http2

HTTP/2

HTTP/2 is a newer version of the HTTP protocol that improves performance and security over the older HTTP/1.1 version. It's used by websites and applications to communicate with servers, and it's designed to be more efficient and scalable.

Node.js's HTTP/2 Module

Node.js provides an HTTP/2 module that allows you to easily use HTTP/2 in your applications. It's an implementation of the HTTP/2 protocol that you can use to send and receive HTTP/2 requests and responses.

HTTP/2 Features

HTTP/2 has several features that make it more efficient than HTTP/1.1, including:

Multiplexing: HTTP/2 allows multiple requests and responses to be sent over a single TCP connection. This means that applications can make multiple requests without having to wait for each response to come back before sending the next one.
Header compression: HTTP/2 uses a header compression algorithm to reduce the size of request and response headers. This can improve performance, especially for requests and responses that have large headers.
Prioritization: HTTP/2 allows applications to prioritize requests. This means that applications can tell the server which requests are more important and should be processed first.

HTTP/2 Applications

HTTP/2 is used in a wide variety of applications, including:

Web browsers: Web browsers use HTTP/2 to load websites and applications more quickly and efficiently.
Mobile applications: Mobile applications use HTTP/2 to communicate with servers.
APIs: APIs use HTTP/2 to provide faster and more scalable access to data and services.

Code Example

Here's a simple example of how to use the HTTP/2 module to send an HTTP/2 request:

const http2 = require('node:http2');

const client = http2.connect('https://example.com');

const req = client.request({
  ':path': '/'
});

req.on('response', (headers, flags) => {
  console.log(headers);
});

req.setEncoding('utf8');
req.on('data', (chunk) => {
  console.log(chunk);
});

req.on('end', () => {
  client.close();
});

req.end();

Simplified Explanation of Node.js http2 Module Crypto Support

What is the http2 module?

The http2 module in Node.js allows you to use the HTTP/2 protocol for faster and more efficient communication over the web.

What is crypto support?

Crypto support refers to the use of encryption and decryption to keep data secure during communication.

When is crypto support unavailable?

Node.js can be built without including support for the node:crypto module, which is necessary for HTTP/2 to function properly.

How to check if crypto support is unavailable?

CommonJS (require() method):

try {
  const http2 = require("node:http2");
} catch (err) {
  console.error("HTTP/2 support is disabled!");
}

If require('node:http2') throws an error, crypto support is unavailable.

ESM (import keyword):

try {
  const http2 = await import("node:http2");
} catch (err) {
  console.error("HTTP/2 support is disabled!");
}

You need to register a handler for process.on('uncaughtException') before attempting to load the module.

Solution:

If crypto support is unavailable, you can use the following alternative:

// Create a secure server without HTTP/2 support
const https = require("https");
const fs = require("fs");

const server = https.createServer({
  key: fs.readFileSync("key.pem"),
  cert: fs.readFileSync("cert.pem"),
});

server.listen(3000, () => {
  console.log("HTTPS server listening on port 3000");
});

Real-World Applications:

HTTP/2 with crypto support is widely used in web applications, APIs, and other online services that require secure and efficient data transfer.

Potential Applications:

Online banking and financial transactions
Secure messaging and communication platforms
E-commerce and online marketplaces
Data-intensive applications like video streaming and file sharing

HTTP/2 Core API

The HTTP/2 Core API is a low-level interface that lets you use the features of the HTTP/2 protocol. It's not meant to be compatible with the older HTTP/1 API, but they offer a Compatibility API for that purpose.

The HTTP/2 Core API is similar for both clients and servers. For example, both can trigger events like 'error', 'connect', and 'stream'.

How it Works

Imagine you have a client and a server communicating using HTTP/2.

Client-side

The client creates an HTTP/2 client object and connects it to the server.
The client can then create multiple HTTP/2 streams, each of which is like a separate connection for sending and receiving data.
Each stream allows the client to send HTTP/2 frames, which contain data and control information.
The client can also pause and resume streams to optimize data flow.

Server-side

The server creates an HTTP/2 server object and listens for incoming connections.
When a client connects, the server creates an HTTP/2 stream for each request/response cycle.
The server can also process HTTP/1 requests using the Compatibility API, and automatically convert them to HTTP/2 internally.

Real-World Applications

HTTP/2 is used in various applications to improve performance:

Online Banking: Faster page loading and secure data transfer.
E-commerce: Enhanced shopping experiences with quick product browsing and checkout processes.
Streaming Media: Smooth and reliable streaming of videos and music.
API Communication: Efficient data exchange between microservices and mobile apps.

Example: Creating a Client

const http2 = require("http2");

const client = http2.connect("https://example.com");

client.on("stream", (stream) => {
  stream.write("Hello from the client");
});

Example: Creating a Server

const http2 = require("http2");

const server = http2.createSecureServer();

server.on("stream", (stream) => {
  stream.respond({
    ":status": 200,
    "content-type": "text/plain",
  });
  stream.end("Hello from the server");
});

HTTP/2 Server with Node.js

HTTP/2 is a newer version of the HTTP protocol that is faster and more efficient than its predecessor, HTTP/1.1. Node.js provides a Core API for creating HTTP/2 servers.

Creating an HTTP/2 Server

To create an HTTP/2 server, you can use the http2.createSecureServer() method. This method takes an options object as an argument, which includes the key and certificate to use for SSL encryption.

const http2 = require("node:http2");
const fs = require("node:fs");

const server = http2.createSecureServer({
  key: fs.readFileSync("localhost-privkey.pem"),
  cert: fs.readFileSync("localhost-cert.pem"),
});

Handling HTTP/2 Requests

When a client sends a request to the HTTP/2 server, a new HTTP/2 stream is created. The server can listen for events on this stream, such as the data event when the client sends data, and the end event when the client finishes sending data.

The server can respond to the request by calling the respond() method on the stream. This method takes an options object as an argument, which includes the response status code and headers. The server can then send data to the client by calling the write() method on the stream.

server.on("stream", (stream, headers) => {
  // stream is a Duplex
  stream.respond({
    "content-type": "text/html; charset=utf-8",
    ":status": 200,
  });
  stream.end("<h1>Hello World</h1>");
});

Real-World Applications

HTTP/2 is used in a variety of real-world applications, including:

Web browsers: Major web browsers, such as Chrome and Firefox, support HTTP/2. This means that websites can load faster and more efficiently when using HTTP/2.
Mobile applications: Many mobile applications use HTTP/2 to communicate with servers. This can improve the performance of mobile applications by reducing latency and improving data transfer speeds.
API servers: API servers can use HTTP/2 to provide faster and more efficient access to their APIs. This can improve the performance of applications that use these APIs.

Improved Code Example

Here is an improved version of the HTTP/2 server example:

const http2 = require("node:http2");
const fs = require("node:fs");

const server = http2.createSecureServer({
  key: fs.readFileSync("localhost-privkey.pem"),
  cert: fs.readFileSync("localhost-cert.pem"),
});

server.on("stream", (stream, headers) => {
  const path = headers[":path"];

  switch (path) {
    case "/":
      stream.respond({
        "content-type": "text/html; charset=utf-8",
        ":status": 200,
      });
      stream.end("<h1>Hello World</h1>");
      break;

    case "/about":
      stream.respond({
        "content-type": "text/html; charset=utf-8",
        ":status": 200,
      });
      stream.end("<h1>About Page</h1>");
      break;

    default:
      stream.respond({
        ":status": 404,
      });
      stream.end();
  }
});

server.listen(8443);

This example handles multiple HTTP/2 requests, based on the path of the request.

HTTP/2 Client

HTTP/2 is a newer version of the HTTP protocol that provides faster and more efficient communication between web browsers and servers. Node.js includes a client module for HTTP/2, which allows you to create HTTP/2 requests from your Node.js applications.

Simple Example

Here's a simplified example of an HTTP/2 client:

const http2 = require("http2");

const client = http2.connect("https://localhost:8443");

const req = client.request({ ":path": "/" });

req.on("response", (headers, flags) => {
  console.log("Headers:", headers);
});

req.setEncoding("utf8");
let data = "";
req.on("data", (chunk) => {
  data += chunk;
});
req.on("end", () => {
  console.log("Data:", data);
  client.close();
});
req.end();

Explanation

http2.connect: Establishes an HTTP/2 connection to the specified server.
client.request: Creates a new HTTP/2 request with the specified path.
req.on('response'): The response event is emitted when the server responds to the request. It provides the response headers and flags.
req.setEncoding('utf8'): Sets the encoding of the response data to UTF-8.
req.on('data'): The data event is emitted whenever the server sends chunks of data.
req.on('end'): The end event is emitted when the server has finished sending data.
client.close: Closes the HTTP/2 connection.

Real-World Applications

HTTP/2 clients can be used in any application that needs to communicate with a server using the HTTP/2 protocol. Here are some potential applications:

Web browsers: Modern web browsers support HTTP/2, which can improve the speed and performance of web browsing.
Web APIs: Third-party web APIs can use HTTP/2 to provide faster and more responsive services.
Mobile applications: Mobile applications can use HTTP/2 to communicate with backend servers more efficiently.
IoT devices: IoT devices can use HTTP/2 to send and receive data from the cloud.

What is HTTP/2?

HTTP/2 is a newer version of the HTTP protocol used to transfer data over the internet. It's faster and more efficient than HTTP/1.1, which is the version used by most websites today.

What is an HTTP/2 Session?

An HTTP/2 session is a connection between an HTTP/2 client and server. It's like a tunnel that allows data to be transferred between the two parties.

How are HTTP/2 Sessions Created?

On the server side, HTTP/2 sessions are created when a new HTTP/2 connection is received. On the client side, HTTP/2 sessions are created using the http2.connect() method.

What Can You Do with HTTP/2 Sessions?

HTTP/2 sessions are used to transfer data between clients and servers. This data can include web pages, images, videos, and other types of content.

Real-World Applications of HTTP/2

HTTP/2 is being used by a number of major websites, including Google, Facebook, and Amazon. It's also being used by a number of mobile applications.

Here is a simplified example of how an HTTP/2 session works:

A client sends a request to a server.
The server responds by sending data to the client.
The client and server continue to exchange data until the session is closed.

Here is a simplified code example of how to use the http2.connect() method to create an HTTP/2 session:

const http2 = require("http2");
const client = http2.connect("https://example.com");

client.on("error", (err) => {
  console.error(err);
});

client.on("data", (chunk) => {
  console.log(chunk.toString());
});

client.write("Hello, world!");
client.end();

This code will create an HTTP/2 session to the example.com website. The client will then send the data "Hello, world!" to the server and close the session.

Http2Session and Sockets

In Node.js, every Http2Session (an HTTP/2 session) is connected to exactly one socket, which can be either a regular socket (net.Socket) or a TLS (encrypted) socket (tls.TLSSocket). When either the Socket or the Http2Session is destroyed, both will be destroyed.

Why not read or write directly to the Socket?

The HTTP/2 protocol has specific rules for how data is serialized and processed. If user code tries to read or write data directly to the socket, it can mess up these rules and cause the session to become unusable.

Real-World Example

Imagine a website that uses HTTP/2 for faster page loading. The Http2Session is responsible for managing the connection between the client (the browser) and the server. If the client tries to read or write data directly to the socket, it could mess up the session and cause the website to load slowly or even fail to load.

Potential Applications

Faster web browsing
Improved performance for applications that use HTTP/2
Secure communication for applications that use TLS

Code Snippet

// Create a TLS socket and bind it to an Http2Session
const tlsSocket = tls.connect(8000, {
  host: "example.com",
  rejectUnauthorized: false,
});

// Create an Http2 session bound to the socket
const session = http2.connect(tlsSocket);

// Send a request using the session
session.request(
  {
    ":path": "/index.html",
  },
  (err, res) => {
    res.on("data", (chunk) => {
      // Received data from the server
    });

    res.on("end", () => {
      // Finished receiving data from the server
    });
  }
);

Event: 'close'

The 'close' event is emitted when the Http2Session is destroyed. This can happen for several reasons, such as:

The connection is closed by the remote peer.
The connection is terminated due to an error.
The Http2Session is explicitly destroyed by calling session.destroy().

When the 'close' event is emitted, the listener function will not receive any arguments.

Example:

const http2 = require("http2");

const session = http2.connect("https://example.com");

session.on("close", () => {
  console.log("The HTTP/2 session has been closed.");
});

Real-world applications:

The 'close' event can be used to perform cleanup tasks when the HTTP/2 session is destroyed. For example, you could close any open streams or release any resources that were allocated for the session.

Event: `'connect'`

Meaning:

When a Http2Session (a connection used for HTTP/2 communication) successfully establishes a connection with the other end, this event is emitted.

Details:

Two arguments are passed to the event listener function:
- session: The Http2Session object that represents the connection.
- socket: The underlying TCP socket used for the connection.

Example:

const { Http2Session } = require("http2");

const session = new Http2Session();

// Listen for the 'connect' event
session.on("connect", (session, socket) => {
  // Do something with the connected session and socket
});

// Initiate the connection
session.connect();

Real-World Application:

When you want to monitor the progress or handle any issues during the connection establishment phase.

Event: 'error'

Simplified Explanation:

When a problem occurs while using the Http2Session, this event is triggered.

Detailed Explanation:

The Http2Session class in the HTTP/2 module handles communication with HTTP/2 servers. If an error occurs during this communication, such as network issues or protocol violations, the 'error' event is emitted.

Code Snippet:

const http2 = require("http2");

// Create an HTTP/2 session
const session = http2.connect("https://example.com");

// Handle the 'error' event
session.on("error", (err) => {
  console.error(err);
});

Real-World Applications:

Detecting and handling communication errors while using HTTP/2 services.
Retrying requests or failing gracefully in case of connection issues.
Logging errors for debugging and analysis.

Event: 'frameError'

Explanation

The 'frameError' event is triggered when an error occurs while sending a frame (a unit of data) on an HTTP/2 session. This error can be associated with a specific stream (a logical connection within the HTTP/2 session) or with the session itself.

Details

When Error Occurs with a Stream:

type: The type of frame that caused the error (e.g., DATA, HEADERS, etc.).
code: The error code associated with the frame.
id: The unique identifier of the stream that the frame was intended for.

In this scenario, the stream is immediately closed and destroyed, and the 'frameError' event is emitted on the stream object.

When Error Occurs with the Session:

type: The type of frame that was being sent when the error occurred.
code: The error code associated with the frame.
id: 0 (since the error is not associated with a specific stream).

In this scenario, the HTTP/2 session is shut down immediately, and the 'frameError' event is emitted on the session object.

Real-World Applications

The 'frameError' event can help identify and handle errors that occur during HTTP/2 communication, allowing applications to gracefully handle such situations. For example:

Error Recovery: Applications can detect frame errors, log the details, and attempt to recover by retrying the frame or initiating a new stream.
Error Reporting: Errors can be reported to monitoring or logging systems for tracking and analysis.
Performance Optimization: Identifying and resolving frame errors can improve the overall performance and reliability of HTTP/2 communication.

Example

// Example for handling frame error on a stream
const { Http2Session } = require("http2");

const session = new Http2Session();

session.on("stream", (stream) => {
  stream.on("error", (error) => {
    if (error.code === Http2Session.errors.PROTOCOL_ERROR) {
      console.error(
        `Error sending frame on stream ${stream.id}: ${error.message}`
      );
    }
  });
});

// Example for handling frame error on the session
session.on("frameError", (error) => {
  console.error(`Error sending frame on session: ${error.message}`);
});

Understanding the `'goaway'` Event in Node.js's HTTP/2 Module

Event Overview

The 'goaway' event is triggered when a client or server receives a GOAWAY frame. This frame is sent to indicate that the other party wants to end the HTTP/2 connection.

Event Parameters

The 'goaway' event passes three parameters:

errorCode: The HTTP/2 error code provided in the GOAWAY frame.
lastStreamID: The ID of the last stream that was successfully processed before the GOAWAY frame was received (or 0 if no ID was specified).
opaqueData: Any additional data included in the GOAWAY frame, provided as a Buffer object.

Event Handling

When the 'goaway' event is emitted, the Http2Session instance will automatically shut down. This means that any pending streams will be closed and no new streams can be created.

Real-World Applications

The 'goaway' event can be useful in several real-world scenarios:

Graceful Shutdown: If a server wants to gracefully shut down its HTTP/2 connection, it can send a GOAWAY frame to indicate that it's no longer accepting new requests.
Error Handling: If a server or client encounters an error that makes it unable to continue the HTTP/2 connection, it can send a GOAWAY frame to terminate the connection.
Load Balancing: A load balancer can use GOAWAY frames to redirect traffic to different servers based on their load or availability.

Example Code

Here's an example of handling the 'goaway' event on a server:

const http2 = require("http2");

const server = http2.createSecureServer({
  // ... SSL options ...
});

server.on("goaway", (errorCode, lastStreamID, opaqueData) => {
  console.log(`Received GOAWAY frame with error code: ${errorCode}`);
  console.log(`Last accepted stream ID: ${lastStreamID}`);

  // Gracefully shut down the connection
  server.close();
});

Here's an example of handling the 'goaway' event on a client:

const http2 = require("http2");

const client = http2.connect("https://example.com");

client.on("goaway", (errorCode, lastStreamID, opaqueData) => {
  console.log(`Received GOAWAY frame with error code: ${errorCode}`);
  console.log(`Last accepted stream ID: ${lastStreamID}`);

  // Clean up any pending streams
  client.close();
});

What is the 'localSettings' event

The 'localSettings' event is emitted when an acknowledgment SETTINGS frame has been received.
When using http2session.settings() to submit new settings, the modified settings do not take effect until the 'localSettings' event is emitted.

In detail and simplified manner:

When you use the http2session.settings() method to change the settings for an HTTP/2 session, the changes you make are not immediately applied.
Instead, the session sends a SETTINGS frame to the other end of the connection, and waits for an acknowledgment.
Once the acknowledgment is received, the 'localSettings' event is emitted, and the new settings take effect.

Code snippet:

session.settings({ enablePush: false });

session.on("localSettings", (settings) => {
  /* Use the new settings */
});

Real world example:

You might use the 'localSettings' event to track changes to the HTTP/2 settings for a particular connection.

For example, you could use the event to log the new settings, or to update a user interface to reflect the changes.

Potential applications:

Logging and monitoring HTTP/2 connections
Debugging HTTP/2 issues
Building tools that manage HTTP/2 connections

What is the 'ping' event?

The 'ping' event is emitted by the HTTP/2 module whenever a PING frame is received from the connected peer.

What is a `PING` frame?

A PING frame is a special type of frame that is used to check if the connection is still alive. It consists of an 8-byte payload, which is typically just a timestamp.

Why is the `'ping'` event useful?

The 'ping' event can be used to monitor the health of the connection. If the event is not emitted for a long period of time, it is possible that the connection has been lost.

How to use the `'ping'` event?

To use the 'ping' event, you can add a listener to it using the on() method. The listener will be called every time a PING frame is received.

const http2 = require("http2");

const client = http2.connect("https://example.com");

client.on("ping", (payload) => {
  console.log("Received PING frame with payload:", payload.toString());
});

Real-world applications

One real-world application of the 'ping' event is to monitor the health of a connection between a client and a server. If the event is not emitted for a long period of time, the client can assume that the connection has been lost and take appropriate action, such as reconnecting.

Code snippet for `'ping'` event

const http2 = require("http2");
const fs = require("fs");

const server = http2.createServer();

server.on("ping", (payload) => {
  console.log("Received PING frame with payload:", payload.toString());
  server.ping();
});

server.listen(8000);

Simplified Explanation of the `'remoteSettings'` Event in Node.js' HTTP/2 Module

What is HTTP/2?

HTTP/2 is a newer version of the HTTP protocol that was designed to improve the speed and efficiency of web communication.

What is a SETTINGS Frame?

In HTTP/2, a SETTINGS frame is a type of message that is used to exchange configuration information between the client and server. This information includes settings such as the maximum size of data that can be sent in a single message.

What is the 'remoteSettings' Event?

The 'remoteSettings' event is emitted by the HTTP/2 session object when it receives a new SETTINGS frame from the remote peer (either the client or server). This event provides access to a copy of the SETTINGS frame's contents.

Example Code:

const http2 = require("http2");

const session = http2.connect("https://example.com");

session.on("remoteSettings", (settings) => {
  console.log(settings);
});

Real-World Applications:

The 'remoteSettings' event can be used to track and respond to changes in the remote peer's settings. This information can be used to optimize the performance of the HTTP/2 connection and to ensure that both parties are using compatible settings.

Potential Applications:

Performance Monitoring: The 'remoteSettings' event can be used to monitor changes in the remote peer's settings over time. This information can be used to identify potential performance bottlenecks and to optimize the connection accordingly.
Compatibility Management: The 'remoteSettings' event can be used to ensure that both parties are using compatible settings. This helps to prevent errors and connection failures.
Security Monitoring: The 'remoteSettings' event can be used to detect changes in the remote peer's settings that could indicate a security issue. This information can be used to take appropriate action to protect the connection.

Event: `'stream'`

stream : Reference to the new Http2Stream created.
headers : Object describing the headers sent with the stream.
flags : Numeric flags associated with the stream.
rawHeaders : Array containing the raw header names and values.

Explanation

The 'stream' event is triggered when a new HTTP/2 stream is created. This event is mostly handled internally by Node.js, but you can use it to listen for new streams and respond to them.

Example

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream, headers, flags) => {
  const method = headers[":method"];
  const path = headers[":path"];

  // Handle the stream here

  stream.respond({
    ":status": 200,
    "content-type": "text/plain",
  });
  stream.write("Hello World");
  stream.end();
});

server.listen(8000);

Applications

The 'stream' event can be used for various applications, such as:

Handling incoming HTTP requests
Sending responses to clients
Streaming data between the server and client

Potential use-cases of HTTP/2 streams in the real world

HTTP/2 push streams: HTTP/2 push streams can be used to improve the performance of web pages by sending resources to the client before they are requested. This can reduce the time it takes for a page to load and improve the user experience.
Server-sent events (SSEs): SSEs are a type of HTTP/2 stream that allows the server to send real-time updates to the client. This can be used for applications such as live chat, stock tickers, and news feeds.
gRPC: gRPC is a framework for building high-performance RPC services. gRPC uses HTTP/2 streams to transport RPC messages. This makes it possible to build RPC services that are fast, efficient, and reliable.

Event: 'timeout'

What is it?

The 'timeout' event is emitted when there is no activity on an Http2Session (a type of network connection) after a certain amount of time (timeout period). This event is triggered by the http2session.setTimeout() method, which sets the timeout period for the Http2Session.

How to use it?

To listen for the 'timeout' event, you can use the on() method of the Http2Session object:

session.on("timeout", () => {
  // Code to run when the timeout event occurs
});

Code snippet:

const http2 = require("http2");

// Create an Http2Session
const session = http2.connect("https://example.com");

// Set the timeout period to 2 seconds
session.setTimeout(2000);

// Listen for the 'timeout' event
session.on("timeout", () => {
  console.log("Timeout occurred");
});

Real-world applications:

Preventing Denial of Service (DoS) attacks: By setting a timeout period, you can prevent attackers from keeping an Http2Session open indefinitely and consuming resources.
Monitoring network activity: The 'timeout' event can be used to monitor the activity of an Http2Session and detect when it has become inactive, allowing you to take appropriate actions such as closing the session.

HTTP/2 Session ALPN Protocol

Simplified Explanation:

An ALPN protocol is like a special handshake between a server and a client. It tells them which protocol they'll be using to communicate, in this case, HTTP/2.

In-depth Explanation:

HTTP/2 is a newer, more efficient version of HTTP, the protocol used for most web communication. To establish an HTTP/2 connection, the client and server need to agree on an "Application Layer Protocol Negotiation" (ALPN).

The alpnProtocol property of an Http2Session instance tells you which ALPN protocol was used when the session was established.

Code Snippet:

const http2 = require('http2');

const session = http2.connect('https://example.com');

session.on('connect', () => {
  console.log(session.alpnProtocol);
});

Output:

'h2'

Real World Application:

Identifying the ALPN protocol used can be helpful for debugging or understanding how your application is communicating with an HTTP/2 server.

Potential Applications:

Ensuring that an HTTP/2 connection is being established correctly.
Identifying the specific ALPN protocol used for a particular connection.
Troubleshooting compatibility issues between clients and servers.

`http2session.close([callback])`

Simplified Explanation:

The close() method gracefully shuts down an HTTP/2 session, allowing any ongoing "streams" (connections) to finish before closing. It prevents any new streams from being created and may eventually destroy the session if there are no more open streams.

Callback Function:

You can optionally provide a callback function as an argument to close(), which will be called when the session is successfully closed. The callback will receive an error object, which will be null if the session closed without any errors.

Real-World Example:

Consider the following code:

const http2 = require("http2");

// Create an HTTP/2 session
const session = http2.connect("example.com", 443);

// Send a request and listen for the response
session
  .request({
    ":path": "/",
  })
  .on("response", (headers) => {
    console.log(headers);
  });

// Gracefully close the session after the response is received
session.close((err) => {
  if (err) {
    console.error(err);
  }
  console.log("Session closed");
});

In this example:

An HTTP/2 session is created using the connect() function.
A request is sent using the request() method and a listener is added to handle the response.
Once the response is received, the close() method is called to gracefully shut down the session.
The callback function is provided to handle any potential errors during the closure process.

Potential Applications:

Gracefully closing HTTP/2 sessions is useful in real-world applications to:

Cleanly terminate connections when they are no longer needed, improving resource efficiency.
Handle error scenarios gracefully by providing clear error messages and enabling recovery.
Implement custom session management strategies, such as setting timeouts or limiting the number of concurrent streams.

`http2session.closed`

What it is: A property that indicates whether this Http2Session has been closed.
Type: Boolean
Value: true if the Http2Session is closed, false if it is open.

Example

const http2 = require("http2");

// Create an HTTP2 session
const session = http2.connect("https://example.com");

// Check if the session has been closed
if (session.closed) {
  // The session is closed.
} else {
  // The session is open.
}

Simplified Explanation:

http2session.connecting

This property is a flag that indicates whether an Http2Session is still in the process of connecting or not.
If true, it means the connection is being established.
If false, it means the connection is fully established.

Real-World Example:

Imagine you are trying to connect to a website over a secure connection (HTTPS). Before you can actually access the website, your browser will establish a connection to the server using HTTP/2. During this initial connection phase, the http2session.connecting flag will be true. Once the connection is fully established, the flag will be set to false and you will be able to access the website.

Potential Applications:

Monitoring connection attempts: You can use this property to monitor the progress of HTTP/2 connections and identify any connection issues that may arise.
Debugging connection errors: If you encounter errors with HTTP/2 connections, you can check the value of this property to determine if the connection is still in progress or not.

Code Example:

const http2 = require("http2");

const client = http2.connect("https://example.com");

client.on("connect", () => {
  // The connection is now established
  console.log("Connected!");
});

client.on("error", (err) => {
  // Handle connection error
  if (err.code === "ECONNREFUSED" && client.connecting) {
    // Connection attempt was refused, retry later
    console.log("Connection attempt refused, retrying...");
  }
});

client.on("close", () => {
  // The connection has closed
  console.log("Connection closed");
});

Simplified Explanation of `http2session.destroy()` Method

What is http2session.destroy()?

http2session.destroy() is a method in Node.js's HTTP/2 module that allows you to immediately close an HTTP/2 session and its associated socket.

When to Use http2session.destroy()?

You might use http2session.destroy() when:

You want to abruptly end the HTTP/2 session due to an error or unexpected behavior.
You have finished using the session and want to release associated resources.

Parameters:

The http2session.destroy() method takes two optional parameters:

error: An Error object if the session is being destroyed due to an error.
code: An HTTP/2 error code to send in the final GOAWAY frame.

Behavior:

The session and the underlying socket will be immediately closed.
If error is provided, an 'error' event will be emitted before the 'close' event.
Any open HTTP/2 streams associated with the session will also be destroyed.

Example:

const { Http2Server } = require("http2");

const server = Http2Server.create();

server.on("session", (session) => {
  session.on("error", (err) => {
    session.destroy(err); // Close the session due to an error
  });

  session.on("close", () => {
    console.log("Session closed");
  });
});

server.listen(3000);

In this example, if an error occurs on the session (e.g., a stream error), the session is immediately closed and an error event is emitted.

Real-World Applications:

http2session.destroy() can be useful in situations such as:

Handling errors in HTTP/2 streams and closing the session to prevent further issues.
Gracefully shutting down HTTP/2 servers or clients and releasing resources.

What is http2session.destroyed?

http2session.destroyed is a property of an Http2Session object that indicates whether or not the session has been destroyed. A destroyed session can no longer be used to send or receive data.

How do I check if a session has been destroyed?

You can check if a session has been destroyed by accessing the http2session.destroyed property. The value of this property will be true if the session has been destroyed, and false otherwise.

Example

const http2 = require("http2");

const session = http2.connect("https://example.com");

session.on("error", (err) => {
  if (err.code === "ERR_HTTP2_SESSION_ERROR") {
    // The session has been destroyed.
    console.log("The session has been destroyed.");
  }
});

session.on("close", () => {
  // The session has been closed.
  console.log("The session has been closed.");
});

// Check if the session has been destroyed.
console.log(session.destroyed); // false

// Destroy the session.
session.destroy();

// Check if the session has been destroyed.
console.log(session.destroyed); // true

Real-world applications

http2session.destroyed can be used to check if a session has been destroyed before attempting to send or receive data. This can help to prevent errors from occurring.

encrypted Property

Definition:

The encrypted property of an Http2Session object indicates whether the session is encrypted using Transport Layer Security (TLS).

Possible Values:

undefined: The session is not yet connected.
true: The session is connected using TLS.
false: The session is connected without TLS.

How to Determine if a Session is Encrypted:

const http2 = require("http2");

const server = http2.createServer();

server.on("session", (session) => {
  const isEncrypted = session.encrypted;
  console.log(`Session is encrypted: ${isEncrypted}`);
});

Real-World Example:

TLS encryption is essential for securing sensitive data transmitted over the network. In an e-commerce website, for example, customer information and financial transactions need to be protected during transmission. By ensuring that the HTTP/2 connection is encrypted, we can prevent eavesdropping and data breaches.

Potential Applications:

Secure web applications: Protect user data and privacy by encrypting HTTP/2 connections.
Encrypted file transfers: Ensure the integrity and confidentiality of file transfers using HTTP/2.
Secure remote desktop access: Transmit sensitive data securely over HTTP/2 connections.

`http2session.goaway([code[, lastStreamID[, opaqueData]]])`

code {number} An HTTP/2 error code.
lastStreamID {number} The numeric ID of the last processed Http2Stream.
opaqueData {Buffer|TypedArray|DataView} A TypedArray or DataView instance containing additional data to be carried within the GOAWAY frame.

Sends a GOAWAY frame to the connected peer without shutting down the Http2Session.

What is a `GOAWAY` frame?

A GOAWAY frame is a way for a server to tell a client that it is going to stop accepting new streams. The frame contains a numeric error code and a stream ID, which indicates the last stream that the server will accept.

Why would a server send a `GOAWAY` frame?

A server might send a GOAWAY frame for a number of reasons, including:

The server is overloaded and needs to reduce the number of active streams.
The server is shutting down and needs to terminate all active streams.
The server has detected an error and needs to terminate all active streams.

What happens when a client receives a `GOAWAY` frame?

When a client receives a GOAWAY frame, it must:

Stop sending new streams to the server.
Close all active streams that have a stream ID less than or equal to the stream ID specified in the GOAWAY frame.
Send a GOAWAY frame to the server to acknowledge receipt of the GOAWAY frame.

Code example

The following code example shows how to send a GOAWAY frame:

const http2 = require("http2");

const session = http2.connect("localhost:8000");

session.goaway(http2.constants.NGHTTP2_NO_ERROR, 100);

Real-world applications

GOAWAY frames are used in a number of real-world applications, including:

Load balancing: A load balancer can send a GOAWAY frame to a server that is overloaded to redirect traffic to another server.
Graceful shutdown: A server can send a GOAWAY frame to clients when it is shutting down to give them time to close their connections.
Error handling: A server can send a GOAWAY frame to clients when it encounters an error to terminate all active streams.

HTTP/2 Settings Object

HTTP/2 settings are used to control how an HTTP/2 session operates. They allow each endpoint to specify its preferences for things like the maximum frame size, the maximum concurrent streams, and the initial window size.

The http2session.localSettings property is a prototype-less object that describes the current local settings of an Http2Session instance. These settings are local to that specific instance and do not affect other sessions.

Properties

The http2session.localSettings object has the following properties:

settingsTimeout: The amount of time (in milliseconds) that the session will wait for the peer to send its settings frame.
maxDeflateDynamicTableSize: The maximum size (in bytes) of the dynamic table used for HPACK compression.
initialWindowSize: The initial window size (in bytes) for new streams.
maxConcurrentStreams: The maximum number of concurrent streams that the session can have open.
maxFrameSize: The maximum size (in bytes) of a single frame.
maxHeaderListSize: The maximum size (in bytes) of the header list for a single frame.

Example

The following code snippet shows how to access the local settings of an Http2Session instance:

const http2 = require('http2');
const session = http2.connect('https://example.com');

session.on('connect', () => {
  console.log(session.localSettings);
});

Potential Applications

HTTP/2 settings can be used to optimize the performance of an HTTP/2 session. For example, increasing the maxConcurrentStreams value can improve throughput on connections with high latency. Decreasing the maxFrameSize value can reduce the risk of head-of-line blocking.

What is `http2session.originSet`?

When using Node.js's http2 module to establish a secure TLS connection, the originSet property of an Http2Session object provides a list of origins (domains or addresses) for which the session can be considered an authoritative source.

How does it work?

Imagine you have a website called example.com and you want to use HTTPS to create a secure connection between your server and clients' browsers. When a client connects to your website, a TLS handshake is performed to establish a secure channel. During this handshake, the client may send a list of origins (e.g., example.com, www.example.com) that it considers to be authoritative.

The http2session.originSet property allows you to access this list of origins and verify if a particular origin is included. This is useful for situations where you need to restrict access to certain origins or enforce security policies based on the origin of the request.

Example

The following code snippet demonstrates how to check the originSet property:

const http2 = require("http2");

const server = http2.createServer();
server.on("session", (session) => {
  // Get the origin set for the session
  const originSet = session.originSet;

  // Check if a specific origin is included in the origin set
  const isOriginAuthorized = originSet.includes("example.com");

  // Do something based on the authorization result
});

Real-World Applications

Enforcing access control: You can use the originSet property to restrict access to certain origins. For example, if you have a user profile page that should only be accessible from your own website, you can check the originSet property and deny access if the origin is not included.
Implementing Cross-Origin Resource Sharing (CORS): CORS is a security mechanism that allows you to specify which origins can access your resources. By using the originSet property, you can check if the origin of the request is allowed to access the resource.

Simplified Explanation of `http2session.pendingSettingsAck`

What is `http2session.pendingSettingsAck`?

In HTTP/2, a SETTINGS frame is used to configure the connection between the client and server. It contains settings that control various aspects of the connection, such as the maximum data frame size and whether to allow HTTP/1.1 requests.

The http2session.pendingSettingsAck property indicates whether the Http2Session is waiting for the other side (client or server) to acknowledge a SETTINGS frame that it has sent.

When is `http2session.pendingSettingsAck` true?

http2session.pendingSettingsAck is set to true after the http2session.settings() method is called. This method allows you to modify the settings for the connection by sending a SETTINGS frame.

When is `http2session.pendingSettingsAck` false?

http2session.pendingSettingsAck is set to false once all sent SETTINGS frames have been acknowledged. The other side will send an acknowledgment frame to indicate that it has received and processed the SETTINGS frame.

Real-World Applications

Using http2session.pendingSettingsAck allows you to control the flow of data on the HTTP/2 connection. By waiting for the other side to acknowledge a SETTINGS frame before sending more data, you can ensure that the other side is ready to receive the data.

Example

The following code shows an example of using http2session.settings() to modify the connection settings and then waiting for the acknowledgment:

const { createServer } = require("http2");

const server = createServer();

server.on("stream", (stream) => {
  // Send an initial SETTINGS frame
  server.settings({
    maxFrameSize: 16384,
    headerTableSize: 4096,
  });

  // Wait for the acknowledgment before sending any data
  server.pendingSettingsAck = true;

  // Send the data
  stream.end("Hello World");
});

server.listen(8080);

Pinging with HTTP/2

HTTP/2 allows you to send a "ping" to the server to check if it's still alive. It's like poking it with a stick to see if it responds.

Sending a Ping

To send a ping, use the ping() method. It takes two arguments:

payload (optional): A buffer, typed array, or data view containing 8 bytes of data to send with the ping.
callback (required): A function that will be called when the server responds to the ping.

The callback function takes three arguments:

err: An error object, which will be null if the ping was successful.
duration: The number of milliseconds it took for the server to respond to the ping.
payload: The 8-byte payload that was returned by the server.

If you don't specify a payload, the default payload will be a 64-bit timestamp marking the start of the ping duration.

// Send a ping with a custom payload
const payload = Buffer.from("abcdefgh");

session.ping(payload, (err, duration, payload) => {
  if (!err) {
    console.log(`Ping acknowledged in ${duration} milliseconds`);
    console.log(`With payload '${payload.toString()}'`);
  }
});

// Send a ping with the default payload
session.ping((err, duration) => {
  if (!err) {
    console.log(`Ping acknowledged in ${duration} milliseconds`);
  }
});

Real World Example

Pinging can be useful for detecting if a server has crashed or become unresponsive. You can periodically send pings to the server and if you don't receive a response within a certain amount of time, you know that something is wrong.

Here's an example of how you could use pinging to monitor a server:

// Create an HTTP/2 session
const session = createSession();

// Set up a timer to periodically send pings
setInterval(() => {
  session.ping((err, duration) => {
    if (err) {
      // The server is not responding to pings, so something is wrong
    } else {
      // The server is alive and responding to pings
    }
  });
}, 1000); // Send a ping every 1 second

`http2session.ref()`

Purpose:

http2session.ref() allows you to prevent the underlying socket of the Http2Session from being closed automatically when there are no more references to the Http2Session object.

How it works:

When you create an Http2Session, it is associated with an underlying TCP socket. By default, when there are no more references to the Http2Session object, the socket will be automatically closed.

However, you can use the http2session.ref() method to keep the socket open even after the Http2Session object has been GC'd. This can be useful if you want to keep the socket open for future use, such as for pooling.

Example:

const { Http2Session } = require("http2");

const session = new Http2Session();

// Keep the socket open even after the session is GC'd
session.ref();

// Later, when you're ready to close the session...
session.unref();

Real-world application:

HTTP/2 pooling is a technique used to improve the performance of HTTP/2 connections by reusing existing connections instead of creating new ones. By using http2session.ref(), you can keep the sockets associated with HTTP/2 sessions open in a pool, so that they can be reused for future requests. This can reduce the overhead of creating new connections and improve the overall performance of your application.

`http2session.remoteSettings`

Explanation: remoteSettings is an object that contains the settings received from the remote HTTP/2 peer. These settings control the behavior of the HTTP/2 connection.

Properties:

headerTableSize: The size of the header table that the remote peer is using.
enablePush: Whether the remote peer is allowing push streams.
maxConcurrentStreams: The maximum number of concurrent streams that the remote peer can handle.
initialWindowSize: The initial window size for new streams.
maxFrameSize: The maximum size of a frame that the remote peer can handle.
maxHeaderListSize: The maximum size of a header list that the remote peer can handle.

Real-World Example:

Consider a web server that uses HTTP/2 to serve content to clients. The server can use the remoteSettings to determine the optimal settings for each connection. For example, if the client has a small header table size, the server can send smaller headers to reduce overhead. If the client has a low maxConcurrentStreams value, the server can limit the number of concurrent streams to improve performance.

Potential Applications:

Performance tuning: The remoteSettings can be used to tune the performance of HTTP/2 connections. By adjusting the settings, you can optimize the connection for the specific needs of the client and server.
Error handling: The remoteSettings can be used to detect errors in the HTTP/2 connection. For example, if the maxConcurrentStreams value is exceeded, the server can send an error frame.

`http2session.setLocalWindowSize(windowSize)`

Description

This method sets the local endpoint's window size in the HTTP/2 session. The window size determines the maximum amount of data that can be sent before waiting for acknowledgment from the other endpoint.

Parameters

windowSize: The new window size to set.

Return Value

None.

Example

The following code sets the local window size to 2 MB:

const http2 = require("http2");

const server = http2.createServer();

// Set the local window size to 2 MB
server.on("session", (session) => {
  session.setLocalWindowSize(2 * 1024 * 1024);
});

Real-World Applications

Setting the window size appropriately can improve performance and prevent data loss in HTTP/2 connections. For example, if the network has high latency, increasing the window size can allow more data to be sent before waiting for acknowledgment. This can reduce the number of round trips and improve throughput.

Conversely, if the network is unreliable, decreasing the window size can help prevent data loss. This is because if data is lost, the sender will only need to retransmit a smaller amount of data.

`http2session.setTimeout(msecs, callback)`

The setTimeout() method of the http2session class in http2 module is used to set a callback function that is called when there is no activity on the Http2Session after msecs milliseconds. The given callback is registered as a listener on the 'timeout' event.

Syntax:

setTimeout(msecs: number, callback: Function): void;

Parameters:

msecs: The number of milliseconds to wait before calling the callback.
callback: The callback function to be called when the Http2Session times out. The callback function takes no arguments.

Example:

const http2 = require("http2");

const session = http2.connect("https://example.com");

session.setTimeout(5000, () => {
  console.log("The HTTP/2 session timed out after 5 seconds.");
});

Applications:

The setTimeout() method can be used to handle situations where there is no activity on the Http2Session for an extended period of time. This can be useful for preventing resource leaks and improving performance.

For example, if a client application is making a request to a server and does not receive a response within a certain amount of time, the client application can use the setTimeout() method to automatically close the connection. This will prevent the client application from wasting resources waiting for a response that will never come.

HTTP/2 Session Socket

Overview

http2session.socket creates a proxy that wraps a net.Socket or tls.TLSSocket. It limits the available methods to those that are safe to use with HTTP/2.

Why is this Important?

HTTP/2 is a newer version of the HTTP protocol that uses multiplexing to improve efficiency. However, some methods in the net.Socket API can disrupt HTTP/2's operation. For example, calling pause on the socket can prevent HTTP/2 streams from being sent.

The http2session.socket proxy prevents these unsafe methods from being called, ensuring that HTTP/2 works correctly.

Limited Methods

The http2session.socket proxy allows the following methods:

destroy (throws an error)
emit (throws an error)
end (throws an error)
pause (throws an error)
read
resume
write (throws an error)
setTimeout (calls setTimeout on the Http2Session)

All other interactions are routed directly to the socket.

Code Example

const http2 = require("http2");

const session = http2.connect("https://example.com");

const socket = session.socket;

socket.on("data", (chunk) => {
  // Handle received data
});

socket.write("Hello, HTTP/2!");

socket.setTimeout(5000); // Calls 'setTimeout' on the 'Http2Session'

Real-World Applications

The http2session.socket proxy is used in many Node.js HTTP/2 applications, including:

Web servers that support HTTP/2
HTTP/2 clients
HTTP/2 proxies

`http2session.state`

This object provides information about the current state of the Http2Session.

Properties:

effectiveLocalWindowSize: The maximum number of bytes that the remote peer can send without receiving a WINDOW_UPDATE.
effectiveRecvDataLength: The current number of bytes that have been received since the last flow control WINDOW_UPDATE.
nextStreamID: The numeric identifier to be used the next time a new Http2Stream is created by this Http2Session.
localWindowSize: The current local (receive) flow control window size for the Http2Session.
lastProcStreamID: The numeric id of the most recently received HEADERS or DATA frame.
remoteWindowSize: The number of bytes that this Http2Session may send without receiving a WINDOW_UPDATE.
outboundQueueSize: The number of frames currently within the outbound queue for this Http2Session.
deflateDynamicTableSize: The current size in bytes of the outbound header compression state table.
inflateDynamicTableSize: The current size in bytes of the inbound header compression state table.

Real-world applications:

This object can be used to monitor the flow of data and frames for troubleshooting and performance analysis.

HTTP/2 Session Settings

In HTTP/2, both the client and server can adjust the settings of the connection to optimize performance. These settings control factors like the maximum frame size, the initial window size, and the number of concurrent streams.

http2session.settings() Method

The http2session.settings() method allows you to update the local settings for an HTTP/2 session. You can pass an object with the new settings as an argument. The method also takes an optional callback function that is called once the session has been updated or if it is already connected.

Usage:

const settings = {
  enablePush: true,
  maxHeaderListSize: 1024
};

http2session.settings(settings, (err, updatedSettings) => {
  if (err) {
    // Handle error
  }

  console.log(`Updated settings: ${JSON.stringify(updatedSettings)}`);
});

Real-World Example:

Imagine you have an HTTP/2 server that is handling a high volume of requests. By increasing the maximum frame size and the initial window size, you can improve the performance of the connection.

Applications:

Performance Optimization: By adjusting the settings, you can optimize the performance of the HTTP/2 connection to meet the specific needs of your application.
Resource Management: The settings allow you to control the resources used by the HTTP/2 session, such as the number of concurrent streams and the size of the connection window.
Security: Some settings, such as the maximum frame size, can be used to enhance the security of the connection.

`http2session.type`

The http2session.type property of the http2.Http2Session class in Node.js is a number that indicates the type of the HTTP/2 session.

If the value is http2.constants.NGHTTP2_SESSION_SERVER, the session is a server session.
If the value is http2.constants.NGHTTP2_SESSION_CLIENT, the session is a client session.

Here is a simplified explanation of the http2session.type property:

Server Session

A server session is created when a client connects to an HTTP/2 server. The server session is responsible for managing the connection and handling requests from the client.

Client Session

A client session is created when a client connects to an HTTP/2 server. The client session is responsible for managing the connection and sending requests to the server.

Real-World Example

The following code snippet shows how to create an HTTP/2 server and listen for client connections:

const http2 = require("http2");

const server = http2.createSecureServer({
  key: fs.readFileSync("server.key"),
  cert: fs.readFileSync("server.crt"),
});

server.on("stream", (stream, headers) => {
  stream.respond({
    "content-type": "text/plain",
    ":status": 200,
  });
  stream.end("Hello, world!");
});

server.listen(8443);

In this example, the server is an HTTP/2 server. When a client connects to the server, the server will create a new http2.Http2Session instance to manage the connection. The http2.Http2Session instance will have a type of http2.constants.NGHTTP2_SESSION_SERVER.

The following code snippet shows how to create an HTTP/2 client and connect to a server:

const http2 = require("http2");

const client = http2.connect("https://localhost:8443");

const request = client.request({
  ":path": "/",
});

request.on("data", (chunk) => {
  console.log(chunk.toString());
});

request.on("end", () => {
  client.close();
});

In this example, the client is an HTTP/2 client. When the client connects to the server, the client will create a new http2.Http2Session instance to manage the connection. The http2.Http2Session instance will have a type of http2.constants.NGHTTP2_SESSION_CLIENT.

Potential Applications

HTTP/2 is a high-performance protocol that can be used to improve the performance of web applications. HTTP/2 is particularly well-suited for applications that require high throughput and low latency. Some potential applications of HTTP/2 include:

Web applications that require high throughput and low latency, such as online games and video streaming services.
Mobile applications that require low latency, such as messaging and social media applications.
API services that require high throughput, such as payment processing and content delivery networks (CDNs).

`http2session.unref()`

Explanation

HTTP/2 sessions are built on top of TCP sockets. The unref() method allows you to detach the HTTP/2 session from its underlying TCP socket. This means that the HTTP/2 session will not be automatically closed when the TCP socket is closed.

Code Snippet

const http2 = require("http2");
const session = http2.connect("https://example.com");

// Detach the HTTP/2 session from its underlying TCP socket.
session.unref();

// The HTTP/2 session will now remain open even if the TCP socket is closed.

Real-World Use Case

This method can be useful in scenarios where you want to keep the HTTP/2 session open even after the TCP socket has been closed. For example, you might want to do this if you are using HTTP/2 for long-lived connections, such as websockets.

Potential Applications

Long-lived HTTP/2 connections: Keeping HTTP/2 sessions open for extended periods of time can improve performance by reducing the overhead of establishing new connections.
Websockets: HTTP/2 can be used to implement websockets, which are long-lived, bi-directional connections that allow for real-time communication between a client and server.

Class: ServerHttp2Session

Description:

The ServerHttp2Session class represents a server-side HTTP/2 session. It manages the HTTP/2 connection and provides methods for handling incoming and outgoing HTTP/2 requests and responses.

Extends:

Http2Session: The ServerHttp2Session class extends the Http2Session class, which defines the basic functionality for managing HTTP/2 connections.

Public Methods:

1. getServer: Returns the Http2Server instance associated with this session.

2. sendHeaders: Sends HTTP/2 headers for a given request.

3. sendBody: Sends the body data for a given request.

4. end: Ends the response for a given request.

5. close: Closes the HTTP/2 session.

Real-World Applications:

Server-side HTTP/2 sessions are used in web servers to handle and respond to HTTP/2 requests from clients. This allows for faster and more efficient communication between the server and client.

Example:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream) => {
  stream.respond({
    ":status": 200,
    "content-type": "text/plain",
  });

  stream.end("Hello, world!");
});

server.listen(8000);

In this example, the http2.createServer() method creates an HTTP/2 server. When a new HTTP/2 stream is received, the 'stream' event is emitted. Inside the event handler, the stream.respond() method is used to send the HTTP/2 response headers, and the stream.end() method is used to send the response body.

`serverhttp2session.altsvc(alt, originOrStream)`

The altsvc() method of the serverhttp2session class in Node.js's http2 module is used to send an ALTSVC frame to the connected client. This frame advertises alternative service configurations as defined by [RFC 7838][].

Parameters

alt: A string describing the alternative service configuration as defined by [RFC 7838][].
originOrStream: Either a URL string specifying the origin or an Object with an origin property, or the numeric identifier of an active Http2Stream as given by the http2stream.id property.

Usage

To use the altsvc() method, you can do the following:

const http2 = require("node:http2");

const server = http2.createServer();
server.on("session", (session) => {
  // Set altsvc for origin https://example.org:80
  session.altsvc('h2=":8000"', "https://example.org:80");
});

server.on("stream", (stream) => {
  // Set altsvc for a specific stream
  stream.session.altsvc('h2=":8000"', stream.id);
});

In the first example, we set the alternative service configuration for the origin https://example.org:80. In the second example, we set the alternative service configuration for a specific stream.

Real-World Applications

The altsvc() method can be used to advertise alternative service configurations to clients. This can be useful for load balancing or for providing clients with faster access to resources. For example, a server could use the altsvc() method to advertise an alternative service configuration that uses a different port or protocol.

Potential Applications

Here are some potential applications of the altsvc() method:

Load balancing: A server can use the altsvc() method to advertise alternative service configurations for different servers. This can help to distribute traffic across multiple servers and improve performance.
Failover: A server can use the altsvc() method to advertise an alternative service configuration that can be used if the primary server fails. This can help to ensure that clients can still access resources even if the primary server is unavailable.
Performance optimization: A server can use the altsvc() method to advertise an alternative service configuration that uses a faster protocol or port. This can help to improve the performance of clients that access resources from the server.

Specifying Alternative Services

Imagine you have a website that you want to make faster. One way to do this is to use HTTP/2, a newer protocol that is more efficient than the traditional HTTP/1.1.

However, not all browsers support HTTP/2 yet. So, you need a way to tell browsers that they can use HTTP/2 if they support it, but to fall back to HTTP/1.1 if they don't.

This is where "alternative services" come in. You can specify alternative services in the HTTP header of your website. This tells browsers that they can use a different protocol or port to connect to your website.

For example, you could specify that browsers can use HTTP/2 on port 81 or HTTP/1.1 on port 80. This would allow browsers that support HTTP/2 to connect to your website on port 81, while browsers that don't support HTTP/2 would connect on port 80.

Here's an example of how you would specify alternative services in the HTTP header of your website:

Alt-Svc: h2="example.org:81"; ma=2592000

Alt-Svc: This is the name of the HTTP header that specifies alternative services.
h2: This is the protocol identifier for HTTP/2.
example.org: This is the host of the website.
81: This is the port number for HTTP/2.
ma=2592000: This specifies how long the alternative service will be valid for, in seconds.

Real-World Applications

Alternative services can be used to improve the performance of any website or application that uses HTTP. Some potential applications include:

Serving static content: Static content, such as images, videos, and CSS files, can be served using HTTP/2 to improve performance.
Improving the performance of web applications: Web applications can be made more responsive by using HTTP/2 for communication between the client and server.
Reducing the latency of live streaming: Live streaming applications can benefit from using HTTP/2 to reduce the latency of video delivery.

Code Implementations

Here is an example of how to use the http2 module to specify alternative services:

const http2 = require("http2");

const server = http2.createSecureServer({
  // ...
  altSvc: [
    // Specify the alternative service for HTTP/2 on port 81.
    {
      port: 81,
      protocol: "h2",
    },
  ],
});

This will tell browsers that they can use HTTP/2 on port 81 to connect to your website.

`serverhttp2session.origin(...origins)`

origins { string | URL | Object } One or more URL Strings passed as separate arguments.

This method allows you to specify the origins that your server can handle requests for. An origin is the combination of a scheme, hostname, and port.

For example, the following code would specify that your server can handle requests from the following origins:

const http2 = require("http2");
const server = http2.createSecureServer(options);
server.on("session", (session) => {
  session.origin("https://example.com", "https://example.org");
});

You can also pass in a URL object, or any object with an origin property. The value of the origin property must be a properly serialized ASCII origin.

For example, the following code would specify the same origins as the previous example:

const http2 = require("http2");
const server = http2.createSecureServer(options);
server.on("session", (session) => {
  session.origin(
    {
      origin: "https://example.com",
    },
    {
      origin: "https://example.org",
    }
  );
});

Alternatively, you can use the origins option when creating a new HTTP/2 server using the http2.createSecureServer() method:

const http2 = require("http2");
const options = getSecureOptionsSomehow();
options.origins = ["https://example.com", "https://example.org"];
const server = http2.createSecureServer(options);
server.on("stream", (stream) => {
  stream.respond();
  stream.end("ok");
});

Real-world applications

This method can be used to improve the performance of your HTTP/2 server. By specifying the origins that your server can handle requests for, you can reduce the number of round-trips required to establish a connection.

This method can also be used to improve the security of your HTTP/2 server. By only allowing requests from specified origins, you can reduce the risk of cross-origin attacks.

Potential applications

Improving the performance of your HTTP/2 server
Improving the security of your HTTP/2 server
Enforcing origin-based access control

Class: ClientHttp2Session

Extends: {Http2Session}

Description:

ClientHttp2Session is a class representing a client HTTP/2 session. It inherits from the Http2Session class, which provides the core HTTP/2 functionality.

Simplified Explanation:

A ClientHttp2Session is like a special connection that allows you to send HTTP/2 requests to a server. It's like a package that contains the rules and information needed for your requests to be sent and processed correctly.

Real-World Implementations:

Here's an example of how you might use a ClientHttp2Session to fetch data from a server:

const http2 = require("http2");
const client = http2.connect("https://example.com");

const request = client.request({
  ":method": "GET",
  ":path": "/",
});

request.on("data", (data) => {
  console.log(data.toString());
});

In this example, client is a ClientHttp2Session object that's connected to the "example.com" server. The request object is used to send a GET request to the root URL "/". When the server responds, the data event is emitted with the server's response.

Potential Applications:

Client HTTP/2 sessions are commonly used in:

Web browsers to load web pages faster and more efficiently.
Mobile apps to communicate with servers more efficiently and reduce data usage.
Microservices and distributed systems to improve communication between different components.

Event: 'altsvc'

Event details

alt {string}: The value of the ALTSVC frame.
origin {string}: The origin of the frame. If no origin is provided, origin will be an empty string.
streamId {number}: The stream ID of the frame.

Description

The 'altsvc' event is emitted whenever an ALTSVC frame is received by the client. The ALTSVC frame is used to advertise alternative service mappings to the client. These mappings can be used to improve performance by directing the client to a closer or faster server.

Usage

To listen for the 'altsvc' event, you can use the following code:

const http2 = require("http2");
const client = http2.connect("https://example.org");

client.on("altsvc", (alt, origin, streamId) => {
  console.log(alt);
  console.log(origin);
  console.log(streamId);
});

Real-world applications

The 'altsvc' event can be used to improve performance by directing the client to a closer or faster server. This can be especially useful for websites that are accessed by users in different geographical locations.

Code example

The following code shows how to use the 'altsvc' event to improve performance:

const http2 = require("http2");
const client = http2.connect("https://example.org");

client.on("altsvc", (alt, origin, streamId) => {
  // If the `alt` value contains a different hostname, we can assume that the
  // server is advertising a closer or faster server.
  if (alt.includes("hostname=") !== origin) {
    // Update the client's connection settings to use the new hostname.
    client.settings({
      altsvc: alt,
    });
  }
});

What is the 'origin' event?

The 'origin' event is a special event emitted by the HTTP/2 client when it receives an ORIGIN frame from the server. The server sends this frame to indicate which origins (websites) it allows the client to request resources from.

What is the purpose of the 'origin' event?

The purpose of the 'origin' event is to inform the client which websites it is allowed to request resources from. This helps to prevent the client from accessing resources from unauthorized websites.

What is an ORIGIN frame?

An ORIGIN frame is a special type of HTTP/2 frame used to indicate which origins are allowed to be requested by the client. The frame contains a list of origin strings, each representing a website that the client is allowed to access.

What is the http2session.originSet property?

The http2session.originSet property is a set of origin strings that have been received by the client in ORIGIN frames. This set is used to track which origins the client is allowed to request resources from.

Usage Example:

The following code snippet shows how to use the 'origin' event:

const http2 = require("http2");
const client = http2.connect("https://example.org");

client.on("origin", (origins) => {
  for (let n = 0; n < origins.length; n++) {
    console.log(origins[n]);
  }
});

Real-World Applications:

The 'origin' event is used in a variety of real-world applications, including:

Preventing Cross-Site Request Forgery (CSRF): CSRF attacks occur when a malicious website tricks a user into submitting a request to a legitimate website. The 'origin' event can be used to prevent CSRF attacks by ensuring that the client only sends requests to origins that have been approved by the server.
Enforcing Content Security Policies (CSP): CSPs are policies that restrict the types of resources that a browser can load from a given origin. The 'origin' event can be used to enforce CSPs by ensuring that the client only requests resources from origins that are included in the CSP.

Potential Applications:

The 'origin' event can be used in a variety of other potential applications, including:

Tracking Origin Usage: The 'origin' event can be used to track which origins are being requested by the client. This information can be used to identify popular origins and to detect suspicious activity.
Enforcing Rate Limiting: The 'origin' event can be used to enforce rate limiting policies. By tracking the number of requests that are made to each origin, the server can prevent clients from making too many requests.

`clienthttp2session.request(headers[, options])`

Simplified Explanation:

Imagine you're running an online store, and customers can add items to their carts and checkout. Each customer has their own "session" with the store, similar to how each web browser has its own session when you visit a website.

Inside the store, each customer's session is like a separate counter. When a customer wants to buy something, they make a "request" to the counter. The counter receives the request and responds with the item's price, and the customer can decide whether to buy it.

Detailed Explanation:

The clienthttp2session.request() method allows you to create a new "request" for a specific customer's session.

Parameters:

headers: This is like a list of items that the customer wants to buy and their quantities.
options: This is an optional list of settings for the request, such as whether the counter should close the connection after sending the response (similar to the customer leaving the counter).

Return Value:

The method returns an Http2Stream object, which represents the customer's request. You can use this object to send data to the counter and receive data back.

Real-World Examples:

Online Store Checkout:

Customer visits an online store and adds items to their cart.
Customer clicks the checkout button, creating a new HTTP/2 request.
The server receives the request and sends the customer's total bill.
The customer confirms the purchase and sends a confirmation request.

Video Streaming:

User opens a video streaming app and selects a video to watch.
The app sends an HTTP/2 request to the server, specifying the video and other settings.
The server sends back a stream of video data, which the app plays for the user.

Potential Applications:

HTTP/2 is commonly used in applications where high performance and low latency are crucial, such as:

Web browsers
Web servers
Streaming services
Social media apps

By enabling multiple requests to be sent concurrently and using compression techniques, HTTP/2 significantly improves the speed and efficiency of online communication.

Http2Stream Class

Each Http2Stream represents a way to communicate between two computers using HTTP/2 protocol. It's like a special channel where computers can send and receive data to each other. A single connection can have many Http2Stream channels, like a highway with multiple lanes.

The Http2Stream class is a parent class for two other classes: ServerHttp2Stream and ClientHttp2Stream. These are more specific types of Http2Stream that are used on the server side or the client side, respectively.

To create a Http2Stream, you don't create it directly. Instead, you use the Http2Session class, which manages Http2Stream for you. On the server side, you create a Http2Stream when a client sends a request or when you want to send a push message to the client. On the client side, you create a Http2Stream when you make a request to the server or when you receive a push message from the server.

Http2Stream is a "duplex" stream, meaning it can both send and receive data. The "writable" side of the stream is used to send data, and the "readable" side is used to receive data.

By default, Http2Stream uses UTF-8 encoding for text data. If you want to use a different encoding, you need to specify it in the "content-type" header.

Real-World Applications

Http2Stream is used in many real-world applications, including:

Web servers: Http2Stream is used to handle HTTP requests and responses.
Web browsers: Http2Stream is used to communicate with web servers.
Streaming services: Http2Stream is used to stream video and audio content.
Chat applications: Http2Stream is used to send and receive chat messages.

Example

Here's a simplified example of how to use Http2Stream on the server side:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream) => {
  // Handle the stream
});

server.listen(8000);

Here's a simplified example of how to use Http2Stream on the client side:

const http2 = require("http2");

const client = http2.connect("https://example.com");

const req = client.request({ ":path": "/" });

req.on("data", (chunk) => {
  // Handle the data
});

req.on("end", () => {
  // Handle the end of the stream
});

req.end();

HTTP/2 Streams

HTTP/2 introduces the concept of streams, which are bidirectional, independent virtual channels that allow multiplexed communication over a single TCP connection.

Benefits of Streams:

Multiplexing: Allows multiple requests and responses to be sent and received concurrently, increasing efficiency and reducing latency.
Independent: Streams do not share bandwidth, so one slow stream will not affect other streams.
Bidirectional: Both the client and server can send data on the same stream, enabling features like server push.

Stream Lifecycle

1. Stream Creation:

Streams are created by either the client or server. The client creates streams by sending a HEADERS frame, while the server creates streams by sending a PUSH_PROMISE frame.

// Client creates a stream to send a request
const stream = http2Session.request({
  ":path": "/request",
});

// Server creates a stream to send a push promise
const stream = http2Session.pushStream({
  ":path": "/pushed-resource",
});

2. Data Flow:

Once a stream is created, data can be sent and received. Data is sent using DATA frames, which can be fragmented into smaller units.

// Client sends data on the stream
stream.write("Hello world");

// Server receives data on the stream
stream.on("data", (chunk) => {
  console.log(`Received data: ${chunk}`);
});

3. Stream Closure:

Streams are closed when all data has been sent and received. Streams can be closed by either the client or server by sending an END_STREAM frame.

// Client closes the stream
stream.end();

// Server closes the stream
stream.close();

Real-World Applications

1. Multiplexing:

Multiple requests can be sent simultaneously, reducing page load times.
Server push can be used to pre-fetch resources, further improving performance.

2. Stream Prioritization:

Streams can be prioritized, ensuring that critical data is delivered first.
This is useful for applications like video streaming or real-time chat.

3. Bidirectional Communication:

Server push allows servers to proactively send data to clients, enabling features like real-time notifications.
Bidirectional streams can be used for interactive applications like online games or chatbots.

HTTP/2 Streams

HTTP/2 Streams are a way to send and receive data over a network connection. They are used in the HTTP/2 protocol, which is a newer and more efficient version of HTTP.

On the server side, streams are created when a client sends a new HTTP request. Each request is assigned a unique stream ID. The server can then send multiple responses back to the client over the same stream, even if the responses are for different requests.

On the client side, streams are created when a client makes a new HTTP request. The client can then send multiple requests over the same stream, even if the requests are for different resources.

Streams are bidirectional, meaning that data can flow in both directions. This allows for more efficient communication than with HTTP/1.1, which uses separate connections for each request and response.

Real-world applications of HTTP/2 streams include:

Streaming video and audio
Real-time data updates
Server-push

Example: Server-Side

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream, headers) => {
  stream.respond({
    ":status": 200,
    "content-type": "text/html",
  });
  stream.end("<h1>Hello, HTTP/2!</h1>");
});

server.listen(3000);

This code creates an HTTP/2 server that listens on port 3000. When a client sends a request to the server, the server creates a new stream and sends back a response. The response includes a status code of 200, a content type of text/html, and the body of the response is <h1>Hello, HTTP/2!</h1>.

Example: Client-Side

const http2 = require("http2");

const client = http2.connect("http://localhost:3000");

const stream = client.request({
  ":path": "/",
});

stream.on("data", (chunk) => {
  console.log(chunk.toString());
});

stream.on("end", () => {
  client.close();
});

This code creates an HTTP/2 client that connects to the server running on port 3000. The client then sends a request to the server for the root URL (/). The server responds with a status code of 200 and the body of the response is <h1>Hello, HTTP/2!</h1>. The client logs the response to the console.

Destruction of HTTP/2 Streams

What is an HTTP/2 Stream?

HTTP/2 uses streams to handle communication between devices. Imagine a stream as a pipe that carries data back and forth.

When Are Streams Destroyed?

Streams can be destroyed in three ways:

RST_STREAM Frame: The other device sends a special message (RST_STREAM) to close the stream.
http2stream.close() Method: You call this method to close the stream.
http2stream.destroy() or http2session.destroy() Methods: These methods also close the stream.

What Happens When a Stream Is Destroyed?

When a stream is destroyed:

The device tries to send an RST_STREAM message to the other device.
The 'close' event is emitted.
If the stream is still flowing, the 'end' event is also emitted.
If you called http2stream.destroy() with an error, the 'error' event is emitted.

After Destruction:

Once a stream is destroyed:

http2stream.destroyed will be true.
http2stream.rstCode will show the error code of the RST_STREAM message.
You cannot use the stream anymore.

Real-World Code Examples

Example 1: Closing a Stream

const http2 = require("http2");

const client = http2.connect("https://example.com");

const req = client.request({ ":path": "/index.html" });

// When data is received, close the stream
req.on("data", () => {
  req.close();
});

Example 2: Receiving an RST_STREAM Frame

const http2 = require("http2");

const server = http2.createSecureServer();

server.on("stream", (stream, headers) => {
  const error = new Error("Something went wrong");
  stream.sendRSTStream(7, error); // 7 is the error code for protocol error
});

server.listen(443);

Potential Applications

HTTP/2 streams are used in various real-world applications:

Web Browsing: HTTP/2 optimizes web browsing by allowing multiple resources to be loaded simultaneously.
File Downloads: HTTP/2 makes file downloads faster by using multiple connections for a single file.
Video Streaming: HTTP/2 improves video streaming quality by providing better bandwidth utilization.

Simplified Explanation of the 'aborted' Event in Node.js's HTTP/2 Module:

Imagine you're having a conversation over the phone with a friend. Suddenly, the line gets disconnected unexpectedly before you could finish your sentence. That's what the 'aborted' event is like for HTTP/2 streams, which are like phone lines for web communications.

Technical Details:

'aborted' is an event that occurs when an HTTP/2 stream closes unexpectedly while it's still actively sending or receiving data.
The listener for this event doesn't receive any arguments.
The event is only triggered if the stream hasn't been fully closed on the sending end.

Code Example:

const { createServer } = require("http2");

createServer((request, response) => {
  request.on("aborted", () => {
    // Handle the unexpected stream closure
  });

  response.writeHead(200);
  response.end("Hello, World!");
});

Real-World Application:

The 'aborted' event can be useful in scenarios where a stream might be prematurely terminated, such as:

Network errors or connection drops
Client timeouts
Server shutdowns
Malicious attacks

By handling this event, you can log errors, clean up resources, or send notifications to other parts of your application to respond to the unexpected closure.

Potential Implementations:

Logging Errors: Record the fact that a stream was aborted along with any relevant details.
Resource Cleanup: Release any resources that were allocated to the stream, such as buffers or file handles.
Notification to Other Components: Inform other components in your application, such as a message queue or monitoring system, about the aborted stream.

By handling the 'aborted' event effectively, you can improve the reliability and robustness of your HTTP/2 applications.

Event: 'close'

The 'close' event is triggered when an HTTP/2 stream is closed. This can happen for various reasons, such as:

The client or server sending a special message to close the stream.
A network error causing the stream to be lost.
An HTTP error occurring while processing the request.

When the 'close' event happens, the HTTP/2 stream can no longer be used. Its error code can be accessed using the http2stream.rstCode property. If the error code is not NGHTTP2_NO_ERROR (0), an 'error' event will also have been triggered.

Real-world example:

Let's say you have a server that handles HTTP requests and sends responses back to clients. If a client closes their connection prematurely, the 'close' event will be fired on the server's end. This allows the server to release any resources associated with the client's connection and handle any cleanup tasks.

Code example:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream, headers) => {
  stream.on("close", () => {
    console.log(`Stream closed with error code ${stream.rstCode}`);
  });
});

server.listen(8000);

In this example, the 'close' event handler logs the error code of the closed stream. This information can help diagnose any issues that caused the stream to be closed prematurely.

Simplified Explanation:

When you're using HTTP/2, each connection can have multiple streams of data flowing through it. Each stream is like a separate channel for sending and receiving data.

The 'error' event happens when something goes wrong with a stream. For example, if the other end of the connection closes the stream unexpectedly or sends invalid data, the 'error' event will be emitted.

Details:

error: This is the error that occurred. It can be any type of error, such as a TypeError, SyntaxError, or Error.

Code Snippet:

const { Http2Server } = require("http2");

const server = new Http2Server();

server.on("error", (err) => {
  console.error(err);
});

Real-World Examples:

One potential application of the 'error' event is to handle errors that occur when receiving data from a client. For example, if the client sends data that is too large or in the wrong format, the 'error' event can be used to close the stream and send an error response to the client.

const { Http2Server } = require("http2");

const server = new Http2Server();

server.on("error", (err, stream) => {
  if (stream) {
    stream.close();
    stream.respond({
      ":status": 400,
      "content-type": "text/plain",
    });
    stream.end("Invalid data");
  }
});

`'frameError'` Event

Explanation:

When the HTTP/2 library encounters an error while trying to send a frame (a data packet), it emits the 'frameError' event. This error indicates that the library was unable to successfully transmit the frame.

Arguments:

type: An integer representing the type of frame that failed to send.
code: An integer representing the error code associated with the failure.
id: An integer representing the ID of the stream (or 0 if the frame was not associated with any stream).

Real-World Example:

Imagine you're sending a file over the internet using HTTP/2. Each piece of the file is sent in a frame. If there's a problem with the network connection or the frame is too large, the HTTP/2 library may encounter an error and emit the 'frameError' event.

const http2 = require('http2');

const client = http2.connect('https://example.com');

// Define a request handler function
const requestHandler = (req, res) => {
  // Send a frame with large data
  res.write(Buffer.alloc(1024 * 1024));

  // Listen for the 'frameError' event
  res.on('frameError', (type, code, id) => {
    console.error(`Error sending frame. Type: ${type}, Code: ${code}, Id: ${id}`);
  });
};

// Create a new HTTP/2 stream and add the request handler
const stream = client.request({ ':method': 'POST' }, requestHandler);

In this code, if the frame is too large for the network, the res.write() function will throw an error. The 'frameError' event will be emitted, and the error information will be logged to the console.

Potential Applications:

Error handling in HTTP/2 servers and clients.
Debugging and troubleshooting issues with HTTP/2 frame transmission.
Monitoring and collecting metrics on HTTP/2 frame errors.

Event: 'ready'

The 'ready' event is emitted by the Http2Stream object when it has been successfully opened, assigned an ID, and is ready for use.

How it works:

Imagine Http2Stream as a water pipe in your house. When you turn on the tap, the pipe opens and water starts flowing. Once the water is flowing, it means the pipe is ready to use. Similarly, when you create an Http2Stream object, it needs to be opened and assigned an ID before it can be used to send and receive data. The 'ready' event indicates that this process has been completed and the stream is ready for action.

Importance:

The 'ready' event is important because it lets you know when the stream is ready to go. Without this event, you would not be sure if the stream was open and could be used properly.

Example:

Here's an example of how you might use the 'ready' event:

const http2 = require("http2");
const client = http2.connect("https://example.com:443");

client.on("connect", () => {
  console.log("Connected to server");

  // Create a new stream
  const stream = client.request({ ":path": "/" });

  // Wait for the stream to be ready before writing to it
  stream.on("ready", () => {
    console.log("Stream is ready");
    stream.write("Hello, world!");
  });
});

This example creates a new Http2Stream object and listens for the 'ready' event. Once the event is emitted, it signifies that the stream is open and can be used to send data to the server.

Applications:

The 'ready' event is essential for using Http2Stream objects in real-world applications. Here are a few examples:

Sending and receiving data over HTTP/2 connections
Building web servers that use HTTP/2
Creating HTTP/2 clients to interact with remote servers

Simplified Explanation

Event: 'timeout'

What is it?

The 'timeout' event is triggered when there's no activity on an HTTP/2 stream for a certain amount of time. This time is set using the http2stream.setTimeout() method.

Why is it useful?

It helps prevent resources from being wasted on idle streams. For example, a server could use this event to close streams that have been inactive for too long.

How to use it?

You can listen for the 'timeout' event using the on() method:

const http2 = require("http2");

const stream = http2.connect();

stream.on("timeout", () => {
  // Handle timeout
});

Real-World Example

Application:

A web server that handles many HTTP/2 connections.

Code:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream) => {
  stream.setTimeout(30000); // 30 seconds timeout

  stream.on("timeout", () => {
    // Close the stream
    stream.close();
  });
});

server.listen(8080);

Benefits

Improved performance: By closing idle streams, resources are freed up for other tasks.
Increased security: Timeouts can help prevent denial-of-service attacks by closing streams that are not actively used.

Event: `'trailers'`

Explanation:

When you send data using HTTP/2, additional headers can be added to the end of the data stream. These extra headers are called "trailers."

When your code receives trailers from the other end, the 'trailers' event is triggered.

Parameters:

The 'trailers' event passes two parameters:

headers: An object containing the trailer headers.
flags: A number representing the flags associated with the headers.

Code Snippet:

Here's an example of how to listen for the 'trailers' event:

// Create a new HTTP/2 stream.
const stream = http2.connect().stream();

// Listen for the 'trailers' event.
stream.on("trailers", (headers, flags) => {
  console.log("Received trailers:");
  console.log(headers);
  console.log("Flags:", flags);
});

Real-World Application:

Trailers are useful for providing additional information about the data that has been sent. For example, they can be used to indicate the size of the data or to specify the type of data.

Simplified Example:

Imagine you're sending an email with an attachment. The trailer headers could contain information about the size and type of the attachment. This would allow the recipient to know how much time it will take to download the attachment and what program to use to open it.

Event: `'wantTrailers'`

The 'wantTrailers' event is a notification in Node.js's http2 module that is emitted by the Http2Stream class when it has queued the final DATA frame to be sent for a particular HTTP request or response. It essentially signifies that the Http2Stream is ready to receive trailing headers.

Simplified Explanation:

Imagine you're at a restaurant, and you've finished eating your main course. The server comes by to clear your plate, but before they do, you notice that you still have some bread left on the plate. You tell the server that you want to keep the bread, and they add it to your bill. In this scenario, the server is the Http2Stream, the main course is the DATA frames, and the bread is the trailing headers.

Technical Details:

Trailing headers are additional HTTP headers that can be sent after the DATA frames in an HTTP message. These headers typically contain information about the message, such as checksums or timestamps.

The waitForTrailers option must be set to true when initiating a request or response to enable the emission of the 'wantTrailers' event. This allows the Http2Stream to buffer the trailing headers until it receives the notification from the application that it is ready to send them.

Real-World Applications:

Checksum Calculation: Trailing headers can be used to calculate checksums for the entire HTTP message, ensuring data integrity.
Timestamping: Trailing headers can contain timestamps indicating when the message was created or modified.
Custom Metadata: Applications can use trailing headers to send additional metadata or contextual information about the message.

Complete Code Implementation:

const { Http2Session } = require("http2");

const session = Http2Session.connect({
  createConnection: () => net.connect({ port: 8080, host: "localhost" }),
  waitForTrailers: true,
});

session.on("stream", (stream) => {
  stream.on("wantTrailers", () => {
    stream.end(null, {
      foo: "bar",
      baz: "qux",
    });
  });
});

In this example, the waitForTrailers option is set to true on the session. When a request stream is created, the 'wantTrailers' event will be emitted when the stream is ready to receive trailing headers. The application can then send the headers using the stream.end() method.

`http2stream.aborted`

Simplified Explanation:

An Http2Stream can be abnormally ended or "aborted". This property indicates whether the stream has been aborted.

Example:

// Create an HTTP/2 server
const http2 = require('http2');
const server = http2.createSecureServer();

server.on('stream', (stream) => {
  // Check if the stream was aborted
  if (stream.aborted) {
    console.log('Stream was aborted!');
  }

  // Do something with the stream...
});

server.listen(8000);

Real-World Applications:

Aborted streams can occur due to network issues or errors, such as:

A client closing the connection before receiving a response.
A server terminating the stream due to an error.

Potential Applications:

Error Handling: Logging or handling aborted streams can help diagnose network or server issues.
Graceful Shutdown: If a stream is aborted, the server can clean up any resources associated with the stream.

`http2stream.bufferSize`

{number}

This property shows the number of characters currently buffered to be written, specifically for this stream.

In simpler terms, it shows how many characters are waiting to be sent to the other end of the connection.

Potential applications in real world:

Monitoring the buffer size can help identify potential bottlenecks in the communication process.
If the buffer size is too large, it may indicate that the network is congested or the receiving end is slow to process the data.
If the buffer size is too small, it may indicate that the sending end is producing data too quickly or the network is not able to handle the traffic load.

Example:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream, headers) => {
  // Handle the stream and send data
  stream.write("Hello World!");

  // Check the buffer size
  console.log(`Buffer size: ${stream.bufferSize}`);
});

server.listen(8000);

In this example, the server sends the message "Hello World!" to the client. The bufferSize property is logged to the console after sending the data. This helps the developer understand how much data is buffered in the stream and can be used to identify potential bottlenecks in the communication process.

`http2stream.close(code[, callback])`

Description

The close() method of the http2stream class in http2 closes the HTTP/2 stream by sending an RST_STREAM frame to the connected HTTP/2 peer.

Parameters

The close() method takes two parameters:

code (number): An unsigned 32-bit integer identifying the error code. The default value is http2.constants.NGHTTP2_NO_ERROR (0x00).
callback (function): An optional function registered to listen for the 'close' event.

Return value

The close() method returns the Http2Stream instance.

Code sample

The following code sample shows you how to use the close() method:

const { Http2Session } = require("http2");

const session = new Http2Session();

const stream = session.request();

stream.close(http2.constants.NGHTTP2_NO_ERROR);

Real-world applications

The close() method can be used to close an HTTP/2 stream in a variety of situations, such as:

When the stream has been completed successfully.
When the stream has encountered an error.
When the stream is no longer needed.

Potential applications

The close() method can be used in a variety of applications, such as:

Web servers
Web clients
HTTP/2 proxies
HTTP/2 load balancers

Simplified explanation

The close() method is used to tell the other end of the HTTP/2 connection that you are done with the stream. This is important because it allows the other end to clean up any resources that are associated with the stream.

The code parameter is used to indicate why you are closing the stream. The default value is http2.constants.NGHTTP2_NO_ERROR, which means that the stream was closed without any errors.

The callback parameter is an optional function that will be called when the stream has been closed. This function can be used to perform any necessary cleanup on your end.

Improved code sample

The following code sample is a more complete example of how to use the close() method:

const { Http2Session } = require("http2");

const session = new Http2Session();

const stream = session.request();

stream.on("close", () => {
  // The stream has been closed.
});

stream.close(http2.constants.NGHTTP2_NO_ERROR);

`http2stream.closed`

Type: boolean
Description: Indicates whether the Http2Stream instance has been closed.

Example:

const http2 = require("http2");

const server = http2.createServer();
server.on("stream", (stream) => {
  stream.on("close", () => {
    console.log("The stream has been closed.");
  });
});

// The client closes the stream.
stream.end();

Output:

The stream has been closed.

What is http2stream.destroyed?

http2stream.destroyed is a property of Http2Stream objects in Node.js's HTTP/2 module. It indicates whether the stream has been destroyed and is no longer usable.

How to use http2stream.destroyed?

You can check the value of http2stream.destroyed to determine if the stream has been destroyed. For example:

const http2 = require('http2');

const server = http2.createServer();

server.on('stream', (stream) => {
  stream.on('close', () => {
    console.log(`Stream ${stream.id} is destroyed: ${stream.destroyed}`);
  });
});

When is http2stream.destroyed set to true?

http2stream.destroyed is set to true when the stream is closed or destroyed. This can happen for a variety of reasons, such as:

The client or server closes the connection.
The stream receives a RST_STREAM frame.
The stream times out.
The stream is destroyed explicitly using the destroy() method.

Why is http2stream.destroyed useful?

http2stream.destroyed is useful because it allows you to determine if a stream is still usable. This is important for performing cleanup tasks, such as closing file descriptors or releasing memory.

Real-world applications of http2stream.destroyed

http2stream.destroyed can be used in a variety of real-world applications, such as:

Closing file descriptors: When a stream is destroyed, you can close any file descriptors that are associated with the stream. This helps to prevent resource leaks.
Releasing memory: When a stream is destroyed, you can release any memory that is associated with the stream. This helps to improve performance.
Performing cleanup tasks: When a stream is destroyed, you can perform any other cleanup tasks that are necessary. For example, you could log the event or notify other parts of your application.

`http2stream.endAfterHeaders`

Simplified Explanation:

Imagine a conversation between a client and a server using HTTP/2. When the client sends a request to the server, it can indicate whether it expects the server to send any more data after the initial response headers. This is controlled by the END_STREAM flag in the request's HEADERS frame.

If the END_STREAM flag is set, it means that the server will not send any additional data for that request. The endAfterHeaders property of the corresponding Http2Stream object will be set to true to indicate this.

Detailed Explanation:

HTTP/2 is a protocol for efficient communication over a network. It uses multiple streams to transfer data in parallel, and each stream is represented by an instance of Http2Stream.

When a client sends a request to a server, it includes a HEADERS frame. This frame contains the request's headers and also includes the END_STREAM flag. If the END_STREAM flag is set, it indicates that the client does not expect the server to send any more data in response to that request.

Example:

const http2 = require("http2");

const client = http2.connect("https://example.com");

client.on("stream", (stream) => {
  stream.on("headers", (headers) => {
    if (stream.endAfterHeaders) {
      // The server has indicated that there will be no more data for this response.
    }
  });
});

Real-World Applications:

The endAfterHeaders property is useful for optimizing network performance. If the server knows that it will not be sending any more data for a particular request, it can close the corresponding stream immediately. This frees up resources on both the client and server sides.

Potential Applications:

Static content delivery: When serving static content from a web server, the server can set the END_STREAM flag in the HEADERS frame to indicate that there is no additional data to be sent. This allows the client to receive the content as quickly as possible.
API responses: When an API endpoint returns a JSON response with no additional data, the server can set the END_STREAM flag to optimize performance.

`http2stream.id`

{number|undefined}

The numeric stream identifier of this Http2Stream instance. Set to undefined if the stream identifier has not yet been assigned.

Simplified Explanation:

http2stream.id is a unique number that identifies a specific stream within an HTTP2 connection. Each stream is like a separate channel of communication between the client and server, and this ID helps to differentiate between them.

Real-World Example:

Consider a website with multiple sections, such as a news feed, a chat window, and a video player. Each of these sections could use a separate HTTP2 stream. The news feed stream would have its own unique http2stream.id, while the chat window and video player would have their own IDs.

This allows the server to send data to the correct section of the website without mixing up the content. For example, if the server receives a message to update the news feed, it can use the http2stream.id to identify the appropriate stream and deliver the update.

Potential Applications:

Multiplexing: Allows multiple requests and responses to be sent and received simultaneously on a single connection.
Prioritization: Streams can be prioritized, so that critical data can be sent faster than non-critical data.
Flow control: Prevents one side from sending data faster than the other side can handle it.

`http2stream.pending`

Variable Type: Boolean
Default Value: False

The http2stream.pending property indicates whether the HTTP/2 stream has been assigned a numeric stream identifier.

Simplified Explanation:

Imagine you have a group of people at a party, and you need to give each person a unique number to identify them. Before you can give them the numbers, you have to figure out how many people there are. The pending property is like a flag that tells you if you still need to figure out how many people there are before you can assign numbers.

Code Snippet:

const { Http2ServerRequest } = require("http2");

const server = http2.createSecureServer();
server.on("stream", (stream, headers, flags) => {
  if (stream.pending) {
    // The stream has not yet been assigned a stream identifier.
  } else {
    // The stream has been assigned a stream identifier.
  }
});

Real-World Example:

When a client sends a request to an HTTP/2 server, the server will create a new HTTP/2 stream to handle the request. Initially, the stream will have a pending property set to true. Once the server has assigned a stream identifier to the stream, the pending property will be set to false.

Potential Applications:

Tracking the progress of stream assignment: You can use the pending property to track the progress of stream assignment. This can be useful for debugging or performance monitoring.
Preventing duplicate stream assignments: You can use the pending property to prevent duplicate stream assignments. This can happen if the server receives multiple requests for the same stream before it has assigned a stream identifier to the stream.

HTTP/2 Streams and Priority

HTTP/2 is a protocol that allows for multiple requests and responses to be sent and received simultaneously over a single connection. Each request and response is handled by a separate stream.

The priority of a stream determines how it is handled in relation to other streams. A higher priority stream will be given more resources (e.g., bandwidth) than a lower priority stream.

http2stream.priority(options)

The http2stream.priority() method allows you to update the priority of a stream. It takes an options object with the following properties:

exclusive: When set to true, this stream becomes the sole direct dependency of its parent stream, and all other existing dependents are made a dependent of this stream. Default: false.
parent: The numeric identifier of the stream that this stream is dependent on.
weight: A number between 1 and 256 (inclusive) that specifies the relative dependency of this stream in relation to other streams with the same parent.
silent: When set to true, the priority changes are made locally without sending a PRIORITY frame to the connected peer. Default: false.

Usage

To update the priority of a stream, you can use the following code:

const { Http2Server } = require("http2");
const server = new Http2Server();

server.on("stream", (stream, headers) => {
  // Update the priority of the stream
  stream.priority({
    parent: 1, // The stream with ID 1 is the parent of this stream
    weight: 256, // This stream has the highest priority among its siblings
    exclusive: true, // This stream is the sole direct dependency of its parent
  });
});

Real-World Applications

Priority can be used to prioritize certain requests and responses over others. For example, a web server could use priority to ensure that critical requests, such as loading the home page, are handled before less important requests, such as loading images.

Potential Applications

Prioritizing real-time data over non-real-time data in a streaming application.
Ensuring that critical requests are handled before less important requests in a web application.
Optimizing the performance of a server by giving priority to requests from high-paying customers.

`http2stream.rstCode`

The http2stream.rstCode property represents the error code that was received when the Http2Stream was closed. This error code indicates the reason why the stream was closed.

The rstCode property is set to one of the following values:

0: The stream was closed normally.
1: The stream was closed due to a protocol error.
2: The stream was closed due to an internal error.
3: The stream was closed due to a flow control error.
4: The stream was closed due to a stream limit error.
5: The stream was closed due to a connection error.
6: The stream was closed due to an enhancement error.
7: The stream was closed due to a compression error.

The rstCode property can be used to determine the reason why a stream was closed. This information can be useful for debugging purposes.

Real-world example:

The following code snippet shows how to use the http2stream.rstCode property to determine the reason why a stream was closed:

const http2 = require('http2');

const server = http2.createServer();

server.on('stream', (stream) => {
  stream.on('close', (rstCode) => {
    console.log(`Stream closed with error code: ${rstCode}`);
  });
});

server.listen(8000);

In this example, the http2.createServer() function is used to create a new HTTP/2 server. The server.on('stream') event listener is used to listen for new streams. When a new stream is created, the stream.on('close') event listener is used to listen for the stream to be closed. When the stream is closed, the rstCode parameter will be set to the error code that was received when the stream was closed.

Potential applications

The http2stream.rstCode property can be used to debug HTTP/2 applications. For example, if a stream is closed unexpectedly, the rstCode property can be used to determine the reason why the stream was closed. This information can help to identify and fix problems with HTTP/2 applications.

http2stream.sentHeaders

Explanation: When an HTTP/2 stream is created, headers are exchanged between the client and server. http2stream.sentHeaders contains the headers that were sent from the server to the client.

Real-World Implementation:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream) => {
  stream.respond({
    ":status": 200,
    "content-type": "text/plain",
  });

  stream.end("Hello, world!");

  console.log(stream.sentHeaders); // Will contain the outbound headers sent to the client
});

Applications:

Debugging HTTP/2 communication
Verifying that the correct headers were sent to the client

http2stream.sentInfoHeaders

Explanation:

When you send data using HTTP/2, you can include additional headers that provide more information about the request or response. These headers are called "informational headers" or "additional headers."

sentInfoHeaders is a property of the Http2Stream object. It contains an array of objects representing all the informational headers that were sent for the current stream.

Simplified Analogy:

Imagine you're sending a birthday present in a gift box. The box has a label with the recipient's name and address. This is like the main headers.

But you also want to include a note saying, "Happy Birthday!" and a list of the gift items inside. These extra messages are like informational headers. They provide additional details but are not essential for delivering the gift.

Real-World Applications:

Informational headers can be used for various purposes, such as:

Providing more context about the request or response
Debugging and troubleshooting
Monitoring and logging

Example Code:

const http2 = require("http2");

// Create an HTTP/2 server
const server = http2.createServer();

// Handle incoming requests
server.on("request", (request, response) => {
  // Send a response with informational headers
  response.writeHead(200, {
    "Content-Type": "text/html",
    // Custom informational header
    "X-Custom-Header": "Hello, world!",
  });

  // End the response
  response.end("<h1>Hello, world!</h1>");
});

// Start the server
server.listen(8000);

In this example, we're sending a custom informational header called X-Custom-Header with the value Hello, world!. By checking the sentInfoHeaders property of the corresponding Http2Stream object, you can access and process these additional headers.

HTTP/2 Outbound Trailers

HTTP/2 trailers are a set of key-value pairs that are sent at the end of a request or response to provide additional information about the message. In Node.js's http2 module, the sentTrailers property of an HttpStream object represents the outbound trailers that were sent for that stream.

How to Use sentTrailers

To access the outbound trailers for a stream, you can use the sentTrailers property of the stream object. This property will contain an object with the trailer key-value pairs, where the keys are strings and the values are strings or buffers.

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream) => {
  stream.on("trailers", (trailers) => {
    console.log(trailers); // { 'content-type': 'text/plain' }
  });
});

Real-World Applications

Outbound trailers can be used to provide additional information about a request or response. For example, they could be used to specify the encoding of the response body or to provide a checksum for the data.

One potential application of outbound trailers is in content negotiation. A client can send trailers with a request to specify the preferred encoding or language for the response. The server can then use these trailers to select the appropriate content to send back to the client.

Another potential application of outbound trailers is in error handling. A server can send trailers with a response to provide additional information about the error that occurred. This information can be helpful for debugging purposes.

`http2stream.session`

Http2Session

The session property of the Http2Stream class refers to the Http2Session instance that owns the stream. After the stream is destroyed, the value of the session property will be set to undefined.

Simplified Explanation

A stream in the HTTP/2 protocol is always associated with a session. A session is a connection between two endpoints that can have multiple streams. When a stream is created, it is assigned to a specific session. The session property of the stream provides access to the session that owns the stream.

Code Snippet

const { Http2Session, Http2ServerRequest } = require("http2");

const server = http2.createServer();

server.on("stream", (stream, headers) => {
  // `stream.session` refers to the session that owns the stream
  const session = stream.session;
});

Real-World Applications

The session property is useful for scenarios where you need to access the session associated with a stream. For example, you might need to access the session to:

Get the session ID
Get the session settings
Get the session's list of active streams
Close the session

Potential Applications

Load balancing: Use the session ID to distribute incoming requests across multiple instances of a service.
Error handling: Access the session's list of active streams to identify and terminate streams that are experiencing errors.
Session management: Close the session when all of its streams have been destroyed.

Summary:

The setTimeout() method allows you to specify a timeout for an HTTP/2 stream. If the stream is inactive for the specified amount of time, the method invokes a callback function. This helps prevent the stream from hanging indefinitely.

Details:

Parameters:

msecs: The number of milliseconds after which to invoke the callback.
callback: The function to execute when the timeout expires. It receives no arguments.

Usage:

To set a timeout for a stream, call the setTimeout() method on the stream object. Pass in the desired timeout value in milliseconds and a callback function to be executed when the timeout expires.

const http2 = require("http2");
const client = http2.connect("http://example.org:8000");
const { NGHTTP2_CANCEL } = http2.constants;
const req = client.request({ ":path": "/" });

// Cancel the stream if there's no activity after 5 seconds
req.setTimeout(5000, () => req.close(NGHTTP2_CANCEL));

In this example, a timeout of 5 seconds is set for the stream. If there is no activity on the stream for 5 seconds after the method is called, the callback function will be executed. The callback function in this case closes the stream with the NGHTTP2_CANCEL error code.

Real-World Applications:

Setting timeouts for HTTP/2 streams can help prevent performance issues and improve overall reliability. For example, if a server or client is slow to respond, the stream can be automatically closed after a certain amount of time to prevent it from blocking other requests.

Improved Code Example:

The following example demonstrates how to use setTimeout() to automatically retry a request after a timeout:

const http2 = require("http2");
const client = http2.connect("http://example.org:8000");
const { NGHTTP2_CANCEL } = http2.constants;
const req = client.request({ ":path": "/" });

// Set a timeout of 5 seconds for the request
req.setTimeout(5000, () => {
  // If the timeout expires, close the request and retry
  req.close(NGHTTP2_CANCEL);
  client.request(req.headers);
});

In this example, if the request does not complete within 5 seconds, the stream is closed and the request is retried. This helps ensure that requests are not lost due to unexpected delays.

`http2stream.state`

Explanation

The http2stream.state object provides information about the current state of an HTTP/2 stream. This includes:

localWindowSize: The number of bytes that the other side can send before we need to send a WINDOW_UPDATE frame.
state: A low-level code indicating the stream's state as determined by the nghttp2 library.
localClose: A flag indicating whether the stream has been closed locally.
remoteClose: A flag indicating whether the stream has been closed remotely.
sumDependencyWeight: The sum of the weights of all streams that depend on this stream.
weight: The stream's priority weight.

Real-World Example

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream) => {
  stream.on("stateChange", (state) => {
    console.log("Stream state changed:", state);
  });
});

server.listen(8000);

In this example, we create an HTTP/2 server and listen on port 8000. When a stream is created, we attach a listener to the stateChange event. This event will fire whenever the stream's state changes. We log the new state to the console.

Potential Applications

The http2stream.state object can be used to track the progress of a stream and to make decisions about how to handle it. For example, if a stream is in the CLOSED state, we know that we can no longer send or receive data on it.

Another potential application is to use the sumDependencyWeight property to prioritize streams. Streams with a higher weight will be given more resources, such as bandwidth.

Simplified Explanation

Imagine you are playing a video game with a friend. Your friend is sending you data over the internet. The http2stream.state object is like a dashboard that shows you information about the data transfer. It tells you how much data you have received, whether the data transfer is still in progress, and how much data your friend can still send before you need to tell them to stop.

`http2stream.sendTrailers(headers)`

Explanation

The sendTrailers method is used in HTTP/2 to send additional headers (called trailers) after the request or response body has been sent. Trailers are used to provide additional information about the request or response, such as the content encoding or the transfer-encoding.

How to Use

To use the sendTrailers method, you first need to create an HTTP/2 stream using the http2.connect function. Once you have a stream, you can send trailers by calling the sendTrailers method with an object containing the trailer headers. The stream will then be closed automatically.

// Create an HTTP/2 client
const client = http2.connect("https://example.com");

// Create a new request stream
const stream = client.request({
  ":method": "GET",
  ":path": "/",
});

// Send trailers after the request body has been sent
stream.on("data", () => {
  stream.sendTrailers({
    "content-encoding": "gzip",
  });
});

Real-World Applications

Trailers are commonly used in the following scenarios:

To provide information about the content encoding of a response body.
To provide information about the transfer-encoding of a response body.
To provide additional information about a request or response that cannot be fit into the initial headers.

Potential Applications

Content encoding: Trailers can be used to specify the content encoding of a response body, which can help to reduce the size of the response and improve performance.
Transfer encoding: Trailers can be used to specify the transfer encoding of a response body, which can help to improve performance and reliability.
Additional information: Trailers can be used to provide additional information about a request or response that cannot be fit into the initial headers. For example, trailers can be used to provide information about the user agent or the origin of a request.

Class: ClientHttp2Stream

Purpose:

The ClientHttp2Stream class in Node.js's HTTP/2 module is designed specifically for use on HTTP/2 clients. It extends the Http2Stream class, which is the base class for all HTTP/2 streams.

Key Features:

Provides events like 'response' and 'push', which are only relevant on the client side.
Allows clients to receive and handle HTTP/2 responses and pushed resources.

Example:

Here's a simple example of using ClientHttp2Stream to create an HTTP/2 GET request:

const http2 = require("http2");

// Create an HTTP/2 client and connect to a remote server
const client = http2.connect("https://example.com");

// Create a new HTTP/2 stream
const stream = client.request({
  ":method": "GET",
  ":path": "/",
});

// Listen for the 'response' event to receive the HTTP/2 response
stream.on("response", (headers, flags) => {
  console.log(`Received response with headers: ${JSON.stringify(headers)}`);
});

// Listen for the 'data' event to receive data from the response
stream.on("data", (chunk) => {
  console.log(`Received data: ${chunk.toString()}`);
});

// Listen for the 'end' event to indicate the end of the response
stream.on("end", () => {
  console.log("Done receiving response");
});

Potential Applications:

Building high-performance HTTP/2 clients for web applications and services.
Utilizing HTTP/2 features like stream multiplexing and server push for improved website and application responsiveness.

Event: 'continue'

The 'continue' event is emitted by the http2 module when the server sends a 100 Continue status code. This usually happens when the request contains an Expect: 100-continue header, which indicates that the client is expecting the server to acknowledge that it's ready to receive the request body.

Simplified Explanation:

When you make a request to a server, the server can respond with a 100 Continue status code. This means that the server is ready to receive the body of your request. The 'continue' event is emitted when the client receives a 100 Continue status code, allowing it to continue sending the request body.

Real World Example:

A real-world example of using the 'continue' event would be when you're uploading a large file to a server. The client would send a request with the Expect: 100-continue header, and the server would respond with a 100 Continue status code. The client would then continue sending the file data to the server.

Code Example:

const http2 = require("http2");

// Create a client
const client = http2.connect("https://example.com");

// Send a request with the Expect: 100-continue header
const req = client.request({
  ":method": "POST",
  ":path": "/",
  expect: "100-continue",
});

// Listen for the 'continue' event
req.on("continue", () => {
  // Send the request body
  req.write("Hello, world!");
  req.end();
});

Potential Applications:

The 'continue' event can be used in any situation where the client needs to know that the server is ready to receive the request body. This is especially useful for large file uploads or other requests that could take a long time to complete.

Event: `'headers'`

headers {HTTP/2 Headers Object}
flags {number}

The 'headers' event is emitted when an additional block of headers is received for a stream. This can happen when a block of 1xx informational headers is received. The listener callback is passed the [HTTP/2 Headers Object][] and flags associated with the headers.

Example

const { Http2Session } = require('http2');

const session = new Http2Session();

session.on('headers', (headers, flags) => {
  console.log(headers);
});

session.receive({
  :status: 200,
  'content-type': 'text/plain'
});

// {
//   ':status': '200',
//   'content-type': 'text/plain'
// }

Real-World Applications

The 'headers' event can be used to handle additional blocks of headers that are received for a stream. This can be useful for handling 1xx informational headers or for handling trailers that are sent at the end of a stream.

Potential Applications

Handling 1xx informational headers
Handling trailers
Customizing HTTP/2 header processing

'push' Event

The 'push' event is emitted when a server sends a Push Stream. A Push Stream is a special type of HTTP/2 stream that allows the server to send additional responses to the client without the client having to request them.

This can be useful for sending related content to the client, such as images, stylesheets, or scripts.

Parameters

The 'push' event is passed the following parameters:

headers: An object representing the HTTP/2 headers for the Push Stream.
flags: A number representing the flags associated with the headers.

Example

The following code shows how to listen for the 'push' event:

const http2 = require("http2");

const client = http2.connect("https://example.com");

client.on("push", (headers, flags) => {
  console.log(headers);
});

When the server sends a Push Stream, the 'push' event will be emitted and the headers and flags parameters will be passed to the callback function.

Applications

Push Streams can be used for a variety of applications, such as:

Preloading resources: The server can send Push Streams for resources that the client is likely to need in the future. This can speed up the loading of the page.
Sending related content: The server can send Push Streams for related content, such as images, stylesheets, or scripts. This can help to create a more immersive experience for the user.
Updating content: The server can send Push Streams to update content on the client. This can be useful for keeping the client's view of the data up to date.

Event: 'response'

Explanation:

When sending an HTTP/2 request, the client expects a response from the server. The 'response' event is triggered when the server sends the headers of this response.

Arguments:

headers: An object containing the HTTP/2 headers sent by the server.
flags: A number representing additional information about the response headers.

Code Snippet:

const http2 = require("http2");
const client = http2.connect("https://example.com");

const req = client.request({ ":path": "/" });
req.on("response", (headers, flags) => {
  console.log(`Status code: ${headers[":status"]}`);
});

Real-World Application:

When sending an HTTP/2 request to fetch a web page, the 'response' event will be triggered when the server sends the HTML code of the web page.

Flags:

The flags parameter can have the following values:

0x1: End of stream, indicating that the headers are the last frame of the response.
0x4: Push promise, indicating that the server is sending additional resources that may be needed to fulfill this request.

Potential Applications:

Monitoring the performance of HTTP/2 requests by measuring the time between sending the request and receiving the response headers.
Handling push promises to prefetch resources and improve page loading speed.

Class: ServerHttp2Stream

Explanation:

A ServerHttp2Stream is a type of stream used in HTTP/2 and is specifically designed for servers. It provides additional methods compared to Http2Stream, which is used on both servers and clients.

Extension of Http2Stream:

ServerHttp2Stream inherits all the properties and methods of Http2Stream, but it does not have access to the properties and methods that are exclusive to Http2Stream on the client.

Additional Server-Specific Methods:

http2stream.pushStream(): Send data to the client without the client requesting it. This is useful for sending prefetch hints, comet messages, or server-driven updates.
http2stream.respond(): Send a response back to the client.

Real-World Applications:

PushStream: A news website can push breaking news updates to subscribers without them having to manually refresh the page.
Respond: A server can respond to client requests with additional metadata or custom headers.

Example of Creating a ServerHttp2Stream:

const http2 = require("http2");
const server = http2.createServer();

server.on("stream", (stream) => {
  // stream is a ServerHttp2Stream object
});

Example of Using PushStream:

const http2 = require("http2");
const server = http2.createServer();

server.on("stream", (stream) => {
  stream.pushStream((err, pushStream) => {
    if (err) {
      console.error("Failed to create a push stream:", err);
    } else {
      pushStream.respond({
        "Content-Type": "text/html",
        ":status": 200,
      });
      pushStream.end("<h1>Hello from your push stream!</h1>");
    }
  });
});

Example of Using Respond:

const http2 = require("http2");
const server = http2.createServer();

server.on("stream", (stream) => {
  stream.respond({
    "Content-Type": "text/html",
    ":status": 200,
  });
  stream.end("<h1>Hello from your server!</h1>");
});

`http2stream.additionalHeaders(headers)`

Purpose: Sends additional informational HEADERS frame to the connected HTTP/2 peer.
Parameters:
- headers: An object containing HTTP/2 headers.

Simplified Explanation

After establishing an HTTP/2 connection, you can send additional HEADERS frames to provide extra information about the current request or response. This is useful for sending things like progress updates or additional metadata.

Example

const http2 = require("http2");

const client = http2.connect("https://example.com");

const request = client.request({
  ":method": "GET",
  ":path": "/",
});

// Send an additional HEADERS frame with a progress update
request.additionalHeaders({
  "x-progress": "50%",
});

request.on("response", (headers) => {
  console.log(headers);
});

request.on("finish", () => {
  client.close();
});

Real-World Applications

Progress updates: You can use additional HEADERS frames to send progress updates to the client. This is especially useful for large downloads or uploads.
Additional metadata: You can use additional HEADERS frames to send additional metadata about the request or response. This could include things like the content type, encoding, or language.

Simplified Explanation of headersSent Property

The headersSent property in Node.js's http2 module is a read-only boolean value that indicates whether HTTP/2 headers have been sent for the current stream.

In Plain English:

Imagine you're sending a letter in the mail. Before you put the letter in the envelope and address it, you need to write the recipient's address on the envelope. In HTTP/2, the "envelope" is the headers, and the "address" is the information about the receiver (like the URL). The headersSent property tells you if you've already written the address on the envelope (i.e., sent the headers).

Code Snippet:

const { Http2ServerRequest, Http2ServerResponse } = require("http2");

const server = http2.createServer();

server.on("stream", (stream, headers) => {
  if (stream.headersSent) {
    // Headers have already been sent for this stream
  } else {
    // Headers have not yet been sent
  }
});

Real-World Applications:

Controlling the timing of header sending: You might want to delay sending headers until you have more data available to reduce the number of header updates.
Error handling: If an error occurs while sending headers, you can check the headersSent property to see if the headers were actually sent.

Potential Applications:

Streaming large files: Instead of sending the entire file in one go, you can stream it in chunks. By checking the headersSent property, you can ensure that the headers are sent before the first chunk is sent.
API endpoints: You can use the headersSent property to control when and how headers are sent in response to API requests.

`http2stream.pushAllowed`

Simplified Explanation

HTTP/2 push streams allow a server to send content to a client without the client having to explicitly request it. This can improve performance by reducing the number of requests that need to be made.

The pushAllowed property tells you whether the client you're connected to supports push streams. It will be true if they do, and false if they don't.

Detailed Explanation

HTTP/2 push streams are a way to improve the performance of web pages by allowing the server to send content to the client before the client even requests it. This can be useful for things like preloading images or CSS stylesheets that are likely to be needed by the client.

To use push streams, the server must first send a SETTINGS frame to the client with the SETTINGS_ENABLE_PUSH flag set to true. If the client supports push streams, it will respond with a SETTINGS frame of its own with the SETTINGS_ENABLE_PUSH flag set to true.

Once push streams are enabled, the server can send push promises to the client. A push promise is a promise to send a push stream. The push promise includes the headers for the push stream, and the client can use these headers to decide whether or not to accept the push stream.

If the client accepts the push stream, the server will send the push stream to the client. The client can then use the data from the push stream to render the content on the web page.

The pushAllowed property tells you whether the client you're connected to supports push streams. It will be true if they do, and false if they don't.

Code Examples

The following code shows how to check if the client supports push streams:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream) => {
  if (stream.pushAllowed) {
    // The client supports push streams.
  } else {
    // The client does not support push streams.
  }
});

The following code shows how to send a push stream to the client:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream) => {
  if (stream.pushAllowed) {
    const pushStream = stream.pushStream({ ":path": "/style.css" });
    pushStream.respondWithFile("/style.css");
  }
});

Real-World Applications

HTTP/2 push streams can be used to improve the performance of web pages by reducing the number of requests that need to be made. This can be especially useful for things like preloading images or CSS stylesheets that are likely to be needed by the client.

One potential application of HTTP/2 push streams is to improve the performance of e-commerce websites. E-commerce websites often have a lot of images and CSS stylesheets that need to be loaded before the page can be rendered. By using HTTP/2 push streams, the server can send these files to the client before the client even requests them, which can reduce the amount of time it takes for the page to load.

Another potential application of HTTP/2 push streams is to improve the performance of mobile web pages. Mobile devices often have limited bandwidth and processing power, so reducing the number of requests that need to be made can help to improve the performance of web pages on mobile devices.

HTTP/2 Push Streams

Imagine you're browsing a website and you click on a link that loads a new page. However, before the new page loads, the website sends you some additional resources, such as images or stylesheets, that you might need for the new page. This way, when you open the new page, it loads faster since the resources are already downloaded. This process is called HTTP/2 push streaming.

Initiating a Push Stream

To initiate a push stream, use the http2stream.pushStream() method. This method takes a few parameters:

Headers: This is an object that contains information about the new stream, such as the path to the resource and the HTTP status code.
Options: This is an optional object that can contain additional settings for the push stream, such as whether it should be the exclusive dependent of its parent stream.
Callback: This is a function that will be called once the push stream has been created.

Example

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream) => {
  stream.respond({ ":status": 200 });
  stream.pushStream({ ":path": "/" }, (err, pushStream, headers) => {
    if (err) throw err;
    pushStream.respond({ ":status": 200 });
    pushStream.end("some pushed data");
  });
  stream.end("some data");
});

In this example, the server responds to the client's request with the status code 200 (OK). It then initiates a push stream for the root path '/'. The push stream is created with the status code 200 and the payload 'some pushed data'. The client will receive the pushed data before it receives the response to its original request.

Applications in the Real World

HTTP/2 push streaming is used in many real-world applications:

Preloading resources: Websites can push resources, such as images or scripts, to the client before the user clicks on a link to a new page. This way, the resources are already downloaded when the user opens the new page, making the page load faster.
Background fetching: Websites can push updates to the client in the background, without the user having to refresh the page. This is useful for applications that need to display real-time data, such as stock quotes or news feeds.
Personalized content: Websites can push personalized content to the client based on their browsing history or preferences. This allows websites to provide a more tailored experience for each user.

`http2stream.respond([headers[, options]])`

This method is part of Node.js's http2 module and is used to respond to an incoming HTTP/2 stream.

Simplified Explanation:

When receiving a request from a client over an HTTP/2 connection, the server can use the respond method to send a response back. This method allows the server to specify the response headers and optionally indicate whether the response will have any payload data.

Detailed Explanation:

The respond method takes an optional headers object as its first argument. This object specifies the HTTP/2 headers that will be sent in the response. The headers object can contain any valid HTTP/2 header fields, such as ':status', 'content-type', and custom headers.

The respond method also takes an optional options object as its second argument. This object can contain the following options:

endStream: If set to true, indicates that the response will not include any payload data. This is useful for responses that only need to send headers, such as 204 No Content responses.
waitForTrailers: If set to true, the Http2Stream will emit the 'wantTrailers' event after the final DATA frame has been sent. This allows the server to send trailing header fields to the client after the payload data has been sent.

Real World Complete Code Implementation:

const http2 = require("node:http2");
const server = http2.createServer();
server.on("stream", (stream) => {
  // Send a 200 OK response with some data
  stream.respond({ ":status": 200 }, { waitForTrailers: true });
  stream.on("wantTrailers", () => {
    // Send trailing headers after payload data
    stream.sendTrailers({ "X-Custom-Trailer": "some value" });
  });
  stream.end("Hello World!");
});

Potential Applications:

The respond method is essential for building HTTP/2 servers. It allows the server to send responses to incoming requests, including responses with payload data and trailing header fields. HTTP/2 is a modern protocol that provides performance and efficiency benefits over HTTP/1.1, and the respond method helps to harness these benefits.

`http2stream.respondWithFD(fd[, headers[, options]])`

Summary:

Responds to an HTTP/2 request by reading data from a file descriptor.

Parameters:

fd: A file descriptor or FileHandle to read data from.
headers (optional): HTTP/2 headers to send in the response.
options (optional): Additional options:
- statCheck: A function to perform additional checks on the file descriptor.
- waitForTrailers: Wait for trailers to be sent before closing the stream.
- offset: The starting position to read data from.
- length: The maximum amount of data to read.

How it works:

This method creates a response stream and starts reading data from the given file descriptor. As data is read, it is sent to the client.

Code Snippet:

const http2 = require("http2");
const fs = require("fs");

const server = http2.createServer();
server.on("stream", (stream) => {
  const fd = fs.openSync("/path/to/file", "r");
  const headers = {
    "content-length": fs.fstatSync(fd).size,
    "content-type": "text/plain",
  };
  stream.respondWithFD(fd, headers);
});

Real-World Applications:

Serving static files efficiently.
Streaming large amounts of data without buffering in memory.
Supporting partial content requests (HTTP Range).

Additional Notes:

The file descriptor or FileHandle should not be closed during the response.
If waitForTrailers is set to true, the stream will wait for trailers to be sent before closing.
Using the same file descriptor concurrently for multiple streams is not supported.

HTTP2: Respond with a File

HTTP2 is a network protocol for sending data quickly and efficiently. It's often used for web pages and streaming media.

respondWithFile()

This method lets you quickly send a file as the response to an HTTP2 request.

Arguments:

path: The path to the file you want to send. It can be a regular file or a URL.
headers (optional): Extra headers to add to the response. This could include things like content-type or cache-control.
options (optional):
- statCheck: A function that allows you to check the file's metadata and set additional headers based on that information.
- onError: A function that handles errors that occur while trying to read the file.
- waitForTrailers: When set to true, the method will wait for you to send any trailing headers before closing the stream.
- offset: The starting point from where to read the file.
- length: The number of bytes to read from the file.

Example:

const http2 = require("node:http2");
const server = http2.createServer();

server.on("stream", (stream) => {
  stream.respondWithFile("/path/to/file.txt");
});

This will send the file /path/to/file.txt as the response to the HTTP2 request.

Real-World Applications:

Sending images, videos, or other files as responses to web requests.
Creating file-sharing applications where users can upload and download files through HTTP2.
Streaming large files, such as movies or software updates, to clients.

Benefits:

Fast and efficient file transfer.
Allows for additional headers and options to customize the response.
Can be used in conjunction with HTTP Range requests to support partial file transfer.
Supports trailing headers when waitForTrailers is enabled.

Class: Http2Server

Simplified Explanation:

Imagine you're running an online store, and your customers want to send orders and payments over the internet. For this, you need a secure and efficient way to communicate with your customers' devices. Http2Server helps you do that.

Technical Details:

Http2Server is like a virtual server that runs on your computer. It listens for special requests called HTTP/2 requests from other devices (like customers' browsers or mobile apps).
HTTP/2 is a newer and faster way to send and receive data over the internet compared to the earlier HTTP protocol.
When a customer sends an HTTP/2 request, Http2Server processes it, sends back a response, and closes the connection. The connection is later automatically re-established as needed, making it efficient and faster for subsequent requests.

Real-World Code Example:

const http2 = require("http2");

// Create an `Http2Server` instance
const server = http2.createServer();

// Handle HTTP/2 requests
server.on("request", (req, res) => {
  res.writeHead(200, { "Content-Type": "text/plain" });
  res.end("Hello, HTTP/2!");
});

// Listen for incoming HTTP/2 connections on port 8443
server.listen(8443);

Potential Applications in Real World:

E-commerce websites to handle secure and fast online transactions.
Online streaming platforms to deliver high-quality video and audio content efficiently.
Instant messaging applications to provide a real-time and responsive communication experience.

Event: 'checkContinue'

When a client sends an HTTP request with an "Expect: 100-continue" header, it means that the client wants to send a large request body and is waiting for the server to tell it if it can continue sending the request. The server can respond with a 100 Continue status code to indicate that the client should continue sending the request body, or it can respond with an appropriate HTTP response code (e.g., 400 Bad Request) if the client should not continue sending the request body.

Example:

const http2 = require("http2");

const server = http2.createServer((request, response) => {
  if (request.headers["expect"] === "100-continue") {
    // Server can continue sending request body

    // Tell the client to continue sending the request body
    response.writeContinue();
  } else {
    // Server cannot continue sending request body

    // Send an appropriate HTTP response code
    response.writeHead(400, "Bad Request");
    response.end();
  }
});

server.listen(8000);

Real-World Applications:

This event is used to handle HTTP requests that may have large request bodies. By responding with a 100 Continue status code, the server can ensure that the client does not waste time and resources sending a large request body that the server will not accept.

Event: 'connection'

Simplified Explanation:

When a new connection is made to the HTTP/2 server, this event is triggered. The socket parameter represents the TCP stream over which the data is being sent and received.

Detailed Explanation:

HTTP/2 is a protocol for transmitting data over a TCP connection. When a client connects to an HTTP/2 server, a new TCP stream is established. The 'connection' event is emitted on the server side when this new stream is created.

The socket parameter is an object of type [net.Socket][]. It represents the TCP stream and provides methods for sending and receiving data.

Typically, users will not need to access this event. However, it can be useful for debugging purposes or for injecting connections into the HTTP/2 server.

Real-World Code Implementation:

// Create an HTTP/2 server
const http2 = require("http2");
const server = http2.createSecureServer({
  // ... server options ...
});

// Listen for 'connection' event
server.on("connection", (socket) => {
  console.log(`New connection established: ${socket.remoteAddress}`);
});

// Start the server
server.listen(8443);

Potential Applications:

Debugging: The 'connection' event can be used to track when new connections are established to the server. This can be helpful for troubleshooting connection issues.
Injecting Connections: In some cases, it may be necessary to inject connections into the HTTP/2 server. For example, this could be done to simulate a connection from a specific client or to test a specific scenario.

Additional Notes:

The 'connection' event is only emitted for new connections. It is not emitted for existing connections that are reused.
The 'connection' event can be used to set up event listeners on the socket object. For example, you could listen for the 'data' event to receive data from the client.
The 'connection' event can be used to set up TLS encryption for the connection. This is typically done by setting the secureProtocol option when creating the HTTP/2 server.

Event: `'request'`

Explanation:

The 'request' event is emitted by the http2 module whenever a new request is received over an HTTP/2 connection. When a client establishes a connection and wants to send data to your server, it sends a request.

Parameters:

request: An Http2ServerRequest object representing the incoming request. It contains information about the request method, headers, and body.
response: An Http2ServerResponse object that you can use to send a response back to the client.

Real-World Example:

Here's an example of handling a request in Node.js using the HTTP/2 module:

const http2 = require("http2");

const server = http2.createServer();

server.on("request", (request, response) => {
  // Handle the request here
  const body = "Hello, world!";

  // Send a response
  response.writeHead(200);
  response.end(body);
});

server.listen(8000);

Potential Applications:

The 'request' event is essential for any server that needs to handle HTTP/2 traffic. It allows you to receive requests from clients and respond with data or status codes. Some real-world applications include:

Web servers
APIs
Microservices

Event: 'session'

Purpose: The 'session' event is emitted when a new Http2Session is created by the Http2Server.
Data: The event data is the newly created Http2Session object.

Example:

const http2 = require("http2");

const server = http2.createHttp2Server();

server.on("session", (session) => {
  console.log("New HTTP/2 session established.");
});

server.listen(8000);

Real-World Application:

Tracking the number of active HTTP/2 sessions in a server.
Debugging HTTP/2 session setup and negotiation.

Event: 'sessionError'

imagine you are using a mobile app and you see an error message saying 'network error', this event is emitted when the 'error' event is emitted by the 'Http2Session' object which is associated with the 'Http2Server' which you are using to listen to incoming HTTP/2 requests.

Parameters:

error: An Error object representing the error that occurred.
session: The ServerHttp2Session object that emitted the error.

Real-world Applications:

This event can be used to handle errors that occur during HTTP/2 sessions. For example, you could use it to log the error, or to close the session and restart it.

Code Example:

const http2 = require("http2");

const server = http2.createServer();

server.on("sessionError", (error, session) => {
  console.error("HTTP/2 session error:", error);
  session.close();
});

server.listen(8080);

Potential Applications:

Logging errors for debugging purposes
Restarting sessions that have encountered errors
Closing sessions that are no longer usable

Event: `'stream'`

Simplified Explanation:

When a new incoming HTTP/2 stream is received by the server, this event is triggered. It provides access to the stream object, the headers sent by the client, and flags indicating the state of the stream.

Code Snippet:

const { createServer } = require("http2");
const {
  HTTP2_HEADER_METHOD,
  HTTP2_HEADER_PATH,
  HTTP2_HEADER_STATUS,
  HTTP2_HEADER_CONTENT_TYPE,
} = require("http2").constants;

const server = createServer();
server.on("stream", (stream, headers, flags) => {
  const method = headers[HTTP2_HEADER_METHOD];
  const path = headers[HTTP2_HEADER_PATH];
  console.log(`Received request: ${method} ${path}`);

  // Send back a response
  stream.respond({
    [HTTP2_HEADER_STATUS]: 200,
    [HTTP2_HEADER_CONTENT_TYPE]: "text/plain; charset=utf-8",
  });
  stream.write("Hello world!");
  stream.end();
});

Real-World Application:

HTTP/2 is a protocol used for high-performance and low-latency web applications. It allows servers to handle multiple simultaneous requests from a single client efficiently. Event handling in HTTP/2 enables servers to respond to incoming streams quickly and efficiently.

For example, an e-commerce website may use HTTP/2 to handle multiple user requests for product listings, shopping carts, and checkout processes concurrently. This would provide a smoother and faster experience for users.

Event: `'timeout'`

The 'timeout' event is emitted when the server has been inactive for a specified amount of time. This event is useful for detecting idle connections that can be terminated to free up resources.

Features

The timeout duration can be set using the http2server.setTimeout() method.
The default timeout duration is 0, which means there is no timeout.
When the timeout occurs, the 'timeout' event is emitted with the following arguments:
- socket - The socket that timed out.

Usage

The following code snippet shows how to set a timeout duration of 10 seconds for an HTTP/2 server:

const http2 = require("http2");

const server = http2.createServer();

server.setTimeout(10000);

server.on("timeout", (socket) => {
  // Handle the timeout event.
});

server.listen(8080);

Applications

The 'timeout' event can be used in a variety of applications, including:

Detecting and terminating idle connections.
Monitoring server performance.
Implementing load balancing and failover mechanisms.

`server.close([callback])`

Purpose:

This method stops the server from accepting new connections but allows existing connections to continue.

Parameters:

callback: (Optional) A function that is invoked when all existing connections are closed.

How it works:

When server.close() is called without a callback, the server immediately stops accepting new connections. Existing connections are not affected and will continue to be processed. When the last existing connection closes, the server's 'close' event will be emitted.

If a callback is provided, the server will not emit the 'close' event until the callback has been invoked. This allows you to perform any necessary cleanup operations before the server is considered fully closed.

Real-world example:

In a typical HTTP/2 server application, you might want to gracefully shut down the server when a shutdown signal is received. You can do this by calling server.close(), providing a callback function to handle the cleanup.

const http2 = require("http2");
const server = http2.createServer();

server.on("error", (err) => {
  console.error(err);
});

// Handle shutdown signal
process.on("SIGINT", () => {
  server.close((err) => {
    if (err) {
      console.error(err);
    }
    process.exit(0);
  });
});

// Start the server
server.listen(8080);

This example ensures that all existing connections are closed before the server exits completely.

Potential applications:

Gracefully shutting down HTTP/2 servers
Handling server restarts or reconfigurations
Cleaning up server resources before exiting

`server[Symbol.asyncDispose]()`

The server[Symbol.asyncDispose]() method in http2 calls [server.close()][] and returns a promise that fulfills when the server has closed.

Example:

const http2 = require("http2");

const server = http2.createServer();

server.listen(3000);

server[Symbol.asyncDispose]().then(() => {
  console.log("Server closed");
});

Simplified Explanation of server.setTimeout()

What is server.setTimeout()?

It's a method that allows you to define a timeout for requests made to your HTTP/2 server. If a request stays idle for longer than this timeout, it triggers an action.

How to use it:

You can use it like this:

const http2 = require("http2");
const server = http2.createServer();

// Set a timeout of 5 seconds
server.setTimeout(5000);

// Register a callback to be called when the timeout occurs
server.on("timeout", () => {
  // This code will run when a request goes idle for more than 5 seconds
  console.log("Request timed out!");
});

Parameters:

msecs: The number of milliseconds before the timeout occurs. By default, it's set to 0, which means no timeout.
callback: A function that will be called when the timeout occurs. This is optional.

Return Value:

The method returns the Http2Server object, allowing you to chain other operations.

Applications:

Preventing server overload: You can use it to prevent your server from getting overloaded by automatically closing idle connections after a certain period.
Resource optimization: It helps optimize server resources by closing inactive connections, making way for new requests.

`server.timeout`

Simplified Explanation:

The server.timeout setting determines how long a socket connection can remain inactive before the server closes it automatically.

Example:

const http2 = require("http2");

const server = http2.createServer();

// Set the timeout to 5 minutes (5 * 60 * 1000 milliseconds)
server.timeout = 5 * 60 * 1000;

server.listen(8443);

In this example, any socket that remains inactive for more than 5 minutes will be closed by the server.

Real-World Applications:

Preventing idling connections: Setting a timeout helps prevent sockets from staying open indefinitely, which can lead to resource leakage and performance issues.
Detecting and recovering from failed connections: By automatically closing idle sockets, the server can detect and recover from failed connections more quickly.
Scaling and load balancing: Timeouts can help balance server load by ensuring that inactive sockets are not consuming resources unnecessarily.

Improved Code Snippet:

To set a custom timeout value, use the setTimeout method on the server object.

const http2 = require("http2");

const server = http2.createServer();

// Set the timeout to 10 minutes (10 * 60 * 1000 milliseconds)
server.setTimeout(10 * 60 * 1000);

server.listen(8443);

Additional Notes:

A timeout value of 0 disables the timeout behavior.
Changing the timeout value only affects new connections.
Timeouts are only applied to incoming connections; outgoing connections are not affected.

`server.updateSettings([settings])`

This method is used to update the settings of an HTTP/2 server with the provided settings.

Parameters:

settings: An object containing the new settings to be applied to the server. The settings object can contain any of the following properties:
- headerTableSize: The maximum size of the server's header table.
- enablePush: A boolean value indicating whether or not the server should enable push streams.
- maxConcurrentStreams: The maximum number of concurrent streams that the server can handle.
- initialWindowSize: The initial window size for new streams.
- maxFrameSize: The maximum frame size that the server can handle.
- maxHeaderListSize: The maximum size of the header list for new streams.

Errors:

ERR_HTTP2_INVALID_SETTING_VALUE: Thrown if any of the provided settings values are invalid.
ERR_INVALID_ARG_TYPE: Thrown if the settings argument is not an object.

Example:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream, headers) => {
  // Update the server's settings
  server.updateSettings({
    headerTableSize: 4096,
    enablePush: true,
    maxConcurrentStreams: 100,
    initialWindowSize: 1024,
    maxFrameSize: 16384,
    maxHeaderListSize: 65536,
  });
});

server.listen(8080);

Applications:

This method can be used to dynamically adjust the settings of an HTTP/2 server in response to changing conditions. For example, if the server is experiencing high traffic, it could increase the maxConcurrentStreams setting to allow more connections. Or, if the server is running on a resource-constrained system, it could decrease the maxFrameSize setting to reduce memory usage.

Class: `Http2SecureServer`

The Http2SecureServer class is a secure HTTP/2 server that extends the tls.Server class. It is used to create secure HTTP/2 servers that encrypt data in transit using TLS.

Creation

To create an Http2SecureServer, use the http2.createSecureServer() function, which takes an options object as an argument. The following code snippet shows how to create an Http2SecureServer:

const http2 = require("http2");

const server = http2.createSecureServer({
  key: fs.readFileSync("server.key"),
  cert: fs.readFileSync("server.crt"),
});

Usage

Once you have created an Http2SecureServer, you can use it to listen for incoming connections on a specified port. The following code snippet shows how to listen for incoming connections on port 443:

server.listen(443);

When a client connects to the server, the server will automatically negotiate a secure connection using TLS. Once the connection is established, the server will start receiving and responding to HTTP/2 requests.

Real-world applications

Http2SecureServer can be used in a variety of real-world applications, including:

Secure web servers
Secure APIs
Secure messaging applications

Potential applications

Here are some potential applications for Http2SecureServer:

A secure e-commerce website that allows users to purchase products online.
A secure API that allows developers to access data and functionality from a remote server.
A secure messaging application that allows users to send and receive messages over the internet.

Event: 'checkContinue'

This event is emitted when a client requests the server to send a 100 Continue response to indicate that the server is ready to receive the request body.

Simplified Explanation:

Imagine you're ordering food at a restaurant. You call the waiter and say, "I'm thinking about ordering the steak." The waiter replies, "Okay, let me check with the kitchen first to make sure we have steak available."

The waiter goes to the kitchen and returns. He says, "Yes, we have steak. You can go ahead and order it." This is like the server's checkContinue event. The server is asking the client if it should continue to receive the request body.

Handling the Event:

If you want the client to continue sending the request body, you call the writeContinue() method on the response object:

response.writeContinue();

If you don't want the client to continue sending the request body, you can generate an appropriate HTTP response, such as 400 Bad Request.

Real-World Application:

This event is useful when you need to check if the server is ready to receive a large request body. For example, if you're uploading a large file to a cloud storage service, you would use this event to make sure that the service is ready to receive the file before you start uploading it.

The 'connection' event in HTTP/2

What is it?

The 'connection' event is emitted when a new TCP connection is established to the HTTP/2 server. This happens before the TLS handshake begins (if TLS is being used).

What is socket?

socket is the underlying TCP stream that is used to communicate with the client. It is typically an object of type [net.Socket][].

Why would I want to listen for this event?

Usually, you would not want to listen for this event. However, there are some cases where it can be useful. For example, you could use this event to inject connections into the HTTP/2 server. This could be useful for testing or for debugging purposes.

Here is an example of how to listen for the 'connection' event:

const http2 = require("http2");

const server = http2.createServer();

server.on("connection", (socket) => {
  // Do something with the socket
});

server.listen(8000);

Real-world applications

One real-world application for listening to the 'connection' event is for testing. For example, you could use this event to test the behavior of your HTTP/2 server when it receives a large number of concurrent connections.

Another real-world application for listening to the 'connection' event is for debugging. For example, you could use this event to track the number of connections that are being made to your HTTP/2 server. This could help you identify any potential performance issues.

Simplified version

In very plain English, the 'connection' event is like the doorbell ringing on your house. It tells you that someone is trying to connect to your HTTP/2 server. socket is like the door itself. You can use the door to let the person in or to keep them out.

Event: 'request'

What is it?

The 'request' event is emitted each time a request is received by the server. There can be multiple requests for each HTTP/2 connection.

Arguments:

request: The incoming HTTP/2 request object.
response: The HTTP/2 response object to be sent back to the client.

How to use it:

To handle incoming requests, you can listen for the 'request' event on the HTTP/2 server object. Here's an example:

const http2 = require("http2");

// Create an HTTP/2 server
const server = http2.createServer();

// Listen for the 'request' event
server.on("request", (request, response) => {
  // Handle the request and send a response
  response.end("Hello World!");
});

// Start the server
server.listen(3000);

Real-world applications:

HTTP/2 is used in many real-world applications, such as:

Web servers
Streaming services
Mobile applications

Potential applications:

HTTP/2 can be used for any application that requires high-performance communication, such as:

Gaming
Video conferencing
Financial trading

`'session'` Event

Summary: When a new HTTP/2 session is established on the server, this event is triggered.

Detailed Explanation: HTTP/2 is a network protocol that allows for faster and more efficient communication between web servers and clients. When a client connects to an HTTP/2 server, the server creates a session to handle the communication. This session is a dedicated channel over which the client and server can exchange data.

The 'session' event is emitted by the HTTP/2 server when a new session is created. This event provides the ServerHttp2Session object, which represents the newly created session.

Real-World Example: Imagine you have a web server that handles a lot of requests from clients. By using HTTP/2, you can improve the performance of your server by establishing multiple sessions with each client. Each session can handle a separate stream of data, allowing for faster and more efficient communication.

Code Example:

const http2 = require("http2");

const server = http2.createServer();

server.on("session", (session) => {
  // Do something with the new session
});

server.listen(8080);

Potential Applications: HTTP/2 is widely used in various applications, including:

Web hosting: To improve the performance of websites and applications
Streaming services: To deliver high-quality video and audio streaming
Enterprise messaging: To facilitate real-time communication and collaboration
Mobile applications: To optimize data transfer and improve user experience

Event: 'sessionError'

This event is emitted when an error occurs on the HTTP/2 session associated with the HTTP/2 secure server.

Parameters:

error: An instance of the Error class representing the error.
session: The HTTP/2 session that emitted the error.

Example:

const http2 = require("http2");
const server = http2.createSecureServer();

server.on("sessionError", (error, session) => {
  console.error(error);
});

Applications in the Real World:

This event can be used to handle errors that occur on the HTTP/2 session, such as protocol errors or connection errors. By handling these errors, the server can take appropriate action, such as closing the connection or retrying the request.

Simplified Explanation of the `'stream'` Event

Introduction:

HTTP/2 is a protocol for efficient communication between a client and a server. When a client makes a request to a server over HTTP/2, the request is handled by a stream.

The 'stream' Event:

The 'stream' event is emitted by the server when a new stream is created. It provides information about the stream and the headers sent by the client.

Understanding the Event Parameters:

stream: This parameter is a reference to the newly created stream.
headers: This is an object containing the HTTP headers sent by the client.
flags: This is a numeric value representing the flags associated with the stream.
rawHeaders: This is an array containing the raw header names and values sent by the client.

Example:

const http2 = require("node:http2");
const { HTTP2_HEADER_METHOD, HTTP2_HEADER_PATH } = http2.constants;

const server = http2.createSecureServer();
server.on("stream", (stream, headers) => {
  // Get the request method and path from the headers
  const method = headers[HTTP2_HEADER_METHOD];
  const path = headers[HTTP2_HEADER_PATH];

  // Respond to the client with a 200 status code
  stream.respond({
    [HTTP2_HEADER_STATUS]: 200,
  });

  // Write a response body
  stream.write("Hello World!");

  // End the stream
  stream.end();
});

Applications:

The 'stream' event is used to handle incoming requests from clients. It allows developers to create and respond to streams, which are used to transfer data between the client and the server.

Real-World Examples:

HTTP/2 is used in various applications, including:

Web servers
Email servers
Streaming platforms
Mobile applications

`'timeout'` Event

Simplified Explanation:

Imagine a child playing on the playground. If the child doesn't play with any toys or friends for several minutes, a teacher blows a whistle to remind them that it's time to do something.

Similarly, when using the HTTP/2 protocol, if there's no activity (such as sending or receiving data) for a certain amount of time, the HTTP2 server can emit the 'timeout' event to notify you.

Usage:

You can use the http2secureServer.setTimeout() method to specify the time in milliseconds before the 'timeout' event is emitted. The default timeout is 120,000 milliseconds (2 minutes).

const http2 = require("http2");
const server = http2.createSecureServer();

// Set the timeout to 30 seconds
server.setTimeout(30000);

Event Handling:

When the 'timeout' event is emitted, your code will receive an object with the following properties:

socket: The socket that timed out
timeout: The timeout in milliseconds that was set

You can handle this event by listening to it using the 'timeout' property of the server:

server.on("timeout", (socket, timeout) => {
  console.log(`Socket ${socket.id} timed out after ${timeout}ms`);
});

Real World Applications:

The 'timeout' event can be useful in the following scenarios:

Preventing Idle Connections: If a client suddenly stops sending data, the server can close the connection after a set period of inactivity to free up resources.
Monitoring Client Activity: You can use the 'timeout' event to keep track of client activity and identify any unresponsive connections.
Enforcing Session Timeouts: You can set a timeout for client sessions to ensure users are logged out after a certain period of inactivity.

Sure, here is a simplified explanation of the 'unknownProtocol' event in Node.js's HTTP/2 module:

What is the 'unknownProtocol' event?

The 'unknownProtocol' event is emitted when a client tries to connect to an HTTP/2 server, but the client does not support HTTP/2 or the server does not allow HTTP/1.1 connections. This can happen if the client is using an old version of a web browser or if the server is configured to only allow HTTP/2 connections.

What happens when the 'unknownProtocol' event is emitted?

When the 'unknownProtocol' event is emitted, the server passes the socket to the event handler. The event handler can then decide what to do with the socket, such as sending an error message to the client or closing the connection. If no event handler is registered for this event, the connection is terminated.

How can I use the 'unknownProtocol' event?

You can use the 'unknownProtocol' event to handle clients that do not support HTTP/2. For example, you could send an error message to the client and close the connection, or you could redirect the client to a different server that supports HTTP/1.1.

Here is an example of how you can use the 'unknownProtocol' event:

const http2 = require('http2');

const server = http2.createSecureServer();

server.on('unknownProtocol', (socket) => {
  socket.end('HTTP/2 not supported');
});

server.listen(8443);

This example will send an error message to clients that do not support HTTP/2 and close the connection.

Potential applications in the real world

The 'unknownProtocol' event can be used in a variety of real-world applications, such as:

Enforcing HTTP/2-only connections to improve performance and security
Redirecting clients to a different server based on their protocol support
Debugging and troubleshooting HTTP/2 connections

I hope this explanation is helpful. Please let me know if you have any other questions.

`server.close([callback])`

callback {Function}

Stops the server from accepting new connections.

Simplified Explanation

Imagine your server is like a store. When you call server.close(), it's like closing the store's door. Customers can't enter (make new connections), but customers who are already inside (active connections) can still finish their shopping (finish their requests).

To completely close the store (shut down gracefully), you need to wait for all the customers to leave (close all active connections). You can do this by calling http2session.close() on all active sessions.

Code Example

const http2 = require("http2");

const server = http2.createServer();

server.listen(3000);

setTimeout(() => {
  server.close(() => {
    console.log("Server closed gracefully.");
  });
}, 1000); // Wait 1 second for any active connections to finish

Real-World Application

Consider a web server that uses HTTP/2. When the server is under heavy load, you may want to stop accepting new connections to prevent the server from crashing. You can do this by calling server.close() and waiting for all active connections to finish. This will allow existing users to finish their requests while preventing new users from connecting.

Simplified Explanation:

Imagine you have a web server that uses HTTP/2 secured connections.

Timeout Value:

You can set a timeout period for each request made to your web server. This means that if a client (e.g., a web browser) doesn't send or receive any data for a certain amount of milliseconds (by default, 2 minutes), the server will automatically close the connection.

Callback Function:

You can also specify a callback function that the server will call when a request times out. This callback function allows you to perform custom actions, such as logging the timeout or sending a response to the client.

Example Code:

const http2 = require("http2");

// Create an HTTP/2 secure server
const server = http2.createSecureServer();

// Set the timeout value to 1 minute (60000 milliseconds)
server.setTimeout(60000);

// Define a callback function to be called when a request times out
server.on("timeout", (socket) => {
  // Log the timeout
  console.log("Request timed out");

  // Send a response to the client
  socket.end("The request timed out");
});

// Listen for incoming requests
server.listen(8443);

Real-World Applications:

Preventing malicious attacks: Limiting the amount of time a client can remain connected without activity helps prevent denial-of-service (DoS) attacks where malicious actors try to keep connections open indefinitely to exhaust resources.
Improving performance: Managing timeouts efficiently allows the server to handle more active requests and avoid wasting resources on inactive connections.
Custom error handling: Implementing the timeout callback function gives you the flexibility to customize how your server responds to timed-out requests, such as displaying specific error messages or logging additional information.

`server.timeout`

Meaning:

The amount of time in milliseconds (thousandths of a second) that a server will wait for a client to send data before closing the connection.

Default Value:

0 (no timeout)

How it works:

When a client connects to a server, the server starts a timer. If the client doesn't send any data within the timeout period, the server closes the connection.

Benefits:

Prevents idle connections from tying up resources on the server.
Improves performance by reducing the number of unnecessary connections.

Real-World Examples:

A web server can set a timeout to prevent clients from leaving open connections indefinitely, keeping the server from being overwhelmed.
A chat application can set a timeout to automatically close inactive chat sessions, freeing up resources for active users.

Code Example:

const http2 = require("http2");

const server = http2.createServer();

server.on("session", (session) => {
  session.setTimeout(10000); // Set a 10-second timeout for new connections.
});

server.listen(8000);

Potential Applications:

Web Servers: Set a timeout to prevent clients from leaving open connections indefinitely, keeping the server from being overwhelmed.
Chat Applications: Set a timeout to automatically close inactive chat sessions, freeing up resources for active users.
Streaming Services: Set a timeout to prevent streams from hanging indefinitely if the client stops receiving data.

Simplified Explanation

server.updateSettings() allows you to change the settings of the HTTP/2 server.

Explanation of Each Topic

HTTP/2 Settings:
- These are parameters that control how the HTTP/2 server behaves, such as the maximum frame size or the maximum number of concurrent streams.
- Example: {headerTableSize: 4096, maxConcurrentStreams: 100}
Valid settings Values:
- Each setting has a minimum and maximum allowed value.
- Exceeding these limits results in an ERR_HTTP2_INVALID_SETTING_VALUE error.
Invalid settings Arguments:
- The settings argument must be an object.
- Passing a non-object argument results in an ERR_INVALID_ARG_TYPE error.

Real-World Code Implementations

// Example usage
const http2 = require("http2");
const server = http2.createSecureServer();

server.on("stream", (stream) => {
  // Update settings during the stream
  server.updateSettings({ initialWindowSize: 8192 });
});

// Update settings before accepting any streams
server.updateSettings({ maxConcurrentStreams: 100 });

Potential Applications

Adjusting Performance: You can fine-tune the server's performance by modifying settings such as the maximum frame size or the maximum number of streams.
Enforcing Limits: You can set limits on certain settings, such as the maximum header table size, to prevent clients from abusing the server's resources.
Debugging: If you encounter HTTP/2 errors, you can try modifying the settings to see if they resolve the issue.

HTTP/2 Server

HTTP/2 is a newer version of HTTP that is faster and more efficient than HTTP/1.1. It uses binary framing, header compression, and multiplexing to improve performance.

To create an HTTP/2 server, you can use the http2.createServer() method. This method takes an optional options object and a request handler function as arguments.

The options object can be used to configure various settings for the HTTP/2 server, such as the maximum number of concurrent streams, the maximum size of header blocks, and the padding strategy to use.

The request handler function is called for each incoming HTTP/2 request. It receives the request stream and the request headers as arguments. The request handler function is responsible for sending a response to the client.

Example

The following code shows how to create a simple HTTP/2 server:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream, headers) => {
  stream.respond({
    "content-type": "text/html; charset=utf-8",
    ":status": 200,
  });
  stream.end("<h1>Hello World</h1>");
});

server.listen(8000);

Applications

HTTP/2 is used in a variety of real-world applications, including:

Web servers
Reverse proxies
Load balancers
WebSocket servers
gRPC servers

HTTP/2 can improve the performance of these applications by reducing latency and increasing throughput.

Potential Applications

Here are some potential applications for HTTP/2:

Web servers: HTTP/2 can be used to improve the performance of web servers by reducing latency and increasing throughput. This can lead to a better user experience for website visitors.
Reverse proxies: HTTP/2 can be used to improve the performance of reverse proxies by reducing latency and increasing throughput. This can lead to a better user experience for clients accessing web applications through a reverse proxy.
Load balancers: HTTP/2 can be used to improve the performance of load balancers by reducing latency and increasing throughput. This can lead to a more reliable and scalable load balancing solution.
WebSocket servers: HTTP/2 can be used to improve the performance of WebSocket servers by reducing latency and increasing throughput. This can lead to a better user experience for clients using WebSocket connections.
gRPC servers: HTTP/2 can be used to improve the performance of gRPC servers by reducing latency and increasing throughput. This can lead to a more efficient and scalable gRPC solution.

`http2.createSecureServer(options[, onRequestHandler])`

The http2.createSecureServer() method in Node.js is used to create a secure HTTP/2 server. It takes two parameters:

options: An object containing the following optional properties:
- allowHTTP1: A boolean value that indicates whether the server should allow HTTP/1.1 connections. Defaults to false.
- maxDeflateDynamicTableSize: A number that specifies the maximum size of the dynamic table used for deflating header fields. Defaults to 4 KiB.
- maxSettings: A number that specifies the maximum number of settings entries per SETTINGS frame. Defaults to 32.
- maxSessionMemory: A number that specifies the maximum amount of memory that the Http2Session is permitted to use. Defaults to 10 MB.
- maxHeaderListPairs: A number that specifies the maximum number of header entries. Defaults to 128.
- maxOutstandingPings: A number that specifies the maximum number of outstanding, unacknowledged pings. Defaults to 10.
- maxSendHeaderBlockLength: A number that specifies the maximum allowed size for a serialized, compressed block of headers. Defaults to 16 KiB.
- paddingStrategy: A number that specifies the strategy used for determining the amount of padding to use for HEADERS and DATA frames. Defaults to http2.constants.PADDING_STRATEGY_NONE.
- peerMaxConcurrentStreams: A number that specifies the maximum number of concurrent streams for the remote peer. Defaults to 100.
- maxSessionInvalidFrames: A number that specifies the maximum number of invalid frames that will be tolerated before the session is closed. Defaults to 1000.
- maxSessionRejectedStreams: A number that specifies the maximum number of rejected upon creation streams that will be tolerated before the session is closed. Defaults to 100.
- settings: An object containing the initial settings to send to the remote peer upon connection.
- remoteCustomSettings: An array of integer values that determines the settings types, which are included in the customSettings-property of the received remoteSettings.
- origins: An array of origin strings to send within an ORIGIN frame immediately following creation of a new server Http2Session.
- unknownProtocolTimeout: A number that specifies a timeout in milliseconds that a server should wait when an ['unknownProtocol'][] event is emitted. If the socket has not been destroyed by that time the server will destroy it. Defaults to 10000.
onRequestHandler: A function that is called when a new HTTP/2 request is received. The function takes two parameters:
- stream: The Http2Stream object for the new request.
- headers: An object containing the headers for the request.

The following code sample shows you how to create a secure HTTP/2 server:

const http2 = require("http2");
const fs = require("fs");

const options = {
  key: fs.readFileSync("server-key.pem"),
  cert: fs.readFileSync("server-cert.pem"),
};

// Create a secure HTTP/2 server
const server = http2.createSecureServer(options);

server.on("stream", (stream, headers) => {
  stream.respond({
    "content-type": "text/html; charset=utf-8",
    ":status": 200,
  });
  stream.end("<h1>Hello World</h1>");
});

server.listen(8443);

Potential applications in the real world

HTTP/2 is a more efficient protocol than HTTP/1.1, so it can be used to improve the performance of web applications. For example, HTTP/2 can be used to reduce the latency of page loads and to improve the throughput of data transfers.

HTTP/2 is also more secure than HTTP/1.1, so it can be used to protect web applications from attacks. For example, HTTP/2 can be used to prevent man-in-the-middle attacks and to protect data from being intercepted.

HTTP/2 Client Connection

HTTP/2 is a network protocol for transferring data efficiently between a client and a server. It's an improvement over HTTP/1.1, providing faster speeds, reduced latency, and more efficient use of resources.

To use HTTP/2, you need to create a client connection. This is done using the http2.connect() function.

Simplified Explanation:

Imagine you're building a Lego tower. You can build it one block at a time (HTTP/1.1), or you can send multiple blocks at once in a package (HTTP/2). HTTP/2 makes it faster to build because it sends more data at once.

Creating an HTTP/2 Client Connection

Function Signature

http2.connect(authority[, options][, listener])

Parameters

authority: The URL of the server you want to connect to. This should include the protocol (http:// or https://), the hostname, and the port (if not the default port).
options: An optional object containing configuration options.
listener: An optional function that will be executed once the connection is established.

Configuration Options

The following configuration options are available:

maxDeflateDynamicTableSize: The maximum size of the dynamic table used for deflating header fields.
maxSettings: The maximum number of settings entries per SETTINGS frame.
maxSessionMemory: The maximum memory that the Http2Session is permitted to use.
maxHeaderListPairs: The maximum number of header entries.
maxOutstandingPings: The maximum number of outstanding, unacknowledged pings.
maxReservedRemoteStreams: The maximum number of reserved push streams the client will accept at any given time.
maxSendHeaderBlockLength: The maximum allowed size for a serialized, compressed block of headers.
paddingStrategy: The strategy used for determining the amount of padding to use for HEADERS and DATA frames.
peerMaxConcurrentStreams: The maximum number of concurrent streams for the remote peer.
protocol: The protocol to connect with, if not set in the authority.
settings: The initial settings to send to the remote peer upon connection.
remoteCustomSettings: The array of integer values determines the settings types, which are included in the CustomSettings-property of the received remoteSettings.
createConnection: An optional callback that receives the URL instance passed to connect and the options object, and returns any [Duplex][] stream that is to be used as the connection for this session.
unknownProtocolTimeout: Specifies a timeout in milliseconds that a server should wait when an ['unknownProtocol'][] event is emitted.

Return Value

The http2.connect() function returns a ClientHttp2Session instance. This instance represents the HTTP/2 connection and can be used to send and receive data.

Example

const http2 = require("node:http2");
const client = http2.connect("https://localhost:1234");

client.on("error", (err) => {
  console.error(err);
});

client.on("connect", () => {
  // The connection has been established.
});

client.on("data", (data) => {
  // Data has been received from the server.
});

client.on("close", () => {
  // The connection has been closed.
});

// Send data to the server.
client.write("Hello, world!");

// Close the connection.
client.close();

Real-World Applications

HTTP/2 is used in a wide variety of applications, including:

Web browsing: HTTP/2 is supported by all major web browsers, which makes it faster to load web pages and reduce latency.
API communication: HTTP/2 is a popular protocol for communicating with APIs, as it provides high performance and reliability.
Streaming media: HTTP/2 is well-suited for streaming media, as it can provide low latency and high throughput.

HTTP/2 Constants

HTTP/2 defines a set of constants that are used to identify different aspects of the protocol. These constants are defined in the http2.constants module.

Connection Options

The following constants are used to configure the connection options for an HTTP/2 server or client:

HTTP2_HEADER_SETTINGS_TIMEOUT: The maximum amount of time (in milliseconds) that the server will wait for the client to send its initial header settings frame.
HTTP2_SETTINGS_TIMEOUT: The maximum amount of time (in milliseconds) that the server will wait for the client to send its settings frame.
HTTP2_KEEP_ALIVE_TIMEOUT: The maximum amount of time (in milliseconds) that the server will keep the connection alive after the last request has been processed.
HTTP2_PING_TIMEOUT: The maximum amount of time (in milliseconds) that the server will wait for the client to respond to a PING frame.

Frame Types

The following constants are used to identify the different types of frames that can be sent over an HTTP/2 connection:

HTTP2_FRAME_DATA: A data frame carries the payload of an HTTP message.
HTTP2_FRAME_HEADERS: A headers frame carries the HTTP headers for a request or response.
HTTP2_FRAME_PRIORITY: A priority frame specifies the priority of a request or stream.
HTTP2_FRAME_RST_STREAM: A RST_STREAM frame is used to reset a stream.
HTTP2_FRAME_SETTINGS: A SETTINGS frame is used to communicate settings between the client and server.
HTTP2_FRAME_PUSH_PROMISE: A PUSH_PROMISE frame is used to indicate that the server is pushing a new resource to the client.
HTTP2_FRAME_PING: A PING frame is used to check if the connection is still alive.
HTTP2_FRAME_GOAWAY: A GOAWAY frame is used to indicate that the server is closing the connection.

Error Codes

The following constants are used to identify the different error codes that can be returned by an HTTP/2 server or client:

HTTP2_ERROR_NO_ERROR: No error occurred.
HTTP2_ERROR_PROTOCOL_ERROR: A protocol error occurred.
HTTP2_ERROR_INTERNAL_ERROR: An internal error occurred.
HTTP2_ERROR_FLOW_CONTROL_ERROR: A flow control error occurred.
HTTP2_ERROR_SETTINGS_TIMEOUT: The settings timeout was exceeded.
HTTP2_ERROR_STREAM_CLOSED: The stream was closed.
HTTP2_ERROR_FRAME_SIZE_ERROR: The frame size was too large.
HTTP2_ERROR_REFUSED_STREAM: The stream was refused.
HTTP2_ERROR_CANCEL: The stream was cancelled.
HTTP2_ERROR_COMPRESSION_ERROR: A compression error occurred.
HTTP2_ERROR_CONNECT_ERROR: A connect error occurred.
HTTP2_ERROR_ENHANCE_YOUR_CALM: The server is experiencing problems and is asking the client to slow down.

Potential Applications

HTTP/2 constants are used to configure and manage HTTP/2 connections. They can be used to set timeouts, identify frame types, and handle errors.

Here is a real-world example of how HTTP/2 constants can be used:

const http2 = require("http2");

// Create an HTTP/2 server with a custom settings timeout
const server = http2.createSecureServer({
  settingsTimeout: 10000, // 10 seconds
});

// Listen for new connections
server.on("connection", (stream) => {
  // Handle the stream
});

In this example, the HTTP2_SETTINGS_TIMEOUT constant is used to set the maximum amount of time that the server will wait for the client to send its settings frame. This can be useful for preventing Denial of Service (DoS) attacks.

Error Codes for RST_STREAM and GOAWAY Frames

When a client or server closes a stream or sends a GOAWAY frame, they can include an error code to indicate why the stream is being closed. The following error codes are defined:

Error Code

Name

Description

0x00

No Error

The stream was closed normally.

0x01

Protocol Error

The stream was closed due to a protocol error.

0x02

Internal Error

The stream was closed due to an internal error on the server.

0x03

Flow Control Error

The stream was closed due to a flow control error.

0x04

Settings Timeout

The stream was closed because the server did not receive a SETTINGS frame from the client within the specified timeout period.

0x05

Stream Closed

The stream was closed because the stream was already closed.

0x06

Frame Size Error

The stream was closed because the client sent a frame that was too large.

0x07

Refused Stream

The stream was closed because the server refused to open the stream.

0x08

Cancel

The stream was closed because the client canceled the stream.

0x09

Compression Error

The stream was closed because the client sent a compressed frame that could not be decompressed.

0x0a

Connect Error

The stream was closed because the client could not connect to the server.

0x0b

Enhance Your Calm

The stream was closed because the server is overloaded and needs to slow down.

0x0c

Inadequate Security

The stream was closed because the security level of the client is not sufficient.

0x0d

HTTP/1.1 Required

The stream was closed because the server requires HTTP/1.1.

'timeout' Event

The 'timeout' event is emitted when there is no activity on the server for a given number of milliseconds set using http2server.setTimeout(). This can be useful for detecting when a client has stopped sending data and the server can close the stream.

Real-World Applications

These error codes and the 'timeout' event can be used to handle errors and manage streams in HTTP/2 applications. For example, a server could use the 'timeout' event to close streams that have been inactive for a long period of time, or a client could use the error codes to determine why a stream was closed by the server.

Complete Code Implementation

The following code shows how to handle the 'timeout' event:

const http2 = require("http2");

const server = http2.createSecureServer();

server.setTimeout(1000);

server.on("timeout", (stream, timedOut) => {
  if (timedOut) {
    // The stream has been inactive for more than 1000 milliseconds.
    stream.close();
  }
});

server.listen(443);

`http2.getDefaultSettings()`

Returns: HTTP/2 Settings Object

Simplified Explanation:

Imagine you're creating a secret code and you want to establish some rules or settings for how the code will work. getDefaultSettings() helps you set up these default rules for encrypting and decrypting your secret messages using HTTP/2.

Detailed Explanation:

HTTP/2 is a protocol used for fast and efficient communication over the internet. getDefaultSettings() provides a starting point for configuring the settings of an HTTP/2 connection. It returns an object with default values for various settings, such as the maximum size of messages and the number of concurrent requests allowed.

Real-World Example:

Suppose you're building an e-commerce website that needs to handle many customer requests quickly. You can use getDefaultSettings() to set up the initial configuration for your HTTP/2 connections, ensuring that they can handle a high volume of traffic efficiently.

Potential Applications:

Secure communication: HTTP/2 provides encryption and security features, making it ideal for transmitting sensitive data, such as financial transactions or medical records.
Performance optimization: HTTP/2 can significantly improve the speed and efficiency of web applications and online services.
Mobile optimization: HTTP/2 is particularly valuable for mobile devices, as it reduces data usage and improves responsiveness.

http2.getPackedSettings([settings])

settings {HTTP/2 Settings Object}
Returns: {Buffer}

Converts an HTTP/2 settings object into a packed buffer representation, as specified in the [HTTP/2][] specification. This is intended for use with the HTTP2-Settings header field.

const http2 = require('node:http2')

// Initialize a settings object to pack
const settings = {
  enablePush: false,
  headerTableSize: 4096
}

// Pack the settings object into a buffer
const packedSettings = http2.getPackedSettings(settings)

// Print the base64-encoded packed settings
console.log(packedSettings.toString('base64')) // 'AAIAAAAA'

Simplified Explanation

Imagine HTTP/2 settings like dials on your kitchen oven. Each dial represents a different setting, like temperature or timer. The http2.getPackedSettings() function is like pressing all the dials into a single button so you can send it to your friend over text.

The friend can then read the text message (the packed buffer) and use it to adjust their oven dials to match yours. This allows you to quickly share your oven settings with others without having to explain each dial individually.

Note: What's different from the kitchen oven example is that http2.getPackedSettings() actually converts the settings into a binary code (the buffer), not a text message. However, the concept of packing all the settings into a single message is the same.

Real-World Applications

Efficiently sharing HTTP/2 settings: Sharing packed settings in the HTTP2-Settings header field allows endpoints to quickly and efficiently negotiate the desired settings for the HTTP/2 connection.

`http2.getUnpackedSettings(buf)`

Simplified Explanation

HTTP/2 settings are used to negotiate various aspects of the connection, such as the maximum frame size and the initial window size.

http2.getUnpackedSettings() takes a buffer of packed settings and returns a JavaScript object with the unpacked settings.

Detailed Explanation

HTTP/2 Settings

HTTP/2 settings are a way for the client and server to negotiate various aspects of the connection, such as:

Maximum Frame Size: The maximum size of a frame that can be sent.
Initial Window Size: The amount of data that can be sent before receiving an acknowledgment.
Max Concurrent Streams: The maximum number of concurrent streams that can be open.

Packed Settings

Settings are sent in a packed format to save space. The packed format is a buffer of bytes, where each byte represents a setting.

Unpacked Settings

http2.getUnpackedSettings() takes a buffer of packed settings and returns a JavaScript object with the unpacked settings. The object has properties for each setting, with the value of the property being the unpacked value.

Real-World Application

HTTP/2 settings are used to optimize the performance of HTTP/2 connections. By negotiating the appropriate settings, the client and server can improve the efficiency of the connection and reduce latency.

Code Example

const http2 = require("http2");

const buf = Buffer.from([
  0x01,
  0x00,
  0x00,
  0x00, // Maximum Frame Size: 16384 bytes
  0x04,
  0x00,
  0x00,
  0x00, // Initial Window Size: 262144 bytes
  0x05,
  0x00,
  0x00,
  0x00, // Max Concurrent Streams: 100
]);

const settings = http2.getUnpackedSettings(buf);

console.log(settings);
// {
//   maxFrameSize: 16384,
//   initialWindowSize: 262144,
//   maxConcurrentStreams: 100
// }

`http2.performServerHandshake(socket[, options])`

Creates an HTTP/2 server session from an existing socket.

Parameters

socket {stream.Duplex}
options {Object}
- ...: Any [http2.createServer()][] option can be provided.

Returns

{ServerHttp2Session}

Example

const http2 = require('http2');
const net = require('net');

const socket = net.connect(8000);

// Create an HTTP/2 server session from the existing socket
const session = http2.performServerHandshake(socket);

// Now that we have an HTTP/2 session, we can create and send HTTP/2 requests
const request = session.request({
  ':method': 'GET',
  ':path': '/'
});

// Optionally, wait for the 'response' event to handle the response
request.on('response', (headers, flags) => {
  ...
});

// Or, retrieve the response directly
session.submitRequest(request, (err, headers) => {
  if (err) {
    ...
  }
  const response = session.recvResponse(headers, flags);
  ...
});

Real-World Applications

HTTP/2 is a binary protocol that provides significant performance improvements over HTTP/1.1. It is particularly useful for applications that require high throughput and low latency, such as websockets and real-time streaming.

By using http2.performServerHandshake(), you can create an HTTP/2 server session from an existing socket, which allows you to take advantage of HTTP/2's performance benefits without having to implement the entire HTTP/2 protocol stack yourself.

`http2.sensitiveHeaders`

Type: Symbol
Purpose: This symbol is used to mark HTTP/2 headers as "sensitive". Sensitive headers are treated specially by HTTP/2 clients and servers, and may not be transmitted over the wire in plaintext.
How to Use: To mark a header as sensitive, set the http2.sensitiveHeaders property on the headers object to an array of header names.

const headers = {
  'content-type': 'application/json',
  'x-api-key': 'my-secret-api-key'
};

headers[http2.sensitiveHeaders] = ['x-api-key'];

Potential Applications: Sensitive headers can be used to protect sensitive information, such as API keys, passwords, and other tokens. By marking a header as sensitive, you can ensure that it is not transmitted over the wire in plaintext, which could prevent it from being intercepted and compromised.

Real-World Example

The following is a real-world example of how to use http2.sensitiveHeaders to protect an API key:

const http2 = require('http2');

const server = http2.createServer((req, res) => {
  // Check if the request contains a sensitive header.

  if (req.headers[http2.sensitiveHeaders] && req.headers[http2.sensitiveHeaders].includes('x-api-key')) {
    // If the request contains a sensitive header, do not transmit it over the wire in plaintext.

    res.writeHead(403, {
      'content-type': 'application/json'
    });

    res.end(JSON.stringify({
      error: 'Forbidden'
    }));

    return;
  }

  // If the request does not contain a sensitive header, proceed as normal.

  res.writeHead(200, {
    'content-type': 'application/json'
  });

  res.end(JSON.stringify({
    message: 'Hello, world!'
  }));
});

server.listen(8000);

In this example, the server checks if the request contains a sensitive header with the name x-api-key. If the header is present, the server responds with a 403 Forbidden error. This prevents the API key from being transmitted over the wire in plaintext, which could prevent it from being intercepted and compromised.

Headers in HTTP2

What are Headers?

Headers are like labels that are added to HTTP messages. They provide information about the message, such as the type of data being sent, the sender's location, or the desired action.

Headers in HTTP2

In HTTP2, headers are represented as objects, with keys and values. The keys are always in lowercase, and the values can be strings or arrays of strings.

Example:

const headers = {
  ":status": "200",
  "content-type": "text-plain",
  abc: ["has", "more", "than", "one", "value"],
};

Special Headers

Some headers have special meanings:

:status: The HTTP status code, such as 200 for "OK".
:method: The HTTP method, such as "GET" or "POST".
:authority: The authority of the request, such as "example.com".
:scheme: The scheme of the request, such as "https".
:path: The path of the request, such as "/index.html".
:protocol: The HTTP protocol version, such as "HTTP/2".

Duplicate Headers

HTTP2 allows duplicate headers. For example, the following headers are allowed:

const headers = {
  "content-type": "text/html",
  "content-type": "application/json",
};

When duplicate headers are received, they are combined into a single header value. In this case, the content-type header would have the value text/html, application/json.

Incoming Headers

When HTTP2 receives a message, it processes the headers as follows:

The :status, :method, :authority, :scheme, :path, and :protocol headers are converted to their appropriate types (number, string, etc.).
Duplicate headers are discarded, except for set-cookie and cookie.
set-cookie is always an array. Duplicates are added to the array.
cookie values are joined together with '; '.

Real-World Applications

Headers are used in a variety of ways, including:

Authentication: The Authorization header is used to send a user's credentials to the server.
Content negotiation: The Accept header is used to specify the types of data that the client can accept.
Caching: The Cache-Control header is used to control how responses are cached.
Security: The X-Content-Type-Options header is used to prevent cross-site scripting attacks.

Sensitive Headers in HTTP2

Imagine that you are sending a secret letter to a friend. You want to protect the contents of this letter, so you use a special code to encrypt it. This way, only your friend with the key can read your message.

In the same way, there are certain headers in HTTP2 that can be considered "sensitive". These headers contain information that should not be shared with just anyone. For example, your friend's name, address, or phone number shouldn't be shared with everyone.

To protect these headers, HTTP2 has a way to mark them as "sensitive". This means that the special code (HTTP/2 header compression algorithm) that normally helps make HTTP2 faster will not include these sensitive headers in its calculations. This way, it's harder for attackers to guess or predict the values of these headers.

Code Example:

const headers = {
  ":status": "200",
  "content-type": "text/plain",
  cookie: "your-friend-is-cool",
  "secret-info": "shhh...",
  [http2.sensitiveHeaders]: ["cookie", "secret-info"],
};

stream.respond(headers);

In this example, we are sending a response with two sensitive headers: "cookie" and "secret-info". By adding these headers to the [http2.sensitiveHeaders] property, we are telling HTTP2 to keep them private.

Potential Applications:

Sensitive headers are important for protecting user privacy and security. They can be used to safeguard information such as:

Passwords
Credit card numbers
Social Security numbers
Medical records
Other personal data

By marking these headers as sensitive, businesses and organizations can help prevent unauthorized access to sensitive information and protect their users from potential harm.

Settings Object in HTTP/2

In HTTP/2, settings configure how communication happens between the client and server. They define details like the size of data frames and the number of concurrent streams allowed.

Properties:

headerTableSize: Determines the maximum size of a compressed header table, reducing data transmission overhead.
enablePush: Controls whether the server can "push" (send) resources to the client without a client request. This can improve performance for commonly used assets.
initialWindowSize: Sets the initial size of the window for exchanging data, preventing buffer overflows.
maxFrameSize: Specifies the maximum size of a single data frame, ensuring the receiver can handle incoming data efficiently.
maxConcurrentStreams: Limits the number of concurrent streams allowed, balancing resource consumption and communication speed.
maxHeaderListSize: Defines the maximum uncompressed size of header fields, controlling the amount of data sent in request and response headers.
enableConnectProtocol: Enables the extended connect protocol, allowing HTTP/2 to establish connections over HTTP/1.1.
customSettings: Allows for additional, non-standard settings to be defined and exchanged.

Code Example:

const http2 = require("http2");

const settings = {
  headerTableSize: 4096,
  enablePush: true,
  initialWindowSize: 65535,
  maxFrameSize: 16384,
  maxConcurrentStreams: 100,
  maxHeaderListSize: 65535,
  customSettings: {
    17: 12345, // Custom setting with ID 17 set to value 12345
  },
};

const server = http2.createServer(settings);
server.on("stream", (stream, headers) => {
  // Handle incoming streams...
});
server.listen(8000);

Real-World Applications:

Header Compression: Reducing header size with headerTableSize improves webpage loading speed.
Push Streaming: Preloading resources with enablePush enhances user experience on slow networks.
Optimized Data Exchange: initialWindowSize and maxFrameSize prevent data loss and optimize communication efficiency.
Managing Concurrency: maxConcurrentStreams regulates the number of simultaneous requests, balancing server load and responsiveness.
Customizable Settings: customSettings allows for customization to suit specific application needs.

Error Handling in Node.js' HTTP/2 Module

Types of Errors

The HTTP/2 module can throw different types of errors:

1. Validation Errors:

Occur when you pass incorrect values to the module, like an invalid input.
Example: Trying to send data on a closed stream.

2. State Errors:

Occur when you try to perform an action at the wrong time.
Example: Attempting to write data to a closed stream.

3. Internal Errors:

Unexpected failures within the HTTP/2 session.
Example: A bug in the HTTP/2 implementation.

4. Protocol Errors:

Violations of HTTP/2 protocol rules.
Example: A client sending a header with an invalid value.

Error Handling

1. Synchronous Errors (Validation and State Errors):

Thrown immediately using throw.
Example:

try {
  const invalidStream = new Http2Stream(); // Creates an invalid stream
  invalidStream.write('Hello'); // Throws a validation error
} catch (err) {
  console.error(err); // Handle the error
}

2. Asynchronous Errors (Internal and Protocol Errors):

Reported through an 'error' event on the relevant object (e.g., stream, session, server).
Example:

const server = http2.createServer();

server.on('error', (err) => {
  console.error(err); // Handle the internal error on the server
});

Real-World Applications

1. Validating Client Requests:

Use validation errors to check if client requests meet required expectations before processing them.

2. Handling Connection Issues:

Monitor for state errors to detect connection problems and take appropriate actions (e.g., reconnect).

3. Debugging Internal Server Errors:

Use internal errors to identify and fix bugs within the HTTP/2 server implementation.

4. Enforcing Protocol Compliance:

Detect protocol errors to ensure that clients and servers follow HTTP/2 standards, preventing potential security risks.

Invalid Character Handling in HTTP/2 Headers

What is HTTP/2?

HTTP/2 is a newer version of the HTTP protocol used for faster and more efficient communication on the web.

What are HTTP Headers?

HTTP headers are pieces of information that are sent at the beginning of a request or response. They provide details about the data being sent.

Invalid Characters in Headers

HTTP/2 has stricter rules about which characters can be used in header names and values. Specifically, header names can only contain these characters:

a-z, A-Z, 0-9, !, #, $, %, &, ', *, +, -, ., ^, _, `, |, ~

Header values should not contain newlines or carriage returns and should ideally be limited to US-ASCII characters.

What Happens if Invalid Characters Are Used?

If an invalid character is used in a header name, the HTTP/2 stream will be closed with an error. This is because invalid characters can cause confusion and security issues.

How Node.js Handles Headers

Node.js allows you to specify header names in mixed case (e.g., Content-Type), but it will automatically convert them to lowercase (e.g., content-type) before sending them.

Real-World Example

Consider a request header:

Content-TYPE: application/json

This header contains an invalid character ("TYPE" instead of "Type") in the name. If sent over HTTP/2, it will cause an error.

Potential Applications

Ensuring valid characters in HTTP headers is essential for:

Security: Invalid characters can be used for malicious purposes, such as cross-site scripting attacks.
Compatibility: HTTP/2 devices and servers may not handle invalid characters correctly, leading to errors.
Data Integrity: Incorrectly formatted headers can corrupt the data being sent or received.

Simplified Explanation:

HTTP/2 allows a server to "push" streams (data) to the client without the client explicitly requesting them. This is useful for sending additional resources or data that the client may need, such as stylesheets or scripts.

Client-Side Implementation:

Set a Stream Listener:
```
client.on('stream', (pushedStream, requestHeaders) => { ... });
```
This listens for incoming pushed streams. When a stream is received, pushedStream will be the stream object, and requestHeaders will contain the headers sent by the server.
Handle Push Events:
```
pushedStream.on('push', (responseHeaders) => { ... });
```
When a push event occurs, this listener will receive the response headers from the server.
Process Pushed Data:
```
pushedStream.on('data', (chunk) => { ... });
```
This listener handles incoming data from the pushed stream. It allows the client to process and use the data as needed.

Real-World Example:

A website can push a CSS stylesheet to the client as soon as it establishes a connection. This way, the stylesheet is loaded even before the user requests a specific page, resulting in a faster and smoother experience.

Code Example:

const http2 = require("node:http2");

const client = http2.connect("http://localhost");

client.on("stream", (pushedStream, requestHeaders) => {
  console.log("Received pushed stream with headers:", requestHeaders);

  pushedStream.on("push", (responseHeaders) => {
    console.log("Received push event with headers:", responseHeaders);
  });

  pushedStream.on("data", (chunk) => {
    console.log(`Received data from pushed stream: ${chunk}`);
  });
});

const req = client.request({ ":path": "/" });

This code sets up a listener for pushed streams and logs information about the headers and data received from the stream.

HTTP/2 CONNECT Method

The CONNECT method in HTTP/2 allows an HTTP/2 server to act as a proxy for TCP/IP connections. This means that a client can use an HTTP/2 connection to establish a connection to a different server.

Simple TCP Server

A simple TCP server listens for incoming connections on a specified port. When a client connects to the server, it can send and receive data.

const net = require("node:net");

const server = net.createServer((socket) => {
  let name = "";
  socket.setEncoding("utf8");
  socket.on("data", (chunk) => (name += chunk));
  socket.on("end", () => socket.end(`hello ${name}`));
});

server.listen(8000);

HTTP/2 CONNECT Proxy

An HTTP/2 CONNECT proxy acts as an intermediary between an HTTP/2 client and a TCP server. When an HTTP/2 client sends a CONNECT request to the proxy, the proxy establishes a connection to the specified TCP server and then forwards all data between the client and the server.

const http2 = require("node:http2");
const { NGHTTP2_REFUSED_STREAM } = http2.constants;
const net = require("node:net");

const proxy = http2.createServer();
proxy.on("stream", (stream, headers) => {
  if (headers[":method"] !== "CONNECT") {
    // Only accept CONNECT requests
    stream.close(NGHTTP2_REFUSED_STREAM);
    return;
  }
  const auth = new URL(`tcp://${headers[":authority"]}`);
  // It's a very good idea to verify that hostname and port are
  // things this proxy should be connecting to.
  const socket = net.connect(auth.port, auth.hostname, () => {
    stream.respond();
    socket.pipe(stream);
    stream.pipe(socket);
  });
  socket.on("error", (error) => {
    stream.close(http2.constants.NGHTTP2_CONNECT_ERROR);
  });
});

proxy.listen(8001);

HTTP/2 CONNECT Client

An HTTP/2 CONNECT client sends a CONNECT request to a proxy server, specifying the destination server that it wants to connect to. The proxy server establishes the connection and then forwards all data between the client and the destination server.

const http2 = require("node:http2");

const client = http2.connect("http://localhost:8001");

// Must not specify the ':path' and ':scheme' headers
// for CONNECT requests or an error will be thrown.
const req = client.request({
  ":method": "CONNECT",
  ":authority": "localhost:8000",
});

req.on("response", (headers) => {
  console.log(headers[http2.constants.HTTP2_HEADER_STATUS]);
});
let data = "";
req.setEncoding("utf8");
req.on("data", (chunk) => (data += chunk));
req.on("end", () => {
  console.log(`The server says: ${data}`);
  client.close();
});
req.end("Jane");

Real-World Applications

The HTTP/2 CONNECT method can be used for a variety of applications, including:

Secure tunneling: CONNECT can be used to create a secure tunnel between a client and a server. This tunnel can be used to send sensitive data, such as passwords or financial information, over an insecure network.
Proxy servers: CONNECT can be used to create proxy servers that allow clients to access blocked websites or content.
Load balancing: CONNECT can be used to load balance traffic across multiple servers.

Extended CONNECT Protocol

What is it?

The Extended CONNECT Protocol is an extension to HTTP/2 that allows you to use the CONNECT method to establish a tunnel for other communication protocols, such as WebSockets.

How to enable it?

On the server side, you can enable the Extended CONNECT Protocol by setting the enableConnectProtocol option to true when creating the HTTP/2 server:

const http2 = require("node:http2");
const server = http2.createServer({ enableConnectProtocol: true });

How to use it?

Once the client receives the SETTINGS frame from the server indicating that the extended CONNECT may be used, it can send CONNECT requests that use the ':protocol' HTTP/2 pseudo-header:

const http2 = require("node:http2");
const client = http2.connect("http://localhost:8080");

client.on("remoteSettings", (settings) => {
  if (settings.enableConnectProtocol) {
    const req = client.request({ ":method": "CONNECT", ":protocol": "foo" });
  }
});

Real-world applications

One potential application of the Extended CONNECT Protocol is to enable WebSockets over HTTP/2. This can provide performance benefits over using a separate WebSocket connection.

Example

Here is a complete example of using the Extended CONNECT Protocol to establish a WebSocket connection:

Server:

const http2 = require("node:http2");

const server = http2.createServer({ enableConnectProtocol: true });

server.on("request", (req, res) => {
  if (
    req.headers[":method"] === "CONNECT" &&
    req.headers[":protocol"] === "websocket"
  ) {
    res.writeHead(200, { "Content-Type": "application/octet-stream" });
    res.end();
  } else {
    res.end();
  }
});

server.listen(8080);

Client:

const http2 = require("node:http2");

const client = http2.connect("http://localhost:8080");

client.on("remoteSettings", (settings) => {
  if (settings.enableConnectProtocol) {
    const req = client.request({
      ":method": "CONNECT",
      ":protocol": "websocket",
    });
    req.on("response", (res) => {
      if (res.statusCode === 200) {
        // WebSocket connection established
      }
    });
    req.end();
  }
});

This example shows how to use the Extended CONNECT Protocol to establish a WebSocket connection over HTTP/2. The client sends a CONNECT request to the server, and the server responds with a 200 OK status code. This indicates that the WebSocket connection has been established, and the client can now send and receive WebSocket messages.

Compatibility API

What is it?

The Compatibility API in Node.js helps you use HTTP/2 while still working with code written for HTTP/1. It gives you a similar developer experience for both protocols.

How does it work?

The Compatibility API creates a bridge between HTTP/1 and HTTP/2, allowing you to use HTTP/1 functions and methods with HTTP/2.

Example

Let's say you have an HTTP/1 server like this:

const http = require("http");

const server = http.createServer((req, res) => {
  res.writeHead(200, { "Content-Type": "text/plain" });
  res.end("Hello, HTTP/1!");
});

To make it compatible with HTTP/2, you can use the Compatibility API:

const http2 = require("http2");

const server = http2.createServer((req, res) => {
  res.setHeader("Content-Type", "text/html");
  res.writeHead(200, { "Content-Type": "text/plain; charset=utf-8" });
  res.end("ok");
});

This code creates an HTTP/2 server that behaves like the HTTP/1 server. It sets the same headers and responds with the same content.

Real-world Applications

The Compatibility API is useful for:

Upgrading existing HTTP/1 applications to HTTP/2 without major code changes
Developing applications that support both HTTP/1 and HTTP/2 clients

Additional Notes

The Compatibility API targets only the public API of HTTP/1.
Internal methods and state of HTTP/1 modules are not supported.
Upgrading from non-TLS HTTP/1 servers to HTTP/2 is not supported.

ALPN Negotiation

Simplified Explanation:

ALPN (Application-Layer Protocol Negotiation) lets you use both HTTPS and HTTP/2 over the same internet connection. It's like having two lanes on a highway, one for old cars (HTTP/1) and one for newer cars (HTTP/2).

How it Works:

When a client (e.g., a browser) connects to a server, it tells the server which protocols it supports.
The server checks if it also supports any of those protocols.
If there's a match, ALPN chooses the highest-supported protocol (usually HTTP/2 if available).

Real-World Application:

ALPN allows you to use HTTP/2 for features like multiplexing (sending multiple requests over the same connection) and server push (server sending data to client without being asked). This can improve website performance and speed.

Example Code

Server:

const https = require("https");
const fs = require("fs");

const options = {
  key: fs.readFileSync("server.key"),
  cert: fs.readFileSync("server.crt"),
  allowHTTP1: true, // Allow both HTTP/1 and HTTP/2 on the same port
};

const server = https.createServer(options, (req, res) => {
  const alpnProtocol = req.alpnProtocol || "HTTP/1.1";
  res.writeHead(200, { "Content-Type": "text/plain" });
  res.write(`ALPN Protocol: ${alpnProtocol}`);
  res.end();
});

server.listen(443);

Client:

const https = require("https");

const options = {
  port: 443,
  servername: "localhost",
  alpnProtocols: ["h2", "http/1.1"], // List of supported protocols in order of preference
};

const req = https.request(options, (res) => {
  console.log(`ALPN Protocol: ${res.alpnProtocol}`);
});

req.end();

Output:

ALPN Protocol: h2

In this example, the server and client agree on HTTP/2 as the preferred protocol and use it for their communication.

Class: http2.Http2ServerRequest

Purpose: Represents an HTTP/2 server request.

Inheritance:

Extends: stream.Readable (a Node.js class for reading data in a stream)

What it is:

A Http2ServerRequest object is created when an HTTP/2 client sends a request to an HTTP/2 server. It contains information about the request, such as the HTTP method, headers, and data.

Properties and Methods:

Headers: A dictionary containing the HTTP request headers. For example, if the request contains a header 'Content-Type' with a value of 'application/json', the headers property would contain { 'Content-Type': 'application/json' }.
Method: The HTTP method used in the request. For example, 'GET', 'POST', 'PUT'.
Url: The URL of the requested resource.
Protocol: The HTTP protocol version used in the request. For HTTP/2, it's usually 'HTTP/2'.
Pipe(destination): Pipes the request data to the specified destination stream.

Real-World Example:

const { Http2Server } = require("http2");

// Create an HTTP/2 server and listen on port 8000
const server = new Http2Server();
server.listen(8000);

// Handle incoming requests
server.on("request", (req, res) => {
  // Get the request method and URL
  const method = req.method;
  const url = req.url;

  // Send a response with a status code of 200 and a body of "Hello World!"
  res.writeHead(200, { "Content-Type": "text/plain" });
  res.end("Hello World!");
});

Potential Applications:

Building HTTP/2 servers that handle client requests and send responses.
Creating request handlers for custom HTTP/2 request processing.
Monitoring HTTP/2 traffic and analyzing request patterns.

'aborted' Event

Explanation:

Imagine you're having a phone conversation when suddenly, the line goes dead. That's like the 'aborted' event. It means a communication (HTTP/2 request) was interrupted unexpectedly.

Example:

const http2 = require("http2");

const server = http2.createSecureServer();

server.on("request", (req, res) => {
  // If the request is abnormally ended...
  req.on("aborted", () => {
    console.log("Oops, the communication was cut off!");
    res.end();
  });
});

server.listen(8000);

Real-World Applications

Potential applications:

Graceful handling of interrupted requests: To prevent data loss or avoid leaving the client in an incomplete state.
Debugging and diagnostics: To identify communication issues.
Error reporting: To notify administrators or monitoring systems of unexpected terminations.

Event: `'close'`

Explanation:

When you use the http2 module in Node.js to make requests and receive responses, each response is associated with a stream. When the server closes the stream, the 'close' event is emitted. This event indicates that the server has finished sending the response and there will be no more data received.

Example:

const http2 = require("http2");

const client = http2.connect("https://example.com");

const req = client.request({ ":path": "/" });

req.on("close", () => {
  console.log("Response received and server has closed the stream.");
});

Potential Applications:

Logging the completion of server responses for debugging and monitoring purposes.
Handling the end of a streaming response where data is received incrementally.
Closing the client connection after all responses have been received and processed.

Simplified Explanation of request.aborted Property

The request.aborted property of an HTTP/2 request object indicates whether the request has been canceled or stopped before completion.

How it Works

When a request is made, it's assigned a unique identifier called a request ID. If the request is aborted, the request ID is removed from the list of active requests, and the request is no longer processed. The request.aborted property is set to true to indicate this.

Real-World Example

Imagine you're sending a request to a server to load a web page. Suddenly, you change your mind and want to navigate to a different page. The browser will automatically abort the first request, and the request.aborted property of that request will be set to true.

Applications in the Real World

Performance Optimization: Aborting requests that are no longer needed can improve performance, especially in applications that make numerous HTTP/2 requests concurrently.
Error Handling: If a request encounters an error, it can be aborted to prevent further processing and to handle the error gracefully.
Security: Aborting requests from unauthorized sources can enhance the security of web applications.

Code Example

The following code checks if a request has been aborted:

const http2 = require('http2');

const client = http2.connect('https://example.com');

const request = client.request({ ':path': '/' });

request.on('aborted', () => {
  console.log('The request was aborted!');
});

HTTP Request Authority Pseudo-Header Field

In HTTP/2 protocol, requests can set either the :authority or host header field to identify the server they are connecting to.

request.authority Property

The request.authority property of the request object in Node.js's http2 module provides the value of the :authority pseudo-header field. This value is derived from the :authority header if it is present in the request, or from the host header otherwise.

Simplified Explanation

Think of :authority as the name of the website or service you are trying to connect to. When you type a URL like "example.com" into your browser, your browser sends an HTTP request to "example.com". The :authority header in this request would be "example.com".

Real-World Example

const http2 = require("http2");

const server = http2.createSecureServer();

server.on("request", (req, res) => {
  // Get the request authority.
  const authority = req.authority;

  // Do something with the authority, such as:
  console.log(`Request to ${authority}`);

  // Send a response.
  res.end("Hello, world!");
});

server.listen(8443);

In this example, the server listens on port 8443 and handles incoming HTTP/2 requests. When a request is received, the server logs the :authority header to the console and sends a response with the message "Hello, world!".

Potential Applications

The :authority header is useful for:

Identifying the server to connect to.
Load balancing requests across multiple servers.
Securing communications by ensuring that requests are only sent to authorized servers.

What is request.complete?

In Node.js, the request.complete property of the http2 module indicates whether an HTTP/2 request has been finished.

Simplified Explanation:

Imagine you're making an online order. When you click "submit", the request is sent to the server. The request.complete property will be false while the order is being processed. Once the order is complete, request.complete will change to true.

Why is request.complete useful?

Knowing when a request is complete is helpful for:

Error handling: If request.complete is true and the response contains an error, you can handle the error accordingly.
Resource release: If request.complete is true, you can release any resources associated with the request, such as memory or network connections.
Performance optimization: By checking request.complete, you can avoid unnecessary processing or waiting for incomplete requests.

Real-World Example:

The following code shows how to handle a request.complete event:

const http2 = require("http2");
const fs = require("fs");

// Create an HTTP/2 server
const server = http2.createServer();

// Define a request listener
server.on("request", (request, response) => {
  // The request is not complete yet
  console.log(`Request complete: ${request.complete}`); // false

  // Process the request...

  // Once the request is complete, respond to the client
  request.on("end", () => {
    console.log(`Request complete: ${request.complete}`); // true
    response.end();
  });
});

// Start the server
server.listen(8000);

Potential Applications:

Web servers: Handle requests efficiently and release resources when requests are complete.
REST APIs: Track the progress of API requests and provide real-time updates to clients.
Streaming services: Ensure smooth streaming by handling incomplete requests gracefully.

`request.connection`

The request.connection property in Node.js is deprecated and you should use the request.socket property instead. Both properties return a reference to the underlying network socket or TLS socket used to communicate with the remote peer.

Here's a simplified explanation:

What is `request.connection`?

When you make an HTTP/2 request using the http2 module, a network socket or TLS socket is created to establish a connection with the remote server. The request.connection property allows you to access this socket object.

Why is `request.connection` deprecated?

The request.connection property is deprecated because it can be confusing to use. The request.socket property provides a more consistent and reliable way to access the underlying socket.

How to use `request.socket`?

You can access the underlying socket using the request.socket property. This property returns a reference to a net.Socket or tls.TLSSocket object.

Here's an example:

const http2 = require("http2");

const client = http2.connect("https://example.com");

client.on("stream", (stream) => {
  stream.on("data", (data) => {
    console.log(`Received data: ${data}`);
  });

  stream.socket.on("close", () => {
    console.log("Socket closed");
  });
});

In this example, the stream.socket property refers to the underlying socket used to communicate with the remote server. You can use this socket object to listen for events, such as the 'close' event in this example.

Potential applications in real world

Accessing the underlying socket can be useful for debugging purposes or for implementing custom network features, such as rate limiting or traffic shaping.

Destroy Request

Imagine you have a request coming in through an HTTP/2 connection. This request is like a letter you receive in the mail.

When you're done with a letter, you can tear it up and throw it away. Similarly, when you're done processing an HTTP/2 request, you can tell the server to "destroy" it.

The request.destroy() method does just that. It tells the server, "Hey, I'm finished with this request. You can close the connection now."

What happens when you destroy a request?

If you provide an error as an argument to request.destroy(), the server will emit an 'error' event and pass the error to any listeners on the event. This is useful for handling errors during request processing.

For example, if you encounter an error while parsing the request body, you could destroy the request with the error:

request.on("error", (err) => {
  console.error(err);
  request.destroy(err);
});

What if the request is already destroyed?

If you try to destroy a request that has already been destroyed, nothing happens. The server will simply ignore the request.

Real-world applications:

Using request.destroy() can be useful in the following situations:

You want to close the connection after processing a request.
You encounter an error while processing the request.
You want to release any resources associated with the request.

request.headers

In HTTP/2, the request/response headers object is a collection of key-value pairs that provide additional information about the request or response. The keys are the header names, which are always in lower case, and the values are the header values.

Example:

const headers = {
  "user-agent": "curl/7.22.0",
  host: "127.0.0.1:8000",
  accept: "*/*",
};

In this example, the user-agent header indicates the type of client that is making the request, the host header specifies the server that the request is being sent to, and the accept header indicates the types of content that the client is willing to accept.

Special Headers

In HTTP/2, the request path, host name, protocol, and method are represented as special headers prefixed with the : character (e.g. ':path'). These special headers are included in the request.headers object.

Example:

const headers = {
  ":path": "/index.html",
  ":host": "127.0.0.1:8000",
  ":method": "GET",
  "user-agent": "curl/7.22.0",
  accept: "*/*",
};

In this example, the special headers ':path', ':host', and ':method' indicate the request path, host name, and method, respectively.

Removing Headers

It is important to note that removing all headers from the request will cause errors to occur.

Example:

const headers = {
  ":path": "/index.html",
  ":host": "127.0.0.1:8000",
  ":method": "GET",
  "user-agent": "curl/7.22.0",
  accept: "*/*",
};

delete headers[":path"];

assert(headers[":path"]); // Fails because the :path header has been removed

Real-World Applications

The request/response headers object is used in a variety of real-world applications, including:

Authentication: The Authorization header is used to authenticate the client to the server.
Content negotiation: The Accept and Content-Type headers are used to negotiate the format of the response.
Caching: The Cache-Control header is used to control how the response is cached.
Security: The X-XSS-Protection and X-Content-Type-Options headers are used to protect against cross-site scripting and MIME type sniffing attacks.

request.httpVersion

Explanation:

It's a string that represents the HTTP version sent by the client in a server request or the HTTP version of the server your client is connected to in a client response.
By default, it's always '2.0', which means HTTP/2.

Simplified Example:

// Server request
const request = {
  httpVersion: '2.0', // HTTP/2
};

// Client response
const response = {
  httpVersion: '2.0', // HTTP/2
};

message.httpVersionMajor and message.httpVersionMinor

Explanation:

httpVersionMajor is the first integer in the HTTP version string.
httpVersionMinor is the second integer in the HTTP version string.

Simplified Example:

// HTTP/2
const httpVersionMajor = 2;
const httpVersionMinor = 0;

Real-World Example:

HTTP/2 is faster and more efficient than previous HTTP versions, so it's commonly used in modern web applications to improve performance.

For example, a website that streams videos or downloads large files would benefit from using HTTP/2 because it allows for faster transfer speeds.

request.method

The request.method property in http2 is a string representing the HTTP method of the request. Read-only. Examples: 'GET', 'DELETE'.

Example:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream, headers) => {
  stream.respond({
    ":status": 200,
    "content-type": "text/plain",
  });
  stream.end("Hello World\n");
});

server.listen(8000);

// Create a client
const client = http2.connect("http://localhost:8000");

// Create a request
const req = client.request({
  ":method": "GET",
  ":path": "/",
});

// Send the request
req.end();

// Listen for a response
req.on("response", (headers, flags) => {
  headers[":status"]; // 200
});

What is request.rawHeaders?

In Node.js's http2 module, request.rawHeaders is a property of an HTTP request object that contains a list of all the headers sent by the client.

Why is it important?

The request.rawHeaders property is useful for accessing the original headers sent by the client, including any that have been modified or removed by middleware or other components. This can be helpful for debugging and troubleshooting purposes.

How to use it

To access the request.rawHeaders property, you can use the following code:

const headers = request.rawHeaders;

The headers variable will now contain an array of strings representing the raw headers sent by the client.

Example

The following example shows how to use the request.rawHeaders property to access the original headers sent by the client:

const http2 = require("http2");

const server = http2.createSecureServer({
  key: fs.readFileSync("key.pem"),
  cert: fs.readFileSync("cert.pem"),
});

server.on("request", (request, response) => {
  const headers = request.rawHeaders;

  console.log(headers);

  response.end();
});

server.listen(8443);

When a client sends a request to this server, the headers variable will contain an array of strings representing the raw headers sent by the client.

Potential applications

The request.rawHeaders property can be used for a variety of purposes, including:

Debugging and troubleshooting
Accessing the original headers sent by the client
Modifying or removing headers before they are processed by middleware or other components

request.rawTrailers

Simplified Explanation:

When sending an HTTP/2 request, you can add extra information known as "trailers" at the very end of the request. These trailers provide additional details that can be accessed by the server.

Detailed Explanation:

Trailers are key-value pairs that are sent after the request body. They are similar to headers, but they are sent at the end of the request instead of the beginning. This allows you to specify information that may not be available until after the request body has been generated.

For example, you could use trailers to provide information about the total size of the request body, or to indicate that the request was chunked.

Code Snippet:

// Create an HTTP/2 client request
const client = http2.connect("https://example.com");
const request = client.request({
  ":method": "POST",
  ":path": "/",
});

// Add a trailer to the request
request.trailer("content-size", "1024");

// Send the request
request.end();

// Listen for the 'response' event
request.on("response", (headers, flags) => {
  console.log(headers);
});

Real-World Applications:

Trailers can be used in a variety of real-world applications, such as:

Chunking large request bodies: Trailers can be used to provide information about the total size of a request body, which is useful for chunking large files into smaller, more manageable chunks.
Providing additional context: Trailers can be used to provide additional context about a request, such as the user agent or the source IP address.
Error handling: Trailers can be used to indicate that an error occurred during the request, and to provide additional details about the error.

`request.scheme`

The request.scheme pseudo header field is a string that indicates the scheme portion of the target URL. The scheme is the protocol used to communicate with the server, such as http or https.

Simplified Explanation

Imagine you're sending a letter to your friend. The request.scheme is like the envelope that you use to send the letter. It tells the postal service how to deliver the letter, whether by regular mail, express mail, or some other method.

Code Snippet

const http2 = require("http2");

const server = http2.createServer();

server.on("request", (request, response) => {
  console.log(request.scheme); // 'https'
});

server.listen(8000);

Real-World Example

Let's say you're developing a website that allows users to securely log in. You would use the request.scheme to determine if the user is connecting over a secure (HTTPS) connection. If the user is not using a secure connection, you could redirect them to the HTTPS version of your website.

const http2 = require("http2");

const server = http2.createServer();

server.on("request", (request, response) => {
  if (request.scheme !== "https") {
    response.writeHead(301, { Location: "https://example.com" });
    response.end();
  } else {
    // Allow the user to log in.
  }
});

server.listen(8000);

Potential Applications

Security: Ensure that users are connecting to your website over a secure connection.
Performance: Optimize the delivery of content based on the user's connection type.
Troubleshooting: Identify and resolve issues related to the request scheme.

`request.setTimeout(msecs, callback)`

Sets the timeout for the HTTP/2 request to msecs milliseconds.

If a callback function is provided, it will be added as a listener for the 'timeout' event on the request object.

If no 'timeout' listener is added to the request, the response, or the server, then HTTP/2 streams are destroyed when they time out. If a handler is assigned to the request, the response, or the server's 'timeout' events, timed out sockets must be handled explicitly.

Here's a simplified example:

const http2 = require('http2');

const server = http2.createServer();
server.on('request', (req, res) => {
  req.setTimeout(10000, () => {
    res.writeHead(503);
    res.end();
  });
});
server.listen(3000);

In this example, the server will automatically destroy any HTTP/2 stream that does not receive a response within 10 seconds.

Here's another example that demonstrates how to handle timed out sockets explicitly:

const http2 = require('http2');

const server = http2.createServer();
server.on('request', (req, res) => {
  req.setTimeout(10000, () => {
    console.log('Request timed out!');
    res.writeHead(503);
    res.end();
  });
});
server.on('timeout', (socket) => {
  console.log('Socket timed out!');
  socket.destroy();
});
server.listen(3000);

In this example, the server will log a message when a request times out, and it will destroy the timed out socket.

Potential applications

HTTP/2 timeouts can be used to prevent long-lived connections from being kept open indefinitely. This can improve the performance of your HTTP/2 server by reducing the number of open connections and freeing up resources.

Timeouts can also be used to prevent clients from sending requests that are too large or that take too long to process. This can help to protect your server from denial-of-service attacks.

What is request.socket?

request.socket is a special object in the HTTP/2 module that allows you to access the underlying network socket for a particular HTTP/2 request. It's like a proxy that sits between your request and the actual socket, and it lets you do things like:

Get information about the socket, such as the remote address and port
Set options on the socket, such as the timeout
Send data to the socket
Receive data from the socket

Why would you use request.socket?

You might use request.socket if you need to access the underlying socket for a specific reason. For example, you might need to set a custom timeout for the request, or you might need to send data to the socket directly.

How to use request.socket

To use request.socket, you can simply access it from the request object. For example:

const http2 = require("http2");

const client = http2.connect("https://example.com");

client.on("stream", (stream) => {
  stream.on("data", (chunk) => {
    console.log(`Received data: ${chunk.toString()}`);
  });

  // Get the underlying socket for the stream
  const socket = stream.socket;

  // Set a custom timeout for the socket
  socket.setTimeout(10000);

  // Send data to the socket
  socket.write("Hello, world!");
});

Real-world applications of request.socket

Here are some real-world applications of request.socket:

Custom timeouts: You can use request.socket to set custom timeouts for individual requests. This can be useful if you have some requests that are more important than others and you want to make sure they don't timeout.
Direct data sending: You can use request.socket to send data to the socket directly. This can be useful if you need to send data that is not part of the HTTP request, such as a custom header or a file upload.
Socket manipulation: You can use request.socket to manipulate the socket in other ways. For example, you can set the socket to keep-alive mode, or you can close the socket prematurely.

Conclusion

request.socket is a powerful tool that allows you to access and manipulate the underlying network socket for a particular HTTP/2 request. It can be used for a variety of purposes, including custom timeouts, direct data sending, and socket manipulation.

`request.stream`

A representation of an HTTP2 stream on the client side.

Usage

The following code sample shows you how to use the request.stream property:

const { HTTP2_HEADER_CONTENT_TYPE, HTTP2_HEADER_STATUS } = require("http2");
const http2 = require("http2");

const client = http2.connect("localhost:8080");

const req = client.request({
  ":method": "GET",
  ":path": "/",
});

req.on("response", (headers, flags) => {
  const contentType = headers[HTTP2_HEADER_CONTENT_TYPE];
  const statusCode = headers[HTTP2_HEADER_STATUS];

  console.log(`Received status ${statusCode} with headers:`);
  for (const pair of Array.from(headers.entries()))
    console.log(`  ${pair[0]}: ${pair[1]}`);

  req.on("data", (data) => {
    console.log(`Received data: ${data.toString()}`);
  });

  req.on("end", () => {
    console.log("End of data");
  });

  req.resume();
});

req.on("error", (err) => {
  console.error(`Request failed with error: ${err.message}`);
});

req.end();

`request.trailers`

request.trailers is an object that contains a key-value pairs of the trailers sent with the request. Trailers are the headers sent at the end of a HTTP/2 request or response. They are useful for providing additional information about the request or response that cannot be fit into the regular headers.

Example

const http2 = require("http2");

const client = http2.connect("https://localhost:3000");

const req = client.request({
  ":path": "/",
  ":method": "GET",
});

req.on("trailers", (trailers) => {
  console.log(trailers);
});

In this example, the req.on('trailers', (trailers) => { ... }) event listener is called when the trailers are received from the server. The trailers will be a key-value pairs object.

Potential applications

Trailers can be used for a variety of purposes, such as:

Providing additional information about the request or response
Providing authentication information
Providing information about the client or server
Providing information about the network connection

Real-world examples

Trailers are used in a variety of real-world applications, such as:

Authenticating requests using OAuth 2.0
Providing cache control information
Providing information about the client's browser or operating system
Providing information about the network connection

request.url is a string that contains the URL from the HTTP request.

Example:

GET /status?name=ryan HTTP/1.1
Accept: text/plain

In this example, request.url would be:

"/status?name=ryan";

This can be parsed further, using new URL():

$ node
> new URL('/status?name=ryan', 'http://example.com')
URL {
  href: 'http://example.com/status?name=ryan',
  origin: 'http://example.com',
  protocol: 'http:',
  username: '',
  password: '',
  host: 'example.com',
  hostname: 'example.com',
  port: '',
  pathname: '/status',
  search: '?name=ryan',
  searchParams: URLSearchParams { 'name' => 'ryan' },
  hash: ''
}

Real-world application:

This can be used to retrieve the URL from an HTTP request and parse it into its individual parts, such as the protocol, host, and path. This can be useful for logging, analytics, or redirecting requests.

Class: `http2.Http2ServerResponse`

An Http2ServerResponse object is created internally by an HTTP server and passed as the second parameter to the 'request' event.

Properties of an Http2ServerResponse Object:

stream: The underlying HTTP/2 stream object.
statusCode: The HTTP status code of the response.
headers: The HTTP response headers.
trailers: The HTTP response trailers.

Methods of an Http2ServerResponse Object:

writeHead(statusCode, headers): Sets the HTTP status code and headers for the response.
end(data): Ends the HTTP response and sends the data to the client.
addTrailers(headers): Adds HTTP trailers to the response.
close(): Closes the HTTP/2 stream.

Real-World Example:

const http2 = require("http2");

const server = http2.createServer();

server.on("request", (req, res) => {
  res.writeHead(200, { "Content-Type": "text/plain" });
  res.end("Hello, HTTP/2!");
});

server.listen(8000);

In this example, we create an HTTP/2 server using the createServer() method of the http2 module. When a client sends a request to the server, the 'request' event is emitted. We handle the event by setting the HTTP status code and headers, and then sending the response data using the end() method.

Potential Applications:

HTTP/2 ServerResponse objects are used in a variety of real-world applications, including:

Web servers
Proxies
Load balancers
Gateways

Event: 'close'

Explanation:

When you're using an HTTP/2 stream, the 'close' event indicates that the stream has been closed. This can happen for a few reasons:

The other end (the client or server) has closed the stream.
There was an error in the HTTP/2 protocol.
The stream has reached its maximum number of data frames.

Simplified Analogy:

Think of HTTP/2 as a two-way street where data is exchanged between two cars (the client and server). The 'close' event happens when one car drives away or there's a roadblock on the street.

Code Example:

const http2 = require("http2");

const client = http2.connect("...");

const request = client.request({ ":path": "/" });

request.on("close", () => {
  console.log("The HTTP/2 stream has been closed.");
});

Real-World Application:

When you close a tab in your browser, it sends a 'close' event to the HTTP/2 stream that was handling the request for that page.
If there's a network error while downloading a file, the 'close' event can be used to report the error.
Servers can use the 'close' event to clean up resources associated with a stream after it's been closed, like closing file handles or database connections.

Simplified Explanation of the 'finish' Event in Node.js's HTTP/2 Module:

What is the 'finish' Event?

When you send a response to a client using the HTTP/2 protocol, the 'finish' event is emitted. This means that all the data (headers and body) that makes up the response has been prepared and handed over to the network for transmission.

What happens after the 'finish' Event?

After this event, there will be no more events emitted for that particular response. This is because the response has been fully sent and there is nothing left to do.

Real-World Example:

Imagine you're sending a website page to a visitor. The 'finish' event would be emitted when the last bit of the page, including the text, images, and styles, has been sent to the visitor's browser.

Applications in Real World:

The 'finish' event is used in various applications, such as:

Monitoring: Knowing when a response has been sent can help you track performance and identify any delays in response delivery.
Error Handling: If the 'finish' event is not emitted within a certain time frame, it could indicate an issue with the network or the client, allowing you to address it promptly.
Caching: Some caching strategies use the 'finish' event to determine when a response has been fully cached and can be used to serve future requests.

Code Examples:

// Example 1: Listen for the 'finish' event on a response object
const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream) => {
  stream.respond({
    ":status": 200,
    "content-type": "text/plain",
  });

  stream.end("Hello, world!");

  stream.on("finish", () => {
    console.log("Response sent!");
  });
});

server.listen(8000);

// Example 2: Use the 'finish' event to track response performance
const http2 = require("http2");
const startTimes = {};

const server = http2.createServer();

server.on("stream", (stream) => {
  const startTime = Date.now();
  startTimes[stream.id] = startTime;

  stream.respond({
    ":status": 200,
    "content-type": "text/plain",
  });

  stream.on("finish", () => {
    const endTime = Date.now();
    const responseTime = endTime - startTimes[stream.id];
    console.log(`Response sent for stream ${stream.id} in ${responseTime}ms`);
  });
});

server.listen(8000);

`response.addTrailers(headers)`

Simplified Explanation:

This method is used to add extra headers at the end of the HTTP response. This is useful for sending information that can't be included in the main response headers.

Technical Explanation:

HTTP trailing headers are added after the main response headers and body have been sent. They are typically used for additional metadata or information that doesn't fit into the regular headers.

Code Snippet:

const http2 = require("http2");

// Create an HTTP/2 server
const server = http2.createServer();

// Handle requests
server.on("request", (req, res) => {
  // Add trailing headers
  res.addTrailers({
    "x-custom-header": "value",
  });

  // Send the response
  res.send();
});

// Start the server
server.listen(3000);

Real-World Application:

Trailing headers can be used for various purposes, such as:

Providing additional content-type information for multipart responses
Sending security-related information, such as authorizations or authentication tokens
Adding debugging or diagnostic information

Potential Applications:

Content Delivery Networks (CDNs): CDNs could use trailing headers to include additional information about cached content, such as its origin server.
Web Analytics: Analytics tools could add trailing headers to track user behavior, such as page views or session times.
Load Balancing: Load balancers could add trailing headers to indicate which server a request was routed to.

What is response.appendHeader()?

In Node.js, when you create an HTTP2 server, you can use the response object to control the HTTP response sent to the client. The response.appendHeader() method allows you to add one or more values to a specific HTTP header.

How do I use response.appendHeader()?

The response.appendHeader() method takes two parameters:

name: The name of the HTTP header you want to append a value to.
value: The value you want to append to the header. This can be a single string or an array of strings.

For example, the following code adds the value "a" to the "set-cookie" header:

res.appendHeader("set-cookie", "a");

If you want to append multiple values to the same header, you can call response.appendHeader() multiple times, like this:

res.appendHeader("set-cookie", "a");
res.appendHeader("set-cookie", "b");

This will result in the following headers being sent to the client:

set-cookie: a
set-cookie: b

When should I use response.appendHeader()?

You can use response.appendHeader() to add any type of HTTP header to the response. However, it is most commonly used to add multiple values to the "set-cookie" header. This is because the "set-cookie" header can contain multiple values, each of which represents a different cookie that you want to set on the client's browser.

Real-world example

The following code creates an HTTP2 server that sets two cookies on the client's browser:

const http2 = require("http2");

const server = http2.createServer();

server.on("request", (req, res) => {
  res.appendHeader("set-cookie", "a");
  res.appendHeader("set-cookie", "b");
  res.writeHead(200);
  res.end("ok");
});

server.listen(3000);

When a client makes a request to this server, the server will send a response with the following headers:

set-cookie: a
set-cookie: b

This will cause the client's browser to create two cookies, one with the name "a" and one with the name "b".

Potential applications

response.appendHeader() can be used in a variety of applications, including:

Setting cookies on the client's browser
Adding additional security headers to the response
Providing additional information about the response to the client

`response.connection`

The response.connection property of the http2 module is a net.Socket or tls.TLSSocket object representing the connection to the client. Note: This property is deprecated and should not be used. Use the response.socket property instead.

Example:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream, headers) => {
  const connection = stream.connection;

  // Do something with the connection.
});

Sure, here is a simplified explanation of the response.createPushResponse(headers, callback) method of the http2 module in Node.js:

What is the response.createPushResponse() method?

The response.createPushResponse() method allows you to create a new HTTP/2 push stream. A push stream is a stream that is initiated by the server, rather than the client. This can be useful for sending resources to the client that they may need in the future, before they actually request them.

How do I use the response.createPushResponse() method?

To use the response.createPushResponse() method, you first need to create an HTTP/2 server. Once you have created a server, you can listen for incoming requests on a specific port. When a request is received, you can use the response.createPushResponse() method to create a new push stream.

The response.createPushResponse() method takes two arguments:

headers: An object describing the headers for the push stream.
callback: A function that will be called once the push stream has been created.

The callback function will be passed two arguments:

err: An error object, if any.
res: The newly-created Http2ServerResponse object.

Example

The following code shows how to use the response.createPushResponse() method:

const http2 = require("http2");

const server = http2.createServer();

server.on("request", (req, res) => {
  // Create a new push stream.
  res.createPushResponse({ ":path": "/style.css" }, (err, pushRes) => {
    if (err) {
      console.error(err);
    } else {
      // Send the response body.
      pushRes.end("body");
    }
  });
});

server.listen(3000);

Real-world applications

The response.createPushResponse() method can be used in a variety of real-world applications, such as:

Preloading resources: You can use the response.createPushResponse() method to send resources to the client that they may need in the future, before they actually request them. This can improve the performance of your website by reducing the amount of time it takes for the client to load the resources.
Lazy loading: You can use the response.createPushResponse() method to send resources to the client only when they are needed. This can help to reduce the amount of bandwidth used by your website.
Server-side rendering: You can use the response.createPushResponse() method to send the HTML for a page to the client before the client has requested it. This can improve the performance of your website by reducing the amount of time it takes for the client to render the page.

Conclusion

The response.createPushResponse() method is a powerful tool that can be used to improve the performance and efficiency of your HTTP/2 server.

What is response.end()?

When you send a response to a client (like a web browser), you need to tell the server that you're finished sending everything. response.end() is the method that does this.

How to use response.end():

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream, headers) => {
  stream.respond({
    ":status": 200,
  });

  stream.end("Hello, world!"); // This will send the data and close the stream
});

server.listen(3000);

In this example, we're sending the response "Hello, world!" to the client. Once the stream is closed, the client will know that it has received all of the data.

When to use response.end():

You should always call response.end() after you've sent all of the data to the client. If you don't, the client will continue to wait for more data, and your server will eventually time out.

Potential applications:

response.end() is used in any situation where you need to send data to a client over HTTP. This includes web applications, APIs, and file downloads.

What is response.finished?

response.finished is a property of the HTTP2 Response object. It is used to determine if the response has been completed, meaning that all data has been sent to the client.

How to use response.finished?

You can access the response.finished property at any time during the lifetime of the response. It will start out as false and will be set to true once the response has been completed.

Here is an example of how you might use response.finished:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream, headers) => {
  // ...

  stream.respond({
    ":status": 200,
    "content-type": "text/plain",
  });

  stream.end("Hello, world!");

  // After the response has been completed, `response.finished` will be `true`.
  console.log(`Response finished: ${stream.response.finished}`); // true
});

server.listen(3000);

When to use response.finished?

response.finished can be useful in a number of scenarios. For example, you might use it to:

Log when a response has been completed.
Perform cleanup tasks after a response has been completed.
Determine if a response has been completed before sending another response to the client.

Real-world applications of response.finished

Here are some real-world applications of response.finished:

Logging: You can use response.finished to log when a response has been completed. This can be useful for debugging purposes or for tracking the performance of your application.
Cleanup tasks: You can use response.finished to perform cleanup tasks after a response has been completed. For example, you might use it to close a database connection or to delete temporary files.
Determining if a response has been completed: You can use response.finished to determine if a response has been completed before sending another response to the client. This can be useful for preventing duplicate responses from being sent.

Improved code example

Here is an improved version of the code example from above:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream, headers) => {
  // ...

  stream.respond({
    ":status": 200,
    "content-type": "text/plain",
  });

  stream.end("Hello, world!");

  // After the response has been completed, log the fact that it has been completed.
  console.log(`Response finished: ${stream.response.finished}`); // true
});

server.listen(3000);

`response.getHeader(name)`

The response.getHeader(name) method in http2 reads out a header that has already been queued but not sent to the client.

The following code sample shows you how to use the response.getHeader(name) method:

const contentType = response.getHeader("content-type");

`response.getHeaderNames()`

Returns: An array containing the unique names of the current outgoing headers. All header names are lowercase.

Simplified Explanation

Imagine you're writing a letter to a friend, and you need to include some information in the header (like the date, subject, etc.). The response.getHeaderNames() method is like a list of all the different types of information you can include in the header.

Code Example

const http2 = require("http2");

// Create a server
const server = http2.createServer();

// Listen for incoming requests
server.on("request", (request, response) => {
  // Set some headers
  response.setHeader("Content-Type", "text/html");
  response.setHeader("X-Powered-By", "Node.js");

  // Get the header names
  const headerNames = response.getHeaderNames();

  // Print the header names
  console.log(headerNames); // ['content-type', 'x-powered-by']
});

// Start the server
server.listen(8000);

Real-World Applications

Getting a list of all the headers that are being sent in a response.
Checking if a specific header is being sent.
Removing a header from the response.

`response.getHeaders()`

Returns: A shallow copy of the outgoing headers. The returned object is in lowercase for headers name. Array values may be mutated without additional calls methods.

Usage Example:

const { connect } = require('http2');

const client = connect('localhost', 3000);

client.on('connect', () => {
  const headers = {
    ':method': 'GET',
    ':path': '/hello'
  };

  const req = client.request(headers);

  req.on('response', (headers, flags) => {
    console.log('Got response headers:', headers);
  });
});
// output:
// Got response headers: { ':status': '200' }

Simplified Explanation of response.hasHeader(name)

What it does:

Imagine you're sending a letter. You can add labels or notes to the envelope, called "headers." This method checks if a specific label exists on the envelope.

Parameters:

name: The name of the label you want to check for. It's like asking, "Do you have a label named 'URGENT' on this envelope?"

Return Value:

boolean: True if the label exists, false if it doesn't. So, if the envelope has the "URGENT" label, it would return true.

Breakdown of the Code Snippet:

const hasContentType = response.hasHeader("content-type");

This code checks if the response from a server has a header named "content-type." Headers are used to describe the content of the response, such as its format (HTML, JSON, etc.).

Real-World Implementation:

You could use this method to check if a response from a server has certain headers set, such as those required for authentication.
You could also use it to verify that a response contains specific content types, ensuring you receive the data you expect.

Potential Applications:

Authentication: Verifying that a request is authorized by checking for headers like "Authorization."
Content Validation: Ensuring that a response contains the expected content type, such as JSON or HTML.
Debugging: Checking if a specific header is present or missing while troubleshooting issues with HTTP requests and responses.

`response.headersSent`

Type: boolean
Read-only: true

The response.headersSent property in the http2 module indicates whether the headers have been sent to the client. This property is read-only and returns true if the headers have been sent, and false otherwise.

Example:

const http2 = require("http2");

const server = http2.createServer();

server.on("stream", (stream) => {
  stream.respond({
    ":status": 200,
    "content-type": "text/plain",
  });

  stream.end("Hello World");

  // Check if headers have been sent
  console.log("Headers sent:", stream.headersSent); // true
});

server.listen(8000);

Real-world applications:

The response.headersSent property can be used to:

Verify that headers have been sent before sending the response body.
Avoid sending duplicate headers.
Implement custom header handling logic.

`response.removeHeader(name)` Method

Simplified Explanation:
- A website can sometimes add extra bits of information called "headers" to a response. For example, the header "Content-Encoding" might contain information about the (encoded) data in the response.
- The response.removeHeader() method allows you to remove a specific header from the list of headers that will be sent to the client. This can be useful if you decide that you don't want to send that particular header after all.
Technical Explanation:
- The response.removeHeader(name) method takes a name argument, which is a string representing the name of the header to remove.
- It removes the header with the specified name from the list of headers that will be sent to the client when the response is sent.
- If the specified name is not found, the method does nothing.
Code Snippet:

// Remove the "Content-Encoding" header from the response.
response.removeHeader("Content-Encoding");

Real-World Example:
- You might use the response.removeHeader() method if you realize that you don't want to send a particular header that you had previously added to the response. For example, you might remove the "Content-Encoding" header if you change your mind about how you want to encode the data in the response.
Potential Applications:
- Modifying the headers sent to the client
- Removing headers that are no longer necessary or relevant
- Correcting errors in headers that were previously added

`response.req`

Represents the original HTTP2 request object.

Real-World Example

const http2 = require("http2");

// Create an HTTP2 server
const server = http2.createServer();

// Listen on port 8443
server.listen(8443);

// Handle incoming requests
server.on("request", (req, res) => {
  // Log the request method and path
  console.log(`Received request: ${req.method} ${req.url}`);

  // Get a reference to the original HTTP2 request object
  const originalRequest = req.req;

  // Log the original request object's properties
  console.log(`Original request object: ${JSON.stringify(originalRequest)}`);

  // Send a response
  res.end("Hello, world!");
});

This script creates an HTTP2 server and listens on port 8443. When a request is received, it logs the request method and path, then gets a reference to the original HTTP2 request object. The original request object's properties are then logged. Finally, a response is sent back to the client.

response.sendDate

What it is: It's an option in Node.js that you can use when creating HTTP responses. When you set it to true, Node.js will automatically add a Date header to the response if it's not already there.

Why you might use it: The Date header tells the client when the response was generated. This can be useful for debugging, caching, and other purposes. It's generally considered good practice to include a Date header in HTTP responses.

How to use it: You can set the sendDate option when you call the writeHead() method to send the response headers:

const http = require("http");

const server = http.createServer((req, res) => {
  res.writeHead(200, {
    "Content-Type": "text/plain",
    // Set the `sendDate` option to `true`
    Date: new Date().toUTCString(),
  });
  res.end("Hello World!");
});

server.listen(3000);

Potential applications:

Debugging: The Date header can be used to troubleshoot issues with HTTP requests and responses, such as if the server is responding too slowly.
Caching: The Date header can be used to control how long a response can be cached by the client.
Security: The Date header can be used to prevent replay attacks, where an attacker tries to reuse an old request to trick the server into performing an action it shouldn't.

response.setHeader(name, value) method

Definition:

The setHeader() method allows you to set a header in the HTTP response that your server sends to the client.

Parameters:

name: The name of the header, e.g., Content-Type.
value: The value of the header, e.g., text/html. You can also provide an array of strings to set multiple headers with the same name.

Explanation:

Headers are like meta-information about the HTTP response. They contain details like the type of content being sent (e.g., HTML, JSON), the language used, and any cookies or session information.

Example:

response.setHeader('Content-Type', 'text/html');
response.setHeader('Set-Cookie', ['type=ninja', 'language=javascript']);

In this example, we're setting the Content-Type header to text/html, which means the response contains HTML content. We're also setting two cookies named type and language.

Real-World Applications:

Setting the Content-Type header ensures that the browser knows how to interpret the response.
Setting cookies allows you to store information about the user's session, such as their preferences or login status.

Simplified Explanation:

Imagine you're sending a letter to your friend. The setHeader() method is like writing the address and other details on the envelope. These details tell your friend where the letter is coming from, who it's intended for, and any special instructions (like "Do Not Bend").

Improved Code Snippet:

// Serve HTML content with a cookie
const server = http2.createServer((req, res) => {
  res.setHeader('Content-Type', 'text/html');
  res.setHeader('Set-Cookie', ['type=ninja']); // Set a single cookie
  res.writeHead(200); // Send the header and status code
  res.end('<h1>Hello, ninja!</h1>'); // Send the response body
});

Topic: Setting HTTP/2 Response Timeouts

Simplified Explanation:

When you set a timeout on an HTTP/2 response, you're specifying the maximum amount of time the server will wait for a response from the client before closing the connection.

Code Snippet:

const http2 = require("http2");

const server = http2.createServer();

server.on("request", (request, response) => {
  // Set a 10-second timeout on the response
  response.setTimeout(10000);
});

Improved Code Snippets:

You can also use the callback parameter to add a function that will be executed when the timeout occurs.

const http2 = require("http2");

const server = http2.createServer();

server.on("request", (request, response) => {
  // Set a 10-second timeout on the response
  response.setTimeout(10000, () => {
    console.log("Response timed out!");
  });
});

Real-World Applications:

HTTP/2 timeouts are useful in preventing long-lived HTTP connections from consuming excessive server resources. By setting an appropriate timeout, you can ensure that inactive connections will be closed and freed up.

Potential Applications:

Web servers to handle incoming HTTP/2 requests
Proxy servers to forward HTTP/2 requests to upstream servers
Load balancers to distribute HTTP/2 traffic across multiple servers

Simplified Explanation of `response.socket` in Node.js

What is `response.socket`?

Imagine you're sending a letter to a friend. The letter travels through the postal service and is delivered to your friend's mailbox. The postal service is like the network, and the mailbox is like the response.socket. It's the point of contact where your friend receives your letter (the HTTP response).

How does `response.socket` work?

The response.socket is an object that looks and acts like a normal network socket, but it's actually a "proxy" controlled by HTTP/2 logic. This means that when you read or write to the socket, HTTP/2 rules are applied to make sure the data is sent and received correctly.

What can you do with `response.socket`?

You can use response.socket to get information about the network connection, such as the IP address and port of the client. You can also use it to set properties like timeouts. However, you can't directly pause, resume, or manipulate the data stream flowing through the socket. HTTP/2 does this automatically.

Real-World Example

Here's an example that demonstrates how to use response.socket to get the client's IP address:

const http2 = require("node:http2");

const server = http2.createServer((req, res) => {
  const ip = req.socket.remoteAddress;
  const port = req.socket.remotePort;
  res.end(`Your IP address is ${ip} and your source port is ${port}.`);
});

server.listen(3000);

When a client sends a request to this server, the ip and port variables will contain the client's IP address and port.

Potential Applications

response.socket can be used in a variety of applications, such as:

Getting diagnostic information about the client
Setting up custom timeouts
Debugging HTTP/2 connections

`response.statusCode` explained for a child

What is a status code in HTTP?

When you send a request to a website, the website responds with a status code. This code tells you if your request was successful or if there was an error.

What is response.statusCode?

response.statusCode is a property of the response object in Node.js's HTTP2 module. It controls the status code that will be sent to the client when the response is sent.

How to use response.statusCode?

You can use response.statusCode to set the status code that will be sent to the client. For example:

response.statusCode = 404;

This will set the status code to 404, which means "Not Found".

When to use response.statusCode?

You should use response.statusCode to set the status code of a response whenever you want to send a specific status code to the client. For example, you might want to send a 404 status code if the client requested a page that does not exist, or a 200 status code if the request was successful.

Real-world examples of response.statusCode

Here are some examples of how response.statusCode can be used in real-world applications:

A web server could use response.statusCode to send a 404 status code to a client if the client requested a page that does not exist.
A shopping website could use response.statusCode to send a 200 status code to a client if the client successfully added an item to their shopping cart.
A social networking website could use response.statusCode to send a 401 status code to a client if the client tries to access a page that they do not have permission to access.

Benefits of using response.statusCode

Using response.statusCode can help you to send specific status codes to clients, which can help to improve the user experience of your website or application. By sending the correct status code, you can also help to prevent clients from receiving confusing or misleading error messages.

`response.statusMessage`

response.statusMessage is a string that represents the status message associated with the HTTP response.
HTTP/2 doesn't support status messages, so response.statusMessage will always return an empty string.

Example:

const http2 = require('http2');

// Create an HTTP/2 server
const server = http2.createServer();

// Handle incoming requests
server.on('request', (req, res) => {
  // Send a response with a status code of 200 and no status message
  res.writeHead(200, {});
  res.end();
});

// Start the server
server.listen(8000);

In this example, the server will send a response with a status code of 200 and no status message. The client will receive the response and will see the status code, but will not see a status message.

Potential Applications

response.statusMessage can be used to provide additional information about the HTTP response. For example, it can be used to provide a more detailed explanation of the status code or to provide a custom message to the client.

`response.stream`

An Http2Stream object represents the underlying HTTP/2 stream associated with the response.

Usage

const { createServer } = require("http2");

createServer((request, response) => {
  response.on("stream", (stream) => {
    stream.on("data", (chunk) => {
      // Handle received data.
    });
  });
}).listen(8000);

response.writableEnded

What is it?

response.writableEnded is a property that indicates whether the response object has finished writing data to the network. It becomes true after the response.end() method has been called.

How to use it?

You can use the response.writableEnded property to check if the response has finished sending data. This can be useful for debugging or for ensuring that all data has been sent before closing the connection.

Example:

const http2 = require("http2");

const server = http2.createServer();

server.on("request", (req, res) => {
  // Send a response
  res.writeHead(200);
  res.end("Hello, world!");

  // Check if the response has finished writing data
  if (res.writableEnded) {
    console.log("Response has finished writing data");
  }
});

server.listen(8000);

Real-world applications:

Debugging: You can use response.writableEnded to check if a response has finished sending data before closing the connection. This can help you identify and fix any issues with your code.
Ensuring data integrity: You can use response.writableEnded to ensure that all data has been sent before closing the connection. This can help prevent data loss or corruption.

HTTP Response: Sending Data to the Client

When you build web servers, you need a way to send data to the client who made the request. In Node.js, the response.write() method is responsible for this task.

How it Works:

Prepare the Data: You have a chunk of data that you want to send to the client. It can be text, HTML, JSON, or any other format.
Call response.write(): You call response.write() with the data chunk you want to send.
Send the Data: Node.js will handle the technical details of packaging the data into the correct format and sending it to the client.

Important Notes:

If you haven't already set the HTTP headers using response.writeHead(), response.write() will do it for you.
You can call response.write() multiple times to send multiple chunks of data.
If you pass a string as the data chunk, you can optionally specify the encoding (e.g., 'utf8').

Real-World Example:

Imagine you're building a simple server that returns a plain text message. Your code might look like this:

const http = require("http");

const server = http.createServer();

server.on("request", (request, response) => {
  response.writeHead(200, { "Content-Type": "text/plain" });
  response.write("Hello from Node.js!");
  response.end();
});

server.listen(3000);

In this example:

We import the http module.
We create a server object (server).
When a request comes in, we set the response status code (200) and content type ('text/plain').
We send the data ("Hello from Node.js!") using response.write().
Finally, we end the response to indicate that there's no more data to send.

Potential Applications:

Sending HTML pages to browsers
Returning JSON data for AJAX requests
Streaming large files (e.g., videos)

Simplified Explanation:

The response.writeContinue() method in Node.js's http2 module allows you to send a special status code (100 Continue) to the client during an HTTP/2 request. This code indicates to the client that it should continue sending the request body.

Technical Details:

In HTTP/2, certain requests need to send a large request body. To improve efficiency, HTTP/2 introduced a mechanism called "flow control." Flow control ensures that the server can handle the load of receiving a large request body before it is actually received.

When a client starts sending a request body, the server can send a 100 Continue status code. This tells the client that the server is ready to receive the body. If the server doesn't send this status code, the client will wait for a certain amount of time before sending the body, which can lead to performance issues.

Real-World Example:

Consider a scenario where a user is uploading a large video file to a web server. Without flow control, the server might start processing the file even before it has fully received it. This could lead to errors and wasted resources.

By using response.writeContinue() and flow control, the server can indicate to the client that it is ready to receive the file. The client will then start sending the file, and the server will process it only after fully receiving it.

Code Example:

const http2 = require("http2");
const server = http2.createSecureServer({
  key: fs.readFileSync("key.pem"),
  cert: fs.readFileSync("cert.pem"),
});

server.on("request", (req, res) => {
  // Check if the request body is present
  if (req.headers["content-length"]) {
    // Send the '100 Continue' status code
    res.writeContinue();
  }

  // Process the request body...
});

Potential Applications:

response.writeContinue() is particularly useful for applications that handle large file uploads, such as video or image sharing websites, or cloud storage services. It ensures efficient and reliable data transfer by preventing the server from overloading before receiving the entire request body.

HTTP Early Hints

When a user visits a website, the browser typically sends a request to the server for the page's contents. The server processes the request and sends back a response. In some cases, the server can send back a partial response, called an "early hints" response, before it has fully processed the request.

Purpose of Early Hints

Early hints responses are used to send partial information to the browser, such as information about the resources that the browser will need to load in order to display the page. This information can help the browser to start preloading these resources, which can speed up the loading of the page.

How Early Hints Responses Work

Early hints responses are sent using the writeEarlyHints() method of the http2 module. The writeEarlyHints() method takes an object as its argument. This object can contain the following properties:

link: A string containing a link to a resource that the browser should preload. Multiple links can be provided in an array.
content-type: A string containing the content type of the resource that the browser should preload.

Example

The following code sends an early hints response with a link to a CSS file:

const response = http2.response();
response.writeEarlyHints({
  link: "</styles.css>; rel=preload; as=style",
});

Potential Applications

Early hints responses can be used to improve the performance of any website that loads a large number of resources. For example, they can be used to speed up the loading of images, videos, and JavaScript files.

Real-World Implementation

The following is a real-world example of how early hints responses can be used to improve the performance of a website:

const express = require("express");
const app = express();

app.get("/", (req, res) => {
  const response = res.writeHead(200, {
    "Content-Type": "text/html",
  });
  response.writeEarlyHints({
    link: [
      "</styles.css>; rel=preload; as=style",
      "</scripts.js>; rel=preload; as=script",
    ],
  });
  res.end();
});

app.listen(3000);

This code creates a simple web application that returns a HTML page with a link to a CSS file and a JavaScript file. The writeEarlyHints() method is used to send an early hints response with links to these resources. This will help the browser to start preloading these resources, which will speed up the loading of the page.

Understanding `response.writeHead()` Method in HTTP/2

What is HTTP/2?

HTTP/2 is a faster and more efficient version of HTTP, the protocol used to transfer data over the web.

What is response.writeHead()?

response.writeHead() is a method used in HTTP/2 to send a response to a client's request. It sets the status code and headers for the response.

Arguments

statusCode: A three-digit number that indicates the status of the response, such as 200 for a successful request.
statusMessage: (Optional) A human-readable message that describes the status code (e.g., "OK"). This is ignored in HTTP/2.
headers: (Optional) An object or array of header values that specify additional information about the response (e.g., Content-Length, Content-Type).

Return Value

The method returns a reference to the Http2ServerResponse object, which allows you to chain additional calls.

Example

const http2 = require("http2");

// Create an HTTP/2 server
const server = http2.createServer();

// Event listener for client requests
server.on("request", (req, res) => {
  // Send a response with status code 200 and a header for the content length
  res.writeHead(200, { "Content-Length": Buffer.byteLength("Hello, world!") });

  // Send the response body
  res.end("Hello, world!");
});

// Start listening on port 8000
server.listen(8000);

How does it work?

When a client sends a request to the server, the server's request event listener is triggered.
Inside the event listener, the server calls response.writeHead() to send a response back to the client.
The response.writeHead() method sets the status code and headers for the response.
After setting the response headers, the server uses response.end() to send the response body to the client.

Real-World Applications

response.writeHead() is used in countless applications that rely on HTTP/2, including:

Web servers: Sending responses to web browser requests
Streaming services: Broadcasting video and audio content
API gateways: Facilitating communication between clients and backend systems

Collecting HTTP/2 Performance Metrics

Performance Observer API

This API allows you to collect performance metrics for Http2Session and Http2Stream instances.

Creating a Performance Observer

const { PerformanceObserver } = require("node:perf_hooks");

const obs = new PerformanceObserver((items) => {
  const entry = items.getEntries()[0];
  console.log(entry.entryType); // prints 'http2'
  if (entry.name === "Http2Session") {
    // Entry contains statistics about the Http2Session
  } else if (entry.name === "Http2Stream") {
    // Entry contains statistics about the Http2Stream
  }
});
obs.observe({ entryTypes: ["http2"] });

Metrics for Http2Stream

bytesRead: Number of DATA frame bytes received
bytesWritten: Number of DATA frame bytes sent
id: Identifier of the Http2Stream
timeToFirstByte: Time (in milliseconds) from start until first DATA frame
timeToFirstByteSent: Time (in milliseconds) from start until first DATA frame sent
timeToFirstHeader: Time (in milliseconds) from start until first header received

Metrics for Http2Session

bytesRead: Total bytes received
bytesWritten: Total bytes sent
framesReceived: Number of HTTP/2 frames received
framesSent: Number of HTTP/2 frames sent
maxConcurrentStreams: Maximum number of open streams at once
pingRTT: Ping round-trip time (if PING frame was used)
streamAverageDuration: Average duration of Http2Stream instances (in milliseconds)
streamCount: Number of Http2Stream instances handled
type: Type of Http2Session (either 'server' or 'client')

Real-World Applications

These metrics can help you:

Optimize HTTP/2 performance by identifying bottlenecks
Troubleshoot latency issues
Understand the performance characteristics of your server and clients

What is HTTP/2?

HTTP/2 is a newer version of the HTTP protocol that is used to transfer data over the internet. It is faster and more efficient than the older HTTP/1 protocol, and it is used by many websites and applications today.

What is :authority and host?

The :authority pseudo-header and the host header are both used to identify the server that a request is being sent to. The :authority pseudo-header is used in HTTP/2 requests, while the host header is used in HTTP/1 requests.

Why is :authority preferred?

:authority is preferred because it is more concise and it can be used in both HTTP/2 and HTTP/1 requests. The host header, on the other hand, can only be used in HTTP/1 requests.

How to use :authority and host

If you are creating an HTTP/2 request, you should use the :authority pseudo-header. If you are converting an HTTP/1 request to an HTTP/2 request, you should use the host header.

// Create an HTTP/2 request with the :authority pseudo-header
const request = http2.createClientRequest({
  :authority: 'example.com',
  path: '/'
});

// Create an HTTP/1 request with the host header
const request = http.request({
  host: 'example.com',
  path: '/'
});

Real-world applications

HTTP/2 is used by many popular websites and applications, including Google, Facebook, and Amazon. It is also used by many content delivery networks (CDNs), such as Cloudflare and Akamai.

HTTP/2 offers a number of benefits over HTTP/1, including:

Faster performance: HTTP/2 is faster than HTTP/1 because it uses a number of techniques to improve performance, such as header compression and multiplexing.
Improved security: HTTP/2 is more secure than HTTP/1 because it uses encryption by default.
Reduced overhead: HTTP/2 uses a smaller number of bytes to send requests and responses than HTTP/1, which can reduce bandwidth usage.

Conclusion

HTTP/2 is a faster, more efficient, and more secure version of the HTTP protocol. It is used by many popular websites and applications, and it is becoming increasingly common.

Previousindex Nextinspector

HTTP/2 Core API

How it Works

Client-side

Server-side

Real-World Applications

Example: Creating a Client

Example: Creating a Server

Creating an HTTP/2 Server

Handling HTTP/2 Requests

Real-World Applications

Improved Code Example

Simple Example

Explanation

Real-World Applications

Http2Session and Sockets

Why not read or write directly to the Socket?

Real-World Example

Potential Applications

Code Snippet

Event: 'connect'

Event: 'frameError'

Explanation

Details

Real-World Applications

Example

Understanding the 'goaway' Event in Node.js's HTTP/2 Module

Event Overview

Event Parameters

Event Handling

Real-World Applications

Example Code

What is the 'ping' event?

What is a PING frame?

Why is the 'ping' event useful?

How to use the 'ping' event?

Real-world applications

Code snippet for 'ping' event

Simplified Explanation of the 'remoteSettings' Event in Node.js' HTTP/2 Module

Event: 'stream'

Explanation

Example

Applications

Potential use-cases of HTTP/2 streams in the real world

HTTP/2 Session ALPN Protocol

http2session.close([callback])

http2session.closed

Example

Simplified Explanation of http2session.destroy() Method

http2session.goaway([code[, lastStreamID[, opaqueData]]])

What is a GOAWAY frame?

Why would a server send a GOAWAY frame?

What happens when a client receives a GOAWAY frame?

Code example

Real-world applications

What is http2session.originSet?

How does it work?

Example

Real-World Applications

Simplified Explanation of http2session.pendingSettingsAck

What is http2session.pendingSettingsAck?

When is http2session.pendingSettingsAck true?

When is http2session.pendingSettingsAck false?

Real-World Applications

Example

Pinging with HTTP/2

Sending a Ping

Real World Example

http2session.ref()

http2session.remoteSettings

Properties:

Real-World Example:

Potential Applications:

http2session.setLocalWindowSize(windowSize)

Description

Parameters

Return Value

Example

Real-World Applications

http2session.setTimeout(msecs, callback)

HTTP/2 Session Socket

Event: `'connect'`

Understanding the `'goaway'` Event in Node.js's HTTP/2 Module

What is a `PING` frame?

Why is the `'ping'` event useful?

How to use the `'ping'` event?

Code snippet for `'ping'` event

Simplified Explanation of the `'remoteSettings'` Event in Node.js' HTTP/2 Module

Event: `'stream'`

`http2session.close([callback])`

`http2session.closed`

Simplified Explanation of `http2session.destroy()` Method

`http2session.goaway([code[, lastStreamID[, opaqueData]]])`

What is a `GOAWAY` frame?

Why would a server send a `GOAWAY` frame?

What happens when a client receives a `GOAWAY` frame?

What is `http2session.originSet`?

Simplified Explanation of `http2session.pendingSettingsAck`

What is `http2session.pendingSettingsAck`?

When is `http2session.pendingSettingsAck` true?

When is `http2session.pendingSettingsAck` false?

`http2session.ref()`

`http2session.remoteSettings`

`http2session.setLocalWindowSize(windowSize)`

`http2session.setTimeout(msecs, callback)`

`http2session.state`

`http2session.type`

`http2session.unref()`

`serverhttp2session.altsvc(alt, originOrStream)`

`serverhttp2session.origin(...origins)`

`clienthttp2session.request(headers[, options])`

`'frameError'` Event

Event: `'trailers'`

Event: `'wantTrailers'`

`http2stream.aborted`

`http2stream.bufferSize`

`http2stream.close(code[, callback])`

`http2stream.closed`

`http2stream.endAfterHeaders`

`http2stream.id`

`http2stream.pending`

`http2stream.rstCode`