node_modules/socket.io/Readme.md - devtools/devtools-frontend - Git at Google


            
            # socket.io

            
            [![Run on Repl.it](https://repl.it/badge/github/socketio/socket.io)](https://replit.com/@socketio/socketio-minimal-example)

            
            [![Backers on Open Collective](https://opencollective.com/socketio/backers/badge.svg)](#backers) [![Sponsors on Open Collective](https://opencollective.com/socketio/sponsors/badge.svg)](#sponsors)

            
            [![Build Status](https://github.com/socketio/socket.io/workflows/CI/badge.svg)](https://github.com/socketio/socket.io/actions)

            
            [![NPM version](https://badge.fury.io/js/socket.io.svg)](https://www.npmjs.com/package/socket.io)

            
            ![Downloads](https://img.shields.io/npm/dm/socket.io.svg?style=flat)

            
            [![](https://slackin-socketio.now.sh/badge.svg)](https://slackin-socketio.now.sh)


            ## Features


            Socket.IO enables real-time bidirectional event-based communication. It consists of:


            - a Node.js server (this repository)

            
            - a [Javascript client library](https://github.com/socketio/socket.io-client) for the browser (or a Node.js client)


            Some implementations in other languages are also available:


            - [Java](https://github.com/socketio/socket.io-client-java)

            
            - [C++](https://github.com/socketio/socket.io-client-cpp)

            
            - [Swift](https://github.com/socketio/socket.io-client-swift)

            
            - [Dart](https://github.com/rikulo/socket.io-client-dart)

            
            - [Python](https://github.com/miguelgrinberg/python-socketio)

            
            - [.NET](https://github.com/doghappy/socket.io-client-csharp)

            
            - [Rust](https://github.com/1c3t3a/rust-socketio)

            
            - [PHP](https://github.com/ElephantIO/elephant.io)


            Its main features are:


            #### Reliability


            Connections are established even in the presence of:

            
              - proxies and load balancers.

            
              - personal firewall and antivirus software.


            For this purpose, it relies on [Engine.IO](https://github.com/socketio/engine.io), which first establishes a long-polling connection, then tries to upgrade to better transports that are "tested" on the side, like WebSocket. Please see the [Goals](https://github.com/socketio/engine.io#goals) section for more information.


            #### Auto-reconnection support


            Unless instructed otherwise a disconnected client will try to reconnect forever, until the server is available again. Please see the available reconnection options [here](https://socket.io/docs/v3/client-api/#new-Manager-url-options).


            #### Disconnection detection


            A heartbeat mechanism is implemented at the Engine.IO level, allowing both the server and the client to know when the other one is not responding anymore.


            That functionality is achieved with timers set on both the server and the client, with timeout values (the `pingInterval` and `pingTimeout` parameters) shared during the connection handshake. Those timers require any subsequent client calls to be directed to the same server, hence the `sticky-session` requirement when using multiples nodes.


            #### Binary support


            Any serializable data structures can be emitted, including:


            - [ArrayBuffer](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) and [Blob](https://developer.mozilla.org/en-US/docs/Web/API/Blob) in the browser

            
            - [ArrayBuffer](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) and [Buffer](https://nodejs.org/api/buffer.html) in Node.js


            #### Simple and convenient API


            Sample code:


            ```js

            
            io.on('connection', socket => {

            
              socket.emit('request', /* … */); // emit an event to the socket

            
              io.emit('broadcast', /* … */); // emit an event to all connected sockets

            
              socket.on('reply', () => { /* … */ }); // listen to the event

            
            });

            
            ```


            #### Cross-browser


            Browser support is tested in Sauce Labs:


            [![Sauce Test Status](https://saucelabs.com/browser-matrix/socket.svg)](https://saucelabs.com/u/socket)


            #### Multiplexing support


            In order to create separation of concerns within your application (for example per module, or based on permissions), Socket.IO allows you to create several `Namespaces`, which will act as separate communication channels but will share the same underlying connection.


            #### Room support


            Within each `Namespace`, you can define arbitrary channels, called `Rooms`, that sockets can join and leave. You can then broadcast to any given room, reaching every socket that has joined it.


            This is a useful feature to send notifications to a group of users, or to a given user connected on several devices for example.


            **Note:** Socket.IO is not a WebSocket implementation. Although Socket.IO indeed uses WebSocket as a transport when possible, it adds some metadata to each packet: the packet type, the namespace and the ack id when a message acknowledgement is needed. That is why a WebSocket client will not be able to successfully connect to a Socket.IO server, and a Socket.IO client will not be able to connect to a WebSocket server (like `ws://echo.websocket.org`) either. Please see the protocol specification [here](https://github.com/socketio/socket.io-protocol).


            ## Installation


            ```bash

            
            // with npm

            
            npm install socket.io


            // with yarn

            
            yarn add socket.io

            
            ```


            ## How to use


            The following example attaches socket.io to a plain Node.JS

            
            HTTP server listening on port `3000`.


            ```js

            
            const server = require('http').createServer();

            
            const io = require('socket.io')(server);

            
            io.on('connection', client => {

            
              client.on('event', data => { /* … */ });

            
              client.on('disconnect', () => { /* … */ });

            
            });

            
            server.listen(3000);

            
            ```


            ### Standalone


            ```js

            
            const io = require('socket.io')();

            
            io.on('connection', client => { ... });

            
            io.listen(3000);

            
            ```


            ### Module syntax


            ```js

            
            import { Server } from "socket.io";

            
            const io = new Server(server);

            
            io.listen(3000);

            
            ```


            ### In conjunction with Express


            Starting with **3.0**, express applications have become request handler

            
            functions that you pass to `http` or `http` `Server` instances. You need

            
            to pass the `Server` to `socket.io`, not the express application

            
            function. Also make sure to call `.listen` on the `server`, not the `app`.


            ```js

            
            const app = require('express')();

            
            const server = require('http').createServer(app);

            
            const io = require('socket.io')(server);

            
            io.on('connection', () => { /* … */ });

            
            server.listen(3000);

            
            ```


            ### In conjunction with Koa


            Like Express.JS, Koa works by exposing an application as a request

            
            handler function, but only by calling the `callback` method.


            ```js

            
            const app = require('koa')();

            
            const server = require('http').createServer(app.callback());

            
            const io = require('socket.io')(server);

            
            io.on('connection', () => { /* … */ });

            
            server.listen(3000);

            
            ```


            ### In conjunction with Fastify


            To integrate Socket.io in your Fastify application you just need to

            
            register `fastify-socket.io` plugin. It will create a `decorator`

            
            called `io`.


            ```js

            
            const app = require('fastify')();

            
            app.register(require('fastify-socket.io'));

            
            app.ready().then(() => {

            
                app.io.on('connection', () => { /* … */ });

            
            })

            
            app.listen(3000);

            
            ```


            ## Documentation


            Please see the documentation [here](https://socket.io/docs/).


            The source code of the website can be found [here](https://github.com/socketio/socket.io-website). Contributions are welcome!


            ## Debug / logging


            Socket.IO is powered by [debug](https://github.com/visionmedia/debug).

            
            In order to see all the debug output, run your app with the environment variable

            
            `DEBUG` including the desired scope.


            To see the output from all of Socket.IO's debugging scopes you can use:


            ```

            
            DEBUG=socket.io* node myapp

            
            ```


            ## Testing


            ```

            
            npm test

            
            ```

            
            This runs the `gulp` task `test`. By default the test will be run with the source code in `lib` directory.


            Set the environmental variable `TEST_VERSION` to `compat` to test the transpiled es5-compat version of the code.


            The `gulp` task `test` will always transpile the source code into es5 and export to `dist` first before running the test.


            ## Backers


            Support us with a monthly donation and help us continue our activities. [[Become a backer](https://opencollective.com/socketio#backer)]


            <a href="https://opencollective.com/socketio/backer/0/website" target="_blank"><img src="https://opencollective.com/socketio/backer/0/avatar.svg"></a>

            
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            ## Sponsors


            Become a sponsor and get your logo on our README on Github with a link to your site. [[Become a sponsor](https://opencollective.com/socketio#sponsor)]


            <a href="https://opencollective.com/socketio/sponsor/0/website" target="_blank"><img src="https://opencollective.com/socketio/sponsor/0/avatar.svg"></a>

            
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            ## License


            [MIT](LICENSE)
	# socket.io
	[![Run on Repl.it](https://repl.it/badge/github/socketio/socket.io)](https://replit.com/@socketio/socketio-minimal-example)
	[![Backers on Open Collective](https://opencollective.com/socketio/backers/badge.svg)](#backers) [![Sponsors on Open Collective](https://opencollective.com/socketio/sponsors/badge.svg)](#sponsors)
	[![Build Status](https://github.com/socketio/socket.io/workflows/CI/badge.svg)](https://github.com/socketio/socket.io/actions)
	[![NPM version](https://badge.fury.io/js/socket.io.svg)](https://www.npmjs.com/package/socket.io)
	![Downloads](https://img.shields.io/npm/dm/socket.io.svg?style=flat)
	[![](https://slackin-socketio.now.sh/badge.svg)](https://slackin-socketio.now.sh)

	## Features

	Socket.IO enables real-time bidirectional event-based communication. It consists of:

	- a Node.js server (this repository)
	- a [Javascript client library](https://github.com/socketio/socket.io-client) for the browser (or a Node.js client)

	Some implementations in other languages are also available:

	- [Java](https://github.com/socketio/socket.io-client-java)
	- [C++](https://github.com/socketio/socket.io-client-cpp)
	- [Swift](https://github.com/socketio/socket.io-client-swift)
	- [Dart](https://github.com/rikulo/socket.io-client-dart)
	- [Python](https://github.com/miguelgrinberg/python-socketio)
	- [.NET](https://github.com/doghappy/socket.io-client-csharp)
	- [Rust](https://github.com/1c3t3a/rust-socketio)
	- [PHP](https://github.com/ElephantIO/elephant.io)

	Its main features are:

	#### Reliability

	Connections are established even in the presence of:
	- proxies and load balancers.
	- personal firewall and antivirus software.

	For this purpose, it relies on [Engine.IO](https://github.com/socketio/engine.io), which first establishes a long-polling connection, then tries to upgrade to better transports that are "tested" on the side, like WebSocket. Please see the [Goals](https://github.com/socketio/engine.io#goals) section for more information.

	#### Auto-reconnection support

	Unless instructed otherwise a disconnected client will try to reconnect forever, until the server is available again. Please see the available reconnection options [here](https://socket.io/docs/v3/client-api/#new-Manager-url-options).

	#### Disconnection detection

	A heartbeat mechanism is implemented at the Engine.IO level, allowing both the server and the client to know when the other one is not responding anymore.

	That functionality is achieved with timers set on both the server and the client, with timeout values (the `pingInterval` and `pingTimeout` parameters) shared during the connection handshake. Those timers require any subsequent client calls to be directed to the same server, hence the `sticky-session` requirement when using multiples nodes.

	#### Binary support

	Any serializable data structures can be emitted, including:

	- [ArrayBuffer](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) and [Blob](https://developer.mozilla.org/en-US/docs/Web/API/Blob) in the browser
	- [ArrayBuffer](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer) and [Buffer](https://nodejs.org/api/buffer.html) in Node.js

	#### Simple and convenient API

	Sample code:

	```js
	io.on('connection', socket => {
	socket.emit('request', /* … */); // emit an event to the socket
	io.emit('broadcast', /* … */); // emit an event to all connected sockets
	socket.on('reply', () => { /* … */ }); // listen to the event
	});
	```

	#### Cross-browser

	Browser support is tested in Sauce Labs:

	[![Sauce Test Status](https://saucelabs.com/browser-matrix/socket.svg)](https://saucelabs.com/u/socket)

	#### Multiplexing support

	In order to create separation of concerns within your application (for example per module, or based on permissions), Socket.IO allows you to create several `Namespaces`, which will act as separate communication channels but will share the same underlying connection.

	#### Room support

	Within each `Namespace`, you can define arbitrary channels, called `Rooms`, that sockets can join and leave. You can then broadcast to any given room, reaching every socket that has joined it.

	This is a useful feature to send notifications to a group of users, or to a given user connected on several devices for example.


	Note: Socket.IO is not a WebSocket implementation. Although Socket.IO indeed uses WebSocket as a transport when possible, it adds some metadata to each packet: the packet type, the namespace and the ack id when a message acknowledgement is needed. That is why a WebSocket client will not be able to successfully connect to a Socket.IO server, and a Socket.IO client will not be able to connect to a WebSocket server (like `ws://echo.websocket.org`) either. Please see the protocol specification [here](https://github.com/socketio/socket.io-protocol).

	## Installation

	```bash
	// with npm
	npm install socket.io

	// with yarn
	yarn add socket.io
	```

	## How to use

	The following example attaches socket.io to a plain Node.JS
	HTTP server listening on port `3000`.

	```js
	const server = require('http').createServer();
	const io = require('socket.io')(server);
	io.on('connection', client => {
	client.on('event', data => { /* … */ });
	client.on('disconnect', () => { /* … */ });
	});
	server.listen(3000);
	```

	### Standalone

	```js
	const io = require('socket.io')();
	io.on('connection', client => { ... });
	io.listen(3000);
	```

	### Module syntax

	```js
	import { Server } from "socket.io";
	const io = new Server(server);
	io.listen(3000);
	```

	### In conjunction with Express

	Starting with 3.0, express applications have become request handler
	functions that you pass to `http` or `http` `Server` instances. You need
	to pass the `Server` to `socket.io`, not the express application
	function. Also make sure to call `.listen` on the `server`, not the `app`.

	```js
	const app = require('express')();
	const server = require('http').createServer(app);
	const io = require('socket.io')(server);
	io.on('connection', () => { /* … */ });
	server.listen(3000);
	```

	### In conjunction with Koa

	Like Express.JS, Koa works by exposing an application as a request
	handler function, but only by calling the `callback` method.

	```js
	const app = require('koa')();
	const server = require('http').createServer(app.callback());
	const io = require('socket.io')(server);
	io.on('connection', () => { /* … */ });
	server.listen(3000);
	```

	### In conjunction with Fastify

	To integrate Socket.io in your Fastify application you just need to
	register `fastify-socket.io` plugin. It will create a `decorator`
	called `io`.

	```js
	const app = require('fastify')();
	app.register(require('fastify-socket.io'));
	app.ready().then(() => {
	app.io.on('connection', () => { /* … */ });
	})
	app.listen(3000);
	```

	## Documentation

	Please see the documentation [here](https://socket.io/docs/).

	The source code of the website can be found [here](https://github.com/socketio/socket.io-website). Contributions are welcome!

	## Debug / logging

	Socket.IO is powered by [debug](https://github.com/visionmedia/debug).
	In order to see all the debug output, run your app with the environment variable
	`DEBUG` including the desired scope.

	To see the output from all of Socket.IO's debugging scopes you can use:

	```
	DEBUG=socket.io* node myapp
	```

	## Testing

	```
	npm test
	```
	This runs the `gulp` task `test`. By default the test will be run with the source code in `lib` directory.

	Set the environmental variable `TEST_VERSION` to `compat` to test the transpiled es5-compat version of the code.

	The `gulp` task `test` will always transpile the source code into es5 and export to `dist` first before running the test.


	## Backers

	Support us with a monthly donation and help us continue our activities. [[Become a backer](https://opencollective.com/socketio#backer)]

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	## Sponsors

	Become a sponsor and get your logo on our README on Github with a link to your site. [[Become a sponsor](https://opencollective.com/socketio#sponsor)]

	<a href="https://opencollective.com/socketio/sponsor/0/website" target="_blank"><img src="https://opencollective.com/socketio/sponsor/0/avatar.svg"></a>
	<a href="https://opencollective.com/socketio/sponsor/1/website" target="_blank"><img src="https://opencollective.com/socketio/sponsor/1/avatar.svg"></a>
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	## License

	[MIT](LICENSE)