273 lines
17 KiB
Markdown
273 lines
17 KiB
Markdown
# socket.io
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[](https://replit.com/@socketio/socketio-minimal-example)
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[](#backers) [](#sponsors)
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[](https://github.com/socketio/socket.io/actions)
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[](https://www.npmjs.com/package/socket.io)
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[](https://slackin-socketio.now.sh)
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## Features
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Socket.IO enables real-time bidirectional event-based communication. It consists of:
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- a Node.js server (this repository)
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- a [Javascript client library](https://github.com/socketio/socket.io-client) for the browser (or a Node.js client)
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Some implementations in other languages are also available:
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- [Java](https://github.com/socketio/socket.io-client-java)
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- [C++](https://github.com/socketio/socket.io-client-cpp)
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- [Swift](https://github.com/socketio/socket.io-client-swift)
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- [Dart](https://github.com/rikulo/socket.io-client-dart)
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- [Python](https://github.com/miguelgrinberg/python-socketio)
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- [.NET](https://github.com/doghappy/socket.io-client-csharp)
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- [Rust](https://github.com/1c3t3a/rust-socketio)
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- [PHP](https://github.com/ElephantIO/elephant.io)
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Its main features are:
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#### Reliability
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Connections are established even in the presence of:
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- proxies and load balancers.
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- personal firewall and antivirus software.
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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.
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#### Auto-reconnection support
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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).
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#### Disconnection detection
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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.
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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.
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#### Binary support
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Any serializable data structures can be emitted, including:
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- [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
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- [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
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#### Simple and convenient API
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Sample code:
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```js
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io.on('connection', socket => {
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socket.emit('request', /* … */); // emit an event to the socket
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io.emit('broadcast', /* … */); // emit an event to all connected sockets
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socket.on('reply', () => { /* … */ }); // listen to the event
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});
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```
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#### Cross-browser
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Browser support is tested in Sauce Labs:
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[](https://saucelabs.com/u/socket)
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#### Multiplexing support
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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.
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#### Room support
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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.
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This is a useful feature to send notifications to a group of users, or to a given user connected on several devices for example.
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**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).
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## Installation
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```bash
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// with npm
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npm install socket.io
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// with yarn
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yarn add socket.io
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```
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## How to use
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The following example attaches socket.io to a plain Node.JS
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HTTP server listening on port `3000`.
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```js
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const server = require('http').createServer();
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const io = require('socket.io')(server);
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io.on('connection', client => {
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client.on('event', data => { /* … */ });
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client.on('disconnect', () => { /* … */ });
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});
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server.listen(3000);
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```
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### Standalone
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```js
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const io = require('socket.io')();
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io.on('connection', client => { ... });
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io.listen(3000);
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```
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### Module syntax
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```js
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import { Server } from "socket.io";
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const io = new Server(server);
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io.listen(3000);
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```
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### In conjunction with Express
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Starting with **3.0**, express applications have become request handler
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functions that you pass to `http` or `http` `Server` instances. You need
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to pass the `Server` to `socket.io`, not the express application
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function. Also make sure to call `.listen` on the `server`, not the `app`.
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```js
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const app = require('express')();
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const server = require('http').createServer(app);
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const io = require('socket.io')(server);
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io.on('connection', () => { /* … */ });
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server.listen(3000);
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```
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### In conjunction with Koa
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Like Express.JS, Koa works by exposing an application as a request
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handler function, but only by calling the `callback` method.
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```js
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const app = require('koa')();
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const server = require('http').createServer(app.callback());
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const io = require('socket.io')(server);
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io.on('connection', () => { /* … */ });
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server.listen(3000);
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```
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### In conjunction with Fastify
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To integrate Socket.io in your Fastify application you just need to
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register `fastify-socket.io` plugin. It will create a `decorator`
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called `io`.
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```js
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const app = require('fastify')();
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app.register(require('fastify-socket.io'));
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app.ready().then(() => {
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app.io.on('connection', () => { /* … */ });
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})
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app.listen(3000);
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```
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## Documentation
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Please see the documentation [here](https://socket.io/docs/).
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The source code of the website can be found [here](https://github.com/socketio/socket.io-website). Contributions are welcome!
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## Debug / logging
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Socket.IO is powered by [debug](https://github.com/visionmedia/debug).
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In order to see all the debug output, run your app with the environment variable
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`DEBUG` including the desired scope.
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To see the output from all of Socket.IO's debugging scopes you can use:
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```
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DEBUG=socket.io* node myapp
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```
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## Testing
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```
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npm test
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```
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This runs the `gulp` task `test`. By default the test will be run with the source code in `lib` directory.
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Set the environmental variable `TEST_VERSION` to `compat` to test the transpiled es5-compat version of the code.
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The `gulp` task `test` will always transpile the source code into es5 and export to `dist` first before running the test.
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## Backers
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Support us with a monthly donation and help us continue our activities. [[Become a backer](https://opencollective.com/socketio#backer)]
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<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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<a href="https://opencollective.com/socketio/backer/1/website" target="_blank"><img src="https://opencollective.com/socketio/backer/1/avatar.svg"></a>
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## Sponsors
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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)]
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## License
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[MIT](LICENSE)
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