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authorYaroslav De La Peña Smirnov <yaros.rus_89@live.com.mx>2017-11-29 11:44:34 +0300
committerYaroslav De La Peña Smirnov <yaros.rus_89@live.com.mx>2017-11-29 11:44:34 +0300
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+
+# Engine.IO: the realtime engine
+
+[![Build Status](https://travis-ci.org/socketio/engine.io.svg?branch=master)](http://travis-ci.org/socketio/engine.io)
+[![NPM version](https://badge.fury.io/js/engine.io.svg)](http://badge.fury.io/js/engine.io)
+
+`Engine.IO` is the implementation of transport-based
+cross-browser/cross-device bi-directional communication layer for
+[Socket.IO](http://github.com/socketio/socket.io).
+
+## How to use
+
+### Server
+
+#### (A) Listening on a port
+
+```js
+var engine = require('engine.io');
+var server = engine.listen(80);
+
+server.on('connection', function(socket){
+ socket.send('utf 8 string');
+ socket.send(new Buffer([0, 1, 2, 3, 4, 5])); // binary data
+});
+```
+
+#### (B) Intercepting requests for a http.Server
+
+```js
+var engine = require('engine.io');
+var http = require('http').createServer().listen(3000);
+var server = engine.attach(http);
+
+server.on('connection', function (socket) {
+ socket.on('message', function(data){ });
+ socket.on('close', function(){ });
+});
+```
+
+#### (C) Passing in requests
+
+```js
+var engine = require('engine.io');
+var server = new engine.Server();
+
+server.on('connection', function(socket){
+ socket.send('hi');
+});
+
+// …
+httpServer.on('upgrade', function(req, socket, head){
+ server.handleUpgrade(req, socket, head);
+});
+httpServer.on('request', function(req, res){
+ server.handleRequest(req, res);
+});
+```
+
+### Client
+
+```html
+<script src="/path/to/engine.io.js"></script>
+<script>
+ var socket = new eio.Socket('ws://localhost/');
+ socket.on('open', function(){
+ socket.on('message', function(data){});
+ socket.on('close', function(){});
+ });
+</script>
+```
+
+For more information on the client refer to the
+[engine-client](http://github.com/learnboost/engine.io-client) repository.
+
+## What features does it have?
+
+- **Maximum reliability**. Connections are established even in the presence of:
+ - proxies and load balancers.
+ - personal firewall and antivirus software.
+ - for more information refer to **Goals** and **Architecture** sections
+- **Minimal client size** aided by:
+ - lazy loading of flash transports.
+ - lack of redundant transports.
+- **Scalable**
+ - load balancer friendly
+- **Future proof**
+- **100% Node.JS core style**
+ - No API sugar (left for higher level projects)
+ - Written in readable vanilla JavaScript
+
+## API
+
+### Server
+
+<hr><br>
+
+#### Top-level
+
+These are exposed by `require('engine.io')`:
+
+##### Events
+
+- `flush`
+ - Called when a socket buffer is being flushed.
+ - **Arguments**
+ - `Socket`: socket being flushed
+ - `Array`: write buffer
+- `drain`
+ - Called when a socket buffer is drained
+ - **Arguments**
+ - `Socket`: socket being flushed
+
+##### Properties
+
+- `protocol` _(Number)_: protocol revision number
+- `Server`: Server class constructor
+- `Socket`: Socket class constructor
+- `Transport` _(Function)_: transport constructor
+- `transports` _(Object)_: map of available transports
+
+##### Methods
+
+- `()`
+ - Returns a new `Server` instance. If the first argument is an `http.Server` then the
+ new `Server` instance will be attached to it. Otherwise, the arguments are passed
+ directly to the `Server` constructor.
+ - **Parameters**
+ - `http.Server`: optional, server to attach to.
+ - `Object`: optional, options object (see `Server#constructor` api docs below)
+
+ The following are identical ways to instantiate a server and then attach it.
+ ```js
+ var httpServer; // previously created with `http.createServer();` from node.js api.
+
+ // create a server first, and then attach
+ var eioServer = require('engine.io').Server();
+ eioServer.attach(httpServer);
+
+ // or call the module as a function to get `Server`
+ var eioServer = require('engine.io')();
+ eioServer.attach(httpServer);
+
+ // immediately attach
+ var eioServer = require('engine.io')(httpServer);
+ ```
+
+- `listen`
+ - Creates an `http.Server` which listens on the given port and attaches WS
+ to it. It returns `501 Not Implemented` for regular http requests.
+ - **Parameters**
+ - `Number`: port to listen on.
+ - `Object`: optional, options object
+ - `Function`: callback for `listen`.
+ - **Options**
+ - All options from `Server.attach` method, documented below.
+ - **Additionally** See Server `constructor` below for options you can pass for creating the new Server
+ - **Returns** `Server`
+- `attach`
+ - Captures `upgrade` requests for a `http.Server`. In other words, makes
+ a regular http.Server WebSocket-compatible.
+ - **Parameters**
+ - `http.Server`: server to attach to.
+ - `Object`: optional, options object
+ - **Options**
+ - All options from `Server.attach` method, documented below.
+ - **Additionally** See Server `constructor` below for options you can pass for creating the new Server
+ - **Returns** `Server` a new Server instance.
+
+<hr><br>
+
+#### Server
+
+The main server/manager. _Inherits from EventEmitter_.
+
+##### Events
+
+- `connection`
+ - Fired when a new connection is established.
+ - **Arguments**
+ - `Socket`: a Socket object
+
+##### Properties
+
+**Important**: if you plan to use Engine.IO in a scalable way, please
+keep in mind the properties below will only reflect the clients connected
+to a single process.
+
+- `clients` _(Object)_: hash of connected clients by id.
+- `clientsCount` _(Number)_: number of connected clients.
+
+##### Methods
+
+- **constructor**
+ - Initializes the server
+ - **Parameters**
+ - `Object`: optional, options object
+ - **Options**
+ - `pingTimeout` (`Number`): how many ms without a pong packet to
+ consider the connection closed (`60000`)
+ - `pingInterval` (`Number`): how many ms before sending a new ping
+ packet (`25000`)
+ - `upgradeTimeout` (`Number`): how many ms before an uncompleted transport upgrade is cancelled (`10000`)
+ - `maxHttpBufferSize` (`Number`): how many bytes or characters a message
+ can be, before closing the session (to avoid DoS). Default
+ value is `10E7`.
+ - `allowRequest` (`Function`): A function that receives a given handshake
+ or upgrade request as its first parameter, and can decide whether to
+ continue or not. The second argument is a function that needs to be
+ called with the decided information: `fn(err, success)`, where
+ `success` is a boolean value where false means that the request is
+ rejected, and err is an error code.
+ - `transports` (`<Array> String`): transports to allow connections
+ to (`['polling', 'websocket']`)
+ - `allowUpgrades` (`Boolean`): whether to allow transport upgrades
+ (`true`)
+ - `perMessageDeflate` (`Object|Boolean`): parameters of the WebSocket permessage-deflate extension
+ (see [ws module](https://github.com/einaros/ws) api docs). Set to `false` to disable. (`true`)
+ - `threshold` (`Number`): data is compressed only if the byte size is above this value (`1024`)
+ - `httpCompression` (`Object|Boolean`): parameters of the http compression for the polling transports
+ (see [zlib](http://nodejs.org/api/zlib.html#zlib_options) api docs). Set to `false` to disable. (`true`)
+ - `threshold` (`Number`): data is compressed only if the byte size is above this value (`1024`)
+ - `cookie` (`String|Boolean`): name of the HTTP cookie that
+ contains the client sid to send as part of handshake response
+ headers. Set to `false` to not send one. (`io`)
+ - `cookiePath` (`String|Boolean`): path of the above `cookie`
+ option. If false, no path will be sent, which means browsers will only send the cookie on the engine.io attached path (`/engine.io`).
+ Set false to not save io cookie on all requests. (`/`)
+ - `cookieHttpOnly` (`Boolean`): If `true` HttpOnly io cookie cannot be accessed by client-side APIs, such as JavaScript. (`true`) _This option has no effect if `cookie` or `cookiePath` is set to `false`._
+ - `wsEngine` (`String`): what WebSocket server implementation to use. Specified module must conform to the `ws` interface (see [ws module api docs](https://github.com/websockets/ws/blob/master/doc/ws.md)). Default value is `uws` (see [µWebSockets](https://github.com/uWebSockets/uWebSockets)).
+ - `initialPacket` (`Object`): an optional packet which will be concatenated to the handshake packet emitted by Engine.IO.
+- `close`
+ - Closes all clients
+ - **Returns** `Server` for chaining
+- `handleRequest`
+ - Called internally when a `Engine` request is intercepted.
+ - **Parameters**
+ - `http.IncomingMessage`: a node request object
+ - `http.ServerResponse`: a node response object
+ - **Returns** `Server` for chaining
+- `handleUpgrade`
+ - Called internally when a `Engine` ws upgrade is intercepted.
+ - **Parameters** (same as `upgrade` event)
+ - `http.IncomingMessage`: a node request object
+ - `net.Stream`: TCP socket for the request
+ - `Buffer`: legacy tail bytes
+ - **Returns** `Server` for chaining
+- `attach`
+ - Attach this Server instance to an `http.Server`
+ - Captures `upgrade` requests for a `http.Server`. In other words, makes
+ a regular http.Server WebSocket-compatible.
+ - **Parameters**
+ - `http.Server`: server to attach to.
+ - `Object`: optional, options object
+ - **Options**
+ - `path` (`String`): name of the path to capture (`/engine.io`).
+ - `destroyUpgrade` (`Boolean`): destroy unhandled upgrade requests (`true`)
+ - `destroyUpgradeTimeout` (`Number`): milliseconds after which unhandled requests are ended (`1000`)
+ - `handlePreflightRequest` (`Boolean|Function`): whether to let engine.io handle the OPTIONS requests. You can also pass a custom function to handle the requests (`true`)
+- `generateId`
+ - Generate a socket id.
+ - Overwrite this method to generate your custom socket id.
+ - **Parameters**
+ - `http.IncomingMessage`: a node request object
+ - **Returns** A socket id for connected client.
+
+<hr><br>
+
+#### Socket
+
+A representation of a client. _Inherits from EventEmitter_.
+
+##### Events
+
+- `close`
+ - Fired when the client is disconnected.
+ - **Arguments**
+ - `String`: reason for closing
+ - `Object`: description object (optional)
+- `message`
+ - Fired when the client sends a message.
+ - **Arguments**
+ - `String` or `Buffer`: Unicode string or Buffer with binary contents
+- `error`
+ - Fired when an error occurs.
+ - **Arguments**
+ - `Error`: error object
+- `flush`
+ - Called when the write buffer is being flushed.
+ - **Arguments**
+ - `Array`: write buffer
+- `drain`
+ - Called when the write buffer is drained
+- `packet`
+ - Called when a socket received a packet (`message`, `ping`)
+ - **Arguments**
+ - `type`: packet type
+ - `data`: packet data (if type is message)
+- `packetCreate`
+ - Called before a socket sends a packet (`message`, `pong`)
+ - **Arguments**
+ - `type`: packet type
+ - `data`: packet data (if type is message)
+
+##### Properties
+
+- `id` _(String)_: unique identifier
+- `server` _(Server)_: engine parent reference
+- `request` _(http.IncomingMessage)_: request that originated the Socket
+- `upgraded` _(Boolean)_: whether the transport has been upgraded
+- `readyState` _(String)_: opening|open|closing|closed
+- `transport` _(Transport)_: transport reference
+
+##### Methods
+
+- `send`:
+ - Sends a message, performing `message = toString(arguments[0])` unless
+ sending binary data, which is sent as is.
+ - **Parameters**
+ - `String` | `Buffer` | `ArrayBuffer` | `ArrayBufferView`: a string or any object implementing `toString()`, with outgoing data, or a Buffer or ArrayBuffer with binary data. Also any ArrayBufferView can be sent as is.
+ - `Object`: optional, options object
+ - `Function`: optional, a callback executed when the message gets flushed out by the transport
+ - **Options**
+ - `compress` (`Boolean`): whether to compress sending data. This option might be ignored and forced to be `true` when using polling. (`true`)
+ - **Returns** `Socket` for chaining
+- `close`
+ - Disconnects the client
+ - **Returns** `Socket` for chaining
+
+### Client
+
+<hr><br>
+
+Exposed in the `eio` global namespace (in the browser), or by
+`require('engine.io-client')` (in Node.JS).
+
+For the client API refer to the
+[engine-client](http://github.com/learnboost/engine.io-client) repository.
+
+## Debug / logging
+
+Engine.IO is powered by [debug](http://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 Engine.IO's debugging scopes you can use:
+
+```
+DEBUG=engine* node myapp
+```
+
+## Transports
+
+- `polling`: XHR / JSONP polling transport.
+- `websocket`: WebSocket transport.
+
+## Plugins
+
+- [engine.io-conflation](https://github.com/EugenDueck/engine.io-conflation): Makes **conflation and aggregation** of messages straightforward.
+
+## Support
+
+The support channels for `engine.io` are the same as `socket.io`:
+ - irc.freenode.net **#socket.io**
+ - [Google Groups](http://groups.google.com/group/socket_io)
+ - [Website](http://socket.io)
+
+## Development
+
+To contribute patches, run tests or benchmarks, make sure to clone the
+repository:
+
+```
+git clone git://github.com/LearnBoost/engine.io.git
+```
+
+Then:
+
+```
+cd engine.io
+npm install
+```
+
+## Tests
+
+Tests run with `make test`. It runs the server tests that are aided by
+the usage of `engine.io-client`.
+
+Make sure `npm install` is run first.
+
+## Goals
+
+The main goal of `Engine` is ensuring the most reliable realtime communication.
+Unlike the previous Socket.IO core, it always establishes a long-polling
+connection first, then tries to upgrade to better transports that are "tested" on
+the side.
+
+During the lifetime of the Socket.IO projects, we've found countless drawbacks
+to relying on `HTML5 WebSocket` or `Flash Socket` as the first connection
+mechanisms.
+
+Both are clearly the _right way_ of establishing a bidirectional communication,
+with HTML5 WebSocket being the way of the future. However, to answer most business
+needs, alternative traditional HTTP 1.1 mechanisms are just as good as delivering
+the same solution.
+
+WebSocket based connections have two fundamental benefits:
+
+1. **Better server performance**
+ - _A: Load balancers_<br>
+ Load balancing a long polling connection poses a serious architectural nightmare
+ since requests can come from any number of open sockets by the user agent, but
+ they all need to be routed to the process and computer that owns the `Engine`
+ connection. This negatively impacts RAM and CPU usage.
+ - _B: Network traffic_<br>
+ WebSocket is designed around the premise that each message frame has to be
+ surrounded by the least amount of data. In HTTP 1.1 transports, each message
+ frame is surrounded by HTTP headers and chunked encoding frames. If you try to
+ send the message _"Hello world"_ with xhr-polling, the message ultimately
+ becomes larger than if you were to send it with WebSocket.
+ - _C: Lightweight parser_<br>
+ As an effect of **B**, the server has to do a lot more work to parse the network
+ data and figure out the message when traditional HTTP requests are used
+ (as in long polling). This means that another advantage of WebSocket is
+ less server CPU usage.
+
+2. **Better user experience**
+
+ Due to the reasons stated in point **1**, the most important effect of being able
+ to establish a WebSocket connection is raw data transfer speed, which translates
+ in _some_ cases in better user experience.
+
+ Applications with heavy realtime interaction (such as games) will benefit greatly,
+ whereas applications like realtime chat (Gmail/Facebook), newsfeeds (Facebook) or
+ timelines (Twitter) will have negligible user experience improvements.
+
+Having said this, attempting to establish a WebSocket connection directly so far has
+proven problematic:
+
+1. **Proxies**<br>
+ Many corporate proxies block WebSocket traffic.
+
+2. **Personal firewall and antivirus software**<br>
+ As a result of our research, we've found that at least 3 personal security
+ applications block WebSocket traffic.
+
+3. **Cloud application platforms**<br>
+ Platforms like Heroku or No.de have had trouble keeping up with the fast-paced
+ nature of the evolution of the WebSocket protocol. Applications therefore end up
+ inevitably using long polling, but the seamless installation experience of
+ Socket.IO we strive for (_"require() it and it just works"_) disappears.
+
+Some of these problems have solutions. In the case of proxies and personal programs,
+however, the solutions many times involve upgrading software. Experience has shown
+that relying on client software upgrades to deliver a business solution is
+fruitless: the very existence of this project has to do with a fragmented panorama
+of user agent distribution, with clients connecting with latest versions of the most
+modern user agents (Chrome, Firefox and Safari), but others with versions as low as
+IE 5.5.
+
+From the user perspective, an unsuccessful WebSocket connection can translate in
+up to at least 10 seconds of waiting for the realtime application to begin
+exchanging data. This **perceptively** hurts user experience.
+
+To summarize, **Engine** focuses on reliability and user experience first, marginal
+potential UX improvements and increased server performance second. `Engine` is the
+result of all the lessons learned with WebSocket in the wild.
+
+## Architecture
+
+The main premise of `Engine`, and the core of its existence, is the ability to
+swap transports on the fly. A connection starts as xhr-polling, but it can
+switch to WebSocket.
+
+The central problem this poses is: how do we switch transports without losing
+messages?
+
+`Engine` only switches from polling to another transport in between polling
+cycles. Since the server closes the connection after a certain timeout when
+there's no activity, and the polling transport implementation buffers messages
+in between connections, this ensures no message loss and optimal performance.
+
+Another benefit of this design is that we workaround almost all the limitations
+of **Flash Socket**, such as slow connection times, increased file size (we can
+safely lazy load it without hurting user experience), etc.
+
+## FAQ
+
+### Can I use engine without Socket.IO ?
+
+Absolutely. Although the recommended framework for building realtime applications
+is Socket.IO, since it provides fundamental features for real-world applications
+such as multiplexing, reconnection support, etc.
+
+`Engine` is to Socket.IO what Connect is to Express. An essential piece for building
+realtime frameworks, but something you _probably_ won't be using for building
+actual applications.
+
+### Does the server serve the client?
+
+No. The main reason is that `Engine` is meant to be bundled with frameworks.
+Socket.IO includes `Engine`, therefore serving two clients is not necessary. If
+you use Socket.IO, including
+
+```html
+<script src="/socket.io/socket.io.js">
+```
+
+has you covered.
+
+### Can I implement `Engine` in other languages?
+
+Absolutely. The [engine.io-protocol](https://github.com/LearnBoost/engine.io-protocol)
+repository contains the most up to date description of the specification
+at all times, and the parser implementation in JavaScript.
+
+## License
+
+(The MIT License)
+
+Copyright (c) 2014 Guillermo Rauch &lt;guillermo@learnboost.com&gt;
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+'Software'), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.