565 lines
21 KiB
Markdown
565 lines
21 KiB
Markdown
|
||
# Engine.IO: the realtime engine
|
||
|
||
[](https://github.com/socketio/engine.io/actions)
|
||
[](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(Buffer.from([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);
|
||
|
||
// with custom options
|
||
var eioServer = require('engine.io')(httpServer, {
|
||
maxHttpBufferSize: 1e3
|
||
});
|
||
```
|
||
|
||
- `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`
|
||
|
||
```js
|
||
var engine = require('engine.io');
|
||
var server = engine.listen(3000, {
|
||
pingTimeout: 2000,
|
||
pingInterval: 10000
|
||
});
|
||
|
||
server.on('connection', /* ... */);
|
||
```
|
||
|
||
- `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.
|
||
|
||
```js
|
||
var engine = require('engine.io');
|
||
var httpServer = require('http').createServer().listen(3000);
|
||
var server = engine.attach(httpServer, {
|
||
wsEngine: 'uws' // requires having uws as dependency
|
||
});
|
||
|
||
server.on('connection', /* ... */);
|
||
```
|
||
|
||
#### 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 (`5000`)
|
||
- `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 `true` to enable. (`false`)
|
||
- `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 `ws`. An alternative c++ addon is also available by installing `uws` module.
|
||
- `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 `npm 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 <guillermo@learnboost.com>
|
||
|
||
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.
|