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https://github.com/faye/websocket-driver-ruby

WebSocket protocol handler with pluggable I/O
https://github.com/faye/websocket-driver-ruby

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WebSocket protocol handler with pluggable I/O

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# websocket-driver



This module provides a complete implementation of the WebSocket protocols that

can be hooked up to any TCP library. It aims to simplify things by decoupling

the protocol details from the I/O layer, such that users only need to implement

code to stream data in and out of it without needing to know anything about how

the protocol actually works. Think of it as a complete WebSocket system with

pluggable I/O.



Due to this design, you get a lot of things for free. In particular, if you hook

this module up to some I/O object, it will do all of this for you:



- Select the correct server-side driver to talk to the client

- Generate and send both server- and client-side handshakes

- Recognize when the handshake phase completes and the WS protocol begins

- Negotiate subprotocol selection based on `Sec-WebSocket-Protocol`

- Negotiate and use extensions via the

  [websocket-extensions](https://github.com/faye/websocket-extensions-ruby)

  module

- Buffer sent messages until the handshake process is finished

- Deal with proxies that defer delivery of the draft-76 handshake body

- Notify you when the socket is open and closed and when messages arrive

- Recombine fragmented messages

- Dispatch text, binary, ping, pong and close frames

- Manage the socket-closing handshake process

- Automatically reply to ping frames with a matching pong

- Apply masking to messages sent by the client



This library was originally extracted from the [Faye](http://faye.jcoglan.com)

project but now aims to provide simple WebSocket support for any Ruby server or

I/O system.



## Installation



```

$ gem install websocket-driver

```



## Usage



To build either a server-side or client-side socket, the only requirement is

that you supply a `socket` object with these methods:



- `socket.url` - returns the full URL of the socket as a string.

- `socket.write(string)` - writes the given string to a TCP stream.



Server-side sockets require one additional method:



- `socket.env` - returns a Rack-style env hash that will contain some of the

  following fields. Their values are strings containing the value of the named

  header, unless stated otherwise.

  * `HTTP_CONNECTION`

  * `HTTP_HOST`

  * `HTTP_ORIGIN`

  * `HTTP_SEC_WEBSOCKET_EXTENSIONS`

  * `HTTP_SEC_WEBSOCKET_KEY`

  * `HTTP_SEC_WEBSOCKET_KEY1`

  * `HTTP_SEC_WEBSOCKET_KEY2`

  * `HTTP_SEC_WEBSOCKET_PROTOCOL`

  * `HTTP_SEC_WEBSOCKET_VERSION`

  * `HTTP_UPGRADE`

  * `rack.input`, an `IO` object representing the request body

  * `REQUEST_METHOD`, the request's HTTP verb



### Server-side with Rack



To handle a server-side WebSocket connection, you need to check whether the

request is a WebSocket handshake, and if so create a protocol driver for it.

You must give the driver an object with the `env`, `url` and `write` methods. A

simple example might be:



```ruby

require 'websocket/driver'

require 'eventmachine'



class WS

  attr_reader :env, :url



  def initialize(env)

    @env = env



    secure = Rack::Request.new(env).ssl?

    scheme = secure ? 'wss:' : 'ws:'

    @url = scheme + '//' + env['HTTP_HOST'] + env['REQUEST_URI']



    @driver = WebSocket::Driver.rack(self)



    env['rack.hijack'].call

    @io = env['rack.hijack_io']



    EM.attach(@io, Reader) { |conn| conn.driver = @driver }



    @driver.start

  end



  def write(string)

    @io.write(string)

  end



  module Reader

    attr_writer :driver



    def receive_data(string)

      @driver.parse(string)

    end

  end

end

```



To explain what's going on here: the `WS` class implements the `env`, `url` and

`write(string)` methods as required. When instantiated with a Rack environment,

it stores the environment and infers the complete URL from it.  Having set up

the `env` and `url`, it asks `WebSocket::Driver` for a server-side driver for

the socket. Then it uses the Rack hijack API to gain access to the TCP stream,

and uses EventMachine to stream in incoming data from the client, handing

incoming data off to the driver for parsing. Finally, we tell the driver to

`start`, which will begin sending the handshake response.  This will invoke the

`WS#write` method, which will send the response out over the TCP socket.



Having defined this class we could use it like this when handling a request:



```ruby

if WebSocket::Driver.websocket?(env)

  socket = WS.new(env)

end

```



The driver API is described in full below.



### Server-side with TCP



You can also handle WebSocket connections in a bare TCP server, if you're not

using Rack and don't want to implement HTTP parsing yourself. For this, your

socket object only needs a `write` method.



The driver will emit a `:connect` event when a request is received, and at this

point you can detect whether it's a WebSocket and handle it as such. Here's an

example using an EventMachine TCP server.



```ruby

module Connection

  def initialize

    @driver = WebSocket::Driver.server(self)



    @driver.on :connect, -> (event) do

      if WebSocket::Driver.websocket?(@driver.env)

        @driver.start

      else

        # handle other HTTP requests, for example

        body = '
hello
'

        response = [

          'HTTP/1.1 200 OK',

          'Content-Type: text/plain',

          "Content-Length: #{body.bytesize}",

          '',

          body

        ]

        send_data response.join("\r\n")

      end

    end



    @driver.on :message, -> (e) { @driver.text(e.data) }

    @driver.on :close,   -> (e) { close_connection_after_writing }

  end



  def receive_data(data)

    @driver.parse(data)

  end



  def write(data)

    send_data(data)

  end

end



EM.run {

  EM.start_server('127.0.0.1', 4180, Connection)

}

```



In the `:connect` event, `@driver.env` is a Rack env representing the request.

If the request has a body, it will be in the `@driver.env['rack.input']` stream,

but only as much of the body as you have so far routed to it using the `parse`

method.



### Client-side



Similarly, to implement a WebSocket client you need an object with `url` and

`write` methods. Once you have one such object, you ask for a driver for it:



```ruby

driver = WebSocket::Driver.client(socket)

```



After this you use the driver API as described below to process incoming data

and send outgoing data.



Client drivers have two additional methods for reading the HTTP data that was

sent back by the server:



- `driver.status` - the integer value of the HTTP status code

- `driver.headers` - a hash-like object containing the response headers



### HTTP Proxies



The client driver supports connections via HTTP proxies using the `CONNECT`

method. Instead of sending the WebSocket handshake immediately, it will send a

`CONNECT` request, wait for a `200` response, and then proceed as normal.



To use this feature, call `proxy = driver.proxy(url)` where `url` is the origin

of the proxy, including a username and password if required. This produces an

object that manages the process of connecting via the proxy. You should call

`proxy.start` to begin the connection process, and pass data you receive via the

socket to `proxy.parse(data)`. When the proxy emits `:connect`, you should then

start sending incoming data to `driver.parse(data)` as normal, and call

`driver.start`.



```rb

proxy = driver.proxy('http://username:[email protected]')



proxy.on :connect, -> (event) do

  driver.start

end

```



The proxy's `:connect` event is also where you should perform a TLS handshake on

your TCP stream, if you are connecting to a `wss:` endpoint.



In the event that proxy connection fails, `proxy` will emit an `:error`. You can

inspect the proxy's response via `proxy.status` and `proxy.headers`.



```rb

proxy.on :error, -> (error) do

  puts error.message

  puts proxy.status

  puts proxy.headers.inspect

end

```



Before calling `proxy.start` you can set custom headers using

`proxy.set_header`:



```rb

proxy.set_header('User-Agent', 'ruby')

proxy.start

```



### Driver API



Drivers are created using one of the following methods:



```ruby

driver = WebSocket::Driver.rack(socket, options)

driver = WebSocket::Driver.server(socket, options)

driver = WebSocket::Driver.client(socket, options)

```



The `rack` method returns a driver chosen using the socket's `env`. The `server`

method returns a driver that will parse an HTTP request and then decide which

driver to use for it using the `rack` method. The `client` method always returns

a driver for the RFC version of the protocol with masking enabled on outgoing

frames.



The `options` argument is optional, and is a hash. It may contain the following

keys:



- `:max_length` - the maximum allowed size of incoming message frames, in bytes.

  The default value is `2^26 - 1`, or 1 byte short of 64 MiB.

- `:protocols` - an array of strings representing acceptable subprotocols for

  use over the socket. The driver will negotiate one of these to use via the

  `Sec-WebSocket-Protocol` header if supported by the other peer.



All drivers respond to the following API methods, but some of them are no-ops

depending on whether the client supports the behaviour.



Note that most of these methods are commands: if they produce data that should

be sent over the socket, they will give this to you by calling

`socket.write(string)`.



#### `driver.on :open, -> (event) {}`



Adds a callback block to execute when the socket becomes open.



#### `driver.on :message, -> (event) {}`



Adds a callback block to execute when a message is received. `event` will have a

`data` attribute containing either a string in the case of a text message or an

array of integers in the case of a binary message.



#### `driver.on :error, -> (event) {}`



Adds a callback to execute when a protocol error occurs due to the other peer

sending an invalid byte sequence. `event` will have a `message` attribute

describing the error.



#### `driver.on :close, -> (event) {}`



Adds a callback block to execute when the socket becomes closed. The `event`

object has `code` and `reason` attributes.



#### `driver.on :ping, -> (event) {}`



Adds a callback block to execute when a ping is received. You do not need to

handle this by sending a pong frame yourself; the driver handles this for you.



#### `driver.on :pong, -> (event) {}`



Adds a callback block to execute when a pong is received. If this was in

response to a ping you sent, you can also handle this event via the

`driver.ping(message) { ... }` callback.



#### `driver.add_extension(extension)`



Registers a protocol extension whose operation will be negotiated via the

`Sec-WebSocket-Extensions` header. `extension` is any extension compatible with

the [websocket-extensions](https://github.com/faye/websocket-extensions-ruby)

framework.



#### `driver.set_header(name, value)`



Sets a custom header to be sent as part of the handshake response, either from

the server or from the client. Must be called before `start`, since this is when

the headers are serialized and sent.



#### `driver.start`



Initiates the protocol by sending the handshake - either the response for a

server-side driver or the request for a client-side one. This should be the

first method you invoke.  Returns `true` if and only if a handshake was sent.



#### `driver.parse(string)`



Takes a string and parses it, potentially resulting in message events being

emitted (see `on('message')` above) or in data being sent to `socket.write`.

You should send all data you receive via I/O to this method.



#### `driver.text(string)`



Sends a text message over the socket. If the socket handshake is not yet

complete, the message will be queued until it is. Returns `true` if the message

was sent or queued, and `false` if the socket can no longer send messages.



#### `driver.binary(array)`



Takes an array of byte-sized integers and sends them as a binary message. Will

queue and return `true` or `false` the same way as the `text` method. It will

also return `false` if the driver does not support binary messages.



#### `driver.ping(string = '', &callback)`



Sends a ping frame over the socket, queueing it if necessary. `string` and the

`callback` block are both optional. If a callback is given, it will be invoked

when the socket receives a pong frame whose content matches `string`. Returns

`false` if frames can no longer be sent, or if the driver does not support

ping/pong.



#### `driver.pong(string = '')`



Sends a pong frame over the socket, queueing it if necessary. `string` is

optional. Returns `false` if frames can no longer be sent, or if the driver does

not support ping/pong.



You don't need to call this when a ping frame is received; pings are replied to

automatically by the driver. This method is for sending unsolicited pongs.



#### `driver.close`



Initiates the closing handshake if the socket is still open. For drivers with no

closing handshake, this will result in the immediate execution of the

`on('close')` callback. For drivers with a closing handshake, this sends a

closing frame and `emit('close')` will execute when a response is received or a

protocol error occurs.



#### `driver.version`



Returns the WebSocket version in use as a string. Will either be `hixie-75`,

`hixie-76` or `hybi-$version`.



#### `driver.protocol`



Returns a string containing the selected subprotocol, if any was agreed upon

using the `Sec-WebSocket-Protocol` mechanism. This value becomes available after

`emit('open')` has fired.