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:

This library was originally extracted from the Faye 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:

Server-side sockets require one additional method:

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:

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:

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.

module Connection
  def initialize
    @driver = WebSocket::Driver.server(self)

    @driver.on(:connect) do
      if WebSocket::Driver.websocket?(@driver.env)
        @driver.start
      else
        # handle other HTTP requests
      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:

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 API ↑

Drivers are created using one of the following methods:

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:

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| } ↑

Sets the callback block to execute when the socket becomes open.

driver.on('message') { |event| } ↑

Sets the 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| } ↑

Sets the 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| } ↑

Sets the callback block to execute when the socket becomes closed. The event object has code and reason attributes.

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 iff 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.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.

License ↑

(The MIT License)

Copyright © 2010-2014 James Coglan

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.