Posted on Wed 21 August 2013

How to Create a Websocket Server in Ruby

This is a short tutorial on creating a websocket server in Ruby using James Coglan's websocket driver. The complete example is available on github.

About Websocket Driver

The websocket-driver gem decouples the websocket protocol from the I/O layer, providing drivers that handle the websocket procotol (handshakes, upgrades etc) on any compatible I/O. It can be used with Rack, EventMachine, or just plain TCP. The examples for EventMachine and Rack are available in the documentation.

Using Plain TCP

This echo server was adapted from code found in poltergeist. It defines an EchoServer class, which is used as follows

server = EchoServer.new
server.listen  # blocking

Within #listen, the server accepts clients connections in a continuous loop and spins off new threads to handle each client. The connected socket is passed to WebSocket::Driver#server, which selects, instantiates, and returns an appropriate driver.

driver = ::WebSocket::Driver.server(socket)
driver.on(:connect) { driver.start }
driver.on(:message) { |e| driver.text e.data }
driver.on(:close)   { puts "Connection with #{socket.addr[2]} closed." }
loop do
  IO.select([socket], [], [], 30) or raise Errno::EWOULDBLOCK
  data = socket.recv(RECV_SIZE)
  break if data.empty?
  driver.parse data
end

In general, data received on the socket should be passed to driver#parse, and driver#text or driver#bytes can be used to send data to the other end. The echo server can be tested from any modern browser with the following JavaScript snippet.

connection = new WebSocket('ws://localhost:54398/');
// Log errors
connection.onerror = function (error) { console.log('WebSocket Error ' + error); };
// Log messages from the server
connection.onmessage = function (e) { console.log('Server: ' + e.data); };

Category: Software

Tags: ruby

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