websocket_server.rb

require 'socket'
require 'digest/sha1'
require 'base64'

require_relative 'websocket_connection'

class WebSocketServer
  WS_MAGIC_STRING = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"

  def initialize(options={path: '/', port: 4567, host: 'localhost'})
    @path, port, host = options[:path], options[:port], options[:host]
    @tcp_server = TCPServer.new(host, port)
  end

  def accept
    socket = @tcp_server.accept
    send_handshake(socket) && WebSocketConnection.new(socket)
  end

  private

    def send_handshake(socket)
      request_line = socket.gets
      header = get_header(socket)
      if (request_line =~ /GET #{@path} HTTP\/1.1/) && (header =~ /Sec-WebSocket-Key: (.*)\r\n/)
        ws_accept = create_websocket_accept($1)
        send_handshake_response(socket, ws_accept)
        return true
      end
      send_400(socket)
      false # reject the handshake
    end

    def get_header(socket, header = "")
      (line = socket.gets) == "\r\n" ? header : get_header(socket, header + line)
    end

    def create_websocket_accept(key)
      digest = Digest::SHA1.digest(key + WS_MAGIC_STRING)
      Base64.encode64(digest)
    end

    def send_handshake_response(socket, ws_accept)
      socket << "HTTP/1.1 101 Switching Protocols\r\n" +
                "Upgrade: websocket\r\n" +
                "Connection: Upgrade\r\n" +
                "Sec-WebSocket-Accept: #{ws_accept}\r\n"
    end

    def send_400(socket)
      socket << "HTTP/1.1 400 Bad Request\r\n" +
                "Content-Type: text/plain\r\n" +
                "Connection: close\r\n" +
                "\r\n" +
                "Incorrect request"
      socket.close
    end

end