Ruby TCPSocket keeps losing connection

Question

I have a client and server. I start up the server, and run the client, and the first time it works fine. The second time I run the client(without restarting the server), the client appears to hang. Can anyone see what is wrong?

I have a client:

# Code example originated from p069dtclient.rb at http://rubylearning.com/satishtalim/ruby_socket_programming.html
    require 'socket'
    x = 0;

    streamSock = TCPSocket.new( 'localhost', 20000 )
    while x < 10
      streamSock.send( "Hello #{x}",0 )
      str = streamSock.recv( 100 )
      puts "#{x} " + str
      x=x+1
    end
    streamSock.close

And server:

    # p068dtserver.rb
    require "socket"
    dts = TCPServer.new('localhost', 20000)
    s = dts.accept
    print(s, " is accepted\n")
    loopCount = 0;
    loop do
      Thread.start(s) do
      loopCount = loopCount + 1
        lineRcvd = s.recv(1024)
        if ( !lineRcvd.empty? )
          puts("#{loopCount} Received: #{lineRcvd}")
          s.write(Time.now)
        end
      end
    end
    s.close
    print(s, " is gone\n")

Answer 1

Each connection to the server requires a separate accept call in order to be received. What's happening is that you're accepting the first, working with it, and then effectively terminating while leaving the socket in a listening state. This means connections will be opened, but not accepted, so they hang as you describe.

You might be better off using a more robust server framework. EventMachine (http://rubyeventmachine.com/) is a little tricky to learn, but is far more powerful than a roll your own solution.

Here's a quick fix that might help:

require "socket"
dts = TCPServer.new('localhost', 20000)
while (s = dts.accept)
  print(s, " is accepted\n")
  loopCount = 0;
  loop do
    Thread.start(s) do
    loopCount = loopCount + 1
      lineRcvd = s.recv(1024)
      if ( !lineRcvd.empty? )
        puts("#{loopCount} Received: #{lineRcvd}")
        s.write(Time.now)
      end
    end
  end
  s.close
  print(s, " is gone\n")
end

Now the accept call is wrapped in a loop so more than one connection can be processed.