#!/usr/bin/env python
     # encoding: utf-8
     #
     # Copyright (c) 2010 Doug Hellmann.  All rights reserved.
     #
     """Server half of echo example.
     """
     #end_pymotw_header
     
     import select
     import socket
     import sys
     import Queue
     
     # Create a TCP/IP socket
     server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
     server.setblocking(0)
     
     # Bind the socket to the port
     server_address = ('localhost', 10000)
     print >>sys.stderr, 'starting up on %s port %s' % server_address
     server.bind(server_address)
     
     # Listen for incoming connections
     server.listen(5)
     
     # Sockets from which we expect to read
     inputs = [ server ]
     
     # Sockets to which we expect to write
     outputs = [ ]
     
     # Outgoing message queues (socket:Queue)
     message_queues = {}
     
     while inputs:
     
         # Wait for at least one of the sockets to be ready for processing
         print >>sys.stderr, '\nwaiting for the next event'
         readable, writable, exceptional = select.select(inputs, outputs, inputs)
     
         # Handle inputs
         for s in readable:
     
             if s is server:
                 # A "readable" server socket is ready to accept a connection
                 connection, client_address = s.accept()
                 print >>sys.stderr, 'new connection from', client_address
                 connection.setblocking(0)
                 inputs.append(connection)
     
                 # Give the connection a queue for data we want to send
                 message_queues[connection] = Queue.Queue()
     
             else:
                 data = s.recv(1024)
                 if data:
                     # A readable client socket has data
                     print >>sys.stderr, 'received "%s" from %s' % (data, s.getpeername())
                     message_queues[s].put(data)
                     # Add output channel for response
                     if s not in outputs:
                         outputs.append(s)
                         
                 else:
                     # Interpret empty result as closed connection
                     print >>sys.stderr, 'closing', client_address, 'after reading no data'
                     # Stop listening for input on the connection
                     if s in outputs:
                         outputs.remove(s)
                     inputs.remove(s)
                     s.close()
     
         # Handle outputs
         for s in writable:
             try:
                 next_msg = message_queues[s].get_nowait()
             except Queue.Empty:
                 # No messages waiting so stop checking for writability.
                 print >>sys.stderr, 'output queue for', s.getpeername(), 'is empty'
                 outputs.remove(s)
             else:
                 print >>sys.stderr, 'sending "%s" to %s' % (next_msg, s.getpeername())
                 s.send(next_msg)
     
         # Handle "exceptional conditions"
         for s in exceptional:
             print >>sys.stderr, 'handling exceptional condition for', s.getpeername()
             # Stop listening for input on the connection
             inputs.remove(s)
             if s in outputs:
                 outputs.remove(s)
             s.close()