select python

1import select
2import socket
3import sys
4import Queue
5
6# Create a TCP/IP socket
7server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
8server.setblocking(0)
9
10# Bind the socket to the port
11server_addr = ('localhost', 10000)
12print('starting server on {server_addr[0]}:{server_addr[1]}')
13server.bind(server_address)
14server.listen(5)
15
16# Sockets from which we expect to read
17inputs = [ server ]
18
19# Sockets to which we expect to write
20outputs = [ ]
21
22# Outgoing message queues (socket:Queue)
23message_queues = {}
24
25while inputs:
26
27    # Wait for at least one of the sockets to be ready for processing
28    print('waiting for the next event')
29    readable, writable, exceptional = select.select(inputs, outputs, inputs)
30
31    # Handle inputs
32    for s in readable:
33        if s is server:
34            # A "readable" server socket is ready to accept a connection
35            connection, client_address = s.accept()
36            print(f'new connection from {client_address}')
37            connection.setblocking(False)
38            inputs.append(connection)
39
40            # Give the connection a queue for data we want to send
41            message_queues[connection] = Queue.Queue()
42        else:
43            data = s.recv(1024)
44            if data:
45                # A readable client socket has data
46                print(f'received "{data}" from {s.getpeername()}')
47                message_queues[s].put(data)
48                # Add output channel for response
49                if s not in outputs:
50                    outputs.append(s)
51            else:
52                # Interpret empty result as closed connection
53                print(f'closing {client_address} after reading no data')
54                # Stop listening for input on the connection
55                if s in outputs:
56                    outputs.remove(s)
57                inputs.remove(s)
58                s.close()
59                
60                # Remove message queue
61                del message_queues[s]
62
63    # Handle outputs
64    for s in writable:
65        try:
66            next_msg = message_queues[s].get_nowait()
67        except Queue.Empty:
68            # No messages waiting so stop checking for writability.
69            print(f'output queue for {s.getpeername()} is empty')
70            outputs.remove(s)
71        else:
72            print(f'sending "{next_msg}" to {s.getpeername()}')
73            s.send(next_msg)
74
75    # Handle "exceptional conditions"
76    for s in exceptional:
77        print(f'handling exceptional condition for {s.getpeername()}')
78        # Stop listening for input on the connection
79        inputs.remove(s)
80        if s in outputs:
81            outputs.remove(s)
82        s.close()
83        # Remove message queue
84        del message_queues[s]