Python Programming On Win32

A Simple Socket Server

The following function implements a short socket server:

# socketserver1.py - runs forever,
# reverse each message received.
from socket import *
import string

HOST = ''     # this means local
PORT = 8578   #arbitrary, high number

def serve():
    # this reverses each message received, lasts forever
    serversock = socket(AF_INET, SOCK_STREAM)
    serversock.bind((HOST, PORT))
    serversock.listen(1)   # max bcklog of 1-5 connections
    print 'socket listening for connections...'
    while 1:
        handlersock, addr = serversock.accept()  

        # now do something with the handler socket
        print 'handler connected by', addr
        data = handlersock.recv(1024)
        print 'received', data
        handlersock.send(string.upper(data))
        handlersock.close()
        print 'handler closed'

if __name__ == '__main__':
    serve()

You can start this server by running it from a DOS prompt. Let’s step through a line at a time:

serversock = socket(AF_INET, SOCK_STREAM)

This creates the server socket. Don’t worry about the constants; there are other types of sockets, but their use is unusual and definitely out of scope for this chapter.

serversock.bind(HOST, PORT)

This associates the socket with a TCP/IP hostname and port number. An empty string, the hostname (if you know it), or the result of the function gethostname() all mean the local machine. PORT is a number between and 65535 and can be thought of like a radio channel or telephone line. The lower port numbers are used for standard services, so pick a big one.

serversock.listen(1)

This places ...