""" Server side: open a socket on a port, listen for a message from a client, and send an echo reply; forks a process to handle each client connection; child processes share parent's socket descriptors; fork is less portable than threads--not yet on Windows, unless Cygwin or similar installed; """
import os, time, sys from socket import * # get socket constructor and constants myHost = '' # server machine, '' means local host myPort = 50007 # listen on a non-reserved port number
sockobj = socket(AF_INET, SOCK_STREAM) # make a TCP socket object sockobj.bind((myHost, myPort)) # bind it to server port number sockobj.listen(5) # allow 5 pending connects
def now(): # current time on server return time.ctime(time.time())
activeChildren = [] def reapChildren(): # reap any dead child processes while activeChildren: # else may fill up system table pid, stat = os.waitpid(0, os.WNOHANG) # don't hang if no child exited if not pid: break activeChildren.remove(pid)
def handleClient(connection): # child process: reply, exit time.sleep(5) # simulate a blocking activity while True: # read, write a client socket data = connection.recv(1024) # till eof when socket closed if not data: break reply = 'Echo=>%s at %s' % (data, now()) connection.send(reply.encode()) connection.close() os._exit(0)
def dispatcher(): # listen until process killed while True: # wait for next connection, connection, address = sockobj.accept() # pass to process for service print('Server connected by', address, end=' ') print('at', now()) reapChildren() # clean up exited children now childPid = os.fork() # copy this process if childPid == 0: # if in child process: handle handleClient(connection) else: # else: go accept next connect activeChildren.append(childPid) # add to active child pid list
dispatcher()
