File: class/Extras/Code/Internet/select-server.py

#################################################################
# Server: handle multiple clients in parallel with select.
# use the select module to multiplex among a set of sockets:
# main sockets which accept new client connections, and 
# input sockets connected to accepted clients; select can
# take an optional 4th arg--0 to poll, n.m to wait n.m secs, 
# ommitted to wait till any socket is ready for processing.
#################################################################
import sys, time
from select import select
from socket import socket, AF_INET, SOCK_STREAM
def now(): return time.ctime(time.time())
myHost = '' # server machine, '' means local host
myPort = 50007 # listen on a non-reserved port number
if len(sys.argv) == 3: # allow host/port as cmdline args too
 myHost, myPort = sys.argv[1:]
numPortSocks = 2 # number of ports for client connects
# make main sockets for accepting new client requests
mainsocks, readsocks, writesocks = [], [], []
for i in range(numPortSocks):
 portsock = socket(AF_INET, SOCK_STREAM) # make a TCP/IP spocket object
 portsock.bind((myHost, myPort)) # bind it to server port number
 portsock.listen(5) # listen, allow 5 pending connects
 mainsocks.append(portsock) # add to main list to identify
 readsocks.append(portsock) # add to select inputs list 
 myPort = myPort + 1 # bind on consecutive ports 
# event loop: listen and multiplex until server process killed
print 'select-server loop starting'
while 1:
 #print readsocks
 readables, writeables, exceptions = select(readsocks, writesocks, [])
 for sockobj in readables:
 if sockobj in mainsocks: # for ready input sockets
 # port socket: accept new client
 newsock, address = sockobj.accept() # accept should not block
 print 'Connect:', address, id(newsock) # newsock is a new socket
 readsocks.append(newsock) # add to select list, wait
 else:
 # client socket: read next line
 data = sockobj.recv(1024) # recv should not block
 print '\tgot', data, 'on', id(sockobj)
 if not data: # if closed by the clients 
 sockobj.close() # close here and remv from
 readsocks.remove(sockobj) # del list else reselected 
 else:
 # this may block: should really select for writes too
 sockobj.send('Echo=>%s at %s' % (data, now()))