#! /usr/bin/env python

# Client and server for udp (datagram) echo.

#

# Usage: udpecho -s [port]            (to start a server)

# or:    udpecho -c host [port] <file (client)

import sys

from socket import *

ECHO_PORT = 50000 + 7

BUFSIZE = 1024

def main():

    if len(sys.argv) < 2:

        usage()

    if sys.argv[1] == '-s':

        server()

    elif sys.argv[1] == '-c':

        client()

    else:

        usage()

def usage():

    sys.stdout = sys.stderr

    print 'Usage: udpecho -s [port]            (server)'

    print 'or:    udpecho -c host [port] <file (client)'

    sys.exit(2)

def server():

    if len(sys.argv) > 2:

        port = eval(sys.argv[2])

    else:

        port = ECHO_PORT

    s = socket(AF_INET, SOCK_DGRAM)

    s.bind(('', port))

    print 'udp echo server ready'

    while 1:

        data, addr = s.recvfrom(BUFSIZE)

        print 'server received %r from %r' % (data, addr)

        s.sendto(data, addr)

def client():

    if len(sys.argv) < 3:

        usage()

    host = sys.argv[2]

    if len(sys.argv) > 3:

        port = eval(sys.argv[3])

    else:

        port = ECHO_PORT

    addr = host, port

    s = socket(AF_INET, SOCK_DGRAM)

    s.bind(('', 0))

    print 'udp echo client ready, reading stdin'

    while 1:

        line = sys.stdin.readline()

        if not line:

            break

        s.sendto(line, addr)

        data, fromaddr = s.recvfrom(BUFSIZE)

        print 'client received %r from %r' % (data, fromaddr)

main()