O'Reilly logo

Perl Cookbook by Nathan Torkington, Tom Christiansen

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

Setting Up a UDP Server

Problem

You want to write a UDP server.

Solution

First bind to the port the server is to be contacted on. With IO::Socket, this is easily accomplished:

use IO::Socket;
$server = IO::Socket::INET->new(LocalPort => $server_port,
                                Proto     => "udp")
    or die "Couldn't be a udp server on port $server_port : $@\n";

Then, go into a loop receiving messages:

while ($him = $server->recv($datagram, $MAX_TO_READ, $flags)) {
    # do something
}

Discussion

Life with UDP is much simpler than life with TCP. Instead of accepting client connections one at a time and committing yourself to a long-term relationship, take messages from clients as they come in. The recv function returns the address of the sender, which you must then decode.

Example 17.2 is a small UDP-based server that just sits around waiting for messages. Every time a message comes in, we find out who sent it and send them a message based on the previous message, and then save the new message.

Example 17-2. udpqotd

#!/usr/bin/perl -w
# udpqotd - UDP message server use strict; use IO::Socket; my($sock, $oldmsg, $newmsg, $hisaddr, $hishost, $MAXLEN, $PORTNO); $MAXLEN = 1024; $PORTNO = 5151; $sock = IO::Socket::INET->new(LocalPort => $PORTNO, Proto => 'udp') or die "socket: $@"; print "Awaiting UDP messages on port $PORTNO\n"; $oldmsg = "This is the starting message."; while ($sock->recv($newmsg, $MAXLEN)) { my($port, $ipaddr) = sockaddr_in($sock->peername); $hishost = gethostbyaddr($ipaddr, AF_INET); print "Client $hishost ...

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required