Using Perl To Send Heartbeat To A Python Server

I’ve been brushing up on my networking and Python skills lately.

One example in the Python Cookbook is recipe 13.11 Detecting Inactive Computers. Here there are two scripts, one that sends a heartbeat, and another that listens for heartbeats. The idea is a simple UDP packet containing the short string “PyHB” is sent every 5 seconds or so by a client. A server then listens for these datagrams, stores the addresses of the clients which it receives messages from, and if it fails to receive a message in a certain time period it flags this up on the console.

I thought I’d just check how easy it would be to create a Perl client to talk to the Python backend. As it’s all through sockets it should be fairly easy.

To start with we define a few constants that cover the address of the server we want to connect to, the port to send the datagram to, how often we want to send it and if we want debugging information displayed or not.

use constant SERVER_IP   => '127.0.0.1';

use constant SERVER_PORT => 43278;

use constant BEAT_PERIOD => 5;

use constant DEBUG       => 1;

Now we need to create the socket, in this case we’ll create a new IO::Socket object.

my $hbsocket = IO::Socket::INET->new(Proto    => 'udp',

PeerPort => SERVER_PORT,

PeerAddr => SERVER_IP)

or die "Creating socket: $!n";

Next we need to send our message, the string “PyHB” over the socket.

$hbsocket->send('PyHB') or die "send: $!";

Finally we need to wrap this up in a loop and sleep BEAT_PERIOD seconds before repeating our message.

Here’s the final script.

#!/usr/bin/perl -w

use strict;

use IO::Socket;

use constant SERVER_IP   => '127.0.0.1';

use constant SERVER_PORT => 43278;

use constant BEAT_PERIOD => 5;

use constant DEBUG       => 1;

print "Sending heatbeat to IP " . SERVER_IP ." , port " . SERVER_PORT . "n";

print "press Ctrl-C to stopn";

while (1) {

my $hbsocket = IO::Socket::INET->new(Proto    => 'udp',

PeerPort => SERVER_PORT,

PeerAddr => SERVER_IP)

or die "Creating socket: $!n";

$hbsocket->send('PyHB') or die "send: $!";

print "Time: " . localtime(time) . "n"  if (DEBUG);

sleep(BEAT_PERIOD);

}

Just set the value of DEBUG to 0 if you don’t want to see the time each time we send a message to the server.

To test this you’ll have to be running the server from recipe 13.11 in the Python Cookbook. You can download a zip file of the examples in the Python Cookbook from the O’Reilly website to test this.