Perl TCP client/server sample code

#perl #network

This post explains how to implement a simple Perl client/server using TCP sockets 🎉

I use IO::Socket::INET which is a core module (no need to install). How to know it's a core module? Check the list of core modules in perldoc or simply use corelist:

$ corelist IO::Socket::INET

Data for 2019-05-22
IO::Socket::INET was first released with perl v5.6.0

Without waiting, let's move on to the Perl TCP client implementation 👍

Perl TCP Client

A very simple client, sending a message (containing "japh - " + the client timestamp) every 3 sec and stopping on signal (Control-C).

The target is localhost (for demo I'm running client and server on same machine) but it could be totally another IP or hostname (obviously... 😀).

#!/usr/bin/env perl

use strict;
use warnings;

use IO::Socket::INET;
# auto-flush on socket
$| = 1;

my $continue = 1;
$SIG{INT} = sub { $continue = 0 };


while ($continue) {
    my $timestamp = localtime(time);
    my $msg = "japh - $timestamp";

    # Create a connecting socket
    my $socket = new IO::Socket::INET (
        PeerHost => 'localhost',
        PeerPort => '7777',
        Proto => 'tcp',
    );

    if($socket) {
        my $size = $socket->send($msg);
        print "Sent!\n";
        $socket->close();
    }

    sleep 3;
}

Start client:

$ perl client.pl

The client sends data then wait 3 seconds, then sends data again and wait, and do it again and again...

As soon as we have the server running, a client live run will look like this:

If you wonder, if the server is not available, no problem, the client will stay alive (and send to nobody until a server is started).

Perl TCP Server

The server looks the same, but is just a bit more complicated with more parameters to $socket constructor and an accept() step:

#!/usr/bin/env perl

use strict;
use warnings;

use IO::Socket::INET;
# auto-flush on socket
$| = 1;


# Creating a listening socket
my $socket = new IO::Socket::INET (
    LocalHost => '0.0.0.0',
    LocalPort => '7777',
    Proto => 'tcp',
    Listen => 5,
    Reuse => 1
);
die "Cannot create socket $!\n" unless $socket;

$SIG{INT} = sub { $socket->close(); exit 0; };

while(1) {
    my $client_socket = $socket->accept();

    # Get information about a newly connected client
    my $client_address = $client_socket->peerhost();

    # Read up to 1024 characters from the connected client
    my $data = "";
    $client_socket->recv($data, 1024);
    print "$client_address - $data\n";
}

The $socket->accept() is blocking and will unblock when the client initiates the connection (new IO::Socket::INET on client side).

The server will retrieve the message ($msg) but also the IP address ($client_address via peerhost() method). It is listening forever and can handle multiple clients.

Below a demo of a running server: