server.pl:

use strict;
use IO::Socket;

my $server = IO::Socket::INET->new(Proto => "tcp",
                                   Listen => 5,
                                   LocalPort => "3000",
                                   Timeout => 2000)
             || die "failed to start server\n";
print "server wait for client to connect ...\n";
my $connection = $server->accept;
print "a client connected\n";
while (1) {
    my $req;
    $connection->recv($req, 7000);
    print "server received $req\n";
    my $res = $req + 1;
    print $connection $res;
    print "server responsed $res\n";
}

client.pl

use strict;
use IO::Socket;

my $client = IO::Socket::INET->new(Proto => "tcp",
                                   PeerAddr => "172.135.2.54",
                                   PeerPort => "3000",
                                   Timeout => 2)
             || die "failed to connect to a server\n";
my $req = 1;
while (1) {
    print $client $req;
    print "client sent $req\n";
    my $res;
    $client->recv($res, 7000);
    print "client received $res\n";
    $req = $res;
}
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