#!/usr/bin/perl

use strict;
use warnings;
use IO::Socket;

my $pid = fork();  die "couldn't fork" unless defined($pid);
if ($pid) {  # SERVER
    my $server = IO::Socket::INET->new(
        Proto     => 'tcp',
        LocalPort => 9999,
        Listen    => 1,
        ReuseAddr => 1,
    );
    die "couldn't setup server" unless $server;
    
    my $client = $server->accept();
    $client->autoflush(1);
    while (<$client>) {
         
       print "DUMP:\n";
       use Data::Dumper;
       print Dumper($_); 
       print "DUMP END\n";       

        if    (/hello/) { print $client "nice to meet you\n" }
        elsif (/quit/)  { print $client "bye\n"; }
        else{ print $client "??\n"; }
    }
    close $client;

} else {     # CLIENT
    sleep 1; # wait for server to get ready
    
    my $sock1 = IO::Socket::INET->new( 
        Proto     => 'tcp',
        PeerAddr  => "localhost",  
        PeerPort  => 9999, 
    );
    die "couldn't connect" unless $sock1;
    
    open my $sock2, '+<&='.$sock1->fileno() or die $!;
    
    printf "sock1         = %s\n",   $sock1;
    printf "fileno(sock1) = %d\n",   $sock1->fileno();
    printf "autoflush     = %s\n\n", $sock1->autoflush() ? "ON":"OFF";
    
    printf "sock2         = %s\n",   $sock2;
    printf "fileno(sock2) = %d\n",   $sock2->fileno();
    printf "autoflush     = %s\n\n", $sock2->autoflush() ? "ON":"OFF";

    my $resp;

    print $sock1 "hello\n";
    $resp = <$sock1>;  print $resp;
    print $sock1 "quit\n";
    $resp = <$sock1>;  print $resp;
    exit;
}

##</code><code>##

sock1         = IO::Socket::INET=GLOB(0xd9327c)
fileno(sock1) = 4
autoflush     = ON

sock2         = GLOB(0xe424b4)
fileno(sock2) = 4
autoflush     = OFF

DUMP:
$VAR1 = 'hello
';
DUMP END
nice to meet you
DUMP:
$VAR1 = 'quit
';
DUMP END
bye

##</code><code>##

sock1         = IO::Socket::INET=GLOB(0xd93504)
fileno(sock1) = 4
autoflush     = ON

sock2         = GLOB(0xe42714)
fileno(sock2) = 4
autoflush     = OFF

DUMP:
$VAR1 = 'hello
';
DUMP END
nice to meet you
DUMP:
$VAR1 = 'nice to meet you
';
DUMP END
??
DUMP:
$VAR1 = 'quit
';
DUMP END