#!/usr/bin/perl -w
use strict;
use IO::Socket;
my $sock = new IO::Socket::INET(
                   LocalHost => 'localhost',
                   LocalPort => 7890,
                   Proto     => 'tcp',
                   Listen    => SOMAXCONN,
                   Reuse     => 1);
$sock or die "no socket :$!";
STDOUT->autoflush(1);

my $req_name = "Enter Name: \n";
my $req_pass = "Enter Password: \n";
my $req_none = "Enter \n";

sub verify_passw {
    my ($name, $pass) = @_;
    # print STDERR "name=$name, pass=$pass\n";  # debug
    # ...
    return 1;
}

while (my $new_sock = $sock->accept())
{
    my $name = "";  # lifetime is connection
    my $auth = 0;   # ditto (storing state of session)

    while (<$new_sock>)
    {
        /^HELLO$/ and print($new_sock $req_name), next;
     
        /^NAME: (\w*)/ and do {
            $name = $1;
            if ($name && length($name)<=8) {
               print $new_sock "Ok, name: $name\n";
               print $new_sock $req_pass;
            } else {
               print $new_sock "Invalid name: '$name'\n";
               print $new_sock $req_name;
            }
            next
        };

        /^PASS: (\w*)/ and do {
            my $pass = $1;
            if ($auth = verify_passw($name, $pass)) {  # =, not ==
               print $new_sock "Login ok\n";
               print $new_sock $req_none;
            } else {
               print $new_sock "Invalid password!\n";
               print $new_sock $req_pass;
            }
            next
        };
          
        /^DATE$/  and print($new_sock scalar(localtime), "\n"), next;
    
         print $new_sock "DEFAULT\n";
    }
    close $new_sock;
}