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

# auto-flush on socket
$| = 1;

my $port_client = 9000; # Port fuer Client-Anfragen
my $port_server = 9001; # Port des echten Servers
my $host_server = "127.0.0.1"; # IP-Adresse des echten Servers

# example data
# $data     = "\x00\x01\x12\x34\x5A\x86";
# $response = "\x00\x03\x05\x27";

# creating a listening socket
# => Wir sind der Server fuer den Anwender
my $socket_server = new IO::Socket::INET (
  LocalHost => '0.0.0.0',
  LocalPort => $port_client,
  Proto => 'tcp',
  Listen => 5,
  Reuse => 1
);
die "cannot create socket $!\n" unless $socket_server;
print "server waiting for client connection on port ".$port_client."\n";


while(1)
{
  print "\n\n\n";
  
  # waiting for a new client connection
  my $client_socket = $socket_server->accept();
  
  # get information about a newly connected client
  my $client_address = $client_socket->peerhost();
  my $client_port = $client_socket->peerport();
  print "connection from $client_address:$client_port\n";
  
  # read up to 1024 characters from the connected client
  my $data = "";
  $client_socket->recv($data, 1024);
  my $data_hex = $data;
  $data_hex =~ s/(.)/sprintf("\\x%02X",ord($1))/eg;
  print "mitm server received data: $data\n";
  print " hex: (".$data_hex.")\n";
  
  #####################
  ### MITM-PART ###
  #####################
  
  # create a connecting socket
  # => Wir sind der Client fuer das Endgeraet
  my $socket_client = new IO::Socket::INET (
    PeerHost => $host_server,
    PeerPort => $port_server,
    Proto => 'tcp',
  );
  die "cannot connect to the server $!\n" unless $socket_client;
  print "client-part connected to the server (endpoint)\n";
  
  my $size = $socket_client->send($data);
  print "mitm client sent data of length ".$size." (".$data.")\n";
  
  if (undef($size) || $size == 0)
  {
    my $size2 = $socket_client->send($data_hex);
    print "mitm client sent hex-data of length ".$size2." (".$data_hex.")\n";
  }
  
  # notify server that request has been sent
  shutdown($socket_client, 1);
  
  # receive a response of up to 1024 characters from server
  my $response = "";
  $socket_client->recv($response, 1024);
  my $response_hex = $response;
  $response_hex =~ s/(.)/sprintf("\\x%02X",ord($1))/eg;
  print "mitm client received response: $response\n";
  print " hex: (".$response_hex.")\n";
  
  $socket_client->close();
  
  #####################
  ### MITM-PART ###
  #####################
  
  # write response data to the connected client
  print "mitm server is sending data to real client\n";
  $client_socket->send($response);
  print "mitm server has send data to real client\n";
  print " data: (".$response.")\n";
  print " hex: (".$response_hex.")\n";
  
  # notify client that response has been sent
  shutdown($client_socket, 1);
}

$socket_server->close();