Hi, Monks!

I'm writing an application which is going to use UDP-based protocol and STUN as a way to build connections between users. I found STUN::RFC_5389 on CPAN. But how do I actually use it?

My code is:

#!/usr/bin/perl

use warnings;
use strict;

use STUN::RFC_5389;
use IO::Socket::INET;

die "$0 <server> [port]\n" unless $#ARGV >= 0;
my ($server,$port) = @ARGV;
$port = $port // 3478;

my $request = Client STUN::RFC_5389 { request => 1 };
my $lport = 10000+(int rand 55536);

my $socket = new IO::Socket::INET (
    LocalPort => $lport,
    PeerAddr => $server,
    PeerPort => $port,
    Proto => 'udp',
) || die "connect: $@\n";
send($socket,$request,0);

my $response;
recv($socket,$response,1024,0);
close($socket);

my $mapped_address = ${Client STUN::RFC_5389 $response}{attributes}->{
+'MAPPED-ADDRESS'};
print $mapped_address->{address},":",$mapped_address->{port},"\n";

my $listen = new IO::Socket::INET (
    LocalPort => $lport,
    Proto => 'udp',
) || die "bind: $@\n";

my $buf;
$|=1;
while ($listen->recv($buf,1)) { print $buf }
die "recv: $!\n";
[download]

When I then try to send some data to the received address and port (using nc -u <ip address> <port>), nothing shows up there. I even tried sniffing with Wireshark, but there is no incoming traffic.

It looks that I should somehow open the socket, send the STUN request from it, receive it and stay working with it without closing. After reading UDP: Message Passing I have rewritten the code:

#!/usr/bin/perl

use warnings;
use strict;

use STUN::RFC_5389;
use Socket;

die "$0 <server> [port]\n" unless $#ARGV >= 0;
my ($server,$port) = @ARGV;
$port = $port // 3478;

$|=1;

my $request = Client STUN::RFC_5389 { request => 1 };
my $lport = 10000+(int rand 55536);

my $lpaddr = sockaddr_in($port, inet_aton("0.0.0.0")) || die "sockaddr
+_in: $!\n";
print "socket: ";
socket(SOCKET, PF_INET, SOCK_DGRAM, getprotobyname("udp")) && print "\
+n" || die "$!\n";
print "bind: ";
bind(SOCKET, $lpaddr) && print "\n" || die "$!\n";

my $siaddr = inet_aton($server) || die "inet_aton: $!\n";
my $spaddr = sockaddr_in($port, $siaddr) || die "sockaddr_in: $!\n";
print "send: ";
defined(send(SOCKET, 0, 0, $spaddr)) && print "\n" || die "$!\n";

my $response;
print "recv: ";
recv(SOCKET, $response, 1024, 0) && print "\n" || die "$!\n";

my $mapped_address = ${Client STUN::RFC_5389 $response}{attributes}->{
+'MAPPED-ADDRESS'};
print $mapped_address->{address},":",$mapped_address->{port},"\n";

print "Listening\n";
my $buf;
$|=1;
while (recv(SOCKET,$buf,1,0)) { print $buf }
die "recv: $!\n";
[download]

but it hangs on the first recv(). I tried to enable non-blocking mode (using Fcntl), sleep for some time, then recv 1024 bytes and print received data, and nothing showed up. I guess that I'm doing something wrong again.

How do I use STUN properly?

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