Perl

SSH Tunnel Static (Fixed-Destination) Port Forwarding

Demonstrates fixed-destination port forwarding with the DestHostname, DestPort, ListenBindIpAddress, and ListenPort properties. Every local connection accepted by the listener is forwarded to the same fixed destination through the SSH server.

Background: This is the classic ssh -L scenario: expose a single remote service — a database, an internal web app — at a local port. Binding the listener to 127.0.0.1 keeps the tunnel private to the local machine, whereas 0.0.0.0 would let other hosts route through it. Passing 0 to BeginAccepting lets the OS pick a free port, which ListenPort then reports — handy when a fixed port might already be in use.

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use strict;
use warnings;
use Chilkat2;

# Demonstrates fixed-destination (static) port forwarding with the SshTunnel properties
# DestHostname, DestPort, ListenBindIpAddress, and ListenPort.
#
# Every local connection accepted by the listener is forwarded to the same fixed destination
# through the SSH server.

my $tunnel = Chilkat2::SshTunnel->new;

# The fixed destination that accepted connections are forwarded to.
$tunnel->DestHostname('db.internal.example.com');
$tunnel->DestPort(5432);

# Bind the listener to loopback so only local processes can use the tunnel.  Use "0.0.0.0" to
# accept connections from other machines (less secure).
$tunnel->ListenBindIpAddress('127.0.0.1');

my $sshPort = 22;
my $success = $tunnel->Connect('ssh.example.com', $sshPort);
if (!$success) {
    print $tunnel->LastErrorText, "\n";
    exit;
}

# Normally you would not hard-code the password in source.  You should instead obtain it
# from an interactive prompt, environment variable, or a secrets vault.
my $password = 'mySshPassword';

$success = $tunnel->AuthenticatePw('mySshLogin', $password);
if (!$success) {
    print $tunnel->LastErrorText, "\n";
    exit;
}

# Pass 0 to let the operating system choose an available port.  After BeginAccepting succeeds,
# ListenPort contains the actual port that was bound.
$success = $tunnel->BeginAccepting(0);
if (!$success) {
    print $tunnel->LastErrorText, "\n";
    exit;
}

print 'Listening on 127.0.0.1 port ', $tunnel->ListenPort, "\n";

# Applications now connect to 127.0.0.1:ListenPort as if it were the database server.

my $waitForThreadExit = 1;
$success = $tunnel->CloseTunnel($waitForThreadExit);
if (!$success) {
    print $tunnel->LastErrorText, "\n";
    exit;
}