https-ssh-switch.pl

#!/usr/bin/env perl
# https-ssh-switch.pl: Turn on https → ssh redirect for the source IP of
# an http request. Allows you to dodge some aggressive firewalls resp.
# paywalls.
# Sample sudo rule: www-data ALL=(root) NOEXEC:NOPASSWD: /sbin/iptables -t nat -I PREROUTING -i [[\:alnum\:]]* -s [[\:digit\:].]* -p tcp --dport 443 -j REDIRECT --to-ports 22
# 2014-02-10 Daniel Albers <[email protected]>, released under GPL license
# TODO: IPv6 support

use strict;
use warnings;

use CGI;

my $ipregex = qr([0-9.]+);
my $q = CGI->new;
my $ip = $q->remote_addr();

print $q->header();

my $get_interface = sub ($) {
  my $ip = shift;
  die unless $ip =~ /^${ipregex}$/;

  my $route = `/usr/bin/env ip -o route get "$ip"`;
  $route =~ m/^${ipregex}(?:\s+via\s+${ipregex})?\s+dev\s+([a-z0-9.-]+)/p;
  my $interface = $1;

  return $interface;
};

my $interface = $get_interface->($ip);
die unless $interface;

print $ip;

print `/usr/bin/sudo /sbin/iptables -t nat -I PREROUTING -i "$interface" -s "$ip" -p tcp --dport 443 -j REDIRECT --to-ports 22`;