https://github.com/pkrumins/perl-tcp-proxy/raw/master/tcp-proxy.pl

diff --git a/tcp-proxy.pl b/tcp-proxy.pl
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+#!/usr/bin/perl
+#
+# Peteris Krumins (peter@catonmat.net)
+# http://www.catonmat.net  --  good coders code, great reuse
+#
+# A simple TCP proxy that implements IP-based access control
+# Currently the ports are hard-coded, and it proxies
+# 0.0.0.0:1080 to localhost:55555.
+#
+# Written for the article "Turn any Linux computer into SOCKS5
+# proxy in one command," which can be read here:
+#
+# http://www.catonmat.net/blog/linux-socks5-proxy
+#
+
+use warnings;
+use strict;
+
+use IO::Socket;
+use IO::Select;
+
+my @allowed_ips = ('1.2.3.4', '5.6.7.8', '127.0.0.1', '192.168.1.2');
+my $ioset = IO::Select->new;
+my %socket_map;
+
+my $debug = 1;
+
+sub new_conn {
+    my ($host, $port) = @_;
+    return IO::Socket::INET->new(
+        PeerAddr => $host,
+        PeerPort => $port
+    ) || die "Unable to connect to $host:$port: $!";
+}
+
+sub new_server {
+    my ($host, $port) = @_;
+    my $server = IO::Socket::INET->new(
+        LocalAddr => $host,
+        LocalPort => $port,
+        ReuseAddr => 1,
+        Listen    => 100
+    ) || die "Unable to listen on $host:$port: $!";
+}
+
+sub new_connection {
+    my $server = shift;
+    my $client = $server->accept;
+    my $client_ip = client_ip($client);
+
+    unless (client_allowed($client)) {
+        print "Connection from $client_ip denied.\n" if $debug;
+        $client->close;
+        return;
+    }
+    print "Connection from $client_ip accepted.\n" if $debug;
+
+    my $remote = new_conn('localhost', 55555);
+    $ioset->add($client);
+    $ioset->add($remote);
+
+    $socket_map{$client} = $remote;
+    $socket_map{$remote} = $client;
+}
+
+sub close_connection {
+    my $client = shift;
+    my $client_ip = client_ip($client);
+    my $remote = $socket_map{$client};
+    
+    $ioset->remove($client);
+    $ioset->remove($remote);
+
+    delete $socket_map{$client};
+    delete $socket_map{$remote};
+
+    $client->close;
+    $remote->close;
+
+    print "Connection from $client_ip closed.\n" if $debug;
+}
+
+sub client_ip {
+    my $client = shift;
+    return inet_ntoa($client->sockaddr);
+}
+
+sub client_allowed {
+    my $client = shift;
+    my $client_ip = client_ip($client);
+    return grep { $_ eq $client_ip } @allowed_ips;
+}
+
+print "Starting a server on 0.0.0.0:1080\n";
+my $server = new_server('0.0.0.0', 1080);
+$ioset->add($server);
+
+while (1) {
+    for my $socket ($ioset->can_read) {
+        if ($socket == $server) {
+            new_connection($server);
+        }
+        else {
+            next unless exists $socket_map{$socket};
+            my $remote = $socket_map{$socket};
+            my $buffer;
+            my $read = $socket->sysread($buffer, 4096);
+            if ($read) {
+                $remote->syswrite($buffer);
+            }
+            else {
+                close_connection($socket);
+            }
+        }
+    }
+}
+