TCP forwarding: a language battle

This repository contains the implementations of the same program in different languages/frameworks. The goal is simple: fun. I found this simple "problem" and it has some complications making it just difficult enough to hit the rougher edges of a language (or framework). Also, I found it provides a nice way of learning a new language.

The "problem"

Context

Forwarding the port 443 to your ssh server is a very good way of making sure you can escape most hotel/airport/company versions of internet.

However, I was already using port 443 to host some personal HTTPS sites. Not wanting to lose those, I required a special kind of port forwarding: based on the first packet it would have to redirect everything to either the ssh server or the https server. Much later I found out that sslh already solves hit problem. But my programmer mind was triggered. After writing the first version in nodejs, I started experimenting with other languages :).

Requirements

Basic functionality

• Acccept connections on a port (for example 8443)
• Check the first byte of a new connection, if it has the value 0x16 or 0x80 redirect it to the https server (for example port 9443) else to the ssh server (port 22)
• After redirecting, just forward the bytes along in both directions.
• If either the client or the server closes the connection, close the other end.

This is all for a first working version of the program.

Timeouts

There are however two features which are quite important especially for resource consumption and compatibility. They are both related to timeouts. Normally the application server has some timeout/connection-lost semantics, but we break that.

• If a new connection does not send anything for 3 seconds, redirect it to the ssh server (Some SSH clients wait for the server banner).
• If both client and server have not send anything for 15 minutes, close both the connections.

Testing/benchmarking

Testing

• basic forwarding: use scp to transfer a big file and check if the md5sum is correct
• timeout: Open a connection to the program using netcat and after 3 seconds it should be connected to the SSH server.
• multiple clients: Apache ab is a very good tool to show multi-threadings/asynchronous errors. -c 200 -n 2000 tends to show even the strangest kind of bugs.

Benchmarking

The goal is not to compare programming languages/framework using this problem. However, I did some rough benchmarks to see the overhead of the tunneling, or the choice of buffers.

• one-stream performance: ssh -c arcfour -C -p 8443 localhost 'cat /dev/zero' | dd of=/dev/null bs=1m count=400 will stream 400MB trough ssh and report the speed (which you should compare with -p 22). Alternativly you could put a big file on the http host and download it with curl/wget.
• multiple clients: Again, apache ab is a very nice tool to analyse how the forwarder performs under stress of multiple connections. Limited of course by the underlying server to handle concurrent the connections.

Related & Larger approaches

• TodoMVC: Compares MVC frameworks based on a todo app use case. tastejs/todomvc
• The Computer Language Benchmarks Game: Comparing languages for different algorithms/challenges. (Same toy program, same computer, same workload)
• 101companies: Different implementations of a HRM system. 101companies/101repo
• Exercises in Programming Style: Comparing programming styles for the same program. crista/exercises-in-programming-style