yasp

YASP - Yet Another (SOCKS) Proxy, but with UDP support for SOCKS-5

What it is

A simple SOCKS proxy server based on Go. It supports SOCKS-4 and SOCKS-5. Supplementary to most of the already existing proxy implementations it also supports UDP connections via SOCKS-5. This facilitates forwarding of UDP traffic without the need for cumbersome workarounds like using socat to convert UDP to TCP and vice versa.

How it works

YASP opens two sockets on the server:

• A TCP socket to listen for SOCKS proxy requests
• A UDP socket acting as forwarder for proxied UDP connections

A SOCKS client requests a SOCKS-5 UDP port association via the TCP socket which responds with the IP and port of the UDP forwarder. The client then directs its UDP traffic towards the UDP forwarder.

The forwarder strips the SOCKS header from the clients' packets and forwards them to the destination depicted in the header. Packets returning from the destination are processed the other way round: the forwarder prepends them with the SOCKS header and returns them to the client.

Installation

Assuming your GOPATH is set to ~/go:

~$ go get github.com/chcon/yasp
~$ cd go/src/github.com/chcon/yasp/
~/go/src/github.com/chcon/yasp$ go build
~/go/src/github.com/chcon/yasp$ ls -l yasp
-rwxrwxr-x 1 user user 3195966 Jul  1 16:31 yasp

This creates the yasp executable in the current directory. Move it anywhere you want and run it.

You can also run go install, which builds the executable inside the directory ~/go/bin/.

Usage

$ ./yasp -h
Usage of ./yasp:
  -p string
        Socks proxy bind address [IP:port] (default "127.0.0.1:3180")
  -t int
        Timeout [seconds] (default 300)
  -u string
        UDP forwarder bind address [IP:port] (default "127.0.0.1:49111")

In this example YASP is running on 192.168.1.100, with the SOCKS proxy running on port 3180, and the UDP forwarder running on port 41234, and the timeout for idle connections in the UDP forwarder is set to one hour:

$ ./yasp -p 192.168.1.100:3180 -u 192.168.1.100:41234 -t 3600
2022/07/01 10:10:56 Proxy connection from 192.168.1.20:24531 
2022/07/01 10:10:57 target address in client's packet is 0.0.0.0:0 (may be 0.0.0.0:0 for UDP port association requests)
2022/07/01 10:10:57 Starting UDP Port Association
2022/07/01 10:10:57 Registered new client with forwarder:  192.168.1.20
2022/07/01 10:10:57 New source connected:  192.168.1.20:24307->10.10.10.200:1337
2022/07/01 10:11:12 Currently connected:  192.168.1.20:24307->10.10.10.200:1337
2022/07/01 10:11:42 Currently connected:  192.168.1.20:24307->10.10.10.200:1337

Limitations

• IPv6 support is not yet finalized, especially the UDP forwarder bind address currently must be an IPv4 address.
• Currently no authentication/registration; the bind ports on the proxy server should be restricted by firewall to trusted source IP addresses

TODO

• Unit tests (shame on me)
• Finalize IPv6 support
• Implement proxy authorization
• Register clients from the proxy to the forwarder
• Improve logging

Acknowledgements

This is not written from scratch. I combined an existing SOCKS proxy implementation and an existing UDP forwarder implementation and added the code to handle UDP traffic via SOCKS-5 to both. Acknowledgements go to the maintainers of these two projects:

• https://github.com/fangdingjun/socks-go
• https://github.com/1lann/udp-forward