transocks - a transparent SOCKS5/HTTP proxy

transocks is a background service to redirect TCP connections transparently to a SOCKS5 server or a HTTP proxy server like Squid.

Currently, transocks supports only Linux iptables with DNAT/REDIRECT target.

Features

• IPv4 and IPv6

  Both IPv4 and IPv6 are supported. Note that nf_conntrack_ipv4 or nf_conntrack_ipv6 kernel modules must be loaded beforehand.

• SOCKS5 and HTTP proxy (CONNECT)

  We recommend using SOCKS5 server if available. Take a look at our SOCKS server usocksd if you are looking for.

  HTTP proxies often prohibits CONNECT method to make connections to ports other than 443. Make sure your HTTP proxy allows CONNECT to the ports you want.

• Graceful stop & restart

  • On SIGINT/SIGTERM, transocks stops gracefully.
  • On SIGHUP, transocks restarts gracefully.

• Library and executable

  transocks comes with a handy executable. You may use the library to create your own.

Install

Use Go 1.7 or better.

go get -u github.com/cybozu-go/transocks/...

Usage

transocks [-h] [-f CONFIG]

The default configuration file path is /etc/transocks.toml.

In addition, transocks implements the common spec from cybozu-go/cmd.

transocks does not have daemon mode. Use systemd to run it as a background service.

Configuration file format

transocks.toml is a TOML file.

proxy_url is mandatory. Other items are optional.

# listening address of transocks.
listen = "localhost:1081"    # default is "localhost:1081"

proxy_url = "socks5://10.20.30.40:1080"  # for SOCKS5 server
#proxy_url = "http://10.20.30.40:3128"   # for HTTP proxy server

[log]
filename = "/path/to/file"   # default to stderr
level = "info"               # critical", error, warning, info, debug
format = "json"              # plain, logfmt, json

Redirecting connections by iptables

Use DNAT or REDIRECT target in OUTPUT chain of the nat table.

Save the following example to a file, then execute: sudo iptables-restore < FILE

*nat
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
:TRANSOCKS - [0:0]
-A OUTPUT -p tcp -j TRANSOCKS
-A TRANSOCKS -d 0.0.0.0/8 -j RETURN
-A TRANSOCKS -d 10.0.0.0/8 -j RETURN
-A TRANSOCKS -d 127.0.0.0/8 -j RETURN
-A TRANSOCKS -d 169.254.0.0/16 -j RETURN
-A TRANSOCKS -d 172.16.0.0/12 -j RETURN
-A TRANSOCKS -d 192.168.0.0/16 -j RETURN
-A TRANSOCKS -d 224.0.0.0/4 -j RETURN
-A TRANSOCKS -d 240.0.0.0/4 -j RETURN
-A TRANSOCKS -p tcp -j REDIRECT --to-ports 1081
COMMIT

Use ip6tables to redirect IPv6 connections.

NOTE: If you are going to use transocks on Linux gateway to redirect transit traffic, you have to bind transocks on primary address of internal network interface because iptables REDIRECT action in PREROUTING chain changes packet destination IP to primary address of incoming interface.

Library usage

Read the documentation.

License

MIT