tcp-proxy

A small TCP proxy written in Go

This project was intended for debugging text-based protocols. The next version will address binary protocols.

Install

Binaries

Install latest release now with curl https://i.jpillora.com/go-tcp-proxy! | bash

Source

$ go get -v github.com/jpillora/go-tcp-proxy/cmd/tcp-proxy

Usage

$ tcp-proxy --help
Usage of tcp-proxy:
  -c: output ansi colors
  -h: output hex
  -l="localhost:9999": local address
  -n: disable nagles algorithm
  -r="localhost:80": remote address
  -match="": match regex (in the form 'regex')
  -replace="": replace regex (in the form 'regex~replacer')
  -v: display server actions
  -vv: display server actions and all tcp data

Note: Regex match and replace only works on text strings and does NOT work across packet boundaries

Simple Example

Since HTTP runs over TCP, we can also use tcp-proxy as a primitive HTTP proxy:

$ tcp-proxy -r echo.jpillora.com:80
Proxying from localhost:9999 to echo.jpillora.com:80

Then test with curl:

$ curl -H 'Host: echo.jpillora.com' localhost:9999/foo
{
  "method": "GET",
  "url": "/foo"
  ...
}

Match Example

$ tcp-proxy -r echo.jpillora.com:80 -match 'Host: (.+)'
Proxying from localhost:9999 to echo.jpillora.com:80
Matching Host: (.+)

#run curl again...

Connection #001 Match #1: Host: echo.jpillora.com

Replace Example

$ tcp-proxy -r echo.jpillora.com:80 -replace '"ip": "([^"]+)"~"ip": "REDACTED"'
Proxying from localhost:9999 to echo.jpillora.com:80
Replacing "ip": "([^"]+)" with "ip": "REDACTED"

#run curl again...
{
  "ip": "REDACTED",
  ...

Note: The -replace option is in the form regex~replacer. Where replacer may contain $N to substitute in group N.

Todo

Implement tcpproxy.Conn which provides accounting and hooks into the underlying net.Conn
Verify wire protocols by providing encoding.BinaryUnmarshaler to a tcpproxy.Conn
Modify wire protocols by also providing a map function
Implement SOCKS v5 to allow for user-decided remote addresses