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.

Usage

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

$ 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

MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.