tcpprepend

Simple TCP forwarder that prepends some fixed bytes to responses and ignores some fixed header on requests

Install it by building (cargo install --path .) or download pre-built executables from Github Releases.

Example

A$ echo -n 'ABC' | base64
A: QUJD

A$ echo -n 'XYZ' | base64
A: WFla

A$ tcpprepend 127.0.0.1:1234 QUJD 127.0.0.1:1235 WFla&
A: [1] 30101

B$ nc -lvp 1235
B: Listening on 0.0.0.0 1235

C$ nc 127.0.0.1 1234
A: Incoming connection from 127.0.0.1:40834
C> 12345
C> asdfg
C> 67ABC890
A:  found matching request bytes
A:   connected to upstream
A:   wrote prepender bytes
B: Connection received on localhost 44242
B: 890
A: XYZ
C> tttyyy
B: tttyyy
B> 555666
C: 555666

Psedo-HTTP server mode:

$ tcpprepend 127.0.0.1:8080 DQoNCg== 127.0.0.1:1235 SFRUUC8xLjAgMjAwIE9LDQoNCg==
$ curl http://127.0.0.1:8080/

Usage line

ARGS:
    <listen>

    <request_needle_base64>

    <connect>

    <response_prepend_base64>