fd-proxy - glue for making a tcp proxy, using ucspi-tcp tools

fd-proxy

fd-proxy is a very small program, written in C. Its purpose is to connect the I/Os of a tcpserver and tcpclient pair, from the ucspi-tcp suite, in order to implement a TCP proxy. Setting up such a proxy can be done in a singe line:

The above proxy will relay all TCP traffic between port 22 and port 8000 on localhost. So, as a simple test, you can run:

The advantage of using the tcpserver and tcpclient programs is that all the related ucspi-tcp programs can be used in combination with tcpserver and tcpclient. One can for example define access restrictions with tcprules, define what needs to get looked up via DNS, etc.

The fd-proxy, tcpserver and tcpclient combination supply, even a non-privileged user with a simple, fast and light-weight way to selectively forward TCP traffic.

At the moment, logging of the data, flowing between server and client is not possible.

fd-proxy honors no environment variables.

On success, 0 is returned. On error, errno is returned, as set by the POSIX calls: open, read, write or select.

ucspi-tcp, tcpserver, tcpclient, tcprules

• Make it possible to override the read buffer size with an environment variable.
• Let fd-proxy take a single cdb-style file name as an argument. This file shall exist and either be empty (eg. /dev/null), or contain cdb-style rules. The rules can then be used to set up a proxy filter, eg: - 'ls:regexp' will log all responses that match the regexp, coming from the server-side. - 'lc:regexp' will log all requests that match the regexp, coming from the client-side. - 'is:regexp' ignore data that match the regexp, coming from the server. - 'ts:regexp' terminate the connection to a server that receives data that match the regexp.
• Use the tcpserver and tcpclient environment variables in the logging, so that it is clear from where data comes, and where data goes to.
• Build at least a Debian package for this.

The only alternative that I could find for fd-proxy, is redirfd. In order to get redirfd working, follow the instructions in this post. You'll need to install execline as well.

Copyright (C) 2014 Pieter du Preez [email protected]

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.