cproxy

cproxy can redirect TCP and UDP traffic made by a program to a proxy, without requiring the program supporting a proxy.

Compared to many existing complicated transparent proxy setup, cproxy usage is as easy as proxychains, but unlike proxychains, it works on any program (including static linked Go programs) and redirects DNS requests.

Note: The proxy used by cproxy should be a transparent proxy port (such as V2Ray's dokodemo-door inbound and shadowsocks ss-redir). A good news is that even if you only have a SOCKS5 or HTTP proxy, there are tools that can convert it to a transparent proxy for you (for example, transocks, ipt2socks and ip2socks-go).

Installation

You can install by downloading the binary from the release page or install with cargo:

cargo install cproxy

Usage

Simple usage: just like proxychains

You can launch a new program with cproxy with:

cproxy --port <destination-local-port> -- <your-program> --arg1 --arg2 ...

All TCP connections and DNS requests will be proxied. In this case, your local transparent proxy should support DNS address overriding to make DNS requests redirection work properly. For an example setup, see wiki. If you don't want to proxy DNS requests, run with

cproxy --port <destination-local-port> --no-dns -- <your-program> --arg1 --arg2 ...

Simple usage: use iptables tproxy

If your system support tproxy, you can use tproxy with --use-tproxy flag:

```bash cproxy --port --use-tproxy -- --arg1 --arg2 ...

or for existing process

cproxy --port --use-tproxy --pid ```

With --use-tproxy, there are several differences:

• All UDP traffic are proxied instead of only DNS UDP traffic to port 53.
• Your V2Ray or shadowsocks service should have tproxy enabled on the inbound port. For V2Ray, you need "tproxy": "tproxy" as in V2Ray Documentation. For shadowsocks, you need -u as shown in shadowsocks manpage.

An example setup can be found here.

Note that when you are using the tproxy mode, you can override the DNS server address with cproxy --use-tproxy --override-dns <your-dns-server-addr> .... This is useful when you want to use a different DNS server for a specific application.

Advanced usage: proxy an existing process

With cproxy, you can even proxy an existing process. This is very handy when you want to proxy existing system services such as docker. To do this, just run

cproxy --port <destination-local-port> --pid <existing-process-pid>

The target process will be proxied as long as this cproxy command is running. You can press Ctrl-C to stop proxying.

How does it work?

cproxy creates a unique cgroup for the proxied program, and redirect its traffic with packet rules.

Limitations

• cproxy requires sudo and root access to modify cgroup.
• Currently only tested on Linux.

Similar projects

There are some awesome existing work:

• graftcp: work on most programs, but cannot proxy UDP (such as DNS) requests. graftcp also has performance hit on the underlying program, since it uses ptrace.
• proxychains: easy to use, but not working on static linked programs (such as Go programs).
• proxychains-ng: similar to proxychains.
• cgproxy: cgproxy also uses cgroup to do transparent proxy, and the idea is similar to cproxy's. There are some differences in UX and system requirements:
  • cgproxy requires system cgroup v2 support, while cproxy requires v1.
  • cgproxy requires a background daemon process cgproxyd running, while cproxy does not.
  • cgproxy requires tproxy, which is optional in cproxy.
  • cgproxy can be used to do global proxy, while cproxy does not intended to support global proxy.