So this is a tiny helper tool that is able to wrap a TCP connection to a tunnel provided by a HTTP connect proxy, all the thing fully transparently (iptables REDIRECT).
My goal was to be able to intercept TLS sessions of my mobile phone using mitmproxy. The idea of running that awesome software on my openwrt router turned out to be too naive, so I started looking for some proxy tool to do that. Solutions like tinyproxy or redsocks didn't do the job (I actually wasted more time on evaluating the available tools than writing this one), so I ended up implementing this thing. (Wanted to do that in lua first using luaposix, but the version of the package on openwrt is way too outdated.)
Setup a REDIRECT rule something like this:
iptables -t nat -I zone_lan_prerouting -p tcp -s 10.6.6.149 --dport 443 -j REDIRECT --to-port 8081
Execute this tool:
./tcp-http-proxy 8081 10.6.6.111 8080
Where 10.6.6.111:8080 is where mitmproxy is listening (eg. in a Kali VM).
The binary was built for the ath79 MIPS SoC with musl libc.