Implement support for pluggable transports over proxies
Currently, if we have PTs enabled we block any other kinds of proxy when we parse the torrc:
/* Check if more than one proxy type has been enabled. */ if (!!options->Socks4Proxy + !!options->Socks5Proxy + !!options->HTTPSProxy + !!options->ClientTransportPlugin > 1) REJECT("You have configured more than one proxy type. " "(Socks4Proxy|Socks5Proxy|HTTPSProxy|ClientTransportPlugin|" "Socks5ProxyUsername|Socks5ProxyPassword)");
During a previous dev meeting, Arturo and Nick discussed how we could enable support for pluggable transport through proxies, and Arturo wrote a proposal: https://lists.torproject.org/pipermail/tor-dev/2012-February/003318.html
We should re-evaluate the proposal and implement it.