Add reverse proxy mode

[joshcooper]

Adds a reverse proxy mode whereby clients connect directly to the reverse proxy, and the proxy forwards the connection to a target host and port specified on the command line or config. For example:

$ python -m nogotofail.mitm -A invalidhostname \
  --mode reverse --port 443 --serverssl server.crt \
  --target_addr www.example.com --target_port 443

The reverse proxy mode makes it trivial to test a client that always connects to a specific server port, as it doesn't require socks or transparent proxy.

That said, the mode has some limitations. It cannot be used in cases where the client needs to connect to multiple servers/ports. Also, it doesn't rewrite HTTP headers, e.g. Host, so the values may be incorrect when received by the real server, and when responses are received by the client.

[joshcooper]

Hi, I was wondering if there's anything I can do to help move this forward? I assume using ValueError is sufficient?

[chadbrubaker]

Sorry for the delay

[joshcooper]

No worries, thanks @chadbrubaker!