relay_server
=====

An OTP application with an esockd-based UDP server.

Build
-----

    $ rebar3 compile

Run
---

    $ rebar3 shell

The UDP listener is configured in `config/sys.config` and listens on port `16380`
by default. It accepts RelayKit UDP relay frames.

Protocol
--------

Each UDP datagram is one `RKP1` frame:

    magic(4) = "RKP1", version(1) = 1, type(1), reserved(2),
    stream_id(8), payload_len(4), payload(payload_len)

Frame types are `open = 1`, `data = 2`, `close = 3`, and `error = 4`.
`open` payload is RelayKit JSON: `host`, `port`, `useTLS`, and `method`.
The server is a transparent TCP relay: `useTLS` is parsed for client
compatibility, but the upstream connection is always raw TCP.