feature request: sip003 mux / multiplexing spec

There is no relay in sip003, currenty it's implemented by plugin self.

• v2ray-plugin: use Mux.Cool
  • Mux.Cool can be turned off by set mux to 0

As it's shadowsocks is based on socks, entire payload can be encrypted, so there is no mux solution on shadowsocks payload.

Then, the mux should be done on plugin:

1. mux on payload, add mux header before payload
   1. Mux.Cool
   2. please note: it seems no way to compatible mux and non mux solution as mux header is not optional
2. mux on plugin's underlying protocol
   1. websockets based on http/1.1, use websockets's rsv and/or opcode.
      1. please note, there should be some simple stream flow control
   2. http2/http3, special stream and stream flow control
   3. other: I don't think other protocol can be supported by cdn

Start with the SIP003 feature request and compare the approaches it lists: Mux.Cool, plugin-payload headers, WebSockets, HTTP/2, and HTTP/3. No implementation files or tests are named. Done would require an agreed multiplexing specification addressing compatibility, stream flow control, and supported underlying protocols.