The entity whose traffic needs to be forwarded
The host that runs rathole in the server mode
The host behind the NAT that runs rathole in the client mode. It has some services that need to be forwarded.
Who visists a service, via the server
A control channel is a TCP connection between the server and the client that only carries rathole control commands for one service.
A data channel is a TCP connection between the server and the client that only carries the encapsulated data that needs forwarding for one service.
TODO: Add more details about the protocol
When rathole starts in the client mode, it creates connections to server.common.bind_addr for each service. These connection acts as control channels.
When a control channel starts, the server challenge the client by a nonce, the client is required to authenticate as the service it wants to represent. Then the forwarding of that service is set up.
When the server accepts a connection on a service's bind_port, it sends a control command to the client via the corresponding contorl channel. Then the client connects to the server to create a data channel. In this way, a forwarding is set up. The server also creates a few data channels in advance to improve the latency.