e11ea68240
Currently, the primary UDP socket is polled within the `Eventloop`. In order to not block the `Server` on the readiness of the socket, we buffer all outgoing packets in a `VecDeque`. This isn't particularly ergonomic. In addition, whilst implementing the IPv6 support, I ran into a limitation with this model. In case we operate in dual-stack mode, I need to poll two UDP sockets but it is not clear in which order they should be polled. The solution I am going for now is to have two separate tasks, one per IP family and have them both write into the same channel. In order to keep #1814 smaller, I this PR represents a pure refactoring towards that solution.
relay
This crate houses a minimalistic STUN & TURN server.
Features
We aim to support the following feature set:
- STUN binding requests
- TURN allocate requests
- TURN refresh requests
- TURN channel bind requests
- TURN channel data requests
Relaying of data through other means such as DATA frames is not supported.
Building
You can build the server using: cargo build --release --bin relay
Running
For an up-to-date documentation on the available configurations options and a detailed help text, run cargo run --bin relay -- --help.
All command-line options can be overridden using environment variables.
Those variables are listed in the --help output at the bottom of each command.
The relay listens on port 3478.
This is the standard port for STUN/TURN and not configurable.
Additionally, the relay needs to have access to the port range 49152 - 65535 for the allocations.
Portal connection
When given a portal endpoint, the relay will connect to it and wait for an init message before commencing relay operations.
Design
The relay is designed in a sans-IO fashion, meaning the core components do not cause side effects but operate as pure, synchronous state machines. They take in data and emit commands: wake me at this point in time, send these bytes to this peer, etc.
This allows us to very easily unit-test all kinds of scenarios because all inputs are simple values.
The main server runs in a single task and spawns one additional task for each allocation. Incoming data that needs to be relayed is forwarded to the main task where it gets authenticated and relayed on success.