The Rust Nakama Client consists of high level traits with implementations for various frameworks and protocols.
Most traits are defined using async_trait of the async_trait crate, because currently using async in traits is not supported.
This means every function call has an overhead of one heap allocation.
The Client trait declares async functions to call the Nakama server endpoints. It has an
associated Error type because the trait cannot know what errors the implementation can generate.
The ClientAdapter trait declares a single function send as an abstract interface to
send data to the Nakama server. For now, there is only a single implementation RestHttpAdapter that
uses REST to communicate with the Nakama server.
In the future, a gRPC adapter can be added.
The DefaultClient is an implementation of Client. It has a type parameter specifying the
underlying ClientAdapter to use. The DefaultClient is stateless and can be sent and accessed between threads. This
also means that futures awaiting on its async functions can be sent between threads.
The Socket trait declares async functions to communicate with the realtime multiplayer engine.
It also declares functions to specify callbacks for received messages that have no corresponding request.
The SocketAdapter trait declares low-level functions to communicate with the realtime multiplayer engine.
Handling messages is done using callbacks. In order to execute the callbacks, the tick function needs to be called.
WebSocketAdapter is an implementation of SocketAdapter using the qws library.
WebSocket is an implementation of Socket. It has a type parameter specifying the underlying SocketAdapter implementation to use.
WebSocket can be sent and accessed between threads.
Because some messages are handled using callbacks, the tick function needs to be called on
a thread. The callbacks will be invoked on the calling thread. The callback functions can be registered on
any thread, but the callback needs to be able to be sent between threads.
For WASM, the following properties need to be considered:
- WASM is single-threaded
- WASM should generate a small library
The library does not use any async runtime. By replacing the SocketAdapter and ClientAdapter with implementation
for WASM, it should be possible to target WASM.
An async runtime targeting WASM would poll futures every frame instead of using a thread pool.