Remove unused fields from RpcServer

RpcServer::create() will create a lambda that wraps around the user's callback. That wrapper will be registered with UTransport. Since the wrapper is already a lambda, all the parameters it needs to produce replies can be captured. As such, there is no need for the RpcServer instance itself to hold those values.

This simplifies the code for implementing RpcServer and reduces the risks of mistakes around setup.

The intent is that the body of RpcServer::create() will look approximately like this:

ServerOrStatus create(
        std::shared_ptr<transport::UTransport> transport,
        const v1::UUri& method_name, RpcCallback&& callback,
        std::optional<v1::UPayloadFormat> payload_format = {},
        std::optional<std::chrono::milliseconds> ttl = {}) {

    // Create a connection to the callback that was provided
    // something like: auto [handle, callable] = connection::Connection::establish(std::move(callback))

    // Create the wrapper
    auto wrapper = [transport, callback = std::move(callable),
                    payload_format = std::move(payload_format), ttl = std::move(ttl)] (const v1::UMessage& m) {
        // Call the callable and pass m (returns optional payload)
        // create a response message builder, passing m
        // if payload_format is set, set it on the message builder
        // if ttl is set, set it on the message builder
        // if payload was returned by the callable, call builder.build(*payload)
            // otherwise call builder.build()
        // Send the response message on the transport
    };

    // Register the wrapper with the transport
    // If successful, construct RpcServer with the handle from registerListener and return the handle for the wrapper
        // Otherwise, return the UStatus returned by registerListener
}

eclipse-uprotocol / up-cpp

Remove unused fields from RpcServer #168