This minimal ScalaJS Akka-Http project is an example of using Sloth and Boopickle for type safe and fast RPC using Ajax to pull data from server to client both sharing the same API. Sloth allows to use any Functor server return type - here a Future is used.
The client initiates the Ajax call by serializing the API method arguments and sending them to the server. The Server then de-serializes the arguments and calls the requested method. The result of this call is serialized and sent back as the Ajax response to the client where it is de-serialized.
Since we use Futures as the higher-kind return type in our API, the result from calling the methods on the server can both return successful data, but also failed futures containing Throwable exceptions. Both are serialized as ByteBuffers. This makes it a bit trickier on the client side where we need to know if the byte data should be de-serialized to a successful future of data matching the API method result type - OR a failed future with a Throwable!
Optimally, we would like to receive a response header telling us if data should be de-serialized as an exception or successful data. For some reason I couldn't get this to work, so as a temporary solution, I added a single bit in the beginning of the ByteBuffer with a 1 for Throwable and 0 for successful data that I then remove before de-serializing on the client.
If there's a more straightforward way to accomplish this exercise, I'd appreciate feedback!
To test, first download this repo and start the Akka-Http server in one process:
git clone https://github.com/marcgrue/scalajs-rpc-exception-test.git
cd scalajs-rpc-exception-test
sbt rpcJVM/run
In another process, run
sbt test
Enjoy!