PolyGlot- Enable capability to write external triggers in C# and .NET core and many other languages -New features

Hi,

This feature is for allowing to create triggers in other languages like C# or Java. As of today, I see the triggers can all be built only using the RUST language. I also understand that Triggers can be any microservice. The one reason why only RUST can be used is that the triggers are doing a call-back to the Spin code that is RUST. I saw the code in main. rs. Though I'm not good at Rust I see the callback module loader and engine of the SPIN.

f that understanding is correct then additional thing needs to be done. Apart from exposing the engine and modules as an API, Is it also possible to provide a gRPC endpoint of the spin execution engine? The external polyglot language triggers can be clients of the Spin engine. Once the trigger starts running the first request will register itself as a client along with the wasm module that the spin SDK needs to invoke when triggering conditions are met. When a triggering condition occurs say a modification in the database or packet in the queue, we can invoke the gRPC endpoint called to execute with the instance id as a parameter and the record or message packet as another parameter.

There are similar components like DAPR or KEDA engines that are allowing external calling using gRPC. For Dapr this is still in the experimental stage.

If for some reason you decide the gRPC is not good candidate(though my personal preference will be gRPC) you can also look into RSockets

Start with examples/spin-timer/src/main.rs and the callback module loader and execution engine referenced in the issue. Review how Dapr and KEDA expose external calls, then clarify the supported polyglot trigger model and whether gRPC or RSockets is appropriate. Done requires an agreed design for registering external triggers and invoking the Spin engine.