Generate Kotlin gRPC Stubs

[t0rr3sp3dr0]

This patch modifies build configuration files to generate gRPC Stubs for Kotlin and place them inside the built artifact. The changes were based on official tutorials on how to configure maven-protobuf-plugin to generate Kotlin gRPC Stubs (https://github.com/grpc/grpc-kotlin/tree/master/compiler) and how to build Kotlin with Maven (https://kotlinlang.org/docs/maven.html).

In the built JAR, for each ServiceGrpc class generated from a gRPC service definition on proto files, a new class called ServiceGrpcKt is introduced with the Kotlin interface. I've tested it on a Java-only project to make sure it doesn't cause any problem.

The built artifact is available on JitPack: https://jitpack.io/#t0rr3sp3dr0/java-control-plane/3bd90153d9.

Closes #168

[codecov-commenter]

Codecov Report

Merging #169 (3bd9015) into main (06f2735) will decrease coverage by 0.10%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main     #169      +/-   ##
============================================
- Coverage     88.26%   88.16%   -0.11%     
+ Complexity      298      297       -1     
============================================
  Files            31       31              
  Lines           980      980              
  Branches         78       78              
============================================
- Hits            865      864       -1     
  Misses           85       85              
- Partials         30       31       +1     

Impacted Files	Coverage Δ
.../io/envoyproxy/controlplane/cache/SimpleCache.java	82.97% <0.00%> (-0.71%)	⬇️

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[slonka]

Hi, I will test it in Envoy-Control and check if it works and if it does i'll review it and merge it.

[t0rr3sp3dr0]

Hi @slonka! Were you able to verify this works?

[slonka]

Why do we need coroutines for that?

[t0rr3sp3dr0]

In Kotlin, the base implementations of gRPC services use coroutines to deal with blocking operations. This way, developers don't need to deal with StreamObservers like they have to do in Java and just implement a suspend function that returns the object directly.

Java implementation:
https://github.com/grpc/grpc-java/blob/c540229d79c6d8d29da34d22c3c5add2138bdc87/examples/src/main/java/io/grpc/examples/helloworld/HelloWorldServer.java#L81-L89

Kotlin implementation:
https://github.com/grpc/grpc-kotlin/blob/b7d06483bf597cd4a10e3ed2ef52b21ca95c80ad/examples/server/src/main/kotlin/io/grpc/examples/helloworld/HelloWorldServer.kt#L48-L53

[slonka]

Hi @t0rr3sp3dr0 - sorry for the delay. I've run into a bit of a problem, after leaving Allegro I no longer can release SNAPSHOTs of java-control-plane. I'm getting permissions denied. Maybe @lukidzi can help out. I'm using the same token as before, and even created a new one.

[t0rr3sp3dr0]

@slonka and @lukidzi, do you have an update here?

[t0rr3sp3dr0]

@slonka and @lukidzi, sorry to bother you again, but I really need to get this PR merged.

We have been using a fork of the project with this patch applied so we could move forward internally while this PR wasn’t merged. But we weren’t expecting to still be relying on the fork 6 months later.

[t0rr3sp3dr0]

@rulex123 and @onemanbucket, are you able to take a look on this PR?

[t0rr3sp3dr0]

@rulex123 and @onemanbucket, sorry to ping you again, but it seems you are the only ones contributing to this repository at the moment. I even sent a message on the control-plane-dev channel on Slack to find other maintainers, but got no answer (https://envoyproxy.slack.com/archives/C7LDJTM6Z/p1644537207034489).

I would appreciate if you could review this patch.

[t0rr3sp3dr0]

Hi everyone!

Sorry to tag all the project maintainers here, but I've been trying to get someone to review this PR for over 9 months now and I've had no success so far.

If someone can take a look here, I'd really appreciate it! 🙂

@Automaat @Ferdudas97 @b-hoyt @chemicL @gawarz @joeyb @kukulam-allegro @lukidzi @mpuncel @ramaraochavali @slonka @snowp

[nothrow]

hello, is any update on this PR/item? I'd really appreciate it as well.