Remove grpc-protobuf dependency for stub runtime

[devkanro]

I found the grpc-kotlin-stub doesn't use any classes from grpc-protobuf/grpc-protobuf-lite, maybe we can use the grpc-api/grpc-stub instead?
Then we can just provide one package for both protobuf and protobuf-lite cases and for non-google official protobuf runtime cases.

[jamesward]

I think we can do that and I gave it a try:
https://github.com/grpc/grpc-kotlin/tree/no-lite

Downside is that the user has to specify a protobuf dep, like:

api("io.grpc:grpc-protobuf:3.13.0")

And in the case of lite they have to also add a guava dep:

api("io.grpc:grpc-protobuf-lite:${rootProject.ext["grpcVersion"]}")
api("com.google.guava:guava:28.2-jre") // or `-android`

WDYT?

[devkanro]

Looks good.
User has to specify a protobuf dep is not a downside I think, the grpc-kotlin-stub is not just can be used in google official protobuf runtime.

But I have some confusion for guava.
Why do we need api dep for guava in the lite case?
Do we use guava classes for grpc-kotlin-stub or generated codes?

I found there are runtimeOnly dep for guava in grpc-protobuf already, and there are no guava dep in grpc-kotlin-stub or grpc-kotlin-stub-lite now.

[jamesward]

The guava dep is transitive for io.grpc:grpc-api:

+--- io.grpc:grpc-stub:1.29.0
|    \--- io.grpc:grpc-api:1.29.0
|         +--- io.grpc:grpc-context:1.29.0
|         +--- com.google.errorprone:error_prone_annotations:2.3.4
|         +--- com.google.code.findbugs:jsr305:3.0.2
|         +--- org.codehaus.mojo:animal-sniffer-annotations:1.18
|         \--- com.google.guava:guava:28.2-android
|              +--- com.google.guava:failureaccess:1.0.1
|              +--- com.google.guava:listenablefuture:9999.0-empty-to-avoid-conflict-with-guava
|              +--- com.google.code.findbugs:jsr305:3.0.2
|              +--- org.checkerframework:checker-compat-qual:2.5.5
|              +--- com.google.errorprone:error_prone_annotations:2.3.4
|              \--- com.google.j2objc:j2objc-annotations:1.3

But is marked as runtime. Not including it with stub-lite usage results in:

/home/jamesward/projects/grpc-kotlin/examples/stub-lite/build/generated/source/proto/main/grpc/io/grpc/examples/routeguide/RouteGuideGrpc.java:433: error: package com.google.common.util.concurrent does not exist
    public com.google.common.util.concurrent.ListenableFuture<io.grpc.examples.routeguide.Feature> getFeature(

We don't see this error with stub usage (in the examples) because the dependency on com.google.protobuf:protobuf-java-util brings it in transitively.

[devkanro]

I found the reason for this problem is the version of grpc-stub is not match with grpc-api.

Before grpc-stub 1.30.0, the guava was a compile dep of grpc-api.
After the 1.30.0 version, the guava is a runtime dep for grpc-api, but it will be a compile dep for grpc-stub.

If you using a low version for grpc-stub but a high version for grpc-api, the problem will have happened.
Upgrade the grpc version of grpc-kotlin in ext can resolve this problem.

Reference:
grpc/grpc-java@v1.30.0

Note: gRPC-Java no longer exposes many transitive dependencies as "compile" dependencies,
    but instead specifies them as "runtime" dependencies. Consuming projects using these
    dependencies directly will need to explicitly add the dependencies to their compile-time classpath.

[jamesward]

So maybe we should make the grpc-stub dependency in grpc-kotlin-stub non-transitive?

[devkanro]

No, I think. The grpc-stub should be a compile dep for grpc-kotlin-stub.

1. AbstractCoroutineStub extends from AbstractStub.
2. Kotlin gRPC codes based on Java gRPC codes, and the Java gRPC codes need the grpc-stub classes.

[jamesward]

Looks like it might work to make the grpc-stub dependency provided so that it isn't transitive: https://github.com/grpc/grpc-kotlin/compare/no-lite#diff-483f493fdd56e587549eb080ba6af32d0f88765702675df3474f6e507ea612d3R31

[devkanro]

Yes, it works. But I still think grpc-stub should be a api dep for grpc-kotlin-stub.

[jamesward]

Isn't that the source of the version incompatibilities though?

[devkanro]

Ummm...How about upgrade grpc-stub version to match grpc-api?
In my opinion, the version of grpc-stub must be matched with grpc-api.

[jamesward]

If we include the grpc-stub dependency and make it transitive, then the versions do match, as long as there isn't another dependency that brings in a newer grpc-api.

[devkanro]

Yes, and users do not need to add grpc-stub to their project in most case.
If users need to upgrade grpc-stub to a higher version than which gprc-kotlin-stub depend on, just add this grpc-stub to their build.gradle.

api("io.grpc:grpc-kotlin-stub:1.1.1")
api("io.grpc:grpc-stub:1.35.6")

[jamesward]

Finally getting the chance to come back to this. So I think we can do is make grpc-kotlin-stub have a transitive dependency on io.grpc:grpc-stub but not depend on grpc-protobuf, protobuf-java-util, io.grpc:grpc-protobuf-lite, or com.google.protobuf:protobuf-javalite.

That seems to be working and I've updated the no-lite branch to reflect the changes:
https://github.com/grpc/grpc-kotlin/compare/no-lite

Does that seem right?

[devkanro]

Good work! just wait for the release.