Experimental grpc-web support for ScalaPB

This library provides a code generator and runtime that enables calling gRPC services from your Scala.js code using grpc-web.

1. Add the following to your project/plugins.sbt:

   val grpcWebVersion = "0.3.0"
   
   resolvers += "Sonatype OSS Snapshots" at "https://oss.sonatype.org/content/repositories/snapshots"
   
   addSbtPlugin("com.thesamet" % "sbt-protoc" % "0.99.31")
   
   libraryDependencies += "com.thesamet.scalapb" %% "compilerplugin" % "0.10.2"
   
   libraryDependencies += "com.thesamet.scalapb.grpcweb" %% "scalapb-grpcweb-code-gen" % grpcWebVersion
   
   addSbtPlugin("ch.epfl.scala" % "sbt-scalajs-bundler" % "0.17.0")
   

2. Add a cross-project with the protos that will be shared by Scala.js and JVM:

   lazy val protos =
     crossProject(JSPlatform, JVMPlatform)
        .crossType(CrossType.Pure)
        .in(file("protos"))
        .settings(
          PB.protoSources in Compile := Seq(
            (baseDirectory in ThisBuild).value / "protos" / "src" / "main" / "protobuf"
          ),
          libraryDependencies += "com.thesamet.scalapb" %%% "scalapb-runtime" % scalapb.compiler.Version.scalapbVersion
        )
        .jvmSettings(
          libraryDependencies += "com.thesamet.scalapb" %% "scalapb-runtime-grpc" % scalapb.compiler.Version.scalapbVersion,
          PB.targets in Compile := Seq(
            scalapb.gen() -> (sourceManaged in Compile).value
          ),
        )
        .jsSettings(
          // publish locally and update the version for test
          libraryDependencies += "com.thesamet.scalapb.grpcweb" %%% "scalapb-grpcweb" % scalapb.grpcweb.BuildInfo.version,
          PB.targets in Compile := Seq(
            scalapb.gen(grpc=false) -> (sourceManaged in Compile).value,
            scalapb.grpcweb.GrpcWebCodeGenerator -> (sourceManaged in Compile).value
          )
        )
   

3. In your client code, instantiate the stub like this:

   val stub = TestServiceStub.stub(Channels.grpcwebChannel("http://localhost:8081"))
   

4. Now, you can call it like:

   // Make an async unary call
   stub.unary(req).onComplete {
     f => println("Unary", f)
   }
   
   // You can also pass metadata
   // Make sure header1 is accepted on the envoy config, otherwise the request will be rejected
   stub.unary(req, Metadata("header1" -> "value1")).onComplete {
     f => println("Unary", f)
   }
   
   // Make an async server streaming call
   stub.serverStreaming(req, new StreamObserver[Res] {
     override def onNext(value: Res): Unit = {
       println("Next: " + value)
     }
   
     override def onError(throwable: Throwable): Unit = {
       println("Error! " + throwable)
     }
   
     override def onCompleted(): Unit = {
       println("Completed!")
     }
   })
   

Check the full example