GRPC Monix

Use Monix's Tasks and Observables to implement your GRPC services instead of Java's StreamObservers.

Unary calls return a Task[T] for the response returned by the server
Server streaming calls return an Observable[T] for the elements returned by the server
Client streaming calls take an Observable[T] for the elements emitted by the client and return a Task[U] for the server response
Bidi streaming calls take an Observable[T] for the elements emitted by the client and return an Observable[U] for the elements returned by the server

Installation

You need to enable sbt-protoc plugin to generate source code for the proto definitions. You can do it by adding a protoc.sbt file into your project folder with the following lines:

addSbtPlugin("com.thesamet" % "sbt-protoc" % "0.99.17")

resolvers += Resolver.bintrayRepo("beyondthelines", "maven")

libraryDependencies ++= Seq(
  "com.thesamet.scalapb" %% "compilerplugin" % "0.7.0",
  "beyondthelines"       %% "grpcmonixgenerator" % "0.0.7"
)

Here we add a dependency to the GRPCMonix protobuf generator.

Then we need to trigger the generation from the build.sbt:

PB.targets in Compile := Seq(
  // compile your proto files into scala source files
  scalapb.gen() -> (sourceManaged in Compile).value,
  // generate the GRPCMonix source code
  grpcmonix.generators.GrpcMonixGenerator() -> (sourceManaged in Compile).value
)

resolvers += Resolver.bintrayRepo("beyondthelines", "maven")

libraryDependencies += "beyondthelines" %% "grpcmonixruntime" % "0.0.7"

Usage

You're now ready to implement your GRPC service using Monix's Tasks and Observables.

To implement your service's business logic you simply extend the GRPC monix generated trait.

E.g. for the RouteGuide service:

class RouteGuideMonixService(features: Seq[Feature]) extends RouteGuideGrpcMonix.RouteGuide {
  // Unary call
  override def getFeature(request: Point): Task[Feature] = ???
  // Server streaming
  override def listFeatures(request: Rectangle): Observable[Feature] = ???
  // Client streaming
  override def recordRoute(points: Observable[Point]): Task[RouteSummary] = ???
  // Bidi streaming
  override def routeChat(notes: Observable[RouteNote]): Observable[RouteNote] = ???
}

The server creation is similar except you need to provide a Monix's Scheduler instead of an ExecutionContext when binding the service

val server = ServerBuilder
  .forPort(8980)
  .addService(
    RouteGuideGrpcMonix.bindService(
      new RouteGuideMonixService(features), // the service implemented above
      monix.execution.Scheduler.global
    )
  )
  .build()

Tasks and Observables are also available on the client side:

val channel = ManagedChannelBuilder
  .forAddress("localhost", 8980)
  .usePlainText(true)
  .build()

val stub = RouteGuideGrpcMonix.stub(channel) // only an async stub is provided

// Unary call
val feature: Task[Feature] = stub.getFeature(408031728, -748645385)
// Server streaming
val request = Rectangle(
  lo = Some(Point(408031728, -748645385)),
  hi = Some(Point(413700272, -742135189))
)
val features: Observable[Feature] = stub.listFeatures(request)
// Client streaming
val route: Observable[Feature] = Observable
  .fromIterable(features.map(_.getLocation)) 
  .delayOnNext(100.millis)
val summary: Task[RouteSummary] = stub.recordRoute(route)
// Bidi streaming
val notes: Observable[RouteNote] = Observable(
  RouteNote(message = "First message", location = Some(Point(0, 0))),
  RouteNote(message = "Second message", location = Some(Point(0, 1))),
  RouteNote(message = "Third message", location = Some(Point(1, 0))),
  RouteNote(message = "Fourth message", location = Some(Point(1, 1)))
).delayOnNext(1.second)
val allNotes = stub.routeChat(notes)