Scala Grpc failed with error io.grpc.StatusRuntimeException: CANCELLED: Failed to read message

Question

I am trying to write a streaming service in Scala using GRPC. Towards this I wrote this proto file

syntax = "proto3";
package com.abhi.grpc;

message TimeRequest{}
message TimeResponse {
    int64 currentTime = 1;
}

service Clock {
    rpc StreamTime(TimeRequest) returns (stream TimeResponse);
}

This is my server side code

import com.abhi.grpc.clock.{ClockGrpc, TimeRequest, TimeResponse}
import io.grpc.stub.StreamObserver
import monix.execution.Scheduler
import monix.execution.Scheduler.{global => scheduler}
import scala.concurrent.duration._

object ClockGrpcServer extends GrpcServer with App {
   val ssd = ClockGrpc.bindService(new ClockGRPC(), Scheduler.global)
   runServer(ssd, "Clock")
}

class ClockGRPC extends ClockGrpc.Clock {
   override def streamTime(request: TimeRequest, responseObserver: StreamObserver[TimeResponse]): Unit = {
      scheduler.scheduleWithFixedDelay(0.seconds, 3.seconds) {
         responseObserver.onNext(TimeResponse(System.currentTimeMillis))
      }
   }
}

and this is my client

object ClockGrpcClient extends App {
   val channel = ManagedChannelBuilder.forAddress("localhost", 50051).usePlaintext(true).build()
   val stub = ClockGrpc.stub(channel)
   val observer = new StreamObserver[TimeResponse] {
      override def onError(t: Throwable): Unit = println(s"failed with error ${t}")
      override def onCompleted(): Unit = println("closing observer")
      override def onNext(value: TimeResponse): Unit = println(s"received time ${new DateTime(value)}")
   }
   stub.streamTime(TimeRequest(), observer)
   StdIn.readLine()
}

When I run the server and the client. The server throws the following error as soon as it receives any message from the client

io.grpc.StatusRuntimeException: CANCELLED
        at io.grpc.Status.asRuntimeException(Status.java:534)
        at io.grpc.stub.ServerCalls$ServerCallStreamObserverImpl.onNext(ServerCalls.java:279)
        at com.abhi.ClockGRPC.$anonfun$streamTime$1(ClockGRPC.scala:22)
        at monix.execution.internal.RunnableAction.run(RunnableAction.scala:25)
        at monix.execution.schedulers.ReferenceScheduler$$anon$1.run(ReferenceScheduler.scala:45)
        at scala.concurrent.impl.ExecutionContextImpl$AdaptedForkJoinTask.exec(ExecutionContextImpl.scala:140)
        at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
        at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
        at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
        at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)

I googled a little and found this article

https://blog.codecentric.de/en/2017/01/hello-grpc-scalapb/

based on this I changed my server to use the java.util scheduler

class ClockGRPC extends ClockGrpc.Clock {
   val scheduler = Executors.newSingleThreadScheduledExecutor()
   override def streamTime(request: TimeRequest, responseObserver: StreamObserver[TimeResponse]): Unit = {
      val tick = new Runnable {
         val counter = new AtomicInteger(10)
         def run() =
            if (counter.getAndDecrement() >= 0) {
               val currentTime = System.currentTimeMillis()
               responseObserver.onNext(TimeResponse(currentTime))
            } else {
               scheduler.shutdown()
               responseObserver.onCompleted()
            }
      }
      scheduler.scheduleAtFixedRate(tick, 0l, 3000l, TimeUnit.SECONDS)
   }
}

But I still get the CANCELLED error. So i cannot get the streaming example to work.

[info] Running com.abhi.ClockGrpcClient failed with error io.grpc.StatusRuntimeException: CANCELLED: Failed to read message. — Knows Not Much

Knows Not Much Knows Not Much · Accepted Answer · 2017-09-11T02:26:08

I had almost given up on this problem. But came back today and resolved it.

The problem is with the line

override def onNext(value: TimeResponse): Unit = println(s"received time ${new DateTime(value)}")

value cannot be passed to new DateTime

To further make the matters worse. if the exception occurs in the callback method. Grpc Swallows it and replaces it with a generic error message

info] Running com.abhi.ClockGrpcClient failed with error io.grpc.StatusRuntimeException: CANCELLED: Failed to read message.

My bad luck that he DateTime uses an object as a parameter so the compilation succeeded, but the call failed at runtime and the exception was swallowed by the Grpc.

I am leaving this here so that it helps someone else.

[info] Running com.abhi.ClockGrpcClient failed with error io.grpc.StatusRuntimeException: CANCELLED: Failed to read message

Means the someone went wrong in the callback function.

Scala Grpc failed with error io.grpc.StatusRuntimeException: CANCELLED: Failed to read message

1 Answers