gRPC – Error Handling

Define protobuff file

Protocol buffer file is the base template for the communication between the server and the client.

//protobuff version
syntax = "proto3";
//package for protobuff
package calculator;
//package for java
option java_package = "com.thebytecloud.calculator";
//This option will create classes as separate files.
//If this is false, all classes will be created in the same java file.
option java_multiple_files = true;
//Error Handling
message SquareRootRequest {
    int32 number = 1;
}
message SquareRootResponse {
    double number_root = 1;
}
//Service is like a class which has methods for the communication.
service CalculatorService {
    //Error handling
    //Error will be sent if request number is negative. Error type will be  INVALID_ARGUMENT
    rpc FindSquareRoot(SquareRootRequest) returns (SquareRootResponse) {};
}

Generating the java classes

Running below command in the terminal will generate java files in package com.thebytecloud.calculator (option java_package)

mvn clean generate-sources

Implementing protobuff service methods

package com.thebytecloud.server;
import com.thebytecloud.calculator.*;
import io.grpc.Status;
import io.grpc.stub.StreamObserver;
public class CalculatorServiceImpl extends CalculatorServiceGrpc.CalculatorServiceImplBase {
    @Override
    public void findSquareRoot(SquareRootRequest request, StreamObserver<SquareRootResponse> responseObserver) {
        Integer number = request.getNumber();
        if(number >= 0){
            double numberRoot = Math.sqrt(number);
            responseObserver.onNext(SquareRootResponse.newBuilder().setNumberRoot(numberRoot).build());
            responseObserver.onCompleted();
        }else{
            responseObserver.onError(Status.INVALID_ARGUMENT
                    .withDescription("The number is not positive")
                    .augmentDescription("Number sent: "+ number)
                    .asRuntimeException()
            );
            responseObserver.onCompleted();
        }
    }
}

Client Implementation

package com.thebytecloud.client;
import com.thebytecloud.calculator.*;
import io.grpc.ManagedChannel;
import io.grpc.ManagedChannelBuilder;
import io.grpc.StatusRuntimeException;
import io.grpc.stub.StreamObserver;
import java.util.Arrays;
import java.util.Iterator;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
public class CalculatorClient {
    private final ManagedChannel managedChannel;
    public CalculatorClient(ManagedChannel managedChannel) {
        this.managedChannel = managedChannel;
    }
    public static void main(String[] args) throws InterruptedException {
        String server = "localhost";
        int serverPort = 7070;
        if(System.getenv("SERVER_PORT") != null)
            serverPort = Integer.parseInt(System.getenv("SERVER_PORT"));
        if(System.getenv("SERVER") != null)
            server = System.getenv("SERVER");
        System.out.println("server = " + server+":"+serverPort);
        Thread.sleep(2000);
        ManagedChannel managedChannel = ManagedChannelBuilder.forAddress(server, serverPort)
                .usePlaintext()
                .build();
        CalculatorClient calculatorClient = new CalculatorClient(managedChannel);
        calculatorClient.errorHandling();
    }
    private void errorHandling() {
        CalculatorServiceGrpc.CalculatorServiceBlockingStub stub = CalculatorServiceGrpc.newBlockingStub(managedChannel);
        int number = -1;
        try{
            stub.findSquareRoot(SquareRootRequest.newBuilder().setNumber(number).build());
        } catch (StatusRuntimeException e){
            System.out.println("Exception on Square Root..."+ e.getLocalizedMessage());
            e.printStackTrace();
        }
    }
}

Executing server and client

Executing server and client can be done via IDE or command line. Following are the commands to execute in terminal.

gRPC Server

grpc-java-examples$ mvn clean install
grpc-java-examples$ java -cp target/grpc-java-examples-1.0-SNAPSHOT-jar-with-dependencies.jar com.thebytecloud.server.CalculatorServer
serverBindPort = 7070
Starting gRPC Server...!

gRPC Client

grpc-java-examples$ java -cp target/grpc-java-examples-1.0-SNAPSHOT-jar-with-dependencies.jar com.thebytecloud.client.CalculatorClient
server = localhost:7070
Exception on Square Root...INVALID_ARGUMENT: The number is not positive
Number sent: -1
io.grpc.StatusRuntimeException: INVALID_ARGUMENT: The number is not positive
Number sent: -1
	at io.grpc.stub.ClientCalls.toStatusRuntimeException(ClientCalls.java:233)
	at io.grpc.stub.ClientCalls.getUnchecked(ClientCalls.java:214)
	at io.grpc.stub.ClientCalls.blockingUnaryCall(ClientCalls.java:139)
	at com.thebytecloud.calculator.CalculatorServiceGrpc$CalculatorServiceBlockingStub.findSquareRoot(CalculatorServiceGrpc.java:430)
	at com.thebytecloud.client.CalculatorClient.errorHandling(CalculatorClient.java:185)
	at com.thebytecloud.client.CalculatorClient.main(CalculatorClient.java:51)
grpc-java-examples$ 

Here client sending negative number for finding square root. Server found that parameter is invalid and throws error response with custom message with the number sent.