grpc unhandled exception StatusCode=Unknown when invoking a method generated from a proto file

Question

I have a c# client and server and get an unhandled exception of type Grpc.Core.RpcException with Status(StatusCode=Unknown, Detail="Exception was thrown by handler.") when invoking the SendMessage function in client (generated from a proto file).

The stack trace is:

Got response: True
RPC failed Grpc.Core.RpcException: Status(StatusCode=Unknown, Detail="Exception was thrown by handler.")
   at Grpc.Core.Internal.AsyncCall`2.UnaryCall(TRequest msg) in T:\src\github\grpc\src\csharp\Grpc.Core\Internal\AsyncCall.cs:line 75
   at Grpc.Core.DefaultCallInvoker.BlockingUnaryCall[TRequest,TResponse](Method`2 method, String host, CallOptions options, TRequest request) in T:\src\github\grpc\src\csharp\Grpc.Core\DefaultCallInvoker.cs:line 46
   at Grpc.Core.Interceptors.InterceptingCallInvoker.<BlockingUnaryCall>b__3_0[TRequest,TResponse](TRequest req, ClientInterceptorContext`2 ctx) in T:\src\github\grpc\src\csharp\Grpc.Core\Interceptors\InterceptingCallInvoker.cs:line 51
   at Grpc.Core.ClientBase.ClientBaseConfiguration.ClientBaseConfigurationInterceptor.BlockingUnaryCall[TRequest,TResponse](TRequest request, ClientInterceptorContext`2 context, BlockingUnaryCallContinuation`2 continuation) in T:\src\github\grpc\src\csharp\Grpc.Core\ClientBase.cs:line 174
   at Grpc.Core.Interceptors.InterceptingCallInvoker.BlockingUnaryCall[TRequest,TResponse](Method`2 method, String host, CallOptions options, TRequest request) in T:\src\github\grpc\src\csharp\Grpc.Core\Interceptors\InterceptingCallInvoker.cs:line 48
   at MessageService.MessageServiceClient.SendMessage(Message request, CallOptions options) in C:\Work\Dev\sphirra\hub-communication\message-hub\Hub-Messenger\MessageGrpc.cs:line 95
   at MessageService.MessageServiceClient.SendMessage(Message request, Metadata headers, Nullable`1 deadline, CancellationToken cancellationToken) in C:\Work\Dev\sphirra\hub-communication\message-hub\Hub-Messenger\MessageGrpc.cs:line 91

The sendMessage method in the proto file is as follows:

service MessageService{

rpc SendMessage(Message) returns (Empty){}
}

message Message{
    bytes msg = 1;
    int32 senderId = 2;
    int32 receiverId = 3;
}

message Empty {}

The SendMessage implementation in Client:

public void SendMessage(String msg, int receiverId)
            {
                try
                {
                    client.SendMessage(NewMsg(msg, ID, receiverId)); //this is where it gets stuck
                    Log("sending: ", msg);
                }
                catch (RpcException e)
                {
                    Log("RPC failed " + e);
                    throw;
                }
            }

The server-side implementation of the method:

public override Task<Empty> SendMessage(Message request, ServerCallContext context)
        {
            try
            {
                Task<Empty> empty = null;
                messages.Add(request);
                return empty;
            }
            catch (RpcException e){
                Console.WriteLine("Remote procedure call failed: " + e);
                throw;
            }

        }

Camisole

Any output from the server? This error usually happens when your handler code throws an exception that is not caught. Maybe try to wrap the entire SendMessage() server handler in a big try-catch-all block and see if any exceptions are thrown. – Fighterbomber

Answer 1

In my case, the issue was not wrapping object in Task.FromResult() while returning it.

Old code:

return new Object{};

Corrected Code

return Task.fromResult(new Object{});

Also always avoid null object or null properties in objects in return statement.

Aloisia