gRPC - Unary Call C#

Question

I am trying to learn gRPC by making a simple project server/client which the client send 2 Int Variable and the server will responed with a string and the 2 variable that the client sent The Protocol Buffer code is :

syntax = "proto3";
option  csharp_namespace = "MapPB";

service MapRoute {

    rpc Gps(Location) returns (LocationName) {}
}


message Location {

    int32 la = 1;
    int32 lo = 2;
}

message LocationName {

    string Name = 1;
}

Server

using Grpc.Core;
using static MapPB.MapRoute;
using MapPB;

namespace gServer
{
    public class gS : MapRouteBase
    {
        public override async Task<LocationName> Gps(Location request, ServerCallContext context)
        {

            return await base.Gps(new LocationName { Name = "Your Location is " + request.La + ":" + request.Lo } );

        }

    }
    class Program
    {
        const int Port = 50051;
        static void Main(string[] args)
        {

            Server server = new Server
            {
                Services = { MapRoute.BindService(new gS()) },
                Ports = { new ServerPort("localhost", Port, ServerCredentials.Insecure) }
            };
            server.Start();

            Console.WriteLine("Map server listening on port " + Port);
            Console.WriteLine("Press any key to stop the server...");
            Console.ReadKey();

            server.ShutdownAsync().Wait();

        }
    }
}

Client

using Grpc.Core;
using Map;
using static MapPB.MapRoute;


namespace Map
{
    class Program : MapRouteClient
    {

        static void Main(string[] args)
        {
            Channel channel = new Channel("127.0.0.1:50021", ChannelCredentials.Insecure);

            var client = new MapRouteClient(channel);

            int la = 1;
            int lo = 2;

            var reply = client.Gps(new MapPB.Location { La = la , Lo = lo });

            Console.WriteLine(reply.Name);


            channel.ShutdownAsync().Wait();
            Console.WriteLine("Press any key to exit...");
            Console.ReadKey();

        }
    }
}

Am getting an red squiggle at the server code under .Gps

There is no argument given that corresponds to the required formal parameter 'context' of 'MapRoute.MapRouteBase.Gps(Location, ServerCallContext)'

I tried to add context to the parameter but I got another error

cannot convert from 'MapPB.LocationName' to 'MapPB.Location'

can someone explain what wrong am doing Please ?

Answer 1

Your service function implementation should look like:

public override async Task<LocationName> Gps(Location request, ServerCallContext context)
{
    return new LocationName { Name = "Your Location is " + request.La + ":" + request.Lo };
}

The idea is that the function is automatically invoked whenever a client calls it. It passes you the defined parameters (location here). You are expected to return the result - which is the location name here.

What you did wrong here was delegating the processing to the base class instead of handling the request yourself.

Answer 2

As an update on Matthias247's answer, I would prefer to see it like this (even tho his answer is also correct):

public override Task<LocationName> Gps(Location request, ServerCallContext context)
    {
        return Task.FromResult(new LocationName
        {
            Name = "Your Location is " + request.La + ":" + request.Lo
        });
    }

And change your client to async:

static async Task Main(string[] args)
    {
        Channel channel = new Channel("127.0.0.1:50021", ChannelCredentials.Insecure);

        var client = new MapRouteClient(channel);

        int la = 1;
        int lo = 2;

        var reply = await client.GpsAsync(new MapPB.Location { La = la , Lo = lo });

        Console.WriteLine(reply.Name);


        channel.ShutdownAsync().Wait();
        Console.WriteLine("Press any key to exit...");
        Console.ReadKey();

    }