gRPC services with C#

This document outlines the concepts needed to write gRPC apps in C#. The topics covered here apply to both C-core-based and ASP.NET Core-based gRPC apps.

proto file

gRPC uses a contract-first approach to API development. Protocol buffers (protobuf) are used as the Interface Design Language (IDL) by default. The *.proto file contains:

  • The definition of the gRPC service.
  • The messages sent between clients and servers.

For more information on the syntax of protobuf files, see the official documentation (protobuf).

For example, consider the greet.proto file used in Get started with gRPC service:

  • Defines a Greeter service.
  • The Greeter service defines a SayHello call.
  • SayHello sends a HelloRequest message and receives a HelloReply message:
syntax = "proto3";

option csharp_namespace = "GrpcGreeter";

package greet;

// The greeting service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply);
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings.
message HelloReply {
  string message = 1;
}

Add a .proto file to a C# app

The *.proto file is included in a project by adding it to the <Protobuf> item group:

<ItemGroup>
  <Protobuf Include="Protos\greet.proto" GrpcServices="Server" />
</ItemGroup>

C# Tooling support for .proto files

The tooling package Grpc.Tools is required to generate the C# assets from *.proto files. The generated assets (files):

  • Are generated on an as-needed basis each time the project is built.
  • Aren't added to the project or checked into source control.
  • Are a build artifact contained in the obj directory.

This package is required by both the server and client projects. The Grpc.AspNetCore metapackage includes a reference to Grpc.Tools. Server projects can add Grpc.AspNetCore using the Package Manager in Visual Studio or by adding a <PackageReference> to the project file:

<PackageReference Include="Grpc.AspNetCore" Version="2.23.2" />

Client projects should directly reference Grpc.Tools alongside the other packages required to use the gRPC client. The tooling package isn't required at runtime, so the dependency is marked with PrivateAssets="All":

<PackageReference Include="Google.Protobuf" Version="3.9.2" />
<PackageReference Include="Grpc.Net.Client" Version="2.23.2" />
<PackageReference Include="Grpc.Tools" Version="2.23.0" PrivateAssets="All" />

Generated C# assets

The tooling package generates the C# types representing the messages defined in the included *.proto files.

For server-side assets, an abstract service base type is generated. The base type contains the definitions of all the gRPC calls contained in the .proto file. Create a concrete service implementation that derives from this base type and implements the logic for the gRPC calls. For the greet.proto, the example described previously, an abstract GreeterBase type that contains a virtual SayHello method is generated. A concrete implementation GreeterService overrides the method and implements the logic handling the gRPC call.

public class GreeterService : Greeter.GreeterBase
{
    public override Task<HelloReply> SayHello(
        HelloRequest request, ServerCallContext context)
    {
        return Task.FromResult(new HelloReply
        {
            Message = "Hello " + request.Name
        });
    }
}

For client-side assets, a concrete client type is generated. The gRPC calls in the .proto file are translated into methods on the concrete type, which can be called. For the greet.proto, the example described previously, a concrete GreeterClient type is generated. Call GreeterClient.SayHelloAsync to initiate a gRPC call to the server.

static async Task Main(string[] args)
{
    // The port number(5001) must match the port of the gRPC server.
    var channel = GrpcChannel.ForAddress("https://localhost:5001");
    var client =  new Greeter.GreeterClient(channel);
    var reply = await client.SayHelloAsync(
                      new HelloRequest { Name = "GreeterClient" });
    Console.WriteLine("Greeting: " + reply.Message);
    Console.WriteLine("Press any key to exit...");
    Console.ReadKey();
}

By default, server and client assets are generated for each *.proto file included in the <Protobuf> item group. To ensure only the server assets are generated in a server project, the GrpcServices attribute is set to Server.

<ItemGroup>
  <Protobuf Include="Protos\greet.proto" GrpcServices="Server" />
</ItemGroup>

Similarly, the attribute is set to Client in client projects.

gRPC not supported on Azure App Service

Warning

ASP.NET Core gRPC is not currently supported on Azure App Service or IIS. The HTTP/2 implementation of Http.Sys does not support HTTP response trailing headers which gRPC relies on. For more information, see this GitHub issue.

Additional resources