gRPC client factory integration in .NET Core

gRPC integration with HttpClientFactory offers a centralized way to create gRPC clients. It can be used as an alternative to configuring stand-alone gRPC client instances. Factory integration is available in the Grpc.Net.ClientFactory NuGet package.

The factory offers the following benefits:

  • Provides a central location for configuring logical gRPC client instances
  • Manages the lifetime of the underlying HttpClientMessageHandler
  • Automatic propagation of deadline and cancellation in an ASP.NET Core gRPC service

Register gRPC clients

To register a gRPC client, the generic AddGrpcClient extension method can be used within Startup.ConfigureServices, specifying the gRPC typed client class and service address:

services.AddGrpcClient<Greeter.GreeterClient>(o =>
{
    o.Address = new Uri("https://localhost:5001");
});

The gRPC client type is registered as transient with dependency injection (DI). The client can now be injected and consumed directly in types created by DI. ASP.NET Core MVC controllers, SignalR hubs and gRPC services are places where gRPC clients can automatically be injected:

public class AggregatorService : Aggregator.AggregatorBase
{
    private readonly Greeter.GreeterClient _client;

    public AggregatorService(Greeter.GreeterClient client)
    {
        _client = client;
    }

    public override async Task SayHellos(HelloRequest request,
        IServerStreamWriter<HelloReply> responseStream, ServerCallContext context)
    {
        // Forward the call on to the greeter service
        using (var call = _client.SayHellos(request))
        {
            await foreach (var response in call.ResponseStream.ReadAllAsync())
            {
                await responseStream.WriteAsync(response);
            }
        }
    }
}

Configure HttpClient

HttpClientFactory creates the HttpClient used by the gRPC client. Standard HttpClientFactory methods can be used to add outgoing request middleware or to configure the underlying HttpClientHandler of the HttpClient:

services
    .AddGrpcClient<Greeter.GreeterClient>(o =>
    {
        o.Address = new Uri("https://localhost:5001");
    })
    .ConfigurePrimaryHttpMessageHandler(() =>
    {
        var handler = new HttpClientHandler();
        handler.ClientCertificates.Add(LoadCertificate());
        return handler;
    });

For more information, see Make HTTP requests using IHttpClientFactory.

Configure Channel and Interceptors

gRPC-specific methods are available to:

  • Configure a gRPC client's underlying channel.
  • Add Interceptor instances that the client will use when making gRPC calls.
services
    .AddGrpcClient<Greeter.GreeterClient>(o =>
    {
        o.Address = new Uri("https://localhost:5001");
    })
    .AddInterceptor(() => new LoggingInterceptor())
    .ConfigureChannel(o =>
    {
        o.Credentials = new CustomCredentials();
    });

Deadline and cancellation propagation

gRPC clients created by the factory in a gRPC service can be configured with EnableCallContextPropagation() to automatically propagate the deadline and cancellation token to child calls. The EnableCallContextPropagation() extension method is available in the Grpc.AspNetCore.Server.ClientFactory NuGet package.

Call context propagation works by reading the deadline and cancellation token from the current gRPC request context and automatically propagating them to outgoing calls made by the gRPC client. Call context propagation is an excellent way of ensuring that complex, nested gRPC scenarios always propagate the deadline and cancellation.

services
    .AddGrpcClient<Greeter.GreeterClient>(o =>
    {
        o.Address = new Uri("https://localhost:5001");
    })
    .EnableCallContextPropagation();

For more information about deadlines and RPC cancellation, see RPC life cycle.

Additional resources