gRPC for .NET

Overview

gRPC is a high-performance RPC framework that uses Protocol Buffers (protobuf) for service contracts and HTTP/2 for transport. In .NET, Grpc.AspNetCore hosts gRPC services inside ASP.NET Core, and Grpc.Net.Client provides a strongly-typed client. gRPC supports four communication patterns: unary (request-response), server streaming, client streaming, and bidirectional streaming.

gRPC is the preferred choice for internal service-to-service communication where strong typing, code generation, and streaming are more valuable than REST's human-readability. The .proto files serve as the single source of truth for the service contract, generating both server stubs and client proxies at build time.

Proto File Definition

Define the service contract in a .proto file. The protobuf compiler generates C# types and service stubs.

protobuf

syntax = "proto3";

option csharp_namespace = "MyApp.Protos";

package orders;

service OrderService {
  rpc GetOrder (GetOrderRequest) returns (OrderReply);
  rpc ListOrders (ListOrdersRequest) returns (stream OrderReply);
  rpc UploadOrders (stream CreateOrderRequest) returns (UploadSummary);
  rpc OrderChat (stream OrderMessage) returns (stream OrderMessage);
}

message GetOrderRequest {
  string order_id = 1;
}

message ListOrdersRequest {
  int32 page_size = 1;
  string page_token = 2;
}

message CreateOrderRequest {
  string customer_name = 1;
  double total = 2;
  repeated OrderItemRequest items = 3;
}

message OrderItemRequest {
  string product_name = 1;
  int32 quantity = 2;
}

message OrderReply {
  string order_id = 1;
  string customer_name = 2;
  double total = 3;
  string created_at = 4;
}

message UploadSummary {
  int32 orders_created = 1;
}

message OrderMessage {
  string sender = 1;
  string content = 2;
}

Server Implementation

Implement the generated base class on the server side.

csharp

using Grpc.Core;
using MyApp.Protos;

namespace MyApp.Services;

public class OrderGrpcService : OrderService.OrderServiceBase
{
    private readonly IOrderRepository _repository;
    private readonly ILogger<OrderGrpcService> _logger;

    public OrderGrpcService(
        IOrderRepository repository,
        ILogger<OrderGrpcService> logger)
    {
        _repository = repository;
        _logger = logger;
    }

    public override async Task<OrderReply> GetOrder(
        GetOrderRequest request, ServerCallContext context)
    {
        var order = await _repository.GetByIdAsync(request.OrderId);
        if (order is null)
        {
            throw new RpcException(new Status(
                StatusCode.NotFound,
                $"Order {request.OrderId} not found"));
        }

        return new OrderReply
        {
            OrderId = order.Id.ToString(),
            CustomerName = order.CustomerName,
            Total = (double)order.Total,
            CreatedAt = order.CreatedAt.ToString("O")
        };
    }

    public override async Task ListOrders(
        ListOrdersRequest request,
        IServerStreamWriter<OrderReply> responseStream,
        ServerCallContext context)
    {
        var orders = _repository.GetOrdersAsync(request.PageSize);

        await foreach (var order in orders
            .WithCancellation(context.CancellationToken))
        {
            await responseStream.WriteAsync(new OrderReply
            {
                OrderId = order.Id.ToString(),
                CustomerName = order.CustomerName,
                Total = (double)order.Total,
                CreatedAt = order.CreatedAt.ToString("O")
            });
        }
    }
}

Server Registration

csharp

using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.DependencyInjection;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddGrpc(options =>
{
    options.MaxReceiveMessageSize = 16 * 1024 * 1024; // 16 MB
    options.MaxSendMessageSize = 16 * 1024 * 1024;
    options.EnableDetailedErrors = builder.Environment.IsDevelopment();
});

var app = builder.Build();
app.MapGrpcService<MyApp.Services.OrderGrpcService>();
app.Run();

Client with GrpcClientFactory

Use the typed client factory for DI-integrated gRPC clients with resilience.

csharp

using Microsoft.Extensions.DependencyInjection;
using MyApp.Protos;

var builder = WebApplication.CreateBuilder(args);

builder.Services
    .AddGrpcClient<OrderService.OrderServiceClient>(options =>
    {
        options.Address = new Uri("https://localhost:5001");
    })
    .ConfigureChannel(options =>
    {
        options.MaxReceiveMessageSize = 16 * 1024 * 1024;
    })
    .AddCallCredentials(async (context, metadata) =>
    {
        var token = await GetTokenAsync();
        metadata.Add("Authorization", $"Bearer {token}");
    });

var app = builder.Build();
app.Run();

static Task<string> GetTokenAsync()
    => Task.FromResult("my-jwt-token");

Client Usage with Deadlines and Cancellation

Always set deadlines on gRPC calls to prevent indefinite waits.

csharp

using Grpc.Core;
using MyApp.Protos;

namespace MyApp.Services;

public class OrderClientService
{
    private readonly OrderService.OrderServiceClient _client;

    public OrderClientService(
        OrderService.OrderServiceClient client)
    {
        _client = client;
    }

    public async Task<OrderReply> GetOrderAsync(
        string orderId, CancellationToken ct)
    {
        var request = new GetOrderRequest { OrderId = orderId };

        var callOptions = new CallOptions(
            deadline: DateTime.UtcNow.AddSeconds(5),
            cancellationToken: ct);

        try
        {
            return await _client.GetOrderAsync(request, callOptions);
        }
        catch (RpcException ex) when (
            ex.StatusCode == StatusCode.DeadlineExceeded)
        {
            throw new TimeoutException(
                $"GetOrder timed out for {orderId}", ex);
        }
        catch (RpcException ex) when (
            ex.StatusCode == StatusCode.NotFound)
        {
            throw new KeyNotFoundException(
                $"Order {orderId} not found", ex);
        }
    }

    public async IAsyncEnumerable<OrderReply> ListOrdersAsync(
        int pageSize,
        [System.Runtime.CompilerServices.EnumeratorCancellation]
        CancellationToken ct = default)
    {
        var request = new ListOrdersRequest { PageSize = pageSize };

        using var call = _client.ListOrders(
            request,
            deadline: DateTime.UtcNow.AddSeconds(30),
            cancellationToken: ct);

        await foreach (var reply in call.ResponseStream
            .ReadAllAsync(ct))
        {
            yield return reply;
        }
    }
}

Interceptors

Interceptors provide cross-cutting concerns (logging, metrics, auth) for gRPC calls.

csharp

using Grpc.Core;
using Grpc.Core.Interceptors;
using Microsoft.Extensions.Logging;

namespace MyApp.Interceptors;

public class LoggingInterceptor : Interceptor
{
    private readonly ILogger<LoggingInterceptor> _logger;

    public LoggingInterceptor(ILogger<LoggingInterceptor> logger)
    {
        _logger = logger;
    }

    public override async Task<TResponse> UnaryServerHandler<TRequest, TResponse>(
        TRequest request,
        ServerCallContext context,
        UnaryServerMethod<TRequest, TResponse> continuation)
    {
        _logger.LogInformation(
            "gRPC call: {Method}", context.Method);

        var sw = System.Diagnostics.Stopwatch.StartNew();
        try
        {
            var response = await continuation(request, context);
            sw.Stop();
            _logger.LogInformation(
                "gRPC {Method} completed in {ElapsedMs}ms",
                context.Method, sw.ElapsedMilliseconds);
            return response;
        }
        catch (Exception ex)
        {
            sw.Stop();
            _logger.LogError(ex,
                "gRPC {Method} failed after {ElapsedMs}ms",
                context.Method, sw.ElapsedMilliseconds);
            throw;
        }
    }
}

gRPC Communication Patterns

Pattern	Client	Server	Use Case
Unary	Single request	Single response	CRUD operations
Server streaming	Single request	Stream of responses	Feed/list retrieval
Client streaming	Stream of requests	Single response	Batch upload
Bidirectional streaming	Stream of requests	Stream of responses	Chat, real-time sync

Best Practices

•Always set deadlines on client calls using CallOptions.Deadline or deadline: parameter to prevent indefinite waits when the server is unresponsive.
•Use .proto files as the single source of truth for service contracts and share them via a NuGet package or git submodule across client and server repositories.
•Use GrpcClientFactory (AddGrpcClient<T>) instead of manually creating channels, so clients benefit from HttpClientFactory pooling, resilience handlers, and DI integration.
•Enable server reflection in development (builder.Services.AddGrpcReflection()) so tools like grpcurl and grpcui can discover and test services without the .proto file.
•Handle RpcException by StatusCode on the client side and throw RpcException with appropriate status codes on the server side instead of returning error payloads in the response message.
•Use server streaming for large result sets instead of returning a single response with a large repeated field, to reduce memory pressure and enable progressive rendering.
•Register interceptors for cross-cutting concerns (logging, metrics, auth token injection) rather than duplicating the logic in every service method.
•Set MaxReceiveMessageSize and MaxSendMessageSize explicitly on both client and server to prevent out-of-memory errors from oversized messages (default is 4 MB).
•Use gRPC-Web (app.MapGrpcService<T>().EnableGrpcWeb()) when browser clients need to call gRPC services, as browsers do not support HTTP/2 trailers natively.
•Version proto packages using the package directive (e.g., orders.v1) and maintain backward compatibility by never removing or renumbering existing fields.