Dotnet Grpc

Cross-references: [skill:dotnet-resilience] for retry/circuit-breaker on gRPC channels, [skill:dotnet-serialization] for Protobuf wire format details. See [skill:dotnet-integration-testing] for testing gRPC services.

Proto Definition and Code Generation

Project Setup

gRPC uses Protocol Buffers as its interface definition language. The Grpc.Tools package generates C# code from .proto files at build time.

Server project:

<ItemGroup>
  <PackageReference Include="Grpc.AspNetCore" Version="2.*" />
</ItemGroup>

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

Client project:

<ItemGroup>
  <PackageReference Include="Google.Protobuf" Version="3.*" />
  <PackageReference Include="Grpc.Net.Client" Version="2.*" />
  <PackageReference Include="Grpc.Tools" Version="2.*" PrivateAssets="All" />
</ItemGroup>

<ItemGroup>
  <Protobuf Include="Protos\*.proto" GrpcServices="Client" />
</ItemGroup>

Shared contracts project (recommended for larger services):

<ItemGroup>
  <PackageReference Include="Google.Protobuf" Version="3.*" />
  <PackageReference Include="Grpc.Tools" Version="2.*" PrivateAssets="All" />
</ItemGroup>

<ItemGroup>
  <Protobuf Include="Protos\*.proto" GrpcServices="Both" />
</ItemGroup>

Proto File Definition

syntax = "proto3";

option csharp_namespace = "MyApp.Grpc";

package myapp;

import "google/protobuf/timestamp.proto";
import "google/protobuf/empty.proto";

// Service definition with all 4 streaming patterns
service OrderService {
  rpc GetOrder (GetOrderRequest) returns (OrderResponse);
  rpc ListOrders (ListOrdersRequest) returns (stream OrderResponse);
  rpc UploadOrders (stream CreateOrderRequest) returns (UploadOrdersResponse);
  rpc ProcessOrders (stream CreateOrderRequest) returns (stream OrderResponse);
}

message GetOrderRequest {
  int32 id = 1;
}

message ListOrdersRequest {
  string customer_id = 1;
  int32 page_size = 2;
  string page_token = 3;
}

message CreateOrderRequest {
  string customer_id = 1;
  repeated OrderItemMessage items = 2;
}

message OrderResponse {
  int32 id = 1;
  string customer_id = 2;
  repeated OrderItemMessage items = 3;
  google.protobuf.Timestamp created_at = 4;
}

message OrderItemMessage {
  string product_id = 1;
  int32 quantity = 2;
  double unit_price = 3;
}

message UploadOrdersResponse {
  int32 orders_created = 1;
}

Code-Gen Workflow

The Grpc.Tools package runs the Protobuf compiler (protoc) and C# gRPC plugin at build time. Generated files appear in obj/ and are included automatically:

1. Add .proto files to the project via <Protobuf> items
2. Set GrpcServices to Server, Client, or Both
3. Build the project -- generated C# types and service stubs appear in obj/Debug/net10.0/Protos/
4. Implement the generated abstract base class (server) or use the generated client class

The gRPC code-gen toolchain uses source generation to produce the C# stubs from .proto definitions. This is conceptually similar to [skill:dotnet-csharp-source-generators] but uses protoc rather than Roslyn incremental generators.

Streaming Patterns Summary

gRPC supports four communication patterns:

Status Codes

Map domain errors to gRPC status codes:

gRPC-Web Limitations

• Unary and server streaming only -- client streaming and bidirectional streaming are not supported by gRPC-Web
• No HTTP/2 trailers -- status and trailing metadata are encoded in the response body
• CORS required -- cross-origin requests need explicit CORS configuration on the server
• Consider SignalR for full-duplex browser communication -- see [skill:dotnet-realtime-communication] for alternatives when bidirectional streaming is required

Key Principles

• Use .proto files as the contract -- they are the single source of truth for the API shape, shared between client and server
• Set GrpcServices on <Protobuf> items -- Server for service projects, Client for consumer projects, Both for shared contracts
• Reuse channels -- GrpcChannel manages HTTP/2 connections; creating a new channel per call wastes resources
• Register gRPC clients via DI -- AddGrpcClient integrates with IHttpClientFactory for connection pooling and resilience
• Always set deadlines -- calls without deadlines can hang indefinitely if the server is slow or unreachable
• Use L7 load balancers -- L4 load balancers pin all traffic to one backend because HTTP/2 multiplexes on a single TCP connection
• Implement the gRPC health check protocol -- enables Kubernetes probes and load balancers to monitor service health
• Use gRPC-Web for browser clients -- native gRPC requires HTTP/2 trailers which browsers do not support; gRPC-Web bridges this gap

See [skill:dotnet-native-aot] for Native AOT compilation pipeline and [skill:dotnet-aot-architecture] for AOT-compatible patterns when building gRPC services with ahead-of-time compilation.

Agent Gotchas

1. Do not create a new GrpcChannel per request -- channels are expensive to create and manage HTTP/2 connections. Reuse them or use DI-registered clients.
2. Do not omit GrpcServices on <Protobuf> items -- the default is Both, which generates server and client stubs. This bloats client projects with unused server code and vice versa.
3. Do not use L4 load balancers for gRPC without enabling EnableMultipleHttp2Connections -- HTTP/2 multiplexing means a single connection handles all RPCs, defeating load distribution.
4. Do not throw generic Exception from gRPC services -- throw RpcException with appropriate StatusCode and descriptive messages. Unhandled exceptions become StatusCode.Internal with no useful detail.
5. Do not forget to call CompleteAsync() on client streams -- the server waits for stream completion before sending its response. Forgetting this causes the call to hang.
6. Do not use grpc.health.v1.Health without registering health checks -- an empty health service always reports Serving, which defeats the purpose of health monitoring.
7. Do not enable gRPC-Web globally without CORS -- UseGrpcWeb() without a CORS policy allows any origin to call your gRPC services. Always pair with explicit RequireCors().
8. Do not attempt client streaming or bidirectional streaming with gRPC-Web -- the gRPC-Web protocol only supports unary and server streaming. Use SignalR or native gRPC for full-duplex browser communication.

Attribution

Adapted from Aaronontheweb/dotnet-skills (MIT license).

References

• gRPC for .NET overview
• Create a gRPC client and server
• gRPC client factory integration
• gRPC services with ASP.NET Core
• gRPC health checks
• gRPC load balancing
• gRPC authentication
• gRPC interceptors
• gRPC-Web for .NET
• Protocol Buffers language guide