Imported from bobmatnyc/claude-mpm-skills (toolchains/golang/golang-grpc/SKILL.md) via skills.sh. Install upstream with npx skills add bobmatnyc/claude-mpm-skills --skill golang-grpc. Copyright stays with the author (MIT).

Go gRPC (Production)

Overview

gRPC provides strongly-typed RPC APIs backed by Protocol Buffers, with first-class streaming support and excellent performance for service-to-service communication. This skill focuses on production defaults: versioned protos, deadlines, error codes, interceptors, health checks, TLS, and testability.

Quick Start

1) Define a versioned protobuf API

✅ Correct: versioned package

// proto/users/v1/users.proto
syntax = "proto3";

package users.v1;
option go_package = "example.com/myapp/gen/users/v1;usersv1";

service UsersService {
  rpc GetUser(GetUserRequest) returns (GetUserResponse);
  rpc ListUsers(ListUsersRequest) returns (stream User);
}

message GetUserRequest { string id = 1; }
message GetUserResponse { User user = 1; }
message ListUsersRequest { int32 page_size = 1; string page_token = 2; }

message User {
  string id = 1;
  string email = 2;
  string display_name = 3;
}

❌ Wrong: unversioned package (hard to evolve)

package users;

2) Generate Go code

Install generators:

go install google.golang.org/protobuf/cmd/protoc-gen-go@latest
go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@latest

Generate:

protoc -I proto \
  --go_out=./gen --go_opt=paths=source_relative \
  --go-grpc_out=./gen --go-grpc_opt=paths=source_relative \
  proto/users/v1/users.proto

3) Implement server with deadlines and status codes

✅ Correct: validate + map errors to gRPC codes

package usersvc

import (
    "context"

    "google.golang.org/grpc/codes"
    "google.golang.org/grpc/status"

    usersv1 "example.com/myapp/gen/users/v1"
)

type Service struct {
    usersv1.UnimplementedUsersServiceServer
    Repo Repo
}

type Repo interface {
    GetUser(ctx context.Context, id string) (User, error)
}

type User struct {
    ID, Email, DisplayName string
}

func (s *Service) GetUser(ctx context.Context, req *usersv1.GetUserRequest) (*usersv1.GetUserResponse, error) {
    if req.GetId() == "" {
        return nil, status.Error(codes.InvalidArgument, "id is required")
    }

    u, err := s.Repo.GetUser(ctx, req.GetId())
    if err != nil {
        if err == ErrNotFound {
            return nil, status.Error(codes.NotFound, "user not found")
        }
        return nil, status.Error(codes.Internal, "internal error")
    }

    return &usersv1.GetUserResponse{
        User: &usersv1.User{
            Id:          u.ID,
            Email:       u.Email,
            DisplayName: u.DisplayName,
        },
    }, nil
}

❌ Wrong: return raw errors (clients lose code semantics)

return nil, errors.New("user not found")

Core Concepts

Deadlines and cancellation

Make every call bounded; enforce server-side timeouts for expensive handlers.

✅ Correct: require deadline

if _, ok := ctx.Deadline(); !ok {
    return nil, status.Error(codes.InvalidArgument, "deadline required")
}

Metadata

Use metadata for auth/session correlation, not for primary request data.

✅ Correct: read auth token from metadata

md, _ := metadata.FromIncomingContext(ctx)
auth := ""
if vals := md.Get("authorization"); len(vals) > 0 {
    auth = vals[0]
}

Interceptors (Middleware)

Use interceptors for cross-cutting concerns: auth, logging, metrics, tracing, request IDs.

✅ Correct: unary interceptor with request ID

func unaryRequestID() grpc.UnaryServerInterceptor {
    return func(ctx context.Context, req any, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (any, error) {
        id := uuid.NewString()
        ctx = context.WithValue(ctx, requestIDKey{}, id)
        resp, err := handler(ctx, req)
        return resp, err
    }
}

Streaming patterns

Server streaming (paginate or stream results)

✅ Correct: stop on ctx.Done()

func (s *Service) ListUsers(req *usersv1.ListUsersRequest, stream usersv1.UsersService_ListUsersServer) error {
    users, err := s.Repo.ListUsers(stream.Context(), int(req.GetPageSize()))
    if err != nil {
        return status.Error(codes.Internal, "internal error")
    }

    for _, u := range users {
        select {
        case <-stream.Context().Done():
            return stream.Context().Err()
        default:
        }

        if err := stream.Send(&usersv1.User{
            Id:          u.ID,
            Email:       u.Email,
            DisplayName: u.DisplayName,
        }); err != nil {
            return err
        }
    }
    return nil
}

Unary vs streaming decision

• Use unary for single request/response and simple retries.
• Use server streaming for large result sets or continuous updates.
• Use client streaming for bulk uploads with one final response.
• Use bidirectional streaming for interactive protocols.

Production Hardening

Health checks and reflection

Add health service; enable reflection only in non-production environments.

✅ Correct: health + conditional reflection

hs := health.NewServer()
grpc_health_v1.RegisterHealthServer(s, hs)

if env != "production" {
    reflection.Register(s)
}

Graceful shutdown

Prefer GracefulStop with a deadline.

✅ Correct: graceful stop

stopped := make(chan struct{})
go func() {
    grpcServer.GracefulStop()
    close(stopped)
}()

select {
case <-stopped:
case <-time.After(10 * time.Second):
    grpcServer.Stop()
}

TLS

Use TLS (or mTLS) in production; avoid insecure credentials outside local dev.

✅ Correct: server TLS

creds, err := credentials.NewServerTLSFromFile("server.crt", "server.key")
if err != nil { return err }

grpcServer := grpc.NewServer(grpc.Creds(creds))

Testing (bufconn)

Test gRPC handlers without opening real sockets using bufconn.

✅ Correct: in-memory gRPC test server

const bufSize = 1024 * 1024

lis := bufconn.Listen(bufSize)
srv := grpc.NewServer()
usersv1.RegisterUsersServiceServer(srv, &Service{Repo: repo})

go func() { _ = srv.Serve(lis) }()

ctx := context.Background()
conn, err := grpc.DialContext(
    ctx,
    "bufnet",
    grpc.WithContextDialer(func(context.Context, string) (net.Conn, error) { return lis.Dial() }),
    grpc.WithTransportCredentials(insecure.NewCredentials()),
)
if err != nil { t.Fatal(err) }
defer conn.Close()

client := usersv1.NewUsersServiceClient(conn)
resp, err := client.GetUser(ctx, &usersv1.GetUserRequest{Id: "1"})
_ = resp
_ = err

Anti-Patterns

• Ignore deadlines: unbounded handlers cause tail latency and resource exhaustion.

• Return string errors: map domain errors to codes.* with status.Error or status.Errorf.

• Stream without backpressure: stop on ctx.Done() and handle Send errors.

• Expose reflection in production: treat reflection as a discovery surface.

Troubleshooting

Symptom: clients see UNKNOWN errors

Actions:

• Return status.Error(codes.X, "...") instead of raw errors.
• Wrap domain errors into typed errors, then map to gRPC codes.

Symptom: slow/hanging requests

Actions:

• Require deadlines and propagate ctx to downstream calls.
• Add server-side timeouts and bounded concurrency in repositories.

Symptom: flaky streaming

Actions:

• Stop streaming on ctx.Done() and handle stream.Send errors.
• Avoid buffering entire result sets before sending.

Resources

• gRPC Go: https://github.com/grpc/grpc-go
• Protobuf Go: https://pkg.go.dev/google.golang.org/protobuf
• gRPC error codes: https://grpc.io/docs/guides/error/