# rpc error: code = Unimplemented desc = method /helloworld.Greeter/SayHello not implemented

- **ID:** `go/grpc-unimplemented-method-not-found`
- **Domain:** go
- **Category:** type_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

The server does not have a handler registered for the requested RPC method, often due to a mismatch between protobuf definitions and server implementation.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 1.0 | active | — | — |
| 1.1 | active | — | — |

## Workarounds

1. **Ensure the server registers the exact method from the protobuf service definition.** (95% success)
   ```
   type server struct {
    pb.UnimplementedGreeterServer
}
func (s *server) SayHello(ctx context.Context, req *pb.HelloRequest) (*pb.HelloReply, error) {
    return &pb.HelloReply{Message: "Hello " + req.Name}, nil
}
// Then register: pb.RegisterGreeterServer(grpcServer, &server{})
   ```
2. **Regenerate protobuf code and rebuild both client and server.** (90% success)
   ```
   protoc --go_out=. --go-grpc_out=. helloworld.proto
go build ./...
   ```

## Dead Ends

- **Restart the server without updating the protobuf definition.** — The server code is missing the method implementation; restarting does not add it. (100% fail)
- **Call a different method with similar name hoping it works.** — The client is designed to call a specific method; using another may cause data inconsistency. (95% fail)