How Does gRPC's `mustEmbedUnimplemented` Enhance Server Forward Compatibility?

Forward Compatibility in gRPC with mustEmbedUnimplemented*

The gRPC-go library has introduced the mustEmbedUnimplemented*** method to enhance forward compatibility in server implementations.

In the past, gRPC servers would fail compilation if required methods were not implemented. To mitigate this, developers had to manually implement unimplemented methods, even if they were not intended to be used.

mustEmbedUnimplemented* solves this issue by making forward compatibility opt-out. This means that:

• Servers must now explicitly embed Unimplemented*** interfaces to opt out of forward compatibility.
• By embedding Unimplemented***, servers will not receive compile-time errors for missing method implementations, but will instead fail at runtime if unimplemented methods are called.

For example, if you have a GreetService interface:

type GreetService interface {
    Greet(ctx context.Context, req *pb.GreetRequest, opts ...gax.CallOption) (*pb.GreetResponse, error)
}

You would previously implement it as:

type server struct {...}
func (s *server) Greet(ctx context.Context, req *pb.GreetRequest, opts ...gax.CallOption) (*pb.GreetResponse, error) {...}
func (s *server) MustEmbeddUnimplementedGreetServiceServer() {...}

Now, with mustEmbedUnimplemented***, you can opt out of forward compatibilty by embedding Unsafe*** interfaces instead:

type server struct {
    grpc.UnsafeGreetServiceServer
    ...
}

This change provides greater flexibility and prevents unnecessary code in your server implementations.

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