How Does `mustEmbedUnimplemented*` in gRPC-go Ensure Forward Compatibility for Server Implementations?

MustEmbedUnimplemented* Methods in gRPC for Forward Compatibility

grpc-go has recently introduced the mustEmbedUnimplemented* method to ensure forward compatibility in server implementations. Previously, server implementations could register a service without implementing all the methods defined in the proto definition. This led to cases where new methods added to the proto would result in compile-time errors due to missing implementations in the server.

With the mustEmbedUnimplemented* method:

• Forward-compatibility: Server implementations must now embed Unimplemented*ServiceServer, allowing for the addition of new methods without compile-time errors. However, any attempt to call an unimplemented method will result in a run-time error with code.Unimplemented.
• Opt-out: Developers can opt out of forward-compatibility by embedding Unsafe*ServiceServer instead. This will avoid run-time errors but retain compile-time errors in cases of unimplemented methods.

For example:

// Implements gRPC FooBarServiceServer
type FooBarService struct {
    grpc.UnsafeFooBarServiceServer // Opt out of forward compatibility
    // other fields
}

To disable forward-compatibility in code generation:

protoc --go-grpc_out=require_unimplemented_servers=false:.

The mustEmbedUnimplemented* method ensures that server implementations are always up to date with the latest proto definition, preventing potential inconsistencies. It provides a graceful way to add new methods without breaking existing code while still maintaining backwards compatibility.

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