ServerReflection doesn't respond with transitive dependencies as its supposed to by the standard

[renbou]

As seen in the implementation of gRPC reflection inside grpclib, only the single requested file descriptor proto is returned instead of the whole transitive dependency chain:

grpclib/grpclib/reflection/service.py

Lines 57 to 67 in 3c0fa03

	def _file_descriptor_response(
	self,
	file_descriptor: FileDescriptor,
	) -> ServerReflectionResponse:
	proto = FileDescriptorProto()
	file_descriptor.CopyToProto(proto) # type: ignore
	return ServerReflectionResponse(
	file_descriptor_response=FileDescriptorResponse(
	file_descriptor_proto=[proto.SerializeToString()],
	),
	)

It is specified in the gRPC reflection design doc and in the proto definition that File* queries should return the whole dependency chain, since otherwise it's pretty much impossible to use the returned descriptors. Of course this isn't a massive problem for the base case where a file imports some well-known protos, wrapperspb for example, but if a file depends on other files, then they aren't returned and the whole process fails. This pretty much means that the reflection client has to manually go requesting for each of the dependencies, which isn't really a solution when the dependency chain is large (proto by default supports dependency chains up to 10k in length).

Is this something that can be resolved in grpclib? This is honestly the only usable gRPC library for Python :P

[vmagamedov]

Our reflection implementation was written by using grpcio-reflection as a reference. Maybe you can point where it currently differs from original implementation or even create a PR with a fix?