What is the role of a gRPC stub?

A gRPC stub (also called a client stub or simply "client") is the auto-generated client-side code that provides a local interface to call remote gRPC service methods as if they were local functions. When you compile a .proto file with protoc and the gRPC plugin, it generates stub code in your target language. The stub handles: serializing method arguments to Protobuf, establishing the HTTP/2 connection, sending the request, receiving and deserializing the response, managing stream lifecycle, and propagating errors and metadata. There are two types of stubs in some languages: blocking stubs (synchronous calls that block the thread until the response arrives) and async stubs (non-blocking calls using futures, callbacks, or coroutines). The stub abstracts all network details, letting developers call remote methods with the same syntax as local ones.