StreamObserver for the request messages.StreamObserver.ServerCallHandler for a streaming request call method of the service.StreamObserver.ServerCallHandler for a unary request call method of the service.Iterator of request messages.Iterator over the
response stream.ServerMethodDefinition.MethodDescriptor for a given method.ListenableFuture for the first value received from the stream.ServerCallHandlers to application service implementation,
meant to be used by the generated code.StreamObserver used in testing.ListenableFuture to the response.