@Override
            public void onCompleted() {
                if (!dispatcher.isCancelled()) {
                    // Tell the dispatcher that all input has been received.
                    dispatcher.completeInput();
                }
            }
True bi-directional streaming. Processes requests as they come in. Begins streaming results
immediately.
grpc/src/test/java/com/linecorp/armeria/internal/common/grpc/TestServiceImpl.java