code: def request_handler_fn(self, request, **kwargs):
      self.requests_handled.append(request)
  
      async def task():
          rand_sleep = random.uniform(0.1, 0.6)
          await asyncio.sleep(rand_sleep)
          docs = request.docs
          docs[0].tags["request_handled"] = True
          request.data.docs = docs
          return request
  
      future = asyncio.ensure_future(task())
      return future, None
  
file_path: jina/tests/unit/serve/stream/test_stream.py
imports: import asyncio
  import random
  import pytest
  from docarray import Document, DocumentArray
  from jina.helper import Namespace, random_identity
  from jina.serve.stream import RequestStreamer
  from jina.types.request.data import DataRequest
label_desc: Use image node_id 2 for calling the RequestStreamerWrapper obj's underlying member method code with example usage: obj.request_handler_fn(request) and returns: future,  None, request