code: def read_body(response, max_bytes=None):
      
      finished = Deferred()
      response.deliverBody(TruncatingReadBodyProtocol(
          response.code, response.phrase, finished, max_bytes))
      return finished
docs: Return a `Deferred` yielding at most *max_bytes* bytes from the
      body of a Twisted Web *response*, or the whole body if *max_bytes*
      is `None`.