code: def _BuildStreamingResponse(self, binary_stream, method_name=None):
      
      precondition.AssertType(method_name, Text)
  
      # We get a first chunk of the output stream. This way the likelihood
      # of catching an exception that may happen during response generation
      # is much higher.
      content = binary_stream.GenerateContent()
      try:
        peek = content.next()
        stream = itertools.chain([peek], content)
      except StopIteration:
        stream = []
  
      response = werkzeug_wrappers.Response(
          response=stream,
          content_type="binary/octet-stream",
          direct_passthrough=True)
      response.headers["Content-Disposition"] = ((
          "attachment; filename=%s" % binary_stream.filename).encode("utf-8"))
      if method_name:
        response.headers["X-API-Method"] = method_name.encode("utf-8")
  
      if binary_stream.content_length:
        response.content_length = binary_stream.content_length
  
      return response
docs: Builds HTTPResponse object for streaming.