storage_api.py 文件源码

def _get_segment(self, start, request_size, check_response=True):
    """Get a segment of the file from Google Storage.

    Args:
      start: start offset of the segment. Inclusive. Have to be within the
        range of the file.
      request_size: number of bytes to request. Have to be small enough
        for a single urlfetch request. May go over the logical range of the
        file.
      check_response: True to check the validity of GCS response automatically
        before the future returns. False otherwise. See Yields section.

    Yields:
      If check_response is True, the segment [start, start + request_size)
      of the file.
      Otherwise, a tuple. The first element is the unverified file segment.
      The second element is a closure that checks response. Caller should
      first invoke the closure before consuing the file segment.

    Raises:
      ValueError: if the file has changed while reading.
    """
    end = start + request_size - 1
    content_range = '%d-%d' % (start, end)
    headers = {'Range': 'bytes=' + content_range}
    status, resp_headers, content = yield self._api.get_object_async(
        self._path, headers=headers)
    def _checker():
      errors.check_status(status, [200, 206], self._path, headers,
                          resp_headers, body=content)
      self._check_etag(resp_headers.get('etag'))
    if check_response:
      _checker()
      raise ndb.Return(content)
    raise ndb.Return(content, _checker)