def CheckHash(self, responses):
    """Adds the block hash to the file tracker responsible for this vfs URN."""
    index = responses.request_data["index"]

    if index not in self.state.pending_files:
      # This is a blobhash for a file we already failed to read and logged as
      # below, check here to avoid logging dups.
      return

    file_tracker = self.state.pending_files[index]

    hash_response = responses.First()
    if not responses.success or not hash_response:
      urn = file_tracker["stat_entry"].pathspec.AFF4Path(self.client_urn)
      self.Log("Failed to read %s: %s", urn, responses.status)
      self._FileFetchFailed(index, responses.request.request.name)
      return

    file_tracker.setdefault("hash_list", []).append(hash_response)

    self.state.blob_hashes_pending += 1

    if self.state.blob_hashes_pending > self.MIN_CALL_TO_FILE_STORE:
      self.FetchFileContent()
Adds the block hash to the file tracker responsible for this vfs URN.