docs: def AppendContent(self, src_fd):
      """Create new blob hashes and append to BlobImage.
  
      We don't support writing at arbitrary file offsets, but this method provides
      a convenient way to add blobs for a new file, or append content to an
      existing one.
  
      Args:
        src_fd: source file handle open for read
  
      Raises:
        IOError: if blob has already been finalized.
      """
      while 1:
        blob = src_fd.read(self.chunksize)
        if not blob:
          break
  
        blob_id = data_store.BLOBS.WriteBlobWithUnknownHash(blob)
        self.AddBlob(blob_id, len(blob))
  
      self.Flush()