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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _UploadChunk(self, chunk):
 """Uploads a single chunk to the transfer store flow. Args: chunk: A chunk to upload. Returns: A `BlobImageChunkDescriptor` object. """

    blob = _CompressedDataBlob(chunk)

    self._action.ChargeBytesToSession(len(chunk.data))
    self._action.SendReply(blob, session_id=self._TRANSFER_STORE_SESSION_ID)

    return rdf_client_fs.BlobImageChunkDescriptor(
        digest=hashlib.sha256(chunk.data).digest(),
        offset=chunk.offset,
        length=len(chunk.data))