limit the chunks that we send over PB to 128k, since it has a hardwired
        string-size limit of 640k.

def _chunkForSend(self, data):
        """
        limit the chunks that we send over PB to 128k, since it has a hardwired
        string-size limit of 640k.
        """
        LIMIT = self.CHUNK_LIMIT
        for i in range(0, len(data), LIMIT):
            yield data[i:i + LIMIT]