async def dump_blob(writer, elem, elem_type, params=None):
elem_is_blob = isinstance(elem, x.BlobType)<EOL>data = bytes(getattr(elem, x.BlobType.DATA_ATTR) if elem_is_blob else elem)<EOL>await dump_varint(writer, len(elem))<EOL>await writer.awrite(data)<EOL>
Dumps blob to a binary stream

:param writer:
:param elem:
:param elem_type:
:param params:
:return: