if not changed(url, properties, now):
# ETag didn't change, same content, just update headers
api.collections().update(uuid=item["uuid"], body={"collection":{"properties": properties}}).execute()
cr = arvados.collection.CollectionReader(item["portable_data_hash"], api_client=api)
if not changed(url, properties, now):
# ETag didn't change, same content, just update headers
api.collections().update(uuid=item["uuid"], body={"collection":{"properties": properties}}).execute()
cr = arvados.collection.CollectionReader(item["portable_data_hash"], api_client=api)