Summary: Some log readers care about the substring rather than the entire line, so fetching an entire line is optional.
Reviewed By: nqmtuan, marekcirkos
Differential Revision: D3035471
fb-gh-sync-id: d7727817f650a4c87dbfff59be6b7fe6136693de
shipit-source-id: d7727817f650a4c87dbfff59be6b7fe6136693de