Faraday.Flushed_reasontype t = | Shiftshift t was called, normally indicating that bytes were written successfully.
| Draindrain t was called, normally indicating that the downstream consumer of t's bytes stopped accepting new input.
| Nothing_pendingPassed to f when flush_with_reason t f is called when there is not any pending output, so t is considered immediately flushed.
Indicates why a flush callback was called.