Read a fixed amount of data
public function readFixedSizeAsync( int $size, ?int $timeout_ns = NULL, ): Awaitable<string>;
Will fail with
EPIPE if the file is closed before that much data is
It is possible for this to never return, e.g. if called on a pipe or or socket which the other end keeps open forever. Set a timeout if you do not want this to happen.
?int $timeout_ns = NULL