The containing class is available as
IO\ReadHandle in the www repository.
Read until there is no more data to read
public function readAllAsync( ?int $max_bytes = NULL, ?int $timeout_ns = NULL, ): Awaitable<string>;
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.
$max_bytes may be allocated in a buffer; large values may lead to
unnecessarily hitting the request memory limit.
?int $max_bytes = NULL
?int $timeout_ns = NULL