file_get_contents.async.php

<?php

function file_get_contents(string $pathname): string
{
    $result = '';
    $fp = fopen($pathname, 'rb');

    while (!feof($fp)) {
        $chunk = 1024;
        Fiber::getCurrent() && ($chunk = (Fiber::suspend() ?: 1024));
        $result .= fread($fp, $chunk);
    }

    return $result;
}