To read byte wise and multi line you can check the line_buffer from readline_info:

<?php

function read(int $count, string $prompt = null): string
{
    $previous = '';
    readline_callback_handler_install($prompt ?? " \e[D", function ($str) use (&$previous) {
        $previous .= $str . PHP_EOL;
    });
    do {
        $r = array(STDIN);
        $n = stream_select($r, $w, $e, null);
        if ($n && in_array(STDIN, $r)) {
            readline_callback_read_char();
            $str = $previous . readline_info('line_buffer');
        }
    } while (mb_strlen($str) < $count); // use strlen if you need the exact byte count
    readline_callback_handler_remove();

    return $str;
}