<?php
declare(strict_types=1);

function requireJsonDocument(string $json): string
{
    if (strlen($json) > 65536) {
        throw new InvalidArgumentException('JSON exceeds the 64 KiB limit.');
    }
    if (!json_validate($json, 64)) {
        throw new InvalidArgumentException(json_last_error_msg());
    }
    return $json;
}

foreach (['{"enabled":true}', '{"enabled":}', 'null'] as $fixture) {
    try {
        echo requireJsonDocument($fixture), PHP_EOL;
    } catch (InvalidArgumentException $error) {
        echo 'Rejected: ', $error->getMessage(), PHP_EOL;
    }
}