แจกโค้ดตรวจสอบว่าสตริงนั้น base64 encode ถูกต้องหรือไม่

function isValidBase64($string): bool
{
    if (!is_string($string)) {
        return false;
    }

    $decoded = base64_decode($string, true);

    if (false === $decoded) {
        return false;
    }

    if (false === json_encode($decoded)) {
        return false;
    }
    unset($decoded);

    return true;
}// isValidBase64

$strings = [
    'NTU1NQ==' => true,
    'dGVzdA==' => true,
    'aGVsbG8=' => true,
    '4Liq4Lin4Lix4Liq4LiU4Li1' => true,
    '5555' => false,
    'test' => false,
    'hello' => false,
    'สวัสดี' => false,
];

assert_options(ASSERT_BAIL, 1);
foreach ($strings as $string => $assert) {
    $decoded = base64_decode($string);
    $isValid = isValidBase64($string);
    echo '<strong>' . $string . '</strong> decoded: ' . str_replace(['<', '>'], ['&lt;', '&gt;'], (var_export($decoded, true))) . '<br>' . PHP_EOL;
    echo '&nbsp; is valid: ' . ($isValid === true ? '<span style="color: green;">YES</span>' : '<span style="color: red;">NO</span>') . '<br>' . PHP_EOL;
    assert($isValid === $assert, 'Failed assert for ' . $string);
}