<?php
/*  debug_update.php  – verbosely logs a DynDNS call from the FRITZ!Box
 *  Drop it next to your existing update.php.
 *  chmod 640 and make it readable by the web server user (nobody, lsadm, …)
 */

$logFile = '/tmp/fritz_dyndns.log';          // writeable by webserver
$now     = date('c');

/* ---- collect request data ------------------------------------------ */

$lines   = [];
$lines[] = "==== $now =================================================";
$lines[] = 'REMOTE_ADDR='.($_SERVER['REMOTE_ADDR'] ?? '');
$lines[] = 'REQUEST_URI='.$_SERVER['REQUEST_URI'];
$lines[] = 'REQUEST_METHOD='.$_SERVER['REQUEST_METHOD'];
$lines[] = '-- HEADERS ------------------------------------------------';
foreach (getallheaders() as $k => $v) {
    $lines[] = "$k: $v";
}
$lines[] = '-- GET ----------------------------------------------------';
foreach ($_GET as $k => $v) {
    $lines[] = "$k = $v";
}
$lines[] = '-- AUTH ---------------------------------------------------';
$lines[] = 'PHP_AUTH_USER='.($_SERVER['PHP_AUTH_USER'] ?? '');
$lines[] = 'PHP_AUTH_PW  ='.($_SERVER['PHP_AUTH_PW']   ?? '');
$lines[] = "================================================================\n";

/* ---- write log atomically ----------------------------------------- */

file_put_contents($logFile, implode("\n", $lines), FILE_APPEND | LOCK_EX);

/* ---- minimal DynDNS response so the box thinks “success” ---------- */

$ip = $_GET['myip'] ?? $_SERVER['REMOTE_ADDR'];
if (!filter_var($ip, FILTER_VALIDATE_IP)) {
    echo "911 bad ip\n";                     // Box will log Fehlergrund 13
    exit;
}

echo "good $ip\n";                           // makes the box think update OK