php-curl times out when calling a php on the same domain - php-curl

Question

I do have a very strange problem where I cannot find any way for debugging. I have a server running Arch Linux, Apache 2.4 and PHP versions 7.4, 8.0 and recent 8.1 as php-fpm. All PHP configurations are identically (modules and configs). But 8.1 has a very strange behaviour regarding php-curl.
I install this php (curltest.php) on my server:
<?php
// this was the originally intended code:
// define ('HTTP_URL', 'https://'.$_SERVER['HTTP_HOST'].'/curltest.php?test=1');
// this doeas not work, too:
define ('HTTP_URL', 'https://'.$_SERVER['HTTP_HOST'].'/any_php_script.php');
// all commented following lines are for testing if $_GET is the cause
// if (empty($_GET['test'])) {
$curlHandle = curl_init();
$fp = fopen('/tmp/error.txt', 'w+');
curl_setopt_array($curlHandle, array(
CURLOPT_URL => HTTP_URL,
CURLOPT_VERBOSE => true,
CURLOPT_STDERR => $fp,
CURLOPT_FAILONERROR => false,
CURLOPT_FOLLOWLOCATION => true,
CURLOPT_CONNECTTIMEOUT => 5,
CURLOPT_TIMEOUT => 5,
CURLOPT_RETURNTRANSFER => true
));
$response = curl_exec($curlHandle);
if (curl_errno($curlHandle)) {
$response = 'Curl error: ' . curl_error($curlHandle);
}
curl_close($curlHandle);
//} else {
$response = 'Erfolg';
//}
echo $response;
The script works perfectly if I run it with PHP 7.4 and 8.0. If I use PHP8.1 I get a "timeout" - no response, nothing in the logs. I dug a bit deeper and tested with calling a text or html file instead of the script itself: this works flawlessly. If I call another php on the same domain the issue pops up again. But if I call a php on the same server but a different domain it works! So the problem only exists:
when using PHP 8.1 (8.1.13-1)
calling a php script which resides on the same domain as my testscript
So it cannot be a dns issue (calling text or html files is working). And it cannot be a problem that I cannot access php via a php-curl: using different domain (on the same server running the same php version) is also working. Any hint for debugging this is welcome.
As already stated I tested with different file types and different domains (on the same server using the same php version). I increased php log level and activated curl to be verbose writing STDERR to file output without success.

Answer 1

You are getting a timeout because you are running in an endless loop. It looks like in that one setup the $_GET variable is not populated and so the if condition always evaluates to true, opening another curl request.
The reason for this can be a misconfiguration of variables_order (php.ini) or FPM parameters (sometimes in a file like fastcgiparams or fastcgi_param params in nginx).
You can verify this by putting a small message after opening the error log:
fwrite($fp, 'Opening socket ' . (string)$curlHandle . PHP_EOL);
Make sure you got G in ini_get('variables_order');