Trusted proxy cannot resolve hostname (docker), only IP or CIDR-ip

The problem

A Nextcloud instance running behind an NGINX reverse-proxy (both in Docker) cannot reliably trust the reverse proxy due to the IP-address of the reverse-proxy changing every time the containers are restarted. Normally one would use the container_name as the hostname, but the relevant code in Nextcloud cannot resolve hostnames - only IP addresses or CIDR-ranges. I have pinpointed the source of the problem - but do not know how to proceed/solve it.

Problem example

Relevant Nextcloud config.php part that does not work:

'trusted_proxies' =>
   array (
      0 => 'nginx_container_name',
   ),

Relevant Nextcloud config.php part that does work:

'trusted_proxies' =>
   array (
      0 => '192.168.160.4',
   ),

(192.168.160.4 is the IP of the nginx-proxy container within Docker, this changes every time one starts the Docker containers)

Problem source

The problem originates from lib/private/AppFramework/Http/Request.php#L607:

protected function matchesTrustedProxy($trustedProxy, $remoteAddress) {
   $cidrre = '/^([0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3})\/([0-9]{1,2})$/';

   if (preg_match($cidrre, $trustedProxy, $match)) {
      $net = $match[1];
      $shiftbits = min(32, max(0, 32 - intval($match[2])));
      $netnum = ip2long($net) >> $shiftbits;
      $ipnum = ip2long($remoteAddress) >> $shiftbits;

      return $ipnum === $netnum;
   }

   return $trustedProxy === $remoteAddress;
}

It cannot resolve trusted_proxy host names, only CIDR comparison or literal IP-comparison.

Examples in config where 'container_name' does work

For example in the DB or Redis configuration one can use the host name within docker:

'dbhost' => 'db_container_name',

'redis' =>
  array (
    'host' => 'redis_container_name',
    ...
  ),

The big question

Is it possible to add host name resolving to the lib/private/AppFramework/Http/Request.php code?
This would make Nextcloud in Docker work flawless without requiring 'overwritehost'/'overwriteprotocol'/etc.

Looking forward to anyone's thoughts on this.

Start with lib/private/AppFramework/Http/Request.php and the matchesTrustedProxy method identified in the issue. Check how trusted_proxies currently handles CIDR ranges and literal IPs, then determine the expected hostname behavior for Docker deployments while preserving existing comparisons. Done means a configured proxy hostname can be trusted reliably after container IP changes.