TLDR: When using horde/mail_autoconfig or other features using pear/net_dns2 under PHP 8.x, use the “master” branch or wait for a release of version 1.5.3 or higher.

While upgrading the Maintaina Horde codebase for PHP 8.1, I stumbled upon a problem:

[Sun May 15 12:15:15.026499 2022] [php:error] [pid 156] [client 172.23.0.1:43894] PHP Fatal error:  Uncaught ValueError: fread(): Argument #2 ($length) must be greater than 0 in /srv/www/horde/vendor/pear/net_dns2/Net/DNS2/Cache/File.php:147\nStack trace:\n#0 /srv/www/horde/vendor/pear/net_dns2/Net/DNS2/Cache/File.php(147): fread()\n#1 [internal function]: Net_DNS2_Cache_File->__destruct()\n#2 {main}\n  thrown in /srv/www/horde/vendor/pear/net_dns2/Net/DNS2/Cache/File.php on line 147, referer: http://localhost/horde/admin/config/config.php

It turns out Net_DNS2 as of latest version 1.5.2 has a problem in its filesystem cache when run under PHP 8.x – it tries to read the cache file content even if the file size is 0 or the file does not yet exist. In PHP 8.x this yields a ValueError because reading with a length 0 should not be attempted.

Mike Pultz, the maintainer of Net_DNS2 already has a fix in his master branch. I have kindly asked him to release a stable version with this fix. However I understand it may take a while or may not be very high on the daily priority list of todos. I am not sure what other changes the master branch contains which might impair its usefulness to your use case. I am hesitant to put work into a problem somebody else already fixed. I will only provide a downstream-packaged version in case no update happens within reasonable time.