Bug #73518 [Opn->Fbk]: gethostbyaddr unnecessarily attempts to resolve the domain name back to IP addr

Edit report at https://bugs.php.net/bug.php?id=73518&edit=1 ID: 73518 Updated by: requinix@php.net Reported by: teo8976 at gmail dot com Summary: gethostbyaddr unnecessarily attempts to resolve the domain name back to IP addr -Status: Open +Status: Feedback Type: Bug Package: HTTP related Operating System: linux PHP Version: 5.6.28 Block user comment: N Private report: N New Comment: https://github.com/php/php-src/blob/PHP-5.6.28/ext/standard/dns.c#L153 As you can see PHP calls gethostbyaddr(3) and only does so once. Do you have any evidence to support the claim that there are two lookups? Is there something on your system, or in an upstream DNS server, that is responsible instead of PHP? Previous Comments: ------------------------------------------------------------------------ [2016-11-20 20:32:05] php at duncanc dot co dot uk I don't think this is a PHP issue. As far as I'm aware this functionality comes from a C library (libc) ------------------------------------------------------------------------ [2016-11-14 20:32:11] teo8976 at gmail dot com Description: ------------ When you call gethostbyaddr($someip), it does 2 DNS lookups: 1 - looks up the IP to find the corresponding domain name, i.e. does its job 2 - then looks up the domain name, as if it needed to find the corresponding IP address The second is completely unnecessary, especially considering that, if it times out, it nonetheless returns the host name found at step 1 (if, in this case, it returned false or the IP address, one may perhaps argue that it makes sense in order to verify that the host name is correct or something). Test script: --------------- <?php echo gethostbyaddr('95.232.181.106'); Expected result: ---------------- should immediately print: host106-181-dynamic.232-95-r.retail.telecomitalia.it At http://mxtoolbox.com/SuperTool.aspx?action=ptr%3a95.232.181.106&run=toolpage# you can verify that it takes a fraction of a second to do the reverse lookup Actual result: -------------- From most servers, it takes more than 15 seconds (I guess it depends on how long it takes for the DNS resolver to time out), and then it prints the expected domain name. Apparently, there is something wrong with this domain which prevents the name from being resolved to an IP: http://mxtoolbox.com/SuperTool.aspx?action=a%3ahost106-181-dynamic.232-95-r.retail.telecomitalia.it&run=toolpage However, as explained above, the name->IP lookup is completely unnecessary. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=73518&edit=1