DNS Validation Issue

[BenHarris]

I hit an issue today where the DNS validation wasn't working. It looks like there is a bug in alpine Linux (I was using the php:7.4-fpm-alpine docker image), which means checkdnsrr returns true even if the domain doesn't exist. See the bug reports below:

• https://bugs.php.net/bug.php?id=78008
• https://gitlab.alpinelinux.org/alpine/aports/-/issues/7392

Whilst I appreciate this is not a bug in this library, I wonder if it might be worth switching to dns_get_record in DNSCheckValidation instead, which is unaffected, allows us the same validation and was also somewhat faster in my tests.

dns_get_record returns an array or false, so the equivalent implementation would just be to do something like $MXresult = !empty(dns_get_record($host, DNS_MX));

Invalid domain test

Function	Result	Runtime
checkdnsrr('notavaliddomain.c2.', 'MX')	bool(false)	0.00630
dns_get_record('notavaliddomain.d2.', DNS_MX)	array(0){}	0.00497

Valid domain

Function	Result	Runtime
checkdnsrr('google.com.', 'MX')	bool(true)	0.00152
dns_get_record('google.com.', DNS_MX)	array(5) { [0]=> array(6) { ["host"]=> string(10) "google.com" ["class"]=> string(2) "IN" ["ttl"]=> int(600) ["type"]=> string(2) "MX" ["pri"]=> int(40) ["target"]=> string(23) "alt3.aspmx.l.google.com" } ... }	0.00115

[BenHarris]

Another benefit to this approach would be handling the "Null MX" case RFC 7505.

checkdnsrr('example.com.', 'MX') returns bool(true) as the MX record exists. As there is no target, it should be considered invalid and return false. dns_get_record() returns the DNS records, so we can simply validate that a) there is an MX record and b) it is a valid record.

[egulias]

Hi @BenHarris ,
Thanks for informing about this issue.
I see the benefits you state and i'd be a great improvement for that validation.
I encourage you to do the change and send a PR ;), I will be more than happy to review and merge.

Looking forward to that PR!

[egulias]

I'll do the port to V3.