DNS Checking on OS X

[technosailor]

Seems OS X Server chokes on checkdnsrr(). We only use this on registration so it should be low impact. This patch adds a new $is_osx global variable and patched the validate_email() function where DNS checking is done.

In versions of WPMU <= 2.9.x, the $check_dns argument for validate_email() was set to true by default. With WPMS, the argument is set to false which solves most of core's issues. However, this patch also overrides this argument in case plugin developers need it on OS X server.

[nacin]

We don't use $check_dns anywhere in core at this point, except for the deprecated validate_email(). We added them just because we could in #9316, but if it's going to cause environment issues, is it something still worth it to keep in core?

[technosailor]

In that case, rip it out.

[nacin]

Can you confirm you're running PHP 5+ but less than PHP 5.2.9? Looks like it may have been fixed there, per ​http://mu.wordpress.org/forums/topic/12710 and ​http://bugs.php.net/46873.

It also doesn't seem to affect PHP4, only PHP5. I'm wondering if we can simply add a filter that a plugin can use to force $check_dns to false.

[technosailor]

Yeah that bug was fixed by Scott MacVicar (@scottmac) after I talked to him about it. It is fixed in PHP 5.3. If $check_dns is fault, regardless of PHP support, we should remove it. Worst case we use a filter but I don't see the benefit of keeping it. Even when we do require PHP5, we probably won't jump to PHP 5.3 immediately and, by the numbers, most people actually do use PHP5. Not worth risking it.

[nacin]

(In [14381]) Deprecate checkdnsrr from is_email. Unused in core, and wonky on some server setups (Mac OS X < PHP 5.3 specifically). A plugin can always add it back. props technosailor, fixes #12503.