WP Object Cache global can be easily hijacked, so some functions return fatal errors

[wonderboymusic]

I noticed this when uploading images in Multisite mode with Memcached WP Object Cache backend installed - cache methods produce fatal errors because the $wp_object_cache global var has been hijacked and the competing class doesn't implement the same methods as the built-in WP cache class

A good long-term solution would be to require any WP Object Cache class to implement the same interface (fat chance), so in the meantime, I have hardened all of the cache functions so they can't call a method that the referenced at runtime WP_Object_Cache class doesn't have

[wonderboymusic]

Patch for this ticket

[dd32]

I would argue that this is part of the life of using "advanced dropins" - to ensure that they're kept up to date when you upgrade core.

All the methods/functions which you've patched here, are ideally, a "core functionality" of the class and are required.. When new functionality is introduced, the best has been done to prevent fataling completely: ​through the usage of function_exists().

If anything, My only thought here is that dropins should have some kind of update notification - perhaps tied into a plugin, like most caching plugins do.

[ryan]

Alternative caches should be using object-cache.php thus avoiding cache.php being loaded at all.

The Memcached and APC backends maintained by myself and Mark do have the same public interfaces as core. Direct access through $wp_object_cache is not public, but we generally try to keep that API in sync too. If there are bugs here, let's fix them in memcached and apc.

[mikeschinkel]

Replying to dd32:

I would argue that this is part of the life of using "advanced dropins" - to ensure that they're kept up to date when you upgrade core.

Related #21412