Multisite support

[pdclark]

Multisite support basically comes down to three things:

The allowed path filter

class-404-template.php#L92
UBP checks to see if the requested $path from $_SERVER['REQUEST_URI'] contains $uploads['basedir'] with ABSPATH stripped out. So, for example, when requesting an image:

/wp-content/uploads/2012/10/image.jpg

$uploads['basedir'] without ABSPATH on a single site is:
wp-content/uploads
which exists in the requested path, so it passes.

On multisite, the requested $path would be:
/files/2012/10/image.jpg

But $uploads['basedir'] would be something like:
/wp-content/blogs.dir/3/files/ (where "3" is a blog ID)

So they don't match up. The check needs to be revised to accomidate multisite uploads directory path rewrites.

Download Path

class-404-template.php#L41
When an image is found, it's downloaded and saved to the local uploads directory. The download method, like allow_path, makes the assumption that the path to save the image to matches the path the image was requested from. In multisite, this isn't the case.

For example, single site:
image requested from: http://site.com/wp-content/uploads/2012/10/image.jpg
image saved to: ABSPATH.'/wp-content/uploads/2012/10/image.jpg'

But multisite:
image requested from: http://site.com/subsite/wp-content/uploads/2012/10/image.jpg
image saved to: ABSPATH.'/wp-content/blogs.dir/3/files/2012/10/image.jpg'

And "subsite" could also be a subdomain (subsite.site.com), or a mapped domain name. (subsite.com)

*Changes in 3.5 *

Trac ticket #19235

I haven't tested Nacin's final version of this in the 3.5 betas, but I'm pretty sure it's slated for release. Basically, in 3.5, there they'll be using wp-content/uploads/sites instead of wp-content/blogs.dir. wp_upload_dir() should account for this, but it of course needs to be tested, and the solutions for #1 and #2 need to be agnostic to whether they're running on 3.4- or 3.5+

To test any of these, you'd need to comment out the hook for requiring multisite to activate. But maybe you already did that? I was surprised to hear you activated the plugin on a multisite at all. Did it let you do it on the master site?

[Dreamsorcerer]

This seems to be working correctly for us on a multisite. The only thing that needed to be changed was the server rewriterule in the config/htaccess.

The default WP .htaccess has this:
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
Which essentially rewrites the path to strip out the subdirectory. The problem with this, is that when the file doesn't exist and it falls through to index.php the REQUEST_URI is still the original path. To solve this, change [L] to [P] which will perform a proxy redirect and use the rewritten URI instead. Note, you'll need to enable mod_proxy_http for this to work correctly.

Given that is all I needed to do to fix multisite support, can we replace the fail message with an admin notice that can instead give some tips on how to set it up?

[Dreamsorcerer]

My actual rules in a <Directory> block as part of a VirtualHost, in case anybody has any trouble (this has actually been tweaked to work with multisites that use multiple levels of subdirectories).

<IfModule mod_rewrite.c>
    RewriteEngine On

    # add a trailing slash to /wp-admin
    RewriteRule ^(.*/)?wp-admin$ $1wp-admin/ [R=301,L]

    RewriteCond %{REQUEST_FILENAME} -f [OR]
    RewriteCond %{REQUEST_FILENAME} -d
    RewriteRule ^ - [L]
    RewriteRule "/.+(/(wp-content|wp-admin|wp-includes|.*\.php$).*)" $1 [P]
    RewriteRule ^ /index.php [L]
</IfModule>

If you have SSL enabled, you'll also need to add to your SSL section:

SSLProxyEngine on