How to initialize WP_Filesystem object?

What method does plugin upgrades choose?

Apache having read/write access to the directory is not enough to cause the direct class to be initialized, This is due to the class checking file ownership as well as RW attributes.

The cause for ownership testing is mainly related to Shared Hosting. On some shared hosts, infact, many shared hosts, Apache will have write access to the users folders. This in itself is not a problem, but when combined with the host using mod_php or fcgi without suPHP/suExec, this results in ALL users on the server being able to write to other directories. Limiting it to only creating the files if the ownership matches allows us to somewhat, mitigate some of these poor security hosts, If the file is owned by apache, then other users can surely Write to the file, If it’s owned by the user, say, dd32, and we apply RW/Owner, R/Group, R/World (644) this results in other users on the server not being able to modify the .php files. Directly modifying the files has been the root cause of many hoster/server-wide exploitation attacks in the last few years.

Now, As for what you need to pass WP_Filesystem() to get it to return a Direct context on a server which nativly supports it in wordpress: Nothing, It’ll automatically select it, and in your case, it sounds like WordPress has decided using the Direct class is not an option.

You may want to have a read of this function: http://core.trac.wordpress.org/browser/trunk/wp-admin/includes/class-wp-upgrader.php#L64

and you may also want to look at the selection method: get_filesystem_method() – http://core.trac.wordpress.org/browser/trunk/wp-admin/includes/file.php#L816 specifically, the filter there, ‘filesystem_method’

If you wish to force it, then my suggestion would be something such as this, But i fear it may still cause issues if something else is using WP_Filesystem on the same page load.

function _return_direct() { return 'direct'; }
add_filter('filesystem_method', '_return_direct');
WP_Filesystem();
remove_filter('filesystem_method', '_return_direct');