URL aliases: racing conditions and existing directories

Creating URL aliases on a Drupal site is a piece of cake. Core path in combination with pathauto and token modules are a real winner. However, there are some annoying cases which you should look out for because they can lead to painfull debugging sessions - especially when you've already encountered them in the past but totally forgot those. So for myself and all of you out there, here are 2 - in some way funny - URL alias pitfalls.

1. Existing directories

When you download Drupal and look at the root folder, you see a couple of subfolders like 'misc', 'sites', 'includes' etc. After installing, go to example.com/sites and you'll get the 403 forbidden page served by Apache (I assume the same happens on other webservers). This means you can't actually create an URL alias for a node (or a view, etc ..) called 'sites' or any of those other subfolders. The .htaccess will not rewrite to index.php?q= to lookup an existing path in your Drupal site or throw a 404 in case it doesn't exist. I've been experimenting with rewrite rules and while following code in the .htaccess will process the request for 'sites', do not use this in production because other http requests for images, javascript and css files in the sites/*/ folders will fail.

# Again, don't use this in production!
RewriteCond %{REQUEST_URI} "/sites/"
RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]

I gave up after a while - needed to solve this for a client - and simply renamed the URL alias for now. If anyone has a better idea, please let us know in the issue on d.o dedicated to this problem.

2. Racing conditions

This is really easy to reproduce: install the views module and enable the default frontpage view. Surf to example.com/frontpage and you'll get a list of all nodes promoted to frontpage. Now create a node and fill in 'frontpage' as the URL alias. You will be redirected to example.com/frontpage and you'll see your node instead of the view you have just enabled and there is absolutely no way to get back to that view unless you rename the alias of the node you've just created. This behaviour is very normal if you look at the code of drupal_lookup_path which is called by drupal_init_path in the bootstrap trying to rewrite the $_GET['q'] variable before menu_execute_active_handler() can find a path in the menu_router table. As with my first case, I simply had to rename the URL alias again to get my view back.

Any other pitfalls people know of ? Let me know!


dalin on Sun, 04/07/2010 - 06:21

Fun debugging.

Though the second case isn't really a race condition:

It's the by-design system where Drupal allows you to override stuff.

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