Apache mod_rewrite and question marks "?"

Quick note to self in case I (inevitably) forget later. If you are using Apache mod_rewrite to make nice, clean URLs, and are also supporting JSONP, you may run into the situation where you have code that wants to append "?callback=xxx" to your URL (e.g., a cross-domain AJAX call in jQuery). Imagine you have a nice clean URL /user/123, which actually corresponds to user.php?id=123. If you append ?callback=xxx to the URL then chances are the code will break, because mod_rewrite will rewrite the URL to something like user.php?id=123?callback=xxx. What you actually want to send to your web server is user.php?id=123&callback=xxx (note the & before "callback"). After much grief trying to figure out how to coerce Apache mod_rewrite into handling this situation I found the answer, of course, on Stack Overflow. If you use the [QSA] flag, Apache will append the additional callback parameter onto the end of the rewritten URL, so JSONP will now work. Once again, Stack Overflow turned a show-stopper into a learning experience.

Rewriting DOIs

One problem with my cunning plan to use Mediawiki REDIRECTs to handle DOIs is that some DOIs, such as those that BioOne serves based on SICIs contain square brackets, [ ], which conflicts with wiki syntax. For example, doi:10.1206/0003-0090(2006)297[0001:TATOL]2.0.CO;2 I want to enable users to enter a raw DOI, so I've been playing with a simple URL rewrite in Appache httd.conf, namely:

RewriteRule ^/wiki/doi:(.*)\[(.*)\](.*)$ /w/index.php?title=Doi:$1-$2-$3 [NC,R]

This rewrites the [ and ] in the original DOI, then forces a new HTTP request (hence the [NC,R] at the end of the line). This keeps Mediawiki happy, at the cost of the REDIRECT page having a DOI that looks a slightly different from the original. However, it means the user can enter the original DOI in the URL, and not have to manually edit it.