htaccess 301 redirect not working

Question

I'm trying to add a simple 301 rule to the .htaccess file of a codeigniter site.

redirect 301 /newsletter http://sub.domain.com/newsletters/may2010

When I visit http://sub.domain.com/newsletter the redirect goes to

http://sub.domain.com/newsletters/may2010/?/newsletter

I'm not sure where the ?/newsletter is coming from. Full .htaccess file:

<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteBase /    

    redirect 301 /newsletter http://sub.domain.com/newsletters/may2010

    #Removes access to the system folder by users.
    #Additionally this will allow you to create a System.php controller,
    #previously this would not have been possible.
    #'system' can be replaced if you have renamed your system folder.
    RewriteCond %{REQUEST_URI} ^system.*
    RewriteRule ^(.*)$ /index.php?/$1 [L]

    #Checks to see if the user is attempting to access a valid file,
    #such as an image or css document, if this isn't true it sends the
    #request to index.php
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule ^(.*)$ index.php?/$1 [L]
</IfModule>



<IfModule !mod_rewrite.c>
    # If we don't have mod_rewrite installed, all 404's
    # can be sent to index.php, and everything works as normal.
    # Submitted by: ElliotHaughin

    ErrorDocument 404 /index.php
</IfModule>

#####################################################
# CONFIGURE media caching
#
Header unset ETag
FileETag None
<FilesMatch "(?i)^.*\.(ico|flv|jpg|jpeg|png|gif|js|css)$">
Header unset Last-Modified
Header set Expires "Fri, 21 Dec 2012 00:00:00 GMT"
Header set Cache-Control "public, no-transform"
</FilesMatch>
#
#####################################################

<IfModule mod_deflate.c>
<FilesMatch "\.(js|css)$">
SetOutputFilter DEFLATE
</FilesMatch>
</IfModule>

How can I fix this?

Answer 1

Heh, this is Apache pulling a sneaky order-of-processing trick on you. As it turns out, the fact that you put your Rewrite command at the top of the file doesn't mean that it's what's actually executed first. What happens instead is that mod_rewrite is run first, followed by mod_alias (which is responsible for handling your Rewrite).

This results in the following transformation, per mod_rewrite:

newsletter --> index.php?/newsletter

mod_rewrite happily sets the query string to ?/newsletter, but because you don't have the PT flag specified, does not passthrough the rewritten URL index.php to mod_alias. Therefore, mod_alias still sees the /newsleter path, redirects it to http://sub.domain.com/newsletters/may2010, and appends the (now changed) query string ?/newsletter to the end to seal the deal. Fun stuff, right?

Anyway, a quick-fix for this scenario would be to ignore requests for just newsletter:

#Checks to see if the user is attempting to access a valid file,
#such as an image or css document, if this isn't true it sends the
#request to index.php
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !newsletter$
RewriteRule ^(.*)$ index.php?/$1 [L]