redirect /app.php to prevent duplicate content

This time it's compatible with Apache < 2.3.9 by not using the END flag. It also features default compatibility with apache aliases (inspired by Zend). And it improves the rewriting performance for the homepage by preventing the process to apply to each DirectoryIndex file

Author: Tobion

web/.htaccess

@@ -1,10 +1,36 @@
 <IfModule mod_rewrite.c>
     RewriteEngine On
 
-    #<IfModule mod_vhost_alias.c>
-    #    RewriteBase /
-    #</IfModule>
+    # This reduces the matching process for the startpage (path "/") because
+    # otherwise apache will apply the rewritting rules to each configured
+    # DirectoryIndex file needlessly (e.g. index.php, index.html, index.pl).
+    DirectoryIndex
 
-    RewriteCond %{REQUEST_FILENAME} !-f
-    RewriteRule ^(.*)$ app.php [QSA,L]
+    # Redirect to URI without front controller to prevent duplicate content
+    # (with and without `/app.php`). Only do this redirect on the initial
+    # rewrite by apache and not on subsequent cycles. Otherwise we would get an
+    # endless redirect loop (request -> rewrite to front controller ->
+    # redirect -> request -> ...).
+    # So in case you get a "too many redirects" error because your apache does
+    # not expose the REDIRECT_STATUS environment variable, you have 2 choices:
+    # - disable this feature by commenting the following 2 lines or
+    # - use apache >= 2.3.9 and replace all L flags by END flags and remove the
+    #   following RewriteCond (best solution)
+    RewriteCond %{ENV:REDIRECT_STATUS} ^$
+    RewriteRule ^app\.php(/(.*)|$) %{CONTEXT_PREFIX}/$2 [R=301,L]
+
+    # If the requested filename exists, simply serve it.
+    # We only want to let apache serve files and not directories.
+    RewriteCond %{REQUEST_FILENAME} -f
+    RewriteRule .? - [L]
+
+    # The following rewrites all other queries to app.php. The
+    # condition ensures that if you are using Apache aliases to do
+    # mass virtual hosting, the base path will be prepended to
+    # allow proper resolution of the app.php file; it will work
+    # in non-aliased environments as well, providing a safe, one-size
+    # fits all solution.
+    RewriteCond %{REQUEST_URI}::$1 ^(/.+)(.+)::\2$
+    RewriteRule ^(.*) - [E=BASE:%1]
+    RewriteRule .? %{ENV:BASE}app.php [L]
 </IfModule>