mod_rewrite omit html extension loop - apache

Question

I have the following scenario:
Two frontcontrollers in a web directory (document root):
web/frontend.php # handles all *.html requests
web/backend.php # direct calls only
Rewriting is easy so far:
RewriteCond %{REQUEST_URI} !^/backend.php
RewriteRule (.+)\.html$ /frontend.php [L]
So now when I call example.org/backend.php I'm in the backend, nothing special happens. And when I call something like example.org/ or example.org/team/john.html it is handled by frontend.php.
Works so far!
Now I want the possibility to omit the *.html extension so that example.org/team/john is internally handled as example.org/team/john.html.
RewriteCond %{REQUEST_FILENAME}.html -f
RewriteRule !.*\.html$ %{REQUEST_URI}.html [L]
Last but not least I want to redirect requests to john.html to john to avoid duplicate content.
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} -f
RewriteCond %{REQUEST_URI} ^(.+)\.html$
RewriteRule (.*)\.html$ /$1 [R=301,L]
Every part works on it's own but put together I get a loop, which doesn't surprise me but I don't know how to avoid this. I searched the docs, tried several flags and conditions but I'm totally stuck and I need help.
Here is the whole .htaccess file:
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteBase /
# extend html extension internally
RewriteCond %{REQUEST_FILENAME}.html -f
RewriteRule !.*\.html$ %{REQUEST_URI}.html [L]
# redirect example.html to example
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} -f
RewriteCond %{REQUEST_URI} ^(.+)\.html$
RewriteRule (.*)\.html$ /$1 [R=301,L]
# frontcontroller
RewriteCond %{REQUEST_URI} !^/backend.php
RewriteRule (.+)\.html$ /frontend.php [L]
</IfModule>
Any help would be great.

Answer 1

To avoid a loop, you can use THE_REQUEST
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} -f
RewriteCond %{THE_REQUEST} "\.html "
RewriteRule ^(.*)\.html$ /$1 [R,L]
Unrelated, but you can simplify your rules. First one
RewriteCond %{REQUEST_URI} !^/backend.php
RewriteRule (.+)\.html$ /frontend.php [L]
You already check for (.+)\.html, so you can omit the RewriteCond. Next, you don't use the captured part (.+). Replace it with . to ensure it's not empty. This gives then
RewriteRule .\.html$ /frontend.php [L]
Second one, unless you have *.html.html files in your site, you don't need to check for !html and can just use ^ for the RewriteRule pattern
RewriteCond %{REQUEST_FILENAME}.html -f
RewriteRule ^ %{REQUEST_URI}.html [L]

Answer 2

The loop is because of the multiple internal redirections, You can use END flag to prevent the rewrite loop
RewriteRule ^(.+)\.html$ /$1 [L,R=301]
RewriteCond %{REQUEST_FILENAME}.html -f
RewriteRule !.*\.html$ %{REQUEST_URI}.html [END]