Looking for a RewriteBase equivalent using RewriteRule - apache

Question

I'm facing an Apache configuration issue which can be summarized like follows.
On a unique hosting system I have a lot of different test sites, each one in its own subdirectory, so they are accessible through an url like myhostname.fr/sitename.
Hence in the corresponding .htaccess, the common practice is to have a RewriteBase /sitename before any of the RewriteCond+RewriteRule sets, and it works fine.
Now for one of these sites (say in the specialsite subdirectory) I had to create a dedicated domain so the url looks like domainname.myhostname.fr.
Then for this site to work the .htaccess now needs RewriteBase / instead of RewriteBase /specialsite, and it works fine too.
Here is the trick: being not so familiar with Apache I decided to experiment and wanted to also keep allowed to access this site through the common url myhostname.fr/specialsite.
So I had to find a way to conditionally use one of the above RewriteBase, depending on which is the current url.
The first way I tried was to work like this:
<If "%(HTTP_HOST) =~ domainname\.myhostname\.fr">
RewriteBase /
</If>
<If "%(HTTP_HOST) =~ myhostname\.fr/specialsite">
RewriteBase /specialsite
</If>
But I got a HTTP 500 error, and I take much time to understand that the <If> directive is available as of Apache 2.4, while my hosting only offers Apache 1.3!
So (thanks to some other SO answers) I thinked to another way, which is to first do:
RewriteCond %{HTTP_HOST} domainname\.myhostname\.fr
RewriteRule ^ - [E=VirtualRewriteBase:/]
RewriteCond %{HTTP_HOST} myhostname\.fr/specialsite
RewriteRule ^ - [E=VirtualRewriteBase:/specialsite/]
Then prepend all further RewriteRule replacement with the given VirtualRewriteBase, like in this one:
RewriteRule ^ %{ENV:VirtualRewriteBase}index.php [L]
But while it works fine for the domain-access version, it gives me an HTTP 404 error for the subdirectory-access version.
So in order to watch at how the replacement applied I changed the above rule for:
RewriteRule ^ %{ENV:VirtualRewriteBase}index.php [R,L]
And I observed that the redirected url looked like this:
http://myhostname.fr/kunden/homepages/7/d265580839/htdocs/specialsite/index.php
where kunden/homepages/7/d265580839/htdocs/ is the full document-root of my hosting.
You can notice that the document-root has been inserted between the two parts of the original url.
Moreover, the result is exactly the same whatever I put in place of /specialsite/ in my VirtualRewriteBase!
So here is my main question: why and how does this happen?
Also I'm obviously interested to a possible alternative solution to achieve the double-access availibility.
But above all I would like to understand...

Answer 1

But while it works fine for the domain-access version, it gives me an
HTTP 404 error for the subdirectory-access version.
That's because your second condition is never matched. Indeed, HTTP_HOST only contains the... http host ! The /specialsite is part of the REQUEST_URI (or can also be matched in RewriteRule directly).
This code should work (anyway, i don't know if it would solve totally your problem, but that's a first step)
RewriteCond %{HTTP_HOST} ^domainname\.myhostname\.fr$ [NC]
RewriteRule ^ - [E=VirtualRewriteBase:/]
RewriteCond %{HTTP_HOST} ^myhostname\.fr$ [NC]
RewriteCond %{REQUEST_URI} ^/specialsite(?:/|$) [NC]
RewriteRule ^ - [E=VirtualRewriteBase:/specialsite/]