mod rewrite - How does Apache process a path with a percent-encoded URL in it?

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I ran into an unexpected case of
Apache giving me a 404 error instead of letting mod_rewrite handle the path, when one of
the percent-encoded path parts was itself a HTTP
URL.

e.g. "GET
/myfolder/http%3A%2F%2Flocalhost%2Fnotify
HTTP/1.0"

I have an extremely simple rule in the
/myfolder/.htaccess file which sends everything that's not a file
in /myfolder/ to a script. It works fine with other percent-encoded values, but in this
case Apache never processes the RewriteRule from the .htaccess file. I can double-encode
the value as a workaround, but it seems that Apache should still process the mod_rewrite
phases. I intend the URL merely to be an input parameter to the
script.

Here are the (ir)relevant
mod_rewrite directives in
/myfolder/.htaccess:

RewriteCond
            %{REQUEST_FILENAME} !-s
RewriteRule .*
            ./script-the-world.php

The
rewrite rules are NOT being processed. In the server configuration I've got
RewriteLogLevel 5, etc., and tail -f /var/log/http/rewrite.log shows all my requests to
/myfolder/ being rewritten... except for the one mentioned above. I mean to say that
something internal is happening in the special case above, but I have no clue what it
is. I'm hoping someone might know of another module that is interfering with what I'm
trying to accomplish.

This is Apache
2.2.16.

Answer

You'll need to enable href="http://httpd.apache.org/docs/2.0/mod/core.html#allowencodedslashes" rel="nofollow
noreferrer">AllowEncodedSlashes, which will cause Apache to allow URLs with
%2F and %5C in them, instead of throwing a 404. You will still, of course, have to make
sure that your php script is handling the decoding of the URL correctly, as that's not
Apache's duty.