URL Rewriting Guide

-

Introduction to `mod_rewrite`

- - - -

The Apache module mod_rewrite is a killer - one, i.e. it is a really sophisticated module which provides - a powerful way to do URL manipulations. With it you can do nearly - all types of URL manipulations you ever dreamed about. - The price you have to pay is to accept complexity, because - mod_rewrite's major drawback is that it is - not easy to understand and use for the beginner. And even - Apache experts sometimes discover new aspects where - mod_rewrite can help.

- -

In other words: With mod_rewrite you either - shoot yourself in the foot the first time and never use it again - or love it for the rest of your life because of its power. - This paper tries to give you a few initial success events to - avoid the first case by presenting already invented solutions - to you.

- -

-

Practical Solutions

- - - -

Here come a lot of practical solutions I've either invented - myself or collected from other people's solutions in the past. - Feel free to learn the black magic of URL rewriting from - these examples.

- -

ATTENTION: Depending on your server-configuration - it can be necessary to slightly change the examples for your - situation, e.g. adding the [PT] flag when - additionally using mod_alias and - mod_userdir, etc. Or rewriting a ruleset - to fit in .htaccess context instead - of per-server context. Always try to understand what a - particular ruleset really does before you use it. It - avoids problems.

- -

-

URL Layout

- - - -

Canonical URLs

- - - -

Description:

-

On some webservers there are more than one URL for a - resource. Usually there are canonical URLs (which should be - actually used and distributed) and those which are just - shortcuts, internal ones, etc. Independent of which URL the - user supplied with the request he should finally see the - canonical one only.

-

Solution:

-

We do an external HTTP redirect for all non-canonical - URLs to fix them in the location view of the Browser and - for all subsequent requests. In the example ruleset below - we replace /~user by the canonical - /u/user and fix a missing trailing slash for - /u/user.

- -

-RewriteRule   ^/~([^/]+)/?(.*)    /u/$1/$2  [R]
-RewriteRule   ^/([uge])/([^/]+)$  /$1/$2/   [R]
-

-

- - - -

Canonical Hostnames

- - - -

Description:

...

Solution:

-

-RewriteCond %{HTTP_HOST}   !^fully\.qualified\.domain\.name [NC]
-RewriteCond %{HTTP_HOST}   !^$
-RewriteCond %{SERVER_PORT} !^80$
-RewriteRule ^/(.*)         http://fully.qualified.domain.name:%{SERVER_PORT}/$1 [L,R]
-RewriteCond %{HTTP_HOST}   !^fully\.qualified\.domain\.name [NC]
-RewriteCond %{HTTP_HOST}   !^$
-RewriteRule ^/(.*)         http://fully.qualified.domain.name/$1 [L,R]
-

-

- - - -

Moved `DocumentRoot`

- - - -

Description:

-

Usually the DocumentRoot - of the webserver directly relates to the URL "/". - But often this data is not really of top-level priority, it is - perhaps just one entity of a lot of data pools. For instance at - our Intranet sites there are /e/www/ - (the homepage for WWW), /e/sww/ (the homepage for - the Intranet) etc. Now because the data of the DocumentRoot stays at /e/www/ we had - to make sure that all inlined images and other stuff inside this - data pool work for subsequent requests.

-

Solution:

-

We redirect the URL / to - /e/www/: -

- -

-RewriteEngine on
-RewriteRule   ^/$  /e/www/  [R]
-

- -

Note that this can also be handled using the RedirectMatch directive:

- -

- RedirectMatch ^/$ http://example.com/e/www/ -

-

- - - -

Trailing Slash Problem

- - - -

Description:

-

Every webmaster can sing a song about the problem of - the trailing slash on URLs referencing directories. If they - are missing, the server dumps an error, because if you say - /~quux/foo instead of /~quux/foo/ - then the server searches for a file named - foo. And because this file is a directory it - complains. Actually it tries to fix it itself in most of - the cases, but sometimes this mechanism need to be emulated - by you. For instance after you have done a lot of - complicated URL rewritings to CGI scripts etc.

-

Solution:

-

The solution to this subtle problem is to let the server - add the trailing slash automatically. To do this - correctly we have to use an external redirect, so the - browser correctly requests subsequent images etc. If we - only did a internal rewrite, this would only work for the - directory page, but would go wrong when any images are - included into this page with relative URLs, because the - browser would request an in-lined object. For instance, a - request for image.gif in - /~quux/foo/index.html would become - /~quux/image.gif without the external - redirect!

- -

So, to do this trick we write:

- -

-RewriteEngine  on
-RewriteBase    /~quux/
-RewriteRule    ^foo$  foo/  [R]
-

- -

The crazy and lazy can even do the following in the - top-level .htaccess file of their homedir. - But notice that this creates some processing - overhead.

- -

-RewriteEngine  on
-RewriteBase    /~quux/
-RewriteCond    %{REQUEST_FILENAME}  -d
-RewriteRule    ^(.+[^/])$           $1/  [R]
-

-

- - - -

Webcluster through Homogeneous URL Layout

- - - -

Description:

-

We want to create a homogeneous and consistent URL - layout over all WWW servers on a Intranet webcluster, i.e. - all URLs (per definition server local and thus server - dependent!) become actually server independent! - What we want is to give the WWW namespace a consistent - server-independent layout: no URL should have to include - any physically correct target server. The cluster itself - should drive us automatically to the physical target - host.

-

Solution:

-

First, the knowledge of the target servers come from - (distributed) external maps which contain information - where our users, groups and entities stay. The have the - form

- -

-user1  server_of_user1
-user2  server_of_user2
-:      :
-

- -

We put them into files map.xxx-to-host. - Second we need to instruct all servers to redirect URLs - of the forms

- -

-/u/user/anypath
-/g/group/anypath
-/e/entity/anypath
-

- -

to

- -

-http://physical-host/u/user/anypath
-http://physical-host/g/group/anypath
-http://physical-host/e/entity/anypath
-

- -

when the URL is not locally valid to a server. The - following ruleset does this for us by the help of the map - files (assuming that server0 is a default server which - will be used if a user has no entry in the map):

- -

-RewriteEngine on
-
-RewriteMap      user-to-host   txt:/path/to/map.user-to-host
-RewriteMap     group-to-host   txt:/path/to/map.group-to-host
-RewriteMap    entity-to-host   txt:/path/to/map.entity-to-host
-
-RewriteRule   ^/u/([^/]+)/?(.*)   http://${user-to-host:$1|server0}/u/$1/$2
-RewriteRule   ^/g/([^/]+)/?(.*)  http://${group-to-host:$1|server0}/g/$1/$2
-RewriteRule   ^/e/([^/]+)/?(.*) http://${entity-to-host:$1|server0}/e/$1/$2
-
-RewriteRule   ^/([uge])/([^/]+)/?$          /$1/$2/.www/
-RewriteRule   ^/([uge])/([^/]+)/([^.]+.+)   /$1/$2/.www/$3\
-

-

- - - -

Move Homedirs to Different Webserver

- - - -

Description:

-

Many webmasters have asked for a solution to the - following situation: They wanted to redirect just all - homedirs on a webserver to another webserver. They usually - need such things when establishing a newer webserver which - will replace the old one over time.

-

Solution:

-

The solution is trivial with mod_rewrite. - On the old webserver we just redirect all - /~user/anypath URLs to - http://newserver/~user/anypath.

- -

-RewriteEngine on
-RewriteRule   ^/~(.+)  http://newserver/~$1  [R,L]
-

-

- - - -

Structured Homedirs

- - - -

Description:

-

Some sites with thousands of users usually use a - structured homedir layout, i.e. each homedir is in a - subdirectory which begins for instance with the first - character of the username. So, /~foo/anypath - is /home/f/foo/.www/anypath - while /~bar/anypath is - /home/b/bar/.www/anypath.

-

Solution:

-

We use the following ruleset to expand the tilde URLs - into exactly the above layout.

- -

-RewriteEngine on
-RewriteRule   ^/~(([a-z])[a-z0-9]+)(.*)  /home/$2/$1/.www$3
-

-

- - - -

Filesystem Reorganization

- - - -

Description:

-

This really is a hardcore example: a killer application - which heavily uses per-directory - RewriteRules to get a smooth look and feel - on the Web while its data structure is never touched or - adjusted. Background: net.sw is - my archive of freely available Unix software packages, - which I started to collect in 1992. It is both my hobby - and job to to this, because while I'm studying computer - science I have also worked for many years as a system and - network administrator in my spare time. Every week I need - some sort of software so I created a deep hierarchy of - directories where I stored the packages:

- -

-drwxrwxr-x   2 netsw  users    512 Aug  3 18:39 Audio/
-drwxrwxr-x   2 netsw  users    512 Jul  9 14:37 Benchmark/
-drwxrwxr-x  12 netsw  users    512 Jul  9 00:34 Crypto/
-drwxrwxr-x   5 netsw  users    512 Jul  9 00:41 Database/
-drwxrwxr-x   4 netsw  users    512 Jul 30 19:25 Dicts/
-drwxrwxr-x  10 netsw  users    512 Jul  9 01:54 Graphic/
-drwxrwxr-x   5 netsw  users    512 Jul  9 01:58 Hackers/
-drwxrwxr-x   8 netsw  users    512 Jul  9 03:19 InfoSys/
-drwxrwxr-x   3 netsw  users    512 Jul  9 03:21 Math/
-drwxrwxr-x   3 netsw  users    512 Jul  9 03:24 Misc/
-drwxrwxr-x   9 netsw  users    512 Aug  1 16:33 Network/
-drwxrwxr-x   2 netsw  users    512 Jul  9 05:53 Office/
-drwxrwxr-x   7 netsw  users    512 Jul  9 09:24 SoftEng/
-drwxrwxr-x   7 netsw  users    512 Jul  9 12:17 System/
-drwxrwxr-x  12 netsw  users    512 Aug  3 20:15 Typesetting/
-drwxrwxr-x  10 netsw  users    512 Jul  9 14:08 X11/
-

- -

In July 1996 I decided to make this archive public to - the world via a nice Web interface. "Nice" means that I - wanted to offer an interface where you can browse - directly through the archive hierarchy. And "nice" means - that I didn't wanted to change anything inside this - hierarchy - not even by putting some CGI scripts at the - top of it. Why? Because the above structure should be - later accessible via FTP as well, and I didn't want any - Web or CGI stuff to be there.

-

Solution:

-

The solution has two parts: The first is a set of CGI - scripts which create all the pages at all directory - levels on-the-fly. I put them under - /e/netsw/.www/ as follows:

- -

--rw-r--r--   1 netsw  users    1318 Aug  1 18:10 .wwwacl
-drwxr-xr-x  18 netsw  users     512 Aug  5 15:51 DATA/
--rw-rw-rw-   1 netsw  users  372982 Aug  5 16:35 LOGFILE
--rw-r--r--   1 netsw  users     659 Aug  4 09:27 TODO
--rw-r--r--   1 netsw  users    5697 Aug  1 18:01 netsw-about.html
--rwxr-xr-x   1 netsw  users     579 Aug  2 10:33 netsw-access.pl
--rwxr-xr-x   1 netsw  users    1532 Aug  1 17:35 netsw-changes.cgi
--rwxr-xr-x   1 netsw  users    2866 Aug  5 14:49 netsw-home.cgi
-drwxr-xr-x   2 netsw  users     512 Jul  8 23:47 netsw-img/
--rwxr-xr-x   1 netsw  users   24050 Aug  5 15:49 netsw-lsdir.cgi
--rwxr-xr-x   1 netsw  users    1589 Aug  3 18:43 netsw-search.cgi
--rwxr-xr-x   1 netsw  users    1885 Aug  1 17:41 netsw-tree.cgi
--rw-r--r--   1 netsw  users     234 Jul 30 16:35 netsw-unlimit.lst
-

- -

The DATA/ subdirectory holds the above - directory structure, i.e. the real - net.sw stuff and gets - automatically updated via rdist from time to - time. The second part of the problem remains: how to link - these two structures together into one smooth-looking URL - tree? We want to hide the DATA/ directory - from the user while running the appropriate CGI scripts - for the various URLs. Here is the solution: first I put - the following into the per-directory configuration file - in the DocumentRoot - of the server to rewrite the announced URL - /net.sw/ to the internal path - /e/netsw:

- -

-RewriteRule  ^net.sw$       net.sw/        [R]
-RewriteRule  ^net.sw/(.*)$  e/netsw/$1
-

- -

The first rule is for requests which miss the trailing - slash! The second rule does the real thing. And then - comes the killer configuration which stays in the - per-directory config file - /e/netsw/.www/.wwwacl:

- -

-Options       ExecCGI FollowSymLinks Includes MultiViews
-
-RewriteEngine on
-
-#  we are reached via /net.sw/ prefix
-RewriteBase   /net.sw/
-
-#  first we rewrite the root dir to
-#  the handling cgi script
-RewriteRule   ^$                       netsw-home.cgi     [L]
-RewriteRule   ^index\.html$            netsw-home.cgi     [L]
-
-#  strip out the subdirs when
-#  the browser requests us from perdir pages
-RewriteRule   ^.+/(netsw-[^/]+/.+)$    $1                 [L]
-
-#  and now break the rewriting for local files
-RewriteRule   ^netsw-home\.cgi.*       -                  [L]
-RewriteRule   ^netsw-changes\.cgi.*    -                  [L]
-RewriteRule   ^netsw-search\.cgi.*     -                  [L]
-RewriteRule   ^netsw-tree\.cgi$        -                  [L]
-RewriteRule   ^netsw-about\.html$      -                  [L]
-RewriteRule   ^netsw-img/.*$           -                  [L]
-
-#  anything else is a subdir which gets handled
-#  by another cgi script
-RewriteRule   !^netsw-lsdir\.cgi.*     -                  [C]
-RewriteRule   (.*)                     netsw-lsdir.cgi/$1
-

- -

Some hints for interpretation:

- -

Notice the L (last) flag and no - substitution field ('-') in the forth part
Notice the ! (not) character and - the C (chain) flag at the first rule - in the last part
Notice the catch-all pattern in the last rule

-

- - - -

NCSA imagemap to Apache `mod_imagemap`

- - - -

Description:

-

When switching from the NCSA webserver to the more - modern Apache webserver a lot of people want a smooth - transition. So they want pages which use their old NCSA - imagemap program to work under Apache with the - modern mod_imagemap. The problem is that there - are a lot of hyperlinks around which reference the - imagemap program via - /cgi-bin/imagemap/path/to/page.map. Under - Apache this has to read just - /path/to/page.map.

-

Solution:

-

We use a global rule to remove the prefix on-the-fly for - all requests:

- -

-RewriteEngine  on
-RewriteRule    ^/cgi-bin/imagemap(.*)  $1  [PT]
-

-

- - - -

Search pages in more than one directory

- - - -

Description:

-

Sometimes it is necessary to let the webserver search - for pages in more than one directory. Here MultiViews or - other techniques cannot help.

-

Solution:

-

We program a explicit ruleset which searches for the - files in the directories.

- -

-RewriteEngine on
-
-#   first try to find it in custom/...
-#   ...and if found stop and be happy:
-RewriteCond         /your/docroot/dir1/%{REQUEST_FILENAME}  -f
-RewriteRule  ^(.+)  /your/docroot/dir1/$1  [L]
-
-#   second try to find it in pub/...
-#   ...and if found stop and be happy:
-RewriteCond         /your/docroot/dir2/%{REQUEST_FILENAME}  -f
-RewriteRule  ^(.+)  /your/docroot/dir2/$1  [L]
-
-#   else go on for other Alias or ScriptAlias directives,
-#   etc.
-RewriteRule   ^(.+)  -  [PT]
-

-

- - - -

Set Environment Variables According To URL Parts

- - - -

Description:

-

Perhaps you want to keep status information between - requests and use the URL to encode it. But you don't want - to use a CGI wrapper for all pages just to strip out this - information.

-

Solution:

-

We use a rewrite rule to strip out the status information - and remember it via an environment variable which can be - later dereferenced from within XSSI or CGI. This way a - URL /foo/S=java/bar/ gets translated to - /foo/bar/ and the environment variable named - STATUS is set to the value "java".

- -

-RewriteEngine on
-RewriteRule   ^(.*)/S=([^/]+)/(.*)    $1/$3 [E=STATUS:$2]
-

-

- - - -

Virtual User Hosts

- - - -

Description:

-

Assume that you want to provide - www.username.host.domain.com - for the homepage of username via just DNS A records to the - same machine and without any virtualhosts on this - machine.

-

Solution:

-

For HTTP/1.0 requests there is no solution, but for - HTTP/1.1 requests which contain a Host: HTTP header we - can use the following ruleset to rewrite - http://www.username.host.com/anypath - internally to /home/username/anypath:

- -

-RewriteEngine on
-RewriteCond   %{HTTP_HOST}                 ^www\.[^.]+\.host\.com$
-RewriteRule   ^(.+)                        %{HTTP_HOST}$1          [C]
-RewriteRule   ^www\.([^.]+)\.host\.com(.*) /home/$1$2
-

-

- - - -

Redirect Homedirs For Foreigners

- - - -

Description:

-

We want to redirect homedir URLs to another webserver - www.somewhere.com when the requesting user - does not stay in the local domain - ourdomain.com. This is sometimes used in - virtual host contexts.

-

Solution:

-

Just a rewrite condition:

- -

-RewriteEngine on
-RewriteCond   %{REMOTE_HOST}  !^.+\.ourdomain\.com$
-RewriteRule   ^(/~.+)         http://www.somewhere.com/$1 [R,L]
-

-

- - - -

Redirect Failing URLs To Other Webserver

- - - -

Description:

-

A typical FAQ about URL rewriting is how to redirect - failing requests on webserver A to webserver B. Usually - this is done via ErrorDocument CGI-scripts in Perl, but - there is also a mod_rewrite solution. - But notice that this performs more poorly than using an - ErrorDocument - CGI-script!

-

Solution:

-

The first solution has the best performance but less - flexibility, and is less error safe:

- -

-RewriteEngine on
-RewriteCond   /your/docroot/%{REQUEST_FILENAME} !-f
-RewriteRule   ^(.+)                             http://webserverB.dom/$1
-

- -

The problem here is that this will only work for pages - inside the DocumentRoot. While you can add more - Conditions (for instance to also handle homedirs, etc.) - there is better variant:

- -

-RewriteEngine on
-RewriteCond   %{REQUEST_URI} !-U
-RewriteRule   ^(.+)          http://webserverB.dom/$1
-

- -

This uses the URL look-ahead feature of mod_rewrite. - The result is that this will work for all types of URLs - and is a safe way. But it does a performance impact on - the webserver, because for every request there is one - more internal subrequest. So, if your webserver runs on a - powerful CPU, use this one. If it is a slow machine, use - the first approach or better a ErrorDocument CGI-script.

-

- - - -

Extended Redirection

- - - -

Description:

-

Sometimes we need more control (concerning the - character escaping mechanism) of URLs on redirects. - Usually the Apache kernels URL escape function also - escapes anchors, i.e. URLs like "url#anchor". - You cannot use this directly on redirects with - mod_rewrite because the - uri_escape() function of Apache - would also escape the hash character. - How can we redirect to such a URL?

-

Solution:

-

We have to use a kludge by the use of a NPH-CGI script - which does the redirect itself. Because here no escaping - is done (NPH=non-parseable headers). First we introduce a - new URL scheme xredirect: by the following - per-server config-line (should be one of the last rewrite - rules):

- -

-RewriteRule ^xredirect:(.+) /path/to/nph-xredirect.cgi/$1 \
-            [T=application/x-httpd-cgi,L]
-

- -

This forces all URLs prefixed with - xredirect: to be piped through the - nph-xredirect.cgi program. And this program - just looks like:

- -

-#!/path/to/perl
-##
-##  nph-xredirect.cgi -- NPH/CGI script for extended redirects
-##  Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved.
-##
-
-$| = 1;
-$url = $ENV{'PATH_INFO'};
-
-print "HTTP/1.0 302 Moved Temporarily\n";
-print "Server: $ENV{'SERVER_SOFTWARE'}\n";
-print "Location: $url\n";
-print "Content-type: text/html\n";
-print "\n";
-print "<html>\n";
-print "<head>\n";
-print "<title>302 Moved Temporarily (EXTENDED)</title>\n";
-print "</head>\n";
-print "<body>\n";
-print "<h1>Moved Temporarily (EXTENDED)</h1>\n";
-print "The document has moved <a HREF=\"$url\">here</a>.<p>\n";
-print "</body>\n";
-print "</html>\n";
-
-##EOF##
-

- -

This provides you with the functionality to do - redirects to all URL schemes, i.e. including the one - which are not directly accepted by mod_rewrite. - For instance you can now also redirect to - news:newsgroup via

- -

-RewriteRule ^anyurl  xredirect:news:newsgroup
-

- -

Notice: You have not to put [R] or - [R,L] to the above rule because the - xredirect: need to be expanded later - by our special "pipe through" rule above.

-

- - - -

Archive Access Multiplexer

- - - -

Description:

-

Do you know the great CPAN (Comprehensive Perl Archive - Network) under http://www.perl.com/CPAN? - This does a redirect to one of several FTP servers around - the world which carry a CPAN mirror and is approximately - near the location of the requesting client. Actually this - can be called an FTP access multiplexing service. While - CPAN runs via CGI scripts, how can a similar approach - implemented via mod_rewrite?

-

Solution:

-

First we notice that from version 3.0.0 - mod_rewrite can - also use the "ftp:" scheme on redirects. - And second, the location approximation can be done by a - RewriteMap - over the top-level domain of the client. - With a tricky chained ruleset we can use this top-level - domain as a key to our multiplexing map.

- -

-RewriteEngine on
-RewriteMap    multiplex                txt:/path/to/map.cxan
-RewriteRule   ^/CxAN/(.*)              %{REMOTE_HOST}::$1                 [C]
-RewriteRule   ^.+\.([a-zA-Z]+)::(.*)$  ${multiplex:$1|ftp.default.dom}$2  [R,L]
-

- -

-##
-##  map.cxan -- Multiplexing Map for CxAN
-##
-
-de        ftp://ftp.cxan.de/CxAN/
-uk        ftp://ftp.cxan.uk/CxAN/
-com       ftp://ftp.cxan.com/CxAN/
- :
-##EOF##
-

-

- - - -

Time-Dependent Rewriting

- - - -

Description:

-

When tricks like time-dependent content should happen a - lot of webmasters still use CGI scripts which do for - instance redirects to specialized pages. How can it be done - via mod_rewrite?

-

Solution:

-

There are a lot of variables named TIME_xxx - for rewrite conditions. In conjunction with the special - lexicographic comparison patterns <STRING, - >STRING and =STRING we can - do time-dependent redirects:

- -

-RewriteEngine on
-RewriteCond   %{TIME_HOUR}%{TIME_MIN} >0700
-RewriteCond   %{TIME_HOUR}%{TIME_MIN} <1900
-RewriteRule   ^foo\.html$             foo.day.html
-RewriteRule   ^foo\.html$             foo.night.html
-

- -

This provides the content of foo.day.html - under the URL foo.html from - 07:00-19:00 and at the remaining time the - contents of foo.night.html. Just a nice - feature for a homepage...

-

- - - -

Backward Compatibility for YYYY to XXXX migration

- - - -

Description:

-

How can we make URLs backward compatible (still - existing virtually) after migrating document.YYYY - to document.XXXX, e.g. after translating a - bunch of .html files to .phtml?

-

Solution:

-

We just rewrite the name to its basename and test for - existence of the new extension. If it exists, we take - that name, else we rewrite the URL to its original state.

- - -

-#   backward compatibility ruleset for
-#   rewriting document.html to document.phtml
-#   when and only when document.phtml exists
-#   but no longer document.html
-RewriteEngine on
-RewriteBase   /~quux/
-#   parse out basename, but remember the fact
-RewriteRule   ^(.*)\.html$              $1      [C,E=WasHTML:yes]
-#   rewrite to document.phtml if exists
-RewriteCond   %{REQUEST_FILENAME}.phtml -f
-RewriteRule   ^(.*)$ $1.phtml                   [S=1]
-#   else reverse the previous basename cutout
-RewriteCond   %{ENV:WasHTML}            ^yes$
-RewriteRule   ^(.*)$ $1.html
-

-

- - - -

-

Content Handling

- - - -

From Old to New (intern)

- - - -

Description:

-

Assume we have recently renamed the page - foo.html to bar.html and now want - to provide the old URL for backward compatibility. Actually - we want that users of the old URL even not recognize that - the pages was renamed.

-

Solution:

-

We rewrite the old URL to the new one internally via the - following rule:

- -

-RewriteEngine  on
-RewriteBase    /~quux/
-RewriteRule    ^foo\.html$  bar.html
-

-

- - - -

From Old to New (extern)

- - - -

Description:

-

Assume again that we have recently renamed the page - foo.html to bar.html and now want - to provide the old URL for backward compatibility. But this - time we want that the users of the old URL get hinted to - the new one, i.e. their browsers Location field should - change, too.

-

Solution:

-

We force a HTTP redirect to the new URL which leads to a - change of the browsers and thus the users view:

- -

-RewriteEngine  on
-RewriteBase    /~quux/
-RewriteRule    ^foo\.html$  bar.html  [R]
-

-

- - - -

Browser Dependent Content

- - - -

Description:

-

At least for important top-level pages it is sometimes - necessary to provide the optimum of browser dependent - content, i.e. one has to provide a maximum version for the - latest Netscape variants, a minimum version for the Lynx - browsers and a average feature version for all others.

-

Solution:

-

We cannot use content negotiation because the browsers do - not provide their type in that form. Instead we have to - act on the HTTP header "User-Agent". The following condig - does the following: If the HTTP header "User-Agent" - begins with "Mozilla/3", the page foo.html - is rewritten to foo.NS.html and and the - rewriting stops. If the browser is "Lynx" or "Mozilla" of - version 1 or 2 the URL becomes foo.20.html. - All other browsers receive page foo.32.html. - This is done by the following ruleset:

- -

-RewriteCond %{HTTP_USER_AGENT}  ^Mozilla/3.*
-RewriteRule ^foo\.html$         foo.NS.html          [L]
-
-RewriteCond %{HTTP_USER_AGENT}  ^Lynx/.*         [OR]
-RewriteCond %{HTTP_USER_AGENT}  ^Mozilla/[12].*
-RewriteRule ^foo\.html$         foo.20.html          [L]
-
-RewriteRule ^foo\.html$         foo.32.html          [L]
-

-

- - - -

Dynamic Mirror

- - - -

Description:

-

Assume there are nice webpages on remote hosts we want - to bring into our namespace. For FTP servers we would use - the mirror program which actually maintains an - explicit up-to-date copy of the remote data on the local - machine. For a webserver we could use the program - webcopy which acts similar via HTTP. But both - techniques have one major drawback: The local copy is - always just as up-to-date as often we run the program. It - would be much better if the mirror is not a static one we - have to establish explicitly. Instead we want a dynamic - mirror with data which gets updated automatically when - there is need (updated data on the remote host).

-

Solution:

-

To provide this feature we map the remote webpage or even - the complete remote webarea to our namespace by the use - of the Proxy Throughput feature - (flag [P]):

- -

-RewriteEngine  on
-RewriteBase    /~quux/
-RewriteRule    ^hotsheet/(.*)$  http://www.tstimpreso.com/hotsheet/$1  [P]
-

- -

-RewriteEngine  on
-RewriteBase    /~quux/
-RewriteRule    ^usa-news\.html$   http://www.quux-corp.com/news/index.html  [P]
-

-

- - - -

Reverse Dynamic Mirror

- - - -

Description:

...

Solution:

-

-RewriteEngine on
-RewriteCond   /mirror/of/remotesite/$1           -U
-RewriteRule   ^http://www\.remotesite\.com/(.*)$ /mirror/of/remotesite/$1
-

-

- - - -

Retrieve Missing Data from Intranet

- - - -

Description:

-

This is a tricky way of virtually running a corporate - (external) Internet webserver - (www.quux-corp.dom), while actually keeping - and maintaining its data on a (internal) Intranet webserver - (www2.quux-corp.dom) which is protected by a - firewall. The trick is that on the external webserver we - retrieve the requested data on-the-fly from the internal - one.

-

Solution:

-

First, we have to make sure that our firewall still - protects the internal webserver and that only the - external webserver is allowed to retrieve data from it. - For a packet-filtering firewall we could for instance - configure a firewall ruleset like the following:

- -

-ALLOW Host www.quux-corp.dom Port >1024 --> Host www2.quux-corp.dom Port 80
-DENY  Host *                 Port *     --> Host www2.quux-corp.dom Port 80
-

- -

Just adjust it to your actual configuration syntax. - Now we can establish the mod_rewrite - rules which request the missing data in the background - through the proxy throughput feature:

- -

-RewriteRule ^/~([^/]+)/?(.*)          /home/$1/.www/$2
-RewriteCond %{REQUEST_FILENAME}       !-f
-RewriteCond %{REQUEST_FILENAME}       !-d
-RewriteRule ^/home/([^/]+)/.www/?(.*) http://www2.quux-corp.dom/~$1/pub/$2 [P]
-

-

- - - -

Load Balancing

- - - -

Description:

-

Suppose we want to load balance the traffic to - www.foo.com over www[0-5].foo.com - (a total of 6 servers). How can this be done?

-

Solution:

-

There are a lot of possible solutions for this problem. - We will discuss first a commonly known DNS-based variant - and then the special one with mod_rewrite:

- -

- DNS Round-Robin - -
The simplest method for load-balancing is to use - the DNS round-robin feature of BIND. - Here you just configure www[0-9].foo.com - as usual in your DNS with A(address) records, e.g.
- -
```
-www0   IN  A       1.2.3.1
-www1   IN  A       1.2.3.2
-www2   IN  A       1.2.3.3
-www3   IN  A       1.2.3.4
-www4   IN  A       1.2.3.5
-www5   IN  A       1.2.3.6
-
```
- -
Then you additionally add the following entry:
- -
```
-www   IN  A       1.2.3.1
-www   IN  A       1.2.3.2
-www   IN  A       1.2.3.3
-www   IN  A       1.2.3.4
-www   IN  A       1.2.3.5
-
```
- -
Now when www.foo.com gets - resolved, BIND gives out www0-www5 - - but in a slightly permutated/rotated order every time. - This way the clients are spread over the various - servers. But notice that this not a perfect load - balancing scheme, because DNS resolve information - gets cached by the other nameservers on the net, so - once a client has resolved www.foo.com - to a particular wwwN.foo.com, all - subsequent requests also go to this particular name - wwwN.foo.com. But the final result is - ok, because the total sum of the requests are really - spread over the various webservers.
-
- DNS Load-Balancing - -
A sophisticated DNS-based method for - load-balancing is to use the program - lbnamed which can be found at - http://www.stanford.edu/~schemers/docs/lbnamed/lbnamed.html. - It is a Perl 5 program in conjunction with auxilliary - tools which provides a real load-balancing for - DNS.
-
- Proxy Throughput Round-Robin - -
In this variant we use mod_rewrite - and its proxy throughput feature. First we dedicate - www0.foo.com to be actually - www.foo.com by using a single
- -
```
-www    IN  CNAME   www0.foo.com.
-
```
- -
entry in the DNS. Then we convert - www0.foo.com to a proxy-only server, - i.e. we configure this machine so all arriving URLs - are just pushed through the internal proxy to one of - the 5 other servers (www1-www5). To - accomplish this we first establish a ruleset which - contacts a load balancing script lb.pl - for all URLs.
- -
```
-RewriteEngine on
-RewriteMap    lb      prg:/path/to/lb.pl
-RewriteRule   ^/(.+)$ ${lb:$1}           [P,L]
-
```
- -
Then we write lb.pl:
- -
```
-#!/path/to/perl
-##
-##  lb.pl -- load balancing script
-##
-
-$| = 1;
-
-$name   = "www";     # the hostname base
-$first  = 1;         # the first server (not 0 here, because 0 is myself)
-$last   = 5;         # the last server in the round-robin
-$domain = "foo.dom"; # the domainname
-
-$cnt = 0;
-while (<STDIN>) {
-    $cnt = (($cnt+1) % ($last+1-$first));
-    $server = sprintf("%s%d.%s", $name, $cnt+$first, $domain);
-    print "http://$server/$_";
-}
-
-##EOF##
-
```
- -
A last notice: Why is this useful? Seems like - www0.foo.com still is overloaded? The - answer is yes, it is overloaded, but with plain proxy - throughput requests, only! All SSI, CGI, ePerl, etc. - processing is completely done on the other machines. - This is the essential point.
-
- Hardware/TCP Round-Robin - -
There is a hardware solution available, too. Cisco - has a beast called LocalDirector which does a load - balancing at the TCP/IP level. Actually this is some - sort of a circuit level gateway in front of a - webcluster. If you have enough money and really need - a solution with high performance, use this one.
-

-

- - - -

New MIME-type, New Service

- - - -

Description:

-

On the net there are a lot of nifty CGI programs. But - their usage is usually boring, so a lot of webmaster - don't use them. Even Apache's Action handler feature for - MIME-types is only appropriate when the CGI programs - don't need special URLs (actually PATH_INFO - and QUERY_STRINGS) as their input. First, - let us configure a new file type with extension - .scgi (for secure CGI) which will be processed - by the popular cgiwrap program. The problem - here is that for instance we use a Homogeneous URL Layout - (see above) a file inside the user homedirs has the URL - /u/user/foo/bar.scgi. But - cgiwrap needs the URL in the form - /~user/foo/bar.scgi/. The following rule - solves the problem:

- -

-RewriteRule ^/[uge]/([^/]+)/\.www/(.+)\.scgi(.*) ...
-... /internal/cgi/user/cgiwrap/~$1/$2.scgi$3  [NS,T=application/x-http-cgi]
-

- -

Or assume we have some more nifty programs: - wwwlog (which displays the - access.log for a URL subtree and - wwwidx (which runs Glimpse on a URL - subtree). We have to provide the URL area to these - programs so they know on which area they have to act on. - But usually this ugly, because they are all the times - still requested from that areas, i.e. typically we would - run the swwidx program from within - /u/user/foo/ via hyperlink to

- -

-/internal/cgi/user/swwidx?i=/u/user/foo/
-

- -

which is ugly. Because we have to hard-code - both the location of the area - and the location of the CGI inside the - hyperlink. When we have to reorganize the area, we spend a - lot of time changing the various hyperlinks.

-

Solution:

-

The solution here is to provide a special new URL format - which automatically leads to the proper CGI invocation. - We configure the following:

- -

-RewriteRule   ^/([uge])/([^/]+)(/?.*)/\*  /internal/cgi/user/wwwidx?i=/$1/$2$3/
-RewriteRule   ^/([uge])/([^/]+)(/?.*):log /internal/cgi/user/wwwlog?f=/$1/$2$3
-

- -

Now the hyperlink to search at - /u/user/foo/ reads only

- -

-HREF="*"
-

- -

which internally gets automatically transformed to

- -

-/internal/cgi/user/wwwidx?i=/u/user/foo/
-

- -

The same approach leads to an invocation for the - access log CGI program when the hyperlink - :log gets used.

-

- - - -

From Static to Dynamic

- - - -

Description:

-

How can we transform a static page - foo.html into a dynamic variant - foo.cgi in a seamless way, i.e. without notice - by the browser/user.

-

Solution:

-

We just rewrite the URL to the CGI-script and force the - correct MIME-type so it gets really run as a CGI-script. - This way a request to /~quux/foo.html - internally leads to the invocation of - /~quux/foo.cgi.

- -

-RewriteEngine  on
-RewriteBase    /~quux/
-RewriteRule    ^foo\.html$  foo.cgi  [T=application/x-httpd-cgi]
-

-

- - - -

On-the-fly Content-Regeneration

- - - -

Description:

-

Here comes a really esoteric feature: Dynamically - generated but statically served pages, i.e. pages should be - delivered as pure static pages (read from the filesystem - and just passed through), but they have to be generated - dynamically by the webserver if missing. This way you can - have CGI-generated pages which are statically served unless - one (or a cronjob) removes the static contents. Then the - contents gets refreshed.

-

Solution:

- This is done via the following ruleset: - -

-RewriteCond %{REQUEST_FILENAME}   !-s
-RewriteRule ^page\.html$          page.cgi   [T=application/x-httpd-cgi,L]
-

- -

Here a request to page.html leads to a - internal run of a corresponding page.cgi if - page.html is still missing or has filesize - null. The trick here is that page.cgi is a - usual CGI script which (additionally to its STDOUT) - writes its output to the file page.html. - Once it was run, the server sends out the data of - page.html. When the webmaster wants to force - a refresh the contents, he just removes - page.html (usually done by a cronjob).

-

- - - -

Document With Autorefresh

- - - -

Description:

-

Wouldn't it be nice while creating a complex webpage if - the webbrowser would automatically refresh the page every - time we write a new version from within our editor? - Impossible?

-

Solution:

-

No! We just combine the MIME multipart feature, the - webserver NPH feature and the URL manipulation power of - mod_rewrite. First, we establish a new - URL feature: Adding just :refresh to any - URL causes this to be refreshed every time it gets - updated on the filesystem.

- -

-RewriteRule   ^(/[uge]/[^/]+/?.*):refresh  /internal/cgi/apache/nph-refresh?f=$1
-

- -

Now when we reference the URL

- -

-/u/foo/bar/page.html:refresh
-

- -

this leads to the internal invocation of the URL

- -

-/internal/cgi/apache/nph-refresh?f=/u/foo/bar/page.html
-

- -

The only missing part is the NPH-CGI script. Although - one would usually say "left as an exercise to the reader" - ;-) I will provide this, too.

- -

-#!/sw/bin/perl
-##
-##  nph-refresh -- NPH/CGI script for auto refreshing pages
-##  Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved.
-##
-$| = 1;
-
-#   split the QUERY_STRING variable
-@pairs = split(/&/, $ENV{'QUERY_STRING'});
-foreach $pair (@pairs) {
-    ($name, $value) = split(/=/, $pair);
-    $name =~ tr/A-Z/a-z/;
-    $name = 'QS_' . $name;
-    $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg;
-    eval "\$$name = \"$value\"";
-}
-$QS_s = 1 if ($QS_s eq '');
-$QS_n = 3600 if ($QS_n eq '');
-if ($QS_f eq '') {
-    print "HTTP/1.0 200 OK\n";
-    print "Content-type: text/html\n\n";
-    print "&lt;b&gt;ERROR&lt;/b&gt;: No file given\n";
-    exit(0);
-}
-if (! -f $QS_f) {
-    print "HTTP/1.0 200 OK\n";
-    print "Content-type: text/html\n\n";
-    print "&lt;b&gt;ERROR&lt;/b&gt;: File $QS_f not found\n";
-    exit(0);
-}
-
-sub print_http_headers_multipart_begin {
-    print "HTTP/1.0 200 OK\n";
-    $bound = "ThisRandomString12345";
-    print "Content-type: multipart/x-mixed-replace;boundary=$bound\n";
-    &print_http_headers_multipart_next;
-}
-
-sub print_http_headers_multipart_next {
-    print "\n--$bound\n";
-}
-
-sub print_http_headers_multipart_end {
-    print "\n--$bound--\n";
-}
-
-sub displayhtml {
-    local($buffer) = @_;
-    $len = length($buffer);
-    print "Content-type: text/html\n";
-    print "Content-length: $len\n\n";
-    print $buffer;
-}
-
-sub readfile {
-    local($file) = @_;
-    local(*FP, $size, $buffer, $bytes);
-    ($x, $x, $x, $x, $x, $x, $x, $size) = stat($file);
-    $size = sprintf("%d", $size);
-    open(FP, "&lt;$file");
-    $bytes = sysread(FP, $buffer, $size);
-    close(FP);
-    return $buffer;
-}
-
-$buffer = &readfile($QS_f);
-&print_http_headers_multipart_begin;
-&displayhtml($buffer);
-
-sub mystat {
-    local($file) = $_[0];
-    local($time);
-
-    ($x, $x, $x, $x, $x, $x, $x, $x, $x, $mtime) = stat($file);
-    return $mtime;
-}
-
-$mtimeL = &mystat($QS_f);
-$mtime = $mtime;
-for ($n = 0; $n &lt; $QS_n; $n++) {
-    while (1) {
-        $mtime = &mystat($QS_f);
-        if ($mtime ne $mtimeL) {
-            $mtimeL = $mtime;
-            sleep(2);
-            $buffer = &readfile($QS_f);
-            &print_http_headers_multipart_next;
-            &displayhtml($buffer);
-            sleep(5);
-            $mtimeL = &mystat($QS_f);
-            last;
-        }
-        sleep($QS_s);
-    }
-}
-
-&print_http_headers_multipart_end;
-
-exit(0);
-
-##EOF##
-

-

- - - -

Mass Virtual Hosting

- - - -

Description:

-

The <VirtualHost> feature of Apache is nice - and works great when you just have a few dozens - virtual hosts. But when you are an ISP and have hundreds of - virtual hosts to provide this feature is not the best - choice.

-

Solution:

-

To provide this feature we map the remote webpage or even - the complete remote webarea to our namespace by the use - of the Proxy Throughput feature (flag [P]):

- -

-##
-##  vhost.map
-##
-www.vhost1.dom:80  /path/to/docroot/vhost1
-www.vhost2.dom:80  /path/to/docroot/vhost2
-     :
-www.vhostN.dom:80  /path/to/docroot/vhostN
-

- -

-##
-##  httpd.conf
-##
-    :
-#   use the canonical hostname on redirects, etc.
-UseCanonicalName on
-
-    :
-#   add the virtual host in front of the CLF-format
-CustomLog  /path/to/access_log  "%{VHOST}e %h %l %u %t \"%r\" %>s %b"
-    :
-
-#   enable the rewriting engine in the main server
-RewriteEngine on
-
-#   define two maps: one for fixing the URL and one which defines
-#   the available virtual hosts with their corresponding
-#   DocumentRoot.
-RewriteMap    lowercase    int:tolower
-RewriteMap    vhost        txt:/path/to/vhost.map
-
-#   Now do the actual virtual host mapping
-#   via a huge and complicated single rule:
-#
-#   1. make sure we don't map for common locations
-RewriteCond   %{REQUEST_URL}  !^/commonurl1/.*
-RewriteCond   %{REQUEST_URL}  !^/commonurl2/.*
-    :
-RewriteCond   %{REQUEST_URL}  !^/commonurlN/.*
-#
-#   2. make sure we have a Host header, because
-#      currently our approach only supports
-#      virtual hosting through this header
-RewriteCond   %{HTTP_HOST}  !^$
-#
-#   3. lowercase the hostname
-RewriteCond   ${lowercase:%{HTTP_HOST}|NONE}  ^(.+)$
-#
-#   4. lookup this hostname in vhost.map and
-#      remember it only when it is a path
-#      (and not "NONE" from above)
-RewriteCond   ${vhost:%1}  ^(/.*)$
-#
-#   5. finally we can map the URL to its docroot location
-#      and remember the virtual host for logging puposes
-RewriteRule   ^/(.*)$   %1/$1  [E=VHOST:${lowercase:%{HTTP_HOST}}]
-

-

- - - -

-

Access Restriction

- - - -

Blocking of Robots

- - - -

Description:

-

How can we block a really annoying robot from - retrieving pages of a specific webarea? A - /robots.txt file containing entries of the - "Robot Exclusion Protocol" is typically not enough to get - rid of such a robot.

-

Solution:

-

We use a ruleset which forbids the URLs of the webarea - /~quux/foo/arc/ (perhaps a very deep - directory indexed area where the robot traversal would - create big server load). We have to make sure that we - forbid access only to the particular robot, i.e. just - forbidding the host where the robot runs is not enough. - This would block users from this host, too. We accomplish - this by also matching the User-Agent HTTP header - information.

- -

-RewriteCond %{HTTP_USER_AGENT}   ^NameOfBadRobot.*
-RewriteCond %{REMOTE_ADDR}       ^123\.45\.67\.[8-9]$
-RewriteRule ^/~quux/foo/arc/.+   -   [F]
-

-

- - - -

Blocked Inline-Images

- - - -

Description:

-

Assume we have under http://www.quux-corp.de/~quux/ - some pages with inlined GIF graphics. These graphics are - nice, so others directly incorporate them via hyperlinks to - their pages. We don't like this practice because it adds - useless traffic to our server.

-

Solution:

-

While we cannot 100% protect the images from inclusion, - we can at least restrict the cases where the browser - sends a HTTP Referer header.

- -

-RewriteCond %{HTTP_REFERER} !^$
-RewriteCond %{HTTP_REFERER} !^http://www.quux-corp.de/~quux/.*$ [NC]
-RewriteRule .*\.gif$        -                                    [F]
-

- -

-RewriteCond %{HTTP_REFERER}         !^$
-RewriteCond %{HTTP_REFERER}         !.*/foo-with-gif\.html$
-RewriteRule ^inlined-in-foo\.gif$   -                        [F]
-

-

- - - -

Host Deny

- - - -

Description:

-

How can we forbid a list of externally configured hosts - from using our server?

-

Solution:

-

For Apache >= 1.3b6:

- -

-RewriteEngine on
-RewriteMap    hosts-deny  txt:/path/to/hosts.deny
-RewriteCond   ${hosts-deny:%{REMOTE_HOST}|NOT-FOUND} !=NOT-FOUND [OR]
-RewriteCond   ${hosts-deny:%{REMOTE_ADDR}|NOT-FOUND} !=NOT-FOUND
-RewriteRule   ^/.*  -  [F]
-

- -

For Apache <= 1.3b6:

- -

-RewriteEngine on
-RewriteMap    hosts-deny  txt:/path/to/hosts.deny
-RewriteRule   ^/(.*)$ ${hosts-deny:%{REMOTE_HOST}|NOT-FOUND}/$1
-RewriteRule   !^NOT-FOUND/.* - [F]
-RewriteRule   ^NOT-FOUND/(.*)$ ${hosts-deny:%{REMOTE_ADDR}|NOT-FOUND}/$1
-RewriteRule   !^NOT-FOUND/.* - [F]
-RewriteRule   ^NOT-FOUND/(.*)$ /$1
-

- -

-##
-##  hosts.deny
-##
-##  ATTENTION! This is a map, not a list, even when we treat it as such.
-##             mod_rewrite parses it for key/value pairs, so at least a
-##             dummy value "-" must be present for each entry.
-##
-
-193.102.180.41 -
-bsdti1.sdm.de  -
-192.76.162.40  -
-

-

- - - -

Proxy Deny

- - - -

Description:

-

How can we forbid a certain host or even a user of a - special host from using the Apache proxy?

-

Solution:

-

We first have to make sure mod_rewrite - is below(!) mod_proxy in the Configuration - file when compiling the Apache webserver. This way it gets - called before mod_proxy. Then we - configure the following for a host-dependent deny...

- -

-RewriteCond %{REMOTE_HOST} ^badhost\.mydomain\.com$
-RewriteRule !^http://[^/.]\.mydomain.com.*  - [F]
-

- -

...and this one for a user@host-dependent deny:

- -

-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST}  ^badguy@badhost\.mydomain\.com$
-RewriteRule !^http://[^/.]\.mydomain.com.*  - [F]
-

-

- - - -

Special Authentication Variant

- - - -

Description:

-

Sometimes a very special authentication is needed, for - instance a authentication which checks for a set of - explicitly configured users. Only these should receive - access and without explicit prompting (which would occur - when using the Basic Auth via mod_auth_basic).

-

Solution:

-

We use a list of rewrite conditions to exclude all except - our friends:

- -

-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} !^friend1@client1.quux-corp\.com$
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} !^friend2@client2.quux-corp\.com$
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} !^friend3@client3.quux-corp\.com$
-RewriteRule ^/~quux/only-for-friends/      -                                 [F]
-

-

- - - -

Referer-based Deflector

- - - -

Description:

-

How can we program a flexible URL Deflector which acts - on the "Referer" HTTP header and can be configured with as - many referring pages as we like?

-

Solution:

-

Use the following really tricky ruleset...

- -

-RewriteMap  deflector txt:/path/to/deflector.map
-
-RewriteCond %{HTTP_REFERER} !=""
-RewriteCond ${deflector:%{HTTP_REFERER}} ^-$
-RewriteRule ^.* %{HTTP_REFERER} [R,L]
-
-RewriteCond %{HTTP_REFERER} !=""
-RewriteCond ${deflector:%{HTTP_REFERER}|NOT-FOUND} !=NOT-FOUND
-RewriteRule ^.* ${deflector:%{HTTP_REFERER}} [R,L]
-

- -

... in conjunction with a corresponding rewrite - map:

- -

-##
-##  deflector.map
-##
-
-http://www.badguys.com/bad/index.html    -
-http://www.badguys.com/bad/index2.html   -
-http://www.badguys.com/bad/index3.html   http://somewhere.com/
-

- -

This automatically redirects the request back to the - referring page (when "-" is used as the value - in the map) or to a specific URL (when an URL is specified - in the map as the second argument).

-

- - - -

-

Other

- - - -

External Rewriting Engine

- - - -

Description:

-

A FAQ: How can we solve the FOO/BAR/QUUX/etc. - problem? There seems no solution by the use of - mod_rewrite...

-

Solution:

-

Use an external RewriteMap, i.e. a program which acts - like a RewriteMap. It is run once on startup of Apache - receives the requested URLs on STDIN and has - to put the resulting (usually rewritten) URL on - STDOUT (same order!).

- -

-RewriteEngine on
-RewriteMap    quux-map       prg:/path/to/map.quux.pl
-RewriteRule   ^/~quux/(.*)$  /~quux/${quux-map:$1}
-

- -

-#!/path/to/perl
-
-#   disable buffered I/O which would lead
-#   to deadloops for the Apache server
-$| = 1;
-
-#   read URLs one per line from stdin and
-#   generate substitution URL on stdout
-while (<>) {
-    s|^foo/|bar/|;
-    print $_;
-}
-

- -

This is a demonstration-only example and just rewrites - all URLs /~quux/foo/... to - /~quux/bar/.... Actually you can program - whatever you like. But notice that while such maps can be - used also by an average user, only the - system administrator can define it.

-

- - - -

How-To / Tutorials

Introduction to mod_rewrite

Practical Solutions

URL Layout

Canonical URLs

Canonical Hostnames

Moved DocumentRoot

Trailing Slash Problem

Webcluster through Homogeneous URL Layout

Move Homedirs to Different Webserver

Structured Homedirs

Filesystem Reorganization

NCSA imagemap to Apache mod_imagemap

Search pages in more than one directory

Set Environment Variables According To URL Parts

Virtual User Hosts

Redirect Homedirs For Foreigners

Redirect Failing URLs To Other Webserver

Extended Redirection

Archive Access Multiplexer

Time-Dependent Rewriting

Backward Compatibility for YYYY to XXXX migration

Content Handling

From Old to New (intern)

From Old to New (extern)

Browser Dependent Content

Dynamic Mirror

Reverse Dynamic Mirror

Retrieve Missing Data from Intranet

Load Balancing

New MIME-type, New Service

From Static to Dynamic

On-the-fly Content-Regeneration

Document With Autorefresh

Mass Virtual Hosting

Access Restriction

Blocking of Robots

Blocked Inline-Images

Host Deny

Proxy Deny

Special Authentication Variant

Referer-based Deflector

Other

External Rewriting Engine

Introduction to `mod_rewrite`

Moved `DocumentRoot`

NCSA imagemap to Apache `mod_imagemap`