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-<title>URL Rewriting Guide - Apache HTTP Server</title>
-<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
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-<body id="manual-page"><div id="page-header">
-<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
-<p class="apache">Apache HTTP Server Version 2.3</p>
-<img alt="" src="../images/feather.gif" /></div>
-<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
-<div id="path">
-<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.3</a> > <a href="./">Miscellaneous Documentation</a></div><div id="page-content"><div id="preamble"><h1>URL Rewriting Guide</h1>
-<div class="toplang">
-<p><span>Available Languages: </span><a href="../en/misc/rewriteguide.html" title="English"> en </a> |
-<a href="../ko/misc/rewriteguide.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
-</div>
-
- <div class="note">
- <p>Originally written by<br />
- <cite>Ralf S. Engelschall <rse@apache.org></cite><br />
- December 1997</p>
- </div>
-
- <p>This document supplements the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
- <a href="../mod/mod_rewrite.html">reference documentation</a>.
- It describes how one can use Apache's <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
- to solve typical URL-based problems with which webmasters are
- commonly confronted. We give detailed descriptions on how to
- solve each problem by configuring URL rewriting rulesets.</p>
-
- </div>
-<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#ToC1">Introduction to <code>mod_rewrite</code></a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#ToC2">Practical Solutions</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#url">URL Layout</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#content">Content Handling</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#access">Access Restriction</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#other">Other</a></li>
-</ul></div>
-<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="ToC1" id="ToC1">Introduction to <code>mod_rewrite</code></a></h2>
-
-
-
- <p>The Apache module <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> 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
- <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>'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
- <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> can help.</p>
-
- <p>In other words: With <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> 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.</p>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="ToC2" id="ToC2">Practical Solutions</a></h2>
-
-
-
- <p>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.</p>
-
- <div class="warning">ATTENTION: Depending on your server-configuration
- it can be necessary to slightly change the examples for your
- situation, e.g. adding the <code>[PT]</code> flag when
- additionally using <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> and
- <code class="module"><a href="../mod/mod_userdir.html">mod_userdir</a></code>, etc. Or rewriting a ruleset
- to fit in <code>.htaccess</code> context instead
- of per-server context. Always try to understand what a
- particular ruleset really does before you use it. It
- avoids problems.</div>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="url" id="url">URL Layout</a></h2>
-
-
-
- <h3>Canonical URLs</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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 <code>/~user</code> by the canonical
- <code>/u/user</code> and fix a missing trailing slash for
- <code>/u/user</code>.</p>
-
-<div class="example"><pre>
-RewriteRule ^/<strong>~</strong>([^/]+)/?(.*) /<strong>u</strong>/$1/$2 [<strong>R</strong>]
-RewriteRule ^/([uge])/(<strong>[^/]+</strong>)$ /$1/$2<strong>/</strong> [<strong>R</strong>]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Canonical Hostnames</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>...</dd>
-
- <dt>Solution:</dt>
-
- <dd>
-<div class="example"><pre>
-RewriteCond %{HTTP_HOST} !^fully\.qualified\.domain\.name [NC]
-RewriteCond %{HTTP_HOST} !^$
-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/$1 [L,R]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Moved <code>DocumentRoot</code></h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Usually the <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code>
- of the webserver directly relates to the URL "<code>/</code>".
- But often this data is not really of top-level priority, it is
- perhaps just one entity of a lot of data pools. For instance at
- our Intranet sites there are <code>/e/www/</code>
- (the homepage for WWW), <code>/e/sww/</code> (the homepage for
- the Intranet) etc. Now because the data of the <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code> stays at <code>/e/www/</code> we had
- to make sure that all inlined images and other stuff inside this
- data pool work for subsequent requests.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We redirect the URL <code>/</code> to
- <code>/e/www/</code>:
- </p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteRule <strong>^/$</strong> /e/www/ [<strong>R</strong>]
-</pre></div>
-
- <p>Note that this can also be handled using the <code class="directive"><a href="../mod/mod_alias.html#redirectmatch">RedirectMatch</a></code> directive:</p>
-
- <div class="example"><p><code>
- RedirectMatch ^/$ http://example.com/e/www/
- </code></p></div>
- </dd>
- </dl>
-
-
-
- <h3>Trailing Slash Problem</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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
- <code>/~quux/foo</code> instead of <code>/~quux/foo/</code>
- then the server searches for a <em>file</em> named
- <code>foo</code>. 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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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 <code>image.gif</code> in
- <code>/~quux/foo/index.html</code> would become
- <code>/~quux/image.gif</code> without the external
- redirect!</p>
-
- <p>So, to do this trick we write:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^foo<strong>$</strong> foo<strong>/</strong> [<strong>R</strong>]
-</pre></div>
-
- <p>The crazy and lazy can even do the following in the
- top-level <code>.htaccess</code> file of their homedir.
- But notice that this creates some processing
- overhead.</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteCond %{REQUEST_FILENAME} <strong>-d</strong>
-RewriteRule ^(.+<strong>[^/]</strong>)$ $1<strong>/</strong> [R]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Webcluster through Homogeneous URL Layout</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>We want to create a homogeneous and consistent URL
- layout over all WWW servers on a Intranet webcluster, i.e.
- all URLs (per definition server local and thus server
- dependent!) become actually server <em>independent</em>!
- What we want is to give the WWW namespace a consistent
- server-independent layout: no URL should have to include
- any physically correct target server. The cluster itself
- should drive us automatically to the physical target
- host.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>First, the knowledge of the target servers come from
- (distributed) external maps which contain information
- where our users, groups and entities stay. The have the
- form</p>
-
-<div class="example"><pre>
-user1 server_of_user1
-user2 server_of_user2
-: :
-</pre></div>
-
- <p>We put them into files <code>map.xxx-to-host</code>.
- Second we need to instruct all servers to redirect URLs
- of the forms</p>
-
-<div class="example"><pre>
-/u/user/anypath
-/g/group/anypath
-/e/entity/anypath
-</pre></div>
-
- <p>to</p>
-
-<div class="example"><pre>
-http://physical-host/u/user/anypath
-http://physical-host/g/group/anypath
-http://physical-host/e/entity/anypath
-</pre></div>
-
- <p>when the URL is not locally valid to a server. The
- following ruleset does this for us by the help of the map
- files (assuming that server0 is a default server which
- will be used if a user has no entry in the map):</p>
-
-<div class="example"><pre>
-RewriteEngine on
-
-RewriteMap user-to-host txt:/path/to/map.user-to-host
-RewriteMap group-to-host txt:/path/to/map.group-to-host
-RewriteMap entity-to-host txt:/path/to/map.entity-to-host
-
-RewriteRule ^/u/<strong>([^/]+)</strong>/?(.*) http://<strong>${user-to-host:$1|server0}</strong>/u/$1/$2
-RewriteRule ^/g/<strong>([^/]+)</strong>/?(.*) http://<strong>${group-to-host:$1|server0}</strong>/g/$1/$2
-RewriteRule ^/e/<strong>([^/]+)</strong>/?(.*) http://<strong>${entity-to-host:$1|server0}</strong>/e/$1/$2
-
-RewriteRule ^/([uge])/([^/]+)/?$ /$1/$2/.www/
-RewriteRule ^/([uge])/([^/]+)/([^.]+.+) /$1/$2/.www/$3\
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Move Homedirs to Different Webserver</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>The solution is trivial with <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.
- On the old webserver we just redirect all
- <code>/~user/anypath</code> URLs to
- <code>http://newserver/~user/anypath</code>.</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteRule ^/~(.+) http://<strong>newserver</strong>/~$1 [R,L]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Structured Homedirs</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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, <code>/~foo/anypath</code>
- is <code>/home/<strong>f</strong>/foo/.www/anypath</code>
- while <code>/~bar/anypath</code> is
- <code>/home/<strong>b</strong>/bar/.www/anypath</code>.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We use the following ruleset to expand the tilde URLs
- into exactly the above layout.</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteRule ^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*) /home/<strong>$2</strong>/$1/.www$3
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Filesystem Reorganization</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>This really is a hardcore example: a killer application
- which heavily uses per-directory
- <code>RewriteRules</code> to get a smooth look and feel
- on the Web while its data structure is never touched or
- adjusted. Background: <strong><em>net.sw</em></strong> 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:</p>
-
-<div class="example"><pre>
-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/
-</pre></div>
-
- <p>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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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
- <code>/e/netsw/.www/</code> as follows:</p>
-
-<div class="example"><pre>
--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
-</pre></div>
-
- <p>The <code>DATA/</code> subdirectory holds the above
- directory structure, i.e. the real
- <strong><em>net.sw</em></strong> stuff and gets
- automatically updated via <code>rdist</code> 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 <code>DATA/</code> 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 <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code>
- of the server to rewrite the announced URL
- <code>/net.sw/</code> to the internal path
- <code>/e/netsw</code>:</p>
-
-<div class="example"><pre>
-RewriteRule ^net.sw$ net.sw/ [R]
-RewriteRule ^net.sw/(.*)$ e/netsw/$1
-</pre></div>
-
- <p>The first rule is for requests which miss the trailing
- slash! The second rule does the real thing. And then
- comes the killer configuration which stays in the
- per-directory config file
- <code>/e/netsw/.www/.wwwacl</code>:</p>
-
-<div class="example"><pre>
-Options ExecCGI FollowSymLinks Includes MultiViews
-
-RewriteEngine on
-
-# we are reached via /net.sw/ prefix
-RewriteBase /net.sw/
-
-# first we rewrite the root dir to
-# the handling cgi script
-RewriteRule ^$ 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
-</pre></div>
-
- <p>Some hints for interpretation:</p>
-
- <ol>
- <li>Notice the <code>L</code> (last) flag and no
- substitution field ('<code>-</code>') in the forth part</li>
-
- <li>Notice the <code>!</code> (not) character and
- the <code>C</code> (chain) flag at the first rule
- in the last part</li>
-
- <li>Notice the catch-all pattern in the last rule</li>
- </ol>
- </dd>
- </dl>
-
-
-
- <h3>NCSA imagemap to Apache <code>mod_imagemap</code></h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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
- <code>imagemap</code> program to work under Apache with the
- modern <code class="module"><a href="../mod/mod_imagemap.html">mod_imagemap</a></code>. The problem is that there
- are a lot of hyperlinks around which reference the
- <code>imagemap</code> program via
- <code>/cgi-bin/imagemap/path/to/page.map</code>. Under
- Apache this has to read just
- <code>/path/to/page.map</code>.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We use a global rule to remove the prefix on-the-fly for
- all requests:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteRule ^/cgi-bin/imagemap(.*) $1 [PT]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Search pages in more than one directory</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Sometimes it is necessary to let the webserver search
- for pages in more than one directory. Here MultiViews or
- other techniques cannot help.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We program a explicit ruleset which searches for the
- files in the directories.</p>
-
-<div class="example"><pre>
-RewriteEngine on
-
-# first try to find it in custom/...
-# ...and if found stop and be happy:
-RewriteCond /your/docroot/<strong>dir1</strong>/%{REQUEST_FILENAME} -f
-RewriteRule ^(.+) /your/docroot/<strong>dir1</strong>/$1 [L]
-
-# second try to find it in pub/...
-# ...and if found stop and be happy:
-RewriteCond /your/docroot/<strong>dir2</strong>/%{REQUEST_FILENAME} -f
-RewriteRule ^(.+) /your/docroot/<strong>dir2</strong>/$1 [L]
-
-# else go on for other Alias or ScriptAlias directives,
-# etc.
-RewriteRule ^(.+) - [PT]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Set Environment Variables According To URL Parts</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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 <code>/foo/S=java/bar/</code> gets translated to
- <code>/foo/bar/</code> and the environment variable named
- <code>STATUS</code> is set to the value "java".</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteRule ^(.*)/<strong>S=([^/]+)</strong>/(.*) $1/$3 [E=<strong>STATUS:$2</strong>]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Virtual User Hosts</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Assume that you want to provide
- <code>www.<strong>username</strong>.host.domain.com</code>
- for the homepage of username via just DNS A records to the
- same machine and without any virtualhosts on this
- machine.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>For HTTP/1.0 requests there is no solution, but for
- HTTP/1.1 requests which contain a Host: HTTP header we
- can use the following ruleset to rewrite
- <code>http://www.username.host.com/anypath</code>
- internally to <code>/home/username/anypath</code>:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteCond %{<strong>HTTP_HOST</strong>} ^www\.<strong>[^.]+</strong>\.host\.com$
-RewriteRule ^(.+) %{HTTP_HOST}$1 [C]
-RewriteRule ^www\.<strong>([^.]+)</strong>\.host\.com(.*) /home/<strong>$1</strong>$2
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Redirect Homedirs For Foreigners</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>We want to redirect homedir URLs to another webserver
- <code>www.somewhere.com</code> when the requesting user
- does not stay in the local domain
- <code>ourdomain.com</code>. This is sometimes used in
- virtual host contexts.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>Just a rewrite condition:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteCond %{REMOTE_HOST} <strong>!^.+\.ourdomain\.com$</strong>
-RewriteRule ^(/~.+) http://www.somewhere.com/$1 [R,L]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Redirect Failing URLs To Other Webserver</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>A typical FAQ about URL rewriting is how to redirect
- failing requests on webserver A to webserver B. Usually
- this is done via <code class="directive"><a href="../mod/core.html#errordocument">ErrorDocument</a></code> CGI-scripts in Perl, but
- there is also a <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> solution.
- But notice that this performs more poorly than using an
- <code class="directive"><a href="../mod/core.html#errordocument">ErrorDocument</a></code>
- CGI-script!</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>The first solution has the best performance but less
- flexibility, and is less error safe:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteCond /your/docroot/%{REQUEST_FILENAME} <strong>!-f</strong>
-RewriteRule ^(.+) http://<strong>webserverB</strong>.dom/$1
-</pre></div>
-
- <p>The problem here is that this will only work for pages
- inside the <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code>. While you can add more
- Conditions (for instance to also handle homedirs, etc.)
- there is better variant:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteCond %{REQUEST_URI} <strong>!-U</strong>
-RewriteRule ^(.+) http://<strong>webserverB</strong>.dom/$1
-</pre></div>
-
- <p>This uses the URL look-ahead feature of <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.
- 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 <code class="directive"><a href="../mod/core.html#errordocument">ErrorDocument</a></code> CGI-script.</p>
- </dd>
- </dl>
-
-
-
- <h3>Extended Redirection</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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 "<code>url#anchor</code>".
- You cannot use this directly on redirects with
- <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> because the
- <code>uri_escape()</code> function of Apache
- would also escape the hash character.
- How can we redirect to such a URL?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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 <code>xredirect:</code> by the following
- per-server config-line (should be one of the last rewrite
- rules):</p>
-
-<div class="example"><pre>
-RewriteRule ^xredirect:(.+) /path/to/nph-xredirect.cgi/$1 \
- [T=application/x-httpd-cgi,L]
-</pre></div>
-
- <p>This forces all URLs prefixed with
- <code>xredirect:</code> to be piped through the
- <code>nph-xredirect.cgi</code> program. And this program
- just looks like:</p>
-
-<div class="example"><pre>
-#!/path/to/perl
-##
-## nph-xredirect.cgi -- NPH/CGI script for extended redirects
-## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved.
-##
-
-$| = 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##
-</pre></div>
-
- <p>This provides you with the functionality to do
- redirects to all URL schemes, i.e. including the one
- which are not directly accepted by <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.
- For instance you can now also redirect to
- <code>news:newsgroup</code> via</p>
-
-<div class="example"><pre>
-RewriteRule ^anyurl xredirect:news:newsgroup
-</pre></div>
-
- <div class="note">Notice: You have not to put <code>[R]</code> or
- <code>[R,L]</code> to the above rule because the
- <code>xredirect:</code> need to be expanded later
- by our special "pipe through" rule above.</div>
- </dd>
- </dl>
-
-
-
- <h3>Archive Access Multiplexer</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Do you know the great CPAN (Comprehensive Perl Archive
- Network) under <a href="http://www.perl.com/CPAN">http://www.perl.com/CPAN</a>?
- 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 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>First we notice that from version 3.0.0
- <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> can
- also use the "<code>ftp:</code>" scheme on redirects.
- And second, the location approximation can be done by a
- <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>
- 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.</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteMap multiplex txt:/path/to/map.cxan
-RewriteRule ^/CxAN/(.*) %{REMOTE_HOST}::$1 [C]
-RewriteRule ^.+\.<strong>([a-zA-Z]+)</strong>::(.*)$ ${multiplex:<strong>$1</strong>|ftp.default.dom}$2 [R,L]
-</pre></div>
-
-<div class="example"><pre>
-##
-## map.cxan -- Multiplexing Map for CxAN
-##
-
-de ftp://ftp.cxan.de/CxAN/
-uk ftp://ftp.cxan.uk/CxAN/
-com ftp://ftp.cxan.com/CxAN/
- :
-##EOF##
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Time-Dependent Rewriting</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>When tricks like time-dependent content should happen a
- lot of webmasters still use CGI scripts which do for
- instance redirects to specialized pages. How can it be done
- via <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>There are a lot of variables named <code>TIME_xxx</code>
- for rewrite conditions. In conjunction with the special
- lexicographic comparison patterns <code><STRING</code>,
- <code>>STRING</code> and <code>=STRING</code> we can
- do time-dependent redirects:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteCond %{TIME_HOUR}%{TIME_MIN} >0700
-RewriteCond %{TIME_HOUR}%{TIME_MIN} <1900
-RewriteRule ^foo\.html$ foo.day.html
-RewriteRule ^foo\.html$ foo.night.html
-</pre></div>
-
- <p>This provides the content of <code>foo.day.html</code>
- under the URL <code>foo.html</code> from
- <code>07:00-19:00</code> and at the remaining time the
- contents of <code>foo.night.html</code>. Just a nice
- feature for a homepage...</p>
- </dd>
- </dl>
-
-
-
- <h3>Backward Compatibility for YYYY to XXXX migration</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>How can we make URLs backward compatible (still
- existing virtually) after migrating <code>document.YYYY</code>
- to <code>document.XXXX</code>, e.g. after translating a
- bunch of <code>.html</code> files to <code>.phtml</code>?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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.</p>
-
-
-<div class="example"><pre>
-# 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 ^(.*)$ $1.html
-</pre></div>
- </dd>
- </dl>
-
-
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="content" id="content">Content Handling</a></h2>
-
-
-
- <h3>From Old to New (intern)</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Assume we have recently renamed the page
- <code>foo.html</code> to <code>bar.html</code> and now want
- to provide the old URL for backward compatibility. Actually
- we want that users of the old URL even not recognize that
- the pages was renamed.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We rewrite the old URL to the new one internally via the
- following rule:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^<strong>foo</strong>\.html$ <strong>bar</strong>.html
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>From Old to New (extern)</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Assume again that we have recently renamed the page
- <code>foo.html</code> to <code>bar.html</code> 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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We force a HTTP redirect to the new URL which leads to a
- change of the browsers and thus the users view:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^<strong>foo</strong>\.html$ <strong>bar</strong>.html [<strong>R</strong>]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Browser Dependent Content</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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 <code>foo.html</code>
- is rewritten to <code>foo.NS.html</code> and and the
- rewriting stops. If the browser is "Lynx" or "Mozilla" of
- version 1 or 2 the URL becomes <code>foo.20.html</code>.
- All other browsers receive page <code>foo.32.html</code>.
- This is done by the following ruleset:</p>
-
-<div class="example"><pre>
-RewriteCond %{HTTP_USER_AGENT} ^<strong>Mozilla/3</strong>.*
-RewriteRule ^foo\.html$ foo.<strong>NS</strong>.html [<strong>L</strong>]
-
-RewriteCond %{HTTP_USER_AGENT} ^<strong>Lynx/</strong>.* [OR]
-RewriteCond %{HTTP_USER_AGENT} ^<strong>Mozilla/[12]</strong>.*
-RewriteRule ^foo\.html$ foo.<strong>20</strong>.html [<strong>L</strong>]
-
-RewriteRule ^foo\.html$ foo.<strong>32</strong>.html [<strong>L</strong>]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Dynamic Mirror</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Assume there are nice webpages on remote hosts we want
- to bring into our namespace. For FTP servers we would use
- the <code>mirror</code> 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
- <code>webcopy</code> 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).</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>To provide this feature we map the remote webpage or even
- the complete remote webarea to our namespace by the use
- of the <dfn>Proxy Throughput</dfn> feature
- (flag <code>[P]</code>):</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^<strong>hotsheet/</strong>(.*)$ <strong>http://www.tstimpreso.com/hotsheet/</strong>$1 [<strong>P</strong>]
-</pre></div>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^<strong>usa-news\.html</strong>$ <strong>http://www.quux-corp.com/news/index.html</strong> [<strong>P</strong>]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Reverse Dynamic Mirror</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>...</dd>
-
- <dt>Solution:</dt>
-
- <dd>
-<div class="example"><pre>
-RewriteEngine on
-RewriteCond /mirror/of/remotesite/$1 -U
-RewriteRule ^http://www\.remotesite\.com/(.*)$ /mirror/of/remotesite/$1
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Retrieve Missing Data from Intranet</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>This is a tricky way of virtually running a corporate
- (external) Internet webserver
- (<code>www.quux-corp.dom</code>), while actually keeping
- and maintaining its data on a (internal) Intranet webserver
- (<code>www2.quux-corp.dom</code>) 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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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:</p>
-
-<div class="example"><pre>
-<strong>ALLOW</strong> Host www.quux-corp.dom Port >1024 --> Host www2.quux-corp.dom Port <strong>80</strong>
-<strong>DENY</strong> Host * Port * --> Host www2.quux-corp.dom Port <strong>80</strong>
-</pre></div>
-
- <p>Just adjust it to your actual configuration syntax.
- Now we can establish the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
- rules which request the missing data in the background
- through the proxy throughput feature:</p>
-
-<div class="example"><pre>
-RewriteRule ^/~([^/]+)/?(.*) /home/$1/.www/$2
-RewriteCond %{REQUEST_FILENAME} <strong>!-f</strong>
-RewriteCond %{REQUEST_FILENAME} <strong>!-d</strong>
-RewriteRule ^/home/([^/]+)/.www/?(.*) http://<strong>www2</strong>.quux-corp.dom/~$1/pub/$2 [<strong>P</strong>]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Load Balancing</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Suppose we want to load balance the traffic to
- <code>www.foo.com</code> over <code>www[0-5].foo.com</code>
- (a total of 6 servers). How can this be done?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>:</p>
-
- <ol>
- <li>
- <strong>DNS Round-Robin</strong>
-
- <p>The simplest method for load-balancing is to use
- the DNS round-robin feature of <code>BIND</code>.
- Here you just configure <code>www[0-9].foo.com</code>
- as usual in your DNS with A(address) records, e.g.</p>
-
-<div class="example"><pre>
-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
-</pre></div>
-
- <p>Then you additionally add the following entry:</p>
-
-<div class="example"><pre>
-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
-</pre></div>
-
- <p>Now when <code>www.foo.com</code> gets
- resolved, <code>BIND</code> gives out <code>www0-www5</code>
- - 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 <code>www.foo.com</code>
- to a particular <code>wwwN.foo.com</code>, all
- subsequent requests also go to this particular name
- <code>wwwN.foo.com</code>. But the final result is
- ok, because the total sum of the requests are really
- spread over the various webservers.</p>
- </li>
-
- <li>
- <strong>DNS Load-Balancing</strong>
-
- <p>A sophisticated DNS-based method for
- load-balancing is to use the program
- <code>lbnamed</code> which can be found at <a href="http://www.stanford.edu/~schemers/docs/lbnamed/lbnamed.html">
- http://www.stanford.edu/~schemers/docs/lbnamed/lbnamed.html</a>.
- It is a Perl 5 program in conjunction with auxilliary
- tools which provides a real load-balancing for
- DNS.</p>
- </li>
-
- <li>
- <strong>Proxy Throughput Round-Robin</strong>
-
- <p>In this variant we use <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
- and its proxy throughput feature. First we dedicate
- <code>www0.foo.com</code> to be actually
- <code>www.foo.com</code> by using a single</p>
-
-<div class="example"><pre>
-www IN CNAME www0.foo.com.
-</pre></div>
-
- <p>entry in the DNS. Then we convert
- <code>www0.foo.com</code> 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 (<code>www1-www5</code>). To
- accomplish this we first establish a ruleset which
- contacts a load balancing script <code>lb.pl</code>
- for all URLs.</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteMap lb prg:/path/to/lb.pl
-RewriteRule ^/(.+)$ ${lb:$1} [P,L]
-</pre></div>
-
- <p>Then we write <code>lb.pl</code>:</p>
-
-<div class="example"><pre>
-#!/path/to/perl
-##
-## lb.pl -- load balancing script
-##
-
-$| = 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##
-</pre></div>
-
- <div class="note">A last notice: Why is this useful? Seems like
- <code>www0.foo.com</code> 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.</div>
- </li>
-
- <li>
- <strong>Hardware/TCP Round-Robin</strong>
-
- <p>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.</p>
- </li>
- </ol>
- </dd>
- </dl>
-
-
-
- <h3>New MIME-type, New Service</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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 <code>PATH_INFO</code>
- and <code>QUERY_STRINGS</code>) as their input. First,
- let us configure a new file type with extension
- <code>.scgi</code> (for secure CGI) which will be processed
- by the popular <code>cgiwrap</code> 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
- <code>/u/user/foo/bar.scgi</code>. But
- <code>cgiwrap</code> needs the URL in the form
- <code>/~user/foo/bar.scgi/</code>. The following rule
- solves the problem:</p>
-
-<div class="example"><pre>
-RewriteRule ^/[uge]/<strong>([^/]+)</strong>/\.www/(.+)\.scgi(.*) ...
-... /internal/cgi/user/cgiwrap/~<strong>$1</strong>/$2.scgi$3 [NS,<strong>T=application/x-http-cgi</strong>]
-</pre></div>
-
- <p>Or assume we have some more nifty programs:
- <code>wwwlog</code> (which displays the
- <code>access.log</code> for a URL subtree and
- <code>wwwidx</code> (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 <code>swwidx</code> program from within
- <code>/u/user/foo/</code> via hyperlink to</p>
-
-<div class="example"><pre>
-/internal/cgi/user/swwidx?i=/u/user/foo/
-</pre></div>
-
- <p>which is ugly. Because we have to hard-code
- <strong>both</strong> the location of the area
- <strong>and</strong> 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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>The solution here is to provide a special new URL format
- which automatically leads to the proper CGI invocation.
- We configure the following:</p>
-
-<div class="example"><pre>
-RewriteRule ^/([uge])/([^/]+)(/?.*)/\* /internal/cgi/user/wwwidx?i=/$1/$2$3/
-RewriteRule ^/([uge])/([^/]+)(/?.*):log /internal/cgi/user/wwwlog?f=/$1/$2$3
-</pre></div>
-
- <p>Now the hyperlink to search at
- <code>/u/user/foo/</code> reads only</p>
-
-<div class="example"><pre>
-HREF="*"
-</pre></div>
-
- <p>which internally gets automatically transformed to</p>
-
-<div class="example"><pre>
-/internal/cgi/user/wwwidx?i=/u/user/foo/
-</pre></div>
-
- <p>The same approach leads to an invocation for the
- access log CGI program when the hyperlink
- <code>:log</code> gets used.</p>
- </dd>
- </dl>
-
-
-
- <h3>From Static to Dynamic</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>How can we transform a static page
- <code>foo.html</code> into a dynamic variant
- <code>foo.cgi</code> in a seamless way, i.e. without notice
- by the browser/user.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We just rewrite the URL to the CGI-script and force the
- correct MIME-type so it gets really run as a CGI-script.
- This way a request to <code>/~quux/foo.html</code>
- internally leads to the invocation of
- <code>/~quux/foo.cgi</code>.</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^foo\.<strong>html</strong>$ foo.<strong>cgi</strong> [T=<strong>application/x-httpd-cgi</strong>]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>On-the-fly Content-Regeneration</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- This is done via the following ruleset:
-
-<div class="example"><pre>
-RewriteCond %{REQUEST_FILENAME} <strong>!-s</strong>
-RewriteRule ^page\.<strong>html</strong>$ page.<strong>cgi</strong> [T=application/x-httpd-cgi,L]
-</pre></div>
-
- <p>Here a request to <code>page.html</code> leads to a
- internal run of a corresponding <code>page.cgi</code> if
- <code>page.html</code> is still missing or has filesize
- null. The trick here is that <code>page.cgi</code> is a
- usual CGI script which (additionally to its <code>STDOUT</code>)
- writes its output to the file <code>page.html</code>.
- Once it was run, the server sends out the data of
- <code>page.html</code>. When the webmaster wants to force
- a refresh the contents, he just removes
- <code>page.html</code> (usually done by a cronjob).</p>
- </dd>
- </dl>
-
-
-
- <h3>Document With Autorefresh</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>No! We just combine the MIME multipart feature, the
- webserver NPH feature and the URL manipulation power of
- <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>. First, we establish a new
- URL feature: Adding just <code>:refresh</code> to any
- URL causes this to be refreshed every time it gets
- updated on the filesystem.</p>
-
-<div class="example"><pre>
-RewriteRule ^(/[uge]/[^/]+/?.*):refresh /internal/cgi/apache/nph-refresh?f=$1
-</pre></div>
-
- <p>Now when we reference the URL</p>
-
-<div class="example"><pre>
-/u/foo/bar/page.html:refresh
-</pre></div>
-
- <p>this leads to the internal invocation of the URL</p>
-
-<div class="example"><pre>
-/internal/cgi/apache/nph-refresh?f=/u/foo/bar/page.html
-</pre></div>
-
- <p>The only missing part is the NPH-CGI script. Although
- one would usually say "left as an exercise to the reader"
- ;-) I will provide this, too.</p>
-
-<div class="example"><pre>
-#!/sw/bin/perl
-##
-## nph-refresh -- NPH/CGI script for auto refreshing pages
-## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved.
-##
-$| = 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($QS_s);
- }
-}
-
-&print_http_headers_multipart_end;
-
-exit(0);
-
-##EOF##
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Mass Virtual Hosting</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>The <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code> feature of Apache is nice
- and works great when you just have a few dozens
- virtual hosts. But when you are an ISP and have hundreds of
- virtual hosts to provide this feature is not the best
- choice.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>To provide this feature we map the remote webpage or even
- the complete remote webarea to our namespace by the use
- of the <dfn>Proxy Throughput</dfn> feature (flag <code>[P]</code>):</p>
-
-<div class="example"><pre>
-##
-## vhost.map
-##
-www.vhost1.dom:80 /path/to/docroot/vhost1
-www.vhost2.dom:80 /path/to/docroot/vhost2
- :
-www.vhostN.dom:80 /path/to/docroot/vhostN
-</pre></div>
-
-<div class="example"><pre>
-##
-## httpd.conf
-##
- :
-# use the canonical hostname on redirects, etc.
-UseCanonicalName on
-
- :
-# add the virtual host in front of the CLF-format
-CustomLog /path/to/access_log "%{VHOST}e %h %l %u %t \"%r\" %>s %b"
- :
-
-# enable the rewriting engine in the main server
-RewriteEngine on
-
-# define two maps: one for fixing the URL and one which defines
-# the available virtual hosts with their corresponding
-# DocumentRoot.
-RewriteMap lowercase int:tolower
-RewriteMap vhost txt:/path/to/vhost.map
-
-# Now do the actual virtual host mapping
-# via a huge and complicated single rule:
-#
-# 1. make sure we don't map for common locations
-RewriteCond %{REQUEST_URL} !^/commonurl1/.*
-RewriteCond %{REQUEST_URL} !^/commonurl2/.*
- :
-RewriteCond %{REQUEST_URL} !^/commonurlN/.*
-#
-# 2. make sure we have a Host header, because
-# currently our approach only supports
-# virtual hosting through this header
-RewriteCond %{HTTP_HOST} !^$
-#
-# 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}}]
-</pre></div>
- </dd>
- </dl>
-
-
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="access" id="access">Access Restriction</a></h2>
-
-
-
- <h3>Blocking of Robots</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>How can we block a really annoying robot from
- retrieving pages of a specific webarea? A
- <code>/robots.txt</code> file containing entries of the
- "Robot Exclusion Protocol" is typically not enough to get
- rid of such a robot.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We use a ruleset which forbids the URLs of the webarea
- <code>/~quux/foo/arc/</code> (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.</p>
-
-<div class="example"><pre>
-RewriteCond %{HTTP_USER_AGENT} ^<strong>NameOfBadRobot</strong>.*
-RewriteCond %{REMOTE_ADDR} ^<strong>123\.45\.67\.[8-9]</strong>$
-RewriteRule ^<strong>/~quux/foo/arc/</strong>.+ - [<strong>F</strong>]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Blocked Inline-Images</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Assume we have under <code>http://www.quux-corp.de/~quux/</code>
- 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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>While we cannot 100% protect the images from inclusion,
- we can at least restrict the cases where the browser
- sends a HTTP Referer header.</p>
-
-<div class="example"><pre>
-RewriteCond %{HTTP_REFERER} <strong>!^$</strong>
-RewriteCond %{HTTP_REFERER} !^http://www.quux-corp.de/~quux/.*$ [NC]
-RewriteRule <strong>.*\.gif$</strong> - [F]
-</pre></div>
-
-<div class="example"><pre>
-RewriteCond %{HTTP_REFERER} !^$
-RewriteCond %{HTTP_REFERER} !.*/foo-with-gif\.html$
-RewriteRule <strong>^inlined-in-foo\.gif$</strong> - [F]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Host Deny</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>How can we forbid a list of externally configured hosts
- from using our server?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>For Apache >= 1.3b6:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteMap hosts-deny txt:/path/to/hosts.deny
-RewriteCond ${hosts-deny:%{REMOTE_HOST}|NOT-FOUND} !=NOT-FOUND [OR]
-RewriteCond ${hosts-deny:%{REMOTE_ADDR}|NOT-FOUND} !=NOT-FOUND
-RewriteRule ^/.* - [F]
-</pre></div>
-
- <p>For Apache <= 1.3b6:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteMap hosts-deny txt:/path/to/hosts.deny
-RewriteRule ^/(.*)$ ${hosts-deny:%{REMOTE_HOST}|NOT-FOUND}/$1
-RewriteRule !^NOT-FOUND/.* - [F]
-RewriteRule ^NOT-FOUND/(.*)$ ${hosts-deny:%{REMOTE_ADDR}|NOT-FOUND}/$1
-RewriteRule !^NOT-FOUND/.* - [F]
-RewriteRule ^NOT-FOUND/(.*)$ /$1
-</pre></div>
-
-<div class="example"><pre>
-##
-## hosts.deny
-##
-## ATTENTION! This is a map, not a list, even when we treat it as such.
-## mod_rewrite parses it for key/value pairs, so at least a
-## dummy value "-" must be present for each entry.
-##
-
-193.102.180.41 -
-bsdti1.sdm.de -
-192.76.162.40 -
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Proxy Deny</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>How can we forbid a certain host or even a user of a
- special host from using the Apache proxy?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We first have to make sure <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
- is below(!) <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> in the Configuration
- file when compiling the Apache webserver. This way it gets
- called <em>before</em> <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code>. Then we
- configure the following for a host-dependent deny...</p>
-
-<div class="example"><pre>
-RewriteCond %{REMOTE_HOST} <strong>^badhost\.mydomain\.com$</strong>
-RewriteRule !^http://[^/.]\.mydomain.com.* - [F]
-</pre></div>
-
- <p>...and this one for a user@host-dependent deny:</p>
-
-<div class="example"><pre>
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>^badguy@badhost\.mydomain\.com$</strong>
-RewriteRule !^http://[^/.]\.mydomain.com.* - [F]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Special Authentication Variant</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Sometimes a very special authentication is needed, for
- instance a authentication which checks for a set of
- explicitly configured users. Only these should receive
- access and without explicit prompting (which would occur
- when using the Basic Auth via <code class="module"><a href="../mod/mod_auth_basic.html">mod_auth_basic</a></code>).</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We use a list of rewrite conditions to exclude all except
- our friends:</p>
-
-<div class="example"><pre>
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>!^friend1@client1.quux-corp\.com$</strong>
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>!^friend2</strong>@client2.quux-corp\.com$
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>!^friend3</strong>@client3.quux-corp\.com$
-RewriteRule ^/~quux/only-for-friends/ - [F]
-</pre></div>
- </dd>
- </dl>
-
-
-
- <h3>Referer-based Deflector</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>Use the following really tricky ruleset...</p>
-
-<div class="example"><pre>
-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 ^.* ${deflector:%{HTTP_REFERER}} [R,L]
-</pre></div>
-
- <p>... in conjunction with a corresponding rewrite
- map:</p>
-
-<div class="example"><pre>
-##
-## deflector.map
-##
-
-http://www.badguys.com/bad/index.html -
-http://www.badguys.com/bad/index2.html -
-http://www.badguys.com/bad/index3.html http://somewhere.com/
-</pre></div>
-
- <p>This automatically redirects the request back to the
- referring page (when "<code>-</code>" is used as the value
- in the map) or to a specific URL (when an URL is specified
- in the map as the second argument).</p>
- </dd>
- </dl>
-
-
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="other" id="other">Other</a></h2>
-
-
-
- <h3>External Rewriting Engine</h3>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>A FAQ: How can we solve the FOO/BAR/QUUX/etc.
- problem? There seems no solution by the use of
- <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>...</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>Use an external <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>, i.e. a program which acts
- like a <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>. It is run once on startup of Apache
- receives the requested URLs on <code>STDIN</code> and has
- to put the resulting (usually rewritten) URL on
- <code>STDOUT</code> (same order!).</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteMap quux-map <strong>prg:</strong>/path/to/map.quux.pl
-RewriteRule ^/~quux/(.*)$ /~quux/<strong>${quux-map:$1}</strong>
-</pre></div>
-
-<div class="example"><pre>
-#!/path/to/perl
-
-# disable buffered I/O which would lead
-# to deadloops for the Apache server
-$| = 1;
-
-# read URLs one per line from stdin and
-# generate substitution URL on stdout
-while (<>) {
- s|^foo/|bar/|;
- print $_;
-}
-</pre></div>
-
- <p>This is a demonstration-only example and just rewrites
- all URLs <code>/~quux/foo/...</code> to
- <code>/~quux/bar/...</code>. Actually you can program
- whatever you like. But notice that while such maps can be
- <strong>used</strong> also by an average user, only the
- system administrator can <strong>define</strong> it.</p>
- </dd>
- </dl>
-
-
-
- </div></div>
-<div class="bottomlang">
-<p><span>Available Languages: </span><a href="../en/misc/rewriteguide.html" title="English"> en </a> |
-<a href="../ko/misc/rewriteguide.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
-</div><div id="footer">
-<p class="apache">Copyright 2008 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
-<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>
-</body></html>
\ No newline at end of file
+++ /dev/null
-<?xml version="1.0" encoding="UTF-8" ?>
-<!DOCTYPE manualpage SYSTEM "../style/manualpage.dtd">
-<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
-<!-- $LastChangedRevision$ -->
-
-<!--
- Licensed to the Apache Software Foundation (ASF) under one or more
- contributor license agreements. See the NOTICE file distributed with
- this work for additional information regarding copyright ownership.
- The ASF licenses this file to You under the Apache License, Version 2.0
- (the "License"); you may not use this file except in compliance with
- the License. You may obtain a copy of the License at
-
- http://www.apache.org/licenses/LICENSE-2.0
-
- Unless required by applicable law or agreed to in writing, software
- distributed under the License is distributed on an "AS IS" BASIS,
- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- See the License for the specific language governing permissions and
- limitations under the License.
--->
-
-<manualpage metafile="rewriteguide.xml.meta">
- <parentdocument href="./">Miscellaneous Documentation</parentdocument>
-
- <title>URL Rewriting Guide</title>
-
- <summary>
- <note>
- <p>Originally written by<br />
- <cite>Ralf S. Engelschall <rse@apache.org></cite><br />
- December 1997</p>
- </note>
-
- <p>This document supplements the <module>mod_rewrite</module>
- <a href="../mod/mod_rewrite.html">reference documentation</a>.
- It describes how one can use Apache's <module>mod_rewrite</module>
- to solve typical URL-based problems with which webmasters are
- commonly confronted. We give detailed descriptions on how to
- solve each problem by configuring URL rewriting rulesets.</p>
-
- </summary>
-
- <section id="ToC1">
-
- <title>Introduction to <code>mod_rewrite</code></title>
-
- <p>The Apache module <module>mod_rewrite</module> 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
- <module>mod_rewrite</module>'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
- <module>mod_rewrite</module> can help.</p>
-
- <p>In other words: With <module>mod_rewrite</module> 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.</p>
-
- </section>
-
- <section id="ToC2">
-
- <title>Practical Solutions</title>
-
- <p>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.</p>
-
- <note type="warning">ATTENTION: Depending on your server-configuration
- it can be necessary to slightly change the examples for your
- situation, e.g. adding the <code>[PT]</code> flag when
- additionally using <module>mod_alias</module> and
- <module>mod_userdir</module>, etc. Or rewriting a ruleset
- to fit in <code>.htaccess</code> context instead
- of per-server context. Always try to understand what a
- particular ruleset really does before you use it. It
- avoids problems.</note>
-
- </section>
-
- <section id="url">
-
- <title>URL Layout</title>
-
- <section>
-
- <title>Canonical URLs</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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 <code>/~user</code> by the canonical
- <code>/u/user</code> and fix a missing trailing slash for
- <code>/u/user</code>.</p>
-
-<example><pre>
-RewriteRule ^/<strong>~</strong>([^/]+)/?(.*) /<strong>u</strong>/$1/$2 [<strong>R</strong>]
-RewriteRule ^/([uge])/(<strong>[^/]+</strong>)$ /$1/$2<strong>/</strong> [<strong>R</strong>]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Canonical Hostnames</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>...</dd>
-
- <dt>Solution:</dt>
-
- <dd>
-<example><pre>
-RewriteCond %{HTTP_HOST} !^fully\.qualified\.domain\.name [NC]
-RewriteCond %{HTTP_HOST} !^$
-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/$1 [L,R]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Moved <code>DocumentRoot</code></title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Usually the <directive module="core">DocumentRoot</directive>
- of the webserver directly relates to the URL "<code>/</code>".
- But often this data is not really of top-level priority, it is
- perhaps just one entity of a lot of data pools. For instance at
- our Intranet sites there are <code>/e/www/</code>
- (the homepage for WWW), <code>/e/sww/</code> (the homepage for
- the Intranet) etc. Now because the data of the <directive module="core"
- >DocumentRoot</directive> stays at <code>/e/www/</code> we had
- to make sure that all inlined images and other stuff inside this
- data pool work for subsequent requests.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We redirect the URL <code>/</code> to
- <code>/e/www/</code>:
- </p>
-
-<example><pre>
-RewriteEngine on
-RewriteRule <strong>^/$</strong> /e/www/ [<strong>R</strong>]
-</pre></example>
-
- <p>Note that this can also be handled using the <directive
- module="mod_alias">RedirectMatch</directive> directive:</p>
-
- <example>
- RedirectMatch ^/$ http://example.com/e/www/
- </example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Trailing Slash Problem</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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
- <code>/~quux/foo</code> instead of <code>/~quux/foo/</code>
- then the server searches for a <em>file</em> named
- <code>foo</code>. 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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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 <code>image.gif</code> in
- <code>/~quux/foo/index.html</code> would become
- <code>/~quux/image.gif</code> without the external
- redirect!</p>
-
- <p>So, to do this trick we write:</p>
-
-<example><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^foo<strong>$</strong> foo<strong>/</strong> [<strong>R</strong>]
-</pre></example>
-
- <p>The crazy and lazy can even do the following in the
- top-level <code>.htaccess</code> file of their homedir.
- But notice that this creates some processing
- overhead.</p>
-
-<example><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteCond %{REQUEST_FILENAME} <strong>-d</strong>
-RewriteRule ^(.+<strong>[^/]</strong>)$ $1<strong>/</strong> [R]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Webcluster through Homogeneous URL Layout</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>We want to create a homogeneous and consistent URL
- layout over all WWW servers on a Intranet webcluster, i.e.
- all URLs (per definition server local and thus server
- dependent!) become actually server <em>independent</em>!
- What we want is to give the WWW namespace a consistent
- server-independent layout: no URL should have to include
- any physically correct target server. The cluster itself
- should drive us automatically to the physical target
- host.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>First, the knowledge of the target servers come from
- (distributed) external maps which contain information
- where our users, groups and entities stay. The have the
- form</p>
-
-<example><pre>
-user1 server_of_user1
-user2 server_of_user2
-: :
-</pre></example>
-
- <p>We put them into files <code>map.xxx-to-host</code>.
- Second we need to instruct all servers to redirect URLs
- of the forms</p>
-
-<example><pre>
-/u/user/anypath
-/g/group/anypath
-/e/entity/anypath
-</pre></example>
-
- <p>to</p>
-
-<example><pre>
-http://physical-host/u/user/anypath
-http://physical-host/g/group/anypath
-http://physical-host/e/entity/anypath
-</pre></example>
-
- <p>when the URL is not locally valid to a server. The
- following ruleset does this for us by the help of the map
- files (assuming that server0 is a default server which
- will be used if a user has no entry in the map):</p>
-
-<example><pre>
-RewriteEngine on
-
-RewriteMap user-to-host txt:/path/to/map.user-to-host
-RewriteMap group-to-host txt:/path/to/map.group-to-host
-RewriteMap entity-to-host txt:/path/to/map.entity-to-host
-
-RewriteRule ^/u/<strong>([^/]+)</strong>/?(.*) http://<strong>${user-to-host:$1|server0}</strong>/u/$1/$2
-RewriteRule ^/g/<strong>([^/]+)</strong>/?(.*) http://<strong>${group-to-host:$1|server0}</strong>/g/$1/$2
-RewriteRule ^/e/<strong>([^/]+)</strong>/?(.*) http://<strong>${entity-to-host:$1|server0}</strong>/e/$1/$2
-
-RewriteRule ^/([uge])/([^/]+)/?$ /$1/$2/.www/
-RewriteRule ^/([uge])/([^/]+)/([^.]+.+) /$1/$2/.www/$3\
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Move Homedirs to Different Webserver</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>The solution is trivial with <module>mod_rewrite</module>.
- On the old webserver we just redirect all
- <code>/~user/anypath</code> URLs to
- <code>http://newserver/~user/anypath</code>.</p>
-
-<example><pre>
-RewriteEngine on
-RewriteRule ^/~(.+) http://<strong>newserver</strong>/~$1 [R,L]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Structured Homedirs</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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, <code>/~foo/anypath</code>
- is <code>/home/<strong>f</strong>/foo/.www/anypath</code>
- while <code>/~bar/anypath</code> is
- <code>/home/<strong>b</strong>/bar/.www/anypath</code>.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We use the following ruleset to expand the tilde URLs
- into exactly the above layout.</p>
-
-<example><pre>
-RewriteEngine on
-RewriteRule ^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*) /home/<strong>$2</strong>/$1/.www$3
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Filesystem Reorganization</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>This really is a hardcore example: a killer application
- which heavily uses per-directory
- <code>RewriteRules</code> to get a smooth look and feel
- on the Web while its data structure is never touched or
- adjusted. Background: <strong><em>net.sw</em></strong> 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:</p>
-
-<example><pre>
-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/
-</pre></example>
-
- <p>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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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
- <code>/e/netsw/.www/</code> as follows:</p>
-
-<example><pre>
--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
-</pre></example>
-
- <p>The <code>DATA/</code> subdirectory holds the above
- directory structure, i.e. the real
- <strong><em>net.sw</em></strong> stuff and gets
- automatically updated via <code>rdist</code> 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 <code>DATA/</code> 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 <directive module="core">DocumentRoot</directive>
- of the server to rewrite the announced URL
- <code>/net.sw/</code> to the internal path
- <code>/e/netsw</code>:</p>
-
-<example><pre>
-RewriteRule ^net.sw$ net.sw/ [R]
-RewriteRule ^net.sw/(.*)$ e/netsw/$1
-</pre></example>
-
- <p>The first rule is for requests which miss the trailing
- slash! The second rule does the real thing. And then
- comes the killer configuration which stays in the
- per-directory config file
- <code>/e/netsw/.www/.wwwacl</code>:</p>
-
-<example><pre>
-Options ExecCGI FollowSymLinks Includes MultiViews
-
-RewriteEngine on
-
-# we are reached via /net.sw/ prefix
-RewriteBase /net.sw/
-
-# first we rewrite the root dir to
-# the handling cgi script
-RewriteRule ^$ 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
-</pre></example>
-
- <p>Some hints for interpretation:</p>
-
- <ol>
- <li>Notice the <code>L</code> (last) flag and no
- substitution field ('<code>-</code>') in the forth part</li>
-
- <li>Notice the <code>!</code> (not) character and
- the <code>C</code> (chain) flag at the first rule
- in the last part</li>
-
- <li>Notice the catch-all pattern in the last rule</li>
- </ol>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>NCSA imagemap to Apache <code>mod_imagemap</code></title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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
- <code>imagemap</code> program to work under Apache with the
- modern <module>mod_imagemap</module>. The problem is that there
- are a lot of hyperlinks around which reference the
- <code>imagemap</code> program via
- <code>/cgi-bin/imagemap/path/to/page.map</code>. Under
- Apache this has to read just
- <code>/path/to/page.map</code>.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We use a global rule to remove the prefix on-the-fly for
- all requests:</p>
-
-<example><pre>
-RewriteEngine on
-RewriteRule ^/cgi-bin/imagemap(.*) $1 [PT]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Search pages in more than one directory</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Sometimes it is necessary to let the webserver search
- for pages in more than one directory. Here MultiViews or
- other techniques cannot help.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We program a explicit ruleset which searches for the
- files in the directories.</p>
-
-<example><pre>
-RewriteEngine on
-
-# first try to find it in custom/...
-# ...and if found stop and be happy:
-RewriteCond /your/docroot/<strong>dir1</strong>/%{REQUEST_FILENAME} -f
-RewriteRule ^(.+) /your/docroot/<strong>dir1</strong>/$1 [L]
-
-# second try to find it in pub/...
-# ...and if found stop and be happy:
-RewriteCond /your/docroot/<strong>dir2</strong>/%{REQUEST_FILENAME} -f
-RewriteRule ^(.+) /your/docroot/<strong>dir2</strong>/$1 [L]
-
-# else go on for other Alias or ScriptAlias directives,
-# etc.
-RewriteRule ^(.+) - [PT]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Set Environment Variables According To URL Parts</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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 <code>/foo/S=java/bar/</code> gets translated to
- <code>/foo/bar/</code> and the environment variable named
- <code>STATUS</code> is set to the value "java".</p>
-
-<example><pre>
-RewriteEngine on
-RewriteRule ^(.*)/<strong>S=([^/]+)</strong>/(.*) $1/$3 [E=<strong>STATUS:$2</strong>]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Virtual User Hosts</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Assume that you want to provide
- <code>www.<strong>username</strong>.host.domain.com</code>
- for the homepage of username via just DNS A records to the
- same machine and without any virtualhosts on this
- machine.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>For HTTP/1.0 requests there is no solution, but for
- HTTP/1.1 requests which contain a Host: HTTP header we
- can use the following ruleset to rewrite
- <code>http://www.username.host.com/anypath</code>
- internally to <code>/home/username/anypath</code>:</p>
-
-<example><pre>
-RewriteEngine on
-RewriteCond %{<strong>HTTP_HOST</strong>} ^www\.<strong>[^.]+</strong>\.host\.com$
-RewriteRule ^(.+) %{HTTP_HOST}$1 [C]
-RewriteRule ^www\.<strong>([^.]+)</strong>\.host\.com(.*) /home/<strong>$1</strong>$2
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Redirect Homedirs For Foreigners</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>We want to redirect homedir URLs to another webserver
- <code>www.somewhere.com</code> when the requesting user
- does not stay in the local domain
- <code>ourdomain.com</code>. This is sometimes used in
- virtual host contexts.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>Just a rewrite condition:</p>
-
-<example><pre>
-RewriteEngine on
-RewriteCond %{REMOTE_HOST} <strong>!^.+\.ourdomain\.com$</strong>
-RewriteRule ^(/~.+) http://www.somewhere.com/$1 [R,L]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Redirect Failing URLs To Other Webserver</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>A typical FAQ about URL rewriting is how to redirect
- failing requests on webserver A to webserver B. Usually
- this is done via <directive module="core"
- >ErrorDocument</directive> CGI-scripts in Perl, but
- there is also a <module>mod_rewrite</module> solution.
- But notice that this performs more poorly than using an
- <directive module="core">ErrorDocument</directive>
- CGI-script!</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>The first solution has the best performance but less
- flexibility, and is less error safe:</p>
-
-<example><pre>
-RewriteEngine on
-RewriteCond /your/docroot/%{REQUEST_FILENAME} <strong>!-f</strong>
-RewriteRule ^(.+) http://<strong>webserverB</strong>.dom/$1
-</pre></example>
-
- <p>The problem here is that this will only work for pages
- inside the <directive module="core">DocumentRoot</directive>. While you can add more
- Conditions (for instance to also handle homedirs, etc.)
- there is better variant:</p>
-
-<example><pre>
-RewriteEngine on
-RewriteCond %{REQUEST_URI} <strong>!-U</strong>
-RewriteRule ^(.+) http://<strong>webserverB</strong>.dom/$1
-</pre></example>
-
- <p>This uses the URL look-ahead feature of <module>mod_rewrite</module>.
- 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 <directive module="core"
- >ErrorDocument</directive> CGI-script.</p>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Extended Redirection</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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 "<code>url#anchor</code>".
- You cannot use this directly on redirects with
- <module>mod_rewrite</module> because the
- <code>uri_escape()</code> function of Apache
- would also escape the hash character.
- How can we redirect to such a URL?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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 <code>xredirect:</code> by the following
- per-server config-line (should be one of the last rewrite
- rules):</p>
-
-<example><pre>
-RewriteRule ^xredirect:(.+) /path/to/nph-xredirect.cgi/$1 \
- [T=application/x-httpd-cgi,L]
-</pre></example>
-
- <p>This forces all URLs prefixed with
- <code>xredirect:</code> to be piped through the
- <code>nph-xredirect.cgi</code> program. And this program
- just looks like:</p>
-
-<example><pre>
-#!/path/to/perl
-##
-## nph-xredirect.cgi -- NPH/CGI script for extended redirects
-## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved.
-##
-
-$| = 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##
-</pre></example>
-
- <p>This provides you with the functionality to do
- redirects to all URL schemes, i.e. including the one
- which are not directly accepted by <module>mod_rewrite</module>.
- For instance you can now also redirect to
- <code>news:newsgroup</code> via</p>
-
-<example><pre>
-RewriteRule ^anyurl xredirect:news:newsgroup
-</pre></example>
-
- <note>Notice: You have not to put <code>[R]</code> or
- <code>[R,L]</code> to the above rule because the
- <code>xredirect:</code> need to be expanded later
- by our special "pipe through" rule above.</note>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Archive Access Multiplexer</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Do you know the great CPAN (Comprehensive Perl Archive
- Network) under <a href="http://www.perl.com/CPAN"
- >http://www.perl.com/CPAN</a>?
- 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 <module>mod_rewrite</module>?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>First we notice that from version 3.0.0
- <module>mod_rewrite</module> can
- also use the "<code>ftp:</code>" scheme on redirects.
- And second, the location approximation can be done by a
- <directive module="mod_rewrite">RewriteMap</directive>
- 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.</p>
-
-<example><pre>
-RewriteEngine on
-RewriteMap multiplex txt:/path/to/map.cxan
-RewriteRule ^/CxAN/(.*) %{REMOTE_HOST}::$1 [C]
-RewriteRule ^.+\.<strong>([a-zA-Z]+)</strong>::(.*)$ ${multiplex:<strong>$1</strong>|ftp.default.dom}$2 [R,L]
-</pre></example>
-
-<example><pre>
-##
-## map.cxan -- Multiplexing Map for CxAN
-##
-
-de ftp://ftp.cxan.de/CxAN/
-uk ftp://ftp.cxan.uk/CxAN/
-com ftp://ftp.cxan.com/CxAN/
- :
-##EOF##
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Time-Dependent Rewriting</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>When tricks like time-dependent content should happen a
- lot of webmasters still use CGI scripts which do for
- instance redirects to specialized pages. How can it be done
- via <module>mod_rewrite</module>?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>There are a lot of variables named <code>TIME_xxx</code>
- for rewrite conditions. In conjunction with the special
- lexicographic comparison patterns <code><STRING</code>,
- <code>>STRING</code> and <code>=STRING</code> we can
- do time-dependent redirects:</p>
-
-<example><pre>
-RewriteEngine on
-RewriteCond %{TIME_HOUR}%{TIME_MIN} >0700
-RewriteCond %{TIME_HOUR}%{TIME_MIN} <1900
-RewriteRule ^foo\.html$ foo.day.html
-RewriteRule ^foo\.html$ foo.night.html
-</pre></example>
-
- <p>This provides the content of <code>foo.day.html</code>
- under the URL <code>foo.html</code> from
- <code>07:00-19:00</code> and at the remaining time the
- contents of <code>foo.night.html</code>. Just a nice
- feature for a homepage...</p>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Backward Compatibility for YYYY to XXXX migration</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>How can we make URLs backward compatible (still
- existing virtually) after migrating <code>document.YYYY</code>
- to <code>document.XXXX</code>, e.g. after translating a
- bunch of <code>.html</code> files to <code>.phtml</code>?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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.</p>
-
-
-<example><pre>
-# 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 ^(.*)$ $1.html
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- </section>
-
- <section id="content">
-
- <title>Content Handling</title>
-
- <section>
-
- <title>From Old to New (intern)</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Assume we have recently renamed the page
- <code>foo.html</code> to <code>bar.html</code> and now want
- to provide the old URL for backward compatibility. Actually
- we want that users of the old URL even not recognize that
- the pages was renamed.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We rewrite the old URL to the new one internally via the
- following rule:</p>
-
-<example><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^<strong>foo</strong>\.html$ <strong>bar</strong>.html
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>From Old to New (extern)</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Assume again that we have recently renamed the page
- <code>foo.html</code> to <code>bar.html</code> 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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We force a HTTP redirect to the new URL which leads to a
- change of the browsers and thus the users view:</p>
-
-<example><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^<strong>foo</strong>\.html$ <strong>bar</strong>.html [<strong>R</strong>]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Browser Dependent Content</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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 <code>foo.html</code>
- is rewritten to <code>foo.NS.html</code> and and the
- rewriting stops. If the browser is "Lynx" or "Mozilla" of
- version 1 or 2 the URL becomes <code>foo.20.html</code>.
- All other browsers receive page <code>foo.32.html</code>.
- This is done by the following ruleset:</p>
-
-<example><pre>
-RewriteCond %{HTTP_USER_AGENT} ^<strong>Mozilla/3</strong>.*
-RewriteRule ^foo\.html$ foo.<strong>NS</strong>.html [<strong>L</strong>]
-
-RewriteCond %{HTTP_USER_AGENT} ^<strong>Lynx/</strong>.* [OR]
-RewriteCond %{HTTP_USER_AGENT} ^<strong>Mozilla/[12]</strong>.*
-RewriteRule ^foo\.html$ foo.<strong>20</strong>.html [<strong>L</strong>]
-
-RewriteRule ^foo\.html$ foo.<strong>32</strong>.html [<strong>L</strong>]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Dynamic Mirror</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Assume there are nice webpages on remote hosts we want
- to bring into our namespace. For FTP servers we would use
- the <code>mirror</code> 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
- <code>webcopy</code> 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).</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>To provide this feature we map the remote webpage or even
- the complete remote webarea to our namespace by the use
- of the <dfn>Proxy Throughput</dfn> feature
- (flag <code>[P]</code>):</p>
-
-<example><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^<strong>hotsheet/</strong>(.*)$ <strong>http://www.tstimpreso.com/hotsheet/</strong>$1 [<strong>P</strong>]
-</pre></example>
-
-<example><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^<strong>usa-news\.html</strong>$ <strong>http://www.quux-corp.com/news/index.html</strong> [<strong>P</strong>]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Reverse Dynamic Mirror</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>...</dd>
-
- <dt>Solution:</dt>
-
- <dd>
-<example><pre>
-RewriteEngine on
-RewriteCond /mirror/of/remotesite/$1 -U
-RewriteRule ^http://www\.remotesite\.com/(.*)$ /mirror/of/remotesite/$1
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Retrieve Missing Data from Intranet</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>This is a tricky way of virtually running a corporate
- (external) Internet webserver
- (<code>www.quux-corp.dom</code>), while actually keeping
- and maintaining its data on a (internal) Intranet webserver
- (<code>www2.quux-corp.dom</code>) 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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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:</p>
-
-<example><pre>
-<strong>ALLOW</strong> Host www.quux-corp.dom Port >1024 --> Host www2.quux-corp.dom Port <strong>80</strong>
-<strong>DENY</strong> Host * Port * --> Host www2.quux-corp.dom Port <strong>80</strong>
-</pre></example>
-
- <p>Just adjust it to your actual configuration syntax.
- Now we can establish the <module>mod_rewrite</module>
- rules which request the missing data in the background
- through the proxy throughput feature:</p>
-
-<example><pre>
-RewriteRule ^/~([^/]+)/?(.*) /home/$1/.www/$2
-RewriteCond %{REQUEST_FILENAME} <strong>!-f</strong>
-RewriteCond %{REQUEST_FILENAME} <strong>!-d</strong>
-RewriteRule ^/home/([^/]+)/.www/?(.*) http://<strong>www2</strong>.quux-corp.dom/~$1/pub/$2 [<strong>P</strong>]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Load Balancing</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Suppose we want to load balance the traffic to
- <code>www.foo.com</code> over <code>www[0-5].foo.com</code>
- (a total of 6 servers). How can this be done?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>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 <module>mod_rewrite</module>:</p>
-
- <ol>
- <li>
- <strong>DNS Round-Robin</strong>
-
- <p>The simplest method for load-balancing is to use
- the DNS round-robin feature of <code>BIND</code>.
- Here you just configure <code>www[0-9].foo.com</code>
- as usual in your DNS with A(address) records, e.g.</p>
-
-<example><pre>
-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
-</pre></example>
-
- <p>Then you additionally add the following entry:</p>
-
-<example><pre>
-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
-</pre></example>
-
- <p>Now when <code>www.foo.com</code> gets
- resolved, <code>BIND</code> gives out <code>www0-www5</code>
- - 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 <code>www.foo.com</code>
- to a particular <code>wwwN.foo.com</code>, all
- subsequent requests also go to this particular name
- <code>wwwN.foo.com</code>. But the final result is
- ok, because the total sum of the requests are really
- spread over the various webservers.</p>
- </li>
-
- <li>
- <strong>DNS Load-Balancing</strong>
-
- <p>A sophisticated DNS-based method for
- load-balancing is to use the program
- <code>lbnamed</code> which can be found at <a
- href="http://www.stanford.edu/~schemers/docs/lbnamed/lbnamed.html">
- http://www.stanford.edu/~schemers/docs/lbnamed/lbnamed.html</a>.
- It is a Perl 5 program in conjunction with auxilliary
- tools which provides a real load-balancing for
- DNS.</p>
- </li>
-
- <li>
- <strong>Proxy Throughput Round-Robin</strong>
-
- <p>In this variant we use <module>mod_rewrite</module>
- and its proxy throughput feature. First we dedicate
- <code>www0.foo.com</code> to be actually
- <code>www.foo.com</code> by using a single</p>
-
-<example><pre>
-www IN CNAME www0.foo.com.
-</pre></example>
-
- <p>entry in the DNS. Then we convert
- <code>www0.foo.com</code> 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 (<code>www1-www5</code>). To
- accomplish this we first establish a ruleset which
- contacts a load balancing script <code>lb.pl</code>
- for all URLs.</p>
-
-<example><pre>
-RewriteEngine on
-RewriteMap lb prg:/path/to/lb.pl
-RewriteRule ^/(.+)$ ${lb:$1} [P,L]
-</pre></example>
-
- <p>Then we write <code>lb.pl</code>:</p>
-
-<example><pre>
-#!/path/to/perl
-##
-## lb.pl -- load balancing script
-##
-
-$| = 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##
-</pre></example>
-
- <note>A last notice: Why is this useful? Seems like
- <code>www0.foo.com</code> 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.</note>
- </li>
-
- <li>
- <strong>Hardware/TCP Round-Robin</strong>
-
- <p>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.</p>
- </li>
- </ol>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>New MIME-type, New Service</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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 <code>PATH_INFO</code>
- and <code>QUERY_STRINGS</code>) as their input. First,
- let us configure a new file type with extension
- <code>.scgi</code> (for secure CGI) which will be processed
- by the popular <code>cgiwrap</code> 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
- <code>/u/user/foo/bar.scgi</code>. But
- <code>cgiwrap</code> needs the URL in the form
- <code>/~user/foo/bar.scgi/</code>. The following rule
- solves the problem:</p>
-
-<example><pre>
-RewriteRule ^/[uge]/<strong>([^/]+)</strong>/\.www/(.+)\.scgi(.*) ...
-... /internal/cgi/user/cgiwrap/~<strong>$1</strong>/$2.scgi$3 [NS,<strong>T=application/x-http-cgi</strong>]
-</pre></example>
-
- <p>Or assume we have some more nifty programs:
- <code>wwwlog</code> (which displays the
- <code>access.log</code> for a URL subtree and
- <code>wwwidx</code> (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 <code>swwidx</code> program from within
- <code>/u/user/foo/</code> via hyperlink to</p>
-
-<example><pre>
-/internal/cgi/user/swwidx?i=/u/user/foo/
-</pre></example>
-
- <p>which is ugly. Because we have to hard-code
- <strong>both</strong> the location of the area
- <strong>and</strong> 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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>The solution here is to provide a special new URL format
- which automatically leads to the proper CGI invocation.
- We configure the following:</p>
-
-<example><pre>
-RewriteRule ^/([uge])/([^/]+)(/?.*)/\* /internal/cgi/user/wwwidx?i=/$1/$2$3/
-RewriteRule ^/([uge])/([^/]+)(/?.*):log /internal/cgi/user/wwwlog?f=/$1/$2$3
-</pre></example>
-
- <p>Now the hyperlink to search at
- <code>/u/user/foo/</code> reads only</p>
-
-<example><pre>
-HREF="*"
-</pre></example>
-
- <p>which internally gets automatically transformed to</p>
-
-<example><pre>
-/internal/cgi/user/wwwidx?i=/u/user/foo/
-</pre></example>
-
- <p>The same approach leads to an invocation for the
- access log CGI program when the hyperlink
- <code>:log</code> gets used.</p>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>From Static to Dynamic</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>How can we transform a static page
- <code>foo.html</code> into a dynamic variant
- <code>foo.cgi</code> in a seamless way, i.e. without notice
- by the browser/user.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We just rewrite the URL to the CGI-script and force the
- correct MIME-type so it gets really run as a CGI-script.
- This way a request to <code>/~quux/foo.html</code>
- internally leads to the invocation of
- <code>/~quux/foo.cgi</code>.</p>
-
-<example><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^foo\.<strong>html</strong>$ foo.<strong>cgi</strong> [T=<strong>application/x-httpd-cgi</strong>]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>On-the-fly Content-Regeneration</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- This is done via the following ruleset:
-
-<example><pre>
-RewriteCond %{REQUEST_FILENAME} <strong>!-s</strong>
-RewriteRule ^page\.<strong>html</strong>$ page.<strong>cgi</strong> [T=application/x-httpd-cgi,L]
-</pre></example>
-
- <p>Here a request to <code>page.html</code> leads to a
- internal run of a corresponding <code>page.cgi</code> if
- <code>page.html</code> is still missing or has filesize
- null. The trick here is that <code>page.cgi</code> is a
- usual CGI script which (additionally to its <code>STDOUT</code>)
- writes its output to the file <code>page.html</code>.
- Once it was run, the server sends out the data of
- <code>page.html</code>. When the webmaster wants to force
- a refresh the contents, he just removes
- <code>page.html</code> (usually done by a cronjob).</p>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Document With Autorefresh</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>No! We just combine the MIME multipart feature, the
- webserver NPH feature and the URL manipulation power of
- <module>mod_rewrite</module>. First, we establish a new
- URL feature: Adding just <code>:refresh</code> to any
- URL causes this to be refreshed every time it gets
- updated on the filesystem.</p>
-
-<example><pre>
-RewriteRule ^(/[uge]/[^/]+/?.*):refresh /internal/cgi/apache/nph-refresh?f=$1
-</pre></example>
-
- <p>Now when we reference the URL</p>
-
-<example><pre>
-/u/foo/bar/page.html:refresh
-</pre></example>
-
- <p>this leads to the internal invocation of the URL</p>
-
-<example><pre>
-/internal/cgi/apache/nph-refresh?f=/u/foo/bar/page.html
-</pre></example>
-
- <p>The only missing part is the NPH-CGI script. Although
- one would usually say "left as an exercise to the reader"
- ;-) I will provide this, too.</p>
-
-<example><pre>
-#!/sw/bin/perl
-##
-## nph-refresh -- NPH/CGI script for auto refreshing pages
-## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved.
-##
-$| = 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($QS_s);
- }
-}
-
-&print_http_headers_multipart_end;
-
-exit(0);
-
-##EOF##
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Mass Virtual Hosting</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>The <directive type="section" module="core"
- >VirtualHost</directive> feature of Apache is nice
- and works great when you just have a few dozens
- virtual hosts. But when you are an ISP and have hundreds of
- virtual hosts to provide this feature is not the best
- choice.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>To provide this feature we map the remote webpage or even
- the complete remote webarea to our namespace by the use
- of the <dfn>Proxy Throughput</dfn> feature (flag <code>[P]</code>):</p>
-
-<example><pre>
-##
-## vhost.map
-##
-www.vhost1.dom:80 /path/to/docroot/vhost1
-www.vhost2.dom:80 /path/to/docroot/vhost2
- :
-www.vhostN.dom:80 /path/to/docroot/vhostN
-</pre></example>
-
-<example><pre>
-##
-## httpd.conf
-##
- :
-# use the canonical hostname on redirects, etc.
-UseCanonicalName on
-
- :
-# add the virtual host in front of the CLF-format
-CustomLog /path/to/access_log "%{VHOST}e %h %l %u %t \"%r\" %>s %b"
- :
-
-# enable the rewriting engine in the main server
-RewriteEngine on
-
-# define two maps: one for fixing the URL and one which defines
-# the available virtual hosts with their corresponding
-# DocumentRoot.
-RewriteMap lowercase int:tolower
-RewriteMap vhost txt:/path/to/vhost.map
-
-# Now do the actual virtual host mapping
-# via a huge and complicated single rule:
-#
-# 1. make sure we don't map for common locations
-RewriteCond %{REQUEST_URL} !^/commonurl1/.*
-RewriteCond %{REQUEST_URL} !^/commonurl2/.*
- :
-RewriteCond %{REQUEST_URL} !^/commonurlN/.*
-#
-# 2. make sure we have a Host header, because
-# currently our approach only supports
-# virtual hosting through this header
-RewriteCond %{HTTP_HOST} !^$
-#
-# 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}}]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- </section>
-
- <section id="access">
-
- <title>Access Restriction</title>
-
- <section>
-
- <title>Blocking of Robots</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>How can we block a really annoying robot from
- retrieving pages of a specific webarea? A
- <code>/robots.txt</code> file containing entries of the
- "Robot Exclusion Protocol" is typically not enough to get
- rid of such a robot.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We use a ruleset which forbids the URLs of the webarea
- <code>/~quux/foo/arc/</code> (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.</p>
-
-<example><pre>
-RewriteCond %{HTTP_USER_AGENT} ^<strong>NameOfBadRobot</strong>.*
-RewriteCond %{REMOTE_ADDR} ^<strong>123\.45\.67\.[8-9]</strong>$
-RewriteRule ^<strong>/~quux/foo/arc/</strong>.+ - [<strong>F</strong>]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Blocked Inline-Images</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Assume we have under <code>http://www.quux-corp.de/~quux/</code>
- 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.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>While we cannot 100% protect the images from inclusion,
- we can at least restrict the cases where the browser
- sends a HTTP Referer header.</p>
-
-<example><pre>
-RewriteCond %{HTTP_REFERER} <strong>!^$</strong>
-RewriteCond %{HTTP_REFERER} !^http://www.quux-corp.de/~quux/.*$ [NC]
-RewriteRule <strong>.*\.gif$</strong> - [F]
-</pre></example>
-
-<example><pre>
-RewriteCond %{HTTP_REFERER} !^$
-RewriteCond %{HTTP_REFERER} !.*/foo-with-gif\.html$
-RewriteRule <strong>^inlined-in-foo\.gif$</strong> - [F]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Host Deny</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>How can we forbid a list of externally configured hosts
- from using our server?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>For Apache >= 1.3b6:</p>
-
-<example><pre>
-RewriteEngine on
-RewriteMap hosts-deny txt:/path/to/hosts.deny
-RewriteCond ${hosts-deny:%{REMOTE_HOST}|NOT-FOUND} !=NOT-FOUND [OR]
-RewriteCond ${hosts-deny:%{REMOTE_ADDR}|NOT-FOUND} !=NOT-FOUND
-RewriteRule ^/.* - [F]
-</pre></example>
-
- <p>For Apache <= 1.3b6:</p>
-
-<example><pre>
-RewriteEngine on
-RewriteMap hosts-deny txt:/path/to/hosts.deny
-RewriteRule ^/(.*)$ ${hosts-deny:%{REMOTE_HOST}|NOT-FOUND}/$1
-RewriteRule !^NOT-FOUND/.* - [F]
-RewriteRule ^NOT-FOUND/(.*)$ ${hosts-deny:%{REMOTE_ADDR}|NOT-FOUND}/$1
-RewriteRule !^NOT-FOUND/.* - [F]
-RewriteRule ^NOT-FOUND/(.*)$ /$1
-</pre></example>
-
-<example><pre>
-##
-## hosts.deny
-##
-## ATTENTION! This is a map, not a list, even when we treat it as such.
-## mod_rewrite parses it for key/value pairs, so at least a
-## dummy value "-" must be present for each entry.
-##
-
-193.102.180.41 -
-bsdti1.sdm.de -
-192.76.162.40 -
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Proxy Deny</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>How can we forbid a certain host or even a user of a
- special host from using the Apache proxy?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We first have to make sure <module>mod_rewrite</module>
- is below(!) <module>mod_proxy</module> in the Configuration
- file when compiling the Apache webserver. This way it gets
- called <em>before</em> <module>mod_proxy</module>. Then we
- configure the following for a host-dependent deny...</p>
-
-<example><pre>
-RewriteCond %{REMOTE_HOST} <strong>^badhost\.mydomain\.com$</strong>
-RewriteRule !^http://[^/.]\.mydomain.com.* - [F]
-</pre></example>
-
- <p>...and this one for a user@host-dependent deny:</p>
-
-<example><pre>
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>^badguy@badhost\.mydomain\.com$</strong>
-RewriteRule !^http://[^/.]\.mydomain.com.* - [F]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Special Authentication Variant</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Sometimes a very special authentication is needed, for
- instance a authentication which checks for a set of
- explicitly configured users. Only these should receive
- access and without explicit prompting (which would occur
- when using the Basic Auth via <module>mod_auth_basic</module>).</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We use a list of rewrite conditions to exclude all except
- our friends:</p>
-
-<example><pre>
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>!^friend1@client1.quux-corp\.com$</strong>
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>!^friend2</strong>@client2.quux-corp\.com$
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>!^friend3</strong>@client3.quux-corp\.com$
-RewriteRule ^/~quux/only-for-friends/ - [F]
-</pre></example>
- </dd>
- </dl>
-
- </section>
-
- <section>
-
- <title>Referer-based Deflector</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>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?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>Use the following really tricky ruleset...</p>
-
-<example><pre>
-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 ^.* ${deflector:%{HTTP_REFERER}} [R,L]
-</pre></example>
-
- <p>... in conjunction with a corresponding rewrite
- map:</p>
-
-<example><pre>
-##
-## deflector.map
-##
-
-http://www.badguys.com/bad/index.html -
-http://www.badguys.com/bad/index2.html -
-http://www.badguys.com/bad/index3.html http://somewhere.com/
-</pre></example>
-
- <p>This automatically redirects the request back to the
- referring page (when "<code>-</code>" is used as the value
- in the map) or to a specific URL (when an URL is specified
- in the map as the second argument).</p>
- </dd>
- </dl>
-
- </section>
-
- </section>
-
- <section id="other">
-
- <title>Other</title>
-
- <section>
-
- <title>External Rewriting Engine</title>
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>A FAQ: How can we solve the FOO/BAR/QUUX/etc.
- problem? There seems no solution by the use of
- <module>mod_rewrite</module>...</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>Use an external <directive module="mod_rewrite"
- >RewriteMap</directive>, i.e. a program which acts
- like a <directive module="mod_rewrite"
- >RewriteMap</directive>. It is run once on startup of Apache
- receives the requested URLs on <code>STDIN</code> and has
- to put the resulting (usually rewritten) URL on
- <code>STDOUT</code> (same order!).</p>
-
-<example><pre>
-RewriteEngine on
-RewriteMap quux-map <strong>prg:</strong>/path/to/map.quux.pl
-RewriteRule ^/~quux/(.*)$ /~quux/<strong>${quux-map:$1}</strong>
-</pre></example>
-
-<example><pre>
-#!/path/to/perl
-
-# disable buffered I/O which would lead
-# to deadloops for the Apache server
-$| = 1;
-
-# read URLs one per line from stdin and
-# generate substitution URL on stdout
-while (<>) {
- s|^foo/|bar/|;
- print $_;
-}
-</pre></example>
-
- <p>This is a demonstration-only example and just rewrites
- all URLs <code>/~quux/foo/...</code> to
- <code>/~quux/bar/...</code>. Actually you can program
- whatever you like. But notice that while such maps can be
- <strong>used</strong> also by an average user, only the
- system administrator can <strong>define</strong> it.</p>
- </dd>
- </dl>
-
- </section>
-
- </section>
-
-</manualpage>
-
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