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<title>URL Rewriting Guide - Advanced topics － Apache 2.2 中文版参考手册</title>
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<div id="page-content"><div id="preamble"><h1>URL Rewriting Guide - Advanced topics</h1>
<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
commonony confronted. We give detailed descriptions on how to
solve each problem by configuring URL rewriting rulesets.</p>
<div class="warning">ATTENTION: Depending on your server configuration
it may 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>和<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. This
avoids many 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="cluster" id="cluster">Webcluster through Homogeneous URL Layout</a></h2>
<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>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="structuredhomedirs" id="structuredhomedirs">Structured Homedirs</a></h2>
<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>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="filereorg" id="filereorg">Filesystem Reorganization</a></h2>
<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><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>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="redirect404" id="redirect404">Redirect Failing URLs To Other Webserver</a></h2>
<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>
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