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10 <title>Using RewriteMap - Apache HTTP Server Version 2.4</title>
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20 <p class="apache">Apache HTTP Server Version 2.4</p>
21 <img alt="" src="../images/feather.png" /></div>
22 <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
24 <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 2.4</a> > <a href="./">Rewrite</a></div><div id="page-content"><div id="preamble"><h1>Using RewriteMap</h1>
26 <p><span>Available Languages: </span><a href="../en/rewrite/rewritemap.html" title="English"> en </a> |
27 <a href="../fr/rewrite/rewritemap.html" hreflang="fr" rel="alternate" title="Français"> fr </a></p>
31 <p>This document supplements the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
32 <a href="../mod/mod_rewrite.html">reference documentation</a>. It describes
33 the use of the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive,
34 and provides examples of each of the various <code>RewriteMap</code> types.</p>
36 <div class="warning">Note that many of these examples won't work unchanged in your
37 particular server configuration, so it's important that you understand
38 them, rather than merely cutting and pasting the examples into your
42 <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#introduction">Introduction</a></li>
43 <li><img alt="" src="../images/down.gif" /> <a href="#txt">txt: Plain text maps</a></li>
44 <li><img alt="" src="../images/down.gif" /> <a href="#rnd">rnd: Randomized Plain Text</a></li>
45 <li><img alt="" src="../images/down.gif" /> <a href="#dbm">dbm: DBM Hash File</a></li>
46 <li><img alt="" src="../images/down.gif" /> <a href="#int">int: Internal Function</a></li>
47 <li><img alt="" src="../images/down.gif" /> <a href="#prg">prg: External Rewriting Program</a></li>
48 <li><img alt="" src="../images/down.gif" /> <a href="#dbd">dbd or fastdbd: SQL Query</a></li>
49 <li><img alt="" src="../images/down.gif" /> <a href="#summary">Summary</a></li>
50 </ul><h3>See also</h3><ul class="seealso"><li><a href="../mod/mod_rewrite.html">Module documentation</a></li><li><a href="intro.html">mod_rewrite introduction</a></li><li><a href="remapping.html">Redirection and remapping</a></li><li><a href="access.html">Controlling access</a></li><li><a href="vhosts.html">Virtual hosts</a></li><li><a href="proxy.html">Proxying</a></li><li><a href="advanced.html">Advanced techniques</a></li><li><a href="avoid.html">When not to use mod_rewrite</a></li></ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
51 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
53 <h2><a name="introduction" id="introduction">Introduction</a></h2>
57 The <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive
58 defines an external function which can be called in the context of
59 <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> or
60 <code class="directive"><a href="../mod/mod_rewrite.html#rewritecond">RewriteCond</a></code> directives to
61 perform rewriting that is too complicated, or too specialized to be
62 performed just by regular expressions. The source of this lookup can
63 be any of the types listed in the sections below, and enumerated in
64 the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> reference
67 <p>The syntax of the <code>RewriteMap</code> directive is as
70 <pre class="prettyprint lang-config">RewriteMap <em>MapName</em> <em>MapType</em>:<em>MapSource</em>
74 <p>The <a id="mapfunc" name="mapfunc"><em>MapName</em></a> is an
75 arbitray name that you assign to the map, and which you will use in
76 directives later on. Arguments are passed to the map via the
81 <code>${</code> <em>MapName</em> <code>:</code> <em>LookupKey</em>
82 <code>}</code> <br /> <code>${</code> <em>MapName</em> <code>:</code>
83 <em>LookupKey</em> <code>|</code> <em>DefaultValue</em> <code>}</code>
87 <p>When such a construct occurs, the map <em>MapName</em> is
88 consulted and the key <em>LookupKey</em> is looked-up. If the
89 key is found, the map-function construct is substituted by
90 <em>SubstValue</em>. If the key is not found then it is
91 substituted by <em>DefaultValue</em> or by the empty string
92 if no <em>DefaultValue</em> was specified.</p>
94 <p>For example, you might define a
95 <code class="directive">RewriteMap</code> as:</p>
96 <pre class="prettyprint lang-config">RewriteMap examplemap "txt:/path/to/file/map.txt"</pre>
98 <p>You would then be able to use this map in a
99 <code class="directive">RewriteRule</code> as follows:</p>
100 <pre class="prettyprint lang-config">RewriteRule "^/ex/(.*)" "${examplemap:$1}"</pre>
103 <p>A default value can be specified in the event that nothing is found
106 <pre class="prettyprint lang-config">RewriteRule "^/ex/(.*)" "${examplemap:$1|/not_found.html}"</pre>
109 <div class="note"><h3>Per-directory and .htaccess context</h3>
111 The <code>RewriteMap</code> directive may not be used in
112 <Directory> sections or <code>.htaccess</code> files. You must
113 declare the map in server or virtualhost context. You may use the map,
114 once created, in your <code>RewriteRule</code> and
115 <code>RewriteCond</code> directives in those scopes. You just can't
116 <strong>declare</strong> it in those scopes.
120 <p>The sections that follow describe the various <em>MapType</em>s that
121 may be used, and give examples of each.</p>
122 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
123 <div class="section">
124 <h2><a name="txt" id="txt">txt: Plain text maps</a></h2>
127 <p>When a MapType of <code>txt</code> is used, the MapSource is a filesystem path to a
128 plain-text mapping file, containing space-separated key/value pair
129 per line. Optionally, a line may be contain a comment, starting with
132 <p>For example, the following might be valid entries in a map
137 <strong><em>MatchingKey</em> <em>SubstValue</em></strong><br />
138 <strong><em>MatchingKey</em> <em>SubstValue</em></strong> # comment<br />
141 <p>When the RewriteMap is invoked the argument is looked for in the
142 first argument of a line, and, if found, the substitution value is
145 <p>For example, we might use a mapfile to translate product names to
146 product IDs for easier-to-remember URLs, using the following
148 <p><strong>Product to ID configuration</strong></p>
149 <pre class="prettyprint lang-config">RewriteMap product2id "txt:/etc/apache2/productmap.txt"
150 RewriteRule "^/product/(.*)" "/prods.php?id=${product2id:$1|NOTFOUND}" [PT]</pre>
153 <p>We assume here that the <code>prods.php</code> script knows what
154 to do when it received an argument of <code>id=NOTFOUND</code> when
155 a product is not found in the lookup map.</p>
157 <p>The file <code>/etc/apache2/productmap.txt</code> then contains
160 <div class="example"><h3>Product to ID map</h3><p><code>
162 ## productmap.txt - Product to ID map file<br />
172 <p>Thus, when <code>http://example.com/product/television</code> is
173 requested, the <code>RewriteRule</code> is applied, and the request
174 is internally mapped to <code>/prods.php?id=993</code>.</p>
176 <div class="note"><h3>Note: .htaccess files</h3>
177 The example given is crafted to be used in server or virtualhost
178 scope. If you're planning to use this in a <code>.htaccess</code>
179 file, you'll need to remove the leading slash from the rewrite
180 pattern in order for it to match anything:
181 <pre class="prettyprint lang-config">RewriteRule "^product/(.*)" "/prods.php?id=${product2id:$1|NOTFOUND}" [PT]</pre>
185 <div class="note"><h3>Cached lookups</h3>
187 The looked-up keys are cached by httpd until the <code>mtime</code>
188 (modified time) of the mapfile changes, or the httpd server is
189 restarted. This ensures better performance on maps that are called
194 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
195 <div class="section">
196 <h2><a name="rnd" id="rnd">rnd: Randomized Plain Text</a></h2>
199 <p>When a MapType of <code>rnd</code> is used, the MapSource is a
200 filesystem path to a plain-text mapping file, each line of which
201 contains a key, and one or more values separated by <code>|</code>.
202 One of these values will be chosen at random if the key is
205 <p>For example, you might use the following map
206 file and directives to provide a random load balancing between
207 several back-end servers, via a reverse-proxy. Images are sent
208 to one of the servers in the 'static' pool, while everything
209 else is sent to one of the 'dynamic' pool.</p>
211 <div class="example"><h3>Rewrite map file</h3><p><code>
213 ## map.txt -- rewriting map<br />
216 static www1|www2|www3|www4<br />
219 <p><strong>Configuration directives</strong></p>
220 <pre class="prettyprint lang-config">RewriteMap servers "rnd:/path/to/file/map.txt"
222 RewriteRule "^/(.*\.(png|gif|jpg))" "http://${servers:static}/$1" [NC,P,L]
223 RewriteRule "^/(.*)" "http://${servers:dynamic}/$1" [P,L]</pre>
226 <p>So, when an image is requested and the first of these rules is
227 matched, <code>RewriteMap</code> looks up the string
228 <code>static</code> in the map file, which returns one of the
229 specified hostnames at random, which is then used in the
230 <code>RewriteRule</code> target.</p>
232 <p>If you wanted to have one of the servers more likely to be chosen
233 (for example, if one of the server has more memory than the others,
234 and so can handle more requests) simply list it more times in the
237 <div class="example"><p><code>
238 static www1|www1|www2|www3|www4
241 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
242 <div class="section">
243 <h2><a name="dbm" id="dbm">dbm: DBM Hash File</a></h2>
246 <p>When a MapType of <code>dbm</code> is used, the MapSource is a
247 filesystem path to a DBM database file containing key/value pairs to
248 be used in the mapping. This works exactly the same way as the
249 <code>txt</code> map, but is much faster, because a DBM is indexed,
250 whereas a text file is not. This allows more rapid access to the
253 <p>You may optionally specify a particular dbm type:</p>
255 <pre class="prettyprint lang-config">RewriteMap examplemap "dbm=sdbm:/etc/apache/mapfile.dbm"</pre>
258 <p>The type can be sdbm, gdbm, ndbm or db.
259 However, it is recommended that you just use the <a href="../programs/httxt2dbm.html">httxt2dbm</a> utility that is
260 provided with Apache HTTP Server, as it will use the correct DBM library,
261 matching the one that was used when httpd itself was built.</p>
263 <p>To create a dbm file, first create a text map file as described
264 in the <a href="#txt">txt</a> section. Then run
265 <code>httxt2dbm</code>:</p>
267 <div class="example"><p><code>
268 $ httxt2dbm -i mapfile.txt -o mapfile.map
271 <p>You can then reference the resulting file in your
272 <code>RewriteMap</code> directive:</p>
274 <pre class="prettyprint lang-config">RewriteMap mapname "dbm:/etc/apache/mapfile.map"</pre>
278 <p>Note that with some dbm types, more than one file is generated, with
279 a common base name. For example, you may have two files named
280 <code>mapfile.map.dir</code> and <code>mapfiile.map.pag</code>. This is
281 normal, and you need only use the base name <code>mapfile.map</code> in
282 your <code>RewriteMap</code> directive.</p>
285 <div class="note"><h3>Cached lookups</h3>
287 The looked-up keys are cached by httpd until the <code>mtime</code>
288 (modified time) of the mapfile changes, or the httpd server is
289 restarted. This ensures better performance on maps that are called
294 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
295 <div class="section">
296 <h2><a name="int" id="int">int: Internal Function</a></h2>
299 <p>When a MapType of <code>int</code> is used, the MapSource is one
300 of the available internal RewriteMap functions. Module authors can provide
301 additional internal functions by registering them with the
302 <code>ap_register_rewrite_mapfunc</code> API.
303 The functions that are provided by default are:
307 <li><strong>toupper</strong>:<br />
308 Converts the key to all upper case.</li>
309 <li><strong>tolower</strong>:<br />
310 Converts the key to all lower case.</li>
311 <li><strong>escape</strong>:<br />
312 Translates special characters in the key to
314 <li><strong>unescape</strong>:<br />
315 Translates hex-encodings in the key back to
316 special characters.</li>
320 To use one of these functions, create a <code>RewriteMap</code> referencing
321 the int function, and then use that in your <code>RewriteRule</code>:
324 <p> <strong>Redirect a URI to an all-lowercase version of itself</strong></p>
325 <pre class="prettyprint lang-config">RewriteMap lc int:tolower
326 RewriteRule "(.*)" "${lc:$1}" [R]</pre>
330 <p>Please note that the example offered here is for
331 illustration purposes only, and is not a recommendation. If you want
332 to make URLs case-insensitive, consider using
333 <code class="module"><a href="../mod/mod_speling.html">mod_speling</a></code> instead.
337 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
338 <div class="section">
339 <h2><a name="prg" id="prg">prg: External Rewriting Program</a></h2>
341 <p>When a MapType of <code>prg</code> is used, the MapSource is a
342 filesystem path to an executable program which will providing the
343 mapping behavior. This can be a compiled binary file, or a program
344 in an interpreted language such as Perl or Python.</p>
346 <p>This program is started once, when the Apache HTTP Server is
347 started, and then communicates with the rewriting engine via
348 <code>STDIN</code> and <code>STDOUT</code>. That is, for each map
349 function lookup, it expects one argument via <code>STDIN</code>, and
350 should return one new-line terminated response string on
351 <code>STDOUT</code>. If there is no corresponding lookup value, the
352 map program should return the four-character string
353 "<code>NULL</code>" to indicate this.</p>
355 <p>External rewriting programs are not started if they're defined in
356 a context that does not have <code class="directive"><a href="../mod/mod_rewrite.html#rewriteengine">RewriteEngine</a></code> set to
359 <p>This feature utilizes the <code>rewrite-map</code> mutex,
360 which is required for reliable communication with the program.
361 The mutex mechanism and lock file can be configured with the
362 <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive.</p>
364 <p>A simple example is shown here which will replace all dashes with
365 underscores in a request URI.</p>
367 <p><strong>Rewrite configuration</strong></p>
368 <pre class="prettyprint lang-config">RewriteMap d2u "prg:/www/bin/dash2under.pl"<br />
369 RewriteRule "-" "${d2u:%{REQUEST_URI}}"</pre>
372 <p><strong>dash2under.pl</strong></p>
373 <pre class="prettyprint lang-perl">#!/usr/bin/perl
374 $| = 1; # Turn off I/O buffering
375 while (<STDIN>) {
376 s/-/_/g; # Replace dashes with underscores
381 <div class="note"><h3>Caution!</h3>
383 <li>Keep your rewrite map program as simple as possible. If the program
384 hangs, it will cause httpd to wait indefinitely for a response from the
385 map, which will, in turn, cause httpd to stop responding to
387 <li>Be sure to turn off buffering in your program. In Perl this is done
388 by the second line in the example script: <code>$| = 1;</code> This will
389 of course vary in other languages. Buffered I/O will cause httpd to wait
390 for the output, and so it will hang.</li>
391 <li>Remember that there is only one copy of the program, started at
392 server startup. All requests will need to go through this one bottleneck.
393 This can cause significant slowdowns if many requests must go through
394 this process, or if the script itself is very slow.</li>
398 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
399 <div class="section">
400 <h2><a name="dbd" id="dbd">dbd or fastdbd: SQL Query</a></h2>
403 <p>When a MapType of <code>dbd</code> or <code>fastdbd</code> is
404 used, the MapSource is a SQL SELECT statement that takes a single
405 argument and returns a single value.</p>
407 <p><code class="module"><a href="../mod/mod_dbd.html">mod_dbd</a></code> will need to be configured to point at
408 the right database for this statement to be executed.</p>
410 <p>There are two forms of this MapType.
411 Using a MapType of <code>dbd</code> causes the query to be
412 executed with each map request, while using <code>fastdbd</code>
413 caches the database lookups internally. So, while
414 <code>fastdbd</code> is more efficient, and therefore faster, it
415 won't pick up on changes to the database until the server is
418 <p>If a query returns more than one row, a random row from
419 the result set is used.</p>
421 <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">RewriteMap myquery "fastdbd:SELECT destination FROM rewrite WHERE source = %s"</pre>
424 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
425 <div class="section">
426 <h2><a name="summary" id="summary">Summary</a></h2>
429 <p>The <code class="directive">RewriteMap</code> directive can occur more than
430 once. For each mapping-function use one
431 <code class="directive">RewriteMap</code> directive to declare its rewriting
434 <p>While you cannot <strong>declare</strong> a map in
435 per-directory context (<code>.htaccess</code> files or
436 <Directory> blocks) it is possible to
437 <strong>use</strong> this map in per-directory context. </p>
440 <div class="bottomlang">
441 <p><span>Available Languages: </span><a href="../en/rewrite/rewritemap.html" title="English"> en </a> |
442 <a href="../fr/rewrite/rewritemap.html" hreflang="fr" rel="alternate" title="Français"> fr </a></p>
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