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17 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
18 <p class="apache">Apache HTTP Server Version 2.4</p>
19 <img alt="" src="../images/feather.gif" /></div>
20 <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
22 <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>
24 <p><span>Available Languages: </span><a href="../en/rewrite/rewritemap.html" title="English"> en </a></p>
28 <p>This document supplements the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
29 <a href="../mod/mod_rewrite.html">reference documentation</a>. It describes
30 the use of the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive,
31 and provides examples of each of the various <code>RewriteMap</code> types.</p>
33 <div class="warning">Note that many of these examples won't work unchanged in your
34 particular server configuration, so it's important that you understand
35 them, rather than merely cutting and pasting the examples into your
39 <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#introduction">Introduction</a></li>
40 <li><img alt="" src="../images/down.gif" /> <a href="#txt">txt: Plain text maps</a></li>
41 <li><img alt="" src="../images/down.gif" /> <a href="#rnd">rnd: Randomized Plain Text</a></li>
42 <li><img alt="" src="../images/down.gif" /> <a href="#dbm">dbm: DBM Hash File</a></li>
43 <li><img alt="" src="../images/down.gif" /> <a href="#int">int: Internal Function</a></li>
44 <li><img alt="" src="../images/down.gif" /> <a href="#prg">prg: External Rewriting Program</a></li>
45 <li><img alt="" src="../images/down.gif" /> <a href="#dbd">dbd or fastdbd: SQL Query</a></li>
46 <li><img alt="" src="../images/down.gif" /> <a href="#summary">Summary</a></li>
47 </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></div>
48 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
50 <h2><a name="introduction" id="introduction">Introduction</a></h2>
54 The <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive
55 defines an external function which can be called in the context of
56 <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> or
57 <code class="directive"><a href="../mod/mod_rewrite.html#rewritecond">RewriteCond</a></code> directives to
58 perform rewriting that is too complicated, or too specialized to be
59 performed just by regular expressions. The source of this lookup can
60 be any of the types listed in the sections below, and enumerated in
61 the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> reference
64 <p>The syntax of the <code>RewriteMap</code> directive is as
67 <div class="example"><p><code>
68 RewriteMap <em>MapName</em> <em>MapType</em>:<em>MapSource</em>
71 <p>The <a id="mapfunc" name="mapfunc"><em>MapName</em></a> is an
72 arbitray name that you assign to the map, and which you will use in
73 directives later on. Arguments are passed to the map via the
78 <code>${</code> <em>MapName</em> <code>:</code> <em>LookupKey</em>
79 <code>}</code> <br /> <code>${</code> <em>MapName</em> <code>:</code>
80 <em>LookupKey</em> <code>|</code> <em>DefaultValue</em> <code>}</code>
84 <p>When such a construct occurs, the map <em>MapName</em> is
85 consulted and the key <em>LookupKey</em> is looked-up. If the
86 key is found, the map-function construct is substituted by
87 <em>SubstValue</em>. If the key is not found then it is
88 substituted by <em>DefaultValue</em> or by the empty string
89 if no <em>DefaultValue</em> was specified.</p>
91 <p>For example, you might define a
92 <code class="directive">RewriteMap</code> as:</p>
93 <div class="example"><p><code>
94 RewriteMap examplemap txt:/path/to/file/map.txt
96 <p>You would then be able to use this map in a
97 <code class="directive">RewriteRule</code> as follows:</p>
98 <div class="example"><p><code>
99 RewriteRule ^/ex/(.*) ${examplemap:$1}
102 <p>A default value can be specified in the event that nothing is found
105 <div class="example"><p><code>
106 RewriteRule ^/ex/(.*) ${examplemap:$1|/not_found.html}
109 <div class="note"><h3>Per-directory and .htaccess context</h3>
111 The <code>RewriteMap</code> directive may not be used in
112 <Directory> sections or <code>.htaccess</code> files. You must
113 declare the map in server or virtualhost context. You may use the map,
114 once created, in your <code>RewriteRule</code> and
115 <code>RewriteCond</code> directives in those scopes. You just can't
116 <strong>declare</strong> it in those scopes.
120 <p>The sections that follow describe the various <em>MapType</em>s that
121 may be used, and give examples of each.</p>
122 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
123 <div class="section">
124 <h2><a name="txt" id="txt">txt: Plain text maps</a></h2>
127 <p>When a MapType of <code>txt</code> is used, the MapSource is a filesystem path to a
128 plain-text mapping file, containing space-separated key/value pair
129 per line. Optionally, a line may be contain a comment, starting with
132 <p>For example, the following might be valid entries in a map
137 <strong><em>MatchingKey</em> <em>SubstValue</em></strong><br />
138 <strong><em>MatchingKey</em> <em>SubstValue</em></strong> # comment<br />
141 <p>When the RewriteMap is invoked the argument is looked for in the
142 first argument of a line, and, if found, the substitution value is
145 <p>For example, we might use a mapfile to translate product names to
146 product IDs for easier-to-remember URLs, using the following
149 <div class="example"><h3>Product to ID configuration</h3><p><code>
150 RewriteMap product2id txt:/etc/apache2/productmap.txt<br />
151 RewriteRule ^/product/(.*) /prods.php?id=${product2id:$1|NOTFOUND} [PT]
154 <p>We assume here that the <code>prods.php</code> script knows what
155 to do when it received an argument of <code>id=NOTFOUND</code> when
156 a product is not found in the lookup map.</p>
158 <p>The file <code>/etc/apache2/productmap.txt</code> then contains
161 <div class="example"><h3>Product to ID map</h3><p><code>
163 ## productmap.txt - Product to ID map file<br />
173 <p>Thus, when <code>http://example.com/product/television</code> is
174 requested, the <code>RewriteRule</code> is applied, and the request
175 is internally mapped to <code>/prods.php?id=993</code>.</p>
177 <div class="note"><h3>Note: .htaccess files</h3>
178 The example given is crafted to be used in server or virtualhost
179 scope. If you're planning to use this in a <code>.htaccess</code>
180 file, you'll need to remove the leading slash from the rewrite
181 pattern in order for it to match anything:
182 <div class="example"><p><code>
183 RewriteRule ^product/(.*) /prods.php?id=${product2id:$1|NOTFOUND} [PT]
187 <div class="note"><h3>Cached lookups</h3>
189 The looked-up keys are cached by httpd until the <code>mtime</code>
190 (modified time) of the mapfile changes, or the httpd server is
191 restarted. This ensures better performance on maps that are called
196 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
197 <div class="section">
198 <h2><a name="rnd" id="rnd">rnd: Randomized Plain Text</a></h2>
201 <p>When a MapType of <code>rnd</code> is used, the MapSource is a
202 filesystem path to a plain-text mapping file, each line of which
203 contains a key, and one or more values separated by <code>|</code>.
204 One of these values will be chosen at random if the key is
207 <p>For example, you might use the following map
208 file and directives to provide a random load balancing between
209 several back-end servers, via a reverse-proxy. Images are sent
210 to one of the servers in the 'static' pool, while everything
211 else is sent to one of the 'dynamic' pool.</p>
213 <div class="example"><h3>Rewrite map file</h3><p><code>
215 ## map.txt -- rewriting map<br />
218 static www1|www2|www3|www4<br />
222 <div class="example"><h3>Configuration directives</h3><p><code>
223 RewriteMap servers rnd:/path/to/file/map.txt<br />
225 RewriteRule ^/(.*\.(png|gif|jpg)) http://${servers:static}/$1 [NC,P,L]<br />
226 RewriteRule ^/(.*) http://${servers:dynamic}/$1 [P,L]
229 <p>So, when an image is requested and the first of these rules is
230 matched, <code>RewriteMap</code> looks up the string
231 <code>static</code> in the map file, which returns one of the
232 specified hostnames at random, which is then used in the
233 <code>RewriteRule</code> target.</p>
235 <p>If you wanted to have one of the servers more likely to be chosen
236 (for example, if one of the server has more memory than the others,
237 and so can handle more requests) simply list it more times in the
240 <div class="example"><p><code>
241 static www1|www1|www2|www3|www4
244 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
245 <div class="section">
246 <h2><a name="dbm" id="dbm">dbm: DBM Hash File</a></h2>
249 <p>When a MapType of <code>dbm</code> is used, the MapSource is a
250 filesystem path to a DBM database file containing key/value pairs to
251 be used in the mapping. This works exactly the same way as the
252 <code>txt</code> map, but is much faster, because a DBM is indexed,
253 whereas a text file is not. This allows more rapid access to the
256 <p>You may optionally specify a particular dbm type:</p>
258 <div class="example"><p><code>
259 RewriteMap examplemap dbm=sdbm:/etc/apache/mapfile.dbm
262 <p>The type can be sdbm, gdbm, ndbm or db.
263 However, it is recommended that you just use the <a href="../programs/httxt2dbm.html">httxt2dbm</a> utility that is
264 provided with Apache HTTP Server, as it will use the correct DBM library,
265 matching the one that was used when httpd itself was built.</p>
267 <p>To create a dbm file, first create a text map file as described
268 in the <a href="#txt">txt</a> section. Then run
269 <code>httxt2dbm</code>:</p>
271 <div class="example"><p><code>
272 $ httxt2dbm -i mapfile.txt -o mapfile.map
275 <p>You can then reference the resulting file in your
276 <code>RewriteMap</code> directive:</p>
278 <div class="example"><p><code>
279 RewriteMap mapname dbm:/etc/apache/mapfile.map
283 <p>Note that with some dbm types, more than one file is generated, with
284 a common base name. For example, you may have two files named
285 <code>mapfile.map.dir</code> and <code>mapfiile.map.pag</code>. This is
286 normal, and you need only use the base name <code>mapfile.map</code> in
287 your <code>RewriteMap</code> directive.</p>
290 <div class="note"><h3>Cached lookups</h3>
292 The looked-up keys are cached by httpd until the <code>mtime</code>
293 (modified time) of the mapfile changes, or the httpd server is
294 restarted. This ensures better performance on maps that are called
299 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
300 <div class="section">
301 <h2><a name="int" id="int">int: Internal Function</a></h2>
304 <p>When a MapType of <code>int</code> is used, the MapSource is one
305 of the available internal RewriteMap functions. Module authors can provide
306 additional internal functions by registering them with the
307 <code>ap_register_rewrite_mapfunc</code> API.
308 The functions that are provided by default are:
312 <li><strong>toupper</strong>:<br />
313 Converts the key to all upper case.</li>
314 <li><strong>tolower</strong>:<br />
315 Converts the key to all lower case.</li>
316 <li><strong>escape</strong>:<br />
317 Translates special characters in the key to
319 <li><strong>unescape</strong>:<br />
320 Translates hex-encodings in the key back to
321 special characters.</li>
325 To use one of these functions, create a <code>RewriteMap</code> referencing
326 the int function, and then use that in your <code>RewriteRule</code>:
329 <div class="example"><h3>Redirect a URI to an all-lowercase version of itself</h3><p><code>
330 RewriteMap lc int:tolower<br />
331 RewriteRule (.*?[A-Z]+.*) ${lc:$1} [R]
335 <p>Please note that the example offered here is for
336 illustration purposes only, and is not a recommendation. If you want
337 to make URLs case-insensitive, consider using
338 <code class="module"><a href="../mod/mod_speling.html">mod_speling</a></code> instead.
342 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
343 <div class="section">
344 <h2><a name="prg" id="prg">prg: External Rewriting Program</a></h2>
346 <p>When a MapType of <code>prg</code> is used, the MapSource is a
347 filesystem path to an executable program which will providing the
348 mapping behavior. This can be a compiled binary file, or a program
349 in an interpreted language such as Perl or Python.</p>
351 <p>This program is started once, when the Apache HTTP Server is
352 started, and then communicates with the rewriting engine via
353 <code>STDIN</code> and <code>STDOUT</code>. That is, for each map
354 function lookup, it expects one argument via <code>STDIN</code>, and
355 should return one new-line terminated response string on
356 <code>STDOUT</code>. If there is no corresponding lookup value, the
357 map program should return the four-character string
358 "<code>NULL</code>" to indicate this.</p>
360 <p>External rewriting programs are not started if they're defined in
361 a context that does not have <code class="directive"><a href="../mod/mod_rewrite.html#rewriteengine">RewriteEngine</a></code> set to
364 <p>This feature utilizes the <code>rewrite-map</code> mutex,
365 which is required for reliable communication with the program.
366 The mutex mechanism and lock file can be configured with the
367 <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive.</p>
369 <p>A simple example is shown here which will replace all dashes with
370 underscores in a request URI.</p>
372 <div class="example"><h3>Rewrite configuration</h3><p><code>
373 RewriteMap d2u prg:/www/bin/dash2under.pl<br />
374 RewriteRule - ${d2u:%{REQUEST_URI}}
377 <div class="example"><h3>dash2under.pl</h3><p><code>
378 #!/usr/bin/perl<br />
379 $| = 1; # Turn off I/O buffering<br />
380 while (<STDIN>) {<br />
381 <span class="indent">
382 s/-/_/g; # Replace dashes with underscores<br />
388 <div class="note"><h3>Caution!</h3>
390 <li>Keep your rewrite map program as simple as possible. If the program
391 hangs, it will cause httpd to wait indefinitely for a response from the
392 map, which will, in turn, cause httpd to stop responding to
394 <li>Be sure to turn off buffering in your program. In Perl this is done
395 by the second line in the example script: <code>$| = 1;</code> This will
396 of course vary in other languages. Buffered I/O will cause httpd to wait
397 for the output, and so it will hang.</li>
398 <li>Remember that there is only one copy of the program, started at
399 server startup. All requests will need to go through this one bottleneck.
400 This can cause significant slowdowns if many requests must go through
401 this process, or if the script itself is very slow.</li>
405 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
406 <div class="section">
407 <h2><a name="dbd" id="dbd">dbd or fastdbd: SQL Query</a></h2>
410 <p>When a MapType of <code>dbd</code> or <code>fastdbd</code> is
411 used, the MapSource is a SQL SELECT statement that takes a single
412 argument and returns a single value.</p>
414 <p><code class="module"><a href="../mod/mod_dbd.html">mod_dbd</a></code> will need to be configured to point at
415 the right database for this statement to be executed.</p>
417 <p>There are two forms of this MapType.
418 Using a MapType of <code>dbd</code> causes the query to be
419 executed with each map request, while using <code>fastdbd</code>
420 caches the database lookups internally. So, while
421 <code>fastdbd</code> is more efficient, and therefore faster, it
422 won't pick up on changes to the database until the server is
425 <p>If a query returns more than one row, a random row from
426 the result set is used.</p>
428 <div class="example"><h3>Example</h3><p><code>
429 RewriteMap myquery "fastdbd:SELECT destination FROM rewrite WHERE source = %s"
432 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
433 <div class="section">
434 <h2><a name="summary" id="summary">Summary</a></h2>
437 <p>The <code class="directive">RewriteMap</code> directive can occur more than
438 once. For each mapping-function use one
439 <code class="directive">RewriteMap</code> directive to declare its rewriting
442 <p>While you cannot <strong>declare</strong> a map in
443 per-directory context (<code>.htaccess</code> files or
444 <Directory> blocks) it is possible to
445 <strong>use</strong> this map in per-directory context. </p>
448 <div class="bottomlang">
449 <p><span>Available Languages: </span><a href="../en/rewrite/rewritemap.html" title="English"> en </a></p>
450 </div><div id="footer">
451 <p class="apache">Copyright 2012 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>
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