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17 <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>
18 <p class="apache">Apache HTTP Server Version 2.5</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 2.5</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 <pre class="prettyprint lang-config">RewriteMap <em>MapName</em> <em>MapType</em>:<em>MapSource</em></pre>
70 <p>The <a id="mapfunc" name="mapfunc"><em>MapName</em></a> is an
71 arbitray name that you assign to the map, and which you will use in
72 directives later on. Arguments are passed to the map via the
77 <code>${</code> <em>MapName</em> <code>:</code> <em>LookupKey</em>
78 <code>}</code> <br /> <code>${</code> <em>MapName</em> <code>:</code>
79 <em>LookupKey</em> <code>|</code> <em>DefaultValue</em> <code>}</code>
83 <p>When such a construct occurs, the map <em>MapName</em> is
84 consulted and the key <em>LookupKey</em> is looked-up. If the
85 key is found, the map-function construct is substituted by
86 <em>SubstValue</em>. If the key is not found then it is
87 substituted by <em>DefaultValue</em> or by the empty string
88 if no <em>DefaultValue</em> was specified.</p>
90 <p>For example, you might define a
91 <code class="directive">RewriteMap</code> as:</p>
92 <pre class="prettyprint lang-config">RewriteMap examplemap txt:/path/to/file/map.txt</pre>
94 <p>You would then be able to use this map in a
95 <code class="directive">RewriteRule</code> as follows:</p>
96 <pre class="prettyprint lang-config">RewriteRule ^/ex/(.*) ${examplemap:$1}</pre>
99 <p>A default value can be specified in the event that nothing is found
102 <pre class="prettyprint lang-config">RewriteRule ^/ex/(.*) ${examplemap:$1|/not_found.html}</pre>
105 <div class="note"><h3>Per-directory and .htaccess context</h3>
107 The <code>RewriteMap</code> directive may not be used in
108 <Directory> sections or <code>.htaccess</code> files. You must
109 declare the map in server or virtualhost context. You may use the map,
110 once created, in your <code>RewriteRule</code> and
111 <code>RewriteCond</code> directives in those scopes. You just can't
112 <strong>declare</strong> it in those scopes.
116 <p>The sections that follow describe the various <em>MapType</em>s that
117 may be used, and give examples of each.</p>
118 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
119 <div class="section">
120 <h2><a name="txt" id="txt">txt: Plain text maps</a></h2>
123 <p>When a MapType of <code>txt</code> is used, the MapSource is a filesystem path to a
124 plain-text mapping file, containing space-separated key/value pair
125 per line. Optionally, a line may be contain a comment, starting with
128 <p>For example, the following might be valid entries in a map
133 <strong><em>MatchingKey</em> <em>SubstValue</em></strong><br />
134 <strong><em>MatchingKey</em> <em>SubstValue</em></strong> # comment<br />
137 <p>When the RewriteMap is invoked the argument is looked for in the
138 first argument of a line, and, if found, the substitution value is
141 <p>For example, we might use a mapfile to translate product names to
142 product IDs for easier-to-remember URLs, using the following
145 <pre class="prettyprint lang-config"><strong>#Product to ID configuration</strong>
146 RewriteMap product2id txt:/etc/apache2/productmap.txt
147 RewriteRule ^/product/(.*) /prods.php?id=${product2id:$1|NOTFOUND} [PT]
151 <p>We assume here that the <code>prods.php</code> script knows what
152 to do when it received an argument of <code>id=NOTFOUND</code> when
153 a product is not found in the lookup map.</p>
155 <p>The file <code>/etc/apache2/productmap.txt</code> then contains
158 <div class="example"><h3>Product to ID map</h3><p><code>
160 ## productmap.txt - Product to ID map file<br />
170 <p>Thus, when <code>http://example.com/product/television</code> is
171 requested, the <code>RewriteRule</code> is applied, and the request
172 is internally mapped to <code>/prods.php?id=993</code>.</p>
174 <div class="note"><h3>Note: .htaccess files</h3>
175 The example given is crafted to be used in server or virtualhost
176 scope. If you're planning to use this in a <code>.htaccess</code>
177 file, you'll need to remove the leading slash from the rewrite
178 pattern in order for it to match anything:
179 <pre class="prettyprint lang-config">RewriteRule ^product/(.*) /prods.php?id=${product2id:$1|NOTFOUND} [PT]</pre>
183 <div class="note"><h3>Cached lookups</h3>
185 The looked-up keys are cached by httpd until the <code>mtime</code>
186 (modified time) of the mapfile changes, or the httpd server is
187 restarted. This ensures better performance on maps that are called
192 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
193 <div class="section">
194 <h2><a name="rnd" id="rnd">rnd: Randomized Plain Text</a></h2>
197 <p>When a MapType of <code>rnd</code> is used, the MapSource is a
198 filesystem path to a plain-text mapping file, each line of which
199 contains a key, and one or more values separated by <code>|</code>.
200 One of these values will be chosen at random if the key is
203 <p>For example, you might use the following map
204 file and directives to provide a random load balancing between
205 several back-end servers, via a reverse-proxy. Images are sent
206 to one of the servers in the 'static' pool, while everything
207 else is sent to one of the 'dynamic' pool.</p>
209 <div class="example"><h3>Rewrite map file</h3><p><code>
211 ## map.txt -- rewriting map<br />
214 static www1|www2|www3|www4<br />
218 <pre class="prettyprint lang-config"><strong>#Configuration directives</strong>
219 RewriteMap servers rnd:/path/to/file/map.txt
221 RewriteRule ^/(.*\.(png|gif|jpg)) http://${servers:static}/$1 [NC,P,L]
222 RewriteRule ^/(.*) http://${servers:dynamic}/$1 [P,L]
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">
256 RewriteMap examplemap dbm=sdbm:/etc/apache/mapfile.dbm
260 <p>The type can be sdbm, gdbm, ndbm or db.
261 However, it is recommended that you just use the <a href="../programs/httxt2dbm.html">httxt2dbm</a> utility that is
262 provided with Apache HTTP Server, as it will use the correct DBM library,
263 matching the one that was used when httpd itself was built.</p>
265 <p>To create a dbm file, first create a text map file as described
266 in the <a href="#txt">txt</a> section. Then run
267 <code>httxt2dbm</code>:</p>
269 <div class="example"><p><code>
270 $ httxt2dbm -i mapfile.txt -o mapfile.map
273 <p>You can then reference the resulting file in your
274 <code>RewriteMap</code> directive:</p>
276 <pre class="prettyprint lang-config">
277 RewriteMap mapname dbm:/etc/apache/mapfile.map
282 <p>Note that with some dbm types, more than one file is generated, with
283 a common base name. For example, you may have two files named
284 <code>mapfile.map.dir</code> and <code>mapfiile.map.pag</code>. This is
285 normal, and you need only use the base name <code>mapfile.map</code> in
286 your <code>RewriteMap</code> directive.</p>
289 <div class="note"><h3>Cached lookups</h3>
291 The looked-up keys are cached by httpd until the <code>mtime</code>
292 (modified time) of the mapfile changes, or the httpd server is
293 restarted. This ensures better performance on maps that are called
298 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
299 <div class="section">
300 <h2><a name="int" id="int">int: Internal Function</a></h2>
303 <p>When a MapType of <code>int</code> is used, the MapSource is one
304 of the available internal RewriteMap functions. Module authors can provide
305 additional internal functions by registering them with the
306 <code>ap_register_rewrite_mapfunc</code> API.
307 The functions that are provided by default are:
311 <li><strong>toupper</strong>:<br />
312 Converts the key to all upper case.</li>
313 <li><strong>tolower</strong>:<br />
314 Converts the key to all lower case.</li>
315 <li><strong>escape</strong>:<br />
316 Translates special characters in the key to
318 <li><strong>unescape</strong>:<br />
319 Translates hex-encodings in the key back to
320 special characters.</li>
324 To use one of these functions, create a <code>RewriteMap</code> referencing
325 the int function, and then use that in your <code>RewriteRule</code>:
328 <pre class="prettyprint lang-config"><strong>#Redirect a URI to an all-lowercase version of itself</strong>
329 RewriteMap lc int:tolower
330 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 <pre class="prettyprint lang-config"><strong>#Rewrite configuration</strong>
373 RewriteMap d2u prg:/www/bin/dash2under.pl<br />
374 RewriteRule - ${d2u:%{REQUEST_URI}}
378 <p><strong>dash2under.pl</strong></p>
379 <pre class="prettyprint lang-perl">
381 $| = 1; # Turn off I/O buffering
382 while (<STDIN>) {
383 s/-/_/g; # Replace dashes with underscores
389 <div class="note"><h3>Caution!</h3>
391 <li>Keep your rewrite map program as simple as possible. If the program
392 hangs, it will cause httpd to wait indefinitely for a response from the
393 map, which will, in turn, cause httpd to stop responding to
395 <li>Be sure to turn off buffering in your program. In Perl this is done
396 by the second line in the example script: <code>$| = 1;</code> This will
397 of course vary in other languages. Buffered I/O will cause httpd to wait
398 for the output, and so it will hang.</li>
399 <li>Remember that there is only one copy of the program, started at
400 server startup. All requests will need to go through this one bottleneck.
401 This can cause significant slowdowns if many requests must go through
402 this process, or if the script itself is very slow.</li>
406 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
407 <div class="section">
408 <h2><a name="dbd" id="dbd">dbd or fastdbd: SQL Query</a></h2>
411 <p>When a MapType of <code>dbd</code> or <code>fastdbd</code> is
412 used, the MapSource is a SQL SELECT statement that takes a single
413 argument and returns a single value.</p>
415 <p><code class="module"><a href="../mod/mod_dbd.html">mod_dbd</a></code> will need to be configured to point at
416 the right database for this statement to be executed.</p>
418 <p>There are two forms of this MapType.
419 Using a MapType of <code>dbd</code> causes the query to be
420 executed with each map request, while using <code>fastdbd</code>
421 caches the database lookups internally. So, while
422 <code>fastdbd</code> is more efficient, and therefore faster, it
423 won't pick up on changes to the database until the server is
426 <p>If a query returns more than one row, a random row from
427 the result set is used.</p>
429 <pre class="prettyprint lang-config"><strong>Example</strong>
430 RewriteMap myquery "fastdbd:SELECT destination FROM rewrite WHERE source = %s"
434 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
435 <div class="section">
436 <h2><a name="summary" id="summary">Summary</a></h2>
439 <p>The <code class="directive">RewriteMap</code> directive can occur more than
440 once. For each mapping-function use one
441 <code class="directive">RewriteMap</code> directive to declare its rewriting
444 <p>While you cannot <strong>declare</strong> a map in
445 per-directory context (<code>.htaccess</code> files or
446 <Directory> blocks) it is possible to
447 <strong>use</strong> this map in per-directory context. </p>
450 <div class="bottomlang">
451 <p><span>Available Languages: </span><a href="../en/rewrite/rewritemap.html" title="English"> en </a></p>
452 </div><div id="footer">
453 <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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