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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 class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></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"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><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="#int">int: Internal Function</a></li>
44 <li><img alt="" src="../images/down.gif" /> <a href="#txt">txt: Plain text maps</a></li>
45 <li><img alt="" src="../images/down.gif" /> <a href="#rnd">rnd: Randomized Plain Text</a></li>
46 <li><img alt="" src="../images/down.gif" /> <a href="#dbm">dbm: DBM Hash File</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><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 class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>
68 directive is as follows:</p>
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 can define a
95 <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></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"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></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 class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive may not be
112 used in <code class="directive"><a href="../mod/core.html#directory"><Directory></a></code> sections or
113 <code>.htaccess</code> files. You must
114 declare the map in server or virtualhost context. You may use the map,
115 once created, in your <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> and
116 <code class="directive"><a href="../mod/mod_rewrite.html#rewritecond">RewriteCond</a></code> directives in those
117 scopes. You just can't <strong>declare</strong> it in those scopes.</p>
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="int" id="int">int: Internal Function</a></h2>
127 <p>When a MapType of <code>int</code> is used, the MapSource is one
128 of the available internal <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>
129 functions. Module authors can provide
130 additional internal functions by registering them with the
131 <code>ap_register_rewrite_mapfunc</code> API.
132 The functions that are provided by default are:
136 <li><strong>toupper</strong>:<br />
137 Converts the key to all upper case.</li>
138 <li><strong>tolower</strong>:<br />
139 Converts the key to all lower case.</li>
140 <li><strong>escape</strong>:<br />
141 Translates special characters in the key to
143 <li><strong>unescape</strong>:<br />
144 Translates hex-encodings in the key back to
145 special characters.</li>
149 To use one of these functions, create a <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> referencing
150 the int function, and then use that in your <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code>:
153 <p> <strong>Redirect a URI to an all-lowercase version of itself</strong></p>
154 <pre class="prettyprint lang-config">RewriteMap lc int:tolower
155 RewriteRule "(.*)" "${lc:$1}" [R]</pre>
159 <p>Please note that the example offered here is for
160 illustration purposes only, and is not a recommendation. If you want
161 to make URLs case-insensitive, consider using
162 <code class="module"><a href="../mod/mod_speling.html">mod_speling</a></code> instead.
166 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
167 <div class="section">
168 <h2><a name="txt" id="txt">txt: Plain text maps</a></h2>
171 <p>When a MapType of <code>txt</code> is used, the MapSource is a filesystem path to a
172 plain-text mapping file, containing one space-separated key/value pair
173 per line. Optionally, a line may contain a comment, starting with
176 <p>A valid text rewrite map file will have the following syntax:</p>
178 <div class="example"><p><code>
180 <strong><em>MatchingKey</em> <em>SubstValue</em></strong><br />
181 <strong><em>MatchingKey</em> <em>SubstValue</em></strong> # comment<br />
184 <p>When the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> is invoked
185 the argument is looked for in the
186 first argument of a line, and, if found, the substitution value is
189 <p>For example, we can use a mapfile to translate product names to
190 product IDs for easier-to-remember URLs, using the following
192 <p><strong>Product to ID configuration</strong></p>
193 <pre class="prettyprint lang-config">RewriteMap product2id "txt:/etc/apache2/productmap.txt"
194 RewriteRule "^/product/(.*)" "/prods.php?id=${product2id:$1|NOTFOUND}" [PT]</pre>
197 <p>We assume here that the <code>prods.php</code> script knows what
198 to do when it received an argument of <code>id=NOTFOUND</code> when
199 a product is not found in the lookup map.</p>
201 <p>The file <code>/etc/apache2/productmap.txt</code> then contains
204 <div class="example"><h3>Product to ID map</h3><p><code>
206 ## productmap.txt - Product to ID map file<br />
216 <p>Thus, when <code>http://example.com/product/television</code> is
217 requested, the <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> is
218 applied, and the request
219 is internally mapped to <code>/prods.php?id=993</code>.</p>
221 <div class="note"><h3>Note: .htaccess files</h3>
222 The example given is crafted to be used in server or virtualhost
223 scope. If you're planning to use this in a <code>.htaccess</code>
224 file, you'll need to remove the leading slash from the rewrite
225 pattern in order for it to match anything:
226 <pre class="prettyprint lang-config">RewriteRule "^product/(.*)" "/prods.php?id=${product2id:$1|NOTFOUND}" [PT]</pre>
230 <div class="note"><h3>Cached lookups</h3>
232 The looked-up keys are cached by httpd until the <code>mtime</code>
233 (modified time) of the mapfile changes, or the httpd server is
234 restarted. This ensures better performance on maps that are called
239 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
240 <div class="section">
241 <h2><a name="rnd" id="rnd">rnd: Randomized Plain Text</a></h2>
244 <p>When a MapType of <code>rnd</code> is used, the MapSource is a
245 filesystem path to a plain-text mapping file, each line of which
246 contains a key, and one or more values separated by <code>|</code>.
247 One of these values will be chosen at random if the key is
250 <p>For example, you can use the following map
251 file and directives to provide a random load balancing between
252 several back-end servers, via a reverse-proxy. Images are sent
253 to one of the servers in the 'static' pool, while everything
254 else is sent to one of the 'dynamic' pool.</p>
256 <div class="example"><h3>Rewrite map file</h3><p><code>
258 ## map.txt -- rewriting map<br />
261 static www1|www2|www3|www4<br />
264 <p><strong>Configuration directives</strong></p>
265 <pre class="prettyprint lang-config">RewriteMap servers "rnd:/path/to/file/map.txt"
267 RewriteRule "^/(.*\.(png|gif|jpg))" "http://${servers:static}/$1" [NC,P,L]
268 RewriteRule "^/(.*)" "http://${servers:dynamic}/$1" [P,L]</pre>
271 <p>So, when an image is requested and the first of these rules is
272 matched, <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> looks up the string
273 <code>static</code> in the map file, which returns one of the
274 specified hostnames at random, which is then used in the
275 <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> target.</p>
277 <p>If you wanted to have one of the servers more likely to be chosen
278 (for example, if one of the server has more memory than the others,
279 and so can handle more requests) simply list it more times in the
282 <div class="example"><p><code>
283 static www1|www1|www2|www3|www4
286 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
287 <div class="section">
288 <h2><a name="dbm" id="dbm">dbm: DBM Hash File</a></h2>
291 <p>When a MapType of <code>dbm</code> is used, the MapSource is a
292 filesystem path to a DBM database file containing key/value pairs to
293 be used in the mapping. This works exactly the same way as the
294 <code>txt</code> map, but is much faster, because a DBM is indexed,
295 whereas a text file is not. This allows more rapid access to the
298 <p>You may optionally specify a particular dbm type:</p>
300 <pre class="prettyprint lang-config">RewriteMap examplemap "dbm=sdbm:/etc/apache/mapfile.dbm"</pre>
303 <p>The type can be <code>sdbm</code>, <code>gdbm</code>, <code>ndbm</code>
305 However, it is recommended that you just use the <a href="../programs/httxt2dbm.html">httxt2dbm</a> utility that is
306 provided with Apache HTTP Server, as it will use the correct DBM library,
307 matching the one that was used when httpd itself was built.</p>
309 <p>To create a dbm file, first create a text map file as described
310 in the <a href="#txt">txt</a> section. Then run
311 <code>httxt2dbm</code>:</p>
313 <div class="example"><p><code>
314 $ httxt2dbm -i mapfile.txt -o mapfile.map
317 <p>You can then reference the resulting file in your
318 <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive:</p>
320 <pre class="prettyprint lang-config">RewriteMap mapname "dbm:/etc/apache/mapfile.map"</pre>
324 <p>Note that with some dbm types, more than one file is generated, with
325 a common base name. For example, you may have two files named
326 <code>mapfile.map.dir</code> and <code>mapfiile.map.pag</code>. This is
327 normal, and you need only use the base name <code>mapfile.map</code> in
328 your <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive.</p>
331 <div class="note"><h3>Cached lookups</h3>
333 The looked-up keys are cached by httpd until the <code>mtime</code>
334 (modified time) of the mapfile changes, or the httpd server is
335 restarted. This ensures better performance on maps that are called
340 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
341 <div class="section">
342 <h2><a name="prg" id="prg">prg: External Rewriting Program</a></h2>
344 <p>When a MapType of <code>prg</code> is used, the MapSource is a
345 filesystem path to an executable program which will providing the
346 mapping behavior. This can be a compiled binary file, or a program
347 in an interpreted language such as Perl or Python.</p>
349 <p>This program is started once, when the Apache HTTP Server is
350 started, and then communicates with the rewriting engine via
351 <code>STDIN</code> and <code>STDOUT</code>. That is, for each map
352 function lookup, it expects one argument via <code>STDIN</code>, and
353 should return one new-line terminated response string on
354 <code>STDOUT</code>. If there is no corresponding lookup value, the
355 map program should return the four-character string
356 "<code>NULL</code>" to indicate this.</p>
358 <p>External rewriting programs are not started if they're defined in
359 a context that does not have <code class="directive"><a href="../mod/mod_rewrite.html#rewriteengine">RewriteEngine</a></code> set to
362 <p>This feature utilizes the <code>rewrite-map</code> mutex,
363 which is required for reliable communication with the program.
364 The mutex mechanism and lock file can be configured with the
365 <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive.</p>
367 <p>A simple example is shown here which will replace all dashes with
368 underscores in a request URI.</p>
370 <p><strong>Rewrite configuration</strong></p>
371 <pre class="prettyprint lang-config">RewriteMap d2u "prg:/www/bin/dash2under.pl"
372 RewriteRule "-" "${d2u:%{REQUEST_URI}}"</pre>
375 <p><strong>dash2under.pl</strong></p>
376 <pre class="prettyprint lang-perl">#!/usr/bin/perl
377 $| = 1; # Turn off I/O buffering
378 while (<STDIN>) {
379 s/-/_/g; # Replace dashes with underscores
384 <div class="note"><h3>Caution!</h3>
386 <li>Keep your rewrite map program as simple as possible. If the program
387 hangs, it will cause httpd to wait indefinitely for a response from the
388 map, which will, in turn, cause httpd to stop responding to
390 <li>Be sure to turn off buffering in your program. In Perl this is done
391 by the second line in the example script: <code>$| = 1;</code> This will
392 of course vary in other languages. Buffered I/O will cause httpd to wait
393 for the output, and so it will hang.</li>
394 <li>Remember that there is only one copy of the program, started at
395 server startup. All requests will need to go through this one bottleneck.
396 This can cause significant slowdowns if many requests must go through
397 this process, or if the script itself is very slow.</li>
401 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
402 <div class="section">
403 <h2><a name="dbd" id="dbd">dbd or fastdbd: SQL Query</a></h2>
406 <p>When a MapType of <code>dbd</code> or <code>fastdbd</code> is
407 used, the MapSource is a SQL SELECT statement that takes a single
408 argument and returns a single value.</p>
410 <p><code class="module"><a href="../mod/mod_dbd.html">mod_dbd</a></code> will need to be configured to point at
411 the right database for this statement to be executed.</p>
413 <p>There are two forms of this MapType.
414 Using a MapType of <code>dbd</code> causes the query to be
415 executed with each map request, while using <code>fastdbd</code>
416 caches the database lookups internally. So, while
417 <code>fastdbd</code> is more efficient, and therefore faster, it
418 won't pick up on changes to the database until the server is
421 <p>If a query returns more than one row, a random row from
422 the result set is used.</p>
424 <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">RewriteMap myquery "fastdbd:SELECT destination FROM rewrite WHERE source = %s"</pre>
427 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
428 <div class="section">
429 <h2><a name="summary" id="summary">Summary</a></h2>
432 <p>The <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive can
433 occur more than once. For each mapping-function use one
434 <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive to declare
435 its rewriting mapfile.</p>
437 <p>While you cannot <strong>declare</strong> a map in
438 per-directory context (<code>.htaccess</code> files or
439 <code class="directive"><a href="../mod/core.html#directory"><Directory></a></code> blocks) it is
440 possible to <strong>use</strong> this map in per-directory context.</p>
443 <div class="bottomlang">
444 <p><span>Available Languages: </span><a href="../en/rewrite/rewritemap.html" title="English"> en </a> |
445 <a href="../fr/rewrite/rewritemap.html" hreflang="fr" rel="alternate" title="Français"> fr </a></p>
446 </div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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