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22 <div id="preamble"><h1>Apache Module mod_expires</h1>
24 <p><span>Available Languages: </span><a href="../en/mod/mod_expires.html" title="English"> en </a> |
25 <a href="../ja/mod/mod_expires.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
26 <a href="../ko/mod/mod_expires.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
28 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Generation of <code>Expires</code> and
29 <code>Cache-Control</code> HTTP headers according to user-specified
31 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
32 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>expires_module</td></tr>
33 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_expires.c</td></tr></table>
36 <p>This module controls the setting of the <code>Expires</code>
37 HTTP header and the <code>max-age</code> directive of the
38 <code>Cache-Control</code> HTTP header in server responses. The
39 expiration date can set to be relative to either the time the
40 source file was last modified, or to the time of the client
43 <p>These HTTP headers are an instruction to the client about the
44 document's validity and persistence. If cached, the document may
45 be fetched from the cache rather than from the source until this
46 time has passed. After that, the cache copy is considered
47 "expired" and invalid, and a new copy must be obtained from the
50 <p>To modify <code>Cache-Control</code> directives other than
51 <code>max-age</code> (see <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9">RFC
52 2616 section 14.9</a>), you can use the <code class="directive"><a href="../mod/mod_headers.html#header">Header</a></code> directive.</p>
55 <div id="quickview"><h3 class="directives">Directives</h3>
57 <li><img alt="" src="../images/down.gif" /> <a href="#expiresactive">ExpiresActive</a></li>
58 <li><img alt="" src="../images/down.gif" /> <a href="#expiresbytype">ExpiresByType</a></li>
59 <li><img alt="" src="../images/down.gif" /> <a href="#expiresdefault">ExpiresDefault</a></li>
63 <li><img alt="" src="../images/down.gif" /> <a href="#AltSyn">Alternate Interval Syntax</a></li>
65 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
67 <h2><a name="AltSyn" id="AltSyn">Alternate Interval Syntax</a></h2>
68 <p>The <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code> and
69 <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> directives
70 can also be defined in a more readable syntax of the form:</p>
72 <div class="example"><p><code>
73 ExpiresDefault "<base> [plus] {<num>
75 ExpiresByType type/encoding "<base> [plus]
76 {<num> <type>}*"
79 <p>where <base> is one of:</p>
82 <li><code>access</code></li>
84 <li><code>now</code> (equivalent to
85 '<code>access</code>')</li>
87 <li><code>modification</code></li>
90 <p>The <code>plus</code> keyword is optional. <num>
91 should be an integer value [acceptable to <code>atoi()</code>],
92 and <type> is one of:</p>
95 <li><code>years</code></li>
96 <li><code>months</code></li>
97 <li><code>weeks</code></li>
98 <li><code>days</code></li>
99 <li><code>hours</code></li>
100 <li><code>minutes</code></li>
101 <li><code>seconds</code></li>
104 <p>For example, any of the following directives can be used to
105 make documents expire 1 month after being accessed, by
108 <div class="example"><p><code>
109 ExpiresDefault "access plus 1 month"<br />
110 ExpiresDefault "access plus 4 weeks"<br />
111 ExpiresDefault "access plus 30 days"
114 <p>The expiry time can be fine-tuned by adding several
115 '<num> <type>' clauses:</p>
117 <div class="example"><p><code>
118 ExpiresByType text/html "access plus 1 month 15
120 ExpiresByType image/gif "modification plus 5 hours 3
124 <p>Note that if you use a modification date based setting, the
125 Expires header will <strong>not</strong> be added to content
126 that does not come from a file on disk. This is due to the fact
127 that there is no modification time for such content.</p>
129 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
130 <div class="directive-section"><h2><a name="ExpiresActive" id="ExpiresActive">ExpiresActive</a> <a name="expiresactive" id="expiresactive">Directive</a></h2>
131 <table class="directive">
132 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enables generation of <code>Expires</code>
134 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresActive On|Off</code></td></tr>
135 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
136 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
137 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
138 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
140 <p>This directive enables or disables the generation of the
141 <code>Expires</code> and <code>Cache-Control</code> headers for
142 the document realm in question. (That is, if found in an
143 <code>.htaccess</code> file, for instance, it applies only to
144 documents generated from that directory.) If set to
145 <code>Off</code>, the headers will not be generated for any
146 document in the realm (unless overridden at a lower level, such as
147 an <code>.htaccess</code> file overriding a server config
148 file). If set to <code>On</code>, the headers will be added to
149 served documents according to the criteria defined by the
150 <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> and
151 <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code>
152 directives (<em>q.v.</em>).</p>
154 <p>Note that this directive does not guarantee that an
155 <code>Expires</code> or <code>Cache-Control</code> header will be
156 generated. If the criteria aren't met, no header will be sent, and
157 the effect will be as though this directive wasn't even
161 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
162 <div class="directive-section"><h2><a name="ExpiresByType" id="ExpiresByType">ExpiresByType</a> <a name="expiresbytype" id="expiresbytype">Directive</a></h2>
163 <table class="directive">
164 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Value of the <code>Expires</code> header configured
165 by MIME type</td></tr>
166 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresByType <var>MIME-type</var>
167 <var><code>seconds</var></code></td></tr>
168 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
169 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
170 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
171 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
173 <p>This directive defines the value of the <code>Expires</code>
174 header and the <code>max-age</code> directive of the
175 <code>Cache-Control</code> header generated for documents of the
176 specified type (<em>e.g.</em>, <code>text/html</code>). The second
177 argument sets the number of seconds that will be added to a base
178 time to construct the expiration date. The <code>Cache-Control:
179 max-age</code> is calculated by subtracting the request time from
180 the expiration date and expressing the result in seconds.</p>
182 <p>The base time is either the last modification time of the
183 file, or the time of the client's access to the document. Which
184 should be used is specified by the
185 <code><var><code></var></code> field; <code>M</code>
186 means that the file's last modification time should be used as
187 the base time, and <code>A</code> means the client's access
188 time should be used.</p>
190 <p>The difference in effect is subtle. If <code>M</code> is used,
191 all current copies of the document in all caches will expire at
192 the same time, which can be good for something like a weekly
193 notice that's always found at the same URL. If <code>A</code> is
194 used, the date of expiration is different for each client; this
195 can be good for image files that don't change very often,
196 particularly for a set of related documents that all refer to
197 the same images (<em>i.e.</em>, the images will be accessed
198 repeatedly within a relatively short timespan).</p>
200 <div class="example"><h3>Example:</h3><p><code>
201 # enable expirations<br />
202 ExpiresActive On<br />
203 # expire GIF images after a month in the client's cache<br />
204 ExpiresByType image/gif A2592000<br />
205 # HTML documents are good for a week from the<br />
206 # time they were changed<br />
207 ExpiresByType text/html M604800
210 <p>Note that this directive only has effect if
211 <code>ExpiresActive On</code> has been specified. It overrides,
212 for the specified MIME type <em>only</em>, any expiration date
213 set by the <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code>
216 <p>You can also specify the expiration time calculation using
217 an <a href="#AltSyn">alternate syntax</a>, described earlier in
221 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
222 <div class="directive-section"><h2><a name="ExpiresDefault" id="ExpiresDefault">ExpiresDefault</a> <a name="expiresdefault" id="expiresdefault">Directive</a></h2>
223 <table class="directive">
224 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Default algorithm for calculating expiration time</td></tr>
225 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresDefault <var><code>seconds</var></code></td></tr>
226 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
227 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
228 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
229 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
231 <p>This directive sets the default algorithm for calculating the
232 expiration time for all documents in the affected realm. It can be
233 overridden on a type-by-type basis by the <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> directive. See the
234 description of that directive for details about the syntax of the
235 argument, and the <a href="#AltSyn">alternate syntax</a>
236 description as well.</p>
240 <div class="bottomlang">
241 <p><span>Available Languages: </span><a href="../en/mod/mod_expires.html" title="English"> en </a> |
242 <a href="../ja/mod/mod_expires.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
243 <a href="../ko/mod/mod_expires.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
244 </div><div id="footer">
245 <p class="apache">Copyright 2009 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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