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| <modulesynopsis metafile="mod_expires.xml.meta"> |
| |
| <name>mod_expires</name> |
| <description>Generation of <code>Expires</code> and |
| <code>Cache-Control</code> HTTP headers according to user-specified |
| criteria</description> |
| <status>Extension</status> |
| <sourcefile>mod_expires.c</sourcefile> |
| <identifier>expires_module</identifier> |
| |
| <summary> |
| <p>This module controls the setting of the <code>Expires</code> |
| HTTP header and the <code>max-age</code> directive of the |
| <code>Cache-Control</code> HTTP header in server responses. The |
| expiration date can set to be relative to either the time the |
| source file was last modified, or to the time of the client |
| access.</p> |
| |
| <p>These HTTP headers are an instruction to the client about the |
| document's validity and persistence. If cached, the document may |
| be fetched from the cache rather than from the source until this |
| time has passed. After that, the cache copy is considered |
| "expired" and invalid, and a new copy must be obtained from the |
| source.</p> |
| |
| <p>To modify <code>Cache-Control</code> directives other than |
| <code>max-age</code> (see <a |
| href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9">RFC |
| 2616 section 14.9</a>), you can use the <directive |
| module="mod_headers">Header</directive> directive.</p> |
| |
| <p> When the <code>Expires</code> header is already part of the response |
| generated by the server, for example when generated by a CGI script or |
| proxied from an origin server, this module does not change or add |
| an <code>Expires</code> or <code>Cache-Control</code> header.</p> |
| </summary> |
| |
| <section id="AltSyn"><title>Alternate Interval Syntax</title> |
| <p>The <directive module="mod_expires">ExpiresDefault</directive> and |
| <directive module="mod_expires">ExpiresByType</directive> directives |
| can also be defined in a more readable syntax of the form:</p> |
| |
| <highlight language="config"> |
| ExpiresDefault "<var>base</var> [plus <var>num</var> <var>type</var>] [<var>num</var> <var>type</var>] ..." |
| ExpiresByType type/encoding "<var>base</var> [plus <var>num</var> <var>type</var>] [<var>num</var> <var>type</var>] ..." |
| </highlight> |
| |
| <p>where <var>base</var> is one of:</p> |
| |
| <ul> |
| <li><code>access</code></li> |
| |
| <li><code>now</code> (equivalent to |
| '<code>access</code>')</li> |
| |
| <li><code>modification</code></li> |
| </ul> |
| |
| <p>The <code>plus</code> keyword is optional. <var>num</var> |
| should be an integer value [acceptable to <code>atoi()</code>], |
| and <var>type</var> is one of:</p> |
| |
| <ul> |
| <li><code>years</code></li> |
| <li><code>months</code></li> |
| <li><code>weeks</code></li> |
| <li><code>days</code></li> |
| <li><code>hours</code></li> |
| <li><code>minutes</code></li> |
| <li><code>seconds</code></li> |
| </ul> |
| |
| <p>For example, any of the following directives can be used to |
| make documents expire 1 month after being accessed, by |
| default:</p> |
| |
| <highlight language="config"> |
| ExpiresDefault "access plus 1 month" |
| ExpiresDefault "access plus 4 weeks" |
| ExpiresDefault "access plus 30 days" |
| </highlight> |
| |
| <p>The expiry time can be fine-tuned by adding several |
| '<var>num</var> <var>type</var>' clauses:</p> |
| |
| <highlight language="config"> |
| ExpiresByType text/html "access plus 1 month 15 days 2 hours" |
| ExpiresByType image/gif "modification plus 5 hours 3 minutes" |
| </highlight> |
| |
| <p>Note that if you use a modification date based setting, the |
| Expires header will <strong>not</strong> be added to content |
| that does not come from a file on disk. This is due to the fact |
| that there is no modification time for such content.</p> |
| </section> |
| |
| <directivesynopsis> |
| <name>ExpiresActive</name> |
| <description>Enables generation of <code>Expires</code> |
| headers</description> |
| <syntax>ExpiresActive On|Off</syntax> |
| <default>ExpiresActive Off</default> |
| <contextlist><context>server config</context> |
| <context>virtual host</context><context>directory</context> |
| <context>.htaccess</context></contextlist> |
| <override>Indexes</override> |
| |
| <usage> |
| <p>This directive enables or disables the generation of the |
| <code>Expires</code> and <code>Cache-Control</code> headers for |
| the document realm in question. (That is, if found in an |
| <code>.htaccess</code> file, for instance, it applies only to |
| documents generated from that directory.) If set to |
| <code>Off</code>, the headers will not be generated for any |
| document in the realm (unless overridden at a lower level, such as |
| an <code>.htaccess</code> file overriding a server config |
| file). If set to <code>On</code>, the headers will be added to |
| served documents according to the criteria defined by the |
| <directive module="mod_expires">ExpiresByType</directive> and |
| <directive module="mod_expires">ExpiresDefault</directive> |
| directives (<em>q.v.</em>).</p> |
| |
| <p>Note that this directive does not guarantee that an |
| <code>Expires</code> or <code>Cache-Control</code> header will be |
| generated. If the criteria aren't met, no header will be sent, and |
| the effect will be as though this directive wasn't even |
| specified.</p> |
| </usage> |
| </directivesynopsis> |
| |
| <directivesynopsis> |
| <name>ExpiresByType</name> |
| <description>Value of the <code>Expires</code> header configured |
| by MIME type</description> |
| <syntax>ExpiresByType <var>MIME-type</var> |
| <var><code>seconds</var></syntax> |
| <contextlist><context>server config</context><context>virtual host</context> |
| <context>directory</context><context>.htaccess</context></contextlist> |
| <override>Indexes</override> |
| |
| <usage> |
| <p>This directive defines the value of the <code>Expires</code> |
| header and the <code>max-age</code> directive of the |
| <code>Cache-Control</code> header generated for documents of the |
| specified type (<em>e.g.</em>, <code>text/html</code>). The second |
| argument sets the number of seconds that will be added to a base |
| time to construct the expiration date. The <code>Cache-Control: |
| max-age</code> is calculated by subtracting the request time from |
| the expiration date and expressing the result in seconds.</p> |
| |
| <p>The base time is either the last modification time of the |
| file, or the time of the client's access to the document. Which |
| should be used is specified by the |
| <code><var><code></var></code> field; <code>M</code> |
| means that the file's last modification time should be used as |
| the base time, and <code>A</code> means the client's access |
| time should be used.</p> |
| |
| <p>The difference in effect is subtle. If <code>M</code> is used, |
| all current copies of the document in all caches will expire at |
| the same time, which can be good for something like a weekly |
| notice that's always found at the same URL. If <code>A</code> is |
| used, the date of expiration is different for each client; this |
| can be good for image files that don't change very often, |
| particularly for a set of related documents that all refer to |
| the same images (<em>i.e.</em>, the images will be accessed |
| repeatedly within a relatively short timespan).</p> |
| |
| <example><title>Example:</title> |
| <highlight language="config"> |
| # enable expirations |
| ExpiresActive On |
| # expire GIF images after a month in the client's cache |
| ExpiresByType image/gif A2592000 |
| # HTML documents are good for a week from the |
| # time they were changed |
| ExpiresByType text/html M604800 |
| </highlight> |
| </example> |
| |
| <p>Note that this directive only has effect if |
| <code>ExpiresActive On</code> has been specified. It overrides, |
| for the specified MIME type <em>only</em>, any expiration date |
| set by the <directive module="mod_expires">ExpiresDefault</directive> |
| directive.</p> |
| |
| <p>You can also specify the expiration time calculation using |
| an <a href="#AltSyn">alternate syntax</a>, described earlier in |
| this document.</p> |
| </usage> |
| </directivesynopsis> |
| |
| <directivesynopsis> |
| <name>ExpiresDefault</name> |
| <description>Default algorithm for calculating expiration time</description> |
| <syntax>ExpiresDefault <var><code>seconds</var></syntax> |
| <contextlist><context>server config</context><context>virtual host</context> |
| <context>directory</context><context>.htaccess</context></contextlist> |
| <override>Indexes</override> |
| |
| <usage> |
| <p>This directive sets the default algorithm for calculating the |
| expiration time for all documents in the affected realm. It can be |
| overridden on a type-by-type basis by the <directive |
| module="mod_expires">ExpiresByType</directive> directive. See the |
| description of that directive for details about the syntax of the |
| argument, and the <a href="#AltSyn">alternate syntax</a> |
| description as well.</p> |
| </usage> |
| </directivesynopsis> |
| </modulesynopsis> |
| |