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| <modulesynopsis> |
| |
| <name>mod_expires</name> |
| <description>Generation of |
| <code>Expires</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 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>The <code>Expires</code> HTTP header is 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> |
| </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> |
| |
| <example> |
| ExpiresDefault "<base> [plus] {<num> |
| <type>}*"<br /> |
| ExpiresByType type/encoding "<base> [plus] |
| {<num> <type>}*" |
| </example> |
| |
| <p>where <base> 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. <num> |
| should be an integer value [acceptable to <code>atoi()</code>], |
| and <type> 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> |
| |
| <example> |
| ExpiresDefault "access plus 1 month"<br /> |
| ExpiresDefault "access plus 4 weeks"<br /> |
| ExpiresDefault "access plus 30 days" |
| </example> |
| |
| <p>The expiry time can be fine-tuned by adding several |
| '<num> <type>' clauses:</p> |
| |
| <example> |
| ExpiresByType text/html "access plus 1 month 15 |
| days 2 hours"<br /> |
| ExpiresByType image/gif "modification plus 5 hours 3 |
| minutes" |
| </example> |
| |
| <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> |
| <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> header 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 <em><code>Off</code></em>, no |
| <code>Expires</code> header will 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 <em><code>On</code></em>, the header 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> 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 |
| <em>MIME-type <code>seconds</em></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 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.</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><em><code></em></code> field; <strong>M</strong> |
| means that the file's last modification time should be used as |
| the base time, and <strong>A</strong> means the client's access |
| time should be used.</p> |
| |
| <p>The difference in effect is subtle. If <em>M</em> 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 <em>A</em> 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> |
| |
| <p><strong>Example:</strong></p> |
| <example> |
| # enable expirations<br /> |
| ExpiresActive On<br /> |
| # expire GIF images after a month in the client's cache<br /> |
| ExpiresByType image/gif A2592000<br /> |
| # HTML documents are good for a week from the time they were changed<br /> |
| ExpiresByType text/html M604800 |
| </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 <em><code>seconds</em></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> |
| |