How can I effectively leverage HTTP headers for caching with PHP?

Understanding HTTP Caching with PHP Headers

Q: What HTTP headers are essential for effective caching with PHP?

A: When implementing HTTP caching for a website, specific headers play a crucial role in guiding browsers on how to manage cached content. Essential headers include:

• Vary: This header specifies that the content varies based on parameters like language or user agent, ensuring browsers retrieve the appropriate cached version.
• Last-Modified: Indicates the last time the content was modified. Browsers compare this value to the If-Modified-Since header in subsequent requests to determine if content needs to be refreshed.
• ETag: This header represents an entity tag or checksum of the content. Browsers compare this value to the If-None-Match header to avoid re-requesting unchanged content.

Implementation:

1. Set Cache Policy:

   <code class="php">session_cache_limiter('private_no_expire'); // Allow caching but do not reveal cache expiry time</code>

2. Set Expiration:

   <code class="php">header("Cache-Control: max-age=" . (60 * 60 * 24 * 30)); // Set cache expiration to 30 days</code>

3. Manage If-Modified-Since and If-None-Match Headers:
   Compare the values of these headers to the Last-Modified and ETag headers to avoid unnecessary re-requests:

   <code class="php">$tsstring = gmdate('D, d M Y H:i:s ', $timestamp) . 'GMT';
   $etag = $language . $timestamp;
   
   $if_modified_since = isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) ? $_SERVER['HTTP_IF_MODIFIED_SINCE'] : false;
   $if_none_match = isset($_SERVER['HTTP_IF_NONE_MATCH']) ? $_SERVER['HTTP_IF_NONE_MATCH'] : false;
   
   if ((($if_none_match && $if_none_match == $etag) || (!$if_none_match)) &&
       ($if_modified_since && $if_modified_since == $tsstring))
   {
       header('HTTP/1.1 304 Not Modified');
       exit();
   }
   else
   {
       header("Last-Modified: $tsstring");
       header("ETag: \"{$etag}\"");
   }</code>

The above is the detailed content of How can I effectively leverage HTTP headers for caching with PHP?. For more information, please follow other related articles on the PHP Chinese website!