


How can I effectively implement HTTP caching with PHP for dynamic websites with static content?
Nov 04, 2024 am 09:35 AMIntegrating HTTP Caching with PHP
In situations where page content remains primarily static but surrounded by a dynamic template, leveraging HTTP cache headers can optimize page delivery. Here's a simplified guide to implementing effective caching using PHP:
Essential Headers for Caching
To enable caching, consider sending the following headers:
- Content-Type: Specify the MIME type and character set of the response.
- Vary: Accept: Indicate that the response can vary based on the client's Accept header, controlling content negotiation.
- Cache-Control: Set directives like private_no_expire to allow private caching but prevent revalidation. Alternatively, use public to allow shared caching.
- Last-Modified: Provide the date and time when the content was last modified.
- ETag: Assign a unique identifier to the content, which clients can use to determine if the cached version is still current.
Conditional Requests and Handling
Process incoming conditional requests using if-modified-since and if-none-match:
- if-modified-since: Compare the request header with the Last-Modified header. If the cached version is still valid, return a 304 (Not Modified) status code.
- if-none-match: Validate against the ETag header. If the cached version matches, return a 304.
Determining Cache Validity
When generating the ETag, consider using a checksum or a combination of factors like user ID, language, and timestamp. For longer-lasting static content, set a longer expiration.
Example Implementation
<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>
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