HTTP/2 200 server: nginx date: Sat, 11 Oct 2025 20:34:43 GMT content-type: text/plain vary: Accept-Encoding last-modified: Mon, 23 Jan 2023 06:59:36 GMT etag: W/"2852729//wp-super-cache/trunk/plugins/dynamic-cache-test.php" cache-control: max-age=604800 alt-svc: h3=":443"; ma=86400 content-encoding: gzip ', $cachedata ); } add_cacheaction( 'wpsc_cachedata', 'dynamic_cache_test_filter' ); function dynamic_cache_test_template_tag() { echo DYNAMIC_CACHE_TEST_TAG; // This is the template tag. } function dynamic_cache_test_init() { add_action( 'wp_footer', 'dynamic_cache_test_template_tag' ); } add_cacheaction( 'add_cacheaction', 'dynamic_cache_test_init' ); } /* * EXAMPLE 2 * * This is going to be complicated. Hang on! * * When the cache file for a new page is generated the plugin uses an output * buffer to capture the page. A callback function processes the buffer and * writes to the cache file. The placeholder tag for any dynamic content has * to be written to that cache file but also, it has to be replaced with * dynamic content before the page is shown to the user. * More on output buffers here: https://php.net/ob_start * * Unfortunately an extra output buffer is often required when capturing dynamic * content such as sidebar widgets. Due to a quirk of the way PHP works it's * not possible to have an output buffer run in an output buffer callback. That * dynamic content has to be generated before the callback function is reached. * The following error occurs when an output buffer is created in the * callback function of another output buffer: * "PHP Fatal error: ob_start(): Cannot use output buffering in output buffering display handlers in..." * * In this example the function add_action() isn't available when this file is * loaded so dynamic_output_buffer_init() is hooked on to the "add_cacheaction" * cacheaction. That function then hooks dynamic_output_buffer_test() on to the * familiar wp_footer action. * * The first time dynamic_output_buffer_test() runs it generates the dynamic * content and captures it with ob_start() in the DYNAMIC_OB_TEXT constant. * * When the main WP Super Cache output buffer is ready the callback is called. * This fires the wpsc_cachedata_safety filter. If the DYNAMIC_OB_TEXT constant * is set, which means dynamic content is ready, then it returns 1, a signal * that everything is ok. * Finally, the wpsc_cachedata filter is run. The function * dynamic_output_buffer_test() is hooked on to it. Since DYNAMIC_OB_TEXT is * set it replaces the placeholder text with that constant. * The resulting html is then sent to the browser. * * Already cached pages call the safety filter, and then the wpsc_cachedata * filter so any hooked function must be ready to generate dynamic content. The * very last line of dynamic_output_buffer_test() replaces the placeholder tag * with the dynamic content in the cache file. * * Use an output buffer to capture dynamic content while the page is generated * and insert into the right place: * Remember to add the DYNAMIC_OUTPUT_BUFFER_TAG text (as defined below) to * your theme where the dynamic content should be. * * dynamic_output_buffer_test() is a function that uses the wpsc_cachedata * filter to add a small message and the current server time to every web * page. The time increments on every reload. * */ define( 'DYNAMIC_OUTPUT_BUFFER_TAG', '' ); // Change this to a secret placeholder tag. if ( '' !== DYNAMIC_OUTPUT_BUFFER_TAG ) { function dynamic_output_buffer_test( $cachedata = 0 ) { if ( defined( 'DYNAMIC_OB_TEXT' ) ) { return str_replace( DYNAMIC_OUTPUT_BUFFER_TAG, DYNAMIC_OB_TEXT, $cachedata ); } ob_start(); // call the sidebar function, do something dynamic echo '

This is a test. The current time on the server is: ' . date( 'H:i:s' ) . '

'; $text = ob_get_contents(); ob_end_clean(); if ( 0 === $cachedata ) { // called directly from the theme so store the output. define( 'DYNAMIC_OB_TEXT', $text ); } else { // called via the wpsc_cachedata filter. We only get here in cached pages in wp-cache-phase1.php. return str_replace( DYNAMIC_OUTPUT_BUFFER_TAG, $text, $cachedata ); } } add_cacheaction( 'wpsc_cachedata', 'dynamic_output_buffer_test' ); function dynamic_output_buffer_init() { add_action( 'wp_footer', 'dynamic_output_buffer_test' ); } add_cacheaction( 'add_cacheaction', 'dynamic_output_buffer_init' ); function dynamic_output_buffer_test_safety( $safety ) { if ( defined( 'DYNAMIC_OB_TEXT' ) ) {// this is set when you call dynamic_output_buffer_test() from the theme. return 1; // ready to replace tag with dynamic content. } else { return 0; // tag cannot be replaced. } } add_cacheaction( 'wpsc_cachedata_safety', 'dynamic_output_buffer_test_safety' ); }