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<?php /* * On the Advanced Settings page enable "Enable dynamic caching" and clear * the cache. * * Plugin authors: NEVER define the template tag for your users. Make them * choose one so it will be unique to their site. * * There are two examples in this file. Both use template tags that must be * kept secret. * * GLOSSARY: * * Dynamic content: the text or widget you want to show visitors to your site * that changes every time it's viewed. * Placeholder/template tag: the string of random characters placed in your * theme file or printed in an action where the dynamic content will go. * Output buffer (ob): any text that is printed by PHP to be sent to the browser * but captured by PHP for further manipulation. * OB Callback function: A function that is called when the output buffer is * filled with a html page. The contents of the page are passed to the function * for processing. * * ** MAKE SURE YOU KEEP THE TEMPLATE TAG SECRET ** * You should probably add 'deny from all' to the .htaccess in the cache directory * so visitors can't directly load any cached html files and discover the secret * tag. Or you can move the cache directory out of the web path and set the * cache location to that new directory on the advanced settings page. * / / * EXAMPLE 1 * http://ocaoimh.ie/2013/10/21/shiny-new-dynamic-content-wp-super-cache/ * Replace a string in your theme with the dynamic content. * * dynamic_cache_test_init() * This function is the first one to be called. This function hooks * dynamic_cache_test_template() to the WordPress action, wp_footer. * This script is loaded before WordPress is and the add_action() * function isn't defined at this time. * This init function hooks onto the cache action "add_cacheaction" * that fires after WordPress (and add_action) is loaded. * * * dynamic_cache_test_template_tag() * This function hooks on to wp_footer and displays the secret template * tag that will be replaced by our dynamic content on each page view. * * * dynamic_cache_test_filter() * This function hooks on to the filter through which all the cached data * sent to visitors is sent. * In this simple example the template tag is replaced by a html comment * containing the text "Hello world at " and the current server time. * If you want to use the output of a WordPress plugin or command you * must enable "late init" on the settings page. Each time you reload * the cached page this time will change. View the page source to examine * this text. * * Chronology of a request: * 1. dynamic_cache_test_init() hooks dynamic_cache_test_template_tag() on * to the wp_footer action. dynamic_cache_test_filter() is hooked on to * the wpsc_cachedata filter. * 2. An output buffer is created by WP Super Cache. * 3. Most of the page is generated by WordPress. * 4. The wp_footer action fires and the TAG is printed to the page. * 5. Processing continues and the page is created. * 6. The output buffer finishes. A WP Super Cache callback function runs * and saves the output buffer to a cache file. The wpsc_cachedata * filter is called. * 7. The function dynamic_cache_test_filter() runs and replaces the TAG in * the buffer with the "Hello world" string. * 8. The output buffer is pushed to the browser to be displayed. / define( 'DYNAMIC_CACHE_TEST_TAG', '' ); // Change this to a secret placeholder tag. if ( '' !== DYNAMIC_CACHE_TEST_TAG ) { function dynamic_cache_test_safety( $safety ) { return 1; } add_cacheaction( 'wpsc_cachedata_safety', 'dynamic_cache_test_safety' ); function dynamic_cache_test_filter( $cachedata ) { return str_replace( DYNAMIC_CACHE_TEST_TAG, '<!-- Hello world at ' . date( 'H:i:s' ) . ' -->', $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: http://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 '<p>This is a test. The current time on the server is: ' . date( 'H:i:s' ) . '</p>'; $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' ); }

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