Changeset 28972 for trunk/src/wp-includes/class-wp-embed.php

Timestamp:

07/03/2014 04:44:15 PM (12 years ago)

Author:

helen

Message:

Improve oEmbed caching. Introduces the concept of a TTL for oEmbed caches and a filter for oembed_ttl.

We will no longer replace previously valid oEmbed responses with an {{unknown}} cache value. When this happens due to reaching a rate limit or a service going down, it is data loss, and is not acceptable. This means that oEmbed caches for a post are no longer deleted indiscriminately every time that post is saved.

oEmbed continues to be cached in post meta, with the addition of a separate meta key containing the timestamp of the last retrieval, which is used to avoid re-requesting a recently cached oEmbed response. By default, we consider a valued cached in the past day to be fresh. This can greatly reduce the number of outbound requests, especially in cases where a post containing multiple embeds is saved frequently.

The TTL used to determine whether or not to request a response can be filtered using oembed_ttl, thus allowing for the possibility of respecting the optional oEmbed response parameter cache_age or altering the period of time a cached value is considered to be fresh.

Now that oEmbeds are previewed in the visual editor as well as the media modal, oEmbed caches are often populated before a post is saved or published. By pre-populating and avoiding having to re-request that response, we also greatly reduce the chances of a stampede happening when a published post is visible before oEmbed caching is complete.

As it previously stood, a stampede was extremely likely to happen, as the AJAX caching was only triggered when $_GET['message'] was 1. The published message is 6. We now trigger the caching every time $_GET['message'] is present on the edit screen, as we are able to avoid triggering so many HTTP requests overall.

props markjaquith. fixes #14759. see #17210.

File:

• trunk/src/wp-includes/class-wp-embed.php (modified) (6 diffs)

trunk/src/wp-includes/class-wp-embed.php

@@ -32 +32 @@
                 add_filter( 'the_content', array( $this, 'autoembed' ), 8 );
 
-                // When a post is saved, invalidate the oEmbed cache
-                add_action( 'pre_post_update', array( $this, 'delete_oembed_caches' ) );
-
                 // After a post is saved, cache oEmbed items via AJAX
                 add_action( 'edit_form_advanced', array( $this, 'maybe_run_ajax_cache' ) );
@@ -79 +76 @@
                 $post = get_post();
 
-                if ( ! $post || empty($_GET['message']) || 1 != $_GET['message'] )
+                if ( ! $post || empty( $_GET['message'] ) )
                         return;
 
@@ -193 +190 @@
 
                         // Check for a cached result (stored in the post meta)
-                        $cachekey = '_oembed_' . md5( $url . serialize( $attr ) );
-                        if ( $this->usecache ) {
-                                $cache = get_post_meta( $post_ID, $cachekey, true );
-
-                                // Failures are cached
+                        $key_suffix = md5( $url . serialize( $attr ) );
+                        $cachekey = '_oembed_' . $key_suffix;
+                        $cachekey_time = '_oembed_time_' . $key_suffix;
+
+                        /**
+                         * Filter the oEmbed TTL (time to live).
+                         *
+                         * @since 4.0.0
+                         *
+                         * @param string $url     The attempted embed URL.
+                         * @param array  $attr    An array of shortcode attributes.
+                         * @param int    $post_ID Post ID.
+                         */
+                        $ttl = apply_filters( 'oembed_ttl', DAY_IN_SECONDS, $url, $attr, $post_ID );
+
+                        $cache = get_post_meta( $post_ID, $cachekey, true );
+                        $cache_time = get_post_meta( $post_ID, $cachekey_time, true );
+
+                        if ( ! $cache_time ) {
+                                $cache_time = 0;
+                        }
+
+                        $cached_recently = ( time() - $cache_time ) < $ttl;
+
+                        if ( $this->usecache || $cached_recently ) {
+                                // Failures are cached. Serve one if we're using the cache.
                                 if ( '{{unknown}}' === $cache )
                                         return $this->maybe_make_link( $url );
 
-                                if ( ! empty( $cache ) )
+                                if ( ! empty( $cache ) ) {
                                         /**
                                          * Filter the cached oEmbed HTML.
@@ -215 +233 @@
                                          */
                                         return apply_filters( 'embed_oembed_html', $cache, $url, $attr, $post_ID );
+                                }
                         }
 
@@ -231 +250 @@
                         $html = wp_oembed_get( $url, $attr );
 
-                        // Cache the result
-                        $cache = ( $html ) ? $html : '{{unknown}}';
-                        update_post_meta( $post_ID, $cachekey, $cache );
+                        // Maybe cache the result
+                        if ( $html ) {
+                                update_post_meta( $post_ID, $cachekey, $html );
+                                update_post_meta( $post_ID, $cachekey_time, time() );
+                        } elseif ( ! $cache ) {
+                                update_post_meta( $post_ID, $cachekey, '{{unknown}}' );
+                        }
 
                         // If there was a result, return it
@@ -247 +270 @@
 
         /**
-         * Delete all oEmbed caches.
+         * Delete all oEmbed caches. Unused by core as of 4.0.0.
          *
          * @param int $post_ID Post ID to delete the caches for.