Support HTTP ETags

classes/theme.php

@@ -315,6 +315,97 @@ public function act_display( $paramarray = array( 'user_filters'=> array() ) )
 				}
 			}
 		}
+
+		// @todo probably need to make this private if the user is logged in so proxy's don't cache it?
+		// @todo this shouldn't be necessary at all after we sort out starting a session only for logged-in users
+		header('Pragma: public', true);
+		header('Cache-Control: public, max-age=' . HabariDateTime::DAY * 30, true);
+
+		// we need to manually build a representation of the current content displayed to be sure comments are included
+		$displayed_content = array();
+
+		// while we're at it, we'll also look for the most recently modified post, rather than iterating back over everything again later
+		$last_modified = null;
+
+		// is there actually anything?
+		if ( isset( $posts ) ) {
+
+			// if $posts is actually a single post (ie: we are displaying a single entry), wrap it up as an array isntead
+			if ( $posts instanceof Post ) {
+				$available_posts = array( $posts );
+			}
+			else {
+				$available_posts = $posts;
+			}
+
+			foreach ( $available_posts as $post ) {
+
+				// hash this post in possibly the most crude way possible
+				$displayed_content[] = sha1( serialize( $post ) );
+
+				// if the post was modified more recently than the last (or we don't have one, duh), use that date
+				if ( $last_modified == null || $post->modified > $last_modified ) {
+					$last_modified = $post->modified;
+				}
+
+				// if there are approved comments, we want to take those into account, too
+				foreach ( $post->comments->moderated->comments as $comment ) {
+
+					// hash the post comment too
+					$displayed_content[] = sha1( serialize( $comment ) );
+
+					// if it was modified more recently than anything else we've seen, use that
+					if ( $last_modified == null || $comment->date > $last_modified ) {
+						$last_modified = $comment->date;
+					}
+
+				}
+
+			}
+
+		}
+
+		// now generate an etag from the content we are displaying
+		$etag = sha1( serialize( $displayed_content ) );
+
+		// let the client know what content is on the page currently
+		header('ETag: "' . $etag . '"', true);
+
+		// and check to see if they gave us an etag they have cached
+		if ( isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) ) {
+			if ( $etag == trim( $_SERVER->raw('HTTP_IF_NONE_MATCH'), '"' ) ) {
+				header( 'HTTP/1.1 304 Not Modified', true, 304);
+				header( 'X-Habari-Cache-Match: ETag');
+				// don't send any further content
+				die();
+			}
+		}
+
+		// if we didn't match the etag, but we have a last modified date to check, do that as a fallback
+		if ( $last_modified != null ) {
+
+			// go ahead and send the header to let them know when it last changed, even if we match
+			header( 'Last-Modified: ' . $last_modified->set_timezone( 'UTC' )->format( 'D, d M Y H:i:s e'), true );
+
+			// does their browser already have something cached?
+			if ( isset( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) ) {
+				$if_modified_since = HabariDateTime::date_create( $_SERVER['HTTP_IF_MODIFIED_SINCE'] );
+
+				// if we don't have content modified more recently, tell them just to use what they have
+				if ( $last_modified <= $if_modified_since ) {
+					header( 'HTTP/1.1 304 Not Modified', true, 304 );
+					header( 'X-Habari-Cache-Match: Modified' );
+					// do not send any further content
+					die();
+				}
+			}
+
+			// and tell them how long they should expect this to be valid
+			$expires = HabariDateTime::date_create( '30 days' )->set_timezone( 'UTC' )->format( 'D, d M Y H:i:s e' );
+			header( 'Expires: ' . $expires, true );
+
+		}
+
 		return $this->display_fallback( $fallback );
 	}