Fix $wgFileCache DB outage fallback

Change-Id: I5c41b4669ca29d119de5c08a2c61dbadae7cf55c

includes/MediaWiki.php

@@ -528,6 +528,24 @@ class MediaWiki {
 				$e->report(); // display the GUI error
 			}
 		} catch ( Exception $e ) {
+			$context = $this->context;
+			if (
+				$e instanceof DBConnectionError &&
+				$context->hasTitle() &&
+				$context->getTitle()->canExist() &&
+				$context->getRequest()->getVal( 'action', 'view' ) === 'view' &&
+				HTMLFileCache::useFileCache( $this->context, HTMLFileCache::MODE_OUTAGE )
+			) {
+				// Try to use any (even stale) file during outages...
+				$cache = new HTMLFileCache( $context->getTitle(), 'view' );
+				if ( $cache->isCached() ) {
+					$cache->loadFromFileCache( $context, HTMLFileCache::MODE_OUTAGE );
+					print MWExceptionRenderer::getHTML( $e );
+					exit;
+				}
+
+			}
+
 			MWExceptionHandler::handleException( $e );
 		}
 
@@ -819,8 +837,7 @@ class MediaWiki {
 			}
 		}
 
-		if ( $this->config->get( 'UseFileCache' ) && $title->getNamespace() >= 0 ) {
+		if ( $title->canExist() && HTMLFileCache::useFileCache( $this->context ) ) {
-			if ( HTMLFileCache::useFileCache( $this->context ) ) {
 			// Try low-level file cache hit
 			$cache = new HTMLFileCache( $title, $action );
 			if ( $cache->isCacheGood( /* Assume up to date */ ) ) {
@@ -829,8 +846,8 @@ class MediaWiki {
 				if ( !$output->checkLastModified( $timestamp ) ) {
 					$cache->loadFromFileCache( $this->context );
 				}
-					// Do any stats increment/watchlist stuff
+				// Do any stats increment/watchlist stuff, assuming user is viewing the
-					// Assume we're viewing the latest revision (this should always be the case with file cache)
+				// latest revision (which should always be the case for file cache)
 				$this->context->getWikiPage()->doViewUpdates( $this->context->getUser() );
 				// Tell OutputPage that output is taken care of
 				$output->disable();
@@ -838,7 +855,6 @@ class MediaWiki {
 				return;
 			}
 		}
-		}
 
 		// Actually do the work of the request and build up any output
 		$this->performRequest();

includes/cache/HTMLFileCache.php

@@ -29,6 +29,9 @@
  * @ingroup Cache
  */
 class HTMLFileCache extends FileCacheBase {
+	const MODE_NORMAL = 0; // normal cache mode
+	const MODE_OUTAGE = 1; // fallback cache for DB outages
+
 	/**
 	 * Construct an HTMLFileCache object from a Title and an action
 	 *
@@ -93,10 +96,12 @@ class HTMLFileCache extends FileCacheBase {
 	/**
 	 * Check if pages can be cached for this request/user
 	 * @param IContextSource $context
+	 * @param integer $mode One of the HTMLFileCache::MODE_* constants
 	 * @return bool
 	 */
-	public static function useFileCache( IContextSource $context ) {
+	public static function useFileCache( IContextSource $context, $mode = self::MODE_NORMAL ) {
 		global $wgUseFileCache, $wgDebugToolbar, $wgContLang;
+
 		if ( !$wgUseFileCache ) {
 			return false;
 		}
@@ -121,15 +126,23 @@ class HTMLFileCache extends FileCacheBase {
 
 			return false;
 		}
+
 		$user = $context->getUser();
 		// Check for non-standard user language; this covers uselang,
 		// and extensions for auto-detecting user language.
 		$ulang = $context->getLanguage();
 
 		// Check that there are no other sources of variation
-		if ( $user->getId() || $user->getNewtalk() || !$ulang->equals( $wgContLang ) ) {
+		if ( $user->getId() || !$ulang->equals( $wgContLang ) ) {
 			return false;
 		}
+
+		if ( $mode === self::MODE_NORMAL ) {
+			if ( $user->getNewtalk() ) {
+				return false;
+			}
+		}
+
 		// Allow extensions to disable caching
 		return Hooks::run( 'HTMLFileCache::useFileCache', [ $context ] );
 	}
@@ -137,14 +150,20 @@ class HTMLFileCache extends FileCacheBase {
 	/**
 	 * Read from cache to context output
 	 * @param IContextSource $context
+	 * @param integer $mode One of the HTMLFileCache::MODE_* constants
 	 * @return void
 	 */
-	public function loadFromFileCache( IContextSource $context ) {
+	public function loadFromFileCache( IContextSource $context, $mode = self::MODE_NORMAL ) {
 		global $wgMimeType, $wgLanguageCode;
 
 		wfDebug( __METHOD__ . "()\n" );
 		$filename = $this->cachePath();
 
+		if ( $mode === self::MODE_OUTAGE ) {
+			// Avoid DB errors for queries in sendCacheControl()
+			$context->getTitle()->resetArticleID( 0 );
+		}
+
 		$context->getOutput()->sendCacheControl();
 		header( "Content-Type: $wgMimeType; charset=UTF-8" );
 		header( "Content-Language: $wgLanguageCode" );

includes/exception/MWExceptionRenderer.php

@@ -209,7 +209,7 @@ class MWExceptionRenderer {
 	 * @param Exception $e
 	 * @return string Html to output
 	 */
-	private static function getHTML( Exception $e ) {
+	public static function getHTML( Exception $e ) {
 		if ( self::showBackTrace( $e ) ) {
 			$html = "<div class=\"errorbox\"><p>" .
 				nl2br( htmlspecialchars( MWExceptionHandler::getLogMessage( $e ) ) ) .