(bug 31044) Make ResourceLoader behave in read-only mode

When the database is in read-only mode or writes fail for some other
reason, ResourceLoader should make every attempt to still serve JS and
CSS correctly.

* Surround a bunch of DB write code in MessageBlobStore.php in try-catch
  blocks.
* Surround the DB write in ResourceLoaderFileModule.php in a try-catch
  block rather than checking wfReadOnly(), because the DB may fail for
  other reasons.
* In ResourceLoader::respond() and helpers, set a short cache timeout on
  responses that include commented-out error messages.

Change-Id: Idc83a0fe042806263f9337c40ade8c38c56aa3cd

1 files changed, 116 insertions, 102 deletions

diff --git a/includes/MessageBlobStore.php b/includes/MessageBlobStore.php
index 09561bd78ae7..6322be7565b3 100644
--- a/includes/MessageBlobStore.php
+++ b/includes/MessageBlobStore.php
@@ -80,42 +80,45 @@ class MessageBlobStore {
 			return false;
 		}
 
-		$dbw = wfGetDB( DB_MASTER );
-		$success = $dbw->insert( 'msg_resource', array(
-				'mr_lang' => $lang,
-				'mr_resource' => $name,
-				'mr_blob' => $blob,
-				'mr_timestamp' => $dbw->timestamp()
-			),
-			__METHOD__,
-			array( 'IGNORE' )
-		);
-
-		if ( $success ) {
-			if ( $dbw->affectedRows() == 0 ) {
-				// Blob was already present, fetch it
-				$blob = $dbw->selectField( 'msg_resource', 'mr_blob', array(
-						'mr_resource' => $name,
-						'mr_lang' => $lang,
-					),
-					__METHOD__
-				);
-			} else {
-				// Update msg_resource_links
-				$rows = array();
+		try {
+			$dbw = wfGetDB( DB_MASTER );
+			$success = $dbw->insert( 'msg_resource', array(
+					'mr_lang' => $lang,
+					'mr_resource' => $name,
+					'mr_blob' => $blob,
+					'mr_timestamp' => $dbw->timestamp()
+				),
+				__METHOD__,
+				array( 'IGNORE' )
+			);
 
-				foreach ( $module->getMessages() as $key ) {
-					$rows[] = array(
-						'mrl_resource' => $name,
-						'mrl_message' => $key
+			if ( $success ) {
+				if ( $dbw->affectedRows() == 0 ) {
+					// Blob was already present, fetch it
+					$blob = $dbw->selectField( 'msg_resource', 'mr_blob', array(
+							'mr_resource' => $name,
+							'mr_lang' => $lang,
+						),
+						__METHOD__
+					);
+				} else {
+					// Update msg_resource_links
+					$rows = array();
+
+					foreach ( $module->getMessages() as $key ) {
+						$rows[] = array(
+							'mrl_resource' => $name,
+							'mrl_message' => $key
+						);
+					}
+					$dbw->insert( 'msg_resource_links', $rows,
+						__METHOD__, array( 'IGNORE' )
 					);
 				}
-				$dbw->insert( 'msg_resource_links', $rows,
-					__METHOD__, array( 'IGNORE' )
-				);
 			}
+		} catch ( Exception $e ) {
+			wfDebug( __METHOD__ . " failed to update DB: $e\n" );
 		}
-
 		return $blob;
 	}
 
@@ -141,48 +144,51 @@ class MessageBlobStore {
 		$oldBlob = $row->mr_blob;
 		$newBlob = self::generateMessageBlob( $module, $lang );
 
-		$newRow = array(
-			'mr_resource' => $name,
-			'mr_lang' => $lang,
-			'mr_blob' => $newBlob,
-			'mr_timestamp' => $dbw->timestamp()
-		);
+		try {
+			$newRow = array(
+				'mr_resource' => $name,
+				'mr_lang' => $lang,
+				'mr_blob' => $newBlob,
+				'mr_timestamp' => $dbw->timestamp()
+			);
 
-		$dbw->replace( 'msg_resource',
-			array( array( 'mr_resource', 'mr_lang' ) ),
-			$newRow, __METHOD__
-		);
+			$dbw->replace( 'msg_resource',
+				array( array( 'mr_resource', 'mr_lang' ) ),
+				$newRow, __METHOD__
+			);
 
-		// Figure out which messages were added and removed
-		$oldMessages = array_keys( FormatJson::decode( $oldBlob, true ) );
-		$newMessages = array_keys( FormatJson::decode( $newBlob, true ) );
-		$added = array_diff( $newMessages, $oldMessages );
-		$removed = array_diff( $oldMessages, $newMessages );
+			// Figure out which messages were added and removed
+			$oldMessages = array_keys( FormatJson::decode( $oldBlob, true ) );
+			$newMessages = array_keys( FormatJson::decode( $newBlob, true ) );
+			$added = array_diff( $newMessages, $oldMessages );
+			$removed = array_diff( $oldMessages, $newMessages );
 
-		// Delete removed messages, insert added ones
-		if ( $removed ) {
-			$dbw->delete( 'msg_resource_links', array(
-					'mrl_resource' => $name,
-					'mrl_message' => $removed
-				), __METHOD__
-			);
-		}
+			// Delete removed messages, insert added ones
+			if ( $removed ) {
+				$dbw->delete( 'msg_resource_links', array(
+						'mrl_resource' => $name,
+						'mrl_message' => $removed
+					), __METHOD__
+				);
+			}
 
-		$newLinksRows = array();
+			$newLinksRows = array();
 
-		foreach ( $added as $message ) {
-			$newLinksRows[] = array(
-				'mrl_resource' => $name,
-				'mrl_message' => $message
-			);
-		}
+			foreach ( $added as $message ) {
+				$newLinksRows[] = array(
+					'mrl_resource' => $name,
+					'mrl_message' => $message
+				);
+			}
 
-		if ( $newLinksRows ) {
-			$dbw->insert( 'msg_resource_links', $newLinksRows, __METHOD__,
-				 array( 'IGNORE' ) // just in case
-			);
+			if ( $newLinksRows ) {
+				$dbw->insert( 'msg_resource_links', $newLinksRows, __METHOD__,
+					array( 'IGNORE' ) // just in case
+				);
+			}
+		} catch ( Exception $e ) {
+			wfDebug( __METHOD__ . " failed to update DB: $e\n" );
 		}
-
 		return $newBlob;
 	}
 
@@ -192,50 +198,58 @@ class MessageBlobStore {
 	 * @param $key String: message key
 	 */
 	public static function updateMessage( $key ) {
-		$dbw = wfGetDB( DB_MASTER );
-
-		// Keep running until the updates queue is empty.
-		// Due to update conflicts, the queue might not be emptied
-		// in one iteration.
-		$updates = null;
-		do {
-			$updates = self::getUpdatesForMessage( $key, $updates );
-
-			foreach ( $updates as $k => $update ) {
-				// Update the row on the condition that it
-				// didn't change since we fetched it by putting
-				// the timestamp in the WHERE clause.
-				$success = $dbw->update( 'msg_resource',
-					array(
-						'mr_blob' => $update['newBlob'],
-						'mr_timestamp' => $dbw->timestamp() ),
-					array(
-						'mr_resource' => $update['resource'],
-						'mr_lang' => $update['lang'],
-						'mr_timestamp' => $update['timestamp'] ),
-					__METHOD__
-				);
+		try {
+			$dbw = wfGetDB( DB_MASTER );
+
+			// Keep running until the updates queue is empty.
+			// Due to update conflicts, the queue might not be emptied
+			// in one iteration.
+			$updates = null;
+			do {
+				$updates = self::getUpdatesForMessage( $key, $updates );
+
+				foreach ( $updates as $k => $update ) {
+					// Update the row on the condition that it
+					// didn't change since we fetched it by putting
+					// the timestamp in the WHERE clause.
+					$success = $dbw->update( 'msg_resource',
+						array(
+							'mr_blob' => $update['newBlob'],
+							'mr_timestamp' => $dbw->timestamp() ),
+						array(
+							'mr_resource' => $update['resource'],
+							'mr_lang' => $update['lang'],
+							'mr_timestamp' => $update['timestamp'] ),
+						__METHOD__
+					);
 
-				// Only requeue conflicted updates.
-				// If update() returned false, don't retry, for
-				// fear of getting into an infinite loop
-				if ( !( $success && $dbw->affectedRows() == 0 ) ) {
-					// Not conflicted
-					unset( $updates[$k] );
+					// Only requeue conflicted updates.
+					// If update() returned false, don't retry, for
+					// fear of getting into an infinite loop
+					if ( !( $success && $dbw->affectedRows() == 0 ) ) {
+						// Not conflicted
+						unset( $updates[$k] );
+					}
 				}
-			}
-		} while ( count( $updates ) );
+			} while ( count( $updates ) );
 
-		// No need to update msg_resource_links because we didn't add
-		// or remove any messages, we just changed their contents.
+			// No need to update msg_resource_links because we didn't add
+			// or remove any messages, we just changed their contents.
+		} catch ( Exception $e ) {
+			wfDebug( __METHOD__ . " failed to update DB: $e\n" );
+		}
 	}
 
 	public static function clear() {
 		// TODO: Give this some more thought
 		// TODO: Is TRUNCATE better?
-		$dbw = wfGetDB( DB_MASTER );
-		$dbw->delete( 'msg_resource', '*', __METHOD__ );
-		$dbw->delete( 'msg_resource_links', '*', __METHOD__ );
+		try {
+			$dbw = wfGetDB( DB_MASTER );
+			$dbw->delete( 'msg_resource', '*', __METHOD__ );
+			$dbw->delete( 'msg_resource_links', '*', __METHOD__ );
+		} catch ( Exception $e ) {
+			wfDebug( __METHOD__ . " failed to update DB: $e\n" );
+		}
 	}
 
 	/**