* Use ApiBase::dieDebug() to render maxlag error properly

* Allow modules to ignore maxlag attribute

includes/api/ApiBase.php

@@ -532,6 +532,14 @@ abstract class ApiBase {
 		return $this->mRawFormat;
 	}
 
+	/**
+	 * Indicates if API needs to check maxlag
+	 */
+	public function shouldCheckMaxlag() {
+		return true;
+	}
+
+
 	/**
 	 * Profiling: total module execution time
 	 */

includes/api/ApiHelp.php

@@ -46,6 +46,10 @@ class ApiHelp extends ApiBase {
 		$this->dieUsage('', 'help');
 	}
 
+	public function shouldCheckMaxlag() {
+		return false;
+	}
+
 	protected function getDescription() {
 		return array (
 			'Display this help screen.'

includes/api/ApiMain.php

@@ -186,17 +186,6 @@ class ApiMain extends ApiBase {
 	 * have been accumulated, and replace it with an error message and a help screen.
 	 */
 	protected function executeActionWithErrorHandling() {
-		$params = $this->extractRequestParams();
-		if( isset( $params['maxlag'] ) ) {
-			// Check for maxlag
-			global $wgLoadBalancer;
-			$maxLag = $params['maxlag'];
-			list( $host, $lag ) = $wgLoadBalancer->getMaxLag();
-			if ( $lag > $maxLag ) {
-				wfMaxlagError( $host, $lag, $maxLag );
-				return;
-			}
-		}
 
 		// In case an error occurs during data output,
 		// clear the output buffer and print just the error information
@@ -301,6 +290,21 @@ class ApiMain extends ApiBase {
 
 		// Instantiate the module requested by the user
 		$module = new $this->mModules[$this->mAction] ($this, $this->mAction);
+		
+		if( $module->shouldCheckMaxlag() && isset( $params['maxlag'] ) ) {
+			// Check for maxlag
+			global $wgLoadBalancer, $wgShowHostnames;
+			$maxLag = $params['maxlag'];
+			list( $host, $lag ) = $wgLoadBalancer->getMaxLag();
+			if ( $lag > $maxLag ) {
+				if( $wgShowHostnames ) {
+					ApiBase :: dieUsage( "Waiting for $host: $lag seconds lagged", 'maxlag' );
+				} else {
+					ApiBase :: dieUsage( "Waiting for a database server: $lag seconds lagged", 'maxlag' );
+				}
+				return;
+			}
+		}
 
 		if (!$this->mInternalMode) {
 

includes/api/ApiQuery.php

@@ -456,6 +456,11 @@ class ApiQuery extends ApiBase {
 		$psModule = new ApiPageSet($this);
 		return $psModule->makeHelpMsgParameters() . parent :: makeHelpMsgParameters();
 	}
+	
+	// @todo should work correctly
+	public function shouldCheckMaxlag() {
+		return true;
+	}
 
 	protected function getParamDescription() {
 		return array (