Avoid hang on WMS legends with missing graphics (fix #12234)

Author: nyalldawson

src/providers/wms/qgswmsprovider.cpp

@@ -3041,6 +3041,7 @@ QImage QgsWmsProvider::getLegendGraphic( double scale, bool forceRefresh, const
   mLegendGraphicFetcher.reset( new QgsWmsLegendDownloadHandler( *QgsNetworkAccessManager::instance(), mSettings, url ) );
   if ( ! mLegendGraphicFetcher ) return QImage();
   connect( mLegendGraphicFetcher.data(), SIGNAL( finish( const QImage& ) ), this, SLOT( getLegendGraphicReplyFinished( const QImage& ) ) );
+  connect( mLegendGraphicFetcher.data(), SIGNAL( error( const QString& ) ), this, SLOT( getLegendGraphicReplyErrored( const QString& ) ) );
   connect( mLegendGraphicFetcher.data(), SIGNAL( progress( qint64, qint64 ) ), this, SLOT( getLegendGraphicReplyProgress( qint64, qint64 ) ) );
   mLegendGraphicFetcher->start( );
 
@@ -3119,6 +3120,21 @@ void QgsWmsProvider::getLegendGraphicReplyFinished( const QImage& img )
   }
 }
 
+void QgsWmsProvider::getLegendGraphicReplyErrored( const QString& message )
+{
+  QgsDebugMsg( QString( "get legend failed: %1" ).arg( message ) );
+
+  QObject* reply = sender();
+
+  if ( reply == mLegendGraphicFetcher.data() )
+  {
+    QEventLoop *loop = qobject_cast< QEventLoop *>( reply->property( "eventLoop" ).value< QObject *>() );
+    if ( loop )
+      QMetaObject::invokeMethod( loop, "quit", Qt::QueuedConnection );
+    mLegendGraphicFetcher.reset();
+  }
+}
+
 void QgsWmsProvider::getLegendGraphicReplyProgress( qint64 bytesReceived, qint64 bytesTotal )
 {
   QString msg = tr( "%1 of %2 bytes of GetLegendGraphic downloaded." ).arg( bytesReceived ).arg( bytesTotal < 0 ? QString( "unknown number of" ) : QString::number( bytesTotal ) );

src/providers/wms/qgswmsprovider.h

@@ -367,6 +367,7 @@ class QgsWmsProvider : public QgsRasterDataProvider
   private slots:
     void identifyReplyFinished();
     void getLegendGraphicReplyFinished( const QImage& );
+    void getLegendGraphicReplyErrored( const QString& message );
     void getLegendGraphicReplyProgress( qint64, qint64 );
 
   private: