Support external WMS layers in GetPrint and GetMap requests

Author: mhugent

src/server/services/wms/qgswmsrenderer.cpp

@@ -2610,7 +2610,17 @@ namespace QgsWms
     {
       QString nickname = param.mNickname;
       QString style = param.mStyle;
-      if ( mNicknameLayers.contains( nickname ) && !mRestrictedLayers.contains( nickname ) )
+      if ( nickname.startsWith( "EXTERNAL_WMS:" ) )
+      {
+        QString externalLayerId = nickname;
+        externalLayerId.remove( 0, 13 );
+        QgsMapLayer *externalWMSLayer = createExternalWMSLayer( externalLayerId );
+        if ( externalWMSLayer )
+        {
+          layers.append( externalWMSLayer );
+        }
+      }
+      else if ( mNicknameLayers.contains( nickname ) && !mRestrictedLayers.contains( nickname ) )
       {
         if ( !style.isEmpty() )
         {
@@ -2633,6 +2643,35 @@ namespace QgsWms
     return layers;
   }
 
+  QgsMapLayer *QgsRenderer::createExternalWMSLayer( const QString &externalLayerId ) const
+  {
+    QgsMapLayer *wmsLayer = 0;
+    QgsDataSourceUri wmsUri;
+
+    QgsServerRequest::Parameters::const_iterator it = mParameters.lowerBound( externalLayerId.toUpper() + ":" );
+    while ( it != mParameters.constEnd() )
+    {
+      if ( !it.key().startsWith( externalLayerId.toUpper() + ":" ) )
+      {
+        break;
+      }
+
+      QString paramKey = it.key();
+      paramKey.remove( 0, externalLayerId.size() + 1 );
+      wmsUri.setParam( paramKey.toLower(), it.value() );
+      ++it;
+    }
+
+    wmsLayer = new QgsRasterLayer( wmsUri.encodedUri(), externalLayerId, QStringLiteral( "wms" ) );
+    if ( !wmsLayer->isValid() )
+    {
+      delete wmsLayer;
+      return 0;
+    }
+
+    return wmsLayer;
+  }
+
   QPainter *QgsRenderer::layersRendering( const QgsMapSettings &mapSettings, QImage &image, HitTest *hitTest ) const
   {
     QPainter *painter = nullptr;

src/server/services/wms/qgswmsrenderer.h

@@ -274,6 +274,9 @@ namespace QgsWms
       //! configure the composition for the GetPrint request
       bool configureComposition( QgsComposition *c, const QgsMapSettings &mapSettings );
 
+      //! Creates external WMS layer. Caller takes ownership
+      QgsMapLayer *createExternalWMSLayer( const QString &externalLayerId ) const;
+
     private:
 
       const QgsServerRequest::Parameters &mParameters;