Cleanup virtual layer error handling, and avoid copying an unterminated

string

src/providers/virtual/qgsvirtuallayersqlitehelper.cpp

@@ -165,7 +165,8 @@ namespace Sqlite
     const int r = sqlite3_exec( db, sql.toUtf8().constData(), nullptr, nullptr, &errMsg );
     if ( r )
     {
-      const QString err = QStringLiteral( "Query execution error on %1: %2 - %3" ).arg( sql ).arg( r ).arg( errMsg );
+      const QString err = QStringLiteral( "Query execution error on %1: %2 - %3" ).arg( sql ).arg( r ).arg( QString::fromUtf8( errMsg ) );
+      sqlite3_free( errMsg );
       throw std::runtime_error( err.toUtf8().constData() );
     }
   }

src/providers/virtual/qgsvirtuallayersqlitemodule.cpp

@@ -118,10 +118,10 @@ struct VTable
       , mValid( true )
     {
       QgsDataProvider::ProviderOptions providerOptions;
-      mProvider = static_cast<QgsVectorDataProvider *>( QgsProviderRegistry::instance()->createProvider( provider, source, providerOptions ) );
+      mProvider = qobject_cast<QgsVectorDataProvider *>( QgsProviderRegistry::instance()->createProvider( provider, source, providerOptions ) );
       if ( !mProvider )
       {
-        throw std::runtime_error( "Invalid provider" );
+        throw std::runtime_error( QStringLiteral( "Invalid provider: Cannot use %1 source layers in virtual layers" ).arg( provider ).toUtf8().constData() );
       }
       else if ( mProvider && !mProvider->isValid() )
       {
@@ -333,13 +333,20 @@ int vtableCreateConnect( sqlite3 *sql, void *aux, int argc, const char *const *a
   Q_UNUSED( aux )
   Q_UNUSED( isCreated )
 
-#define RETURN_CSTR_ERROR(err) if (outErr) {size_t s = strlen(err); *outErr=reinterpret_cast<char*>(sqlite3_malloc( static_cast<int>( s ) +1)); strncpy(*outErr, err, s);}
-#define RETURN_CPPSTR_ERROR(err) if (outErr) {*outErr=reinterpret_cast<char*>(sqlite3_malloc( static_cast<int>( err.toUtf8().size() )+1)); strncpy(*outErr, err.toUtf8().constData(), err.toUtf8().size());}
+  auto returnStrError = [&outErr]( const QString & err )
+  {
+    if ( outErr )
+    {
+      const int size = err.toUtf8().size();
+      *outErr = reinterpret_cast<char *>( sqlite3_malloc( size + 1 ) );
+      strncpy( *outErr, err.toUtf8().constData(), size + 1 );
+    }
+  };
 
   if ( argc < 4 )
   {
-    QString err( QStringLiteral( "Missing arguments: layer_id | provider, source" ) );
-    RETURN_CPPSTR_ERROR( err );
+    const QString err( QStringLiteral( "Missing arguments: layer_id | provider, source" ) );
+    returnStrError( err );
     return SQLITE_ERROR;
   }
 
@@ -363,11 +370,11 @@ int vtableCreateConnect( sqlite3 *sql, void *aux, int argc, const char *const *a
       {
         QString err( QStringLiteral( "Cannot find layer " ) );
         err += QString::fromUtf8( argv[3] );
-        RETURN_CPPSTR_ERROR( err );
+        returnStrError( err );
       }
       return SQLITE_ERROR;
     }
-    newVtab.reset( new VTable( sql, static_cast<QgsVectorLayer *>( l ) ) );
+    newVtab.reset( new VTable( sql, qobject_cast<QgsVectorLayer *>( l ) ) );
 
   }
   else if ( argc == 5 || argc == 6 )
@@ -400,21 +407,20 @@ int vtableCreateConnect( sqlite3 *sql, void *aux, int argc, const char *const *a
     }
     catch ( std::runtime_error &e )
     {
-      RETURN_CSTR_ERROR( e.what() );
+      returnStrError( e.what() );
       return SQLITE_ERROR;
     }
   }
 
   r = sqlite3_declare_vtab( sql, newVtab->creationString().toUtf8().constData() );
   if ( r )
   {
-    RETURN_CSTR_ERROR( sqlite3_errmsg( sql ) );
+    returnStrError( sqlite3_errmsg( sql ) );
     return r;
   }
 
   *outVtab = reinterpret_cast< sqlite3_vtab * >( newVtab.release() );
   return SQLITE_OK;
-#undef RETURN_CSTR_ERROR
 #undef RETURN_CPPSTR_ERROR
 }