Workaround double slot calling causing empty replies to overwrite

nyalldawson · rldhont · commit 6f5302fcd0c8 · 2020-05-21T20:14:52.000+02:00
valid reply content
diff --git a/src/core/qgsabstractcontentcache.h b/src/core/qgsabstractcontentcache.h
@@ -402,7 +402,12 @@ class CORE_EXPORT QgsAbstractContentCache : public QgsAbstractContentCacheBase
         if ( ok )
         {
           // read the content data
-          mRemoteContentCache.insert( path, new QByteArray( reply->readAll() ) );
+          const QByteArray ba = reply->readAll();
+
+          // because of the fragility listed below in waitForTaskFinished, this slot may get called twice. In that case
+          // the second time will have an empty reply (we've already read it all...)
+          if ( !ba.isEmpty() )
+            mRemoteContentCache.insert( path, new QByteArray( ba ) );
         }
         QMetaObject::invokeMethod( const_cast< QgsAbstractContentCacheBase * >( qobject_cast< const QgsAbstractContentCacheBase * >( this ) ), "onRemoteContentFetched", Qt::QueuedConnection, Q_ARG( QString, path ), Q_ARG( bool, true ) );
       } );
@@ -466,6 +471,8 @@ class CORE_EXPORT QgsAbstractContentCache : public QgsAbstractContentCacheBase
         if ( task->status() == QgsTask::Complete )
         {
           // Fourth step, force the signal fetched to be sure reply has been checked
+
+          // ARGH this is BAD BAD BAD. The connection will get called twice as a result!!!
           task->fetched();
           return true;
         }

Original file line number	Diff line number	Diff line change
`@@ -402,7 +402,12 @@ class CORE_EXPORT QgsAbstractContentCache : public QgsAbstractContentCacheBase`
`402`	`402`	`if ( ok )`
`403`	`403`	`{`
`404`	`404`	`// read the content data`
`405`		`- mRemoteContentCache.insert( path, new QByteArray( reply->readAll() ) );`
	`405`	`+ const QByteArray ba = reply->readAll();`
	`406`	`+`
	`407`	`+ // because of the fragility listed below in waitForTaskFinished, this slot may get called twice. In that case`
	`408`	`+ // the second time will have an empty reply (we've already read it all...)`
	`409`	`+ if ( !ba.isEmpty() )`
	`410`	`+ mRemoteContentCache.insert( path, new QByteArray( ba ) );`
`406`	`411`	`}`
`407`	`412`	`QMetaObject::invokeMethod( const_cast< QgsAbstractContentCacheBase * >( qobject_cast< const QgsAbstractContentCacheBase * >( this ) ), "onRemoteContentFetched", Qt::QueuedConnection, Q_ARG( QString, path ), Q_ARG( bool, true ) );`
`408`	`413`	`} );`
`@@ -466,6 +471,8 @@ class CORE_EXPORT QgsAbstractContentCache : public QgsAbstractContentCacheBase`
`466`	`471`	`if ( task->status() == QgsTask::Complete )`
`467`	`472`	`{`
`468`	`473`	`// Fourth step, force the signal fetched to be sure reply has been checked`
	`474`	`+`
	`475`	`+ // ARGH this is BAD BAD BAD. The connection will get called twice as a result!!!`
`469`	`476`	`task->fetched();`
`470`	`477`	`return true;`
`471`	`478`	`}`