QGrpcOperation: handle failed deserialization directly

Originally motivated by Axivion(SV3), which nagged about the const
errorOccurred signal; this patch removes signal emission for failed
deserialization in the read() functions. Immediately handling this can
lead to better user code as an fallback mechanism can avoid further
execution of unneeded logic.

This patch makes the errorOcurred signal non-const and changes the
signature of the read methods to either return an optional or bool to
signal failure immediately.

Users can then retrieve the error through 'deserializationError()' or
'deserializationErrorString()'. This can be seen in the generated QML
integration code, which uses those to still emit the 'errorOcurred'
signal on deserialization failure.

Change-Id: Ie6761753145536a42d5dd5bf1eac18afa555581a
Reviewed-by:  Alexey Edelev <alexey.edelev@qt.io>

1 files changed, 6 insertions, 4 deletions

diff --git a/src/grpc/doc/src/qtgrpcclientinterceptor-logging.qdoc b/src/grpc/doc/src/qtgrpcclientinterceptor-logging.qdoc
index 936db77..45ab2a2 100644
--- a/src/grpc/doc/src/qtgrpcclientinterceptor-logging.qdoc
+++ b/src/grpc/doc/src/qtgrpcclientinterceptor-logging.qdoc
@@ -55,8 +55,10 @@ protected:
         auto responsePtr = response.get();
         QObject::connect(responsePtr, &QGrpcServerStream::messageReceived, responsePtr,
                         [responsePtr]{
-                            SimpleStringMessage mess = responsePtr->read<SimpleStringMessage>();
-                            qDebug() << "Response received:" << mess.testFieldString();
+                            const auto mess = responsePtr->read<SimpleStringMessage>();
+                            if (!mess)
+                                qDebug() << "Failed deserialization";
+                            qDebug() << "Response received:" << mess->testFieldString();
                         });
     }
 
@@ -67,8 +69,8 @@ protected:
         // Intercept the response
         QObject::connect(stream.get(), &QGrpcServerStream::messageReceived, this,
                              [stream] {
-                                SimpleStringMessage mess = stream->read<SimpleStringMessage>();
-                                qDebug() << "Response received:" << mess.testFieldString();
+                                if (const auto mess = responsePtr->read<SimpleStringMessage>())
+                                    qDebug() << "Response received:" << mess->testFieldString();
                              });
 
         // Log incoming and outgoing requests here