QtNfc: Fix iOS session invalidation/restart

Fix a problem where the user is able to get into a state, where iOS NFC
implementation deadlocks itself, so the whole app has to be restarted
to get it working again.

Basically, if we (or the user) abort a scan sessionStoppedByApplication
will be set, preventing a new scan until the session is invalidated by
the system and sessionStoppedByApplication is cleared. The problem is
that sometimes the invalidation by the system takes some time, especially
if the sessions is transmitting and waiting for a timeout. In that case,
the user is able to quickly start a new scan, which will of course wait
for the flag to be cleared. However, if that scan is immediately stopped
again self.session will be set to nil. This then becomes a problem, when
the original session finally invalidates and we now think it's an
unexpected session and return. This means self.sessionStoppedByApplication
will never be cleared, preventing any start of the scan.

To fix this we should always wait for the system to invalidate the
session and not just clear it ourselves. Similarly, if we already have
a session don't just to restartPolling, since it has no effect on
an invalidated session, so invalidate it to make sure and wait for
it to clear and start a new one.

Change-Id: I341a114d6ba5c761aa3c61df66b1a17636ec3946
Reviewed-by: Juha Vuolle <juha.vuolle@insta.fi>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
(cherry picked from commit a113cea72806e3b1302d36532df3a8a58c6640fe)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 11 insertions, 15 deletions

diff --git a/src/nfc/ios/qiostagreaderdelegate.mm b/src/nfc/ios/qiostagreaderdelegate.mm
index 03a2554c..3540aa0a 100644
--- a/src/nfc/ios/qiostagreaderdelegate.mm
+++ b/src/nfc/ios/qiostagreaderdelegate.mm
@@ -63,13 +63,13 @@ QT_USE_NAMESPACE
 
 - (void)startSession
 {
-    if (self.sessionStoppedByApplication) {
-        Q_EMIT self.listener->didInvalidateWithError(true);
-        return;
+    if (self.session && !self.sessionStoppedByApplication) {
+        [self.session invalidateSession];
+        self.sessionStoppedByApplication = true;
     }
 
-    if (self.session) {
-        [self.session restartPolling];
+    if (self.sessionStoppedByApplication) {
+        Q_EMIT self.listener->didInvalidateWithError(true);
         return;
     }
 
@@ -85,16 +85,12 @@ QT_USE_NAMESPACE
 
 - (void)stopSession:(QString)message
 {
-    if (self.session) {
-        if (self.session.ready) {
-            if (message.isNull())
-                [self.session invalidateSession];
-            else
-               [self.session invalidateSessionWithErrorMessage:message.toNSString()];
-           self.sessionStoppedByApplication = true;
-        } else {
-            self.session = nil;
-        }
+    if (self.session && !self.sessionStoppedByApplication) {
+        if (message.isNull())
+            [self.session invalidateSession];
+        else
+            [self.session invalidateSessionWithErrorMessage:message.toNSString()];
+        self.sessionStoppedByApplication = true;
     }
 }