Emit finished() and delete remotely cancelled verification session

KeyVerificationSession emits finished() and self-deletes on any wrong
situation but only changes state if a remote device simply cancels the
verification, as if it were not an endgame. This commit pulls the common
code from cancelVerification() into handleCancel() and calls that new
function when KeyVerificationCancelEvent is received. It also makes sure
now not to call cancelVerification() twice with different error codes.

Quotient/keyverificationsession.cpp

@@ -130,11 +130,9 @@ void KeyVerificationSession::setupTimeout(milliseconds timeout)
 
 void KeyVerificationSession::handleEvent(const KeyVerificationEvent& baseEvent)
 {
-    if (!switchOnType(
-            baseEvent,
+    if (!baseEvent.switchOnType( // true if state transition is correct; false otherwise
             [this](const KeyVerificationCancelEvent& event) {
-                setError(stringToError(event.code()));
-                setState(CANCELED);
+                handleCancel(stringToError(event.code()));
                 return true;
             },
             [this](const KeyVerificationStartEvent& event) {
@@ -162,13 +160,13 @@ void KeyVerificationSession::handleEvent(const KeyVerificationEvent& baseEvent)
                 }
                 if (m_commonMacCodes.isEmpty()) {
                     cancelVerification(UNKNOWN_METHOD);
-                    return false;
+                    return true;
                 }
                 m_commitment = event.commitment().toLatin1();
                 if (!QByteArray::fromBase64Encoding(m_commitment,
                                                     QByteArray::AbortOnBase64DecodingErrors)) {
                     cancelVerification(INVALID_MESSAGE);
-                    return false;
+                    return true;
                 }
                 sendKey();
                 setState(WAITINGFORKEY);
@@ -361,15 +359,13 @@ void KeyVerificationSession::sendKey()
                                m_encrypted);
 }
 
-
 void KeyVerificationSession::cancelVerification(Error error)
 {
-    sendEvent(m_remoteUserId, m_remoteDeviceId, KeyVerificationCancelEvent(m_transactionId,
-                                                          errorToString(error)), m_encrypted);
-    setState(CANCELED);
-    setError(error);
-    emit finished();
-    deleteLater();
+    if (QUO_ALARM(state() == CANCELED))
+        return; // Make sure not to overwrite previous error
+    sendEvent(m_remoteUserId, m_remoteDeviceId,
+              KeyVerificationCancelEvent(m_transactionId, errorToString(error)), m_encrypted);
+    handleCancel(error);
 }
 
 void KeyVerificationSession::sendReady()
@@ -499,6 +495,14 @@ void KeyVerificationSession::handleMac(const KeyVerificationMacEvent& event)
     }
 }
 
+void KeyVerificationSession::handleCancel(Error error)
+{
+    setState(CANCELED);
+    setError(error);
+    emit finished();
+    deleteLater();
+}
+
 void KeyVerificationSession::trustKeys()
 {
     m_connection->database()->setSessionVerified(m_pendingEdKeyId);

Quotient/keyverificationsession.h

@@ -170,6 +170,7 @@ public Q_SLOTS:
     void handleStart(const KeyVerificationStartEvent& event);
     void handleKey(const KeyVerificationKeyEvent& event);
     void handleMac(const KeyVerificationMacEvent& event);
+    void handleCancel(Error error);
     void setupTimeout(std::chrono::milliseconds timeout);
     void setState(State state);
     void setError(Error error);