Remove invalid assert, add documentation, and fix uses (owncloud#12095)

A response timestamp can be missing for multiple reasons: aborted job
before a header came in, many possible network errors, and just missing
in a response. So instead of an assert over all these cases, handle the
absence when it is about to be used. This was already done in some
cases.

Author: erikjv

src/gui/scheduling/etagwatcher.cpp

@@ -105,7 +105,12 @@ void ETagWatcher::startOC10EtagJob(Folder *f)
             connect(requestEtagJob, &RequestEtagJob::finishedSignal, this, [requestEtagJob, f, this] {
                 if (requestEtagJob->httpStatusCode() == 207) {
                     if (OC_ENSURE_NOT(requestEtagJob->etag().isEmpty())) {
-                        f->accountState()->tagLastSuccessfullETagRequest(requestEtagJob->responseQTimeStamp());
+                        auto lastResponse = requestEtagJob->responseQTimeStamp();
+                        if (!lastResponse.isValid()) {
+                            // If the responose had no valid "Date" header, use "now", as the job just finished.
+                            lastResponse = QDateTime::currentDateTimeUtc();
+                        }
+                        f->accountState()->tagLastSuccessfullETagRequest(lastResponse);
                         updateEtag(f, requestEtagJob->etag());
                     } else {
                         qCWarning(lcEtagWatcher) << "Invalid empty etag received for" << f->displayName() << f->path() << requestEtagJob;

src/libsync/abstractnetworkjob.cpp

@@ -238,7 +238,6 @@ void AbstractNetworkJob::slotFinished()
 
 QByteArray AbstractNetworkJob::responseTimestamp() const
 {
-    OC_ASSERT(!_responseTimestamp.isEmpty() || _aborted || (reply() && reply()->error() == QNetworkReply::RemoteHostClosedError));
     return _responseTimestamp;
 }
 

src/libsync/abstractnetworkjob.h

@@ -74,7 +74,18 @@ class OWNCLOUDSYNC_EXPORT AbstractNetworkJob : public QObject
     void setForceIgnoreCredentialFailure(bool ignore);
     bool ignoreCredentialFailure() const;
 
+    /**
+     * @brief Returns the timestamp from the reply
+     *
+     * @return Empty if the job was aborted, or an error occurred and no response was received.
+     *         Otherwise the timestamp from the reply header. Note that the timestamp might be
+     *         absent if the reply didn't contain one.
+     */
     QByteArray responseTimestamp() const;
+    /**
+     * See responseTimestamp(), now converted to a QDateTime. If there was no response timestamp,
+     * return an invalid `QDateTime`.
+     */
     QDateTime responseQTimeStamp() const;
 
     int httpStatusCode() const;

src/libsync/discoveryphase.cpp

@@ -422,7 +422,14 @@ void DiscoverySingleDirectoryJob::lsJobFinishedWithoutErrorSlot()
         deleteLater();
         return;
     }
-    Q_EMIT etag(_firstEtag, _proFindJob->responseQTimeStamp());
+
+    auto lastResponse = _proFindJob->responseQTimeStamp();
+    if (!lastResponse.isValid()) {
+        // If the responose had no valid "Date" header, use "now", as the job just finished.
+        lastResponse = QDateTime::currentDateTimeUtc();
+    }
+
+    Q_EMIT etag(_firstEtag, lastResponse);
     Q_EMIT finished(_results);
     deleteLater();
 }