Fix sending UTC-offset QTimeZones through QDataStream

QTimeZone("UTC") should be valid, as "UTC" appears in the list of
availableTimeZoneIds(), and tst_QTimeZone::dataStreamTest() constructs
timezones like this, which are considered valid.

The internal representation of a QTimeZone("UTC") as created by
QTimeZone::QTimeZone(const QByteArray &ianaId) is a QUtcTimeZonePrivate
which isValid(), so the containing QTimeZone isValid() too.

When QTimeZone is serialized into a QDataStream, it calls
tz.d->serialize(ds) which is QUtcTimeZonePrivate::serialize. This
writes QStringLiteral("OffsetFromUtc") followed by the IANA ID and
the offset (etc.) to the datastream.

When QTimeZone is deserialized it looks for this marker string, and if
present, it passed all of the parameters to the QTimeZone constructor
(not just the name). However, that constructor does not support standard
IANA timezones (only custom ones), and when it detects that the supplied
IANA ID is actually listed in availableTimeZoneIds(), it leaves the
pointer to the QTimeZonePrivate uninitialized (NULL), which leaves
the QTimeZone invalid (isValid() returns false).

Thus, a valid timezone which was serialized and then deserialized has
become invalid. This also affects serialization of QDateTimes with
timezones.

Fixed by calling the name-only constructor first, which works (only) for
IANA standard timezones and leaves the QTimeZone invalid (isValid()
returns false) otherwise. In which case, we can call the many-argument
contructor to create a custom timezone with the same offset as the one
which was originally serialized.

[ChangeLog][QtCore][QTimeZone] Fixed sending IANA standard UTC-offset
QTimeZones through QDataStream, which previously came out invalid after
deserialization.

Task-number: QTBUG-60595
Change-Id: Id9c47e8bda701faae4d800e012afb6db545b2fe9
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 7 insertions, 1 deletions

diff --git a/src/corelib/tools/qtimezone.cpp b/src/corelib/tools/qtimezone.cpp
index ec2f7c4af6..c4cd76c59c 100644
--- a/src/corelib/tools/qtimezone.cpp
+++ b/src/corelib/tools/qtimezone.cpp
@@ -961,7 +961,13 @@ QDataStream &operator>>(QDataStream &ds, QTimeZone &tz)
         int country;
         QString comment;
         ds >> ianaId >> utcOffset >> name >> abbreviation >> country >> comment;
-        tz = QTimeZone(ianaId.toUtf8(), utcOffset, name, abbreviation, (QLocale::Country) country, comment);
+        // Try creating as a system timezone, which succeeds (producing a valid
+        // zone) iff ianaId is valid; we can then ignore the other data.
+        tz = QTimeZone(ianaId.toUtf8());
+        // If not, then construct a custom timezone using all the saved values:
+        if (!tz.isValid())
+            tz = QTimeZone(ianaId.toUtf8(), utcOffset, name, abbreviation,
+                           QLocale::Country(country), comment);
     } else {
         tz = QTimeZone(ianaId.toUtf8());
     }