Apple OS: Handle QSetting strings with embedded zero-bytes

Saving strings with embedded zero-bytes (\0) as CFStrings would
sometimes fail, and only write the part of the string leading
up to the first zero-byte, instead of all the way to the final
zero-terminator. This bug was revealed by the code-path that
falls back to storing e.g. QTime as strings, via the helper
method QSettingsPrivate::variantToString().

We now use the same approach as on platforms such as Windows
and WinRT, where the string produced by variantToString() is
checked for null-bytes, and if so, stored using a binary
representation instead of as a string. For our case that
means we fall back to CFData when detecting the null-byte.

To separate strings from regular byte arrays, new logic has
been added to variantToString() that wraps the null-byte
strings in @String(). That way we can implement a fast-path
when converting back from CFData, that doesn't go via the
slow and lossy conversion via UTF8, and the resulting QVariant
will be of type QVariant::ByteArray. The reason for using
UTF-8 as the binary representation of the string is that
in the case of storing a QByteArray("@foo") we need to
still be able to convert it back to the same byte array,
which doesn't work if the on-disk format is UTF-16.

Task-number: QTBUG-56124
Change-Id: Iab2f71cf96cf3225de48dc5e71870d74b6dde1e8
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/src/corelib/io/qsettings.cpp b/src/corelib/io/qsettings.cpp
index fcdc1e362b..47108d057b 100644
--- a/src/corelib/io/qsettings.cpp
+++ b/src/corelib/io/qsettings.cpp
@@ -416,7 +416,9 @@ QString QSettingsPrivate::variantToString(const QVariant &v)
         case QVariant::Double:
         case QVariant::KeySequence: {
             result = v.toString();
-            if (result.startsWith(QLatin1Char('@')))
+            if (result.contains(QChar::Null))
+                result = QLatin1String("@String(") + result + QLatin1Char(')');
+            else if (result.startsWith(QLatin1Char('@')))
                 result.prepend(QLatin1Char('@'));
             break;
         }
@@ -476,6 +478,8 @@ QVariant QSettingsPrivate::stringToVariant(const QString &s)
         if (s.endsWith(QLatin1Char(')'))) {
             if (s.startsWith(QLatin1String("@ByteArray("))) {
                 return QVariant(s.midRef(11, s.size() - 12).toLatin1());
+            } else if (s.startsWith(QLatin1String("@String("))) {
+                return QVariant(s.midRef(8, s.size() - 9).toString());
             } else if (s.startsWith(QLatin1String("@Variant("))
                        || s.startsWith(QLatin1String("@DateTime("))) {
 #ifndef QT_NO_DATASTREAM