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, 2 insertions, 11 deletions

diff --git a/src/corelib/io/qsettings_win.cpp b/src/corelib/io/qsettings_win.cpp
index 3f06ab7043..1c10548cbc 100644
--- a/src/corelib/io/qsettings_win.cpp
+++ b/src/corelib/io/qsettings_win.cpp
@@ -667,15 +667,6 @@ void QWinSettingsPrivate::remove(const QString &uKey)
     }
 }
 
-static bool stringContainsNullChar(const QString &s)
-{
-    for (int i = 0; i < s.length(); ++i) {
-        if (s.at(i).unicode() == 0)
-            return true;
-    }
-    return false;
-}
-
 void QWinSettingsPrivate::set(const QString &uKey, const QVariant &value)
 {
     if (writeHandle() == 0) {
@@ -704,7 +695,7 @@ void QWinSettingsPrivate::set(const QString &uKey, const QVariant &value)
             QStringList l = variantListToStringList(value.toList());
             QStringList::const_iterator it = l.constBegin();
             for (; it != l.constEnd(); ++it) {
-                if ((*it).length() == 0 || stringContainsNullChar(*it)) {
+                if ((*it).length() == 0 || it->contains(QChar::Null)) {
                     type = REG_BINARY;
                     break;
                 }
@@ -748,7 +739,7 @@ void QWinSettingsPrivate::set(const QString &uKey, const QVariant &value)
             // If the string does not contain '\0', we can use REG_SZ, the native registry
             // string type. Otherwise we use REG_BINARY.
             QString s = variantToString(value);
-            type = stringContainsNullChar(s) ? REG_BINARY : REG_SZ;
+            type = s.contains(QChar::Null) ? REG_BINARY : REG_SZ;
             if (type == REG_BINARY) {
                 regValueBuff = QByteArray((const char*)s.utf16(), s.length() * 2);
             } else {