Win32: Consolidate registry code

Add a RAII class for registry keys and use it throughout
the code base.

Change-Id: I666b2fbb790f83436443101d6bc1e3c0525e78df
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

17 files changed, 375 insertions, 207 deletions

diff --git a/src/corelib/global/qglobal.cpp b/src/corelib/global/qglobal.cpp
index 17aab17fe4..6ae5bf299a 100644
--- a/src/corelib/global/qglobal.cpp
+++ b/src/corelib/global/qglobal.cpp
@@ -47,12 +47,11 @@
 #include "qoperatingsystemversion.h"
 #include "qoperatingsystemversion_p.h"
 #if defined(Q_OS_WIN) || defined(Q_OS_CYGWIN) || defined(Q_OS_WINRT)
-#include "qoperatingsystemversion_win_p.h"
-#  if QT_CONFIG(settings)
-#    include "qsettings.h"
-#    include "qvariant.h"
+#  include "qoperatingsystemversion_win_p.h"
+#  ifndef Q_OS_WINRT
+#    include "private/qwinregistry_p.h"
 #  endif
-#endif
+#endif // Q_OS_WIN || Q_OS_CYGWIN
 #include <private/qlocale_tools_p.h>
 
 #include <qmutex.h>
@@ -2190,28 +2189,25 @@ const QSysInfo::WinVersion QSysInfo::WindowsVersion = QSysInfo::windowsVersion()
 QT_WARNING_POP
 #endif
 
-static QString readRegistryString(const QString &key, const QString &subKey)
+static QString readVersionRegistryString(const wchar_t *subKey)
 {
-#if QT_CONFIG(settings)
-    QSettings settings(key, QSettings::NativeFormat);
-    return settings.value(subKey).toString();
+#if !defined(QT_BUILD_QMAKE) && !defined(Q_OS_WINRT)
+     return QWinRegistryKey(HKEY_LOCAL_MACHINE, LR"(SOFTWARE\Microsoft\Windows NT\CurrentVersion)")
+            .stringValue(subKey);
 #else
-    Q_UNUSED(key);
-    Q_UNUSED(subKey);
-    return QString();
+     Q_UNUSED(subKey);
+     return QString();
 #endif
 }
 
-static inline QString windowsVersionKey() { return QStringLiteral(R"(HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion)"); }
-
 static inline QString windows10ReleaseId()
 {
-    return readRegistryString(windowsVersionKey(), QStringLiteral("ReleaseId"));
+    return readVersionRegistryString(L"ReleaseId");
 }
 
 static inline QString windows7Build()
 {
-    return readRegistryString(windowsVersionKey(), QStringLiteral("CurrentBuild"));
+    return readVersionRegistryString(L"CurrentBuild");
 }
 
 static QString winSp_helper()
@@ -3078,6 +3074,7 @@ QByteArray QSysInfo::machineUniqueId()
     }
 #elif defined(Q_OS_WIN) && !defined(Q_OS_WINRT)
     // Let's poke at the registry
+    // ### Qt 6: Use new helpers from qwinregistry.cpp (once bootstrap builds are obsolete)
     HKEY key = NULL;
     if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, L"SOFTWARE\\Microsoft\\Cryptography", 0, KEY_READ | KEY_WOW64_64KEY, &key)
             == ERROR_SUCCESS) {
diff --git a/src/corelib/io/qsettings_win.cpp b/src/corelib/io/qsettings_win.cpp
index 679212ea21..6eb318006e 100644
--- a/src/corelib/io/qsettings_win.cpp
+++ b/src/corelib/io/qsettings_win.cpp
@@ -136,6 +136,8 @@ static void mergeKeySets(NameSet *dest, const QStringList &src)
 ** Wrappers for the insane windows registry API
 */
 
+// ### Qt 6: Use new helpers from qwinregistry.cpp (once bootstrap builds are obsolete)
+
 // Open a key with the specified "perms".
 // "access" is to explicitly use the 32- or 64-bit branch.
 static HKEY openKey(HKEY parentHandle, REGSAM perms, const QString &rSubKey, REGSAM access = 0)
diff --git a/src/corelib/kernel/kernel.pri b/src/corelib/kernel/kernel.pri
index 789bcb7927..bd3cabc01a 100644
--- a/src/corelib/kernel/kernel.pri
+++ b/src/corelib/kernel/kernel.pri
@@ -88,8 +88,10 @@ win32 {
             SOURCES += kernel/qeventdispatcher_winrt.cpp
             HEADERS += kernel/qeventdispatcher_winrt_p.h
         } else {
-            SOURCES += kernel/qeventdispatcher_win.cpp
-            HEADERS += kernel/qeventdispatcher_win_p.h
+            SOURCES += kernel/qeventdispatcher_win.cpp \
+                       kernel/qwinregistry.cpp
+            HEADERS += kernel/qeventdispatcher_win_p.h \
+                       kernel/qwinregistry_p.h
         }
 
         !winrt: LIBS_PRIVATE += -lversion
diff --git a/src/corelib/kernel/qwinregistry.cpp b/src/corelib/kernel/qwinregistry.cpp
new file mode 100644
index 0000000000..6566dd3c76
--- /dev/null
+++ b/src/corelib/kernel/qwinregistry.cpp
@@ -0,0 +1,120 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qwinregistry_p.h"
+
+#include <QtCore/qvarlengtharray.h>
+
+#include <algorithm>
+
+QT_BEGIN_NAMESPACE
+
+QWinRegistryKey::QWinRegistryKey() :
+    m_key(nullptr)
+{
+}
+
+// Open a key with the specified permissions (KEY_READ/KEY_WRITE).
+// "access" is to explicitly use the 32- or 64-bit branch.
+QWinRegistryKey::QWinRegistryKey(HKEY parentHandle, QStringView subKey,
+                                 REGSAM permissions, REGSAM access)
+{
+    if (RegOpenKeyEx(parentHandle, reinterpret_cast<const wchar_t *>(subKey.utf16()),
+                     0, permissions | access, &m_key) != ERROR_SUCCESS) {
+        m_key = nullptr;
+    }
+}
+
+QWinRegistryKey::~QWinRegistryKey()
+{
+    close();
+}
+
+void QWinRegistryKey::close()
+{
+    if (isValid()) {
+        RegCloseKey(m_key);
+        m_key = nullptr;
+    }
+}
+
+QString QWinRegistryKey::stringValue(QStringView subKey) const
+{
+    QString result;
+    if (!isValid())
+        return result;
+    DWORD type;
+    DWORD size;
+    auto subKeyC = reinterpret_cast<const wchar_t *>(subKey.utf16());
+    if (RegQueryValueEx(m_key, subKeyC, nullptr, &type, nullptr, &size) != ERROR_SUCCESS
+        || (type != REG_SZ && type != REG_EXPAND_SZ) || size <= 2) {
+        return result;
+    }
+    // Reserve more for rare cases where trailing '\0' are missing in registry,
+    // otherwise chop off the '\0' received.
+    QString buffer(int(size / sizeof(wchar_t)), Qt::Uninitialized);
+    if (RegQueryValueEx(m_key, subKeyC, nullptr, &type,
+                        reinterpret_cast<LPBYTE>(buffer.data()), &size) == ERROR_SUCCESS) {
+        if (buffer.endsWith(QChar::Null))
+            buffer.chop(1);
+    } else {
+        buffer.clear();
+    }
+    return buffer;
+}
+
+QPair<DWORD, bool> QWinRegistryKey::dwordValue(QStringView subKey) const
+{
+    if (!isValid())
+        return qMakePair(0, false);
+    DWORD type;
+    auto subKeyC = reinterpret_cast<const wchar_t *>(subKey.utf16());
+    if (RegQueryValueEx(m_key, subKeyC, nullptr, &type, nullptr, nullptr) != ERROR_SUCCESS
+        || type != REG_DWORD) {
+        return qMakePair(0, false);
+    }
+    DWORD value = 0;
+    DWORD size = sizeof(value);
+    const bool ok =
+        RegQueryValueEx(m_key, subKeyC, nullptr, nullptr,
+                        reinterpret_cast<unsigned char *>(&value), &size) == ERROR_SUCCESS;
+    return qMakePair(value, ok);
+}
+
+QT_END_NAMESPACE
diff --git a/src/corelib/kernel/qwinregistry_p.h b/src/corelib/kernel/qwinregistry_p.h
new file mode 100644
index 0000000000..d249a97988
--- /dev/null
+++ b/src/corelib/kernel/qwinregistry_p.h
@@ -0,0 +1,89 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QWINREGISTRY_H
+#define QWINREGISTRY_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API. It exists purely as an
+// implementation detail. This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtCore/qpair.h>
+#include <QtCore/qstring.h>
+#include <QtCore/qstringview.h>
+#include <QtCore/qt_windows.h>
+
+QT_BEGIN_NAMESPACE
+
+class Q_CORE_EXPORT QWinRegistryKey
+{
+public:
+    Q_DISABLE_COPY(QWinRegistryKey)
+
+    QWinRegistryKey();
+    explicit QWinRegistryKey(HKEY parentHandle, QStringView subKey,
+                             REGSAM permissions = KEY_READ, REGSAM access = 0);
+    ~QWinRegistryKey();
+
+    QWinRegistryKey(QWinRegistryKey &&other) noexcept { swap(other); }
+    QWinRegistryKey &operator=(QWinRegistryKey &&other) noexcept { swap(other); return *this; }
+
+    void swap(QWinRegistryKey &other) noexcept { qSwap(m_key, other.m_key); }
+
+    bool isValid() const { return m_key != nullptr; }
+    operator HKEY() const { return m_key; }
+    void close();
+
+    QString stringValue(QStringView subKey) const;
+    QPair<DWORD, bool> dwordValue(QStringView subKey) const;
+
+private:
+    HKEY m_key;
+};
+
+QT_END_NAMESPACE
+
+#endif // QWINREGISTRY_H
diff --git a/src/corelib/time/qtimezoneprivate_win.cpp b/src/corelib/time/qtimezoneprivate_win.cpp
index 5a480222e0..0fec5355b2 100644
--- a/src/corelib/time/qtimezoneprivate_win.cpp
+++ b/src/corelib/time/qtimezoneprivate_win.cpp
@@ -46,13 +46,14 @@
 
 #include <algorithm>
 
-QT_BEGIN_NAMESPACE
-
 #ifndef Q_OS_WINRT
+#include <private/qwinregistry_p.h>
 // The registry-based timezone backend is not available on WinRT, which falls back to equivalent APIs.
 #define QT_USE_REGISTRY_TIMEZONE 1
 #endif
 
+QT_BEGIN_NAMESPACE
+
 /*
     Private
 
@@ -71,8 +72,8 @@ QT_BEGIN_NAMESPACE
 // Vista introduced support for historic data, see MSDN docs on DYNAMIC_TIME_ZONE_INFORMATION
 // http://msdn.microsoft.com/en-gb/library/windows/desktop/ms724253%28v=vs.85%29.aspx
 #ifdef QT_USE_REGISTRY_TIMEZONE
-static const char tzRegPath[] = "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Time Zones";
-static const char currTzRegPath[] = "SYSTEM\\CurrentControlSet\\Control\\TimeZoneInformation";
+static const wchar_t tzRegPath[] = LR"(SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones)";
+static const wchar_t currTzRegPath[] = LR"(SYSTEM\CurrentControlSet\Control\TimeZoneInformation)";
 #endif
 
 enum {
@@ -138,27 +139,6 @@ bool equalTzi(const TIME_ZONE_INFORMATION &tzi1, const TIME_ZONE_INFORMATION &tz
 }
 
 #ifdef QT_USE_REGISTRY_TIMEZONE
-bool openRegistryKey(const QString &keyPath, HKEY *key)
-{
-    return RegOpenKeyEx(HKEY_LOCAL_MACHINE, reinterpret_cast<const wchar_t*>(keyPath.utf16()),
-                        0, KEY_READ, key) == ERROR_SUCCESS;
-}
-
-QString readRegistryString(const HKEY &key, const wchar_t *value)
-{
-    wchar_t buffer[MAX_PATH] = {0};
-    DWORD size = sizeof(wchar_t) * MAX_PATH;
-    RegQueryValueEx(key, value, nullptr, nullptr, reinterpret_cast<LPBYTE>(buffer), &size);
-    return QString::fromWCharArray(buffer);
-}
-
-int readRegistryValue(const HKEY &key, const wchar_t *value)
-{
-    DWORD buffer;
-    DWORD size = sizeof(buffer);
-    RegQueryValueEx(key, value, nullptr, nullptr, reinterpret_cast<LPBYTE>(&buffer), &size);
-    return buffer;
-}
 
 QWinTimeZonePrivate::QWinTransitionRule readRegistryRule(const HKEY &key,
                                                          const wchar_t *value, bool *ok)
@@ -185,12 +165,11 @@ TIME_ZONE_INFORMATION getRegistryTzi(const QByteArray &windowsId, bool *ok)
     TIME_ZONE_INFORMATION tzi;
     REG_TZI_FORMAT regTzi;
     DWORD regTziSize = sizeof(regTzi);
-    HKEY key = NULL;
-    const QString tziKeyPath = QString::fromUtf8(tzRegPath) + QLatin1Char('\\')
+    const QString tziKeyPath = QString::fromWCharArray(tzRegPath) + QLatin1Char('\\')
                                + QString::fromUtf8(windowsId);
 
-    if (openRegistryKey(tziKeyPath, &key)) {
-
+    QWinRegistryKey key(HKEY_LOCAL_MACHINE, tziKeyPath);
+    if (key.isValid()) {
         DWORD size = sizeof(tzi.DaylightName);
         RegQueryValueEx(key, L"Dlt", nullptr, nullptr, reinterpret_cast<LPBYTE>(tzi.DaylightName), &size);
 
@@ -206,8 +185,6 @@ TIME_ZONE_INFORMATION getRegistryTzi(const QByteArray &windowsId, bool *ok)
             tzi.DaylightDate = regTzi.DaylightDate;
             *ok = true;
         }
-
-        RegCloseKey(key);
     }
 
     return tzi;
@@ -299,8 +276,8 @@ QList<QByteArray> availableWindowsIds()
 #ifdef QT_USE_REGISTRY_TIMEZONE
     // TODO Consider caching results in a global static, very unlikely to change.
     QList<QByteArray> list;
-    HKEY key = NULL;
-    if (openRegistryKey(QString::fromUtf8(tzRegPath), &key)) {
+    QWinRegistryKey key(HKEY_LOCAL_MACHINE, tzRegPath);
+    if (key.isValid()) {
         DWORD idCount = 0;
         if (RegQueryInfoKey(key, 0, 0, 0, &idCount, 0, 0, 0, 0, 0, 0, 0) == ERROR_SUCCESS
             && idCount > 0) {
@@ -311,7 +288,6 @@ QList<QByteArray> availableWindowsIds()
                     list.append(QString::fromWCharArray(buffer).toUtf8());
             }
         }
-        RegCloseKey(key);
     }
     return list;
 #else // QT_USE_REGISTRY_TIMEZONE
@@ -325,15 +301,10 @@ QByteArray windowsSystemZoneId()
 {
 #ifdef QT_USE_REGISTRY_TIMEZONE
     // On Vista and later is held in the value TimeZoneKeyName in key currTzRegPath
-    QString id;
-    HKEY key = NULL;
-    QString tziKeyPath = QString::fromUtf8(currTzRegPath);
-    if (openRegistryKey(tziKeyPath, &key)) {
-        id = readRegistryString(key, L"TimeZoneKeyName");
-        RegCloseKey(key);
-        if (!id.isEmpty())
-            return std::move(id).toUtf8();
-    }
+    const QString id = QWinRegistryKey(HKEY_LOCAL_MACHINE, currTzRegPath)
+                       .stringValue(L"TimeZoneKeyName");
+    if (!id.isEmpty())
+        return id.toUtf8();
 
     // On XP we have to iterate over the zones until we find a match on
     // names/offsets with the current data
@@ -575,22 +546,22 @@ void QWinTimeZonePrivate::init(const QByteArray &ianaId)
     if (!m_windowsId.isEmpty()) {
 #ifdef QT_USE_REGISTRY_TIMEZONE
         // Open the base TZI for the time zone
-        HKEY baseKey = NULL;
-        const QString baseKeyPath = QString::fromUtf8(tzRegPath) + QLatin1Char('\\')
+        const QString baseKeyPath = QString::fromWCharArray(tzRegPath) + QLatin1Char('\\')
                                    + QString::fromUtf8(m_windowsId);
-        if (openRegistryKey(baseKeyPath, &baseKey)) {
+        QWinRegistryKey baseKey(HKEY_LOCAL_MACHINE, baseKeyPath);
+        if (baseKey.isValid()) {
             //  Load the localized names
-            m_displayName = readRegistryString(baseKey, L"Display");
-            m_standardName = readRegistryString(baseKey, L"Std");
-            m_daylightName = readRegistryString(baseKey, L"Dlt");
+            m_displayName = baseKey.stringValue(L"Display");
+            m_standardName = baseKey.stringValue(L"Std");
+            m_daylightName = baseKey.stringValue(L"Dlt");
             // On Vista and later the optional dynamic key holds historic data
             const QString dynamicKeyPath = baseKeyPath + QLatin1String("\\Dynamic DST");
-            HKEY dynamicKey = NULL;
-            if (openRegistryKey(dynamicKeyPath, &dynamicKey)) {
+            QWinRegistryKey dynamicKey(HKEY_LOCAL_MACHINE, dynamicKeyPath);
+            if (dynamicKey.isValid()) {
                 // Find out the start and end years stored, then iterate over them
-                int startYear = readRegistryValue(dynamicKey, L"FirstEntry");
-                int endYear = readRegistryValue(dynamicKey, L"LastEntry");
-                for (int year = startYear; year <= endYear; ++year) {
+                const auto startYear = dynamicKey.dwordValue(L"FirstEntry");
+                const auto endYear = dynamicKey.dwordValue(L"LastEntry");
+                for (int year = int(startYear.first); year <= int(endYear.first); ++year) {
                     bool ruleOk;
                     QWinTransitionRule rule = readRegistryRule(dynamicKey,
                                                                reinterpret_cast<LPCWSTR>(QString::number(year).utf16()),
@@ -611,7 +582,6 @@ void QWinTimeZonePrivate::init(const QByteArray &ianaId)
                         m_tranRules.append(rule);
                     }
                 }
-                RegCloseKey(dynamicKey);
             } else {
                 // No dynamic data so use the base data
                 bool ruleOk;
@@ -620,7 +590,6 @@ void QWinTimeZonePrivate::init(const QByteArray &ianaId)
                 if (ruleOk)
                     m_tranRules.append(rule);
             }
-            RegCloseKey(baseKey);
         }
 #else // QT_USE_REGISTRY_TIMEZONE
         if (gTimeZones->isEmpty())
diff --git a/src/platformsupport/fontdatabases/windows/qwindowsfontdatabase.cpp b/src/platformsupport/fontdatabases/windows/qwindowsfontdatabase.cpp
index 79f7eb3d43..011476cf13 100644
--- a/src/platformsupport/fontdatabases/windows/qwindowsfontdatabase.cpp
+++ b/src/platformsupport/fontdatabases/windows/qwindowsfontdatabase.cpp
@@ -53,6 +53,7 @@
 #include <QtCore/QtEndian>
 #include <QtCore/QThreadStorage>
 #include <QtCore/private/qsystemlibrary_p.h>
+#include <QtCore/private/qwinregistry_p.h>
 
 #include <wchar.h>
 
@@ -1210,33 +1211,8 @@ static int QT_WIN_CALLBACK populateFontFamilies(const LOGFONT *logFont, const TE
 
 void QWindowsFontDatabase::addDefaultEUDCFont()
 {
-    QString path;
-    {
-        HKEY key;
-        if (RegOpenKeyEx(HKEY_CURRENT_USER,
-                         L"EUDC\\1252",
-                         0,
-                         KEY_READ,
-                         &key) != ERROR_SUCCESS) {
-            return;
-        }
-
-        WCHAR value[MAX_PATH];
-        DWORD bufferSize = sizeof(value);
-        ZeroMemory(value, bufferSize);
-
-        if (RegQueryValueEx(key,
-                            L"SystemDefaultEUDCFont",
-                            nullptr,
-                            nullptr,
-                            reinterpret_cast<LPBYTE>(value),
-                            &bufferSize) == ERROR_SUCCESS) {
-            path = QString::fromWCharArray(value);
-        }
-
-        RegCloseKey(key);
-    }
-
+    const QString path = QWinRegistryKey(HKEY_CURRENT_USER, LR"(EUDC\1252)")
+                         .stringValue(L"SystemDefaultEUDCFont");
     if (!path.isEmpty()) {
         QFile file(path);
         if (!file.open(QIODevice::ReadOnly)) {
@@ -2105,28 +2081,6 @@ int QWindowsFontDatabase::defaultVerticalDPI()
     return vDPI;
 }
 
-QString QWindowsFontDatabase::readRegistryString(HKEY parentHandle, const wchar_t *keyPath, const wchar_t *keyName)
-{
-    QString result;
-    HKEY handle = 0;
-    if (RegOpenKeyEx(parentHandle, keyPath, 0, KEY_READ, &handle) == ERROR_SUCCESS) {
-        // get the size and type of the value
-        DWORD dataType;
-        DWORD dataSize;
-        if (RegQueryValueEx(handle, keyName, 0, &dataType, 0, &dataSize) == ERROR_SUCCESS) {
-            if (dataType == REG_SZ || dataType == REG_EXPAND_SZ) {
-                dataSize += 2; // '\0' missing?
-                QVarLengthArray<unsigned char> data(dataSize);
-                data[dataSize - 2] = data[dataSize - 1] = '\0';
-                if (RegQueryValueEx(handle, keyName, 0, 0, data.data(), &dataSize) == ERROR_SUCCESS)
-                    result = QString::fromWCharArray(reinterpret_cast<const wchar_t *>(data.data()));
-            }
-        }
-        RegCloseKey(handle);
-    }
-    return result;
-}
-
 bool QWindowsFontDatabase::isPrivateFontFamily(const QString &family) const
 {
     return m_eudcFonts.contains(family) || QPlatformFontDatabase::isPrivateFontFamily(family);
diff --git a/src/platformsupport/fontdatabases/windows/qwindowsfontdatabase_p.h b/src/platformsupport/fontdatabases/windows/qwindowsfontdatabase_p.h
index a1cab17a87..f132e69d4d 100644
--- a/src/platformsupport/fontdatabases/windows/qwindowsfontdatabase_p.h
+++ b/src/platformsupport/fontdatabases/windows/qwindowsfontdatabase_p.h
@@ -133,8 +133,6 @@ public:
     static void setFontOptions(unsigned options);
     static unsigned fontOptions();
 
-    static QString readRegistryString(HKEY parentHandle, const wchar_t *keyPath, const wchar_t *keyName);
-
 private:
     void removeApplicationFonts();
     void addDefaultEUDCFont();
diff --git a/src/platformsupport/fontdatabases/windows/qwindowsfontenginedirectwrite.cpp b/src/platformsupport/fontdatabases/windows/qwindowsfontenginedirectwrite.cpp
index a4490a6664..e796c18e79 100644
--- a/src/platformsupport/fontdatabases/windows/qwindowsfontenginedirectwrite.cpp
+++ b/src/platformsupport/fontdatabases/windows/qwindowsfontenginedirectwrite.cpp
@@ -47,6 +47,7 @@
 #include <QtCore/QFile>
 #include <private/qstringiterator_p.h>
 #include <QtCore/private/qsystemlibrary_p.h>
+#include <QtCore/private/qwinregistry_p.h>
 #include <QtGui/private/qguiapplication_p.h>
 #include <qpa/qplatformintegration.h>
 #include <QtGui/private/qhighdpiscaling_p.h>
@@ -945,10 +946,10 @@ void QWindowsFontEngineDirectWrite::initFontInfo(const QFontDef &request,
 
 QString QWindowsFontEngineDirectWrite::fontNameSubstitute(const QString &familyName)
 {
-    const wchar_t key[] = L"Software\\Microsoft\\Windows NT\\CurrentVersion\\FontSubstitutes";
     const QString substitute =
-        QWindowsFontDatabase::readRegistryString(HKEY_LOCAL_MACHINE, key,
-                                                 reinterpret_cast<const wchar_t *>(familyName.utf16()));
+        QWinRegistryKey(HKEY_LOCAL_MACHINE,
+                        LR"(Software\Microsoft\Windows NT\CurrentVersion\FontSubstitutes)")
+        .stringValue(familyName);
     return substitute.isEmpty() ? familyName : substitute;
 }
 
diff --git a/src/plugins/platforms/windows/qwindowscontext.cpp b/src/plugins/platforms/windows/qwindowscontext.cpp
index bb349f08a7..f7d04b667d 100644
--- a/src/plugins/platforms/windows/qwindowscontext.cpp
+++ b/src/plugins/platforms/windows/qwindowscontext.cpp
@@ -79,6 +79,7 @@
 #include <QtCore/qscopedpointer.h>
 #include <QtCore/quuid.h>
 #include <QtCore/private/qsystemlibrary_p.h>
+#include <QtCore/private/qwinregistry_p.h>
 
 #include <QtEventDispatcherSupport/private/qwindowsguieventdispatcher_p.h>
 
@@ -1518,28 +1519,13 @@ QTouchDevice *QWindowsContext::touchDevice() const
         d->m_pointerHandler.touchDevice() : d->m_mouseHandler.touchDevice();
 }
 
-static DWORD readDwordRegistrySetting(const wchar_t *regKey, const wchar_t *subKey, DWORD defaultValue)
-{
-    DWORD result = defaultValue;
-    HKEY handle;
-    if (RegOpenKeyEx(HKEY_CURRENT_USER, regKey, 0, KEY_READ, &handle) == ERROR_SUCCESS) {
-        DWORD type;
-        if (RegQueryValueEx(handle, subKey, nullptr, &type, nullptr, nullptr) == ERROR_SUCCESS
-            && type == REG_DWORD) {
-            DWORD value;
-            DWORD size = sizeof(result);
-            if (RegQueryValueEx(handle, subKey, nullptr, nullptr, reinterpret_cast<unsigned char *>(&value), &size) == ERROR_SUCCESS)
-                result = value;
-        }
-        RegCloseKey(handle);
-    }
-    return result;
-}
-
 DWORD QWindowsContext::readAdvancedExplorerSettings(const wchar_t *subKey, DWORD defaultValue)
 {
-    return readDwordRegistrySetting(L"Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Advanced",
-                                    subKey, defaultValue);
+    const auto value =
+        QWinRegistryKey(HKEY_CURRENT_USER,
+                        LR"(Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced)")
+                       .dwordValue(subKey);
+    return value.second ? value.first : defaultValue;
 }
 
 static inline bool isEmptyRect(const RECT &rect)
diff --git a/src/plugins/platforms/windows/qwindowsservices.cpp b/src/plugins/platforms/windows/qwindowsservices.cpp
index b2b1dee232..83b052bb49 100644
--- a/src/plugins/platforms/windows/qwindowsservices.cpp
+++ b/src/plugins/platforms/windows/qwindowsservices.cpp
@@ -45,6 +45,8 @@
 #include <QtCore/qdebug.h>
 #include <QtCore/qdir.h>
 
+#include <QtCore/private/qwinregistry_p.h>
+
 #include <shlobj.h>
 #include <intshcut.h>
 
@@ -78,35 +80,24 @@ static inline QString mailCommand()
 
     const wchar_t mailUserKey[] = L"Software\\Microsoft\\Windows\\Shell\\Associations\\UrlAssociations\\mailto\\UserChoice";
 
-    wchar_t command[MAX_PATH] = {0};
     // Check if user has set preference, otherwise use default.
-    HKEY handle;
-    QString keyName;
-    if (!RegOpenKeyEx(HKEY_CURRENT_USER, mailUserKey, 0, KEY_READ, &handle)) {
-        DWORD bufferSize = BufferSize;
-        if (!RegQueryValueEx(handle, L"Progid", nullptr, nullptr, reinterpret_cast<unsigned char*>(command), &bufferSize))
-            keyName = QString::fromWCharArray(command);
-        RegCloseKey(handle);
-    }
+    QString keyName = QWinRegistryKey(HKEY_CURRENT_USER, mailUserKey)
+                      .stringValue( L"Progid");
     const QLatin1String mailto = keyName.isEmpty() ? QLatin1String("mailto") : QLatin1String();
     keyName += mailto + QLatin1String("\\Shell\\Open\\Command");
     if (debug)
         qDebug() << __FUNCTION__ << "keyName=" << keyName;
-    command[0] = 0;
-    if (!RegOpenKeyExW(HKEY_CLASSES_ROOT, reinterpret_cast<const wchar_t*>(keyName.utf16()), 0, KEY_READ, &handle)) {
-        DWORD bufferSize = BufferSize;
-        RegQueryValueEx(handle, L"", nullptr, nullptr, reinterpret_cast<unsigned char*>(command), &bufferSize);
-        RegCloseKey(handle);
-    }
+    const QString command = QWinRegistryKey(HKEY_CLASSES_ROOT, keyName).stringValue(L"");
     // QTBUG-57816: As of Windows 10, if there is no mail client installed, an entry like
     // "rundll32.exe .. url.dll,MailToProtocolHandler %l" is returned. Launching it
     // silently fails or brings up a broken dialog after a long time, so exclude it and
     // fall back to ShellExecute() which brings up the URL assocation dialog.
-    if (!command[0] || wcsstr(command, L",MailToProtocolHandler") != nullptr)
+    if (command.isEmpty() || command.contains(QLatin1String(",MailToProtocolHandler")))
         return QString();
     wchar_t expandedCommand[MAX_PATH] = {0};
-    return ExpandEnvironmentStrings(command, expandedCommand, MAX_PATH) ?
-           QString::fromWCharArray(expandedCommand) : QString::fromWCharArray(command);
+    return ExpandEnvironmentStrings(reinterpret_cast<const wchar_t *>(command.utf16()),
+                                    expandedCommand, MAX_PATH)
+        ? QString::fromWCharArray(expandedCommand) : command;
 }
 
 static inline bool launchMail(const QUrl &url)
diff --git a/src/tools/bootstrap/bootstrap.pro b/src/tools/bootstrap/bootstrap.pro
index 09a1c68001..9863ff5e69 100644
--- a/src/tools/bootstrap/bootstrap.pro
+++ b/src/tools/bootstrap/bootstrap.pro
@@ -126,6 +126,7 @@ win32:SOURCES += ../../corelib/global/qoperatingsystemversion_win.cpp \
                  ../../corelib/kernel/qsharedmemory_win.cpp \
                  ../../corelib/kernel/qsystemsemaphore_win.cpp \
                  ../../corelib/plugin/qsystemlibrary.cpp \
+                 ../../corelib/kernel/qwinregistry.cpp \
 
 mac {
     SOURCES += \
diff --git a/tests/auto/corelib/global/global.pro b/tests/auto/corelib/global/global.pro
index 139e073644..0f77d191ee 100644
--- a/tests/auto/corelib/global/global.pro
+++ b/tests/auto/corelib/global/global.pro
@@ -12,3 +12,6 @@ SUBDIRS=\
     qtendian \
     qglobalstatic \
     qhooks
+
+win32:!winrt: SUBDIRS += \
+    qwinregistry
diff --git a/tests/auto/corelib/global/qwinregistry/qwinregistry.pro b/tests/auto/corelib/global/qwinregistry/qwinregistry.pro
new file mode 100644
index 0000000000..eab5df9dc3
--- /dev/null
+++ b/tests/auto/corelib/global/qwinregistry/qwinregistry.pro
@@ -0,0 +1,8 @@
+CONFIG   += testcase
+QT       += testlib core-private
+QT       -= gui
+
+TARGET = tst_qwinregistry
+CONFIG   += console
+
+SOURCES += tst_qwinregistry.cpp
diff --git a/tests/auto/corelib/global/qwinregistry/tst_qwinregistry.cpp b/tests/auto/corelib/global/qwinregistry/tst_qwinregistry.cpp
new file mode 100644
index 0000000000..ac811de2a1
--- /dev/null
+++ b/tests/auto/corelib/global/qwinregistry/tst_qwinregistry.cpp
@@ -0,0 +1,68 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtTest/QtTest>
+
+#include <QtCore/qoperatingsystemversion.h>
+
+#include <QtCore/private/qwinregistry_p.h>
+
+class tst_QWinRegistry : public QObject
+{
+    Q_OBJECT
+
+public Q_SLOTS:
+    void initTestCase();
+
+private Q_SLOTS:
+    void values();
+};
+
+void tst_QWinRegistry::initTestCase()
+{
+    if (QOperatingSystemVersion::current() < QOperatingSystemVersion::Windows10)
+        QSKIP("This test requires registry values present in Windows 10");
+}
+
+void tst_QWinRegistry::values()
+{
+    QWinRegistryKey key(HKEY_LOCAL_MACHINE, LR"(SOFTWARE\Microsoft\Windows NT\CurrentVersion)");
+    QVERIFY(key.isValid());
+    QVERIFY(!key.stringValue(L"ProductName").isEmpty());
+    QVERIFY(key.stringValue(L"NonExistingKey").isEmpty());
+    auto majorVersion = key.dwordValue(L"CurrentMajorVersionNumber");
+    QVERIFY(majorVersion.second);
+    QVERIFY(majorVersion.first > 0);
+    auto nonExistingValue = key.dwordValue(L"NonExistingKey");
+    QVERIFY(!nonExistingValue.second);
+    QCOMPARE(nonExistingValue.first, 0u);
+}
+
+QTEST_APPLESS_MAIN(tst_QWinRegistry);
+
+#include "tst_qwinregistry.moc"
diff --git a/tests/auto/corelib/io/qfileinfo/tst_qfileinfo.cpp b/tests/auto/corelib/io/qfileinfo/tst_qfileinfo.cpp
index 16fcafa248..0597a7d521 100644
--- a/tests/auto/corelib/io/qfileinfo/tst_qfileinfo.cpp
+++ b/tests/auto/corelib/io/qfileinfo/tst_qfileinfo.cpp
@@ -49,6 +49,7 @@
 #ifdef Q_OS_WIN
 #include <qt_windows.h>
 #if !defined(Q_OS_WINRT)
+#include <private/qwinregistry_p.h>
 #include <lm.h>
 #endif
 #endif
@@ -1243,17 +1244,12 @@ void tst_QFileInfo::fileTimes()
     //In Vista the last-access timestamp is not updated when the file is accessed/touched (by default).
     //To enable this the HKLM\SYSTEM\CurrentControlSet\Control\FileSystem\NtfsDisableLastAccessUpdate
     //is set to 0, in the test machine.
-    HKEY key;
-    if (ERROR_SUCCESS == RegOpenKeyEx(HKEY_LOCAL_MACHINE, L"SYSTEM\\CurrentControlSet\\Control\\FileSystem",
-        0, KEY_READ, &key)) {
-            DWORD disabledAccessTimes = 0;
-            DWORD size = sizeof(DWORD);
-            LONG error = RegQueryValueEx(key, L"NtfsDisableLastAccessUpdate"
-                , NULL, NULL, (LPBYTE)&disabledAccessTimes, &size);
-            if (ERROR_SUCCESS == error && disabledAccessTimes)
-                noAccessTime = true;
-            RegCloseKey(key);
-    }
+    const auto disabledAccessTimes =
+        QWinRegistryKey(HKEY_LOCAL_MACHINE,
+                        LR"(SYSTEM\CurrentControlSet\Control\FileSystem)")
+        .dwordValue(L"NtfsDisableLastAccessUpdate");
+    if (disabledAccessTimes.second && disabledAccessTimes.first != 0)
+        noAccessTime = true;
 #endif
 
     if (noAccessTime)
diff --git a/tests/auto/corelib/io/qsettings/tst_qsettings.cpp b/tests/auto/corelib/io/qsettings/tst_qsettings.cpp
index 289590a233..0f07ba4bb2 100644
--- a/tests/auto/corelib/io/qsettings/tst_qsettings.cpp
+++ b/tests/auto/corelib/io/qsettings/tst_qsettings.cpp
@@ -54,6 +54,9 @@
 
 #if defined(Q_OS_WIN)
 #include <QtCore/qt_windows.h>
+#ifndef Q_OS_WINRT
+#  include <private/qwinregistry_p.h>
+#endif
 #else
 #include <unistd.h>
 #endif
@@ -3623,16 +3626,13 @@ void tst_QSettings::recursionBug()
 
 #if defined(Q_OS_WIN) && !defined(Q_OS_WINRT)
 
-static DWORD readKeyType(HKEY handle, const QString &rSubKey)
+static DWORD readKeyType(HKEY handle, QStringView rSubKey)
 {
     DWORD dataType;
     DWORD dataSize;
-    LONG res = RegQueryValueEx(handle, reinterpret_cast<const wchar_t *>(rSubKey.utf16()), 0, &dataType, 0, &dataSize);
-
-    if (res == ERROR_SUCCESS)
-        return dataType;
-
-    return 0;
+    LONG res = RegQueryValueEx(handle, reinterpret_cast<const wchar_t *>(rSubKey.utf16()),
+                               nullptr, &dataType, nullptr, &dataSize);
+    return res == ERROR_SUCCESS ? dataType : 0;
 }
 
 // This is a regression test for QTBUG-13249, where QSettings was storing
@@ -3652,29 +3652,12 @@ void tst_QSettings::consistentRegistryStorage()
     QCOMPARE(settings1.value("quint64_value").toULongLong(), (quint64)1024);
     settings1.sync();
 
-    HKEY handle;
-    LONG res;
-    QString keyName = "Software\\software.org\\KillerAPP";
-    res = RegOpenKeyEx(HKEY_CURRENT_USER, reinterpret_cast<const wchar_t *>(keyName.utf16()), 0, KEY_READ, &handle);
-    if (res == ERROR_SUCCESS)
-    {
-        DWORD dataType;
-        dataType = readKeyType(handle, QString("qint32_value"));
-        if (dataType != 0) {
-            QCOMPARE((int)REG_DWORD, (int)dataType);
-        }
-        dataType = readKeyType(handle, QString("quint32_value"));
-        if (dataType != 0) {
-            QCOMPARE((int)REG_DWORD, (int)dataType);
-        }
-        dataType = readKeyType(handle, QString("qint64_value"));
-        if (dataType != 0) {
-            QCOMPARE((int)REG_QWORD, (int)dataType);
-        }
-        dataType = readKeyType(handle, QString("quint64_value"));
-        if (dataType != 0) {
-            QCOMPARE((int)REG_QWORD, (int)dataType);
-        }
+    QWinRegistryKey handle(HKEY_CURRENT_USER, LR"(Software\software.org\KillerAPP)");
+    if (handle.isValid()) {
+        QCOMPARE(readKeyType(handle, L"qint32_value"), DWORD(REG_DWORD));
+        QCOMPARE(readKeyType(handle, L"quint32_value"), DWORD(REG_DWORD));
+        QCOMPARE(readKeyType(handle, L"qint64_value"), DWORD(REG_QWORD));
+        QCOMPARE(readKeyType(handle, L"quint64_value"), DWORD(REG_QWORD));
         RegCloseKey(handle);
     }
 }