QByteArray: add compare() with case sensitivity options

Need to do the same for startsWith() and endsWith(). indexOf() is a lot
harder.

[ChangeLog][QtCore][QByteArray] Added compare(), which takes
Qt::CaseSensitivity as one of the parameters. This function is more
efficient than using toLower() or toUpper() and then comparing.

Change-Id: Ib48364abee9f464c96c6fffd152e69bde4194df7
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

17 files changed, 183 insertions, 53 deletions

diff --git a/src/corelib/io/qsettings.cpp b/src/corelib/io/qsettings.cpp
index 4b1b9888d8..1134c6bb85 100644
--- a/src/corelib/io/qsettings.cpp
+++ b/src/corelib/io/qsettings.cpp
@@ -1694,10 +1694,10 @@ bool QConfFileSettingsPrivate::readIniFile(const QByteArray &data,
 
             iniSection = iniSection.trimmed();
 
-            if (qstricmp(iniSection.constData(), "general") == 0) {
+            if (iniSection.compare("general", Qt::CaseInsensitive) == 0) {
                 currentSection.clear();
             } else {
-                if (qstricmp(iniSection.constData(), "%general") == 0) {
+                if (iniSection.compare("%general", Qt::CaseInsensitive) == 0) {
                     currentSection = QLatin1String(iniSection.constData() + 1);
                 } else {
                     currentSection.clear();
@@ -1857,7 +1857,7 @@ bool QConfFileSettingsPrivate::writeIniFile(QIODevice &device, const ParsedSetti
 
         if (realSection.isEmpty()) {
             realSection = "[General]";
-        } else if (qstricmp(realSection.constData(), "general") == 0) {
+        } else if (realSection.compare("general", Qt::CaseInsensitive) == 0) {
             realSection = "[%General]";
         } else {
             realSection.prepend('[');
diff --git a/src/corelib/tools/qbytearray.cpp b/src/corelib/tools/qbytearray.cpp
index 3468580bf1..4d2003334c 100644
--- a/src/corelib/tools/qbytearray.cpp
+++ b/src/corelib/tools/qbytearray.cpp
@@ -356,7 +356,8 @@ char *qstrncpy(char *dst, const char *src, uint len)
     Special case 2: Returns an arbitrary non-zero value if \a str1 is
     nullptr or \a str2 is nullptr (but not both).
 
-    \sa qstrncmp(), qstricmp(), qstrnicmp(), {8-bit Character Comparisons}
+    \sa qstrncmp(), qstricmp(), qstrnicmp(), {8-bit Character Comparisons},
+        QByteArray::compare()
 */
 int qstrcmp(const char *str1, const char *str2)
 {
@@ -381,7 +382,8 @@ int qstrcmp(const char *str1, const char *str2)
     Special case 2: Returns a random non-zero value if \a str1 is nullptr
     or \a str2 is nullptr (but not both).
 
-    \sa qstrcmp(), qstricmp(), qstrnicmp(), {8-bit Character Comparisons}
+    \sa qstrcmp(), qstricmp(), qstrnicmp(), {8-bit Character Comparisons},
+        QByteArray::compare()
 */
 
 /*! \relates QByteArray
@@ -400,7 +402,8 @@ int qstrcmp(const char *str1, const char *str2)
     Special case 2: Returns a random non-zero value if \a str1 is nullptr
     or \a str2 is nullptr (but not both).
 
-    \sa qstrcmp(), qstrncmp(), qstrnicmp(), {8-bit Character Comparisons}
+    \sa qstrcmp(), qstrncmp(), qstrnicmp(), {8-bit Character Comparisons},
+        QByteArray::compare()
 */
 
 int qstricmp(const char *str1, const char *str2)
@@ -434,7 +437,8 @@ int qstricmp(const char *str1, const char *str2)
     Special case 2: Returns a random non-zero value if \a str1 is nullptr
     or \a str2 is nullptr (but not both).
 
-    \sa qstrcmp(), qstrncmp(), qstricmp(), {8-bit Character Comparisons}
+    \sa qstrcmp(), qstrncmp(), qstricmp(), {8-bit Character Comparisons},
+        QByteArray::compare()
 */
 
 int qstrnicmp(const char *str1, const char *str2, uint len)
@@ -456,6 +460,55 @@ int qstrnicmp(const char *str1, const char *str2, uint len)
 
 /*!
     \internal
+    \since 5.12
+
+    A helper for QByteArray::compare. Compares \a len1 bytes from \a str1 to \a
+    len2 bytes from \a str2. If \a len2 is -1, then \a str2 is expected to be
+    null-terminated.
+ */
+int qstrnicmp(const char *str1, qsizetype len1, const char *str2, qsizetype len2)
+{
+    Q_ASSERT(str1);
+    Q_ASSERT(len1 >= 0);
+    Q_ASSERT(len2 >= -1);
+    const uchar *s1 = reinterpret_cast<const uchar *>(str1);
+    const uchar *s2 = reinterpret_cast<const uchar *>(str2);
+    if (!s2)
+        return len1 == 0 ? 0 : 1;
+
+    int res;
+    uchar c;
+    if (len2 == -1) {
+        // null-terminated str2
+        qsizetype i;
+        for (i = 0; i < len1; ++i) {
+            c = latin1_lowercased[s2[i]];
+            if (!c)
+                return 1;
+
+            res = latin1_lowercased[s1[i]] - c;
+            if (res)
+                return res;
+        }
+        c = latin1_lowercased[s2[i]];
+        return c ? -1 : 0;
+    } else {
+        // not null-terminated
+        for (qsizetype i = 0; i < qMin(len1, len2); ++i) {
+            c = latin1_lowercased[s2[i]];
+            res = latin1_lowercased[s1[i]] - c;
+            if (res)
+                return res;
+        }
+        if (len1 == len2)
+            return 0;
+        return len1 < len2 ? -1 : 1;
+    }
+}
+
+/*!
+    \internal
+    ### Qt6: replace the QByteArray parameter with [pointer,len] pair
  */
 int qstrcmp(const QByteArray &str1, const char *str2)
 {
@@ -483,6 +536,7 @@ int qstrcmp(const QByteArray &str1, const char *str2)
 
 /*!
     \internal
+    ### Qt6: replace the QByteArray parameter with [pointer,len] pair
  */
 int qstrcmp(const QByteArray &str1, const QByteArray &str2)
 {
@@ -2864,6 +2918,31 @@ int QByteArray::count(char ch) const
 */
 
 /*!
+    \fn int QByteArray::compare(const char *c, Qt::CaseSensitivity cs = Qt::CaseSensitive) const
+    \since 5.12
+
+    Returns an integer less than, equal to, or greater than zero depending on
+    whether this QByteArray sorts before, at the same position, or after the
+    string pointed to by \a c. The comparison is performed according to case
+    sensitivity \a cs.
+
+    \sa operator==
+*/
+
+/*!
+    \fn int QByteArray::compare(const QByteArray &a, Qt::CaseSensitivity cs = Qt::CaseSensitive) const
+    \overload
+    \since 5.12
+
+    Returns an integer less than, equal to, or greater than zero depending on
+    whether this QByteArray sorts before, at the same position, or after the
+    QByteArray \a a. The comparison is performed according to case sensitivity
+    \a cs.
+
+    \sa operator==
+*/
+
+/*!
     Returns \c true if this byte array starts with byte array \a ba;
     otherwise returns \c false.
 
@@ -3367,6 +3446,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if byte array \a a1 is equal to byte array \a a2;
     otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator==(const QByteArray &a1, const char *a2)
@@ -3376,6 +3457,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if byte array \a a1 is equal to string \a a2;
     otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator==(const char *a1, const QByteArray &a2)
@@ -3385,6 +3468,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if string \a a1 is equal to byte array \a a2;
     otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator!=(const QByteArray &a1, const QByteArray &a2)
@@ -3394,6 +3479,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if byte array \a a1 is not equal to byte array \a a2;
     otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator!=(const QByteArray &a1, const char *a2)
@@ -3403,6 +3490,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if byte array \a a1 is not equal to string \a a2;
     otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator!=(const char *a1, const QByteArray &a2)
@@ -3412,6 +3501,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if string \a a1 is not equal to byte array \a a2;
     otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator<(const QByteArray &a1, const QByteArray &a2)
@@ -3421,6 +3512,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if byte array \a a1 is lexically less than byte array
     \a a2; otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn inline bool operator<(const QByteArray &a1, const char *a2)
@@ -3430,6 +3523,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if byte array \a a1 is lexically less than string
     \a a2; otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator<(const char *a1, const QByteArray &a2)
@@ -3439,6 +3534,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if string \a a1 is lexically less than byte array
     \a a2; otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator<=(const QByteArray &a1, const QByteArray &a2)
@@ -3448,6 +3545,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if byte array \a a1 is lexically less than or equal
     to byte array \a a2; otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator<=(const QByteArray &a1, const char *a2)
@@ -3457,6 +3556,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if byte array \a a1 is lexically less than or equal
     to string \a a2; otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator<=(const char *a1, const QByteArray &a2)
@@ -3466,6 +3567,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if string \a a1 is lexically less than or equal
     to byte array \a a2; otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator>(const QByteArray &a1, const QByteArray &a2)
@@ -3475,6 +3578,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if byte array \a a1 is lexically greater than byte
     array \a a2; otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator>(const QByteArray &a1, const char *a2)
@@ -3484,6 +3589,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if byte array \a a1 is lexically greater than string
     \a a2; otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator>(const char *a1, const QByteArray &a2)
@@ -3493,6 +3600,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if string \a a1 is lexically greater than byte array
     \a a2; otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator>=(const QByteArray &a1, const QByteArray &a2)
@@ -3502,6 +3611,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if byte array \a a1 is lexically greater than or
     equal to byte array \a a2; otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator>=(const QByteArray &a1, const char *a2)
@@ -3511,6 +3622,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if byte array \a a1 is lexically greater than or
     equal to string \a a2; otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn bool operator>=(const char *a1, const QByteArray &a2)
@@ -3520,6 +3633,8 @@ QDataStream &operator>>(QDataStream &in, QByteArray &ba)
 
     Returns \c true if string \a a1 is lexically greater than or
     equal to byte array \a a2; otherwise returns \c false.
+
+    \sa QByteArray::compare()
 */
 
 /*! \fn const QByteArray operator+(const QByteArray &a1, const QByteArray &a2)
diff --git a/src/corelib/tools/qbytearray.h b/src/corelib/tools/qbytearray.h
index bed710c597..8ee3a29ecc 100644
--- a/src/corelib/tools/qbytearray.h
+++ b/src/corelib/tools/qbytearray.h
@@ -99,6 +99,7 @@ inline int qstrncmp(const char *str1, const char *str2, uint len)
 }
 Q_CORE_EXPORT int qstricmp(const char *, const char *);
 Q_CORE_EXPORT int qstrnicmp(const char *, const char *, uint len);
+Q_CORE_EXPORT int qstrnicmp(const char *, qsizetype, const char *, qsizetype = -1);
 
 // implemented in qvsnprintf.cpp
 Q_CORE_EXPORT int qvsnprintf(char *str, size_t n, const char *fmt, va_list ap);
@@ -231,6 +232,9 @@ public:
     int count(const char *a) const;
     int count(const QByteArray &a) const;
 
+    inline int compare(const char *c, Qt::CaseSensitivity cs = Qt::CaseSensitive) const;
+    inline int compare(const QByteArray &a, Qt::CaseSensitivity cs = Qt::CaseSensitive) const;
+
     Q_REQUIRED_RESULT QByteArray left(int len) const;
     Q_REQUIRED_RESULT QByteArray right(int len) const;
     Q_REQUIRED_RESULT QByteArray mid(int index, int len = -1) const;
@@ -603,6 +607,16 @@ inline bool QByteArray::contains(const QByteArray &a) const
 { return indexOf(a) != -1; }
 inline bool QByteArray::contains(char c) const
 { return indexOf(c) != -1; }
+inline int QByteArray::compare(const char *c, Qt::CaseSensitivity cs) const
+{
+    return cs == Qt::CaseSensitive ? qstrcmp(*this, c) :
+                                     qstrnicmp(data(), size(), c, -1);
+}
+inline int QByteArray::compare(const QByteArray &a, Qt::CaseSensitivity cs) const
+{
+    return cs == Qt::CaseSensitive ? qstrcmp(*this, a) :
+                                     qstrnicmp(data(), size(), a.data(), a.size());
+}
 inline bool operator==(const QByteArray &a1, const QByteArray &a2) Q_DECL_NOTHROW
 { return (a1.size() == a2.size()) && (memcmp(a1.constData(), a2.constData(), a1.size())==0); }
 inline bool operator==(const QByteArray &a1, const char *a2) Q_DECL_NOTHROW
diff --git a/src/corelib/tools/qstring.cpp b/src/corelib/tools/qstring.cpp
index 712e058c9c..c2e62a47f7 100644
--- a/src/corelib/tools/qstring.cpp
+++ b/src/corelib/tools/qstring.cpp
@@ -1076,14 +1076,12 @@ static int qt_compare_strings(QLatin1String lhs, QStringView rhs, Qt::CaseSensit
 
 static int qt_compare_strings(QLatin1String lhs, QLatin1String rhs, Qt::CaseSensitivity cs) Q_DECL_NOTHROW
 {
+    if (cs == Qt::CaseInsensitive)
+        return qstrnicmp(lhs.data(), lhs.size(), rhs.data(), rhs.size());
     if (lhs.isEmpty())
         return lencmp(0, rhs.size());
     const auto l = std::min(lhs.size(), rhs.size());
-    int r;
-    if (cs == Qt::CaseSensitive)
-        r = qstrncmp(lhs.data(), rhs.data(), l);
-    else
-        r = qstrnicmp(lhs.data(), rhs.data(), l);
+    int r = qstrncmp(lhs.data(), rhs.data(), l);
     return r ? r : lencmp(lhs.size(), rhs.size());
 }
 
diff --git a/src/gui/kernel/qhighdpiscaling.cpp b/src/gui/kernel/qhighdpiscaling.cpp
index 8689f9f3b1..a455aa639d 100644
--- a/src/gui/kernel/qhighdpiscaling.cpp
+++ b/src/gui/kernel/qhighdpiscaling.cpp
@@ -244,7 +244,8 @@ static inline bool usePixelDensity()
         return false;
     return QCoreApplication::testAttribute(Qt::AA_EnableHighDpiScaling)
         || (screenEnvValueOk && screenEnvValue > 0)
-        || (qEnvironmentVariableIsSet(legacyDevicePixelEnvVar) && qgetenv(legacyDevicePixelEnvVar).toLower() == "auto");
+        || (qEnvironmentVariableIsSet(legacyDevicePixelEnvVar) &&
+            qgetenv(legacyDevicePixelEnvVar).compare("auto", Qt::CaseInsensitive) == 0);
 }
 
 void QHighDpiScaling::initHighDpiScaling()
diff --git a/src/network/access/http2/http2protocol.cpp b/src/network/access/http2/http2protocol.cpp
index f51af4be5c..0be72042c6 100644
--- a/src/network/access/http2/http2protocol.cpp
+++ b/src/network/access/http2/http2protocol.cpp
@@ -287,7 +287,8 @@ bool is_protocol_upgraded(const QHttpNetworkReply &reply)
         // Do some minimal checks here - we expect 'Upgrade: h2c' to be found.
         const auto &header = reply.header();
         for (const QPair<QByteArray, QByteArray> &field : header) {
-            if (field.first.toLower() == "upgrade" && field.second.toLower() == "h2c")
+            if (field.first.compare("upgrade", Qt::CaseInsensitive) == 0 &&
+                    field.second.compare("h2c", Qt::CaseInsensitive) == 0)
                 return true;
         }
     }
diff --git a/src/network/access/qhsts.cpp b/src/network/access/qhsts.cpp
index 43a8a3663e..a015feb044 100644
--- a/src/network/access/qhsts.cpp
+++ b/src/network/access/qhsts.cpp
@@ -453,8 +453,7 @@ bool QHstsHeaderParser::processDirective(const QByteArray &name, const QByteArra
 {
     Q_ASSERT(name.size());
     // RFC6797 6.1/3 Directive names are case-insensitive
-    const auto lcName = name.toLower();
-    if (lcName == "max-age") {
+    if (name.compare("max-age", Qt::CaseInsensitive) == 0) {
         // RFC 6797, 6.1.1
         // The syntax of the max-age directive's REQUIRED value (after
         // quoted-string unescaping, if necessary) is defined as:
@@ -477,7 +476,7 @@ bool QHstsHeaderParser::processDirective(const QByteArray &name, const QByteArra
 
         maxAge = age;
         maxAgeFound = true;
-    } else if (lcName == "includesubdomains") {
+    } else if (name.compare("includesubdomains", Qt::CaseInsensitive) == 0) {
         // RFC 6797, 6.1.2.  The includeSubDomains Directive.
         // The OPTIONAL "includeSubDomains" directive is a valueless directive.
 
diff --git a/src/network/access/qhttp2protocolhandler.cpp b/src/network/access/qhttp2protocolhandler.cpp
index c207d6e240..df7f87efd4 100644
--- a/src/network/access/qhttp2protocolhandler.cpp
+++ b/src/network/access/qhttp2protocolhandler.cpp
@@ -97,16 +97,18 @@ HPack::HttpHeader build_headers(const QHttpNetworkRequest &request, quint32 maxH
         if (size.second > maxHeaderListSize)
             break;
 
-        QByteArray key(field.first.toLower());
-        if (key == "connection" || key == "host" || key == "keep-alive"
-            || key == "proxy-connection" || key == "transfer-encoding")
+        if (field.first.compare("connection", Qt::CaseInsensitive) == 0 ||
+                field.first.compare("host", Qt::CaseInsensitive) == 0 ||
+                field.first.compare("keep-alive", Qt::CaseInsensitive) == 0 ||
+                field.first.compare("proxy-connection", Qt::CaseInsensitive) == 0 ||
+                field.first.compare("transfer-encoding", Qt::CaseInsensitive) == 0)
             continue; // Those headers are not valid (section 3.2.1) - from QSpdyProtocolHandler
         // TODO: verify with specs, which fields are valid to send ....
         // toLower - 8.1.2 .... "header field names MUST be converted to lowercase prior
         // to their encoding in HTTP/2.
         // A request or response containing uppercase header field names
         // MUST be treated as malformed (Section 8.1.2.6)".
-        header.push_back(HeaderField(key, field.second));
+        header.push_back(HeaderField(field.first.toLower(), field.second));
     }
 
     return header;
@@ -1404,8 +1406,9 @@ bool QHttp2ProtocolHandler::tryReserveStream(const Http2::Frame &pushPromiseFram
         return false;
     }
 
-    const auto method = pseudoHeaders[":method"].toLower();
-    if (method != "get" && method != "head")
+    const QByteArray method = pseudoHeaders[":method"];
+    if (method.compare("get", Qt::CaseInsensitive) != 0 &&
+            method.compare("head", Qt::CaseInsensitive) != 0)
         return false;
 
     QUrl url;
diff --git a/src/network/access/qhttpnetworkconnection.cpp b/src/network/access/qhttpnetworkconnection.cpp
index 0e2c257952..c58fd24a44 100644
--- a/src/network/access/qhttpnetworkconnection.cpp
+++ b/src/network/access/qhttpnetworkconnection.cpp
@@ -528,7 +528,7 @@ QUrl QHttpNetworkConnectionPrivate::parseRedirectResponse(QAbstractSocket *socke
     QUrl redirectUrl;
     const QList<QPair<QByteArray, QByteArray> > fields = reply->header();
     for (const QNetworkReply::RawHeaderPair &header : fields) {
-        if (header.first.toLower() == "location") {
+        if (header.first.compare("location", Qt::CaseInsensitive) == 0) {
             redirectUrl = QUrl::fromEncoded(header.second);
             break;
         }
diff --git a/src/network/access/qhttpnetworkheader.cpp b/src/network/access/qhttpnetworkheader.cpp
index 3326f89d2f..8ad01174b4 100644
--- a/src/network/access/qhttpnetworkheader.cpp
+++ b/src/network/access/qhttpnetworkheader.cpp
@@ -64,7 +64,7 @@ qint64 QHttpNetworkHeaderPrivate::contentLength() const
     QList<QPair<QByteArray, QByteArray> >::ConstIterator it = fields.constBegin(),
                                                         end = fields.constEnd();
     for ( ; it != end; ++it)
-        if (qstricmp("content-length", it->first) == 0) {
+        if (it->first.compare("content-length", Qt::CaseInsensitive) == 0) {
             value = it->second;
             break;
         }
@@ -95,7 +95,7 @@ QList<QByteArray> QHttpNetworkHeaderPrivate::headerFieldValues(const QByteArray
     QList<QPair<QByteArray, QByteArray> >::ConstIterator it = fields.constBegin(),
                                                         end = fields.constEnd();
     for ( ; it != end; ++it)
-        if (qstricmp(name.constData(), it->first) == 0)
+        if (name.compare(it->first, Qt::CaseInsensitive) == 0)
             result += it->second;
 
     return result;
@@ -104,7 +104,7 @@ QList<QByteArray> QHttpNetworkHeaderPrivate::headerFieldValues(const QByteArray
 void QHttpNetworkHeaderPrivate::setHeaderField(const QByteArray &name, const QByteArray &data)
 {
     auto firstEqualsName = [&name](const QPair<QByteArray, QByteArray> &header) {
-        return qstricmp(name.constData(), header.first) == 0;
+        return name.compare(header.first, Qt::CaseInsensitive) == 0;
     };
     fields.erase(std::remove_if(fields.begin(), fields.end(),
                                 firstEqualsName),
diff --git a/src/network/access/qhttpnetworkreply.cpp b/src/network/access/qhttpnetworkreply.cpp
index a657346958..c9c3172304 100644
--- a/src/network/access/qhttpnetworkreply.cpp
+++ b/src/network/access/qhttpnetworkreply.cpp
@@ -390,7 +390,8 @@ qint64 QHttpNetworkReplyPrivate::bytesAvailable() const
 bool QHttpNetworkReplyPrivate::isCompressed()
 {
     QByteArray encoding = headerField("content-encoding");
-    return qstricmp(encoding.constData(), "gzip") == 0 || qstricmp(encoding.constData(), "deflate") == 0;
+    return encoding.compare("gzip", Qt::CaseInsensitive) == 0 ||
+            encoding.compare("deflate", Qt::CaseInsensitive) == 0;
 }
 
 void QHttpNetworkReplyPrivate::removeAutoDecompressHeader()
@@ -401,7 +402,7 @@ void QHttpNetworkReplyPrivate::removeAutoDecompressHeader()
     QList<QPair<QByteArray, QByteArray> >::Iterator it = fields.begin(),
                                                    end = fields.end();
     while (it != end) {
-        if (qstricmp(name.constData(), it->first.constData()) == 0) {
+        if (name.compare(it->first, Qt::CaseInsensitive) == 0) {
             removedContentLength = strtoull(it->second.constData(), nullptr, 0);
             fields.erase(it);
             break;
diff --git a/src/network/access/qnetworkdiskcache.cpp b/src/network/access/qnetworkdiskcache.cpp
index c9d658225e..df2e4902a4 100644
--- a/src/network/access/qnetworkdiskcache.cpp
+++ b/src/network/access/qnetworkdiskcache.cpp
@@ -189,7 +189,7 @@ QIODevice *QNetworkDiskCache::prepare(const QNetworkCacheMetaData &metaData)
 
     const auto headers = metaData.rawHeaders();
     for (const auto &header : headers) {
-        if (header.first.toLower() == "content-length") {
+        if (header.first.compare("content-length", Qt::CaseInsensitive) == 0) {
             const qint64 size = header.second.toLongLong();
             if (size > (maximumCacheSize() * 3)/4)
                 return 0;
@@ -642,7 +642,7 @@ bool QCacheItem::canCompress() const
     bool typeOk = false;
     const auto headers = metaData.rawHeaders();
     for (const auto &header : headers) {
-        if (header.first.toLower() == "content-length") {
+        if (header.first.compare("content-length", Qt::CaseInsensitive) == 0) {
             qint64 size = header.second.toLongLong();
             if (size > MAX_COMPRESSION_SIZE)
                 return false;
@@ -650,7 +650,7 @@ bool QCacheItem::canCompress() const
                 sizeOk = true;
         }
 
-        if (header.first.toLower() == "content-type") {
+        if (header.first.compare("content-type", Qt::CaseInsensitive) == 0) {
             QByteArray type = header.second;
             if (type.startsWith("text/")
                     || (type.startsWith("application/")
diff --git a/src/network/access/qnetworkreplyhttpimpl.cpp b/src/network/access/qnetworkreplyhttpimpl.cpp
index 96016453c2..3c6f4aadfa 100644
--- a/src/network/access/qnetworkreplyhttpimpl.cpp
+++ b/src/network/access/qnetworkreplyhttpimpl.cpp
@@ -1318,7 +1318,7 @@ void QNetworkReplyHttpImplPrivate::replyDownloadMetaData(const QList<QPair<QByte
         if (!value.isEmpty()) {
             // Why are we appending values for headers which are already
             // present?
-            if (qstricmp(it->first.constData(), "set-cookie") == 0)
+            if (it->first.compare("set-cookie", Qt::CaseInsensitive) == 0)
                 value += '\n';
             else
                 value += ", ";
@@ -1584,7 +1584,7 @@ bool QNetworkReplyHttpImplPrivate::sendCacheContents(const QNetworkCacheMetaData
     QUrl redirectUrl;
     for ( ; it != end; ++it) {
         if (httpRequest.isFollowRedirects() &&
-            !qstricmp(it->first.toLower().constData(), "location"))
+            !it->first.compare("location", Qt::CaseInsensitive))
             redirectUrl = QUrl::fromEncoded(it->second);
         setRawHeader(it->first, it->second);
     }
diff --git a/src/network/access/qnetworkrequest.cpp b/src/network/access/qnetworkrequest.cpp
index 70a7f4e8bd..c2b388bbce 100644
--- a/src/network/access/qnetworkrequest.cpp
+++ b/src/network/access/qnetworkrequest.cpp
@@ -918,11 +918,11 @@ static int parseHeaderName(const QByteArray &headerName)
 
     switch (tolower(headerName.at(0))) {
     case 'c':
-        if (qstricmp(headerName.constData(), "content-type") == 0)
+        if (headerName.compare("content-type", Qt::CaseInsensitive) == 0)
             return QNetworkRequest::ContentTypeHeader;
-        else if (qstricmp(headerName.constData(), "content-length") == 0)
+        else if (headerName.compare("content-length", Qt::CaseInsensitive) == 0)
             return QNetworkRequest::ContentLengthHeader;
-        else if (qstricmp(headerName.constData(), "cookie") == 0)
+        else if (headerName.compare("cookie", Qt::CaseInsensitive) == 0)
             return QNetworkRequest::CookieHeader;
         else if (qstricmp(headerName.constData(), "content-disposition") == 0)
             return QNetworkRequest::ContentDispositionHeader;
@@ -943,21 +943,21 @@ static int parseHeaderName(const QByteArray &headerName)
         break;
 
     case 'l':
-        if (qstricmp(headerName.constData(), "location") == 0)
+        if (headerName.compare("location", Qt::CaseInsensitive) == 0)
             return QNetworkRequest::LocationHeader;
-        else if (qstricmp(headerName.constData(), "last-modified") == 0)
+        else if (headerName.compare("last-modified", Qt::CaseInsensitive) == 0)
             return QNetworkRequest::LastModifiedHeader;
         break;
 
     case 's':
-        if (qstricmp(headerName.constData(), "set-cookie") == 0)
+        if (headerName.compare("set-cookie", Qt::CaseInsensitive) == 0)
             return QNetworkRequest::SetCookieHeader;
-        else if (qstricmp(headerName.constData(), "server") == 0)
+        else if (headerName.compare("server", Qt::CaseInsensitive) == 0)
             return QNetworkRequest::ServerHeader;
         break;
 
     case 'u':
-        if (qstricmp(headerName.constData(), "user-agent") == 0)
+        if (headerName.compare("user-agent", Qt::CaseInsensitive) == 0)
             return QNetworkRequest::UserAgentHeader;
         break;
     }
@@ -1100,7 +1100,7 @@ QNetworkHeadersPrivate::findRawHeader(const QByteArray &key) const
     RawHeadersList::ConstIterator it = rawHeaders.constBegin();
     RawHeadersList::ConstIterator end = rawHeaders.constEnd();
     for ( ; it != end; ++it)
-        if (qstricmp(it->first.constData(), key.constData()) == 0)
+        if (it->first.compare(key, Qt::CaseInsensitive) == 0)
             return it;
 
     return end;                 // not found
@@ -1181,7 +1181,7 @@ void QNetworkHeadersPrivate::setCookedHeader(QNetworkRequest::KnownHeaders heade
 void QNetworkHeadersPrivate::setRawHeaderInternal(const QByteArray &key, const QByteArray &value)
 {
     auto firstEqualsKey = [&key](const RawHeaderPair &header) {
-        return qstricmp(header.first.constData(), key.constData()) == 0;
+        return header.first.compare(key, Qt::CaseInsensitive) == 0;
     };
     rawHeaders.erase(std::remove_if(rawHeaders.begin(), rawHeaders.end(),
                                     firstEqualsKey),
diff --git a/src/network/kernel/qauthenticator.cpp b/src/network/kernel/qauthenticator.cpp
index a3ccf13e82..11ea40dbce 100644
--- a/src/network/kernel/qauthenticator.cpp
+++ b/src/network/kernel/qauthenticator.cpp
@@ -412,7 +412,7 @@ void QAuthenticatorPrivate::parseHttpResponse(const QList<QPair<QByteArray, QByt
     QByteArray headerVal;
     for (int i = 0; i < values.size(); ++i) {
         const QPair<QByteArray, QByteArray> &current = values.at(i);
-        if (current.first.toLower() != search)
+        if (current.first.compare(search, Qt::CaseInsensitive) != 0)
             continue;
         QByteArray str = current.second.toLower();
         if (method < Basic && str.startsWith("basic")) {
@@ -443,7 +443,7 @@ void QAuthenticatorPrivate::parseHttpResponse(const QList<QPair<QByteArray, QByt
         break;
     case DigestMd5: {
         this->options[QLatin1String("realm")] = realm = QString::fromLatin1(options.value("realm"));
-        if (options.value("stale").toLower() == "true")
+        if (options.value("stale").compare("true", Qt::CaseInsensitive) == 0)
             phase = Start;
         if (user.isEmpty() && password.isEmpty())
             phase = Done;
@@ -630,7 +630,7 @@ static QByteArray digestMd5ResponseHelper(
     hash.addData(":", 1);
     hash.addData(password);
     QByteArray ha1 = hash.result();
-    if (alg.toLower() == "md5-sess") {
+    if (alg.compare("md5-sess", Qt::CaseInsensitive) == 0) {
         hash.reset();
         // RFC 2617 contains an error, it was:
         // hash.addData(ha1);
@@ -650,7 +650,7 @@ static QByteArray digestMd5ResponseHelper(
     hash.addData(method);
     hash.addData(":", 1);
     hash.addData(digestUri);
-    if (qop.toLower() == "auth-int") {
+    if (qop.compare("auth-int", Qt::CaseInsensitive) == 0) {
         hash.addData(":", 1);
         hash.addData(hEntity);
     }
diff --git a/src/network/socket/qhttpsocketengine.cpp b/src/network/socket/qhttpsocketengine.cpp
index b543ea7981..9427c3b00d 100644
--- a/src/network/socket/qhttpsocketengine.cpp
+++ b/src/network/socket/qhttpsocketengine.cpp
@@ -627,10 +627,9 @@ void QHttpSocketEngine::slotSocketReadNotification()
         // from http spec is also allowed.
         if (proxyConnectionHeader.isEmpty())
             proxyConnectionHeader = d->reply->headerField("Connection");
-        proxyConnectionHeader = proxyConnectionHeader.toLower();
-        if (proxyConnectionHeader == "close") {
+        if (proxyConnectionHeader.compare("close", Qt::CaseSensitive) == 0) {
             willClose = true;
-        } else if (proxyConnectionHeader == "keep-alive") {
+        } else if (proxyConnectionHeader.compare("keep-alive", Qt::CaseInsensitive) == 0) {
             willClose = false;
         } else {
             // no Proxy-Connection header, so use the default
diff --git a/src/plugins/platforms/eglfs/api/qeglfsintegration.cpp b/src/plugins/platforms/eglfs/api/qeglfsintegration.cpp
index 33878a5f50..43f2e31a49 100644
--- a/src/plugins/platforms/eglfs/api/qeglfsintegration.cpp
+++ b/src/plugins/platforms/eglfs/api/qeglfsintegration.cpp
@@ -415,8 +415,7 @@ static void *eglContextForContext(QOpenGLContext *context)
 QPlatformNativeInterface::NativeResourceForContextFunction QEglFSIntegration::nativeResourceFunctionForContext(const QByteArray &resource)
 {
 #ifndef QT_NO_OPENGL
-    QByteArray lowerCaseResource = resource.toLower();
-    if (lowerCaseResource == "get_egl_context")
+    if (resource.compare("get_egl_context", Qt::CaseInsensitive) == 0)
         return NativeResourceForContextFunction(eglContextForContext);
 #else
     Q_UNUSED(resource);