qDecodeDataUrl(): treat ";base64" marker as case-insensitive

RFC2397 doesn't explicitly mention it, but references RFC2045, which,
in Section 2, states:

> All media type values, subtype values, and parameter names as
> defined are case-insensitive.

and goes on, in 6.1:

>   mechanism := "7bit" / "8bit" / "binary" /
>                  "quoted-printable" / "base64" /
>                  ietf-token / x-token
>
>   These values are not case sensitive

So regardless of whether "base64" is a parameter name, or a mechanism,
we need to treat it case-insensitively.

Use QLatin1String::endsWith() instead of QByteArray::endsWith(),
because the former takes Qt::CaseInsensitive while the latter would
need a toLower().

Add a test.

As a drive-by, use the same trick for the existing case-insensitive
comparison with "charset".

As a further drive-by, fix inappropriate uses of QLatin1String (=
where they don't prevent allocations).

[ChangeLog][QtCore][QUrl] Now recognizes the ";base64" marker in
"data:" URLs case-insensitively.

Pick-to: 6.3 6.2
Change-Id: Ife6ba771553aaad3b7c119c1fa631f41ffa8f590
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qdataurl.cpp

@@ -43,6 +43,8 @@
 
 QT_BEGIN_NAMESPACE
 
+using namespace Qt::Literals;
+
 /*!
     \internal
 
@@ -54,7 +56,7 @@ Q_CORE_EXPORT bool qDecodeDataUrl(const QUrl &uri, QString &mimeType, QByteArray
     if (uri.scheme() != QLatin1String("data") || !uri.host().isEmpty())
         return false;
 
-    mimeType = QLatin1String("text/plain;charset=US-ASCII");
+    mimeType = QStringLiteral("text/plain;charset=US-ASCII");
 
     // the following would have been the correct thing, but
     // reality often differs from the specification. People have
@@ -70,12 +72,12 @@ Q_CORE_EXPORT bool qDecodeDataUrl(const QUrl &uri, QString &mimeType, QByteArray
         data = data.trimmed();
 
         // find out if the payload is encoded in Base64
-        if (data.endsWith(";base64")) {
+        if (QLatin1String{data}.endsWith(";base64"_L1, Qt::CaseInsensitive)) {
             payload = QByteArray::fromBase64(payload);
             data.chop(7);
         }
 
-        if (data.toLower().startsWith("charset")) {
+        if (QLatin1String{data}.startsWith("charset"_L1, Qt::CaseInsensitive)) {
             int i = 7;      // strlen("charset")
             while (data.at(i) == ' ')
                 ++i;
@@ -84,7 +86,7 @@ Q_CORE_EXPORT bool qDecodeDataUrl(const QUrl &uri, QString &mimeType, QByteArray
         }
 
         if (!data.isEmpty())
-            mimeType = QLatin1String(data.trimmed());
+            mimeType = QString::fromLatin1(data.trimmed());
 
     }
 

tests/auto/corelib/io/qdataurl/tst_qdataurl.cpp

@@ -57,6 +57,8 @@ void tst_QDataUrl::decode_data()
         "text/plain;charset=US-ASCII"_L1);
     row("alreadyPercentageEncoded", "data:text/plain,%E2%88%9A", true,
         "text/plain"_L1, QByteArray::fromPercentEncoding("%E2%88%9A"));
+    row("everythingIsCaseInsensitive", "Data:texT/PlaiN;charSet=iSo-8859-1;Base64,SGVsbG8=", true,
+        "texT/PlaiN;charSet=iSo-8859-1"_L1, QByteArrayLiteral("Hello"));
 }
 
 void tst_QDataUrl::decode()