QNetworkRequest: Make header parsing locale-independent

The existing header parsing used C's tolower() function for
case-insensitive switching over the first character of the
header. However, that function's result depends on the current locale.

Since the parser is supposed to match the likes of "If-Match" and
"If-None-Match", matching may fail in locales, such as Turkish, where
tolower(I) is ı (LATIN SMALL LETTER DOTLESS I) (or I, if the former
isn't representable in the current charset), causing a False Negative.

To fix, use the US-ASCII-only QtMiscUtils::toAsciiLower() function,
which has the added advantage that it's inline.

Replace at(0) with front() as a drive-by.

The WASM copy of the function is hopelessly outdated (recognizes less
headers than the QNetworkRequest original).

[ChangeLog][QtNetwork] Fixed a bug where certain
QNetworkRequest::KnownHeaders wouldn't be recognized as such in
certain locales.

Pick-to: 6.4 6.2 5.15
Task-number: QTBUG-109235
Change-Id: Ib147ab64803bb868647dd07ad657d785071242ea
Reviewed-by: Thiago Macieira <[email protected]>
Reviewed-by: Qt CI Bot <[email protected]>
Reviewed-by: Mårten Nordheim <[email protected]>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/network/access/qnetworkreplywasmimpl.cpp b/src/network/access/qnetworkreplywasmimpl.cpp
index 70d2a6be440..b05fae73db5 100644
--- a/src/network/access/qnetworkreplywasmimpl.cpp
+++ b/src/network/access/qnetworkreplywasmimpl.cpp
@@ -9,6 +9,7 @@
 #include <QtCore/qcoreapplication.h>
 #include <QtCore/qfileinfo.h>
 #include <QtCore/qthread.h>
+#include <QtCore/private/qtools_p.h>
 
 #include <private/qnetworkaccessmanager_p.h>
 #include <private/qnetworkfile_p.h>
@@ -346,7 +347,7 @@ static int parseHeaderName(const QByteArray &headerName)
     if (headerName.isEmpty())
         return -1;
 
-    switch (tolower(headerName.at(0))) {
+    switch (QtMiscUtils::toAsciiLower(headerName.front())) {
     case 'c':
         if (qstricmp(headerName.constData(), "content-type") == 0)
             return QNetworkRequest::ContentTypeHeader;