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The WASM copy of the function is hopelessly outdated (recognizes less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 <thiago.macieira@intel.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

0 files changed, 0 insertions, 0 deletions