This just complicates the code, for the small benefit of avoiding a
messageHash seeding from an empty key that then has to be reset.
This lazy initialization is in the way of using QCH's SmallByteArray
for the key, which this author thinks is the more important
optimization, because it will allow passing keys by QByteArrayView,
removing the impedance mismatch between QMAC and QCH.
Since the QMAC API doesn't distinguish between the absence of a key,
and the presence of a null (ie. empty) key, we can't not call
initMessageHash() when the key is empty, so we should suggest to pass
the actual key to the constructor as often as possible, and use
setKey() only to change the key afterwards.
[ChangeLog][QtCore][QMessageAuthenticationCode] No longer delays
processing of the key to the first setData() or result() call. While
passing a default-constructed key to the constructor and then calling
setKey() continues to work, for optimal performance, we suggest to
pass the actual key as a constructor argument and call setKey() only
to change the key.
Pick-to: 6.5
Change-Id: If0a078f37a16f8306f77d2b2bd5dacf23ce5c3e2
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
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