QMessageAuthenticationCode: add hashInto() overloads

Same change as previously done for QCryptographicHash; same rationale
applies.

[ChangeLog][QtCore][QMessageAuthenticationCode] Added hashInto()
methods, see QCryptographicHash for more information.

Fixes: QTBUG-125431
Change-Id: I88a15479b020b39ff0669a9615793886289c83f7
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/tools/qcryptographichash.cpp

@@ -1671,15 +1671,52 @@ void QMessageAuthenticationCodePrivate::finalizeUnchecked() noexcept
     the key \a key and the method \a method.
 
     \include qcryptographichash.cpp {qba-to-qbav-6.6}
+
+    \sa hashInto()
 */
 QByteArray QMessageAuthenticationCode::hash(QByteArrayView message, QByteArrayView key,
                                             QCryptographicHash::Algorithm method)
+{
+    QByteArray ba(hashLengthInternal(method), Qt::Uninitialized);
+    [[maybe_unused]] const auto r = hashInto(ba, message, key, method);
+    Q_ASSERT(r.size() == ba.size());
+    return ba;
+}
+
+/*!
+    \since 6.8
+    \fn QMessageAuthenticationCode::hashInto(QSpan<char> buffer, QSpan<const QByteArrayView> messageParts, QByteArrayView key, QCryptographicHash::Algorithm method);
+    \fn QMessageAuthenticationCode::hashInto(QSpan<uchar> buffer, QSpan<const QByteArrayView> messageParts, QByteArrayView key, QCryptographicHash::Algorithm method);
+    \fn QMessageAuthenticationCode::hashInto(QSpan<std::byte> buffer, QSpan<const QByteArrayView> messageParts, QByteArrayView key, QCryptographicHash::Algorithm method);
+    \fn QMessageAuthenticationCode::hashInto(QSpan<char> buffer, QByteArrayView message, QByteArrayView key, QCryptographicHash::Algorithm method);
+    \fn QMessageAuthenticationCode::hashInto(QSpan<uchar> buffer, QByteArrayView message, QByteArrayView key, QCryptographicHash::Algorithm method);
+    \fn QMessageAuthenticationCode::hashInto(QSpan<std::byte> buffer, QByteArrayView message, QByteArrayView key, QCryptographicHash::Algorithm method);
+
+    Returns the authentication code for the message (\a message or, for the
+    QSpan overloads, the concatenation of \a messageParts) using the key \a key
+    and the method \a method.
+
+    The return value will be a sub-span of \a buffer, unless \a buffer is of
+    insufficient size, in which case a null QByteArrayView is returned.
+
+    \sa hash()
+*/
+QByteArrayView QMessageAuthenticationCode::hashInto(QSpan<std::byte> buffer,
+                                                    QSpan<const QByteArrayView> messageParts,
+                                                    QByteArrayView key,
+                                                    QCryptographicHash::Algorithm method) noexcept
 {
     QMessageAuthenticationCodePrivate mac(method);
     mac.setKey(key);
-    mac.messageHash.addData(message);
+    for (QByteArrayView part : messageParts)
+        mac.messageHash.addData(part);
     mac.finalizeUnchecked();
-    return mac.messageHash.resultView().toByteArray();
+    auto result = mac.messageHash.resultView();
+    if (buffer.size() < result.size())
+        return {}; // buffer too small
+    // ### optimize: have the method directly write into `buffer`
+    memcpy(buffer.data(), result.data(), result.size());
+    return buffer.first(result.size());
 }
 
 QT_END_NAMESPACE

src/corelib/tools/qmessageauthenticationcode.h

@@ -55,6 +55,30 @@ public:
     static QByteArray hash(QByteArrayView message, QByteArrayView key,
                            QCryptographicHash::Algorithm method);
 
+    static QByteArrayView
+    hashInto(QSpan<char> buffer, QByteArrayView message, QByteArrayView key,
+             QCryptographicHash::Algorithm method) noexcept
+    { return hashInto(as_writable_bytes(buffer), {&message, 1}, key, method); }
+    static QByteArrayView
+    hashInto(QSpan<uchar> buffer, QByteArrayView message, QByteArrayView key,
+             QCryptographicHash::Algorithm method) noexcept
+    { return hashInto(as_writable_bytes(buffer), {&message, 1}, key, method); }
+    static QByteArrayView
+    hashInto(QSpan<std::byte> buffer, QByteArrayView message,
+             QByteArrayView key, QCryptographicHash::Algorithm method) noexcept
+    { return hashInto(buffer, {&message, 1}, key, method); }
+    static QByteArrayView
+    hashInto(QSpan<char> buffer, QSpan<const QByteArrayView> messageParts,
+             QByteArrayView key, QCryptographicHash::Algorithm method) noexcept
+    { return hashInto(as_writable_bytes(buffer), messageParts, key, method); }
+    static QByteArrayView
+    hashInto(QSpan<uchar> buffer, QSpan<const QByteArrayView> messageParts,
+             QByteArrayView key, QCryptographicHash::Algorithm method) noexcept
+    { return hashInto(as_writable_bytes(buffer), messageParts, key, method); }
+    static QByteArrayView
+    hashInto(QSpan<std::byte> buffer, QSpan<const QByteArrayView> message,
+             QByteArrayView key, QCryptographicHash::Algorithm method) noexcept;
+
 private:
     Q_DISABLE_COPY(QMessageAuthenticationCode)
     QMessageAuthenticationCodePrivate *d;