Add QHttpHeaders methods to QNetworkProxy

[ChangeLog][QtNetwork][QNetworkProxy] Added headers() and setHeaders()
methods to QNetworkProxy to provide an interface to work with
QHttpHeaders.

Task-number: QTBUG-107751
Change-Id: I8a82f56f0262c9f44d0cb52b2e411bf75626b926
Reviewed-by: Juha Vuolle <juha.vuolle@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/network/kernel/qnetworkproxy.cpp

@@ -751,6 +751,53 @@ QNetworkProxy QNetworkProxy::applicationProxy()
     return QNetworkProxy();
 }
 
+/*!
+    \since 6.8
+
+    Returns headers that are set in this network request.
+
+    If the proxy is not of type HttpProxy or HttpCachingProxy,
+    default constructed QHttpHeaders is returned.
+
+    \sa setHeaders()
+*/
+QHttpHeaders QNetworkProxy::headers() const
+{
+    if (d->type != HttpProxy && d->type != HttpCachingProxy)
+        return {};
+    return d->headers.headers();
+}
+
+/*!
+    \since 6.8
+
+    Sets \a newHeaders as headers in this network request, overriding
+    any previously set headers.
+
+    If some headers correspond to the known headers, the values will
+    be parsed and the corresponding parsed form will also be set.
+
+    If the proxy is not of type HttpProxy or HttpCachingProxy this has no
+    effect.
+
+    \sa headers(), QNetworkRequest::KnownHeaders
+*/
+void QNetworkProxy::setHeaders(QHttpHeaders &&newHeaders)
+{
+    if (d->type == HttpProxy || d->type == HttpCachingProxy)
+        d->headers.setHeaders(std::move(newHeaders));
+}
+
+/*!
+    \overload
+    \since 6.8
+*/
+void QNetworkProxy::setHeaders(const QHttpHeaders &newHeaders)
+{
+    if (d->type == HttpProxy || d->type == HttpCachingProxy)
+        d->headers.setHeaders(newHeaders);
+}
+
 /*!
     \since 5.0
     Returns the value of the known network header \a header if it is

src/network/kernel/qnetworkproxy.h

@@ -136,6 +136,10 @@ public:
     static void setApplicationProxy(const QNetworkProxy &proxy);
     static QNetworkProxy applicationProxy();
 
+    QHttpHeaders headers() const;
+    void setHeaders(const QHttpHeaders &newHeaders);
+    void setHeaders(QHttpHeaders &&newHeaders);
+
     // "cooked" headers
     QVariant header(QNetworkRequest::KnownHeaders header) const;
     void setHeader(QNetworkRequest::KnownHeaders header, const QVariant &value);