QNAM: Add Q*Socket abstractions in new namespace

Functions to unify certain aspects of QAbstractSocket and QLocalSocket.
To be used in follow-up commits.

Task-number: QTBUG-102855
Change-Id: I4fb39e626c8a4054196f5985a9ccc2532117e4a7
Reviewed-by: Mate Barany <mate.barany@qt.io>

src/network/CMakeLists.txt

@@ -142,6 +142,7 @@ qt_internal_extend_target(Network CONDITION QT_FEATURE_http
         access/qnetworkrequestfactory.h
         access/qrestaccessmanager.cpp access/qrestaccessmanager.h access/qrestaccessmanager_p.h
         access/qrestreply.cpp access/qrestreply.h access/qrestreply_p.h
+        access/qsocketabstraction_p.h
         socket/qhttpsocketengine.cpp socket/qhttpsocketengine_p.h
 )
 

src/network/access/qsocketabstraction_p.h

@@ -0,0 +1,91 @@
+// Copyright (C) 2024 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#ifndef QSOCKETABSTRACTION_P_H
+#define QSOCKETABSTRACTION_P_H
+
+#include <private/qtnetworkglobal_p.h>
+
+#include <QtNetwork/qabstractsocket.h>
+#include <QtNetwork/qlocalsocket.h>
+
+#include <QtCore/qxpfunctional.h>
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API. It exists for the convenience
+// of the Network Access API. This header file may change from
+// version to version without notice, or even be removed.
+//
+// We mean it.
+//
+
+QT_BEGIN_NAMESPACE
+
+// Helper functions to deal with a QIODevice that is either a socket or a local
+// socket.
+namespace QSocketAbstraction {
+template <typename Fn, typename... Args>
+auto visit(Fn &&fn, QIODevice *socket, Args &&...args)
+{
+    if (auto *s = qobject_cast<QAbstractSocket *>(socket))
+        return std::forward<Fn>(fn)(s, std::forward<Args>(args)...);
+    if (auto *s = qobject_cast<QLocalSocket *>(socket))
+        return std::forward<Fn>(fn)(s, std::forward<Args>(args)...);
+    Q_UNREACHABLE();
+}
+
+// Since QLocalSocket's LocalSocketState's values are defined as being equal
+// to some of QAbstractSocket's SocketState's values, we can use the superset
+// of the two as the return type.
+inline QAbstractSocket::SocketState socketState(QIODevice *device)
+{
+    auto getState = [](auto *s) {
+        using T = std::remove_pointer_t<decltype(s)>;
+        if constexpr (std::is_same_v<T, QAbstractSocket>) {
+            return s->state();
+        } else if constexpr (std::is_same_v<T, QLocalSocket>) {
+            QLocalSocket::LocalSocketState st = s->state();
+            return static_cast<QAbstractSocket::SocketState>(st);
+        }
+        Q_UNREACHABLE();
+    };
+    return visit(getState, device);
+}
+
+// Same as for socketState(), but for the errors
+inline QAbstractSocket::SocketError socketError(QIODevice *device)
+{
+    auto getError = [](auto *s) {
+        using T = std::remove_pointer_t<decltype(s)>;
+        if constexpr (std::is_same_v<T, QAbstractSocket>) {
+            return s->error();
+        } else if constexpr (std::is_same_v<T, QLocalSocket>) {
+            QLocalSocket::LocalSocketError st = s->error();
+            return static_cast<QAbstractSocket::SocketError>(st);
+        }
+        Q_UNREACHABLE();
+    };
+    return visit(getError, device);
+}
+
+inline QString socketPeerName(QIODevice *device)
+{
+    auto getPeerName = [](auto *s) {
+        using T = std::remove_pointer_t<decltype(s)>;
+        if constexpr (std::is_same_v<T, QAbstractSocket>) {
+            return s->peerName();
+        } else if constexpr (std::is_same_v<T, QLocalSocket>) {
+            return s->serverName();
+        }
+        Q_UNREACHABLE();
+    };
+    return visit(getPeerName, device);
+}
+} // namespace QSocketAbstraction
+
+QT_END_NAMESPACE
+
+#endif // QSOCKETABSTRACTION_P_H