feat: Use string for logind session id instead of int

Although the logind session id is exactly an integer in current
systemd-logind, but this is an UB according to systemd documentation.
Systemd advertise us to treat it as a string and we shall adapt it.

Author: calsys456

src/greeter/usermodel.h

@@ -85,7 +85,7 @@ class UserModel : public QAbstractListModel
     void currentUserNameChanged();
     void updateTranslations(const QLocale &locale);
     void countChanged();
-    void userLoggedIn(const QString &username, int sessionId);
+    void userLoggedIn(const QString &username, const QString &session);
 
 private Q_SLOTS:
     void onUserAdded(quint64 uid);

src/session/session.cpp

@@ -61,7 +61,7 @@ Session::~Session()
     }
 }
 
-int Session::id() const
+QString Session::id() const
 {
     return m_id;
 }
@@ -187,7 +187,7 @@ void SessionManager::removeSession(std::shared_ptr<Session> session)
  * @param username Username to ensure session for
  * @returns Session for the given username, or nullptr on failure
  */
-std::shared_ptr<Session> SessionManager::ensureSession(int id, QString username)
+std::shared_ptr<Session> SessionManager::ensureSession(QString id, QString username)
 {
     // Helper lambda to create WSocket and WXWayland
     auto createWSocket = [this]() {
@@ -314,7 +314,7 @@ std::shared_ptr<Session> SessionManager::ensureSession(int id, QString username)
  * @param id Session ID to find session for
  * @returns Session for the given id, or nullptr if not found
  */
-std::shared_ptr<Session> SessionManager::sessionForId(int id) const
+std::shared_ptr<Session> SessionManager::sessionForId(const QString &id) const
 {
     for (auto session : m_sessions) {
         if (session && session->m_id == id)
@@ -389,8 +389,9 @@ std::shared_ptr<Session> SessionManager::sessionForSocket(WSocket *socket) const
  * active session changed.
  *
  * @param username Username to set as active session
+ * @param session Logind session ID to set as active session
  */
-void SessionManager::updateActiveUserSession(const QString &username, int id)
+void SessionManager::updateActiveUserSession(const QString &username, const QString &id)
 {
     // Get previous active session
     auto previous = m_activeSession.lock();

src/session/session.h

@@ -21,7 +21,7 @@ class Session : public QObject {
 public:
     ~Session();
 
-    int id() const;
+    QString id() const;
     uid_t uid() const;
     const QString &username() const;
     WSocket *socket() const;
@@ -34,7 +34,7 @@ class Session : public QObject {
 private:
     friend class SessionManager;
 
-    int m_id = 0;
+    QString m_id = {};
     uid_t m_uid = 0;
     QString m_username = {};
     WSocket *m_socket = nullptr;
@@ -61,9 +61,9 @@ class SessionManager : public QObject {
     bool activeSocketEnabled() const;
     void setActiveSocketEnabled(bool newEnabled);
 
-    void updateActiveUserSession(const QString &username, int id);
+    void updateActiveUserSession(const QString &username, const QString &id);
     void removeSession(std::shared_ptr<Session> session);
-    std::shared_ptr<Session> sessionForId(int id) const;
+    std::shared_ptr<Session> sessionForId(const QString &id) const;
     std::shared_ptr<Session> sessionForUid(uid_t uid) const;
     std::shared_ptr<Session> sessionForUser(const QString &username) const;
     std::shared_ptr<Session> sessionForXWayland(WXWayland *xwayland) const;
@@ -74,7 +74,7 @@ class SessionManager : public QObject {
     void sessionChanged();
 
 private:
-    std::shared_ptr<Session> ensureSession(int id, QString username);
+    std::shared_ptr<Session> ensureSession(QString id, QString username);
 
     std::weak_ptr<Session> m_activeSession;
     QList<std::shared_ptr<Session>> m_sessions;