new class to isolate UpdateChannel connections

cockatrice/src/client/network/client_update_checker.h

@@ -0,0 +1,45 @@
+#ifndef CLIENT_UPDATE_CHECKER_H
+#define CLIENT_UPDATE_CHECKER_H
+#include <QObject>
+
+class Release;
+
+/**
+ * We use a singleton instance of UpdateChannel, which can cause interference and feedback loops when multiple objects
+ * connect to it.
+ *
+ * This class encapsulates the usage of that UpdateChannel to ensure that the check only happens once per connection and
+ * the connection is destroyed after it's been used.
+ */
+class ClientUpdateChecker : public QObject
+{
+    Q_OBJECT
+
+    QMetaObject::Connection finishedCheckConnection;
+    QMetaObject::Connection errorConnection;
+
+    void actFinishedCheck(bool needToUpdate, bool isCompatible, Release *release);
+    void actError(const QString &errorString);
+
+public:
+    explicit ClientUpdateChecker(QObject *parent = nullptr);
+    /**
+     * Actually performs the check, using the currently selected update channel in the settings.
+     * Any resulting signals will only be sent once.
+     * This method should only be called ONCE per instance.
+     */
+    void check();
+
+signals:
+    /**
+     * Forwarded from UpdateChannel::finishedCheck
+     */
+    void finishedCheck(bool needToUpdate, bool isCompatible, Release *release);
+
+    /**
+     * Forwarded from UpdateChannel::error
+     */
+    void error(const QString &errorString);
+};
+
+#endif // CLIENT_UPDATE_CHECKER_H