fix: rewrite linux router dns flusher (#1335)

Co-authored-by: sund3RRR <evenquantity@gamil.com>

service/server/router_linux.cpp

@@ -152,21 +152,29 @@ bool RouterLinux::routeDeleteList(const QString &gw, const QStringList &ips)
     return cnt;
 }
 
+bool RouterLinux::isServiceActive(const QString &serviceName) {
+    QProcess process;
+    process.start("systemctl", { "is-active", "--quiet", serviceName });
+    process.waitForFinished();
+
+    return process.exitCode() == 0;
+}
+
 void RouterLinux::flushDns()
 {
     QProcess p;
     p.setProcessChannelMode(QProcess::MergedChannels);
 
     //check what the dns manager use
-    if (QFileInfo::exists("/usr/bin/nscd")
+    if (isServiceActive("nscd.service")) {
-        || QFileInfo::exists("/usr/sbin/nscd")
+        qDebug() << "Restarting nscd.service";
-        || QFileInfo::exists("/usr/lib/systemd/system/nscd.service"))
-    {
         p.start("systemctl", { "restart", "nscd" });
-    }
+    } else if (isServiceActive("systemd-resolved.service")) {
-    else
+        qDebug() << "Restarting systemd-resolved.service";
-    {
         p.start("systemctl", { "restart", "systemd-resolved" });
+    } else {
+        qDebug() << "No suitable DNS manager found.";
+        return;
     }
 
     p.waitForFinished();

service/server/router_linux.h

@@ -43,6 +43,7 @@ private:
     RouterLinux(RouterLinux const &) = delete;
     RouterLinux& operator= (RouterLinux const&) = delete;
 
+    bool isServiceActive(const QString &serviceName);
     QList<Route> m_addedRoutes;
     DnsUtilsLinux *m_dnsUtil;
 };