Change basic connection to DNS SRV lookup for master server failover

aoapplication.cpp

@@ -12,6 +12,7 @@
 AOApplication::AOApplication(int &argc, char **argv) : QApplication(argc, argv)
 {
   net_manager = new NetworkManager(this);
+  QObject::connect(net_manager, SIGNAL(ms_connect_finished(bool)), SLOT(ms_connect_finished(bool)));
 }
 
 AOApplication::~AOApplication()
@@ -134,3 +135,20 @@ void AOApplication::loading_cancelled()
 
   w_lobby->hide_loading_overlay();
 }
+
+void AOApplication::ms_connect_finished(bool connected)
+{
+  if (connected)
+  {
+    AOPacket *f_packet = new AOPacket("ALL#%");
+    send_ms_packet(f_packet);
+  }
+  else
+  {
+    call_error("There was an error connecting to the master server.\n"
+               "We deploy multiple master servers to mitigate any possible downtime,"
+               "but the client appears to have exhausted all possible methods of finding"
+               "and connecting to one.\n"
+               "Please check your Internet connection and firewall, and please try again.");
+  }
+}

aoapplication.h

@@ -146,6 +146,9 @@ private:
   QVector<server_type> server_list;
   QVector<server_type> favorite_list;
 
+private slots:
+  void ms_connect_finished(bool connected);
+
 public slots:
   void server_disconnected();
   void loading_cancelled();

main.cpp

@@ -14,8 +14,6 @@ int main(int argc, char *argv[])
     AOApplication main_app(argc, argv);
     main_app.construct_lobby();
     main_app.net_manager->connect_to_master();
-    AOPacket *f_packet = new AOPacket("ALL#%");
-    main_app.send_ms_packet(f_packet);
     main_app.w_lobby->show();
 
     return main_app.exec();

networkmanager.cpp

@@ -27,7 +27,7 @@ void NetworkManager::connect_to_master()
   ms_socket->close();
   ms_socket->abort();
 
-  ms_socket->connectToHost(ms_hostname, ms_port);
+  perform_srv_lookup();
 }
 
 void NetworkManager::connect_to_server(server_type p_server)
@@ -82,6 +82,59 @@ void NetworkManager::handle_ms_packet()
   }
 }
 
+void NetworkManager::perform_srv_lookup()
+{
+  ms_dns = new QDnsLookup(QDnsLookup::SRV, ms_hostname, this);
+
+  connect(ms_dns, SIGNAL(finished()), this, SLOT(on_srv_lookup()));
+  ms_dns->lookup();
+}
+
+void NetworkManager::on_srv_lookup()
+{
+  bool connected = false;
+  if (ms_dns->error() != QDnsLookup::NoError)
+  {
+    qWarning("SRV lookup of the master server DNS failed.");
+    ms_dns->deleteLater();
+  }
+  else
+  {
+    const auto srv_records = ms_dns->serviceRecords();
+
+    for (const QDnsServiceRecord &record : srv_records)
+    {
+      qDebug() << "Connecting to " << record.target();
+      ms_socket->connectToHost(record.target(), record.port());
+      QTime timer;
+      timer.start();
+      do
+      {
+        ao_app->processEvents();
+        if (ms_socket->state() == QAbstractSocket::ConnectedState)
+        {
+          connected = true;
+          break;
+        }
+        else if (ms_socket->error() != -1)
+        {
+          qWarning(QString("Error connecting to master server: %1").arg(ms_socket->errorString()).toStdString().c_str());
+          ms_socket->abort();
+          ms_socket->close();
+          break;
+        }
+      } while (timer.elapsed() < timeout_milliseconds); // Very expensive spin-wait loop - it will bring CPU to 100%!
+      if (connected) break;
+      else
+      {
+        ms_socket->abort();
+        ms_socket->close();
+      }
+    }
+  }
+  emit ms_connect_finished(connected);
+}
+
 void NetworkManager::handle_server_packet()
 {
   char buffer[16384] = {0};

networkmanager.h

@@ -5,6 +5,8 @@
 #include "aoapplication.h"
 
 #include <QTcpSocket>
+#include <QDnsLookup>
+#include <QTime>
 
 class NetworkManager : public QObject
 {
@@ -17,9 +19,11 @@ public:
   AOApplication *ao_app;
   QTcpSocket *ms_socket;
   QTcpSocket *server_socket;
+  QDnsLookup *ms_dns;
 
-  QString ms_hostname = "master.aceattorneyonline.com";
+  QString ms_hostname = "_aoms._tcp.aceattorneyonline.com";
   int ms_port = 27016;
+  const int timeout_milliseconds = 2000;
 
   bool ms_partial_packet = false;
   QString ms_temp_packet = "";
@@ -36,7 +40,14 @@ public slots:
   void ship_ms_packet(QString p_packet);
   void ship_server_packet(QString p_packet);
 
+signals:
+  void ms_connect_finished(bool success);
+
+private:
+  void perform_srv_lookup();
+
 private slots:
+  void on_srv_lookup();
   void handle_ms_packet();
   void handle_server_packet();
 };