Ensure multicast UDP is sent to at least the loop-back interface

Also send multicast UDP to every selected network interface.

Configuration.cpp

@@ -443,7 +443,8 @@ private:
   void load_audio_devices (QAudio::Mode, QComboBox *, QAudioDeviceInfo *);
   void update_audio_channels (QComboBox const *, int, QComboBox *, bool);
 
-  void load_network_interfaces (CheckableItemComboBox *, QStringList const& current);
+  void load_network_interfaces (CheckableItemComboBox *, QStringList current);
+  void validate_network_interfaces (CheckableItemComboBox *);
   QStringList get_selected_network_interfaces (CheckableItemComboBox *);
   Q_SLOT void host_info_results (QHostInfo);
   void check_multicast (QHostAddress const&);
@@ -656,6 +657,7 @@ private:
   int dns_lookup_id_;
   port_type udp_server_port_;
   QStringList udp_interface_names_;
+  QString loopback_interface_name_;
   int udp_TTL_;
   QString n1mm_server_name_;
   port_type n1mm_server_port_;
@@ -1085,6 +1087,9 @@ Configuration::impl::impl (Configuration * self, QNetworkAccessManager * network
       load_network_interfaces (ui_->udp_interfaces_combo_box, udp_interface_names_);
       QGuiApplication::restoreOverrideCursor ();
     });
+  connect (ui_->udp_interfaces_combo_box, &QComboBox::currentTextChanged, [this] (QString const& /*text*/) {
+      validate_network_interfaces (ui_->udp_interfaces_combo_box);
+    });
 
   // set up LoTW users CSV file fetching
   connect (&lotw_users_, &LotWUsers::load_finished, [this] () {
@@ -2995,7 +3000,7 @@ void Configuration::impl::load_audio_devices (QAudio::Mode mode, QComboBox * com
 }
 
 // load the available network interfaces into the selection combo box
-void Configuration::impl::load_network_interfaces (CheckableItemComboBox * combo_box, QStringList const& current)
+void Configuration::impl::load_network_interfaces (CheckableItemComboBox * combo_box, QStringList current)
 {
   combo_box->clear ();
   for (auto const& net_if : QNetworkInterface::allInterfaces ())
@@ -3003,11 +3008,13 @@ void Configuration::impl::load_network_interfaces (CheckableItemComboBox * combo
       auto flags = QNetworkInterface::IsUp | QNetworkInterface::CanMulticast;
       if ((net_if.flags () & flags) == flags)
         {
-          auto is_loopback = net_if.flags () & QNetworkInterface::IsLoopBack;
+          if (net_if.flags () & QNetworkInterface::IsLoopBack)
+            {
+              loopback_interface_name_ = net_if.name ();
+            }
           auto item = combo_box->addCheckItem (net_if.humanReadableName ()
                                                , net_if.name ()
-                                               , is_loopback || current.contains (net_if.name ()) ? Qt::Checked : Qt::Unchecked);
+                                               , current.contains (net_if.name ()) ? Qt::Checked : Qt::Unchecked);
-          item->setEnabled (!is_loopback);
           auto tip = QString {"name(index): %1(%2) - %3"}.arg (net_if.name ()).arg (net_if.index ())
                        .arg (net_if.flags () & QNetworkInterface::IsUp ? "Up" : "Down");
           auto hw_addr = net_if.hardwareAddress ();
@@ -3029,6 +3036,33 @@ void Configuration::impl::load_network_interfaces (CheckableItemComboBox * combo
     }
 }
 
+// get the select network interfaces from the selection combo box
+void Configuration::impl::validate_network_interfaces (CheckableItemComboBox * combo_box)
+{
+  auto model = static_cast<QStandardItemModel *> (combo_box->model ());
+  bool has_checked {false};
+  int loopback_row {-1};
+  for (int row = 0; row < model->rowCount (); ++row)
+    {
+      if (model->item (row)->data ().toString () == loopback_interface_name_)
+        {
+          loopback_row = row;
+        }
+      else if (Qt::Checked == model->item (row)->checkState ())
+        {
+          has_checked = true;
+        }
+    }
+  if (loopback_row >= 0)
+    {
+      if (!has_checked)
+        {
+          model->item (loopback_row)->setCheckState (Qt::Checked);
+        }
+      model->item (loopback_row)->setEnabled (has_checked);
+    }
+}
+
 // get the select network interfaces from the selection combo box
 QStringList Configuration::impl::get_selected_network_interfaces (CheckableItemComboBox * combo_box)
 {

Configuration.ui

@@ -1885,7 +1885,7 @@ and DX Grid fields when a 73 or free text message is sent.</string>
             <item row="1" column="1">
              <widget class="QSpinBox" name="udp_server_port_spin_box">
               <property name="toolTip">
-               <string>&lt;html&gt;&lt;head/&gt;&lt;body&gt;&lt;p&gt;Enter the service port number of the UDP server that WSJT-X should send updates to. If this is zero no updates will be broadcast.&lt;/p&gt;&lt;/body&gt;&lt;/html&gt;</string>
+               <string>&lt;html&gt;&lt;head/&gt;&lt;body&gt;&lt;p&gt;Enter the service port number of the UDP server that WSJT-X should send updates to. If this is zero no updates will be sent.&lt;/p&gt;&lt;/body&gt;&lt;/html&gt;</string>
               </property>
               <property name="maximum">
                <number>65534</number>
@@ -1903,10 +1903,17 @@ and DX Grid fields when a 73 or free text message is sent.</string>
              </widget>
             </item>
             <item row="2" column="1">
-             <widget class="CheckableItemComboBox" name="udp_interfaces_combo_box"/>
+             <widget class="CheckableItemComboBox" name="udp_interfaces_combo_box">
+              <property name="toolTip">
+               <string>&lt;html&gt;&lt;head/&gt;&lt;body&gt;&lt;p&gt;When sending updates to a multicast group address it is necessary to specify which network interface(s) to send them to. If the loop-back interface is multicast capable then at least that one will be selected.&lt;/p&gt;&lt;p&gt;For most users the loop-back interface is all that is needed, that will allow multiple other applications on the same machine to interoperate with WSJT-X. If applications running on other hosts are to receive status updates then a suitable network interface should be used.&lt;/p&gt;&lt;p&gt;On some Linux systems it may be necessary to enable multicast on the loop-back network interface.&lt;/p&gt;&lt;/body&gt;&lt;/html&gt;</string>
+              </property>
+             </widget>
             </item>
             <item row="3" column="1">
              <widget class="QSpinBox" name="udp_TTL_spin_box">
+              <property name="toolTip">
+               <string>&lt;html&gt;&lt;head/&gt;&lt;body&gt;&lt;p&gt;Sets the number or router hops that multicast datagrams are allowed to make. Almost everyone should set this to 1 to keep outgoing multicast traffic withn the local subnet.&lt;/p&gt;&lt;/body&gt;&lt;/html&gt;</string>
+              </property>
               <property name="maximum">
                <number>255</number>
               </property>

Network/MessageClient.cpp

@@ -103,6 +103,7 @@ public:
 
 void MessageClient::impl::set_server (QString const& server_name, QStringList const& network_interface_names)
 {
+  // qDebug () << "MessageClient server:" << server_name << "port:" << server_port_ << "interfaces:" << network_interface_names;
   server_.setAddress (server_name);
   network_interfaces_.clear ();
   for (auto const& net_if_name : network_interface_names)
@@ -447,9 +448,19 @@ void MessageClient::impl::send_message (QByteArray const& message, bool queue_if
         {
           if (message != last_message_) // avoid duplicates
             {
-              for (auto const& net_if : network_interfaces_)
+              if (is_multicast_address (server_))
                 {
+                  // send datagram on each selected network interface
+                  std::for_each (network_interfaces_.begin (), network_interfaces_.end ()
+                                 , [&] (QNetworkInterface const& net_if) {
                                      setMulticastInterface (net_if);
+                                     // qDebug () << "Multicast UDP datagram sent to:" << server_ << "port:" << server_port_ << "on:" << multicastInterface ().humanReadableName ();
+                                     writeDatagram (message, server_, server_port_);
+                                   });
+                }
+              else
+                {
+                  // qDebug () << "Unicast UDP datagram sent to:" << server_ << "port:" << server_port_;
                   writeDatagram (message, server_, server_port_);
                 }
               last_message_ = message;