From a4d496cdb067155cb3b988a93e0ec967168cf20f Mon Sep 17 00:00:00 2001
From: Bill Somerville <bill@classdesign.com>
Date: Fri, 11 Jan 2019 23:17:43 +0000
Subject: [PATCH] UDP Message Server now joins a multicast group on all
 available multicast capable network interfaces

---
 MessageServer.cpp | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/MessageServer.cpp b/MessageServer.cpp
index 609d24a9a..0748bcaa0 100644
--- a/MessageServer.cpp
+++ b/MessageServer.cpp
@@ -2,6 +2,7 @@
 
 #include <stdexcept>
 
+#include <QNetworkInterface>
 #include <QUdpSocket>
 #include <QString>
 #include <QTimer>
@@ -95,16 +96,30 @@ MessageServer::impl::BindMode constexpr MessageServer::impl::bind_mode_;
 
 void MessageServer::impl::leave_multicast_group ()
 {
-  if (!multicast_group_address_.isNull () && BoundState == state ())
+  if (!multicast_group_address_.isNull () && BoundState == state ()
+#if QT_VERSION >= 0x050600
+      && multicast_group_address_.isMulticast ()
+#endif
+      )
     {
-      leaveMulticastGroup (multicast_group_address_);
+      for (auto const& interface : QNetworkInterface::allInterfaces ())
+        {
+          if (QNetworkInterface::CanMulticast & interface.flags ())
+            {
+              leaveMulticastGroup (multicast_group_address_, interface);
+            }
+        }
     }
 }
 
 void MessageServer::impl::join_multicast_group ()
 {
   if (BoundState == state ()
-      && !multicast_group_address_.isNull ())
+      && !multicast_group_address_.isNull ()
+#if QT_VERSION >= 0x050600
+      && multicast_group_address_.isMulticast ()
+#endif
+      )
     {
       if (IPv4Protocol == multicast_group_address_.protocol ()
           && IPv4Protocol != localAddress ().protocol ())
@@ -112,7 +127,15 @@ void MessageServer::impl::join_multicast_group ()
           close ();
           bind (QHostAddress::AnyIPv4, port_, bind_mode_);
         }
-      if (!joinMulticastGroup (multicast_group_address_))
+      bool joined {false};
+      for (auto const& interface : QNetworkInterface::allInterfaces ())
+        {
+          if (QNetworkInterface::CanMulticast & interface.flags ())
+            {
+              joined |= joinMulticastGroup (multicast_group_address_, interface);
+            }
+        }
+      if (!joined)
         {
           multicast_group_address_.clear ();
         }