fix: don't set UdpClient.DontFragment on OSX (#116)

* Wrap DontFragment assignment in a catch for OSX

dotnet/runtime#27653

Fixes #115

* Don't attempt to set fragmentation on OSX

Transport/BacnetIpUdpProtocolTransport.cs

@@ -100,7 +100,7 @@ private void Open()
                 if (!string.IsNullOrEmpty(_localEndpoint)) ep = new IPEndPoint(IPAddress.Parse(_localEndpoint), SharedPort);
                 DisableConnReset(_sharedConn);
                 _sharedConn.Client.Bind(ep);
-                _sharedConn.DontFragment = _dontFragment;
+                SetDontFragment(_sharedConn, _dontFragment);
                 Log.Info($"Binded shared {ep} using UDP");
             }
             /* This is our own exclusive port. We'll recieve everything sent to this. */
@@ -120,10 +120,9 @@ private void Open()
                 // minutes ... yes it's like this at least on several systems
                 _exclusiveConn = new UdpClient(ep)
                 {
-                    DontFragment = _dontFragment,
                     EnableBroadcast = true
                 };
-
+                SetDontFragment(_exclusiveConn, _dontFragment);
                 DisableConnReset(_exclusiveConn);
             }
         }
@@ -134,20 +133,43 @@ private void Open()
             _exclusiveConn = new UdpClient { ExclusiveAddressUse = true };
             DisableConnReset(_exclusiveConn);
             _exclusiveConn.Client.Bind(ep);
-            _exclusiveConn.DontFragment = _dontFragment;
+            SetDontFragment(_exclusiveConn, _dontFragment);
             _exclusiveConn.EnableBroadcast = true;
             Log.Info($"Binded exclusively to {ep} using UDP");
         }
 
         Bvlc = new BVLC(this);
     }
 
-    /// <summary>
-    ///   Done to prevent exceptions in Socket.BeginReceive()
-    /// </summary>
-    /// <remarks>
-    ///   http://microsoft.public.win32.programmer.networks.narkive.com/RlxW2V6m/udp-comms-and-connection-reset-problem
-    /// </remarks>
+    /// <summary>
+    ///   Prevent exception on setting Don't Fragment on OSX
+    /// </summary>
+    /// <remarks>
+    ///   https://github.com/dotnet/runtime/issues/27653
+    /// </remarks>
+    /// <param name="client"></param>
+    /// <param name="dontFragment"></param>
+    private void SetDontFragment(UdpClient client, bool dontFragment)
+    {
+        if (Environment.OSVersion.Platform != PlatformID.MacOSX)
+        {
+            try
+            {
+                client.DontFragment = dontFragment;
+            }
+            catch (SocketException e)
+            {
+                Log.WarnFormat("Unable to set DontFragment", e);
+            }
+        }
+    }
+
+    /// <summary>
+    ///   Done to prevent exceptions in Socket.BeginReceive()
+    /// </summary>
+    /// <remarks>
+    ///   http://microsoft.public.win32.programmer.networks.narkive.com/RlxW2V6m/udp-comms-and-connection-reset-problem
+    /// </remarks>
     private static void DisableConnReset(UdpClient client)
     {
         if (Environment.OSVersion.Platform == PlatformID.Win32NT)