Announce a service

src/MulticastService.cs

@@ -132,6 +132,7 @@ public MulticastService(Func<IEnumerable<NetworkInterface>, IEnumerable<NetworkI
 
             UseIpv4 = Socket.OSSupportsIPv4;
             UseIpv6 = Socket.OSSupportsIPv6;
+            IgnoreDuplicateMessages = true;
         }
 
         /// <summary>
@@ -150,6 +151,18 @@ public MulticastService(Func<IEnumerable<NetworkInterface>, IEnumerable<NetworkI
         /// </value>
         public bool UseIpv6 { get; set; }
 
+        /// <summary>
+        ///   Determines if received messages are checked for duplicates.
+        /// </summary>
+        /// <value>
+        ///   <b>true</b> to ignore duplicate messages. Defaults to <b>true</b>.
+        /// </value>
+        /// <remarks>
+        ///   When set, a message that has been received within the last minute
+        ///   will be ignored.
+        /// </remarks>
+        public bool IgnoreDuplicateMessages { get; set; }
+
         /// <summary>
         ///   The interval for discovering network interfaces.
         /// </summary>
@@ -619,7 +632,7 @@ void Send(Message msg, bool checkDuplicate, IPEndPoint remoteEndPoint = null)
         public void OnDnsMessage(object sender, UdpReceiveResult result)
         {
             // If recently received, then ignore.
-            if (!receivedMessages.TryAdd(result.Buffer))
+            if (IgnoreDuplicateMessages && !receivedMessages.TryAdd(result.Buffer))
             {
                 return;
             }

src/ServiceDiscovery.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading.Tasks;
 using Common.Logging;
 using Makaretu.Dns.Resolving;
 
@@ -256,6 +257,40 @@ public void Advertise(ServiceProfile service)
             catalog.IncludeReverseLookupRecords();
         }
 
+        /// <summary>
+        ///    Sends an unsolicited MDNS response describing the
+        ///    service profile.
+        /// </summary>
+        /// <param name="profile">
+        ///   The profile to describe.
+        /// </param>
+        /// <remarks>
+        ///   Sends a MDNS response <see cref="Message"/> containing the pointer
+        ///   and resource records of the <paramref name="profile"/>.
+        ///   <para>
+        ///   To provide increased robustness against packet loss,
+        ///   two unsolicited responses are sent one second apart.
+        ///   </para>
+        /// </remarks>
+        public void Announce(ServiceProfile profile)
+        {
+            var message = new Message { QR = true };
+
+            // Add the shared records.
+            var ptrRecord = new PTRRecord { Name = profile.QualifiedServiceName, DomainName = profile.FullyQualifiedName };
+            message.Answers.Add(ptrRecord);
+
+            // Add the resource records.
+            profile.Resources.ForEach((resource) =>
+            {
+                message.Answers.Add(resource);
+            });
+
+            Mdns.SendAnswer(message, checkDuplicate: false);
+            Task.Delay(1000).Wait();
+            Mdns.SendAnswer(message, checkDuplicate: false);
+        }
+
         /// <summary>
         /// Sends a goodbye message for the provided
         /// profile and removes its pointer from the name sever.

test/MulticastServiceTest.cs

@@ -19,6 +19,7 @@ public void Can_Create()
         {
             var mdns = new MulticastService();
             Assert.IsNotNull(mdns);
+            Assert.IsTrue(mdns.IgnoreDuplicateMessages);
         }
 
         [TestMethod]

test/ServiceDiscoveryTest.cs

@@ -454,5 +454,104 @@ public void ResourceRecords()
             }
         }
 
+        [TestMethod]
+        public void Announce_ContainsSharedRecords()
+        {
+            var service = new ServiceProfile("z", "_sdtest-4._udp", 1024, new[] { IPAddress.Loopback });
+            var done = new ManualResetEvent(false);
+
+            var mdns = new MulticastService();
+            mdns.AnswerReceived += (s, e) =>
+            {
+                var msg = e.Message;
+                if (msg.Answers.OfType<PTRRecord>().Any(p => p.DomainName == service.FullyQualifiedName))
+                {
+                    done.Set();
+                }
+            };
+            try
+            {
+                using (var sd = new ServiceDiscovery(mdns))
+                {
+                    mdns.NetworkInterfaceDiscovered += (s, e) => sd.Announce(service);
+                    mdns.Start();
+                    Assert.IsTrue(done.WaitOne(TimeSpan.FromSeconds(3)), "announce timeout");
+                }
+            }
+            finally
+            {
+                mdns.Stop();
+            }
+        }
+
+        [TestMethod]
+        public void Announce_ContainsResourceRecords()
+        {
+            var service = new ServiceProfile("z", "_sdtest-4._udp", 1024, new[] { IPAddress.Loopback });
+            var done = new ManualResetEvent(false);
+
+            var mdns = new MulticastService();
+            mdns.AnswerReceived += (s, e) =>
+            {
+                var msg = e.Message;
+                foreach (var r in service.Resources)
+                {
+                    if (!msg.Answers.Contains(r))
+                    {
+                        return;
+                    }
+                }
+                done.Set();
+            };
+            try
+            {
+                using (var sd = new ServiceDiscovery(mdns))
+                {
+                    mdns.NetworkInterfaceDiscovered += (s, e) => sd.Announce(service);
+                    mdns.Start();
+                    Assert.IsTrue(done.WaitOne(TimeSpan.FromSeconds(3)), "announce timeout");
+                }
+            }
+            finally
+            {
+                mdns.Stop();
+            }
+        }
+
+        [TestMethod]
+        public void Announce_SentTwice()
+        {
+            var service = new ServiceProfile("z", "_sdtest-4._udp", 1024, new[] { IPAddress.Loopback });
+            var done = new ManualResetEvent(false);
+            var nanswers = 0;
+            var mdns = new MulticastService
+            {
+                IgnoreDuplicateMessages = false
+            };
+            mdns.AnswerReceived += (s, e) =>
+            {
+                var msg = e.Message;
+                if (msg.Answers.OfType<PTRRecord>().Any(p => p.DomainName == service.FullyQualifiedName))
+                {
+                    if (++nanswers == 2)
+                    {
+                        done.Set();
+                    }
+                }
+            };
+            try
+            {
+                using (var sd = new ServiceDiscovery(mdns))
+                {
+                    mdns.NetworkInterfaceDiscovered += (s, e) => sd.Announce(service);
+                    mdns.Start();
+                    Assert.IsTrue(done.WaitOne(TimeSpan.FromSeconds(4)), "announce timeout");
+                }
+            }
+            finally
+            {
+                mdns.Stop();
+            }
+        }
     }
 }