feat(ServiceDiscovery): ServiceInstanceShutdown event #58

src/ServiceDiscovery.cs

@@ -116,6 +116,19 @@ public ServiceDiscovery(MulticastService mdns)
         /// </remarks>
         public event EventHandler<ServiceInstanceDiscoveryEventArgs> ServiceInstanceDiscovered;
 
+        /// <summary>
+        ///   Raised when a servive instance is shutting down.
+        /// </summary>
+        /// <value>
+        ///   Contains the service instance name.
+        /// </value>
+        /// <remarks>
+        ///   <b>ServiceDiscovery</b> passively monitors the network for any answers.
+        ///   When an answer containing a PTR to a service instance with a
+        ///   TTL of zero is received this event is raised.
+        /// </remarks>
+        public event EventHandler<ServiceInstanceShutdownEventArgs> ServiceInstanceShutdown;
+
         /// <summary>
         ///    Asks other MDNS services to send their service names.
         /// </summary>
@@ -232,6 +245,14 @@ public void Unadvertise()
         void OnAnswer(object sender, MessageEventArgs e)
         {
             var msg = e.Message;
+            if (log.IsDebugEnabled)
+            {
+                log.Debug($"Answer from {e.RemoteEndPoint}");
+            }
+            if (log.IsTraceEnabled)
+            {
+                log.Trace(msg);
+            }
 
             // Any DNS-SD answers?
             var sd = msg.Answers.OfType<PTRRecord>();
@@ -241,6 +262,15 @@ void OnAnswer(object sender, MessageEventArgs e)
                 {
                     ServiceDiscovered?.Invoke(this, ptr.DomainName);
                 }
+                else if (ptr.TTL == TimeSpan.Zero)
+                {
+                    var args = new ServiceInstanceShutdownEventArgs
+                    {
+                        ServiceInstanceName = ptr.DomainName,
+                        Message = msg
+                    };
+                    ServiceInstanceShutdown?.Invoke(this, args);
+                }
                 else
                 {
                     var args = new ServiceInstanceDiscoveryEventArgs

src/ServiceInstanceShutdownEventArgs.cs

@@ -0,0 +1,23 @@
+using Makaretu.Dns;
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Makaretu.Dns
+{
+    /// <summary>
+    ///   The event data for <see cref="ServiceDiscovery.ServiceInstanceShutdown"/>.
+    /// </summary>
+    public class ServiceInstanceShutdownEventArgs : MessageEventArgs
+    {
+        /// <summary>
+        ///   The fully qualified name of the service instance.
+        /// </summary>
+        /// <value>
+        ///   Typically of the form "<i>instance</i>._<i>service</i>._tcp.local".
+        /// </value>
+        /// <seealso cref="ServiceProfile.FullyQualifiedName"/>
+        public string ServiceInstanceName { get; set; }
+    }
+}
+

test/ServiceDiscoveryTest.cs

@@ -291,5 +291,35 @@ public void Discover_ServiceInstance_WithAnswersContainingAdditionRecords()
                 Assert.AreEqual(additionalRecordsCount + 1, discovered.Answers.Count);
             }
         }
+
+        [TestMethod]
+        public void Unadvertise()
+        {
+            var service = new ServiceProfile("z", "_sdtest-7._udp", 1024);
+            var done = new ManualResetEvent(false);
+            var mdns = new MulticastService();
+            var sd = new ServiceDiscovery(mdns);
+
+            mdns.NetworkInterfaceDiscovered += (s, e) => sd.QueryAllServices();
+            sd.ServiceInstanceShutdown += (s, e) =>
+            {
+                if (e.ServiceInstanceName == service.FullyQualifiedName)
+                {
+                    done.Set();
+                }
+            };
+            try
+            {
+                sd.Advertise(service);
+                mdns.Start();
+                sd.Unadvertise(service);
+                Assert.IsTrue(done.WaitOne(TimeSpan.FromSeconds(1)), "goodbye timeout");
+            }
+            finally
+            {
+                sd.Dispose();
+                mdns.Stop();
+            }
+        }
     }
 }