fix: process questions requesting unicast responses #50

src/MulticastService.cs

@@ -371,6 +371,43 @@ public void SendQuery(string name, DnsClass klass = DnsClass.IN, DnsType type =
             SendQuery(msg);
         }
 
+        /// <summary>
+        ///   Ask for answers about a name and accept unicast and/or broadcast response.
+        /// </summary>
+        /// <param name="name">
+        ///   A domain name that should end with ".local", e.g. "myservice.local".
+        /// </param>
+        /// <param name="klass">
+        ///   The class, defaults to <see cref="DnsClass.IN"/>.
+        /// </param>
+        /// <param name="type">
+        ///   The question type, defaults to <see cref="DnsType.ANY"/>.
+        /// </param>
+        /// <remarks>
+        ///   Send a "QU" question (unicast).  The most significat bit of the Class is set.
+        ///   Answers to any query are obtained on the <see cref="AnswerReceived"/>
+        ///   event.
+        /// </remarks>
+        /// <exception cref="InvalidOperationException">
+        ///   When the service has not started.
+        /// </exception>
+        public void SendUnicastQuery(string name, DnsClass klass = DnsClass.IN, DnsType type = DnsType.ANY)
+        {
+            var msg = new Message
+            {
+                Opcode = MessageOperation.Query,
+                QR = false
+            };
+            msg.Questions.Add(new Question
+            {
+                Name = name,
+                Class = (DnsClass) ((ushort)klass | 0x8000),
+                Type = type
+            });
+
+            SendQuery(msg);
+        }
+
         /// <summary>
         ///   Ask for answers.
         /// </summary>

src/ServiceDiscovery.cs

@@ -127,6 +127,18 @@ public void QueryAllServices()
             Mdns.SendQuery(ServiceName, type: DnsType.PTR);
         }
 
+        /// <summary>
+        ///    Asks other MDNS services to send their service names;
+        ///    accepts unicast and/or broadcast answers.
+        /// </summary>
+        /// <remarks>
+        ///   When an answer is received the <see cref="ServiceDiscovered"/> event is raised.
+        /// </remarks>
+        public void QueryUnicastAllServices()
+        {
+            Mdns.SendUnicastQuery(ServiceName, type: DnsType.PTR);
+        }
+
         /// <summary>
         ///   Asks instances of the specified service to send details.
         /// </summary>
@@ -142,6 +154,22 @@ public void QueryServiceInstances(string service)
             Mdns.SendQuery(service + ".local", type: DnsType.PTR);
         }
 
+        /// <summary>
+        ///   Asks instances of the specified service to send details.
+        ///   accepts unicast and/or broadcast answers.
+        /// </summary>
+        /// <param name="service">
+        ///   The service name to query. Typically of the form "_<i>service</i>._tcp".
+        /// </param>
+        /// <remarks>
+        ///   When an answer is received the <see cref="ServiceInstanceDiscovered"/> event is raised.
+        /// </remarks>
+        /// <seealso cref="ServiceProfile.ServiceName"/>
+        public void QueryUnicastServiceInstances(string service)
+        {
+            Mdns.SendUnicastQuery(service + ".local", type: DnsType.PTR);
+        }
+
         /// <summary>
         ///   Advertise a service profile.
         /// </summary>
@@ -200,7 +228,19 @@ void OnQuery(object sender, MessageEventArgs e)
 
             if (log.IsDebugEnabled)
             {
-                log.Debug($"got query from: {e.RemoteEndPoint.Address},  for {request.Questions[0].Name} {request.Questions[0].Type}");
+                log.Debug($"got query from: {e.RemoteEndPoint},  for {request.Questions[0].Name} {request.Questions[0].Type}");
+            }
+
+            // Determine if this query is requesting a unicast response
+            // and normalise the Class.
+            var QU = false; // unicast query response?
+            foreach (var r in request.Questions)
+            {
+                if (((ushort)r.Class & 0x8000) != 0)
+                {
+                    QU = true;
+                    r.Class = (DnsClass)((ushort)r.Class & 0x7fff);
+                }
             }
 
             var response = NameServer.ResolveAsync(request).Result;
@@ -222,7 +262,15 @@ void OnQuery(object sender, MessageEventArgs e)
                 response.Answers.AddRange(response.AdditionalRecords);
             }
 
-            Mdns.SendAnswer(response);
+            if (QU)
+            {
+                // TODO: Send a Unicast response if required.
+                Mdns.SendAnswer(response);
+            }
+            else
+            {
+                Mdns.SendAnswer(response);
+            }
 
             if (log.IsDebugEnabled)
             {

test/MulticastServiceTest.cs

@@ -58,6 +58,35 @@ public void SendQuery()
             }
         }
 
+        [TestMethod]
+        public void SendUnicastQuery()
+        {
+            var ready = new ManualResetEvent(false);
+            var done = new ManualResetEvent(false);
+            Message msg = null;
+
+            var mdns = new MulticastService();
+            mdns.NetworkInterfaceDiscovered += (s, e) => ready.Set();
+            mdns.QueryReceived += (s, e) =>
+            {
+                msg = e.Message;
+                done.Set();
+            };
+            try
+            {
+                mdns.Start();
+                Assert.IsTrue(ready.WaitOne(TimeSpan.FromSeconds(1)), "ready timeout");
+                mdns.SendUnicastQuery("some-service.local");
+                Assert.IsTrue(done.WaitOne(TimeSpan.FromSeconds(1)), "query timeout");
+                Assert.AreEqual("some-service.local", msg.Questions.First().Name);
+                Assert.AreEqual(DnsClass.IN + 0x8000, msg.Questions.First().Class);
+            }
+            finally
+            {
+                mdns.Stop();
+            }
+        }
+
         [TestMethod]
         public void ReceiveAnswer()
         {

test/ServiceDiscoveryTest.cs

@@ -150,6 +150,35 @@ public void Discover_AllServices()
             }
         }
 
+        [TestMethod]
+        public void Discover_AllServices_Unicast()
+        {
+            var service = new ServiceProfile("x", "_sdtest-5._udp", 1024);
+            var done = new ManualResetEvent(false);
+            var mdns = new MulticastService();
+            var sd = new ServiceDiscovery(mdns);
+
+            mdns.NetworkInterfaceDiscovered += (s, e) => sd.QueryUnicastAllServices();
+            sd.ServiceDiscovered += (s, serviceName) =>
+            {
+                if (serviceName == service.QualifiedServiceName)
+                {
+                    done.Set();
+                }
+            };
+            try
+            {
+                sd.Advertise(service);
+                mdns.Start();
+                Assert.IsTrue(done.WaitOne(TimeSpan.FromSeconds(1)), "DNS-SD query timeout");
+            }
+            finally
+            {
+                sd.Dispose();
+                mdns.Stop();
+            }
+        }
+
         [TestMethod]
         public void Discover_ServiceInstance()
         {
@@ -184,6 +213,40 @@ public void Discover_ServiceInstance()
             }
         }
 
+        [TestMethod]
+        public void Discover_ServiceInstance_Unicast()
+        {
+            var service = new ServiceProfile("y", "_sdtest-5._udp", 1024);
+            var done = new ManualResetEvent(false);
+            var mdns = new MulticastService();
+            var sd = new ServiceDiscovery(mdns);
+
+            mdns.NetworkInterfaceDiscovered += (s, e) =>
+            {
+                sd.QueryUnicastServiceInstances(service.ServiceName);
+            };
+
+            sd.ServiceInstanceDiscovered += (s, e) =>
+            {
+                if (e.ServiceInstanceName == service.FullyQualifiedName)
+                {
+                    Assert.IsNotNull(e.Message);
+                    done.Set();
+                }
+            };
+            try
+            {
+                sd.Advertise(service);
+                mdns.Start();
+                Assert.IsTrue(done.WaitOne(TimeSpan.FromSeconds(1)), "instance not found");
+            }
+            finally
+            {
+                sd.Dispose();
+                mdns.Stop();
+            }
+        }
+
         [TestMethod]
         public void Discover_ServiceInstance_WithAnswersContainingAdditionRecords()
         {