implement probing richardschneider#60

jdomnitz · May 5, 2023 · bd9992d · bd9992d
1 parent 7ef60f6
commit bd9992d
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Showing 4 changed files with 62 additions and 12 deletions.
diff --git a/src/MulticastService.cs b/src/MulticastService.cs
@@ -584,7 +584,7 @@ public void SendAnswer(Message answer, MessageEventArgs query, bool checkDuplica
             Send(answer, checkDuplicate, query.RemoteEndPoint);
         }
 
-        void Send(Message msg, bool checkDuplicate, IPEndPoint remoteEndPoint = null)
+        internal void Send(Message msg, bool checkDuplicate, IPEndPoint remoteEndPoint = null)
         {
             var packet = msg.ToByteArray();
             if (packet.Length > maxPacketSize)

diff --git a/src/ServiceDiscovery.cs b/src/ServiceDiscovery.cs
@@ -1,7 +1,9 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Security.Claims;
 using System.Threading.Tasks;
+using System.Xml.Linq;
 using Common.Logging;
 using Makaretu.Dns.Resolving;
 
@@ -17,6 +19,7 @@ public class ServiceDiscovery : IDisposable
         static readonly ILog log = LogManager.GetLogger(typeof(ServiceDiscovery));
         static readonly DomainName LocalDomain = new DomainName("local");
         static readonly DomainName SubName = new DomainName("_sub");
+        static readonly ushort transaction = (ushort)new Random().Next(10000, int.MaxValue);
 
         /// <summary>
         ///   The service discovery service name.
@@ -28,6 +31,7 @@ public class ServiceDiscovery : IDisposable
 
         readonly bool ownsMdns;
         List<ServiceProfile> profiles = new List<ServiceProfile>();
+        bool conflict;
 
         /// <summary>
         ///   Creates a new instance of the <see cref="ServiceDiscovery"/> class.
@@ -257,6 +261,40 @@ public void Advertise(ServiceProfile service)
             catalog.IncludeReverseLookupRecords();
         }
 
+        /// <summary>
+        /// Probe the network to ensure the service is unique.
+        /// </summary>
+        /// <param name="profile"></param>
+        /// <returns>True if thise service conflicts with an existing network service</returns>
+        public bool Probe(ServiceProfile profile)
+        {
+            conflict = false;
+            Message msg = new Message
+            {
+                Opcode = MessageOperation.Query,
+                QR = false,
+                Id = transaction
+            };
+            msg.Questions.Add(new Question
+            {
+                Name = profile.HostName,
+                Class = DnsClass.IN,
+                Type = DnsType.ANY
+            });
+
+            Task.Delay(new Random().Next(0, 250)).Wait();
+            Mdns.Send(msg, false);
+
+            Task.Delay(250).Wait();
+            Mdns.Send(msg, false);
+
+            Task.Delay(250).Wait();
+            Mdns.Send(msg, false);
+
+            Task.Delay(250).Wait();
+            return conflict;
+        }
+
         /// <summary>
         ///    Sends an unsolicited MDNS response describing the
         ///    service profile.
@@ -335,6 +373,11 @@ void OnAnswer(object sender, MessageEventArgs e)
             }
 
             // Any DNS-SD answers?
+            if (msg.Id == transaction)
+            {
+                if (msg.Answers.Count > 0)
+                    conflict = true;
+            }
 
             var sd = msg.Answers
                 .OfType<PTRRecord>()

diff --git a/test/ServiceDiscoveryTest.cs b/test/ServiceDiscoveryTest.cs
@@ -473,7 +473,11 @@ public void Announce_ContainsSharedRecords()
             {
                 using (var sd = new ServiceDiscovery(mdns))
                 {
-                    mdns.NetworkInterfaceDiscovered += (s, e) => sd.Announce(service);
+                    mdns.NetworkInterfaceDiscovered += (s, e) =>
+                    {
+                        Assert.IsFalse(sd.Probe(service));
+                        sd.Announce(service);
+                    };
                     mdns.Start();
                     Assert.IsTrue(done.WaitOne(TimeSpan.FromSeconds(3)), "announce timeout");
                 }
@@ -507,7 +511,12 @@ public void Announce_ContainsResourceRecords()
             {
                 using (var sd = new ServiceDiscovery(mdns))
                 {
-                    mdns.NetworkInterfaceDiscovered += (s, e) => sd.Announce(service);
+                    mdns.NetworkInterfaceDiscovered +=
+                    (s, e) =>
+                    {
+                        Assert.IsFalse(sd.Probe(service));
+                        sd.Announce(service);
+                    };
                     mdns.Start();
                     Assert.IsTrue(done.WaitOne(TimeSpan.FromSeconds(3)), "announce timeout");
                 }
@@ -543,7 +552,11 @@ public void Announce_SentTwice()
             {
                 using (var sd = new ServiceDiscovery(mdns))
                 {
-                    mdns.NetworkInterfaceDiscovered += (s, e) => sd.Announce(service);
+                    mdns.NetworkInterfaceDiscovered += (s, e) =>
+                    {
+                        Assert.IsFalse(sd.Probe(service));
+                        sd.Announce(service);
+                    };
                     mdns.Start();
                     Assert.IsTrue(done.WaitOne(TimeSpan.FromSeconds(4)), "announce timeout");
                 }

diff --git a/test/ServiceProfileTest.cs b/test/ServiceProfileTest.cs
@@ -1,17 +1,11 @@
-using Makaretu.Dns;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 using System;
-using System.Collections.Generic;
 using System.Linq;
 using System.Net;
-using System.Net.NetworkInformation;
-using System.Net.Sockets;
-using System.Threading;
-using System.Threading.Tasks;
 
 namespace Makaretu.Dns
 {
-    
+
     [TestClass]
     public class ServiveProfileTest
     {