[WIP] message validation

src/Message.cs

@@ -9,7 +9,7 @@ namespace Makaretu.Dns
     ///   All communications inside of the domain protocol are carried in a single
     ///   format called a message.
     /// </summary>
-    public class Message : DnsObject
+    public partial class Message : DnsObject
     {
         /// <summary>
         ///   The least significant 4 bits of the opcode.
@@ -134,7 +134,7 @@ public MessageOperation Opcode
         ///    authority for the domain name in question section.
         ///    
         ///    Note that the contents of the answer section may have
-        ///    multiple owner names because of aliases.The AA bit
+        ///    multiple owner names because of aliases. The AA bit
         ///    corresponds to the name which matches the query name, or
         ///    the first owner name in the answer section.
         /// </summary>
@@ -144,7 +144,7 @@ public MessageOperation Opcode
         public bool AA { get; set; }
 
         /// <summary>
-        ///   TrunCation - specifies that this message was truncated
+        ///   Truncation - specifies that this message was truncated
         ///   due to length greater than that permitted on the
         ///   transmission channel.
         /// </summary>
@@ -167,7 +167,7 @@ public MessageOperation Opcode
         public bool RD { get; set; }
 
         /// <summary>
-        ///    Recursion Available - this be is set or cleared in a
+        ///    Recursion Available - this bit is set or cleared in a
         ///    response, and denotes whether recursive query support is
         ///    available in the name server.
         /// </summary>

src/MessageValidation.cs

@@ -0,0 +1,81 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Makaretu.Dns
+{
+    public partial class Message
+    {
+        /// <summary>
+        ///   Throws if the response is invalid.
+        /// </summary>
+        /// <param name="response">
+        ///   The response to this query.
+        /// </param>
+        /// <param name="resolver">
+        ///   Used to obtain the <see cref="DNSKEYRecord"/> and <see cref="DSRecord"/>
+        ///   resource records when doing DNSEC validations.
+        /// </param>
+        /// <param name="cancel">
+        ///   Is used to stop the task.  When cancelled, the <see cref="TaskCanceledException"/> is raised.
+        /// </param>
+        /// <exception cref="Exception">
+        ///   When the <paramref name="response"/> is not valid.
+        /// </exception>
+        /// <seealso cref="ValidateResponseAsync"/>
+        public async Task EnsureValidResponseAsync(
+            Message response,
+            IResolver resolver,
+            CancellationToken cancel = default(CancellationToken)
+            )
+        {
+            var reason = await ValidateResponseAsync(response, resolver, cancel);
+            if (reason != null)
+                throw new Exception(reason);
+        }
+
+        /// <summary>
+        ///   Validate the response to a query.
+        /// </summary>
+        /// <param name="response">
+        ///   The response to this query.
+        /// </param>
+        /// <param name="resolver">
+        ///   Used to obtain the <see cref="DNSKEYRecord"/> and <see cref="DSRecord"/>
+        ///   resource records when doing DNSEC validations.
+        /// </param>
+        /// <param name="cancel">
+        ///   Is used to stop the task.  When cancelled, the <see cref="TaskCanceledException"/> is raised.
+        /// </param>
+        /// <returns>
+        ///   A task that represents the asynchronous operation. The task's value is
+        ///  <b>null</b> if the <paramref name="response"/> is valid; otherwise, a
+        ///  <see cref="string"/> containing the reason why the response is invalid.
+        /// </returns>
+        /// <seealso cref="EnsureValidResponseAsync"/>
+        public async Task<string> ValidateResponseAsync(
+            Message response,
+            IResolver resolver,
+            CancellationToken cancel = default(CancellationToken)
+            )
+        {
+            if (!response.QR)
+                return "Not a response, QR is not set.";
+            if (Id != response.Id)
+                return "Response and query IDs are not equal.";
+            if (response.Status == MessageStatus.NoError 
+                && (response.Answers.Count + response.AuthorityRecords.Count == 0))
+                return "No answers.";
+            // TODO: if MXDOMAIN needs an SOA authority record
+
+            // TODO: DNSSEC
+
+            // Everything is good.
+            return null;
+        }
+
+    }
+}

test/MessageValidationTest.cs

@@ -0,0 +1,103 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net;
+using System.Threading.Tasks;
+
+namespace Makaretu.Dns
+{
+
+    [TestClass]
+    public class MessageValidationTest
+    {
+        [TestMethod]
+        public async Task EnsureValidResponse()
+        {
+            var query = new Message
+            {
+                Id = 1234,
+                Questions = { new Question { Name = "foo.bar", Type = DnsType.A } }
+            };
+            var response = query.CreateResponse();
+            response.Answers.Add(AddressRecord.Create("foo.bar", IPAddress.Loopback));
+
+            await query.EnsureValidResponseAsync(response, null);
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(Exception))]
+        public async Task EnsureValidResponse_Throws()
+        {
+            var query = new Message
+            {
+                Id = 1234,
+                Questions = { new Question { Name = "foo.bar", Type = DnsType.A } }
+            };
+            var response = query.CreateResponse();
+            response.Id = 4321;
+            response.Answers.Add(AddressRecord.Create("foo.bar", IPAddress.Loopback));
+
+            await query.EnsureValidResponseAsync(response, null);
+        }
+
+
+        [TestMethod]
+        public async Task ValidateResponse()
+        {
+            var query = new Message
+            {
+                Id = 1234,
+                Questions = { new Question { Name = "foo.bar", Type = DnsType.A } }
+            };
+            var response = query.CreateResponse();
+            response.Answers.Add(AddressRecord.Create("foo.bar", IPAddress.Loopback));
+
+            var failure = await query.ValidateResponseAsync(response, null);
+            Assert.AreEqual(null, failure);
+        }
+
+        [TestMethod]
+        public async Task ValidateResponse_WrongID()
+        {
+            var query = new Message
+            {
+                Id = 1234,
+                Questions = { new Question { Name = "foo.bar", Type = DnsType.A } }
+            };
+            var response = query.CreateResponse();
+            response.Id = 4321;
+            response.Answers.Add(AddressRecord.Create("foo.bar", IPAddress.Loopback));
+
+            var failure = await query.ValidateResponseAsync(response, null);
+            Assert.IsNotNull(failure);
+        }
+
+        [TestMethod]
+        public async Task ValidateResponse_QR()
+        {
+            var query = new Message
+            {
+                Id = 1234,
+                Questions = { new Question { Name = "foo.bar", Type = DnsType.A } }
+            };
+
+            var failure = await query.ValidateResponseAsync(query, null);
+            Assert.IsNotNull(failure);
+        }
+
+        [TestMethod]
+        public async Task ValidateResponse_MissingAnswer()
+        {
+            var query = new Message
+            {
+                Id = 1234,
+                Questions = { new Question { Name = "foo.bar", Type = DnsType.A } }
+            };
+            var response = query.CreateResponse();
+
+            var failure = await query.ValidateResponseAsync(response, null);
+            Assert.IsNotNull(failure);
+        }
+    }
+}