CSHARP-5200: Allow valid SRV hostnames with less than 3 parts (#1527)

* CSHARP-5200: Allow valid SRV hostnames with less than 3 parts

* Some corrections

* Small simplification

* Corrections according to PR

* Permalink

* Improved check

* Small fix

Author: papafe

src/MongoDB.Driver/Core/Configuration/ConnectionString.cs

@@ -1358,33 +1358,24 @@ private void ValidateResolvedHosts(string original, List<string> resolved)
 
         internal static bool HasValidParentDomain(string original, DnsEndPoint resolvedEndPoint)
         {
-            // Helper functions...
-            Func<string, string[]> getParentParts = x => x.Split('.').Skip(1).ToArray();
-
-            // Indicates whether "a" ends with "b"
-            Func<string[], string[], bool> endsWith = (a, b) =>
-            {
-                if (a.Length < b.Length)
-                {
-                    return false;
-                }
+            var host = resolvedEndPoint.Host;
 
-                // loop from back to front making sure that all of b is at the back of a, in order.
-                for (int ai = a.Length - 1, bi = b.Length - 1; bi >= 0; ai--, bi--)
-                {
-                    if (a[ai] != b[bi])
-                    {
-                        return false;
-                    }
-                }
+            var hostDotCount = host.Count(c => c == '.');
+            var originalDotCount = original.Count(c => c == '.');
 
-                return true;
-            };
+            // If original has less than 3 dot separated parts,
+            // the returned hostname must have at least one more domain level than original
+            if (originalDotCount < 2)
+            {
+                return host.Length > original.Length &&
+                       hostDotCount > originalDotCount &&
+                       host.EndsWith(original, StringComparison.Ordinal) &&
+                       host[host.Length - original.Length -1 ] == '.';
+            }
 
-            // make sure that the resolve host ends with domain of the parent.
-            var originalParentParts = getParentParts(original);
-            var host = resolvedEndPoint.Host;
-            return endsWith(getParentParts(host), originalParentParts);
+            // We check that the returned hostname has the same domain name as original
+            var originalFirstDotIndex = original.IndexOf('.');
+            return hostDotCount >= originalDotCount && host.AsSpan().EndsWith(original.AsSpan(originalFirstDotIndex), StringComparison.Ordinal);
         }
 
         private void ValidateResolvedOptions(IEnumerable<string> optionNames)

tests/MongoDB.Driver.Tests/Specifications/initial-dns-seedlist-discovery/prose-tests/SrvPartsTests.cs

@@ -0,0 +1,101 @@
+/* Copyright 2010-present MongoDB Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+using System;
+using System.Collections.Generic;
+using System.Net;
+using System.Threading;
+using System.Threading.Tasks;
+using FluentAssertions;
+using MongoDB.Driver.Core.Configuration;
+using MongoDB.Driver.Core.Misc;
+using Xunit;
+
+namespace MongoDB.Driver.Tests.Specifications.initial_dns_seedlist_discovery.prose_tests
+{
+    public class SrvPartsTests
+    {
+        // https://github.com/mongodb/specifications/blob/master/source/initial-dns-seedlist-discovery/tests/README.md#1-allow-srvs-with-fewer-than-3--separated-parts
+        [Theory]
+        [InlineData("mongodb+srv://localhost")]
+        [InlineData("mongodb+srv://mongo.local")]
+        public void Allow_srv_with_fewer_than_3_parts(string uri)
+        {
+            var exception = Record.Exception(() => new ConnectionString(uri));
+
+            exception.Should().BeNull();
+        }
+
+        // https://github.com/mongodb/specifications/blob/master/source/initial-dns-seedlist-discovery/tests/README.md#2-throw-when-return-address-does-not-end-with-srv-domain
+        [Theory]
+        [InlineData("mongodb+srv://localhost", "localhost.mongodb")]
+        [InlineData("mongodb+srv://mongo.local", "test_1.evil.local")]
+        [InlineData("mongodb+srv://blogs.mongodb.com", "blogs.evil.com")]
+        public void Throw_when_return_address_does_not_end_with_srv_domain(string uri, string resolvedHost)
+        {
+            var connectionString = new ConnectionString(uri, true, new MockDnsResolver(resolvedHost));
+            var exception = Record.Exception(() => connectionString.Resolve());
+
+            exception.Should().BeOfType<MongoConfigurationException>().
+                Which.Message.Should().Be("Hosts in the SRV record must have the same parent domain as the seed host.");
+        }
+
+        // https://github.com/mongodb/specifications/blob/master/source/initial-dns-seedlist-discovery/tests/README.md#3-throw-when-return-address-is-identical-to-srv-hostname
+        [Theory]
+        [InlineData("mongodb+srv://localhost", "localhost")]
+        [InlineData("mongodb+srv://mongo.local", "mongo.local")]
+        public void Throw_when_return_address_is_identical_to_srv_hostname(string uri, string resolvedHost)
+        {
+            var connectionString = new ConnectionString(uri, true, new MockDnsResolver(resolvedHost));
+            var exception = Record.Exception(() => connectionString.Resolve());
+
+            exception.Should().BeOfType<MongoConfigurationException>().
+                Which.Message.Should().Be("Hosts in the SRV record must have the same parent domain as the seed host.");
+        }
+
+        // https://github.com/mongodb/specifications/blob/master/source/initial-dns-seedlist-discovery/tests/README.md#4-throw-when-return-address-does-not-contain--separating-shared-part-of-domain
+        [Theory]
+        [InlineData("mongodb+srv://localhost", "test_1.cluster_1localhost")]
+        [InlineData("mongodb+srv://mongo.local", "test_1.my_hostmongo.local")]
+        [InlineData("mongodb+srv://blogs.mongodb.com", "cluster.testmongodb.com")]
+        public void Throw_when_return_address_does_not_contain_dot_separating_shared_part_of_domain(string uri, string resolvedHost)
+        {
+            var connectionString = new ConnectionString(uri, true, new MockDnsResolver(resolvedHost));
+            var exception = Record.Exception(() => connectionString.Resolve());
+
+            exception.Should().BeOfType<MongoConfigurationException>().
+                Which.Message.Should().Be("Hosts in the SRV record must have the same parent domain as the seed host.");
+        }
+
+        private class MockDnsResolver(string dnsEndPointString) : IDnsResolver
+        {
+            public List<SrvRecord> ResolveSrvRecords(string service, CancellationToken cancellation)
+            {
+                return new List<SrvRecord>
+                    { new SrvRecord(new DnsEndPoint(dnsEndPointString, 2090), TimeSpan.MaxValue) };
+            }
+
+            public List<TxtRecord> ResolveTxtRecords(string domainName, CancellationToken cancellation)
+                => throw new NotImplementedException();
+
+            public Task<List<SrvRecord>> ResolveSrvRecordsAsync(string service, CancellationToken cancellation)
+                => throw new NotImplementedException();
+
+            public Task<List<TxtRecord>> ResolveTxtRecordsAsync(string domainName, CancellationToken cancellation)
+                => throw new NotImplementedException();
+
+        }
+    }
+}