CSHARP-1255: fixed issue with prefixed mapped fields interferring wit…

…h other unmapped and ignored fields.

src/MongoDB.Bson.Tests/IO/TrieNameDecoderTests.cs

@@ -0,0 +1,69 @@
+/* Copyright 2010-2014 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.IO;
+using FluentAssertions;
+using MongoDB.Bson.IO;
+using NUnit.Framework;
+
+namespace MongoDB.Bson.Tests.IO
+{
+    public class TrieNameDecoderTests
+    {
+        [Test]
+        public void Should_read_name_when_trie_does_not_know_about_the_name()
+        {
+            var trie = new BsonTrie<int>();
+            trie.Add("known", 10);
+
+            Assert(trie, "different");
+        }
+
+        [Test]
+        public void Should_read_name_when_trie_holds_a_longer_version_of_the_name()
+        {
+            var trie = new BsonTrie<int>();
+            trie.Add("longer", 10);
+
+            Assert(trie, "long");
+        }
+
+        [Test]
+        public void Should_read_name_when_trie_knows_about_the_name()
+        {
+            var trie = new BsonTrie<int>();
+            trie.Add("known", 10);
+
+            Assert(trie, "known");
+        }
+
+        private void Assert(BsonTrie<int> trie, string name)
+        {
+            var subject = new TrieNameDecoder<int>(trie);
+
+            using (var memoryStream = new MemoryStream())
+            using (var bsonStream = new BsonStreamAdapter(memoryStream))
+            {
+                bsonStream.WriteCString(name);
+                bsonStream.WriteInt32(20);
+                bsonStream.Position = 0;
+
+                var result = subject.Decode(bsonStream, Utf8Encodings.Strict);
+
+                result.Should().Be(name);
+            }
+        }
+    }
+}

src/MongoDB.Bson.Tests/MongoDB.Bson.Tests.csproj

@@ -97,6 +97,7 @@
     <Compile Include="IO\MultiChunkBufferTests.cs" />
     <Compile Include="IO\OutputBufferChunkSourceTests.cs" />
     <Compile Include="IO\SingleChunkBufferTests.cs" />
+    <Compile Include="IO\TrieNameDecoderTests.cs" />
     <Compile Include="Jira\CSharp728Tests.cs" />
     <Compile Include="Jira\CSharp708Tests.cs" />
     <Compile Include="Jira\CSharp476Tests.cs" />

src/MongoDB.Bson/IO/TrieNameDecoder.cs

@@ -77,6 +77,7 @@ public TValue Value
         public string Decode(BsonStream stream, UTF8Encoding encoding)
         {
             BsonTrieNode<TValue> node;
+            var oldPosition = stream.Position;
             if (_trie.TryGetNode(stream, out node))
             {
                 if (node.HasValue)
@@ -85,6 +86,8 @@ public string Decode(BsonStream stream, UTF8Encoding encoding)
                     _value = node.Value;
                     return node.ElementName;
                 }
+
+                stream.Position = oldPosition;
             }
 
             return stream.ReadCString(encoding);