CSHARP-4475: Add an AllowedTypes filter to ObjectSerializer.

src/MongoDB.Bson/Serialization/BsonSerializer.cs

@@ -678,6 +678,28 @@ public static void RegisterSerializer(Type type, IBsonSerializer serializer)
             serializer.Serialize(context, args, value);
         }
 
+        /// <summary>
+        /// Tries to register a serializer for a type.
+        /// </summary>
+        /// <param name="serializer">The serializer.</param>
+        /// <param name="type">The type.</param>
+        /// <returns>True if the serializer was registered on this call, false if the same serializer was already registered on a previous call, throws an exception if a different serializer was already registered.</returns>
+        public static bool TryRegisterSerializer(Type type, IBsonSerializer serializer)
+        {
+            return __serializerRegistry.TryRegisterSerializer(type, serializer);
+        }
+
+        /// <summary>
+        /// Tries to register a serializer for a type.
+        /// </summary>
+        /// <typeparam name="T">The type.</typeparam>
+        /// <param name="serializer">The serializer.</param>
+        /// <returns>True if the serializer was registered on this call, false if the same serializer was already registered on a previous call, throws an exception if a different serializer was already registered.</returns>
+        public static bool TryRegisterSerializer<T>(IBsonSerializer<T> serializer)
+        {
+            return TryRegisterSerializer(typeof(T), serializer);
+        }
+
         // internal static methods
         internal static void EnsureKnownTypesAreRegistered(Type nominalType)
         {

src/MongoDB.Bson/Serialization/BsonSerializerRegistry.cs

@@ -93,17 +93,7 @@ public void RegisterSerializer(Type type, IBsonSerializer serializer)
             {
                 throw new ArgumentNullException("serializer");
             }
-            var typeInfo = type.GetTypeInfo();
-            if (typeof(BsonValue).GetTypeInfo().IsAssignableFrom(type))
-            {
-                var message = string.Format("A serializer cannot be registered for type {0} because it is a subclass of BsonValue.", BsonUtils.GetFriendlyTypeName(type));
-                throw new BsonSerializationException(message);
-            }
-            if (typeInfo.IsGenericType && typeInfo.ContainsGenericParameters)
-            {
-                var message = string.Format("Generic type {0} has unassigned type parameters.", BsonUtils.GetFriendlyTypeName(type));
-                throw new ArgumentException(message, "type");
-            }
+            EnsureRegisteringASerializerForThisTypeIsAllowed(type);
 
             if (!_cache.TryAdd(type, serializer))
             {
@@ -127,6 +117,40 @@ public void RegisterSerializationProvider(IBsonSerializationProvider serializati
             _serializationProviders.Push(serializationProvider);
         }
 
+        /// <summary>
+        /// Tries to register the serializer.
+        /// </summary>
+        /// <param name="type">The type.</param>
+        /// <param name="serializer">The serializer.</param>
+        /// <returns>True if the serializer was registered on this call, false if the same serializer was already registered on a previous call, throws an exception if a different serializer was already registered.</returns>
+        public bool TryRegisterSerializer(Type type, IBsonSerializer serializer)
+        {
+            if (type == null)
+            {
+                throw new ArgumentNullException(nameof(type));
+            }
+            if (serializer == null)
+            {
+                throw new ArgumentNullException(nameof(serializer));
+            }
+            EnsureRegisteringASerializerForThisTypeIsAllowed(type);
+
+            if (_cache.TryAdd(type, serializer))
+            {
+                return true;
+            }
+            else
+            {
+                var existingSerializer = _cache[type];
+                if (!existingSerializer.Equals(serializer))
+                {
+                    var message = $"There is already a different serializer registered for type {BsonUtils.GetFriendlyTypeName(type)}.";
+                    throw new BsonSerializationException(message);
+                }
+                return false;
+            }
+        }
+
         // private methods
         private IBsonSerializer CreateSerializer(Type type)
         {
@@ -153,5 +177,20 @@ private IBsonSerializer CreateSerializer(Type type)
             var message = string.Format("No serializer found for type {0}.", type.FullName);
             throw new BsonSerializationException(message);
         }
+
+        private void EnsureRegisteringASerializerForThisTypeIsAllowed(Type type)
+        {
+            var typeInfo = type.GetTypeInfo();
+            if (typeof(BsonValue).GetTypeInfo().IsAssignableFrom(type))
+            {
+                var message = string.Format("A serializer cannot be registered for type {0} because it is a subclass of BsonValue.", BsonUtils.GetFriendlyTypeName(type));
+                throw new BsonSerializationException(message);
+            }
+            if (typeInfo.IsGenericType && typeInfo.ContainsGenericParameters)
+            {
+                var message = string.Format("Generic type {0} has unassigned type parameters.", BsonUtils.GetFriendlyTypeName(type));
+                throw new ArgumentException(message, "type");
+            }
+        }
     }
 }

src/MongoDB.Bson/Serialization/Serializers/BsonClassMapSerializer.cs

@@ -651,13 +651,23 @@ private void SerializeDiscriminator(BsonSerializationContext context, Type nomin
 
         private void SerializeMember(BsonSerializationContext context, object obj, BsonMemberMap memberMap)
         {
-            if (memberMap != _classMap.ExtraElementsMemberMap)
+            try
             {
-                SerializeNormalMember(context, obj, memberMap);
+                if (memberMap != _classMap.ExtraElementsMemberMap)
+                {
+                    SerializeNormalMember(context, obj, memberMap);
+                }
+                else
+                {
+                    SerializeExtraElements(context, obj, memberMap);
+                }
             }
-            else
+            catch (Exception ex)
             {
-                SerializeExtraElements(context, obj, memberMap);
+                var message = string.Format(
+                    "An error occurred while serializing the {0} {1} of class {2}: {3}", // terminating period provided by nested message
+                    memberMap.MemberName, (memberMap.MemberInfo is FieldInfo) ? "field" : "property", memberMap.ClassMap.ClassType.FullName, ex.Message);
+                throw new BsonSerializationException(message, ex);
             }
         }
 

src/MongoDB.Bson/Serialization/Serializers/DictionarySerializerBase.cs

@@ -16,7 +16,6 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
-using System.Linq.Expressions;
 using MongoDB.Bson.IO;
 using MongoDB.Bson.Serialization.Options;
 
@@ -59,7 +58,7 @@ public DictionarySerializerBase()
         /// </summary>
         /// <param name="dictionaryRepresentation">The dictionary representation.</param>
         public DictionarySerializerBase(DictionaryRepresentation dictionaryRepresentation)
-            : this(dictionaryRepresentation, new ObjectSerializer(), new ObjectSerializer())
+            : this(dictionaryRepresentation, BsonSerializer.LookupSerializer<object>(), BsonSerializer.LookupSerializer<object>())
         {
         }
 

src/MongoDB.Bson/Serialization/Serializers/DiscriminatedInterfaceSerializer.cs

@@ -81,7 +81,7 @@ public DiscriminatedInterfaceSerializer(IDiscriminatorConvention discriminatorCo
 
             _interfaceType = typeof(TInterface);
             _discriminatorConvention = discriminatorConvention;
-            _objectSerializer = new ObjectSerializer(_discriminatorConvention);
+            _objectSerializer = ((ObjectSerializer)BsonSerializer.LookupSerializer<object>()).WithDiscriminatorConvention(_discriminatorConvention);
             _interfaceSerializer = interfaceSerializer;
         }