Protobuf-net不会从Protobuf.js反序列化数据。

Question

我使用Protobuf进行web客户端和服务器(C#)之间的通信，使用WebSocket。在客户机上，反序列化是通过Protobuf.js完成的，在服务器上使用protobuf。

问题是，当使用带有抽象类的聚合时，Protobuf.js无法对Protobuf.js发送的数据进行反序列化。

这是堆栈跟踪：

ProtoException: No parameterless constructor found for Base.
at ProtoBuf.Meta.TypeModel.ThrowCannotCreateInstance(Type type) na c:\Dev\protobuf-net\protobuf-net\Meta\TypeModel.cs:line 1397
at proto_6(Object , ProtoReader )
at ProtoBuf.Serializers.CompiledSerializer.ProtoBuf.Serializers.IProtoSerializer.Read(Object value, ProtoReader source) na c:\Dev\protobuf-net\protobuf-net\Serializers\CompiledSerializer.cs:line 57
at ProtoBuf.Meta.RuntimeTypeModel.Deserialize(Int32 key, Object value, ProtoReader source) na c:\Dev\protobuf-net\protobuf-net\Meta\RuntimeTypeModel.cs:line 775
at ProtoBuf.ProtoReader.ReadTypedObject(Object value, Int32 key, ProtoReader reader, Type type) na c:\Dev\protobuf-net\protobuf-net\ProtoReader.cs:line 579
at ProtoBuf.ProtoReader.ReadObject(Object value, Int32 key, ProtoReader reader) na c:\Dev\protobuf-net\protobuf-net\ProtoReader.cs:line 566
at proto_2(Object , ProtoReader )
at ProtoBuf.Serializers.CompiledSerializer.ProtoBuf.Serializers.IProtoSerializer.Read(Object value, ProtoReader source) na c:\Dev\protobuf-net\protobuf-net\Serializers\CompiledSerializer.cs:line 57
at ProtoBuf.Meta.RuntimeTypeModel.Deserialize(Int32 key, Object value, ProtoReader source) na c:\Dev\protobuf-net\protobuf-net\Meta\RuntimeTypeModel.cs:line 775
at ProtoBuf.Meta.TypeModel.DeserializeCore(ProtoReader reader, Type type, Object value, Boolean noAutoCreate) na c:\Dev\protobuf-net\protobuf-net\Meta\TypeModel.cs:line 700
at ProtoBuf.Meta.TypeModel.Deserialize(Stream source, Object value, Type type, SerializationContext context) na c:\Dev\protobuf-net\protobuf-net\Meta\TypeModel.cs:line 589
at ProtoBuf.Meta.TypeModel.Deserialize(Stream source, Object value, Type type) na c:\Dev\protobuf-net\protobuf-net\Meta\TypeModel.cs:line 566
at ProtoBuf.Serializer.Deserialize[T](Stream source) na c:\Dev\protobuf-net\protobuf-net\Serializer.cs:line 77
at ProtobufPolymorphismTest.Program.Main(String[] args) na c:\Desenvolvimento\Testes\ProtobufPolymorphismTest\ProtobufPolymorphismTest\Program.cs:line 30
at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()

这是合同：

[ProtoContract]
[ProtoInclude(100, typeof(Child))]
abstract class Base
{
    [ProtoMember(1)]
    public int BaseProperty { get; set; }
}

[ProtoContract]
class Child : Base
{
    [ProtoMember(1)]
    public float ChildProperty { get; set; }
}

[ProtoContract]
class Request
{
    [ProtoMember(1)]
    public Base Aggregate { get; set; }
}

这是再现错误的代码。由于序列化工作，我只提供一个字节数组的结果。如果有帮助，我可以提供获得序列化值的步骤。

// This is the object serialized
Child child = new Child() { ChildProperty = 0.5f, BaseProperty = 10 };
Request request = new Request() { Aggregate = child };

// This is the byte representation generated by protobuf-net and Protobuf.js
byte[] protoNet = new byte[] { 10, 10, 162, 6, 5, 13, 0, 0, 0, 63, 8, 10 };
byte[] protoJS = new byte[] { 10, 10, 8, 10, 162, 6, 5, 13, 0, 0, 0, 63 };

// Try to deserialize the protobuf-net data
using (System.IO.MemoryStream ms = new System.IO.MemoryStream(protoNet))
{
    request = Serializer.Deserialize<Request>(ms); // Success
}

// Try to deserialize the Protobuf.js data
using (System.IO.MemoryStream ms = new System.IO.MemoryStream(protoJS))
{
    request = Serializer.Deserialize<Request>(ms); // ProtoException: No parameterless constructor found for Base.
}

如果在基类定义中添加SkipConstructor = true，则错误将更改为"MemberAccessException:无法创建抽象类“，并具有以下堆栈跟踪。如果我从基类定义中删除抽象，它将按预期工作。

System.MemberAccessException: Cannot create an abstract class.
at System.Runtime.Serialization.FormatterServices.nativeGetUninitializedObject(RuntimeType type)
at ProtoBuf.BclHelpers.GetUninitializedObject(Type type) na c:\Dev\protobuf-net\protobuf-net\BclHelpers.cs:line 38
at proto_6(Object , ProtoReader )
at ProtoBuf.Serializers.CompiledSerializer.ProtoBuf.Serializers.IProtoSerializer.Read(Object value, ProtoReader source) na c:\Dev\protobuf-net\protobuf-net\Serializers\CompiledSerializer.cs:line 57
at ProtoBuf.Meta.RuntimeTypeModel.Deserialize(Int32 key, Object value, ProtoReader source) na c:\Dev\protobuf-net\protobuf-net\Meta\RuntimeTypeModel.cs:line 775
at ProtoBuf.ProtoReader.ReadTypedObject(Object value, Int32 key, ProtoReader reader, Type type) na c:\Dev\protobuf-net\protobuf-net\ProtoReader.cs:line 579
at ProtoBuf.ProtoReader.ReadObject(Object value, Int32 key, ProtoReader reader) na c:\Dev\protobuf-net\protobuf-net\ProtoReader.cs:line 566
at proto_2(Object , ProtoReader )
at ProtoBuf.Serializers.CompiledSerializer.ProtoBuf.Serializers.IProtoSerializer.Read(Object value, ProtoReader source) na c:\Dev\protobuf-net\protobuf-net\Serializers\CompiledSerializer.cs:line 57
at ProtoBuf.Meta.RuntimeTypeModel.Deserialize(Int32 key, Object value, ProtoReader source) na c:\Dev\protobuf-net\protobuf-net\Meta\RuntimeTypeModel.cs:line 775
at ProtoBuf.Meta.TypeModel.DeserializeCore(ProtoReader reader, Type type, Object value, Boolean noAutoCreate) na c:\Dev\protobuf-net\protobuf-net\Meta\TypeModel.cs:line 700
at ProtoBuf.Meta.TypeModel.Deserialize(Stream source, Object value, Type type, SerializationContext context) na c:\Dev\protobuf-net\protobuf-net\Meta\TypeModel.cs:line 589
at ProtoBuf.Meta.TypeModel.Deserialize(Stream source, Object value, Type type) na c:\Dev\protobuf-net\protobuf-net\Meta\TypeModel.cs:line 566
at ProtoBuf.Serializer.Deserialize[T](Stream source) na c:\Dev\protobuf-net\protobuf-net\Serializer.cs:line 77
at ProtobufPolymorphismTest.Program.Main(String[] args) na c:\Desenvolvimento\Testes\ProtobufPolymorphismTest\ProtobufPolymorphismTest\Program.cs:line 30
at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()

我不知道通过protobuf和Protobuf.js生成的二进制表示为何不同，但是如果基类不是抽象的，它们看起来都是有效的。

对于为什么会发生这种情况，或者如何在不从基类中删除抽象的情况下进行工作，有什么想法吗？

提前感谢！

更新

这是我用来通过Protobuf.js生成字节序列化的代码：

<script src="//raw.githubusercontent.com/dcodeIO/ByteBuffer.js/master/dist/ByteBufferAB.min.js"></script>
<script src="//cdn.rawgit.com/dcodeIO/ProtoBuf.js/master/dist/ProtoBuf.js"></script>
<script type="text/javascript">
    // Proto file
    var proto = "";
    proto += "package ProtobufPolymorphismTest;\r\n\r\n";
    proto += "message Base {\r\n";
    proto += "    optional int32 BaseProperty = 1 [default = 0];\r\n";
    proto += "    // the following represent sub-types; at most 1 should have a value\r\n";
    proto += "    optional Child Child = 100;\r\n";
    proto += "}\r\n\r\n";
    proto += "message Child {\r\n";
    proto += "    optional float ChildProperty = 1 [default = 0];\r\n";
    proto += "}\r\n\r\n";
    proto += "message Request {\r\n";
    proto += "    optional Base Aggregate = 1;\r\n";
    proto += "}";

    // Build the entities
    var protoFile = dcodeIO.ProtoBuf.loadProto(proto);
    var requestClass = protoFile.build("ProtobufPolymorphismTest.Request");
    var baseClass = protoFile.build("ProtobufPolymorphismTest.Base");
    var childClass = protoFile.build("ProtobufPolymorphismTest.Child");

    // Build the request
    var base = new baseClass();
    base.BaseProperty = 10;
    base.Child = new childClass();
    base.Child.ChildProperty = 0.5;
    var request = new requestClass();
    request.Aggregate = base;

    // Serialize
    var bytes = new Uint8Array(request.toArrayBuffer());
    var str = "new byte[] { " + bytes.join(", ") + " };";
    console.log(str);
</script>

解决方案

正如Marc解释的，当字段顺序倒置时，protobuf-net不支持多态性。作为一种解决方法，特定于Protobuf.js，您可以更改.proto文件中字段的顺序，以便按正确的顺序序列化。

在我的例子中，将.proto文件更改为以下内容解决了这个问题：

package ProtobufPolymorphismTest;

message Base {
   // the following represent sub-types; at most 1 should have a value
   optional Child Child = 100;
   optional int32 BaseProperty = 1 [default = 0];
}
message Child {
   optional float ChildProperty = 1 [default = 0];
}
message Request {
   optional Base Aggregate = 1;
}

(注意optional Child Child = 100;之前的BaseProperty)

Answer 1

它的长短在于，protobuf的多形性支持期望子类型在消息中是first (或者更具体地说:对于任何对象，在提供数据之前，该类型将是固定的)。在js输出中，BaseProperty的字段数据是first --也许是非常合理的。但是，由于没有关于继承应该如何运行的覆盖式协议定义，所以protobuf的实现实际上只打算与自己一起工作。就字节而言，这实际上是字段标记"162，6“(以及相关的长度/数据，"5，13，0，0，63")出现的地方。

该库可能会被重新处理，以允许任何字段顺序的多态性，但是:它将需要一些努力。我知道它通常会按任何顺序处理字段，但是由于这已经超出了规范的范围，所以我没有关注这个问题。所有其他数据字段都可以以任何顺序的纯多态性方式工作。

在一般情况下:由于多态性不是规范的一部分，我强烈建议在库之间工作时避免多态性。

注意:您可能可以通过确保多态字段为、比数据字段更低的(数字)来强制它工作。