protobuf-net AddField 忽略 IgnoreListHandling

Question

我有这个数据结构声明：

[ProtoContract]
public class NotACollectionHolder
{
    public NotACollection some_objects;
}

[ProtoContract(IgnoreListHandling = true, ImplicitFields = ImplicitFields.AllPublic)]
public class NotACollection : IEnumerable<int>
{
    public int some_data;

    // something looks like a collection API
    public void Add(int a) { }
    public IEnumerator<int> GetEnumerator() { throw new NotImplementedException(); }
    IEnumerator IEnumerable.GetEnumerator() { throw new NotImplementedException(); }
}

我正在通过以下代码手动将字段注册到 MetaType：

MetaType meta = RuntimeTypeModel.Default.Add(typeof(NotACollectionHolder), false);
ValueMember member = meta.AddField(1, "some_objects", itemType: null, defaultType: null);
string proto = Serializer.GetProto<NotACollectionHolder>();

我用IgnoreListHandling标记NotACollection。我试图通过提供 itemType: null, defaultType: null.

来强制 AddField 忽略 NotACollection 看起来像集合的事实

然而，我有 member.ItemType is not null，并且 member.DefaultType is not null either。 some_objects 成为生成的 proto:

中的一个 repeated 字段

message NotACollectionHolder {
    repeated int32 some_objects = 1;
}

我希望 proto 看起来像这样：

message NotACollection {
   optional int32 some_data = 1 [default = 0];
}
message NotACollectionHolder {
   optional NotACollection some_objects = 1;
}

我怎样才能做到这一点？我究竟做错了什么？如何强制 protobuf-net 将此字段视为非集合字段？

提前致谢。

Answer 1

我认为这可能是 RuntimeTypeModel API 的错误或限制。

判断是否为ValueMember is a collection is RuntimeTypeModel.ResolveListTypes()的方法。当传入的 itemType 为 null 时，它会尝试推断集合项类型。仅使用静态属性为 NotACollectionHolder 构建合约时，例如通过执行以下操作：

var model = TypeModel.Create();
var schema = model.GetSchema(typeof(NotACollectionHolder));

然后调用 ProtoBuf.Meta.MetaType.ApplyDefaultBehaviour(bool isEnum, ProtoMemberAttribute normalizedAttribute) 来创建初始化 ValueMember。它具有以下逻辑：

        // check for list types
        ResolveListTypes(model, effectiveType, ref itemType, ref defaultType);
        // but take it back if it is explicitly excluded
        if(itemType != null)
        { // looks like a list, but double check for IgnoreListHandling
            int idx = model.FindOrAddAuto(effectiveType, false, true, false);
            if(idx >= 0 && model[effectiveType].IgnoreListHandling)
            {
                itemType = null;
                defaultType = null;
            }
        }

注意到 IgnoreListHandling 的显式检查了吗？这正确地防止了 some_objects 被序列化为一个集合。

相反，如果以编程方式添加 ValueMember，如下所示：

var model = TypeModel.Create();
var meta = model.Add(typeof(NotACollectionHolder), false);
var member = meta.AddField(1, "some_objects", null, null);
var schema = model.GetSchema(typeof(NotACollectionHolder));

然后 MetaType.AddField(int fieldNumber, string memberName, Type itemType, Type defaultType, object defaultValue) 被调用，它只是做：

        ResolveListTypes(model, miType, ref itemType, ref defaultType);

请注意没有检查 IgnoreListHandling？这是你的问题的原因。

不幸的是，ValueType.itemType is read-only and MetaType[int fieldNumber] is get-only so there doesn't seem to be a simple API to call to fix this. You might consider reporting an issue。

我能找到的唯一解决方法是为 NotACollectionHolder 类型引入一个代理项，如下所示：

[ProtoContract]
internal class NotACollectionHolderSurrogate
{
    [ProtoMember(1)]
    internal NotACollectionSurrogate some_objects;

    public static implicit operator NotACollectionHolder(NotACollectionHolderSurrogate input)
    {
        if (input == null)
            return null;
        return new NotACollectionHolder { some_objects = input.some_objects };
    }

    public static implicit operator NotACollectionHolderSurrogate(NotACollectionHolder input)
    {
        if (input == null)
            return null;
        return new NotACollectionHolderSurrogate { some_objects = input.some_objects };
    }
}

[ProtoContract]
internal class NotACollectionSurrogate
{
    [ProtoMember(1)]
    public int some_data;

    public static implicit operator NotACollection(NotACollectionSurrogate input)
    {
        if (input == null)
            return null;
        return new NotACollection { some_data = input.some_data };
    }

    public static implicit operator NotACollectionSurrogate(NotACollection input)
    {
        if (input == null)
            return null;
        return new NotACollectionSurrogate { some_data = input.some_data };
    }
}

然后做：

var model = TypeModel.Create();
model.Add(typeof(NotACollectionHolder), false).SetSurrogate(typeof(NotACollectionHolderSurrogate));

var schema = model.GetSchema(typeof(NotACollectionHolder));

按要求生成的合约：

message NotACollectionHolderSurrogate {
   optional NotACollectionSurrogate some_objects = 1;
}
message NotACollectionSurrogate {
   optional int32 some_data = 1 [default = 0];
}

Answer 2

我发现这确实是protobuf-net的一个bug。修复它的第一种方法是更改 protobuf-net 的源代码：在文件 MetaType.cs 中在函数

中

private ValueMember AddField(int fieldNumber, string memberName, Type itemType, Type defaultType, object defaultValue)

替换行

ResolveListTypes(model, miType, ref itemType, ref defaultType);

和

if (model.FindWithoutAdd(miType)?.IgnoreListHandling == true)
{
    itemType = null;
    defaultType = null;
}
else
    ResolveListTypes(model, miType, ref itemType, ref defaultType);

另一种方法是使用反射将对象ValueMember的私有字段itemType和defaultType设置为添加字段后的null：

ValueMember m = meta.AddField(++last_field_number, f.Name, f.ItemType, f.DefaultType);
m.GetType().GetField("itemType", BindingFlags.NonPublic | BindingFlags.Instance).SetValue(m, null);
m.GetType().GetField("defaultType", BindingFlags.NonPublic | BindingFlags.Instance).SetValue(m, null);

希望这对某人有所帮助。

protobuf-net AddField 忽略 IgnoreListHandling

protobuf-net AddField ignores IgnoreListHandling

c#

protobuf-net