Empty 'Any' type field values cannot be correctly serialized/deserialized to JSON text in the C# library

[tltsaia]

What version of protobuf and what language are you using? Version: main/v29.2 Language: C#

What operating system (Linux, Windows, ...) and version? Windows 10 22H2 What runtime / compiler are you using (e.g., python version or gcc version) Visual Studio 2022 What did you do? Steps to reproduce the behavior:

The "Any" type fields do not accept null values for packing; only an empty object instantiated with new Any() can be passed to represent a null value. An empty "Any" object is represented as {"@type": "", "@value": ""}. The current C# JsonFormatter and JsonParser both do not accept this input value, and both throw an error: Type registry has no descriptor for type name ''.

For example:

        var rep = new MsgFromProtoFile(); // IMessage instance
        rep.SomeAnyField = Any.Pack(new MyAnyField{ strField= "string", 
            anyField= new Any() // empty Any object, this will be {"@type": "", "@value": ""}
        });

        var tr = TypeRegistry.FromMessages(MyAnyField.Descriptor);
        var json_parser = new JsonParser(JsonParser.Settings.Default.WithTypeRegistry(tr));
        var formater = new JsonFormatter(new JsonFormatter.Settings(true).WithTypeRegistry(tr));

        var json_text = formater.Format(rep); // throw exception as above
        var rep0 = json_parser.Parse<MsgFromProtoFile>(json_text); // throw exception as above

What did you expect to see formater return json text with null value, ex: {"anyField": null} parser return empty Any object as expect, even if {"@type": "", "@value": ""}

What did you see instead? throw an error: Type registry has no descriptor for type name ''.

Make sure you include information that can help us debug (full error message, exception listing, stack trace, logs).

Anything else we should know about your project / environment In the Golang library, an empty "Any" object represented as {"@type": "", "@value": ""} can be processed normally.

It is recommended to handle this in the function MergeAny() of Google.Protobuf.JsonParser

        string typeUrl = token.StringValue;
        string typeName = Any.GetTypeName(typeUrl);

        if (string.IsNullOrEmpty(typeName))
        {
            tokenizer.Next(); // @value
            tokenizer.Next(); // string
            tokenizer.Next(); // EndObject
            return;
        }

to handle this in the function WriteAny() of Google.Protobuf.JsonFormatter

  string typeName = Any.GetTypeName(typeUrl);

        if (string.IsNullOrEmpty(typeName))
        {
            WriteNull(writer);
            return;
        }

[jskeet]

I will look at this in January.

[jskeet]

Fundamentally, an Any without a populated type isn't valid. That said, I'd rather be able to deserialize it to the same value than it just fail.

Will consult internally to find out what other languages do.

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[tltsaia]

This issue remains unresolved. Do you have any further suggestions? Thank you.

[esrauchg]

Hey, sorry for slow updates here.

We had checked the other language's behavior on this case and they pretty much were all matching in behavior on this case, so we also updated the conformance test suite to match the behavior that ~all other impls already had.

The behavior that everyone else had that is now in the conformance tests is:

• null mean that the Any field unset
• Any with no type_url should round trip as {}
• {"@type_url": "", "value":""} is malformed and should parse fail

csharp diverging from this is reflected by these lines in the conformance test known failures: https://github.com/protocolbuffers/protobuf/blob/main/conformance/failure_list_csharp.txt#L36-L38

So the right step forward is basically to match that behavior in a way that makes those lines of the conformance test known failures can be removed.

[jskeet]

https://github.com/protocolbuffers/protobuf/commit/dc4e4295a4515c593cd8b96e63b3581cc99ac97f implements the change described above. I'll close this issue now, as although it isn't exactly as requested, it's where we want to end up (across all languages).