Weird serialization behaviour

Consider the following message definition in C#:

public interface CreateUser
{
    string UserId { get; }
    string UnverifiedPrimaryEmail { get; }
    string Language { get; }
}

F# has explicit interface implementations. The syntax looks like this:

type CreateUserMsg(uid, email, lang) =
  interface CreateUser with
    member _.UserId = uid
    member _.UnverifiedPrimaryEmail = lang
    member _.Language = email

For some reason, instantiating and sending this will send a message where all the properties are null.

As a counter-example, the following works fine:

type CreateUserMsg(uid, email, lang) =
  member _.UserId = uid
  member _.UnverifiedPrimaryEmail = email
  member _.Language = lang

  interface CreateUser with
    member _.UserId = "some"
    member _.UnverifiedPrimaryEmail = "other"
    member _.Language = "value"

Note that if one of the non-interface members are removed or renamed, that member will be serialized to null even though the interface contains the correct value. And that the actual (explicit) interface members are not used at all.

It might seem like MassTransit assumes the class itself contains members corresponding to those in the interface, and does not account for explicit interface implementations (which AFAIK is supported in C# too, by the way).

[cmeeren]

Adapt this huge thing here? No thanks, that’s a maintenance burden I’d rather be without. I’ll look for other workarounds instead. 😃

For example, have C# contract projects where in addition to the message interfaces, I could add message classes implementing them. It’s not idiomatic, but it seems that’s the only way of sending strongly typed interface-based messages from F#, given the current serialization implementation.

Thanks for the help, though!

[phatboyg]

You can certainly create a new serializer by implementing the interfaces and adding it to the supported serializers/deserializers.

You can configure the entire bus instance (all receive endpoints) or a single receive endpoint to use a serializer, as well as support the deserializer, using:

configurator.SetMessageSerializer(() => new RawJsonMessageSerializer());

configurator.AddMessageDeserializer(RawJsonMessageSerializer.RawJsonContentType,
    () => new RawJsonMessageDeserializer(RawJsonMessageSerializer.Deserializer));

That’s an example, you’d need your own content type. If you call:

configurator.ClearMessageDeserializers();

That will remove all of the default serializer/deserializers.

(In this example, RawJsonMessageSerializer is an example – if you wanted to support System.Text.Json, I’d suggest using the built-in JsonMessageSerializer as a base).