Publish NServiceBus event from v6 JSON to v4 XML environment

Question

I'm looking for a way to publish events from our new NServiceBus 6 endpoint environment to an older v4 endpoint environment. To make matters more interesting, the v6 is using JSON and the v4 is using XML.

• Do I need to simply add a mutator on the incoming v4 endpoint?
• How do I convert the JSON message to an XML message? In the above mentioned mutator?
• Do I need to add any specific v4 message headers on the outgoing event message?

I'm using MSMQ as the underlying transport layer.

Answer 1

Potentially the simplest way to move forward is to write a custom serializer definition. The following example assumes the default XmlSerializer and JsonSerializer available in NServiceBus v6 are used.

Write a custom serializer definition

public class CustomJsonSerializer : SerializationDefinition
{
    public override Func<IMessageMapper, IMessageSerializer> Configure(ReadOnlySettings settings)
    {
        var xmlSerializerDefinition = new XmlSerializer();
        var xmlSerializerFactory = xmlSerializerDefinition.Configure(settings);

        var jsonSerializerDefinition = new JsonSerializer();
        var jsonSerializerFactory = jsonSerializerDefinition.Configure(settings);
        return mapper => new DecoratorSerializer(xmlSerializerFactory(mapper), jsonSerializerFactory(mapper));
    }
}

Write a serializer decorator that has custom logic to forward message types to the XmlSerializer if they are targetted towards the V4 endpoint.

class DecoratorSerializer : IMessageSerializer
{
    IMessageSerializer xmlSerializer;
    IMessageSerializer jsonSerializer;

    public DecoratorSerializer(IMessageSerializer xmlSerializer, IMessageSerializer jsonSerializer)
    {
        this.xmlSerializer = xmlSerializer;
        this.jsonSerializer = jsonSerializer;
    }

    public void Serialize(object message, Stream stream)
    {
        if (message.GetType() == typeof(MyMessage))
        {
            xmlSerializer.Serialize(message, stream);
        }
        else
        {
            jsonSerializer.Serialize(message, stream);
        }
    }

    public object[] Deserialize(Stream stream, IList<Type> messageTypes = null)
    {
        return jsonSerializer.Deserialize(stream, messageTypes);
    }

    public string ContentType
    {
        get { return jsonSerializer.ContentType; }
    }
}

use the CustomSerializer like the following

endpointConfiguration.UseSerializer<CustomJsonSerializer>();

A working sample can be found on this github repo. The sample uses commands but the approach should also work for PubSub. The only caveat is that a specific message type will always use one format. So it is not possible to publish the same event once in Xml and for other publishes in Json.