Interoperability

Hey, it's a complicated world and Wolverine is a relative newcomer, so it's somewhat likely you'll find yourself needing to make a Wolverine application talk via GCP Pub/Sub to a non-Wolverine application. Not to worry (too much), Wolverine has you covered with the ability to customize Wolverine to GCP Pub/Sub mapping.

You can create interoperability with non-Wolverine applications by writing a custom IPubsubEnvelopeMapper as shown in the following sample:

public class CustomPubsubMapper : EnvelopeMapper<ReceivedMessage, PubsubMessage>, IPubsubEnvelopeMapper
{
    public CustomPubsubMapper(PubsubEndpoint endpoint) : base(endpoint)
    {
    }

    public void MapIncomingToEnvelope(PubsubEnvelope envelope, ReceivedMessage incoming)
    {
        envelope.AckId = incoming.AckId;

        // You will have to help Wolverine out by either telling Wolverine
        // what the message type is, or by reading the actual message object,
        // or by telling Wolverine separately what the default message type
        // is for a listening endpoint
        envelope.MessageType = typeof(Message1).ToMessageTypeName();
    }

    public void MapOutgoingToMessage(OutgoingMessageBatch outgoing, PubsubMessage message)
    {
        message.Data = ByteString.CopyFrom(outgoing.Data);
    }

    protected override void writeOutgoingHeader(PubsubMessage outgoing, string key, string value)
    {
        outgoing.Attributes[key] = value;
    }

    protected override void writeIncomingHeaders(ReceivedMessage incoming, Envelope envelope)
    {
        if (incoming.Message.Attributes is null)
        {
            return;
        }

        foreach (var pair in incoming.Message.Attributes) envelope.Headers[pair.Key] = pair.Value;
    }

    protected override bool tryReadIncomingHeader(ReceivedMessage incoming, string key, out string? value)
    {
        if (incoming.Message.Attributes.TryGetValue(key, out var header))
        {
            value = header;

            return true;
        }

        value = null;

        return false;
    }
}

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To apply that mapper to specific endpoints, use this syntax on any type of GCP Pub/Sub endpoint:

using var host = await Host.CreateDefaultBuilder()
    .UseWolverine(opts =>
    {
        opts.UsePubsub("your-project-id")
            .UseConventionalRouting()
            .ConfigureListeners(l => l.InteropWith(e => new CustomPubsubMapper(e)))
            .ConfigureSenders(s => s.InteropWith(e => new CustomPubsubMapper(e)));
    }).StartAsync();

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