Jasper

Publishing and Sending Messages

Publish/Subscribe is a messaging pattern where the senders of messages do not need to specifically know what the specific subscribers are for a given message. In this case, some kind of middleware or infrastructure is responsible for either allowing subscribers to express interest in what messages they need to receive or apply routing rules to send the published messages to the right places. Jasper's messaging support was largely built to support the publish/subscibe messaging patterm.

To send a message with Jasper, use the IMessagePublisher interface or the bigger IExecutionContext interface that are registered in your application's IoC container. The sample below shows the most common usage:

public ValueTask SendMessage(IExecutionContext bus)
{
    // In this case, we're sending an "InvoiceCreated"
    // message
    var @event = new InvoiceCreated
    {
        Time = DateTimeOffset.Now,
        Purchaser = "Guy Fieri",
        Amount = 112.34,
        Item = "Cookbook"
    };

    return bus.SendAsync(@event);
}

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That by itself will send the InvoiceCreated message to whatever subscribers are interested in that message. The SendAsync() method will throw an exception if Jasper doesn't know where to send the message. In other words, there has to be a subscriber of some sort for that message.

On the other hand, the PublishAsync() method will send a message if there is a known subscriber and ignore the message if there is no subscriber:

public ValueTask PublishMessage(IExecutionContext bus)
{
    // In this case, we're sending an "InvoiceCreated"
    // message
    var @event = new InvoiceCreated
    {
        Time = DateTimeOffset.Now,
        Purchaser = "Guy Fieri",
        Amount = 112.34,
        Item = "Cookbook"
    };

    return bus.PublishAsync(@event);
}

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Send Messages to a Specific Endpoint or Topic

// TODO

Customizing Message Delivery

TODO -- more text here

public static async Task SendMessagesWithDeliveryOptions(IMessagePublisher publisher)
{
    await publisher.PublishAsync(new Message1(), new DeliveryOptions
    {
        AckRequested = true,
        ContentType = "text/xml", // you can do this, but I'm not sure why you'd want to override this
        DeliverBy = DateTimeOffset.Now.AddHours(1), // set a message expiration date
        DeliverWithin = 1.Hours(), // convenience method to set the deliver-by expiration date
        ScheduleDelay = 1.Hours(), // Send this in one hour, or...
        ScheduledTime = DateTimeOffset.Now.AddHours(1),
        ResponseType = typeof(Message2) // ask the receiver to send this message back to you if it can
    }
        // There's a chained fluent interface for adding header values too
        .WithHeader("tenant", "one"));

}

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