The RSVP methods allow developers to define a request/response model using the messagebroker. Unlike a normal publish, publishing on an RSVP channel is a synchronous call that will ask all subscribers to respond with some value.

An RSVP message must be sent on a special RSVP channel. In order to create on of those, you should extend the IRSVPConfig interface in your Contract interface, which will require you to specify an rsvp section. In this section, you can provide a channel name as usual, and it must have a payload and response section in it.

interface IContract extends IRSVPConfig {
    nonRSVPChannel : string;
    rsvp: {
        myRSVPChannel: {
            payload: { data: string };
            response: number;
        };
    };
}

Publish

With your contract defined, you can now publish a message.

Remember, this call will be synchronous, so it will block until all the subscribers have completed their work and returned a value.

When all return values have been gathered, they will be returned by the rsvp method.

const results: number[] = messagebroker<IMessageChannels>()
                            .rsvp('myRSVPChannel', { data: 'abcde'});

Respond

Subscribing to an RSVP channel looks much the same as publishing, with the key difference being that the second parameter is a function rather than an object. This function must take a parameter of the type that matches the payload type in your contract. It must then return a value which is of the same type as the response type in your contract.

messagebroker<IMessageChannels>()
    .rsvp('myRSVPChannel', payload => {
        // Perform some work on payload
        return len(payload.data);
    }
);

Respond with manual disconnect

If for some reason you would like to stop responding to RSVP messages on a certain channel, the rsvp function returns a responder handler which has a disconnect method on it. Calling this method will prevent any further messages being received.

const responder = messagebroker<IMessageChannels>()
                    .rsvp('myRSVPChannel', payload => {
                        return len(payload.data);
                    });

// Manually disconnect the responder to
// avoid handling further rsvp requests.
responder.disconnect();