A last will is a regular application message, but the client can set it up and send while connecting to the broker. The broker will distribute this last-will only when the client goes offline and the last-will's Delay Interval expires.

Creating a Last-Will

A last-will can be created in the connect packget builder callback using ConnectPacketBuilder’s WithLastWill and a new LastWillBuilder. The following code creates a last-will that will be published to the "client/last-will" topic 60 seconds after the client gone offline.

private ConnectPacketBuilder ConnectPacketBuilderCallback(MQTTClient client, ConnectPacketBuilder builder)
    return builder.WithLastWill(new LastWillBuilder()
                                    .WithPayload("This is my last will!"));