MQTT

The MQTT binding. The emitted member is mqtt, and every object carries bindingVersion: 0.2.0.

@mqttServer

extern dec mqttServer(target: Namespace, config: valueof AsyncAPIMqttServerBinding);

Field	Type	Required
clientId	string	no
cleanSession	boolean	no
lastWill	AsyncAPIMqttLastWill	no
keepAlive	int32	no
sessionExpiryInterval	unknown	no
maximumPacketSize	unknown	no

Apply it to the service namespace. Every server that namespace declares gets its own copy.

lastWill is the message the broker sends when the client disconnects without a DISCONNECT packet. Its qos is 0, 1 or 2. Any other value is reported through invalid-binding-field. The field is dropped and the rest of the will is kept.

sessionExpiryInterval and maximumPacketSize are MQTT 5 fields. Write each one as a number, or as a Schema Object describing the number.

@service(#{ title: "Sensors" })
@server("prod", #{ host: "mqtt.example.com:8883", protocol: "mqtt" })
@mqttServer(#{
  clientId: "sensor-gateway",
  cleanSession: true,
  keepAlive: 60,
  lastWill: #{ topic: "sensors/status", qos: 1, message: "offline", retain: true }
})
namespace Sensors;

servers:
  prod:
    host: mqtt.example.com:8883
    protocol: mqtt
    bindings:
      mqtt:
        clientId: sensor-gateway
        cleanSession: true
        lastWill:
          topic: sensors/status
          qos: 1
          message: offline
          retain: true
        keepAlive: 60
        bindingVersion: 0.2.0

@mqttOperation

extern dec mqttOperation(target: Operation, config: valueof AsyncAPIMqttOperationBinding);

Field	Type	Required
qos	int32	no
retain	boolean	no
messageExpiryInterval	unknown	no

Apply it to an operation that carries @send or @receive.

qos is 0, 1 or 2. Any other value is reported through invalid-binding-field. The field is dropped and the rest of the binding is kept.

@send
@mqttOperation(#{ qos: 1, retain: false, messageExpiryInterval: 3600 })
op publish(event: Reading): void;

operations:
  publish:
    action: send
    channel:
      $ref: "#/channels/sensors~1reading"
    bindings:
      mqtt:
        qos: 1
        retain: false
        messageExpiryInterval: 3600
        bindingVersion: 0.2.0

@mqttMessage

extern dec mqttMessage(target: Model, config: valueof AsyncAPIMqttMessageBinding);

Field	Type	Required
payloadFormatIndicator	int32	no
correlationData	unknown	no
contentType	string	no
responseTopic	unknown	no

Apply it to a model that also carries @message. All four fields are MQTT 5 fields.

payloadFormatIndicator is 0 for unspecified bytes and 1 for UTF-8. correlationData is a Schema Object. responseTopic is a topic name, or a Schema Object describing the name.

@message
@mqttMessage(#{
  payloadFormatIndicator: 1,
  contentType: "application/json",
  responseTopic: "sensors/reply"
})
model Reading {
  value: float64;
}

components:
  messages:
    Reading:
      name: Reading
      payload:
        $ref: "#/components/schemas/Reading"
      bindings:
        mqtt:
          payloadFormatIndicator: 1
          contentType: application/json
          responseTopic: sensors/reply
          bindingVersion: 0.2.0