MQTT-SN Gateway: Core

This module is part of mqttsngw. It is responsible for handling parsed MQTT-SN packets from the event bus and maintaining state machines for connected sensors. If necessary it requests a connection to the broker on the event bus.

Factory

const Core = require('mqttsngw-core');
mqttsngw.attach(Core(opts));

Creates a new Core factory and attaches it to an existing instance of mqttsngw. opts has the following fields:

• log: Optional. An object containing logging callbacks for all log levels (error, warn, info, debug). Every callback is called with a human-readable message as the first argument followed by an object containing more information regarding the event: { error: (msg, info) => { ... }, ...}.
• enforceUniqueClientIds: If set to true, existing connections will be disconnected if a new connection with the same MQTT Client ID is established.

State Machines

[Core] Main

• init: Preparing the state machine
• listening: Listens for incoming connection requests from the sensor network. If a request is received, a new instance of [Core] Client is created and started.

[Core] Client

Reflects the current sensor state.

• init: Preparing the state machine.
• willTopic: Waits for a will topic sent by the sensor.
• willMessage: Waits for a will message sent by the sensor.
• connectBroker: Tries to connect to the broker.
• active: The sensor is connected. Depending on the received sensor messages, it will start the state machines [Core] Subscribe, [Core] PublishToBroker or [Core] PublishToClient.
• sleep: The sensor may enter sleep state by stating a non-zero duration in the DISCONNECT packet. The gateway will collect ingress publishes from the broker and sends them to the sensores once it's active again.

[Core] Subscribe

Handles topic subscription requested sent by sensors.

• init: Checks subscription request.
• brokerSubscribe: Subscribes the topic at the broker.

[Core] PublishToBroker

Sends a message to the broker

• init: Checks the publish request and translates the topicId to the topic name.
• publishToBroker: Sends the message to the broker.

[Core] PublishToClient

Sends a message to the sensor

• init: Lookup the topicId to the given topic name or register one.
• registerTopic: Registers a topic at the sensor.
• publishToClient: Sends the message to the sensor.

Events

Several events are consumed and emitted by the Core module on the event bus.

Consumed

| Event | State Machine | Description | | ------------------------------ | ---------------------- | ----------- | | snUnicastIngress,,connect | [Core] Main | Incoming connection requests packet | | brokerConnect,,res | [Core] Client | Response to a broker connection request | | snUnicastIngress,,disconnect | [Core] Client | Sensor sent disconnect | | snUnicastIngress,,register | [Core] Client | Sensor registers a new topic name | | snUnicastIngress,,subscribe | [Core] Client | Sensor subscribes to a new topic | | snUnicastIngress,,unsubscribe | [Core] Client | Sensor unsubscribes from a topic | | snUnicastIngress,,publish | [Core] Client | Sensor publishes a message | | snUnicastIngress,,pingreq | [Core] Client | Sensor sent ping request | | brokerDisconnect,,notify | [Core] Client | Connection to the broker has been disconnected | | brokerPublishToClient,,req | [Core] Client | A message shall be sent from the broker to the sensor | | brokerSubscribe,,res | [Core] Subscribe | Response to a subscription request | | brokerUnsubscribe,,res | [Core] Unsubscribe | Response to a desubscription request | | brokerPublishFromClient,,res | [Core] PublishToBroker | Response to a publish to broker request | | snUnicastIngress,,regack | [Core] PublishToClient | Reaction to a register request from the sensor | | snUnicastIngress,*,puback | [Core] PublishToClient | Reaction to a publish request from the sensor |

Emitted

| Event | State Machine | Description | | ------------------------------ | ---------------------- | ----------- | | brokerConnect,,req | [Core] Client | Request a connection to the broker | | brokerDisconnect,,call | [Core] Client | Disconnect from the broker | | snUnicastOutgress,,connack | [Core] Client | Send a CONNACK to the sensor | | snUnicastOutgress,,disconnect | [Core] Client | Disconnect from sensor | | snUnicastOutgress,,regack | [Core] Client | Send a REGACK to the sensor | | snUnicastOutgress,,pingresp | [Core] Client | Respond to a ping request | | brokerSubscribe,,req | [Core] Subscribe | Subscribes a topic at the broker | | snUnicastOutgress,,suback | [Core] Subscribe | Respond to a subscription request | | brokerUnsubscribe,,req | [Core] Unsubscribe | Unsubscribes a topic at the broker | | snUnicastOutgress,,unsuback | [Core] Unsubscribe | Respond to a desubscription request | | brokerPublishFromClient,,req | [Core] PublishToBroker | Publish a message to the broker | | snUnicastOutgress,,puback | [Core] PublishToBroker | Send PUBACK to the sensor | | snUnicastOutgress,,register | [Core] PublishToClient | Register a topic at the sensor | | snUnicastOutgress,,publish | [Core] PublishToClient | Publish a message to the sensor | | brokerPublishToClient,*,res | [Core] PublishToClient | Respond to publish request from the broker |