Eclipse Ditto Client SDK for Golang

This repository contains the Golang client SDK for Eclipse Ditto.

Currently, Eclipse Hono MQTT is the only one supported transport.

Table of Contents

• Installation
• Creating and connecting a client
• Working with features
  • Create a new feature instance
  • Modify a feature's property
• Subscribing and handling messages

Installation

go get github.com/eclipse/ditto-clients-golang

Creating and connecting a client

Each client instance requires a ditto.Configuration object.

config := ditto.NewConfiguration().
    WithKeepAlive(30 * time.Second). // default keep alive is 30 seconds
    // WithCredentials(&ditto.Credentials{Username: "John", Password: "qwerty"}). if such are available or required
    WithBroker("mqtt-host:1883").
    WithConnectHandler(connectHandler)

func connectHandler(client *ditto.Client) {
    // add logic to be executed when the client is connected
}

With this configuration a client instance could be created.

client = ditto.NewClient(config)

NOTE: In some cases an external Paho instance could be provided for the communication. If this is the case, there is a ditto.NewClientMQTT() create function available.

After you have configured and created your client instance, it's ready to be connected.

if err := client.Connect(); err != nil {
    panic(fmt.Errorf("cannot connect to broker: %v", err))
}
defer disconnect(client)

Working with features

Create a new feature instance

Define the feature to be created.

myFeature := &model.Feature{}
myFeature.
    WithDefinitionFrom("my.model.namespace:FeatureModel:1.0.0"). // you can provide a semantic definition of your feature
    WithProperty("myProperty", "myValue")

Create your Ditto command. Modify acts as an upsert - it either updates or creates features.

command := things.
    NewCommand(model.NewNamespacedIDFrom("my.namespace:thing.id")). // specify which thing you will send the command to
    Twin().
    Feature("MyFeature").
    Modify(myFeature) // the payload for the modification - i.e. the feature's JSON representation

Send the Ditto command.

envelope := command.Envelope(protocol.WithResponseRequired(false))
if err := client.Send(envelope); err != nil {
    fmt.Printf("could not send Ditto message: %v\n", err)
}

Modify a feature's property

Modify overrides the current feature's property.

command = things.
    NewCommand(model.NewNamespacedIDFrom("my.namespace:thing.id")). // specify which thing you will send the command to
    Twin().
    FeatureProperty("MyFeature", "myProperty").
    Modify("myNewValue") // the payload for the modification - i.e. the new property's value JSON representation

Subscribing and handling messages

Subscribe for incoming Ditto messages.

func connectHandler(client *ditto.Client) {
    // it's a good practise to subscribe after the client is connected
    client.Subscribe(messagesHandler)
}

NOTE: You can add multiple handlers for Ditto messages processing.

It's a good practice to clear all subscriptions on client disconnect.

func disconnect(client *ditto.Client) {
    // add any resources clearing logic
    client.Unsubscribe()
    client.Disconnect()
}

NOTE: If no message handler is provided then all would be removed.

Handle and reply to Ditto messages.

func messagesHandler(requestID string, msg *protocol.Envelope) {
    if msg.Topic.Namespace == "my.namespace" && msg.Topic.EntityID == "thing.id" &&
            msg.Path == "/features/MyFeature/inbox/messages/myCommand" {
        // respond to the message by using the outbox
        response := things.NewMessage(model.NewNamespacedID(msg.Topic.Namespace, msg.Topic.EntityID)).
            Feature("MyFeature").Outbox("myCommand").WithPayload("responsePayload")
        responseMsg := response.Envelope(protocol.WithCorrelationID(msg.Headers.CorrelationID()), protocol.WithResponseRequired(false))
        responseMsg.Status = 200
        if replyErr := client.Reply(requestID, responseMsg); replyErr != nil {
            fmt.Printf("failed to send response to request Id %s: %v\n", requestID, replyErr)
        }
    }
}

Logging

A custom logger could be implemented based on ditto.Logger interface. For example:

type logger struct {
	prefix string
}

func (l logger) Println(v ...interface{}) {
    fmt.Println(l.prefix, fmt.Sprint(v...))
}

func (l logger) Printf(format string, v ...interface{}) {
    fmt.Printf(fmt.Sprint(l.prefix, " ", format), v...)
}

Then the Ditto library could be configured to use the logger by assigning the logging endpoints - ERROR, WARN, INFO and DEBUG.

func init() {
    ditto.ERROR = logger{prefix: "ERROR  "}
    ditto.WARN  = logger{prefix: "WARN   "}
    ditto.INFO  = logger{prefix: "INFO   "}
    ditto.DEBUG = logger{prefix: "DEBUG  "}
}