go-mod-messaging

Messaging client library for use by Go implementation of EdgeX micro services. This project contains the abstract Message Bus interface and an implementation for ZeroMQ, MQTT, and Redis Pub/Sub. These interface functions connect, publish, subscribe and disconnect to/from the Message Bus.

What is this repository for?

Create new MessageClient
Connect to the Message Bus
Public messages to the Message Bus
Subscribe to and receives messages from the Messsage Bus
Disconnect from the Message Bus

Installation

Make sure you have modules enabled, i.e. have an initialized go.mod file
If your code is in your GOPATH then make sure GO111MODULE=on is set
Run go get github.com/edgexfoundry/go-mod-messaging/v2
- This will add the go-mod-messaging to the go.mod file and download it into the module cache

How to Use

This library is used by Go programs for interacting with the Message Bus (i.e. redis).

The Message Bus connection information as well as which implementation to use is stored in the service's toml configuration as:

[MessageQueue]
Protocol = "redis"
Host = "localhost"
Port = 6379
Type = "redis"

MQTT Configuration

The MQTT client abstraction allows for the following additional configuration properties:

Username
Password
ClientId
Qos
KeepAlive
Retained
AutoReconnect
CleanSession
CertFile
KeyFile
CertPEMBlock
KeyPEMBlock
SkipCertVerify

Which can be provided via TOML:

[MessageQueue]
Protocol = "tcp"
Host = "localhost"
Port = 1883
Type = "mqtt"
Topic = "events"
    [MessageQueue.Optional]
    ClientId = "MyClient"
    Username = "MyUsername"
    ...

Or programmatically in the Optional field of the MessageBusConfig struct. For example,

types.MessageBusConfig{
				PublishHost: types.HostInfo{Host: "example.com", Port: 9090, Protocol: "tcp"},
				Optional: map[string]string{
					"ClientId":          "MyClientID",
					"Username":          "MyUser",
					"Password":          "MyPassword",
					...
				}}

NOTE
The best way to construct the Optional map is to use the provided mqttOptionalConfigurationBuilder struct which gives the additional benefit of ensuring the expected types for each property is correct.

Redis Pub/Sub

Requirement: Redis version 5+

The Redis Pub/Sub client implementation uses Redis to accept, store, and distribute messages to appropriate consumer. This is achieved by treating each topic as a Redis Pub/Sub channel. Publishing and subscribing takes place within a Redis Pub/Sub and is abstracted by the Redis Pub/Sub client, so you can interact with the Redis Pub/Sub implementation of the MessagingClient as you would with other implementations.

The Redis Pub/Sub client abstraction allows for the following additional configuration properties:

Password

Which can be provided via TOML:

[MessageQueue]
Protocol = "redis"
Host = "localhost"
Port = 6379
Type = "redis"
    [MessageQueue.Optional]
    Password = "MyPassword"

Or programmatically in the Optional field of the MessageBusConfig struct. For example,

types.MessageBusConfig{
				PublishHost: types.HostInfo{Host: "localhost", Port: 6379, Protocol: "redis"},
				Optional: map[string]string{
					"Password":          "MyPassword",
				}}

NOTE
The best way to construct the Optional map is to use the provided redisOptionalConfigurationBuilder struct which gives the additional benefit of ensuring the expected types for each property is correct.

The following code snippets demonstrate how a service uses this messaging module to create a connection, send messages, and receive messages.

This code snippet shows how to connect to the abstract message bus.

var messageBus messaging.MessageClient

var err error
messageBus, err = msgFactory.NewMessageClient(types.MessageBusConfig{
  PublishHost: types.HostInfo{
  Host:     Configuration.MessageQueue.Host,
  Port:     Configuration.MessageQueue.Port,
  Protocol: Configuration.MessageQueue.Protocol,
  },
  Type: Configuration.MessageQueue.Type,})

if err != nil {
  LoggingClient.Error("failed to create messaging client: " + err.Error())
}

err = messsageBus.Connect()

if err != nil {
  LoggingClient.Error("failed to connect to message bus: " + err.Error())
}

This code snippet shows how to publish a message to the abstract message bus.

...
payload, err := json.Marshal(evt)
...
msgEnvelope := types.MessageEnvelope{
  CorrelationID: evt.CorrelationId,
  Payload:       payload,
  ContentType:   clients.ContentJson,
}

err = messageBus.Publish(msgEnvelope, Configuration.MessageQueue.Topic)

This code snippet shows how to subscribe to the abstract message bus.

messageBus, err := factory.NewMessageClient(types.MessageBusConfig{
  SubscribeHost: types.HostInfo{
  Host:     Configuration.MessageQueue.Host,
  Port:     Configuration.MessageQueue.Port,
  Protocol: Configuration.MessageQueue.Protocol,
  },
  Type: Configuration.MessageQueue.Type,
})

if err != nil {
  LoggingClient.Error("failed to create messaging client: " + err.Error())
return
}

if err := messageBus.Connect(); err != nil {
  LoggingClient.Error("failed to connect to message bus: " + err.Error())
  return
}

topics := []types.TopicChannel{
    {
      Topic:    Configuration.MessageQueue.Topic,
      Messages: messages,
    },
}

err = messageBus.Subscribe(topics, messageErrors)
if err != nil {
  LoggingClient.Error("failed to subscribe for event messages: " + err.Error())
  return
}

This code snippet shows how to receive data on the message channel after you have subscribed to the bus.