Perfect-Mosquitto

This project provides a Swift class wrapper of mosquitto client library which implements the MQTT protocol version 3.1 and 3.1.1.

This package builds with Swift Package Manager and is part of the Perfect project, however, it can work independently as a Server Side Swift component.

Ensure you have installed and activated the latest Swift 3.0 tool chain.

OS X Notes

Homebrew Installation

This project depends on mosquitto library. To install on mac OS, try command brew:

$ brew install mosquitto

PC File

A package configuration file is needed, for example, /usr/local/lib/pkgconfig/mosquitto.pc as below:

Name: mosquitto
Description: Mosquitto Client Library
Version: 1.4.11
Requires:
Libs: -L/usr/local/lib -lmosquitto
Cflags: -I/usr/local/include

Please also export an environmental variable called $PKG_CONFIG_PATH:

$ export PKG_CONFIG_PATH="/usr/local/lib/pkgconfig:/usr/lib/pkgconfig"

Linux Notes

This project depends on Ubuntu 16.04 library libmosquitto-dev:

$ apt-get libmosquitto-dev

Quick Start

Library Open / Close

Before using any functions of Perfect Mosquitto, please initialize the function set by calling Mosquitto.OpenLibrary(). Also, Mosquitto.CloseLibrary() is highly recommended once program quitted.

Note Both operations are not thread safe, so please perform the operation prior to any threads.

Initialize a Mosquitto Client

Mosquitto instance can be constructed by calling with or without any parameters. The simplest form can be:

let m = Mosquitto()

Which means assigning a random client id to this new instance, while all messages and subscriptions will be cleared once disconnected.

However, you can also assign it with a customized client id with instruction of keeping all messages and subscription by this specific name. This is useful for resuming work in case of connection loss.

let mosquitto = Mosquitto(id: "myInstanceId", cleanSession: false)

Connect to a Message Broker

A message broker is a server that implements MQTT protocol and serves all clients in terms of messaging - receiving messages from producer and dispatching them to message subscribers.

Although connection to a message broker can be asynchronous, keeping alive or binding to a specific network address, api connect() can be as express as demo below - only a host name and a port (usually 1883) are required:

try moosquitto.connect(host: "mybroker.com", port: 1883)

Although the instance can disconnect() from a broker automatically when no longer uses the object, it is recommended to call this function explicitly for a better practice. Besides, a reconnect() function is available for the same instance.

Threading Model

Start / Stop

Perfect Mosquitto is flexible in dealing with threads. Clients can call start() to run the mosquitto thread in background, which will automatically execute message publishing / receiving without any extra operations in the main thread, i.e., the thread will do the actual sending after calling publish() and activate callbacks for incoming messages. If no longer running, you can also stop the service thread at any time by calling stop()

// start the messaging thread as a background service, it will not block the main thread and will return immediately.
try mosquitto.start()

// do your other work in the main thread, such as publishing etc., and the messages received will go to the callbacks

// stop the background messaging service if no longer need.
try mosquitto.stop()

Wait for Event

Or, alternatively, you can process events in the main thread, by calling wait() method frequently in a message polling style:

// wait a minimal while for events. 
// In this specific moment, mosquitto will perform actual message sending,
// and pull messages from broker / run call backs.
try mosquitto.wait(0)

The only parameter of wait() is the timeout value for message polling in milliseconds. Zero represents the minimal period of the system wait and negative value will be treated the same as 1000 (1 second).

⚠️ NOTE ⚠️ DO NOT MIX start()/stop() with wait()

Publish a Message

Once connected to a broker, you can send messages at any time you want:

var msg = Mosquitto.Message()
msg.id = 100 // input your message id here
msg.topic = "publish/test"
msg.string = "publication test 🇨🇳🇨🇦"

let mid = try mosquitto.publish(message: msg)

As demo above, firstly setup an empty message structure, then assign an message id (integer), a topic for this message and the message content; Then call publish() method to send it to the broker with a returned message id.

Note Message content can also be a binary buffer, for example: swift // send a [Int8] array msg.payload = [40, 41, 42, 43, 44, 45]

Once published, call start() or wait() to perform the actual message sending as described in the Thread Model.

Message Subscription and Receiving

The only way to receive a MQTT message in Perfect Mosquitto is messaging callback:

mosquitto.OnMessage = { msg in

    // print out message id
    print(msg.id)

    // print out message topic
    print(msg.topic)

    // print out message content
    print(msg.string)

    // print out message body, in a binary array form
    print(msg.payload)
}//end on Message

Once set the callback, you can call subscribe() to complete the message subscription on client side:

try mosquitto.subscribe(topic: "publish/test")

Once subscribed, call start() or wait() to perform actual receiving process as described in the Thread Model.

More API

Perfect Mosquitto also provides a rich set of functions beside the above ones, please check the project references for detail information.

Event Callbacks

Please set the following event callbacks for your mosquitto objects if need:

API Parameters Description
OnConnect { status in } ConnectionStatus Triggered on connection
OnDisconnected { status in } ConnectionStatus Triggered on disconnection
OnPublish { msg in } Message Triggered when message sent
OnMessage { msg in } Message Triggered on message arrival
OnSubscribe { id, qos in } (Int32, [Int32]) Triggered on subscription
OnUnsubscribe { id in } Int32 (message id) Triggered on unsubscription
OnLog { level, content in } (LogLevel, String) Triggered on log output

TLS Configuration

  • Set TLS certification file: func setTLS(caFile: String, caPath: String, certFile: String? = nil, keyFile: String? = nil, keyPass: String? = nil) throws

  • Set TLS verification method: func setTLS(verify: SSLVerify = .PEER, version: String? = nil, ciphers: String? = nil) throws

  • Set pre shared key: func setTLS(psk: String, identity: String, ciphers: String? = nil) throws

Miscellaneous Functions

  • Configure will information for a mosquitto instance: func setConfigWill(message: Message?) throws

  • Configure username and password for a mosquitton instance: func login(username: String? = nil, password: String? = nil) throws

  • Set the number of seconds to wait before retrying messages: func setMessageRetry(max: UInt32 = 20)

  • Set the number of QoS 1 and 2 messages that can be “in flight” at one time: func setInflightMessages(max: UInt32 = 20) throws

  • Control the behaviour of the client when it has unexpectedly disconnected: func reconnectSetDelay(delay: UInt32 = 2, delayMax: UInt32 = 10, backOff: Bool = false) throws

  • Reconnecting to a broker after a connection has been lost: func reconnect(_ asynchronous: Bool = true) throws

  • Reuse an existing mosquitto instance: func reset(id: String? = nil, cleanSession: Bool = true) throws

  • Set MQTT Version: func setClientOption(_ version: MQTTVersion = .V31, value: UnsafeMutableRawPointer) throws

  • Explain an exception (in English): static func Explain(_ fault: Exception) -> String