bharathbob/apple-mqtt-example

MQTT usage example for iOS

MQTT example

This example walks you through the basic complete usage of Paho MQTT.

Introduction

The MQTT library used is the C library developed by Eclipse Paho (is an OpenSource project). You can find more information here:

• Paho C Client.
• Git repository with the code: http://git.eclipse.org/c/paho/org.eclipse.paho.mqtt.c.git

Update 25/05/2015

If you are trying to use MQTT for an iOS application I will highly recommend you to use a native (Objective-C/Swift) iOS library. Using C or wrapper libraries usually means you are using POSIX networking calls at some point. Apple forbids the use of third party networking libraries from using the mobile internet antenna. Thus if you use Paho or something similar, you can only use MQTT when you are connected to a WiFi network.

Name	Type	Programming Language	Code
Paho	Original	C	Open-Source. Eclipse project
IBM	Original	C	Close Source. IBM SDK
Mosquitto	Original	C	Open-Source. Eclipse project
MQTTKit	Wrapper (Mosquitto)	Objective-C	Open-Source. Github
Marquette	Wrapper (Mosquitto)	Objective-C	Open-Source. Github
Moscapsule	Wrapper (Mosquitto)	Swift	Open-Source. Github
Musqueteer	Wrapper (Mosquitto)	Objective-C
MQTT-Client	Native	Objective-C	Open-Source. Github
MQTTSDK	Native	Objective-C
CocoaMQTT	Native	Swift	Open-Source. Github

MQTT C Client

The Paho MQTT C Client offers two APIs, one synchronous and one asynchronous. For any professional usage, you should target the asynchronous one since you don't want to stall any thread waiting or receiving messages. Thus, the examples given only offer the Asynchronous Calls.

Dependencies and binaries

I have build the MQTT Paho source code into a static library called libMQTT.a with three headers: MQTTAsync.h, MQTTClient.h, MQTTClientPersistance.h. It can be found under Paho > external > MQTT.

The binary supports all iOS devices (ARMv7, ARMv7s, ARMv64, and i386 simulator) and OSX machines (x86_64).

The libMQTT.a static library needs the OpenSSL static library. I have compiled the latest OpenSSL library (1.0.2) into the file you can find in Paho > external > MQTT.

I decided to make two separate static libraries instead of one binary blob, for three reasons:

1. It is easy to update each library separately.
2. Right now each static library is too big (since it supports all those CPU architectures), you can reduce its size greatly by just releasing the static library for platform you are targeting. For example, in your distribution release for the app store, you can take the Simulator and x86_64 code from the binaries reducing the size of both MQTT and OpenSSL by 40% of the size (8.2 MB of the total size).
3. Once you have set up the XCode project for static libraries it doesn't really matter whether you add one or two. Having the benefit of using one or the other independently (if you need that).

Adding static libraries to XCode

You need to do three steps:

1. Go to your project > Build Settings and in the search box look for Header Search Path. In the value of that plist array you should include the location of the folder where you have the external library. In my example: $(PROJECT_DIR)/external.
2. Go to your project > Build Settings and in the search box look for Library Search Path. In the value of that plist array you should also include the location of the folder where you have the external library ($(PROJECT_DIR)/external as before), but be sure to change the property to recursive (by default is non-recursive).
3. Go to your project > Build Phases and in the Link Binary With Librariessection drag and drop the static library binaries. In this case: libcrypto.a, libssl.a, libMQTT.a.

Using MQTT

To use the MQTT code add the following headers to the files targeting MQTT communications.

#import <MQTT/MQTTClient.h>
#import <MQTT/MQTTAsync.h>