Monday, 17 July 2017

Using MQTT on Mac and iOS

About a year ago we wanted to see how we could move the robot car with the phone. One option was to create an Message Queue Telemetry Transport (MQTT) broker on the operating system of the robot (raspberry pi) and then control it using simple commands like "Left" "Right" "Forward" and "Backwards".

To test this I connected my phone to my laptop using the laptop as my robot car operating system. At the time I forgot to do this write up so I'm doing so now so that others can do a similar test / play with MQTT with just their phone and laptop.

So the devices I'm going to be using are a MacBook Pro (macOS Sierra v10.12.5) and an iPhone 6S (v10.3.2). Here are the steps you need to follow:

1. Installing an MQTT Broker
I first installed eclipse Mosquitto open source MQTT, which - at the time of writing - implements MQTT protocol version 3.1 with the Arduino and other small "internet of things" devices in minds.

MQTT works using a publish / subscribe model. Read here to learn more, or get it straight from the Mosquitto's mouth here!
To install on the mac, go to your terminal and open a session.
  > brew install mosquitto

This will take several minutes. The version I am using is "mosquitto-1.4.8_1"
Upon completion the broker will usually start by default using port 1883 on the local network. (In my case my wifi)
For a full guide you can see here, the author also goes into a bit more detail about installing "brew" and the options for starting the broker / editing the configuration.

I simply use:
 > brew services start mosquitto
or if the service is already running, I use:
 > brew services restart mosquitto
to change the default settings i.e. port or use TLS/SSL you need to change the config:
 > /usr/local/etc/mosquitto/mosquitto.conf

2. Find your network IP address
In my case I was using my wifi so I went directly to:
 > system preferences / network / wifi
underneath the "connected" status was my IP Address.

To find your IP on smartphone or other device there's a useful guide here.

3. MQTT for your Phone
When I first tried this last year there was a very good utility called MQTTool for the iPhone but it has since disappeared!

Instead I tried MQTT Probe, MqttClient and StompClient. These simply didn't work on my phone. The connection kept dropping with the mac or the buttons simply didn't work. I finally found Mqttt which worked well and allowed you to view publish and subscribe on the same screen!

Android has a much wider variety of options as can be seen here though Hive MQ suggests MyMQTT or MQTT Client.

Mqttt application
My demonstration will look at using Mqttt though all the apps look and feel much the same so it would be easy to follow these instructions for all of them.

4. Connecting Mqttt to your MQTT broker
To achieve this we simple need to give ip address we had earlier in the "Host" section and set the port to "1883" or whatever you have changed your default to be. The "Client ID" will automatically fill for you. Selecting "Clean Session" will provide a new client view each time. Press "Connect" to connect to the broker.

Connection Page
5. Testing our mobile to mac publish
After we have connected we come to the publish / subscribe screen. The smaller boxes allow you to type the topic strings and the bigger boxes are used for the messages.

For our first test we will use the bottom group (Publish) and give a topic string. This could be
 > anything/You/Like
though I will be using
 > topic/Aiden
for my example. Refer to the Pub / Sub model links for guidance on topic syntax, do's and do nots.

In the message box for our simple test we will type
 > Hello

We need to go to our mac terminal and run the following command:
 > mosquitto_sub -h -p 1883 -v -t 'topic/Aiden'

This command runs an MQTT Client and subscribes to the ip address defined with "-h" and to the port defined with "-p". "-v" says to print any published messages verbosely and "-t" says which topic to subscribe to. This process to will continue to run, waiting for any published messages to arrive to the topic string.

In our iOS Application Mqttt we can now press "Publish". We should now see the "Hello" message on the mac terminal as can be seen below.
Published Output
Subscription Output

5a. Publishing from the mac
To achieve the same test from the mac, we would need to simply open a new terminal (leaving the subscribe command running where it currently is) and run the following command:
> mosquitto_pub -t topic/Aiden -m “blah blah”

We would then expect to see the message "topic/Aiden blah blah" appear bellow the "topic/Aiden Hello" we had previously received in the subscription terminal. We can cancel the subscribe process in the terminal now.

6. Event Handling 
I then wanted to test pushing messages back to the Mqttt tool from the broker after it has received a message from the subscribed string. The total flow will go: Phone publish -> broker interpret -> broker publish to response string.

In the Mqttt tool we want to add a Subscription in the Subscription area, we first assign a topic:
 > topic/Fred
and press "Subscribe"

This is now doing what the broker had been doing previously but a different topic and instead from the phone, waiting for published messages to come through on the topic. For this example we will use the phone to publish to "topic/Aiden", the mac will then pick up that message in a shell script and forward the message to "topic/Fred".

In the mac in an open terminal and a dedicated folder we want to complete the following commands:
 > touch
 > touch mqtt.log

The MQTT shell script will have a constant loop which take the top line of the log file (where we will send published messages). It will then delete the top line that has been processed. If the top line was empty (i.e. no published messages to process) the loop restarts. If the top line held data, we trim the topic string from the message and publish the message only to the "topic/Fred" topic.

#get the log file name
echo "Check the shell script log file"
while true; do
        #get the top line of the log file
        line=$(head -n 1 ${filename})
        #delete the top line of the log file
        echo "$(tail -n +2 ${filename})" > ${filename}
        #if the top line was not blank
        if [[ ${line} != "" ]]; then
        #remove the topic string from the message
        newOutput=${line#* }
         #publish the string to topic/Fred
        mosquitto_pub -t topic/Fred -m "\"$newOutput\""

7. Test the Event Handling shell script
On the mac we open two terminals to the location of the and log file.

Terminal 1:
 > chmod 755
 > ./
Terminal 2:
 > mosquitto_sub -h -p 1883 -v -t 'topic/Aiden' >> mqtt.log

On Mqttt we write a message in the publish box and publish it.
I will try the following:
 > hello
 > hello
 > hello my name is Aiden

Replace "Aiden" with your own name.

The subscription on one terminal will write to the log file to be processed by the running shell script.
If successful we will see the message appear in the "topic/Fred" subscription message box.

Example Response Output
There’s lots we can make the laptop do other then reply. i.e. invoke an API call, move a robot, turn on bedroom lights, run a function to unlock the door for a guest coming around the house, open a garage door.

The reply sent back could be “done” “incomplete” “failed”. This is also important for when you want to audit messages being sent and received as we can send to a dedicated topic which stores the messages in some way.

8. Load Testing
Very briefly, we can load test MQTT using several existing tools. One such tool is MQTT Box which can be found here.

I hope this was helpful, Enjoy using MQTT!

Any questions feel free to email me!

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