Unable to read Azure IoT hub MQTT subscription message data

1
votes

I have successfully connected my ESP8266 Arduino project to the Azure IoT hub by following the steps outlined here:

https://azure.microsoft.com/en-gb/documentation/articles/iot-hub-mqtt-support/

The MQTT library that I am using is the following library:

https://github.com/Imroy/pubsubclient

Using the code I have been able to publish events to azure. The problem starts when trying to read the messages that are passed to the device.

Here is the code:

http://pastebin.com/7AVLQfFh

When I sue the Azure Device Explorer to send a message to the device the I get the following results:

Capture of results
As you can see the payload length is the same as the number of characters in the message but the characters are not the same. And also if I vary the string sent then the vales in the result are the same.

As a sanity check I have tried the code against a different MQTT service (Adafruit IO) and the results are as to be expected (here the message is 'ON' or 'OFF'):

Adafruit IO image The Azure MQTT service must be doing something different when it sends the messages to the device, what I needs to know is what it does differently.

2
azurearduinomqttesp8266azure-iot-hub

2 Answers

2
votes

Just a couple of hours ago I managed to get the messages flowing from Azure IoT hub to my ESP8266 using the original PubSubClient - link here. You are using the fork of that library that has been made more object oriented and probably has more enhancements.. but if you aren't very hooked on using the newer version I'd recommend getting the original one and trying it out.

I have my code on github if you need some reference: link

One important mention: the PubSubClient.h needs changing the #defineMQTT_MAX_PACKET_SIZE 128 to #defineMQTT_MAX_PACKET_SIZE 256 or more if you work with big packets

Also, I haven't tried to send any messages so I don't know how that'll work.

Update: I've also written a short blog post on how to set it up: link

1
votes

According to this documentation page, property_bag is RFC2396 encoded.

RFC 2396-encoded(<PropertyName1>)=RFC 2396-encoded(<PropertyValue1>)&RFC 2396-encoded(<PropertyName2>)=RFC 2396-encoded(<PropertyValue2>)…

But isn't ABCD the same in plain text vs URI encoded you ask... Well, yes.

Install stunnel (https://www.stunnel.org/index.html), open a TLS 1.2 connection to IoT Hub on 8883/TCP and then point MQTT.fx or Paho to it and sniff the traffic with Wireshark, see what you get.

I was able to read all messages in plain ASCII text while talking to IoT Hub over REST, so whatever this is i think it's MQTT specific.

If you haven't done so already you should open an issue on their GitHub. They seem to be quite responsive: https://github.com/Azure/azure-iot-sdks/issues