Demo application that uses the AWS IoT Device Shadow library, MQTT Client library, and JSON library to interact with the AWS IoT Device Shadow service.

The device is assumed to have the powerOn state, which can be 1 or 0 depending on whether or not the device is powered on. This state is maintained in the device's shadow. The demo does the following operations:

• Establish a MQTT connection. ( step 1. )
• Assemble MQTT topic strings for device shadow operations using macros defined by the Device Shadow library. ( step 6. )
• Subscribe to the MQTT topics for shadow update operations. ( step 8. )
• Publish a desired powerOn state. This causes a device shadow update delta message to be sent to the device. ( step 13 ~ step 14. )
• Handle the incoming MQTT message in the MQTT event callback and determine whether the message is related to the device shadow using Shadow_MatchTopic. If the message is a device shadow update delta message, set a flag for the main function to know. The main function will then publish a second message to update the reported powerOn state. ( step 15 ~ step 26. )
• Handle the incoming MQTT message again in the MQTT event callback and determine whether the message is related to the device shadow. If the message is a device shadow update accepted message, verify that it is for the update operation initiated previously by ensuring that it contains the same clientToken as sent in the update operation. ( step 27 ~ step 33. )