Subscribing to when a shadow changes and retrieving that change

Question

I am having issues using this mostly default code to get a change in shadow. The code is very slightly adapted from AWS tutorial code. I just removed the arg section and changes it to hard coded variables. I also added a print statement in the callback.
```
import sys
import time
import traceback

from awsiot.greengrasscoreipc.clientv2 import GreengrassCoreIPCClientV2
from awsiot.greengrasscoreipc.model import (
    SubscriptionResponseMessage,
    UnauthorizedError
)

def main():

try:
        message = 'script initialized'
        topic = 'dsvvefvfq'
        ipc_client = GreengrassCoreIPCClientV2()
        # Subscription operations return a tuple with the response and the operation.
        _, operation = ipc_client.subscribe_to_topic(topic=topic, on_stream_event=on_stream_event,
                                                     on_stream_error=on_stream_error, on_stream_closed=on_stream_closed)
        print('Successfully subscribed to topic: ' + topic)

# Keep the main thread alive, or the process will exit.
        try:
            while True:
                time.sleep(10)
        except InterruptedError:
            print('Subscribe interrupted.')

# To stop subscribing, close the stream.
        operation.close()
    except UnauthorizedError:
        print('Unauthorized error while subscribing to topic')
        traceback.print_exc()
        exit(1)
    except Exception:
        print('Exception occurred', file=sys.stderr)
        traceback.print_exc()
        exit(1)

def on_stream_event(event: SubscriptionResponseMessage) -> None:
    try:
        print("Callback was involked")
        message = str(event.binary_message.message, 'utf-8')
        topic = event.binary_message.context.topic
        print('Received new message on topic %s: %s' % (topic, message))
    except:
        traceback.print_exc()

def on_stream_error(error: Exception) -> bool:
    print('Received a stream error.', file=sys.stderr)
    traceback.print_exc()
    return False  # Return True to close stream, False to keep stream open.

def on_stream_closed() -> None:
    print('Subscribe to topic stream closed.')

if __name__ == '__main__':
    main()
```
My shadowmanager configuration looks like this:
```
{
  "reset": [],
  "merge": {
    "reset": [],
    "merge": {
      "strategy": {
        "type": "realTime"
      },
      "synchronize": {
        "coreThing": {
          "classic": true
        },
        "namedShadows": [
          "test",
          "dsvvefvfq"
        ],
        "direction": "betweenDeviceAndCloud"
      }
    }
  }
}
```
My component code looks like this:
```
{
  "accessControl": {
    "aws.greengrass.ShadowManager": {
      "com.xxxxxxxx.productivity.cycle_count:shadow:1": {
        "policyDescription": "allow access to shadows",
        "operations": [
          "aws.greengrass#GetThingShadow",
          "aws.greengrass#UpdateThingShadow",
          "aws.greengrass#ListNamedShadowsForThing"
        ],
        "resources": [
          "*"
        ]
      }
    },
    "aws.greengrass.ipc.pubsub": {
      "com.xxxxxxxx.productivity.cycle_count:pubsub:1": {
        "policyDescription": "Allows access to publish/subscribe to all topics.",
        "operations": [
          "aws.greengrass#PublishToTopic",
          "aws.greengrass#SubscribeToTopic"
        ],
        "resources": [
          "*"
        ]
      }
    }
  }
}
```

I am expecting that python code to "see" that the shadow has changed and execute the callback function `on_stream_event`. It is not.

Why?

MichaelDombrowski-AWS · Answer

Hi again @flycast,

A couple things I notice:

1. Your shadow manager configuration is not in the correct format
```
{
  "reset": [],
  "merge": {
    "reset": [],
    "merge": {
```

You have `merge` inside of another `merge`. Please make sure that the configuration is correctly set.

2. You are subscribing to the topic named `dsvvefvfq`. Who or what do you expect to be publishing to `dsvvefvfq`?

Shadow manager publishes to local pubsub topics using the device shadow topics (https://docs.aws.amazon.com/iot/latest/developerguide/device-shadow-mqtt.html) as explained here: https://docs.aws.amazon.com/greengrass/v2/developerguide/interact-with-shadows-in-components.html#react-shadow-events.

Therefore, you should be subscribing to `$aws/things//shadow/name/dsvvefvfq/#`

You can subscribe to `$aws/things/#` which is a wildcard, you will then be able to see all traffic to the topics beginning with `$aws/things/` and update your code accordingly.

Cheers,

Michael

flycast · Answer

Too long for a comment:
To answer your question  #2 - I expect to publish data in a shadow for the core device to use to publish with.

When I publish an update to a shadow I am seeing the updates get logged in the greengrass.log so I know shadowmanager is getting them.

My current component config looks like:
```
{
  "accessControl": {
    "aws.greengrass.ShadowManager": {
      "com.xxxxxxxx.productivity.cycle_count:shadow:1": {
        "policyDescription": "",
        "operations": [
          "aws.greengrass#GetThingShadow",
          "aws.greengrass#UpdateThingShadow",
          "aws.greengrass#DeleteThingShadow",
          "aws.greengrass#ListNamedShadowsForThing"
        ],
        "resources": [
          "*"
        ]
      }
    },
    "aws.greengrass.ipc.pubsub": {
      "com.xxxxxxxx.productivity.cycle_count:pubsub:1": {
        "policyDescription": "",
        "operations": [
          "aws.greengrass#SubscribeToTopic"
        ],
        "resources": [
          "*"
        ]
      }
    }
  }
}
```

As I understand this the component configuration will get all shadow traffic from shadowManager and any mqtt packets from pubsub.

When I update the shadow `dsvvefvfq` I see the changes logged by shadowManager but nothing happens in my custom component log. I am expecting to see the callback execute. Bare minimum I expect to see the `print("Callback was involked")` message in the component log.

```
def on_stream_event(event: SubscriptionResponseMessage) -> None:
    try:
        print("Callback was involked")
        message = str(event.binary_message.message, 'utf-8')
        topic = event.binary_message.context.topic
        print('Received new message on topic %s: %s' % (topic, message))
    except:
        traceback.print_exc()

```

Subscribing to when a shadow changes and retrieving that change

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