Parsing binary data published by Auto-Event into Redis

[satyam1990]

Hi Team,

My Environment Info:
EdgeX Version: 2.1
EdgeX C SDK Version: 2.2

As I was implementing a sample device service using EdgeX C SDK I had few queries around Auto-Events.
I have configured auto events for my sample device to be triggered on every 10 seconds:
"autoEvents": [ {"interval":"10s","sourceName":"temperature","onChange":false} ]

I can see in my device service logs auto-events are being triggered and sent to Redis message bus, from stdout logs of my device service:

level=INFO ts=2022-11-15T11:44:40Z app=device-template correlation-id=c8d66f0c-d7af-48e4-b1a5-0a7d96b30bba msg="AutoEvent: Temp-Device01/temperature"
level=DEBUG ts=2022-11-15T11:44:40Z app=device-template correlation-id=c8d66f0c-d7af-48e4-b1a5-0a7d96b30bba msg="GET on device:"
level=DEBUG ts=2022-11-15T11:44:40Z app=device-template correlation-id=c8d66f0c-d7af-48e4-b1a5-0a7d96b30bba msg=" [Other] protocol:"
level=DEBUG ts=2022-11-15T11:44:40Z app=device-template correlation-id=c8d66f0c-d7af-48e4-b1a5-0a7d96b30bba msg="    Address = random"
level=DEBUG ts=2022-11-15T11:44:40Z app=device-template correlation-id=c8d66f0c-d7af-48e4-b1a5-0a7d96b30bba msg="    Port = 300"
level=DEBUG ts=2022-11-15T11:44:40Z app=device-template correlation-id=c8d66f0c-d7af-48e4-b1a5-0a7d96b30bba msg="Resource name: temperature"
level=DEBUG ts=2022-11-15T11:44:40Z app=device-template correlation-id=c8d66f0c-d7af-48e4-b1a5-0a7d96b30bba msg="iot_threadpool_add_work jobs/max: 1/4294967295"

I have written a small python client which subscribes to the events in redis published by my device service:

import redis

# connect with redis server
redis_conn = redis.Redis(host='localhost', port=6379, db=0)
redis_conn.auth(username="default", password="pT0lXEgTnf6wmX7943WGSScnrrzYsiEFaRXRZFHqFPnc")

my_subscription = redis_conn.pubsub()
my_subscription.subscribe('edgex.events.device.Temp-Device.Temp-Device01.temperature')
for message in my_subscription.listen():
    print(message)

I see output something as below, payload is not what I expected it to be:

-bash-4.4 /scratch/redis_client$ ./redis_subscribe.py 
{'type': 'subscribe', 'pattern': None, 'channel': b'edgex.events.device.Temp-Device.Temp-Device01.temperature', 'data': 1}

{'type': 'message', 
'pattern': None, 
'channel': b'edgex.events.device.Temp-Device.Temp-Device01.temperature', 
'data': b'{"CorrelationID":"cd3d6fad-02c7-424c-a149-6b82e3e83a42",
"Payload":"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",
"ContentType":"application/json"}'}

But If I get the same ResourceAttribute via Core Command REST API, I get valid data as below:

GET: http://<IP>:59882/api/v2/device/name/Temp-Device01/temperature
{
    "apiVersion": "v2",
    "statusCode": 200,
    "event": {
        "apiVersion": "v2",
        "id": "4e3c3efe-3f49-405f-8cf6-38244708e5e4",
        "deviceName": "Temp-Device01",
        "profileName": "Temp-Device",
        "sourceName": "temperature",
        "origin": 1668513227987209926,
        "readings": [
            {
                "id": "dc58133f-7fc9-4526-bd16-dc7b60c5c11a",
                "origin": 1668513227987209926,
                "deviceName": "Temp-Device01",
                "resourceName": "temperature",
                "profileName": "Temp-Device",
                "valueType": "Int32",
                "value": "18"
            }
        ]
    }
}

So my question is there some parsing that we need to do on "Payload" when getting data through redis PUB/SUB? Because as you can see above we see some binary data when we read through redis.

Also few general questions I had around Auto-Events:
Are the auto-events triggered by the EdgeX C SDK?
How auto-events communicate with the device service, do they also use same REST API which Core Command Exposes?

[iain-anderson]

Hi, the Payload string is base-64 encoded. Decoded it reads:

{
  "apiVersion": "v2",
  "event": {
    "apiVersion": "v2",
    "deviceName": "Temp-Device01",
    "id": "26843afe-b558-4b0c-a2ca-44bd9dc6207f",
    "origin": 1668513120403444500,
    "profileName": "Temp-Device",
    "readings": [
      {
        "apiVersion": "v2",
        "deviceName": "Temp-Device01",
        "id": "765573d8-0d84-4f1f-8651-681d53dc7655",
        "origin": 1668513120403444500,
        "profileName": "Temp-Device",
        "resourceName": "temperature",
        "value": "7",
        "valueType": "Int32"
      }
    ],
    "sourceName": "temperature"
  },
  "statusCode": 200
}

so you should be okay working from that.
The autoevents are triggered in the SDK. The SDK calls the get handler in the device service in the same way as it would if it had received a REST request.

[satyam1990]

Thanks a ton @iain-anderson