Etag

flask.py

from flask import Flask, request
from flask_restful import Resource, Api

from azure.appconfiguration import AzureAppConfigurationClient

app = Flask(__name__)
api = Api(app)

class Config(Resource):
    def __init__(self):
        self.client = AzureAppConfigurationClient.from_connection_string(connection_str)
        self.cache = {}
  
    def _refresh_cache():
        # Let's have a thread running this in parallel every 10 seconds or so
        # Shoudl lock but, meee, let's assume the cache is a locked one like.
        for key, value in self.cache.items():
            if (result := self.client.get_configuration_setting(key, etag=value.etag)) is not None:
                self.cache[key] = result

    def get(self, key_id):
        cache = self.cache.get(key_id, None)
        etag = cache.etag if cache else None # Means I have no etag, probably should be '*' under the hood? As a client, impl detail.
        try:
          # Assuming I get None
          return (self.client.get_configuration_setting(mykey, etag=etag) or cache).value
        except ResourceNotFoundError:
          return f"Resource {key_id} doesn't exist", 404

    def put(self, key_id):
        value = request.form['value']
        # I want to cache it first if it exists already, so I have the etag
        try:
          cache = self.cache.setdefault(key_id, self.client.get_configuration_setting(mykey))
          etag = cache.etag
          raise_condition = MatchConditions.IfModified
        except ResourceNotFoundError:
          etag = None # Means I have no etag, probably should be '*' under the hood? As a client, impl detail.
          raise_condition = MatchConditions.IfExists
        settings_to_send = ConfigurationSetting(
            key=key_id,
            value=value,
            content_type="text/plain"
          )
        try:
          self.set_configuration_setting(settings_to_send, etag=etag, raise_condition=raise_condition)
        except ResourceExists:
          return f"You can't create resource {key_id} anymore, someone did it before you", 400
        except ResourceModifed:
          return f"Since the last time you saw resource {key_id} it has changed, can't write", 400
        except ResourceReadOnlyError:
          return f"Resource {key_id} not writable, can't write", 400
        return f"Resource {key_id} updated"

api.add_resource(TodoSimple, '/<string:todo_id>')

if __name__ == '__main__':
    app.run(debug=True)

iot_notif.py

import time

from azure.core.exceptions import ResourceNotFoundError, ResourceModified
from azure.core import MatchConditions
from azure.appconfiguration import AzureAppConfigurationClient
from azure.eventhub import IotHubClient

client = AzureAppConfigurationClient.from_connection_string(connection_str)
iothub_client = IotHubClient.from_connection_string(connection_str2)
mykey = 'key'

# Monitor value and send a notification if anything changes
#
# Version 1
# I belive if nothing changed, I should receive None, since I don't think
# it's possible to store the None value. Discard this impl if it's possible
# to store a None value
cache = client.get_configuration_setting(mykey)
while True:
  print(f"My value {cache.value}")
  try:
    if (current := client.get_configuration_setting(mykey, etag=cache.etag)) is not None:
      iothub_client.send(f"Key {cache.key} changed")
      cache = current
      continue
  except ResourceNotFoundError:
    iothub_client.send(f"Resource {cache.key} doesn't exist anymore")
    break
  time.sleep(10)

# Version 2
# If None is a possible value, use exception instead
cache = client.get_configuration_setting(mykey)
while True:
  print(f"My value {cache.value}")
  try:
    cache = client.get_configuration_setting(mykey, etag=cache.etag, raise_condition=MatchConditions.IfModified)
  except ResourceModifiedError as err:
    iothub_client.send(f"Key {cache.key} changed")
    cache = err.model
  except ResourceNotFoundError:
    iothub_client.send(f"Resource {cache.key} doesn't exist anymore")
    break
  time.sleep(10)

print_value.py

import time

from azure.core.exceptions import ResourceNotFoundError
from azure.appconfiguration import AzureAppConfigurationClient

client = AzureAppConfigurationClient.from_connection_string(connection_str)
mykey = 'key'

# Refresh as needed
# I want to show this value every 10 seconds. I expect to receive None if nothing has changed, so I use the one in cache
# Under the hood I probably received a 304 and I don't care at my level
cache = client.get_configuration_setting(mykey)
while True:
  print(f"My value {cache.value}")
  try:
    cache = client.get_configuration_setting(mykey, etag=cache.etag)
  except ResourceNotFoundError:
    print(f"Resource {cache.key} doesn't exist anymore, quit")
    break
  time.sleep(10)