Delay app startup until mqtt is available

[FredericG-BE]

I have an app that registers on mqtt events. At startup the app fails as the registering on the mqtt events fail.

What would be the best way to delay the startup of the app until the mqtt service is started?

Thanks!

[craigbarratt]

Can you post some code? One hack would be to have a @startup function that includes the mqtt event trigger function in a try... except... loop that tries every few seconds until it succeeds.

[FredericG-BE]

Yes, I suppose I will try that. From what I have now, I will make some simplified code to test this approach.
Thanks a lot

[niklaspeura]

How do you deploy your stack? If you use docker you can set dependencies, and make sure mqtt is running before home assistant starts.

[FredericG-BE]

I use a standard HA OS on a PI, so no docker I suppose (this is still a bit of a blind spot for me to be honest). Are you referring to the mqtt broker that could be started first? I think it is the HA mqtt integration not being ready.
Thanks a lot

[FredericG-BE]

I made some simplified code for testing. What I found out:

• In most cases the registration on the mqtt events works fine when the app is started while HA/pyscript starts. So, I need to try multiple times to reproduce. I suppose that unrelated changes to the code or configuration can make the issue appear or disappear, the nice thing about race conditions
• There does not seem to be exception raised. There is a message in the log after the trigger was created, see log below
• When this failure occurred during startup, reloading the code (and so registering to the mqtt messages again) seems to fail silently; no error messages but no reception oven event either.
• When the registration failed at startup, there is an exception happening when restarting HA as pyscript tries to unregister (or this is what I think it is), see also below

2024-01-31 08:07:22.102 WARNING (SyncWorker_2) [homeassistant.loader] We found a custom integration openhasp which has not been tested by Home Assistant. This component might cause stability problems, be sure to disable it if you experience issues with Home Assistant
 ....
2024-01-31 08:07:37.379 INFO (MainThread) [custom_components.pyscript.global_ctx] Loaded /config/pyscript/modules/haspTest.py
2024-01-31 08:07:37.380 INFO (MainThread) [custom_components.pyscript.apps.mqttTest] HaspManager.__init__(plateName=plate_test) ref=1706684857.3804057
==> 2024-01-31 08:07:37.381 INFO (MainThread) [custom_components.pyscript.apps.mqttTest] >>> Setting up trigger - Done trigFunc=<custom_components.pyscript.eval.EvalFuncVar object at 0x7f8739c2d0>
==> 2024-01-31 08:07:37.381 INFO (MainThread) [custom_components.pyscript.global_ctx] Reloaded /config/pyscript/apps/mqttTest.py
==> 2024-01-31 08:07:37.397 ERROR (MainThread) [custom_components.pyscript.trigger] modules.haspTest.trigFunc: Cannot subscribe to topic 'hasp/discovery/#', make sure MQTT is set up correctly
2024-01-31 08:07:37.427 INFO (MainThread) [custom_components.pyscript.global_ctx] Loaded /config/pyscript/modules/fgLib.py
2024-01-31 08:07:37.432 INFO (MainThread) [custom_components.pyscript.global_ctx] Loaded /config/pyscript/dobissinterface.py
2024-01-31 08:07:37.442 INFO (MainThread) [custom_components.pyscript.global_ctx] Loaded /config/pyscript/example.py
2024-01-31 08:07:38.284 INFO (MainThread) [custom_components.pyscript.global_ctx] Loaded /config/pyscript/modules/openhasp.py
2024-01-31 08:07:38.285 INFO (MainThread) [custom_components.pyscript.global_ctx] Loaded /config/pyscript/haspTests.py
2024-01-31 08:07:38.286 INFO (MainThread) [custom_components.pyscript.global_ctx] Loaded /config/pyscript/louvres.py

While shutting down HA

Traceback (most recent call last):                                                                                                                                                                                                  
  File "/config/custom_components/pyscript/__init__.py", line 347, in hass_stop                                                                                                                                                     
    await unload_scripts(unload_all=True)                                                                                                                                                                                           
  File "/config/custom_components/pyscript/__init__.py", line 395, in unload_scripts                                                                                                                                                
    global_ctx.stop()                                                                                                                                                                                                               
  File "/config/custom_components/pyscript/global_ctx.py", line 81, in stop                                                                                                                                                         
    func.trigger_stop()                                                                                                                                                                                                             
  File "/config/custom_components/pyscript/eval.py", line 575, in trigger_stop                                                                                                                                                      
    trigger.stop()                                                                                                                                                                                                                  
  File "/config/custom_components/pyscript/trigger.py", line 922, in stop                                                                                                                                                           
    Mqtt.notify_del(self.mqtt_trigger[0], self.notify_q)                                                                                                                                                                            
  File "/config/custom_components/pyscript/mqtt.py", line 79, in notify_del                                                                                                                                                         
    cls.notify_remove[topic]()                                                                                                                                                                                                      
    ~~~~~~~~~~~~~~~~~^^^^^^^                                                                                                                                                                                                        
KeyError: 'hasp/discovery/#'            

The code I used:

modules/hapsTest.py:

import time # if only we could do this in real life...

def trigFuncFactory_mqtt(topic, func):

    # log.info(">>> Setting up trigger")

    try:
        @mqtt_trigger(topic)
        def trigFunc(topic, payload):
            func(topic, payload)
    except:
        log.info(">>> Setting up trigger - EXCEPTION")

    log.info(f">>> Setting up trigger - Done trigFunc={trigFunc}")

    return trigFunc

class HaspManager(object):
    def __init__(self, plateName):
        self.ref = time.time()
        log.info(f"HaspManager.__init__(plateName={plateName}) ref={self.ref}")

        self.plateName = plateName
        self.trigFunc = trigFuncFactory_mqtt("hasp/discovery/#", self.onDiscovery)

    def onDiscovery(self, topic, payload):
        log.info(f"HaspManager.onDiscovery(topic=\"{topic}\") ref={self.ref}")

apps/mqttTest.py:

from haspTest import *

hm = HaspManager("plate_test")

Thanks a lot for your help

[FredericG-BE]

For the record, I added
"dependencies": ["mqtt"]
to the manfest.json a few months ago and have never seen the issue again

BTW, still loving pyscript a lot, I use it for all my automations :)