MQTT fan does not work in optimistic mode

[raomin]

Home Assistant release with the issue:
0.91.2

Operating environment (Hass.io/Docker/Windows/etc.):
pip installed; Python 3.7.3rc1

Component/platform:
MQTT Fan

Description of problem:
MQTT fan does not work in optimistic mode. When discovered without state_topic and/or
with "optimistic":"true" the fan behaves in non-optimistic mode: setting up manually to ON and it will turn back to OFF by itself.

Steps to reproduce:

1. With mqtt discovery configured:

mqtt:
    broker: localhost
    discovery: true
    discovery_prefix: "homeassistant"

2. run the following command:
   mosquitto_pub -t 'homeassistant/fan/underground/config' -m '{"name":"fanUnderground","cmd_t":"homeassistant/fanUnderground/set"}'
3. Add the fan in the UI (lovelace).
4. Click on the switch to set it on.

2 sec later the fans turns back to off by itself.

Same behaviour when I set a state_topic and/or "optimistic":"true" in the mqtt configuration message.

[emontnemery]

Optimistic mode is simply not implemented in MQTT Fan even though the configuration option is there, I'll fix that + add tests soon.
Out of curiousity: Why doesn't your fan send a state message back?

[github-actions]

Hey there @home-assistant/core, mind taking a look at this issue as its been labeled with a integration (mqtt) you are listed as a codeowner for? Thanks!

[raomin]

Thanks for the feedbacl @emontnemery. It's also described in the documentation.
My 'fan' is actually an esp8266 controlling a powerful server fan.
I'll probably drop the 'fan' component for a number input slider to mqtt as my 'fan' can get control the power from 0-1024 and I couldn't find any MQTT component that could receive a numeric value (like a MQTT binarynumeric sensor). Maybe I'll code one...?

[emontnemery]

I couldn't find any MQTT component that could receive a numeric value

I guess you mean you want the MQTT component to SEND a numeric value, not receive one?
If so, you could perhaps use MQTT light, with brightness support + custom icon.

[raomin]

Correct. I needed an HA MQTT component to SEND to my esp8266 in mqtt.
Thanks for the excellent suggestion @emontnemery I now have a nice fan ui controller :)

BTW the MQTT light was not optimistic until I forced it to true despite not having a state topic... Should I open a new bug?
-edit-
It appears that HASS defaults a 'state_topic': 'homeassistant/light/underground2/state' for the MQTT light although it is not part of the config mqtt message. Hence it is not optimistic because it finds a state_topic

[emontnemery]

Yes, that's an undocumented "feature" of MQTT discovery. Are you using that?

[raomin]

Yes, I'm using MQTT discovery. It just that in the documentation of (all?) MQTT components, it says that

When a state topic is not available, the light will work in optimistic mode.

If MQTT forces one, then this is not true anymore.

[emontnemery]

Yes, it's not intuitive. I opened PR #22998 to deprecate the implicit setting of state_topic. Can you verify optimistic mode works for you with that change?

[raomin]

Hi @emontnemery , I did test #22998 . Now the light has no implicit state_topic and operates with implicit optimism :) thanks and good job!

The fan still doesn't work on optimistic mode, so I keep the bug open for now.

[emontnemery]

Fan optimistic mode should be fixed with #22998 (which is now merged to dev) + #22976, did you try that?

[raomin]

I did test #22976. The fan is not optimistic.
What I did:

1. Get the PR: (is it enough?)
   python3 -m pip install git+https://github.com/home-assistant/home-assistant.git@refs/pull/22976/merge

2. (restart) Version is 0.92.0.dev0

3. Declare a mqtt fan:
   mosquitto_pub -t 'homeassistant/fan/underground4/config' -m '{"name":"fanUnderground4","cmd_t":"homeassistant/fanUnderground/set"}'

4. Add fan.underground4 to the UI

5. Click on the ⚡icon; a ON message is published to homeassistant/fanUnderground/set
   2 secs later, the state is back to OFF (no OFF message is published)

[emontnemery]

Aha, I think step 1 is not correct because it will remove #22998.

Edit: I rebased #22976 so #22998 is included, can you try again with same steps as before?

[raomin]

I tested again #22976 and it works. MQTT fans with no state_topic are optimistic and when declared with a state_topic, they are not. All works as expected.
Thanks @emontnemery, good job!