Expected behavior of on_update_callback ?

[SantiagoSotoC]

I would like to know what is the expected functionality of this method, should I get notifications when the volume of a cleinte changes?

[luar123]

on_update_callback_func() which can be set with set_on_update_callback() is called whenever a Server.OnUpdate notification is received:

def _on_server_update(self, data):
        """Handle server update."""
        self.synchronize(data)
        if self._on_update_callback_func and callable(self._on_update_callback_func):
            self._on_update_callback_func()

Check Snapcast API docu to find out when this notification is send.

For your use case a Client.OnVolumeChanged notification is send.
This will update the volume here:

    def _on_client_volume_changed(self, data):
        """Handle client volume change."""
        self._clients.get(data.get('id')).update_volume(data)

and then here:

    def update_volume(self, data):
        """Update volume."""
        self._client['config']['volume'] = data['volume']
        _LOGGER.debug('updated volume on %s', self.friendly_name)
        self._server.group(self.group.identifier).callback()
        self.callback()

So in the end the client and group callback function is called.
In HA snapcast integration it is used like this:

    async def async_added_to_hass(self) -> None:
        """Subscribe to client events."""
        self._client.set_callback(self.schedule_update_ha_state)
        self.hass.data[DOMAIN][self._entry_id].clients.append(self)

    async def async_will_remove_from_hass(self) -> None:
        """Disconnect client object when removed."""
        self._client.set_callback(None)
        self.hass.data[DOMAIN][self._entry_id].clients.remove(self)

[SantiagoSotoC]

Well, to summarize the method

async def client_volume(self, identifier, volume):
“”“Set client volume.”“””
return await await self._request(CLIENT_SETVOLUME, identifier, 'volume', volume)

of the snapserver class does not call the callback, you have to use the methods inside the Snapclient class, thanks for the quick answer, I think it is something that could be clarified.