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45 lines
2.4 KiB
Markdown
45 lines
2.4 KiB
Markdown
---
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layout: page
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title: "Component Discovery"
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description: "How to make component discovery work."
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date: 2016-04-16 14:24 -07:00
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sidebar: true
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comments: false
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sharing: true
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footer: true
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---
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<p class='note warning'>
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This option is only available for built-in components.
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</p>
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Home Assistant has a discovery service running in the background to discover new devices. Whenever a new device is discovered, a `SERVICE_DISCOVERED` event will be fired with the found service and the information. The `discovery` component has some knowledge about which components handle which type of services and will ensure those are loaded and listening before firing the `SERVICE_DISCOVERED` event.
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### {% linkable_title Add discovery instructions %}
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Device discovery for Home Assistant has been extracted into an external library called [NetDisco](https://github.com/home-assistant/netdisco). This library is integrated using [the `discovery` component](https://github.com/home-assistant/home-assistant/blob/dev/homeassistant/components/discovery.py) and scans the network in intervals for uPnP and zeroconf/mDNS services.
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To have your device be discovered, you will have to extend the NetDisco library to be able to find your device. This is done by adding a new discoverable. [See the repository for examples of existing discoverable.](https://github.com/home-assistant/netdisco/tree/master/netdisco/discoverables)
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### {% linkable_title Listening to `SERVICE_DISCOVERED` events %}
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From your component, you will have to set up the listening for specific services. Given below is an example how one would listen for discovered Chromecasts:
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```python
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from homeassistant.loader import get_component
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def setup(hass, config):
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discovery = get_component('discovery')
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def chromecast_discovered(service, info):
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""" Called when a Chromecast has been discovered. """
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print("Discovered a new Chromecast: {}".format(info))
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discovery.listen(
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hass, discovery.services.GOOGLE_CAST, chromecast_discovered)
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```
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### {% linkable_title Auto-loading your component upon discovery %}
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The Discovery component is capable of setting up your components before firing the `SERVICE_DISCOVERD` event. To do this you will have to update the [`SERVICE_HANDLERS`](https://github.com/home-assistant/home-assistant/blob/dev/homeassistant/components/discovery.py#L29) constant in [the `discovery` component](https://github.com/home-assistant/home-assistant/blob/dev/homeassistant/components/discovery.py).
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