An adapter add-on essentially adapts an existing device into a web thing. For instance, the Zigbee adapter communicates with Zigbee devices via the Zigbee protocol and represents them as web things with properties, actions, and events.
This type of add-on can also handle directly connected hardware devices, such as GPIO pins, as well as cloud services, such as a weather website.
A notifier add-on allows a user to be notified via some specific mechanism, e.g. email or SMS. The notifier is used as an output for a rule.
An extension add-on allows a developer to modify the gateway's UI through a set of predefined extension points.
There are certain things that add-ons should and should not do. Some things will prevent the add-on from being accepted into the official add-on list.
If the add-on needs to store something persistently, it should only do so in
the gateway's profile directory, i.e. ~/.mozilla-iot/data/your-addon-id. This
directory is guaranteed to persist through system, gateway, and add-on updates.
Device IDs should be prefixed by the name of the adapter, e.g. zigbee-ABCDEF.
This prevents conflicts with other adapters.
Add-ons MUST NOT install system-wide dependencies. Doing so affects everything on the system, so it makes it impossible to guarantee the stability of the gateway and other add-ons.
Add-ons MUST NOT use root privileges to do anything on the system. If such things are required, there may be ways for the gateway to facilitate that in a safer manner. Likewise, the system image could potentially be modified, if necessary. Please file issues to the gateway for discussion.
Add-ons should not crash when they first start up. Necessary configurations and such should be properly checked such that exceptions are not thrown, causing things to crash. This is just good practice.
Using an IP address or some other ephemeral data as part of a device's ID can lead to numerous issues. For instance, if the router assigns a new IP address to the device, it will no longer be usable via the WebThings UI. Instead, something more static should be used.
Device IDs are eventually used directly in thing URLs for the gateway. As such, using spaces, slashes, etc. in the ID can lead to issues. If your ID is generated from user input, you should instead hash the input, or better yet, generate a random ID, such that you are only using valid characters for a URL path component.