Device Variable Conventions

Every device exposes its state and control points through the use of variables.

There are three different types of variables:

• Read-write - variables that provide both state and control of some device facet
• Read-only - variables that provide only state about some device facet
• Write-only - variables that facilitate only control of some device facet

Variable Naming

What variables a device exposes define the device's capabilities and ultimately how clients will perceive and interact with that device. Therefore, it is important that variable naming remain consistent for functions that are common across different devices.

The below list defines commonly used variable names:

Image & Video Status URLs

There are two variables the Hobson runtime treats differently than the others – imageStatusUrl and videoStatusUrl. As indicated in the table above, the value a device provides for these variables is a URL or JSON URL (which we'll refer to as the source URL) which can include user credentials. However, those variable values are not returned directly via the REST API. Instead, the value returned by the REST API is a generic proxy URL that provides the image or video stream data from the source URL. It is therefore safe for devices to include user credentials in the value they provide for imageStatusUrl and videoStatusUrl because they will not be exposed.

JSON URL

As of Hobson 0.3.1 and higher, some variables support a value referred to as a JSON URL. This is a JSON object that contains an URL string and associated metadata. The JSON URL object should have the following pairs:

Here's an example:

{
  "url": "http://www.foo.com",
  "headers": {
    "Accept": "text/xml"
  },
  "auth": {
    "username": "username",
    "password": "password",
    "type": "basic"
  }
}