watchers/DBus

godoc

import dbusWatcher "barista.run/base/watchers/dbus"

The dbus package provides watchers for dbus properties and signals. All watchers must be cleaned up when no longer needed, by calling their Unsubscribe() method.

NameOwnerWatcher

A NameOwherWatcher watches for changes to the owner for a named service. It supports both single name and namespaced wildcard names.

• WatchNameOwner(name string) watches only the specified service.

• WatchNameOwners(pattern string) watches all services within the namespace pattern.

Any updates to relevant service owners will trigger a notification on the .Updates channel, with the name and new owner of the triggering name. Calling GetOwner() will return the service owner, while GetOwners() will return a map of service names to owners (useful in case of multiple services within the namespace active at the same time).

PropertiesWatcher

A PropertiesWatcher watches for changes to the properties of a DBus object. It signals each change to the .Updates channel, in a map that contains both the previous and the current value for each updated property.

It also provides AddSignalHandler(string, func(*Signal, Fetcher) map[string]interface{}) to run custom signal handlers in case there are properties on the object that trigger signals other than PropertiesChanged. The handler function is provided both the received Signal, as well as a Fetcher to query additional properties from the object (even properties that are not marked for updates during construction).

Created using WatchProperties(...):

• busType BusType: The bus to use: Session or System.
• service string: The service that exports the object.
• object dbus.ObjectPath: The path to the exported object.
• iface string: A namespace under which the properties are provided. You can still use other properties by providing fully-qualified names, but any short names (no .s) will default to this interface.

Properties can be added in different ways depending on how updates to the property are expected:

• Add(...string): Adds properties that emit PropertiesChanged. These properties are only updated from signals, and cached values are returned on calls to Get().
• FetchOnSignal(...string): Adds properties that change when one or more of the signalling properties change. These properties are fetched from the object if they’re not present in a change signal, but are otherwise equivalent to signalling properties. Cached values are used, and they are part of the change objects.
• Fetch(...string): Adds properties that are “computed”, and changes cannot be reasonably tracked. These properties are always fetched from the object when calling Get().