Component capabilities

Components obtain privileges to access various parts of the wider system through capabilities. Each component can declare new capabilities that they offer to the system and capabilities provided by other components (or the framework) that they require to function.

As you just saw, runner is an example of a capability declaring the runtime used by the component. Other examples of common capability types are directory to access filesystem resources and protocol for communicating with other components.

Developers declare the capability types required by the component using the component manifest. Below is an example of a component manifest requesting two capabilities: read access to an example-data directory and a service described by the fuchsia.example.Foo FIDL protocol.

use: [
        directory: "example-data",
        rights: [ "r*" ],
        path: "/example/data",
        protocol: "fuchsia.example.Foo",

Component manager uses the capability declarations to populate each component's namespace with the necessary directory handles. For this example, the component would receive /example/data and /svc/fuchsia.example.Foo in their namespace.