Command select

The Remote Control Service offers an API for querying and connecting to arbitrary FIDL services on the target.

Queries can match an arbitrary number of services on the system, and select will output all of the matches, formatted according to their place in the component topology.

In the special case of a query that uniquely matches a single service, RCS can connect to that service and pass a handle to it to the host for FFX to use. This is how the FHO subtool framework is able to create FIDL proxies using the component selector mapping.

To query for services on a target, write a selector to match the service(s) of interest.

Selector syntax

Many ffx commands that interact with components or services take component selectors as a parameter. Component selectors in ffx use the same syntax as the diagnostics selectors.

Here are some example selectors, all of which select the Remote Control Service:

core/remote-control:out:fuchsia.developer.remotecontrol.RemoteControl
core/*:out:fuchsia.developer.remotecontrol.RemoteControl
core/*:expose:fuchsia.developer.remotecontrol.RemoteControl
core/remote-control:out:*
core/*:expose:fuchsia.developer.remotecontrol.R*

Selector segments

There are three constituent segments of a selector: <component moniker>:<node selector>:<property selector>. Each is discussed below. The wildcard (*) is valid in each segment of a selector.

Consider this example: core/remote-control:out:fuchsia.developer.remotecontrol.RemoteControl

core/remote-control is the component moniker. This uniquely specifies a path in the component topology.

Note: You can use * to wildcard a particular level in the topology, but * is not recursive. That is, a/*/c will match a/b/c but would not match a/b/b2/c.
out is the node selector. In ffx, this must be one of the following values, which correspond to the routing terminology used in the component manifest and defined in routing terminology documentation.
- out: services offered by the component. Corresponds to offer in the component manifest.
- expose: services exposed by the component. Corresponds to expose in the component manifest.
- in: services depended upon by the component. Corresponds to use in the component manifest.
fuchsia.developer.remotecontrol.RemoteControl is the property selector and is matched against fully-qualified FIDL service names in the routing directories matched by the node selector.

You may optionally omit the property selector: core/remote-control:out is equivalent to core/remote-control:out:*.