Trait DevtoolsBackend 

pub trait DevtoolsBackend: Send + 'static {
    // Required methods
    fn widget_tree(&self) -> WidgetTreeDump;
    fn widget_props(&self, id: u64) -> Option<WidgetProps>;
    fn metrics_snapshot(&self) -> MetricsSnapshot;
    fn inject_tap(&self, params: InputTapParams) -> Result<(), BackendError>;
    fn inject_scroll(
        &self,
        params: InputScrollParams,
    ) -> Result<(), BackendError>;
    fn inject_text(&self, text: &str) -> Result<(), BackendError>;

    // Provided methods
    fn handshake_info(&self, app: &AppInfo) -> HandshakeInfo { ... }
    fn screenshot(&self) -> Result<ScreenshotResult, BackendError> { ... }
}

What the devtools service asks the app for.

Threading

Every method here is called from the service’s own backend thread, one call at a time, never from the frame/UI thread and never concurrently. An implementation that needs UI-thread state does the hop itself (post to the UI thread and block on the answer) — that is the one thing this trait cannot do for it, because only the shell knows what its UI thread is. The service caps every call with a timeout, so a hop that never comes back costs the caller an error response, never a hung client (crate::hop::BackendClient).

handshake_info is the exception: it is called once, on the thread that calls crate::Service::start, and the answer is cached for the process lifetime — which is what lets handshake be answered statelessly at any time, including while the UI thread is wedged.

Required Methods

fn widget_tree(&self) -> WidgetTreeDump

A snapshot of the retained widget tree.

Infallible on purpose: “nothing built yet” is an empty WidgetTreeDump::roots, not an error — a client polling a just-launched app should see an empty tree, not a failure it has to distinguish from a broken backend.

fn widget_props(&self, id: u64) -> Option<WidgetProps>

One widget’s inspectable properties, or None when id names no live widget (the service turns that into INVALID_PARAMS — a stale id from a tree the app has since rebuilt is an ordinary, expected case, not a backend failure).

fn metrics_snapshot(&self) -> MetricsSnapshot

Process-level metrics (uptime, best-effort RSS). Infallible for Self::widget_tree’s reason — an unavailable RSS is MetricsSnapshot::rss_bytes None, not a failed call.

fn inject_tap(&self, params: InputTapParams) -> Result<(), BackendError>

Synthesize a tap at the given logical-px point.

fn inject_scroll(&self, params: InputScrollParams) -> Result<(), BackendError>

Synthesize a scroll at the given logical-px point.

fn inject_text(&self, text: &str) -> Result<(), BackendError>

Synthesize text input against the focused widget.

Provided Methods

fn handshake_info(&self, app: &AppInfo) -> HandshakeInfo

Server identity + the capability set clients gate on. Called once at startup, on the starting thread (see the trait doc).

The default answers with everything except Capability::Screenshot, matching the default Self::screenshot below — override this together with screenshot, never one alone.

fn screenshot(&self) -> Result<ScreenshotResult, BackendError>

Capture the current frame as a PNG.

Defaults to BackendError::NotSupported: a screenshot needs a readback path the backend may not have, so it is capability-gated rather than mandatory (RpcError::NOT_SUPPORTED on the wire). A backend that overrides this must also declare Capability::Screenshot in Self::handshake_info.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors