USB hub power: read the USB tree at launch and when a status is requested

ControlBooth/ControlBoothApp.swift

@@ -42,6 +42,7 @@ struct ControlBoothApp: App {
                     // receiver competing for port 5000.
                     guard !AppDelegate.isHostingUnitTests else { return }
                     store.seedDsdNeoScannerPipelineIfNeeded()
+                    usbHubPower.refresh()
                     scheduler.reschedule(events: eventStore.events, pipelineStore: store, runner: runner)
                     airPlayReceiverService.setSettingsStore(airPlaySettingsStore)
                     airPlayReceiverService.applySettings(airPlaySettingsStore.settings)

ControlBooth/Services/ScriptingCommands.swift

@@ -329,7 +329,9 @@ private func usbHubPower(reportingTo command: NSScriptCommand) -> USBHubPowerCon
 
 @MainActor
 private func usbHubPowerJSON(_ controller: USBHubPowerController, refreshing: Bool) -> String {
-    if refreshing { controller.refresh() }
+    // A status without the tree still names the chosen port and the RTL-SDRs
+    // on it, which come from the tree.
+    if refreshing { controller.refresh() } else { controller.refreshIfStale() }
     let encoder = JSONEncoder()
     encoder.outputFormatting = [.sortedKeys]
     let data = (try? encoder.encode(controller.status(includingTree: refreshing))) ?? Data("{}".utf8)

ControlBooth/Services/USBHubPowerController.swift

@@ -73,8 +73,23 @@ final class USBHubPowerController {
 
     var canCycle: Bool { settings.isConfigured && cycler.isInstalled && !isCycling }
 
+    /// When the tree was last read; nil before the first read.
+    @ObservationIgnored private var lastRefresh: Date?
+
+    /// How long a read of the tree is good for when a status is asked for.
+    static let statusMaxAge: TimeInterval = 10
+
+    /// Reads the tree unless it was read within `maxAge` seconds, so a status
+    /// poll names the chosen port and its RTL-SDRs without launching ioreg and
+    /// uhubctl on every request.
+    func refreshIfStale(maxAge: TimeInterval = USBHubPowerController.statusMaxAge) {
+        if let lastRefresh, Date().timeIntervalSince(lastRefresh) < maxAge { return }
+        refresh()
+    }
+
     /// Reads the tree and uhubctl's hub list again.
     func refresh() {
+        lastRefresh = Date()
         let cycler = self.cycler
         do {
             let hubs = cycler.isInstalled ? try cycler.listHubs() : []

ControlBoothTests/USBTreeTests.swift

@@ -82,4 +82,20 @@ struct USBTreeTests {
         // A path that merely starts with the same digits isn't below it.
         #expect(!USBTree.devices(affectedBy: mtt, in: rows).contains { $0.path == "2-2.1.3" })
     }
+
+    /// A status asked for before anything read the tree used to name the port by
+    /// its USB ID and list no RTL-SDRs.
+    @MainActor @Test func statusReadsTheTreeWhenItHasNone() {
+        let controller = USBHubPowerController(
+            settings: USBHubPowerSettings(enabled: true, hubLocation: "2-2.1", hubID: "045b:0209",
+                                          port: 1, portDeviceID: "1a40:0101"),
+            cycler: USBHubPowerCycler(executable: nil))
+        #expect(controller.status(includingTree: false).affectedRTLSDRs.isEmpty)
+        controller.refreshIfStale()
+        // The tree was read (whatever this machine has); a second ask within the
+        // age limit doesn't read it again.
+        let first = controller.rows
+        controller.refreshIfStale()
+        #expect(controller.rows == first)
+    }
 }