fix(darwin): make Adapter.Enable callable after first invocation

adapter_darwin.go

@@ -44,21 +44,40 @@ var DefaultAdapter = &Adapter{
 
 // Enable configures the BLE stack. It must be called before any
 // Bluetooth-related calls (unless otherwise indicated).
+//
+// poweredChan doubles as the "Enable currently in flight" sentinel
+// (the upfront non-nil check guards against re-entry) and the
+// channel the central-manager delegate signals on once
+// CoreBluetooth reports powered-on. It is cleared on every exit
+// path — success and timeout — so a subsequent call can run again.
+// Previously the channel was set at the start of Enable and never
+// cleared, so any second Enable on the same Adapter (e.g. from a
+// recovery flow that re-Enables after an error) returned "already
+// calling Enable function" even though no Enable was actually in
+// flight.
 func (a *Adapter) Enable() error {
 	if a.poweredChan != nil {
 		return errors.New("already calling Enable function")
 	}
 
-	// wait until powered
 	a.poweredChan = make(chan error, 1)
 
+	// Attach the central-manager delegate BEFORE checking
+	// cm.State(): a freshly-constructed CBCentralManager fires
+	// DidUpdateState asynchronously, and if SetDelegate happens
+	// after the callback runs we miss the powered-on event entirely
+	// and wait the full 10s timeout for a callback that already
+	// fired. Setting the delegate first guarantees the callback
+	// path is wired before the manager has had a chance to update
+	// state.
 	a.cmd = &centralManagerDelegate{a: a}
 	a.cm.SetDelegate(a.cmd)
 
 	if a.cm.State() != cbgo.ManagerStatePoweredOn {
 		select {
 		case <-a.poweredChan:
 		case <-time.NewTimer(10 * time.Second).C:
+			a.poweredChan = nil
 			return errors.New("timeout enabling CentralManager")
 		}
 	}
@@ -68,10 +87,11 @@ func (a *Adapter) Enable() error {
 		<-a.poweredChan
 	}
 
-	// wait until powered?
 	a.pmd = &peripheralManagerDelegate{a: a}
 	a.pm.SetDelegate(a.pmd)
 
+	a.poweredChan = nil
+
 	return nil
 }
 
@@ -85,9 +105,20 @@ type centralManagerDelegate struct {
 
 // CentralManagerDidUpdateState when central manager state updated.
 func (cmd *centralManagerDelegate) CentralManagerDidUpdateState(cmgr cbgo.CentralManager) {
-	// powered on?
 	if cmgr.State() == cbgo.ManagerStatePoweredOn {
-		cmd.a.poweredChan <- nil
+		// Guard against poweredChan being nil — Enable clears it
+		// once the adapter is powered on, so a late or repeated
+		// state update (CoreBluetooth occasionally fires multiple
+		// times during startup, or after a state-toggle event)
+		// would otherwise block forever on a nil-channel send.
+		// Non-blocking send so we never park the delegate goroutine
+		// even if the channel is set but already buffered full.
+		if cmd.a.poweredChan != nil {
+			select {
+			case cmd.a.poweredChan <- nil:
+			default:
+			}
+		}
 	}
 
 	// TODO: handle other state changes.