bluetooth: add soft rfkill unblock, wait for adapter to become available

instead of forfeiting subscription

fixes #2922
fixes #1537

core/internal/server/bluez/watcher.go

@@ -0,0 +1,46 @@
+package bluez
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/godbus/dbus/v5"
+)
+
+var ErrNoAdapter = errors.New("no bluetooth adapter found")
+
+func WaitForAdapter() error {
+	conn, err := dbus.ConnectSystemBus()
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+
+	if err := conn.AddMatchSignal(
+		dbus.WithMatchInterface(objectMgrIface),
+		dbus.WithMatchMember("InterfacesAdded"),
+	); err != nil {
+		return err
+	}
+
+	signals := make(chan *dbus.Signal, 64)
+	conn.Signal(signals)
+
+	if _, err := findAdapter(conn); err == nil {
+		return nil
+	}
+
+	for sig := range signals {
+		if sig == nil || sig.Name != objectMgrIface+".InterfacesAdded" || len(sig.Body) < 2 {
+			continue
+		}
+		ifaces, ok := sig.Body[1].(map[string]map[string]dbus.Variant)
+		if !ok {
+			continue
+		}
+		if _, ok := ifaces[adapter1Iface]; ok {
+			return nil
+		}
+	}
+	return fmt.Errorf("dbus signal stream closed")
+}