mobile: Add ServiceStatus for retrieving current runtime status of lnd

Used for checking whether lnd is started or not.
ServiceStatus can also be used to determine when lnd has shut down, since
`stopDaemon` returns immediately and does not wait for the gRPC servers
to be fully closed.

Author: hsjoberg

mobile/bindings.go

@@ -156,3 +156,18 @@ func Start(extraArgs string, rpcReady Callback) {
 		rpcReady.OnResponse([]byte{})
 	}()
 }
+
+type LndStatusCallback interface {
+	OnResponse(lndStarted int32)
+}
+
+// Returns 1 if lnd has started up successfully, allowing the caller to interact
+// with the in-memory gRPC servers. If 0 is returned, the caller should invoke
+// `Start` to initialize lnd.
+//
+// ServiceStatus can also be used to determine when lnd has shut down, since
+// `stopDaemon` returns immediately and does not wait for the gRPC servers
+// to be fully closed.
+func ServiceStatus(callback LndStatusCallback) {
+	callback.OnResponse(lndStarted)
+}