refactor: improve code for wait vm to reach the specified state (#75)

In previous implementations, there was a need to maintain a timeout
error variable to ignore while waiting for the VM to stop.
This part of the code was not intuitive enough, and other maintainers
couldn’t grasp its intention at first glance.
This improvement has optimized the `waitForVMState` function by adding a
timeout parameter, making the code more intuitive.

cmd/vfkit/main.go

@@ -20,7 +20,6 @@ limitations under the License.
 package main
 
 import (
-	"errors"
 	"fmt"
 	"os"
 	"os/signal"
@@ -91,9 +90,7 @@ func newVMConfiguration(opts *cmdline.Options) (*config.VirtualMachine, error) {
 	return vmConfig, nil
 }
 
-var errVMStateTimeout = fmt.Errorf("timeout waiting for VM state")
-
-func waitForVMState(vm *vz.VirtualMachine, state vz.VirtualMachineState) error {
+func waitForVMState(vm *vz.VirtualMachine, state vz.VirtualMachineState, timeout <-chan time.Time) error {
 	signalCh := make(chan os.Signal, 1)
 	signal.Notify(signalCh, syscall.SIGPIPE)
 
@@ -108,8 +105,8 @@ func waitForVMState(vm *vz.VirtualMachine, state vz.VirtualMachineState) error {
 			if newState == vz.VirtualMachineStateError {
 				return fmt.Errorf("hypervisor virtualization error")
 			}
-		case <-time.After(5 * time.Second):
-			return errVMStateTimeout
+		case <-timeout:
+			return fmt.Errorf("timeout waiting for VM state")
 		}
 	}
 }
@@ -145,13 +142,11 @@ func runVFKit(vmConfig *config.VirtualMachine, opts *cmdline.Options) error {
 }
 
 func runVirtualMachine(vmConfig *config.VirtualMachine, vm *vz.VirtualMachine) error {
-	err := vm.Start()
-	if err != nil {
+	if err := vm.Start(); err != nil {
 		return err
 	}
 
-	err = waitForVMState(vm, vz.VirtualMachineStateRunning)
-	if err != nil {
+	if err := waitForVMState(vm, vz.VirtualMachineStateRunning, time.After(5*time.Second)); err != nil {
 		return err
 	}
 	log.Infof("virtual machine is running")
@@ -182,18 +177,11 @@ func runVirtualMachine(vmConfig *config.VirtualMachine, vm *vz.VirtualMachine) e
 
 	errCh := make(chan error, 1)
 	go func() {
-		for {
-			err := waitForVMState(vm, vz.VirtualMachineStateStopped)
-			if err == nil {
-				log.Infof("VM is stopped")
-				errCh <- nil
-				return
-			}
-			if !errors.Is(err, errVMStateTimeout) {
-				errCh <- fmt.Errorf("virtualization error: %v", err)
-				return
-			}
-			// errVMStateTimeout -> keep looping
+		if err := waitForVMState(vm, vz.VirtualMachineStateStopped, nil); err != nil {
+			errCh <- fmt.Errorf("virtualization error: %v", err)
+		} else {
+			log.Infof("VM is stopped")
+			errCh <- nil
 		}
 	}()