Maint: loopstate package used in Openvpn state

internal/loopstate/apply.go

@@ -0,0 +1,77 @@
+package loopstate
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/qdm12/gluetun/internal/constants"
+	"github.com/qdm12/gluetun/internal/models"
+)
+
+type Applier interface {
+	ApplyStatus(ctx context.Context, status models.LoopStatus) (
+		outcome string, err error)
+}
+
+var ErrInvalidStatus = errors.New("invalid status")
+
+// ApplyStatus sends signals to the running loop depending on the
+// current status and status requested, such that its next status
+// matches the requested one. It is thread safe and a synchronous call
+// since it waits to the loop to fully change its status.
+func (s *State) ApplyStatus(ctx context.Context, status models.LoopStatus) (
+	outcome string, err error) {
+	// prevent simultaneous loop changes by restricting
+	// multiple ApplyStatus calls to run sequentially.
+	s.loopMu.Lock()
+	defer s.loopMu.Unlock()
+
+	// not a read lock as we want to modify it eventually in
+	// the code below before any other call.
+	s.statusMu.Lock()
+	existingStatus := s.status
+
+	switch status {
+	case constants.Running:
+		if existingStatus != constants.Stopped {
+			return "already " + existingStatus.String(), nil
+		}
+
+		s.status = constants.Starting
+		s.statusMu.Unlock()
+		s.start <- struct{}{}
+
+		// Wait for the loop to react to the start signal
+		newStatus := constants.Starting // for canceled context
+		select {
+		case <-ctx.Done():
+		case newStatus = <-s.running:
+		}
+		s.SetStatus(newStatus)
+
+		return newStatus.String(), nil
+	case constants.Stopped:
+		if existingStatus != constants.Running {
+			return "already " + existingStatus.String(), nil
+		}
+
+		s.status = constants.Stopping
+		s.statusMu.Unlock()
+		s.stop <- struct{}{}
+
+		// Wait for the loop to react to the stop signal
+		newStatus := constants.Stopping // for canceled context
+		select {
+		case <-ctx.Done():
+		case <-s.stopped:
+			newStatus = constants.Stopped
+		}
+		s.SetStatus(newStatus)
+
+		return newStatus.String(), nil
+	default:
+		return "", fmt.Errorf("%w: %s: it can only be one of: %s, %s",
+			ErrInvalidStatus, status, constants.Running, constants.Stopped)
+	}
+}