Loops and HTTP control server rework (#308)

- CRUD REST HTTP server
- `/v1` HTTP server prefix
- Retrocompatible with older routes (redirects to v1 or handles the requests directly)
- DNS, Updater and Openvpn refactored to have a REST-like state with new methods to change their states synchronously
- Openvpn, Unbound and Updater status, see #287

internal/updater/state.go

@@ -0,0 +1,88 @@
+package updater
+
+import (
+	"fmt"
+	"reflect"
+	"sync"
+
+	"github.com/qdm12/gluetun/internal/constants"
+	"github.com/qdm12/gluetun/internal/models"
+	"github.com/qdm12/gluetun/internal/settings"
+)
+
+type state struct {
+	status   models.LoopStatus
+	settings settings.Updater
+	statusMu sync.RWMutex
+	periodMu sync.RWMutex
+}
+
+func (s *state) setStatusWithLock(status models.LoopStatus) {
+	s.statusMu.Lock()
+	defer s.statusMu.Unlock()
+	s.status = status
+}
+
+func (l *looper) GetStatus() (status models.LoopStatus) {
+	l.state.statusMu.RLock()
+	defer l.state.statusMu.RUnlock()
+	return l.state.status
+}
+
+func (l *looper) SetStatus(status models.LoopStatus) (outcome string, err error) {
+	l.state.statusMu.Lock()
+	defer l.state.statusMu.Unlock()
+	existingStatus := l.state.status
+
+	switch status {
+	case constants.Running:
+		switch existingStatus {
+		case constants.Starting, constants.Running, constants.Stopping, constants.Crashed:
+			return fmt.Sprintf("already %s", existingStatus), nil
+		}
+		l.loopLock.Lock()
+		defer l.loopLock.Unlock()
+		l.state.status = constants.Starting
+		l.state.statusMu.Unlock()
+		l.start <- struct{}{}
+		newStatus := <-l.running
+		l.state.statusMu.Lock()
+		l.state.status = newStatus
+		return newStatus.String(), nil
+	case constants.Stopped:
+		switch existingStatus {
+		case constants.Stopped, constants.Stopping, constants.Starting, constants.Crashed:
+			return fmt.Sprintf("already %s", existingStatus), nil
+		}
+		l.loopLock.Lock()
+		defer l.loopLock.Unlock()
+		l.state.status = constants.Stopping
+		l.state.statusMu.Unlock()
+		l.stop <- struct{}{}
+		<-l.stopped
+		l.state.statusMu.Lock()
+		l.state.status = status
+		return status.String(), nil
+	default:
+		return "", fmt.Errorf("status %q can only be %q or %q",
+			status, constants.Running, constants.Stopped)
+	}
+}
+
+func (l *looper) GetSettings() (settings settings.Updater) {
+	l.state.periodMu.RLock()
+	defer l.state.periodMu.RUnlock()
+	return l.state.settings
+}
+
+func (l *looper) SetSettings(settings settings.Updater) (outcome string) {
+	l.state.periodMu.Lock()
+	defer l.state.periodMu.Unlock()
+	settingsUnchanged := reflect.DeepEqual(settings, l.state.settings)
+	if settingsUnchanged {
+		return "settings left unchanged"
+	}
+	l.state.settings = settings
+	l.updateTicker <- struct{}{}
+	return "settings updated"
+}