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/server/dns.go

@@ -0,0 +1,76 @@
+//nolint:dupl
+package server
+
+import (
+	"encoding/json"
+	"net/http"
+	"strings"
+
+	"github.com/qdm12/gluetun/internal/dns"
+	"github.com/qdm12/golibs/logging"
+)
+
+func newDNSHandler(looper dns.Looper, logger logging.Logger) http.Handler {
+	return &dnsHandler{
+		looper: looper,
+		logger: logger,
+	}
+}
+
+type dnsHandler struct {
+	looper dns.Looper
+	logger logging.Logger
+}
+
+func (h *dnsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	r.RequestURI = strings.TrimPrefix(r.RequestURI, "/dns")
+	switch r.RequestURI {
+	case "/status": //nolint:goconst
+		switch r.Method {
+		case http.MethodGet:
+			h.getStatus(w)
+		case http.MethodPut:
+			h.setStatus(w, r)
+		default:
+			http.Error(w, "", http.StatusNotFound)
+		}
+	default:
+		http.Error(w, "", http.StatusNotFound)
+	}
+}
+
+func (h *dnsHandler) getStatus(w http.ResponseWriter) {
+	status := h.looper.GetStatus()
+	encoder := json.NewEncoder(w)
+	data := statusWrapper{Status: string(status)}
+	if err := encoder.Encode(data); err != nil {
+		h.logger.Warn(err)
+		w.WriteHeader(http.StatusInternalServerError)
+		return
+	}
+}
+
+func (h *dnsHandler) setStatus(w http.ResponseWriter, r *http.Request) {
+	decoder := json.NewDecoder(r.Body)
+	var data statusWrapper
+	if err := decoder.Decode(&data); err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+	status, err := data.getStatus()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+	outcome, err := h.looper.SetStatus(status)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+	encoder := json.NewEncoder(w)
+	if err := encoder.Encode(outcomeWrapper{Outcome: outcome}); err != nil {
+		h.logger.Warn(err)
+		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		return
+	}
+}