lib/connections: Add KCP support (fixes #804)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3489

lib/config/wrapper.go

@@ -13,6 +13,7 @@ import (
 	"github.com/syncthing/syncthing/lib/events"
 	"github.com/syncthing/syncthing/lib/osutil"
 	"github.com/syncthing/syncthing/lib/protocol"
+	"github.com/syncthing/syncthing/lib/rand"
 	"github.com/syncthing/syncthing/lib/sync"
 	"github.com/syncthing/syncthing/lib/util"
 )
@@ -404,3 +405,26 @@ func (w *Wrapper) RequiresRestart() bool {
 func (w *Wrapper) setRequiresRestart() {
 	atomic.StoreUint32(&w.requiresRestart, 1)
 }
+
+func (w *Wrapper) StunServers() []string {
+	var addresses []string
+	for _, addr := range w.cfg.Options.StunServers {
+		switch addr {
+		case "default":
+			addresses = append(addresses, DefaultStunServers...)
+		default:
+			addresses = append(addresses, addr)
+		}
+	}
+
+	addresses = util.UniqueStrings(addresses)
+
+	// Shuffle
+	l := len(addresses)
+	for i := range addresses {
+		r := rand.Intn(l)
+		addresses[i], addresses[r] = addresses[r], addresses[i]
+	}
+
+	return addresses
+}