lib/connections: Fix lan detection (fixes #4421)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4487

cmd/syncthing/main.go

@@ -725,24 +725,6 @@ func syncthingMain(runtimeOptions RuntimeOptions) {
 		weakhash.Enabled = true
 	}
 
-	if (opts.MaxRecvKbps > 0 || opts.MaxSendKbps > 0) && !opts.LimitBandwidthInLan {
-		lans, _ = osutil.GetLans()
-		for _, lan := range opts.AlwaysLocalNets {
-			_, ipnet, err := net.ParseCIDR(lan)
-			if err != nil {
-				l.Infoln("Network", lan, "is malformed:", err)
-				continue
-			}
-			lans = append(lans, ipnet)
-		}
-
-		networks := make([]string, len(lans))
-		for i, lan := range lans {
-			networks[i] = lan.String()
-		}
-		l.Infoln("Local networks:", strings.Join(networks, ", "))
-	}
-
 	dbFile := locations[locDatabase]
 	ldb, err := db.Open(dbFile)
 
@@ -818,7 +800,7 @@ func syncthingMain(runtimeOptions RuntimeOptions) {
 
 	// Start connection management
 
-	connectionsService := connections.NewService(cfg, myID, m, tlsCfg, cachedDiscovery, bepProtocolName, tlsDefaultCommonName, lans)
+	connectionsService := connections.NewService(cfg, myID, m, tlsCfg, cachedDiscovery, bepProtocolName, tlsDefaultCommonName)
 	mainService.Add(connectionsService)
 
 	if cfg.Options().GlobalAnnEnabled {

lib/connections/service.go

@@ -19,6 +19,7 @@ import (
 	"github.com/syncthing/syncthing/lib/discover"
 	"github.com/syncthing/syncthing/lib/events"
 	"github.com/syncthing/syncthing/lib/nat"
+	"github.com/syncthing/syncthing/lib/osutil"
 	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/sync"
 	"github.com/syncthing/syncthing/lib/util"
@@ -79,7 +80,6 @@ type Service struct {
 	conns                chan internalConn
 	bepProtocolName      string
 	tlsDefaultCommonName string
-	lans                 []*net.IPNet
 	limiter              *limiter
 	natService           *nat.Service
 	natServiceToken      *suture.ServiceToken
@@ -94,7 +94,7 @@ type Service struct {
 }
 
 func NewService(cfg *config.Wrapper, myID protocol.DeviceID, mdl Model, tlsCfg *tls.Config, discoverer discover.Finder,
-	bepProtocolName string, tlsDefaultCommonName string, lans []*net.IPNet) *Service {
+	bepProtocolName string, tlsDefaultCommonName string) *Service {
 
 	service := &Service{
 		Supervisor: suture.New("connections.Service", suture.Spec{
@@ -110,7 +110,6 @@ func NewService(cfg *config.Wrapper, myID protocol.DeviceID, mdl Model, tlsCfg *
 		conns:                make(chan internalConn),
 		bepProtocolName:      bepProtocolName,
 		tlsDefaultCommonName: tlsDefaultCommonName,
-		lans:                 lans,
 		limiter:              newLimiter(cfg),
 		natService:           nat.NewService(myID, cfg),
 
@@ -429,12 +428,30 @@ func (s *Service) isLAN(addr net.Addr) bool {
 	if !ok {
 		return false
 	}
-	for _, lan := range s.lans {
+
+	if tcpaddr.IP.IsLoopback() {
+		return true
+	}
+
+	for _, lan := range s.cfg.Options().AlwaysLocalNets {
+		_, ipnet, err := net.ParseCIDR(lan)
+		if err != nil {
+			l.Debugln("Network", lan, "is malformed:", err)
+			continue
+		}
+		if ipnet.Contains(tcpaddr.IP) {
+			return true
+		}
+	}
+
+	lans, _ := osutil.GetLans()
+	for _, lan := range lans {
 		if lan.Contains(tcpaddr.IP) {
 			return true
 		}
 	}
-	return tcpaddr.IP.IsLoopback()
+
+	return false
 }
 
 func (s *Service) createListener(factory listenerFactory, uri *url.URL) bool {