Invert initialization dependence on relay/conns

This makes it so we can initialize the relay management and then give
that to the connection management, instead of the other way around.

This is important to me in the discovery revamp I'm doing, as otherwise
I get a circular dependency when constructing stuff, with relaying
depending on connection, connection depending on discovery, and
discovery depending on relaying.

With this fixed, discovery will depend on relaying, and connection will
depend on both discovery and relaying.

cmd/syncthing/connections.go

@@ -22,6 +22,7 @@ import (
 	"github.com/syncthing/syncthing/lib/events"
 	"github.com/syncthing/syncthing/lib/model"
 	"github.com/syncthing/syncthing/lib/osutil"
+	"github.com/syncthing/syncthing/lib/relay"
 
 	"github.com/thejerf/suture"
 )
@@ -44,6 +45,7 @@ type connectionSvc struct {
 	tlsCfg     *tls.Config
 	discoverer *discover.Discoverer
 	conns      chan model.IntermediateConnection
+	relaySvc   *relay.Svc
 
 	lastRelayCheck map[protocol.DeviceID]time.Time
 
@@ -52,7 +54,7 @@ type connectionSvc struct {
 	relaysEnabled bool
 }
 
-func newConnectionSvc(cfg *config.Wrapper, myID protocol.DeviceID, mdl *model.Model, tlsCfg *tls.Config, discoverer *discover.Discoverer) *connectionSvc {
+func newConnectionSvc(cfg *config.Wrapper, myID protocol.DeviceID, mdl *model.Model, tlsCfg *tls.Config, discoverer *discover.Discoverer, relaySvc *relay.Svc) *connectionSvc {
 	svc := &connectionSvc{
 		Supervisor: suture.NewSimple("connectionSvc"),
 		cfg:        cfg,
@@ -60,6 +62,7 @@ func newConnectionSvc(cfg *config.Wrapper, myID protocol.DeviceID, mdl *model.Mo
 		model:      mdl,
 		tlsCfg:     tlsCfg,
 		discoverer: discoverer,
+		relaySvc:   relaySvc,
 		conns:      make(chan model.IntermediateConnection),
 
 		connType:       make(map[protocol.DeviceID]model.ConnectionType),
@@ -104,6 +107,10 @@ func newConnectionSvc(cfg *config.Wrapper, myID protocol.DeviceID, mdl *model.Mo
 	}
 	svc.Add(serviceFunc(svc.handle))
 
+	if svc.relaySvc != nil {
+		svc.Add(serviceFunc(svc.acceptRelayConns))
+	}
+
 	return svc
 }
 
@@ -385,6 +392,12 @@ func (s *connectionSvc) connect() {
 	}
 }
 
+func (s *connectionSvc) acceptRelayConns() {
+	for {
+		s.conns <- s.relaySvc.Accept()
+	}
+}
+
 func (s *connectionSvc) shouldLimit(addr net.Addr) bool {
 	if s.cfg.Options().LimitBandwidthInLan {
 		return true

cmd/syncthing/main.go

@@ -711,16 +711,19 @@ func syncthingMain() {
 
 	setupGUI(mainSvc, cfg, m, apiSub, discoverer)
 
-	// Start connection management
-
-	connectionSvc := newConnectionSvc(cfg, myID, m, tlsCfg, discoverer)
-	mainSvc.Add(connectionSvc)
+	// Start relay management
 
+	var relaySvc *relay.Svc
 	if opts.RelaysEnabled && (opts.GlobalAnnEnabled || opts.RelayWithoutGlobalAnn) {
-		relaySvc = relay.NewSvc(cfg, tlsCfg, connectionSvc.conns)
-		connectionSvc.Add(relaySvc)
+		relaySvc = relay.NewSvc(cfg, tlsCfg)
+		mainSvc.Add(relaySvc)
 	}
 
+	// Start connection management
+
+	connectionSvc := newConnectionSvc(cfg, myID, m, tlsCfg, discoverer, relaySvc)
+	mainSvc.Add(connectionSvc)
+
 	if cpuProfile {
 		f, err := os.Create(fmt.Sprintf("cpu-%d.pprof", os.Getpid()))
 		if err != nil {

lib/relay/relay.go

@@ -25,7 +25,9 @@ import (
 	"github.com/thejerf/suture"
 )
 
-func NewSvc(cfg *config.Wrapper, tlsCfg *tls.Config, conns chan<- model.IntermediateConnection) *Svc {
+func NewSvc(cfg *config.Wrapper, tlsCfg *tls.Config) *Svc {
+	conns := make(chan model.IntermediateConnection)
+
 	svc := &Svc{
 		Supervisor: suture.New("Svc", suture.Spec{
 			Log: func(log string) {
@@ -40,11 +42,11 @@ func NewSvc(cfg *config.Wrapper, tlsCfg *tls.Config, conns chan<- model.Intermed
 		cfg:    cfg,
 		tlsCfg: tlsCfg,
 
-		tokens:  make(map[string]suture.ServiceToken),
-		clients: make(map[string]*client.ProtocolClient),
-		mut:     sync.NewRWMutex(),
-
+		tokens:      make(map[string]suture.ServiceToken),
+		clients:     make(map[string]*client.ProtocolClient),
+		mut:         sync.NewRWMutex(),
 		invitations: make(chan protocol.SessionInvitation),
+		conns:       conns,
 	}
 
 	rcfg := cfg.Raw()
@@ -72,6 +74,7 @@ type Svc struct {
 	clients     map[string]*client.ProtocolClient
 	mut         sync.RWMutex
 	invitations chan protocol.SessionInvitation
+	conns       chan model.IntermediateConnection
 }
 
 func (s *Svc) VerifyConfiguration(from, to config.Configuration) error {
@@ -207,6 +210,10 @@ func (s *Svc) ClientStatus() map[string]bool {
 	return status
 }
 
+func (s *Svc) Accept() model.IntermediateConnection {
+	return <-s.conns
+}
+
 type invitationReceiver struct {
 	invitations chan protocol.SessionInvitation
 	tlsCfg      *tls.Config