tailscale: Add runtime exit node API

protocol/tailscale/endpoint.go

@@ -53,6 +53,7 @@ import (
 	"github.com/sagernet/tailscale/net/netns"
 	"github.com/sagernet/tailscale/net/tsaddr"
 	tsTUN "github.com/sagernet/tailscale/net/tstun"
+	"github.com/sagernet/tailscale/tailcfg"
 	"github.com/sagernet/tailscale/tsnet"
 	"github.com/sagernet/tailscale/types/ipproto"
 	"github.com/sagernet/tailscale/types/nettype"
@@ -487,6 +488,49 @@ func (t *Endpoint) watchState() {
 	}
 }
 
+func (t *Endpoint) SetTailscaleExitNode(ctx context.Context, stableID string) error {
+	if !t.started.Load() {
+		return E.New("Tailscale is not ready yet")
+	}
+	if t.advertiseExitNode && stableID != "" {
+		return E.New("cannot advertise an exit node and use an exit node at the same time")
+	}
+	perfs := &ipn.MaskedPrefs{
+		Prefs: ipn.Prefs{
+			ExitNodeID:             tailcfg.StableNodeID(stableID),
+			ExitNodeAllowLANAccess: t.exitNodeAllowLANAccess,
+		},
+		ExitNodeIDSet:             true,
+		ExitNodeIPSet:             true,
+		ExitNodeAllowLANAccessSet: true,
+	}
+	if stableID != "" {
+		status, err := common.Must1(t.server.LocalClient()).Status(ctx)
+		if err != nil {
+			return E.Cause(err, "get tailscale status")
+		}
+		found := false
+		for _, peer := range status.Peer {
+			if peer.ID != tailcfg.StableNodeID(stableID) {
+				continue
+			}
+			if !peer.ExitNodeOption {
+				return E.New("peer does not offer exit node: ", stableID)
+			}
+			found = true
+			break
+		}
+		if !found {
+			return E.New("peer not found: ", stableID)
+		}
+	}
+	_, err := t.server.ExportLocalBackend().EditPrefs(perfs)
+	if err != nil {
+		return E.Cause(err, "update prefs")
+	}
+	return nil
+}
+
 func (t *Endpoint) Close() error {
 	var err error
 	t.started.Store(false)

protocol/tailscale/status.go

@@ -26,7 +26,7 @@ func (t *Endpoint) SubscribeTailscaleStatus(ctx context.Context, fn func(*adapte
 			return false
 		default:
 		}
-		if roNotify.State != nil || roNotify.NetMap != nil || roNotify.BrowseToURL != nil {
+		if roNotify.State != nil || roNotify.NetMap != nil || roNotify.BrowseToURL != nil || roNotify.Prefs != nil {
 			sendStatus()
 		}
 		return true
@@ -76,6 +76,27 @@ func convertTailscaleStatus(status *ipnstate.Status) *adapter.TailscaleEndpointS
 			return 0
 		})
 	}
+	if status.ExitNodeStatus != nil {
+		for _, peerKey := range status.Peers() {
+			peer := status.Peer[peerKey]
+			if peer.ID == status.ExitNodeStatus.ID {
+				result.ExitNode = convertTailscalePeer(peer)
+				break
+			}
+		}
+		if result.ExitNode == nil {
+			ips := make([]string, 0, len(status.ExitNodeStatus.TailscaleIPs))
+			for _, prefix := range status.ExitNodeStatus.TailscaleIPs {
+				ips = append(ips, prefix.Addr().String())
+			}
+			result.ExitNode = &adapter.TailscalePeer{
+				StableID:     string(status.ExitNodeStatus.ID),
+				TailscaleIPs: ips,
+				Online:       status.ExitNodeStatus.Online,
+				ExitNode:     true,
+			}
+		}
+	}
 	return result
 }
 
@@ -89,6 +110,7 @@ func convertTailscalePeer(peer *ipnstate.PeerStatus) *adapter.TailscalePeer {
 		keyExpiry = peer.KeyExpiry.Unix()
 	}
 	return &adapter.TailscalePeer{
+		StableID:       string(peer.ID),
 		HostName:       peer.HostName,
 		DNSName:        peer.DNSName,
 		OS:             peer.OS,