ipn/ipnstate: add ExitNodeStatus to share the exit node if it is in use, the IP, ID and whether its online. (#4761)

-
Updates #4619

Signed-off-by: nyghtowl <warrick@tailscale.com>

ipn/ipnlocal/local.go

@@ -425,6 +425,20 @@ func (b *LocalBackend) updateStatus(sb *ipnstate.StatusBuilder, extraLocked func
 			s.CurrentTailnet.MagicDNSSuffix = b.netMap.MagicDNSSuffix()
 			s.CurrentTailnet.MagicDNSEnabled = b.netMap.DNS.Proxied
 			s.CurrentTailnet.Name = b.netMap.Domain
+			if b.prefs != nil && !b.prefs.ExitNodeID.IsZero() {
+				if exitPeer, ok := b.netMap.PeerWithStableID(b.prefs.ExitNodeID); ok {
+					var online = false
+					if exitPeer.Online != nil {
+						online = *exitPeer.Online
+					}
+					s.ExitNodeStatus = &ipnstate.ExitNodeStatus{
+						ID:           b.prefs.ExitNodeID,
+						Online:       online,
+						TailscaleIPs: exitPeer.Addresses,
+					}
+				}
+
+			}
 		}
 	})
 	sb.MutateSelfStatus(func(ss *ipnstate.PeerStatus) {

ipn/ipnstate/ipnstate.go

@@ -38,6 +38,10 @@ type Status struct {
 	TailscaleIPs []netaddr.IP // Tailscale IP(s) assigned to this node
 	Self         *PeerStatus
 
+	// ExitNodeStatus describes the current exit node.
+	// If nil, an exit node is not in use.
+	ExitNodeStatus *ExitNodeStatus `json:"ExitNodeStatus,omitempty"`
+
 	// Health contains health check problems.
 	// Empty means everything is good. (or at least that no known
 	// problems are detected)
@@ -81,6 +85,18 @@ type TailnetStatus struct {
 	MagicDNSEnabled bool
 }
 
+// ExitNodeStatus describes the current exit node.
+type ExitNodeStatus struct {
+	// ID is the exit node's ID.
+	ID tailcfg.StableNodeID
+
+	// Online is whether the exit node is alive.
+	Online bool
+
+	// TailscaleIPs are the exit node's IP addresses assigned to the node.
+	TailscaleIPs []netaddr.IPPrefix
+}
+
 func (s *Status) Peers() []key.NodePublic {
 	kk := make([]key.NodePublic, 0, len(s.Peer))
 	for k := range s.Peer {

types/netmap/netmap.go

@@ -122,6 +122,16 @@ func (nm *NetworkMap) VeryConcise() string {
 	return buf.String()
 }
 
+// PeerWithStableID finds and returns the peer associated to the inputted StableNodeID.
+func (nm *NetworkMap) PeerWithStableID(pid tailcfg.StableNodeID) (_ *tailcfg.Node, ok bool) {
+	for _, p := range nm.Peers {
+		if p.StableID == pid {
+			return p, true
+		}
+	}
+	return nil, false
+}
+
 // printConciseHeader prints a concise header line representing nm to buf.
 //
 // If this function is changed to access different fields of nm, keep