ipn/ipnstate, cmd/tailscale: add Online bool to tailscale status & --json

Fixes #3533

Change-Id: I2f6f0d712cf3f987fba1c15be74cdb5c8d565f04
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscale/cli/status.go

@@ -29,7 +29,22 @@
 	Name:       "status",
 	ShortUsage: "status [--active] [--web] [--json]",
 	ShortHelp:  "Show state of tailscaled and its connections",
-	Exec:       runStatus,
+	LongHelp: strings.TrimSpace(`
+
+JSON FORMAT
+
+Warning: this format has changed between releases and might change more
+in the future.
+
+For a description of the fields, see the "type Status" declaration at:
+
+https://github.com/tailscale/tailscale/blob/main/ipn/ipnstate/ipnstate.go
+
+(and be sure to select branch/tag that corresponds to the version
+ of Tailscale you're running)
+
+`),
+	Exec: runStatus,
 	FlagSet: (func() *flag.FlagSet {
 		fs := newFlagSet("status")
 		fs.BoolVar(&statusArgs.json, "json", false, "output in JSON format (WARNING: format subject to change)")
@@ -145,13 +160,19 @@ func runStatus(ctx context.Context, args []string) error {
 		)
 		relay := ps.Relay
 		anyTraffic := ps.TxBytes != 0 || ps.RxBytes != 0
+		var offline string
+		if !ps.Online {
+			offline = "; offline"
+		}
 		if !ps.Active {
 			if ps.ExitNode {
-				f("idle; exit node")
+				f("idle; exit node" + offline)
 			} else if ps.ExitNodeOption {
-				f("idle; offers exit node")
+				f("idle; offers exit node" + offline)
 			} else if anyTraffic {
-				f("idle")
+				f("idle" + offline)
+			} else if !ps.Online {
+				f("offline")
 			} else {
 				f("-")
 			}
@@ -167,6 +188,9 @@ func runStatus(ctx context.Context, args []string) error {
 			} else if ps.CurAddr != "" {
 				f("direct %s", ps.CurAddr)
 			}
+			if !ps.Online {
+				f("; offline")
+			}
 		}
 		if anyTraffic {
 			f(", tx %d rx %d", ps.TxBytes, ps.RxBytes)

ipn/ipnlocal/local.go

@@ -445,6 +445,7 @@ func (b *LocalBackend) populatePeerStatusLocked(sb *ipnstate.StatusBuilder) {
 			KeepAlive:          p.KeepAlive,
 			Created:            p.Created,
 			LastSeen:           lastSeen,
+			Online:             p.Online != nil && *p.Online,
 			ShareeNode:         p.Hostinfo.ShareeNode,
 			ExitNode:           p.StableID != "" && p.StableID == b.prefs.ExitNodeID,
 			ExitNodeOption:     exitNodeOption,

ipn/ipnstate/ipnstate.go

@@ -100,8 +100,9 @@ type PeerStatus struct {
 	TxBytes        int64
 	Created        time.Time // time registered with tailcontrol
 	LastWrite      time.Time // time last packet sent
-	LastSeen       time.Time // last seen to tailcontrol
+	LastSeen       time.Time // last seen to tailcontrol; only present if offline
 	LastHandshake  time.Time // with local wireguard
+	Online         bool      // whether node is connected to the control plane
 	KeepAlive      bool
 	ExitNode       bool // true if this is the currently selected exit node.
 	ExitNodeOption bool // true if this node can be an exit node (offered && approved)
@@ -276,6 +277,9 @@ func (sb *StatusBuilder) AddPeer(peer key.NodePublic, st *PeerStatus) {
 	if v := st.LastWrite; !v.IsZero() {
 		e.LastWrite = v
 	}
+	if st.Online {
+		e.Online = true
+	}
 	if st.InNetworkMap {
 		e.InNetworkMap = true
 	}