cmd/tailscale: change formatting of "tailscale status"

* show DNS name over hostname, removing domain's common MagicDNS suffix.
  only show hostname if there's no DNS name.
  but still show shared devices' MagicDNS FQDN.

* remove nerdy low-level details by default: endpoints, DERP relay,
  public key.  They're available in JSON mode still for those who need
  them.

* only show endpoint or DERP relay when it's active with the goal of
  making debugging easier. (so it's easier for users to understand
  what's happening) The asterisks are gone.

* remove Tx/Rx numbers by default for idle peers; only show them when
  there's traffic.

* include peers' owner login names

* add CLI option to not show peers (matching --self=true, --peers= also
  defaults to true)

* sort by DNS/host name, not public key

* reorder columns

ipn/ipnstate/ipnstate.go

@@ -25,9 +25,10 @@ import (
 
 // Status represents the entire state of the IPN network.
 type Status struct {
-	BackendState string
-	TailscaleIPs []netaddr.IP // Tailscale IP(s) assigned to this node
-	Self         *PeerStatus
+	BackendState   string
+	TailscaleIPs   []netaddr.IP // Tailscale IP(s) assigned to this node
+	Self           *PeerStatus
+	MagicDNSSuffix string // e.g. "userfoo.tailscale.net" (no surrounding dots)
 
 	Peer map[key.Public]*PeerStatus
 	User map[tailcfg.UserID]tailcfg.UserProfile
@@ -103,6 +104,12 @@ func (sb *StatusBuilder) SetBackendState(v string) {
 	sb.st.BackendState = v
 }
 
+func (sb *StatusBuilder) SetMagicDNSSuffix(v string) {
+	sb.mu.Lock()
+	defer sb.mu.Unlock()
+	sb.st.MagicDNSSuffix = v
+}
+
 func (sb *StatusBuilder) Status() *Status {
 	sb.mu.Lock()
 	defer sb.mu.Unlock()

ipn/local.go

@@ -201,6 +201,7 @@ func (b *LocalBackend) UpdateStatus(sb *ipnstate.StatusBuilder) {
 	// TODO: hostinfo, and its networkinfo
 	// TODO: EngineStatus copy (and deprecate it?)
 	if b.netMap != nil {
+		sb.SetMagicDNSSuffix(b.netMap.MagicDNSSuffix())
 		for id, up := range b.netMap.UserProfiles {
 			sb.AddUser(id, up)
 		}
@@ -1232,28 +1233,10 @@ func (b *LocalBackend) authReconfig() {
 // magicDNSRootDomains returns the subset of nm.DNS.Domains that are the search domains for MagicDNS.
 // Each entry has a trailing period.
 func magicDNSRootDomains(nm *controlclient.NetworkMap) []string {
-	searchPathUsedAsDNSSuffix := func(suffix string) bool {
-		if tsdns.NameHasSuffix(nm.Name, suffix) {
-			return true
-		}
-		for _, p := range nm.Peers {
-			if tsdns.NameHasSuffix(p.Name, suffix) {
-				return true
-			}
-		}
-		return false
+	if v := nm.MagicDNSSuffix(); v != "" {
+		return []string{strings.Trim(v, ".") + "."}
 	}
-
-	var ret []string
-	for _, d := range nm.DNS.Domains {
-		if searchPathUsedAsDNSSuffix(d) {
-			if !strings.HasSuffix(d, ".") {
-				d += "."
-			}
-			ret = append(ret, d)
-		}
-	}
-	return ret
+	return nil
 }
 
 // routerConfig produces a router.Config from a wireguard config and IPN prefs.