Keep watching the tunnel after a failed look, and remember peers' names

modules/netcheck/cmd/netcheck/tunnel.go

@@ -20,6 +20,7 @@ import (
 	"sort"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 )
 
@@ -109,11 +110,20 @@ func parseDump(out string, now time.Time) (Tunnel, error) {
 	return t, sc.Err()
 }
 
+// errNoTunnel is a machine without the interface: not a fault, a machine off the private network.
+var errNoTunnel = errors.New("this machine has no " + TunnelInterface)
+
+// names remembers the mesh's name of each peer address once found, so the watcher asks no resolver every look.
+var names sync.Map
+
 // readTunnel asks wg for the interface's state and names each peer by the mesh's names.
 func readTunnel(ctx context.Context) (Tunnel, error) {
 	out, err := exec.CommandContext(ctx, "wg", "show", TunnelInterface, "dump").Output()
 	if err != nil {
 		var ee *exec.ExitError
+		if errors.As(err, &ee) && strings.Contains(string(ee.Stderr), "No such device") {
+			return Tunnel{}, errNoTunnel
+		}
 		if errors.As(err, &ee) && len(ee.Stderr) > 0 {
 			return Tunnel{}, fmt.Errorf("wg show %s: %s", TunnelInterface, strings.TrimSpace(string(ee.Stderr)))
 		}
@@ -124,7 +134,15 @@ func readTunnel(ctx context.Context) (Tunnel, error) {
 		return t, err
 	}
 	for i := range t.Peers {
-		t.Peers[i].Name = nameOf(ctx, t.Peers[i].AllowedIPs)
+		k := peerKey(t.Peers[i])
+		if known, ok := names.Load(k); ok {
+			t.Peers[i].Name = known.(string)
+			continue
+		}
+		if name := nameOf(ctx, t.Peers[i].AllowedIPs); name != "" {
+			names.Store(k, name)
+			t.Peers[i].Name = name
+		}
 	}
 	return t, nil
 }
@@ -204,7 +222,7 @@ func report(err error) {
 }
 
 // watchTunnel looks every 20 seconds while this machine has the interface; a machine without it is
-// looked at again every ten minutes, saying so once.
+// looked at again every ten minutes. A failed look is said once and tried again at the next look.
 func watchTunnel(emit emitter) {
 	var w tunnelWatch
 	said := ""
@@ -217,7 +235,11 @@ func watchTunnel(emit emitter) {
 				say("not watching the tunnel: %v", err)
 				said = err.Error()
 			}
-			time.Sleep(10 * time.Minute)
+			if errors.Is(err, errNoTunnel) {
+				time.Sleep(10 * time.Minute)
+			} else {
+				time.Sleep(20 * time.Second)
+			}
 			continue
 		}
 		said = ""