internal: only delete old ipv6 if it is non-link local

So the client is removed from table only when it's global ipv6 changed.

internal/clientinfo/ndp.go

@@ -15,6 +15,7 @@ import (
 	"github.com/mdlayher/ndp"
 
 	"github.com/Control-D-Inc/ctrld"
+	ctrldnet "github.com/Control-D-Inc/ctrld/internal/net"
 )
 
 // ndpDiscover provides client discovery functionality using NDP protocol.
@@ -70,20 +71,23 @@ func (nd *ndpDiscover) List() []string {
 }
 
 // saveInfo saves ip and mac info to mapping table.
-// If force is true, old ip will be removed before saving.
-func (nd *ndpDiscover) saveInfo(ip, mac string, force bool) {
+func (nd *ndpDiscover) saveInfo(ip, mac string) {
 	ip = normalizeIP(ip)
 	// Store ip => map mapping,
 	nd.mac.Store(ip, mac)
 
-	if force {
-		// If there is old ip => mac mapping, delete it.
-		if old, ok := nd.ip.Load(mac); ok {
-			oldIP := old.(string)
+	// Do not store mac => ip mapping if new ip is a link local unicast.
+	if ctrldnet.IsLinkLocalUnicastIPv6(ip) {
+		return
+	}
+
+	// If there is old ip => mac mapping, delete it.
+	if old, existed := nd.ip.Load(mac); existed {
+		oldIP := old.(string)
+		if oldIP != ip {
 			nd.mac.Delete(oldIP)
 		}
 	}
-
 	// Store mac => ip mapping.
 	nd.ip.Store(mac, ip)
 }
@@ -138,7 +142,7 @@ func (nd *ndpDiscover) listenOnInterface(ctx context.Context, ifi *net.Interface
 		for _, opt := range am.Options {
 			if lla, ok := opt.(*ndp.LinkLayerAddress); ok {
 				mac := lla.Addr.String()
-				nd.saveInfo(fromIP, mac, true)
+				nd.saveInfo(fromIP, mac)
 			}
 		}
 	}
@@ -153,7 +157,7 @@ func (nd *ndpDiscover) scanWindows(r io.Reader) {
 			continue
 		}
 		if mac := parseMAC(fields[1]); mac != "" {
-			nd.saveInfo(fields[0], mac, true)
+			nd.saveInfo(fields[0], mac)
 		}
 	}
 }
@@ -172,7 +176,7 @@ func (nd *ndpDiscover) scanUnix(r io.Reader) {
 			if idx := strings.IndexByte(ip, '%'); idx != -1 {
 				ip = ip[:idx]
 			}
-			nd.saveInfo(ip, mac, true)
+			nd.saveInfo(ip, mac)
 		}
 	}
 }

internal/clientinfo/ndp_linux.go

@@ -24,7 +24,7 @@ func (nd *ndpDiscover) scan() {
 		}
 		ip := n.IP.String()
 		mac := n.HardwareAddr.String()
-		nd.saveInfo(ip, mac, false)
+		nd.saveInfo(ip, mac)
 	}
 }
 
@@ -54,7 +54,7 @@ func (nd *ndpDiscover) subscribe(ctx context.Context) {
 			mac := nu.HardwareAddr.String()
 			switch nu.State {
 			case netlink.NUD_REACHABLE:
-				nd.saveInfo(ip, mac, false)
+				nd.saveInfo(ip, mac)
 			case netlink.NUD_FAILED:
 				ctrld.ProxyLogger.Load().Debug().Msgf("removing NDP neighbor with failed state: %s", ip)
 				nd.mac.Delete(ip)

internal/clientinfo/ndp_test.go

@@ -45,18 +45,17 @@ ff02::c                                       33-33-00-00-00-0c  Permanent
 	nd.scanWindows(r)
 
 	count := 0
-	expectedCount := 5
+	expectedCount := 6
 	nd.mac.Range(func(key, value any) bool {
 		count++
 		return true
 	})
-	// There are 2 entries for 60-57-47-21-dd-00 in the table, but (*ndpDiscover).saveInfo
-	// only saves the last one, that's why the expected count number is 5.
 	if count != expectedCount {
 		t.Errorf("unexpected count, want %d, got: %d", expectedCount, count)
 	}
 
 	count = 0
+	expectedCount = 4
 	nd.ip.Range(func(key, value any) bool {
 		count++
 		return true

internal/net/net.go

@@ -115,6 +115,15 @@ func IsIPv6(ip string) bool {
 	return parsedIP != nil && parsedIP.To4() == nil && parsedIP.To16() != nil
 }
 
+// IsLinkLocalUnicastIPv6 checks if the provided IP is a link local unicast v6 address.
+func IsLinkLocalUnicastIPv6(ip string) bool {
+	parsedIP := net.ParseIP(ip)
+	if parsedIP == nil || parsedIP.To4() != nil || parsedIP.To16() == nil {
+		return false
+	}
+	return parsedIP.To16().IsLinkLocalUnicast()
+}
+
 type parallelDialerResult struct {
 	conn net.Conn
 	err  error