all: generalize vpn client info

VPN clients often have empty MAC address, because they come from virtual
network interface. However, there's other setup/devices also create
virtual interface, but is not VPN.

Changing source of those clients to empty to prevent confustion in
clients list command output.

cmd/cli/cli.go

@@ -626,6 +626,9 @@ NOTE: Uninstalling will set DNS to values provided by DHCP.`,
 			map2Slice := func(m map[string]struct{}) []string {
 				s := make([]string, 0, len(m))
 				for k := range m {
+					if k == "" { // skip empty source from output.
+						continue
+					}
 					s = append(s, k)
 				}
 				sort.Strings(s)

internal/clientinfo/client_info.go

@@ -74,7 +74,7 @@ type Table struct {
 	ptr    *ptrDiscover
 	mdns   *mdns
 	hf     *hostsFile
-	vpn    *vpn
+	vni    *virtualNetworkIface
 	cfg    *ctrld.Config
 	quitCh chan struct{}
 	selfIP string
@@ -202,8 +202,8 @@ func (t *Table) init() {
 	}
 	// VPN clients.
 	if t.discoverDHCP() || t.discoverARP() {
-		t.vpn = &vpn{}
-		t.hostnameResolvers = append(t.hostnameResolvers, t.vpn)
+		t.vni = &virtualNetworkIface{}
+		t.hostnameResolvers = append(t.hostnameResolvers, t.vni)
 	}
 }
 
@@ -288,7 +288,7 @@ func (t *Table) ListClients() []*Client {
 		_ = r.refresh()
 	}
 	ipMap := make(map[string]*Client)
-	il := []ipLister{t.dhcp, t.arp, t.ptr, t.mdns, t.vpn}
+	il := []ipLister{t.dhcp, t.arp, t.ptr, t.mdns, t.vni}
 	for _, ir := range il {
 		for _, ip := range ir.List() {
 			c, ok := ipMap[ip]
@@ -331,11 +331,11 @@ func (t *Table) ListClients() []*Client {
 
 // StoreVPNClient stores client info for VPN clients.
 func (t *Table) StoreVPNClient(ci *ctrld.ClientInfo) {
-	if ci == nil || t.vpn == nil {
+	if ci == nil || t.vni == nil {
 		return
 	}
-	t.vpn.mac.Store(ci.IP, ci.Mac)
-	t.vpn.ip2name.Store(ci.IP, ci.Hostname)
+	t.vni.mac.Store(ci.IP, ci.Mac)
+	t.vni.ip2name.Store(ci.IP, ci.Hostname)
 }
 
 func (t *Table) discoverDHCP() bool {

internal/clientinfo/virtual_iface.go

@@ -4,14 +4,14 @@ import (
 	"sync"
 )
 
-// vpn is the manager for VPN clients info.
-type vpn struct {
+// virtualNetworkIface is the manager for clients from virtual network interface.
+type virtualNetworkIface struct {
 	ip2name sync.Map // ip  => name
 	mac     sync.Map // ip  => mac
 }
 
 // LookupHostnameByIP returns hostname of the given VPN client ip.
-func (v *vpn) LookupHostnameByIP(ip string) string {
+func (v *virtualNetworkIface) LookupHostnameByIP(ip string) string {
 	val, ok := v.ip2name.Load(ip)
 	if !ok {
 		return ""
@@ -20,17 +20,17 @@ func (v *vpn) LookupHostnameByIP(ip string) string {
 }
 
 // LookupHostnameByMac always returns empty string.
-func (v *vpn) LookupHostnameByMac(mac string) string {
+func (v *virtualNetworkIface) LookupHostnameByMac(mac string) string {
 	return ""
 }
 
-// String returns the string representation of vpn struct.
-func (v *vpn) String() string {
-	return "vpn"
+// String returns the string representation of virtualNetworkIface struct.
+func (v *virtualNetworkIface) String() string {
+	return ""
 }
 
 // List lists all known VPN clients IP.
-func (v *vpn) List() []string {
+func (v *virtualNetworkIface) List() []string {
 	if v == nil {
 		return nil
 	}