add -i flag to filter by single interface

arp.go

@@ -37,6 +37,9 @@ func (t *Tendrils) readARPTable() {
 	entries := t.parseARPTable()
 
 	for _, entry := range entries {
+		if t.iface != "" && entry.iface != t.iface {
+			continue
+		}
 		if isBroadcastOrZero(entry.mac) {
 			continue
 		}

cmd/tendrils/main.go

@@ -1,10 +1,15 @@
 package main
 
 import (
+	"flag"
+
 	"github.com/gopatchy/tendrils"
 )
 
 func main() {
-	t := tendrils.New()
+	iface := flag.String("i", "", "interface to use (default: all interfaces)")
+	flag.Parse()
+
+	t := tendrils.New(*iface)
 	t.Run()
 }

tendrils.go

@@ -11,12 +11,14 @@ import (
 type Tendrils struct {
 	activeInterfaces map[string]context.CancelFunc
 	nodes            *Nodes
+	iface            string
 }
 
-func New() *Tendrils {
+func New(iface string) *Tendrils {
 	return &Tendrils{
 		activeInterfaces: map[string]context.CancelFunc{},
 		nodes:            NewNodes(),
+		iface:            iface,
 	}
 }
 
@@ -88,6 +90,9 @@ func (t *Tendrils) listInterfaces() []net.Interface {
 
 	var validInterfaces []net.Interface
 	for _, iface := range interfaces {
+		if t.iface != "" && iface.Name != t.iface {
+			continue
+		}
 		if iface.Flags&net.FlagUp == 0 {
 			continue
 		}