internal/router: normalize ip address from dnsmasq lease file

dnsmasq may put an ip address with the interface index in lease file,
causing bad data sent to the Control-D backend.

internal/router/client_info.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"log"
 	"os"
+	"strings"
 	"time"
 
 	"github.com/fsnotify/fsnotify"
@@ -80,9 +81,18 @@ func readClientInfoFile(name string) error {
 	return lineread.File(name, func(line []byte) error {
 		fields := bytes.Fields(line)
 		mac := string(fields[1])
-		ip := string(fields[2])
+		ip := normalizeIP(string(fields[2]))
 		hostname := string(fields[3])
 		r.mac.Store(mac, &ctrld.ClientInfo{Mac: mac, IP: ip, Hostname: hostname})
 		return nil
 	})
 }
+
+func normalizeIP(in string) string {
+	// dnsmasq may put ip with interface index in lease file, strip it here.
+	ip, _, found := strings.Cut(in, "%")
+	if found {
+		return ip
+	}
+	return in
+}

internal/router/client_info_test.go

@@ -0,0 +1,25 @@
+package router
+
+import "testing"
+
+func Test_normalizeIP(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		want string
+	}{
+		{"v4", "127.0.0.1", "127.0.0.1"},
+		{"v4 with index", "127.0.0.1%lo", "127.0.0.1"},
+		{"v6", "fe80::1", "fe80::1"},
+		{"v6 with index", "fe80::1%22002", "fe80::1"},
+	}
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			if got := normalizeIP(tc.in); got != tc.want {
+				t.Errorf("normalizeIP() = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}