netlink: add func AddrSubscribe on darwin

netlink/addr.go

@@ -0,0 +1,9 @@
+package netlink
+
+import "net"
+
+type AddrUpdate struct {
+	New       bool
+	Addr      net.IPNet
+	LinkIndex int
+}

netlink/addr_darwin.go

@@ -0,0 +1,83 @@
+package netlink
+
+import (
+	"context"
+	"encoding/hex"
+	"fmt"
+	"log/slog"
+	"net"
+	"os"
+	"slices"
+	"syscall"
+
+	"golang.org/x/net/route"
+)
+
+func AddrSubscribe(ctx context.Context, ch chan<- AddrUpdate) error {
+	fd, err := syscall.Socket(syscall.AF_ROUTE, syscall.SOCK_RAW, syscall.AF_UNSPEC)
+	if err != nil {
+		return fmt.Errorf("syscall socket: %w", err)
+	}
+	go func() {
+		err := runAddrMsgReadLoop(fd, ch)
+		if err != nil {
+			slog.Error("AddrSubscribe", "err", fmt.Errorf("msg read loop exited: %w", err))
+		}
+	}()
+	go func() {
+		<-ctx.Done()
+		syscall.Close(fd)
+		close(ch)
+	}()
+	return nil
+}
+
+func runAddrMsgReadLoop(fd int, ch chan<- AddrUpdate) error {
+	buf := make([]byte, os.Getpagesize())
+	for {
+		n, err := syscall.Read(fd, buf)
+		if err != nil {
+			return fmt.Errorf("syscall read: %w", err)
+		}
+		buf[0] = 254
+		msgs, err := route.ParseRIB(route.RIBTypeRoute, buf[:254])
+		if err != nil {
+			slog.Warn("RouteParseRIB", "err", err, "msglen", n, "msg", hex.EncodeToString(buf[:n]))
+			continue
+		}
+		for _, msg := range msgs {
+			m, ok := msg.(*route.InterfaceAddrMessage)
+			if !ok {
+				continue
+			}
+			if !slices.Contains([]int{syscall.RTM_NEWADDR, syscall.RTM_DELADDR}, m.Type) {
+				continue
+			}
+			ipnet := net.IPNet{}
+			for _, addr := range m.Addrs {
+				var ip []byte
+				switch v := addr.(type) {
+				case *route.Inet4Addr:
+					ip = v.IP[:]
+				case *route.Inet6Addr:
+					ip = v.IP[:]
+				default:
+					continue
+				}
+				if ipnet.Mask == nil {
+					ipnet.Mask = ip
+					continue
+				}
+				if ipnet.IP == nil {
+					ipnet.IP = ip
+					break
+				}
+			}
+			ch <- AddrUpdate{
+				New:       m.Type == syscall.RTM_NEWADDR,
+				Addr:      ipnet,
+				LinkIndex: m.Index,
+			}
+		}
+	}
+}