internal/clientinfo: improving mdns discovery

- Prevent duplicated log message.
 - Distinguish in case of create/update hostname.
 - Stop probing if network is unreachable or invalid.

internal/clientinfo/client_info.go

@@ -48,10 +48,11 @@ type Table struct {
 	ptr    *ptrDiscover
 	mdns   *mdns
 	cfg    *ctrld.Config
+	quitCh chan struct{}
 }
 
 func NewTable(cfg *ctrld.Config) *Table {
-	return &Table{cfg: cfg}
+	return &Table{cfg: cfg, quitCh: make(chan struct{})}
 }
 
 func (t *Table) AddLeaseFile(name string, format ctrld.LeaseFileFormat) {
@@ -70,6 +71,7 @@ func (t *Table) RefreshLoop(stopCh chan struct{}) {
 				_ = r.refresh()
 			}
 		case <-stopCh:
+			close(t.quitCh)
 			return
 		}
 	}
@@ -122,7 +124,7 @@ func (t *Table) Init() {
 	if t.discoverMDNS() {
 		t.mdns = &mdns{}
 		ctrld.ProxyLog.Debug().Msg("start mdns discovery")
-		if err := t.mdns.init(); err != nil {
+		if err := t.mdns.init(t.quitCh); err != nil {
 			ctrld.ProxyLog.Error().Err(err).Msg("could not init mDNS discover")
 		} else {
 			t.hostnameResolvers = append(t.hostnameResolvers, t.mdns)

internal/clientinfo/mdns.go

@@ -4,7 +4,9 @@ import (
 	"context"
 	"errors"
 	"net"
+	"os"
 	"sync"
+	"syscall"
 	"time"
 
 	"github.com/miekg/dns"
@@ -41,7 +43,7 @@ func (m *mdns) LookupHostnameByMac(mac string) string {
 	return ""
 }
 
-func (m *mdns) init() error {
+func (m *mdns) init(quitCh chan struct{}) error {
 	ifaces, err := multicastInterfaces()
 	if err != nil {
 		return err
@@ -65,20 +67,35 @@ func (m *mdns) init() error {
 		}
 	}
 
-	go func() {
+	go m.probeLoop(v4ConnList, mdnsV4Addr, quitCh)
-		bo := backoff.NewBackoff("mdns probe", func(format string, args ...any) {}, time.Second*30)
+	go m.probeLoop(v6ConnList, mdnsV6Addr, quitCh)
-		for {
-			err := m.probe(v4ConnList, v6ConnList)
-			if err != nil {
-				ctrld.ProxyLog.Warn().Err(err).Msg("error while probing mdns")
-			}
-			bo.BackOff(context.Background(), errors.New("mdns probe backoff"))
-		}
-	}()
 
 	return nil
 }
 
+func (m *mdns) probeLoop(conns []*net.UDPConn, remoteAddr net.Addr, quitCh chan struct{}) {
+	bo := backoff.NewBackoff("mdns probe", func(format string, args ...any) {}, time.Second*30)
+	for {
+		err := m.probe(conns, remoteAddr, quitCh)
+		if isErrNetUnreachableOrInvalid(err) {
+			ctrld.ProxyLog.Warn().Msgf("stop probing %q: network unreachable or invalid", remoteAddr)
+			break
+		}
+		if err != nil {
+			ctrld.ProxyLog.Warn().Err(err).Msg("error while probing mdns")
+			bo.BackOff(context.Background(), errors.New("mdns probe backoff"))
+		}
+		select {
+		case <-quitCh:
+			break
+		}
+	}
+	<-quitCh
+	for _, conn := range conns {
+		_ = conn.Close()
+	}
+}
+
 func (m *mdns) readLoop(conn *net.UDPConn) {
 	defer conn.Close()
 	buf := make([]byte, dns.MaxMsgSize)
@@ -87,12 +104,10 @@ func (m *mdns) readLoop(conn *net.UDPConn) {
 		_ = conn.SetReadDeadline(time.Now().Add(time.Second * 30))
 		n, _, err := conn.ReadFromUDP(buf)
 		if err != nil {
-			if err, ok := err.(*net.OpError); ok {
+			if err, ok := err.(*net.OpError); ok && (err.Timeout() || err.Temporary()) {
-				if err.Timeout() || err.Temporary() {
+				continue
-					continue
-				}
-				ctrld.ProxyLog.Debug().Err(err).Msg("mdns readLoop error")
 			}
+			ctrld.ProxyLog.Debug().Err(err).Msg("mdns readLoop error")
 			return
 		}
 
@@ -111,14 +126,22 @@ func (m *mdns) readLoop(conn *net.UDPConn) {
 			}
 			if ip != "" && name != "" {
 				name = normalizeHostname(name)
-				ctrld.ProxyLog.Debug().Msgf("Found hostname: %q, ip: %q via mdns", name, ip)
+				if val, loaded := m.name.LoadOrStore(ip, name); !loaded {
-				m.name.Store(ip, name)
+					ctrld.ProxyLog.Debug().Msgf("found hostname: %q, ip: %q via mdns", name, ip)
+				} else {
+					old := val.(string)
+					if old != name {
+						ctrld.ProxyLog.Debug().Msgf("update hostname: %q, ip: %q, old: %q via mdns", name, ip, old)
+						m.name.Store(ip, name)
+					}
+				}
+				ip, name = "", ""
 			}
 		}
 	}
 }
 
-func (m *mdns) probe(v4connList, v6connList []*net.UDPConn) error {
+func (m *mdns) probe(conns []*net.UDPConn, remoteAddr net.Addr, quitCh chan struct{}) error {
 	msg := new(dns.Msg)
 	msg.Question = make([]dns.Question, len(services))
 	for i, service := range services {
@@ -133,16 +156,13 @@ func (m *mdns) probe(v4connList, v6connList []*net.UDPConn) error {
 	if err != nil {
 		return err
 	}
-	do := func(connList []*net.UDPConn, remoteAddr net.Addr) error {
+	for _, conn := range conns {
-		for _, conn := range connList {
+		_ = conn.SetWriteDeadline(time.Now().Add(time.Second * 30))
-			_ = conn.SetWriteDeadline(time.Now().Add(time.Second * 30))
+		if _, werr := conn.WriteTo(buf, remoteAddr); werr != nil {
-			if _, err := conn.WriteTo(buf, remoteAddr); err != nil {
+			err = werr
-				return err
-			}
 		}
-		return nil
 	}
-	return errors.Join(do(v4connList, mdnsV4Addr), do(v6connList, mdnsV6Addr))
+	return err
 }
 
 func multicastInterfaces() ([]net.Interface, error) {
@@ -161,3 +181,11 @@ func multicastInterfaces() ([]net.Interface, error) {
 	}
 	return interfaces, nil
 }
+
+func isErrNetUnreachableOrInvalid(err error) bool {
+	var se *os.SyscallError
+	if errors.As(err, &se) {
+		return se.Err == syscall.ENETUNREACH || se.Err == syscall.EINVAL
+	}
+	return false
+}