Improve mDNS package

pkg/mdns/mdns.go

@@ -1,18 +1,19 @@
 package mdns
 
 import (
+	"context"
+	"errors"
 	"fmt"
-	"github.com/miekg/dns"
 	"net"
 	"strings"
+	"syscall"
 	"time"
+
+	"github.com/miekg/dns" // awesome library for parsing mDNS records
 )
 
 const ServiceHAP = "_hap._tcp.local." // HomeKit Accessory Protocol
 
-const requestTimeout = time.Millisecond * 505
-const responseTimeout = time.Second * 2
-
 type ServiceEntry struct {
 	Name string
 	IP   net.IP
@@ -28,40 +29,191 @@ func (e *ServiceEntry) Addr() string {
 	return fmt.Sprintf("%s:%d", e.IP, e.Port)
 }
 
-func Discovery(service string, onentry func(*ServiceEntry) bool) error {
+var MulticastAddr = &net.UDPAddr{
-	addr := &net.UDPAddr{
+	IP:   net.IP{224, 0, 0, 251},
-		IP:   net.IP{224, 0, 0, 251},
+	Port: 5353,
-		Port: 5353,
+}
-	}
 
-	conn, err := net.ListenMulticastUDP("udp4", nil, addr)
+const sendTimeout = time.Millisecond * 505
+const respTimeout = time.Second * 3
+
+// BasicDiscovery - default golang Multicast UDP listener.
+// Does not work well with multiple interfaces.
+func BasicDiscovery(service string, onentry func(*ServiceEntry) bool) error {
+	conn, err := net.ListenMulticastUDP("udp4", nil, MulticastAddr)
 	if err != nil {
 		return err
 	}
 
-	defer conn.Close()
+	b := Browser{
+		Service:     service,
+		Addr:        MulticastAddr,
+		Recv:        conn,
+		Sends:       []net.PacketConn{conn},
+		RecvTimeout: respTimeout,
+		SendTimeout: sendTimeout,
+	}
 
-	if err = conn.SetDeadline(time.Now().Add(responseTimeout)); err != nil {
+	defer b.Close()
+
+	return b.Browse(onentry)
+}
+
+// Discovery - better discovery version. Works well with multiple interfaces.
+func Discovery(service string, onentry func(*ServiceEntry) bool) error {
+	b := Browser{
+		Service:     service,
+		Addr:        MulticastAddr,
+		RecvTimeout: respTimeout,
+		SendTimeout: sendTimeout,
+	}
+
+	if err := b.ListenMulticastUDP(); err != nil {
 		return err
 	}
 
-	msg := &dns.Msg{
+	defer b.Close()
-		Question: []dns.Question{
+
-			{service, dns.TypePTR, dns.ClassINET},
+	return b.Browse(onentry)
+}
+
+// Query - direct Discovery request on device IP-address. Works even over VPN.
+func Query(host, service string) (entry *ServiceEntry, err error) {
+	conn, err := net.ListenPacket("udp4", ":0") // shouldn't use ":5353"
+	if err != nil {
+		return
+	}
+
+	br := Browser{
+		Service: service,
+		Addr: &net.UDPAddr{
+			IP:   net.ParseIP(host),
+			Port: 5353,
+		},
+		Recv:        conn,
+		Sends:       []net.PacketConn{conn},
+		SendTimeout: time.Millisecond * 255,
+		RecvTimeout: time.Second,
+	}
+
+	defer br.Close()
+
+	err = br.Browse(func(en *ServiceEntry) bool {
+		entry = en
+		return true
+	})
+
+	return
+}
+
+func QueryOrDiscovery(host, service string, onentry func(*ServiceEntry) bool) error {
+	entry, _ := Query(host, service)
+	if entry != nil && onentry(entry) {
+		return nil
+	}
+
+	return Discovery(service, onentry)
+}
+
+type Browser struct {
+	Service string
+
+	Addr  net.Addr
+	Recv  net.PacketConn
+	Sends []net.PacketConn
+
+	RecvTimeout time.Duration
+	SendTimeout time.Duration
+}
+
+// ListenMulticastUDP - creates multiple senders socket (each for IP4 interface).
+// And one receiver with multicast membership for each sender.
+// Receiver will get multicast responses on senders requests.
+func (b *Browser) ListenMulticastUDP() error {
+	// 1. Collect IPv4 interfaces
+	ip4s, err := InterfacesIP4()
+	if err != nil {
+		return err
+	}
+
+	ctx := context.Background()
+
+	// 2. Create senders
+	lc1 := net.ListenConfig{
+		Control: func(network, address string, c syscall.RawConn) error {
+			return c.Control(func(fd uintptr) {
+				// 1. Allow multicast UDP to listen concurrently across multiple listeners
+				_ = syscall.SetsockoptInt(syscall.Handle(fd), syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
+			})
 		},
 	}
 
-	b1, err := msg.Pack()
+	for _, ip4 := range ip4s {
+		conn, err := lc1.ListenPacket(ctx, "udp4", ip4.String()+":5353") // same port important
+		if err != nil {
+			continue
+		}
+		b.Sends = append(b.Sends, conn)
+	}
+
+	if b.Sends == nil {
+		return errors.New("no interfaces for listen")
+	}
+
+	// 3. Create receiver
+	lc2 := net.ListenConfig{
+		Control: func(network, address string, c syscall.RawConn) error {
+			return c.Control(func(fd uintptr) {
+				// 1. Allow multicast UDP to listen concurrently across multiple listeners
+				_ = syscall.SetsockoptInt(syscall.Handle(fd), syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
+
+				// 2. Disable loop responses
+				_ = syscall.SetsockoptInt(syscall.Handle(fd), syscall.IPPROTO_IP, syscall.IP_MULTICAST_LOOP, 0)
+
+				// 3. Allow receive multicast responses on all this addresses
+				mreq := &syscall.IPMreq{
+					Multiaddr: [4]byte{224, 0, 0, 251},
+				}
+				_ = syscall.SetsockoptIPMreq(syscall.Handle(fd), syscall.IPPROTO_IP, syscall.IP_ADD_MEMBERSHIP, mreq)
+
+				for _, send := range b.Sends {
+					addr := send.LocalAddr().(*net.UDPAddr)
+					mreq.Interface = [4]byte(addr.IP.To4())
+					_ = syscall.SetsockoptIPMreq(syscall.Handle(fd), syscall.IPPROTO_IP, syscall.IP_ADD_MEMBERSHIP, mreq)
+				}
+			})
+		},
+	}
+
+	b.Recv, err = lc2.ListenPacket(ctx, "udp4", "0.0.0.0:5353")
+
+	return err
+}
+
+func (b *Browser) Browse(onentry func(*ServiceEntry) bool) error {
+	msg := &dns.Msg{
+		Question: []dns.Question{
+			{b.Service, dns.TypePTR, dns.ClassINET},
+		},
+	}
+
+	query, err := msg.Pack()
 	if err != nil {
 		return err
 	}
 
+	if err = b.Recv.SetDeadline(time.Now().Add(b.RecvTimeout)); err != nil {
+		return err
+	}
+
 	go func() {
 		for {
-			if _, err := conn.WriteToUDP(b1, addr); err != nil {
+			for _, send := range b.Sends {
-				return
+				if _, err := send.WriteTo(query, b.Addr); err != nil {
+					return
+				}
 			}
-			time.Sleep(requestTimeout)
+			time.Sleep(b.SendTimeout)
 		}
 	}()
 
@@ -71,7 +223,7 @@ func Discovery(service string, onentry func(*ServiceEntry) bool) error {
 loop:
 	for {
 		// in the Hass docker network can receive same msg from different address
-		n, _, err := conn.ReadFromUDP(b2)
+		n, _, err := b.Recv.ReadFrom(b2)
 		if err != nil {
 			break
 		}
@@ -82,7 +234,7 @@ loop:
 
 		ptr := GetPTR(msg)
 
-		if !strings.HasSuffix(ptr, service) {
+		if !strings.HasSuffix(ptr, b.Service) {
 			continue
 		}
 
@@ -102,6 +254,16 @@ loop:
 	return nil
 }
 
+func (b *Browser) Close() error {
+	if b.Recv != nil {
+		_ = b.Recv.Close()
+	}
+	for _, send := range b.Sends {
+		_ = send.Close()
+	}
+	return nil
+}
+
 func GetPTR(msg *dns.Msg) string {
 	for _, rr := range msg.Answer {
 		if rr, ok := rr.(*dns.PTR); ok {
@@ -139,3 +301,36 @@ func NewServiceEntry(msg *dns.Msg) *ServiceEntry {
 
 	return entry
 }
+
+func InterfacesIP4() ([]net.IP, error) {
+	intfs, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+
+	var ips []net.IP
+
+loop:
+	for _, intf := range intfs {
+		if intf.Flags&net.FlagUp == 0 || intf.Flags&net.FlagLoopback != 0 {
+			continue
+		}
+
+		addrs, err := intf.Addrs()
+		if err != nil {
+			continue
+		}
+
+		for _, addr := range addrs {
+			switch v := addr.(type) {
+			case *net.IPNet:
+				if ip := v.IP.To4(); ip != nil {
+					ips = append(ips, ip)
+					continue loop
+				}
+			}
+		}
+	}
+
+	return ips, nil
+}