From 1e642e955496ccee198251b16e1435406a2f133f Mon Sep 17 00:00:00 2001
From: Eric Daniels <eric@erdaniels.com>
Date: Thu, 19 Jan 2023 12:56:48 -0500
Subject: [PATCH] Properly add fix from
 https://github.com/grandcat/zeroconf/pull/110

---
 client.go | 24 ++++++++++++++++++++++++
 server.go | 43 ++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/client.go b/client.go
index 93de3de0..4d8e1ceb 100644
--- a/client.go
+++ b/client.go
@@ -4,7 +4,9 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"log"
 	"net"
+	"runtime"
 	"strings"
 	"sync"
 	"time"
@@ -511,16 +513,38 @@ func (c *client) sendQuery(msg *dns.Msg) error {
 		return err
 	}
 	if c.ipv4conn != nil {
+		// See https://pkg.go.dev/golang.org/x/net/ipv4#pkg-note-BUG
+		// As of Golang 1.18.4
+		// On Windows, the ControlMessage for ReadFrom and WriteTo methods of PacketConn is not implemented.
 		var wcm ipv4.ControlMessage
 		for ifi := range c.ifaces {
 			wcm.IfIndex = c.ifaces[ifi].Index
+			switch runtime.GOOS {
+			case "darwin", "ios", "linux":
+				wcm.IfIndex = c.ifaces[ifi].Index
+			default:
+				if err := c.ipv4conn.SetMulticastInterface(&c.ifaces[ifi]); err != nil {
+					log.Printf("[WARN] mdns: Failed to set multicast interface: %v", err)
+				}
+			}
 			c.ipv4conn.WriteTo(buf, &wcm, ipv4Addr)
 		}
 	}
 	if c.ipv6conn != nil {
+		// See https://pkg.go.dev/golang.org/x/net/ipv6#pkg-note-BUG
+		// As of Golang 1.18.4
+		// On Windows, the ControlMessage for ReadFrom and WriteTo methods of PacketConn is not implemented.
 		var wcm ipv6.ControlMessage
 		for ifi := range c.ifaces {
 			wcm.IfIndex = c.ifaces[ifi].Index
+			switch runtime.GOOS {
+			case "darwin", "ios", "linux":
+				wcm.IfIndex = c.ifaces[ifi].Index
+			default:
+				if err := c.ipv6conn.SetMulticastInterface(&c.ifaces[ifi]); err != nil {
+					log.Printf("[WARN] mdns: Failed to set multicast interface: %v", err)
+				}
+			}
 			c.ipv6conn.WriteTo(buf, &wcm, ipv6Addr)
 		}
 	}
diff --git a/server.go b/server.go
index 01c9ff66..b8ef489f 100644
--- a/server.go
+++ b/server.go
@@ -8,6 +8,7 @@ import (
 	"math/rand"
 	"net"
 	"os"
+	"runtime"
 	"strings"
 	"sync"
 	"time"
@@ -561,7 +562,7 @@ func (s *Server) serviceTypeName(resp *dns.Msg, ttl uint32) {
 }
 
 // Perform probing & announcement
-//TODO: implement a proper probing & conflict resolution
+// TODO: implement a proper probing & conflict resolution
 func (s *Server) probe() {
 	q := new(dns.Msg)
 	q.SetQuestion(s.service.ServiceInstanceName(), dns.TypePTR)
@@ -765,26 +766,66 @@ func (s *Server) multicastResponse(msg *dns.Msg, ifIndex int) error {
 		return err
 	}
 	if s.ipv4conn != nil {
+		// See https://pkg.go.dev/golang.org/x/net/ipv4#pkg-note-BUG
+		// As of Golang 1.18.4
+		// On Windows, the ControlMessage for ReadFrom and WriteTo methods of PacketConn is not implemented.
 		var wcm ipv4.ControlMessage
 		if ifIndex != 0 {
 			wcm.IfIndex = ifIndex
+			switch runtime.GOOS {
+			case "darwin", "ios", "linux":
+				wcm.IfIndex = ifIndex
+			default:
+				iface, _ := net.InterfaceByIndex(ifIndex)
+				if err := s.ipv4conn.SetMulticastInterface(iface); err != nil {
+					log.Printf("[WARN] mdns: Failed to set multicast interface: %v", err)
+				}
+			}
 			s.ipv4conn.WriteTo(buf, &wcm, ipv4Addr)
 		} else {
 			for _, intf := range s.ifaces {
 				wcm.IfIndex = intf.Index
+				switch runtime.GOOS {
+				case "darwin", "ios", "linux":
+					wcm.IfIndex = intf.Index
+				default:
+					if err := s.ipv4conn.SetMulticastInterface(&intf); err != nil {
+						log.Printf("[WARN] mdns: Failed to set multicast interface: %v", err)
+					}
+				}
 				s.ipv4conn.WriteTo(buf, &wcm, ipv4Addr)
 			}
 		}
 	}
 
 	if s.ipv6conn != nil {
+		// See https://pkg.go.dev/golang.org/x/net/ipv6#pkg-note-BUG
+		// As of Golang 1.18.4
+		// On Windows, the ControlMessage for ReadFrom and WriteTo methods of PacketConn is not implemented.
 		var wcm ipv6.ControlMessage
 		if ifIndex != 0 {
 			wcm.IfIndex = ifIndex
+			switch runtime.GOOS {
+			case "darwin", "ios", "linux":
+				wcm.IfIndex = ifIndex
+			default:
+				iface, _ := net.InterfaceByIndex(ifIndex)
+				if err := s.ipv6conn.SetMulticastInterface(iface); err != nil {
+					log.Printf("[WARN] mdns: Failed to set multicast interface: %v", err)
+				}
+			}
 			s.ipv6conn.WriteTo(buf, &wcm, ipv6Addr)
 		} else {
 			for _, intf := range s.ifaces {
 				wcm.IfIndex = intf.Index
+				switch runtime.GOOS {
+				case "darwin", "ios", "linux":
+					wcm.IfIndex = intf.Index
+				default:
+					if err := s.ipv6conn.SetMulticastInterface(&intf); err != nil {
+						log.Printf("[WARN] mdns: Failed to set multicast interface: %v", err)
+					}
+				}
 				s.ipv6conn.WriteTo(buf, &wcm, ipv6Addr)
 			}
 		}