From 523279ef67888ecbf894487c2df803b3c8c95c39 Mon Sep 17 00:00:00 2001
From: Nicolai Ommer <nicolai.ommer@gmail.com>
Date: Thu, 15 Jun 2023 20:46:45 +0200
Subject: [PATCH] Detect multicast sources from different network interfaces

---
 cmd/ssl-multicast-sources/main.go | 83 +++++++++++++++++++++++--------
 1 file changed, 61 insertions(+), 22 deletions(-)

diff --git a/cmd/ssl-multicast-sources/main.go b/cmd/ssl-multicast-sources/main.go
index 2d983c3..1eed308 100644
--- a/cmd/ssl-multicast-sources/main.go
+++ b/cmd/ssl-multicast-sources/main.go
@@ -4,66 +4,105 @@ import (
 	"flag"
 	"log"
 	"net"
-	"time"
+	"os"
+	"os/signal"
+	"sync"
+	"syscall"
 )
 
 const maxDatagramSize = 8192
 
-var detectedRemotes map[string][]string
+type Source struct {
+	nif  string
+	ip   string
+	port int
+}
+
+var detectedRemotes map[string][]Source
+var detectedRemotesMutex sync.Mutex
 
 func main() {
 	flag.Parse()
 
-	detectedRemotes = map[string][]string{}
+	detectedRemotes = map[string][]Source{}
 	mcAddresses := flag.Args()
 	if len(mcAddresses) == 0 {
 		mcAddresses = []string{"224.5.23.1:10003", "224.5.23.2:10006", "224.5.23.2:10010", "224.5.23.2:10012"}
 	}
 
+	ifiList := interfaces()
 	for _, address := range mcAddresses {
-		go watchAddress(address)
+		for _, ifi := range ifiList {
+			go receiveOnInterface(address, ifi)
+		}
 	}
 
-	for {
-		time.Sleep(1 * time.Second)
+	signals := make(chan os.Signal, 1)
+	signal.Notify(signals, syscall.SIGINT, syscall.SIGTERM)
+	<-signals
+}
+
+func interfaces() (interfaces []net.Interface) {
+	interfaces = []net.Interface{}
+	ifis, err := net.Interfaces()
+	if err != nil {
+		log.Println("Could not get available interfaces: ", err)
+	}
+	for _, ifi := range ifis {
+		interfaces = append(interfaces, ifi)
 	}
+	return
 }
 
-func watchAddress(address string) {
+func receiveOnInterface(address string, ifi net.Interface) {
 	addr, err := net.ResolveUDPAddr("udp", address)
 	if err != nil {
-		log.Fatal(err)
+		log.Printf("Could resolve multicast address %v: %v", address, err)
+		return
 	}
-	conn, err := net.ListenMulticastUDP("udp", nil, addr)
+
+	conn, err := net.ListenMulticastUDP("udp", &ifi, addr)
 	if err != nil {
-		log.Fatal(err)
+		log.Printf("Could not listen at %v: %v", address, err)
+		return
 	}
+
 	if err := conn.SetReadBuffer(maxDatagramSize); err != nil {
-		log.Printf("Could not set read buffer to %v.", maxDatagramSize)
+		log.Println("Could not set read buffer: ", err)
 	}
-	log.Println("Receiving from", address)
+
+	log.Printf("Listening on %s (%s)", address, ifi.Name)
+
+	data := make([]byte, maxDatagramSize)
 	for {
-		_, udpAddr, err := conn.ReadFromUDP([]byte{0})
+		_, remoteAddr, err := conn.ReadFromUDP(data)
 		if err != nil {
-			log.Print("Could not read: ", err)
-			time.Sleep(1 * time.Second)
-			continue
+			log.Println("ReadFromUDP failed:", err)
+			return
 		}
-		addRemote(address, udpAddr.IP.String())
+
+		addRemote(address, Source{
+			nif:  ifi.Name,
+			ip:   remoteAddr.IP.String(),
+			port: remoteAddr.Port,
+		})
 	}
 }
 
-func addRemote(address string, remote string) {
+func addRemote(address string, source Source) {
+	detectedRemotesMutex.Lock()
+	defer detectedRemotesMutex.Unlock()
+
 	remotes, ok := detectedRemotes[address]
 	if !ok {
-		detectedRemotes[address] = []string{}
+		detectedRemotes[address] = []Source{}
 	}
 	for _, a := range remotes {
-		if a == remote {
+		if a == source {
 			return
 		}
 	}
 
-	detectedRemotes[address] = append(detectedRemotes[address], remote)
-	log.Printf("remote ip on %v: %v\n", address, remote)
+	detectedRemotes[address] = append(detectedRemotes[address], source)
+	log.Printf("New source on %v: %+v\n", address, source)
 }