add multicast.InterfaceForSource (#414)

client_udp_listener.go

@@ -2,7 +2,6 @@ package gortsplib
 
 import (
 	"crypto/rand"
-	"fmt"
 	"math/big"
 	"net"
 	"strconv"
@@ -25,35 +24,6 @@ func randInRange(max int) (int, error) {
 	return int(n.Int64()), nil
 }
 
-func findMulticastInterfaceForSource(ip net.IP) (*net.Interface, error) {
-	if ip.Equal(net.ParseIP("127.0.0.1")) {
-		return nil, fmt.Errorf("IP 127.0.0.1 can't be used as source of a multicast stream. Use the LAN IP of your PC")
-	}
-
-	intfs, err := net.Interfaces()
-	if err != nil {
-		return nil, err
-	}
-
-	for _, intf := range intfs {
-		if (intf.Flags & net.FlagMulticast) == 0 {
-			continue
-		}
-
-		addrs, err := intf.Addrs()
-		if err == nil {
-			for _, addr := range addrs {
-				_, ipnet, err := net.ParseCIDR(addr.String())
-				if err == nil && ipnet.Contains(ip) {
-					return &intf, nil
-				}
-			}
-		}
-	}
-
-	return nil, fmt.Errorf("found no interface that is multicast-capable and can communicate with IP %v", ip)
-}
-
 type clientUDPListener struct {
 	c  *Client
 	pc net.PacketConn
@@ -118,7 +88,7 @@ func newClientUDPListener(
 ) (*clientUDPListener, error) {
 	var pc packetConn
 	if multicastEnable {
-		intf, err := findMulticastInterfaceForSource(multicastSourceIP)
+		intf, err := multicast.InterfaceForSource(multicastSourceIP)
 		if err != nil {
 			return nil, err
 		}

pkg/multicast/multicast.go

@@ -2,6 +2,7 @@
 package multicast
 
 import (
+	"fmt"
 	"net"
 )
 
@@ -10,3 +11,33 @@ type Conn interface {
 	net.PacketConn
 	SetReadBuffer(int) error
 }
+
+// InterfaceForSource returns a multicast-capable interface that can communicate with given IP.
+func InterfaceForSource(ip net.IP) (*net.Interface, error) {
+	if ip.Equal(net.ParseIP("127.0.0.1")) {
+		return nil, fmt.Errorf("IP 127.0.0.1 can't be used as source of a multicast stream. Use the LAN IP of your PC")
+	}
+
+	intfs, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+
+	for _, intf := range intfs {
+		if (intf.Flags & net.FlagMulticast) == 0 {
+			continue
+		}
+
+		addrs, err := intf.Addrs()
+		if err == nil {
+			for _, addr := range addrs {
+				_, ipnet, err := net.ParseCIDR(addr.String())
+				if err == nil && ipnet.Contains(ip) {
+					return &intf, nil
+				}
+			}
+		}
+	}
+
+	return nil, fmt.Errorf("found no interface that is multicast-capable and can communicate with IP %v", ip)
+}