Implement IPv6 multicast again (fixes #346)

beacon/multicast.go

@@ -0,0 +1,70 @@
+// Copyright (C) 2014 Jakob Borg and Contributors (see the CONTRIBUTORS file).
+// All rights reserved. Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file.
+
+package beacon
+
+import "net"
+
+type Multicast struct {
+	conn   *net.UDPConn
+	addr   *net.UDPAddr
+	conns  []dst
+	inbox  chan []byte
+	outbox chan recv
+}
+
+func NewMulticast(addr string) (*Multicast, error) {
+	gaddr, err := net.ResolveUDPAddr("udp", addr)
+	if err != nil {
+		return nil, err
+	}
+	conn, err := net.ListenMulticastUDP("udp", nil, gaddr)
+	if err != nil {
+		return nil, err
+	}
+	b := &Multicast{
+		conn:   conn,
+		addr:   gaddr,
+		inbox:  make(chan []byte),
+		outbox: make(chan recv, 16),
+	}
+
+	go genericReader(b.conn, b.outbox)
+	go b.writer()
+
+	return b, nil
+}
+
+func (b *Multicast) Send(data []byte) {
+	b.inbox <- data
+}
+
+func (b *Multicast) Recv() ([]byte, net.Addr) {
+	recv := <-b.outbox
+	return recv.data, recv.src
+}
+
+func (b *Multicast) writer() {
+	for bs := range b.inbox {
+		intfs, err := net.Interfaces()
+		if err != nil {
+			l.Warnln("multicast interfaces:", err)
+			continue
+		}
+		for _, intf := range intfs {
+			if intf.Flags&net.FlagUp != 0 && intf.Flags&net.FlagMulticast != 0 {
+				addr := *b.addr
+				addr.Zone = intf.Name
+				_, err = b.conn.WriteTo(bs, &addr)
+				if err != nil {
+					if debug {
+						l.Debugln(err, "on write to", addr)
+					}
+				} else if debug {
+					l.Debugf("sent %d bytes to %s", len(bs), addr.String())
+				}
+			}
+		}
+	}
+}