syncthing/beacon/beacon.go

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// Copyright (C) 2014 Jakob Borg and other contributors. All rights reserved.
// Use of this source code is governed by an MIT-style license that can be
// found in the LICENSE file.
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package beacon
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import "net"
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type recv struct {
data []byte
src net.Addr
}
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type dst struct {
intf string
conn *net.UDPConn
}
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type Beacon struct {
conn *net.UDPConn
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port int
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conns []dst
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inbox chan []byte
outbox chan recv
}
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func New(port int) (*Beacon, error) {
conn, err := net.ListenUDP("udp", &net.UDPAddr{Port: port})
if err != nil {
return nil, err
}
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b := &Beacon{
conn: conn,
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port: port,
inbox: make(chan []byte),
outbox: make(chan recv, 16),
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}
go b.reader()
go b.writer()
return b, nil
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}
func (b *Beacon) Send(data []byte) {
b.inbox <- data
}
func (b *Beacon) Recv() ([]byte, net.Addr) {
recv := <-b.outbox
return recv.data, recv.src
}
func (b *Beacon) reader() {
var bs = make([]byte, 65536)
for {
n, addr, err := b.conn.ReadFrom(bs)
if err != nil {
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l.Warnln("Beacon read:", err)
return
}
if debug {
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l.Debugf("recv %d bytes from %s", n, addr)
}
select {
case b.outbox <- recv{bs[:n], addr}:
default:
if debug {
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l.Debugln("dropping message")
}
}
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}
}
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func (b *Beacon) writer() {
for bs := range b.inbox {
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addrs, err := net.InterfaceAddrs()
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if err != nil {
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l.Warnln("Beacon: interface addresses:", err)
continue
}
var dsts []net.IP
for _, addr := range addrs {
if iaddr, ok := addr.(*net.IPNet); ok && iaddr.IP.IsGlobalUnicast() {
baddr := bcast(iaddr)
dsts = append(dsts, baddr.IP)
}
}
if len(dsts) == 0 {
// Fall back to the general IPv4 broadcast address
dsts = append(dsts, net.IP{0xff, 0xff, 0xff, 0xff})
}
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if debug {
l.Debugln("addresses:", dsts)
}
for _, ip := range dsts {
dst := &net.UDPAddr{IP: ip, Port: b.port}
_, err := b.conn.WriteTo(bs, dst)
if err != nil {
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if debug {
l.Debugln(err)
}
} else if debug {
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l.Debugf("sent %d bytes to %s", len(bs), dst)
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}
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}
}
}
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func bcast(ip *net.IPNet) *net.IPNet {
var bc = &net.IPNet{}
bc.IP = make([]byte, len(ip.IP))
copy(bc.IP, ip.IP)
bc.Mask = ip.Mask
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offset := len(bc.IP) - len(bc.Mask)
for i := range bc.IP {
if i-offset > 0 {
bc.IP[i] = ip.IP[i] | ^ip.Mask[i-offset]
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}
}
return bc
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}