syncthing/mc/beacon.go

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package mc
import (
"log"
"net"
)
type recv struct {
data []byte
src net.Addr
}
type Beacon struct {
group string
port int
conns []*net.UDPConn
inbox chan []byte
outbox chan recv
}
func NewBeacon(group string, port int) *Beacon {
b := &Beacon{
group: group,
port: port,
inbox: make(chan []byte),
outbox: make(chan recv),
}
go b.run()
return b
}
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) run() {
group := &net.UDPAddr{IP: net.ParseIP(b.group), Port: b.port}
intfs, err := net.Interfaces()
if err != nil {
log.Fatal(err)
}
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if debug {
dlog.Printf("trying %d interfaces", len(intfs))
}
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for _, intf := range intfs {
intf := intf
if debug {
dlog.Printf("trying interface %q", intf.Name)
}
conn, err := net.ListenMulticastUDP("udp4", &intf, group)
if err != nil {
if debug {
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dlog.Printf("failed to listen for multicast group on %q: %v", intf.Name, err)
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}
} else {
b.conns = append(b.conns, conn)
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if debug {
dlog.Printf("listening for multicast group on %q", intf.Name)
}
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}
}
for _, conn := range b.conns {
conn := conn
go func() {
for {
var bs = make([]byte, 1500)
n, addr, err := conn.ReadFrom(bs)
if err != nil {
dlog.Println(err)
return
}
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if debug {
dlog.Printf("recv %d bytes from %s on %v", n, addr, conn)
}
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b.outbox <- recv{bs[:n], addr}
}
}()
}
go func() {
for bs := range b.inbox {
for _, conn := range b.conns {
_, err := conn.WriteTo(bs, group)
if err != nil {
dlog.Println(err)
return
}
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if debug {
dlog.Printf("sent %d bytes to %s on %v", len(bs), group, conn)
}
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}
}
}()
}