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- // Copyright (C) 2014 The Syncthing Authors.
- //
- // This Source Code Form is subject to the terms of the Mozilla Public
- // License, v. 2.0. If a copy of the MPL was not distributed with this file,
- // You can obtain one at https://mozilla.org/MPL/2.0/.
- package beacon
- import (
- "context"
- "net"
- "time"
- )
- func NewBroadcast(port int) Interface {
- c := newCast("broadcastBeacon")
- c.addReader(func(ctx context.Context) error {
- return readBroadcasts(ctx, c.outbox, port)
- })
- c.addWriter(func(ctx context.Context) error {
- return writeBroadcasts(ctx, c.inbox, port)
- })
- return c
- }
- func writeBroadcasts(ctx context.Context, inbox <-chan []byte, port int) error {
- conn, err := net.ListenUDP("udp4", nil)
- if err != nil {
- l.Debugln(err)
- return err
- }
- doneCtx, cancel := context.WithCancel(ctx)
- defer cancel()
- go func() {
- <-doneCtx.Done()
- conn.Close()
- }()
- for {
- var bs []byte
- select {
- case bs = <-inbox:
- case <-doneCtx.Done():
- return doneCtx.Err()
- }
- intfs, err := net.Interfaces()
- if err != nil {
- l.Debugln("Failed to list interfaces:", err)
- // net.Interfaces() is broken on Android. see https://github.com/golang/go/issues/40569
- // Use the general broadcast address 255.255.255.255 instead.
- }
- var dsts []net.IP
- for _, intf := range intfs {
- if intf.Flags&net.FlagRunning == 0 || intf.Flags&net.FlagBroadcast == 0 {
- continue
- }
- addrs, err := intf.Addrs()
- if err != nil {
- l.Debugln("Failed to list interface addresses:", err)
- // Interface discovery might work while retrieving the addresses doesn't. So log the error and carry on.
- continue
- }
- for _, addr := range addrs {
- if iaddr, ok := addr.(*net.IPNet); ok && len(iaddr.IP) >= 4 && iaddr.IP.IsGlobalUnicast() && iaddr.IP.To4() != nil {
- 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})
- }
- l.Debugln("addresses:", dsts)
- success := 0
- for _, ip := range dsts {
- dst := &net.UDPAddr{IP: ip, Port: port}
- conn.SetWriteDeadline(time.Now().Add(time.Second))
- _, err = conn.WriteTo(bs, dst)
- conn.SetWriteDeadline(time.Time{})
- if nerr, ok := err.(net.Error); ok && nerr.Timeout() {
- // Write timeouts should not happen. We treat it as a fatal
- // error on the socket.
- l.Debugln(err)
- return err
- }
- if err != nil {
- // Some other error that we don't expect. Debug and continue.
- l.Debugln(err)
- continue
- }
- l.Debugf("sent %d bytes to %s", len(bs), dst)
- success++
- }
- if success == 0 {
- l.Debugln("couldn't send any broadcasts")
- return err
- }
- }
- }
- func readBroadcasts(ctx context.Context, outbox chan<- recv, port int) error {
- conn, err := net.ListenUDP("udp4", &net.UDPAddr{Port: port})
- if err != nil {
- l.Debugln(err)
- return err
- }
- doneCtx, cancel := context.WithCancel(ctx)
- defer cancel()
- go func() {
- <-doneCtx.Done()
- conn.Close()
- }()
- bs := make([]byte, 65536)
- for {
- n, addr, err := conn.ReadFrom(bs)
- if err != nil {
- l.Debugln(err)
- return err
- }
- l.Debugf("recv %d bytes from %s", n, addr)
- c := make([]byte, n)
- copy(c, bs)
- select {
- case outbox <- recv{c, addr}:
- case <-doneCtx.Done():
- return doneCtx.Err()
- default:
- l.Debugln("dropping message")
- }
- }
- }
- 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
- 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]
- }
- }
- return bc
- }
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