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control_linux.go
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control_linux.go
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// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ipv4
import (
"os"
"syscall"
"unsafe"
)
// Linux provides a convenient path control option IP_PKTINFO that
// contains IP_SENDSRCADDR, IP_RECVDSTADDR, IP_RECVIF and IP_SENDIF.
const pktinfo = FlagSrc | FlagDst | FlagInterface
func setControlMessage(fd int, opt *rawOpt, cf ControlFlags, on bool) error {
opt.Lock()
defer opt.Unlock()
if cf&FlagTTL != 0 {
if err := setIPv4ReceiveTTL(fd, on); err != nil {
return err
}
if on {
opt.set(FlagTTL)
} else {
opt.clear(FlagTTL)
}
}
if cf&pktinfo != 0 {
if err := setIPv4PacketInfo(fd, on); err != nil {
return err
}
if on {
opt.set(cf & pktinfo)
} else {
opt.clear(cf & pktinfo)
}
}
return nil
}
func newControlMessage(opt *rawOpt) (oob []byte) {
opt.Lock()
defer opt.Unlock()
l, off := 0, 0
if opt.isset(FlagTTL) {
l += syscall.CmsgSpace(1)
}
if opt.isset(pktinfo) {
l += syscall.CmsgSpace(syscall.SizeofInet4Pktinfo)
}
if l > 0 {
oob = make([]byte, l)
if opt.isset(FlagTTL) {
m := (*syscall.Cmsghdr)(unsafe.Pointer(&oob[off]))
m.Level = ianaProtocolIP
m.Type = syscall.IP_RECVTTL
m.SetLen(syscall.CmsgLen(1))
off += syscall.CmsgSpace(1)
}
if opt.isset(pktinfo) {
m := (*syscall.Cmsghdr)(unsafe.Pointer(&oob[off]))
m.Level = ianaProtocolIP
m.Type = syscall.IP_PKTINFO
m.SetLen(syscall.CmsgLen(syscall.SizeofInet4Pktinfo))
off += syscall.CmsgSpace(syscall.SizeofInet4Pktinfo)
}
}
return
}
func parseControlMessage(b []byte) (*ControlMessage, error) {
if len(b) == 0 {
return nil, nil
}
cmsgs, err := syscall.ParseSocketControlMessage(b)
if err != nil {
return nil, os.NewSyscallError("parse socket control message", err)
}
cm := &ControlMessage{}
for _, m := range cmsgs {
if m.Header.Level != ianaProtocolIP {
continue
}
switch m.Header.Type {
case syscall.IP_TTL:
cm.TTL = int(*(*byte)(unsafe.Pointer(&m.Data[:1][0])))
case syscall.IP_PKTINFO:
pi := (*syscall.Inet4Pktinfo)(unsafe.Pointer(&m.Data[0]))
cm.IfIndex = int(pi.Ifindex)
cm.Dst = pi.Addr[:]
}
}
return cm, nil
}
func marshalControlMessage(cm *ControlMessage) (oob []byte) {
if cm == nil {
return
}
l, off := 0, 0
pion := false
if cm.Src.To4() != nil || cm.IfIndex != 0 {
pion = true
l += syscall.CmsgSpace(syscall.SizeofInet4Pktinfo)
}
if l > 0 {
oob = make([]byte, l)
if pion {
m := (*syscall.Cmsghdr)(unsafe.Pointer(&oob[off]))
m.Level = ianaProtocolIP
m.Type = syscall.IP_PKTINFO
m.SetLen(syscall.CmsgLen(syscall.SizeofInet4Pktinfo))
pi := (*syscall.Inet4Pktinfo)(unsafe.Pointer(&oob[off+syscall.CmsgLen(0)]))
if ip := cm.Src.To4(); ip != nil {
copy(pi.Addr[:], ip)
}
if cm.IfIndex != 0 {
pi.Ifindex = int32(cm.IfIndex)
}
off += syscall.CmsgSpace(syscall.SizeofInet4Pktinfo)
}
}
return
}