go.net/ipv4: new package
Package ipv4 implements IP-level socket options for the Internet
Protocol version 4. It also provides raw IP socket access methods
including IPv4 header manipulation.
Fixes golang/go#3684.
Fixes golang/go#3820.
This CL requires CL 6426047;
net: add read, write message methods to IPConn, UDPConn
R=rsc, dave, alex.brainman
CC=gobot, golang-dev
https://golang.org/cl/6482044
diff --git a/ipv4/control_linux.go b/ipv4/control_linux.go
new file mode 100644
index 0000000..16f53d0
--- /dev/null
+++ b/ipv4/control_linux.go
@@ -0,0 +1,116 @@
+// 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 (
+ "net"
+ "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()
+ if opt.isset(FlagTTL) {
+ b := make([]byte, syscall.CmsgSpace(1))
+ cmsg := (*syscall.Cmsghdr)(unsafe.Pointer(&b[0]))
+ cmsg.Level = syscall.IPPROTO_IP
+ cmsg.Type = syscall.IP_RECVTTL
+ cmsg.SetLen(syscall.CmsgLen(1))
+ oob = append(oob, b...)
+ }
+ if opt.isset(pktinfo) {
+ b := make([]byte, syscall.CmsgSpace(syscall.SizeofInet4Pktinfo))
+ cmsg := (*syscall.Cmsghdr)(unsafe.Pointer(&b[0]))
+ cmsg.Level = syscall.IPPROTO_IP
+ cmsg.Type = syscall.IP_PKTINFO
+ cmsg.SetLen(syscall.CmsgLen(syscall.SizeofInet4Pktinfo))
+ oob = append(oob, b...)
+ }
+ return
+}
+
+func parseControlMessage(b []byte) (*ControlMessage, error) {
+ cmsgs, err := syscall.ParseSocketControlMessage(b)
+ if err != nil {
+ return nil, os.NewSyscallError("parse socket control message", err)
+ }
+ if len(b) == 0 {
+ return nil, nil
+ }
+ cm := &ControlMessage{}
+ for _, m := range cmsgs {
+ if m.Header.Level != syscall.IPPROTO_IP {
+ 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 = net.IPv4(pi.Addr[0], pi.Addr[1], pi.Addr[2], pi.Addr[3])
+ }
+ }
+ return cm, nil
+}
+
+func marshalControlMessage(cm *ControlMessage) (oob []byte) {
+ if cm == nil {
+ return
+ }
+ pi := &syscall.Inet4Pktinfo{}
+ pion := false
+ if ip := cm.Src.To4(); ip != nil {
+ copy(pi.Spec_dst[:], ip[0:net.IPv4len])
+ pion = true
+ }
+ if cm.IfIndex != 0 {
+ pi.Ifindex = int32(cm.IfIndex)
+ pion = true
+ }
+ if pion {
+ b := make([]byte, syscall.CmsgSpace(syscall.SizeofInet4Pktinfo))
+ cmsg := (*syscall.Cmsghdr)(unsafe.Pointer(&b[0]))
+ cmsg.Level = syscall.IPPROTO_IP
+ cmsg.Type = syscall.IP_PKTINFO
+ cmsg.SetLen(syscall.CmsgLen(syscall.SizeofInet4Pktinfo))
+ data := b[syscall.CmsgLen(0):]
+ copy(data[0:syscall.SizeofInet4Pktinfo], (*[syscall.SizeofInet4Pktinfo]byte)(unsafe.Pointer(pi))[:syscall.SizeofInet4Pktinfo])
+ oob = append(oob, b...)
+ }
+ return
+}
