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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 (
"fmt"
"net"
"sync"
"golang.org/x/net/internal/iana"
"golang.org/x/net/internal/socket"
)
type rawOpt struct {
sync.RWMutex
cflags ControlFlags
}
func (c *rawOpt) set(f ControlFlags) { c.cflags |= f }
func (c *rawOpt) clear(f ControlFlags) { c.cflags &^= f }
func (c *rawOpt) isset(f ControlFlags) bool { return c.cflags&f != 0 }
type ControlFlags uint
const (
FlagTTL ControlFlags = 1 << iota // pass the TTL on the received packet
FlagSrc // pass the source address on the received packet
FlagDst // pass the destination address on the received packet
FlagInterface // pass the interface index on the received packet
)
// A ControlMessage represents per packet basis IP-level socket options.
type ControlMessage struct {
// Receiving socket options: SetControlMessage allows to
// receive the options from the protocol stack using ReadFrom
// method of PacketConn or RawConn.
//
// Specifying socket options: ControlMessage for WriteTo
// method of PacketConn or RawConn allows to send the options
// to the protocol stack.
//
TTL int // time-to-live, receiving only
Src net.IP // source address, specifying only
Dst net.IP // destination address, receiving only
IfIndex int // interface index, must be 1 <= value when specifying
}
func (cm *ControlMessage) String() string {
if cm == nil {
return "<nil>"
}
return fmt.Sprintf("ttl=%d src=%v dst=%v ifindex=%d", cm.TTL, cm.Src, cm.Dst, cm.IfIndex)
}
// Marshal returns the binary encoding of cm.
func (cm *ControlMessage) Marshal() []byte {
if cm == nil {
return nil
}
var m socket.ControlMessage
if ctlOpts[ctlPacketInfo].name > 0 && (cm.Src.To4() != nil || cm.IfIndex > 0) {
m = socket.NewControlMessage([]int{ctlOpts[ctlPacketInfo].length})
}
if len(m) > 0 {
ctlOpts[ctlPacketInfo].marshal(m, cm)
}
return m
}
// Parse parses b as a control message and stores the result in cm.
func (cm *ControlMessage) Parse(b []byte) error {
ms, err := socket.ControlMessage(b).Parse()
if err != nil {
return err
}
for _, m := range ms {
lvl, typ, l, err := m.ParseHeader()
if err != nil {
return err
}
if lvl != iana.ProtocolIP {
continue
}
switch {
case typ == ctlOpts[ctlTTL].name && l >= ctlOpts[ctlTTL].length:
ctlOpts[ctlTTL].parse(cm, m.Data(l))
case typ == ctlOpts[ctlDst].name && l >= ctlOpts[ctlDst].length:
ctlOpts[ctlDst].parse(cm, m.Data(l))
case typ == ctlOpts[ctlInterface].name && l >= ctlOpts[ctlInterface].length:
ctlOpts[ctlInterface].parse(cm, m.Data(l))
case typ == ctlOpts[ctlPacketInfo].name && l >= ctlOpts[ctlPacketInfo].length:
ctlOpts[ctlPacketInfo].parse(cm, m.Data(l))
}
}
return nil
}
// NewControlMessage returns a new control message.
//
// The returned message is large enough for options specified by cf.
func NewControlMessage(cf ControlFlags) []byte {
opt := rawOpt{cflags: cf}
var l int
if opt.isset(FlagTTL) && ctlOpts[ctlTTL].name > 0 {
l += socket.ControlMessageSpace(ctlOpts[ctlTTL].length)
}
if ctlOpts[ctlPacketInfo].name > 0 {
if opt.isset(FlagSrc | FlagDst | FlagInterface) {
l += socket.ControlMessageSpace(ctlOpts[ctlPacketInfo].length)
}
} else {
if opt.isset(FlagDst) && ctlOpts[ctlDst].name > 0 {
l += socket.ControlMessageSpace(ctlOpts[ctlDst].length)
}
if opt.isset(FlagInterface) && ctlOpts[ctlInterface].name > 0 {
l += socket.ControlMessageSpace(ctlOpts[ctlInterface].length)
}
}
var b []byte
if l > 0 {
b = make([]byte, l)
}
return b
}
// Ancillary data socket options
const (
ctlTTL = iota // header field
ctlSrc // header field
ctlDst // header field
ctlInterface // inbound or outbound interface
ctlPacketInfo // inbound or outbound packet path
ctlMax
)
// A ctlOpt represents a binding for ancillary data socket option.
type ctlOpt struct {
name int // option name, must be equal or greater than 1
length int // option length
marshal func([]byte, *ControlMessage) []byte
parse func(*ControlMessage, []byte)
}
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