// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package ipv4
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import (
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"fmt"
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"net"
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"sync"
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"golang.org/x/net/internal/iana"
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"golang.org/x/net/internal/socket"
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)
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type rawOpt struct {
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sync.RWMutex
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cflags ControlFlags
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}
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func (c *rawOpt) set(f ControlFlags) { c.cflags |= f }
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func (c *rawOpt) clear(f ControlFlags) { c.cflags &^= f }
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func (c *rawOpt) isset(f ControlFlags) bool { return c.cflags&f != 0 }
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type ControlFlags uint
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const (
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FlagTTL ControlFlags = 1 << iota // pass the TTL on the received packet
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FlagSrc // pass the source address on the received packet
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FlagDst // pass the destination address on the received packet
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FlagInterface // pass the interface index on the received packet
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)
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// A ControlMessage represents per packet basis IP-level socket options.
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type ControlMessage struct {
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// Receiving socket options: SetControlMessage allows to
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// receive the options from the protocol stack using ReadFrom
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// method of PacketConn or RawConn.
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//
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// Specifying socket options: ControlMessage for WriteTo
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// method of PacketConn or RawConn allows to send the options
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// to the protocol stack.
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//
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TTL int // time-to-live, receiving only
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Src net.IP // source address, specifying only
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Dst net.IP // destination address, receiving only
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IfIndex int // interface index, must be 1 <= value when specifying
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}
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func (cm *ControlMessage) String() string {
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if cm == nil {
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return "<nil>"
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}
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return fmt.Sprintf("ttl=%d src=%v dst=%v ifindex=%d", cm.TTL, cm.Src, cm.Dst, cm.IfIndex)
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}
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// Marshal returns the binary encoding of cm.
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func (cm *ControlMessage) Marshal() []byte {
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if cm == nil {
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return nil
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}
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var m socket.ControlMessage
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if ctlOpts[ctlPacketInfo].name > 0 && (cm.Src.To4() != nil || cm.IfIndex > 0) {
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m = socket.NewControlMessage([]int{ctlOpts[ctlPacketInfo].length})
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}
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if len(m) > 0 {
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ctlOpts[ctlPacketInfo].marshal(m, cm)
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}
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return m
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}
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// Parse parses b as a control message and stores the result in cm.
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func (cm *ControlMessage) Parse(b []byte) error {
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ms, err := socket.ControlMessage(b).Parse()
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if err != nil {
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return err
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}
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for _, m := range ms {
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lvl, typ, l, err := m.ParseHeader()
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if err != nil {
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return err
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}
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if lvl != iana.ProtocolIP {
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continue
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}
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switch {
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case typ == ctlOpts[ctlTTL].name && l >= ctlOpts[ctlTTL].length:
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ctlOpts[ctlTTL].parse(cm, m.Data(l))
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case typ == ctlOpts[ctlDst].name && l >= ctlOpts[ctlDst].length:
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ctlOpts[ctlDst].parse(cm, m.Data(l))
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case typ == ctlOpts[ctlInterface].name && l >= ctlOpts[ctlInterface].length:
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ctlOpts[ctlInterface].parse(cm, m.Data(l))
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case typ == ctlOpts[ctlPacketInfo].name && l >= ctlOpts[ctlPacketInfo].length:
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ctlOpts[ctlPacketInfo].parse(cm, m.Data(l))
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}
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}
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return nil
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}
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// NewControlMessage returns a new control message.
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//
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// The returned message is large enough for options specified by cf.
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func NewControlMessage(cf ControlFlags) []byte {
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opt := rawOpt{cflags: cf}
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var l int
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if opt.isset(FlagTTL) && ctlOpts[ctlTTL].name > 0 {
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l += socket.ControlMessageSpace(ctlOpts[ctlTTL].length)
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}
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if ctlOpts[ctlPacketInfo].name > 0 {
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if opt.isset(FlagSrc | FlagDst | FlagInterface) {
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l += socket.ControlMessageSpace(ctlOpts[ctlPacketInfo].length)
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}
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} else {
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if opt.isset(FlagDst) && ctlOpts[ctlDst].name > 0 {
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l += socket.ControlMessageSpace(ctlOpts[ctlDst].length)
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}
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if opt.isset(FlagInterface) && ctlOpts[ctlInterface].name > 0 {
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l += socket.ControlMessageSpace(ctlOpts[ctlInterface].length)
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}
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}
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var b []byte
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if l > 0 {
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b = make([]byte, l)
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}
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return b
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}
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// Ancillary data socket options
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const (
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ctlTTL = iota // header field
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ctlSrc // header field
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ctlDst // header field
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ctlInterface // inbound or outbound interface
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ctlPacketInfo // inbound or outbound packet path
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ctlMax
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)
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// A ctlOpt represents a binding for ancillary data socket option.
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type ctlOpt struct {
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name int // option name, must be equal or greater than 1
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length int // option length
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marshal func([]byte, *ControlMessage) []byte
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parse func(*ControlMessage, []byte)
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}
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