--- /dev/null
+// 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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