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// Copyright 2009 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 net
import "errors"
const (
icmpv4EchoRequest = 8
icmpv4EchoReply = 0
icmpv6EchoRequest = 128
icmpv6EchoReply = 129
)
// icmpMessage represents an ICMP message.
type icmpMessage struct {
Type int // type
Code int // code
Checksum int // checksum
Body icmpMessageBody // body
}
// icmpMessageBody represents an ICMP message body.
type icmpMessageBody interface {
Len() int
Marshal() ([]byte, error)
}
// Marshal returns the binary enconding of the ICMP echo request or
// reply message m.
func (m *icmpMessage) Marshal() ([]byte, error) {
b := []byte{byte(m.Type), byte(m.Code), 0, 0}
if m.Body != nil && m.Body.Len() != 0 {
mb, err := m.Body.Marshal()
if err != nil {
return nil, err
}
b = append(b, mb...)
}
switch m.Type {
case icmpv6EchoRequest, icmpv6EchoReply:
return b, nil
}
csumcv := len(b) - 1 // checksum coverage
s := uint32(0)
for i := 0; i < csumcv; i += 2 {
s += uint32(b[i+1])<<8 | uint32(b[i])
}
if csumcv&1 == 0 {
s += uint32(b[csumcv])
}
s = s>>16 + s&0xffff
s = s + s>>16
// Place checksum back in header; using ^= avoids the
// assumption the checksum bytes are zero.
b[2] ^= byte(^s)
b[3] ^= byte(^s >> 8)
return b, nil
}
// parseICMPMessage parses b as an ICMP message.
func parseICMPMessage(b []byte) (*icmpMessage, error) {
msglen := len(b)
if msglen < 4 {
return nil, errors.New("message too short")
}
m := &icmpMessage{Type: int(b[0]), Code: int(b[1]), Checksum: int(b[2])<<8 | int(b[3])}
if msglen > 4 {
var err error
switch m.Type {
case icmpv4EchoRequest, icmpv4EchoReply, icmpv6EchoRequest, icmpv6EchoReply:
m.Body, err = parseICMPEcho(b[4:])
if err != nil {
return nil, err
}
}
}
return m, nil
}
// imcpEcho represenets an ICMP echo request or reply message body.
type icmpEcho struct {
ID int // identifier
Seq int // sequence number
Data []byte // data
}
func (p *icmpEcho) Len() int {
if p == nil {
return 0
}
return 4 + len(p.Data)
}
// Marshal returns the binary enconding of the ICMP echo request or
// reply message body p.
func (p *icmpEcho) Marshal() ([]byte, error) {
b := make([]byte, 4+len(p.Data))
b[0], b[1] = byte(p.ID>>8), byte(p.ID)
b[2], b[3] = byte(p.Seq>>8), byte(p.Seq)
copy(b[4:], p.Data)
return b, nil
}
// parseICMPEcho parses b as an ICMP echo request or reply message
// body.
func parseICMPEcho(b []byte) (*icmpEcho, error) {
bodylen := len(b)
p := &icmpEcho{ID: int(b[0])<<8 | int(b[1]), Seq: int(b[2])<<8 | int(b[3])}
if bodylen > 4 {
p.Data = make([]byte, bodylen-4)
copy(p.Data, b[4:])
}
return p, nil
}
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