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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 icmp provides basic functions for the manipulation of ICMP
// message.
package icmp
import (
"errors"
"net"
"golang.org/x/net/internal/iana"
"golang.org/x/net/ipv4"
"golang.org/x/net/ipv6"
)
// A Type represents an ICMP message type.
type Type interface {
String() string
}
// A Message represents an ICMP message.
type Message struct {
Type Type // type, either ipv4.ICMPType or ipv6.ICMPType
Code int // code
Checksum int // checksum
Body MessageBody // body
}
// Marshal returns the binary enconding of the ICMP message m.
//
// For ICMP for IPv4 message, the returned message always contains the
// calculated checksum field.
//
// For ICMP for IPv6 message, the returned message contains the
// calculated checksum field when psh is not nil, otherwise the kernel
// will compute the checksum field during the message transmission.
// When psh is not nil, it must be the pseudo header for IPv6.
func (m *Message) Marshal(psh []byte) ([]byte, error) {
var mtype int
var icmpv6 bool
switch typ := m.Type.(type) {
case ipv4.ICMPType:
mtype = int(typ)
case ipv6.ICMPType:
mtype = int(typ)
icmpv6 = true
default:
return nil, errors.New("invalid argument")
}
b := []byte{byte(mtype), byte(m.Code), 0, 0}
if icmpv6 && psh != nil {
b = append(psh, b...)
}
if m.Body != nil && m.Body.Len() != 0 {
mb, err := m.Body.Marshal()
if err != nil {
return nil, err
}
b = append(b, mb...)
}
if icmpv6 {
if psh == nil { // cannot calculate checksum here
return b, nil
}
off, l := 2*net.IPv6len, len(b)-len(psh)
b[off], b[off+1], b[off+2], b[off+3] = byte(l>>24), byte(l>>16), byte(l>>8), byte(l)
}
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[len(psh)+2] ^= byte(^s)
b[len(psh)+3] ^= byte(^s >> 8)
return b[len(psh):], nil
}
// ParseMessage parses b as an ICMP message. Proto must be
// iana.ProtocolICMP or iana.ProtocolIPv6ICMP.
func ParseMessage(proto int, b []byte) (*Message, error) {
if len(b) < 4 {
return nil, errors.New("message too short")
}
var err error
switch proto {
case iana.ProtocolICMP:
m := &Message{Type: ipv4.ICMPType(b[0]), Code: int(b[1]), Checksum: int(b[2])<<8 | int(b[3])}
switch m.Type {
case ipv4.ICMPTypeEcho, ipv4.ICMPTypeEchoReply:
m.Body, err = parseEcho(b[4:])
if err != nil {
return nil, err
}
default:
m.Body = &DefaultMessageBody{Data: b[4:]}
}
return m, nil
case iana.ProtocolIPv6ICMP:
m := &Message{Type: ipv6.ICMPType(b[0]), Code: int(b[1]), Checksum: int(b[2])<<8 | int(b[3])}
switch m.Type {
case ipv6.ICMPTypeEchoRequest, ipv6.ICMPTypeEchoReply:
m.Body, err = parseEcho(b[4:])
if err != nil {
return nil, err
}
default:
m.Body = &DefaultMessageBody{Data: b[4:]}
}
return m, nil
default:
return nil, errors.New("unknown protocol")
}
}
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