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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
// messages used in the Internet Control Message Protocols,
// ICMPv4 and ICMPv6.
//
// ICMPv4 and ICMPv6 are defined in RFC 792 and RFC 4443.
// Multi-part message support for ICMP is defined in RFC 4884.
// ICMP extensions for MPLS are defined in RFC 4950.
// ICMP extensions for interface and next-hop identification are
// defined in RFC 5837.
package icmp // import "golang.org/x/net/icmp"
import (
"encoding/binary"
"errors"
"net"
"syscall"
"golang.org/x/net/internal/iana"
"golang.org/x/net/ipv4"
"golang.org/x/net/ipv6"
)
// BUG(mikio): This package is not implemented on NaCl and Plan 9.
var (
errMessageTooShort = errors.New("message too short")
errHeaderTooShort = errors.New("header too short")
errBufferTooShort = errors.New("buffer too short")
errOpNoSupport = errors.New("operation not supported")
errNoExtension = errors.New("no extension")
errInvalidExtension = errors.New("invalid extension")
)
func checksum(b []byte) uint16 {
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
return ^uint16(s)
}
// A Type represents an ICMP message type.
type Type interface {
Protocol() int
}
// 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 encoding of the ICMP message m.
//
// For an ICMPv4 message, the returned message always contains the
// calculated checksum field.
//
// For an ICMPv6 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
switch typ := m.Type.(type) {
case ipv4.ICMPType:
mtype = int(typ)
case ipv6.ICMPType:
mtype = int(typ)
default:
return nil, syscall.EINVAL
}
b := []byte{byte(mtype), byte(m.Code), 0, 0}
if m.Type.Protocol() == iana.ProtocolIPv6ICMP && psh != nil {
b = append(psh, b...)
}
if m.Body != nil && m.Body.Len(m.Type.Protocol()) != 0 {
mb, err := m.Body.Marshal(m.Type.Protocol())
if err != nil {
return nil, err
}
b = append(b, mb...)
}
if m.Type.Protocol() == iana.ProtocolIPv6ICMP {
if psh == nil { // cannot calculate checksum here
return b, nil
}
off, l := 2*net.IPv6len, len(b)-len(psh)
binary.BigEndian.PutUint32(b[off:off+4], uint32(l))
}
s := checksum(b)
// 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
}
var parseFns = map[Type]func(int, []byte) (MessageBody, error){
ipv4.ICMPTypeDestinationUnreachable: parseDstUnreach,
ipv4.ICMPTypeTimeExceeded: parseTimeExceeded,
ipv4.ICMPTypeParameterProblem: parseParamProb,
ipv4.ICMPTypeEcho: parseEcho,
ipv4.ICMPTypeEchoReply: parseEcho,
ipv6.ICMPTypeDestinationUnreachable: parseDstUnreach,
ipv6.ICMPTypePacketTooBig: parsePacketTooBig,
ipv6.ICMPTypeTimeExceeded: parseTimeExceeded,
ipv6.ICMPTypeParameterProblem: parseParamProb,
ipv6.ICMPTypeEchoRequest: parseEcho,
ipv6.ICMPTypeEchoReply: parseEcho,
}
// ParseMessage parses b as an ICMP message.
// Proto must be either the ICMPv4 or ICMPv6 protocol number.
func ParseMessage(proto int, b []byte) (*Message, error) {
if len(b) < 4 {
return nil, errMessageTooShort
}
var err error
m := &Message{Code: int(b[1]), Checksum: int(binary.BigEndian.Uint16(b[2:4]))}
switch proto {
case iana.ProtocolICMP:
m.Type = ipv4.ICMPType(b[0])
case iana.ProtocolIPv6ICMP:
m.Type = ipv6.ICMPType(b[0])
default:
return nil, syscall.EINVAL
}
if fn, ok := parseFns[m.Type]; !ok {
m.Body, err = parseDefaultMessageBody(proto, b[4:])
} else {
m.Body, err = fn(proto, b[4:])
}
if err != nil {
return nil, err
}
return m, nil
}
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