tailscale/net/packet/icmp4.go

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// Copyright (c) 2020 Tailscale Inc & 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 packet
import (
"encoding/binary"
"tailscale.com/types/ipproto"
)
// icmp4HeaderLength is the size of the ICMPv4 packet header, not
// including the outer IP layer or the variable "response data"
// trailer.
const icmp4HeaderLength = 4
// ICMP4Type is an ICMPv4 type, as specified in
// https://www.iana.org/assignments/icmp-parameters/icmp-parameters.xhtml
type ICMP4Type uint8
const (
ICMP4EchoReply ICMP4Type = 0x00
ICMP4EchoRequest ICMP4Type = 0x08
ICMP4Unreachable ICMP4Type = 0x03
ICMP4TimeExceeded ICMP4Type = 0x0b
)
func (t ICMP4Type) String() string {
switch t {
case ICMP4EchoReply:
return "EchoReply"
case ICMP4EchoRequest:
return "EchoRequest"
case ICMP4Unreachable:
return "Unreachable"
case ICMP4TimeExceeded:
return "TimeExceeded"
default:
return "Unknown"
}
}
// ICMP4Code is an ICMPv4 code, as specified in
// https://www.iana.org/assignments/icmp-parameters/icmp-parameters.xhtml
type ICMP4Code uint8
const (
ICMP4NoCode ICMP4Code = 0
)
// ICMP4Header is an IPv4+ICMPv4 header.
type ICMP4Header struct {
IP4Header
Type ICMP4Type
Code ICMP4Code
}
// Len implements Header.
func (h ICMP4Header) Len() int {
return h.IP4Header.Len() + icmp4HeaderLength
}
// Marshal implements Header.
func (h ICMP4Header) Marshal(buf []byte) error {
if len(buf) < h.Len() {
return errSmallBuffer
}
if len(buf) > maxPacketLength {
return errLargePacket
}
// The caller does not need to set this.
h.IPProto = ipproto.ICMPv4
buf[20] = uint8(h.Type)
buf[21] = uint8(h.Code)
h.IP4Header.Marshal(buf)
binary.BigEndian.PutUint16(buf[22:24], ip4Checksum(buf))
return nil
}
// ToResponse implements Header. TODO: it doesn't implement it
// correctly, instead it statically generates an ICMP Echo Reply
// packet.
func (h *ICMP4Header) ToResponse() {
// TODO: this doesn't implement ToResponse correctly, as it
// assumes the ICMP request type.
h.Type = ICMP4EchoReply
h.Code = ICMP4NoCode
h.IP4Header.ToResponse()
}