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