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