golang实现ping命令

// Copyright 2009 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.

// taken from http://golang.org/src/pkg/net/ipraw_test.go

package ping

import (
"bytes"
"errors"
"net"
"os"
"time"
)

const (
icmpv4EchoRequest = 8
icmpv4EchoReply   = 0
icmpv6EchoRequest = 128
icmpv6EchoReply   = 129
)

type icmpMessage struct {
Type     int             // type
Code     int             // code
Checksum int             // checksum
Body     icmpMessageBody // body
}

type icmpMessageBody interface {
Len() int
Marshal() ([]byte, error)
}

// Marshal returns the binary enconding of the ICMP echo request or
// reply message m.
func (m *icmpMessage) Marshal() ([]byte, error) {
b := []byte{byte(m.Type), byte(m.Code), 0, 0}
if m.Body != nil && m.Body.Len() != 0 {
  mb, err := m.Body.Marshal()
  if err != nil {
   return nil, err
  }
  b = append(b, mb...)
}
switch m.Type {
case icmpv6EchoRequest, icmpv6EchoReply:
  return b, nil
}
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[2] ^= byte(^s & 0xff)
b[3] ^= byte(^s >> 8)
return b, nil
}

// parseICMPMessage parses b as an ICMP message.
func parseICMPMessage(b []byte) (*icmpMessage, error) {
msglen := len(b)
if msglen < 4 {
  return nil, errors.New("message too short")
}
m := &icmpMessage{Type: int(b[0]), Code: int(b[1]), Checksum: int(b[2])<<8 | int(b[3])}
if msglen > 4 {
  var err error
  switch m.Type {
  case icmpv4EchoRequest, icmpv4EchoReply, icmpv6EchoRequest, icmpv6EchoReply:
   m.Body, err = parseICMPEcho(b[4:])
   if err != nil {
    return nil, err
   }
  }
}
return m, nil
}

// imcpEcho represenets an ICMP echo request or reply message body.
type icmpEcho struct {
ID   int    // identifier
Seq  int    // sequence number
Data []byte // data
}

func (p *icmpEcho) Len() int {
if p == nil {
  return 0
}
return 4 + len(p.Data)
}

// Marshal returns the binary enconding of the ICMP echo request or
// reply message body p.
func (p *icmpEcho) Marshal() ([]byte, error) {
b := make([]byte, 4+len(p.Data))
b[0], b[1] = byte(p.ID>>8), byte(p.ID&0xff)
b[2], b[3] = byte(p.Seq>>8), byte(p.Seq&0xff)
copy(b[4:], p.Data)
return b, nil
}

// parseICMPEcho parses b as an ICMP echo request or reply message body.
func parseICMPEcho(b []byte) (*icmpEcho, error) {
bodylen := len(b)
p := &icmpEcho{ID: int(b[0])<<8 | int(b[1]), Seq: int(b[2])<<8 | int(b[3])}
if bodylen > 4 {
  p.Data = make([]byte, bodylen-4)
  copy(p.Data, b[4:])
}
return p, nil
}

func Ping(address string, timeout int) (alive bool) {
err := Pinger(address, timeout)
alive = err == nil
return
}

func Pinger(address string, timeout int) (err error) {
c, err := net.Dial("ip4:icmp", address)
if err != nil {
  return
}
c.SetDeadline(time.Now().Add(time.Duration(timeout) * time.Second))
defer c.Close()

typ := icmpv4EchoRequest
xid, xseq := os.Getpid()&0xffff, 1
wb, err := (&icmpMessage{
  Type: typ, Code: 0,
  Body: &icmpEcho{
   ID: xid, Seq: xseq,
   Data: bytes.Repeat([]byte("Go Go Gadget Ping!!!"), 3),
  },
}).Marshal()
if err != nil {
  return
}
if _, err = c.Write(wb); err != nil {
  return
}
var m *icmpMessage
rb := make([]byte, 20+len(wb))
for {
  if _, err = c.Read(rb); err != nil {
   return
  }
  rb = ipv4Payload(rb)
  if m, err = parseICMPMessage(rb); err != nil {
   return
  }
  switch m.Type {
  case icmpv4EchoRequest, icmpv6EchoRequest:
   continue
  }
  break
}
return
}

func ipv4Payload(b []byte) []byte {
if len(b) < 20 {
  return b
}
hdrlen := int(b[0]&0x0f) << 2
return b[hdrlen:]
}

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