我正在尝试发送TTL仅1的icmp消息,并希望收到超时消息。该消息的确出现了(我从wireshark看到了),但是我的程序在上阻塞了syscall.Recvfrom
。有人知道为什么吗?
icmp.go
package main
import (
"bytes"
"encoding/binary"
"fmt"
"net"
"os"
"syscall"
)
type ICMP struct {
Type uint8
Code uint8
Checksum uint16
Identifier uint16
SeqNo uint16
}
func Checksum(data []byte) uint16 {
var (
sum uint32
length int = len(data)
index int
)
for length > 1 {
sum += uint32(data[index])<<8 + uint32(data[index+1])
index += 2
length -= 2
}
if length > 0 {
sum += uint32(data[index])
}
sum += (sum >> 16)
return uint16(^sum)
}
func main() {
h := Header{
Version: 4,
Len: 20,
TotalLen: 20 + 8,
TTL: 1,
Protocol: 1,
// Dst:
}
argc := len(os.Args)
if argc < 2 {
fmt.Println("usage: program + host")
return
}
ipAddr, _ := net.ResolveIPAddr("ip", os.Args[1])
h.Dst = ipAddr.IP
icmpReq := ICMP{
Type: 8,
Code: 0,
Identifier: 0,
SeqNo: 0,
}
out, err := h.Marshal()
if err != nil {
fmt.Println("ip header error", err)
return
}
var icmpBuf bytes.Buffer
binary.Write(&icmpBuf, binary.BigEndian, icmpReq)
icmpReq.Checksum = Checksum(icmpBuf.Bytes())
icmpBuf.Reset()
binary.Write(&icmpBuf, binary.BigEndian, icmpReq)
fd, _ := syscall.Socket(syscall.AF_INET, syscall.SOCK_RAW, syscall.IPPROTO_RAW)
addr := syscall.SockaddrInet4{
Port: 0,
}
copy(addr.Addr[:], ipAddr.IP[12:16])
pkg := append(out, icmpBuf.Bytes()...)
fmt.Println("ip length", len(pkg))
if err := syscall.Sendto(fd, pkg, 0, &addr); err != nil {
fmt.Println("Sendto err:", err)
}
var recvBuf []byte
if nBytes, rAddr, err := syscall.Recvfrom(fd, recvBuf, 0); err == nil {
fmt.Printf("recv %d bytes from %v\n", nBytes, rAddr)
}
}
另外,我使用header.go
并helper.go
从https://github.com/golang/net/tree/master/ipv4
正如Andy指出的那样,raw(7)手册页指出:
仅发送IPPROTO_RAW套接字。如果您确实想接收所有IP数据包,请使用具有ETH_P_IP协议的packet(7)套接字。请注意,与原始套接字不同,数据包套接字不会重组IP片段。
我知道如果IPPROTO_ICMP
在创建套接字时将其设置为协议,则可以收到ICMP答复,但是我需要将其设置TTL
为1,这必须在IP层中完成。因此IPPROTO_RAW
,我使用套接字发送ICMP请求,此后,我用于net.ListenIP
接收ICMP消息。这是代码:
package main
import (
"bytes"
"encoding/binary"
"log"
"net"
"os"
"syscall"
)
const icmpID uint16 = 43565 // use a magic number for now
type ICMP struct {
Type uint8
Code uint8
Checksum uint16
Identifier uint16
SeqNo uint16
}
func Checksum(data []byte) uint16 {
var (
sum uint32
length int = len(data)
index int
)
for length > 1 {
sum += uint32(data[index])<<8 + uint32(data[index+1])
index += 2
length -= 2
}
if length > 0 {
sum += uint32(data[index])
}
sum += (sum >> 16)
return uint16(^sum)
}
func main() {
h := Header{
Version: 4,
Len: 20,
TotalLen: 20 + 8,
TTL: 1,
Protocol: 1,
}
argc := len(os.Args)
if argc < 2 {
log.Println("usage: program + host")
return
}
ipAddr, _ := net.ResolveIPAddr("ip", os.Args[1])
h.Dst = ipAddr.IP
icmpReq := ICMP{
Type: 8,
Code: 0,
Identifier: icmpID,
SeqNo: 1,
}
out, err := h.Marshal()
if err != nil {
log.Println("ip header error", err)
return
}
var icmpBuf bytes.Buffer
binary.Write(&icmpBuf, binary.BigEndian, icmpReq)
icmpReq.Checksum = Checksum(icmpBuf.Bytes())
icmpBuf.Reset()
binary.Write(&icmpBuf, binary.BigEndian, icmpReq)
fd, _ := syscall.Socket(syscall.AF_INET, syscall.SOCK_RAW, syscall.IPPROTO_RAW)
addr := syscall.SockaddrInet4{
Port: 0,
}
copy(addr.Addr[:], ipAddr.IP[12:16])
pkg := append(out, icmpBuf.Bytes()...)
if err := syscall.Sendto(fd, pkg, 0, &addr); err != nil {
log.Println("Sendto err:", err)
}
laddr, err := net.ResolveIPAddr("ip4:icmp", "0.0.0.0")
if err != nil {
log.Fatal(err)
}
c, err := net.ListenIP("ip4:icmp", laddr)
if err != nil {
log.Fatal(err)
}
for {
buf := make([]byte, 2048)
n, raddr, err := c.ReadFrom(buf)
if err != nil {
log.Println(err)
continue
}
icmpType := buf[0]
if icmpType == 11 {
if n == 36 { // Time exceeded messages
// A time exceeded message contain IP header(20 bytes) and first 64 bits of the original payload
id := binary.BigEndian.Uint16(buf[32:34])
log.Println("recv id", id)
if id == icmpID {
log.Println("recv Time Exceeded from", raddr)
}
}
}
}
}
实际上,我在go中编写了一个traceroute,如果有人对此感兴趣,则整个代码都在github中。
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