关于DNS协议的具体内容可以查看RFC1035，如果英语不太好我推荐下面这个人的译文：
http://blog.csdn.net/tigerjibo/article/details/6827736 翻译的足够详尽了。
那么来看下Go的实现：
package main
import (
"bytes"
"encoding/binary"
"fmt"
"net"
"strings"
)
type DNSHeader struct {
ID uint16
Flag uint16
QuestionCount uint16
AnswerRRs uint16 //RRs is Resource Records
AuthorityRRs uint16
AdditionalRRs uint16
}
func (header *DNSHeader) SetFlag(QR uint16, OperationCode uint16, AuthoritativeAnswer uint16, Truncation uint16, RecursionDesired uint16, RecursionAvailable uint16, ResponseCode uint16) {
header.Flag = QR<<15 + OperationCode<<11 + AuthoritativeAnswer<<10 + Truncation<<9 + RecursionDesired<<8 + RecursionAvailable<<7 + ResponseCode
}
type DNSQuery struct {
QuestionType uint16
QuestionClass uint16
}
func ParseDomainName(domain string) []byte {
//要将域名解析成相应的格式，例如：
//"www.google.com"会被解析成"0x03www0x06google0x03com0x00"
//就是长度+内容，长度+内容……最后以0x00结尾
var (
buffer bytes.Buffer
segments []string = strings.Split(domain, ".")
)
for _, seg := range segments {
binary.Write(&buffer, binary.BigEndian, byte(len(seg)))
binary.Write(&buffer, binary.BigEndian, []byte(seg))
}
binary.Write(&buffer, binary.BigEndian, byte(0x00))
return buffer.Bytes()
}
func main() {
var (
dns_header DNSHeader
dns_question DNSQuery
)
//填充dns首部
dns_header.ID = 0xFFFF
dns_header.SetFlag(0, 0, 0, 0, 1, 0, 0)
dns_header.QuestionCount = 1
dns_header.AnswerRRs = 0
dns_header.AuthorityRRs = 0
dns_header.AdditionalRRs = 0
//填充dns查询首部
dns_question.QuestionType = 1 //IPv4
dns_question.QuestionClass = 1
var (
conn net.Conn
err error
buffer bytes.Buffer
)
//DNS服务器的端口一般是53，IP你自己ipconfig查一下
//别忘了DNS是基于UDP协议的
if conn, err = net.Dial("udp", "211.137.191.26:53"); err != nil {
fmt.Println(err.Error())
return
}
defer conn.Close()
//buffer中是我们要发送的数据，里面的内容是DNS首部+查询内容+DNS查询首部
binary.Write(&buffer, binary.BigEndian, dns_header)
binary.Write(&buffer, binary.BigEndian, ParseDomainName("www.baidu.com"))
binary.Write(&buffer, binary.BigEndian, dns_question)
fmt.Println(buffer.Bytes())
if _, err := conn.Write(buffer.Bytes()); err != nil {
fmt.Println(err.Error())
return
}
fmt.Println("send success.")
}
用Wireshark来检查一下是否正确(截一张太长了不方便看，所以截成了两段)：
看看我们构造的DNS请求数据包：
如果转载请注明出处：http://blog.csdn.net/gophers/article/details/22942457
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