概要

DNS协议属于比较简单的网络协议，最近用golang实现了对于dns协议的解包和打包，暂时只实现了一个查询问题与一个回答问题，代码如下。
本文代码地址
https://github.com/changjixiong/goNotes/tree/master/dnsnotes

DNS报文解包与打包

package dnsKitimport ("bytes""encoding/binary""net""strings"
)/*
DNS报文格式，不论是请求报文，还是DNS服务器返回的应答报文，都使用统一的格式。
2个字节(16bit)，标识字段，客户端会解析服务器返回的DNS应答报文，获取ID值与请求报文设置的ID值做比较
如果相同，则认为是同一个DNS会话。
QR  标示该消息是请求消息（该位为0）还是应答消息（该位为1）
QR这一段位 Flag 16bit长度
header0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                      ID                       |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR|  opcode   |AA|TC|RD|RA|   Z    |   RCODE   |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    QDCOUNT                    |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    ANCOUNT                    |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    NSCOUNT                    |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    ARCOUNT                    |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+question0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                     ...                       |
|                    QNAME                      |
|                     ...                       |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    QTYPE                      |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    QCLASS                     |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
*/// DNSHeader 头
type DNSHeader struct {ID uint16//golang 没有bit类型，只能这样处理QR                  uint16 //1bitOperationCode       uint16 //4bitAuthoritativeAnswer uint16 //1bitTruncation          uint16 //1bitRecursionDesired    uint16 //1bitRecursionAvailable  uint16 //1bitZero                uint16 //3bitResponseCode        uint16 //4bitQuestionCount uint16AnswerRRs     uint16AuthorityRRs  uint16AdditionalRRs uint16
}func (dh *DNSHeader) ToBytes() []byte {var buffer bytes.Bufferbinary.Write(&buffer, binary.BigEndian, dh.ID)bits := dh.QR<<15 + dh.OperationCode<<11 + dh.AuthoritativeAnswer<<10 + dh.Truncation<<9bits += dh.RecursionDesired<<8 + dh.RecursionAvailable<<7 + dh.ResponseCodebinary.Write(&buffer, binary.BigEndian, bits)binary.Write(&buffer, binary.BigEndian, dh.QuestionCount)binary.Write(&buffer, binary.BigEndian, dh.AnswerRRs)binary.Write(&buffer, binary.BigEndian, dh.AuthorityRRs)binary.Write(&buffer, binary.BigEndian, dh.AdditionalRRs)return buffer.Bytes()
}func NewDNSHeader(buffer *bytes.Buffer) *DNSHeader {// 读12byteid := binary.BigEndian.Uint16(buffer.Next(2))flag := binary.BigEndian.Uint16(buffer.Next(2))return &DNSHeader{ID: id,QR:                  flag >> 15,OperationCode:       (flag >> 11) % (1 << 4),AuthoritativeAnswer: (flag >> 10) % (1 << 1),Truncation:          (flag >> 9) % (1 << 1),RecursionDesired:    (flag >> 8) % (1 << 1),RecursionAvailable:  (flag >> 7) % (1 << 1),Zero:                (flag >> 4) % (1 << 3),ResponseCode:        flag % (1 << 4),QuestionCount: binary.BigEndian.Uint16(buffer.Next(2)),AnswerRRs:     binary.BigEndian.Uint16(buffer.Next(2)),AuthorityRRs:  binary.BigEndian.Uint16(buffer.Next(2)),AdditionalRRs: binary.BigEndian.Uint16(buffer.Next(2)),}
}//DNSQuestion 请求
type DNSQuestion struct {QuestionName  stringQuestionType  uint16QuestionClass uint16
}func (dq *DNSQuestion) ToBytes() []byte {var buffer bytes.Buffersegments := strings.Split(dq.QuestionName, ".")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))binary.Write(&buffer, binary.BigEndian, dq.QuestionType)binary.Write(&buffer, binary.BigEndian, dq.QuestionClass)return buffer.Bytes()
}func NewDNSQuestion(buffer *bytes.Buffer) *DNSQuestion {//8bit标记每一级域名的长度// buf := bytes.NewBuffer(data)length := uint8(0)binary.Read(buffer, binary.BigEndian, &length)segments := []string{}for length > 0 {seg := make([]byte, length)binary.Read(buffer, binary.BigEndian, &seg)segments = append(segments, string(seg))binary.Read(buffer, binary.BigEndian, &length)// fmt.Println(length)}question := &DNSQuestion{QuestionName: strings.Join(segments, "."),}question.QuestionType = binary.BigEndian.Uint16(buffer.Next(2))question.QuestionClass = binary.BigEndian.Uint16(buffer.Next(2))return question
}//DNSResourceRecode 回答字段，授权字段，附加字段
type DNSResourceRecode struct {Name     stringNamePos  uint16RRType   uint16Class    uint16TTL      uint32RDLength uint16RData    string
}func (drr *DNSResourceRecode) ToBytes() []byte {var buffer bytes.Bufferif drr.NamePos > 0 {binary.Write(&buffer, binary.BigEndian, (0x01<<15)|(0x01<<14)|drr.NamePos)} else {segments := strings.Split(drr.Name, ".")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))}binary.Write(&buffer, binary.BigEndian, drr.RRType)binary.Write(&buffer, binary.BigEndian, drr.Class)binary.Write(&buffer, binary.BigEndian, drr.TTL)binary.Write(&buffer, binary.BigEndian, drr.RDLength)if drr.Class == 1 {binary.Write(&buffer, binary.BigEndian, []byte(net.ParseIP(drr.RData).To4()))} else if drr.Class == 5 {}return buffer.Bytes()
}func NewDNSResourceRecode(buffer *bytes.Buffer) *DNSResourceRecode {tag := buffer.Next(1)[0] >> 6buffer.UnreadByte()drr := &DNSResourceRecode{}if tag == 3 {//最高两位11，右移后是3drr.NamePos = (binary.BigEndian.Uint16(buffer.Next(2)) << 2) >> 2} else {}drr.RRType = binary.BigEndian.Uint16(buffer.Next(2))drr.Class = binary.BigEndian.Uint16(buffer.Next(2))drr.TTL = binary.BigEndian.Uint32(buffer.Next(4))drr.RDLength = binary.BigEndian.Uint16(buffer.Next(2))if drr.RRType == 1 && drr.RDLength == 4 {drr.RData = net.IPv4(buffer.Next(1)[0], buffer.Next(1)[0], buffer.Next(1)[0], buffer.Next(1)[0]).String()} else {//FIXME://域名处理}return drr
}// DNSMessage 消息体
type DNSMessage struct {Header          *DNSHeaderQuestions       []*DNSQuestionResourceRecodes []*DNSResourceRecode
}func (dm *DNSMessage) ToBytes() []byte {result := []byte{}result = append(result, dm.Header.ToBytes()...)for i := uint16(0); i < dm.Header.QuestionCount; i++ {result = append(result, dm.Questions[i].ToBytes()...)}for _, rr := range dm.ResourceRecodes {result = append(result, rr.ToBytes()...)}return result
}func NewDNSMessage(buffer *bytes.Buffer) *DNSMessage {//用bytes.Buffer类型来逐个字节读取后处理的优点就是不需要自己计算读取偏移值//这个对于Question和Answer这种第一段长度不固定的内容处理非常方便dnsMsg := &DNSMessage{Header: NewDNSHeader(buffer),}//FIXME: deal more then 1 QuestionCountdnsMsg.Questions = append(dnsMsg.Questions, NewDNSQuestion(buffer))//FIXME: deal more then 1 ResourceRecodeif buffer.Len() > 0 {dnsMsg.ResourceRecodes = append(dnsMsg.ResourceRecodes, NewDNSResourceRecode(buffer))}return dnsMsg
}

客户端

package mainimport ("bytes""fmt". "goNotes/dnsnotes/dnsKit""net"
)func main() {dnsMsg1 := DNSMessage{Header: &DNSHeader{ID:                  0x0010,QR:                  0,OperationCode:       0,AuthoritativeAnswer: 0,Truncation:          0,RecursionDesired:    1,RecursionAvailable:  0,Zero:                0,ResponseCode:        0,QuestionCount:       1,AnswerRRs:           0,AuthorityRRs:        0,AdditionalRRs:       0,},Questions: []*DNSQuestion{&DNSQuestion{QuestionName:  "www.test1.com",QuestionType:  1,QuestionClass: 1,},},}dnsMsg2 := DNSMessage{Header: &DNSHeader{ID:                  0x0010,QR:                  0,OperationCode:       0,AuthoritativeAnswer: 0,Truncation:          0,RecursionDesired:    1,RecursionAvailable:  0,Zero:                0,ResponseCode:        0,QuestionCount:       1,AnswerRRs:           0,AuthorityRRs:        0,AdditionalRRs:       0,},Questions: []*DNSQuestion{&DNSQuestion{QuestionName:  "www.test2.com",QuestionType:  1,QuestionClass: 1,},},}dnsServer := "127.0.0.1:11153"var conn net.Connvar err errorif conn, err = net.Dial("udp", dnsServer); err != nil {fmt.Println(err.Error())return}defer conn.Close()if _, err := conn.Write(dnsMsg1.ToBytes()); err != nil {fmt.Println(err.Error())return}buf := make([]byte, 1024)if length, err := conn.Read(buf); err == nil {result := NewDNSMessage(bytes.NewBuffer(buf[0:length]))fmt.Println("query:", result.Questions[0].QuestionName, ", get ip:", result.ResourceRecodes[0].RData)} else {fmt.Println(err.Error())}if _, err = conn.Write(dnsMsg2.ToBytes()); err != nil {fmt.Println(err.Error())return}buf = make([]byte, 1024)if length, err := conn.Read(buf); err == nil {result := NewDNSMessage(bytes.NewBuffer(buf[0:length]))fmt.Println("query:", result.Questions[0].QuestionName, ", get ip:", result.ResourceRecodes[0].RData)} else {fmt.Println(err.Error())}}

服务端

对域名返回的ip从10.0.0.1开始，新域名返回的ip加1

package mainimport ("bytes""encoding/binary""fmt". "goNotes/dnsnotes/dnsKit""net""sync"
)const RECV_BUF_LEN = 1024var addr2IP Address2IPtype Address2IP struct {lastIP uint32 //167772160 -> 10.0.0.0sync.RWMutexaddress2ip map[string]uint32
}func (a *Address2IP) getIP(address string) string {a.RLock()ip := uint32(0)ok := falseif ip, ok = a.address2ip[address]; ok {a.RUnlock()} else {a.RUnlock()a.Lock()a.lastIP++a.address2ip[address] = a.lastIPip = a.lastIPa.Unlock()}ipByte := []byte{0, 0, 0, 0}binary.BigEndian.PutUint32(ipByte, ip)return net.IPv4(ipByte[0], ipByte[1], ipByte[2], ipByte[3]).String()
}func main() {addr2IP = Address2IP{lastIP:     167772160,address2ip: map[string]uint32{},}udpAddr, err := net.ResolveUDPAddr("udp", ":11153")if err != nil {panic("error listening:" + err.Error())}fmt.Println("Starting the server")conn, err := net.ListenUDP("udp", udpAddr)defer conn.Close()for {buf := make([]byte, RECV_BUF_LEN)n, raddr, err := conn.ReadFromUDP(buf)if err != nil {panic("Error accept:" + err.Error())}fmt.Println("Accepted the Connection :", conn.RemoteAddr())go echoServer(conn, raddr, buf[0:n])}
}func echoServer(conn *net.UDPConn, raddr *net.UDPAddr, data []byte) {dnsMsg := NewDNSMessage(bytes.NewBuffer(data))dnsMsg.Header.QR = 1dnsMsg.Header.RecursionAvailable = 1dnsMsg.Header.AnswerRRs = 1dnsMsg.ResourceRecodes = append(dnsMsg.ResourceRecodes,&DNSResourceRecode{Name:     "",NamePos:  12,RRType:   1,Class:    1,TTL:      384,RDLength: 4,RData:    addr2IP.getIP(dnsMsg.Questions[0].QuestionName),})fmt.Println("query:", dnsMsg.Questions[0].QuestionName, ", ip:", dnsMsg.ResourceRecodes[0].RData)conn.WriteToUDP(dnsMsg.ToBytes(), raddr)}

DNS协议解析与DNS模拟服务器-基于golang实现

概要

DNS报文解包与打包

客户端

服务端

更多代码

DNS协议解析与DNS模拟服务器-基于golang实现相关推荐

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