var header = {};

  header.id = buf.slice(0,2);
  header.qdcount = buf.slice(4,6);
  header.ancount = buf.slice(6,8);
  header.nscount = buf.slice(8,10);
  header.arcount = buf.slice(10, 12);

  //对第3个字节转成`2`进制字符串然后转换为数值
  var b = buf.slice(2,3).toString('binary', 0, 1).charCodeAt(0);

  var bitSlice = function(b, offset, length) {
      return (b >>> (7-(offset+length-1))) & ~(0xff << length);
  };

  'use strict';

  var buf = Buffer.from([0x2d]);
  var b = buf.toString('binary' , 0,1).charCodeAt(0);

  console.log(bitSlice(b , 0, 1));//0
  console.log(bitSlice(b , 1, 1));//0
  console.log(bitSlice(b , 2, 1));//1
  console.log(bitSlice(b , 3, 1));//0
  console.log(bitSlice(b , 4, 1));//1
  console.log(bitSlice(b , 5, 1));//1
  console.log(bitSlice(b , 6, 1));//0
  console.log(bitSlice(b , 7, 1));//1
  console.log(bitSlice(b , 5, 3));//5  === 0000 0101

  /**
   * 16进制：0x2d
   * 10进制：45
   * 2进制： 0010 1101
   *
   * (45,0,1)：45>>>7 & ~(0xff<<1) 
   *    45>>>7 = 0000 0000
   *    (0xff<<1)  = 0000 0000 0000 0000 0000 0001 1111 1110   510
   *    ~(0xff<<1) = 1111 1111 1111 1111 1111 1110 0000 0001   -511 = -((0xff<<1)+1)
   *
   *      0000 0000 0000 0000 0000 0000 0000 0000  === 45>>>7
   *    & 1111 1111 1111 1111 1111 1110 0000 0001  === ~(0xff<<1)
   *      ----------------------------------------
   *      0000 0000 0000 0000 0000 0000 0000 0000 = 0
   *
   * (45,2,1)：45>>>5 & ~(0xff<<1) 
   *    45>>>5 = 0000 0001
   *    (0xff<<1)  = 0000 0000 0000 0000 0000 0001 1111 1110   510
   *    ~(0xff<<1) = 1111 1111 1111 1111 1111 1110 0000 0001   -511 = -((0xff<<1)+1)
   *
   *      0000 0000 0000 0000 0000 0000 0000 0001  === 45>>>5
   *    & 1111 1111 1111 1111 1111 1110 0000 0001  === ~(0xff<<1)
   *      ----------------------------------------
   *      0000 0000 0000 0000 0000 0000 0000 0001 = 1
   */

  //第3个字节
  var b = buf.slice(2,3).toString('binary', 0, 1).charCodeAt(0);
  header.qr = bitSlice(b,0,1);
  header.opcode = bitSlice(b,1,4);
  header.aa = bitSlice(b,5,1);
  header.tc = bitSlice(b,6,1);
  header.rd = bitSlice(b,7,1);
  
  //第4个字节
  b = buf.slice(3,4).toString('binary', 0, 1).charCodeAt(0);
  header.ra = bitSlice(b,0,1);
  header.z = bitSlice(b,1,3);
  header.rcode = bitSlice(b,4,4);

var question = {};
  question.qname = buf.slice(12, buf.length-4);
  question.qtype = buf.slice(buf.length-4, buf.length-2);
  question.qclass = buf.slice(buf.length-2, buf.length);

  var domainify = function(qname) {
    var parts = [];

    for (var i = 0; i < qname.length && qname[i];) {
      var len = qname[i] , offset = i+1;//获取每一块域名长度

      parts.push(qname.slice(offset,offset+len).toString());//获取每一块域名

      i = offset+len;
    }

    return parts.join('.');//拼凑成完整域名
  };

  'use strict';

  const dgram = require('dgram');
  const dns = require('dns');
  const fs = require('fs');
  const server = dgram.createSocket('udp4');

  var bitSlice = function(b, offset, length) {
      return (b >>> (7-(offset+length-1))) & ~(0xff << length);
  };

  var domainify = function(qname) {
      var parts = [];

      for (var i = 0; i < qname.length && qname[i];) {
          var length = qname[i];
          var offset = i+1;

          parts.push(qname.slice(offset,offset+length).toString());

          i = offset+length;
      }

      return parts.join('.');
  };

  var parse = function(buf) {
      var header = {};
      var question = {};
      var b = buf.slice(2,3).toString('binary', 0, 1).charCodeAt(0);

      header.id = buf.slice(0,2);
      header.qr = bitSlice(b,0,1);
      header.opcode = bitSlice(b,1,4);
      header.aa = bitSlice(b,5,1);
      header.tc = bitSlice(b,6,1);
      header.rd = bitSlice(b,7,1);

      b = buf.slice(3,4).toString('binary', 0, 1).charCodeAt(0);

      header.ra = bitSlice(b,0,1);
      header.z = bitSlice(b,1,3);
      header.rcode = bitSlice(b,4,4);

      header.qdcount = buf.slice(4,6);
      header.ancount = buf.slice(6,8);
      header.nscount = buf.slice(8,10);
      header.arcount = buf.slice(10, 12);

      question.qname = buf.slice(12, buf.length-4);
      question.qtype = buf.slice(buf.length-4, buf.length-2);
      question.qclass = buf.slice(buf.length-2, buf.length);

      return {header:header, question:question};
  };

  server.on('error' , (err)=>{
      console.log(`server error: ${err.stack}`);
  });

  server.on('message' , (msg , rinfo)=>{
      //fs.writeFile('dns.json' ,msg, {flag:'w',endcoding:'utf-8'} ,(err)=>{
      //    console.log(err);
      //});
      var query = parse(msg);
      console.log('标识ID: ' ,query.header.id);
      console.log('标识FLAG: ' , 'QR: ',query.header.qr , 'opcode: ',query.header.opcode , 'AA: ',query.header.aa , 'TC: ',query.header.tc,'RD: ',query.header.rd);
      
      console.log('RA: ',query.header.ra , 'zero: ',query.header.z , 'recode: ',query.header.rcode);

      console.log('QDCOUNT: ',query.header.qdcount , 'ANCOUNT: ' , query.header.ancount, 'NSCOUNT: ' , query.header.nscount,'ARCOUNT: ',query.header.arcount);
          
      console.log('QNAME: ',query.question.qname , 'QTYPE: ', query.question.qtype ,'QCLASS: ' , query.question.qclass);

      console.log('QUESTION STRING: ' ,domainify(query.question.qname));

      server.close();
  });

  server.on('listening' , ()=>{
      var address = server.address();
      console.log(`server listening ${address.address}:${address.port}`);
  });

  server.bind({port:53,address:'8.8.8.8'});//address需要指定到你要用于进行代理的机器ip