为什么dns.resolveMx在多次调用时总是返回错误？

I am trying to validate a list of email addresses (to get rid of spammy ones e.g. asdasdas@waqwqasd.com) by looking up MX records with Node.JS

我试图通过使用Node.JS查找MX记录来验证电子邮件地址列表（以摆脱垃圾邮件地址，例如asdasdas@waqwqasd.com）

My code works on one email address but when I'm calling it a lot of times I get an error from dns.resolveMx with either ETIMEOUT or ECONNREFUSED.

我的代码在一个电子邮件地址上工作，但是当我多次调用它时，我从dns.resolveMx收到ETIMEOUT或ECONNREFUSED的错误。

Here's the relevant bits:

这是相关的位：

This test code works:

此测试代码有效：

(function() {
  var dns = require('dns'); 
  var email = "test@yahoo.co.uk"
   var emailDomain;
    try
    {
      emailDomain = email.split('@')[1];

      console.log('Checking Domain ' + emailDomain);
    }
    catch(e)
    {
      return false;
    }
  dns.resolveMx("yahoo.co.uk", function (err, addresses) {
      if(err)
      {
        console.log(err);
      }
      else
      {
        console.log('Found addresses ' + JSON.stringify(addresses));  
        return true;
      }
    }
  );
})();

This code doesn't:

此代码不：

(function() {

  var dns = require('dns');
  var fs = require('fs');
  var Sync = require('sync');

  var validEmails = [];
  var invalidEmails = [];
  var validDomains = [];

  var checkEmails = function()
  {
    var fileData = fs.readFileSync('emails_only-full.txt').toString().split('\n');

    console.log(fileData.length);
    testValidEmailDomains(fileData);
  }

  var finished = function()
  {
    console.log('Finished parsing database');
    console.log('Found ' + validEmails.length + ' valid emails');
    console.log('Found ' + invalidEmails.length + ' invalid emails');    
  };

  var testValidEmailDomains = function(emails, index)
  {
    if(emails.length == 0)
    {
      finished();
      return;
    }

    var email = emails.pop();
    var emailDomain;
    try
    {
      emailDomain = email.split('@')[1];
      if(validDomains.indexOf(emailDomain) != -1)
      {
        validEmails.push(email);
        return;
      }
    }
    catch(e)
    {
      invalidEmails.push(email);
      return;
    }
    console.log('Checking Domain ' + emailDomain);    
    dns.resolveMx(emailDomain, function (err, addresses) {
      if(err)
      {
        console.log(err);
        invalidEmails.push(email);
      }
      else
      {
        validDomains.push(emailDomain);
        validEmails.push(email);
        console.log('Found addresses ' + JSON.stringify(addresses));  
      }
      testValidEmailDomains(emails.slice(index), index + 1);
    });
  }
  checkEmails();
})();

I was thinking it was to do with calling too many times at once but using Sync/fibers to sleep the thread doesn't seem to work either. Any ideas?

我当时认为它是同时调用太多次，但使用Sync /光纤来休眠线程似乎也不起作用。有任何想法吗？

1 个解决方案

#1

Edit: Appears stable branch (0.10.x) does not support dns.setServers. Use https://github.com/tjfontaine/node-dns instead for dns requests in this case. See the dns.Request method. It lets you manually set the dns server in each request.

编辑：出现稳定分支（0.10.x）不支持dns.setServers。在这种情况下，请使用https://github.com/tjfontaine/node-dns代替dns请求。请参阅dns.Request方法。它允许您在每个请求中手动设置DNS服务器。

DNS servers typically block clients if too many requests are made in quick succession to avoid DNS amplification attacks. Best approach would be to:

如果快速连续发出太多请求以避免DNS放大攻击，DNS服务器通常会阻止客户端。最好的方法是：

Rate limit DNS requests
限制DNS请求
Use multiple servers and cycle through them (might still get blocked by ISP or other intermediaries)
使用多个服务器并循环使用它们（可能仍被ISP或其他中介阻止）
Cache domains that have already been checked to avoid duplicate requests
缓存已经过检查的域以避免重复请求

There's a good list of DNS servers here: http://pcsupport.about.com/od/tipstricks/a/free-public-dns-servers.htm

这里有一个很好的DNS服务器列表：http：//pcsupport.about.com/od/tipstricks/a/free-public-dns-servers.htm

Sample code for cycling through multiple servers:

循环访问多个服务器的示例代码：

// static list of DNS servers to use from the list above
var SERVERS = ['8.8.8.8', ...];
var SERVERS_LENGTH = servers.length;

var dns = require('dns');

// function to resolve mx records   
// loops through emails and launches parallel requests - rate limit as required
function resolve(emails, fn) {
   emails.forEach(function(email, index) {
       var nextServer = SERVERS[index % SERVERS_LENGTH];
       dns.setServers([nextServer]);
       dns.resolveMx(email, fn);
   });
}

#1