XMLHttpRequest（）&网:: ERR_NAME_NOT_RESOLVED [英] XMLHttpRequest() & net::ERR_NAME_NOT_RESOLVED

问题描述

我正在编写一个javascript应用程序，它发出远程服务器的HTTP请求。用户将输入主机名。

I am writing a javascript app that makes an HTTP request of a remote server. The user will enter the host name.

如果他们输入无法解析的DNS名称，我想提供诊断消息。这是当前的代码：

I want to offer a diagnostic message if they enter a DNS name that cannot resolve. Here's the current code:

var req, t, url;
url = 'http://definitelydoesntexist0x314159.com';
req = new XMLHttpRequest();
req.open('GET', url, true);
req.onreadystatechange = function() {
  if (req.readyState == 4) {
    t = req.statusText;
  }
};
req.send();

在onreadystatechange函数中，req的状态为= 0，响应为，所以没有多少出现问题的迹象。然而，控制台显示无法加载资源：net :: ERR_NAME_NOT_RESOLVED，因此浏览器（Chrome）能够弄清楚发生了什么。

In the onreadystatechange function, the req has status=0, response is "", so there's not much indication of what went wrong. Yet the Console shows "Failed to load resource: net::ERR_NAME_NOT_RESOLVED" so the browser (Chrome) was able to figure out what happened.

我如何获得指示ERR_NAME_NOT_RESOLVED？

How can I get an indication of ERR_NAME_NOT_RESOLVED?

更新：我回到了这个问题，使用的策略是任何非超时响应意味着名称已解决，主人回答等等。

Update: I have come back to this question, using the strategy that any response that isn't 'timeout' means that the name resolved, the host answers, etc.

我原来问题的答案似乎是：浏览器本身（在这种情况下是Chrome）检测到无法解决并在控制台中显示它，但XMLHttpRequest API不够丰富，无法指明原因。所以这个可怜的Javascript程序员坚持使用超时作为解决方法。

The answer to my original question seems to be: It appears that the browser itself (Chrome, in this case) detects the failure to resolve and displays it in the Console, but the XMLHttpRequest API isn't rich enough to indicate the cause. So the poor Javascript programmer is stuck with the timeout as a workaround.

我还删除了CORS标题，因为正确指出的评论者之一没有任何价值。

I also removed the CORS header, as one of the commenters correctly noted was of no value.

推荐答案

经过大量的研究，我更清楚地理解问题，并理解答案（不，不可能得到答案）原因 - 例如，ERR_NAME_NOT_RESOLVED - 处于错误状态。）

After a great deal more research, I understand the problem more clearly, and understand the answer (No, it's not possible to get the reason - e.g., ERR_NAME_NOT_RESOLVED - in the error status).

这是设计。 Javascript错误处理例程不会，也不能，返回有关失败原因的更多信息。浏览器这样做是为了防止恶意Javascript代码在本地网络上运行端口扫描程序并将该信息发送到远程服务器。

This is by design. The Javascript error handling routines do not, and must not, return more information about the reason for the failures. Browsers do this to prevent malicious Javascript code from running port scanners on the local network and sending that information to a remote server.

我的报告很清楚地说明了这一点。 Chromium bug记者和其中一位开发人员的回复，请访问： https ：//bugs.chromium.org/p/chromium/issues/detail？id = 718447 特别评论＃2。

This is borne out quite clearly by my report on the Chromium bug reporter and the response from one of the developers, at: https://bugs.chromium.org/p/chromium/issues/detail?id=718447 especially Comment #2.

因此，javascript在窗口在沙箱中运行，只能访问
加载，超时，中止和错误状态，没有任何进一步的粒度。 （浏览器的调试环境，可以显示此信息，因此您可以找出问题所在......）

Thus, the javascript in the window runs in a sandbox, that only has access to load, timeout, abort, and error status, without any further granularity. (The browser's debugging environment, though, can display this information, so you can figure out what went wrong...)

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