XMLHttpRequest() &净::ERR_NAME_NOT_RESOLVED

问题描述

我正在编写一个向远程服务器发出 HTTP 请求的 javascript 应用程序.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.

如果他们输入的 DNS 名称无法解析，我想提供诊断消息.这是当前代码:

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 status=0，response 是 ""，所以没有太多迹象表明出了什么问题.然而，控制台显示加载资源失败: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.

如何获得 ERR_NAME_NOT_RESOLVED 的指示?

How can I get an indication of ERR_NAME_NOT_RESOLVED?

更新:我回到了这个问题，使用的策略是任何不是超时"的响应都意味着名称已解析、主机回答等.

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.

我最初问题的答案似乎是:浏览器本身(在本例中为 Chrome)检测到无法解析并将其显示在控制台中，但 XMLHttpRequest API 不够丰富，无法指示原因.因此，可怜的 Javascript 程序员只能将超时作为一种解决方法.

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 标头，因为其中一位正确指出的评论者没有任何价值.

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

推荐答案

经过大量研究，我更清楚地理解了问题，并且理解了答案(不，不可能得到原因 - 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).

这是设计使然. 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器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.

我对 Chromium 错误报告者的报告和其中一位开发人员的回复非常清楚地证明了这一点，网址为:https://bugs.chromium.org/p/chromium/issues/detail?id=718447 特别是评论 #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，窗口中的 javascript 在沙箱中运行，该沙箱只能访问加载、超时、中止和错误状态，没有任何进一步的粒度.(不过，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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