使用 file://在本地加载的来自移动 WebView 的 CORS

问题描述

请耐心等待，这个需要解释一下.

我正在帮助构建一个混合移动网络应用.主要代码库是 HTML5 和 JavaScript，它们将被封装在原生移动 Web 视图(la Phonegap)中.

部分功能要求应用将信息发布到由我们的一位客户控制的网络服务.由于其他人正在使用此 Web 服务，因此更改的余地很小.我们使用 HTTP POST 发送 JSON 并从服务器接收响应.此响应的一部分是管理我们与服务器的会话的 JSESSIONID cookie.在初始 initSession() 调用之后，我们需要在每个 (AJAX) 请求中发送 JSESSIONID cookie.

当部署在移动设备上时，Web 应用程序被包装在本机 Web 视图中，它通过浏览到 file:///path/to/app/index.html 来启动 Web 应用程序.

我们尝试的第一件事是要求我们的客户端在其响应标头中设置 Access-Control-Allow-Origin: * 以允许 CORS.然后我们尝试发布到服务器:

$.ajax({url: 'http://thirdparty.com/ws',数据:数据，类型:POST"，数据类型:JSON"，成功:成功回调，错误:失败回调});

监控请求，很明显没有包含 cookie.仔细检查后，在 CORS 规范中有一个 用于处理用户凭据的特殊部分，其中包括会话 cookie.所以我修改了 AJAX 调用以包含以下内容:

$.ajax({url: 'http://thirdparty.com/ws',数据:数据，类型:POST"，数据类型:JSON"，成功:成功回调，错误:失败回调，xhrFields { withCredentials: true }});

另一个错误，这次来自浏览器.更多阅读得出以下结论:

如果第三方服务器未使用 Access-Control-Allow-Credentials: true 标头响应，则响应将被忽略且无法用于 Web 内容.

重要提示:服务器在响应凭证请求时，必须在 Access-Control-Allow-Origin 标头中指定域，并且不能使用通配符.

因此我们需要更改服务器的标头以将 Access-Control-Allow-Credentials: true 和 Access-Control-Allow-Origin 包含到我们的 Origin 中.p>

我们终于来到了我的问题:当使用 file://协议加载网页时，从 Web 视图发送的 Origin 请求标头设置为 null.因此它不能被服务器解析，因此服务器不能在 Access-Control-Allow-Origin 中设置它.但是，如果服务器无法将 Access-Control-Allow-Origin 设置为 * 以外的其他值，我们就无法发送凭据，包括 cookie.

所以我被困住了.该怎么办?我在这里看到了一个类似的问题，但我不太明白提议的内容回答.任何帮助将不胜感激！

我意识到这个问题已经过时了，但我想我还是会提出来.对于 CORS 请求，浏览器会对其进行预检.这意味着 - 无论您使用什么 $.ajax() 方法，一个 OPTIONS 请求都会发送到服务器.

这个预检 OPTIONS 请求实际上是在说:

嘿，来自其他域的外部服务器，我想向您发送一个不简单的请求(简单的请求没有预检).我的不简单的请求将具有这些类型的标头和内容类型等等.你能告诉我这是否可以吗?"

然后服务器将做任何事情(可能检查一些配置或数据库)并以允许的来源、允许的标头和/或允许的方法进行响应.

最后 - 如果预检 OPTIONS 请求已收到允许实际 $.ajax() 方法执行的响应 - 它会执行.

CORS 与 JSONP 不同.

所有这些 - 虽然 withCredentials 预检成功需要响应携带 Access-Control-Allow-Credentials 标头(如问题中所述)，即 INAccess-Control-Allow-Origins 和 Access-Control-Allow-Methods 值的补充，这些值必须包括预期请求的各个方面.

例如 - 如果您从源 http://foo-domain.com 发出 CORS POST 请求，标头 somevalue 到http://bar-domain.com，预检 OPTIONS 请求将发出，以便对 http://发出实际的发布请求bar-domain.com，OPTIONS 请求需要接收带有 Access-Control-Allow-Origins 值的响应，其中包含 http://foo-domain.com.这可能是源名称本身或 *.响应还需要包含 POST 的 Access-Control-Allow-Methods 值.这也可能是 *.最后，如果我们希望我们的 somevalue 标头被允许，响应必须包含一个 Access-Control-Allow-Headers 值，其中包含我们的 somevalue标题键或 *.

回过头来——如果您无法控制服务器，或者无法让服务器允许您的 CORS 请求，您可以始终使用 JSONP 或某些 urlEncoded 数据类型和/或发出没有自定义标头的简单请求.GET、HEAD 和完整的 POST 请求通常是简单请求.

Bear with me, this one needs a bit of explanation.

I am helping to build a hybrid mobile web app. The main codebase is HTML5 and JavaScript, which will be wrapped in a native mobile Web View (a la Phonegap).

Part of the functionality requires the app to post information to a web service controlled by one of our clients. There is very little scope to change this web service as it is being used by others. We send JSON using an HTTP POST and receive responses from the server. Part of this response is a JSESSIONID cookie which manages our session with the server. After the initial initSession() call, we need to send the JSESSIONID cookie with every (AJAX) request.

When deployed on a mobile device, the web app is wrapped in the native Web View, which starts the web app by browsing to file:///path/to/app/index.html.

The first thing we tried was asking our client to set Access-Control-Allow-Origin: * in their response header to allow CORS. We then tried posting to the server:

$.ajax({
  url: 'http://thirdparty.com/ws',
  data: data,
  type: "POST",
  dataType: "JSON",
  success: successCallback,
  error: failedCallback
});

Monitoring the requests, it was apparent that the cookies were not being included. On closer inspection there is a special section in the CORS spec for dealing with user credentials, which includes session cookies. So I modified the AJAX call to include this:

$.ajax({
  url: 'http://thirdparty.com/ws',
  data: data,
  type: "POST",
  dataType: "JSON",
  success: successCallback,
  error: failedCallback,
  xhrFields { withCredentials: true }
});

Another error, this time from the Browser. More reading yielded the following:

If the third party server did not respond with an Access-Control-Allow-Credentials: true header the response would be ignored and not made available to web content.

Important note: when responding to a credentialed request, the server must specify a domain in the Access-Control-Allow-Origin header, and cannot use wild carding.

So we need to change the server's headers to include Access-Control-Allow-Credentials: true and Access-Control-Allow-Origin to our Origin.

Here we finally come to my problem: when loading a web page using the file:// protocol, the Origin request header sent from the Web View is set to null. It therefore can't be parsed by the server and so the server can't set it in Access-Control-Allow-Origin. But if the server can't set Access-Control-Allow-Origin to something other than * we can't send credentials, including cookies.

So I'm stuck. What to do? I saw a similar question posted here but I don't really understand the proposed answer. Any help would be much appreciated!

I realize this question is old, but I figured I'd throw in on it anyhow. In the case of CORS requests, the browser preflights them. What this means is - in spite of whatever $.ajax() method you are using, an OPTIONS request is sent to the server.

What this preflighted OPTIONS request is actually doing is saying:

"Hey there, foreign-server-from-some-other-domain, I want to send you a not-simple request (simple req's are not preflighted). My not-simple request going to have these kinds of headers and content type and so on. Can you let me know if this is okay?"

Then the server will do whatever it does (probably check some configuration or database) and respond with the allowable origin(s), the allowable header(s), and/or the allowable method(s).

Finally - if that preflight OPTIONS request has received response that allows the actual $.ajax() method to go - it goes.

CORS is not the same as JSONP.

All that said - while withCredentials preflight success requires the response to carry a Access-Control-Allow-Credentials header (as stated in the question), that is IN ADDITION to Access-Control-Allow-Origins AND Access-Control-Allow-Methods values, which must include the facets of the intended request.

For example - if you are making a CORS POST request from origin http://foo-domain.com with headers somevalue to http://bar-domain.com, a preflight OPTIONS request would go out and in order for the actual post request to be made to http://bar-domain.com, the OPTIONS request would need to receive a response with an Access-Control-Allow-Origins value that included http://foo-domain.com. This could be the origin name itself or *. The response would also need to have an Access-Control-Allow-Methods value that included POST. This may also be *. And Finally if we want our somevalue header to be allowed, the response must contain a Access-Control-Allow-Headers value that includes our somevalue header key or *.

To circle back - if you can't control the server, or have no way to allow the server to allow your CORS requests, you could always use JSONP or some urlEncoded datatype and/or make simple requests without custom headers. GET, HEAD, and full POST requests are usually simple requests.

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