时间使用jQuery ajax的两个CORS请求之间的时间间隔 [英] Time Interval between two CORS requests using jquery ajax

问题描述

我正在使用jQuery $。ajax 向Web服务发出CORS请求。按照标准，有一个预先请求的请求，然后是实际的POST请求。

我注意到，每次尝试创建Web服务时都有两个请求仅在两次请求之间有一段时间间隔。

如果我连续不断地进行Web服务调用时间差距（如两个请求之间少于1秒），则飞行前丢失。

每次我如何避免这个预先请求的请求？

这个时间间隔是什么时间？

这是Chrome浏览器特有的东西吗？

浏览器在实现飞行前缓存方面的差异。不幸的是，W3C规范本身并不能解释您在飞行前高速缓存中观察到的细微差别。

对于阅读这个问题的其他人，我想解释OP何时说

前请求，他指的是 OPTIONS 请求位于跨源 POST 请求之前。  OPTIONS 请求用于查询API并确定哪些HTTP方法可用于跨源请求。通常，您会希望看到对 OPTIONS 请求的这种响应：
 c $ c> Access-Control-Allow-Origin：* 
 Access-Control-Allow-Credentials：true 
 Access-Control-Allow-Headers：Content-Type，X-Requested-With 
 Access-Control-Allow-Methods：POST，GET，OPTIONS，DELETE，PUT 
  

使用谷歌浏览器，我会向您推荐 Webkit 源代码的适用部分：

https://github.com/WebKit/webkit/blob/master /Source/WebCore/loader/CrossOriginPreflightResultCache.cpp

默认的飞行前缓存超时时间为5秒：

  static const auto defaultPreflightCacheTimeout = std :: chrono :: seconds（5）; 
  

最大值为5分钟：

  static const auto maxPreflightCacheTimeout = std :: chrono :: seconds（600）; 
  

服务器可以使用 <$ c $为执行前请求指定超时值c> Access-Control-Max-Age 字段，但是 Webkit浏览器强制执行最大超时为5分钟。

回答您的问题：

我怎样才能避免每次这个预先飞行要求？您需要将 Access-Control-Max-Age 设置为600 在您的API响应标头中对 OPTIONS 请求。 $ b

这是什么时间间隔？

对于Webkit浏览器（即谷歌浏览器），默认的超时值是 5秒即可。这就是为什么你会在每次POST请求之前看到预先请求的请求，但是如果你迅速提交POST请求，那么你就不会看到额外的预先请求。

这是Chrome浏览器的特定功能吗？

是，存在差异浏览器之间如何实现飞行前缓存。 W3C规范并未详细说明在Web浏览器中构建飞行前高速缓存功能所需的一切。

I am making CORS request to a web service using jQuery $.ajax. As per standard there is a pre-flight request and then the actual POST request.

What I have noticed is, there are two requests everytime I try to make a web service call (one pre-flight and one actual POST request) only If there is a time interval between the two requests.

If I keep making the web service call successively without any time gap (like less than 1 second between two requests) then the pre-flight is missing.

How can I avoid this pre-flight request every time?

What is this time interval?

Is this something specific to Chrome browser?

解决方案

There are differences between browsers in how they implement pre-flight caching. Unfortunately the W3C spec alone does not explain the nuances you've observed in pre-flight caching.

For others reading this question, I'd like to explain when the OP says pre-flight request he is referring to the OPTIONS request that precedes a cross-origin POST request. The OPTIONS request is used to query an API and determine which HTTP methods are permissible for cross-origin requests. Typically, you'd expect to see this type of response to an OPTIONS request:

Access-Control-Allow-Origin: *
Access-Control-Allow-Credentials: true
Access-Control-Allow-Headers: Content-Type, X-Requested-With
Access-Control-Allow-Methods: POST, GET, OPTIONS, DELETE, PUT

Since you are working with Google Chrome, I will refer you to the applicable section of the Webkit source code:

https://github.com/WebKit/webkit/blob/master/Source/WebCore/loader/CrossOriginPreflightResultCache.cpp

The default pre-flight cache timeout is 5 seconds:

static const auto defaultPreflightCacheTimeout = std::chrono::seconds(5);

The maximum value is 5 minutes:

static const auto maxPreflightCacheTimeout = std::chrono::seconds(600);

The server can specify a timeout value for pre-flight requests using the Access-Control-Max-Age field in the response header, however the Webkit browser enforces a maximum timeout of 5 minutes.

To answer your questions:

How can I avoid this pre flight request every time?

You need to set Access-Control-Max-Age to 600 in the header of your API response to the OPTIONS request.

What is this time interval?

For Webkit browsers (i.e., Google Chrome) the default timeout value is 5 seconds. That is why you are seeing the pre-flight request before each POST request, but if you rapidly submit POST requests, then you do not see additional pre-flight requests.

Is this something specific to Chrome browser?

Yes, there are differences between browsers in how pre-flight caching is implemented. The W3C spec does not specify everything needed to build out pre-flight caching functionality in a web browser.

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