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watak

If-Unmodified-Since请求的HTTP标头发出请求的条件:服务器会发送回所请求的资源,或者接受它的情况下POST或其他非安全的方法,只要它没有被最后给定的日期之后修改。如果请求在给定日期之后被修改,则该响应将是412(先决条件失败)错误。

有两种常见用例:

  • 像非安全方法一样POST,它可以用来实现积极并发控制,就像一些维基所做的那样:如果存储文档在检索原始文档后被修改,则版本将被拒绝。

  • 结合具有If-Range标题的范围请求,可以使用它来确保请求的新片段来自未修改的文档。

Header type

Request header

Forbidden header name

no

句法

If-Unmodified-Since: <day-name>, <day> <month> <year> <hour>:<minute>:<second> GMT

指令

<day-name>“星期一”,“星期二”,“星期三”,“星期四”,“星期五”,“星期六”或“太阳”之一(区分大小写)。 “04”或“23”<月>“Jan”,“Feb”,“Mar”,“Apr”,“May”,“Jun”,“Jul”,“Aug”,“Sep”,“十进制“,”十一月“,”十二月“(区分大小写)<year> 4位数年份编号,例如”1990“或”2016“。<小时> 2位数小时编号,例如”09“或”23“分钟> 2位数分钟数,例如“04”或“59”。<秒> 2位数秒数,例如“04”或“59”。GMT

格林威治标准时间。HTTP 日期总是以 GMT 表示,从不以本地时间表示。

例子

If-Unmodified-Since: Wed, 21 Oct 2015 07:28:00 GMT

产品规格

Specification

Title

RFC 7232, section 3.4: If-Unmodified-Since

Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests

浏览器兼容性

Feature

Chrome

Firefox

Edge

Internet Explorer

Opera

Safari

Basic Support

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

Feature

Android

Chrome for Android

Edge mobile

Firefox for Android

IE mobile

Opera Android

iOS Safari

Basic Support

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

请参阅

  • If-Unmodified-since

  • If-Match

  • If-None-Match

  • If-Range

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