Warning

警告

Warning一般 HTTP 标头包含有关该消息的状态可能出现的问题的信息。Warning响应中可能会出现多个标题。

Warning 标题字段通常可以应用于任何消息，但某些警告代码是特定于高速缓存的，只能应用于响应消息。

Header type	General header
Forbidden header name	no

Warning: <warn-code> <warn-agent> <warn-text> [<warn-date>]

<警告码>一个三位警告号码。第一位数字表示是否Warning需要在验证后从存储的响应中删除。

<warn-agent>

添加Warning标题的服务器或软件的名称或假名（代理未知时可能为“ - ”）。

<warn-text> 描述错误的建议文本 <warn-date> 可选。如果Warning发送多个标题，请包含与Date标题匹配的日期。

iana.org 上的 HTTP 警告代码注册表定义了警告代码的命名空间。

Code	Text	Description
110	Response is Stale	A response provided by a cache is stale (the expiration time set for it has passed).
111	Revalidation Failed	An attempt to validate the response failed, due to an inability to reach the server.
112	Disconnected Operation	The cache is disconnected from the rest of the network.
113	Heuristic Expiration	Sent If a cache heuristically chose a freshness lifetime greater than 24 hours and the response's age is greater than 24 hours.
199	Miscellaneous Warning	Arbitrary, non-specific warning
214	Transformation Applied	Added by a proxy if it applies any transformation to the representation, such as changing the content-coding, media-type or the like.
299	Miscellaneous Warning	Same as 199, but indicating a persistent warning

Warning: 110 anderson/1.3.37 "Response is stale"

Date: Wed, 21 Oct 2015 07:28:00 GMT 
Warning: 112 - "cache down" "Wed, 21 Oct 2015 07:28:00 GMT"

Specification	Title
RFC 7234, section 5.5: Warning	Hypertext Transfer Protocol (HTTP/1.1): Caching

Feature	Chrome	Edge	Firefox	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)