Warning header has been deprecated; see
(https://github.com/httpwg/http-core/issues/139) and Warning: header &
stale-while-revalidate (https://github.com/whatwg/fetch/issues/913) for more
Warning HTTP header contains information
about possible problems with the status of the message. More than one
Warning header may appear in a response.
Warning header fields can, in general, be applied to any message. However, some warn-codes are specific to caches and can only be applied to response messages.
|Header type||Request header, Response header|
|Forbidden header name||no|
Warning: <warn-code> <warn-agent> <warn-text> [<warn-date>]
A three-digit warning number. The first digit indicates whether the
Warningis required to be deleted from a stored response after validation.
1xxwarn-codes describe the freshness or validation status of the response and will be deleted by a cache after deletion.
2xxwarn-codes describe some aspect of the representation that is not rectified by a validation and will not be deleted by a cache after validation unless a full response is sent.
The name or pseudonym of the server or software adding the
Warningheader (might be "-" when the agent is unknown).
An advisory text describing the error.
A date. This is optional. If more than one
Warningheader is sent, include a date that matches the
The HTTP Warn Codes registry at iana.org defines the namespace for warning codes.
|110||Response is Stale||The response provided by a cache is stale (the expiration time set for the response has passed).|
|111||Revalidation Failed||An attempt to validate the stale response failed due to an inability to reach the server.|
|112||Disconnected Operation||The cache is intentionally disconnected from the rest of the network.|
|113||Heuristic Expiration||A cache heuristically chose a freshness lifetime greater than 24 hours and the age of the response is greater than 24 hours.|
|199||Miscellaneous Warning||Arbitrary information that should be presented to a user or logged.|
|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 Persistent Warning||Arbitrary information that should be presented to a user or logged. This warn-code is similar to the warn-code 199 and additionally indicates 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"
|Hypertext Transfer Protocol (HTTP/1.1): Caching (HTTP/1.1)|
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