Warning  

The Warning header is used to give a little more information about what happened during a request. It provides the server with a way to send additional information that is not in the status code or reason phrase. Several warning codes are defined in the HTTP/1.1 specification:

101 Response Is Stale

When a response message is known to be stale-for instance, if the origin server is unavailable for revalidation-this warning must be included.

111 Revalidation Failed

If a cache attempts to revalidate a response with an origin server and the revalidation fails because the cache cannot reach the origin server, this warning must be included in the response to the client.

112 Disconnected Operation

An informative warning; should be used if a cache's connectivity to the network is removed.

113 Heuristic Expiration

Caches must include this warning if their freshness heuristic is greater than 24 hours and they are returning a response with an age greater than 24 hours.

199 Miscellaneous Warning

Systems receiving this warning must not take any automated response; the message may and probably should contain a body with additional information for the user.

214 Transformation Applied

Must be added by any intermediate application, such as a proxy, if the application performs any transformation that changes the content encoding of the response.

299 Miscellaneous Persistent Warning

Systems receiving this warning must not take any automated reaction; the error may contain a body with more information for the user.

Type

Response header

Basic Syntax

Warning: 1# warning-value

Example

Warning: 113

 


Hypertext Transfer Protocol (HTTP)