Name
Warning
Synopsis
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 ...
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