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HTTP_STATUS_IM_USED
This status belongs to HTTP Delta Encoding. It means the server applied one or more instance manipulations so the response can describe a change relative to a cached representation instead of sending the entire representation again.
Clients must understand the negotiated A-IM and related headers before using the payload. Treating a 226 body as a complete standalone document can produce corrupted content.
RFC 3229: Delta Encoding in HTTP
Operational meaning of HTTP 226 for HTTP_STATUS_IM_USED
HTTP 226 (HTTP_STATUS_IM_USED) is a successful response. AllStat records its meaning as “226 IM Used”. For HTTP_STATUS_IM_USED, interpret it with the request method, selected representation, response headers, and the specification or product that defines the code; the number alone does not prove that application work completed.
Client and server handling for HTTP_STATUS_IM_USED
- Verify what work the response representation says was completed; HTTP_STATUS_IM_USED can still describe asynchronous or partial handling.
- For HTTP_STATUS_IM_USED, use validators, location/status links, and application identifiers supplied by the server.
- For HTTP_STATUS_IM_USED, do not retry a non-idempotent request merely because the client did not understand the response body.
For telemetry, record HTTP 226, method, authority, route template rather than secrets, response headers relevant to caching or retry, latency, upstream identity, and whether the response originated at the application or an intermediary.
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