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Toshiki's HTTP

226 IM Used

IM Used


The HTTP 226 IM Used response status, in the context of delta encodings, is a status code set by the server to indicate that it is returning a delta to the GET request that it received. IM stands for Instance Manipulations, the term used to describe an algorithm generating a delta.

With delta encoding a server responds to GET requests with differences (called deltas) relative to a given base document (rather than the current document). The client uses the A-IM: HTTP header to indicate which differencing algorithm to use and the If-None-Match: header to hint the server about the last version it got. The server generates a delta, sending it back in an HTTP response with the 226 status code and containing the IM: (with the name of the algorithm used) and Delta-Base: (with the ETag matching the base document associated to the delta) HTTP headers.