Note:
Browsers don't support
delta encoding
with HTTP. This status code is sent back by custom servers used by specific clients.
In the context of delta encodings, the HTTP
226 IM Used
status code is set by the server to indicate that it is returning a
delta
to the
GET
request that it received.
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.
IM stands for
instance manipulations
the term used to describe an algorithm generating a
delta
.