Request HeaderIf-Range
Beispiel:
If-Range: Sat, 29 Oct 1994 19:43:31 GMT
Original Beschreibung (engl.):
If a client has a partial copy of an entity in its cache, and wishes
to have an up-to-date copy of the entire entity in its cache, it
could use the Range request-header with a conditional GET (using
either or both of If-Unmodified-Since and If-Match.) However, if the
condition fails because the entity has been modified, the client
would then have to make a second request to obtain the entire current
entity-body.
The If-Range header allows a client to "short-circuit" the second
request. Informally, its meaning is `if the entity is unchanged, send
me the part(s) that I am missing; otherwise, send me the entire new
entity'.
If-Range = "If-Range" ":" ( entity-tag | HTTP-date )
If the client has no entity tag for an entity, but does have a Last-
Modified date, it MAY use that date in an If-Range header. (The
server can distinguish between a valid HTTP-date and any form of
entity-tag by examining no more than two characters.) The If-Range
header SHOULD only be used together with a Range header, and MUST be
ignored if the request does not include a Range header, or if the
server does not support the sub-range operation.
If the entity tag given in the If-Range header matches the current
entity tag for the entity, then the server SHOULD provide the
specified sub-range of the entity using a 206 (Partial content)
response. If the entity tag does not match, then the server SHOULD
return the entire entity using a 200 (OK) response.
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