Dell DX6004S DX Object Storage Application Guide - Page 74
entity-tag by looking for double quotes. The If-Range header should only be used together with
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The value of the header can be either a single quoted string (possibly with some ignored flags outside the quotation marks) or an HTTP-date string (unquoted). Examples of If-Range request headers: If-Range: "508941dc9b52243f64d964b058354b76" If-Range: W/"508941dc9b52243f64d964b058354b76" If-Range: Tue, 07 Jul 2009 16:25:24 GMT If a client has a partial copy of an object in its cache, and wishes to have an up-to-date copy of the entire object 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 an anchor stream has been updated, the client would then have to make a second request to obtain the entire current object. The If-Range header allows a client to "short-circuit" the second request. Informally, its meaning is `if the object is unchanged, send me the part(s) that I am missing; otherwise, send me the entire object'. If the client has no entity tag for an object, but does have a Last-Modified date, it may use that date in an If-Range header. DX Storage can distinguish between a valid HTTP-date and any form of entity-tag by looking for double quotes. The If-Range header should only be used together with a Range header, and will be ignored if the request does not include a Range header. If the entity tag given in the If-Range header matches the current primary UUID of the object, or the HTTP-date given is not before the Last-Modified date of the object, then DX Storage will provide the specified sub-range of the object using a 206 Partial content response. If the entity tag does not match, then DX Storage will return the entire object using a 200 OK response. Copyright © 2010 Caringo, Inc. All rights reserved 69 Version 5.0 December 2010