Comment 5 for bug 1279076

Reviewed: https://review.openstack.org/73162
Committed: https://git.openstack.org/cgit/openstack/swift/commit/?id=1f67eb7403e6000840c44ec702c406f177ea1942
Submitter: Jenkins
Branch: master

commit 1f67eb7403e6000840c44ec702c406f177ea1942
Author: Samuel Merritt <email address hidden>
Date: Wed Feb 12 18:29:12 2014 -0800

    Support If-[None-]Match for object HEAD, SLO, and DLO

    I moved the checking of If-Match and If-None-Match out of the object
    server's GET method and into swob so that everyone can use it. The
    interface is similar to the Range handling; make a response with
    conditional_response=True, and you get handing of If-Match and
    If-None-Match.

    Since the only users of conditional_response are object GET, object
    HEAD, SLO, and DLO, this has the effect of adding support for If-Match
    and If-None-Match to just the latter three places and nowhere
    else. This makes object GET and HEAD consistent for any kind of
    object, large or small.

    This also fixes a bug where various conditional headers (If-*) were
    passed through to the object server on segment requests, which could
    cause segment requests to fail with a 304 or 412 response. Now only
    certain headers are copied to the segment requests, and that doesn't
    include the conditional ones, so they can't goof up the segment
    retrieval.

    Note that I moved SegmentedIterable to swift.common.request_helpers
    because it sprouted a transitive dependency on swob, and leaving it in
    utils caused a circular import.

    Bonus fix: unified the handling of DiskFileQuarantined and
    DiskFileNotFound in object server GET and HEAD. Now in either case, a
    412 will be returned if the client said "If-Match: *". If not, the
    response is a 404, just like before.

    Closes-Bug: 1279076
    Closes-Bug: 1280022
    Closes-Bug: 1280028

    Change-Id: Id2ee78346244d516b980202e990aa38ce6812de5