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From:   Junio C Hamano <gitster@pobox.com>
To:     Taylor Blau <me@ttaylorr.com>
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        Elijah Newren <newren@gmail.com>, git@vger.kernel.org
Subject: Re: [PATCH v3] bulk-checkin: only support blobs in index_bulk_checkin
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Taylor Blau <me@ttaylorr.com> writes:

> I am not sure that I follow. If we have an address in memory from which
> we want to stream raw bytes directly to the packfile, that should work
> for all objects regardless of type, no?

For a single hash world, yes.  For keeping track of "the other hash"
and correspondence, you need to (1) interpret the contents of the
object (e.g., if you received a tree contents for SHA-1 repository,
you'd need to split them into tree entries and know which parts of
the bytestream are SHA-1 hashes of the tree contebnts), (2) come
up with the corresponding tree contents in the SHA-256 world (you
should be able to do that now you know SHA-1 names of the objects
directly referred to by the tree) and hash that using SHA-256, and
(3) remember the SHA-1 and the SHA-256 name correspondence of the
tree object you just hashed, in addition to the usual (4) hashing
the contents using SHA-1 hash algorithm without caring what the byte
stream represents.