From: Matthieu Moy <matthieu.moy@imag.fr>
Date: Fri, 16 Feb 2007 17:14:51 GMT
Subject: Re: suggested feature: someone mails me a blob, git please tell me what it is
Message-ID: <vpqr6sq58j8.fsf@olympe.imag.fr>
In-Reply-To: <3c6c07c20702160823j316c52f4pe4cf5ca8a882e194@mail.gmail.com>

"Mike Coleman" <tutufan@gmail.com> writes:

> It seems like it should be fairly easy, given a blob (the file), for
> git to describe what it knows about it.  For example, it could provide
> a list of commits that it's a part of, etc.  It'd be *really* nice if
> only the output of the sha1sum command on the blob were needed. 

"git cat-file -p" does almost this : given the sha1sum for a blob, it
will give the header and the content of the blob ...

> (I can't recall exactly how git's blob SHA1's are computed--maybe
> this isn't feasible.)

... but this is where it doesn't work :
http://www.kernel.org/pub/software/scm/git/docs/v1.5.0/git.html#Discussion
explains that the sha1sum used by git is the one of the blob _plus_
its header, so it's not the one you get with "sha1sum file".

But it should be possible to recompute the git sha1sum by recomputing
the magic formula sha1sum(<ascii type without space> + <space> +
<ascii decimal size> + <byte\0> + <binary object data>).

-- 
Matthieu