Re: How to use git attributes to configure server-side checks?

From: Michael Haggerty <mhagger@alum.mit.edu>
Date: Feb 17, 2012, 18:42 UTC
Message-ID: <4F3E9F86.3070802@alum.mit.edu>
In-Reply-To: <7vy5xh1whq.fsf@alter.siamese.dyndns.org>

On 09/21/2011 10:17 PM, Junio C Hamano wrote:

Show 14 quoted lines

> Michael Haggerty <mhagger@alum.mit.edu> writes:
>> I was thinking of using git attributes to configure a server-side
>> "update" hook that does some basic sanity checking before accepting a
>> push.  I thought I could do something like
>> [...]
>> I see that there is an (undocumented) API involving
>> git_attr_set_direction() that seems to let gitattributes to be read out
>> of the index instead of the working tree.  But I am still confused:
> 
> The words "server side" automatically mean that there should be no working
> tree, and where there is no working tree there should be no index, so the
> direction should not make any difference.  The attributes that are used to
> help whitespace checks should come from project.git/info/attributes in
> such a case [*...*].

I was just alerted by Scott Chacon's blog [1] to the fact that one can set GIT_INDEX_FILE to an arbitrary filename, thereby causing the index to be read/written from that file instead of $GIT_DIR/index. It occurred to me that this feature, along with the addition of "git check-attr --cached" in 1.7.8, can be used to give server-side access to the gitattributes for an arbitrary commit:

    GIT_INDEX_FILE="$(tempfile)"
    export GIT_INDEX_FILE
    git read-tree $COMMIT
    git check-attr --cached attr -- pathname
    ...
    rm "$GIT_INDEX_FILE"

Empirically it seems to work (and it is surprisingly fast).  The use of
a temporary file prevents simultaneous accesses to the repository from
stepping on each other.  This looks like a clean solution to my problem.
 Or is there some hidden pitfall in this approach?

Michael

[1] http://progit.org/2010/04/11/environment.html

-- 
Michael Haggerty
mhagger@alum.mit.edu
http://softwareswirl.blogspot.com/