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

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

Michael Haggerty [off-list ref] writes:

quoted

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/