Re: svn commit: r1241097 - in /subversion/trunk/subversion: libsvn_client/repos_diff.c libsvn_delta/compat.c libsvn_fs_base/tree.c libsvn_fs_fs/tree.c libsvn_wc/externals.c libsvn_wc/update_editor.c

On Mon, Feb 6, 2012 at 1:28 PM, Greg Stein <gstein_at_gmail.com> wrote:
> On Mon, Feb 6, 2012 at 12:48,  <hwright_at_apache.org> wrote:
>> Author: hwright
>> Date: Mon Feb  6 17:48:36 2012
>> New Revision: 1241097
>>
>> URL: http://svn.apache.org/viewvc?rev=1241097&view=rev
>> Log:
>> Ev2 shims: Truthfully report our base checksum as being that of the empty
>> stream.
>>
>> Note: This breaks several assumptions in various delta-editor receivers about
>> the validity of this checksum.  These have been patched to ignore the checksum
>> if it is that of the empty stream.  This will not affect correctness, as the
>> final checksum, as supplied by close_file() is still used to detect corruption,
>> and it hasn't changed.
>
> How does this even work? Sure, the checksum isn't checked, but the
> delta-editor receiver is going to choose the wrong base contents to
> apply the delta against.

Huh? The delta-editor receiver isn't using this to choose any base
contents, it's simply using it as some kind of intermediate
verification step.

Before this change, we just passed a NULL checksum, which was *always*
ignored, and everything Just Worked. With this change, we started
being honest, and various pieces of the system didn't appreciate that
honesty.

-Hyrum

-- 
uberSVN: Apache Subversion Made Easy
http://www.uberSVN.com/