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Re: enforcing LF-normalization for svn:eol-style=native files (issue #4065)

From: Branko Čibej <brane_at_wandisco.com>
Date: Mon, 10 Dec 2012 11:51:08 +0100

On 10.12.2012 11:31, Daniel Shahaf wrote:
> Branko Čibej wrote on Mon, Dec 10, 2012 at 00:26:20 +0100:
>> On 10.12.2012 00:08, Johan Corveleyn wrote:
>>> On Sun, Dec 9, 2012 at 11:43 PM, Daniel Shahaf <d.s_at_daniel.shahaf.name> wrote:
>>>> Johan Corveleyn wrote on Sun, Dec 09, 2012 at 21:15:24 +0100:
>>>>> 2) Am I the only one who wants to protect his repository against this
>>>>> corruption? Judging from [1], I don't think so. It doesn't make sense
>>>>> that everyone starts writing this pre-commit hook, for something that
>>>>> IMHO is an obvious anti-corruption protection. I think every
>>>>> repository out there deserves to be protected against this.
>>>>>
>>>> FWIW, I suggested a hook because you could implement that in about
>>>> 5 minutes, whereas doing a C code change would take at least 10 times
>>>> that (and several weeks if you have to wait for it to appear in a 1.7.x
>>>> release that you can install at $WORK). I won't object to C code
>>>> verifying the svn:eol-style invariant.
>>> Thanks. And your pre-commit hook example is much appreciated.
>>>
>>> For the moment I get the impression that it's not really doable /
>>> desirable to implement this in the repository. At least until now
>>> no-one has suggested how it could be done, and I don't know enough
>>> myself about the server-side / back-end to figure it out :-).
>> The first obstacle is that the server does not interpret properties.[1]
>> Therefore, you'd have to implement this check at transaction-commit
>> time, because there's no earlier point where you're guaranteed to have
>> all node properties at their final values. This implies that the time to
>> reject a commit would be proportional to the size of the commit (which
>> isn't the case when it comes to conflict detection).
> Can't you do what stefan2 suggested, but in libsvn_repos? The repos
> layer commit editor would remember for each file whether its textdelta
> has added a new 0x0D byte, then at close_edit() it would iterate all
> files in the commit --- and for each file only compare its svn:eol-style
> property to the by-now-precomputed "did it it contain a 0x0D" bit.
>
> I'm not sure how efficient it would be to parse for 0x0D's in
> libsvn_repos, though. Maybe we should make this optional.

It's not enough to just look for \r in the delta stream. Certainly
wouldn't help with historically broken files.

Moreover, if libsvn_repos started looking at svn:eol-style, that'd only
make sense if you verified all normalizations, not just "native". And
why should it just be svn:eol-style, when svn:keywords has potentially
the same problem? Eventually you start verifying everything that affects
file contents.

Maybe that's a good idea, but /why/ put it in libsvn_repos when it's
much easier and cleaner to just provide some standard hooks, written in
C and distributed with releases, that the admin plug in if she feels
like it? Surely that's what hooks are for.

-- Brane

-- 
Branko Čibej
Director of Subversion | WANdisco | www.wandisco.com
Received on 2012-12-10 11:51:49 CET

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