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From: Jeff King <peff@peff.net>
To: Taylor Blau <me@ttaylorr.com>
Cc: git@vger.kernel.org, chriscool@tuxfamily.org, gitster@pobox.com,
	szeder.dev@gmail.com
Subject: Re: [PATCH v3 4/4] upload-pack.c: introduce 'uploadpackfilter.tree.maxDepth'
Date: Fri, 31 Jul 2020 17:36:04 -0400	[thread overview]
Message-ID: <20200731213604.GA1457058@coredump.intra.peff.net> (raw)
In-Reply-To: <20200731212905.GE3409@syl.lan>

On Fri, Jul 31, 2020 at 05:29:05PM -0400, Taylor Blau wrote:

> > > @@ -1029,6 +1040,11 @@ static void die_if_using_banned_filter(struct upload_pack_data *data)
> > >
> > >  	strbuf_addf(&buf, "git upload-pack: filter '%s' not supported",
> > >  		    list_object_filter_config_name(banned->choice));
> > > +	if (banned->choice == LOFC_TREE_DEPTH &&
> > > +	    data->tree_filter_max_depth != ULONG_MAX)
> > > +		strbuf_addf(&buf, _(" (maximum depth: %lu, but got: %lu)"),
> > > +			    data->tree_filter_max_depth,
> > > +			    banned->tree_exclude_depth);
> >
> > Hmm. So I see now why you wanted to go with the strbuf in the earlier
> > patch. This does still feel awkward, though. You check "is it allowed"
> > in an earlier function, we get "nope, it's not allowed", and now we have
> > to reimplement the check here. That seems like a maintenance burden.
> 
> I'm not sure that I follow. Is the earlier function that you're
> referring to 'banned_filter'? If so, the only use of that function is
> within 'die_if_using_banned_filter'. 'banned_filter' exists only insofar
> as to answer the question "return me the first banned filter, if one
> exists, or NULL otherwise".
> 
> Then, dying here is as simple as (1) lookup the banned filter, and (2)
> check if it's NULL or not.
> 
> If you're referring to 'allows_filter_choice', I guess I see what you're
> getting it, but to be honest I'm not sure if I'm buying it.

Yeah, it's allows_filter_choice() that knows "if it's a tree we must
check the depth". And now die_if_using_banned_filter() needs to know
that, too. The policy is implemented twice.

I do appreciate that the way you've written it means that if somebody
forgets to update die_if_using_banned_filter() to match the logic in
allows_filter_choice(), we'd at least still die, just with a less good
error message. But it seems better still not to require the two to match
in the first place.

> If we were
> to combine 'allows_filter_choice', 'banned_filter', and
> 'die_if_using_banned_filter' into one function that traversed the filter
> tree and 'die()'d as soon as it got to a banned one, that function would
> have to know how to:
> 
>   1. Recurse through the tree when it hits a LOFC_COMBINE node.
> 
>   2. At each node, translate the filter->choice into the appropriate key
>   name, look it up, and then figure out how to interpret its allowed
>   status (including falling back to the default if unspecified).
> 
>   3. And, it would have to figure out how to format the message at each
>   step.
> 
> (3) I think is made easier, since we know what message to format based
> on whether or not we're in the 'opts->choice == LOFC_TREE_DEPTH' arm or
> not. But, there are two more things that we now have to cram into that
> same function.

You can still split those things into functions; see the patch I posted.

> Maybe I'm being too strict an adherent to having simpler functions, but
> I'm failing to see how to combine these in a way that's cleaner than
> what's written here.

To me this is less about "clean" and more about "don't ever duplicate
policy code". I don't mind duplicating boilerplate, but introducing a
place where somebody touching function X must remember to also touch Y
(and gets no compiler support to remind them) is a bad thing. I guess
you can call that "clean", but I'd take longer or more functions as a
tradeoff to avoid that.

My suggested patch does introduce more side effects. I think that's OK
because there really is only a single caller here. But if you wanted it
cleaner, then I think having allows_filter_choice() fill out an error
strbuf would eliminate my concern without drastically altering the flow
of your code.

-Peff

  reply	other threads:[~2020-07-31 21:36 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-23  1:48 [PATCH v2 0/4] upload-pack: custom allowed object filters Taylor Blau
2020-07-23  1:48 ` [PATCH v2 1/4] list_objects_filter_options: introduce 'list_object_filter_config_name' Taylor Blau
2020-07-23  1:49 ` [PATCH v2 2/4] upload-pack.c: allow banning certain object filter(s) Taylor Blau
2020-07-23  1:49 ` [PATCH v2 3/4] upload-pack.c: pass 'struct list_objects_filter_options *' Taylor Blau
2020-07-23  1:49 ` [PATCH v2 4/4] upload-pack.c: introduce 'uploadpackfilter.tree.maxDepth' Taylor Blau
2020-07-23 20:43 ` [PATCH v2 0/4] upload-pack: custom allowed object filters SZEDER Gábor
2020-07-24 16:51   ` Taylor Blau
2020-07-24 19:51     ` Jeff King
2020-07-27 14:25       ` Taylor Blau
2020-07-27 19:34     ` SZEDER Gábor
2020-07-27 19:36       ` Taylor Blau
2020-07-27 19:42         ` Jeff King
2020-07-27 19:59         ` SZEDER Gábor
2020-07-27 20:03           ` Taylor Blau
2020-07-31 20:26 ` [PATCH v3 " Taylor Blau
2020-07-31 20:26   ` [PATCH v3 1/4] list_objects_filter_options: introduce 'list_object_filter_config_name' Taylor Blau
2020-07-31 20:26   ` [PATCH v3 2/4] upload-pack.c: allow banning certain object filter(s) Taylor Blau
2020-07-31 20:54     ` Jeff King
2020-07-31 21:20       ` Taylor Blau
2020-07-31 20:26   ` [PATCH v3 3/4] upload-pack.c: pass 'struct list_objects_filter_options *' Taylor Blau
2020-07-31 20:26   ` [PATCH v3 4/4] upload-pack.c: introduce 'uploadpackfilter.tree.maxDepth' Taylor Blau
2020-07-31 21:01     ` Jeff King
2020-07-31 21:22       ` Jeff King
2020-07-31 21:30         ` Taylor Blau
2020-07-31 21:29       ` Taylor Blau
2020-07-31 21:36         ` Jeff King [this message]
2020-07-31 21:43           ` Jeff King
2020-08-03 18:00 ` [PATCH v4 0/3] upload-pack: custom allowed object filters Taylor Blau
2020-08-03 18:00   ` [PATCH v4 2/3] upload-pack.c: allow banning certain object filter(s) Taylor Blau
2020-08-03 18:00   ` [PATCH v4 1/3] list_objects_filter_options: introduce 'list_object_filter_config_name' Taylor Blau
2020-08-03 18:00   ` [PATCH v4 3/3] upload-pack.c: introduce 'uploadpackfilter.tree.maxDepth' Taylor Blau
2020-08-04  0:37   ` [PATCH v4 0/3] upload-pack: custom allowed object filters Jeff King

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