Subject: Re: [PATCH v3 4/4] upload-pack.c: introduce 'uploadpackfilter.tree.maxDepth'

From: Taylor Blau <[email-masked]>
Date: Fri, 31 Jul 2020 17:30:38 -0400

On Fri, Jul 31, 2020 at 05:22:43PM -0400, Jeff King wrote:
> On Fri, Jul 31, 2020 at 05:01:14PM -0400, Jeff King wrote:
>
> > 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 think a more natural flow would be either:
> >
> >   - the "is it allowed" functions calls immediately into the function
> >     that sends the error and dies (this might need a conditional if
> >     there's a caller who doesn't want to die; I didn't check)
> >
> > or
> >
> >   - on failure it populates an error buffer itself, which the caller can
> >     then pass along as it sees fit
>
> The first one is easy to do, because there's no other caller. Worth it?
>
> -- >8 --
> diff --git a/upload-pack.c b/upload-pack.c
> index 131445b212..574a447d5c 100644
> --- a/upload-pack.c
> +++ b/upload-pack.c
> @@ -992,62 +992,63 @@ static int process_deepen_not(const char *line, struct string_list *deepen_not,
>  	return 0;
>  }
>
> -static int allows_filter_choice(struct upload_pack_data *data,
> -				struct list_objects_filter_options *opts)
> +/* probably this helper could be used in lots more places */
> +NORETURN __attribute__((format(printf,2,3)))
> +static void send_err_and_die(struct upload_pack_data *data,
> +			     const char *fmt, ...)
> +{
> +	struct strbuf buf = STRBUF_INIT;
> +	va_list ap;
> +
> +	/* yuck, buf not necessary if we had va_list versions of our helpers */
> +	va_start(ap, fmt);
> +	strbuf_vaddf(&buf, fmt, ap);
> +	va_end(ap);
> +
> +	packet_writer_error(&data->writer, "%s", buf.buf);
> +	die("%s", buf.buf);
> +}
> +
> +static void check_one_filter(struct upload_pack_data *data,
> +			     struct list_objects_filter_options *opts)
>  {
>  	const char *key = list_object_filter_config_name(opts->choice);
>  	struct string_list_item *item = string_list_lookup(&data->allowed_filters,
>  							   key);
> -	int allowed = -1;
> +	int allowed;
>  	if (item)
>  		allowed = (intptr_t) item->util;
> +	else
> +		allowed = data->allow_filter_fallback;
>
> -	if (allowed != 0 &&
> -	    opts->choice == LOFC_TREE_DEPTH &&
> -	    opts->tree_exclude_depth > data->tree_filter_max_depth)
> -		return 0;
> +	if (!allowed)
> +		send_err_and_die(data, "filter '%s' not supported",
> +				 list_object_filter_config_name(opts->choice));
>
> -	if (allowed > -1)
> -		return allowed;
> -	return data->allow_filter_fallback;
> +	if (opts->choice == LOFC_TREE_DEPTH &&
> +	    opts->tree_exclude_depth > data->tree_filter_max_depth)
> +		send_err_and_die(data,
> +				 "tree filter allows max depth %lu, but got %lu",
> +				 data->tree_filter_max_depth,
> +				 opts->tree_exclude_depth);
>  }
>
> -static struct list_objects_filter_options *banned_filter(
> -	struct upload_pack_data *data,
> -	struct list_objects_filter_options *opts)
> +static void check_filter_recurse(struct upload_pack_data *data,
> +				 struct list_objects_filter_options *opts)
>  {
>  	size_t i;
>
> -	if (!allows_filter_choice(data, opts))
> -		return opts;
> +	check_one_filter(data, opts);
>
>  	if (opts->choice == LOFC_COMBINE)
>  		for (i = 0; i < opts->sub_nr; i++) {
> -			struct list_objects_filter_options *sub = &opts->sub[i];
> -			if (banned_filter(data, sub))
> -				return sub;
> +			check_filter_recurse(data, &opts->sub[i]);
>  		}
> -	return NULL;
>  }
>
>  static void die_if_using_banned_filter(struct upload_pack_data *data)
>  {
> -	struct list_objects_filter_options *banned = banned_filter(data,
> -								   &data->filter_options);
> -	struct strbuf buf = STRBUF_INIT;
> -	if (!banned)
> -		return;
> -
> -	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);
> -
> -	packet_writer_error(&data->writer, "%s\n", buf.buf);
> -	die("%s", buf.buf);
> +	check_filter_recurse(data, &data->filter_options);
>  }
>
>  static void receive_needs(struct upload_pack_data *data,

I think that we crossed emails, but I'm still not convinced that this is
any cleaner than what I wrote. Yes, it's a maintenance problem if we add
more filter-specific logic like what we have in the LOFC_TREE_DEPTH
case, but I feel like we're bending over backwards in the meantime to
accommodate a problem that we don't have.

Thanks,
Taylor