Re: [PATCH v3] cat-file: skip expanding default format

> Hi Taylor,
>
> On 8 Mar 2022, at 17:30, Taylor Blau wrote:
>
>> On Tue, Mar 08, 2022 at 10:08:46PM +0000, John Cai via GitGitGadget wrote:
>>> diff --git a/builtin/cat-file.c b/builtin/cat-file.c
>>> index 7b3f42950ec..e2edba70b41 100644
>>> --- a/builtin/cat-file.c
>>> +++ b/builtin/cat-file.c
>>> @@ -351,6 +351,13 @@ static void print_object_or_die(struct batch_options *opt, struct expand_data *d
>>>  	}
>>>  }
>>>
>>> +static int print_default_format(char *buf, int len, struct expand_data *data)
>>> +{
>>> +	return xsnprintf(buf, len, "%s %s %"PRIuMAX"\n", oid_to_hex(&data->oid),
>>> +			 type_name(data->type),
>>> +			 (uintmax_t)*data->info.sizep);
>>> +}
>>
>> Two small nits here. It looks like the indentation on the second and
>> third lines is off a little bit, since we'd typically expect those to be
>> indented to the same margin as the first argument to xsnprintf().
>
> Thanks for bringing this up. I did have a question about indentation in this
> case. for the second line, I did try to indent it to align with buf. I attempted
> to do the same with the third line, but it's the ( that lines up with buf so
> optically it looks a little off.
>
>>
>> The other is that you're reading data->info.sizep by dereferencing it,
>> but we know that it points to data->size. So I think there it makes
>> sense to just read the value directly out of data->size, though note
>> that you'll still need the cast to uintmax_t since you're formatting it
>> with PRIuMAX.
>
> good point, I'll adjust this in the next version.
>
>>
>>> +
>>>  /*
>>>   * If "pack" is non-NULL, then "offset" is the byte offset within the pack from
>>>   * which the object may be accessed (though note that we may also rely on
>>> @@ -381,10 +388,16 @@ static void batch_object_write(const char *obj_name,
>>>  		}
>>>  	}
>>>
>>> -	strbuf_reset(scratch);
>>> -	strbuf_expand(scratch, opt->format, expand_format, data);
>>> -	strbuf_addch(scratch, '\n');
>>> -	batch_write(opt, scratch->buf, scratch->len);
>>> +	if (!opt->format) {
>>> +		char buf[1024];
>>> +		int len = print_default_format(buf, 1024, data);
>>> +		batch_write(opt, buf, len);
>>
>> Just curious (and apologies if this was discussed earlier and I missed
>> it), but: is there a reason that we have to use a scratch buffer here
>> that is separate from the strbuf we already have allocated?
>>
>> That would avoid a large-ish stack variable, but it means that the two
>> paths are a little more similar, and can share the batch_write call
>> outside of the if/else statement.
>
> This was holdover code from before. Looks like the scratch buffer gets passed
> in. Do you mean we don't need to allocate char buf[1024] and instead we can just
> use scratch and pass it into print_default_format?