Re: [RFC WIP PATCH 1/3] tag: factor out tag reading from write_tag_body()

[Junio C Hamano <gitster@pobox.com>]

Lucas Oshiro <lucasseikioshiro@gmail.com> writes:

> +/* 
> + * Returns the tag body of the given oid or NULL, in case of error. If size is
> + * not NULL it is assigned the body size in bytes (excluding the '\0').
> + */
> +static char *get_tag_body(const struct object_id *oid, size_t *size) 
>  {
> +	unsigned long buf_size;
>  	enum object_type type;
> +	char *buf, *sp, *tag_body;
> +	size_t tag_body_size, signature_offset;
>  
> +	buf = read_object_file(oid, &type, &buf_size);
>  	if (!buf)
> +		return NULL;
>  	/* skip header */
>  	sp = strstr(buf, "\n\n");
>  
> +	if (!sp || !buf_size || type != OBJ_TAG) {
>  		free(buf);
> +		return NULL;
>  	}

Returning early when !buf_size before even attempting to strstr
would be cleaner to read, i.e.

	buf = read_object_file(...);
	if (!buf || !buf_size) {
		free(buf);
		return NULL;
	}
	body = strstr(buf, "\n\n");

FWIW, the type check that is done after this point could also be a
part of the early return, as there is no point scanning for the end
of object header part if the object is not a tag (e.g. if it were a
blob, there is no "header part" and scanning for a blank line is
meaningless).
	
>  	sp += 2; /* skip the 2 LFs */
> +	signature_offset = parse_signature(sp, buf + buf_size - sp);
> +	sp[signature_offset] = '\0';
>  
> +	/* detach sp from buf */
> +	tag_body_size = strlen(sp) + 1;
> +	tag_body = xmalloc(tag_body_size);
> +	xsnprintf(tag_body, tag_body_size, "%s", sp);

Isn't this essentially

	tag_body = xstrdup(sp);
        tag_body_size = signature_offset;

(my arith may be off by one or two, but does a separate
tag_body_size need to exist?)

>  	free(buf);
> +	if (size)
> +		*size = tag_body_size - 1; /* exclude '\0' */
> +	return tag_body;
> +}
> +
> +static void write_tag_body(int fd, const struct object_id *oid)
> +{
> +	size_t size;
> +	const char *tag_body = get_tag_body(oid, &size);
> +
> +	if (!tag_body) {
> +		warning("failed to get tag body for %s", oid->hash);

I do not think the original gives any such warning.

 - Do we want to be unconditionally noisy this way?
 - Should this be a fatal error?  If not, why?
 - Should the message be translatable?

As an interface, is it sensible to force any and all callers of
get_tag_body() to supply a pointer to &size?  Is the returned value
always a NUL-terminated string?  I suspect that people would find it
a more natural interface if its were like:

	const char *body = get_tag_body(oid);

	if (!body)		
		...;

	if (this caller needs size) {
		size_t body_size = strlen(body);
		... use both body and body_size ...
		write_or_die(fd, body, body_size);
	} else {
		... just use body ...
		printf("%s", body);
	}
	
> +		return;
> +	}
> +	printf("tag_body: <%s>\n", tag_body);
> +	write_or_die(fd, tag_body, size);

WTH is this double writing?

>  }
>  
>  static int build_tag_object(struct strbuf *buf, int sign, struct object_id *result)