Re: [PATCH v2] strbuf: add and use strbuf_insertstr()

From: Eric Sunshine <sunshine@sunshineco.com>
To: "René Scharfe" <l.s.r@web.de>
Cc: Git Mailing List <git@vger.kernel.org>,
	Junio C Hamano <gitster@pobox.com>, Taylor Blau <me@ttaylorr.com>
Subject: Re: [PATCH v2] strbuf: add and use strbuf_insertstr()
Date: Sun, 9 Feb 2020 12:36:22 -0500	[thread overview]
Message-ID: <CAPig+cQdJ0NJSWZN-2ckeLB7RfU9GZ7LGvVX4y+Q1daPnW8WsA@mail.gmail.com> (raw)
In-Reply-To: <b31c46a8-380b-3528-27a5-a2dddacaf837@web.de>

On Sun, Feb 9, 2020 at 8:45 AM René Scharfe <l.s.r@web.de> wrote:
> Add a function for inserting a C string into a strbuf.  Use it
> throughout the source to get rid of magic string length constants and
> explicit strlen() calls.
>
> Like strbuf_addstr(), implement it as an inline function to avoid the
> implicit strlen() calls to cause runtime overhead.
>
> Signed-off-by: René Scharfe <l.s.r@web.de>
> ---
> diff --git a/mailinfo.c b/mailinfo.c
> @@ -570,7 +570,7 @@ static int check_header(struct mailinfo *mi,
>                 len = strlen("Content-Type: ");
>                 strbuf_add(&sb, line->buf + len, line->len - len);
>                 decode_header(mi, &sb);
> -               strbuf_insert(&sb, 0, "Content-Type: ", len);
> +               strbuf_insertstr(&sb, 0, "Content-Type: ");
>                 handle_content_type(mi, &sb);

Meh. We've already computed the length of "Content-Type: " a few lines
earlier, so taking advantage of that value when inserting the string
literal is perfectly sensible. Thus, I'm not convinced that this
change is an improvement.

Digging deeper, though, I have to wonder why this bothers inserting
"Content-Type: " at all. None of the other cases handled by
check_header() bother re-inserting the header, so why this one? I
thought it might be because handle_content_type() depends upon the
header being present, but from my reading, this does not appear to be
the case. handle_content_type() calls has_attr_value() and
slurp_attr() to examine the incoming line, but neither of those seem
to expect any sort of "<Header>: " either. Thus, it appears that the
insertion of "Content-Type: " is superfluous. If this is indeed the
case, then rather than converting this to strbuf_insertstr(), I could
see it being pulled out into a separate patch which merely removes the
strbuf_insert() call.