Subject: Re: [PATCH 3/6] strbuf_getwholeline: use getc_unlocked

From: Jeff King <[email-masked]>
Date: Sun, 5 Apr 2015 01:27:33 -0400

On Sun, Apr 05, 2015 at 12:56:14AM -0400, Jeff King wrote:

> The big downside is that our input strings are no longer NUL-clean
> (reading "foo\0bar\n" would yield just "foo". I doubt that matters in
> the real world, but it does fail a few of the tests (e.g., t7008 tries
> to read a list of patterns which includes NUL, and we silently truncate
> the pattern rather than read in the NUL and barf).

So there is this trick:

diff --git a/strbuf.c b/strbuf.c
index f319d8d..5ceebb7 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -445,12 +445,13 @@ int strbuf_getwholeline(struct strbuf *sb, FILE *fp, int term)
 	strbuf_reset(sb);
 
 	if (term == '\n') {
+		long pos = ftell(fp);
 		strbuf_grow(sb, 256);
 		if (!fgets(sb->buf, sb->alloc - 1, fp)) {
 			strbuf_release(sb);
 			return EOF;
 		}
-		sb->len = strlen(sb->buf);
+		sb->len = ftell(fp) - pos;
 		if (sb->buf[sb->len - 1] == '\n')
 			return 0;
 	}

but much to my surprise it actually runs slower than the strlen version!
It also has a 32-bit overflow issue. There's fgetpos() as an
alternative, but fpos_t is an opaque type, and we might not be able to
do arithmetic on it (for that matter, I am not sure if arithmetic is
strictly guaranteed on ftell() results). POSIX gives us ftello(), which
returns an off_t. That would probably be fine.

The ftello() version seems slower than the strlen, but faster than
ftell(). Puzzling.

-Peff