fill_sha1_file: write into a strbuf

It's currently the responsibility of the caller to give
fill_sha1_file() enough bytes to write into, leading them to
manually compute the required lengths. Instead, let's just
write into a strbuf so that it's impossible to get this
wrong.

The alt_odb caller already has a strbuf, so this makes
things strictly simpler. The other caller, sha1_file_name(),
uses a static PATH_MAX buffer and dies when it would
overflow. We can convert this to a static strbuf, which
means our allocation cost is amortized (and as a bonus, we
no longer have to worry about PATH_MAX being too short for
normal use).

This does introduce some small overhead in fill_sha1_file(),
as each strbuf_addchar() will check whether it needs to
grow. However, between the optimization in fec501d
(strbuf_addch: avoid calling strbuf_grow, 2015-04-16) and
the fact that this is not generally called in a tight loop
(after all, the next step is typically to access the file!)
this probably doesn't matter. And even if it did, the right
place to micro-optimize is inside fill_sha1_file(), by
calling a single strbuf_grow() there.

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

sha1_file.c

@@ -172,36 +172,28 @@ enum scld_error safe_create_leading_directories_const(const char *path)
 	return result;
 }
 
-static void fill_sha1_path(char *pathbuf, const unsigned char *sha1)
+static void fill_sha1_path(struct strbuf *buf, const unsigned char *sha1)
 {
 	int i;
 	for (i = 0; i < 20; i++) {
 		static char hex[] = "0123456789abcdef";
 		unsigned int val = sha1[i];
-		*pathbuf++ = hex[val >> 4];
-		*pathbuf++ = hex[val & 0xf];
+		strbuf_addch(buf, hex[val >> 4]);
+		strbuf_addch(buf, hex[val & 0xf]);
 		if (!i)
-			*pathbuf++ = '/';
+			strbuf_addch(buf, '/');
 	}
-	*pathbuf = '\0';
 }
 
 const char *sha1_file_name(const unsigned char *sha1)
 {
-	static char buf[PATH_MAX];
-	const char *objdir;
-	int len;
+	static struct strbuf buf = STRBUF_INIT;
 
-	objdir = get_object_directory();
-	len = strlen(objdir);
+	strbuf_reset(&buf);
+	strbuf_addf(&buf, "%s/", get_object_directory());
 
-	/* '/' + sha1(2) + '/' + sha1(38) + '\0' */
-	if (len + 43 > PATH_MAX)
-		die("insanely long object directory %s", objdir);
-	memcpy(buf, objdir, len);
-	buf[len] = '/';
-	fill_sha1_path(buf + len + 1, sha1);
-	return buf;
+	fill_sha1_path(&buf, sha1);
+	return buf.buf;
 }
 
 struct strbuf *alt_scratch_buf(struct alternate_object_database *alt)
@@ -213,14 +205,8 @@ struct strbuf *alt_scratch_buf(struct alternate_object_database *alt)
 static const char *alt_sha1_path(struct alternate_object_database *alt,
 				 const unsigned char *sha1)
 {
-	/* hex sha1 plus internal "/" */
-	size_t len = GIT_SHA1_HEXSZ + 1;
 	struct strbuf *buf = alt_scratch_buf(alt);
-
-	strbuf_grow(buf, len);
-	fill_sha1_path(buf->buf + buf->len, sha1);
-	strbuf_setlen(buf, buf->len + len);
-
+	fill_sha1_path(buf, sha1);
 	return buf->buf;
 }