midx.c: write MIDX filenames to strbuf

To ask for the name of a MIDX and its corresponding .rev file, callers
invoke get_midx_filename() and get_midx_rev_filename(), respectively.
These both invoke xstrfmt(), allocating a chunk of memory which must be
freed later on.

This makes callers in pack-bitmap.c somewhat awkward. Specifically,
midx_bitmap_filename(), which is implemented like:

    return xstrfmt("%s-%s.bitmap",
                   get_midx_filename(midx->object_dir),
                   hash_to_hex(get_midx_checksum(midx)));

this leaks the second argument to xstrfmt(), which itself was allocated
with xstrfmt(). This caller could assign both the result of
get_midx_filename() and the outer xstrfmt() to a temporary variable,
remembering to free() the former before returning. But that involves a
wasteful copy.

Instead, get_midx_filename() and get_midx_rev_filename() take a strbuf
as an output parameter. This way midx_bitmap_filename() can manipulate
and pass around a temporary buffer which it detaches back to its caller.

That allows us to implement the function without copying or open-coding
get_midx_filename() in a way that doesn't leak.

Update the other callers of get_midx_filename() and
get_midx_rev_filename() accordingly.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/pack-bitmap.c b/pack-bitmap.c
index f47a0a7..3f60342 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -292,9 +292,12 @@ static int load_bitmap_entries_v1(struct bitmap_index *index)
 
 char *midx_bitmap_filename(struct multi_pack_index *midx)
 {
-	return xstrfmt("%s-%s.bitmap",
-		       get_midx_filename(midx->object_dir),
-		       hash_to_hex(get_midx_checksum(midx)));
+	struct strbuf buf = STRBUF_INIT;
+
+	get_midx_filename(&buf, midx->object_dir);
+	strbuf_addf(&buf, "-%s.bitmap", hash_to_hex(get_midx_checksum(midx)));
+
+	return strbuf_detach(&buf, NULL);
 }
 
 char *pack_bitmap_filename(struct packed_git *p)
@@ -324,10 +327,12 @@ static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
 	}
 
 	if (bitmap_git->pack || bitmap_git->midx) {
+		struct strbuf buf = STRBUF_INIT;
+		get_midx_filename(&buf, midx->object_dir);
 		/* ignore extra bitmap file; we can only handle one */
-		warning("ignoring extra bitmap file: %s",
-			get_midx_filename(midx->object_dir));
+		warning("ignoring extra bitmap file: %s", buf.buf);
 		close(fd);
+		strbuf_release(&buf);
 		return -1;
 	}