{fetch,receive}-pack: skip sha-1 integrity test on objects from new packnd/optim-connected

When we fetch or push, usually "git rev-list --verify-objects --not
--all --stdin" is used to make sure that all objects between existing
refs and new refs are good. This means no gaps in between, all objects
are well-formed, object content agrees with its sha-1 signature.

For the last one, --verify-objects calls check_sha1_signature() via
parse_object(). check_sha1_signature() is an expensive operation,
especially when new refs are far away from existing ones because all
objects in between are re-hashed. Because objects coming from the new
pack are already hashed by index-pack, we can trust their
integrity. The only objects left to check are existing ones in repo
but has no connection to any current refs.

Pass the new pack id down to--verify-objects and skip
check_sha1_signature() on objects from that pack.

As an (extreme) example, a repository is created with only one commit:
e83c516 (Initial revision of "git", the information manager from hell
- 2005-04-07). The rest of git.git is fetched on top. Without the
patch:

$ time git fetch file:///home/pclouds/w/git/.git
remote: Counting objects: 125656, done.
remote: Compressing objects: 100% (33280/33280), done.
remote: Total 125656 (delta 92585), reused 123464 (delta 90682)
Receiving objects: 100% (125656/125656), 34.60 MiB | 8.47 MiB/s, done.
Resolving deltas: 100% (92585/92585), done.
>From file:///home/pclouds/t/test/
 * branch            HEAD       -> FETCH_HEAD

real    1m30.437s
user    1m31.338s
sys     0m1.687s

With the patch:

$ time git fetch file:///home/pclouds/w/git/.git
remote: Counting objects: 125656, done.
remote: Compressing objects: 100% (33280/33280), done.
remote: Total 125656 (delta 92585), reused 123464 (delta 90682)
Receiving objects: 100% (125656/125656), 34.60 MiB | 7.86 MiB/s, done.
Resolving deltas: 100% (92585/92585), done.
>From file:///home/pclouds/t/test/
 * branch            HEAD       -> FETCH_HEAD

real    0m52.182s
user    0m53.151s
sys     0m1.465s

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 18 insertions, 2 deletions

diff --git a/builtin/rev-list.c b/builtin/rev-list.c
index 4c4d404afc..21d714b528 100644
--- a/builtin/rev-list.c
+++ b/builtin/rev-list.c
@@ -180,8 +180,24 @@ static void finish_object(struct object *obj,
 	struct rev_list_info *info = cb_data;
 	if (obj->type == OBJ_BLOB && !has_sha1_file(obj->sha1))
 		die("missing blob object '%s'", sha1_to_hex(obj->sha1));
-	if (info->revs->verify_objects && !obj->parsed && obj->type != OBJ_COMMIT)
-		parse_object(obj->sha1);
+	if (info->revs->verify_objects &&
+	    !obj->parsed && obj->type != OBJ_COMMIT) {
+		const char *safe_pack = info->revs->safe_pack;
+		struct object_info oi;
+		int safe = 0;
+		memset(&oi, 0, sizeof(oi));
+		if (*safe_pack &&
+		    sha1_object_info_extended(obj->sha1, &oi) >= 0 &&
+		    oi.whence == OI_PACKED) {
+			const char *pack = oi.u.packed.pack->pack_name;
+			int len = strlen(pack);
+			assert(strncmp(pack + len - 51, "/pack-", 6) == 0);
+			assert(strcmp(pack + len - 5, ".pack") == 0);
+			safe = !memcmp(safe_pack, pack + len - 45, 40);
+		}
+		if (!safe)
+			parse_object(obj->sha1);
+	}
 }
 
 static void show_object(struct object *obj,