{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, 23 insertions, 8 deletions

diff --git a/connected.c b/connected.c
index d7624230d4..af81049e7e 100644
--- a/connected.c
+++ b/connected.c
@@ -14,28 +14,43 @@
  *
  * Returns 0 if everything is connected, non-zero otherwise.
  */
-int check_everything_connected(sha1_iterate_fn fn, int quiet, void *cb_data)
+int check_everything_connected(sha1_iterate_fn fn, unsigned int flags,
+			       const char *pack_lockfile, void *cb_data)
 {
 	struct child_process rev_list;
-	const char *argv[] = {"rev-list", "--verify-objects",
-			      "--stdin", "--not", "--all", NULL, NULL};
+	const char *argv[] = {"rev-list", "--verify-objects", "--stdin",
+			      "--not", "--all", NULL, NULL, NULL, NULL };
 	char commit[41];
 	unsigned char sha1[20];
-	int err = 0;
+	int err = 0, ac = 5;
+	struct strbuf packfile = STRBUF_INIT;
 
 	if (fn(cb_data, sha1))
 		return err;
 
-	if (quiet)
-		argv[5] = "--quiet";
+	if (flags & CHECK_CONNECT_QUIET)
+		argv[ac++] = "--quiet";
+	if (pack_lockfile) {
+		strbuf_addstr(&packfile, pack_lockfile);
+		/* xxx/pack-%40s.keep */
+		assert(strcmp(packfile.buf + packfile.len - 5, ".keep") == 0);
+		assert(strncmp(packfile.buf + packfile.len - 51, "/pack-", 6) == 0);
+		strbuf_setlen(&packfile, packfile.len - 5);
+		strbuf_remove(&packfile, 0, packfile.len - 40);
+		argv[ac++] = "--safe-pack";
+		argv[ac++] = packfile.buf;
+	}
+	assert(ac < ARRAY_SIZE(argv) && argv[ac] == NULL);
 
 	memset(&rev_list, 0, sizeof(rev_list));
 	rev_list.argv = argv;
 	rev_list.git_cmd = 1;
 	rev_list.in = -1;
 	rev_list.no_stdout = 1;
-	rev_list.no_stderr = quiet;
-	if (start_command(&rev_list))
+	rev_list.no_stderr = flags & CHECK_CONNECT_QUIET;
+	err = start_command(&rev_list);
+	strbuf_release(&packfile);
+	if (err)
 		return error(_("Could not run 'git rev-list'"));
 
 	sigchain_push(SIGPIPE, SIG_IGN);