Subject: [PATCH v6 4/9] packed-backend: check if header starts with "# pack-refs with: "

From: shejialuo <[email-masked]>
Date: Tue, 25 Feb 2025 21:21:41 +0800

We always write a space after "# pack-refs with:". However, when
creating the packed-ref snapshot, we only check whether the header
starts with "# pack-refs with:". However, we need to make sure that we
would not break compatibility by tightening the rule. The following is
how some third-party libraries handle the header of "packed-ref" file.

1. libgit2 is fine and always writes the space. It also expects the
   whitespace to exist.
2. JGit does not expect th header to have a trailing space, but expects
   the "peeled" capability to have a leading space, which is mostly
   equivalent because that capability is typically the first one we
   write. It always writes the space.
3. gitoxide expects the space t exist and writes it.
4. go-git doesn't create the header by default.

So, we are safe to tighten the rule by checking whether the header
starts with "# pack-refs with: ".

Mentored-by: Patrick Steinhardt <[email-masked]>
Mentored-by: Karthik Nayak <[email-masked]>
Signed-off-by: shejialuo <[email-masked]>
---
 refs/packed-backend.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 6c118119a0..9dabb5e556 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -694,7 +694,7 @@ static struct snapshot *create_snapshot(struct packed_ref_store *refs)
 
 		tmp = xmemdupz(snapshot->buf, eol - snapshot->buf);
 
-		if (!skip_prefix(tmp, "# pack-refs with:", (const char **)&p))
+		if (!skip_prefix(tmp, "# pack-refs with: ", (const char **)&p))
 			die_invalid_line(refs->path,
 					 snapshot->buf,
 					 snapshot->eof - snapshot->buf);
-- 
2.48.1