snapshot: support archive signatures

Read signatures from the notes refs refs/notes/signatures/$FORMAT where
FORMAT is one of our archive formats ("tar", "tar.gz", ...).  The note
is expected to simply contain the signature content to be returned when
the snapshot "${filename}.asc" is requested, so the signature for
cgit-1.1.tar.xz can be stored against the v1.1 tag with:

	git notes --ref=refs/notes/signatures/tar.xz add -C "$(
		gpg --output - --armor --detach-sign cgit-1.1.tar.xz |
		git hash-object -w --stdin
	)" v1.1

and then downloaded by simply appending ".asc" to the archive URL.

Signed-off-by: John Keeping <john@keeping.me.uk>
Reviewed-by: Christian Hesse <mail@eworm.de>

1 files changed, 2 insertions, 0 deletions

@@ -374,6 +374,8 @@ extern void cgit_parse_url(const char *url);
 extern const char *cgit_repobasename(const char *reponame);
 
 extern int cgit_parse_snapshots_mask(const char *str);
+extern const struct object_id *cgit_snapshot_get_sig(const char *ref,
+                                                     const struct cgit_snapshot_format *f);
 
 extern int cgit_open_filter(struct cgit_filter *filter, ...);
 extern int cgit_close_filter(struct cgit_filter *filter);