fsck: consider gpgsig headers expected in tags

When we're creating a tag, we want to make sure that gpgsig and
gpgsig-sha256 headers are allowed for the commit.  The default fsck
behavior is to ignore the fact that they're left over, but some of our
tests enable strict checking which flags them nonetheless.  Add
improved checking for these headers as well as documentation and several
tests.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/fsck.c b/fsck.c
index 171b424dd5..341e100d24 100644
--- a/fsck.c
+++ b/fsck.c
@@ -1067,6 +1067,24 @@ int fsck_tag_standalone(const struct object_id *oid, const char *buffer,
 	else
 		ret = fsck_ident(&buffer, oid, OBJ_TAG, options);
 
+	if (buffer < buffer_end && (skip_prefix(buffer, "gpgsig ", &buffer) || skip_prefix(buffer, "gpgsig-sha256 ", &buffer))) {
+		eol = memchr(buffer, '\n', buffer_end - buffer);
+		if (!eol) {
+			ret = report(options, oid, OBJ_TAG, FSCK_MSG_BAD_GPGSIG, "invalid format - unexpected end after 'gpgsig' or 'gpgsig-sha256' line");
+			goto done;
+		}
+		buffer = eol + 1;
+
+		while (buffer < buffer_end && starts_with(buffer, " ")) {
+			eol = memchr(buffer, '\n', buffer_end - buffer);
+			if (!eol) {
+				ret = report(options, oid, OBJ_TAG, FSCK_MSG_BAD_HEADER_CONTINUATION, "invalid format - unexpected end in 'gpgsig' or 'gpgsig-sha256' continuation line");
+				goto done;
+			}
+			buffer = eol + 1;
+		}
+	}
+
 	if (buffer < buffer_end && !starts_with(buffer, "\n")) {
 		/*
 		 * The verify_headers() check will allow