csum-file: introduce checksum_valid()

Introduce a new function which checks the validity of a file's trailing
checksum. This is similar to hashfd_check(), but different since it is
intended to be used by callers who aren't writing the same data (like
`git index-pack --verify`), but who instead want to validate the
integrity of data that they are reading.

Rewrite the first of two callers which could benefit from this new
function in pack-check.c. Subsequent callers will be added in the
following patches.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 10 deletions

diff --git a/pack-check.c b/pack-check.c
index 4b089fe8ec..c8e560d71a 100644
--- a/pack-check.c
+++ b/pack-check.c
@@ -164,22 +164,13 @@ static int verify_packfile(struct repository *r,
 
 int verify_pack_index(struct packed_git *p)
 {
-	size_t len;
-	const unsigned char *index_base;
-	git_hash_ctx ctx;
-	unsigned char hash[GIT_MAX_RAWSZ];
 	int err = 0;
 
 	if (open_pack_index(p))
 		return error("packfile %s index not opened", p->pack_name);
-	index_base = p->index_data;
-	len = p->index_size - the_hash_algo->rawsz;
 
 	/* Verify SHA1 sum of the index file */
-	the_hash_algo->init_fn(&ctx);
-	the_hash_algo->update_fn(&ctx, index_base, len);
-	the_hash_algo->final_fn(hash, &ctx);
-	if (!hasheq(hash, index_base + len))
+	if (!hashfile_checksum_valid(p->index_data, p->index_size))
 		err = error("Packfile index for %s hash mismatch",
 			    p->pack_name);
 	return err;