[PATCH 05/10] object-file API: provide a hash_object_file_oideq()

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Provide a new hash_object_file_oideq() for those callers of
check_object_signature() that don't care about its streaming
interface. I.e. at the start of that function we do:

	if (map) {
		hash_object_file(r->hash_algo, map, size, type, real_oid);
		return !oideq(oid, real_oid) ? -1 : 0;
	}

These callers always provide a "map" (or "buf[fer]"). Let's have them
call this simpler hash_object_file_oideq() function instead.

None of them use a non-NULL "real_oid" argument, but let's provide it
like check_object_signature() did. This'll make it easy to have these
emit better error messages in the future as was done in
96e41f58fe1 (fsck: report invalid object type-path combinations,
2021-10-01), i.e. the die() calls here can emit not only the OID we
expected, but also what we got.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 builtin/fast-export.c |  4 ++--
 builtin/index-pack.c  |  5 ++---
 builtin/mktag.c       |  5 ++---
 object-file.c         | 13 +++++++++++++
 object-store.h        | 14 ++++++++++++++
 object.c              |  4 ++--
 6 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/builtin/fast-export.c b/builtin/fast-export.c
index 9f1c730e587..f084da198c7 100644
--- a/builtin/fast-export.c
+++ b/builtin/fast-export.c
@@ -299,8 +299,8 @@ static void export_blob(const struct object_id *oid)
 		buf = read_object_file(oid, &type, &size);
 		if (!buf)
 			die("could not read blob %s", oid_to_hex(oid));
-		if (check_object_signature(the_repository, oid, buf, size,
-					   type_name(type), NULL) < 0)
+		if (!hash_object_file_oideq(the_repository->hash_algo, buf,
+					    size, type, oid, NULL))
 			die("oid mismatch in blob %s", oid_to_hex(oid));
 		object = parse_object_buffer(the_repository, oid, type,
 					     size, buf, &eaten);
diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 01574378ce2..5531a6d8bae 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -1412,9 +1412,8 @@ static void fix_unresolved_deltas(struct hashfile *f)
 		if (!data)
 			continue;
 
-		if (check_object_signature(the_repository, &d->oid,
-					   data, size,
-					   type_name(type), NULL))
+		if (!hash_object_file_oideq(the_repository->hash_algo, data,
+					    size, type, &d->oid, NULL))
 			die(_("local object %s is corrupt"), oid_to_hex(&d->oid));
 
 		/*
diff --git a/builtin/mktag.c b/builtin/mktag.c
index 96a3686af53..d8c7cf836b7 100644
--- a/builtin/mktag.c
+++ b/builtin/mktag.c
@@ -61,9 +61,8 @@ static int verify_object_in_tag(struct object_id *tagged_oid, int *tagged_type)
 		    type_name(*tagged_type), type_name(type));
 
 	repl = lookup_replace_object(the_repository, tagged_oid);
-	ret = check_object_signature(the_repository, repl,
-				     buffer, size, type_name(*tagged_type),
-				     NULL);
+	ret = !hash_object_file_oideq(the_repository->hash_algo, buffer, size,
+				      *tagged_type, repl, NULL);
 	free(buffer);
 
 	return ret;
diff --git a/object-file.c b/object-file.c
index 59eb793e0ac..27d10112960 100644
--- a/object-file.c
+++ b/object-file.c
@@ -1862,6 +1862,19 @@ void hash_object_file(const struct git_hash_algo *algo, const void *buf,
 	write_object_file_prepare(algo, buf, len, type, oid, hdr, &hdrlen);
 }
 
+int hash_object_file_oideq(const struct git_hash_algo *algo, const void *buf,
+			   unsigned long len, enum object_type type,
+			   const struct object_id *oid,
+			   struct object_id *real_oidp)
+{
+	struct object_id tmp;
+	struct object_id *real_oid = real_oidp ? real_oidp : &tmp;
+
+	hash_object_file(algo, buf, len, type_name(type), real_oid);
+
+	return oideq(oid, real_oid);
+}
+
 /* Finalize a file on disk, and close it. */
 static void close_loose_object(int fd)
 {
diff --git a/object-store.h b/object-store.h
index eab1e2a967e..95907062682 100644
--- a/object-store.h
+++ b/object-store.h
@@ -249,6 +249,20 @@ void hash_object_file(const struct git_hash_algo *algo, const void *buf,
 		      unsigned long len, const char *type,
 		      struct object_id *oid);
 
+/**
+ * hash_object_file_oideq() is like hash_object_file() except that
+ * asserts that "real_oid" is equivalent to an input "oid", and the
+ * return value is that of oideq(oid, real_oid).
+ *
+ * The "real_oid" can be NULL, when non-NULL the caller provides a
+ * "struct object_id *" that can be used to print what the real OID
+ * was.
+ */
+int hash_object_file_oideq(const struct git_hash_algo *algo, const void *buf,
+			   unsigned long len, enum object_type type,
+			   const struct object_id *oid,
+			   struct object_id *real_oidp);
+
 int write_object_file_flags(const void *buf, unsigned long len,
 			    enum object_type type, struct object_id *oid,
 			    unsigned flags);
diff --git a/object.c b/object.c
index c37501fc120..d7673332582 100644
--- a/object.c
+++ b/object.c
@@ -289,8 +289,8 @@ struct object *parse_object(struct repository *r, const struct object_id *oid)
 
 	buffer = repo_read_object_file(r, oid, &type, &size);
 	if (buffer) {
-		if (check_object_signature(r, repl, buffer, size,
-					   type_name(type), NULL) < 0) {
+		if (!hash_object_file_oideq(r->hash_algo, buffer, size,
+					    type, repl, NULL)) {
 			free(buffer);
 			error(_("hash mismatch %s"), oid_to_hex(repl));
 			return NULL;
-- 
2.35.0.913.g12b4baa2536