git_object__is_valid: use `odb_read_header`

This allows lighter weight validation in `git_object__is_valid` that
does not require reading the entire object.

src/object.c

@@ -467,3 +467,27 @@ int git_object_short_id(git_buf *out, const git_object *obj)
 	return error;
 }
 
+bool git_object__is_valid(
+	git_repository *repo, const git_oid *id, git_otype expected_type)
+{
+	git_odb *odb;
+	git_otype actual_type;
+	size_t len;
+	int error;
+
+	if (!git_object__strict_input_validation)
+		return true;
+
+	if ((error = git_repository_odb__weakptr(&odb, repo)) < 0 ||
+		(error = git_odb_read_header(&len, &actual_type, odb, id)) < 0)
+		return false;
+
+	if (expected_type != GIT_OBJ_ANY && expected_type != actual_type) {
+		giterr_set(GITERR_INVALID,
+			"the requested type does not match the type in the ODB");
+		return false;
+	}
+
+	return true;
+}
+

src/object.h

@@ -7,6 +7,8 @@
 #ifndef INCLUDE_object_h__
 #define INCLUDE_object_h__
 
+#include "repository.h"
+
 extern bool git_object__strict_input_validation;
 
 /** Base git object for inheritance */
@@ -30,21 +32,8 @@ int git_oid__parse(git_oid *oid, const char **buffer_out, const char *buffer_end
 
 void git_oid__writebuf(git_buf *buf, const char *header, const git_oid *oid);
 
-GIT_INLINE(bool) git_object__is_valid(
-	git_repository *repo, const git_oid *id, git_otype type)
-{
-	git_object *obj = NULL;
-	bool valid = true;
-
-	if (git_object__strict_input_validation) {
-		if (git_object_lookup(&obj, repo, id, type) < 0)
-			valid = false;
-
-		git_object_free(obj);
-	}
-
-	return valid;
-}
+bool git_object__is_valid(
+	git_repository *repo, const git_oid *id, git_otype expected_type);
 
 GIT_INLINE(git_otype) git_object__type_from_filemode(git_filemode_t mode)
 {