Deny serialization before PHP 8.1 too

ZEND_ACC_NOT_SERIALIZABLE exists since PHP 8.1. Before, the
zend_class_(un)serialize_deny handlers make serialize() throw, and
unserialize() too for the C: format, while the O: format fails with a
warning without creating the object.

Author: nicolas-grekas

msgpack_class.c

@@ -1,4 +1,5 @@
 #include "php.h"
+#include "zend_interfaces.h"
 
 #include "php_msgpack.h"
 #include "msgpack_pack.h"
@@ -517,6 +518,9 @@ void msgpack_init_class() /* {{{ */ {
     msgpack_ce->create_object = php_msgpack_base_new;
 #if PHP_VERSION_ID >= 80100
     msgpack_ce->ce_flags |= ZEND_ACC_NOT_SERIALIZABLE;
+#else
+    msgpack_ce->serialize = zend_class_serialize_deny;
+    msgpack_ce->unserialize = zend_class_unserialize_deny;
 #endif
     memcpy(&msgpack_handlers, zend_get_std_object_handlers(),sizeof msgpack_handlers);
     msgpack_handlers.offset = offsetof(php_msgpack_base_t, object);
@@ -532,6 +536,9 @@ void msgpack_init_class() /* {{{ */ {
     msgpack_unpacker_ce->create_object = php_msgpack_unpacker_new;
 #if PHP_VERSION_ID >= 80100
     msgpack_unpacker_ce->ce_flags |= ZEND_ACC_NOT_SERIALIZABLE;
+#else
+    msgpack_unpacker_ce->serialize = zend_class_serialize_deny;
+    msgpack_unpacker_ce->unserialize = zend_class_unserialize_deny;
 #endif
     memcpy(&msgpack_unpacker_handlers, zend_get_std_object_handlers(),sizeof msgpack_unpacker_handlers);
     msgpack_unpacker_handlers.offset = offsetof(php_msgpack_unpacker_t, object);

tests/144.phpt

@@ -1,10 +1,5 @@
 --TEST--
 MessagePack and MessagePackUnpacker cannot be serialized
---SKIPIF--
-<?php
-if (PHP_VERSION_ID < 80100) {
-    echo "skip requires PHP 8.1+";
-}
 --FILE--
 <?php
 if(!extension_loaded('msgpack')) {
@@ -19,9 +14,12 @@ foreach ([new MessagePack(), new MessagePackUnpacker()] as $object) {
     }
 }
 
+// Before PHP 8.1, only the C: format reaches the handler that throws
+$format = PHP_VERSION_ID < 80100 ? 'C' : 'O';
+
 foreach (['MessagePack', 'MessagePackUnpacker'] as $class) {
     try {
-        unserialize('O:' . strlen($class) . ':"' . $class . '":0:{}');
+        unserialize($format . ':' . strlen($class) . ':"' . $class . '":0:{}');
     } catch (Exception $e) {
         echo $e->getMessage(), PHP_EOL;
     }