Fix GH-8996: DOMNode serialization on PHP ^8.1

PHP 8.1 introduced a seemingly unintentional BC break in ca94d55a19 by
blocking the (un)serialization of DOM objects.
This was done because the serialization never really worked and just
resulted in an empty object, which upon unserialization just resulted in
an object that you can't use.

Users can however implement their own serialization methods, but the
commit made that impossible as the ACC flag gets passed down to the
child class. An approach was tried in #10307 with a new ACC flag to
selectively allow serialization with subclasses if they implement the
right methods. However, that was found to be too ad hoc.

Instead, let's abuse how the __sleep and __wakeup methods work to throw
the exception instead. If the child class implements the __serialize /
__unserialize method, then the throwing methods won't be called.
Similarly, if the child class implements __sleep and __wakeup, then
they're overridden and it doesn't matter that they throw.

For the user, this PR has the exact same behaviour for (sub)classes that
don't implement the serialization methods: an exception will be thrown.
For code that previously implemented subclasses with these methods, this
approach will make that code work again. This approach should be both BC
preserving and unbreak user's code.

Closes GH-12388.

For the test:
Co-authored-by: wazelin <contact@sergeimikhailov.com>

NEWS

@@ -19,6 +19,7 @@ PHP                                                                        NEWS
 
 - DOM:
   . Restore old namespace reconciliation behaviour. (nielsdos)
+  . Fixed bug GH-8996 (DOMNode serialization on PHP ^8.1). (nielsdos)
 
 - Fileinfo:
   . Fixed bug GH-11891 (fileinfo returns text/xml for some svg files). (usarise)

ext/dom/node.c

@@ -1786,4 +1786,25 @@ PHP_METHOD(DOMNode, getLineNo)
 }
 /* }}} */
 
+/**
+ * We want to block the serialization and unserialization of DOM classes.
+ * However, using @not-serializable makes the child classes also not serializable, even if the user implements the methods.
+ * So instead, we implement the methods wherein we throw exceptions.
+ * The reason we choose these methods is because:
+ *   - If the user implements __serialize / __unserialize, the respective throwing methods are not called.
+ *   - If the user implements __sleep / __wakeup, then it's also not a problem because they will not enter the throwing methods.
+ */
+
+PHP_METHOD(DOMNode, __sleep)
+{
+	zend_throw_exception_ex(NULL, 0, "Serialization of '%s' is not allowed, unless serialization methods are implemented in a subclass", ZSTR_VAL(Z_OBJCE_P(ZEND_THIS)->name));
+	RETURN_THROWS();
+}
+
+PHP_METHOD(DOMNode, __wakeup)
+{
+	zend_throw_exception_ex(NULL, 0, "Unserialization of '%s' is not allowed, unless unserialization methods are implemented in a subclass", ZSTR_VAL(Z_OBJCE_P(ZEND_THIS)->name));
+	RETURN_THROWS();
+}
+
 #endif

ext/dom/php_dom.stub.php

@@ -56,7 +56,6 @@ interface DOMChildNode
     public function replaceWith(...$nodes): void;
 }
 
-/** @not-serializable */
 class DOMNode
 {
     /** @readonly */
@@ -104,6 +103,10 @@ class DOMNode
 
     public string $textContent;
 
+    public function __sleep(): array {}
+
+    public function __wakeup(): void {}
+
     /** @return DOMNode|false */
     public function appendChild(DOMNode $node) {}
 
@@ -156,7 +159,6 @@ class DOMNode
     public function replaceChild(DOMNode $node, DOMNode $child) {}
 }
 
-/** @not-serializable */
 class DOMNameSpaceNode
 {
     /** @readonly */
@@ -182,6 +184,12 @@ class DOMNameSpaceNode
 
     /** @readonly */
     public ?DOMNode $parentNode;
+
+    /** @implementation-alias DOMNode::__sleep */
+    public function __sleep(): array {}
+
+    /** @implementation-alias DOMNode::__wakeup */
+    public function __wakeup(): void {}
 }
 
 class DOMImplementation

ext/dom/php_dom_arginfo.h

@@ -1,5 +1,5 @@
 /* This is a generated file, edit the .stub.php file instead.
- * Stub hash: 20a0ff883af3bbf073d9c8bc8246646ffafe7818 */
+ * Stub hash: 203760d1cf0e063ffd9abe743a0e24a97985767e */
 
 ZEND_BEGIN_ARG_WITH_RETURN_OBJ_INFO_EX(arginfo_dom_import_simplexml, 0, 1, DOMElement, 0)
 	ZEND_ARG_TYPE_INFO(0, node, IS_OBJECT, 0)
@@ -28,6 +28,11 @@ ZEND_END_ARG_INFO()
 
 #define arginfo_class_DOMChildNode_replaceWith arginfo_class_DOMParentNode_append
 
+ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_class_DOMNode___sleep, 0, 0, IS_ARRAY, 0)
+ZEND_END_ARG_INFO()
+
+#define arginfo_class_DOMNode___wakeup arginfo_class_DOMChildNode_remove
+
 ZEND_BEGIN_ARG_INFO_EX(arginfo_class_DOMNode_appendChild, 0, 0, 1)
 	ZEND_ARG_OBJ_INFO(0, node, DOMNode, 0)
 ZEND_END_ARG_INFO()
@@ -100,6 +105,10 @@ ZEND_BEGIN_ARG_INFO_EX(arginfo_class_DOMNode_replaceChild, 0, 0, 2)
 	ZEND_ARG_OBJ_INFO(0, child, DOMNode, 0)
 ZEND_END_ARG_INFO()
 
+#define arginfo_class_DOMNameSpaceNode___sleep arginfo_class_DOMNode___sleep
+
+#define arginfo_class_DOMNameSpaceNode___wakeup arginfo_class_DOMChildNode_remove
+
 ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(arginfo_class_DOMImplementation_getFeature, 0, 2, IS_NEVER, 0)
 	ZEND_ARG_TYPE_INFO(0, feature, IS_STRING, 0)
 	ZEND_ARG_TYPE_INFO(0, version, IS_STRING, 0)
@@ -491,6 +500,8 @@ ZEND_END_ARG_INFO()
 ZEND_FUNCTION(dom_import_simplexml);
 ZEND_METHOD(DOMCdataSection, __construct);
 ZEND_METHOD(DOMComment, __construct);
+ZEND_METHOD(DOMNode, __sleep);
+ZEND_METHOD(DOMNode, __wakeup);
 ZEND_METHOD(DOMNode, appendChild);
 ZEND_METHOD(DOMNode, C14N);
 ZEND_METHOD(DOMNode, C14NFile);
@@ -672,6 +683,8 @@ static const zend_function_entry class_DOMChildNode_methods[] = {
 
 
 static const zend_function_entry class_DOMNode_methods[] = {
+	ZEND_ME(DOMNode, __sleep, arginfo_class_DOMNode___sleep, ZEND_ACC_PUBLIC)
+	ZEND_ME(DOMNode, __wakeup, arginfo_class_DOMNode___wakeup, ZEND_ACC_PUBLIC)
 	ZEND_ME(DOMNode, appendChild, arginfo_class_DOMNode_appendChild, ZEND_ACC_PUBLIC)
 	ZEND_ME(DOMNode, C14N, arginfo_class_DOMNode_C14N, ZEND_ACC_PUBLIC)
 	ZEND_ME(DOMNode, C14NFile, arginfo_class_DOMNode_C14NFile, ZEND_ACC_PUBLIC)
@@ -694,6 +707,8 @@ static const zend_function_entry class_DOMNode_methods[] = {
 
 
 static const zend_function_entry class_DOMNameSpaceNode_methods[] = {
+	ZEND_MALIAS(DOMNode, __sleep, __sleep, arginfo_class_DOMNameSpaceNode___sleep, ZEND_ACC_PUBLIC)
+	ZEND_MALIAS(DOMNode, __wakeup, __wakeup, arginfo_class_DOMNameSpaceNode___wakeup, ZEND_ACC_PUBLIC)
 	ZEND_FE_END
 };
 
@@ -989,7 +1004,6 @@ static zend_class_entry *register_class_DOMNode(void)
 
 	INIT_CLASS_ENTRY(ce, "DOMNode", class_DOMNode_methods);
 	class_entry = zend_register_internal_class_ex(&ce, NULL);
-	class_entry->ce_flags |= ZEND_ACC_NOT_SERIALIZABLE;
 
 	zval property_nodeName_default_value;
 	ZVAL_UNDEF(&property_nodeName_default_value);
@@ -1104,7 +1118,6 @@ static zend_class_entry *register_class_DOMNameSpaceNode(void)
 
 	INIT_CLASS_ENTRY(ce, "DOMNameSpaceNode", class_DOMNameSpaceNode_methods);
 	class_entry = zend_register_internal_class_ex(&ce, NULL);
-	class_entry->ce_flags |= ZEND_ACC_NOT_SERIALIZABLE;
 
 	zval property_nodeName_default_value;
 	ZVAL_UNDEF(&property_nodeName_default_value);

ext/dom/tests/gh8996.phpt

@@ -0,0 +1,120 @@
+--TEST--
+GH-8996: DOMNode serialization on PHP ^8.1
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+
+echo "=== __sleep and __wakeup ===\n";
+
+class SerializableDomDocumentSleepWakeup extends DOMDocument
+{
+    private $xmlData;
+
+    public function __sleep(): array
+    {
+        $this->xmlData = $this->saveXML();
+        return ['xmlData'];
+    }
+
+    public function __wakeup(): void
+    {
+        $this->loadXML($this->xmlData);
+    }
+}
+
+$dom = new SerializableDomDocumentSleepWakeup('1.0', 'UTF-8');
+$dom->loadXML('<tag>value</tag>');
+
+$serialized = serialize($dom);
+var_dump($serialized);
+$unserialized = unserialize($serialized);
+
+echo "Serialized:\n-----------\n$serialized\n-----------\nRestored:\n-----------\n{$unserialized->saveXml()}";
+
+echo "=== __serialize and __unserialize ===\n";
+
+class SerializableDomDocument__Serialize__Unserialize extends DOMDocument
+{
+    public function __serialize(): array
+    {
+        return ['xmlData' => $this->saveXML()];
+    }
+
+    public function __unserialize(array $data): void
+    {
+        $this->loadXML($data['xmlData']);
+    }
+}
+
+$dom = new SerializableDomDocument__Serialize__Unserialize('1.0', 'UTF-8');
+$dom->loadXML('<tag>value</tag>');
+
+$serialized = serialize($dom);
+$unserialized = unserialize($serialized);
+
+echo "Serialized:\n-----------\n$serialized\n-----------\nRestored:\n-----------\n{$unserialized->saveXml()}";
+
+echo "=== serialize and unserialize ===\n";
+
+class SerializableDomDocumentSerializeUnserialize extends DOMDocument implements Serializable
+{
+    public function serialize(): ?string
+    {
+        return $this->saveXML();
+    }
+
+    public function unserialize(string $data): void
+    {
+        $this->loadXML($data);
+    }
+}
+
+$dom = new SerializableDomDocumentSerializeUnserialize('1.0', 'UTF-8');
+$dom->loadXML('<tag>value</tag>');
+
+$serialized = serialize($dom);
+$unserialized = unserialize($serialized);
+
+echo "Serialized:\n-----------\n$serialized\n-----------\nRestored:\n-----------\n{$unserialized->saveXml()}";
+
+?>
+--EXPECTF--
+=== __sleep and __wakeup ===
+string(144) "O:34:"SerializableDomDocumentSleepWakeup":1:{s:43:"%0SerializableDomDocumentSleepWakeup%0xmlData";s:39:"<?xml version="1.0"?>
+<tag>value</tag>
+";}"
+Serialized:
+-----------
+O:34:"SerializableDomDocumentSleepWakeup":1:{s:43:"%0SerializableDomDocumentSleepWakeup%0xmlData";s:39:"<?xml version="1.0"?>
+<tag>value</tag>
+";}
+-----------
+Restored:
+-----------
+<?xml version="1.0"?>
+<tag>value</tag>
+=== __serialize and __unserialize ===
+Serialized:
+-----------
+O:47:"SerializableDomDocument__Serialize__Unserialize":1:{s:7:"xmlData";s:39:"<?xml version="1.0"?>
+<tag>value</tag>
+";}
+-----------
+Restored:
+-----------
+<?xml version="1.0"?>
+<tag>value</tag>
+=== serialize and unserialize ===
+
+Deprecated: SerializableDomDocumentSerializeUnserialize implements the Serializable interface, which is deprecated. Implement __serialize() and __unserialize() instead (or in addition, if support for old PHP versions is necessary) in %s on line %d
+Serialized:
+-----------
+C:43:"SerializableDomDocumentSerializeUnserialize":39:{<?xml version="1.0"?>
+<tag>value</tag>
+}
+-----------
+Restored:
+-----------
+<?xml version="1.0"?>
+<tag>value</tag>

ext/dom/tests/not_serializable.phpt

@@ -36,7 +36,7 @@ try {
 
 ?>
 --EXPECT--
-Serialization of 'DOMDocument' is not allowed
-Serialization of 'DOMElement' is not allowed
+Serialization of 'DOMDocument' is not allowed, unless serialization methods are implemented in a subclass
+Serialization of 'DOMElement' is not allowed, unless serialization methods are implemented in a subclass
 Serialization of 'DOMXPath' is not allowed
-Serialization of 'DOMNameSpaceNode' is not allowed
+Serialization of 'DOMNameSpaceNode' is not allowed, unless serialization methods are implemented in a subclass

ext/dom/tests/not_unserializable.phpt

@@ -0,0 +1,29 @@
+--TEST--
+DOM classes are not unserializable
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+
+$classes = [
+    "DOMXPath",
+    "DOMDocument",
+    "DOMNode",
+    "DOMNameSpaceNode",
+];
+
+foreach ($classes as $class)
+{
+    try {
+        unserialize('O:' . strlen($class) . ':"' . $class . '":0:{}');
+    } catch (Exception $e) {
+        echo $e->getMessage(), "\n";
+    }
+}
+
+?>
+--EXPECT--
+Unserialization of 'DOMXPath' is not allowed
+Unserialization of 'DOMDocument' is not allowed, unless unserialization methods are implemented in a subclass
+Unserialization of 'DOMNode' is not allowed, unless unserialization methods are implemented in a subclass
+Unserialization of 'DOMNameSpaceNode' is not allowed, unless unserialization methods are implemented in a subclass