Fix error paths in dom_xml_serializing_a_document_node()

ext/dom/tests/modern/xml/serialize_document_write_failure.phpt

@@ -0,0 +1,39 @@
+--TEST--
+Dom\XMLDocument: failed write while serializing the document node must not detach its children
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+
+class FailingStream {
+    public $context;
+
+    public function stream_open(string $path, string $mode, int $options, ?string &$opened_path): bool {
+        return true;
+    }
+
+    public function stream_write(string $data): int|false {
+        return false;
+    }
+
+    public function stream_tell(): int {
+        return 0;
+    }
+}
+
+stream_wrapper_register('failing', FailingStream::class);
+
+$doc = Dom\XMLDocument::createFromString('<root><child/></root>');
+var_dump($doc->saveXmlFile('failing://out'));
+
+var_dump($doc->documentElement?->nodeName);
+var_dump($doc->childNodes->length);
+echo $doc->saveXml();
+
+?>
+--EXPECT--
+bool(false)
+string(4) "root"
+int(1)
+<?xml version="1.0" encoding="UTF-8"?>
+<root><child/></root>

ext/dom/tests/modern/xml/serialize_document_write_mutation.phpt

@@ -0,0 +1,40 @@
+--TEST--
+Dom\XMLDocument: mutating the document from a stream write during document serialization
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+
+class MutatingStream {
+    public $context;
+    public static $doc;
+
+    public function stream_open(string $path, string $mode, int $options, ?string &$opened_path): bool {
+        return true;
+    }
+
+    public function stream_write(string $data): int {
+        if (self::$doc !== null) {
+            $doc = self::$doc;
+            self::$doc = null;
+            $doc->append($doc->createComment('injected'));
+        }
+        return strlen($data);
+    }
+}
+
+stream_wrapper_register('mutating', MutatingStream::class);
+
+$doc = Dom\XMLDocument::createFromString('<root><child/></root>');
+MutatingStream::$doc = $doc;
+$doc->saveXmlFile('mutating://out');
+
+$doc->append($doc->createComment('after'));
+var_dump($doc->childNodes->length);
+echo $doc->saveXml(), "\n";
+
+?>
+--EXPECT--
+int(3)
+<?xml version="1.0" encoding="UTF-8"?>
+<root><child/></root><!--injected--><!--after-->

ext/dom/xml_serializer.c

@@ -1228,18 +1228,18 @@ static int dom_xml_serializing_a_document_node(
 	/* 1. Let serialized document be an empty string.
 	 *    => We use the output buffer instead. */
 
-	xmlNodePtr child = node->children;
-	node->children = NULL;
-
 	/* https://github.com/w3c/DOM-Parsing/issues/50 */
 	TRY(xmlOutputBufferFlush(ctx->out));
-	TRY(xmlSaveDoc(ctx->ctxt, (xmlDocPtr) node));
+	/* To gain the xml declaration, use a shallow copy of the document with the children NULLed out.
+	 * Stream wrappers can access the real document, so we cannot modify that. */
+	xmlDoc declaration_doc = *(xmlDocPtr) node;
+	declaration_doc.children = declaration_doc.last = NULL;
+	TRY(xmlSaveDoc(ctx->ctxt, &declaration_doc));
 	TRY(xmlSaveFlush(ctx->ctxt));
 
-	node->children = child;
-
 	/* 2. For each child child of node, in tree order, run the XML serialization algorithm on the child passing along the provided arguments,
 	 *    and append the result to serialized document. */
+	xmlNodePtr child = node->children;
 	while (child != NULL) {
 		TRY(dom_xml_serialization_algorithm(ctx, namespace_prefix_map, child, namespace, prefix_index, indent, require_well_formed));
 		child = child->next;