Avoid regression in the size of XML input that we will accept.

This mostly reverts commit 6082b3d, "Use xmlParseInNodeContext
not xmlParseBalancedChunkMemory".  It turns out that
xmlParseInNodeContext will reject text chunks exceeding 10MB, while
(in most libxml2 versions) xmlParseBalancedChunkMemory will not.
The bleeding-edge libxml2 bug that we needed to work around a year
ago is presumably no longer a factor, and the argument that
xmlParseBalancedChunkMemory is semi-deprecated is not enough to
justify a functionality regression.  Hence, go back to doing it
the old way.

Reported-by: Michael Paquier <[email protected]>
Author: Michael Paquier <[email protected]>
Co-authored-by: Erik Wienhold <[email protected]>
Reviewed-by: Tom Lane <[email protected]>
Discussion: https://postgr.es/m/[email protected]
Backpatch-through: 13

Author: tglsfdc

src/backend/utils/adt/xml.c

@@ -1769,7 +1769,7 @@ xml_doctype_in_content(const xmlChar *str)
  * xmloption_arg, but a DOCTYPE node in the input can force DOCUMENT mode).
  *
  * If parsed_nodes isn't NULL and we parse in CONTENT mode, the list
- * of parsed nodes from the xmlParseInNodeContext call will be returned
+ * of parsed nodes from the xmlParseBalancedChunkMemory call will be returned
  * to *parsed_nodes.  (It is caller's responsibility to free that.)
  *
  * Errors normally result in ereport(ERROR), but if escontext is an
@@ -1795,6 +1795,7 @@ xml_parse(text *data, XmlOptionType xmloption_arg,
 	PgXmlErrorContext *xmlerrcxt;
 	volatile xmlParserCtxtPtr ctxt = NULL;
 	volatile xmlDocPtr doc = NULL;
+	volatile int save_keep_blanks = -1;
 
 	/*
 	 * This step looks annoyingly redundant, but we must do it to have a
@@ -1822,7 +1823,6 @@ xml_parse(text *data, XmlOptionType xmloption_arg,
 	PG_TRY();
 	{
 		bool		parse_as_document = false;
-		int			options;
 		int			res_code;
 		size_t		count = 0;
 		xmlChar    *version = NULL;
@@ -1853,18 +1853,6 @@ xml_parse(text *data, XmlOptionType xmloption_arg,
 				parse_as_document = true;
 		}
 
-		/*
-		 * Select parse options.
-		 *
-		 * Note that here we try to apply DTD defaults (XML_PARSE_DTDATTR)
-		 * according to SQL/XML:2008 GR 10.16.7.d: 'Default values defined by
-		 * internal DTD are applied'.  As for external DTDs, we try to support
-		 * them too (see SQL/XML:2008 GR 10.16.7.e), but that doesn't really
-		 * happen because xmlPgEntityLoader prevents it.
-		 */
-		options = XML_PARSE_NOENT | XML_PARSE_DTDATTR
-			| (preserve_whitespace ? 0 : XML_PARSE_NOBLANKS);
-
 		/* initialize output parameters */
 		if (parsed_xmloptiontype != NULL)
 			*parsed_xmloptiontype = parse_as_document ? XMLOPTION_DOCUMENT :
@@ -1874,11 +1862,26 @@ xml_parse(text *data, XmlOptionType xmloption_arg,
 
 		if (parse_as_document)
 		{
+			int			options;
+
+			/* set up parser context used by xmlCtxtReadDoc */
 			ctxt = xmlNewParserCtxt();
 			if (ctxt == NULL || xmlerrcxt->err_occurred)
 				xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
 							"could not allocate parser context");
 
+			/*
+			 * Select parse options.
+			 *
+			 * Note that here we try to apply DTD defaults (XML_PARSE_DTDATTR)
+			 * according to SQL/XML:2008 GR 10.16.7.d: 'Default values defined
+			 * by internal DTD are applied'.  As for external DTDs, we try to
+			 * support them too (see SQL/XML:2008 GR 10.16.7.e), but that
+			 * doesn't really happen because xmlPgEntityLoader prevents it.
+			 */
+			options = XML_PARSE_NOENT | XML_PARSE_DTDATTR
+				| (preserve_whitespace ? 0 : XML_PARSE_NOBLANKS);
+
 			doc = xmlCtxtReadDoc(ctxt, utf8string,
 								 NULL,	/* no URL */
 								 "UTF-8",
@@ -1900,10 +1903,7 @@ xml_parse(text *data, XmlOptionType xmloption_arg,
 		}
 		else
 		{
-			xmlNodePtr	root;
-			xmlNodePtr	oldroot PG_USED_FOR_ASSERTS_ONLY;
-
-			/* set up document with empty root node to be the context node */
+			/* set up document that xmlParseBalancedChunkMemory will add to */
 			doc = xmlNewDoc(version);
 			if (doc == NULL || xmlerrcxt->err_occurred)
 				xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
@@ -1916,36 +1916,23 @@ xml_parse(text *data, XmlOptionType xmloption_arg,
 							"could not allocate XML document");
 			doc->standalone = standalone;
 
-			root = xmlNewNode(NULL, (const xmlChar *) "content-root");
-			if (root == NULL || xmlerrcxt->err_occurred)
-				xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
-							"could not allocate xml node");
-
-			/*
-			 * This attaches root to doc, so we need not free it separately;
-			 * and there can't yet be any old root to free.
-			 */
-			oldroot = xmlDocSetRootElement(doc, root);
-			Assert(oldroot == NULL);
+			/* set parse options --- have to do this the ugly way */
+			save_keep_blanks = xmlKeepBlanksDefault(preserve_whitespace ? 1 : 0);
 
 			/* allow empty content */
 			if (*(utf8string + count))
 			{
 				xmlNodePtr	node_list = NULL;
-				xmlParserErrors res;
-
-				res = xmlParseInNodeContext(root,
-											(char *) utf8string + count,
-											strlen((char *) utf8string + count),
-											options,
-											&node_list);
 
-				if (res != XML_ERR_OK || xmlerrcxt->err_occurred)
+				res_code = xmlParseBalancedChunkMemory(doc, NULL, NULL, 0,
+													   utf8string + count,
+													   &node_list);
+				if (res_code != 0 || xmlerrcxt->err_occurred)
 				{
-					xmlFreeNodeList(node_list);
 					xml_errsave(escontext, xmlerrcxt,
 								ERRCODE_INVALID_XML_CONTENT,
 								"invalid XML content");
+					xmlFreeNodeList(node_list);
 					goto fail;
 				}
 
@@ -1961,6 +1948,8 @@ xml_parse(text *data, XmlOptionType xmloption_arg,
 	}
 	PG_CATCH();
 	{
+		if (save_keep_blanks != -1)
+			xmlKeepBlanksDefault(save_keep_blanks);
 		if (doc != NULL)
 			xmlFreeDoc(doc);
 		if (ctxt != NULL)
@@ -1972,6 +1961,9 @@ xml_parse(text *data, XmlOptionType xmloption_arg,
 	}
 	PG_END_TRY();
 
+	if (save_keep_blanks != -1)
+		xmlKeepBlanksDefault(save_keep_blanks);
+
 	if (ctxt != NULL)
 		xmlFreeParserCtxt(ctxt);