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

This mostly reverts commit 6082b3d5d, "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 <michael@paquier.xyz>
Author: Michael Paquier <michael@paquier.xyz>
Co-authored-by: Erik Wienhold <ewie@ewie.name>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/aIGknLuc8b8ega2X@paquier.xyz
Backpatch-through: 13

diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index 056d811594909252cc54b1fc07078a825956cb23..28af16fe93eea226a9ab42b3bd03463fe28a0db7 100644 (file)
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -1730,7 +1730,7 @@ 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
@@ -1756,6 +1756,7 @@ 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
@@ -1783,7 +1784,6 @@ 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;
@@ -1814,18 +1814,6 @@ 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 :
@@ -1835,11 +1823,26 @@ 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",
@@ -1861,10 +1864,7 @@ 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,
@@ -1877,36 +1877,23 @@ 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;
                                }
 
@@ -1922,6 +1909,8 @@ fail:
        }
        PG_CATCH();
        {
+               if (save_keep_blanks != -1)
+                       xmlKeepBlanksDefault(save_keep_blanks);
                if (doc != NULL)
                        xmlFreeDoc(doc);
                if (ctxt != NULL)
@@ -1933,6 +1922,9 @@ fail:
        }
        PG_END_TRY();
 
+       if (save_keep_blanks != -1)
+               xmlKeepBlanksDefault(save_keep_blanks);
+
        if (ctxt != NULL)
                xmlFreeParserCtxt(ctxt);