Added support for OPENXML with WITH clause

src/backend/parser/parse_clause.c

@@ -56,6 +56,8 @@ sortby_nulls_hook_type  sortby_nulls_hook = NULL;
 
 optimize_explicit_cast_hook_type optimize_explicit_cast_hook = NULL;
 
+pre_transform_openxml_columns_hook_type pre_transform_openxml_columns_hook = NULL;
+
 static int	extractRemainingColumns(ParseState *pstate,
 									ParseNamespaceColumn *src_nscolumns,
 									List *src_colnames,
@@ -711,6 +713,13 @@ transformRangeTableFunc(ParseState *pstate, RangeTableFunc *rtf)
 	constructName = "XMLTABLE";
 	docType = XMLOID;
 
+	/*
+	 * Hook to allow extensions to pre-process OPENXML column definitions
+	 * before standard XMLTABLE transformation.
+	 */
+	if (pre_transform_openxml_columns_hook && tf->functype == TFT_XMLTABLE)
+		pre_transform_openxml_columns_hook(pstate, rtf);
+
 	/*
 	 * We make lateral_only names of this level visible, whether or not the
 	 * RangeTableFunc is explicitly marked LATERAL.  This is needed for SQL

src/backend/utils/adt/xml.c

@@ -232,6 +232,10 @@ const TableFuncRoutine XmlTableRoutine =
 	.DestroyOpaque = XmlTableDestroyOpaque
 };
 
+#ifdef USE_LIBXML
+openxml_set_namespaces_hook_type openxml_set_namespaces_hook = NULL;
+#endif
+
 #define NO_XML_SUPPORT() \
 	ereport(ERROR, \
 			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED), \
@@ -4795,6 +4799,10 @@ XmlTableSetNamespace(TableFuncScanState *state, const char *name, const char *ur
 				 errmsg("DEFAULT namespace is not supported")));
 	xtCxt = GetXmlTableBuilderPrivateData(state, "XmlTableSetNamespace");
 
+	/* For TSQL OPENXML, following hook will fetch and register namespaces in Xpath context. */
+	if (openxml_set_namespaces_hook)
+        return openxml_set_namespaces_hook(xtCxt->xpathcxt, xtCxt->xmlerrcxt, uri);
+
 	if (xmlXPathRegisterNs(xtCxt->xpathcxt,
 						   pg_xmlCharStrndup(name, strlen(name)),
 						   pg_xmlCharStrndup(uri, strlen(uri))))
@@ -5114,3 +5122,22 @@ XmlTableDestroyOpaque(TableFuncScanState *state)
 	NO_XML_SUPPORT();
 #endif							/* not USE_LIBXML */
 }
+
+#ifdef USE_LIBXML
+xmlDocPtr
+xml_parse_wrapper(text *data, XmlOptionType xmloption_arg,
+		  bool preserve_whitespace, int encoding,
+		  XmlOptionType *parsed_xmloptiontype, xmlNodePtr *parsed_nodes,
+		  Node *escontext)
+{
+	return xml_parse(data, xmloption_arg, preserve_whitespace,
+					encoding, parsed_xmloptiontype, parsed_nodes, escontext);
+}
+
+xmlChar *
+pg_xmlCharStrndup_wrapper(const char *str, size_t len)
+{
+	return pg_xmlCharStrndup(str, len);
+}
+
+#endif							/* USE_LIBXML */

src/include/parser/parse_clause.h

@@ -62,4 +62,8 @@ extern PGDLLEXPORT optimize_explicit_cast_hook_type optimize_explicit_cast_hook;
 /* functions in parse_jsontable.c */
 extern ParseNamespaceItem *transformJsonTable(ParseState *pstate, JsonTable *jt);
 
+/* Hook for preprocessing OPENXML column definitions before XMLTABLE transformation */
+typedef void (*pre_transform_openxml_columns_hook_type) (ParseState *pstate, RangeTableFunc *rtf);
+extern PGDLLIMPORT pre_transform_openxml_columns_hook_type pre_transform_openxml_columns_hook;
+
 #endif							/* PARSE_CLAUSE_H */

src/include/utils/xml.h

@@ -19,6 +19,10 @@
 #include "fmgr.h"
 #include "nodes/execnodes.h"
 #include "nodes/primnodes.h"
+#ifdef USE_LIBXML
+#include <libxml/tree.h>
+#include <libxml/xpath.h>
+#endif
 
 typedef struct varlena xmltype;
 
@@ -85,6 +89,17 @@ extern char *map_sql_identifier_to_xml_name(const char *ident, bool fully_escape
 extern char *map_xml_name_to_sql_identifier(const char *name);
 extern char *map_sql_value_to_xml_value(Datum value, Oid type, bool xml_escape_strings);
 
+#ifdef USE_LIBXML
+extern xmlDocPtr xml_parse_wrapper(text *data, XmlOptionType xmloption_arg,
+							bool preserve_whitespace, int encoding,
+							XmlOptionType *parsed_xmloptiontype, xmlNodePtr *parsed_nodes,
+							Node *escontext);
+extern xmlChar *pg_xmlCharStrndup_wrapper(const char *str, size_t len);
+/* Hook function type for TSQL OPENXML namespace handling */
+typedef void (*openxml_set_namespaces_hook_type) (xmlXPathContext *xpathctx, PgXmlErrorContext *xmlerrcxt, char *doc_id_str);
+extern PGDLLIMPORT openxml_set_namespaces_hook_type openxml_set_namespaces_hook;
+#endif							/* USE_LIBXML */
+
 extern PGDLLIMPORT int xmlbinary;	/* XmlBinaryType, but int for guc enum */
 
 extern PGDLLIMPORT int xmloption;	/* XmlOptionType, but int for guc enum */