Fix namespace handling in xpath function

Previously, the xml value resulting from an xpath query would not have
namespace declarations if the namespace declarations were attached to
an ancestor element in the input xml value.  That means the output value
was not correct XML.  Fix that by running the result value through
xmlCopyNode(), which produces the correct namespace declarations.

Author: Ali Akbar <the.apaan@gmail.com>

4 files changed, 55 insertions, 8 deletions

diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index 335e4d38ca3..92a935ff63a 100644
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -141,9 +141,10 @@ static bool print_xml_decl(StringInfo buf, const xmlChar *version,
 			   pg_enc encoding, int standalone);
 static xmlDocPtr xml_parse(text *data, XmlOptionType xmloption_arg,
 		  bool preserve_whitespace, int encoding);
-static text *xml_xmlnodetoxmltype(xmlNodePtr cur);
+static text *xml_xmlnodetoxmltype(xmlNodePtr cur, PgXmlErrorContext *xmlerrcxt);
 static int xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
-					   ArrayBuildState **astate);
+					   ArrayBuildState **astate,
+					   PgXmlErrorContext *xmlerrcxt);
 #endif   /* USE_LIBXML */
 
 static StringInfo query_to_xml_internal(const char *query, char *tablename,
@@ -3606,26 +3607,41 @@ SPI_sql_row_to_xmlelement(int rownum, StringInfo result, char *tablename,
  * return value otherwise)
  */
 static text *
-xml_xmlnodetoxmltype(xmlNodePtr cur)
+xml_xmlnodetoxmltype(xmlNodePtr cur, PgXmlErrorContext *xmlerrcxt)
 {
 	xmltype    *result;
 
 	if (cur->type == XML_ELEMENT_NODE)
 	{
 		xmlBufferPtr buf;
+		xmlNodePtr	cur_copy;
 
 		buf = xmlBufferCreate();
+
+		/*
+		 * The result of xmlNodeDump() won't contain namespace definitions
+		 * from parent nodes, but xmlCopyNode() duplicates a node along with
+		 * its required namespace definitions.
+		 */
+		cur_copy = xmlCopyNode(cur, 1);
+
+		if (cur_copy == NULL)
+			xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
+						"could not copy node");
+
 		PG_TRY();
 		{
-			xmlNodeDump(buf, NULL, cur, 0, 1);
+			xmlNodeDump(buf, NULL, cur_copy, 0, 1);
 			result = xmlBuffer_to_xmltype(buf);
 		}
 		PG_CATCH();
 		{
+			xmlFreeNode(cur_copy);
 			xmlBufferFree(buf);
 			PG_RE_THROW();
 		}
 		PG_END_TRY();
+		xmlFreeNode(cur_copy);
 		xmlBufferFree(buf);
 	}
 	else
@@ -3667,7 +3683,8 @@ xml_xmlnodetoxmltype(xmlNodePtr cur)
  */
 static int
 xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
-					   ArrayBuildState **astate)
+					   ArrayBuildState **astate,
+					   PgXmlErrorContext *xmlerrcxt)
 {
 	int			result = 0;
 	Datum		datum;
@@ -3689,7 +3706,8 @@ xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
 
 					for (i = 0; i < result; i++)
 					{
-						datum = PointerGetDatum(xml_xmlnodetoxmltype(xpathobj->nodesetval->nodeTab[i]));
+						datum = PointerGetDatum(xml_xmlnodetoxmltype(xpathobj->nodesetval->nodeTab[i],
+																	 xmlerrcxt));
 						*astate = accumArrayResult(*astate, datum,
 												   false, XMLOID,
 												   CurrentMemoryContext);
@@ -3893,9 +3911,9 @@ xpath_internal(text *xpath_expr_text, xmltype *data, ArrayType *namespaces,
 		 * Extract the results as requested.
 		 */
 		if (res_nitems != NULL)
-			*res_nitems = xml_xpathobjtoxmlarray(xpathobj, astate);
+			*res_nitems = xml_xpathobjtoxmlarray(xpathobj, astate, xmlerrcxt);
 		else
-			(void) xml_xpathobjtoxmlarray(xpathobj, astate);
+			(void) xml_xpathobjtoxmlarray(xpathobj, astate, xmlerrcxt);
 	}
 	PG_CATCH();
 	{
diff --git a/src/test/regress/expected/xml.out b/src/test/regress/expected/xml.out
index 382f9df5093..9b7b393c85f 100644
--- a/src/test/regress/expected/xml.out
+++ b/src/test/regress/expected/xml.out
@@ -584,6 +584,21 @@ SELECT xpath('//loc:piece/@id', '<local:data xmlns:local="http://127.0.0.1"><loc
  {1,2}
 (1 row)
 
+SELECT xpath('//loc:piece', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number one</local:piece><local:piece id="2" /></local:data>', ARRAY[ARRAY['loc', 'http://127.0.0.1']]);
+                                                                     xpath                                                                      
+------------------------------------------------------------------------------------------------------------------------------------------------
+ {"<local:piece xmlns:local=\"http://127.0.0.1\" id=\"1\">number one</local:piece>","<local:piece xmlns:local=\"http://127.0.0.1\" id=\"2\"/>"}
+(1 row)
+
+SELECT xpath('//loc:piece', '<local:data xmlns:local="http://127.0.0.1" xmlns="http://127.0.0.2"><local:piece id="1"><internal>number one</internal><internal2/></local:piece><local:piece id="2" /></local:data>', ARRAY[ARRAY['loc', 'http://127.0.0.1']]);
+                                        xpath                                         
+--------------------------------------------------------------------------------------
+ {"<local:piece xmlns:local=\"http://127.0.0.1\" xmlns=\"http://127.0.0.2\" id=\"1\">+
+   <internal>number one</internal>                                                   +
+   <internal2/>                                                                      +
+ </local:piece>","<local:piece xmlns:local=\"http://127.0.0.1\" id=\"2\"/>"}
+(1 row)
+
 SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>');
           xpath          
 -------------------------
diff --git a/src/test/regress/expected/xml_1.out b/src/test/regress/expected/xml_1.out
index a34d1f41dd6..97382499da6 100644
--- a/src/test/regress/expected/xml_1.out
+++ b/src/test/regress/expected/xml_1.out
@@ -498,6 +498,18 @@ LINE 1: SELECT xpath('//loc:piece/@id', '<local:data xmlns:local="ht...
                                         ^
 DETAIL:  This functionality requires the server to be built with libxml support.
 HINT:  You need to rebuild PostgreSQL using --with-libxml.
+SELECT xpath('//loc:piece', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number one</local:piece><local:piece id="2" /></local:data>', ARRAY[ARRAY['loc', 'http://127.0.0.1']]);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xpath('//loc:piece', '<local:data xmlns:local="http:/...
+                                    ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+HINT:  You need to rebuild PostgreSQL using --with-libxml.
+SELECT xpath('//loc:piece', '<local:data xmlns:local="http://127.0.0.1" xmlns="http://127.0.0.2"><local:piece id="1"><internal>number one</internal><internal2/></local:piece><local:piece id="2" /></local:data>', ARRAY[ARRAY['loc', 'http://127.0.0.1']]);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xpath('//loc:piece', '<local:data xmlns:local="http:/...
+                                    ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+HINT:  You need to rebuild PostgreSQL using --with-libxml.
 SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>');
 ERROR:  unsupported XML feature
 LINE 1: SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>'...
diff --git a/src/test/regress/sql/xml.sql b/src/test/regress/sql/xml.sql
index 90d4d67f04e..ce87d426842 100644
--- a/src/test/regress/sql/xml.sql
+++ b/src/test/regress/sql/xml.sql
@@ -174,6 +174,8 @@ SELECT xpath(NULL, NULL) IS NULL FROM xmltest;
 SELECT xpath('', '<!-- error -->');
 SELECT xpath('//text()', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number one</local:piece><local:piece id="2" /></local:data>');
 SELECT xpath('//loc:piece/@id', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number one</local:piece><local:piece id="2" /></local:data>', ARRAY[ARRAY['loc', 'http://127.0.0.1']]);
+SELECT xpath('//loc:piece', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number one</local:piece><local:piece id="2" /></local:data>', ARRAY[ARRAY['loc', 'http://127.0.0.1']]);
+SELECT xpath('//loc:piece', '<local:data xmlns:local="http://127.0.0.1" xmlns="http://127.0.0.2"><local:piece id="1"><internal>number one</internal><internal2/></local:piece><local:piece id="2" /></local:data>', ARRAY[ARRAY['loc', 'http://127.0.0.1']]);
 SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>');
 SELECT xpath('//text()', '<root>&lt;</root>');
 SELECT xpath('//@value', '<root value="&lt;"/>');