/*-------------------------------------------------------------------------
 *
 * xml.c
 *	  XML data type support.
 *
 *
 * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $PostgreSQL: pgsql/src/backend/utils/adt/xml.c,v 1.78 2008/10/09 15:49:04 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */

/*
 * Generally, XML type support is only available when libxml use was
 * configured during the build.  But even if that is not done, the
 * type and all the functions are available, but most of them will
 * fail.  For one thing, this avoids having to manage variant catalog
 * installations.  But it also has nice effects such as that you can
 * dump a database containing XML type data even if the server is not
 * linked with libxml.	Thus, make sure xml_out() works even if nothing
 * else does.
 */

/*
 * Notes on memory management:
 *
 * Via callbacks, libxml is told to use palloc and friends for memory
 * management, within a context that we reset at transaction end (and also at
 * subtransaction abort) to prevent memory leaks.  Resetting at transaction or
 * subtransaction abort is necessary since we might have thrown a longjmp
 * while some data structures were not linked from anywhere persistent.
 * Resetting at transaction commit might not be necessary, but seems a good
 * idea to forestall long-term leaks.
 *
 * Sometimes libxml allocates global structures in the hope that it can reuse
 * them later on.  Therefore, before resetting LibxmlContext, we must tell
 * libxml to discard any global data it has.  The libxml API documentation is
 * not very good about specifying this, but for now we assume that
 * xmlCleanupParser() will get rid of anything we need to worry about.
 *
 * We use palloc --- which will throw a longjmp on error --- for allocation
 * callbacks that officially should act like malloc, ie, return NULL on
 * out-of-memory.  This is a bit risky since there is a chance of leaving
 * persistent libxml data structures in an inconsistent partially-constructed
 * state, perhaps leading to crash in xmlCleanupParser().  However, as of
 * early 2008 it is *known* that libxml can crash on out-of-memory due to
 * inadequate checks for NULL returns, so this behavior seems the lesser
 * of two evils.
 */

#include "postgres.h"

#ifdef USE_LIBXML
#include <libxml/chvalid.h>
#include <libxml/parser.h>
#include <libxml/tree.h>
#include <libxml/uri.h>
#include <libxml/xmlerror.h>
#include <libxml/xmlwriter.h>
#include <libxml/xpath.h>
#include <libxml/xpathInternals.h>
#endif   /* USE_LIBXML */

#include "catalog/namespace.h"
#include "catalog/pg_type.h"
#include "commands/dbcommands.h"
#include "executor/executor.h"
#include "executor/spi.h"
#include "fmgr.h"
#include "lib/stringinfo.h"
#include "libpq/pqformat.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "nodes/execnodes.h"
#include "nodes/nodeFuncs.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/date.h"
#include "utils/datetime.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/xml.h"


/* GUC variables */
int xmlbinary;
int xmloption;

#ifdef USE_LIBXML

static StringInfo xml_err_buf = NULL;
static MemoryContext LibxmlContext = NULL;

static void xml_init(void);
static void xml_memory_init(void);
static void xml_memory_cleanup(void);
static void *xml_palloc(size_t size);
static void *xml_repalloc(void *ptr, size_t size);
static void xml_pfree(void *ptr);
static char *xml_pstrdup(const char *string);
static void xml_ereport(int level, int sqlcode, const char *msg);
static void xml_errorHandler(void *ctxt, const char *msg,...);
static void xml_ereport_by_code(int level, int sqlcode,
					const char *msg, int errcode);
static xmlChar *xml_text2xmlChar(text *in);
static int parse_xml_decl(const xmlChar * str, size_t *lenp,
			   xmlChar ** version, xmlChar ** encoding, int *standalone);
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, xmlChar * encoding);
static text *xml_xmlnodetoxmltype(xmlNodePtr cur);
#endif   /* USE_LIBXML */

static StringInfo query_to_xml_internal(const char *query, char *tablename,
					  const char *xmlschema, bool nulls, bool tableforest,
					  const char *targetns, bool top_level);
static const char *map_sql_table_to_xmlschema(TupleDesc tupdesc, Oid relid,
						 bool nulls, bool tableforest, const char *targetns);
static const char *map_sql_schema_to_xmlschema_types(Oid nspid,
								  List *relid_list, bool nulls,
								  bool tableforest, const char *targetns);
static const char *map_sql_catalog_to_xmlschema_types(List *nspid_list,
								   bool nulls, bool tableforest,
								   const char *targetns);
static const char *map_sql_type_to_xml_name(Oid typeoid, int typmod);
static const char *map_sql_typecoll_to_xmlschema_types(List *tupdesc_list);
static const char *map_sql_type_to_xmlschema_type(Oid typeoid, int typmod);
static void SPI_sql_row_to_xmlelement(int rownum, StringInfo result,
						  char *tablename, bool nulls, bool tableforest,
						  const char *targetns, bool top_level);

#define NO_XML_SUPPORT() \
	ereport(ERROR, \
			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED), \
			 errmsg("unsupported XML feature"), \
			 errdetail("This functionality requires the server to be built with libxml support."), \
			 errhint("You need to rebuild PostgreSQL using --with-libxml.")))


/* from SQL/XML:2003 section 4.7 */
#define NAMESPACE_XSD "http://www.w3.org/2001/XMLSchema"
#define NAMESPACE_XSI "http://www.w3.org/2001/XMLSchema-instance"
#define NAMESPACE_SQLXML "http://standards.iso.org/iso/9075/2003/sqlxml"


#ifdef USE_LIBXML

static int
xmlChar_to_encoding(xmlChar * encoding_name)
{
	int			encoding = pg_char_to_encoding((char *) encoding_name);

	if (encoding < 0)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("invalid encoding name \"%s\"",
						(char *) encoding_name)));
	return encoding;
}
#endif


/*
 * xml_in uses a plain C string to VARDATA conversion, so for the time being
 * we use the conversion function for the text datatype.
 *
 * This is only acceptable so long as xmltype and text use the same
 * representation.
 */
Datum
xml_in(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
	char	   *s = PG_GETARG_CSTRING(0);
	xmltype    *vardata;
	xmlDocPtr	doc;

	vardata = (xmltype *) cstring_to_text(s);

	/*
	 * Parse the data to check if it is well-formed XML data.  Assume that
	 * ERROR occurred if parsing failed.
	 */
	doc = xml_parse(vardata, xmloption, true, NULL);
	xmlFreeDoc(doc);

	PG_RETURN_XML_P(vardata);
#else
	NO_XML_SUPPORT();
	return 0;
#endif
}


#define PG_XML_DEFAULT_VERSION "1.0"


/*
 * xml_out_internal uses a plain VARDATA to C string conversion, so for the
 * time being we use the conversion function for the text datatype.
 *
 * This is only acceptable so long as xmltype and text use the same
 * representation.
 */
static char *
xml_out_internal(xmltype *x, pg_enc target_encoding)
{
	char	   *str = text_to_cstring((text *) x);

#ifdef USE_LIBXML
	size_t		len = strlen(str);
	xmlChar    *version;
	int			standalone;
	int			res_code;

	if ((res_code = parse_xml_decl((xmlChar *) str,
								   &len, &version, NULL, &standalone)) == 0)
	{
		StringInfoData buf;

		initStringInfo(&buf);

		if (!print_xml_decl(&buf, version, target_encoding, standalone))
		{
			/*
			 * If we are not going to produce an XML declaration, eat a single
			 * newline in the original string to prevent empty first lines in
			 * the output.
			 */
			if (*(str + len) == '\n')
				len += 1;
		}
		appendStringInfoString(&buf, str + len);

		if (version)
			xmlFree(version);
		pfree(str);

		return buf.data;
	}

	xml_ereport_by_code(WARNING, ERRCODE_INTERNAL_ERROR,
						"could not parse XML declaration in stored value",
						res_code);
#endif
	return str;
}


Datum
xml_out(PG_FUNCTION_ARGS)
{
	xmltype    *x = PG_GETARG_XML_P(0);

	/*
	 * xml_out removes the encoding property in all cases.	This is because we
	 * cannot control from here whether the datum will be converted to a
	 * different client encoding, so we'd do more harm than good by including
	 * it.
	 */
	PG_RETURN_CSTRING(xml_out_internal(x, 0));
}


Datum
xml_recv(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
	StringInfo	buf = (StringInfo) PG_GETARG_POINTER(0);
	xmltype    *result;
	char	   *str;
	char	   *newstr;
	int			nbytes;
	xmlDocPtr	doc;
	xmlChar    *encoding = NULL;

	/*
	 * Read the data in raw format. We don't know yet what the encoding is, as
	 * that information is embedded in the xml declaration; so we have to
	 * parse that before converting to server encoding.
	 */
	nbytes = buf->len - buf->cursor;
	str = (char *) pq_getmsgbytes(buf, nbytes);

	/*
	 * We need a null-terminated string to pass to parse_xml_decl().  Rather
	 * than make a separate copy, make the temporary result one byte bigger
	 * than it needs to be.
	 */
	result = palloc(nbytes + 1 + VARHDRSZ);
	SET_VARSIZE(result, nbytes + VARHDRSZ);
	memcpy(VARDATA(result), str, nbytes);
	str = VARDATA(result);
	str[nbytes] = '\0';

	parse_xml_decl((xmlChar *) str, NULL, NULL, &encoding, NULL);

	/*
	 * Parse the data to check if it is well-formed XML data.  Assume that
	 * xml_parse will throw ERROR if not.
	 */
	doc = xml_parse(result, xmloption, true, encoding);
	xmlFreeDoc(doc);

	/* Now that we know what we're dealing with, convert to server encoding */
	newstr = (char *) pg_do_encoding_conversion((unsigned char *) str,
												nbytes,
												encoding ?
											  xmlChar_to_encoding(encoding) :
												PG_UTF8,
												GetDatabaseEncoding());

	if (newstr != str)
	{
		pfree(result);
		result = (xmltype *) cstring_to_text(newstr);
		pfree(newstr);
	}

	PG_RETURN_XML_P(result);
#else
	NO_XML_SUPPORT();
	return 0;
#endif
}


Datum
xml_send(PG_FUNCTION_ARGS)
{
	xmltype    *x = PG_GETARG_XML_P(0);
	char	   *outval;
	StringInfoData buf;

	/*
	 * xml_out_internal doesn't convert the encoding, it just prints the right
	 * declaration. pq_sendtext will do the conversion.
	 */
	outval = xml_out_internal(x, pg_get_client_encoding());

	pq_begintypsend(&buf);
	pq_sendtext(&buf, outval, strlen(outval));
	pfree(outval);
	PG_RETURN_BYTEA_P(pq_endtypsend(&buf));
}


#ifdef USE_LIBXML
static void
appendStringInfoText(StringInfo str, const text *t)
{
	appendBinaryStringInfo(str, VARDATA(t), VARSIZE(t) - VARHDRSZ);
}
#endif


static xmltype *
stringinfo_to_xmltype(StringInfo buf)
{
	return (xmltype *) cstring_to_text_with_len(buf->data, buf->len);
}


static xmltype *
cstring_to_xmltype(const char *string)
{
	return (xmltype *) cstring_to_text(string);
}


#ifdef USE_LIBXML
static xmltype *
xmlBuffer_to_xmltype(xmlBufferPtr buf)
{
	return (xmltype *) cstring_to_text_with_len((char *) xmlBufferContent(buf),
												xmlBufferLength(buf));
}
#endif


Datum
xmlcomment(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
	text	   *arg = PG_GETARG_TEXT_P(0);
	char	   *argdata = VARDATA(arg);
	int			len = VARSIZE(arg) - VARHDRSZ;
	StringInfoData buf;
	int			i;

	/* check for "--" in string or "-" at the end */
	for (i = 1; i < len; i++)
	{
		if (argdata[i] == '-' && argdata[i - 1] == '-')
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_XML_COMMENT),
					 errmsg("invalid XML comment")));
	}
	if (len > 0 && argdata[len - 1] == '-')
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_XML_COMMENT),
				 errmsg("invalid XML comment")));

	initStringInfo(&buf);
	appendStringInfo(&buf, "<!--");
	appendStringInfoText(&buf, arg);
	appendStringInfo(&buf, "-->");

	PG_RETURN_XML_P(stringinfo_to_xmltype(&buf));
#else
	NO_XML_SUPPORT();
	return 0;
#endif
}



/*
 * TODO: xmlconcat needs to merge the notations and unparsed entities
 * of the argument values.	Not very important in practice, though.
 */
xmltype *
xmlconcat(List *args)
{
#ifdef USE_LIBXML
	int			global_standalone = 1;
	xmlChar    *global_version = NULL;
	bool		global_version_no_value = false;
	StringInfoData buf;
	ListCell   *v;

	initStringInfo(&buf);
	foreach(v, args)
	{
		xmltype    *x = DatumGetXmlP(PointerGetDatum(lfirst(v)));
		size_t		len;
		xmlChar    *version;
		int			standalone;
		char	   *str;

		len = VARSIZE(x) - VARHDRSZ;
		str = text_to_cstring((text *) x);

		parse_xml_decl((xmlChar *) str, &len, &version, NULL, &standalone);

		if (standalone == 0 && global_standalone == 1)
			global_standalone = 0;
		if (standalone < 0)
			global_standalone = -1;

		if (!version)
			global_version_no_value = true;
		else if (!global_version)
			global_version = xmlStrdup(version);
		else if (xmlStrcmp(version, global_version) != 0)
			global_version_no_value = true;

		appendStringInfoString(&buf, str + len);
		pfree(str);
	}

	if (!global_version_no_value || global_standalone >= 0)
	{
		StringInfoData buf2;

		initStringInfo(&buf2);

		print_xml_decl(&buf2,
					   (!global_version_no_value) ? global_version : NULL,
					   0,
					   global_standalone);

		appendStringInfoString(&buf2, buf.data);
		buf = buf2;
	}

	return stringinfo_to_xmltype(&buf);
#else
	NO_XML_SUPPORT();
	return NULL;
#endif
}


/*
 * XMLAGG support
 */
Datum
xmlconcat2(PG_FUNCTION_ARGS)
{
	if (PG_ARGISNULL(0))
	{
		if (PG_ARGISNULL(1))
			PG_RETURN_NULL();
		else
			PG_RETURN_XML_P(PG_GETARG_XML_P(1));
	}
	else if (PG_ARGISNULL(1))
		PG_RETURN_XML_P(PG_GETARG_XML_P(0));
	else
		PG_RETURN_XML_P(xmlconcat(list_make2(PG_GETARG_XML_P(0),
											 PG_GETARG_XML_P(1))));
}


Datum
texttoxml(PG_FUNCTION_ARGS)
{
	text	   *data = PG_GETARG_TEXT_P(0);

	PG_RETURN_XML_P(xmlparse(data, xmloption, true));
}


Datum
xmltotext(PG_FUNCTION_ARGS)
{
	xmltype    *data = PG_GETARG_XML_P(0);

	/* It's actually binary compatible. */
	PG_RETURN_TEXT_P((text *) data);
}


text *
xmltotext_with_xmloption(xmltype *data, XmlOptionType xmloption_arg)
{
	if (xmloption_arg == XMLOPTION_DOCUMENT && !xml_is_document(data))
		ereport(ERROR,
				(errcode(ERRCODE_NOT_AN_XML_DOCUMENT),
				 errmsg("not an XML document")));

	/* It's actually binary compatible, save for the above check. */
	return (text *) data;
}


xmltype *
xmlelement(XmlExprState *xmlExpr, ExprContext *econtext)
{
#ifdef USE_LIBXML
	XmlExpr    *xexpr = (XmlExpr *) xmlExpr->xprstate.expr;
	xmltype    *result;
	List	   *named_arg_strings;
	List	   *arg_strings;
	int			i;
	ListCell   *arg;
	ListCell   *narg;
	xmlBufferPtr buf;
	xmlTextWriterPtr writer;

	/*
	 * We first evaluate all the arguments, then start up libxml and create
	 * the result.	This avoids issues if one of the arguments involves a call
	 * to some other function or subsystem that wants to use libxml on its own
	 * terms.
	 */
	named_arg_strings = NIL;
	i = 0;
	foreach(arg, xmlExpr->named_args)
	{
		ExprState  *e = (ExprState *) lfirst(arg);
		Datum		value;
		bool		isnull;
		char	   *str;

		value = ExecEvalExpr(e, econtext, &isnull, NULL);
		if (isnull)
			str = NULL;
		else
			str = OutputFunctionCall(&xmlExpr->named_outfuncs[i], value);
		named_arg_strings = lappend(named_arg_strings, str);
		i++;
	}

	arg_strings = NIL;
	foreach(arg, xmlExpr->args)
	{
		ExprState  *e = (ExprState *) lfirst(arg);
		Datum		value;
		bool		isnull;
		char	   *str;

		value = ExecEvalExpr(e, econtext, &isnull, NULL);
		/* here we can just forget NULL elements immediately */
		if (!isnull)
		{
			str = map_sql_value_to_xml_value(value,
											 exprType((Node *) e->expr));
			arg_strings = lappend(arg_strings, str);
		}
	}

	/* now safe to run libxml */
	xml_init();

	buf = xmlBufferCreate();
	writer = xmlNewTextWriterMemory(buf, 0);

	xmlTextWriterStartElement(writer, (xmlChar *) xexpr->name);

	forboth(arg, named_arg_strings, narg, xexpr->arg_names)
	{
		char	   *str = (char *) lfirst(arg);
		char	   *argname = strVal(lfirst(narg));

		if (str)
		{
			xmlTextWriterWriteAttribute(writer,
										(xmlChar *) argname,
										(xmlChar *) str);
			pfree(str);
		}
	}

	foreach(arg, arg_strings)
	{
		char	   *str = (char *) lfirst(arg);

		xmlTextWriterWriteRaw(writer, (xmlChar *) str);
	}

	xmlTextWriterEndElement(writer);
	xmlFreeTextWriter(writer);

	result = xmlBuffer_to_xmltype(buf);
	xmlBufferFree(buf);

	return result;
#else
	NO_XML_SUPPORT();
	return NULL;
#endif
}


xmltype *
xmlparse(text *data, XmlOptionType xmloption_arg, bool preserve_whitespace)
{
#ifdef USE_LIBXML
	xmlDocPtr	doc;

	doc = xml_parse(data, xmloption_arg, preserve_whitespace, NULL);
	xmlFreeDoc(doc);

	return (xmltype *) data;
#else
	NO_XML_SUPPORT();
	return NULL;
#endif
}


xmltype *
xmlpi(char *target, text *arg, bool arg_is_null, bool *result_is_null)
{
#ifdef USE_LIBXML
	xmltype    *result;
	StringInfoData buf;

	if (pg_strcasecmp(target, "xml") == 0)
		ereport(ERROR,
				(errcode(ERRCODE_SYNTAX_ERROR), /* really */
				 errmsg("invalid XML processing instruction"),
				 errdetail("XML processing instruction target name cannot be \"%s\".", target)));

	/*
	 * Following the SQL standard, the null check comes after the syntax check
	 * above.
	 */
	*result_is_null = arg_is_null;
	if (*result_is_null)
		return NULL;

	initStringInfo(&buf);

	appendStringInfo(&buf, "<?%s", target);

	if (arg != NULL)
	{
		char	   *string;

		string = text_to_cstring(arg);
		if (strstr(string, "?>") != NULL)
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_XML_PROCESSING_INSTRUCTION),
					 errmsg("invalid XML processing instruction"),
			errdetail("XML processing instruction cannot contain \"?>\".")));

		appendStringInfoChar(&buf, ' ');
		appendStringInfoString(&buf, string + strspn(string, " "));
		pfree(string);
	}
	appendStringInfoString(&buf, "?>");

	result = stringinfo_to_xmltype(&buf);
	pfree(buf.data);
	return result;
#else
	NO_XML_SUPPORT();
	return NULL;
#endif
}


xmltype *
xmlroot(xmltype *data, text *version, int standalone)
{
#ifdef USE_LIBXML
	char	   *str;
	size_t		len;
	xmlChar    *orig_version;
	int			orig_standalone;
	StringInfoData buf;

	len = VARSIZE(data) - VARHDRSZ;
	str = text_to_cstring((text *) data);

	parse_xml_decl((xmlChar *) str, &len, &orig_version, NULL, &orig_standalone);

	if (version)
		orig_version = xml_text2xmlChar(version);
	else
		orig_version = NULL;

	switch (standalone)
	{
		case XML_STANDALONE_YES:
			orig_standalone = 1;
			break;
		case XML_STANDALONE_NO:
			orig_standalone = 0;
			break;
		case XML_STANDALONE_NO_VALUE:
			orig_standalone = -1;
			break;
		case XML_STANDALONE_OMITTED:
			/* leave original value */
			break;
	}

	initStringInfo(&buf);
	print_xml_decl(&buf, orig_version, 0, orig_standalone);
	appendStringInfoString(&buf, str + len);

	return stringinfo_to_xmltype(&buf);
#else
	NO_XML_SUPPORT();
	return NULL;
#endif
}


/*
 * Validate document (given as string) against DTD (given as external link)
 *
 * This has been removed because it is a security hole: unprivileged users
 * should not be able to use Postgres to fetch arbitrary external files,
 * which unfortunately is exactly what libxml is willing to do with the DTD
 * parameter.
 */
Datum
xmlvalidate(PG_FUNCTION_ARGS)
{
	ereport(ERROR,
			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
			 errmsg("xmlvalidate is not implemented")));
	return 0;
}


bool
xml_is_document(xmltype *arg)
{
#ifdef USE_LIBXML
	bool		result;
	xmlDocPtr	doc = NULL;
	MemoryContext ccxt = CurrentMemoryContext;

	PG_TRY();
	{
		doc = xml_parse((text *) arg, XMLOPTION_DOCUMENT, true, NULL);
		result = true;
	}
	PG_CATCH();
	{
		ErrorData  *errdata;
		MemoryContext ecxt;

		ecxt = MemoryContextSwitchTo(ccxt);
		errdata = CopyErrorData();
		if (errdata->sqlerrcode == ERRCODE_INVALID_XML_DOCUMENT)
		{
			FlushErrorState();
			result = false;
		}
		else
		{
			MemoryContextSwitchTo(ecxt);
			PG_RE_THROW();
		}
	}
	PG_END_TRY();

	if (doc)
		xmlFreeDoc(doc);

	return result;
#else							/* not USE_LIBXML */
	NO_XML_SUPPORT();
	return false;
#endif   /* not USE_LIBXML */
}


/*
 * xml cleanup function for transaction end.  This is also called on
 * subtransaction abort; see notes at top of file for rationale.
 */
void
AtEOXact_xml(void)
{
#ifdef USE_LIBXML
	xml_memory_cleanup();
#endif
}


#ifdef USE_LIBXML

/*
 * Set up for use of libxml --- this should be called by each function that
 * is about to use libxml facilities.
 *
 * TODO: xmlChar is utf8-char, make proper tuning (initdb with enc!=utf8 and
 * check)
 */
static void
xml_init(void)
{
	static bool first_time = true;

	if (first_time)
	{
		/* Stuff we need do only once per session */
		MemoryContext oldcontext;

		/*
		 * Currently, we have no pure UTF-8 support for internals -- check if
		 * we can work.
		 */
		if (sizeof(char) != sizeof(xmlChar))
			ereport(ERROR,
					(errmsg("could not initialize XML library"),
					 errdetail("libxml2 has incompatible char type: sizeof(char)=%u, sizeof(xmlChar)=%u.",
							   (int) sizeof(char), (int) sizeof(xmlChar))));

		/* create error buffer in permanent context */
		oldcontext = MemoryContextSwitchTo(TopMemoryContext);
		xml_err_buf = makeStringInfo();
		MemoryContextSwitchTo(oldcontext);

		/* Now that xml_err_buf exists, safe to call xml_errorHandler */
		xmlSetGenericErrorFunc(NULL, xml_errorHandler);

		/* Set up memory allocation our way, too */
		xml_memory_init();

		/* Check library compatibility */
		LIBXML_TEST_VERSION;

		first_time = false;
	}
	else
	{
		/* Reset pre-existing buffer to empty */
		Assert(xml_err_buf != NULL);
		resetStringInfo(xml_err_buf);

		/*
		 * We re-establish the callback functions every time.  This makes it
		 * safe for other subsystems (PL/Perl, say) to also use libxml with
		 * their own callbacks ... so long as they likewise set up the
		 * callbacks on every use.	It's cheap enough to not be worth worrying
		 * about, anyway.
		 */
		xmlSetGenericErrorFunc(NULL, xml_errorHandler);
		xml_memory_init();
	}
}


/*
 * SQL/XML allows storing "XML documents" or "XML content".  "XML
 * documents" are specified by the XML specification and are parsed
 * easily by libxml.  "XML content" is specified by SQL/XML as the
 * production "XMLDecl? content".  But libxml can only parse the
 * "content" part, so we have to parse the XML declaration ourselves
 * to complete this.
 */

#define CHECK_XML_SPACE(p) \
	do { \
		if (!xmlIsBlank_ch(*(p))) \
			return XML_ERR_SPACE_REQUIRED; \
	} while (0)

#define SKIP_XML_SPACE(p) \
	while (xmlIsBlank_ch(*(p))) (p)++

/* Letter | Digit | '.' | '-' | '_' | ':' | CombiningChar | Extender */
/* Beware of multiple evaluations of argument! */
#define PG_XMLISNAMECHAR(c) \
	(xmlIsBaseChar_ch(c) || xmlIsIdeographicQ(c) \
			|| xmlIsDigit_ch(c) \
			|| c == '.' || c == '-' || c == '_' || c == ':' \
			|| xmlIsCombiningQ(c) \
			|| xmlIsExtender_ch(c))

static int
parse_xml_decl(const xmlChar * str, size_t *lenp,
			   xmlChar ** version, xmlChar ** encoding, int *standalone)
{
	const xmlChar *p;
	const xmlChar *save_p;
	size_t		len;
	int			utf8char;
	int			utf8len;

	xml_init();

	if (version)
		*version = NULL;
	if (encoding)
		*encoding = NULL;
	if (standalone)
		*standalone = -1;

	p = str;

	if (xmlStrncmp(p, (xmlChar *) "<?xml", 5) != 0)
		goto finished;

	/* if next char is name char, it's a PI like <?xml-stylesheet ...?> */
	utf8len = strlen((const char *) (p + 5));
	utf8char = xmlGetUTF8Char(p + 5, &utf8len);
	if (PG_XMLISNAMECHAR(utf8char))
		goto finished;

	p += 5;

	/* version */
	CHECK_XML_SPACE(p);
	SKIP_XML_SPACE(p);
	if (xmlStrncmp(p, (xmlChar *) "version", 7) != 0)
		return XML_ERR_VERSION_MISSING;
	p += 7;
	SKIP_XML_SPACE(p);
	if (*p != '=')
		return XML_ERR_VERSION_MISSING;
	p += 1;
	SKIP_XML_SPACE(p);

	if (*p == '\'' || *p == '"')
	{
		const xmlChar *q;

		q = xmlStrchr(p + 1, *p);
		if (!q)
			return XML_ERR_VERSION_MISSING;

		if (version)
			*version = xmlStrndup(p + 1, q - p - 1);
		p = q + 1;
	}
	else
		return XML_ERR_VERSION_MISSING;

	/* encoding */
	save_p = p;
	SKIP_XML_SPACE(p);
	if (xmlStrncmp(p, (xmlChar *) "encoding", 8) == 0)
	{
		CHECK_XML_SPACE(save_p);
		p += 8;
		SKIP_XML_SPACE(p);
		if (*p != '=')
			return XML_ERR_MISSING_ENCODING;
		p += 1;
		SKIP_XML_SPACE(p);

		if (*p == '\'' || *p == '"')
		{
			const xmlChar *q;

			q = xmlStrchr(p + 1, *p);
			if (!q)
				return XML_ERR_MISSING_ENCODING;

			if (encoding)
				*encoding = xmlStrndup(p + 1, q - p - 1);
			p = q + 1;
		}
		else
			return XML_ERR_MISSING_ENCODING;
	}
	else
	{
		p = save_p;
	}

	/* standalone */
	save_p = p;
	SKIP_XML_SPACE(p);
	if (xmlStrncmp(p, (xmlChar *) "standalone", 10) == 0)
	{
		CHECK_XML_SPACE(save_p);
		p += 10;
		SKIP_XML_SPACE(p);
		if (*p != '=')
			return XML_ERR_STANDALONE_VALUE;
		p += 1;
		SKIP_XML_SPACE(p);
		if (xmlStrncmp(p, (xmlChar *) "'yes'", 5) == 0 ||
			xmlStrncmp(p, (xmlChar *) "\"yes\"", 5) == 0)
		{
			*standalone = 1;
			p += 5;
		}
		else if (xmlStrncmp(p, (xmlChar *) "'no'", 4) == 0 ||
				 xmlStrncmp(p, (xmlChar *) "\"no\"", 4) == 0)
		{
			*standalone = 0;
			p += 4;
		}
		else
			return XML_ERR_STANDALONE_VALUE;
	}
	else
	{
		p = save_p;
	}

	SKIP_XML_SPACE(p);
	if (xmlStrncmp(p, (xmlChar *) "?>", 2) != 0)
		return XML_ERR_XMLDECL_NOT_FINISHED;
	p += 2;

finished:
	len = p - str;

	for (p = str; p < str + len; p++)
		if (*p > 127)
			return XML_ERR_INVALID_CHAR;

	if (lenp)
		*lenp = len;

	return XML_ERR_OK;
}


/*
 * Write an XML declaration.  On output, we adjust the XML declaration
 * as follows.	(These rules are the moral equivalent of the clause
 * "Serialization of an XML value" in the SQL standard.)
 *
 * We try to avoid generating an XML declaration if possible.  This is
 * so that you don't get trivial things like xml '<foo/>' resulting in
 * '<?xml version="1.0"?><foo/>', which would surely be annoying.  We
 * must provide a declaration if the standalone property is specified
 * or if we include an encoding declaration.  If we have a
 * declaration, we must specify a version (XML requires this).
 * Otherwise we only make a declaration if the version is not "1.0",
 * which is the default version specified in SQL:2003.
 */
static bool
print_xml_decl(StringInfo buf, const xmlChar * version,
			   pg_enc encoding, int standalone)
{
	xml_init();

	if ((version && strcmp((char *) version, PG_XML_DEFAULT_VERSION) != 0)
		|| (encoding && encoding != PG_UTF8)
		|| standalone != -1)
	{
		appendStringInfoString(buf, "<?xml");

		if (version)
			appendStringInfo(buf, " version=\"%s\"", version);
		else
			appendStringInfo(buf, " version=\"%s\"", PG_XML_DEFAULT_VERSION);

		if (encoding && encoding != PG_UTF8)
		{
			/*
			 * XXX might be useful to convert this to IANA names (ISO-8859-1
			 * instead of LATIN1 etc.); needs field experience
			 */
			appendStringInfo(buf, " encoding=\"%s\"",
							 pg_encoding_to_char(encoding));
		}

		if (standalone == 1)
			appendStringInfoString(buf, " standalone=\"yes\"");
		else if (standalone == 0)
			appendStringInfoString(buf, " standalone=\"no\"");
		appendStringInfoString(buf, "?>");

		return true;
	}
	else
		return false;
}


/*
 * Convert a C string to XML internal representation
 *
 * TODO maybe, libxml2's xmlreader is better? (do not construct DOM,
 * yet do not use SAX - see xmlreader.c)
 */
static xmlDocPtr
xml_parse(text *data, XmlOptionType xmloption_arg, bool preserve_whitespace,
		  xmlChar * encoding)
{
	int32		len;
	xmlChar    *string;
	xmlChar    *utf8string;
	xmlParserCtxtPtr ctxt;
	xmlDocPtr	doc;

	len = VARSIZE(data) - VARHDRSZ;		/* will be useful later */
	string = xml_text2xmlChar(data);

	utf8string = pg_do_encoding_conversion(string,
										   len,
										   encoding ?
										   xmlChar_to_encoding(encoding) :
										   GetDatabaseEncoding(),
										   PG_UTF8);

	xml_init();
	xmlInitParser();
	ctxt = xmlNewParserCtxt();
	if (ctxt == NULL)
		xml_ereport(ERROR, ERRCODE_OUT_OF_MEMORY,
					"could not allocate parser context");

	if (xmloption_arg == XMLOPTION_DOCUMENT)
	{
		/*
		 * Note, that here we try to apply DTD defaults
		 * (XML_PARSE_DTDATTR) according to SQL/XML: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:10.16.7.e)
		 */
		doc = xmlCtxtReadDoc(ctxt, utf8string,
							 NULL,
							 "UTF-8",
							 XML_PARSE_NOENT | XML_PARSE_DTDATTR
							 | (preserve_whitespace ? 0 : XML_PARSE_NOBLANKS));
		if (doc == NULL)
			xml_ereport(ERROR, ERRCODE_INVALID_XML_DOCUMENT,
						"invalid XML document");
	}
	else
	{
		int			res_code;
		size_t		count;
		xmlChar    *version = NULL;
		int			standalone = -1;

		doc = xmlNewDoc(NULL);

		res_code = parse_xml_decl(utf8string,
								  &count, &version, NULL, &standalone);
		if (res_code != 0)
			xml_ereport_by_code(ERROR, ERRCODE_INVALID_XML_CONTENT,
								"invalid XML content: invalid XML declaration",
								res_code);

		res_code = xmlParseBalancedChunkMemory(doc, NULL, NULL, 0,
											   utf8string + count, NULL);
		if (res_code != 0)
			xml_ereport(ERROR, ERRCODE_INVALID_XML_CONTENT,
						"invalid XML content");

		doc->version = xmlStrdup(version);
		doc->encoding = xmlStrdup((xmlChar *) "UTF-8");
		doc->standalone = standalone;
	}

	xmlFreeParserCtxt(ctxt);

	return doc;
}


/*
 * xmlChar<->text conversions
 */
static xmlChar *
xml_text2xmlChar(text *in)
{
	return (xmlChar *) text_to_cstring(in);
}


/*
 * Manage the special context used for all libxml allocations
 */
static void
xml_memory_init(void)
{
	/*
	 * Create memory context if not there already.  We make it a child of
	 * TopMemoryContext, even though our current policy is that it doesn't
	 * survive past transaction end, because we want to be really really
	 * sure it doesn't go away before we've called xmlCleanupParser().
	 */
	if (LibxmlContext == NULL)
		LibxmlContext = AllocSetContextCreate(TopMemoryContext,
											  "LibxmlContext",
											  ALLOCSET_DEFAULT_MINSIZE,
											  ALLOCSET_DEFAULT_INITSIZE,
											  ALLOCSET_DEFAULT_MAXSIZE);

	/* Re-establish the callbacks even if already set */
	xmlMemSetup(xml_pfree, xml_palloc, xml_repalloc, xml_pstrdup);
}

static void
xml_memory_cleanup(void)
{
	if (LibxmlContext != NULL)
	{
		/* Give libxml a chance to clean up dangling pointers */
		xmlCleanupParser();

		/* And flush the context */
		MemoryContextDelete(LibxmlContext);
		LibxmlContext = NULL;
	}
}

/*
 * Wrappers for memory management functions
 */
static void *
xml_palloc(size_t size)
{
	return MemoryContextAlloc(LibxmlContext, size);
}


static void *
xml_repalloc(void *ptr, size_t size)
{
	return repalloc(ptr, size);
}


static void
xml_pfree(void *ptr)
{
	pfree(ptr);
}


static char *
xml_pstrdup(const char *string)
{
	return MemoryContextStrdup(LibxmlContext, string);
}


/*
 * Wrapper for "ereport" function for XML-related errors.  The "msg"
 * is the SQL-level message; some can be adopted from the SQL/XML
 * standard.  This function adds libxml's native error messages, if
 * any, as detail.
 */
static void
xml_ereport(int level, int sqlcode, const char *msg)
{
	char	   *detail;

	if (xml_err_buf->len > 0)
	{
		detail = pstrdup(xml_err_buf->data);
		resetStringInfo(xml_err_buf);
	}
	else
		detail = NULL;

	/* libxml error messages end in '\n'; get rid of it */
	if (detail)
	{
		size_t		len;

		len = strlen(detail);
		if (len > 0 && detail[len - 1] == '\n')
			detail[len - 1] = '\0';

		ereport(level,
				(errcode(sqlcode),
				 errmsg("%s", msg),
				 errdetail("%s", detail)));
	}
	else
	{
		ereport(level,
				(errcode(sqlcode),
				 errmsg("%s", msg)));
	}
}


/*
 * Error handler for libxml error messages
 */
static void
xml_errorHandler(void *ctxt, const char *msg,...)
{
	/* Append the formatted text to xml_err_buf */
	for (;;)
	{
		va_list		args;
		bool		success;

		/* Try to format the data. */
		va_start(args, msg);
		success = appendStringInfoVA(xml_err_buf, msg, args);
		va_end(args);

		if (success)
			break;

		/* Double the buffer size and try again. */
		enlargeStringInfo(xml_err_buf, xml_err_buf->maxlen);
	}
}


/*
 * Wrapper for "ereport" function for XML-related errors.  The "msg"
 * is the SQL-level message; some can be adopted from the SQL/XML
 * standard.  This function uses "code" to create a textual detail
 * message.  At the moment, we only need to cover those codes that we
 * may raise in this file.
 */
static void
xml_ereport_by_code(int level, int sqlcode,
					const char *msg, int code)
{
	const char *det;

	switch (code)
	{
		case XML_ERR_INVALID_CHAR:
			det = gettext_noop("Invalid character value.");
			break;
		case XML_ERR_SPACE_REQUIRED:
			det = gettext_noop("Space required.");
			break;
		case XML_ERR_STANDALONE_VALUE:
			det = gettext_noop("standalone accepts only 'yes' or 'no'.");
			break;
		case XML_ERR_VERSION_MISSING:
			det = gettext_noop("Malformed declaration: missing version.");
			break;
		case XML_ERR_MISSING_ENCODING:
			det = gettext_noop("Missing encoding in text declaration.");
			break;
		case XML_ERR_XMLDECL_NOT_FINISHED:
			det = gettext_noop("Parsing XML declaration: '?>' expected.");
			break;
		default:
			det = gettext_noop("Unrecognized libxml error code: %d.");
			break;
	}

	ereport(level,
			(errcode(sqlcode),
			 errmsg("%s", msg),
			 errdetail(det, code)));
}


/*
 * Convert one char in the current server encoding to a Unicode codepoint.
 */
static pg_wchar
sqlchar_to_unicode(char *s)
{
	char	   *utf8string;
	pg_wchar	ret[2];			/* need space for trailing zero */

	utf8string = (char *) pg_do_encoding_conversion((unsigned char *) s,
													pg_mblen(s),
													GetDatabaseEncoding(),
													PG_UTF8);

	pg_encoding_mb2wchar_with_len(PG_UTF8, utf8string, ret, pg_mblen(s));

	return ret[0];
}


static bool
is_valid_xml_namefirst(pg_wchar c)
{
	/* (Letter | '_' | ':') */
	return (xmlIsBaseCharQ(c) || xmlIsIdeographicQ(c)
			|| c == '_' || c == ':');
}


static bool
is_valid_xml_namechar(pg_wchar c)
{
	/* Letter | Digit | '.' | '-' | '_' | ':' | CombiningChar | Extender */
	return (xmlIsBaseCharQ(c) || xmlIsIdeographicQ(c)
			|| xmlIsDigitQ(c)
			|| c == '.' || c == '-' || c == '_' || c == ':'
			|| xmlIsCombiningQ(c)
			|| xmlIsExtenderQ(c));
}
#endif   /* USE_LIBXML */


/*
 * Map SQL identifier to XML name; see SQL/XML:2003 section 9.1.
 */
char *
map_sql_identifier_to_xml_name(char *ident, bool fully_escaped,
							   bool escape_period)
{
#ifdef USE_LIBXML
	StringInfoData buf;
	char	   *p;

	/*
	 * SQL/XML doesn't make use of this case anywhere, so it's probably a
	 * mistake.
	 */
	Assert(fully_escaped || !escape_period);

	initStringInfo(&buf);

	for (p = ident; *p; p += pg_mblen(p))
	{
		if (*p == ':' && (p == ident || fully_escaped))
			appendStringInfo(&buf, "_x003A_");
		else if (*p == '_' && *(p + 1) == 'x')
			appendStringInfo(&buf, "_x005F_");
		else if (fully_escaped && p == ident &&
				 pg_strncasecmp(p, "xml", 3) == 0)
		{
			if (*p == 'x')
				appendStringInfo(&buf, "_x0078_");
			else
				appendStringInfo(&buf, "_x0058_");
		}
		else if (escape_period && *p == '.')
			appendStringInfo(&buf, "_x002E_");
		else
		{
			pg_wchar	u = sqlchar_to_unicode(p);

			if ((p == ident)
				? !is_valid_xml_namefirst(u)
				: !is_valid_xml_namechar(u))
				appendStringInfo(&buf, "_x%04X_", (unsigned int) u);
			else
				appendBinaryStringInfo(&buf, p, pg_mblen(p));
		}
	}

	return buf.data;
#else							/* not USE_LIBXML */
	NO_XML_SUPPORT();
	return NULL;
#endif   /* not USE_LIBXML */
}


/*
 * Map a Unicode codepoint into the current server encoding.
 */
static char *
unicode_to_sqlchar(pg_wchar c)
{
	static unsigned char utf8string[5]; /* need trailing zero */

	if (c <= 0x7F)
	{
		utf8string[0] = c;
	}
	else if (c <= 0x7FF)
	{
		utf8string[0] = 0xC0 | ((c >> 6) & 0x1F);
		utf8string[1] = 0x80 | (c & 0x3F);
	}
	else if (c <= 0xFFFF)
	{
		utf8string[0] = 0xE0 | ((c >> 12) & 0x0F);
		utf8string[1] = 0x80 | ((c >> 6) & 0x3F);
		utf8string[2] = 0x80 | (c & 0x3F);
	}
	else
	{
		utf8string[0] = 0xF0 | ((c >> 18) & 0x07);
		utf8string[1] = 0x80 | ((c >> 12) & 0x3F);
		utf8string[2] = 0x80 | ((c >> 6) & 0x3F);
		utf8string[3] = 0x80 | (c & 0x3F);
	}

	return (char *) pg_do_encoding_conversion(utf8string,
											  pg_mblen((char *) utf8string),
											  PG_UTF8,
											  GetDatabaseEncoding());
}


/*
 * Map XML name to SQL identifier; see SQL/XML:2003 section 9.17.
 */
char *
map_xml_name_to_sql_identifier(char *name)
{
	StringInfoData buf;
	char	   *p;

	initStringInfo(&buf);

	for (p = name; *p; p += pg_mblen(p))
	{
		if (*p == '_' && *(p + 1) == 'x'
			&& isxdigit((unsigned char) *(p + 2))
			&& isxdigit((unsigned char) *(p + 3))
			&& isxdigit((unsigned char) *(p + 4))
			&& isxdigit((unsigned char) *(p + 5))
			&& *(p + 6) == '_')
		{
			unsigned int u;

			sscanf(p + 2, "%X", &u);
			appendStringInfoString(&buf, unicode_to_sqlchar(u));
			p += 6;
		}
		else
			appendBinaryStringInfo(&buf, p, pg_mblen(p));
	}

	return buf.data;
}

/*
 * Map SQL value to XML value; see SQL/XML:2003 section 9.16.
 */
char *
map_sql_value_to_xml_value(Datum value, Oid type)
{
	StringInfoData buf;

	if (type_is_array(type))
	{
		ArrayType  *array;
		Oid			elmtype;
		int16		elmlen;
		bool		elmbyval;
		char		elmalign;
		int			num_elems;
		Datum	   *elem_values;
		bool	   *elem_nulls;
		int			i;

		array = DatumGetArrayTypeP(value);
		elmtype = ARR_ELEMTYPE(array);
		get_typlenbyvalalign(elmtype, &elmlen, &elmbyval, &elmalign);

		deconstruct_array(array, elmtype,
						  elmlen, elmbyval, elmalign,
						  &elem_values, &elem_nulls,
						  &num_elems);

		initStringInfo(&buf);

		for (i = 0; i < num_elems; i++)
		{
			if (elem_nulls[i])
				continue;
			appendStringInfoString(&buf, "<element>");
			appendStringInfoString(&buf,
								   map_sql_value_to_xml_value(elem_values[i],
															  elmtype));
			appendStringInfoString(&buf, "</element>");
		}

		pfree(elem_values);
		pfree(elem_nulls);

		return buf.data;
	}
	else
	{
		Oid			typeOut;
		bool		isvarlena;
		char	   *p,
				   *str;

		/*
		 * Special XSD formatting for some data types
		 */
		switch (type)
		{
			case BOOLOID:
				if (DatumGetBool(value))
					return "true";
				else
					return "false";

			case DATEOID:
				{
					DateADT		date;
					struct pg_tm tm;
					char		buf[MAXDATELEN + 1];

					date = DatumGetDateADT(value);
					j2date(date + POSTGRES_EPOCH_JDATE,
						   &(tm.tm_year), &(tm.tm_mon), &(tm.tm_mday));
					EncodeDateOnly(&tm, USE_XSD_DATES, buf);

					return pstrdup(buf);
				}

			case TIMESTAMPOID:
				{
					Timestamp	timestamp;
					struct pg_tm tm;
					fsec_t		fsec;
					char	   *tzn = NULL;
					char		buf[MAXDATELEN + 1];

					timestamp = DatumGetTimestamp(value);

					/* XSD doesn't support infinite values */
					if (TIMESTAMP_NOT_FINITE(timestamp))
						ereport(ERROR,
								(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
								 errmsg("timestamp out of range")));
					else if (timestamp2tm(timestamp, NULL, &tm, &fsec, NULL, NULL) == 0)
						EncodeDateTime(&tm, fsec, NULL, &tzn, USE_XSD_DATES, buf);
					else
						ereport(ERROR,
								(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
								 errmsg("timestamp out of range")));

					return pstrdup(buf);
				}

			case TIMESTAMPTZOID:
				{
					TimestampTz timestamp;
					struct pg_tm tm;
					int			tz;
					fsec_t		fsec;
					char	   *tzn = NULL;
					char		buf[MAXDATELEN + 1];

					timestamp = DatumGetTimestamp(value);

					/* XSD doesn't support infinite values */
					if (TIMESTAMP_NOT_FINITE(timestamp))
						ereport(ERROR,
								(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
								 errmsg("timestamp out of range")));
					else if (timestamp2tm(timestamp, &tz, &tm, &fsec, &tzn, NULL) == 0)
						EncodeDateTime(&tm, fsec, &tz, &tzn, USE_XSD_DATES, buf);
					else
						ereport(ERROR,
								(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
								 errmsg("timestamp out of range")));

					return pstrdup(buf);
				}

#ifdef USE_LIBXML
			case BYTEAOID:
				{
					bytea	   *bstr = DatumGetByteaPP(value);
					xmlBufferPtr buf;
					xmlTextWriterPtr writer;
					char	   *result;

					xml_init();

					buf = xmlBufferCreate();
					writer = xmlNewTextWriterMemory(buf, 0);

					if (xmlbinary == XMLBINARY_BASE64)
						xmlTextWriterWriteBase64(writer, VARDATA_ANY(bstr),
												 0, VARSIZE_ANY_EXHDR(bstr));
					else
						xmlTextWriterWriteBinHex(writer, VARDATA_ANY(bstr),
												 0, VARSIZE_ANY_EXHDR(bstr));

					xmlFreeTextWriter(writer);
					result = pstrdup((const char *) xmlBufferContent(buf));
					xmlBufferFree(buf);
					return result;
				}
#endif   /* USE_LIBXML */

		}

		/*
		 * otherwise, just use the type's native text representation
		 */
		getTypeOutputInfo(type, &typeOut, &isvarlena);
		str = OidOutputFunctionCall(typeOut, value);

		/* ... exactly as-is for XML */
		if (type == XMLOID)
			return str;

		/* otherwise, translate special characters as needed */
		initStringInfo(&buf);

		for (p = str; *p; p++)
		{
			switch (*p)
			{
				case '&':
					appendStringInfoString(&buf, "&amp;");
					break;
				case '<':
					appendStringInfoString(&buf, "&lt;");
					break;
				case '>':
					appendStringInfoString(&buf, "&gt;");
					break;
				case '\r':
					appendStringInfoString(&buf, "&#x0d;");
					break;
				default:
					appendStringInfoCharMacro(&buf, *p);
					break;
			}
		}

		return buf.data;
	}
}


static char *
_SPI_strdup(const char *s)
{
	size_t		len = strlen(s) + 1;
	char	   *ret = SPI_palloc(len);

	memcpy(ret, s, len);
	return ret;
}


/*
 * SQL to XML mapping functions
 *
 * What follows below is intentionally organized so that you can read
 * along in the SQL/XML:2003 standard.	The functions are mostly split
 * up and ordered they way the clauses lay out in the standards
 * document, and the identifiers are also aligned with the standard
 * text.  (SQL/XML:2006 appears to be ordered differently,
 * unfortunately.)
 *
 * There are many things going on there:
 *
 * There are two kinds of mappings: Mapping SQL data (table contents)
 * to XML documents, and mapping SQL structure (the "schema") to XML
 * Schema.	And there are functions that do both at the same time.
 *
 * Then you can map a database, a schema, or a table, each in both
 * ways.  This breaks down recursively: Mapping a database invokes
 * mapping schemas, which invokes mapping tables, which invokes
 * mapping rows, which invokes mapping columns, although you can't
 * call the last two from the outside.	Because of this, there are a
 * number of xyz_internal() functions which are to be called both from
 * the function manager wrapper and from some upper layer in a
 * recursive call.
 *
 * See the documentation about what the common function arguments
 * nulls, tableforest, and targetns mean.
 *
 * Some style guidelines for XML output: Use double quotes for quoting
 * XML attributes.	Indent XML elements by two spaces, but remember
 * that a lot of code is called recursively at different levels, so
 * it's better not to indent rather than create output that indents
 * and outdents weirdly.  Add newlines to make the output look nice.
 */


/*
 * Visibility of objects for XML mappings; see SQL/XML:2003 section
 * 4.8.5.
 */

/*
 * Given a query, which must return type oid as first column, produce
 * a list of Oids with the query results.
 */
static List *
query_to_oid_list(const char *query)
{
	int			i;
	List	   *list = NIL;

	SPI_execute(query, true, 0);

	for (i = 0; i < SPI_processed; i++)
	{
		Datum		oid;
		bool		isnull;

		oid = SPI_getbinval(SPI_tuptable->vals[i],
							SPI_tuptable->tupdesc,
							1,
							&isnull);
		if (!isnull)
			list = lappend_oid(list, DatumGetObjectId(oid));
	}

	return list;
}


static List *
schema_get_xml_visible_tables(Oid nspid)
{
	StringInfoData query;

	initStringInfo(&query);
	appendStringInfo(&query, "SELECT oid FROM pg_catalog.pg_class WHERE relnamespace = %u AND relkind IN ('r', 'v') AND pg_catalog.has_table_privilege (oid, 'SELECT') ORDER BY relname;", nspid);

	return query_to_oid_list(query.data);
}


/*
 * Including the system schemas is probably not useful for a database
 * mapping.
 */
#define XML_VISIBLE_SCHEMAS_EXCLUDE "(nspname ~ '^pg_' OR nspname = 'information_schema')"

#define XML_VISIBLE_SCHEMAS "SELECT oid FROM pg_catalog.pg_namespace WHERE pg_catalog.has_schema_privilege (oid, 'USAGE') AND NOT " XML_VISIBLE_SCHEMAS_EXCLUDE


static List *
database_get_xml_visible_schemas(void)
{
	return query_to_oid_list(XML_VISIBLE_SCHEMAS " ORDER BY nspname;");
}


static List *
database_get_xml_visible_tables(void)
{
	/* At the moment there is no order required here. */
	return query_to_oid_list("SELECT oid FROM pg_catalog.pg_class WHERE relkind IN ('r', 'v') AND pg_catalog.has_table_privilege (pg_class.oid, 'SELECT') AND relnamespace IN (" XML_VISIBLE_SCHEMAS ");");
}


/*
 * Map SQL table to XML and/or XML Schema document; see SQL/XML:2003
 * section 9.3.
 */

static StringInfo
table_to_xml_internal(Oid relid,
					  const char *xmlschema, bool nulls, bool tableforest,
					  const char *targetns, bool top_level)
{
	StringInfoData query;

	initStringInfo(&query);
	appendStringInfo(&query, "SELECT * FROM %s",
					 DatumGetCString(DirectFunctionCall1(regclassout,
												  ObjectIdGetDatum(relid))));
	return query_to_xml_internal(query.data, get_rel_name(relid),
								 xmlschema, nulls, tableforest,
								 targetns, top_level);
}


Datum
table_to_xml(PG_FUNCTION_ARGS)
{
	Oid			relid = PG_GETARG_OID(0);
	bool		nulls = PG_GETARG_BOOL(1);
	bool		tableforest = PG_GETARG_BOOL(2);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));

	PG_RETURN_XML_P(stringinfo_to_xmltype(table_to_xml_internal(relid, NULL,
														  nulls, tableforest,
														   targetns, true)));
}


Datum
query_to_xml(PG_FUNCTION_ARGS)
{
	char	   *query = text_to_cstring(PG_GETARG_TEXT_PP(0));
	bool		nulls = PG_GETARG_BOOL(1);
	bool		tableforest = PG_GETARG_BOOL(2);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));

	PG_RETURN_XML_P(stringinfo_to_xmltype(query_to_xml_internal(query, NULL,
													NULL, nulls, tableforest,
														   targetns, true)));
}


Datum
cursor_to_xml(PG_FUNCTION_ARGS)
{
	char	   *name = text_to_cstring(PG_GETARG_TEXT_PP(0));
	int32		count = PG_GETARG_INT32(1);
	bool		nulls = PG_GETARG_BOOL(2);
	bool		tableforest = PG_GETARG_BOOL(3);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(4));

	StringInfoData result;
	Portal		portal;
	int			i;

	initStringInfo(&result);

	SPI_connect();
	portal = SPI_cursor_find(name);
	if (portal == NULL)
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_CURSOR),
				 errmsg("cursor \"%s\" does not exist", name)));

	SPI_cursor_fetch(portal, true, count);
	for (i = 0; i < SPI_processed; i++)
		SPI_sql_row_to_xmlelement(i, &result, NULL, nulls,
								  tableforest, targetns, true);

	SPI_finish();

	PG_RETURN_XML_P(stringinfo_to_xmltype(&result));
}


/*
 * Write the start tag of the root element of a data mapping.
 *
 * top_level means that this is the very top level of the eventual
 * output.	For example, when the user calls table_to_xml, then a call
 * with a table name to this function is the top level.  When the user
 * calls database_to_xml, then a call with a schema name to this
 * function is not the top level.  If top_level is false, then the XML
 * namespace declarations are omitted, because they supposedly already
 * appeared earlier in the output.	Repeating them is not wrong, but
 * it looks ugly.
 */
static void
xmldata_root_element_start(StringInfo result, const char *eltname,
						   const char *xmlschema, const char *targetns,
						   bool top_level)
{
	/* This isn't really wrong but currently makes no sense. */
	Assert(top_level || !xmlschema);

	appendStringInfo(result, "<%s", eltname);
	if (top_level)
	{
		appendStringInfoString(result, " xmlns:xsi=\"" NAMESPACE_XSI "\"");
		if (strlen(targetns) > 0)
			appendStringInfo(result, " xmlns=\"%s\"", targetns);
	}
	if (xmlschema)
	{
		/* FIXME: better targets */
		if (strlen(targetns) > 0)
			appendStringInfo(result, " xsi:schemaLocation=\"%s #\"", targetns);
		else
			appendStringInfo(result, " xsi:noNamespaceSchemaLocation=\"#\"");
	}
	appendStringInfo(result, ">\n\n");
}


static void
xmldata_root_element_end(StringInfo result, const char *eltname)
{
	appendStringInfo(result, "</%s>\n", eltname);
}


static StringInfo
query_to_xml_internal(const char *query, char *tablename,
					  const char *xmlschema, bool nulls, bool tableforest,
					  const char *targetns, bool top_level)
{
	StringInfo	result;
	char	   *xmltn;
	int			i;

	if (tablename)
		xmltn = map_sql_identifier_to_xml_name(tablename, true, false);
	else
		xmltn = "table";

	result = makeStringInfo();

	SPI_connect();
	if (SPI_execute(query, true, 0) != SPI_OK_SELECT)
		ereport(ERROR,
				(errcode(ERRCODE_DATA_EXCEPTION),
				 errmsg("invalid query")));

	if (!tableforest)
		xmldata_root_element_start(result, xmltn, xmlschema,
								   targetns, top_level);

	if (xmlschema)
		appendStringInfo(result, "%s\n\n", xmlschema);

	for (i = 0; i < SPI_processed; i++)
		SPI_sql_row_to_xmlelement(i, result, tablename, nulls,
								  tableforest, targetns, top_level);

	if (!tableforest)
		xmldata_root_element_end(result, xmltn);

	SPI_finish();

	return result;
}


Datum
table_to_xmlschema(PG_FUNCTION_ARGS)
{
	Oid			relid = PG_GETARG_OID(0);
	bool		nulls = PG_GETARG_BOOL(1);
	bool		tableforest = PG_GETARG_BOOL(2);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
	const char *result;
	Relation	rel;

	rel = heap_open(relid, AccessShareLock);
	result = map_sql_table_to_xmlschema(rel->rd_att, relid, nulls,
										tableforest, targetns);
	heap_close(rel, NoLock);

	PG_RETURN_XML_P(cstring_to_xmltype(result));
}


Datum
query_to_xmlschema(PG_FUNCTION_ARGS)
{
	char	   *query = text_to_cstring(PG_GETARG_TEXT_PP(0));
	bool		nulls = PG_GETARG_BOOL(1);
	bool		tableforest = PG_GETARG_BOOL(2);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
	const char *result;
	SPIPlanPtr	plan;
	Portal		portal;

	SPI_connect();

	if ((plan = SPI_prepare(query, 0, NULL)) == NULL)
		elog(ERROR, "SPI_prepare(\"%s\") failed", query);

	if ((portal = SPI_cursor_open(NULL, plan, NULL, NULL, true)) == NULL)
		elog(ERROR, "SPI_cursor_open(\"%s\") failed", query);

	result = _SPI_strdup(map_sql_table_to_xmlschema(portal->tupDesc,
													InvalidOid, nulls,
													tableforest, targetns));
	SPI_cursor_close(portal);
	SPI_finish();

	PG_RETURN_XML_P(cstring_to_xmltype(result));
}


Datum
cursor_to_xmlschema(PG_FUNCTION_ARGS)
{
	char	   *name = text_to_cstring(PG_GETARG_TEXT_PP(0));
	bool		nulls = PG_GETARG_BOOL(1);
	bool		tableforest = PG_GETARG_BOOL(2);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
	const char *xmlschema;
	Portal		portal;

	SPI_connect();
	portal = SPI_cursor_find(name);
	if (portal == NULL)
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_CURSOR),
				 errmsg("cursor \"%s\" does not exist", name)));

	xmlschema = _SPI_strdup(map_sql_table_to_xmlschema(portal->tupDesc,
													   InvalidOid, nulls,
													 tableforest, targetns));
	SPI_finish();

	PG_RETURN_XML_P(cstring_to_xmltype(xmlschema));
}


Datum
table_to_xml_and_xmlschema(PG_FUNCTION_ARGS)
{
	Oid			relid = PG_GETARG_OID(0);
	bool		nulls = PG_GETARG_BOOL(1);
	bool		tableforest = PG_GETARG_BOOL(2);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
	Relation	rel;
	const char *xmlschema;

	rel = heap_open(relid, AccessShareLock);
	xmlschema = map_sql_table_to_xmlschema(rel->rd_att, relid, nulls,
										   tableforest, targetns);
	heap_close(rel, NoLock);

	PG_RETURN_XML_P(stringinfo_to_xmltype(table_to_xml_internal(relid,
											   xmlschema, nulls, tableforest,
														   targetns, true)));
}


Datum
query_to_xml_and_xmlschema(PG_FUNCTION_ARGS)
{
	char	   *query = text_to_cstring(PG_GETARG_TEXT_PP(0));
	bool		nulls = PG_GETARG_BOOL(1);
	bool		tableforest = PG_GETARG_BOOL(2);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));

	const char *xmlschema;
	SPIPlanPtr	plan;
	Portal		portal;

	SPI_connect();

	if ((plan = SPI_prepare(query, 0, NULL)) == NULL)
		elog(ERROR, "SPI_prepare(\"%s\") failed", query);

	if ((portal = SPI_cursor_open(NULL, plan, NULL, NULL, true)) == NULL)
		elog(ERROR, "SPI_cursor_open(\"%s\") failed", query);

	xmlschema = _SPI_strdup(map_sql_table_to_xmlschema(portal->tupDesc,
								  InvalidOid, nulls, tableforest, targetns));
	SPI_cursor_close(portal);
	SPI_finish();

	PG_RETURN_XML_P(stringinfo_to_xmltype(query_to_xml_internal(query, NULL,
											   xmlschema, nulls, tableforest,
														   targetns, true)));
}


/*
 * Map SQL schema to XML and/or XML Schema document; see SQL/XML:2003
 * section 9.4.
 */

static StringInfo
schema_to_xml_internal(Oid nspid, const char *xmlschema, bool nulls,
					   bool tableforest, const char *targetns, bool top_level)
{
	StringInfo	result;
	char	   *xmlsn;
	List	   *relid_list;
	ListCell   *cell;

	xmlsn = map_sql_identifier_to_xml_name(get_namespace_name(nspid),
										   true, false);
	result = makeStringInfo();

	xmldata_root_element_start(result, xmlsn, xmlschema, targetns, top_level);

	if (xmlschema)
		appendStringInfo(result, "%s\n\n", xmlschema);

	SPI_connect();

	relid_list = schema_get_xml_visible_tables(nspid);

	SPI_push();

	foreach(cell, relid_list)
	{
		Oid			relid = lfirst_oid(cell);
		StringInfo	subres;

		subres = table_to_xml_internal(relid, NULL, nulls, tableforest,
									   targetns, false);

		appendStringInfoString(result, subres->data);
		appendStringInfoChar(result, '\n');
	}

	SPI_pop();
	SPI_finish();

	xmldata_root_element_end(result, xmlsn);

	return result;
}


Datum
schema_to_xml(PG_FUNCTION_ARGS)
{
	Name		name = PG_GETARG_NAME(0);
	bool		nulls = PG_GETARG_BOOL(1);
	bool		tableforest = PG_GETARG_BOOL(2);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));

	char	   *schemaname;
	Oid			nspid;

	schemaname = NameStr(*name);
	nspid = LookupExplicitNamespace(schemaname);

	PG_RETURN_XML_P(stringinfo_to_xmltype(schema_to_xml_internal(nspid, NULL,
									   nulls, tableforest, targetns, true)));
}


/*
 * Write the start element of the root element of an XML Schema mapping.
 */
static void
xsd_schema_element_start(StringInfo result, const char *targetns)
{
	appendStringInfoString(result,
						   "<xsd:schema\n"
						   "    xmlns:xsd=\"" NAMESPACE_XSD "\"");
	if (strlen(targetns) > 0)
		appendStringInfo(result,
						 "\n"
						 "    targetNamespace=\"%s\"\n"
						 "    elementFormDefault=\"qualified\"",
						 targetns);
	appendStringInfoString(result,
						   ">\n\n");
}


static void
xsd_schema_element_end(StringInfo result)
{
	appendStringInfoString(result, "</xsd:schema>");
}


static StringInfo
schema_to_xmlschema_internal(const char *schemaname, bool nulls,
							 bool tableforest, const char *targetns)
{
	Oid			nspid;
	List	   *relid_list;
	List	   *tupdesc_list;
	ListCell   *cell;
	StringInfo	result;

	result = makeStringInfo();

	nspid = LookupExplicitNamespace(schemaname);

	xsd_schema_element_start(result, targetns);

	SPI_connect();

	relid_list = schema_get_xml_visible_tables(nspid);

	tupdesc_list = NIL;
	foreach(cell, relid_list)
	{
		Relation	rel;

		rel = heap_open(lfirst_oid(cell), AccessShareLock);
		tupdesc_list = lappend(tupdesc_list, CreateTupleDescCopy(rel->rd_att));
		heap_close(rel, NoLock);
	}

	appendStringInfoString(result,
						   map_sql_typecoll_to_xmlschema_types(tupdesc_list));

	appendStringInfoString(result,
						 map_sql_schema_to_xmlschema_types(nspid, relid_list,
											  nulls, tableforest, targetns));

	xsd_schema_element_end(result);

	SPI_finish();

	return result;
}


Datum
schema_to_xmlschema(PG_FUNCTION_ARGS)
{
	Name		name = PG_GETARG_NAME(0);
	bool		nulls = PG_GETARG_BOOL(1);
	bool		tableforest = PG_GETARG_BOOL(2);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));

	PG_RETURN_XML_P(stringinfo_to_xmltype(schema_to_xmlschema_internal(NameStr(*name),
											 nulls, tableforest, targetns)));
}


Datum
schema_to_xml_and_xmlschema(PG_FUNCTION_ARGS)
{
	Name		name = PG_GETARG_NAME(0);
	bool		nulls = PG_GETARG_BOOL(1);
	bool		tableforest = PG_GETARG_BOOL(2);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
	char	   *schemaname;
	Oid			nspid;
	StringInfo	xmlschema;

	schemaname = NameStr(*name);
	nspid = LookupExplicitNamespace(schemaname);

	xmlschema = schema_to_xmlschema_internal(schemaname, nulls,
											 tableforest, targetns);

	PG_RETURN_XML_P(stringinfo_to_xmltype(schema_to_xml_internal(nspid,
													  xmlschema->data, nulls,
											  tableforest, targetns, true)));
}


/*
 * Map SQL database to XML and/or XML Schema document; see SQL/XML:2003
 * section 9.5.
 */

static StringInfo
database_to_xml_internal(const char *xmlschema, bool nulls,
						 bool tableforest, const char *targetns)
{
	StringInfo	result;
	List	   *nspid_list;
	ListCell   *cell;
	char	   *xmlcn;

	xmlcn = map_sql_identifier_to_xml_name(get_database_name(MyDatabaseId),
										   true, false);
	result = makeStringInfo();

	xmldata_root_element_start(result, xmlcn, xmlschema, targetns, true);

	if (xmlschema)
		appendStringInfo(result, "%s\n\n", xmlschema);

	SPI_connect();

	nspid_list = database_get_xml_visible_schemas();

	SPI_push();

	foreach(cell, nspid_list)
	{
		Oid			nspid = lfirst_oid(cell);
		StringInfo	subres;

		subres = schema_to_xml_internal(nspid, NULL, nulls,
										tableforest, targetns, false);

		appendStringInfoString(result, subres->data);
		appendStringInfoChar(result, '\n');
	}

	SPI_pop();
	SPI_finish();

	xmldata_root_element_end(result, xmlcn);

	return result;
}


Datum
database_to_xml(PG_FUNCTION_ARGS)
{
	bool		nulls = PG_GETARG_BOOL(0);
	bool		tableforest = PG_GETARG_BOOL(1);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(2));

	PG_RETURN_XML_P(stringinfo_to_xmltype(database_to_xml_internal(NULL, nulls,
													tableforest, targetns)));
}


static StringInfo
database_to_xmlschema_internal(bool nulls, bool tableforest,
							   const char *targetns)
{
	List	   *relid_list;
	List	   *nspid_list;
	List	   *tupdesc_list;
	ListCell   *cell;
	StringInfo	result;

	result = makeStringInfo();

	xsd_schema_element_start(result, targetns);

	SPI_connect();

	relid_list = database_get_xml_visible_tables();
	nspid_list = database_get_xml_visible_schemas();

	tupdesc_list = NIL;
	foreach(cell, relid_list)
	{
		Relation	rel;

		rel = heap_open(lfirst_oid(cell), AccessShareLock);
		tupdesc_list = lappend(tupdesc_list, CreateTupleDescCopy(rel->rd_att));
		heap_close(rel, NoLock);
	}

	appendStringInfoString(result,
						   map_sql_typecoll_to_xmlschema_types(tupdesc_list));

	appendStringInfoString(result,
						   map_sql_catalog_to_xmlschema_types(nspid_list, nulls, tableforest, targetns));

	xsd_schema_element_end(result);

	SPI_finish();

	return result;
}


Datum
database_to_xmlschema(PG_FUNCTION_ARGS)
{
	bool		nulls = PG_GETARG_BOOL(0);
	bool		tableforest = PG_GETARG_BOOL(1);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(2));

	PG_RETURN_XML_P(stringinfo_to_xmltype(database_to_xmlschema_internal(nulls,
													tableforest, targetns)));
}


Datum
database_to_xml_and_xmlschema(PG_FUNCTION_ARGS)
{
	bool		nulls = PG_GETARG_BOOL(0);
	bool		tableforest = PG_GETARG_BOOL(1);
	const char *targetns = text_to_cstring(PG_GETARG_TEXT_PP(2));
	StringInfo	xmlschema;

	xmlschema = database_to_xmlschema_internal(nulls, tableforest, targetns);

	PG_RETURN_XML_P(stringinfo_to_xmltype(database_to_xml_internal(xmlschema->data,
											 nulls, tableforest, targetns)));
}


/*
 * Map a multi-part SQL name to an XML name; see SQL/XML:2003 section
 * 9.2.
 */
static char *
map_multipart_sql_identifier_to_xml_name(char *a, char *b, char *c, char *d)
{
	StringInfoData result;

	initStringInfo(&result);

	if (a)
		appendStringInfo(&result, "%s",
						 map_sql_identifier_to_xml_name(a, true, true));
	if (b)
		appendStringInfo(&result, ".%s",
						 map_sql_identifier_to_xml_name(b, true, true));
	if (c)
		appendStringInfo(&result, ".%s",
						 map_sql_identifier_to_xml_name(c, true, true));
	if (d)
		appendStringInfo(&result, ".%s",
						 map_sql_identifier_to_xml_name(d, true, true));

	return result.data;
}


/*
 * Map an SQL table to an XML Schema document; see SQL/XML:2003
 * section 9.3.
 *
 * Map an SQL table to XML Schema data types; see SQL/XML:2003 section
 * 9.6.
 */
static const char *
map_sql_table_to_xmlschema(TupleDesc tupdesc, Oid relid, bool nulls,
						   bool tableforest, const char *targetns)
{
	int			i;
	char	   *xmltn;
	char	   *tabletypename;
	char	   *rowtypename;
	StringInfoData result;

	initStringInfo(&result);

	if (OidIsValid(relid))
	{
		HeapTuple	tuple;
		Form_pg_class reltuple;

		tuple = SearchSysCache(RELOID,
							   ObjectIdGetDatum(relid),
							   0, 0, 0);
		if (!HeapTupleIsValid(tuple))
			elog(ERROR, "cache lookup failed for relation %u", relid);
		reltuple = (Form_pg_class) GETSTRUCT(tuple);

		xmltn = map_sql_identifier_to_xml_name(NameStr(reltuple->relname),
											   true, false);

		tabletypename = map_multipart_sql_identifier_to_xml_name("TableType",
											 get_database_name(MyDatabaseId),
								  get_namespace_name(reltuple->relnamespace),
												 NameStr(reltuple->relname));

		rowtypename = map_multipart_sql_identifier_to_xml_name("RowType",
											 get_database_name(MyDatabaseId),
								  get_namespace_name(reltuple->relnamespace),
												 NameStr(reltuple->relname));

		ReleaseSysCache(tuple);
	}
	else
	{
		if (tableforest)
			xmltn = "row";
		else
			xmltn = "table";

		tabletypename = "TableType";
		rowtypename = "RowType";
	}

	xsd_schema_element_start(&result, targetns);

	appendStringInfoString(&result,
				   map_sql_typecoll_to_xmlschema_types(list_make1(tupdesc)));

	appendStringInfo(&result,
					 "<xsd:complexType name=\"%s\">\n"
					 "  <xsd:sequence>\n",
					 rowtypename);

	for (i = 0; i < tupdesc->natts; i++)
		appendStringInfo(&result,
			   "    <xsd:element name=\"%s\" type=\"%s\"%s></xsd:element>\n",
		  map_sql_identifier_to_xml_name(NameStr(tupdesc->attrs[i]->attname),
										 true, false),
				   map_sql_type_to_xml_name(tupdesc->attrs[i]->atttypid, -1),
						 nulls ? " nillable=\"true\"" : " minOccurs=\"0\"");

	appendStringInfoString(&result,
						   "  </xsd:sequence>\n"
						   "</xsd:complexType>\n\n");

	if (!tableforest)
	{
		appendStringInfo(&result,
						 "<xsd:complexType name=\"%s\">\n"
						 "  <xsd:sequence>\n"
						 "    <xsd:element name=\"row\" type=\"%s\" minOccurs=\"0\" maxOccurs=\"unbounded\"/>\n"
						 "  </xsd:sequence>\n"
						 "</xsd:complexType>\n\n",
						 tabletypename, rowtypename);

		appendStringInfo(&result,
						 "<xsd:element name=\"%s\" type=\"%s\"/>\n\n",
						 xmltn, tabletypename);
	}
	else
		appendStringInfo(&result,
						 "<xsd:element name=\"%s\" type=\"%s\"/>\n\n",
						 xmltn, rowtypename);

	xsd_schema_element_end(&result);

	return result.data;
}


/*
 * Map an SQL schema to XML Schema data types; see SQL/XML section
 * 9.7.
 */
static const char *
map_sql_schema_to_xmlschema_types(Oid nspid, List *relid_list, bool nulls,
								  bool tableforest, const char *targetns)
{
	char	   *dbname;
	char	   *nspname;
	char	   *xmlsn;
	char	   *schematypename;
	StringInfoData result;
	ListCell   *cell;

	dbname = get_database_name(MyDatabaseId);
	nspname = get_namespace_name(nspid);

	initStringInfo(&result);

	xmlsn = map_sql_identifier_to_xml_name(nspname, true, false);

	schematypename = map_multipart_sql_identifier_to_xml_name("SchemaType",
															  dbname,
															  nspname,
															  NULL);

	appendStringInfo(&result,
					 "<xsd:complexType name=\"%s\">\n", schematypename);
	if (!tableforest)
		appendStringInfoString(&result,
							   "  <xsd:all>\n");
	else
		appendStringInfoString(&result,
							   "  <xsd:sequence>\n");

	foreach(cell, relid_list)
	{
		Oid			relid = lfirst_oid(cell);
		char	   *relname = get_rel_name(relid);
		char	   *xmltn = map_sql_identifier_to_xml_name(relname, true, false);
		char	   *tabletypename = map_multipart_sql_identifier_to_xml_name(tableforest ? "RowType" : "TableType",
																	  dbname,
																	 nspname,
																	relname);

		if (!tableforest)
			appendStringInfo(&result,
							 "    <xsd:element name=\"%s\" type=\"%s\"/>\n",
							 xmltn, tabletypename);
		else
			appendStringInfo(&result,
							 "    <xsd:element name=\"%s\" type=\"%s\" minOccurs=\"0\" maxOccurs=\"unbounded\"/>\n",
							 xmltn, tabletypename);
	}

	if (!tableforest)
		appendStringInfoString(&result,
							   "  </xsd:all>\n");
	else
		appendStringInfoString(&result,
							   "  </xsd:sequence>\n");
	appendStringInfoString(&result,
						   "</xsd:complexType>\n\n");

	appendStringInfo(&result,
					 "<xsd:element name=\"%s\" type=\"%s\"/>\n\n",
					 xmlsn, schematypename);

	return result.data;
}


/*
 * Map an SQL catalog to XML Schema data types; see SQL/XML section
 * 9.8.
 */
static const char *
map_sql_catalog_to_xmlschema_types(List *nspid_list, bool nulls,
								   bool tableforest, const char *targetns)
{
	char	   *dbname;
	char	   *xmlcn;
	char	   *catalogtypename;
	StringInfoData result;
	ListCell   *cell;

	dbname = get_database_name(MyDatabaseId);

	initStringInfo(&result);

	xmlcn = map_sql_identifier_to_xml_name(dbname, true, false);

	catalogtypename = map_multipart_sql_identifier_to_xml_name("CatalogType",
															   dbname,
															   NULL,
															   NULL);

	appendStringInfo(&result,
					 "<xsd:complexType name=\"%s\">\n", catalogtypename);
	appendStringInfoString(&result,
						   "  <xsd:all>\n");

	foreach(cell, nspid_list)
	{
		Oid			nspid = lfirst_oid(cell);
		char	   *nspname = get_namespace_name(nspid);
		char	   *xmlsn = map_sql_identifier_to_xml_name(nspname, true, false);
		char	   *schematypename = map_multipart_sql_identifier_to_xml_name("SchemaType",
																	  dbname,
																	 nspname,
																	   NULL);

		appendStringInfo(&result,
						 "    <xsd:element name=\"%s\" type=\"%s\"/>\n",
						 xmlsn, schematypename);
	}

	appendStringInfoString(&result,
						   "  </xsd:all>\n");
	appendStringInfoString(&result,
						   "</xsd:complexType>\n\n");

	appendStringInfo(&result,
					 "<xsd:element name=\"%s\" type=\"%s\"/>\n\n",
					 xmlcn, catalogtypename);

	return result.data;
}


/*
 * Map an SQL data type to an XML name; see SQL/XML:2003 section 9.9.
 */
static const char *
map_sql_type_to_xml_name(Oid typeoid, int typmod)
{
	StringInfoData result;

	initStringInfo(&result);

	switch (typeoid)
	{
		case BPCHAROID:
			if (typmod == -1)
				appendStringInfo(&result, "CHAR");
			else
				appendStringInfo(&result, "CHAR_%d", typmod - VARHDRSZ);
			break;
		case VARCHAROID:
			if (typmod == -1)
				appendStringInfo(&result, "VARCHAR");
			else
				appendStringInfo(&result, "VARCHAR_%d", typmod - VARHDRSZ);
			break;
		case NUMERICOID:
			if (typmod == -1)
				appendStringInfo(&result, "NUMERIC");
			else
				appendStringInfo(&result, "NUMERIC_%d_%d",
								 ((typmod - VARHDRSZ) >> 16) & 0xffff,
								 (typmod - VARHDRSZ) & 0xffff);
			break;
		case INT4OID:
			appendStringInfo(&result, "INTEGER");
			break;
		case INT2OID:
			appendStringInfo(&result, "SMALLINT");
			break;
		case INT8OID:
			appendStringInfo(&result, "BIGINT");
			break;
		case FLOAT4OID:
			appendStringInfo(&result, "REAL");
			break;
		case FLOAT8OID:
			appendStringInfo(&result, "DOUBLE");
			break;
		case BOOLOID:
			appendStringInfo(&result, "BOOLEAN");
			break;
		case TIMEOID:
			if (typmod == -1)
				appendStringInfo(&result, "TIME");
			else
				appendStringInfo(&result, "TIME_%d", typmod);
			break;
		case TIMETZOID:
			if (typmod == -1)
				appendStringInfo(&result, "TIME_WTZ");
			else
				appendStringInfo(&result, "TIME_WTZ_%d", typmod);
			break;
		case TIMESTAMPOID:
			if (typmod == -1)
				appendStringInfo(&result, "TIMESTAMP");
			else
				appendStringInfo(&result, "TIMESTAMP_%d", typmod);
			break;
		case TIMESTAMPTZOID:
			if (typmod == -1)
				appendStringInfo(&result, "TIMESTAMP_WTZ");
			else
				appendStringInfo(&result, "TIMESTAMP_WTZ_%d", typmod);
			break;
		case DATEOID:
			appendStringInfo(&result, "DATE");
			break;
		case XMLOID:
			appendStringInfo(&result, "XML");
			break;
		default:
			{
				HeapTuple	tuple;
				Form_pg_type typtuple;

				tuple = SearchSysCache(TYPEOID,
									   ObjectIdGetDatum(typeoid),
									   0, 0, 0);
				if (!HeapTupleIsValid(tuple))
					elog(ERROR, "cache lookup failed for type %u", typeoid);
				typtuple = (Form_pg_type) GETSTRUCT(tuple);

				appendStringInfoString(&result,
									   map_multipart_sql_identifier_to_xml_name((typtuple->typtype == TYPTYPE_DOMAIN) ? "Domain" : "UDT",
											 get_database_name(MyDatabaseId),
								  get_namespace_name(typtuple->typnamespace),
												NameStr(typtuple->typname)));

				ReleaseSysCache(tuple);
			}
	}

	return result.data;
}


/*
 * Map a collection of SQL data types to XML Schema data types; see
 * SQL/XML:2002 section 9.10.
 */
static const char *
map_sql_typecoll_to_xmlschema_types(List *tupdesc_list)
{
	List	   *uniquetypes = NIL;
	int			i;
	StringInfoData result;
	ListCell   *cell0;

	/* extract all column types used in the set of TupleDescs */
	foreach(cell0, tupdesc_list)
	{
		TupleDesc	tupdesc = (TupleDesc) lfirst(cell0);

		for (i = 0; i < tupdesc->natts; i++)
		{
			if (tupdesc->attrs[i]->attisdropped)
				continue;
			uniquetypes = list_append_unique_oid(uniquetypes,
												 tupdesc->attrs[i]->atttypid);
		}
	}

	/* add base types of domains */
	foreach(cell0, uniquetypes)
	{
		Oid			typid = lfirst_oid(cell0);
		Oid			basetypid = getBaseType(typid);

		if (basetypid != typid)
			uniquetypes = list_append_unique_oid(uniquetypes, basetypid);
	}

	/* Convert to textual form */
	initStringInfo(&result);

	foreach(cell0, uniquetypes)
	{
		appendStringInfo(&result, "%s\n",
						 map_sql_type_to_xmlschema_type(lfirst_oid(cell0),
														-1));
	}

	return result.data;
}


/*
 * Map an SQL data type to a named XML Schema data type; see SQL/XML
 * sections 9.11 and 9.15.
 *
 * (The distinction between 9.11 and 9.15 is basically that 9.15 adds
 * a name attribute, which this function does.	The name-less version
 * 9.11 doesn't appear to be required anywhere.)
 */
static const char *
map_sql_type_to_xmlschema_type(Oid typeoid, int typmod)
{
	StringInfoData result;
	const char *typename = map_sql_type_to_xml_name(typeoid, typmod);

	initStringInfo(&result);

	if (typeoid == XMLOID)
	{
		appendStringInfo(&result,
						 "<xsd:complexType mixed=\"true\">\n"
						 "  <xsd:sequence>\n"
						 "    <xsd:any name=\"element\" minOccurs=\"0\" maxOccurs=\"unbounded\" processContents=\"skip\"/>\n"
						 "  </xsd:sequence>\n"
						 "</xsd:complexType>\n");
	}
	else
	{
		appendStringInfo(&result,
						 "<xsd:simpleType name=\"%s\">\n", typename);

		switch (typeoid)
		{
			case BPCHAROID:
			case VARCHAROID:
			case TEXTOID:
				appendStringInfo(&result,
								 "  <xsd:restriction base=\"xsd:string\">\n");
				if (typmod != -1)
					appendStringInfo(&result,
									 "    <xsd:maxLength value=\"%d\"/>\n",
									 typmod - VARHDRSZ);
				appendStringInfo(&result,
								 "  </xsd:restriction>\n");
				break;

			case BYTEAOID:
				appendStringInfo(&result,
								 "  <xsd:restriction base=\"xsd:%s\">\n"
								 "  </xsd:restriction>\n",
				xmlbinary == XMLBINARY_BASE64 ? "base64Binary" : "hexBinary");
				break;

			case NUMERICOID:
				if (typmod != -1)
					appendStringInfo(&result,
								 "  <xsd:restriction base=\"xsd:decimal\">\n"
									 "    <xsd:totalDigits value=\"%d\"/>\n"
								   "    <xsd:fractionDigits value=\"%d\"/>\n"
									 "  </xsd:restriction>\n",
									 ((typmod - VARHDRSZ) >> 16) & 0xffff,
									 (typmod - VARHDRSZ) & 0xffff);
				break;

			case INT2OID:
				appendStringInfo(&result,
								 "  <xsd:restriction base=\"xsd:short\">\n"
								 "    <xsd:maxInclusive value=\"%d\"/>\n"
								 "    <xsd:minInclusive value=\"%d\"/>\n"
								 "  </xsd:restriction>\n",
								 SHRT_MAX, SHRT_MIN);
				break;

			case INT4OID:
				appendStringInfo(&result,
								 "  <xsd:restriction base=\"xsd:int\">\n"
								 "    <xsd:maxInclusive value=\"%d\"/>\n"
								 "    <xsd:minInclusive value=\"%d\"/>\n"
								 "  </xsd:restriction>\n",
								 INT_MAX, INT_MIN);
				break;

			case INT8OID:
				appendStringInfo(&result,
								 "  <xsd:restriction base=\"xsd:long\">\n"
					   "    <xsd:maxInclusive value=\"" INT64_FORMAT "\"/>\n"
					   "    <xsd:minInclusive value=\"" INT64_FORMAT "\"/>\n"
								 "  </xsd:restriction>\n",
							   (((uint64) 1) << (sizeof(int64) * 8 - 1)) - 1,
								 (((uint64) 1) << (sizeof(int64) * 8 - 1)));
				break;

			case FLOAT4OID:
				appendStringInfo(&result,
				"  <xsd:restriction base=\"xsd:float\"></xsd:restriction>\n");
				break;

			case FLOAT8OID:
				appendStringInfo(&result,
								 "  <xsd:restriction base=\"xsd:double\"></xsd:restriction>\n");
				break;

			case BOOLOID:
				appendStringInfo(&result,
								 "  <xsd:restriction base=\"xsd:boolean\"></xsd:restriction>\n");
				break;

			case TIMEOID:
			case TIMETZOID:
				{
					const char *tz = (typeoid == TIMETZOID ? "(+|-)\\p{Nd}{2}:\\p{Nd}{2}" : "");

					if (typmod == -1)
						appendStringInfo(&result,
									"  <xsd:restriction base=\"xsd:time\">\n"
										 "    <xsd:pattern value=\"\\p{Nd}{2}:\\p{Nd}{2}:\\p{Nd}{2}(.\\p{Nd}+)?%s\"/>\n"
										 "  </xsd:restriction>\n", tz);
					else if (typmod == 0)
						appendStringInfo(&result,
									"  <xsd:restriction base=\"xsd:time\">\n"
										 "    <xsd:pattern value=\"\\p{Nd}{2}:\\p{Nd}{2}:\\p{Nd}{2}%s\"/>\n"
										 "  </xsd:restriction>\n", tz);
					else
						appendStringInfo(&result,
									"  <xsd:restriction base=\"xsd:time\">\n"
										 "    <xsd:pattern value=\"\\p{Nd}{2}:\\p{Nd}{2}:\\p{Nd}{2}.\\p{Nd}{%d}%s\"/>\n"
							"  </xsd:restriction>\n", typmod - VARHDRSZ, tz);
					break;
				}

			case TIMESTAMPOID:
			case TIMESTAMPTZOID:
				{
					const char *tz = (typeoid == TIMESTAMPTZOID ? "(+|-)\\p{Nd}{2}:\\p{Nd}{2}" : "");

					if (typmod == -1)
						appendStringInfo(&result,
								"  <xsd:restriction base=\"xsd:dateTime\">\n"
										 "    <xsd:pattern value=\"\\p{Nd}{4}-\\p{Nd}{2}-\\p{Nd}{2}T\\p{Nd}{2}:\\p{Nd}{2}:\\p{Nd}{2}(.\\p{Nd}+)?%s\"/>\n"
										 "  </xsd:restriction>\n", tz);
					else if (typmod == 0)
						appendStringInfo(&result,
								"  <xsd:restriction base=\"xsd:dateTime\">\n"
										 "    <xsd:pattern value=\"\\p{Nd}{4}-\\p{Nd}{2}-\\p{Nd}{2}T\\p{Nd}{2}:\\p{Nd}{2}:\\p{Nd}{2}%s\"/>\n"
										 "  </xsd:restriction>\n", tz);
					else
						appendStringInfo(&result,
								"  <xsd:restriction base=\"xsd:dateTime\">\n"
										 "    <xsd:pattern value=\"\\p{Nd}{4}-\\p{Nd}{2}-\\p{Nd}{2}T\\p{Nd}{2}:\\p{Nd}{2}:\\p{Nd}{2}.\\p{Nd}{%d}%s\"/>\n"
							"  </xsd:restriction>\n", typmod - VARHDRSZ, tz);
					break;
				}

			case DATEOID:
				appendStringInfo(&result,
								 "  <xsd:restriction base=\"xsd:date\">\n"
								 "    <xsd:pattern value=\"\\p{Nd}{4}-\\p{Nd}{2}-\\p{Nd}{2}\"/>\n"
								 "  </xsd:restriction>\n");
				break;

			default:
				if (get_typtype(typeoid) == TYPTYPE_DOMAIN)
				{
					Oid			base_typeoid;
					int32		base_typmod = -1;

					base_typeoid = getBaseTypeAndTypmod(typeoid, &base_typmod);

					appendStringInfo(&result,
									 "  <xsd:restriction base=\"%s\"/>\n",
						map_sql_type_to_xml_name(base_typeoid, base_typmod));
				}
				break;
		}
		appendStringInfo(&result,
						 "</xsd:simpleType>\n");
	}

	return result.data;
}


/*
 * Map an SQL row to an XML element, taking the row from the active
 * SPI cursor.	See also SQL/XML:2003 section 9.12.
 */
static void
SPI_sql_row_to_xmlelement(int rownum, StringInfo result, char *tablename,
						  bool nulls, bool tableforest,
						  const char *targetns, bool top_level)
{
	int			i;
	char	   *xmltn;

	if (tablename)
		xmltn = map_sql_identifier_to_xml_name(tablename, true, false);
	else
	{
		if (tableforest)
			xmltn = "row";
		else
			xmltn = "table";
	}

	if (tableforest)
		xmldata_root_element_start(result, xmltn, NULL, targetns, top_level);
	else
		appendStringInfoString(result, "<row>\n");

	for (i = 1; i <= SPI_tuptable->tupdesc->natts; i++)
	{
		char	   *colname;
		Datum		colval;
		bool		isnull;

		colname = map_sql_identifier_to_xml_name(SPI_fname(SPI_tuptable->tupdesc, i),
												 true, false);
		colval = SPI_getbinval(SPI_tuptable->vals[rownum],
							   SPI_tuptable->tupdesc,
							   i,
							   &isnull);
		if (isnull)
		{
			if (nulls)
				appendStringInfo(result, "  <%s xsi:nil=\"true\"/>\n", colname);
		}
		else
			appendStringInfo(result, "  <%s>%s</%s>\n",
							 colname,
							 map_sql_value_to_xml_value(colval,
									SPI_gettypeid(SPI_tuptable->tupdesc, i)),
							 colname);
	}

	if (tableforest)
	{
		xmldata_root_element_end(result, xmltn);
		appendStringInfoChar(result, '\n');
	}
	else
		appendStringInfoString(result, "</row>\n\n");
}


/*
 * XPath related functions
 */

#ifdef USE_LIBXML
/*
 * Convert XML node to text (dump subtree in case of element,
 * return value otherwise)
 */
static text *
xml_xmlnodetoxmltype(xmlNodePtr cur)
{
	xmlChar    *str;
	xmltype    *result;
	xmlBufferPtr buf;

	if (cur->type == XML_ELEMENT_NODE)
	{
		buf = xmlBufferCreate();
		xmlNodeDump(buf, NULL, cur, 0, 1);
		result = xmlBuffer_to_xmltype(buf);
		xmlBufferFree(buf);
	}
	else
	{
		str = xmlXPathCastNodeToString(cur);
		result = (xmltype *) cstring_to_text((char *) str);
		xmlFree(str);
	}

	return result;
}
#endif


/*
 * Evaluate XPath expression and return array of XML values.
 *
 * As we have no support of XQuery sequences yet, this function seems
 * to be the most useful one (array of XML functions plays a role of
 * some kind of substitution for XQuery sequences).
 *
 * Workaround here: we parse XML data in different way to allow XPath for
 * fragments (see "XPath for fragment" TODO comment inside).
 */
Datum
xpath(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
	text	   *xpath_expr_text = PG_GETARG_TEXT_P(0);
	xmltype    *data = PG_GETARG_XML_P(1);
	ArrayType  *namespaces = PG_GETARG_ARRAYTYPE_P(2);
	ArrayBuildState *astate = NULL;
	xmlParserCtxtPtr ctxt;
	xmlDocPtr	doc;
	xmlXPathContextPtr xpathctx;
	xmlXPathCompExprPtr xpathcomp;
	xmlXPathObjectPtr xpathobj;
	char	   *datastr;
	int32		len;
	int32		xpath_len;
	xmlChar    *string;
	xmlChar    *xpath_expr;
	int			i;
	int			res_nitems;
	int			ndim;
	Datum	   *ns_names_uris;
	bool	   *ns_names_uris_nulls;
	int			ns_count;

	/*
	 * Namespace mappings are passed as text[].  If an empty array is passed
	 * (ndim = 0, "0-dimensional"), then there are no namespace mappings.
	 * Else, a 2-dimensional array with length of the second axis being equal
	 * to 2 should be passed, i.e., every subarray contains 2 elements, the
	 * first element defining the name, the second one the URI.  Example:
	 * ARRAY[ARRAY['myns', 'http://example.com'], ARRAY['myns2',
	 * 'http://example2.com']].
	 */
	ndim = ARR_NDIM(namespaces);
	if (ndim != 0)
	{
		int		   *dims;

		dims = ARR_DIMS(namespaces);

		if (ndim != 2 || dims[1] != 2)
			ereport(ERROR,
					(errcode(ERRCODE_DATA_EXCEPTION),
					 errmsg("invalid array for XML namespace mapping"),
					 errdetail("The array must be two-dimensional with length of the second axis equal to 2.")));

		Assert(ARR_ELEMTYPE(namespaces) == TEXTOID);

		deconstruct_array(namespaces, TEXTOID, -1, false, 'i',
						  &ns_names_uris, &ns_names_uris_nulls,
						  &ns_count);

		Assert((ns_count % 2) == 0);	/* checked above */
		ns_count /= 2;			/* count pairs only */
	}
	else
	{
		ns_names_uris = NULL;
		ns_names_uris_nulls = NULL;
		ns_count = 0;
	}

	datastr = VARDATA(data);
	len = VARSIZE(data) - VARHDRSZ;
	xpath_len = VARSIZE(xpath_expr_text) - VARHDRSZ;
	if (xpath_len == 0)
		ereport(ERROR,
				(errcode(ERRCODE_DATA_EXCEPTION),
				 errmsg("empty XPath expression")));

	xml_init();

	/*
	 * To handle both documents and fragments, regardless of the fact whether
	 * the XML datum has a single root (XML well-formedness), we wrap the XML
	 * datum in a dummy element (<x>...</x>) and extend the XPath expression
	 * accordingly.  To do it, throw away the XML prolog, if any.
	 */
	if (len >= 5 &&
		xmlStrncmp((xmlChar *) datastr, (xmlChar *) "<?xml", 5) == 0)
	{
		i = 5;
		while (i < len &&
			   !(datastr[i - 1] == '?' && datastr[i] == '>'))
			i++;

		if (i == len)
			xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
						"could not parse XML data");

		++i;

		datastr += i;
		len -= i;
	}

	string = (xmlChar *) palloc((len + 8) * sizeof(xmlChar));
	memcpy(string, "<x>", 3);
	memcpy(string + 3, datastr, len);
	memcpy(string + 3 + len, "</x>", 5);
	len += 7;

	xpath_expr = (xmlChar *) palloc((xpath_len + 3) * sizeof(xmlChar));
	memcpy(xpath_expr, "/x", 2);
	memcpy(xpath_expr + 2, VARDATA(xpath_expr_text), xpath_len);
	xpath_expr[xpath_len + 2] = '\0';
	xpath_len += 2;

	xmlInitParser();

	/*
	 * redundant XML parsing (two parsings for the same value during one
	 * command execution are possible)
	 */
	ctxt = xmlNewParserCtxt();
	if (ctxt == NULL)
		xml_ereport(ERROR, ERRCODE_OUT_OF_MEMORY,
					"could not allocate parser context");
	doc = xmlCtxtReadMemory(ctxt, (char *) string, len, NULL, NULL, 0);
	if (doc == NULL)
		xml_ereport(ERROR, ERRCODE_INVALID_XML_DOCUMENT,
					"could not parse XML data");
	xpathctx = xmlXPathNewContext(doc);
	if (xpathctx == NULL)
		xml_ereport(ERROR, ERRCODE_OUT_OF_MEMORY,
					"could not allocate XPath context");
	xpathctx->node = xmlDocGetRootElement(doc);
	if (xpathctx->node == NULL)
		xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
					"could not find root XML element");

	/* register namespaces, if any */
	if (ns_count > 0)
	{
		for (i = 0; i < ns_count; i++)
		{
			char	   *ns_name;
			char	   *ns_uri;

			if (ns_names_uris_nulls[i * 2] ||
				ns_names_uris_nulls[i * 2 + 1])
				ereport(ERROR,
						(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
						 errmsg("neither namespace name nor URI may be null")));
			ns_name = TextDatumGetCString(ns_names_uris[i * 2]);
			ns_uri = TextDatumGetCString(ns_names_uris[i * 2 + 1]);
			if (xmlXPathRegisterNs(xpathctx,
								   (xmlChar *) ns_name,
								   (xmlChar *) ns_uri) != 0)
				ereport(ERROR,		/* is this an internal error??? */
						(errmsg("could not register XML namespace with name \"%s\" and URI \"%s\"",
								ns_name, ns_uri)));
		}
	}

	xpathcomp = xmlXPathCompile(xpath_expr);
	if (xpathcomp == NULL)	/* TODO: show proper XPath error details */
		xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
					"invalid XPath expression");

	xpathobj = xmlXPathCompiledEval(xpathcomp, xpathctx);
	if (xpathobj == NULL)	/* TODO: reason? */
		ereport(ERROR,
				(errmsg("could not create XPath object")));

	xmlXPathFreeCompExpr(xpathcomp);

	/* return empty array in cases when nothing is found */
	if (xpathobj->nodesetval == NULL)
		res_nitems = 0;
	else
		res_nitems = xpathobj->nodesetval->nodeNr;

	if (res_nitems)
	{
		for (i = 0; i < xpathobj->nodesetval->nodeNr; i++)
		{
			Datum		elem;
			bool		elemisnull = false;

			elem = PointerGetDatum(xml_xmlnodetoxmltype(xpathobj->nodesetval->nodeTab[i]));
			astate = accumArrayResult(astate, elem,
									  elemisnull, XMLOID,
									  CurrentMemoryContext);
		}
	}

	xmlXPathFreeObject(xpathobj);
	xmlXPathFreeContext(xpathctx);
	xmlFreeDoc(doc);
	xmlFreeParserCtxt(ctxt);

	if (res_nitems == 0)
		PG_RETURN_ARRAYTYPE_P(construct_empty_array(XMLOID));
	else
		PG_RETURN_ARRAYTYPE_P(makeArrayResult(astate, CurrentMemoryContext));
#else
	NO_XML_SUPPORT();
	return 0;
#endif
}
