openGauss-server/src/common/backend/utils/adt/xml.cpp

/* -------------------------------------------------------------------------
 *
 * xml.c
 *    XML data type support.
 *
 *
 * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/backend/utils/adt/xml.c
 *
 * -------------------------------------------------------------------------
 */

/*
 * 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:
 *
 * Sometimes libxml allocates global structures in the hope that it can reuse
 * them later on.  This makes it impractical to change the xmlMemSetup
 * functions on-the-fly; that is likely to lead to trying to pfree_ext() chunks
 * allocated with malloc() or vice versa.  Since libxml might be used by
 * loadable modules, eg libperl, our only safe choices are to change the
 * functions at postmaster/backend launch or not at all.  Since we'd rather
 * not activate libxml in sessions that might never use it, the latter choice
 * is the preferred one.  However, for debugging purposes it can be awfully
 * handy to constrain libxml's allocations to be done in a specific palloc
 * context, where they're easy to track.  Therefore there is code here that
 * can be enabled in debug builds to redirect libxml's allocations into a
 * special context LibxmlContext.  It's not recommended to turn this on in
 * a production build because of the possibility of bad interactions with
 * external modules.
 */

#include "postgres.h"
#include "knl/knl_variable.h"

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

/*
 * We used to check for xmlStructuredErrorContext via a configure test; but
 * that doesn't work on Windows, so instead use this grottier method of
 * testing the library version number.
 */
#if LIBXML_VERSION >= 20704
#define HAVE_XMLSTRUCTUREDERRORCONTEXT 1
#endif
#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/rel.h"
#include "utils/rel_gs.h"
#include "utils/syscache.h"
#include "utils/xml.h"

/* GUC variables */
THR_LOCAL int xmloption;
#ifdef USE_LIBXML

/* random number to identify PgXmlErrorContext */
#define ERRCXT_MAGIC 68275028

struct PgXmlErrorContext {
    int magic;
    /* strictness argument passed to pg_xml_init */
    PgXmlStrictness strictness;
    /* current error status and accumulated message, if any */
    bool err_occurred;
    StringInfoData err_buf;
    /* previous libxml error handling state (saved by pg_xml_init) */
    xmlStructuredErrorFunc saved_errfunc;
    void* saved_errcxt;
    /* previous libxml entity handler (saved by pg_xml_init) */
    xmlExternalEntityLoader saved_entityfunc;
};

static xmlParserInputPtr xml_pg_entity_loader(const char* URL, const char* ID, xmlParserCtxtPtr ctxt);
static void xml_error_handler(void* data, xmlErrorPtr error);
static void xml_ereport_by_code(int level, int sqlcode, const char* msg, int errcode);
static void chop_string_info_new_lines(StringInfo str);
static void append_string_info_line_separator(StringInfo str);

#ifdef USE_LIBXMLCONTEXT

static MemoryContext LibxmlContext = NULL;

static void xml_memory_init(void);
static void* xml_palloc(size_t size);
static void* xml_repalloc(void* ptr, size_t size);
static void xml_pfree_ext(void* ptr);
static char* xml_pstrdup(const char* string);
#endif /* USE_LIBXMLCONTEXT */

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, int encoding);
static text* xml_xmlnodetoxmltype(xmlNodePtr cur);
static int xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj, ArrayBuildState** astate);
#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);
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);
// Empty string to NULL
#define DEF_TARGETNS ""

#ifdef USE_LIBXML
#define NO_XML_SUPPORT()
#else
#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.")))
#endif

/* from SQL/XML:2008 section 4.9 */
#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 xml_char_to_encoding(const xmlChar* encoding_name)
{
    int encoding = pg_char_to_encoding((const char*)encoding_name);
    if (encoding < 0) {
        ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
            errmsg("invalid encoding name \"%s\"", (const 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* var_data = NULL;
    xmlDocPtr doc;

    var_data = (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(var_data, (XmlOptionType)xmloption, true, GetDatabaseEncoding());
    xmlFreeDoc(doc);

    PG_RETURN_XML_P(var_data);
#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 = NULL;
    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);

        pfree_ext(str);

        return buf.data;
    }

    xml_ereport_by_code(
        WARNING, ERRCODE_INVALID_XML_CONTENT, "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, (pg_enc)0));
}

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

    /*
     * 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.
     */
    n_bytes = buf->len - buf->cursor;
    str = (char*)pq_getmsgbytes(buf, n_bytes);

    /*
     * 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 = (xmltype*)palloc(n_bytes + 1 + VARHDRSZ);
    SET_VARSIZE(result, n_bytes + VARHDRSZ);
    int rc = memcpy_s(VARDATA(result), n_bytes, str, n_bytes);
    securec_check(rc, "\0", "\0");
    str = VARDATA(result);
    str[n_bytes] = '\0';

    int res_code = parse_xml_decl((const xmlChar*)str, NULL, NULL, &encoding_str, NULL);
    if (res_code != 0) {
        xml_ereport_by_code(ERROR, ERRCODE_INVALID_XML_CONTENT,
            "invalid XML content: invalid XML declaration", res_code);
    }

    /*
     * If encoding wasn't explicitly specified in the XML header, treat it as
     * UTF-8, as that's the default in XML. This is different from xml_in(),
     * where the input has to go through the normal client to server encoding
     * conversion.
     */
    encoding = encoding_str ? xml_char_to_encoding(encoding_str) : PG_UTF8;

    /*
     * 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, (XmlOptionType)xmloption, true, encoding);
    xmlFreeDoc(doc);

    /* Now that we know what we're dealing with, convert to server encoding */
    new_str = (char*)pg_do_encoding_conversion((unsigned char*)str, n_bytes, encoding, GetDatabaseEncoding());
    if (new_str != str) {
        pfree_ext(result);
        result = (xmltype*)cstring_to_text(new_str);
        pfree_ext(new_str);
    }

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

Datum xml_send(PG_FUNCTION_ARGS)
{
    NO_XML_SUPPORT();

    xmltype* x = PG_GETARG_XML_P(0);
    char* out_val = NULL;
    StringInfoData buf;

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

    pq_begintypsend(&buf);
    pq_sendtext(&buf, out_val, strlen(out_val));
    pfree_ext(out_val);
    PG_RETURN_BYTEA_P(pq_endtypsend(&buf));
}

#ifdef USE_LIBXML
static void append_string_info_text(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((const char*)xmlBufferContent(buf), xmlBufferLength(buf));
}
#endif

Datum xmlcomment(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
    text* arg = PG_GETARG_TEXT_P(0);
    char* arg_data = 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 (arg_data[i] == '-' && arg_data[i - 1] == '-') {
            ereport(ERROR, (errcode(ERRCODE_INVALID_XML_COMMENT), errmsg("invalid XML comment")));
        }
    }
    if (len > 0 && arg_data[len - 1] == '-') {
        ereport(ERROR, (errcode(ERRCODE_INVALID_XML_COMMENT), errmsg("invalid XML comment")));
    }
    initStringInfo(&buf);
    appendStringInfo(&buf, "<!--");
    append_string_info_text(&buf, arg);
    appendStringInfo(&buf, "-->");

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

/*
 * 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 = NULL;

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

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

        int res_code = parse_xml_decl((xmlChar*)str, &len, &version, NULL, &standalone);
        if (res_code != 0) {
            xml_ereport_by_code(
                ERROR, ERRCODE_INVALID_XML_CONTENT, "invalid XML content: invalid XML declaration", res_code);
        }
        if (standalone == 0 && global_standalone == 1) {
            global_standalone = 0;
        }
        if (standalone < 0) {
            global_standalone = -1;
        }
        if (version == NULL) {
            global_version_no_value = true;
        } else if (global_version == NULL) {
            global_version = version;
        } else if (xmlStrcmp(version, global_version) != 0) {
            global_version_no_value = true;
        }
        appendStringInfoString(&buf, str + len);
        pfree_ext(str);
    }

    if (!global_version_no_value || global_standalone >= 0) {
        StringInfoData buf2;
        initStringInfo(&buf2);
        print_xml_decl(&buf2, (!global_version_no_value) ? global_version : NULL, (pg_enc)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)
{
    NO_XML_SUPPORT();

    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)
{
    NO_XML_SUPPORT();
    text* data = PG_GETARG_TEXT_P(0);
    PG_RETURN_XML_P(xmlparse(data, (XmlOptionType)xmloption, true));
}

Datum xmltotext(PG_FUNCTION_ARGS)
{
    NO_XML_SUPPORT();

    /* It's actually binary compatible. */
    xmltype* data = PG_GETARG_XML_P(0);
    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 = NULL;
    List* named_arg_strings = NIL;
    List* arg_strings = NIL;
    int i;
    ListCell* arg = NULL;
    ListCell* narg = NULL;
    PgXmlErrorContext* xml_err_cxt = NULL;
    volatile xmlBufferPtr buf = NULL;
    volatile xmlTextWriterPtr writer = NULL;

    /*
     * 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 is_null = false;
        char* str = NULL;

        value = ExecEvalExpr(e, econtext, &is_null, NULL);
        if (is_null) {
            str = NULL;
        } else {
            str = map_sql_value_to_xml_value(value, exprType((Node*)e->expr), false);
        }
        named_arg_strings = lappend(named_arg_strings, str);
        i++;
    }

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

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

    /* now safe to run libxml */
    xml_err_cxt = pg_xml_init(PG_XML_STRICTNESS_ALL);

    PG_TRY();
    {
        buf = xmlBufferCreate();
        if (buf == NULL || xml_err_cxt->err_occurred) {
            xml_ereport(xml_err_cxt, ERROR, ERRCODE_OUT_OF_MEMORY, "could not allocate xmlBuffer");
        }
        writer = xmlNewTextWriterMemory(buf, 0);
        if (writer == NULL || xml_err_cxt->err_occurred) {
            xml_ereport(xml_err_cxt, ERROR, ERRCODE_OUT_OF_MEMORY, "could not allocate xmlTextWriter");
        }
        xmlTextWriterStartElement(writer, (xmlChar*)xexpr->name);

        forboth(arg, named_arg_strings, narg, xexpr->arg_names)
        {
            char* str = (char*)lfirst(arg);
            char* arg_name = strVal(lfirst(narg));
            if (str != NULL) {
                xmlTextWriterWriteAttribute(writer, (xmlChar*)arg_name, (xmlChar*)str);
            }
        }

        foreach (arg, arg_strings) {
            char* str = (char*)lfirst(arg);
            xmlTextWriterWriteRaw(writer, (xmlChar*)str);
        }

        xmlTextWriterEndElement(writer);

        /* we MUST do this now to flush data out to the buffer ... */
        xmlFreeTextWriter(writer);
        writer = NULL;

        result = xmlBuffer_to_xmltype(buf);
    }
    PG_CATCH();
    {
        if (writer) {
            xmlFreeTextWriter(writer);
        }
        if (buf) {
            xmlBufferFree(buf);
        }
        pg_xml_done(xml_err_cxt, true);

        PG_RE_THROW();
    }
    PG_END_TRY();

    xmlBufferFree(buf);

    pg_xml_done(xml_err_cxt, false);

    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, GetDatabaseEncoding());
    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 = NULL;
    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 = NULL;
        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_ext(string);
    }
    appendStringInfoString(&buf, "?>");

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

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

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

    int res_code = parse_xml_decl((xmlChar*)str, &len, &orig_version, NULL, &orig_standalone);
    if (res_code != 0) {
        xml_ereport_by_code(
            ERROR, ERRCODE_INVALID_XML_CONTENT, "invalid XML content: invalid XML declaration", res_code);
    }
    if (version != NULL) {
        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;
        default:
            break;
    }

    initStringInfo(&buf);
    print_xml_decl(&buf, orig_version, (pg_enc)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 = false;
    volatile xmlDocPtr doc = NULL;
    MemoryContext ccxt = CurrentMemoryContext;

    /* We want to catch ereport(INVALID_XML_DOCUMENT) and return false */
    PG_TRY();
    {
        doc = xml_parse((text*)arg, XMLOPTION_DOCUMENT, true, GetDatabaseEncoding());
        result = true;
    }
    PG_CATCH();
    {
        ErrorData* err_data = NULL;
        MemoryContext ecxt;

        ecxt = MemoryContextSwitchTo(ccxt);
        err_data = CopyErrorData();
        if (err_data->sqlerrcode == ERRCODE_INVALID_XML_DOCUMENT) {
            FlushErrorState();
            result = false;
        } else {
            (void)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 */
}

#ifdef USE_LIBXML

/*
 * pg_xml_init_library --- set up for use of libxml
 *
 * This should be called by each function that is about to use libxml
 * facilities but doesn't require error handling.  It initializes libxml
 * and verifies compatibility with the loaded libxml version.  These are
 * once-per-session activities.
 *
 * XmlChar is utf8-char, need make proper tuning (initdb with enc!=utf8 and
 * check)
 */
void pg_xml_init_library(void)
{
    static bool first_time = true;

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

        /*
         * Currently, we have no pure UTF-8 support for internals -- check if
         * we can work.
         */
        if (sizeof(char) != sizeof(xmlChar)) {
            ereport(ERROR,
                (errcode(ERRCODE_DATATYPE_MISMATCH),
                    errmsg("could not initialize XML library"),
                    errdetail("libxml2 has incompatible char type: sizeof(char)=%u, sizeof(xmlChar)=%u.",
                        (int)sizeof(char),
                        (int)sizeof(xmlChar))));
        }
#ifdef USE_LIBXMLCONTEXT
        /* Set up libxml's memory allocation our way */
        xml_memory_init();
#endif

        /* Check library compatibility */
        LIBXML_TEST_VERSION;

        first_time = false;
    }
}

/*
 * pg_xml_init --- set up for use of libxml and register an error handler
 *
 * This should be called by each function that is about to use libxml
 * facilities and requires error handling.	It initializes libxml with
 * pg_xml_init_library() and establishes our libxml error handler.
 *
 * strictness determines which errors are reported and which are ignored.
 *
 * Calls to this function MUST be followed by a PG_TRY block that guarantees
 * that pg_xml_done() is called during either normal or error exit.
 *
 * This is exported for use by contrib/xml2, as well as other code that might
 * wish to share use of this module's libxml error handler.
 */
PgXmlErrorContext* pg_xml_init(PgXmlStrictness strictness)
{
    PgXmlErrorContext* errcxt = NULL;
    void* new_errcxt = NULL;

    /* Do one-time setup if needed */
    pg_xml_init_library();

    /* Create error handling context structure */
    errcxt = (PgXmlErrorContext*)palloc(sizeof(PgXmlErrorContext));
    errcxt->magic = ERRCXT_MAGIC;
    errcxt->strictness = strictness;
    errcxt->err_occurred = false;
    initStringInfo(&errcxt->err_buf);

    /*
     * Save original error handler and install ours. libxml originally didn't
     * distinguish between the contexts for generic and for structured error
     * handlers.  If we're using an old libxml version, we must thus save the
     * generic error context, even though we're using a structured error
     * handler.
     */
    errcxt->saved_errfunc = xmlStructuredError;

#ifdef HAVE_XMLSTRUCTUREDERRORCONTEXT
    errcxt->saved_errcxt = xmlStructuredErrorContext;
#else
    errcxt->saved_errcxt = xmlGenericErrorContext;
#endif

    xmlSetStructuredErrorFunc((void*)errcxt, xml_error_handler);

    /*
     * Verify that xmlSetStructuredErrorFunc set the context variable we
     * expected it to.	If not, the error context pointer we just saved is not
     * the correct thing to restore, and since that leaves us without a way to
     * restore the context in pg_xml_done, we must fail.
     *
     * The only known situation in which this test fails is if we compile with
     * headers from a libxml2 that doesn't track the structured error context
     * separately (< 2.7.4), but at runtime use a version that does, or vice
     * versa.  The libxml2 authors did not treat that change as constituting
     * an ABI break, so the LIBXML_TEST_VERSION test in pg_xml_init_library
     * fails to protect us from this.
     */
#ifdef HAVE_XMLSTRUCTUREDERRORCONTEXT
    new_errcxt = xmlStructuredErrorContext;
#else
    new_errcxt = xmlGenericErrorContext;
#endif

    if (new_errcxt != (void*)errcxt) {
        ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
            errmsg("could not set up XML error handler"),
            errhint("This probably indicates that the version of libxml2"
                    " being used is not compatible with the libxml2"
                    " header files that PostgreSQL was built with.")));
    }

    /*
     * Also, install an entity loader to prevent unwanted fetches of external
     * files and URLs.
     */
    errcxt->saved_entityfunc = xmlGetExternalEntityLoader();
    xmlSetExternalEntityLoader(xml_pg_entity_loader);

    return errcxt;
}

/*
 * pg_xml_done --- restore previous libxml error handling
 *
 * Resets libxml's global error-handling state to what it was before
 * pg_xml_init() was called.
 *
 * This routine verifies that all pending errors have been dealt with
 * (in assert-enabled builds, anyway).
 */
void pg_xml_done(PgXmlErrorContext* errcxt, bool is_error)
{
    void* cur_errcxt = NULL;

    /* An assert seems like enough protection here */
    Assert(errcxt->magic == ERRCXT_MAGIC);

    /*
     * In a normal exit, there should be no un-handled libxml errors.  But we
     * shouldn't try to enforce this during error recovery, since the longjmp
     * could have been thrown before xml_ereport had a chance to run.
     */
    Assert(!errcxt->err_occurred || is_error);

    /*
     * Check that libxml's global state is correct, warn if not.  This is a
     * real test and not an Assert because it has a higher probability of
     * happening.
     */
#ifdef HAVE_XMLSTRUCTUREDERRORCONTEXT
    cur_errcxt = xmlStructuredErrorContext;
#else
    cur_errcxt = xmlGenericErrorContext;
#endif

    if (cur_errcxt != (void*)errcxt) {
        elog(WARNING, "libxml error handling state is out of sync with xml.c");
    }

    /* Restore the saved handlers */
    xmlSetStructuredErrorFunc(errcxt->saved_errcxt, errcxt->saved_errfunc);
    xmlSetExternalEntityLoader(errcxt->saved_entityfunc);

    /*
     * Mark the struct as invalid, just in case somebody somehow manages to
     * call xml_error_handler or xml_ereport with it.
     */
    errcxt->magic = 0;

    /* Release memory */
    pfree_ext(errcxt->err_buf.data);
    pfree_ext(errcxt);
}

/*
 * pg_xml_error_occurred() --- test the error flag
 */
bool pg_xml_error_occurred(PgXmlErrorContext* errcxt)
{
    return errcxt->err_occurred;
}

/*
 * 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 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))

/* pnstrdup, but deal with xmlChar not char; len is measured in xmlChars */
static xmlChar* xml_pnstrdup(const xmlChar* str, size_t len)
{
    xmlChar* result = NULL;

    result = (xmlChar*)palloc((len + 1) * sizeof(xmlChar));
    MemCpy(result, str, len * sizeof(xmlChar));
    result[len] = 0;
    return result;
}

/*
 * str is the null-terminated input string.  Remaining arguments are
 * output arguments; each can be NULL if value is not wanted.
 * version and encoding are returned as locally-palloc'd strings.
 * Result is 0 if OK, an error code if not.
 */
static int parse_xml_decl(const xmlChar* str, size_t* lenp, xmlChar** version, xmlChar** encoding, int* standalone)
{
    const xmlChar* p = NULL;
    const xmlChar* save_p = NULL;
    size_t len;
    int utf8char;
    int utf8len;

    /*
     * Only initialize libxml.	We don't need error handling here, but we do
     * need to make sure libxml is initialized before calling any of its
     * functions.  Note that this is safe (and a no-op) if caller has already
     * done pg_xml_init().
     */
    pg_xml_init_library();

    /* Initialize output arguments to "not present" */
    if (version != NULL) {
        *version = NULL;
    }
    if (encoding != NULL) {
        *encoding = NULL;
    }
    if (standalone != NULL) {
        *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 */
    if (!xmlIsBlank_ch(*(p))) {
        return XML_ERR_SPACE_REQUIRED;
    }
    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 = NULL;
        q = xmlStrchr(p + 1, *p);
        if (q == NULL) {
            return XML_ERR_VERSION_MISSING;
        }
        if (version != NULL) {
            *version = xml_pnstrdup(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) {
        if (!xmlIsBlank_ch(*(save_p))) {
            return XML_ERR_SPACE_REQUIRED;
        }
        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 = NULL;
            q = xmlStrchr(p + 1, *p);
            if (q == NULL) {
                return XML_ERR_MISSING_ENCODING;
            }
            if (encoding != NULL) {
                *encoding = xml_pnstrdup(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) {
        if (!xmlIsBlank_ch(*(save_p))) {
            return XML_ERR_SPACE_REQUIRED;
        }
        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) {
            if (standalone != NULL) {
                *standalone = 1;
            }
            p += 5;
        } else if (xmlStrncmp(p, (xmlChar*)"'no'", 4) == 0 || xmlStrncmp(p, (xmlChar*)"\"no\"", 4) == 0) {
            if (standalone != NULL) {
                *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 != NULL) {
        *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)
{
    if ((version && strcmp((const char*)version, PG_XML_DEFAULT_VERSION) != 0) ||
        (encoding && encoding != PG_UTF8) || standalone != -1) {
        appendStringInfoString(buf, "<?xml");

        if (version != NULL) {
            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
 *
 * Note: it is caller's responsibility to xmlFreeDoc() the result,
 * else a permanent memory leak will ensue!
 *
 * 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, int encoding)
{
    int32 len;
    xmlChar* string = NULL;
    xmlChar* utf8string = NULL;
    PgXmlErrorContext* xml_errcxt = NULL;
    volatile xmlParserCtxtPtr ctxt = NULL;
    volatile xmlDocPtr doc = NULL;

    len = VARSIZE(data) - VARHDRSZ; /* will be useful later */
    string = xml_text2xmlChar(data);
    utf8string = pg_do_encoding_conversion(string, len, encoding, PG_UTF8);

    /* Start up libxml and its parser */
    xml_errcxt = pg_xml_init(PG_XML_STRICTNESS_WELLFORMED);

    /* Use a TRY block to ensure we clean up correctly */
    PG_TRY();
    {
        xmlInitParser();

        ctxt = xmlNewParserCtxt();
        if (ctxt == NULL || xml_errcxt->err_occurred) {
            xml_ereport(xml_errcxt, 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:2008 GR 10.16.7.d:
             * 'Default values defined by internal DTD are applied'. As for
             * external DTDs, we try to support them too, (see SQL/XML:2008 GR
             * 10.16.7.e)
             */
            doc = xmlCtxtReadDoc(ctxt,
                utf8string,
                NULL,
                "UTF-8",
                XML_PARSE_NOENT | XML_PARSE_DTDATTR | (preserve_whitespace ? 0 : XML_PARSE_NOBLANKS));
            if (doc == NULL || xml_errcxt->err_occurred) {
                xml_ereport(xml_errcxt, ERROR, ERRCODE_INVALID_XML_DOCUMENT, "invalid XML document");
            }
        } else {
            int res_code;
            size_t count;
            xmlChar* version = NULL;
            int standalone;

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

            res_code = xmlParseBalancedChunkMemory(doc, NULL, NULL, 0, utf8string + count, NULL);
            if (res_code != 0 || xml_errcxt->err_occurred) {
                xml_ereport(xml_errcxt, ERROR, ERRCODE_INVALID_XML_CONTENT, "invalid XML content");
            }
        }
    }
    PG_CATCH();
    {
        if (doc != NULL) {
            xmlFreeDoc(doc);
        }
        if (ctxt != NULL) {
            xmlFreeParserCtxt(ctxt);
        }
        pg_xml_done(xml_errcxt, true);

        PG_RE_THROW();
    }
    PG_END_TRY();

    xmlFreeParserCtxt(ctxt);

    pg_xml_done(xml_errcxt, false);

    return doc;
}

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

#ifdef USE_LIBXMLCONTEXT

/*
 * Manage the special context used for all libxml allocations (but only
 * in special debug builds; see notes at top of file)
 */
static void xml_memory_init(void)
{
    /* Create memory context if not there already */
    if (LibxmlContext == NULL) {
        LibxmlContext = AllocSetContextCreate(t_thrd.top_mem_cxt,
            "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);
}

/*
 * 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_ext(void* ptr)
{
    /* At least some parts of libxml assume xmlFree(NULL) is allowed */
    if (ptr != NULL) {
        pfree_ext(ptr);
    }
}

static char* xml_pstrdup(const char* string)
{
    return MemoryContextStrdup(LibxmlContext, string);
}
#endif /* USE_LIBXMLCONTEXT */

/*
 * xml_pg_entity_loader --- entity loader callback function
 *
 * Silently prevent any external entity URL from being loaded.  We don't want
 * to throw an error, so instead make the entity appear to expand to an empty
 * string.
 *
 * We would prefer to allow loading entities that exist in the system's
 * global XML catalog; but the available libxml2 APIs make that a complex
 * and fragile task.  For now, just shut down all external access.
 */
static xmlParserInputPtr xml_pg_entity_loader(const char* URL, const char* ID, xmlParserCtxtPtr ctxt)
{
    return xmlNewStringInputStream(ctxt, (const xmlChar*)"");
}

/*
 * xml_ereport --- report an XML-related error
 *
 * The "msg" is the SQL-level message; some can be adopted from the SQL/XML
 * standard.  This function adds libxml's native error message, if any, as
 * detail.
 *
 * This is exported for modules that want to share the core libxml error
 * handler.  Note that pg_xml_init() *must* have been called previously.
 */
void xml_ereport(PgXmlErrorContext* errcxt, int level, int sqlcode, const char* msg)
{
    char* detail = NULL;

    /* Defend against someone passing us a bogus context struct */
    if (errcxt->magic != ERRCXT_MAGIC) {
        ereport(ERROR,
            (errmodule(MOD_OPT),
                (errcode(ERRCODE_INVALID_XML_ERROR_CONTEXT),
                    errmsg("xml_ereport called with invalid PgXmlErrorContext"))));
    }

    /* Flag that the current libxml error has been reported */
    errcxt->err_occurred = false;

    /* Include detail only if we have some text from libxml */
    if (errcxt->err_buf.len > 0) {
        detail = errcxt->err_buf.data;
    } else {
        detail = NULL;
    }
    ereport(level, (errcode(sqlcode), errmsg_internal("%s", msg), detail ? errdetail_internal("%s", detail) : 0));
}

/*
 * Error handler for libxml errors and warnings
 */
static void xml_error_handler(void* data, xmlErrorPtr error)
{
    PgXmlErrorContext* xml_errcxt = (PgXmlErrorContext*)data;
    xmlParserCtxtPtr ctxt = (xmlParserCtxtPtr)error->ctxt;
    xmlParserInputPtr input = (ctxt != NULL) ? ctxt->input : NULL;
    xmlNodePtr node = (xmlNodePtr)error->node;
    const xmlChar* name = (node != NULL && node->type == XML_ELEMENT_NODE) ? node->name : NULL;
    int domain = error->domain;
    int level = error->level;
    StringInfo error_buf;

    /*
     * Defend against someone passing us a bogus context struct.
     *
     * We force a backend exit if this check fails because longjmp'ing out of
     * libxml would likely render it unsafe to use further.
     */
    if (xml_errcxt->magic != ERRCXT_MAGIC) {
        ereport(FATAL,
            (errmodule(MOD_OPT),
                (errcode(ERRCODE_INVALID_XML_ERROR_CONTEXT),
                    errmsg("xml_error_handler called with invalid PgXmlErrorContext"))));
    }

    /* ----------
     * Older libxml versions report some errors differently.
     * First, some errors were previously reported as coming from the parser
     * domain but are now reported as coming from the namespace domain.
     * Second, some warnings were upgraded to errors.
     * We attempt to compensate for that here.
     * ----------
     */
    switch (error->code) {
        case XML_WAR_NS_URI:
            level = XML_ERR_ERROR;
            domain = XML_FROM_NAMESPACE;
            break;

        case XML_ERR_NS_DECL_ERROR:
        case XML_WAR_NS_URI_RELATIVE:
        case XML_WAR_NS_COLUMN:
        case XML_NS_ERR_XML_NAMESPACE:
        case XML_NS_ERR_UNDEFINED_NAMESPACE:
        case XML_NS_ERR_QNAME:
        case XML_NS_ERR_ATTRIBUTE_REDEFINED:
        case XML_NS_ERR_EMPTY:
            domain = XML_FROM_NAMESPACE;
            break;
        default:
            break;
    }

    /* Decide whether to act on the error or not */
    switch (domain) {
        case XML_FROM_PARSER:
        case XML_FROM_NONE:
        case XML_FROM_MEMORY:
        case XML_FROM_IO:
            /*
             * Suppress warnings about undeclared entities.  We need to do
             * this to avoid problems due to not loading DTD definitions.
             */
            if (error->code == XML_WAR_UNDECLARED_ENTITY) {
                return;
            }

            /* Otherwise, accept error regardless of the parsing purpose */
            break;

        default:
            /* Ignore error if only doing well-formedness check */
            if (xml_errcxt->strictness == PG_XML_STRICTNESS_WELLFORMED) {
                return;
            }
            break;
    }

    /* Prepare error message in error_buf */
    error_buf = makeStringInfo();

    if (error->line > 0) {
        appendStringInfo(error_buf, "line %d: ", error->line);
    }
    if (name != NULL) {
        appendStringInfo(error_buf, "element %s: ", name);
    }
    if (error->message != NULL) {
        appendStringInfoString(error_buf, error->message);
    } else {
        appendStringInfoString(error_buf, "(no message provided)");
    }

    /*
     * Append context information to error_buf.
     *
     * xmlParserPrintFileContext() uses libxml's "generic" error handler to
     * write the context.  Since we don't want to duplicate libxml
     * functionality here, we set up a generic error handler temporarily.
     *
     * We use appendStringInfo() directly as libxml's generic error handler.
     * This should work because it has essentially the same signature as
     * libxml expects, namely (void *ptr, const char *msg, ...).
     */
    if (input != NULL) {
        xmlGenericErrorFunc err_func_saved = xmlGenericError;
        void* err_ctx_saved = xmlGenericErrorContext;

        xmlSetGenericErrorFunc((void*)error_buf, (xmlGenericErrorFunc)appendStringInfo);

        /* Add context information to error_buf */
        append_string_info_line_separator(error_buf);

        xmlParserPrintFileContext(input);

        /* Restore generic error func */
        xmlSetGenericErrorFunc(err_ctx_saved, err_func_saved);
    }

    /* Get rid of any trailing newlines in error_buf */
    chop_string_info_new_lines(error_buf);

    /*
     * Legacy error handling mode.	err_occurred is never set, we just add the
     * message to err_buf.	This mode exists because the xml2 contrib module
     * uses our error-handling infrastructure, but we don't want to change its
     * behaviour since it's deprecated anyway.  This is also why we don't
     * distinguish between notices, warnings and errors here --- the old-style
     * generic error handler wouldn't have done that either.
     */
    if (xml_errcxt->strictness == PG_XML_STRICTNESS_LEGACY) {
        append_string_info_line_separator(&xml_errcxt->err_buf);
        appendStringInfoString(&xml_errcxt->err_buf, error_buf->data);

        pfree_ext(error_buf->data);
        pfree_ext(error_buf);
        return;
    }

    /*
     * We don't want to ereport() here because that'd probably leave libxml in
     * an inconsistent state.  Instead, we remember the error and ereport()
     * from xml_ereport().
     *
     * Warnings and notices can be reported immediately since they won't cause
     * a longjmp() out of libxml.
     */
    if (level >= XML_ERR_ERROR) {
        append_string_info_line_separator(&xml_errcxt->err_buf);
        appendStringInfoString(&xml_errcxt->err_buf, error_buf->data);

        xml_errcxt->err_occurred = true;
    } else if (level >= XML_ERR_WARNING) {
        ereport(WARNING, (errmsg_internal("%s", error_buf->data)));
    } else {
        ereport(NOTICE, (errmsg_internal("%s", error_buf->data)));
    }

    pfree_ext(error_buf->data);
    pfree_ext(error_buf);
}

/*
 * 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 = NULL;

    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_internal("%s", msg), errdetail(det, code)));
}

/*
 * Remove all trailing newlines from a StringInfo string
 */
static void chop_string_info_new_lines(StringInfo str)
{
    while (str->len > 0 && str->data[str->len - 1] == '\n')
        str->data[--str->len] = '\0';
}

/*
 * Append a newline after removing any existing trailing newlines
 */
static void append_string_info_line_separator(StringInfo str)
{
    chop_string_info_new_lines(str);
    if (str->len > 0) {
        appendStringInfoChar(str, '\n');
    }
}

/*
 * Convert one char in the current server encoding to a Unicode codepoint.
 */
static pg_wchar sqlchar_to_unicode(char* s)
{
    char* utf8_string = NULL;
    pg_wchar ret[2]; /* need space for trailing zero */

    utf8_string = (char*)pg_do_encoding_conversion((unsigned char*)s, pg_mblen(s), GetDatabaseEncoding(), PG_UTF8);
    pg_encoding_mb2wchar_with_len(PG_UTF8, utf8_string, ret, pg_encoding_mblen(PG_UTF8, utf8_string));
    if (utf8_string != s) {
        pfree_ext(utf8_string);
    }
    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:2008 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 = NULL;

    /*
     * 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)
{
    unsigned char utf8_string[5]; /* need room for trailing zero */
    char* result = NULL;
    errno_t rc = 0;

    rc = memset_s(utf8_string, sizeof(utf8_string), 0, sizeof(utf8_string));
    securec_check(rc, "\0", "\0");

    unicode_to_utf8(c, utf8_string);

    result = (char*)pg_do_encoding_conversion(
        utf8_string, pg_encoding_mblen(PG_UTF8, (char*)utf8_string), PG_UTF8, GetDatabaseEncoding());
    /* if pg_do_encoding_conversion didn't strdup, we must */
    if (result == (char*)utf8_string) {
        result = pstrdup(result);
    }
    return result;
}

/*
 * Map XML name to SQL identifier; see SQL/XML:2008 section 9.3.
 */
char* map_xml_name_to_sql_identifier(char* name)
{
    StringInfoData buf;
    char* p = NULL;
    errno_t ss_rc = 0;

    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;
            ss_rc = sscanf_s(p + 2, "%X", &u);
            if (ss_rc != 1) {
                ereport(LOG,
                    (errmsg("ERROR at %s : %d : The destination buffer or format is normal but can not read data..\n",
                        __FILE__,
                        __LINE__)));
            }
            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:2008 section 9.8.
 *
 * When xml_escape_strings is true, then certain characters in string
 * values are replaced by entity references (&lt; etc.), as specified
 * in SQL/XML:2008 section 9.8 GR 9) a) iii).	This is normally what is
 * wanted.	The false case is mainly useful when the resulting value
 * is used with xmlTextWriterWriteAttribute() to write out an
 * attribute, because that function does the escaping itself.
 */
char* map_sql_value_to_xml_value(Datum value, Oid type, bool xml_escape_strings)
{
    if (type_is_array_domain(type)) {
        ArrayType* array = NULL;
        Oid elm_type;
        int16 elm_len;
        bool elm_by_val = false;
        char elm_align;
        int num_elems;
        Datum* elem_values = NULL;
        bool* elem_nulls = NULL;
        StringInfoData buf;
        int i;

        array = DatumGetArrayTypeP(value);
        elm_type = ARR_ELEMTYPE(array);
        get_typlenbyvalalign(elm_type, &elm_len, &elm_by_val, &elm_align);

        deconstruct_array(array, elm_type, elm_len, elm_by_val, elm_align, &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], elm_type, true));
            appendStringInfoString(&buf, "</element>");
        }

        pfree_ext(elem_values);
        pfree_ext(elem_nulls);

        return buf.data;
    } else {
        Oid type_out;
        bool is_varlena = false;
        char* str = NULL;

        /*
         * 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);
                /* XSD doesn't support infinite values */
                if (DATE_NOT_FINITE(date)) {
                    ereport(ERROR,
                        (errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
                            errmsg("date out of range"),
                            errdetail("XML does not support infinite date values.")));
                }
                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 time_stamp;
                struct pg_tm tm;
                fsec_t fsec;
                char buf[MAXDATELEN + 1];

                /* XSD doesn't support infinite values */
                time_stamp = DatumGetTimestamp(value);
                if (TIMESTAMP_NOT_FINITE(time_stamp)) {
                    ereport(ERROR,
                        (errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
                            errmsg("timestamp out of range"),
                            errdetail("XML does not support infinite timestamp values.")));
                } else if (timestamp2tm(time_stamp, NULL, &tm, &fsec, NULL, NULL) == 0) {
                    EncodeDateTime(&tm, fsec, false, 0, NULL, 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 time_stamp;
                struct pg_tm tm;
                int tz;
                fsec_t fsec;
                const char* tzn = NULL;
                char buf[MAXDATELEN + 1];

                /* XSD doesn't support infinite values */
                time_stamp = DatumGetTimestamp(value);
                if (TIMESTAMP_NOT_FINITE(time_stamp)) {
                    ereport(ERROR,
                        (errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
                            errmsg("timestamp out of range"),
                            errdetail("XML does not support infinite timestamp values.")));
                } else if (timestamp2tm(time_stamp, &tz, &tm, &fsec, &tzn, NULL) == 0) {
                    EncodeDateTime(&tm, fsec, true, 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* b_str = DatumGetByteaPP(value);
                PgXmlErrorContext* xml_errcxt = NULL;
                volatile xmlBufferPtr buf = NULL;
                volatile xmlTextWriterPtr writer = NULL;
                char* result = NULL;

                xml_errcxt = pg_xml_init(PG_XML_STRICTNESS_ALL);

                PG_TRY();
                {
                    buf = xmlBufferCreate();
                    if (buf == NULL || xml_errcxt->err_occurred) {
                        xml_ereport(xml_errcxt, ERROR, ERRCODE_OUT_OF_MEMORY, "could not allocate xmlBuffer");
                    }
                    writer = xmlNewTextWriterMemory(buf, 0);
                    if (writer == NULL || xml_errcxt->err_occurred) {
                        xml_ereport(xml_errcxt, ERROR, ERRCODE_OUT_OF_MEMORY, "could not allocate xmlTextWriter");
                    }
                    if (u_sess->attr.attr_common.xmlbinary == XMLBINARY_BASE64) {
                        xmlTextWriterWriteBase64(writer, VARDATA_ANY(b_str), 0, VARSIZE_ANY_EXHDR(b_str));
                    } else {
                        xmlTextWriterWriteBinHex(writer, VARDATA_ANY(b_str), 0, VARSIZE_ANY_EXHDR(b_str));
                    }

                    /* we MUST do this now to flush data out to the buffer */
                    xmlFreeTextWriter(writer);
                    writer = NULL;

                    result = pstrdup((const char*)xmlBufferContent(buf));
                }
                PG_CATCH();
                {
                    if (writer) {
                        xmlFreeTextWriter(writer);
                    }
                    if (buf) {
                        xmlBufferFree(buf);
                    }
                    pg_xml_done(xml_errcxt, true);

                    PG_RE_THROW();
                }
                PG_END_TRY();

                xmlBufferFree(buf);

                pg_xml_done(xml_errcxt, false);

                return result;
            }
#endif /* USE_LIBXML */
            default:
                break;
        }

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

        /* ... exactly as-is for XML, and when escaping is not wanted */
        if (type == XMLOID || !xml_escape_strings) {
            return str;
        }
        /* otherwise, translate special characters as needed */
        return escape_xml(str);
    }
}

/*
 * Escape characters in text that have special meanings in XML.
 *
 * Returns a palloc'd string.
 *
 * NB: this is intentionally not dependent on libxml.
 */
char* escape_xml(const char* str)
{
    StringInfoData buf;
    const char* p = NULL;
    int char_len = 0;

    initStringInfo(&buf);
    p = str;
    while (*p) {
        char_len = pg_mblen(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: {
                for (int i = 0; i < char_len; i++) {
                    appendStringInfoCharMacro(&buf, p[i]);
                }
                break;
            }
        }
        p += char_len;
    }
    return buf.data;
}

static char* _SPI_strdup(const char* s)
{
    size_t len = strlen(s) + 1;
    char* ret = (char*)SPI_palloc(len);
    if (ret != NULL) {
        MemCpy(ret, s, len);
    }
    return ret;
}

/*
 * SQL to XML mapping functions
 *
 * What follows below was at one point intentionally organized so that
 * you can read along in the SQL/XML standard. The functions are
 * mostly split up the way the clauses lay out in the standards
 * document, and the identifiers are also aligned with the standard
 * text.  Unfortunately, SQL/XML:2006 reordered the clauses
 * differently than SQL/XML:2003, so the order below doesn't make much
 * sense anymore.
 *
 * 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:2008 section
 * 4.10.8.
 *
 * 
 * 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)
{
    List* list = NIL;
    SPI_execute(query, true, 0);

    for (int i = 0; i < (int)SPI_processed; i++) {
        Datum oid;
        bool is_null = false;

        oid = SPI_getbinval(SPI_tuptable->vals[i], SPI_tuptable->tupdesc, 1, &is_null);
        if (!is_null) {
            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:2008
 * section 9.11.
 */
static StringInfo table_to_xml_internal(
    Oid relid, const char* xml_schema, bool nulls, bool table_forest, 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),
        xml_schema, nulls, table_forest, targetns, top_level);
}

Datum table_to_xml(PG_FUNCTION_ARGS)
{
    NO_XML_SUPPORT();

    Oid relid = PG_GETARG_OID(0);
    bool nulls = PG_GETARG_BOOL(1);
    bool table_forest = PG_GETARG_BOOL(2);
    const char* targetns = NULL;

    if (PG_ARGISNULL(3)) {
        targetns = DEF_TARGETNS;
    } else {
        targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
    }
    PG_RETURN_XML_P(stringinfo_to_xmltype(table_to_xml_internal(relid, NULL, nulls, table_forest, targetns, true)));
}

Datum query_to_xml(PG_FUNCTION_ARGS)
{
    /*
     * If you want to remove the macro, please fix the issue caused by
     * NULL input of first param. Check input of text_to_cstring? or
     * modify the code below? or set proisstrict in pg_proc?
     */
    NO_XML_SUPPORT();

    char* query = text_to_cstring(PG_GETARG_TEXT_PP(0));
    bool nulls = PG_GETARG_BOOL(1);
    bool table_forest = PG_GETARG_BOOL(2);
    const char* targetns = NULL;

    if (PG_ARGISNULL(3)) {
        targetns = DEF_TARGETNS;
    } else {
        targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
    }
    PG_RETURN_XML_P(
        stringinfo_to_xmltype(query_to_xml_internal(query, NULL, NULL, nulls, table_forest, targetns, true)));
}

Datum cursor_to_xml(PG_FUNCTION_ARGS)
{
    /*
     * If you want to remove the macro, please fix the issue caused by
     * NULL input of first param. Check input of text_to_cstring? or
     * modify the code below? or set proisstrict in pg_proc?
     */
    NO_XML_SUPPORT();

    char* name = text_to_cstring(PG_GETARG_TEXT_PP(0));
    int32 count = PG_GETARG_INT32(1);
    bool nulls = PG_GETARG_BOOL(2);
    bool table_forest = PG_GETARG_BOOL(3);
    const char* targetns = NULL;

    StringInfoData result;
    Portal portal;
    int i;
    int rc = 0;

    if (PG_ARGISNULL(4)) {
        targetns = DEF_TARGETNS;
    } else {
        targetns = text_to_cstring(PG_GETARG_TEXT_PP(4));
    }
    initStringInfo(&result);

    /*
     * Connect to SPI manager
     */
    if ((rc = SPI_connect()) != SPI_OK_CONNECT) {
        ereport(ERROR,
            (errmodule(MOD_OPT),
                (errcode(ERRCODE_SPI_CONNECTION_FAILURE),
                    errmsg("SPI_connect failed: %s", SPI_result_code_string(rc)))));
    }
    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 < (int)SPI_processed; i++) {
        SPI_sql_row_to_xmlelement(i, &result, NULL, nulls, table_forest, 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* elt_name, const char* xml_schema, const char* targetns, bool top_level)
{
    /* This isn't really wrong but currently makes no sense. */
    Assert(top_level || !xml_schema);

    appendStringInfo(result, "<%s", elt_name);
    if (top_level) {
        appendStringInfoString(result, " xmlns:xsi=\"" NAMESPACE_XSI "\"");
        if (strlen(targetns) > 0) {
            appendStringInfo(result, " xmlns=\"%s\"", targetns);
        }
    }
    if (xml_schema != NULL) {
        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* elt_name)
{
    appendStringInfo(result, "</%s>\n", elt_name);
}

static StringInfo query_to_xml_internal(const char* query, char* table_name, const char* xml_schema,
    bool nulls, bool table_forest, const char* targetns, bool top_level)
{
    StringInfo result;
    char* xmltn = NULL;
    int rc = 0;

    if (table_name != NULL) {
        xmltn = map_sql_identifier_to_xml_name(table_name, true, false);
    } else {
        xmltn = "table";
    }
    result = makeStringInfo();

    /*
     * Connect to SPI manager
     */
    if ((rc = SPI_connect()) != SPI_OK_CONNECT) {
        ereport(ERROR,
            (errmodule(MOD_OPT),
                (errcode(ERRCODE_SPI_CONNECTION_FAILURE),
                    errmsg("SPI_connect failed: %s", SPI_result_code_string(rc)))));
    }
    if (SPI_execute(query, true, 0) != SPI_OK_SELECT) {
        ereport(ERROR, (errcode(ERRCODE_DATA_EXCEPTION), errmsg("invalid query")));
    }
    if (!table_forest) {
        xmldata_root_element_start(result, xmltn, xml_schema, targetns, top_level);
    }
    if (xml_schema != NULL) {
        appendStringInfo(result, "%s\n\n", xml_schema);
    }
    for (int i = 0; i < (int)SPI_processed; i++) {
        SPI_sql_row_to_xmlelement(i, result, table_name, nulls, table_forest, targetns, top_level);
    }
    if (!table_forest) {
        xmldata_root_element_end(result, xmltn);
    }
    SPI_finish();

    return result;
}

Datum table_to_xmlschema(PG_FUNCTION_ARGS)
{
    NO_XML_SUPPORT();

    Oid relid = PG_GETARG_OID(0);
    bool nulls = PG_GETARG_BOOL(1);
    bool table_forest = PG_GETARG_BOOL(2);
    const char* targetns = NULL;
    const char* result = NULL;
    Relation rel;

    if (PG_ARGISNULL(3)) {
        targetns = DEF_TARGETNS;
    } else {
        targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
    }
    rel = heap_open(relid, AccessShareLock);
    result = map_sql_table_to_xmlschema(rel->rd_att, relid, nulls, table_forest, targetns);
    heap_close(rel, NoLock);

    PG_RETURN_XML_P(cstring_to_xmltype(result));
}

Datum query_to_xmlschema(PG_FUNCTION_ARGS)
{
    /*
     * If you want to remove the macro, please fix the issue caused by
     * NULL input of first param. Check input of text_to_cstring? or
     * modify the code below? or set proisstrict in pg_proc?
     */
    NO_XML_SUPPORT();

    char* query = text_to_cstring(PG_GETARG_TEXT_PP(0));
    bool nulls = PG_GETARG_BOOL(1);
    bool table_forest = PG_GETARG_BOOL(2);
    const char* targetns = NULL;
    const char* result = NULL;
    SPIPlanPtr plan;
    Portal portal;
    int rc = 0;

    if (PG_ARGISNULL(3)) {
        targetns = DEF_TARGETNS;
    } else {
        targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
    }

    /*
     * Connect to SPI manager
     */
    if ((rc = SPI_connect()) != SPI_OK_CONNECT) {
        ereport(ERROR,
            (errmodule(MOD_OPT),
                (errcode(ERRCODE_SPI_CONNECTION_FAILURE),
                    errmsg("SPI_connect failed: %s", SPI_result_code_string(rc)))));
    }
    if ((plan = SPI_prepare(query, 0, NULL)) == NULL) {
        ereport(ERROR, (errmodule(MOD_OPT),
            (errcode(ERRCODE_SPI_PREPARE_FAILURE), errmsg("SPI_prepare(\"%s\") failed", query))));
    }
    if ((portal = SPI_cursor_open(NULL, plan, NULL, NULL, true)) == NULL) {
        ereport(ERROR,
            (errmodule(MOD_OPT),
                (errcode(ERRCODE_SPI_CURSOR_OPEN_FAILURE), errmsg("SPI_cursor_open(\"%s\") failed", query))));
    }
    result = _SPI_strdup(map_sql_table_to_xmlschema(portal->tupDesc, InvalidOid, nulls, table_forest, targetns));
    SPI_cursor_close(portal);
    SPI_finish();

    PG_RETURN_XML_P(cstring_to_xmltype(result));
}

Datum cursor_to_xmlschema(PG_FUNCTION_ARGS)
{
    /*
     * If you want to remove the macro, please fix the issue caused by
     * NULL input of first param. Check input of text_to_cstring? or
     * modify the code below? or set proisstrict in pg_proc?
     */
    NO_XML_SUPPORT();

    char* name = text_to_cstring(PG_GETARG_TEXT_PP(0));
    bool nulls = PG_GETARG_BOOL(1);
    bool table_forest = PG_GETARG_BOOL(2);
    const char* targetns = NULL;
    const char* xml_schema = NULL;
    Portal portal;
    int rc = 0;

    if (PG_ARGISNULL(3)) {
        targetns = DEF_TARGETNS;
    } else {
        targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
    }
    /*
     * Connect to SPI manager
     */
    if ((rc = SPI_connect()) != SPI_OK_CONNECT) {
        ereport(ERROR,
            (errmodule(MOD_OPT),
                (errcode(ERRCODE_SPI_CONNECTION_FAILURE),
                    errmsg("SPI_connect failed: %s", SPI_result_code_string(rc)))));
    }
    portal = SPI_cursor_find(name);
    if (portal == NULL) {
        ereport(ERROR, (errcode(ERRCODE_UNDEFINED_CURSOR), errmsg("cursor \"%s\" does not exist", name)));
    }
    xml_schema = _SPI_strdup(map_sql_table_to_xmlschema(portal->tupDesc, InvalidOid, nulls, table_forest, targetns));
    SPI_finish();

    PG_RETURN_XML_P(cstring_to_xmltype(xml_schema));
}

Datum table_to_xml_and_xmlschema(PG_FUNCTION_ARGS)
{
    NO_XML_SUPPORT();

    Oid relid = PG_GETARG_OID(0);
    bool nulls = PG_GETARG_BOOL(1);
    bool table_forest = PG_GETARG_BOOL(2);
    const char* targetns = NULL;
    Relation rel;
    const char* xml_schema = NULL;

    if (PG_ARGISNULL(3)) {
        targetns = DEF_TARGETNS;
    } else {
        targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
    }
    rel = heap_open(relid, AccessShareLock);
    xml_schema = map_sql_table_to_xmlschema(rel->rd_att, relid, nulls, table_forest, targetns);
    heap_close(rel, NoLock);

    PG_RETURN_XML_P(stringinfo_to_xmltype(table_to_xml_internal(relid,
        xml_schema, nulls, table_forest, targetns, true)));
}

Datum query_to_xml_and_xmlschema(PG_FUNCTION_ARGS)
{
    /*
     * If you want to remove the macro, please fix the issue caused by
     * NULL input of first param. Check input of text_to_cstring? or
     * modify the code below? or set proisstrict in pg_proc?
     */
    NO_XML_SUPPORT();

    char* query = text_to_cstring(PG_GETARG_TEXT_PP(0));
    bool nulls = PG_GETARG_BOOL(1);
    bool table_forest = PG_GETARG_BOOL(2);
    const char* targetns = NULL;

    const char* xml_schema = NULL;
    SPIPlanPtr plan;
    Portal portal;
    int rc = 0;

    if (PG_ARGISNULL(3)) {
        targetns = DEF_TARGETNS;
    } else {
        targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
    }
    /*
     * Connect to SPI manager
     */
    if ((rc = SPI_connect()) != SPI_OK_CONNECT) {
        ereport(ERROR,
            (errmodule(MOD_OPT),
                (errcode(ERRCODE_SPI_CONNECTION_FAILURE),
                    errmsg("SPI_connect failed: %s", SPI_result_code_string(rc)))));
    }
    if ((plan = SPI_prepare(query, 0, NULL)) == NULL) {
        ereport(ERROR,
            (errmodule(MOD_OPT), (errcode(ERRCODE_SPI_PREPARE_FAILURE),
                errmsg("SPI_prepare(\"%s\") failed", query))));
    }
    if ((portal = SPI_cursor_open(NULL, plan, NULL, NULL, true)) == NULL) {
        ereport(ERROR,
            (errmodule(MOD_OPT),
                (errcode(ERRCODE_SPI_CURSOR_OPEN_FAILURE), errmsg("SPI_cursor_open(\"%s\") failed", query))));
    }
    xml_schema = _SPI_strdup(map_sql_table_to_xmlschema(portal->tupDesc, InvalidOid, nulls, table_forest, targetns));
    SPI_cursor_close(portal);
    SPI_finish();

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

/*
 * Map SQL schema to XML and/or XML Schema document; see SQL/XML:2008
 * sections 9.13, 9.14.
 */
static StringInfo schema_to_xml_internal(Oid nspid, const char* xml_schema,
    bool nulls, bool table_forest, const char* targetns, bool top_level)
{
    StringInfo result;
    char* xmlsn = NULL;
    List* relid_list = NIL;
    ListCell* cell = NULL;
    int rc = 0;

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

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

    if (xml_schema != NULL) {
        appendStringInfo(result, "%s\n\n", xml_schema);
    }

    /*
     * Connect to SPI manager
     */
    if ((rc = SPI_connect()) != SPI_OK_CONNECT) {
        ereport(ERROR,
            (errmodule(MOD_OPT),
                (errcode(ERRCODE_SPI_CONNECTION_FAILURE),
                    errmsg("SPI_connect failed: %s", SPI_result_code_string(rc)))));
    }
    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, table_forest, 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)
{
    /*
     * If you want to remove the macro, please fix the issue caused by
     * NULL input of first param. Check input of text_to_cstring? or
     * modify the code below? or set proisstrict in pg_proc?
     */
    NO_XML_SUPPORT();

    Name name = PG_GETARG_NAME(0);
    bool nulls = PG_GETARG_BOOL(1);
    bool table_forest = PG_GETARG_BOOL(2);
    const char* targetns = NULL;

    char* schema_name = NULL;
    Oid nspid;

    if (PG_ARGISNULL(3)) {
        targetns = DEF_TARGETNS;
    } else {
        targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
    }
    schema_name = NameStr(*name);
    nspid = LookupExplicitNamespace(schema_name);

    PG_RETURN_XML_P(stringinfo_to_xmltype(schema_to_xml_internal(nspid, NULL, nulls, table_forest, 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* schema_name, bool nulls, bool table_forest, const char* targetns)
{
    Oid nspid;
    List* relid_list = NIL;
    List* tupdesc_list = NIL;
    ListCell* cell = NULL;
    StringInfo result;
    int rc = 0;

    result = makeStringInfo();

    nspid = LookupExplicitNamespace(schema_name);

    xsd_schema_element_start(result, targetns);

    /*
     * Connect to SPI manager
     */
    if ((rc = SPI_connect()) != SPI_OK_CONNECT) {
        ereport(ERROR,
            (errmodule(MOD_OPT),
                (errcode(ERRCODE_SPI_CONNECTION_FAILURE),
                    errmsg("SPI_connect failed: %s", SPI_result_code_string(rc)))));
    }
    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, table_forest, targetns));

    xsd_schema_element_end(result);

    SPI_finish();

    return result;
}

Datum schema_to_xmlschema(PG_FUNCTION_ARGS)
{
    /*
     * If you want to remove the macro, please fix the issue caused by
     * NULL input of first param. Check input of text_to_cstring? or
     * modify the code below? or set proisstrict in pg_proc?
     */
    NO_XML_SUPPORT();

    Name name = PG_GETARG_NAME(0);
    bool nulls = PG_GETARG_BOOL(1);
    bool table_forest = PG_GETARG_BOOL(2);
    const char* targetns = NULL;

    if (PG_ARGISNULL(3)) {
        targetns = DEF_TARGETNS;
    } else {
        targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
    }
    PG_RETURN_XML_P(stringinfo_to_xmltype(
        schema_to_xmlschema_internal(NameStr(*name), nulls, table_forest, targetns)));
}

Datum schema_to_xml_and_xmlschema(PG_FUNCTION_ARGS)
{
    /*
     * If you want to remove the macro, please fix the issue caused by
     * NULL input of first param. Check input of text_to_cstring? or
     * modify the code below? or set proisstrict in pg_proc?
     */
    NO_XML_SUPPORT();

    Name name = PG_GETARG_NAME(0);
    bool nulls = PG_GETARG_BOOL(1);
    bool table_forest = PG_GETARG_BOOL(2);
    const char* targetns = NULL;
    char* schema_name = NULL;
    Oid nspid;
    StringInfo xml_schema;

    if (PG_ARGISNULL(3)) {
        targetns = DEF_TARGETNS;
    } else {
        targetns = text_to_cstring(PG_GETARG_TEXT_PP(3));
    }
    schema_name = NameStr(*name);
    nspid = LookupExplicitNamespace(schema_name);

    xml_schema = schema_to_xmlschema_internal(schema_name, nulls, table_forest, targetns);

    PG_RETURN_XML_P(stringinfo_to_xmltype(
        schema_to_xml_internal(nspid, xml_schema->data, nulls, table_forest, targetns, true)));
}

/*
 * Map SQL database to XML and/or XML Schema document; see SQL/XML:2008
 * sections 9.16, 9.17.
 */
static StringInfo database_to_xml_internal(const char* xml_schema,
    bool nulls, bool table_forest, const char* targetns)
{
    StringInfo result;
    List* nspid_list = NIL;
    ListCell* cell = NULL;
    char* xmlcn = NULL;
    int rc = 0;
    char* dbname;
    
    dbname = get_database_name(u_sess->proc_cxt.MyDatabaseId);
    if (dbname == NULL) {
        ereport(ERROR, (errcode(ERRCODE_UNDEFINED_DATABASE),
                    errmsg("database with OID %u does not exist",
                        u_sess->proc_cxt.MyDatabaseId)));
    }

    xmlcn = map_sql_identifier_to_xml_name(dbname, true, false);
    result = makeStringInfo();

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

    if (xml_schema != NULL) {
        appendStringInfo(result, "%s\n\n", xml_schema);
    }

    /*
     * Connect to SPI manager
     */
    if ((rc = SPI_connect()) != SPI_OK_CONNECT) {
        ereport(ERROR,
            (errmodule(MOD_OPT),
                (errcode(ERRCODE_SPI_CONNECTION_FAILURE),
                    errmsg("SPI_connect failed: %s", SPI_result_code_string(rc)))));
    }
    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, table_forest, 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)
{
    NO_XML_SUPPORT();

    bool nulls = PG_GETARG_BOOL(0);
    bool table_forest = 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, table_forest, targetns)));
}

static StringInfo database_to_xmlschema_internal(const char* targetns)
{
    List* relid_list = NIL;
    List* nspid_list = NIL;
    List* tupdesc_list = NIL;
    ListCell* cell = NULL;
    StringInfo result;
    int rc = 0;

    result = makeStringInfo();

    xsd_schema_element_start(result, targetns);

    /*
     * Connect to SPI manager
     */
    if ((rc = SPI_connect()) != SPI_OK_CONNECT) {
        ereport(ERROR,
            (errmodule(MOD_OPT),
                (errcode(ERRCODE_SPI_CONNECTION_FAILURE),
                    errmsg("SPI_connect failed: %s", SPI_result_code_string(rc)))));
    }
    relid_list = database_get_xml_visible_tables();
    nspid_list = database_get_xml_visible_schemas();

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

    xsd_schema_element_end(result);

    SPI_finish();

    return result;
}

Datum database_to_xmlschema(PG_FUNCTION_ARGS)
{
    NO_XML_SUPPORT();

    /* the first arg is BOOL, means nulls; the second arg is BOOL, means table_forest */
    const char* targetns = text_to_cstring(PG_GETARG_TEXT_PP(2));
    PG_RETURN_XML_P(stringinfo_to_xmltype(database_to_xmlschema_internal(targetns)));
}

Datum database_to_xml_and_xmlschema(PG_FUNCTION_ARGS)
{
    NO_XML_SUPPORT();

    bool nulls = PG_GETARG_BOOL(0);
    bool table_forest = PG_GETARG_BOOL(1);
    const char* targetns = text_to_cstring(PG_GETARG_TEXT_PP(2));
    StringInfo xml_schema = database_to_xmlschema_internal(targetns);

    PG_RETURN_XML_P(stringinfo_to_xmltype(
        database_to_xml_internal(xml_schema->data, nulls, table_forest, targetns)));
}

/*
 * Map a multi-part SQL name to an XML name; see SQL/XML:2008 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 != NULL) {
        appendStringInfo(&result, "%s", map_sql_identifier_to_xml_name(a, true, true));
    }
    if (b != NULL) {
        appendStringInfo(&result, ".%s", map_sql_identifier_to_xml_name(b, true, true));
    }
    if (c != NULL) {
        appendStringInfo(&result, ".%s", map_sql_identifier_to_xml_name(c, true, true));
    }
    if (d != NULL) {
        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:2008
 * section 9.11.
 *
 * Map an SQL table to XML Schema data types; see SQL/XML:2008 section
 * 9.9.
 */
static const char* map_sql_table_to_xmlschema(
    TupleDesc tupdesc, Oid relid, bool nulls, bool tableforest, const char* targetns)
{
    char* xmltn = NULL;
    char* table_type_name = NULL;
    char* row_type_name = NULL;
    char* dbname = NULL;

    StringInfoData result;
    initStringInfo(&result);

    if (OidIsValid(relid)) {
        Form_pg_class rel_tuple;

        HeapTuple tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
        if (!HeapTupleIsValid(tuple)) {
            ereport(ERROR,
                (errmodule(MOD_OPT),
                    (errcode(ERRCODE_CACHE_LOOKUP_FAILED), errmsg("cache lookup failed for relation %u", relid))));
        }

        rel_tuple = (Form_pg_class)GETSTRUCT(tuple);
        xmltn = map_sql_identifier_to_xml_name(NameStr(rel_tuple->relname), true, false);

        dbname = get_database_name(u_sess->proc_cxt.MyDatabaseId);
        if (dbname == NULL) {
            ereport(ERROR, (errcode(ERRCODE_UNDEFINED_DATABASE),
                        errmsg("database with OID %u does not exist",
                            u_sess->proc_cxt.MyDatabaseId)));
        }

        table_type_name = map_multipart_sql_identifier_to_xml_name("TableType",
            dbname,
            get_namespace_name(rel_tuple->relnamespace),
            NameStr(rel_tuple->relname));

        row_type_name = map_multipart_sql_identifier_to_xml_name("RowType",
            dbname,
            get_namespace_name(rel_tuple->relnamespace),
            NameStr(rel_tuple->relname));

        ReleaseSysCache(tuple);
    } else {
        if (tableforest) {
            xmltn = "row";
        } else {
            xmltn = "table";
        }
        table_type_name = "TableType";
        row_type_name = "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",
        row_type_name);

    for (int i = 0; i < tupdesc->natts; i++) {
        if (tupdesc->attrs[i]->attisdropped) {
            continue;
        }
        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",
            table_type_name,
            row_type_name);

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

    return result.data;
}

/*
 * Map an SQL schema to XML Schema data types; see SQL/XML:2008
 * section 9.12.
 */
static const char* map_sql_schema_to_xmlschema_types(
    Oid nspid, List* relid_list, bool nulls, bool table_forest, const char* targetns)
{
    char* dbname = NULL;
    char* nspname = NULL;
    char* xmlsn = NULL;
    char* schema_type_name = NULL;
    StringInfoData result;
    ListCell* cell = NULL;

    dbname = get_database_name(u_sess->proc_cxt.MyDatabaseId);
    if (dbname == NULL) {
        ereport(ERROR, (errcode(ERRCODE_UNDEFINED_DATABASE),
                    errmsg("database with OID %u does not exist",
                        u_sess->proc_cxt.MyDatabaseId)));
    }

    nspname = get_namespace_name(nspid, true);

    initStringInfo(&result);

    xmlsn = map_sql_identifier_to_xml_name(nspname, true, false);

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

    appendStringInfo(&result, "<xsd:complexType name=\"%s\">\n", schema_type_name);
    if (!table_forest) {
        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* table_type_name = map_multipart_sql_identifier_to_xml_name(
            (char*)(table_forest ? "RowType" : "TableType"), dbname, nspname, relname);

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

    if (!table_forest) {
        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, schema_type_name);

    return result.data;
}

/*
 * Map an SQL catalog to XML Schema data types; see SQL/XML:2008
 * section 9.15.
 */
static const char* map_sql_catalog_to_xmlschema_types(List* nspid_list)
{
    char* dbname = NULL;
    char* xmlcn = NULL;
    char* catalog_type_name = NULL;
    StringInfoData result;
    ListCell* cell = NULL;

    dbname = get_database_name(u_sess->proc_cxt.MyDatabaseId);
    if (dbname == NULL) {
        ereport(ERROR, (errcode(ERRCODE_UNDEFINED_DATABASE),
                    errmsg("database with OID %u does not exist",
                        u_sess->proc_cxt.MyDatabaseId)));
    }

    initStringInfo(&result);

    xmlcn = map_sql_identifier_to_xml_name(dbname, true, false);

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

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

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

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

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

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

    return result.data;
}

/*
 * Map an SQL data type to an XML name; see SQL/XML:2008 section 9.4.
 */
static const char* map_sql_type_to_xml_name(Oid type_oid, int type_mod)
{
    StringInfoData result;
    char* dbname = NULL;
    initStringInfo(&result);

    switch (type_oid) {
        case BPCHAROID:
            if (type_mod == -1) {
                appendStringInfo(&result, "CHAR");
            } else {
                appendStringInfo(&result, "CHAR_%d", type_mod - VARHDRSZ);
            }
            break;
        case VARCHAROID:
            if (type_mod == -1) {
                appendStringInfo(&result, "VARCHAR");
            } else {
                appendStringInfo(&result, "VARCHAR_%d", type_mod - VARHDRSZ);
            }
            break;
        case NUMERICOID:
            if (type_mod == -1) {
                appendStringInfo(&result, "NUMERIC");
            } else {
                appendStringInfo(&result,
                    "NUMERIC_%d_%d",
                    ((unsigned int)(type_mod - VARHDRSZ) >> 16) & 0xffff,
                    (unsigned int)(type_mod - VARHDRSZ) & 0xffff);
            }
            break;
        case INT4OID:
            appendStringInfo(&result, "INTEGER");
            break;
        case INT2OID:
            appendStringInfo(&result, "SMALLINT");
            break;
        case INT1OID:
            appendStringInfo(&result, "TINYINT");
            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 (type_mod == -1) {
                appendStringInfo(&result, "TIME");
            } else {
                appendStringInfo(&result, "TIME_%d", type_mod);
            }
            break;
        case TIMETZOID:
            if (type_mod == -1) {
                appendStringInfo(&result, "TIME_WTZ");
            } else {
                appendStringInfo(&result, "TIME_WTZ_%d", type_mod);
            }
            break;
        case TIMESTAMPOID:
            if (type_mod == -1) {
                appendStringInfo(&result, "TIMESTAMP");
            } else {
                appendStringInfo(&result, "TIMESTAMP_%d", type_mod);
            }
            break;
        case TIMESTAMPTZOID:
            if (type_mod == -1) {
                appendStringInfo(&result, "TIMESTAMP_WTZ");
            } else {
                appendStringInfo(&result, "TIMESTAMP_WTZ_%d", type_mod);
            }
            break;
        case SMALLDATETIMEOID:
            appendStringInfo(&result, "SMALLDATETIME");
            break;
        case DATEOID:
            appendStringInfo(&result, "DATE");
            break;
        case XMLOID:
            appendStringInfo(&result, "XML");
            break;
        default: {
            HeapTuple tuple;
            Form_pg_type type_tuple;

            tuple = SearchSysCache1(TYPEOID, ObjectIdGetDatum(type_oid));
            if (!HeapTupleIsValid(tuple)) {
                ereport(ERROR,
                    (errmodule(MOD_OPT),
                        (errcode(ERRCODE_CACHE_LOOKUP_FAILED), errmsg("cache lookup failed for type %u", type_oid))));
            }

            type_tuple = (Form_pg_type)GETSTRUCT(tuple);

            dbname = get_database_name(u_sess->proc_cxt.MyDatabaseId);
            if (dbname == NULL) {
                ereport(ERROR, (errcode(ERRCODE_UNDEFINED_DATABASE),
                            errmsg("database with OID %u does not exist",
                                u_sess->proc_cxt.MyDatabaseId)));
            }

            appendStringInfoString(&result,
                map_multipart_sql_identifier_to_xml_name(
                    (char*)((type_tuple->typtype == TYPTYPE_DOMAIN) ? "Domain" : "UDT"),
                    dbname,
                    get_namespace_name(type_tuple->typnamespace, true),
                    NameStr(type_tuple->typname)));

            ReleaseSysCache(tuple);
        } break;
    }

    return result.data;
}

/*
 * Map a collection of SQL data types to XML Schema data types; see
 * SQL/XML:2008 section 9.7.
 */
static const char* map_sql_typecoll_to_xmlschema_types(List* tupdesc_list)
{
    List* unique_types = NIL;
    StringInfoData result;
    ListCell* cell0 = NULL;

    /* extract all column types used in the set of TupleDescs */
    foreach (cell0, tupdesc_list) {
        TupleDesc tupdesc = (TupleDesc)lfirst(cell0);
        for (int i = 0; i < tupdesc->natts; i++) {
            if (tupdesc->attrs[i]->attisdropped) {
                continue;
            }
            unique_types = list_append_unique_oid(unique_types, tupdesc->attrs[i]->atttypid);
        }
    }

    /* add base types of domains */
    foreach (cell0, unique_types) {
        Oid typid = lfirst_oid(cell0);
        Oid base_typid = getBaseType(typid);
        if (base_typid != typid) {
            unique_types = list_append_unique_oid(unique_types, base_typid);
        }
    }

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

    foreach (cell0, unique_types) {
        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:2008 sections 9.5 and 9.6.
 *
 * (The distinction between 9.5 and 9.6 is basically that 9.6 adds
 * a name attribute, which this function does.	The name-less version
 * 9.5 doesn't appear to be required anywhere.)
 */
static const char* map_sql_type_to_xmlschema_type(Oid type_oid, int type_mod)
{
    StringInfoData result;
    const char* type_name = map_sql_type_to_xml_name(type_oid, type_mod);

    initStringInfo(&result);

    if (type_oid == 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", type_name);

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

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

            case NUMERICOID:
                if (type_mod != -1) {
                    appendStringInfo(&result,
                        "  <xsd:restriction base=\"xsd:decimal\">\n"
                        "    <xsd:totalDigits value=\"%d\"/>\n"
                        "    <xsd:fractionDigits value=\"%d\"/>\n"
                        "  </xsd:restriction>\n",
                        ((unsigned int)(type_mod - VARHDRSZ) >> 16) & 0xffff,
                        (unsigned int)(type_mod - 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 = (type_oid == TIMETZOID ? "(+|-)\\p{Nd}{2}:\\p{Nd}{2}" : "");

                if (type_mod == -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 (type_mod == 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",
                        type_mod - VARHDRSZ,
                        tz);
                }
                break;
            }

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

                if (type_mod == -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 (type_mod == 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",
                        type_mod - 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(type_oid) == TYPTYPE_DOMAIN) {
                    int32 base_type_mod = -1;
                    Oid base_type_oid = getBaseTypeAndTypmod(type_oid, &base_type_mod);

                    appendStringInfo(&result,
                        "  <xsd:restriction base=\"%s\"/>\n",
                        map_sql_type_to_xml_name(base_type_oid, base_type_mod));
                }
                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:2008 section 9.10.
 */
static void SPI_sql_row_to_xmlelement(int row_num, StringInfo result,
    char* table_name, bool nulls, bool table_forest, const char* targetns, bool top_level)
{
    char* xmltn = NULL;
    if (table_name != NULL) {
        xmltn = map_sql_identifier_to_xml_name(table_name, true, false);
    } else {
        if (table_forest) {
            xmltn = "row";
        } else {
            xmltn = "table";
        }
    }

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

    for (int i = 1; i <= SPI_tuptable->tupdesc->natts; i++) {
        char* col_name = NULL;
        Datum col_val;
        bool is_null = false;

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

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

#ifdef USE_LIBXML

/*
 * Convert XML node to text (dump subtree in case of element,
 * return value otherwise)
 */
static text* xml_xmlnodetoxmltype(xmlNodePtr cur)
{
    xmltype* result = NULL;
    if (cur->type == XML_ELEMENT_NODE) {
        xmlBufferPtr buf = xmlBufferCreate();
        PG_TRY();
        {
            xmlNodeDump(buf, NULL, cur, 0, 1);
            result = xmlBuffer_to_xmltype(buf);
        }
        PG_CATCH();
        {
            xmlBufferFree(buf);
            PG_RE_THROW();
        }
        PG_END_TRY();
        xmlBufferFree(buf);
    } else {
        xmlChar* str = NULL;
        str = xmlXPathCastNodeToString(cur);
        PG_TRY();
        {
            /* Here we rely on XML having the same representation as TEXT */
            char* escaped = escape_xml((char*)str);

            result = (xmltype*)cstring_to_text(escaped);
            pfree_ext(escaped);
        }
        PG_CATCH();
        {
            xmlFree(str);
            PG_RE_THROW();
        }
        PG_END_TRY();
        xmlFree(str);
    }

    return result;
}

/*
 * Convert an XML XPath object (the result of evaluating an XPath expression)
 * to an array of xml values, which is returned at *astate.  The function
 * result value is the number of elements in the array.
 *
 * If "astate" is NULL then we don't generate the array value, but we still
 * return the number of elements it would have had.
 *
 * Nodesets are converted to an array containing the nodes' textual
 * representations.  Primitive values (float, double, string) are converted
 * to a single-element array containing the value's string representation.
 */
static int xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpath_obj, ArrayBuildState** astate)
{
    int result = 0;
    Datum datum;
    Oid datum_type;
    char* result_str = NULL;

    if (astate != NULL) {
        *astate = NULL;
    }

    switch (xpath_obj->type) {
        case XPATH_NODESET:
            if (xpath_obj->nodesetval != NULL) {
                result = xpath_obj->nodesetval->nodeNr;
                if (astate != NULL) {
                    for (int i = 0; i < result; i++) {
                        datum = PointerGetDatum(xml_xmlnodetoxmltype(xpath_obj->nodesetval->nodeTab[i]));
                        *astate = accumArrayResult(*astate, datum, false, XMLOID, CurrentMemoryContext);
                    }
                }
            }
            return result;

        case XPATH_BOOLEAN:
            if (astate == NULL) {
                return 1;
            }
            datum = BoolGetDatum(xpath_obj->boolval);
            datum_type = BOOLOID;
            break;

        case XPATH_NUMBER:
            if (astate == NULL) {
                return 1;
            }
            datum = Float8GetDatum(xpath_obj->floatval);
            datum_type = FLOAT8OID;
            break;

        case XPATH_STRING:
            if (astate == NULL) {
                return 1;
            }
            datum = CStringGetDatum((char*)xpath_obj->stringval);
            datum_type = CSTRINGOID;
            break;

        default:
            ereport(ERROR,
                (errmodule(MOD_OPT),
                    (errcode(ERRCODE_CHECK_VIOLATION),
                        errmsg("xpath expression result type %d is unsupported", xpath_obj->type))));

            return 0; /* keep compiler quiet */
    }

    /* Common code for scalar-value cases */
    result_str = map_sql_value_to_xml_value(datum, datum_type, true);
    datum = PointerGetDatum(cstring_to_xmltype(result_str));
    *astate = accumArrayResult(*astate, datum, false, XMLOID, CurrentMemoryContext);
    return 1;
}

/*
 * Common code for xpath() and xmlexists()
 *
 * Evaluate XPath expression and return number of nodes in res_items
 * and array of XML values in astate.  Either of those pointers can be
 * NULL if the corresponding result isn't wanted.
 *
 * It is up to the user to ensure that the XML passed is in fact
 * an XML document - XPath doesn't work easily on fragments without
 * a context node being known.
 */
static void xpath_internal(
    text* xpath_expr_text, xmltype* data, ArrayType* namespaces, int* res_nitems, ArrayBuildState** astate)
{
    PgXmlErrorContext* xml_errcxt = NULL;
    volatile xmlParserCtxtPtr ctxt = NULL;
    volatile xmlDocPtr doc = NULL;
    volatile xmlXPathContextPtr xpath_ctx = NULL;
    volatile xmlXPathCompExprPtr xpath_comp = NULL;
    volatile xmlXPathObjectPtr xpath_obj = NULL;
    char* data_str = NULL;
    int32 len;
    int32 xpath_len;
    xmlChar* string = NULL;
    xmlChar* xpath_expr = NULL;
    int i;
    int ndim;
    Datum* ns_names_uris = NULL;
    bool* ns_names_uris_nulls = NULL;
    int ns_count;
    errno_t rc = 0;
    /*
     * 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 = namespaces ? ARR_NDIM(namespaces) : 0;
    if (ndim != 0) {
        int* 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;
    }

    data_str = 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")));
    }

    string = (xmlChar*)palloc((len + 1) * sizeof(xmlChar));
    rc = memcpy_s(string, (len + 1) * sizeof(xmlChar), data_str, len);
    securec_check(rc, "\0", "\0");

    string[len] = '\0';

    xpath_expr = (xmlChar*)palloc((xpath_len + 1) * sizeof(xmlChar));
    rc = memcpy_s(xpath_expr, (xpath_len + 1) * sizeof(xmlChar), VARDATA(xpath_expr_text), xpath_len);
    securec_check(rc, "\0", "\0");
    xpath_expr[xpath_len] = '\0';

    xml_errcxt = pg_xml_init(PG_XML_STRICTNESS_ALL);

    PG_TRY();
    {
        xmlInitParser();

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

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

                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(xpath_ctx, (xmlChar*)ns_name, (xmlChar*)ns_uri) != 0) {
                    ereport(ERROR, /* is this an internal error??? */
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                            errmsg(
                                "could not register XML namespace with name \"%s\" and URI \"%s\"", ns_name, ns_uri)));
                }
            }
        }

        xpath_comp = xmlXPathCompile(xpath_expr);
        if (xpath_comp == NULL || xml_errcxt->err_occurred) {
            xml_ereport(xml_errcxt, ERROR, ERRCODE_UNDEFINED_FILE, "invalid XPath expression");
        }

        /*
         * Version 2.6.27 introduces a function named
         * xmlXPathCompiledEvalToBoolean, which would be enough for xmlexists,
         * but we can derive the existence by whether any nodes are returned,
         * thereby preventing a library version upgrade and keeping the code
         * the same.
         */
        xpath_obj = xmlXPathCompiledEval(xpath_comp, xpath_ctx);
        if (xpath_obj == NULL || xml_errcxt->err_occurred) {
            xml_ereport(xml_errcxt, ERROR, ERRCODE_UNEXPECTED_NULL_VALUE, "could not create XPath object");
        }

        /*
         * Extract the results as requested.
         */
        if (res_nitems != NULL) {
            *res_nitems = xml_xpathobjtoxmlarray(xpath_obj, astate);
        } else {
            (void)xml_xpathobjtoxmlarray(xpath_obj, astate);
        }
    }
    PG_CATCH();
    {
        if (xpath_obj) {
            xmlXPathFreeObject(xpath_obj);
        }
        if (xpath_comp) {
            xmlXPathFreeCompExpr(xpath_comp);
        }
        if (xpath_ctx) {
            xmlXPathFreeContext(xpath_ctx);
        }
        if (doc) {
            xmlFreeDoc(doc);
        }
        if (ctxt) {
            xmlFreeParserCtxt(ctxt);
        }
        pg_xml_done(xml_errcxt, true);

        PG_RE_THROW();
    }
    PG_END_TRY();

    xmlXPathFreeObject(xpath_obj);
    xmlXPathFreeCompExpr(xpath_comp);
    xmlXPathFreeContext(xpath_ctx);
    xmlFreeDoc(doc);
    xmlFreeParserCtxt(ctxt);

    pg_xml_done(xml_errcxt, false);
}
#endif /* USE_LIBXML */

/*
 * 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).
 */
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);
    int res_nitems;
    ArrayBuildState* astate = NULL;

    xpath_internal(xpath_expr_text, data, namespaces, &res_nitems, &astate);

    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
}

/*
 * Determines if the node specified by the supplied XPath exists
 * in a given XML document, returning a boolean.
 */
Datum xmlexists(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
    text* xpath_expr_text = PG_GETARG_TEXT_P(0);
    xmltype* data = PG_GETARG_XML_P(1);
    int res_nitems;

    xpath_internal(xpath_expr_text, data, NULL, &res_nitems, NULL);

    PG_RETURN_BOOL(res_nitems > 0);
#else
    NO_XML_SUPPORT();
    return 0;
#endif
}

/*
 * Determines if the node specified by the supplied XPath exists
 * in a given XML document, returning a boolean. Differs from
 * xmlexists as it supports namespaces and is not defined in SQL/XML.
 */
Datum xpath_exists(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);
    int res_nitems;
    xpath_internal(xpath_expr_text, data, namespaces, &res_nitems, NULL);
    PG_RETURN_BOOL(res_nitems > 0);
#else
    NO_XML_SUPPORT();
    return 0;
#endif
}

#ifdef USE_LIBXML
/*
 * Functions for checking well-formed-ness
 */
static bool wellformed_xml(text* data, XmlOptionType xmloption_arg)
{
    bool result = false;
    volatile xmlDocPtr doc = NULL;

    /* We want to catch any exceptions and return false */
    PG_TRY();
    {
        doc = xml_parse(data, xmloption_arg, true, GetDatabaseEncoding());
        result = true;
    }
    PG_CATCH();
    {
        FlushErrorState();
        result = false;
    }
    PG_END_TRY();

    if (doc) {
        xmlFreeDoc(doc);
    }
    return result;
}
#endif

Datum xml_is_well_formed(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
    text* data = PG_GETARG_TEXT_P(0);
    PG_RETURN_BOOL(wellformed_xml(data, (XmlOptionType)xmloption));
#else
    NO_XML_SUPPORT();
    return 0;
#endif /* not USE_LIBXML */
}

Datum xml_is_well_formed_document(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
    text* data = PG_GETARG_TEXT_P(0);
    PG_RETURN_BOOL(wellformed_xml(data, XMLOPTION_DOCUMENT));
#else
    NO_XML_SUPPORT();
    return 0;
#endif /* not USE_LIBXML */
}

Datum xml_is_well_formed_content(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
    text* data = PG_GETARG_TEXT_P(0);
    PG_RETURN_BOOL(wellformed_xml(data, XMLOPTION_CONTENT));
#else
    NO_XML_SUPPORT();
    return 0;
#endif /* not USE_LIBXML */
}