xml.c

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/*-------------------------------------------------------------------------
 *
 * xml.c
 *    XML data type support.
 *
 *
 * Portions Copyright (c) 1996-2016, 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() 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.
 */
/* #define USE_LIBXMLCONTEXT */

#include "postgres.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 "access/htup_details.h"
#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/syscache.h"
#include "utils/xml.h"


/* GUC variables */
int         xmlbinary;
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 xmlPgEntityLoader(const char *URL, const char *ID,
                  xmlParserCtxtPtr ctxt);
static void xml_errorHandler(void *data, xmlErrorPtr error);
static void xml_ereport_by_code(int level, int sqlcode,
                    const char *msg, int errcode);
static void chopStringInfoNewlines(StringInfo str);
static void appendStringInfoLineSeparator(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(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, PgXmlErrorContext *xmlerrcxt);
static int xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
                       ArrayBuildState *astate,
                       PgXmlErrorContext *xmlerrcxt);
#endif   /* USE_LIBXML */

static StringInfo query_to_xml_internal(const char *query, char *tablename,
                      const char *xmlschema, bool nulls, bool tableforest,
                      const char *targetns, bool top_level);
static const char *map_sql_table_to_xmlschema(TupleDesc tupdesc, Oid relid,
                         bool nulls, bool tableforest, const char *targetns);
static const char *map_sql_schema_to_xmlschema_types(Oid nspid,
                                  List *relid_list, bool nulls,
                                  bool tableforest, const char *targetns);
static const char *map_sql_catalog_to_xmlschema_types(List *nspid_list,
                                   bool nulls, bool tableforest,
                                   const char *targetns);
static const char *map_sql_type_to_xml_name(Oid typeoid, int typmod);
static const char *map_sql_typecoll_to_xmlschema_types(List *tupdesc_list);
static const char *map_sql_type_to_xmlschema_type(Oid typeoid, int typmod);
static void SPI_sql_row_to_xmlelement(uint64 rownum, StringInfo result,
                          char *tablename, bool nulls, bool tableforest,
                          const char *targetns, bool top_level);

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


/* from SQL/XML: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
xmlChar_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    *vardata;
    xmlDocPtr   doc;

    vardata = (xmltype *) cstring_to_text(s);

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

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


#define PG_XML_DEFAULT_VERSION "1.0"


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

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

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

        initStringInfo(&buf);

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

        pfree(str);

        return buf.data;
    }

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


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

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


Datum
xml_recv(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
    StringInfo  buf = (StringInfo) PG_GETARG_POINTER(0);
    xmltype    *result;
    char       *str;
    char       *newstr;
    int         nbytes;
    xmlDocPtr   doc;
    xmlChar    *encodingStr = 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.
     */
    nbytes = buf->len - buf->cursor;
    str = (char *) pq_getmsgbytes(buf, nbytes);

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

    parse_xml_decl((const xmlChar *) str, NULL, NULL, &encodingStr, NULL);

    /*
     * 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 = encodingStr ? xmlChar_to_encoding(encodingStr) : 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, xmloption, true, encoding);
    xmlFreeDoc(doc);

    /* Now that we know what we're dealing with, convert to server encoding */
    newstr = pg_any_to_server(str, nbytes, encoding);

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

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


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

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

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


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


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


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


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


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

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

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

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



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

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

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

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

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

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

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

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

        initStringInfo(&buf2);

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

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

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


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


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

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


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

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


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

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


xmltype *
xmlelement(XmlExprState *xmlExpr, ExprContext *econtext)
{
#ifdef USE_LIBXML
    XmlExpr    *xexpr = (XmlExpr *) xmlExpr->xprstate.expr;
    xmltype    *result;
    List       *named_arg_strings;
    List       *arg_strings;
    int         i;
    ListCell   *arg;
    ListCell   *narg;
    PgXmlErrorContext *xmlerrcxt;
    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        isnull;
        char       *str;

        value = ExecEvalExpr(e, econtext, &isnull, NULL);
        if (isnull)
            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        isnull;
        char       *str;

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

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

    PG_TRY();
    {
        buf = xmlBufferCreate();
        if (buf == NULL || xmlerrcxt->err_occurred)
            xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
                        "could not allocate xmlBuffer");
        writer = xmlNewTextWriterMemory(buf, 0);
        if (writer == NULL || xmlerrcxt->err_occurred)
            xml_ereport(xmlerrcxt, 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       *argname = strVal(lfirst(narg));

            if (str)
                xmlTextWriterWriteAttribute(writer,
                                            (xmlChar *) argname,
                                            (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(xmlerrcxt, true);

        PG_RE_THROW();
    }
    PG_END_TRY();

    xmlBufferFree(buf);

    pg_xml_done(xmlerrcxt, 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;
    StringInfoData buf;

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

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

    initStringInfo(&buf);

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

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

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

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

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


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

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

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

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

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

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

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


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


bool
xml_is_document(xmltype *arg)
{
#ifdef USE_LIBXML
    bool        result;
    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  *errdata;
        MemoryContext ecxt;

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

    if (doc)
        xmlFreeDoc(doc);

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


#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.
 *
 * TODO: xmlChar is utf8-char, make proper tuning (initdb with enc!=utf8 and
 * check)
 */
void
pg_xml_init_library(void)
{
    static bool first_time = true;

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

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

#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;
    void       *new_errcxt;

    /* 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_errorHandler);

    /*
     * 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(xmlPgEntityLoader);

    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 isError)
{
    void       *cur_errcxt;

    /* 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 || isError);

    /*
     * 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_errorHandler or xml_ereport with it.
     */
    errcxt->magic = 0;

    /* Release memory */
    pfree(errcxt->err_buf.data);
    pfree(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 CHECK_XML_SPACE(p) \
    do { \
        if (!xmlIsBlank_ch(*(p))) \
            return XML_ERR_SPACE_REQUIRED; \
    } while (0)

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

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

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

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

    p = str;

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

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

    p += 5;

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

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

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

        if (version)
            *version = 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)
    {
        CHECK_XML_SPACE(save_p);
        p += 8;
        SKIP_XML_SPACE(p);
        if (*p != '=')
            return XML_ERR_MISSING_ENCODING;
        p += 1;
        SKIP_XML_SPACE(p);

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

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

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

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

finished:
    len = p - str;

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

    if (lenp)
        *lenp = len;

    return XML_ERR_OK;
}


/*
 * Write an XML declaration.  On output, we adjust the XML declaration
 * as follows.  (These rules are the moral equivalent of the clause
 * "Serialization of an XML value" in the SQL standard.)
 *
 * We try to avoid generating an XML declaration if possible.  This is
 * so that you don't get trivial things like xml '<foo/>' resulting in
 * '<?xml version="1.0"?><foo/>', which would surely be annoying.  We
 * must provide a declaration if the standalone property is specified
 * or if we include an encoding declaration.  If we have a
 * declaration, we must specify a version (XML requires this).
 * Otherwise we only make a declaration if the version is not "1.0",
 * which is the default version specified in SQL:2003.
 */
static bool
print_xml_decl(StringInfo buf, const xmlChar *version,
               pg_enc encoding, int standalone)
{
    if ((version && strcmp((const char *) version, PG_XML_DEFAULT_VERSION) != 0)
        || (encoding && encoding != PG_UTF8)
        || standalone != -1)
    {
        appendStringInfoString(buf, "<?xml");

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

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

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

        return true;
    }
    else
        return false;
}


/*
 * Convert a C string to XML internal representation
 *
 * Note: it is caller's responsibility to xmlFreeDoc() the result,
 * else a permanent memory leak will ensue!
 *
 * TODO maybe libxml2's xmlreader is better? (do not construct DOM,
 * yet do not use SAX - see xmlreader.c)
 */
static xmlDocPtr
xml_parse(text *data, XmlOptionType xmloption_arg, bool preserve_whitespace,
          int encoding)
{
    int32       len;
    xmlChar    *string;
    xmlChar    *utf8string;
    PgXmlErrorContext *xmlerrcxt;
    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 */
    xmlerrcxt = 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 || xmlerrcxt->err_occurred)
            xml_ereport(xmlerrcxt, 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 || xmlerrcxt->err_occurred)
                xml_ereport(xmlerrcxt, ERROR, ERRCODE_INVALID_XML_DOCUMENT,
                            "invalid XML document");
        }
        else
        {
            int         res_code;
            size_t      count;
            xmlChar    *version;
            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;

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

        pg_xml_done(xmlerrcxt, true);

        PG_RE_THROW();
    }
    PG_END_TRY();

    xmlFreeParserCtxt(ctxt);

    pg_xml_done(xmlerrcxt, 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(TopMemoryContext,
                                              "LibxmlContext",
                                              ALLOCSET_DEFAULT_MINSIZE,
                                              ALLOCSET_DEFAULT_INITSIZE,
                                              ALLOCSET_DEFAULT_MAXSIZE);

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

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


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


static void
xml_pfree(void *ptr)
{
    /* At least some parts of libxml assume xmlFree(NULL) is allowed */
    if (ptr)
        pfree(ptr);
}


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


/*
 * xmlPgEntityLoader --- 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
xmlPgEntityLoader(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;

    /* Defend against someone passing us a bogus context struct */
    if (errcxt->magic != ERRCXT_MAGIC)
        elog(ERROR, "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_errorHandler(void *data, xmlErrorPtr error)
{
    PgXmlErrorContext *xmlerrcxt = (PgXmlErrorContext *) data;
    xmlParserCtxtPtr ctxt = (xmlParserCtxtPtr) error->ctxt;
    xmlParserInputPtr input = (ctxt != NULL) ? ctxt->input : NULL;
    xmlNodePtr  node = error->node;
    const xmlChar *name = (node != NULL &&
                         node->type == XML_ELEMENT_NODE) ? node->name : NULL;
    int         domain = error->domain;
    int         level = error->level;
    StringInfo  errorBuf;

    /*
     * 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 (xmlerrcxt->magic != ERRCXT_MAGIC)
        elog(FATAL, "xml_errorHandler 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;
    }

    /* 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 (xmlerrcxt->strictness == PG_XML_STRICTNESS_WELLFORMED)
                return;
            break;
    }

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

    if (error->line > 0)
        appendStringInfo(errorBuf, "line %d: ", error->line);
    if (name != NULL)
        appendStringInfo(errorBuf, "element %s: ", name);
    appendStringInfoString(errorBuf, error->message);

    /*
     * Append context information to errorBuf.
     *
     * 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 errFuncSaved = xmlGenericError;
        void       *errCtxSaved = xmlGenericErrorContext;

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

        /* Add context information to errorBuf */
        appendStringInfoLineSeparator(errorBuf);

        xmlParserPrintFileContext(input);

        /* Restore generic error func */
        xmlSetGenericErrorFunc(errCtxSaved, errFuncSaved);
    }

    /* Get rid of any trailing newlines in errorBuf */
    chopStringInfoNewlines(errorBuf);

    /*
     * 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 (xmlerrcxt->strictness == PG_XML_STRICTNESS_LEGACY)
    {
        appendStringInfoLineSeparator(&xmlerrcxt->err_buf);
        appendStringInfoString(&xmlerrcxt->err_buf, errorBuf->data);

        pfree(errorBuf->data);
        pfree(errorBuf);
        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)
    {
        appendStringInfoLineSeparator(&xmlerrcxt->err_buf);
        appendStringInfoString(&xmlerrcxt->err_buf, errorBuf->data);

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

    pfree(errorBuf->data);
    pfree(errorBuf);
}


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

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

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


/*
 * Remove all trailing newlines from a StringInfo string
 */
static void
chopStringInfoNewlines(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
appendStringInfoLineSeparator(StringInfo str)
{
    chopStringInfoNewlines(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       *utf8string;
    pg_wchar    ret[2];         /* need space for trailing zero */

    /* note we're not assuming s is null-terminated */
    utf8string = pg_server_to_any(s, pg_mblen(s), PG_UTF8);

    pg_encoding_mb2wchar_with_len(PG_UTF8, utf8string, ret,
                                  pg_encoding_mblen(PG_UTF8, utf8string));

    if (utf8string != s)
        pfree(utf8string);

    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;

    /*
     * 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))
            appendStringInfoString(&buf, "_x003A_");
        else if (*p == '_' && *(p + 1) == 'x')
            appendStringInfoString(&buf, "_x005F_");
        else if (fully_escaped && p == ident &&
                 pg_strncasecmp(p, "xml", 3) == 0)
        {
            if (*p == 'x')
                appendStringInfoString(&buf, "_x0078_");
            else
                appendStringInfoString(&buf, "_x0058_");
        }
        else if (escape_period && *p == '.')
            appendStringInfoString(&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)
{
    char        utf8string[8];  /* need room for trailing zero */
    char       *result;

    memset(utf8string, 0, sizeof(utf8string));
    unicode_to_utf8(c, (unsigned char *) utf8string);

    result = pg_any_to_server(utf8string, strlen(utf8string), PG_UTF8);
    /* if pg_any_to_server didn't strdup, we must */
    if (result == utf8string)
        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;

    initStringInfo(&buf);

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

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

    return buf.data;
}

/*
 * Map SQL value to XML value; see SQL/XML: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;
        Oid         elmtype;
        int16       elmlen;
        bool        elmbyval;
        char        elmalign;
        int         num_elems;
        Datum      *elem_values;
        bool       *elem_nulls;
        StringInfoData buf;
        int         i;

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

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

        initStringInfo(&buf);

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

        pfree(elem_values);
        pfree(elem_nulls);

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

        /*
         * Flatten domains; the special-case treatments below should apply to,
         * eg, domains over boolean not just boolean.
         */
        type = getBaseType(type);

        /*
         * 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   timestamp;
                    struct pg_tm tm;
                    fsec_t      fsec;
                    char        buf[MAXDATELEN + 1];

                    timestamp = DatumGetTimestamp(value);

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

                    timestamp = DatumGetTimestamp(value);

                    /* XSD doesn't support infinite values */
                    if (TIMESTAMP_NOT_FINITE(timestamp))
                        ereport(ERROR,
                                (errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
                                 errmsg("timestamp out of range"),
                                 errdetail("XML does not support infinite timestamp values.")));
                    else if (timestamp2tm(timestamp, &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      *bstr = DatumGetByteaPP(value);
                    PgXmlErrorContext *xmlerrcxt;
                    volatile xmlBufferPtr buf = NULL;
                    volatile xmlTextWriterPtr writer = NULL;
                    char       *result;

                    xmlerrcxt = pg_xml_init(PG_XML_STRICTNESS_ALL);

                    PG_TRY();
                    {
                        buf = xmlBufferCreate();
                        if (buf == NULL || xmlerrcxt->err_occurred)
                            xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
                                        "could not allocate xmlBuffer");
                        writer = xmlNewTextWriterMemory(buf, 0);
                        if (writer == NULL || xmlerrcxt->err_occurred)
                            xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
                                        "could not allocate xmlTextWriter");

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

                        /* 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(xmlerrcxt, true);

                        PG_RE_THROW();
                    }
                    PG_END_TRY();

                    xmlBufferFree(buf);

                    pg_xml_done(xmlerrcxt, false);

                    return result;
                }
#endif   /* USE_LIBXML */

        }

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

        /* ... exactly as-is for XML, 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;

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


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

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


/*
 * SQL to XML mapping functions
 *
 * What follows below 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)
{
    uint64      i;
    List       *list = NIL;

    SPI_execute(query, true, 0);

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

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

    return list;
}


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

    initStringInfo(&query);
    appendStringInfo(&query, "SELECT oid FROM pg_catalog.pg_class WHERE relnamespace = %u AND relkind IN ('r', 'm', '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', 'm', '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 *xmlschema, bool nulls, bool tableforest,
                      const char *targetns, bool top_level)
{
    StringInfoData query;

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


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

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


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

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


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

    StringInfoData result;
    Portal      portal;
    uint64      i;

    initStringInfo(&result);

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

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

    SPI_finish();

    PG_RETURN_XML_P(stringinfo_to_xmltype(&result));
}


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

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


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


static StringInfo
query_to_xml_internal(const char *query, char *tablename,
                      const char *xmlschema, bool nulls, bool tableforest,
                      const char *targetns, bool top_level)
{
    StringInfo  result;
    char       *xmltn;
    uint64      i;

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

    result = makeStringInfo();

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

    if (!tableforest)
    {
        xmldata_root_element_start(result, xmltn, xmlschema,
                                   targetns, top_level);
        appendStringInfoChar(result, '\n');
    }

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

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

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

    SPI_finish();

    return result;
}


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

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

    PG_RETURN_XML_P(cstring_to_xmltype(result));
}


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

    SPI_connect();

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

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

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

    PG_RETURN_XML_P(cstring_to_xmltype(result));
}


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

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

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

    PG_RETURN_XML_P(cstring_to_xmltype(xmlschema));
}


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

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

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


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

    const char *xmlschema;
    SPIPlanPtr  plan;
    Portal      portal;

    SPI_connect();

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

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

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

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


/*
 * Map SQL schema to XML and/or XML Schema document; see SQL/XML:2008
 * sections 9.13, 9.14.
 */

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

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

    xmldata_root_element_start(result, xmlsn, xmlschema, targetns, top_level);
    appendStringInfoChar(result, '\n');

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

    SPI_connect();

    relid_list = schema_get_xml_visible_tables(nspid);

    SPI_push();

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

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

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

    SPI_pop();
    SPI_finish();

    xmldata_root_element_end(result, xmlsn);

    return result;
}


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

    char       *schemaname;
    Oid         nspid;

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

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


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


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


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

    result = makeStringInfo();

    nspid = LookupExplicitNamespace(schemaname, false);

    xsd_schema_element_start(result, targetns);

    SPI_connect();

    relid_list = schema_get_xml_visible_tables(nspid);

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

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

    appendStringInfoString(result,
                           map_sql_typecoll_to_xmlschema_types(tupdesc_list));

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

    xsd_schema_element_end(result);

    SPI_finish();

    return result;
}


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

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


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

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

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

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


/*
 * Map SQL database to XML and/or XML Schema document; see SQL/XML:2008
 * sections 9.16, 9.17.
 */

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

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

    xmldata_root_element_start(result, xmlcn, xmlschema, targetns, true);
    appendStringInfoChar(result, '\n');

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

    SPI_connect();

    nspid_list = database_get_xml_visible_schemas();

    SPI_push();

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

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

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

    SPI_pop();
    SPI_finish();

    xmldata_root_element_end(result, xmlcn);

    return result;
}


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

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


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

    result = makeStringInfo();

    xsd_schema_element_start(result, targetns);

    SPI_connect();

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

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

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

    appendStringInfoString(result,
                           map_sql_typecoll_to_xmlschema_types(tupdesc_list));

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

    xsd_schema_element_end(result);

    SPI_finish();

    return result;
}


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

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


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

    xmlschema = database_to_xmlschema_internal(nulls, tableforest, targetns);

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


/*
 * Map a multi-part SQL name to an XML name; see SQL/XML: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)
        appendStringInfoString(&result,
                               map_sql_identifier_to_xml_name(a, true, true));
    if (b)
        appendStringInfo(&result, ".%s",
                         map_sql_identifier_to_xml_name(b, true, true));
    if (c)
        appendStringInfo(&result, ".%s",
                         map_sql_identifier_to_xml_name(c, true, true));
    if (d)
        appendStringInfo(&result, ".%s",
                         map_sql_identifier_to_xml_name(d, true, true));

    return result.data;
}


/*
 * Map an SQL table to an XML Schema document; see SQL/XML: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)
{
    int         i;
    char       *xmltn;
    char       *tabletypename;
    char       *rowtypename;
    StringInfoData result;

    initStringInfo(&result);

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

        tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
        if (!HeapTupleIsValid(tuple))
            elog(ERROR, "cache lookup failed for relation %u", relid);
        reltuple = (Form_pg_class) GETSTRUCT(tuple);

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

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

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

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

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

    xsd_schema_element_start(&result, targetns);

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

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

    for (i = 0; i < tupdesc->natts; i++)
    {
        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",
                         tabletypename, rowtypename);

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

    xsd_schema_element_end(&result);

    return result.data;
}


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

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

    initStringInfo(&result);

    xmlsn = map_sql_identifier_to_xml_name(nspname, true, false);

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

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

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

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

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

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

    return result.data;
}


/*
 * Map an SQL catalog to XML Schema data types; see SQL/XML:2008
 * section 9.15.
 */
static const char *
map_sql_catalog_to_xmlschema_types(List *nspid_list, bool nulls,
                                   bool tableforest, const char *targetns)
{
    char       *dbname;
    char       *xmlcn;
    char       *catalogtypename;
    StringInfoData result;
    ListCell   *cell;

    dbname = get_database_name(MyDatabaseId);

    initStringInfo(&result);

    xmlcn = map_sql_identifier_to_xml_name(dbname, true, false);

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

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

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

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

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

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

    return result.data;
}


/*
 * Map an SQL data type to an XML name; see SQL/XML:2008 section 9.4.
 */
static const char *
map_sql_type_to_xml_name(Oid typeoid, int typmod)
{
    StringInfoData result;

    initStringInfo(&result);

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

                tuple = SearchSysCache1(TYPEOID, ObjectIdGetDatum(typeoid));
                if (!HeapTupleIsValid(tuple))
                    elog(ERROR, "cache lookup failed for type %u", typeoid);
                typtuple = (Form_pg_type) GETSTRUCT(tuple);

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

                ReleaseSysCache(tuple);
            }
    }

    return result.data;
}


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

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

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

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

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

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

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

    return result.data;
}


/*
 * Map an SQL data type to a named XML Schema data type; see
 * SQL/XML: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 typeoid, int typmod)
{
    StringInfoData result;
    const char *typename = map_sql_type_to_xml_name(typeoid, typmod);

    initStringInfo(&result);

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

                    base_typeoid = getBaseTypeAndTypmod(typeoid, &base_typmod);

                    appendStringInfo(&result,
                                     "  <xsd:restriction base=\"%s\"/>\n",
                        map_sql_type_to_xml_name(base_typeoid, base_typmod));
                }
                break;
        }
        appendStringInfoString(&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(uint64 rownum, StringInfo result, char *tablename,
                          bool nulls, bool tableforest,
                          const char *targetns, bool top_level)
{
    int         i;
    char       *xmltn;

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

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

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

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

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


/*
 * XPath related functions
 */

#ifdef USE_LIBXML

/*
 * Convert XML node to text (dump subtree in case of element,
 * return value otherwise)
 */
static text *
xml_xmlnodetoxmltype(xmlNodePtr cur, PgXmlErrorContext *xmlerrcxt)
{
    xmltype    *result;

    if (cur->type == XML_ELEMENT_NODE)
    {
        xmlBufferPtr buf;
        xmlNodePtr  cur_copy;

        buf = xmlBufferCreate();

        /*
         * The result of xmlNodeDump() won't contain namespace definitions
         * from parent nodes, but xmlCopyNode() duplicates a node along with
         * its required namespace definitions.
         */
        cur_copy = xmlCopyNode(cur, 1);

        if (cur_copy == NULL)
            xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
                        "could not copy node");

        PG_TRY();
        {
            xmlNodeDump(buf, NULL, cur_copy, 0, 1);
            result = xmlBuffer_to_xmltype(buf);
        }
        PG_CATCH();
        {
            xmlFreeNode(cur_copy);
            xmlBufferFree(buf);
            PG_RE_THROW();
        }
        PG_END_TRY();
        xmlFreeNode(cur_copy);
        xmlBufferFree(buf);
    }
    else
    {
        xmlChar    *str;

        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(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 are appended to 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 xpathobj,
                       ArrayBuildState *astate,
                       PgXmlErrorContext *xmlerrcxt)
{
    int         result = 0;
    Datum       datum;
    Oid         datumtype;
    char       *result_str;

    switch (xpathobj->type)
    {
        case XPATH_NODESET:
            if (xpathobj->nodesetval != NULL)
            {
                result = xpathobj->nodesetval->nodeNr;
                if (astate != NULL)
                {
                    int         i;

                    for (i = 0; i < result; i++)
                    {
                        datum = PointerGetDatum(xml_xmlnodetoxmltype(xpathobj->nodesetval->nodeTab[i],
                                                                 xmlerrcxt));
                        (void) accumArrayResult(astate, datum, false,
                                                XMLOID, CurrentMemoryContext);
                    }
                }
            }
            return result;

        case XPATH_BOOLEAN:
            if (astate == NULL)
                return 1;
            datum = BoolGetDatum(xpathobj->boolval);
            datumtype = BOOLOID;
            break;

        case XPATH_NUMBER:
            if (astate == NULL)
                return 1;
            datum = Float8GetDatum(xpathobj->floatval);
            datumtype = FLOAT8OID;
            break;

        case XPATH_STRING:
            if (astate == NULL)
                return 1;
            datum = CStringGetDatum((char *) xpathobj->stringval);
            datumtype = CSTRINGOID;
            break;

        default:
            elog(ERROR, "xpath expression result type %d is unsupported",
                 xpathobj->type);
            return 0;           /* keep compiler quiet */
    }

    /* Common code for scalar-value cases */
    result_str = map_sql_value_to_xml_value(datum, datumtype, true);
    datum = PointerGetDatum(cstring_to_xmltype(result_str));
    (void) 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 *xmlerrcxt;
    volatile xmlParserCtxtPtr ctxt = NULL;
    volatile xmlDocPtr doc = NULL;
    volatile xmlXPathContextPtr xpathctx = NULL;
    volatile xmlXPathCompExprPtr xpathcomp = NULL;
    volatile xmlXPathObjectPtr xpathobj = NULL;
    char       *datastr;
    int32       len;
    int32       xpath_len;
    xmlChar    *string;
    xmlChar    *xpath_expr;
    int         i;
    int         ndim;
    Datum      *ns_names_uris;
    bool       *ns_names_uris_nulls;
    int         ns_count;

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

        dims = ARR_DIMS(namespaces);

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

        Assert(ARR_ELEMTYPE(namespaces) == TEXTOID);

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

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

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

    string = (xmlChar *) palloc((len + 1) * sizeof(xmlChar));
    memcpy(string, datastr, len);
    string[len] = '\0';

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

    xmlerrcxt = 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 || xmlerrcxt->err_occurred)
            xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
                        "could not allocate parser context");
        doc = xmlCtxtReadMemory(ctxt, (char *) string, len, NULL, NULL, 0);
        if (doc == NULL || xmlerrcxt->err_occurred)
            xml_ereport(xmlerrcxt, ERROR, ERRCODE_INVALID_XML_DOCUMENT,
                        "could not parse XML document");
        xpathctx = xmlXPathNewContext(doc);
        if (xpathctx == NULL || xmlerrcxt->err_occurred)
            xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
                        "could not allocate XPath context");
        xpathctx->node = xmlDocGetRootElement(doc);
        if (xpathctx->node == NULL || xmlerrcxt->err_occurred)
            xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
                        "could not find root XML element");

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

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

        xpathcomp = xmlXPathCompile(xpath_expr);
        if (xpathcomp == NULL || xmlerrcxt->err_occurred)
            xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
                        "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.
         */
        xpathobj = xmlXPathCompiledEval(xpathcomp, xpathctx);
        if (xpathobj == NULL || xmlerrcxt->err_occurred)
            xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
                        "could not create XPath object");

        /*
         * Extract the results as requested.
         */
        if (res_nitems != NULL)
            *res_nitems = xml_xpathobjtoxmlarray(xpathobj, astate, xmlerrcxt);
        else
            (void) xml_xpathobjtoxmlarray(xpathobj, astate, xmlerrcxt);
    }
    PG_CATCH();
    {
        if (xpathobj)
            xmlXPathFreeObject(xpathobj);
        if (xpathcomp)
            xmlXPathFreeCompExpr(xpathcomp);
        if (xpathctx)
            xmlXPathFreeContext(xpathctx);
        if (doc)
            xmlFreeDoc(doc);
        if (ctxt)
            xmlFreeParserCtxt(ctxt);

        pg_xml_done(xmlerrcxt, true);

        PG_RE_THROW();
    }
    PG_END_TRY();

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

    pg_xml_done(xmlerrcxt, 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);
    ArrayBuildState *astate;

    astate = initArrayResult(XMLOID, CurrentMemoryContext, true);
    xpath_internal(xpath_expr_text, data, namespaces,
                   NULL, astate);
    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
}

/*
 * Functions for checking well-formed-ness
 */

#ifdef USE_LIBXML
static bool
wellformed_xml(text *data, XmlOptionType xmloption_arg)
{
    bool        result;
    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, 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 */
}