/src/postgres/src/backend/utils/adt/xml.c

Source (jump to first uncovered line)
/*-------------------------------------------------------------------------
 *
 * xml.c
 *    XML data type support.
 *
 *
 * Portions Copyright (c) 1996-2025, 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/entities.h>
#include <libxml/parser.h>
#include <libxml/parserInternals.h>
#include <libxml/tree.h>
#include <libxml/uri.h>
#include <libxml/xmlerror.h>
#include <libxml/xmlsave.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

/*
 * libxml2 2.12 decided to insert "const" into the error handler API.
 */
#if LIBXML_VERSION >= 21200
#define PgXmlErrorPtr const xmlError *
#else
#define PgXmlErrorPtr xmlErrorPtr
#endif

#endif              /* USE_LIBXML */

#include "access/htup_details.h"
#include "access/table.h"
#include "catalog/namespace.h"
#include "catalog/pg_class.h"
#include "catalog/pg_type.h"
#include "commands/dbcommands.h"
#include "executor/spi.h"
#include "executor/tablefunc.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/miscnodes.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/rel.h"
#include "utils/syscache.h"
#include "utils/xml.h"


/* GUC variables */
int     xmlbinary = XMLBINARY_BASE64;
int     xmloption = XMLOPTION_CONTENT;

#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_errsave(Node *escontext, PgXmlErrorContext *errcxt,
            int sqlcode, const char *msg);
static void xml_errorHandler(void *data, PgXmlErrorPtr error);
static int  errdetail_for_xml_code(int code);
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 bool xml_doctype_in_content(const xmlChar *str);
static xmlDocPtr xml_parse(text *data, XmlOptionType xmloption_arg,
               bool preserve_whitespace, int encoding,
               XmlOptionType *parsed_xmloptiontype,
               xmlNodePtr *parsed_nodes,
               Node *escontext);
static text *xml_xmlnodetoxmltype(xmlNodePtr cur, PgXmlErrorContext *xmlerrcxt);
static int  xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
                   ArrayBuildState *astate,
                   PgXmlErrorContext *xmlerrcxt);
static xmlChar *pg_xmlCharStrndup(const char *str, size_t len);
#endif              /* USE_LIBXML */

static void xmldata_root_element_start(StringInfo result, const char *eltname,
                     const char *xmlschema, const char *targetns,
                     bool top_level);
static void xmldata_root_element_end(StringInfo result, const char *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);
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);

/* XMLTABLE support */
#ifdef USE_LIBXML
/* random number to identify XmlTableContext */
#define XMLTABLE_CONTEXT_MAGIC  46922182
typedef struct XmlTableBuilderData
{
  int     magic;
  int     natts;
  long int  row_count;
  PgXmlErrorContext *xmlerrcxt;
  xmlParserCtxtPtr ctxt;
  xmlDocPtr doc;
  xmlXPathContextPtr xpathcxt;
  xmlXPathCompExprPtr xpathcomp;
  xmlXPathObjectPtr xpathobj;
  xmlXPathCompExprPtr *xpathscomp;
} XmlTableBuilderData;
#endif

static void XmlTableInitOpaque(struct TableFuncScanState *state, int natts);
static void XmlTableSetDocument(struct TableFuncScanState *state, Datum value);
static void XmlTableSetNamespace(struct TableFuncScanState *state, const char *name,
                 const char *uri);
static void XmlTableSetRowFilter(struct TableFuncScanState *state, const char *path);
static void XmlTableSetColumnFilter(struct TableFuncScanState *state,
                  const char *path, int colnum);
static bool XmlTableFetchRow(struct TableFuncScanState *state);
static Datum XmlTableGetValue(struct TableFuncScanState *state, int colnum,
                Oid typid, int32 typmod, bool *isnull);
static void XmlTableDestroyOpaque(struct TableFuncScanState *state);

const TableFuncRoutine XmlTableRoutine =
{
  .InitOpaque = XmlTableInitOpaque,
  .SetDocument = XmlTableSetDocument,
  .SetNamespace = XmlTableSetNamespace,
  .SetRowFilter = XmlTableSetRowFilter,
  .SetColumnFilter = XmlTableSetColumnFilter,
  .FetchRow = XmlTableFetchRow,
  .GetValue = XmlTableGetValue,
  .DestroyOpaque = XmlTableDestroyOpaque
};

#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.")))


/* 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;

  /* Build the result object. */
  vardata = (xmltype *) cstring_to_text(s);

  /*
   * Parse the data to check if it is well-formed XML data.
   *
   * Note: we don't need to worry about whether a soft error is detected.
   */
  doc = xml_parse(vardata, xmloption, true, GetDatabaseEncoding(),
          NULL, NULL, fcinfo->context);
  if (doc != NULL)
    xmlFreeDoc(doc);

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


#define PG_XML_DEFAULT_VERSION "1.0"


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

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

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

    initStringInfo(&buf);

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

    pfree(str);

    return buf.data;
  }

  ereport(WARNING,
      errcode(ERRCODE_DATA_CORRUPTED),
      errmsg_internal("could not parse XML declaration in stored value"),
      errdetail_for_xml_code(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, NULL, NULL, NULL);
  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_ANY(t), VARSIZE_ANY_EXHDR(t));
}
#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_PP(0);
  char     *argdata = VARDATA_ANY(arg);
  int     len = VARSIZE_ANY_EXHDR(arg);
  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
}


Datum
xmltext(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
  text     *arg = PG_GETARG_TEXT_PP(0);
  text     *result;
  volatile xmlChar *xmlbuf = NULL;
  PgXmlErrorContext *xmlerrcxt;

  /* First we gotta spin up some error handling. */
  xmlerrcxt = pg_xml_init(PG_XML_STRICTNESS_ALL);

  PG_TRY();
  {
    xmlbuf = xmlEncodeSpecialChars(NULL, xml_text2xmlChar(arg));

    if (xmlbuf == NULL || xmlerrcxt->err_occurred)
      xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
            "could not allocate xmlChar");

    result = cstring_to_text_with_len((const char *) xmlbuf,
                      xmlStrlen((const xmlChar *) xmlbuf));
  }
  PG_CATCH();
  {
    if (xmlbuf)
      xmlFree((xmlChar *) xmlbuf);

    pg_xml_done(xmlerrcxt, true);
    PG_RE_THROW();
  }
  PG_END_TRY();

  xmlFree((xmlChar *) xmlbuf);
  pg_xml_done(xmlerrcxt, false);

  PG_RETURN_XML_P(result);
#else
  NO_XML_SUPPORT();
  return 0;
#endif              /* not USE_LIBXML */
}


/*
 * 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);

    appendBinaryStringInfo(&buf2, buf.data, buf.len);
    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_PP(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_options(xmltype *data, XmlOptionType xmloption_arg, bool indent)
{
#ifdef USE_LIBXML
  text     *volatile result;
  xmlDocPtr doc;
  XmlOptionType parsed_xmloptiontype;
  xmlNodePtr  content_nodes;
  volatile xmlBufferPtr buf = NULL;
  volatile xmlSaveCtxtPtr ctxt = NULL;
  ErrorSaveContext escontext = {T_ErrorSaveContext};
  PgXmlErrorContext *volatile xmlerrcxt = NULL;
#endif

  if (xmloption_arg != XMLOPTION_DOCUMENT && !indent)
  {
    /*
     * We don't actually need to do anything, so just return the
     * binary-compatible input.  For backwards-compatibility reasons,
     * allow such cases to succeed even without USE_LIBXML.
     */
    return (text *) data;
  }

#ifdef USE_LIBXML

  /*
   * Parse the input according to the xmloption.
   *
   * preserve_whitespace is set to false in case we are indenting, otherwise
   * libxml2 will fail to indent elements that have whitespace between them.
   */
  doc = xml_parse(data, xmloption_arg, !indent, GetDatabaseEncoding(),
          &parsed_xmloptiontype, &content_nodes,
          (Node *) &escontext);
  if (doc == NULL || escontext.error_occurred)
  {
    if (doc)
      xmlFreeDoc(doc);
    /* A soft error must be failure to conform to XMLOPTION_DOCUMENT */
    ereport(ERROR,
        (errcode(ERRCODE_NOT_AN_XML_DOCUMENT),
         errmsg("not an XML document")));
  }

  /* If we weren't asked to indent, we're done. */
  if (!indent)
  {
    xmlFreeDoc(doc);
    return (text *) data;
  }

  /*
   * Otherwise, we gotta spin up some error handling.  Unlike most other
   * routines in this module, we already have a libxml "doc" structure to
   * free, so we need to call pg_xml_init() inside the PG_TRY and be
   * prepared for it to fail (typically due to palloc OOM).
   */
  PG_TRY();
  {
    size_t    decl_len = 0;

    xmlerrcxt = pg_xml_init(PG_XML_STRICTNESS_ALL);

    /* The serialized data will go into this buffer. */
    buf = xmlBufferCreate();

    if (buf == NULL || xmlerrcxt->err_occurred)
      xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
            "could not allocate xmlBuffer");

    /* Detect whether there's an XML declaration */
    parse_xml_decl(xml_text2xmlChar(data), &decl_len, NULL, NULL, NULL);

    /*
     * Emit declaration only if the input had one.  Note: some versions of
     * xmlSaveToBuffer leak memory if a non-null encoding argument is
     * passed, so don't do that.  We don't want any encoding conversion
     * anyway.
     */
    if (decl_len == 0)
      ctxt = xmlSaveToBuffer(buf, NULL,
                   XML_SAVE_NO_DECL | XML_SAVE_FORMAT);
    else
      ctxt = xmlSaveToBuffer(buf, NULL,
                   XML_SAVE_FORMAT);

    if (ctxt == NULL || xmlerrcxt->err_occurred)
      xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
            "could not allocate xmlSaveCtxt");

    if (parsed_xmloptiontype == XMLOPTION_DOCUMENT)
    {
      /* If it's a document, saving is easy. */
      if (xmlSaveDoc(ctxt, doc) == -1 || xmlerrcxt->err_occurred)
        xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
              "could not save document to xmlBuffer");
    }
    else if (content_nodes != NULL)
    {
      /*
       * Deal with the case where we have non-singly-rooted XML.
       * libxml's dump functions don't work well for that without help.
       * We build a fake root node that serves as a container for the
       * content nodes, and then iterate over the nodes.
       */
      xmlNodePtr  root;
      xmlNodePtr  oldroot;
      xmlNodePtr  newline;

      root = xmlNewNode(NULL, (const xmlChar *) "content-root");
      if (root == NULL || xmlerrcxt->err_occurred)
        xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
              "could not allocate xml node");

      /*
       * This attaches root to doc, so we need not free it separately...
       * but instead, we have to free the old root if there was one.
       */
      oldroot = xmlDocSetRootElement(doc, root);
      if (oldroot != NULL)
        xmlFreeNode(oldroot);

      if (xmlAddChildList(root, content_nodes) == NULL ||
        xmlerrcxt->err_occurred)
        xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
              "could not append xml node list");

      /*
       * We use this node to insert newlines in the dump.  Note: in at
       * least some libxml versions, xmlNewDocText would not attach the
       * node to the document even if we passed it.  Therefore, manage
       * freeing of this node manually, and pass NULL here to make sure
       * there's not a dangling link.
       */
      newline = xmlNewDocText(NULL, (const xmlChar *) "\n");
      if (newline == NULL || xmlerrcxt->err_occurred)
        xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
              "could not allocate xml node");

      for (xmlNodePtr node = root->children; node; node = node->next)
      {
        /* insert newlines between nodes */
        if (node->type != XML_TEXT_NODE && node->prev != NULL)
        {
          if (xmlSaveTree(ctxt, newline) == -1 || xmlerrcxt->err_occurred)
          {
            xmlFreeNode(newline);
            xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
                  "could not save newline to xmlBuffer");
          }
        }

        if (xmlSaveTree(ctxt, node) == -1 || xmlerrcxt->err_occurred)
        {
          xmlFreeNode(newline);
          xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
                "could not save content to xmlBuffer");
        }
      }

      xmlFreeNode(newline);
    }

    if (xmlSaveClose(ctxt) == -1 || xmlerrcxt->err_occurred)
    {
      ctxt = NULL;    /* don't try to close it again */
      xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
            "could not close xmlSaveCtxtPtr");
    }

    /*
     * xmlDocContentDumpOutput may add a trailing newline, so remove that.
     */
    if (xmloption_arg == XMLOPTION_DOCUMENT)
    {
      const char *str = (const char *) xmlBufferContent(buf);
      int     len = xmlBufferLength(buf);

      while (len > 0 && (str[len - 1] == '\n' ||
                 str[len - 1] == '\r'))
        len--;

      result = cstring_to_text_with_len(str, len);
    }
    else
      result = (text *) xmlBuffer_to_xmltype(buf);
  }
  PG_CATCH();
  {
    if (ctxt)
      xmlSaveClose(ctxt);
    if (buf)
      xmlBufferFree(buf);
    xmlFreeDoc(doc);

    if (xmlerrcxt)
      pg_xml_done(xmlerrcxt, true);

    PG_RE_THROW();
  }
  PG_END_TRY();

  xmlBufferFree(buf);
  xmlFreeDoc(doc);

  pg_xml_done(xmlerrcxt, false);

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


xmltype *
xmlelement(XmlExpr *xexpr,
       Datum *named_argvalue, bool *named_argnull,
       Datum *argvalue, bool *argnull)
{
#ifdef USE_LIBXML
  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;

  /*
   * All arguments are already evaluated, and their values are passed in the
   * named_argvalue/named_argnull or argvalue/argnull arrays.  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.  We examine the
   * original XmlExpr to identify the numbers and types of the arguments.
   */
  named_arg_strings = NIL;
  i = 0;
  foreach(arg, xexpr->named_args)
  {
    Expr     *e = (Expr *) lfirst(arg);
    char     *str;

    if (named_argnull[i])
      str = NULL;
    else
      str = map_sql_value_to_xml_value(named_argvalue[i],
                       exprType((Node *) e),
                       false);
    named_arg_strings = lappend(named_arg_strings, str);
    i++;
  }

  arg_strings = NIL;
  i = 0;
  foreach(arg, xexpr->args)
  {
    Expr     *e = (Expr *) lfirst(arg);
    char     *str;

    /* here we can just forget NULL elements immediately */
    if (!argnull[i])
    {
      str = map_sql_value_to_xml_value(argvalue[i],
                       exprType((Node *) e),
                       true);
      arg_strings = lappend(arg_strings, str);
    }
    i++;
  }

  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 (xmlTextWriterStartElement(writer, (xmlChar *) xexpr->name) < 0 ||
      xmlerrcxt->err_occurred)
      xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
            "could not start xml element");

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

      if (str)
      {
        if (xmlTextWriterWriteAttribute(writer,
                        (xmlChar *) argname,
                        (xmlChar *) str) < 0 ||
          xmlerrcxt->err_occurred)
          xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
                "could not write xml attribute");
      }
    }

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

      if (xmlTextWriterWriteRaw(writer, (xmlChar *) str) < 0 ||
        xmlerrcxt->err_occurred)
        xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
              "could not write raw xml text");
    }

    if (xmlTextWriterEndElement(writer) < 0 ||
      xmlerrcxt->err_occurred)
      xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
            "could not end xml element");

    /* 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(), NULL, NULL, NULL);
  xmlFreeDoc(doc);

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


xmltype *
xmlpi(const 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_INVALID_XML_PROCESSING_INSTRUCTION),
         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
  xmlDocPtr doc;
  ErrorSaveContext escontext = {T_ErrorSaveContext};

  /*
   * We'll report "true" if no soft error is reported by xml_parse().
   */
  doc = xml_parse((text *) arg, XMLOPTION_DOCUMENT, true,
          GetDatabaseEncoding(), NULL, NULL, (Node *) &escontext);
  if (doc)
    xmlFreeDoc(doc);

  return !escontext.error_occurred;
#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)=%zu, sizeof(xmlChar)=%zu.",
                 sizeof(char), 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(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 != 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 != 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;
}

/* Ditto, except input is char* */
static xmlChar *
pg_xmlCharStrndup(const char *str, size_t len)
{
  xmlChar    *result;

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

  return result;
}

/*
 * Copy xmlChar string to PostgreSQL-owned memory, freeing the input.
 *
 * The input xmlChar is freed regardless of success of the copy.
 */
static char *
xml_pstrdup_and_free(xmlChar *str)
{
  char     *result;

  if (str)
  {
    PG_TRY();
    {
      result = pstrdup((char *) str);
    }
    PG_FINALLY();
    {
      xmlFree(str);
    }
    PG_END_TRY();
  }
  else
    result = NULL;

  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 a name char, it's a PI like <?xml-stylesheet ...?>
   * rather than an XMLDecl, so we have done what we came to do and found no
   * XMLDecl.
   *
   * We need an input length value for xmlGetUTF8Char, but there's no need
   * to count the whole document size, so use strnlen not strlen.
   */
  utf8len = strnlen((const char *) (p + 5), MAX_MULTIBYTE_CHAR_LEN);
  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;
}

/*
 * Test whether an input that is to be parsed as CONTENT contains a DTD.
 *
 * The SQL/XML:2003 definition of CONTENT ("XMLDecl? content") is not
 * satisfied by a document with a DTD, which is a bit of a wart, as it means
 * the CONTENT type is not a proper superset of DOCUMENT.  SQL/XML:2006 and
 * later fix that, by redefining content with reference to the "more
 * permissive" Document Node of the XQuery/XPath Data Model, such that any
 * DOCUMENT value is indeed also a CONTENT value.  That definition is more
 * useful, as CONTENT becomes usable for parsing input of unknown form (think
 * pg_restore).
 *
 * As used below in parse_xml when parsing for CONTENT, libxml does not give
 * us the 2006+ behavior, but only the 2003; it will choke if the input has
 * a DTD.  But we can provide the 2006+ definition of CONTENT easily enough,
 * by detecting this case first and simply doing the parse as DOCUMENT.
 *
 * A DTD can be found arbitrarily far in, but that would be a contrived case;
 * it will ordinarily start within a few dozen characters.  The only things
 * that can precede it are an XMLDecl (here, the caller will have called
 * parse_xml_decl already), whitespace, comments, and processing instructions.
 * This function need only return true if it sees a valid sequence of such
 * things leading to <!DOCTYPE.  It can simply return false in any other
 * cases, including malformed input; that will mean the input gets parsed as
 * CONTENT as originally planned, with libxml reporting any errors.
 *
 * This is only to be called from xml_parse, when pg_xml_init has already
 * been called.  The input is already in UTF8 encoding.
 */
static bool
xml_doctype_in_content(const xmlChar *str)
{
  const xmlChar *p = str;

  for (;;)
  {
    const xmlChar *e;

    SKIP_XML_SPACE(p);
    if (*p != '<')
      return false;
    p++;

    if (*p == '!')
    {
      p++;

      /* if we see <!DOCTYPE, we can return true */
      if (xmlStrncmp(p, (xmlChar *) "DOCTYPE", 7) == 0)
        return true;

      /* otherwise, if it's not a comment, fail */
      if (xmlStrncmp(p, (xmlChar *) "--", 2) != 0)
        return false;
      /* find end of comment: find -- and a > must follow */
      p = xmlStrstr(p + 2, (xmlChar *) "--");
      if (!p || p[2] != '>')
        return false;
      /* advance over comment, and keep scanning */
      p += 3;
      continue;
    }

    /* otherwise, if it's not a PI <?target something?>, fail */
    if (*p != '?')
      return false;
    p++;

    /* find end of PI (the string ?> is forbidden within a PI) */
    e = xmlStrstr(p, (xmlChar *) "?>");
    if (!e)
      return false;

    /* advance over PI, keep scanning */
    p = e + 2;
  }
}


/*
 * Convert a text object to XML internal representation
 *
 * data is the source data (must not be toasted!), encoding is its encoding,
 * and xmloption_arg and preserve_whitespace are options for the
 * transformation.
 *
 * If parsed_xmloptiontype isn't NULL, *parsed_xmloptiontype is set to the
 * XmlOptionType actually used to parse the input (typically the same as
 * xmloption_arg, but a DOCTYPE node in the input can force DOCUMENT mode).
 *
 * If parsed_nodes isn't NULL and we parse in CONTENT mode, the list
 * of parsed nodes from the xmlParseBalancedChunkMemory call will be returned
 * to *parsed_nodes.  (It is caller's responsibility to free that.)
 *
 * Errors normally result in ereport(ERROR), but if escontext is an
 * ErrorSaveContext, then "safe" errors are reported there instead, and the
 * caller must check SOFT_ERROR_OCCURRED() to see whether that happened.
 *
 * Note: it is caller's responsibility to xmlFreeDoc() the result,
 * else a permanent memory leak will ensue!  But note the result could
 * be NULL after a soft error.
 *
 * 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,
      XmlOptionType *parsed_xmloptiontype, xmlNodePtr *parsed_nodes,
      Node *escontext)
{
  int32   len;
  xmlChar    *string;
  xmlChar    *utf8string;
  PgXmlErrorContext *xmlerrcxt;
  volatile xmlParserCtxtPtr ctxt = NULL;
  volatile xmlDocPtr doc = NULL;
  volatile int save_keep_blanks = -1;

  /*
   * This step looks annoyingly redundant, but we must do it to have a
   * null-terminated string in case encoding conversion isn't required.
   */
  len = VARSIZE_ANY_EXHDR(data);  /* will be useful later */
  string = xml_text2xmlChar(data);

  /*
   * If the data isn't UTF8, we must translate before giving it to libxml.
   *
   * XXX ideally, we'd catch any encoding conversion failure and return a
   * soft error.  However, failure to convert to UTF8 should be pretty darn
   * rare, so for now this is left undone.
   */
  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();
  {
    bool    parse_as_document = false;
    int     res_code;
    size_t    count = 0;
    xmlChar    *version = NULL;
    int     standalone = 0;

    /* Any errors here are reported as hard ereport's */
    xmlInitParser();

    /* Decide whether to parse as document or content */
    if (xmloption_arg == XMLOPTION_DOCUMENT)
      parse_as_document = true;
    else
    {
      /* Parse and skip over the XML declaration, if any */
      res_code = parse_xml_decl(utf8string,
                    &count, &version, NULL, &standalone);
      if (res_code != 0)
      {
        errsave(escontext,
            errcode(ERRCODE_INVALID_XML_CONTENT),
            errmsg_internal("invalid XML content: invalid XML declaration"),
            errdetail_for_xml_code(res_code));
        goto fail;
      }

      /* Is there a DOCTYPE element? */
      if (xml_doctype_in_content(utf8string + count))
        parse_as_document = true;
    }

    /* initialize output parameters */
    if (parsed_xmloptiontype != NULL)
      *parsed_xmloptiontype = parse_as_document ? XMLOPTION_DOCUMENT :
        XMLOPTION_CONTENT;
    if (parsed_nodes != NULL)
      *parsed_nodes = NULL;

    if (parse_as_document)
    {
      int     options;

      /* set up parser context used by xmlCtxtReadDoc */
      ctxt = xmlNewParserCtxt();
      if (ctxt == NULL || xmlerrcxt->err_occurred)
        xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
              "could not allocate parser context");

      /*
       * Select parse options.
       *
       * 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), but that
       * doesn't really happen because xmlPgEntityLoader prevents it.
       */
      options = XML_PARSE_NOENT | XML_PARSE_DTDATTR
        | (preserve_whitespace ? 0 : XML_PARSE_NOBLANKS);

      doc = xmlCtxtReadDoc(ctxt, utf8string,
                 NULL,  /* no URL */
                 "UTF-8",
                 options);

      if (doc == NULL || xmlerrcxt->err_occurred)
      {
        /* Use original option to decide which error code to report */
        if (xmloption_arg == XMLOPTION_DOCUMENT)
          xml_errsave(escontext, xmlerrcxt,
                ERRCODE_INVALID_XML_DOCUMENT,
                "invalid XML document");
        else
          xml_errsave(escontext, xmlerrcxt,
                ERRCODE_INVALID_XML_CONTENT,
                "invalid XML content");
        goto fail;
      }
    }
    else
    {
      /* set up document that xmlParseBalancedChunkMemory will add to */
      doc = xmlNewDoc(version);
      if (doc == NULL || xmlerrcxt->err_occurred)
        xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
              "could not allocate XML document");

      Assert(doc->encoding == NULL);
      doc->encoding = xmlStrdup((const xmlChar *) "UTF-8");
      if (doc->encoding == NULL || xmlerrcxt->err_occurred)
        xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
              "could not allocate XML document");
      doc->standalone = standalone;

      /* set parse options --- have to do this the ugly way */
      save_keep_blanks = xmlKeepBlanksDefault(preserve_whitespace ? 1 : 0);

      /* allow empty content */
      if (*(utf8string + count))
      {
        res_code = xmlParseBalancedChunkMemory(doc, NULL, NULL, 0,
                             utf8string + count,
                             parsed_nodes);
        if (res_code != 0 || xmlerrcxt->err_occurred)
        {
          xml_errsave(escontext, xmlerrcxt,
                ERRCODE_INVALID_XML_CONTENT,
                "invalid XML content");
          goto fail;
        }
      }
    }

fail:
    ;
  }
  PG_CATCH();
  {
    if (save_keep_blanks != -1)
      xmlKeepBlanksDefault(save_keep_blanks);
    if (doc != NULL)
      xmlFreeDoc(doc);
    if (ctxt != NULL)
      xmlFreeParserCtxt(ctxt);

    pg_xml_done(xmlerrcxt, true);

    PG_RE_THROW();
  }
  PG_END_TRY();

  if (save_keep_blanks != -1)
    xmlKeepBlanksDefault(save_keep_blanks);

  if (ctxt != NULL)
    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,
                        "Libxml context",
                        ALLOCSET_DEFAULT_SIZES);

  /* 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));
}


/*
 * xml_errsave --- save an XML-related error
 *
 * If escontext is an ErrorSaveContext, error details are saved into it,
 * and control returns normally.
 *
 * Otherwise, the error is thrown, so that this is equivalent to
 * xml_ereport() with level == ERROR.
 *
 * This should be used only for errors that we're sure we do not need
 * a transaction abort to clean up after.
 */
static void
xml_errsave(Node *escontext, PgXmlErrorContext *errcxt,
      int sqlcode, const char *msg)
{
  char     *detail;

  /* Defend against someone passing us a bogus context struct */
  if (errcxt->magic != ERRCXT_MAGIC)
    elog(ERROR, "xml_errsave 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;

  errsave(escontext,
      (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, PgXmlErrorPtr 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:

      /*
       * XML_ERR_NOT_WELL_BALANCED is typically reported after some
       * other, more on-point error.  Furthermore, libxml2 2.13 reports
       * it under a completely different set of rules than prior
       * versions.  To avoid cross-version behavioral differences,
       * suppress it so long as we already logged some error.
       */
      if (error->code == XML_ERR_NOT_WELL_BALANCED &&
        xmlerrcxt->err_occurred)
        return;
      /* fall through */

    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);
  if (error->message != NULL)
    appendStringInfoString(errorBuf, error->message);
  else
    appendStringInfoString(errorBuf, "(no message provided)");

  /*
   * 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(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);
    appendBinaryStringInfo(&xmlerrcxt->err_buf, errorBuf->data,
                 errorBuf->len);

    destroyStringInfo(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);
    appendBinaryStringInfo(&xmlerrcxt->err_buf, errorBuf->data,
                 errorBuf->len);

    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)));
  }

  destroyStringInfo(errorBuf);
}


/*
 * Convert libxml error codes into textual errdetail messages.
 *
 * This should be called within an ereport or errsave invocation,
 * just as errdetail would be.
 *
 * At the moment, we only need to cover those codes that we
 * may raise in this file.
 */
static int
errdetail_for_xml_code(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;
  }

  return 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(const 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(const char *ident, bool fully_escaped,
                 bool escape_period)
{
#ifdef USE_LIBXML
  StringInfoData buf;
  const 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 XML name to SQL identifier; see SQL/XML:2008 section 9.3.
 */
char *
map_xml_name_to_sql_identifier(const char *name)
{
  StringInfoData buf;
  const 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) == '_')
    {
      char    cbuf[MAX_UNICODE_EQUIVALENT_STRING + 1];
      unsigned int u;

      sscanf(p + 2, "%X", &u);
      pg_unicode_to_server(u, (unsigned char *) cbuf);
      appendStringInfoString(&buf, cbuf);
      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;
  int     spi_result;

  spi_result = SPI_execute(query, true, 0);
  if (spi_result != SPI_OK_SELECT)
    elog(ERROR, "SPI_execute returned %s for %s",
       SPI_result_code_string(spi_result), query);

  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 ("
           CppAsString2(RELKIND_RELATION) ","
           CppAsString2(RELKIND_MATVIEW) ","
           CppAsString2(RELKIND_VIEW) ")"
           " 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 ("
               CppAsString2(RELKIND_RELATION) ","
               CppAsString2(RELKIND_MATVIEW) ","
               CppAsString2(RELKIND_VIEW) ")"
               " 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);

  if (!tableforest)
  {
    xmldata_root_element_start(&result, "table", NULL, targetns, true);
    appendStringInfoChar(&result, '\n');
  }

  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();

  if (!tableforest)
    xmldata_root_element_end(&result, "table");

  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 = table_open(relid, AccessShareLock);
  result = map_sql_table_to_xmlschema(rel->rd_att, relid, nulls,
                    tableforest, targetns);
  table_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)));
  if (portal->tupDesc == NULL)
    ereport(ERROR,
        (errcode(ERRCODE_INVALID_CURSOR_STATE),
         errmsg("portal \"%s\" does not return tuples", 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 = table_open(relid, AccessShareLock);
  xmlschema = map_sql_table_to_xmlschema(rel->rd_att, relid, nulls,
                       tableforest, targetns);
  table_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);

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

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

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

  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 = table_open(lfirst_oid(cell), AccessShareLock);
    tupdesc_list = lappend(tupdesc_list, CreateTupleDescCopy(rel->rd_att));
    table_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();

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

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

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

  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 = table_open(lfirst_oid(cell), AccessShareLock);
    tupdesc_list = lappend(tupdesc_list, CreateTupleDescCopy(rel->rd_att));
    table_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(const char *a, const char *b, const char *c, const 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++)
  {
    Form_pg_attribute att = TupleDescAttr(tupdesc, i);

    if (att->attisdropped)
      continue;
    appendStringInfo(&result,
             "    <xsd:element name=\"%s\" type=\"%s\"%s></xsd:element>\n",
             map_sql_identifier_to_xml_name(NameStr(att->attname),
                            true, false),
             map_sql_type_to_xml_name(att->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++)
    {
      Form_pg_attribute att = TupleDescAttr(tupdesc, i);

      if (att->attisdropped)
        continue;
      uniquetypes = list_append_unique_oid(uniquetypes, att->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:
        appendStringInfoString(&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",
                 PG_INT64_MAX,
                 PG_INT64_MIN);
        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.
 *
 * For attribute and text nodes, return the escaped text.  For anything else,
 * dump the whole subtree.
 */
static text *
xml_xmlnodetoxmltype(xmlNodePtr cur, PgXmlErrorContext *xmlerrcxt)
{
  xmltype    *result = NULL;

  if (cur->type != XML_ATTRIBUTE_NODE && cur->type != XML_TEXT_NODE)
  {
    void    (*volatile nodefree) (xmlNodePtr) = NULL;
    volatile xmlBufferPtr buf = NULL;
    volatile xmlNodePtr cur_copy = NULL;

    PG_TRY();
    {
      int     bytes;

      buf = xmlBufferCreate();
      if (buf == NULL || xmlerrcxt->err_occurred)
        xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
              "could not allocate xmlBuffer");

      /*
       * Produce a dump of the node that we can serialize.  xmlNodeDump
       * does that, but the result of that function won't contain
       * namespace definitions from ancestor nodes, so we first do a
       * xmlCopyNode() which duplicates the node along with its required
       * namespace definitions.
       *
       * Some old libxml2 versions such as 2.7.6 produce partially
       * broken XML_DOCUMENT_NODE nodes (unset content field) when
       * copying them.  xmlNodeDump of such a node works fine, but
       * xmlFreeNode crashes; set us up to call xmlFreeDoc instead.
       */
      cur_copy = xmlCopyNode(cur, 1);
      if (cur_copy == NULL || xmlerrcxt->err_occurred)
        xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
              "could not copy node");
      nodefree = (cur_copy->type == XML_DOCUMENT_NODE) ?
        (void (*) (xmlNodePtr)) xmlFreeDoc : xmlFreeNode;

      bytes = xmlNodeDump(buf, NULL, cur_copy, 0, 0);
      if (bytes == -1 || xmlerrcxt->err_occurred)
        xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
              "could not dump node");

      result = xmlBuffer_to_xmltype(buf);
    }
    PG_FINALLY();
    {
      if (nodefree)
        nodefree(cur_copy);
      if (buf)
        xmlBufferFree(buf);
    }
    PG_END_TRY();
  }
  else
  {
    volatile xmlChar *str = NULL;

    PG_TRY();
    {
      char     *escaped;

      str = xmlXPathCastNodeToString(cur);
      if (str == NULL || xmlerrcxt->err_occurred)
        xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
              "could not allocate xmlChar");

      /* Here we rely on XML having the same representation as TEXT */
      escaped = escape_xml((char *) str);

      result = (xmltype *) cstring_to_text(escaped);
      pfree(escaped);
    }
    PG_FINALLY();
    {
      if (str)
        xmlFree((xmlChar *) str);
    }
    PG_END_TRY();
  }

  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_nitems
 * 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;
  size_t    xmldecl_len = 0;
  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_builtin(namespaces, TEXTOID,
                  &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_ANY_EXHDR(xpath_expr_text);
  if (xpath_len == 0)
    ereport(ERROR,
        (errcode(ERRCODE_INVALID_ARGUMENT_FOR_XQUERY),
         errmsg("empty XPath expression")));

  string = pg_xmlCharStrndup(datastr, len);
  xpath_expr = pg_xmlCharStrndup(VARDATA_ANY(xpath_expr_text), xpath_len);

  /*
   * In a UTF8 database, skip any xml declaration, which might assert
   * another encoding.  Ignore parse_xml_decl() failure, letting
   * xmlCtxtReadMemory() report parse errors.  Documentation disclaims
   * xpath() support for non-ASCII data in non-UTF8 databases, so leave
   * those scenarios bug-compatible with historical behavior.
   */
  if (GetDatabaseEncoding() == PG_UTF8)
    parse_xml_decl(string, &xmldecl_len, NULL, NULL, NULL);

  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 + xmldecl_len,
                len - xmldecl_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 = (xmlNodePtr) doc;

    /* 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)));
      }
    }

    /*
     * Note: here and elsewhere, be careful to use xmlXPathCtxtCompile not
     * xmlXPathCompile.  In libxml2 2.13.3 and older, the latter function
     * fails to defend itself against recursion-to-stack-overflow.  See
     * https://gitlab.gnome.org/GNOME/libxml2/-/issues/799
     */
    xpathcomp = xmlXPathCtxtCompile(xpathctx, xpath_expr);
    if (xpathcomp == NULL || xmlerrcxt->err_occurred)
      xml_ereport(xmlerrcxt, ERROR, ERRCODE_INVALID_ARGUMENT_FOR_XQUERY,
            "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_INVALID_ARGUMENT_FOR_XQUERY,
            "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_PP(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_DATUM(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_PP(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_PP(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)
{
  xmlDocPtr doc;
  ErrorSaveContext escontext = {T_ErrorSaveContext};

  /*
   * We'll report "true" if no soft error is reported by xml_parse().
   */
  doc = xml_parse(data, xmloption_arg, true,
          GetDatabaseEncoding(), NULL, NULL, (Node *) &escontext);
  if (doc)
    xmlFreeDoc(doc);

  return !escontext.error_occurred;
}
#endif

Datum
xml_is_well_formed(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
  text     *data = PG_GETARG_TEXT_PP(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_PP(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_PP(0);

  PG_RETURN_BOOL(wellformed_xml(data, XMLOPTION_CONTENT));
#else
  NO_XML_SUPPORT();
  return 0;
#endif              /* not USE_LIBXML */
}

/*
 * support functions for XMLTABLE
 *
 */
#ifdef USE_LIBXML

/*
 * Returns private data from executor state. Ensure validity by check with
 * MAGIC number.
 */
static inline XmlTableBuilderData *
GetXmlTableBuilderPrivateData(TableFuncScanState *state, const char *fname)
{
  XmlTableBuilderData *result;

  if (!IsA(state, TableFuncScanState))
    elog(ERROR, "%s called with invalid TableFuncScanState", fname);
  result = (XmlTableBuilderData *) state->opaque;
  if (result->magic != XMLTABLE_CONTEXT_MAGIC)
    elog(ERROR, "%s called with invalid TableFuncScanState", fname);

  return result;
}
#endif

/*
 * XmlTableInitOpaque
 *    Fill in TableFuncScanState->opaque for XmlTable processor; initialize
 *    the XML parser.
 *
 * Note: Because we call pg_xml_init() here and pg_xml_done() in
 * XmlTableDestroyOpaque, it is critical for robustness that no other
 * executor nodes run until this node is processed to completion.  Caller
 * must execute this to completion (probably filling a tuplestore to exhaust
 * this node in a single pass) instead of using row-per-call mode.
 */
static void
XmlTableInitOpaque(TableFuncScanState *state, int natts)
{
#ifdef USE_LIBXML
  volatile xmlParserCtxtPtr ctxt = NULL;
  XmlTableBuilderData *xtCxt;
  PgXmlErrorContext *xmlerrcxt;

  xtCxt = palloc0(sizeof(XmlTableBuilderData));
  xtCxt->magic = XMLTABLE_CONTEXT_MAGIC;
  xtCxt->natts = natts;
  xtCxt->xpathscomp = palloc0(sizeof(xmlXPathCompExprPtr) * natts);

  xmlerrcxt = pg_xml_init(PG_XML_STRICTNESS_ALL);

  PG_TRY();
  {
    xmlInitParser();

    ctxt = xmlNewParserCtxt();
    if (ctxt == NULL || xmlerrcxt->err_occurred)
      xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
            "could not allocate parser context");
  }
  PG_CATCH();
  {
    if (ctxt != NULL)
      xmlFreeParserCtxt(ctxt);

    pg_xml_done(xmlerrcxt, true);

    PG_RE_THROW();
  }
  PG_END_TRY();

  xtCxt->xmlerrcxt = xmlerrcxt;
  xtCxt->ctxt = ctxt;

  state->opaque = xtCxt;
#else
  NO_XML_SUPPORT();
#endif              /* not USE_LIBXML */
}

/*
 * XmlTableSetDocument
 *    Install the input document
 */
static void
XmlTableSetDocument(TableFuncScanState *state, Datum value)
{
#ifdef USE_LIBXML
  XmlTableBuilderData *xtCxt;
  xmltype    *xmlval = DatumGetXmlP(value);
  char     *str;
  xmlChar    *xstr;
  int     length;
  volatile xmlDocPtr doc = NULL;
  volatile xmlXPathContextPtr xpathcxt = NULL;

  xtCxt = GetXmlTableBuilderPrivateData(state, "XmlTableSetDocument");

  /*
   * Use out function for casting to string (remove encoding property). See
   * comment in xml_out.
   */
  str = xml_out_internal(xmlval, 0);

  length = strlen(str);
  xstr = pg_xmlCharStrndup(str, length);

  PG_TRY();
  {
    doc = xmlCtxtReadMemory(xtCxt->ctxt, (char *) xstr, length, NULL, NULL, 0);
    if (doc == NULL || xtCxt->xmlerrcxt->err_occurred)
      xml_ereport(xtCxt->xmlerrcxt, ERROR, ERRCODE_INVALID_XML_DOCUMENT,
            "could not parse XML document");
    xpathcxt = xmlXPathNewContext(doc);
    if (xpathcxt == NULL || xtCxt->xmlerrcxt->err_occurred)
      xml_ereport(xtCxt->xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
            "could not allocate XPath context");
    xpathcxt->node = (xmlNodePtr) doc;
  }
  PG_CATCH();
  {
    if (xpathcxt != NULL)
      xmlXPathFreeContext(xpathcxt);
    if (doc != NULL)
      xmlFreeDoc(doc);

    PG_RE_THROW();
  }
  PG_END_TRY();

  xtCxt->doc = doc;
  xtCxt->xpathcxt = xpathcxt;
#else
  NO_XML_SUPPORT();
#endif              /* not USE_LIBXML */
}

/*
 * XmlTableSetNamespace
 *    Add a namespace declaration
 */
static void
XmlTableSetNamespace(TableFuncScanState *state, const char *name, const char *uri)
{
#ifdef USE_LIBXML
  XmlTableBuilderData *xtCxt;

  if (name == NULL)
    ereport(ERROR,
        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
         errmsg("DEFAULT namespace is not supported")));
  xtCxt = GetXmlTableBuilderPrivateData(state, "XmlTableSetNamespace");

  if (xmlXPathRegisterNs(xtCxt->xpathcxt,
               pg_xmlCharStrndup(name, strlen(name)),
               pg_xmlCharStrndup(uri, strlen(uri))))
    xml_ereport(xtCxt->xmlerrcxt, ERROR, ERRCODE_INVALID_ARGUMENT_FOR_XQUERY,
          "could not set XML namespace");
#else
  NO_XML_SUPPORT();
#endif              /* not USE_LIBXML */
}

/*
 * XmlTableSetRowFilter
 *    Install the row-filter Xpath expression.
 */
static void
XmlTableSetRowFilter(TableFuncScanState *state, const char *path)
{
#ifdef USE_LIBXML
  XmlTableBuilderData *xtCxt;
  xmlChar    *xstr;

  xtCxt = GetXmlTableBuilderPrivateData(state, "XmlTableSetRowFilter");

  if (*path == '\0')
    ereport(ERROR,
        (errcode(ERRCODE_INVALID_ARGUMENT_FOR_XQUERY),
         errmsg("row path filter must not be empty string")));

  xstr = pg_xmlCharStrndup(path, strlen(path));

  /* We require XmlTableSetDocument to have been done already */
  Assert(xtCxt->xpathcxt != NULL);

  xtCxt->xpathcomp = xmlXPathCtxtCompile(xtCxt->xpathcxt, xstr);
  if (xtCxt->xpathcomp == NULL || xtCxt->xmlerrcxt->err_occurred)
    xml_ereport(xtCxt->xmlerrcxt, ERROR, ERRCODE_INVALID_ARGUMENT_FOR_XQUERY,
          "invalid XPath expression");
#else
  NO_XML_SUPPORT();
#endif              /* not USE_LIBXML */
}

/*
 * XmlTableSetColumnFilter
 *    Install the column-filter Xpath expression, for the given column.
 */
static void
XmlTableSetColumnFilter(TableFuncScanState *state, const char *path, int colnum)
{
#ifdef USE_LIBXML
  XmlTableBuilderData *xtCxt;
  xmlChar    *xstr;

  Assert(PointerIsValid(path));

  xtCxt = GetXmlTableBuilderPrivateData(state, "XmlTableSetColumnFilter");

  if (*path == '\0')
    ereport(ERROR,
        (errcode(ERRCODE_INVALID_ARGUMENT_FOR_XQUERY),
         errmsg("column path filter must not be empty string")));

  xstr = pg_xmlCharStrndup(path, strlen(path));

  /* We require XmlTableSetDocument to have been done already */
  Assert(xtCxt->xpathcxt != NULL);

  xtCxt->xpathscomp[colnum] = xmlXPathCtxtCompile(xtCxt->xpathcxt, xstr);
  if (xtCxt->xpathscomp[colnum] == NULL || xtCxt->xmlerrcxt->err_occurred)
    xml_ereport(xtCxt->xmlerrcxt, ERROR, ERRCODE_INVALID_ARGUMENT_FOR_XQUERY,
          "invalid XPath expression");
#else
  NO_XML_SUPPORT();
#endif              /* not USE_LIBXML */
}

/*
 * XmlTableFetchRow
 *    Prepare the next "current" tuple for upcoming GetValue calls.
 *    Returns false if the row-filter expression returned no more rows.
 */
static bool
XmlTableFetchRow(TableFuncScanState *state)
{
#ifdef USE_LIBXML
  XmlTableBuilderData *xtCxt;

  xtCxt = GetXmlTableBuilderPrivateData(state, "XmlTableFetchRow");

  /* Propagate our own error context to libxml2 */
  xmlSetStructuredErrorFunc(xtCxt->xmlerrcxt, xml_errorHandler);

  if (xtCxt->xpathobj == NULL)
  {
    xtCxt->xpathobj = xmlXPathCompiledEval(xtCxt->xpathcomp, xtCxt->xpathcxt);
    if (xtCxt->xpathobj == NULL || xtCxt->xmlerrcxt->err_occurred)
      xml_ereport(xtCxt->xmlerrcxt, ERROR, ERRCODE_INVALID_ARGUMENT_FOR_XQUERY,
            "could not create XPath object");

    xtCxt->row_count = 0;
  }

  if (xtCxt->xpathobj->type == XPATH_NODESET)
  {
    if (xtCxt->xpathobj->nodesetval != NULL)
    {
      if (xtCxt->row_count++ < xtCxt->xpathobj->nodesetval->nodeNr)
        return true;
    }
  }

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

/*
 * XmlTableGetValue
 *    Return the value for column number 'colnum' for the current row.  If
 *    column -1 is requested, return representation of the whole row.
 *
 * This leaks memory, so be sure to reset often the context in which it's
 * called.
 */
static Datum
XmlTableGetValue(TableFuncScanState *state, int colnum,
         Oid typid, int32 typmod, bool *isnull)
{
#ifdef USE_LIBXML
  Datum   result = (Datum) 0;
  XmlTableBuilderData *xtCxt;
  volatile xmlXPathObjectPtr xpathobj = NULL;

  xtCxt = GetXmlTableBuilderPrivateData(state, "XmlTableGetValue");

  Assert(xtCxt->xpathobj &&
       xtCxt->xpathobj->type == XPATH_NODESET &&
       xtCxt->xpathobj->nodesetval != NULL);

  /* Propagate our own error context to libxml2 */
  xmlSetStructuredErrorFunc(xtCxt->xmlerrcxt, xml_errorHandler);

  *isnull = false;

  Assert(xtCxt->xpathscomp[colnum] != NULL);

  PG_TRY();
  {
    xmlNodePtr  cur;
    char     *cstr = NULL;

    /* Set current node as entry point for XPath evaluation */
    cur = xtCxt->xpathobj->nodesetval->nodeTab[xtCxt->row_count - 1];
    xtCxt->xpathcxt->node = cur;

    /* Evaluate column path */
    xpathobj = xmlXPathCompiledEval(xtCxt->xpathscomp[colnum], xtCxt->xpathcxt);
    if (xpathobj == NULL || xtCxt->xmlerrcxt->err_occurred)
      xml_ereport(xtCxt->xmlerrcxt, ERROR, ERRCODE_INVALID_ARGUMENT_FOR_XQUERY,
            "could not create XPath object");

    /*
     * There are four possible cases, depending on the number of nodes
     * returned by the XPath expression and the type of the target column:
     * a) XPath returns no nodes.  b) The target type is XML (return all
     * as XML).  For non-XML return types:  c) One node (return content).
     * d) Multiple nodes (error).
     */
    if (xpathobj->type == XPATH_NODESET)
    {
      int     count = 0;

      if (xpathobj->nodesetval != NULL)
        count = xpathobj->nodesetval->nodeNr;

      if (xpathobj->nodesetval == NULL || count == 0)
      {
        *isnull = true;
      }
      else
      {
        if (typid == XMLOID)
        {
          text     *textstr;
          StringInfoData str;

          /* Concatenate serialized values */
          initStringInfo(&str);
          for (int i = 0; i < count; i++)
          {
            textstr =
              xml_xmlnodetoxmltype(xpathobj->nodesetval->nodeTab[i],
                         xtCxt->xmlerrcxt);

            appendStringInfoText(&str, textstr);
          }
          cstr = str.data;
        }
        else
        {
          xmlChar    *str;

          if (count > 1)
            ereport(ERROR,
                (errcode(ERRCODE_CARDINALITY_VIOLATION),
                 errmsg("more than one value returned by column XPath expression")));

          str = xmlXPathCastNodeSetToString(xpathobj->nodesetval);
          cstr = str ? xml_pstrdup_and_free(str) : "";
        }
      }
    }
    else if (xpathobj->type == XPATH_STRING)
    {
      /* Content should be escaped when target will be XML */
      if (typid == XMLOID)
        cstr = escape_xml((char *) xpathobj->stringval);
      else
        cstr = (char *) xpathobj->stringval;
    }
    else if (xpathobj->type == XPATH_BOOLEAN)
    {
      char    typcategory;
      bool    typispreferred;
      xmlChar    *str;

      /* Allow implicit casting from boolean to numbers */
      get_type_category_preferred(typid, &typcategory, &typispreferred);

      if (typcategory != TYPCATEGORY_NUMERIC)
        str = xmlXPathCastBooleanToString(xpathobj->boolval);
      else
        str = xmlXPathCastNumberToString(xmlXPathCastBooleanToNumber(xpathobj->boolval));

      cstr = xml_pstrdup_and_free(str);
    }
    else if (xpathobj->type == XPATH_NUMBER)
    {
      xmlChar    *str;

      str = xmlXPathCastNumberToString(xpathobj->floatval);
      cstr = xml_pstrdup_and_free(str);
    }
    else
      elog(ERROR, "unexpected XPath object type %u", xpathobj->type);

    /*
     * By here, either cstr contains the result value, or the isnull flag
     * has been set.
     */
    Assert(cstr || *isnull);

    if (!*isnull)
      result = InputFunctionCall(&state->in_functions[colnum],
                     cstr,
                     state->typioparams[colnum],
                     typmod);
  }
  PG_FINALLY();
  {
    if (xpathobj != NULL)
      xmlXPathFreeObject(xpathobj);
  }
  PG_END_TRY();

  return result;
#else
  NO_XML_SUPPORT();
  return 0;
#endif              /* not USE_LIBXML */
}

/*
 * XmlTableDestroyOpaque
 *    Release all libxml2 resources
 */
static void
XmlTableDestroyOpaque(TableFuncScanState *state)
{
#ifdef USE_LIBXML
  XmlTableBuilderData *xtCxt;

  xtCxt = GetXmlTableBuilderPrivateData(state, "XmlTableDestroyOpaque");

  /* Propagate our own error context to libxml2 */
  xmlSetStructuredErrorFunc(xtCxt->xmlerrcxt, xml_errorHandler);

  if (xtCxt->xpathscomp != NULL)
  {
    int     i;

    for (i = 0; i < xtCxt->natts; i++)
      if (xtCxt->xpathscomp[i] != NULL)
        xmlXPathFreeCompExpr(xtCxt->xpathscomp[i]);
  }

  if (xtCxt->xpathobj != NULL)
    xmlXPathFreeObject(xtCxt->xpathobj);
  if (xtCxt->xpathcomp != NULL)
    xmlXPathFreeCompExpr(xtCxt->xpathcomp);
  if (xtCxt->xpathcxt != NULL)
    xmlXPathFreeContext(xtCxt->xpathcxt);
  if (xtCxt->doc != NULL)
    xmlFreeDoc(xtCxt->doc);
  if (xtCxt->ctxt != NULL)
    xmlFreeParserCtxt(xtCxt->ctxt);

  pg_xml_done(xtCxt->xmlerrcxt, true);

  /* not valid anymore */
  xtCxt->magic = 0;
  state->opaque = NULL;

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

Coverage Report

Created: 2025-08-12 06:43