postgresql/contrib/xml2/xpath.c
Tom Lane cacd42d62c Rewrite libxml error handling to be more robust.
libxml reports some errors (like invalid xmlns attributes) via the error
handler hook, but still returns a success indicator to the library caller.
This causes us to miss some errors that are important to report.  Since the
"generic" error handler hook doesn't know whether the message it's getting
is for an error, warning, or notice, stop using that and instead start
using the "structured" error handler hook, which gets enough information
to be useful.

While at it, arrange to save and restore the error handler hook setting in
each libxml-using function, rather than assuming we can set and forget the
hook.  This should improve the odds of working nicely with third-party
libraries that also use libxml.

In passing, volatile-ize some local variables that get modified within
PG_TRY blocks.  I noticed this while testing with an older gcc version
than I'd previously tried to compile xml.c with.

Florian Pflug and Tom Lane, with extensive review/testing by Noah Misch
2011-07-20 13:03:49 -04:00

857 lines
20 KiB
C

/*
* contrib/xml2/xpath.c
*
* Parser interface for DOM-based parser (libxml) rather than
* stream-based SAX-type parser
*/
#include "postgres.h"
#include "executor/spi.h"
#include "fmgr.h"
#include "funcapi.h"
#include "lib/stringinfo.h"
#include "miscadmin.h"
#include "utils/builtins.h"
#include "utils/xml.h"
/* libxml includes */
#include <libxml/xpath.h>
#include <libxml/tree.h>
#include <libxml/xmlmemory.h>
#include <libxml/xmlerror.h>
#include <libxml/parserInternals.h>
PG_MODULE_MAGIC;
/* externally accessible functions */
Datum xml_is_well_formed(PG_FUNCTION_ARGS);
Datum xml_encode_special_chars(PG_FUNCTION_ARGS);
Datum xpath_nodeset(PG_FUNCTION_ARGS);
Datum xpath_string(PG_FUNCTION_ARGS);
Datum xpath_number(PG_FUNCTION_ARGS);
Datum xpath_bool(PG_FUNCTION_ARGS);
Datum xpath_list(PG_FUNCTION_ARGS);
Datum xpath_table(PG_FUNCTION_ARGS);
/* exported for use by xslt_proc.c */
PgXmlErrorContext *pgxml_parser_init(PgXmlStrictness strictness);
/* workspace for pgxml_xpath() */
typedef struct
{
xmlDocPtr doctree;
xmlXPathContextPtr ctxt;
xmlXPathObjectPtr res;
} xpath_workspace;
/* local declarations */
static xmlChar *pgxmlNodeSetToText(xmlNodeSetPtr nodeset,
xmlChar *toptagname, xmlChar *septagname,
xmlChar *plainsep);
static text *pgxml_result_to_text(xmlXPathObjectPtr res, xmlChar *toptag,
xmlChar *septag, xmlChar *plainsep);
static xmlChar *pgxml_texttoxmlchar(text *textstring);
static xmlXPathObjectPtr pgxml_xpath(text *document, xmlChar *xpath,
xpath_workspace *workspace);
static void cleanup_workspace(xpath_workspace *workspace);
/*
* Initialize for xml parsing.
*
* As with the underlying pg_xml_init function, calls to this MUST be followed
* by a PG_TRY block that guarantees that pg_xml_done is called.
*/
PgXmlErrorContext *
pgxml_parser_init(PgXmlStrictness strictness)
{
PgXmlErrorContext *xmlerrcxt;
/* Set up error handling (we share the core's error handler) */
xmlerrcxt = pg_xml_init(strictness);
/* Note: we're assuming an elog cannot be thrown by the following calls */
/* Initialize libxml */
xmlInitParser();
xmlSubstituteEntitiesDefault(1);
xmlLoadExtDtdDefaultValue = 1;
return xmlerrcxt;
}
/*
* Returns true if document is well-formed
*
* Note: this has been superseded by a core function. We still have to
* have it in the contrib module so that existing SQL-level references
* to the function won't fail; but in normal usage with up-to-date SQL
* definitions for the contrib module, this won't be called.
*/
PG_FUNCTION_INFO_V1(xml_is_well_formed);
Datum
xml_is_well_formed(PG_FUNCTION_ARGS)
{
text *t = PG_GETARG_TEXT_P(0); /* document buffer */
bool result = false;
int32 docsize = VARSIZE(t) - VARHDRSZ;
xmlDocPtr doctree;
PgXmlErrorContext *xmlerrcxt;
xmlerrcxt = pgxml_parser_init(PG_XML_STRICTNESS_LEGACY);
PG_TRY();
{
doctree = xmlParseMemory((char *) VARDATA(t), docsize);
result = (doctree != NULL);
if (doctree != NULL)
xmlFreeDoc(doctree);
}
PG_CATCH();
{
pg_xml_done(xmlerrcxt, true);
PG_RE_THROW();
}
PG_END_TRY();
pg_xml_done(xmlerrcxt, false);
PG_RETURN_BOOL(result);
}
/* Encodes special characters (<, >, &, " and \r) as XML entities */
PG_FUNCTION_INFO_V1(xml_encode_special_chars);
Datum
xml_encode_special_chars(PG_FUNCTION_ARGS)
{
text *tin = PG_GETARG_TEXT_P(0);
text *tout;
xmlChar *ts,
*tt;
ts = pgxml_texttoxmlchar(tin);
tt = xmlEncodeSpecialChars(NULL, ts);
pfree(ts);
tout = cstring_to_text((char *) tt);
xmlFree(tt);
PG_RETURN_TEXT_P(tout);
}
/*
* Function translates a nodeset into a text representation
*
* iterates over each node in the set and calls xmlNodeDump to write it to
* an xmlBuffer -from which an xmlChar * string is returned.
*
* each representation is surrounded by <tagname> ... </tagname>
*
* plainsep is an ordinary (not tag) separator - if used, then nodes are
* cast to string as output method
*/
static xmlChar *
pgxmlNodeSetToText(xmlNodeSetPtr nodeset,
xmlChar *toptagname,
xmlChar *septagname,
xmlChar *plainsep)
{
xmlBufferPtr buf;
xmlChar *result;
int i;
buf = xmlBufferCreate();
if ((toptagname != NULL) && (xmlStrlen(toptagname) > 0))
{
xmlBufferWriteChar(buf, "<");
xmlBufferWriteCHAR(buf, toptagname);
xmlBufferWriteChar(buf, ">");
}
if (nodeset != NULL)
{
for (i = 0; i < nodeset->nodeNr; i++)
{
if (plainsep != NULL)
{
xmlBufferWriteCHAR(buf,
xmlXPathCastNodeToString(nodeset->nodeTab[i]));
/* If this isn't the last entry, write the plain sep. */
if (i < (nodeset->nodeNr) - 1)
xmlBufferWriteChar(buf, (char *) plainsep);
}
else
{
if ((septagname != NULL) && (xmlStrlen(septagname) > 0))
{
xmlBufferWriteChar(buf, "<");
xmlBufferWriteCHAR(buf, septagname);
xmlBufferWriteChar(buf, ">");
}
xmlNodeDump(buf,
nodeset->nodeTab[i]->doc,
nodeset->nodeTab[i],
1, 0);
if ((septagname != NULL) && (xmlStrlen(septagname) > 0))
{
xmlBufferWriteChar(buf, "</");
xmlBufferWriteCHAR(buf, septagname);
xmlBufferWriteChar(buf, ">");
}
}
}
}
if ((toptagname != NULL) && (xmlStrlen(toptagname) > 0))
{
xmlBufferWriteChar(buf, "</");
xmlBufferWriteCHAR(buf, toptagname);
xmlBufferWriteChar(buf, ">");
}
result = xmlStrdup(buf->content);
xmlBufferFree(buf);
return result;
}
/* Translate a PostgreSQL "varlena" -i.e. a variable length parameter
* into the libxml2 representation
*/
static xmlChar *
pgxml_texttoxmlchar(text *textstring)
{
return (xmlChar *) text_to_cstring(textstring);
}
/* Publicly visible XPath functions */
/*
* This is a "raw" xpath function. Check that it returns child elements
* properly
*/
PG_FUNCTION_INFO_V1(xpath_nodeset);
Datum
xpath_nodeset(PG_FUNCTION_ARGS)
{
text *document = PG_GETARG_TEXT_P(0);
text *xpathsupp = PG_GETARG_TEXT_P(1); /* XPath expression */
xmlChar *toptag = pgxml_texttoxmlchar(PG_GETARG_TEXT_P(2));
xmlChar *septag = pgxml_texttoxmlchar(PG_GETARG_TEXT_P(3));
xmlChar *xpath;
text *xpres;
xmlXPathObjectPtr res;
xpath_workspace workspace;
xpath = pgxml_texttoxmlchar(xpathsupp);
res = pgxml_xpath(document, xpath, &workspace);
xpres = pgxml_result_to_text(res, toptag, septag, NULL);
cleanup_workspace(&workspace);
pfree(xpath);
if (xpres == NULL)
PG_RETURN_NULL();
PG_RETURN_TEXT_P(xpres);
}
/*
* The following function is almost identical, but returns the elements in
* a list.
*/
PG_FUNCTION_INFO_V1(xpath_list);
Datum
xpath_list(PG_FUNCTION_ARGS)
{
text *document = PG_GETARG_TEXT_P(0);
text *xpathsupp = PG_GETARG_TEXT_P(1); /* XPath expression */
xmlChar *plainsep = pgxml_texttoxmlchar(PG_GETARG_TEXT_P(2));
xmlChar *xpath;
text *xpres;
xmlXPathObjectPtr res;
xpath_workspace workspace;
xpath = pgxml_texttoxmlchar(xpathsupp);
res = pgxml_xpath(document, xpath, &workspace);
xpres = pgxml_result_to_text(res, NULL, NULL, plainsep);
cleanup_workspace(&workspace);
pfree(xpath);
if (xpres == NULL)
PG_RETURN_NULL();
PG_RETURN_TEXT_P(xpres);
}
PG_FUNCTION_INFO_V1(xpath_string);
Datum
xpath_string(PG_FUNCTION_ARGS)
{
text *document = PG_GETARG_TEXT_P(0);
text *xpathsupp = PG_GETARG_TEXT_P(1); /* XPath expression */
xmlChar *xpath;
int32 pathsize;
text *xpres;
xmlXPathObjectPtr res;
xpath_workspace workspace;
pathsize = VARSIZE(xpathsupp) - VARHDRSZ;
/*
* We encapsulate the supplied path with "string()" = 8 chars + 1 for NUL
* at end
*/
/* We could try casting to string using the libxml function? */
xpath = (xmlChar *) palloc(pathsize + 9);
strncpy((char *) xpath, "string(", 7);
memcpy((char *) (xpath + 7), VARDATA(xpathsupp), pathsize);
xpath[pathsize + 7] = ')';
xpath[pathsize + 8] = '\0';
res = pgxml_xpath(document, xpath, &workspace);
xpres = pgxml_result_to_text(res, NULL, NULL, NULL);
cleanup_workspace(&workspace);
pfree(xpath);
if (xpres == NULL)
PG_RETURN_NULL();
PG_RETURN_TEXT_P(xpres);
}
PG_FUNCTION_INFO_V1(xpath_number);
Datum
xpath_number(PG_FUNCTION_ARGS)
{
text *document = PG_GETARG_TEXT_P(0);
text *xpathsupp = PG_GETARG_TEXT_P(1); /* XPath expression */
xmlChar *xpath;
float4 fRes;
xmlXPathObjectPtr res;
xpath_workspace workspace;
xpath = pgxml_texttoxmlchar(xpathsupp);
res = pgxml_xpath(document, xpath, &workspace);
pfree(xpath);
if (res == NULL)
PG_RETURN_NULL();
fRes = xmlXPathCastToNumber(res);
cleanup_workspace(&workspace);
if (xmlXPathIsNaN(fRes))
PG_RETURN_NULL();
PG_RETURN_FLOAT4(fRes);
}
PG_FUNCTION_INFO_V1(xpath_bool);
Datum
xpath_bool(PG_FUNCTION_ARGS)
{
text *document = PG_GETARG_TEXT_P(0);
text *xpathsupp = PG_GETARG_TEXT_P(1); /* XPath expression */
xmlChar *xpath;
int bRes;
xmlXPathObjectPtr res;
xpath_workspace workspace;
xpath = pgxml_texttoxmlchar(xpathsupp);
res = pgxml_xpath(document, xpath, &workspace);
pfree(xpath);
if (res == NULL)
PG_RETURN_BOOL(false);
bRes = xmlXPathCastToBoolean(res);
cleanup_workspace(&workspace);
PG_RETURN_BOOL(bRes);
}
/* Core function to evaluate XPath query */
static xmlXPathObjectPtr
pgxml_xpath(text *document, xmlChar *xpath, xpath_workspace *workspace)
{
int32 docsize = VARSIZE(document) - VARHDRSZ;
PgXmlErrorContext *xmlerrcxt;
xmlXPathCompExprPtr comppath;
workspace->doctree = NULL;
workspace->ctxt = NULL;
workspace->res = NULL;
xmlerrcxt = pgxml_parser_init(PG_XML_STRICTNESS_LEGACY);
PG_TRY();
{
workspace->doctree = xmlParseMemory((char *) VARDATA(document),
docsize);
if (workspace->doctree != NULL)
{
workspace->ctxt = xmlXPathNewContext(workspace->doctree);
workspace->ctxt->node = xmlDocGetRootElement(workspace->doctree);
/* compile the path */
comppath = xmlXPathCompile(xpath);
if (comppath == NULL)
xml_ereport(xmlerrcxt, ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
"XPath Syntax Error");
/* Now evaluate the path expression. */
workspace->res = xmlXPathCompiledEval(comppath, workspace->ctxt);
xmlXPathFreeCompExpr(comppath);
}
}
PG_CATCH();
{
cleanup_workspace(workspace);
pg_xml_done(xmlerrcxt, true);
PG_RE_THROW();
}
PG_END_TRY();
if (workspace->res == NULL)
cleanup_workspace(workspace);
pg_xml_done(xmlerrcxt, false);
return workspace->res;
}
/* Clean up after processing the result of pgxml_xpath() */
static void
cleanup_workspace(xpath_workspace *workspace)
{
if (workspace->res)
xmlXPathFreeObject(workspace->res);
workspace->res = NULL;
if (workspace->ctxt)
xmlXPathFreeContext(workspace->ctxt);
workspace->ctxt = NULL;
if (workspace->doctree)
xmlFreeDoc(workspace->doctree);
workspace->doctree = NULL;
}
static text *
pgxml_result_to_text(xmlXPathObjectPtr res,
xmlChar *toptag,
xmlChar *septag,
xmlChar *plainsep)
{
xmlChar *xpresstr;
text *xpres;
if (res == NULL)
return NULL;
switch (res->type)
{
case XPATH_NODESET:
xpresstr = pgxmlNodeSetToText(res->nodesetval,
toptag,
septag, plainsep);
break;
case XPATH_STRING:
xpresstr = xmlStrdup(res->stringval);
break;
default:
elog(NOTICE, "unsupported XQuery result: %d", res->type);
xpresstr = xmlStrdup((const xmlChar *) "<unsupported/>");
}
/* Now convert this result back to text */
xpres = cstring_to_text((char *) xpresstr);
/* Free various storage */
xmlFree(xpresstr);
return xpres;
}
/*
* xpath_table is a table function. It needs some tidying (as do the
* other functions here!
*/
PG_FUNCTION_INFO_V1(xpath_table);
Datum
xpath_table(PG_FUNCTION_ARGS)
{
/* Function parameters */
char *pkeyfield = text_to_cstring(PG_GETARG_TEXT_PP(0));
char *xmlfield = text_to_cstring(PG_GETARG_TEXT_PP(1));
char *relname = text_to_cstring(PG_GETARG_TEXT_PP(2));
char *xpathset = text_to_cstring(PG_GETARG_TEXT_PP(3));
char *condition = text_to_cstring(PG_GETARG_TEXT_PP(4));
/* SPI (input tuple) support */
SPITupleTable *tuptable;
HeapTuple spi_tuple;
TupleDesc spi_tupdesc;
/* Output tuple (tuplestore) support */
Tuplestorestate *tupstore = NULL;
TupleDesc ret_tupdesc;
HeapTuple ret_tuple;
ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
AttInMetadata *attinmeta;
MemoryContext per_query_ctx;
MemoryContext oldcontext;
char **values;
xmlChar **xpaths;
char *pos;
const char *pathsep = "|";
int numpaths;
int ret;
int proc;
int i;
int j;
int rownr; /* For issuing multiple rows from one original
* document */
bool had_values; /* To determine end of nodeset results */
StringInfoData query_buf;
PgXmlErrorContext *xmlerrcxt;
volatile xmlDocPtr doctree = NULL;
/* We only have a valid tuple description in table function mode */
if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("set-valued function called in context that cannot accept a set")));
if (rsinfo->expectedDesc == NULL)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("xpath_table must be called as a table function")));
/*
* We want to materialise because it means that we don't have to carry
* libxml2 parser state between invocations of this function
*/
if (!(rsinfo->allowedModes & SFRM_Materialize))
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("xpath_table requires Materialize mode, but it is not "
"allowed in this context")));
/*
* The tuplestore must exist in a higher context than this function call
* (per_query_ctx is used)
*/
per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
oldcontext = MemoryContextSwitchTo(per_query_ctx);
/*
* Create the tuplestore - work_mem is the max in-memory size before a
* file is created on disk to hold it.
*/
tupstore =
tuplestore_begin_heap(rsinfo->allowedModes & SFRM_Materialize_Random,
false, work_mem);
MemoryContextSwitchTo(oldcontext);
/* get the requested return tuple description */
ret_tupdesc = CreateTupleDescCopy(rsinfo->expectedDesc);
/* must have at least one output column (for the pkey) */
if (ret_tupdesc->natts < 1)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("xpath_table must have at least one output column")));
/*
* At the moment we assume that the returned attributes make sense for the
* XPath specififed (i.e. we trust the caller). It's not fatal if they get
* it wrong - the input function for the column type will raise an error
* if the path result can't be converted into the correct binary
* representation.
*/
attinmeta = TupleDescGetAttInMetadata(ret_tupdesc);
/* Set return mode and allocate value space. */
rsinfo->returnMode = SFRM_Materialize;
rsinfo->setDesc = ret_tupdesc;
values = (char **) palloc(ret_tupdesc->natts * sizeof(char *));
xpaths = (xmlChar **) palloc(ret_tupdesc->natts * sizeof(xmlChar *));
/*
* Split XPaths. xpathset is a writable CString.
*
* Note that we stop splitting once we've done all needed for tupdesc
*/
numpaths = 0;
pos = xpathset;
while (numpaths < (ret_tupdesc->natts - 1))
{
xpaths[numpaths++] = (xmlChar *) pos;
pos = strstr(pos, pathsep);
if (pos != NULL)
{
*pos = '\0';
pos++;
}
else
break;
}
/* Now build query */
initStringInfo(&query_buf);
/* Build initial sql statement */
appendStringInfo(&query_buf, "SELECT %s, %s FROM %s WHERE %s",
pkeyfield,
xmlfield,
relname,
condition);
if ((ret = SPI_connect()) < 0)
elog(ERROR, "xpath_table: SPI_connect returned %d", ret);
if ((ret = SPI_exec(query_buf.data, 0)) != SPI_OK_SELECT)
elog(ERROR, "xpath_table: SPI execution failed for query %s",
query_buf.data);
proc = SPI_processed;
/* elog(DEBUG1,"xpath_table: SPI returned %d rows",proc); */
tuptable = SPI_tuptable;
spi_tupdesc = tuptable->tupdesc;
/* Switch out of SPI context */
MemoryContextSwitchTo(oldcontext);
/*
* Check that SPI returned correct result. If you put a comma into one of
* the function parameters, this will catch it when the SPI query returns
* e.g. 3 columns.
*/
if (spi_tupdesc->natts != 2)
{
ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("expression returning multiple columns is not valid in parameter list"),
errdetail("Expected two columns in SPI result, got %d.", spi_tupdesc->natts)));
}
/*
* Setup the parser. This should happen after we are done evaluating the
* query, in case it calls functions that set up libxml differently.
*/
xmlerrcxt = pgxml_parser_init(PG_XML_STRICTNESS_LEGACY);
PG_TRY();
{
/* For each row i.e. document returned from SPI */
for (i = 0; i < proc; i++)
{
char *pkey;
char *xmldoc;
xmlXPathContextPtr ctxt;
xmlXPathObjectPtr res;
xmlChar *resstr;
xmlXPathCompExprPtr comppath;
/* Extract the row data as C Strings */
spi_tuple = tuptable->vals[i];
pkey = SPI_getvalue(spi_tuple, spi_tupdesc, 1);
xmldoc = SPI_getvalue(spi_tuple, spi_tupdesc, 2);
/*
* Clear the values array, so that not-well-formed documents return
* NULL in all columns. Note that this also means that spare columns
* will be NULL.
*/
for (j = 0; j < ret_tupdesc->natts; j++)
values[j] = NULL;
/* Insert primary key */
values[0] = pkey;
/* Parse the document */
if (xmldoc)
doctree = xmlParseMemory(xmldoc, strlen(xmldoc));
else /* treat NULL as not well-formed */
doctree = NULL;
if (doctree == NULL)
{
/* not well-formed, so output all-NULL tuple */
ret_tuple = BuildTupleFromCStrings(attinmeta, values);
tuplestore_puttuple(tupstore, ret_tuple);
heap_freetuple(ret_tuple);
}
else
{
/* New loop here - we have to deal with nodeset results */
rownr = 0;
do
{
/* Now evaluate the set of xpaths. */
had_values = false;
for (j = 0; j < numpaths; j++)
{
ctxt = xmlXPathNewContext(doctree);
ctxt->node = xmlDocGetRootElement(doctree);
/* compile the path */
comppath = xmlXPathCompile(xpaths[j]);
if (comppath == NULL)
xml_ereport(xmlerrcxt, ERROR,
ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
"XPath Syntax Error");
/* Now evaluate the path expression. */
res = xmlXPathCompiledEval(comppath, ctxt);
xmlXPathFreeCompExpr(comppath);
if (res != NULL)
{
switch (res->type)
{
case XPATH_NODESET:
/* We see if this nodeset has enough nodes */
if (res->nodesetval != NULL &&
rownr < res->nodesetval->nodeNr)
{
resstr = xmlXPathCastNodeToString(res->nodesetval->nodeTab[rownr]);
had_values = true;
}
else
resstr = NULL;
break;
case XPATH_STRING:
resstr = xmlStrdup(res->stringval);
break;
default:
elog(NOTICE, "unsupported XQuery result: %d", res->type);
resstr = xmlStrdup((const xmlChar *) "<unsupported/>");
}
/*
* Insert this into the appropriate column in the
* result tuple.
*/
values[j + 1] = (char *) resstr;
}
xmlXPathFreeContext(ctxt);
}
/* Now add the tuple to the output, if there is one. */
if (had_values)
{
ret_tuple = BuildTupleFromCStrings(attinmeta, values);
tuplestore_puttuple(tupstore, ret_tuple);
heap_freetuple(ret_tuple);
}
rownr++;
} while (had_values);
}
if (doctree != NULL)
xmlFreeDoc(doctree);
doctree = NULL;
if (pkey)
pfree(pkey);
if (xmldoc)
pfree(xmldoc);
}
}
PG_CATCH();
{
if (doctree != NULL)
xmlFreeDoc(doctree);
pg_xml_done(xmlerrcxt, true);
PG_RE_THROW();
}
PG_END_TRY();
if (doctree != NULL)
xmlFreeDoc(doctree);
pg_xml_done(xmlerrcxt, false);
tuplestore_donestoring(tupstore);
SPI_finish();
rsinfo->setResult = tupstore;
/*
* SFRM_Materialize mode expects us to return a NULL Datum. The actual
* tuples are in our tuplestore and passed back through rsinfo->setResult.
* rsinfo->setDesc is set to the tuple description that we actually used
* to build our tuples with, so the caller can verify we did what it was
* expecting.
*/
return (Datum) 0;
}