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XPath fixes:
- Function renamed to "xpath".
- Function is now strict, per discussion.
- Return empty array in case when XPath expression detects nothing
(previously, NULL was returned in such case), per discussion.
- (bugfix) Work with fragments with prologue: select xpath('/a',
'<?xml version="1.0"?><a /><b />'); // now XML datum is always wrapped
with dummy <x>...</x>, XML prologue simply goes away (if any).
- Some cleanup.
Nikolay Samokhvalov
Some code cleanup and documentation work by myself.
This commit is contained in:
Peter Eisentraut
@ -7,7 +7,7 @@
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* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/backend/utils/adt/xml.c,v 1.42 2007/04/06 04:21:43 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/utils/adt/xml.c,v 1.43 2007/05/21 17:10:29 petere Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -2991,90 +2991,94 @@ xml_xmlnodetoxmltype(xmlNodePtr cur)
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}
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#endif
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/*
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* Evaluate XPath expression and return array of XML values.
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* As we have no support of XQuery sequences yet, this functions seems
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* to be the most useful one (array of XML functions plays a role of
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* some kind of substritution for XQuery sequences).
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*
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* Workaround here: we parse XML data in different way to allow XPath for
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* fragments (see "XPath for fragment" TODO comment inside).
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*/
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Datum
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xmlpath(PG_FUNCTION_ARGS)
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xpath(PG_FUNCTION_ARGS)
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{
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#ifdef USE_LIBXML
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ArrayBuildState *astate = NULL;
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text *xpath_expr_text = PG_GETARG_TEXT_P(0);
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xmltype *data = PG_GETARG_XML_P(1);
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ArrayType *namespaces = PG_GETARG_ARRAYTYPE_P(2);
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ArrayBuildState *astate = NULL;
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xmlParserCtxtPtr ctxt = NULL;
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xmlDocPtr doc = NULL;
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xmlXPathContextPtr xpathctx = NULL;
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xmlXPathCompExprPtr xpathcomp = NULL;
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xmlXPathObjectPtr xpathobj = NULL;
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int32 len, xpath_len;
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xmlChar *string, *xpath_expr;
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bool res_is_null = FALSE;
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int i;
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xmltype *data;
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text *xpath_expr_text;
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ArrayType *namespaces;
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int *dims, ndims, ns_count = 0, bitmask = 1;
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char *ptr;
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bits8 *bitmap;
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char **ns_names = NULL, **ns_uris = NULL;
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int16 typlen;
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bool typbyval;
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char typalign;
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/* the function is not strict, we must check first two args */
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if (PG_ARGISNULL(0) || PG_ARGISNULL(1))
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PG_RETURN_NULL();
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xpath_expr_text = PG_GETARG_TEXT_P(0);
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data = PG_GETARG_XML_P(1);
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/* Namespace mappings passed as text[].
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* Assume that 2-dimensional array has been passed,
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* the 1st subarray is array of names, the 2nd -- array of URIs,
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* example: ARRAY[ARRAY['myns', 'myns2'], ARRAY['http://example.com', 'http://example2.com']].
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int32 len;
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int32 xpath_len;
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xmlChar *string;
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xmlChar *xpath_expr;
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int i;
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int res_nitems;
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int ndim;
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int ns_count;
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char **ns_names;
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char **ns_uris;
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/*
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* Namespace mappings are passed as text[]. If an empty array is
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* passed (ndim = 0, "0-dimentional"), then there are no namespace
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* mappings. Else, a 2-dimentional array with length of the
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* second axis being equal to 2 should be passed, i.e., every
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* subarray contains 2 elements, the first element defining the
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* name, the second one the URI. Example: ARRAY[ARRAY['myns',
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* 'http://example.com'], ARRAY['myns2', 'http://example2.com']].
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*/
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if (!PG_ARGISNULL(2))
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ndim = ARR_NDIM(namespaces);
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if (ndim != 0)
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{
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namespaces = PG_GETARG_ARRAYTYPE_P(2);
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ndims = ARR_NDIM(namespaces);
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bits8 *bitmap;
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int bitmask;
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int16 typlen;
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bool typbyval;
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char typalign;
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char *ptr;
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int *dims;
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dims = ARR_DIMS(namespaces);
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/* Sanity check */
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if (ndims != 2)
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ereport(ERROR, (errmsg("invalid array passed for namespace mappings"),
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errdetail("Only 2-dimensional array may be used for namespace mappings.")));
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if (ndim != 2 || dims[1] != 2)
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ereport(ERROR, (errmsg("invalid array for XML namespace mapping"),
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errdetail("The array must be two-dimensional with length of the second axis equal to 2."),
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errcode(ERRCODE_DATA_EXCEPTION)));
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Assert(ARR_ELEMTYPE(namespaces) == TEXTOID);
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ns_count = ArrayGetNItems(ndims, dims) / 2;
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ns_count = ArrayGetNItems(ndim, dims) / 2; /* number of NS mappings */
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get_typlenbyvalalign(ARR_ELEMTYPE(namespaces),
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&typlen, &typbyval, &typalign);
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ns_names = (char **) palloc(ns_count * sizeof(char *));
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ns_uris = (char **) palloc(ns_count * sizeof(char *));
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ns_names = palloc(ns_count * sizeof(char *));
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ns_uris = palloc(ns_count * sizeof(char *));
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ptr = ARR_DATA_PTR(namespaces);
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bitmap = ARR_NULLBITMAP(namespaces);
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bitmask = 1;
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for (i = 0; i < ns_count * 2; i++)
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{
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if (bitmap && (*bitmap & bitmask) == 0)
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ereport(ERROR, (errmsg("neither namespace nor URI may be NULL"))); /* TODO: better message */
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ereport(ERROR, (errmsg("neither namespace name nor URI may be null")));
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else
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{
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if (i < ns_count)
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ns_names[i] = DatumGetCString(DirectFunctionCall1(textout,
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PointerGetDatum(ptr)));
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if (i % 2 == 0)
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ns_names[i / 2] = DatumGetCString(DirectFunctionCall1(textout,
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PointerGetDatum(ptr)));
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else
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ns_uris[i - ns_count] = DatumGetCString(DirectFunctionCall1(textout,
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PointerGetDatum(ptr)));
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ns_uris[i / 2] = DatumGetCString(DirectFunctionCall1(textout,
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PointerGetDatum(ptr)));
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ptr = att_addlength_pointer(ptr, typlen, ptr);
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ptr = (char *) att_align_nominal(ptr, typalign);
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}
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/* advance bitmap pointer if any */
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if (bitmap)
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{
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@ -3087,37 +3091,55 @@ xmlpath(PG_FUNCTION_ARGS)
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}
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}
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}
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else
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{
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ns_count = 0;
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ns_names = NULL;
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ns_uris = NULL;
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}
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len = VARSIZE(data) - VARHDRSZ;
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xpath_len = VARSIZE(xpath_expr_text) - VARHDRSZ;
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if (xpath_len == 0)
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ereport(ERROR, (errmsg("empty XPath expression")));
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if (xmlStrncmp((xmlChar *) VARDATA(data), (xmlChar *) "<?xml", 5) == 0)
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ereport(ERROR, (errmsg("empty XPath expression"),
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errcode(ERRCODE_DATA_EXCEPTION)));
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/*
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* To handle both documents and fragments, regardless of the fact
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* whether the XML datum has a single root (XML well-formedness),
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* we wrap the XML datum in a dummy element (<x>...</x>) and
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* extend the XPath expression accordingly. To do it, throw away
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* the XML prolog, if any.
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*/
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if ((len > 4) && xmlStrncmp((xmlChar *) VARDATA(data), (xmlChar *) "<?xml", 5) == 0)
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{
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string = palloc(len + 1);
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memcpy(string, VARDATA(data), len);
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string[len] = '\0';
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xpath_expr = palloc(xpath_len + 1);
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memcpy(xpath_expr, VARDATA(xpath_expr_text), xpath_len);
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xpath_expr[xpath_len] = '\0';
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i = 5;
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while ((i < len) && (('?' != (VARDATA(data))[i - 1]) || ('>' != (VARDATA(data))[i])))
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i++;
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if (i == len)
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xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
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"could not parse XML data");
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++i;
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string = xmlStrncatNew((xmlChar *) "<x>", (xmlChar *) VARDATA(data) + i, len - i);
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}
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else
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{
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/* use "<x>...</x>" as dummy root element to enable XPath for fragments */
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/* TODO: (XPath for fragment) find better solution to work with XML fragment! */
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string = xmlStrncatNew((xmlChar *) "<x>", (xmlChar *) VARDATA(data), len);
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string = xmlStrncat(string, (xmlChar *) "</x>", 5);
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len += 7;
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xpath_expr = xmlStrncatNew((xmlChar *) "/x", (xmlChar *) VARDATA(xpath_expr_text), xpath_len);
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len += 2;
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}
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string = xmlStrncat(string, (xmlChar *) "</x>", 5);
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len += 7;
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xpath_expr = xmlStrncatNew((xmlChar *) "/x", (xmlChar *) VARDATA(xpath_expr_text), xpath_len);
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xpath_len += 2;
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xml_init();
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PG_TRY();
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{
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/* redundant XML parsing (two parsings for the same value in the same session are possible) */
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/*
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* redundant XML parsing (two parsings for the same value *
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* during one command execution are possible)
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*/
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ctxt = xmlNewParserCtxt();
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if (ctxt == NULL)
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xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
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@ -3133,34 +3155,33 @@ xmlpath(PG_FUNCTION_ARGS)
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xpathctx->node = xmlDocGetRootElement(doc);
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if (xpathctx->node == NULL)
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xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
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"could not find root XML element");
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"could not find root XML element");
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/* register namespaces, if any */
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if ((ns_count > 0) && ns_names && ns_uris)
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for (i = 0; i < ns_count; i++)
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if (0 != xmlXPathRegisterNs(xpathctx, (xmlChar *) ns_names[i], (xmlChar *) ns_uris[i]))
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ereport(ERROR,
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(errmsg("could not register XML namespace with prefix=\"%s\" and href=\"%s\"", ns_names[i], ns_uris[i])));
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ereport(ERROR,
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(errmsg("could not register XML namespace with name \"%s\" and URI \"%s\"",
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ns_names[i], ns_uris[i])));
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xpathcomp = xmlXPathCompile(xpath_expr);
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if (xpathcomp == NULL)
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xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
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"invalid XPath expression"); /* TODO: show proper XPath error details */
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xpathobj = xmlXPathCompiledEval(xpathcomp, xpathctx);
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xmlXPathFreeCompExpr(xpathcomp);
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if (xpathobj == NULL)
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ereport(ERROR, (errmsg("could not create XPath object")));
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ereport(ERROR, (errmsg("could not create XPath object"))); /* TODO: reason? */
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/* return empty array in cases when nothing is found */
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if (xpathobj->nodesetval == NULL)
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res_is_null = TRUE;
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if (!res_is_null && xpathobj->nodesetval->nodeNr == 0)
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/* TODO maybe empty array should be here, not NULL? (if so -- fix segfault) */
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/*PG_RETURN_ARRAYTYPE_P(makeArrayResult(astate, CurrentMemoryContext));*/
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res_is_null = TRUE;
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if (!res_is_null)
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res_nitems = 0;
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else
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res_nitems = xpathobj->nodesetval->nodeNr;
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if (res_nitems)
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for (i = 0; i < xpathobj->nodesetval->nodeNr; i++)
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{
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Datum elem;
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@ -3170,7 +3191,7 @@ xmlpath(PG_FUNCTION_ARGS)
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elemisnull, XMLOID,
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CurrentMemoryContext);
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}
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xmlXPathFreeObject(xpathobj);
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xmlXPathFreeContext(xpathctx);
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xmlFreeParserCtxt(ctxt);
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@ -3194,15 +3215,11 @@ xmlpath(PG_FUNCTION_ARGS)
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PG_RE_THROW();
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}
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PG_END_TRY();
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if (res_is_null)
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{
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PG_RETURN_NULL();
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}
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if (res_nitems == 0)
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PG_RETURN_ARRAYTYPE_P(construct_empty_array(XMLOID));
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else
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{
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PG_RETURN_ARRAYTYPE_P(makeArrayResult(astate, CurrentMemoryContext));
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}
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#else
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NO_XML_SUPPORT();
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return 0;
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