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postgresql/contrib/xml2/xpath.c

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/*
* contrib/xml2/xpath.c
*
* Parser interface for DOM-based parser (libxml) rather than
* stream-based SAX-type parser
*/
#include "postgres.h"
#include "access/htup_details.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;
/* 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* Note: this has been superseded by a core function.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_PP(0); /* document buffer */
bool result = false;
int32 docsize = VARSIZE_ANY_EXHDR(t);
xmlDocPtr doctree;
PgXmlErrorContext *xmlerrcxt;
xmlerrcxt = pgxml_parser_init(PG_XML_STRICTNESS_LEGACY);
PG_TRY();
{
doctree = xmlParseMemory((char *) VARDATA_ANY(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_PP(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_PP(0);
text *xpathsupp = PG_GETARG_TEXT_PP(1); /* XPath expression */
xmlChar *toptag = pgxml_texttoxmlchar(PG_GETARG_TEXT_PP(2));
xmlChar *septag = pgxml_texttoxmlchar(PG_GETARG_TEXT_PP(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_PP(0);
text *xpathsupp = PG_GETARG_TEXT_PP(1); /* XPath expression */
xmlChar *plainsep = pgxml_texttoxmlchar(PG_GETARG_TEXT_PP(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_PP(0);
text *xpathsupp = PG_GETARG_TEXT_PP(1); /* XPath expression */
xmlChar *xpath;
int32 pathsize;
text *xpres;
xmlXPathObjectPtr res;
xpath_workspace workspace;
pathsize = VARSIZE_ANY_EXHDR(xpathsupp);
/*
* 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);
memcpy((char *) xpath, "string(", 7);
memcpy((char *) (xpath + 7), VARDATA_ANY(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_PP(0);
text *xpathsupp = PG_GETARG_TEXT_PP(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_PP(0);
text *xpathsupp = PG_GETARG_TEXT_PP(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_ANY_EXHDR(document);
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_ANY(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;
uint64 proc;
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 specified (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;
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 */
uint64 i;
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;
}
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