Fix significant memory leak in contrib/xml2 functions.

Most of the functions that execute XPath queries leaked the data structures
created by libxml2.  This memory would not be recovered until end of
session, so it mounts up pretty quickly in any serious use of the feature.
Per report from Pavel Stehule, though this isn't his patch.

Back-patch to all supported branches.

diff --git a/contrib/xml2/xpath.c b/contrib/xml2/xpath.c
index dbf0b76f927125244551e2183a4afbe56d0c9fb0..853dd1f8b34c033afe70ea63ccb4e062b37c3805 100644 (file)
--- a/contrib/xml2/xpath.c
+++ b/contrib/xml2/xpath.c
@@ -40,6 +40,15 @@ Datum        xpath_table(PG_FUNCTION_ARGS);
 
 void       pgxml_parser_init(void);
 
+/* workspace for pgxml_xpath() */
+
+typedef struct
+{
+   xmlDocPtr   doctree;
+   xmlXPathContextPtr ctxt;
+   xmlXPathObjectPtr res;
+} xpath_workspace;
+
 /* local declarations */
 
 static xmlChar *pgxmlNodeSetToText(xmlNodeSetPtr nodeset,
@@ -51,7 +60,10 @@ static text *pgxml_result_to_text(xmlXPathObjectPtr res, xmlChar *toptag,
 
 static xmlChar *pgxml_texttoxmlchar(text *textstring);
 
-static xmlXPathObjectPtr pgxml_xpath(text *document, xmlChar *xpath);
+static xmlXPathObjectPtr pgxml_xpath(text *document, xmlChar *xpath,
+                                    xpath_workspace *workspace);
+
+static void cleanup_workspace(xpath_workspace *workspace);
 
 
 /*
@@ -214,25 +226,22 @@ PG_FUNCTION_INFO_V1(xpath_nodeset);
 Datum
 xpath_nodeset(PG_FUNCTION_ARGS)
 {
-   xmlChar    *xpath,
-              *toptag,
-              *septag;
-   int32       pathsize;
-   text       *xpathsupp,
-              *xpres;
-
-   /* PG_GETARG_TEXT_P(0) is document buffer */
-   xpathsupp = PG_GETARG_TEXT_P(1);    /* XPath expression */
+   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;
 
-   toptag = pgxml_texttoxmlchar(PG_GETARG_TEXT_P(2));
-   septag = pgxml_texttoxmlchar(PG_GETARG_TEXT_P(3));
+   xpath = pgxml_texttoxmlchar(xpathsupp);
 
-   pathsize = VARSIZE(xpathsupp) - VARHDRSZ;
+   res = pgxml_xpath(document, xpath, &workspace);
 
-   xpath = pgxml_texttoxmlchar(xpathsupp);
+   xpres = pgxml_result_to_text(res, toptag, septag, NULL);
 
-   xpres = pgxml_result_to_text(pgxml_xpath(PG_GETARG_TEXT_P(0), xpath),
-                                toptag, septag, NULL);
+   cleanup_workspace(&workspace);
 
    pfree(xpath);
 
@@ -250,23 +259,21 @@ PG_FUNCTION_INFO_V1(xpath_list);
 Datum
 xpath_list(PG_FUNCTION_ARGS)
 {
-   xmlChar    *xpath,
-              *plainsep;
-   int32       pathsize;
-   text       *xpathsupp,
-              *xpres;
-
-   /* PG_GETARG_TEXT_P(0) is document buffer */
-   xpathsupp = PG_GETARG_TEXT_P(1);    /* XPath expression */
+   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;
 
-   plainsep = pgxml_texttoxmlchar(PG_GETARG_TEXT_P(2));
+   xpath = pgxml_texttoxmlchar(xpathsupp);
 
-   pathsize = VARSIZE(xpathsupp) - VARHDRSZ;
+   res = pgxml_xpath(document, xpath, &workspace);
 
-   xpath = pgxml_texttoxmlchar(xpathsupp);
+   xpres = pgxml_result_to_text(res, NULL, NULL, plainsep);
 
-   xpres = pgxml_result_to_text(pgxml_xpath(PG_GETARG_TEXT_P(0), xpath),
-                                NULL, NULL, plainsep);
+   cleanup_workspace(&workspace);
 
    pfree(xpath);
 
@@ -281,13 +288,13 @@ 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       *xpathsupp,
-              *xpres;
-
-   /* PG_GETARG_TEXT_P(0) is document buffer */
-   xpathsupp = PG_GETARG_TEXT_P(1);    /* XPath expression */
+   text       *xpres;
+   xmlXPathObjectPtr res;
+   xpath_workspace workspace;
 
    pathsize = VARSIZE(xpathsupp) - VARHDRSZ;
 
@@ -298,13 +305,16 @@ xpath_string(PG_FUNCTION_ARGS)
    /* We could try casting to string using the libxml function? */
 
    xpath = (xmlChar *) palloc(pathsize + 9);
-   memcpy((char *) (xpath + 7), VARDATA(xpathsupp), pathsize);
    strncpy((char *) xpath, "string(", 7);
+   memcpy((char *) (xpath + 7), VARDATA(xpathsupp), pathsize);
    xpath[pathsize + 7] = ')';
    xpath[pathsize + 8] = '\0';
 
-   xpres = pgxml_result_to_text(pgxml_xpath(PG_GETARG_TEXT_P(0), xpath),
-                                NULL, NULL, NULL);
+   res = pgxml_xpath(document, xpath, &workspace);
+
+   xpres = pgxml_result_to_text(res, NULL, NULL, NULL);
+
+   cleanup_workspace(&workspace);
 
    pfree(xpath);
 
@@ -319,21 +329,17 @@ 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;
-   int32       pathsize;
-   text       *xpathsupp;
    float4      fRes;
-
    xmlXPathObjectPtr res;
-
-   /* PG_GETARG_TEXT_P(0) is document buffer */
-   xpathsupp = PG_GETARG_TEXT_P(1);    /* XPath expression */
-
-   pathsize = VARSIZE(xpathsupp) - VARHDRSZ;
+   xpath_workspace workspace;
 
    xpath = pgxml_texttoxmlchar(xpathsupp);
 
-   res = pgxml_xpath(PG_GETARG_TEXT_P(0), xpath);
+   res = pgxml_xpath(document, xpath, &workspace);
+
    pfree(xpath);
 
    if (res == NULL)
@@ -341,6 +347,8 @@ xpath_number(PG_FUNCTION_ARGS)
 
    fRes = xmlXPathCastToNumber(res);
 
+   cleanup_workspace(&workspace);
+
    if (xmlXPathIsNaN(fRes))
        PG_RETURN_NULL();
 
@@ -353,21 +361,17 @@ 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;
-   int32       pathsize;
-   text       *xpathsupp;
    int         bRes;
-
    xmlXPathObjectPtr res;
-
-   /* PG_GETARG_TEXT_P(0) is document buffer */
-   xpathsupp = PG_GETARG_TEXT_P(1);    /* XPath expression */
-
-   pathsize = VARSIZE(xpathsupp) - VARHDRSZ;
+   xpath_workspace workspace;
 
    xpath = pgxml_texttoxmlchar(xpathsupp);
 
-   res = pgxml_xpath(PG_GETARG_TEXT_P(0), xpath);
+   res = pgxml_xpath(document, xpath, &workspace);
+
    pfree(xpath);
 
    if (res == NULL)
@@ -375,6 +379,8 @@ xpath_bool(PG_FUNCTION_ARGS)
 
    bRes = xmlXPathCastToBoolean(res);
 
+   cleanup_workspace(&workspace);
+
    PG_RETURN_BOOL(bRes);
 }
 
@@ -383,49 +389,61 @@ xpath_bool(PG_FUNCTION_ARGS)
 /* Core function to evaluate XPath query */
 
 static xmlXPathObjectPtr
-pgxml_xpath(text *document, xmlChar *xpath)
+pgxml_xpath(text *document, xmlChar *xpath, xpath_workspace *workspace)
 {
-   xmlDocPtr   doctree;
-   xmlXPathContextPtr ctxt;
+   int32       docsize = VARSIZE(document) - VARHDRSZ;
    xmlXPathObjectPtr res;
    xmlXPathCompExprPtr comppath;
-   int32       docsize;
 
-   docsize = VARSIZE(document) - VARHDRSZ;
+   workspace->doctree = NULL;
+   workspace->ctxt = NULL;
+   workspace->res = NULL;
 
    pgxml_parser_init();
 
-   doctree = xmlParseMemory((char *) VARDATA(document), docsize);
-   if (doctree == NULL)
+   workspace->doctree = xmlParseMemory((char *) VARDATA(document), docsize);
+   if (workspace->doctree == NULL)
        return NULL;            /* not well-formed */
 
-   ctxt = xmlXPathNewContext(doctree);
-   ctxt->node = xmlDocGetRootElement(doctree);
+   workspace->ctxt = xmlXPathNewContext(workspace->doctree);
+   workspace->ctxt->node = xmlDocGetRootElement(workspace->doctree);
 
    /* compile the path */
    comppath = xmlXPathCompile(xpath);
    if (comppath == NULL)
    {
-       xmlFreeDoc(doctree);
+       cleanup_workspace(workspace);
        xml_ereport(ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
                    "XPath Syntax Error");
    }
 
    /* Now evaluate the path expression. */
-   res = xmlXPathCompiledEval(comppath, ctxt);
+   res = xmlXPathCompiledEval(comppath, workspace->ctxt);
+   workspace->res = res;
+
    xmlXPathFreeCompExpr(comppath);
 
    if (res == NULL)
-   {
-       xmlXPathFreeContext(ctxt);
-       xmlFreeDoc(doctree);
+       cleanup_workspace(workspace);
 
-       return NULL;
-   }
-   /* xmlFreeDoc(doctree); */
    return 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,