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

1 files changed, 34 insertions, 22 deletions

diff --git a/contrib/xml2/xslt_proc.c b/contrib/xml2/xslt_proc.c
index f8f7d7263f9..a8e481a3ce8 100644
--- a/contrib/xml2/xslt_proc.c
+++ b/contrib/xml2/xslt_proc.c
@@ -38,7 +38,7 @@ Datum		xslt_process(PG_FUNCTION_ARGS);
 #ifdef USE_LIBXSLT
 
 /* declarations to come from xpath.c */
-extern void pgxml_parser_init(void);
+extern PgXmlErrorContext *pgxml_parser_init(PgXmlStrictness strictness);
 
 /* local defs */
 static const char **parse_params(text *paramstr);
@@ -56,13 +56,14 @@ xslt_process(PG_FUNCTION_ARGS)
 	text	   *ssheet = PG_GETARG_TEXT_P(1);
 	text	   *paramstr;
 	const char **params;
-	xsltStylesheetPtr stylesheet = NULL;
-	xmlDocPtr	doctree;
-	xmlDocPtr	restree;
-	xmlDocPtr	ssdoc = NULL;
-	xmlChar    *resstr;
-	int			resstat;
-	int			reslen;
+	PgXmlErrorContext *xmlerrcxt;
+	volatile xsltStylesheetPtr stylesheet = NULL;
+	volatile xmlDocPtr doctree = NULL;
+	volatile xmlDocPtr restree = NULL;
+	volatile xmlDocPtr ssdoc = NULL;
+	volatile int resstat = -1;
+	xmlChar    *resstr = NULL;
+	int			reslen = 0;
 
 	if (fcinfo->nargs == 3)
 	{
@@ -77,9 +78,11 @@ xslt_process(PG_FUNCTION_ARGS)
 	}
 
 	/* Setup parser */
-	pgxml_parser_init();
+	xmlerrcxt = pgxml_parser_init(PG_XML_STRICTNESS_LEGACY);
 
-	/* Check to see if document is a file or a literal */
+	PG_TRY();
+	{
+		/* Check to see if document is a file or a literal */
 
 	if (VARDATA(doct)[0] == '<')
 		doctree = xmlParseMemory((char *) VARDATA(doct), VARSIZE(doct) - VARHDRSZ);
@@ -87,7 +90,7 @@ xslt_process(PG_FUNCTION_ARGS)
 		doctree = xmlParseFile(text_to_cstring(doct));
 
 	if (doctree == NULL)
-		xml_ereport(ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
+		xml_ereport(xmlerrcxt, ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
 					"error parsing XML document");
 
 	/* Same for stylesheet */
@@ -96,35 +99,44 @@ xslt_process(PG_FUNCTION_ARGS)
 		ssdoc = xmlParseMemory((char *) VARDATA(ssheet),
 							   VARSIZE(ssheet) - VARHDRSZ);
 		if (ssdoc == NULL)
-		{
-			xmlFreeDoc(doctree);
-			xml_ereport(ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
+			xml_ereport(xmlerrcxt, ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
 						"error parsing stylesheet as XML document");
-		}
 
 		stylesheet = xsltParseStylesheetDoc(ssdoc);
 	}
 	else
 		stylesheet = xsltParseStylesheetFile((xmlChar *) text_to_cstring(ssheet));
 
-
 	if (stylesheet == NULL)
-	{
-		xmlFreeDoc(doctree);
-		xsltCleanupGlobals();
-		xml_ereport(ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
+		xml_ereport(xmlerrcxt, ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
 					"failed to parse stylesheet");
-	}
 
 	restree = xsltApplyStylesheet(stylesheet, doctree, params);
 	resstat = xsltSaveResultToString(&resstr, &reslen, restree, stylesheet);
+	}
+	PG_CATCH();
+	{
+		if (stylesheet != NULL)
+			xsltFreeStylesheet(stylesheet);
+		if (restree != NULL)
+			xmlFreeDoc(restree);
+		if (doctree != NULL)
+			xmlFreeDoc(doctree);
+		xsltCleanupGlobals();
+
+		pg_xml_done(xmlerrcxt, true);
+
+		PG_RE_THROW();
+	}
+	PG_END_TRY();
 
 	xsltFreeStylesheet(stylesheet);
 	xmlFreeDoc(restree);
 	xmlFreeDoc(doctree);
-
 	xsltCleanupGlobals();
 
+	pg_xml_done(xmlerrcxt, false);
+
 	if (resstat < 0)
 		PG_RETURN_NULL();