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Check to see whether libxml2 handles error context the way we expect.

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It turns out to be possible to link against a libxml2.so that does this
differently than the version we configured and built against, so we need
a runtime check to avoid bizarre behavior.  Per report from Bernd Helmle.
Patch by Florian Pflug.
This commit is contained in:
Tom Lane 2011-07-26 16:29:53 -04:00
parent e67efb01e8
commit c1420fcf7d
1 changed files with 36 additions and 2 deletions
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38
src/backend/utils/adt/xml.c
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@ -928,6 +928,7 @@ PgXmlErrorContext *
pg_xml_init(PgXmlStrictness strictness)
{
PgXmlErrorContext *errcxt;
void *new_errcxt;
/* Do one-time setup if needed */
pg_xml_init_library();
@ -956,6 +957,34 @@ pg_xml_init(PgXmlStrictness strictness)
xmlSetStructuredErrorFunc((void *) errcxt, xml_errorHandler);
/*
* Verify that xmlSetStructuredErrorFunc set the context variable we
* expected it to. If not, the error context pointer we just saved is not
* the correct thing to restore, and since that leaves us without a way to
* restore the context in pg_xml_done, we must fail.
*
* The only known situation in which this test fails is if we compile with
* headers from a libxml2 that doesn't track the structured error context
* separately (<= 2.7.3), but at runtime use a version that does, or vice
* versa. The libxml2 authors did not treat that change as constituting
* an ABI break, so the LIBXML_TEST_VERSION test in pg_xml_init_library
* fails to protect us from this.
*/
#ifdef HAVE_XMLSTRUCTUREDERRORCONTEXT
new_errcxt = xmlStructuredErrorContext;
#else
new_errcxt = xmlGenericErrorContext;
#endif
if (new_errcxt != (void *) errcxt)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("could not set up XML error handler"),
errhint("This probably indicates that the version of libxml2"
" being used is not compatible with the libxml2"
" header files that PostgreSQL was built with.")));
return errcxt;
}
@ -1494,9 +1523,14 @@ xml_errorHandler(void *data, xmlErrorPtr error)
int level = error->level;
StringInfo errorBuf;
/* Defend against someone passing us a bogus context struct */
/*
* Defend against someone passing us a bogus context struct.
*
* We force a backend exit if this check fails because longjmp'ing out of
* libxml would likely render it unsafe to use further.
*/
if (xmlerrcxt->magic != ERRCXT_MAGIC)
elog(ERROR, "xml_errorHandler called with invalid PgXmlErrorContext");
elog(FATAL, "xml_errorHandler called with invalid PgXmlErrorContext");
/*----------
* Older libxml versions report some errors differently.