[issue6697] Check that _PyUnicode_AsString() result is not NULL

[Marc-Andre Lemburg]

Marc-Andre Lemburg <mal at egenix.com> added the comment:

Alexander Belopolsky wrote:
> 
> Alexander Belopolsky <belopolsky at users.sourceforge.net> added the comment:
> 
> I am attaching a revised version of the patch which also includes some tests.  Interestingly, the issue in syslog module is a regression from 3.1 introduced in r80401.  Although it is not a crasher, I don't think it was intentional because although openlog() is happy to accept NULL for indent, the error from  _PyUnicode_AsString() would have to be cleared if the intent was to ignore undecodable indent.

Some notes:

* Rather than just patching in error handling code, please consider
removing use of those APIs and replace their calls with something
more appropriate, e.g. using a parser API.

* When ignoring errors from the API, you have to clear the exception.
This is missing in a couple of places in the patch, e.g. in pyexpat.c

* Please also remove hacks like these:

+#define CMP PyUnicode_CompareWithASCIIString
+        if (CMP(nameobj, "entity") == 0)
+            res = self->entity;
+        else if (CMP(nameobj, "target") == 0)
+            res = self->target;
+        else if (CMP(nameobj, "version") == 0) {
+            return PyUnicode_FromFormat(
+                "Expat %d.%d.%d", XML_MAJOR_VERSION,
                 XML_MINOR_VERSION, XML_MICRO_VERSION);

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<http://bugs.python.org/issue6697>
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