Correct implementation and documentation of os.confstr. Add a simple test

case.  I've yet to figure out how to provoke a None return I can test.

1 files changed, 9 insertions, 6 deletions

diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index d91d8b5eec..4c462a039c 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -6817,15 +6817,18 @@ posix_confstr(PyObject *self, PyObject *args)
         errno = 0;
 	len = confstr(name, buffer, sizeof(buffer));
 
-	if (len == -1) {
-	    posix_error();
-	}
-	else if (len == 0) {
-            result = PyString_FromString("");
+	if (len == 0) {
+	    if (errno) {
+		posix_error();
+	    }
+	    else {
+		result = Py_None;
+		Py_INCREF(Py_None);
+	    }
         }
         else {
 		if ((unsigned int)len >= sizeof(buffer)) {
-                result = PyString_FromStringAndSize(NULL, len);
+                result = PyString_FromStringAndSize(NULL, len+1);
                 if (result != NULL)
                     confstr(name, PyString_AS_STRING(result), len+1);
             }