bpo-31247: xmlrpc.server: break reference cycle (#3166)

xmlrpc.server now explicitly breaks reference cycles when using
sys.exc_info() in code handling exceptions.

Lib/xmlrpc/server.py

@@ -270,10 +270,14 @@ class SimpleXMLRPCDispatcher:
         except:
             # report exception back to server
             exc_type, exc_value, exc_tb = sys.exc_info()
+            try:
                 response = dumps(
                     Fault(1, "%s:%s" % (exc_type, exc_value)),
                     encoding=self.encoding, allow_none=self.allow_none,
                     )
+            finally:
+                # Break reference cycle
+                exc_type = exc_value = exc_tb = None
 
         return response.encode(self.encoding, 'xmlcharrefreplace')
 
@@ -365,10 +369,14 @@ class SimpleXMLRPCDispatcher:
                     )
             except:
                 exc_type, exc_value, exc_tb = sys.exc_info()
+                try:
                     results.append(
                         {'faultCode' : 1,
                          'faultString' : "%s:%s" % (exc_type, exc_value)}
                         )
+                finally:
+                    # Break reference cycle
+                    exc_type = exc_value = exc_tb = None
         return results
 
     def _dispatch(self, method, params):
@@ -630,10 +638,14 @@ class MultiPathXMLRPCServer(SimpleXMLRPCServer):
             # (each dispatcher should have handled their own
             # exceptions)
             exc_type, exc_value = sys.exc_info()[:2]
+            try:
                 response = dumps(
                     Fault(1, "%s:%s" % (exc_type, exc_value)),
                     encoding=self.encoding, allow_none=self.allow_none)
                 response = response.encode(self.encoding, 'xmlcharrefreplace')
+            finally:
+                # Break reference cycle
+                exc_type = exc_value = None
         return response
 
 class CGIXMLRPCRequestHandler(SimpleXMLRPCDispatcher):

Misc/NEWS.d/next/Library/2017-08-21-17-50-27.bpo-31247.8S3zJp.rst

+xmlrpc.server now explicitly breaks reference cycles when using
+sys.exc_info() in code handling exceptions.