From 84524454d0ba77d299741c47bd0f5841ac3f66ce Mon Sep 17 00:00:00 2001
From: Victor Stinner <victor.stinner@gmail.com>
Date: Mon, 21 Aug 2017 18:12:58 +0200
Subject: [PATCH] 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                          | 36 ++++++++++++-------
 .../2017-08-21-17-50-27.bpo-31247.8S3zJp.rst  |  2 ++
 2 files changed, 26 insertions(+), 12 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2017-08-21-17-50-27.bpo-31247.8S3zJp.rst

diff --git a/Lib/xmlrpc/server.py b/Lib/xmlrpc/server.py
index bb86fe6872a..88d0eec786b 100644
--- a/Lib/xmlrpc/server.py
+++ b/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()
-            response = dumps(
-                Fault(1, "%s:%s" % (exc_type, exc_value)),
-                encoding=self.encoding, allow_none=self.allow_none,
-                )
+            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()
-                results.append(
-                    {'faultCode' : 1,
-                     'faultString' : "%s:%s" % (exc_type, exc_value)}
-                    )
+                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]
-            response = dumps(
-                Fault(1, "%s:%s" % (exc_type, exc_value)),
-                encoding=self.encoding, allow_none=self.allow_none)
-            response = response.encode(self.encoding, 'xmlcharrefreplace')
+            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):
diff --git a/Misc/NEWS.d/next/Library/2017-08-21-17-50-27.bpo-31247.8S3zJp.rst b/Misc/NEWS.d/next/Library/2017-08-21-17-50-27.bpo-31247.8S3zJp.rst
new file mode 100644
index 00000000000..6879384eb8f
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2017-08-21-17-50-27.bpo-31247.8S3zJp.rst
@@ -0,0 +1,2 @@
+xmlrpc.server now explicitly breaks reference cycles when using
+sys.exc_info() in code handling exceptions.