Merge lp:~cjwatson/lazr.restful/traceback-reference-cycle into lp:lazr.restful

[Colin Watson]

Avoid traceback reference cycle in ReadWriteResource.__call__.

`sys.exc_info()` called from `ReadWriteResource.__call__` returns a tuple containing the exception's traceback object, which has a reference to the `ReadWriteResource.__call__` frame. Storing that in a local variable creates a reference cycle. Clear that variable in a `finally` block to avoid this.

[Ioana Lasc (ilasc)]

review: Approve

=== modified file 'NEWS.rst'
--- NEWS.rst	2021-02-18 11:03:23 +0000
+++ NEWS.rst	2021-05-14 09:15:23 +0000
@@ -2,6 +2,11 @@
 NEWS for lazr.restful
 =====================
 
+1.0.2
+=====
+
+Avoid traceback reference cycle in ``ReadWriteResource.__call__``.
+
 1.0.1 (2021-02-18)
 ==================
 

=== modified file 'src/lazr/restful/_resource.py'
--- src/lazr/restful/_resource.py	2021-01-21 11:43:07 +0000
+++ src/lazr/restful/_resource.py	2021-05-14 09:15:23 +0000
@@ -940,20 +940,24 @@
                 self.request.response.setHeader("Allow", allow_string)
         except Exception as e:
             exception_info = sys.exc_info()
-            view = getMultiAdapter((e, self.request), name="index.html")
             try:
-                ws_view = IWebServiceExceptionView(view)
-            except TypeError:
-                # There's a view for this exception, but it's not one
-                # we can understand. It was probably designed for a
-                # web application rather than a web service. We'll
-                # re-raise the exception, let the publisher look up
-                # the view, and hopefully handle it better.  Note the careful
-                # reraising that ensures the original traceback is preserved.
-                if six.PY3:
-                    six.raise_from(exception_info[1], None)
-                else:
-                    six.reraise(*exception_info)
+                view = getMultiAdapter((e, self.request), name="index.html")
+                try:
+                    ws_view = IWebServiceExceptionView(view)
+                except TypeError:
+                    # There's a view for this exception, but it's not one we
+                    # can understand.  It was probably designed for a web
+                    # application rather than a web service.  We'll re-raise
+                    # the exception, let the publisher look up the view, and
+                    # hopefully handle it better.  Note the careful
+                    # reraising that ensures the original traceback is
+                    # preserved.
+                    if six.PY3:
+                        six.raise_from(exception_info[1], None)
+                    else:
+                        six.reraise(*exception_info)
+            finally:
+                del exception_info
 
             self.request.response.setStatus(ws_view.status)
             if ws_view.status // 100 == 4: