bpo-34547: Handle client connection terminations in wsgiref.

Previously, long stack traces with Python TypeErrors and AttributeErrors
were printed (see bug).

The wsgiref server is used quite a lot in the community, notably by the
Django development server. I see these huge stack traces daily.

Author: PetterS

Lib/test/test_wsgiref.py

@@ -788,6 +788,18 @@ def flush(self):
             b"Hello, world!",
             written)
 
+    def testConnectionAbortedError(self):
+        class AbortingWriter:
+            def write(self, b):
+                raise ConnectionAbortedError()
+
+            def flush(self):
+                pass
+
+        environ = {"SERVER_PROTOCOL": "HTTP/1.0"}
+        h = SimpleHandler(BytesIO(), AbortingWriter(), sys.stderr, environ)
+        h.run(hello_app)
+
 
 if __name__ == "__main__":
     unittest.main()

Lib/wsgiref/handlers.py

@@ -136,6 +136,10 @@ def run(self, application):
             self.setup_environ()
             self.result = application(self.environ, self.start_response)
             self.finish_response()
+        except ConnectionAbortedError:
+            # We expect the client to close the connection abruptly from time
+            # to time.
+            return
         except:
             try:
                 self.handle_error()

Misc/NEWS.d/next/Library/2018-10-05-16-01-00.bpo-34547.abbaa.rst

@@ -0,0 +1,3 @@
+``wsgiref`` now handles abrupt client connection terminations gracefully.
+Previously, long stack traces with Python TypeErrors and AttributeErrors
+were printed. Patch by Petter Strandmark.