Invoke after_request on exceptions as well. This fixes #59

flask.py

@@ -1362,6 +1362,12 @@ class Flask(_PackageBoundObject):
         Then you still have the original application object around and
         can continue to call methods on it.
 
+        .. versionchanged:: 0.4
+           The :meth:`after_request` functions are now called even if an
+           error handler took over request processing.  This ensures that
+           even if an exception happens database have the chance to
+           properly close the connection.
+
         :param environ: a WSGI environment
         :param start_response: a callable accepting a status code,
                                a list of headers and an optional
@@ -1376,6 +1382,13 @@ class Flask(_PackageBoundObject):
                 response = self.process_response(response)
             except Exception, e:
                 response = self.make_response(self.handle_exception(e))
+                try:
+                    response = self.process_response(response)
+                except Exception, e:
+                    self.logger.exception('after_request handler failed '
+                                          'to postprocess error response. '
+                                          'Depending on uncertain state?')
+
             return response(environ, start_response)
 
     def request_context(self, environ):

tests/flask_tests.py

@@ -16,6 +16,7 @@ import sys
 import flask
 import unittest
 import tempfile
+from logging import StreamHandler
 from contextlib import contextmanager
 from datetime import datetime
 from werkzeug import parse_date, parse_options_header
@@ -240,6 +241,37 @@ class BasicFunctionalityTestCase(unittest.TestCase):
         assert 'after' in evts
         assert rv == 'request|after'
 
+    def test_after_request_errors(self):
+        app = flask.Flask(__name__)
+        called = []
+        @app.after_request
+        def after_request(response):
+            called.append(True)
+            return response
+        @app.route('/')
+        def fails():
+            1/0
+        rv = app.test_client().get('/')
+        assert rv.status_code == 500
+        assert 'Internal Server Error' in rv.data
+        assert len(called) == 1
+
+    def test_after_request_handler_error(self):
+        error_out = StringIO()
+        app = flask.Flask(__name__)
+        app.logger.addHandler(StreamHandler(error_out))
+        @app.after_request
+        def after_request(response):
+            1/0
+            return response
+        @app.route('/')
+        def fails():
+            1/0
+        rv = app.test_client().get('/')
+        assert rv.status_code == 500
+        assert 'Internal Server Error' in rv.data
+        assert 'after_request handler failed' in error_out.getvalue()
+
     def test_error_handling(self):
         app = flask.Flask(__name__)
         @app.errorhandler(404)