bug fix in webmention => activitypub target fetch error handling

fixes https://console.cloud.google.com/errors/CPyMpaulkMKWZA

tests/test_webmention.py

@@ -335,6 +335,16 @@ class WebmentionTest(testutil.TestCase):
                                body=urllib.urlencode({'source': 'http://a/post'}))
         self.assertEquals(400, got.status_int)
 
+    def test_target_fetch_fails(self, mock_get, mock_post):
+        mock_get.side_effect = (
+            requests_response(self.reply_html.replace('http://orig/post', 'bad'),
+                              content_type=CONTENT_TYPE_HTML),
+            requests.Timeout('foo bar'))
+
+        got = app.get_response('/webmention', method='POST',
+                               body=urllib.urlencode({'source': 'http://a/post'}))
+        self.assertEquals(502, got.status_int)
+
     def test_no_backlink(self, mock_get, mock_post):
         mock_get.return_value = requests_response(
             self.reply_html.replace('<a href="http://localhost/"></a>', ''),

webmention.py

@@ -170,9 +170,9 @@ class WebmentionHandler(webapp2.RequestHandler):
         try:
             self.target_resp = common.get_as2(target)
         except (requests.HTTPError, exc.HTTPBadGateway) as e:
-            self.target_resp = e.response
-            if (e.response.status_code // 100 == 2 and
-                common.content_type(e.response).startswith('text/html')):
+            self.target_resp = getattr(e, 'response', None)
+            if (self.target_resp and self.target_resp.status_code // 100 == 2 and
+                common.content_type(self.target_resp).startswith('text/html')):
                 # TODO: pass e.response to try_salmon()'s target_resp
                 return False  # make post() try Salmon
             else: