web feed polling: start using ETag/If-None-Match and Last-Modified/If-Modified-Since

for #791

tests/test_web.py

@@ -1783,8 +1783,11 @@ class WebTest(TestCase):
   <content>I hereby ☕ post</content>
 </entry>
 """
-        mock_get.return_value = requests_response(
-            feed, headers={'Content-Type': atom.CONTENT_TYPE})
+        mock_get.return_value = requests_response(feed, headers={
+            'Content-Type': atom.CONTENT_TYPE,
+            'Last-Modified': 'Sat, 01 Jan 2024 01:02:03 GMT',
+            'ETag': '"abc123"',
+        })
 
         got = self.post('/queue/poll-feed', data={'domain': 'user.com'})
         self.assertEqual(200, got.status_code)
@@ -1792,6 +1795,8 @@ class WebTest(TestCase):
         user = self.user.key.get()
         self.assertEqual(NOW, user.last_polled_feed)
         self.assertEqual('https://user.com/post', user.feed_last_item)
+        self.assertEqual('"abc123"', user.feed_etag)
+        self.assertEqual('Sat, 01 Jan 2024 01:02:03 GMT', user.feed_last_modified)
 
         mock_get.assert_has_calls((
             self.req('https://foo/feed'),
@@ -2074,6 +2079,39 @@ class WebTest(TestCase):
         mock_create_task.assert_not_called()
         mock_get.assert_not_called()
 
+
+    @patch('oauth_dropins.webutil.appengine_config.tasks_client.create_task')
+    def test_poll_feed_etag_last_modified(self, mock_create_task, mock_get, _):
+        common.RUN_TASKS_INLINE = False
+        self.user.obj.mf2 = ACTOR_MF2_REL_FEED_URL
+        self.user.obj.put()
+
+        self.user.feed_etag = '"abc123"'
+        self.user.feed_last_modified ='Sat, 01 Jan 2024 01:02:03 GMT'
+        self.user.put()
+
+        mock_get.return_value = requests_response('', status=304, headers={
+            'Last-Modified': 'Sat, 99 Jan 2024 01:02:03 GMT',
+            'ETag': '"def789"',
+        })
+
+        got = self.post('/queue/poll-feed', data={'domain': 'user.com'})
+        self.assertEqual(200, got.status_code)
+
+        user = self.user.key.get()
+        self.assertEqual(NOW, user.last_polled_feed)
+        self.assertEqual('"def789"', user.feed_etag)
+        self.assertEqual('Sat, 99 Jan 2024 01:02:03 GMT', user.feed_last_modified)
+
+        mock_get.assert_has_calls([self.req('https://foo/feed', headers={
+            'If-None-Match': '"abc123"',
+            'If-Modified-Since': 'Sat, 01 Jan 2024 01:02:03 GMT',
+        })])
+
+        expected_eta = NOW_SECONDS + web.MIN_FEED_POLL_PERIOD.total_seconds()
+        self.assert_task(mock_create_task, 'poll-feed', '/queue/poll-feed',
+                         domain='user.com', eta_seconds=expected_eta)
+
     def _test_verify(self, redirects, hcard, actor, redirects_error=None):
         self.user.has_redirects = False
         self.user.put()

web.py

@@ -102,6 +102,8 @@ class Web(User, Protocol):
     last_webmention_in = ndb.DateTimeProperty(tzinfo=timezone.utc)
     last_polled_feed = ndb.DateTimeProperty(tzinfo=timezone.utc)
     feed_last_item = ndb.StringProperty()  # id (URL)
+    feed_etag = ndb.StringProperty()
+    feed_last_modified = ndb.StringProperty()
 
     # Originally, BF served Web users' AP actor ids on fed.brid.gy, eg
     # https://fed.brid.gy/snarfed.org . When we started adding new protocols, we
@@ -642,25 +644,35 @@ def poll_feed_task():
         return msg
 
     # fetch feed
-    resp = util.requests_get(url)
-    content_type = resp.headers.get('Content-Type') or ''
-    type = FEED_TYPES.get(content_type.split(';')[0])
-    if type == 'atom' or (type == 'xml' and rel_type == 'atom'):
-        try:
-            activities = atom.atom_to_activities(resp.text)
-        except ValueError as e:
-            error(f"Couldn't parse feed as Atom: {e}", status=502)
-        obj_feed_prop = {'atom': resp.text}
-    elif type == 'rss' or (type == 'xml' and rel_type == 'rss'):
-        try:
-            activities = rss.to_activities(resp.text)
-        except ValueError as e:
-            error(f"Couldn't parse feed as RSS: {e}", status=502)
-        obj_feed_prop = {'rss': resp.text}
+    headers = {}
+    if user.feed_etag:
+        headers['If-None-Match'] = user.feed_etag
+    if user.feed_last_modified:
+        headers['If-Modified-Since'] = user.feed_last_modified
+    resp = util.requests_get(url, headers=headers)
+
+    if resp.status_code == 304:
+        logger.info('Feed is unchanged since last poll')
+        activities = []
     else:
-        msg = f'Unknown feed type {content_type}'
-        logger.info(msg)
-        return msg
+        content_type = resp.headers.get('Content-Type') or ''
+        type = FEED_TYPES.get(content_type.split(';')[0])
+        if type == 'atom' or (type == 'xml' and rel_type == 'atom'):
+            try:
+                activities = atom.atom_to_activities(resp.text)
+            except ValueError as e:
+                error(f"Couldn't parse feed as Atom: {e}", status=502)
+            obj_feed_prop = {'atom': resp.text}
+        elif type == 'rss' or (type == 'xml' and rel_type == 'rss'):
+            try:
+                activities = rss.to_activities(resp.text)
+            except ValueError as e:
+                error(f"Couldn't parse feed as RSS: {e}", status=502)
+            obj_feed_prop = {'rss': resp.text}
+        else:
+            msg = f'Unknown feed type {content_type}'
+            logger.info(msg)
+            return msg
 
     # create Objects and receive tasks
     for i, activity in enumerate(activities):
@@ -720,6 +732,8 @@ def poll_feed_task():
 
     # update user
     user.last_polled_feed = util.now()
+    user.feed_etag = resp.headers.get('ETag')
+    user.feed_last_modified = resp.headers.get('Last-Modified')
     user.put()
 
     return 'OK'