Improve readability with early returns

kinto_changes/views.py

@@ -134,6 +134,10 @@ def _handle_old_since_redirect(request):
     See https://bugzilla.mozilla.org/show_bug.cgi?id=1529685
     and https://bugzilla.mozilla.org/show_bug.cgi?id=1665319#c2
     """
+    qs_since = request.validated["querystring"].get("_since")
+    if qs_since is None:
+        return
+
     settings = request.registry.settings
     max_age_since = int(settings.get("changes.since_max_age_days", 21))
     if max_age_since < 0:
@@ -143,25 +147,28 @@ def _handle_old_since_redirect(request):
     min_since_dt = datetime.now() - timedelta(days=max_age_since)
     min_since = min_since_dt.timestamp() * 1000
 
-    http_scheme = request.registry.settings.get("http_scheme") or "https"
-    http_host = request.registry.settings.get(
+    if qs_since >= min_since:
+        # Since value is recent. No redirect.
+        return
+
+    http_scheme = settings.get("http_scheme") or "https"
+    http_host = settings.get(
         "changes.http_host",
         request.registry.settings.get("http_host")
     )
-    redirect = f"{http_scheme}://{http_host}"
-
-    since = request.validated["querystring"].get("_since")
-    if since and since < min_since:
-        redirect += request.route_path(
-            "record-plural",
-            bucket_id=MONITOR_BUCKET,
-            collection_id=CHANGES_COLLECTION
-        )
-        queryparams = request.GET.copy()
-        del queryparams["_since"]
-        if queryparams:
-            redirect += "?" + urlencode(queryparams)
-        raise httpexceptions.HTTPTemporaryRedirect(redirect)
+    host_uri = f"{http_scheme}://{http_host}"
+    redirect = host_uri + request.route_path(
+        "record-plural",
+        bucket_id=MONITOR_BUCKET,
+        collection_id=CHANGES_COLLECTION
+    )
+
+    queryparams = request.GET.copy()
+    del queryparams["_since"]
+    if queryparams:
+        redirect += "?" + urlencode(queryparams)
+
+    raise httpexceptions.HTTPTemporaryRedirect(redirect)
 
 
 @implementer(IAuthorizationPolicy)

tests/test_changes.py

@@ -7,6 +7,7 @@
 
 
 SAMPLE_RECORD = {'data': {'dev-edition': True}}
+HOUR_AGO = int(datetime.datetime.now().timestamp() * 1000) - 3600
 
 
 class UpdateChangesTest(BaseWebTest, unittest.TestCase):
@@ -163,23 +164,22 @@ def test_cache_expires_headers_are_supported(self):
         assert "max-age=60" in resp.headers["Cache-Control"]
 
     def test_cache_expires_header_is_maximum_with_cache_busting(self):
-        resp = self.app.get(self.changes_uri + "?_since=0&_expected=42")
+        resp = self.app.get(self.changes_uri + f"?_since={HOUR_AGO}&_expected=42")
         assert "max-age=3600" in resp.headers["Cache-Control"]
 
     def test_cache_expires_header_is_default_with_filter(self):
         # The _since just filters on lower bound of timestamps, if data changes
         # we don't want to cache for too long.
-        resp = self.app.get(self.changes_uri + "?_since=0")
+        resp = self.app.get(self.changes_uri + f"?_since={HOUR_AGO}")
         assert "max-age=60" in resp.headers["Cache-Control"]
 
     def test_cache_expires_header_is_default_with_concurrency_control(self):
         # The `If-None-Match` header is just a way to obtain a 304 instead of a 200
         # with an empty list. In the client code [0] it is always used in conjonction
         # with _since={last-etag}
         # [0] https://searchfox.org/mozilla-central/rev/93905b66/services/settings/Utils.jsm#70-73
-        hour_ago = int(datetime.datetime.now().timestamp() * 1000) - 3600
-        headers = {"If-None-Match": f'"{hour_ago}"'}
-        resp = self.app.get(self.changes_uri + f'?_since="{hour_ago}"', headers=headers)
+        headers = {"If-None-Match": f'"{HOUR_AGO}"'}
+        resp = self.app.get(self.changes_uri + f'?_since="{HOUR_AGO}"', headers=headers)
         assert "max-age=60" in resp.headers["Cache-Control"]