subscriptions: Avoid sending unneeded subscriber information.

The `users/me/subscriptions` endpoint accidentally started returning
subscriber information for each stream.  This is convenient, but
unnecessarily costly for those clients which either don't need it
(most API apps) or already acquire this information via /register
(including Zulip's apps).

This change removes that data set from the default response.  Clients
which had come to rely on it, or would like to rely on it in future,
may still access it via an additional documented API parameter.

Fixes #12917.

templates/zerver/api/get-subscribed-streams.md

@@ -37,11 +37,18 @@ curl -X GET {{ api_url }}/v1/users/me/subscriptions \
     -u BOT_EMAIL_ADDRESS:BOT_API_KEY
 ```
 
+You may pass the `include_subscribers` query parameter as follows:
+
+``` curl
+curl -X GET {{ api_url }}/v1/users/me/subscriptions?include_subscribers=true \
+    -u BOT_EMAIL_ADDRESS:BOT_API_KEY
+```
+
 {end_tabs}
 
 ## Arguments
 
-This request takes no arguments.
+{generate_api_arguments_table|zulip.yaml|/users/me/subscriptions:get}
 
 ## Response
 
@@ -55,7 +62,7 @@ This request takes no arguments.
     * `invite-only`: Specifies whether a stream is private or not.
       Only people who have been invited can access a private stream.
     * `subscribers`: A list of email addresses of users who are also subscribed
-      to a given stream.
+      to a given stream. Included only if `include_subscribers` is `true`.
     * `desktop_notifications`: A boolean specifiying whether desktop notifications
       are enabled for the given stream.
     * `push_notifications`: A boolean specifiying whether push notifications

zerver/lib/actions.py

@@ -4736,20 +4736,28 @@ def gather_subscriptions_helper(user_profile: UserProfile,
             sorted(unsubscribed, key=lambda x: x['name']),
             sorted(never_subscribed, key=lambda x: x['name']))
 
-def gather_subscriptions(user_profile: UserProfile) -> Tuple[List[Dict[str, Any]], List[Dict[str, Any]]]:
-    subscribed, unsubscribed, never_subscribed = gather_subscriptions_helper(user_profile)
-    user_ids = set()
-    for subs in [subscribed, unsubscribed, never_subscribed]:
-        for sub in subs:
-            if 'subscribers' in sub:
-                for subscriber in sub['subscribers']:
-                    user_ids.add(subscriber)
-    email_dict = get_emails_from_user_ids(list(user_ids))
+def gather_subscriptions(
+    user_profile: UserProfile,
+    include_subscribers: bool=False,
+) -> Tuple[List[Dict[str, Any]], List[Dict[str, Any]]]:
+    subscribed, unsubscribed, _ = gather_subscriptions_helper(
+        user_profile, include_subscribers=include_subscribers)
 
-    for subs in [subscribed, unsubscribed]:
-        for sub in subs:
-            if 'subscribers' in sub:
-                sub['subscribers'] = sorted([email_dict[user_id] for user_id in sub['subscribers']])
+    if include_subscribers:
+        user_ids = set()
+        for subs in [subscribed, unsubscribed]:
+            for sub in subs:
+                if 'subscribers' in sub:
+                    for subscriber in sub['subscribers']:
+                        user_ids.add(subscriber)
+        email_dict = get_emails_from_user_ids(list(user_ids))
+
+        for subs in [subscribed, unsubscribed]:
+            for sub in subs:
+                if 'subscribers' in sub:
+                    sub['subscribers'] = sorted([
+                        email_dict[user_id] for user_id in sub['subscribers']
+                    ])
 
     return (subscribed, unsubscribed)
 

zerver/openapi/zulip.yaml

@@ -1210,6 +1210,16 @@ paths:
   /users/me/subscriptions:
     get:
       description: Get information on every stream the user is subscribed to.
+      parameters:
+      - name: include_subscribers
+        in: query
+        description: Set to `true` if you would like each stream's info to include a
+          list of current subscribers to that stream. (This may be significantly slower
+          in organizations with thousands of users.)
+        schema:
+          type: boolean
+          default: false
+        example: true
       security:
       - basicAuth: []
       responses:

zerver/tests/test_subs.py

@@ -3515,9 +3515,10 @@ class GetSubscribersTest(ZulipTestCase):
         self.assert_user_got_subscription_notification(msg)
 
         with queries_captured() as queries:
-            subscriptions = gather_subscriptions(self.user_profile)
-        self.assertTrue(len(subscriptions[0]) >= 11)
-        for sub in subscriptions[0]:
+            subscribed_streams, _ = gather_subscriptions(
+                self.user_profile, include_subscribers=True)
+        self.assertTrue(len(subscribed_streams) >= 11)
+        for sub in subscribed_streams:
             if not sub["name"].startswith("stream_"):
                 continue
             self.assertTrue(len(sub["subscribers"]) == len(users_to_subscribe))
@@ -3695,10 +3696,11 @@ class GetSubscribersTest(ZulipTestCase):
         self.assert_json_success(ret)
 
         with queries_captured() as queries:
-            subscriptions = gather_subscriptions(mit_user_profile)
+            subscribed_streams, _ = gather_subscriptions(
+                mit_user_profile, include_subscribers=True)
 
-        self.assertTrue(len(subscriptions[0]) >= 2)
-        for sub in subscriptions[0]:
+        self.assertTrue(len(subscribed_streams) >= 2)
+        for sub in subscribed_streams:
             if not sub["name"].startswith("mit_"):
                 raise AssertionError("Unexpected stream!")
             if sub["name"] == "mit_invite_only":
@@ -3752,11 +3754,12 @@ class GetSubscribersTest(ZulipTestCase):
     def test_json_get_subscribers(self) -> None:
         """
         json_get_subscribers in zerver/views/streams.py
-        also returns the list of subscribers for a stream.
+        also returns the list of subscribers for a stream, when requested.
         """
         stream_name = gather_subscriptions(self.user_profile)[0][0]['name']
         stream_id = get_stream(stream_name, self.user_profile.realm).id
-        expected_subscribers = gather_subscriptions(self.user_profile)[0][0]['subscribers']
+        expected_subscribers = gather_subscriptions(
+            self.user_profile, include_subscribers=True)[0][0]['subscribers']
         result = self.client_get("/json/streams/%d/members" % (stream_id,))
         self.assert_json_success(result)
         result_dict = result.json()

zerver/views/streams.py

@@ -180,8 +180,16 @@ def update_stream_backend(
         do_change_stream_invite_only(stream, is_private, history_public_to_subscribers)
     return json_success()
 
-def list_subscriptions_backend(request: HttpRequest, user_profile: UserProfile) -> HttpResponse:
-    return json_success({"subscriptions": gather_subscriptions(user_profile)[0]})
+@has_request_variables
+def list_subscriptions_backend(
+    request: HttpRequest,
+    user_profile: UserProfile,
+    include_subscribers: bool=REQ(validator=check_bool, default=False),
+) -> HttpResponse:
+    subscribed, _ = gather_subscriptions(
+        user_profile, include_subscribers=include_subscribers
+    )
+    return json_success({"subscriptions": subscribed})
 
 FuncKwargPair = Tuple[Callable[..., HttpResponse], Dict[str, Union[int, Iterable[Any]]]]