Welcome notification bug (#3907)

* Add failing test reproducing the issue

* Only create one welcome notification per user

* Add CHANGELOG entry

* Lint

* Test notifications for both clients

changelog.d/3-bug-fixes/welcome-notifications

@@ -0,0 +1 @@
+Fix bug where welcome notifications were generated for each client instead of for each user

integration/integration.cabal

@@ -128,6 +128,7 @@ library
     Test.MLS
     Test.MLS.KeyPackage
     Test.MLS.Message
+    Test.MLS.Notifications
     Test.MLS.One2One
     Test.MLS.SubConversation
     Test.MLS.Unreachable

integration/test/Test/MLS/Notifications.hs

@@ -0,0 +1,30 @@
+module Test.MLS.Notifications where
+
+import API.Gundeck
+import MLS.Util
+import Notifications
+import SetupHelpers
+import Testlib.Prelude
+
+testWelcomeNotification :: HasCallStack => App ()
+testWelcomeNotification = do
+  [alice, bob] <- createAndConnectUsers [OwnDomain, OtherDomain]
+  [alice1, alice2, bob1, bob2] <- traverse (createMLSClient def) [alice, alice, bob, bob]
+  traverse_ uploadNewKeyPackage [alice2, bob1, bob2]
+
+  void $ createNewGroup alice1
+  notif <- withWebSocket bob $ \ws -> do
+    void $ createAddCommit alice1 [alice, bob] >>= sendAndConsumeCommitBundle
+    awaitMatch isWelcomeNotif ws
+
+  notifId <- notif %. "id" & asString
+
+  for_ [bob1, bob2] $ \cid ->
+    getNotifications
+      bob
+      def
+        { since = Just notifId,
+          client = Just cid.client,
+          size = Just 10000
+        }
+      >>= getJSON 200

services/galley/src/Galley/API/MLS/Welcome.hs

@@ -26,13 +26,16 @@ import Data.Aeson qualified as A
 import Data.Domain
 import Data.Id
 import Data.Json.Util
+import Data.List1
+import Data.Map qualified as Map
 import Data.Qualified
 import Data.Time
 import Galley.API.Push
 import Galley.Effects.ExternalAccess
 import Galley.Effects.FederatorAccess
 import Galley.Effects.GundeckAccess
-import Imports
+import Gundeck.Types.Push.V2 (RecipientClients (..))
+import Imports hiding (cs)
 import Network.Wai.Utilities.JSONResponse
 import Polysemy
 import Polysemy.Input
@@ -87,9 +90,17 @@ sendLocalWelcomes ::
   Local [(UserId, ClientId)] ->
   Sem r ()
 sendLocalWelcomes qcnv qusr con now welcome lclients = do
+  -- only create one notification per user
+  let rcpts =
+        map (\(u, cs) -> Recipient u (RecipientClientsSome (List1 cs)))
+          . Map.assocs
+          . foldr
+            (\(u, c) -> Map.insertWith (<>) u (pure c))
+            mempty
+          $ tUnqualified lclients
   let e = Event qcnv Nothing qusr now $ EdMLSWelcome welcome.raw
   runMessagePush lclients (Just qcnv) $
-    newMessagePush mempty con defMessageMetadata (tUnqualified lclients) e
+    newMessagePush mempty con defMessageMetadata rcpts e
 
 sendRemoteWelcomes ::
   ( Member FederatorAccess r,