From d2c0ae35b818ed19af44991c200316ebb5b0488d Mon Sep 17 00:00:00 2001
From: Stefan Berthold <stefan.berthold@wire.com>
Date: Wed, 14 Jun 2023 14:07:43 +0000
Subject: [PATCH] alter group ID serialisation

- 16 bit version
- 16 bit conversation type
---
 changelog.d/5-internal/group-id-subconv-2             | 1 +
 libs/wire-api/src/Wire/API/MLS/Group/Serialisation.hs | 8 ++++----
 2 files changed, 5 insertions(+), 4 deletions(-)
 create mode 100644 changelog.d/5-internal/group-id-subconv-2

diff --git a/changelog.d/5-internal/group-id-subconv-2 b/changelog.d/5-internal/group-id-subconv-2
new file mode 100644
index 0000000000..75eb794702
--- /dev/null
+++ b/changelog.d/5-internal/group-id-subconv-2
@@ -0,0 +1 @@
+change version and conversation type to 16 bit in group ID serialisation
diff --git a/libs/wire-api/src/Wire/API/MLS/Group/Serialisation.hs b/libs/wire-api/src/Wire/API/MLS/Group/Serialisation.hs
index 061a72abd8..3fb9a7dd3d 100644
--- a/libs/wire-api/src/Wire/API/MLS/Group/Serialisation.hs
+++ b/libs/wire-api/src/Wire/API/MLS/Group/Serialisation.hs
@@ -62,8 +62,8 @@ convToGroupId :: GroupIdParts -> GroupId
 convToGroupId parts = GroupId . L.toStrict . runPut $ do
   let cs = qUnqualified parts.qConvId
       subId = foldMap unSubConvId cs.subconv
-  putWord64be 1 -- Version 1 of the GroupId format
-  putWord32be (fromIntegral $ fromEnum parts.convType)
+  putWord16be 1 -- Version 1 of the GroupId format
+  putWord16be (fromIntegral $ fromEnum parts.convType)
   putLazyByteString . UUID.toByteString . toUUID $ cs.conv
   putWord8 $ fromIntegral (T.length subId)
   putByteString $ T.encodeUtf8 subId
@@ -82,8 +82,8 @@ groupIdToConv gid = do
       }
   where
     readConv = do
-      version <- getWord64be
-      ct <- getWord32be
+      version <- getWord16be
+      ct <- getWord16be
       unless (version == 1) $ fail "unsupported groupId version"
       mUUID <- UUID.fromByteString . L.fromStrict <$> getByteString 16
       uuid <- maybe (fail "invalid conversation UUID in groupId") pure mUUID