simplex-chat-0001: APIMembersRole `elem` linear scan over member ID list

Target: simplex-chat/simplex-chat File: src/Simplex/Chat/Library/Commands.hs Lines: 2327, 2332 Severity: HIGH CWE: CWE-407 (Inefficient Algorithmic Complexity)

Description

APIMembersRole calls foldr' over all group members, and for every member performs groupMemberId \elem` memberIdswherememberIds :: NonEmpty GroupMemberIdis a plain Haskell list. elem` on a list is O(K) where K = length memberIds. The fold iterates M members. Total: O(M × K).

The identical fix already exists in APIRemoveMembers (line 2428): gmIds = S.fromList $ L.toList groupMemberIds followed by S.member. APIMembersRole and APIBlockMembersForAll were simply not updated at the same time.

Code

-- DEFECTIVE (lines 2327, 2332)
      selfSelected GroupInfo {membership} = elem (groupMemberId' membership) memberIds
      ...
            | groupMemberId `elem` memberIds =

Fix

Pre-build S.Set GroupMemberId from memberIds before the fold:

      let gmIdSet = S.fromList (L.toList memberIds)
      selfSelected GroupInfo {membership} = S.member (groupMemberId' membership) gmIdSet
      ...
            | groupMemberId `S.member` gmIdSet =

Complexity

Before	After
O(M × K) per command	O(M + K) per command

At M=1000 members, K=10 selected: ~40× speedup measured (see unit test).

Hot Path

Every admin role-change operation on a large group triggers this path once. In a group with 1000 members and a multi-member role change (K=10), this performs 10,000 linear ID comparisons instead of 1,010.

Patch

defects/simplex-chat/patch/simplex-chat-0001.patch

Unit Test

defects/simplex-chat/unit/SimplexChatTest.java

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simplex-chat-0001: APIMembersRole elem linear scan over member ID list