From 9b658366978fb5644eb1a03584a9daa2b588238b Mon Sep 17 00:00:00 2001
From: Anh Nguyen <lananhnt@outlook.com.vn>
Date: Fri, 6 Dec 2024 15:20:21 +0700
Subject: [PATCH] Format and update docs for ra:transfer_leadership/2

---
 src/ra.erl        |  3 ++-
 src/ra_server.erl | 11 +++++++----
 test/ra_SUITE.erl |  2 +-
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/ra.erl b/src/ra.erl
index 91e7124e..d0534491 100644
--- a/src/ra.erl
+++ b/src/ra.erl
@@ -1154,8 +1154,9 @@ initial_members(ServerId) ->
 initial_members(ServerId, Timeout) ->
     ra_server_proc:state_query(ServerId, initial_members, Timeout).
 
-%% @doc Transfers leadership from the leader to a follower.
+%% @doc Transfers leadership from the leader to a voter follower.
 %% Returns `already_leader' if the transfer target is already the leader.
+%% Leadership cannot be transferred to non-voters.
 %% @end
 -spec transfer_leadership(ra_server_id(), ra_server_id()) ->
     ok | already_leader | {error, term()} | {timeout, ra_server_id()}.
diff --git a/src/ra_server.erl b/src/ra_server.erl
index 7532a7ce..877dd55f 100644
--- a/src/ra_server.erl
+++ b/src/ra_server.erl
@@ -830,11 +830,14 @@ handle_leader({transfer_leadership, ServerId},
               #{cfg := #cfg{log_id = LogId},
                 cluster := Cluster} = State) ->
     case Cluster of
-        #{ServerId := #{voter_status := #{membership := Membership}}} when Membership =/= voter ->
-            ?DEBUG("~ts: transfer leadership requested but non-voter member ~w", [LogId, ServerId]),
-            {leader, State, [{reply, {error, non_voter_member}}]};
+        #{ServerId := #{voter_status := #{membership := Membership}}}
+          when Membership =/= voter ->
+            ?INFO("~ts: transfer leadership requested but non-voter member ~w",
+                  [LogId, ServerId]),
+            {leader, State, [{reply, {error, non_voter}}]};
         _ ->
-            ?DEBUG("~ts: transfer leadership to ~w requested", [LogId, ServerId]),
+            ?DEBUG("~ts: transfer leadership to ~w requested",
+                   [LogId, ServerId]),
             %% TODO find a timeout
             gen_statem:cast(ServerId, try_become_leader),
             {await_condition,
diff --git a/test/ra_SUITE.erl b/test/ra_SUITE.erl
index 83d1e55e..2d8cb621 100644
--- a/test/ra_SUITE.erl
+++ b/test/ra_SUITE.erl
@@ -1233,7 +1233,7 @@ transfer_leadership(Config) ->
     {ok, _, _} = ra:add_member(NewLeader, NonVoterMember),
     ok = ra:start_server(default, Name, NonVoterMember, add_machine(), Members),
     ct:pal("Transferring leadership from ~p to ~p", [NewLeader, NonVoterMemberId]),
-    ?assertEqual({error, non_voter_member}, ra:transfer_leadership(NewLeader, NonVoterMemberId)),
+    ?assertEqual({error, non_voter}, ra:transfer_leadership(NewLeader, NonVoterMemberId)),
     terminate_cluster([NonVoterMemberId | Members]).
 
 transfer_leadership_two_node(Config) ->