CompletableFuture transferLeadershipAsync()

in ratis-server/src/main/java/org/apache/ratis/server/impl/RaftServerImpl.java [1248:1292]
36 lines of code
9 McCabe index (conditional complexity)

  CompletableFuture<RaftClientReply> transferLeadershipAsync(TransferLeadershipRequest request)
      throws IOException {
    if (request.getNewLeader() == null) {
      return stepDownLeaderAsync(request);
    }

    LOG.info("{}: receive transferLeadership {}", getMemberId(), request);
    assertLifeCycleState(LifeCycle.States.RUNNING);
    assertGroup(getMemberId(), request);

    synchronized (this) {
      CompletableFuture<RaftClientReply> reply = checkLeaderState(request);
      if (reply != null) {
        return reply;
      }

      if (getId().equals(request.getNewLeader())) {
        return CompletableFuture.completedFuture(newSuccessReply(request));
      }

      final RaftConfigurationImpl conf = getRaftConf();
      final LeaderStateImpl leaderState = role.getLeaderStateNonNull();

      // make sure there is no raft reconfiguration in progress
      if (!conf.isStable() || leaderState.inStagingState() || !state.isConfCommitted()) {
        String msg = getMemberId() + " refused to transfer leadership to peer " + request.getNewLeader() +
            " when raft reconfiguration in progress.";
        return logAndReturnTransferLeadershipFail(request, msg);
      }

      if (!conf.containsInConf(request.getNewLeader())) {
        String msg = getMemberId() + " refused to transfer leadership to peer " + request.getNewLeader() +
            " as it is not in " + conf;
        return logAndReturnTransferLeadershipFail(request, msg);
      }

      if (!conf.isHighestPriority(request.getNewLeader())) {
        String msg = getMemberId() + " refused to transfer leadership to peer " + request.getNewLeader() +
            " as it does not has highest priority in " + conf;
        return logAndReturnTransferLeadershipFail(request, msg);
      }

      return transferLeadership.start(leaderState, request);
    }
  }