[amaliujia]

What changes were proposed in this pull request?

Refactor the appendEntries code in RaftServerImpl and move the code to a self-contained class.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/RATIS-2737

How was this patch tested?

Existing tests

[szetszwo]

@amaliujia , thanks for working on this!

The change looks good. Just have some minor comments inlined.

[szetszwo]

Let's change it to updateCommitInfoCache(..). Then, we don't have to expose commitInfoCache.

  void updateCommitInfoCache(List<CommitInfoProto> commitInfos) {
    commitInfos.forEach(commitInfoCache::update);
  }

[szetszwo]

Let's pass isFollowerInitializing. It is easier to understand the if-condition when initializing ad compareAndTransition are together.

  void startFollowerState(boolean isFollowerInitializing) {
    if (!isFollowerInitializing && lifeCycle.compareAndTransition(State.STARTING, State.RUNNING)) {
      // the follower has caught up (i.e. not initializing).  If it is not already RUNNING, start it up. 
      role.startFollowerState(this, Op.APPEND_ENTRIES);
    }
  }

[szetszwo]

Let's check it in the beginning of appendEntriesAsync(..). Then, we don't need this new method.

//RaftServerImpl
  @Override
  public CompletableFuture<AppendEntriesReplyProto> appendEntriesAsync(AppendEntriesRequestProto r)
      throws IOException {
    if (!startComplete.get()) {
      throw new ServerNotReadyException(getMemberId() + ": The server role is not yet initialized.");
    }
    return appendEntriesHandler.appendEntriesAsync(r);
  }

[szetszwo]

+1 the change looks good.