Unify logic of building raft-loggers for etcd.

1. We had the same code copied 3 times.
2. For no good reason the code was not reusing existing logger if this one is given.

server/etcdserver/raft.go

@@ -461,17 +461,7 @@ func startNode(cfg config.ServerConfig, cl *membership.RaftCluster, ids []types.
  CheckQuorum: true,
  PreVote: cfg.PreVote,
  }
- if cfg.Logger != nil {
- // called after capnslog setting in "init" function
- if cfg.LoggerConfig != nil {
- c.Logger, err = NewRaftLogger(cfg.LoggerConfig)
- if err != nil {
- log.Fatalf("cannot create raft logger %v", err)
- }
- } else if cfg.LoggerCore != nil && cfg.LoggerWriteSyncer != nil {
- c.Logger = NewRaftLoggerFromZapCore(cfg.LoggerCore, cfg.LoggerWriteSyncer)
- }
- }
+ c.Logger, err = getRaftLogger(cfg)
 
  if len(peers) == 0 {
  n = raft.RestartNode(c)
@@ -515,17 +505,10 @@ func restartNode(cfg config.ServerConfig, snapshot *raftpb.Snapshot) (types.ID,
  CheckQuorum: true,
  PreVote: cfg.PreVote,
  }
- if cfg.Logger != nil {
- // called after capnslog setting in "init" function
- var err error
- if cfg.LoggerConfig != nil {
- c.Logger, err = NewRaftLogger(cfg.LoggerConfig)
- if err != nil {
- log.Fatalf("cannot create raft logger %v", err)
- }
- } else if cfg.LoggerCore != nil && cfg.LoggerWriteSyncer != nil {
- c.Logger = NewRaftLoggerFromZapCore(cfg.LoggerCore, cfg.LoggerWriteSyncer)
- }
+ var err error
+ c.Logger, err = getRaftLogger(cfg)
+ if err != nil {
+ log.Fatalf("cannot create raft logger %v", err)
  }
 
  n := raft.RestartNode(c)
@@ -600,21 +583,29 @@ func restartAsStandaloneNode(cfg config.ServerConfig, snapshot *raftpb.Snapshot)
  CheckQuorum: true,
  PreVote: cfg.PreVote,
  }
+
+ c.Logger, err = getRaftLogger(cfg)
+ if err != nil {
+ log.Fatalf("cannot create raft logger %v", err)
+ }
+
+ n := raft.RestartNode(c)
+ raftStatus = n.Status
+ return id, cl, n, s, w
+}
+
+func getRaftLogger(cfg config.ServerConfig) (raft.Logger, error) {
  if cfg.Logger != nil {
  // called after capnslog setting in "init" function
  if cfg.LoggerConfig != nil {
- c.Logger, err = NewRaftLogger(cfg.LoggerConfig)
- if err != nil {
- log.Fatalf("cannot create raft logger %v", err)
- }
+ return NewRaftLogger(cfg.LoggerConfig)
  } else if cfg.LoggerCore != nil && cfg.LoggerWriteSyncer != nil {
- c.Logger = NewRaftLoggerFromZapCore(cfg.LoggerCore, cfg.LoggerWriteSyncer)
+ return NewRaftLoggerFromZapCore(cfg.LoggerCore, cfg.LoggerWriteSyncer), nil
+ } else {
+ return NewRaftLoggerZap(cfg.Logger), nil
  }
  }
-
- n := raft.RestartNode(c)
- raftStatus = n.Status
- return id, cl, n, s, w
+ return nil, nil
 }
 
 // getIDs returns an ordered set of IDs included in the given snapshot and