func NewRaft(conf *Config, fsm FSM, logs LogStore, stable StableStore, snaps SnapshotStore, trans Transport) (*Raft, error) {
	// Validate the configuration.
	if err := ValidateConfig(conf); err != nil {
		return nil, err
	}

	// Ensure we have a LogOutput.
	var logger hclog.Logger
	if conf.Logger != nil {
		logger = conf.Logger
	} else {
		if conf.LogOutput == nil {
			conf.LogOutput = os.Stderr
		}

		logger = hclog.New(&hclog.LoggerOptions{
			Name:   "raft",
			Level:  hclog.LevelFromString(conf.LogLevel),
			Output: conf.LogOutput,
		})
	}

	// Try to restore the current term.
	currentTerm, err := stable.GetUint64(keyCurrentTerm)
	if err != nil && err.Error() != "not found" {
		return nil, fmt.Errorf("failed to load current term: %v", err)
	}

	// Read the index of the last log entry.
	lastIndex, err := logs.LastIndex()
	if err != nil {
		return nil, fmt.Errorf("failed to find last log: %v", err)
	}

	// Get the last log entry.
	var lastLog Log
	if lastIndex > 0 {
		if err = logs.GetLog(lastIndex, &lastLog); err != nil {
			return nil, fmt.Errorf("failed to get last log at index %d: %v", lastIndex, err)
		}
	}

	// Make sure we have a valid server address and ID.
	protocolVersion := conf.ProtocolVersion
	localAddr := ServerAddress(trans.LocalAddr())
	localID := conf.LocalID

	// TODO (slackpad) - When we deprecate protocol version 2, remove this
	// along with the AddPeer() and RemovePeer() APIs.
	if protocolVersion < 3 && string(localID) != string(localAddr) {
		return nil, fmt.Errorf("when running with ProtocolVersion < 3, LocalID must be set to the network address")
	}

	// Create Raft struct.
	r := &Raft{
		protocolVersion: protocolVersion,
		applyCh:         make(chan *logFuture),
		conf:            *conf,
		fsm:             fsm,
		fsmMutateCh:     make(chan interface{}, 128),
		fsmSnapshotCh:   make(chan *reqSnapshotFuture),
		leaderCh:        make(chan bool),
		localID:         localID,
		localAddr:       localAddr,
		logger:          logger,
		logs:            logs,
		configurationChangeCh: make(chan *configurationChangeFuture),
		configurations:        configurations{},
		rpcCh:                 trans.Consumer(),
		snapshots:             snaps,
		userSnapshotCh:        make(chan *userSnapshotFuture),
		userRestoreCh:         make(chan *userRestoreFuture),
		shutdownCh:            make(chan struct{}),
		stable:                stable,
		trans:                 trans,
		verifyCh:              make(chan *verifyFuture, 64),
		configurationsCh:      make(chan *configurationsFuture, 8),
		bootstrapCh:           make(chan *bootstrapFuture),
		observers:             make(map[uint64]*Observer),
	}

	// Initialize as a follower.
	r.setState(Follower)

	// Start as leader if specified. This should only be used
	// for testing purposes.
	if conf.StartAsLeader {
		r.setState(Leader)
		r.setLeader(r.localAddr)
	}

	// Restore the current term and the last log.
	r.setCurrentTerm(currentTerm)
	r.setLastLog(lastLog.Index, lastLog.Term)

	// Attempt to restore a snapshot if there are any.
	if err := r.restoreSnapshot(); err != nil {
		return nil, err
	}

	// Scan through the log for any configuration change entries.
	snapshotIndex, _ := r.getLastSnapshot()
	for index := snapshotIndex + 1; index <= lastLog.Index; index++ {
		var entry Log
		if err := r.logs.GetLog(index, &entry); err != nil {
			r.logger.Error(fmt.Sprintf("Failed to get log at %d: %v", index, err))
			panic(err)
		}
		r.processConfigurationLogEntry(&entry)
	}
	r.logger.Info(fmt.Sprintf("Initial configuration (index=%d): %+v",
		r.configurations.latestIndex, r.configurations.latest.Servers))

	// Setup a heartbeat fast-path to avoid head-of-line
	// blocking where possible. It MUST be safe for this
	// to be called concurrently with a blocking RPC.
	trans.SetHeartbeatHandler(r.processHeartbeat)

	// Start the background work.
	r.goFunc(r.run)
	r.goFunc(r.runFSM)
	r.goFunc(r.runSnapshots)
	return r, nil
}
func NewRaft(conf *Config, fsm FSM, logs LogStore, stable StableStore, snaps SnapshotStore, trans Transport) (*Raft, error) {
	// Validate the configuration.
	if err := ValidateConfig(conf); err != nil {
		return nil, err
	}

	// Ensure we have a LogOutput.
	var logger hclog.Logger
	if conf.Logger != nil {
		logger = conf.Logger
	} else {
		if conf.LogOutput == nil {
			conf.LogOutput = os.Stderr
		}

		logger = hclog.New(&hclog.LoggerOptions{
			Name:   "raft",
			Level:  hclog.LevelFromString(conf.LogLevel),
			Output: conf.LogOutput,
		})
	}

	// Try to restore the current term.
	currentTerm, err := stable.GetUint64(keyCurrentTerm)
	if err != nil && err.Error() != "not found" {
		return nil, fmt.Errorf("failed to load current term: %v", err)
	}

	// Read the index of the last log entry.
	lastIndex, err := logs.LastIndex()
	if err != nil {
		return nil, fmt.Errorf("failed to find last log: %v", err)
	}

	// Get the last log entry.
	var lastLog Log
	if lastIndex > 0 {
		if err = logs.GetLog(lastIndex, &lastLog); err != nil {
			return nil, fmt.Errorf("failed to get last log at index %d: %v", lastIndex, err)
		}
	}

	// Make sure we have a valid server address and ID.
	protocolVersion := conf.ProtocolVersion
	localAddr := ServerAddress(trans.LocalAddr())
	localID := conf.LocalID

	// TODO (slackpad) - When we deprecate protocol version 2, remove this
	// along with the AddPeer() and RemovePeer() APIs.
	if protocolVersion < 3 && string(localID) != string(localAddr) {
		return nil, fmt.Errorf("when running with ProtocolVersion < 3, LocalID must be set to the network address")
	}

	// Create Raft struct.
	r := &Raft{
		protocolVersion: protocolVersion,
		applyCh:         make(chan *logFuture),
		conf:            *conf,
		fsm:             fsm,
		fsmMutateCh:     make(chan interface{}, 128),
		fsmSnapshotCh:   make(chan *reqSnapshotFuture),
		leaderCh:        make(chan bool),
		localID:         localID,
		localAddr:       localAddr,
		logger:          logger,
		logs:            logs,
		configurationChangeCh: make(chan *configurationChangeFuture),
		configurations:        configurations{},
		rpcCh:                 trans.Consumer(),
		snapshots:             snaps,
		userSnapshotCh:        make(chan *userSnapshotFuture),
		userRestoreCh:         make(chan *userRestoreFuture),
		shutdownCh:            make(chan struct{}),
		stable:                stable,
		trans:                 trans,
		verifyCh:              make(chan *verifyFuture, 64),
		configurationsCh:      make(chan *configurationsFuture, 8),
		bootstrapCh:           make(chan *bootstrapFuture),
		observers:             make(map[uint64]*Observer),
	}

	// Initialize as a follower.
	r.setState(Follower)

	// Start as leader if specified. This should only be used
	// for testing purposes.
	if conf.StartAsLeader {
		r.setState(Leader)
		r.setLeader(r.localAddr)
	}

	// Restore the current term and the last log.
	r.setCurrentTerm(currentTerm)
	r.setLastLog(lastLog.Index, lastLog.Term)

	// Attempt to restore a snapshot if there are any.
	if err := r.restoreSnapshot(); err != nil {
		return nil, err
	}

	// Scan through the log for any configuration change entries.
	snapshotIndex, _ := r.getLastSnapshot()
	for index := snapshotIndex + 1; index <= lastLog.Index; index++ {
		var entry Log
		if err := r.logs.GetLog(index, &entry); err != nil {
			r.logger.Error(fmt.Sprintf("Failed to get log at %d: %v", index, err))
			panic(err)
		}
		r.processConfigurationLogEntry(&entry)
	}
	r.logger.Info(fmt.Sprintf("Initial configuration (index=%d): %+v",
		r.configurations.latestIndex, r.configurations.latest.Servers))

	// Setup a heartbeat fast-path to avoid head-of-line
	// blocking where possible. It MUST be safe for this
	// to be called concurrently with a blocking RPC.
	trans.SetHeartbeatHandler(r.processHeartbeat)

	// Start the background work.
	r.goFunc(r.run)
	r.goFunc(r.runFSM)
	r.goFunc(r.runSnapshots)
	return r, nil
}
// NewRaft is used to construct a new Raft node. It takes a configuration, as well
// as implementations of various interfaces that are required. If we have any
// old state, such as snapshots, logs, peers, etc, all those will be restored
// when creating the Raft node.