// newStreamClient starts and returns a new started stream client.
// The caller should call stop when finished, to shut it down.
func newStreamReader(id, to, cid types.ID, term uint64, tr http.RoundTripper, u string, r Raft) (*streamReader, error) {
	s := &streamReader{
		id:   id,
		to:   to,
		term: term,
		r:    r,
		done: make(chan struct{}),
	}

	uu, err := url.Parse(u)
	if err != nil {
		return nil, fmt.Errorf("parse url %s error: %v", u, err)
	}
	uu.Path = path.Join(RaftStreamPrefix, s.id.String())
	req, err := http.NewRequest("GET", uu.String(), nil)
	if err != nil {
		return nil, fmt.Errorf("new request to %s error: %v", u, err)
	}
	req.Header.Set("X-Etcd-Cluster-ID", cid.String())
	req.Header.Set("X-Raft-To", s.to.String())
	req.Header.Set("X-Raft-Term", strconv.FormatUint(s.term, 10))
	resp, err := tr.RoundTrip(req)
	if err != nil {
		return nil, fmt.Errorf("error posting to %q: %v", u, err)
	}
	if resp.StatusCode != http.StatusOK {
		resp.Body.Close()
		return nil, fmt.Errorf("unhandled http status %d", resp.StatusCode)
	}
	s.closer = resp.Body
	go s.handle(resp.Body)
	log.Printf("rafthttp: starting client stream to %s at term %d", s.to, s.term)
	return s, nil
}

// Dial dials to the remote url, and sends streaming request. If it succeeds,
// it returns nil error, and the caller should call Handle function to keep
// receiving appendEntry messages.
func (s *streamClient) start(tr http.RoundTripper, u string, cid types.ID) error {
	uu, err := url.Parse(u)
	if err != nil {
		return fmt.Errorf("parse url %s error: %v", u, err)
	}
	uu.Path = path.Join(RaftStreamPrefix, s.id.String())
	req, err := http.NewRequest("GET", uu.String(), nil)
	if err != nil {
		return fmt.Errorf("new request to %s error: %v", u, err)
	}
	req.Header.Set("X-Etcd-Cluster-ID", cid.String())
	req.Header.Set("X-Raft-To", s.to.String())
	req.Header.Set("X-Raft-Term", strconv.FormatUint(s.term, 10))
	resp, err := tr.RoundTrip(req)
	if err != nil {
		return fmt.Errorf("error posting to %q: %v", u, err)
	}
	if resp.StatusCode != http.StatusOK {
		resp.Body.Close()
		return fmt.Errorf("unhandled http status %d", resp.StatusCode)
	}
	s.closer = resp.Body
	go s.handle(resp.Body)
	log.Printf("rafthttp: starting client stream to %s at term %d", s.to, s.term)
	return nil
}

func isCompatibleWithVers(vers map[string]*version.Versions, local types.ID, minV, maxV *semver.Version) bool {
	var ok bool
	for id, v := range vers {
		// ignore comparasion with local version
		if id == local.String() {
			continue
		}
		if v == nil {
			continue
		}
		clusterv, err := semver.NewVersion(v.Cluster)
		if err != nil {
			plog.Errorf("cannot understand the cluster version of member %s (%v)", id, err)
			continue
		}
		if clusterv.LessThan(*minV) {
			plog.Warningf("the running cluster version(%v) is lower than the minimal cluster version(%v) supported", clusterv.String(), minV.String())
			return false
		}
		if maxV.LessThan(*clusterv) {
			plog.Warningf("the running cluster version(%v) is higher than the maximum cluster version(%v) supported", clusterv.String(), maxV.String())
			return false
		}
		ok = true
	}
	return ok
}

// the caller of this function must have the peers mutex.
func (t *transport) removePeer(id types.ID) {
	if peer, ok := t.peers[id]; ok {
		peer.Stop()
	} else {
		plog.Panicf("unexpected removal of unknown peer '%d'", id)
	}
	delete(t.peers, id)
	delete(t.leaderStats.Followers, id.String())
}

// the caller of this function must have the peers mutex.
func (t *Transport) removePeer(id types.ID) {
	if peer, ok := t.peers[id]; ok {
		peer.stop()
	} else {
		plog.Panicf("unexpected removal of unknown peer '%d'", id)
	}
	delete(t.peers, id)
	delete(t.LeaderStats.Followers, id.String())
	t.prober.Remove(id.String())
	plog.Infof("removed peer %s", id)
}

// checkClusterCompatibilityFromHeader checks the cluster compatibility of
// the local member from the given header.
// It checks whether the version of local member is compatible with
// the versions in the header, and whether the cluster ID of local member
// matches the one in the header.
func checkClusterCompatibilityFromHeader(header http.Header, cid types.ID) error {
	if err := checkVersionCompability(header.Get("X-Server-From"), serverVersion(header), minClusterVersion(header)); err != nil {
		plog.Errorf("request version incompatibility (%v)", err)
		return errIncompatibleVersion
	}
	if gcid := header.Get("X-Etcd-Cluster-ID"); gcid != cid.String() {
		plog.Errorf("request cluster ID mismatch (got %s want %s)", gcid, cid)
		return errClusterIDMismatch
	}
	return nil
}

func (t *transport) AddPeer(id types.ID, us []string) {
	t.mu.Lock()
	defer t.mu.Unlock()
	if _, ok := t.peers[id]; ok {
		return
	}
	urls, err := types.NewURLs(us)
	if err != nil {
		plog.Panicf("newURLs %+v should never fail: %+v", us, err)
	}
	fs := t.leaderStats.Follower(id.String())
	t.peers[id] = startPeer(t.roundTripper, urls, t.id, id, t.clusterID, t.raft, fs, t.errorc, t.term)
}

func (t *Transport) AddPeer(id types.ID, us []string) {
	t.mu.Lock()
	defer t.mu.Unlock()
	if _, ok := t.peers[id]; ok {
		return
	}
	urls, err := types.NewURLs(us)
	if err != nil {
		plog.Panicf("newURLs %+v should never fail: %+v", us, err)
	}
	fs := t.LeaderStats.Follower(id.String())
	t.peers[id] = startPeer(t.streamRt, t.pipelineRt, urls, t.ID, id, t.ClusterID, t.Raft, fs, t.ErrorC, t.V3demo)
	addPeerToProber(t.prober, id.String(), us)
}

// createPostRequest creates a HTTP POST request that sends raft message.
func createPostRequest(u url.URL, path string, body io.Reader, ct string, from, cid types.ID) *http.Request {
	uu := u
	uu.Path = path
	req, err := http.NewRequest("POST", uu.String(), body)
	if err != nil {
		plog.Panicf("unexpected new request error (%v)", err)
	}
	req.Header.Set("Content-Type", ct)
	req.Header.Set("X-Server-From", from.String())
	req.Header.Set("X-Server-Version", version.Version)
	req.Header.Set("X-Min-Cluster-Version", version.MinClusterVersion)
	req.Header.Set("X-Etcd-Cluster-ID", cid.String())
	return req
}

func (t *transport) AddPeer(id types.ID, urls []string) {
	t.mu.Lock()
	defer t.mu.Unlock()
	if _, ok := t.peers[id]; ok {
		return
	}
	// TODO: considering how to switch between all available peer urls
	peerURL := urls[0]
	u, err := url.Parse(peerURL)
	if err != nil {
		log.Panicf("unexpect peer url %s", peerURL)
	}
	u.Path = path.Join(u.Path, RaftPrefix)
	fs := t.leaderStats.Follower(id.String())
	t.peers[id] = NewPeer(t.roundTripper, u.String(), id, t.clusterID, t.raft, fs, t.errorc)
}

func (t *Transport) UpdatePeer(id types.ID, us []string) {
	t.mu.Lock()
	defer t.mu.Unlock()
	// TODO: return error or just panic?
	if _, ok := t.peers[id]; !ok {
		return
	}
	urls, err := types.NewURLs(us)
	if err != nil {
		plog.Panicf("newURLs %+v should never fail: %+v", us, err)
	}
	t.peers[id].update(urls)

	t.prober.Remove(id.String())
	addPeerToProber(t.prober, id.String(), us)
}

func (t *Transport) AddPeer(id types.ID, us []string) {
	t.mu.Lock()
	defer t.mu.Unlock()

	if t.peers == nil {
		panic("transport stopped")
	}
	if _, ok := t.peers[id]; ok {
		return
	}
	urls, err := types.NewURLs(us)
	if err != nil {
		plog.Panicf("newURLs %+v should never fail: %+v", us, err)
	}
	fs := t.LeaderStats.Follower(id.String())
	t.peers[id] = startPeer(t, urls, id, fs)
	addPeerToProber(t.prober, id.String(), us)

	plog.Infof("added peer %s", id)
}

func newEntryReader(r io.Reader, id types.ID) *entryReader {
	return &entryReader{
		r:         r,
		id:        id,
		ents:      metrics.GetMap("rafthttp.stream.entries_received").NewCounter(id.String()),
		bytes:     metrics.GetMap("rafthttp.stream.bytes_received").NewCounter(id.String()),
		lastIndex: metrics.GetMap("rafthttp.stream.last_index_received").NewGauge(id.String()),
	}
}

func newEntryWriter(w io.Writer, id types.ID) *entryWriter {
	ew := &entryWriter{
		w:         w,
		id:        id,
		ents:      metrics.GetMap("rafthttp.stream.entries_sent").NewCounter(id.String()),
		bytes:     metrics.GetMap("rafthttp.stream.bytes_sent").NewCounter(id.String()),
		lastIndex: metrics.GetMap("rafthttp.stream.last_index_sent").NewGauge(id.String()),
	}
	return ew
}

func MemberStoreKey(id types.ID) string {
	return path.Join(StoreMembersPrefix, id.String())
}

// NewServer creates a new EtcdServer from the supplied configuration. The
// configuration is considered static for the lifetime of the EtcdServer.
func NewServer(cfg *ServerConfig) (*EtcdServer, error) {
	st := store.New(StoreClusterPrefix, StoreKeysPrefix)
	var w *wal.WAL
	var n raft.Node
	var s *raft.MemoryStorage
	var id types.ID
	var cl *cluster

	// Run the migrations.
	dataVer, err := version.DetectDataDir(cfg.DataDir)
	if err != nil {
		return nil, err
	}
	if err := upgradeDataDir(cfg.DataDir, cfg.Name, dataVer); err != nil {
		return nil, err
	}

	haveWAL := wal.Exist(cfg.WALDir())
	ss := snap.New(cfg.SnapDir())

	var remotes []*Member
	switch {
	case !haveWAL && !cfg.NewCluster:
		if err := cfg.VerifyJoinExisting(); err != nil {
			return nil, err
		}
		cl, err = newClusterFromURLsMap(cfg.InitialClusterToken, cfg.InitialPeerURLsMap)
		if err != nil {
			return nil, err
		}
		existingCluster, err := GetClusterFromRemotePeers(getRemotePeerURLs(cl, cfg.Name), cfg.Transport)
		if err != nil {
			return nil, fmt.Errorf("cannot fetch cluster info from peer urls: %v", err)
		}
		if err := ValidateClusterAndAssignIDs(cl, existingCluster); err != nil {
			return nil, fmt.Errorf("error validating peerURLs %s: %v", existingCluster, err)
		}
		if !isCompatibleWithCluster(cl, cl.MemberByName(cfg.Name).ID, cfg.Transport) {
			return nil, fmt.Errorf("incomptible with current running cluster")
		}

		remotes = existingCluster.Members()
		cl.SetID(existingCluster.id)
		cl.SetStore(st)
		cfg.Print()
		id, n, s, w = startNode(cfg, cl, nil)
	case !haveWAL && cfg.NewCluster:
		if err := cfg.VerifyBootstrap(); err != nil {
			return nil, err
		}
		cl, err = newClusterFromURLsMap(cfg.InitialClusterToken, cfg.InitialPeerURLsMap)
		if err != nil {
			return nil, err
		}
		m := cl.MemberByName(cfg.Name)
		if isMemberBootstrapped(cl, cfg.Name, cfg.Transport) {
			return nil, fmt.Errorf("member %s has already been bootstrapped", m.ID)
		}
		if cfg.ShouldDiscover() {
			str, err := discovery.JoinCluster(cfg.DiscoveryURL, cfg.DiscoveryProxy, m.ID, cfg.InitialPeerURLsMap.String())
			if err != nil {
				return nil, err
			}
			urlsmap, err := types.NewURLsMap(str)
			if err != nil {
				return nil, err
			}
			if checkDuplicateURL(urlsmap) {
				return nil, fmt.Errorf("discovery cluster %s has duplicate url", urlsmap)
			}
			if cl, err = newClusterFromURLsMap(cfg.InitialClusterToken, urlsmap); err != nil {
				return nil, err
			}
		}
		cl.SetStore(st)
		cfg.PrintWithInitial()
		id, n, s, w = startNode(cfg, cl, cl.MemberIDs())
	case haveWAL:
		if err := fileutil.IsDirWriteable(cfg.DataDir); err != nil {
			return nil, fmt.Errorf("cannot write to data directory: %v", err)
		}

		if err := fileutil.IsDirWriteable(cfg.MemberDir()); err != nil {
			return nil, fmt.Errorf("cannot write to member directory: %v", err)
		}

		if cfg.ShouldDiscover() {
			plog.Warningf("discovery token ignored since a cluster has already been initialized. Valid log found at %q", cfg.WALDir())
		}
		snapshot, err := ss.Load()
		if err != nil && err != snap.ErrNoSnapshot {
			return nil, err
		}
		if snapshot != nil {
			if err := st.Recovery(snapshot.Data); err != nil {
				plog.Panicf("recovered store from snapshot error: %v", err)
			}
			plog.Infof("recovered store from snapshot at index %d", snapshot.Metadata.Index)
//.........这里部分代码省略.........

func backendMemberKey(id types.ID) []byte {
	return []byte(path.Join(id.String(), raftAttributesSuffix))
}

func backendMemberKey(id types.ID) []byte {
	return []byte(id.String())
}

// NewServer creates a new EtcdServer from the supplied configuration. The
// configuration is considered static for the lifetime of the EtcdServer.
func NewServer(cfg *ServerConfig) (srv *EtcdServer, err error) {
	st := store.New(StoreClusterPrefix, StoreKeysPrefix)

	var (
		w  *wal.WAL
		n  raft.Node
		s  *raft.MemoryStorage
		id types.ID
		cl *membership.RaftCluster
	)

	if terr := fileutil.TouchDirAll(cfg.DataDir); terr != nil {
		return nil, fmt.Errorf("cannot access data directory: %v", terr)
	}

	haveWAL := wal.Exist(cfg.WALDir())

	if err = fileutil.TouchDirAll(cfg.SnapDir()); err != nil {
		plog.Fatalf("create snapshot directory error: %v", err)
	}
	ss := snap.New(cfg.SnapDir())

	bepath := path.Join(cfg.SnapDir(), databaseFilename)
	beExist := fileutil.Exist(bepath)

	var be backend.Backend
	beOpened := make(chan struct{})
	go func() {
		be = backend.NewDefaultBackend(bepath)
		beOpened <- struct{}{}
	}()

	select {
	case <-beOpened:
	case <-time.After(time.Second):
		plog.Warningf("another etcd process is running with the same data dir and holding the file lock.")
		plog.Warningf("waiting for it to exit before starting...")
		<-beOpened
	}

	defer func() {
		if err != nil {
			be.Close()
		}
	}()

	prt, err := rafthttp.NewRoundTripper(cfg.PeerTLSInfo, cfg.peerDialTimeout())
	if err != nil {
		return nil, err
	}
	var (
		remotes  []*membership.Member
		snapshot *raftpb.Snapshot
	)

	switch {
	case !haveWAL && !cfg.NewCluster:
		if err = cfg.VerifyJoinExisting(); err != nil {
			return nil, err
		}
		cl, err = membership.NewClusterFromURLsMap(cfg.InitialClusterToken, cfg.InitialPeerURLsMap)
		if err != nil {
			return nil, err
		}
		existingCluster, gerr := GetClusterFromRemotePeers(getRemotePeerURLs(cl, cfg.Name), prt)
		if gerr != nil {
			return nil, fmt.Errorf("cannot fetch cluster info from peer urls: %v", gerr)
		}
		if err = membership.ValidateClusterAndAssignIDs(cl, existingCluster); err != nil {
			return nil, fmt.Errorf("error validating peerURLs %s: %v", existingCluster, err)
		}
		if !isCompatibleWithCluster(cl, cl.MemberByName(cfg.Name).ID, prt) {
			return nil, fmt.Errorf("incompatible with current running cluster")
		}

		remotes = existingCluster.Members()
		cl.SetID(existingCluster.ID())
		cl.SetStore(st)
		cl.SetBackend(be)
		cfg.Print()
		id, n, s, w = startNode(cfg, cl, nil)
	case !haveWAL && cfg.NewCluster:
		if err = cfg.VerifyBootstrap(); err != nil {
			return nil, err
		}
		cl, err = membership.NewClusterFromURLsMap(cfg.InitialClusterToken, cfg.InitialPeerURLsMap)
		if err != nil {
			return nil, err
		}
		m := cl.MemberByName(cfg.Name)
		if isMemberBootstrapped(cl, cfg.Name, prt, cfg.bootstrapTimeout()) {
			return nil, fmt.Errorf("member %s has already been bootstrapped", m.ID)
		}
		if cfg.ShouldDiscover() {
			var str string
			str, err = discovery.JoinCluster(cfg.DiscoveryURL, cfg.DiscoveryProxy, m.ID, cfg.InitialPeerURLsMap.String())
			if err != nil {
				return nil, &DiscoveryError{Op: "join", Err: err}
//.........这里部分代码省略.........

// NewServer creates a new EtcdServer from the supplied configuration. The
// configuration is considered static for the lifetime of the EtcdServer.
func NewServer(cfg *ServerConfig) (*EtcdServer, error) {
	st := store.New()
	var w *wal.WAL
	var n raft.Node
	var s *raft.MemoryStorage
	var id types.ID
	walVersion, err := wal.DetectVersion(cfg.DataDir)
	if err != nil {
		return nil, err
	}
	if walVersion == wal.WALUnknown {
		return nil, fmt.Errorf("unknown wal version in data dir %s", cfg.DataDir)
	}
	haveWAL := walVersion != wal.WALNotExist

	if haveWAL && walVersion != wal.WALv0_5 {
		err := UpgradeWAL(cfg, walVersion)
		if err != nil {
			return nil, err
		}
	}

	ss := snap.New(cfg.SnapDir())
	switch {
	case !haveWAL && !cfg.NewCluster:
		us := getOtherPeerURLs(cfg.Cluster, cfg.Name)
		existingCluster, err := GetClusterFromPeers(us)
		if err != nil {
			return nil, fmt.Errorf("cannot fetch cluster info from peer urls: %v", err)
		}
		if err := ValidateClusterAndAssignIDs(cfg.Cluster, existingCluster); err != nil {
			return nil, fmt.Errorf("error validating peerURLs %s: %v", existingCluster, err)
		}
		cfg.Cluster.SetID(existingCluster.id)
		cfg.Cluster.SetStore(st)
		cfg.Print()
		id, n, s, w = startNode(cfg, nil)
	case !haveWAL && cfg.NewCluster:
		if err := cfg.VerifyBootstrapConfig(); err != nil {
			return nil, err
		}
		if err := checkClientURLsEmptyFromPeers(cfg.Cluster, cfg.Name); err != nil {
			return nil, err
		}
		m := cfg.Cluster.MemberByName(cfg.Name)
		if cfg.ShouldDiscover() {
			s, err := discovery.JoinCluster(cfg.DiscoveryURL, cfg.DiscoveryProxy, m.ID, cfg.Cluster.String())
			if err != nil {
				return nil, err
			}
			if cfg.Cluster, err = NewClusterFromString(cfg.Cluster.token, s); err != nil {
				return nil, err
			}
		}
		cfg.Cluster.SetStore(st)
		cfg.PrintWithInitial()
		id, n, s, w = startNode(cfg, cfg.Cluster.MemberIDs())
	case haveWAL:
		if cfg.ShouldDiscover() {
			log.Printf("etcdserver: discovery token ignored since a cluster has already been initialized. Valid log found at %q", cfg.WALDir())
		}
		var index uint64
		snapshot, err := ss.Load()
		if err != nil && err != snap.ErrNoSnapshot {
			return nil, err
		}
		if snapshot != nil {
			if err := st.Recovery(snapshot.Data); err != nil {
				log.Panicf("etcdserver: recovered store from snapshot error: %v", err)
			}
			log.Printf("etcdserver: recovered store from snapshot at index %d", snapshot.Metadata.Index)
			index = snapshot.Metadata.Index
		}
		cfg.Cluster = NewClusterFromStore(cfg.Cluster.token, st)
		cfg.Print()
		if snapshot != nil {
			log.Printf("etcdserver: loaded cluster information from store: %s", cfg.Cluster)
		}
		if !cfg.ForceNewCluster {
			id, n, s, w = restartNode(cfg, index+1, snapshot)
		} else {
			id, n, s, w = restartAsStandaloneNode(cfg, index+1, snapshot)
		}
	default:
		return nil, fmt.Errorf("unsupported bootstrap config")
	}

	sstats := &stats.ServerStats{
		Name: cfg.Name,
		ID:   id.String(),
	}
	lstats := stats.NewLeaderStats(id.String())

	srv := &EtcdServer{
		cfg:         cfg,
		store:       st,
		node:        n,
		raftStorage: s,
//.........这里部分代码省略.........