func commandEmergencyReparentShard(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	waitSlaveTimeout := subFlags.Duration("wait_slave_timeout", 30*time.Second, "time to wait for slaves to catch up in reparenting")
	keyspaceShard := subFlags.String("keyspace_shard", "", "keyspace/shard of the shard that needs to be reparented")
	newMaster := subFlags.String("new_master", "", "alias of a tablet that should be the new master")
	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() == 2 {
		// Legacy syntax: "<keyspace/shard> <tablet alias>".
		if *newMaster != "" {
			return fmt.Errorf("cannot use legacy syntax and flag -new_master for action EmergencyReparentShard at the same time")
		}
		*keyspaceShard = subFlags.Arg(0)
		*newMaster = subFlags.Arg(1)
	} else if subFlags.NArg() != 0 {
		return fmt.Errorf("action EmergencyReparentShard requires -keyspace_shard=<keyspace/shard> -new_master=<tablet alias>")
	}

	keyspace, shard, err := topoproto.ParseKeyspaceShard(*keyspaceShard)
	if err != nil {
		return err
	}
	tabletAlias, err := topoproto.ParseTabletAlias(*newMaster)
	if err != nil {
		return err
	}
	return wr.EmergencyReparentShard(ctx, keyspace, shard, tabletAlias, *waitSlaveTimeout)
}

func commandRestoreFromBackup(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 1 {
		return fmt.Errorf("The RestoreFromBackup command requires the <tablet alias> argument.")
	}

	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(0))
	if err != nil {
		return err
	}
	tabletInfo, err := wr.TopoServer().GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}
	stream, err := wr.TabletManagerClient().RestoreFromBackup(ctx, tabletInfo.Tablet)
	if err != nil {
		return err
	}
	for {
		e, err := stream.Recv()
		switch err {
		case nil:
			logutil.LogEvent(wr.Logger(), e)
		case io.EOF:
			return nil
		default:
			return err
		}
	}
}

// GetTabletsByCell implements topo.Server.
func (s *Server) GetTabletsByCell(ctx context.Context, cellName string) ([]*topodatapb.TabletAlias, error) {
	cell, err := s.getCell(cellName)
	if err != nil {
		return nil, err
	}

	resp, err := cell.Get(tabletsDirPath, false /* sort */, false /* recursive */)
	if err != nil {
		return nil, convertError(err)
	}

	nodes, err := getNodeNames(resp)
	if err != nil {
		return nil, err
	}

	tablets := make([]*topodatapb.TabletAlias, 0, len(nodes))
	for _, node := range nodes {
		tabletAlias, err := topoproto.ParseTabletAlias(node)
		if err != nil {
			return nil, err
		}
		tablets = append(tablets, tabletAlias)
	}
	return tablets, nil
}

func commandVtTabletRollback(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	connectTimeout := subFlags.Duration("connect_timeout", 30*time.Second, "Connection timeout for vttablet client")
	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 2 {
		return fmt.Errorf("the <tablet_alias> and <transaction_id> arguments are required for the VtTabletRollback command")
	}
	transactionID, err := strconv.ParseInt(subFlags.Arg(1), 10, 64)
	if err != nil {
		return err
	}
	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(0))
	if err != nil {
		return err
	}
	tabletInfo, err := wr.TopoServer().GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}

	conn, err := tabletconn.GetDialer()(tabletInfo.Tablet, *connectTimeout)
	if err != nil {
		return fmt.Errorf("cannot connect to tablet %v: %v", tabletAlias, err)
	}
	defer conn.Close(ctx)

	return conn.Rollback(ctx, &querypb.Target{
		Keyspace:   tabletInfo.Tablet.Keyspace,
		Shard:      tabletInfo.Tablet.Shard,
		TabletType: tabletInfo.Tablet.Type,
	}, transactionID)
}

func commandVtTabletBegin(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	connectTimeout := subFlags.Duration("connect_timeout", 30*time.Second, "Connection timeout for vttablet client")
	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 1 {
		return fmt.Errorf("the <tablet_alias> argument is required for the VtTabletBegin command")
	}
	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(0))
	if err != nil {
		return err
	}
	tabletInfo, err := wr.TopoServer().GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}

	conn, err := tabletconn.GetDialer()(ctx, tabletInfo.Tablet, *connectTimeout)
	if err != nil {
		return fmt.Errorf("cannot connect to tablet %v: %v", tabletAlias, err)
	}
	defer conn.Close()

	transactionID, err := conn.Begin(ctx)
	if err != nil {
		return fmt.Errorf("Begin failed: %v", err)
	}
	result := map[string]int64{
		"transaction_id": transactionID,
	}
	return printJSON(wr.Logger(), result)
}

// handleExplorerRedirect returns the redirect target URL.
func handleExplorerRedirect(ctx context.Context, ts topo.Server, r *http.Request) (string, error) {
	keyspace := r.FormValue("keyspace")
	shard := r.FormValue("shard")
	cell := r.FormValue("cell")

	switch r.FormValue("type") {
	case "keyspace":
		if keyspace == "" {
			return "", errors.New("keyspace is required for this redirect")
		}
		return appPrefix + "#/keyspaces/", nil
	case "shard":
		if keyspace == "" || shard == "" {
			return "", errors.New("keyspace and shard are required for this redirect")
		}
		return appPrefix + fmt.Sprintf("#/shard/%s/%s", keyspace, shard), nil
	case "srv_keyspace":
		if keyspace == "" || cell == "" {
			return "", errors.New("keyspace and cell are required for this redirect")
		}
		return appPrefix + "#/keyspaces/", nil
	case "srv_shard":
		if keyspace == "" || shard == "" || cell == "" {
			return "", errors.New("keyspace, shard, and cell are required for this redirect")
		}
		return appPrefix + fmt.Sprintf("#/shard/%s/%s", keyspace, shard), nil
	case "srv_type":
		tabletType := r.FormValue("tablet_type")
		if keyspace == "" || shard == "" || cell == "" || tabletType == "" {
			return "", errors.New("keyspace, shard, cell, and tablet_type are required for this redirect")
		}
		return appPrefix + fmt.Sprintf("#/shard/%s/%s", keyspace, shard), nil
	case "tablet":
		alias := r.FormValue("alias")
		if alias == "" {
			return "", errors.New("alias is required for this redirect")
		}
		tabletAlias, err := topoproto.ParseTabletAlias(alias)
		if err != nil {
			return "", fmt.Errorf("bad tablet alias %q: %v", alias, err)
		}
		ti, err := ts.GetTablet(ctx, tabletAlias)
		if err != nil {
			return "", fmt.Errorf("can't get tablet %q: %v", alias, err)
		}
		return appPrefix + fmt.Sprintf("#/shard/%s/%s", ti.Keyspace, ti.Shard), nil
	case "replication":
		if keyspace == "" || shard == "" || cell == "" {
			return "", errors.New("keyspace, shard, and cell are required for this redirect")
		}
		return appPrefix + fmt.Sprintf("#/shard/%s/%s", keyspace, shard), nil
	default:
		return "", errors.New("bad redirect type")
	}
}

// handleExplorerRedirect returns the redirect target URL.
func handleExplorerRedirect(r *http.Request) (string, error) {
	keyspace := r.FormValue("keyspace")
	shard := r.FormValue("shard")
	cell := r.FormValue("cell")

	switch r.FormValue("type") {
	case "keyspace":
		if keyspace == "" {
			return "", errors.New("keyspace is required for this redirect")
		}
		return explorer.GetKeyspacePath(keyspace), nil
	case "shard":
		if keyspace == "" || shard == "" {
			return "", errors.New("keyspace and shard are required for this redirect")
		}
		return explorer.GetShardPath(keyspace, shard), nil
	case "srv_keyspace":
		if keyspace == "" || cell == "" {
			return "", errors.New("keyspace and cell are required for this redirect")
		}
		return explorer.GetSrvKeyspacePath(cell, keyspace), nil
	case "srv_shard":
		if keyspace == "" || shard == "" || cell == "" {
			return "", errors.New("keyspace, shard, and cell are required for this redirect")
		}
		return explorer.GetSrvShardPath(cell, keyspace, shard), nil
	case "srv_type":
		tabletType := r.FormValue("tablet_type")
		if keyspace == "" || shard == "" || cell == "" || tabletType == "" {
			return "", errors.New("keyspace, shard, cell, and tablet_type are required for this redirect")
		}
		tt, err := topoproto.ParseTabletType(tabletType)
		if err != nil {
			return "", fmt.Errorf("cannot parse tablet type %v: %v", tabletType, err)
		}
		return explorer.GetSrvTypePath(cell, keyspace, shard, tt), nil
	case "tablet":
		alias := r.FormValue("alias")
		if alias == "" {
			return "", errors.New("alias is required for this redirect")
		}
		tabletAlias, err := topoproto.ParseTabletAlias(alias)
		if err != nil {
			return "", fmt.Errorf("bad tablet alias %q: %v", alias, err)
		}
		return explorer.GetTabletPath(tabletAlias), nil
	case "replication":
		if keyspace == "" || shard == "" || cell == "" {
			return "", errors.New("keyspace, shard, and cell are required for this redirect")
		}
		return explorer.GetReplicationSlaves(cell, keyspace, shard), nil
	default:
		return "", errors.New("bad redirect type")
	}
}

func commandReparentTablet(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 1 {
		return fmt.Errorf("action ReparentTablet requires <tablet alias>")
	}
	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(0))
	if err != nil {
		return err
	}
	return wr.ReparentTablet(ctx, tabletAlias)
}

func commandPlannedReparentShard(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	waitSlaveTimeout := subFlags.Duration("wait_slave_timeout", 30*time.Second, "time to wait for slaves to catch up in reparenting")
	keyspaceShard := subFlags.String("keyspace_shard", "", "keyspace/shard of the shard that needs to be reparented")
	newMaster := subFlags.String("new_master", "", "alias of a tablet that should be the new master")
	avoidMaster := subFlags.String("avoid_master", "", "alias of a tablet that should not be the master, i.e. reparent to any other tablet if this one is the master")
	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() == 2 {
		// Legacy syntax: "<keyspace/shard> <tablet alias>".
		if *keyspaceShard != "" || *newMaster != "" {
			return fmt.Errorf("cannot use legacy syntax and flags -keyspace_shard and -new_master for action PlannedReparentShard at the same time")
		}
		*keyspaceShard = subFlags.Arg(0)
		*newMaster = subFlags.Arg(1)
	} else if subFlags.NArg() != 0 {
		return fmt.Errorf("action PlannedReparentShard requires -keyspace_shard=<keyspace/shard> [-new_master=<tablet alias>] [-avoid_master=<tablet alias>]")
	}

	keyspace, shard, err := topoproto.ParseKeyspaceShard(*keyspaceShard)
	if err != nil {
		return err
	}
	var newMasterAlias, avoidMasterAlias *topodatapb.TabletAlias
	if *newMaster != "" {
		newMasterAlias, err = topoproto.ParseTabletAlias(*newMaster)
		if err != nil {
			return err
		}
	}
	if *avoidMaster != "" {
		avoidMasterAlias, err = topoproto.ParseTabletAlias(*avoidMaster)
		if err != nil {
			return err
		}
	}
	return wr.PlannedReparentShard(ctx, keyspace, shard, newMasterAlias, avoidMasterAlias, *waitSlaveTimeout)
}

func commandVtTabletExecute(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	transactionID := subFlags.Int("transaction_id", 0, "transaction id to use, if inside a transaction.")
	bindVariables := newBindvars(subFlags)
	keyspace := subFlags.String("keyspace", "", "keyspace the tablet belongs to")
	shard := subFlags.String("shard", "", "shard the tablet belongs to")
	tabletType := subFlags.String("tablet_type", "unknown", "tablet type we expect from the tablet (use unknown to use sessionId)")
	connectTimeout := subFlags.Duration("connect_timeout", 30*time.Second, "Connection timeout for vttablet client")
	json := subFlags.Bool("json", false, "Output JSON instead of human-readable table")

	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 2 {
		return fmt.Errorf("the <tablet_alias> and <sql> arguments are required for the VtTabletExecute command")
	}
	tt, err := topoproto.ParseTabletType(*tabletType)
	if err != nil {
		return err
	}
	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(0))
	if err != nil {
		return err
	}
	tabletInfo, err := wr.TopoServer().GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}
	ep, err := topo.TabletEndPoint(tabletInfo.Tablet)
	if err != nil {
		return fmt.Errorf("cannot get EndPoint from tablet record: %v", err)
	}

	conn, err := tabletconn.GetDialer()(ctx, ep, *keyspace, *shard, tt, *connectTimeout)
	if err != nil {
		return fmt.Errorf("cannot connect to tablet %v: %v", tabletAlias, err)
	}
	defer conn.Close()

	qr, err := conn.Execute(ctx, subFlags.Arg(1), *bindVariables, int64(*transactionID))
	if err != nil {
		return fmt.Errorf("Execute failed: %v", err)
	}
	if *json {
		return printJSON(wr.Logger(), qr)
	}
	printQueryResult(loggerWriter{wr.Logger()}, qr)
	return nil
}

func commandVtTabletUpdateStream(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	count := subFlags.Int("count", 1, "number of responses to wait for")
	timestamp := subFlags.Int("timestamp", 0, "timestamp to start the stream from")
	position := subFlags.String("position", "", "position to start the stream from")
	connectTimeout := subFlags.Duration("connect_timeout", 30*time.Second, "Connection timeout for vttablet client")
	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 1 {
		return fmt.Errorf("The <tablet alias> argument is required for the VtTabletUpdateStream command.")
	}
	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(0))
	if err != nil {
		return err
	}
	tabletInfo, err := wr.TopoServer().GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}

	conn, err := tabletconn.GetDialer()(tabletInfo.Tablet, *connectTimeout)
	if err != nil {
		return fmt.Errorf("cannot connect to tablet %v: %v", tabletAlias, err)
	}

	stream, err := conn.UpdateStream(ctx, &querypb.Target{
		Keyspace:   tabletInfo.Tablet.Keyspace,
		Shard:      tabletInfo.Tablet.Shard,
		TabletType: tabletInfo.Tablet.Type,
	}, *position, int64(*timestamp))
	if err != nil {
		return err
	}
	for i := 0; i < *count; i++ {
		se, err := stream.Recv()
		if err != nil {
			return fmt.Errorf("stream ended early: %v", err)
		}
		data, err := json.Marshal(se)
		if err != nil {
			wr.Logger().Errorf("cannot json-marshal structure: %v", err)
		} else {
			wr.Logger().Printf("%v\n", string(data))
		}
	}
	return nil
}

func commandVtTabletStreamHealth(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	count := subFlags.Int("count", 1, "number of responses to wait for")
	connectTimeout := subFlags.Duration("connect_timeout", 30*time.Second, "Connection timeout for vttablet client")
	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 1 {
		return fmt.Errorf("The <tablet alias> argument is required for the VtTabletStreamHealth command.")
	}
	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(0))
	if err != nil {
		return err
	}
	tabletInfo, err := wr.TopoServer().GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}

	ep, err := topo.TabletEndPoint(tabletInfo.Tablet)
	if err != nil {
		return fmt.Errorf("cannot get EndPoint from tablet record: %v", err)
	}

	// pass in a non-UNKNOWN tablet type to not use sessionId
	conn, err := tabletconn.GetDialer()(ctx, ep, "", "", pb.TabletType_MASTER, *connectTimeout)
	if err != nil {
		return fmt.Errorf("cannot connect to tablet %v: %v", tabletAlias, err)
	}

	stream, errFunc, err := conn.StreamHealth(ctx)
	if err != nil {
		return err
	}
	for i := 0; i < *count; i++ {
		shr, ok := <-stream
		if !ok {
			return fmt.Errorf("stream ended early: %v", errFunc())
		}
		data, err := json.Marshal(shr)
		if err != nil {
			wr.Logger().Errorf("cannot json-marshal structure: %v", err)
		} else {
			wr.Logger().Printf("%v\n", string(data))
		}
	}
	return nil
}

func commandVtTabletExecute(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	transactionID := subFlags.Int("transaction_id", 0, "transaction id to use, if inside a transaction.")
	bindVariables := newBindvars(subFlags)
	connectTimeout := subFlags.Duration("connect_timeout", 30*time.Second, "Connection timeout for vttablet client")
	options := subFlags.String("options", "", "execute options values as a text encoded proto of the ExecuteOptions structure")
	json := subFlags.Bool("json", false, "Output JSON instead of human-readable table")

	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 2 {
		return fmt.Errorf("the <tablet_alias> and <sql> arguments are required for the VtTabletExecute command")
	}
	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(0))
	if err != nil {
		return err
	}
	tabletInfo, err := wr.TopoServer().GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}
	executeOptions, err := parseExecuteOptions(*options)
	if err != nil {
		return err
	}

	conn, err := tabletconn.GetDialer()(tabletInfo.Tablet, *connectTimeout)
	if err != nil {
		return fmt.Errorf("cannot connect to tablet %v: %v", tabletAlias, err)
	}
	defer conn.Close(ctx)

	qr, err := conn.Execute(ctx, &querypb.Target{
		Keyspace:   tabletInfo.Tablet.Keyspace,
		Shard:      tabletInfo.Tablet.Shard,
		TabletType: tabletInfo.Tablet.Type,
	}, subFlags.Arg(1), *bindVariables, int64(*transactionID), executeOptions)
	if err != nil {
		return fmt.Errorf("Execute failed: %v", err)
	}
	if *json {
		return printJSON(wr.Logger(), qr)
	}
	printQueryResult(loggerWriter{wr.Logger()}, qr)
	return nil
}

func commandDemoteMaster(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 1 {
		return fmt.Errorf("action DemoteMaster requires <tablet alias>")
	}
	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(0))
	if err != nil {
		return err
	}
	tabletInfo, err := wr.TopoServer().GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}
	_, err = wr.TabletManagerClient().DemoteMaster(ctx, tabletInfo.Tablet)
	return err
}

func commandVtTabletBegin(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	keyspace := subFlags.String("keyspace", "", "keyspace the tablet belongs to")
	shard := subFlags.String("shard", "", "shard the tablet belongs to")
	tabletType := subFlags.String("tablet_type", "unknown", "tablet type we expect from the tablet (use unknown to use sessionId)")
	connectTimeout := subFlags.Duration("connect_timeout", 30*time.Second, "Connection timeout for vttablet client")
	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 1 {
		return fmt.Errorf("the <tablet_alias> argument is required for the VtTabletBegin command")
	}
	tt, err := topoproto.ParseTabletType(*tabletType)
	if err != nil {
		return err
	}
	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(0))
	if err != nil {
		return err
	}
	tabletInfo, err := wr.TopoServer().GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}
	ep, err := topo.TabletEndPoint(tabletInfo.Tablet)
	if err != nil {
		return fmt.Errorf("cannot get EndPoint from tablet record: %v", err)
	}

	conn, err := tabletconn.GetDialer()(ctx, ep, *keyspace, *shard, tt, *connectTimeout)
	if err != nil {
		return fmt.Errorf("cannot connect to tablet %v: %v", tabletAlias, err)
	}
	defer conn.Close()

	transactionID, err := conn.Begin(ctx)
	if err != nil {
		return fmt.Errorf("Begin failed: %v", err)
	}
	result := map[string]int64{
		"transaction_id": transactionID,
	}
	return printJSON(wr, result)
}

func commandEmergencyReparentShard(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	waitSlaveTimeout := subFlags.Duration("wait_slave_timeout", 30*time.Second, "time to wait for slaves to catch up in reparenting")
	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 2 {
		return fmt.Errorf("action EmergencyReparentShard requires <keyspace/shard> <tablet alias>")
	}

	keyspace, shard, err := topoproto.ParseKeyspaceShard(subFlags.Arg(0))
	if err != nil {
		return err
	}
	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(1))
	if err != nil {
		return err
	}
	return wr.EmergencyReparentShard(ctx, keyspace, shard, tabletAlias, *waitSlaveTimeout)
}

func commandInitShardMaster(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	force := subFlags.Bool("force", false, "will force the reparent even if the provided tablet is not a master or the shard master")
	waitSlaveTimeout := subFlags.Duration("wait_slave_timeout", 30*time.Second, "time to wait for slaves to catch up in reparenting")
	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 2 {
		return fmt.Errorf("action InitShardMaster requires <keyspace/shard> <tablet alias>")
	}
	keyspace, shard, err := topoproto.ParseKeyspaceShard(subFlags.Arg(0))
	if err != nil {
		return err
	}
	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(1))
	if err != nil {
		return err
	}
	return wr.InitShardMaster(ctx, keyspace, shard, tabletAlias, *force, *waitSlaveTimeout)
}

//.........这里部分代码省略.........
	// Tablets
	handleCollection("tablets", func(r *http.Request) (interface{}, error) {
		tabletPath := getItemPath(r.URL.Path)

		// List tablets based on query params.
		if tabletPath == "" {
			if err := r.ParseForm(); err != nil {
				return nil, err
			}
			shardRef := r.FormValue("shard")
			cell := r.FormValue("cell")

			if shardRef != "" {
				// Look up by keyspace/shard, and optionally cell.
				keyspace, shard, err := topoproto.ParseKeyspaceShard(shardRef)
				if err != nil {
					return nil, err
				}
				if cell != "" {
					return ts.FindAllTabletAliasesInShardByCell(ctx, keyspace, shard, []string{cell})
				}
				return ts.FindAllTabletAliasesInShard(ctx, keyspace, shard)
			}

			// Get all tablets in a cell.
			if cell == "" {
				return nil, errors.New("cell param required")
			}
			return ts.GetTabletsByCell(ctx, cell)
		}

		// Get tablet health.
		if parts := strings.Split(tabletPath, "/"); len(parts) == 2 && parts[1] == "health" {
			tabletAlias, err := topoproto.ParseTabletAlias(parts[0])
			if err != nil {
				return nil, err
			}
			return tabletHealthCache.Get(ctx, tabletAlias)
		}

		tabletAlias, err := topoproto.ParseTabletAlias(tabletPath)
		if err != nil {
			return nil, err
		}

		// Perform an action on a tablet.
		if r.Method == "POST" {
			if err := r.ParseForm(); err != nil {
				return nil, err
			}
			action := r.FormValue("action")
			if action == "" {
				return nil, errors.New("must specify action")
			}
			return actions.ApplyTabletAction(ctx, action, tabletAlias, r), nil
		}

		// Get the tablet record.
		return ts.GetTablet(ctx, tabletAlias)
	})

	// EndPoints
	handleCollection("endpoints", func(r *http.Request) (interface{}, error) {
		// We expect cell/keyspace/shard/tabletType.
		epPath := getItemPath(r.URL.Path)
		parts := strings.Split(epPath, "/")

//.........这里部分代码省略.........
		if err != nil {
			return nil, fmt.Errorf("can't get list of SrvKeyspaceNames for cell %q: GetSrvKeyspaceNames returned: %v", cell, err)
		}
		for _, keyspaceName := range keyspaceNamesList {
			err := addSrvkeyspace(ctx, ts, cell, keyspaceName, srvKeyspaces)
			if err != nil {
				return nil, err
			}
		}
		return srvKeyspaces, nil

	})

	// Tablets
	handleCollection("tablets", func(r *http.Request) (interface{}, error) {
		tabletPath := getItemPath(r.URL.Path)

		// List tablets based on query params.
		if tabletPath == "" {
			if err := r.ParseForm(); err != nil {
				return nil, err
			}
			shardRef := r.FormValue("shard")
			cell := r.FormValue("cell")

			if shardRef != "" {
				// Look up by keyspace/shard, and optionally cell.
				keyspace, shard, err := topoproto.ParseKeyspaceShard(shardRef)
				if err != nil {
					return nil, err
				}
				if cell != "" {
					return ts.FindAllTabletAliasesInShardByCell(ctx, keyspace, shard, []string{cell})
				}
				return ts.FindAllTabletAliasesInShard(ctx, keyspace, shard)
			}

			// Get all tablets in a cell.
			if cell == "" {
				return nil, errors.New("cell param required")
			}
			return ts.GetTabletsByCell(ctx, cell)
		}

		// Get tablet health.
		if parts := strings.Split(tabletPath, "/"); len(parts) == 2 && parts[1] == "health" {
			tabletAlias, err := topoproto.ParseTabletAlias(parts[0])
			if err != nil {
				return nil, err
			}
			return tabletHealthCache.Get(ctx, tabletAlias)
		}

		tabletAlias, err := topoproto.ParseTabletAlias(tabletPath)
		if err != nil {
			return nil, err
		}

		// Perform an action on a tablet.
		if r.Method == "POST" {
			if err := r.ParseForm(); err != nil {
				return nil, err
			}
			action := r.FormValue("action")
			if action == "" {
				return nil, errors.New("must specify action")
			}
			return actions.ApplyTabletAction(ctx, action, tabletAlias, r), nil
		}

		// Get the tablet record.
		return ts.GetTablet(ctx, tabletAlias)
	})

	// Schema Change
	http.HandleFunc(apiPrefix+"schema/apply", func(w http.ResponseWriter, r *http.Request) {
		req := struct {
			Keyspace, SQL       string
			SlaveTimeoutSeconds int
		}{}
		if err := unmarshalRequest(r, &req); err != nil {
			httpErrorf(w, r, "can't unmarshal request: %v", err)
			return
		}
		if req.SlaveTimeoutSeconds <= 0 {
			req.SlaveTimeoutSeconds = 10
		}

		logger := logutil.NewCallbackLogger(func(ev *logutilpb.Event) {
			w.Write([]byte(logutil.EventString(ev)))
		})
		wr := wrangler.New(logger, ts, tmClient)

		executor := schemamanager.NewTabletExecutor(
			wr, time.Duration(req.SlaveTimeoutSeconds)*time.Second)

		schemamanager.Run(ctx,
			schemamanager.NewUIController(req.SQL, req.Keyspace, w), executor)
	})
}

func main() {
	defer exit.Recover()

	flags := dbconfigs.AppConfig | dbconfigs.AllPrivsConfig | dbconfigs.DbaConfig |
		dbconfigs.FilteredConfig | dbconfigs.ReplConfig
	dbconfigs.RegisterFlags(flags)
	mysqlctl.RegisterFlags()
	flag.Parse()
	tabletserver.Init()
	if len(flag.Args()) > 0 {
		flag.Usage()
		log.Errorf("vttablet doesn't take any positional arguments")
		exit.Return(1)
	}

	servenv.Init()

	if *tabletPath == "" {
		log.Errorf("tabletPath required")
		exit.Return(1)
	}
	tabletAlias, err := topoproto.ParseTabletAlias(*tabletPath)
	if err != nil {
		log.Error(err)
		exit.Return(1)
	}

	mycnf, err := mysqlctl.NewMycnfFromFlags(tabletAlias.Uid)
	if err != nil {
		log.Errorf("mycnf read failed: %v", err)
		exit.Return(1)
	}

	dbcfgs, err := dbconfigs.Init(mycnf.SocketFile, flags)
	if err != nil {
		log.Warning(err)
	}

	// creates and registers the query service
	qsc := tabletserver.NewServer()
	servenv.OnRun(func() {
		qsc.Register()
		addStatusParts(qsc)
	})
	servenv.OnClose(func() {
		// We now leave the queryservice running during lameduck,
		// so stop it in OnClose(), after lameduck is over.
		qsc.StopService()
	})

	if *tableAclConfig != "" {
		// To override default simpleacl, other ACL plugins must set themselves to be default ACL factory
		tableacl.Register("simpleacl", &simpleacl.Factory{})
	} else if *enforceTableACLConfig {
		log.Error("table acl config has to be specified with table-acl-config flag because enforce-tableacl-config is set.")
		exit.Return(1)
	}
	// tabletacl.Init loads ACL from file if *tableAclConfig is not empty
	err = tableacl.Init(
		*tableAclConfig,
		func() {
			qsc.ClearQueryPlanCache()
		},
	)
	if err != nil {
		log.Errorf("Fail to initialize Table ACL: %v", err)
		if *enforceTableACLConfig {
			log.Error("Need a valid initial Table ACL when enforce-tableacl-config is set, exiting.")
			exit.Return(1)
		}
	}

	// Create mysqld and register the health reporter (needs to be done
	// before initializing the agent, so the initial health check
	// done by the agent has the right reporter)
	mysqld := mysqlctl.NewMysqld(mycnf, &dbcfgs.Dba, &dbcfgs.AllPrivs, &dbcfgs.App, &dbcfgs.Repl, true /* enablePublishStats */)
	servenv.OnClose(mysqld.Close)

	// Depends on both query and updateStream.
	gRPCPort := int32(0)
	if servenv.GRPCPort != nil {
		gRPCPort = int32(*servenv.GRPCPort)
	}
	agent, err = tabletmanager.NewActionAgent(context.Background(), mysqld, qsc, tabletAlias, dbcfgs, mycnf, int32(*servenv.Port), gRPCPort)
	if err != nil {
		log.Error(err)
		exit.Return(1)
	}

	servenv.OnClose(func() {
		// We will still use the topo server during lameduck period
		// to update our state, so closing it in OnClose()
		topo.CloseServers()
	})
	servenv.RunDefault()
}