func (s *Server) onConn(c net.Conn) {
	conn := s.newClientConn(c) //新建一个conn

	defer func() {
		err := recover()
		if err != nil {
			const size = 4096
			buf := make([]byte, size)
			buf = buf[:runtime.Stack(buf, false)] //获得当前goroutine的stacktrace
			golog.Error("server", "onConn", "error", 0,
				"remoteAddr", c.RemoteAddr().String(),
				"stack", string(buf),
			)
		}

		conn.Close()
	}()

	if allowConnect := conn.IsAllowConnect(); allowConnect == false {
		err := mysql.NewError(mysql.ER_ACCESS_DENIED_ERROR, "ip address access denied by kingshard.")
		conn.writeError(err)
		conn.Close()
		return
	}
	if err := conn.Handshake(); err != nil {
		golog.Error("server", "onConn", err.Error(), 0)
		c.Close()
		return
	}

	conn.Run()
}

func (c *ClientConn) handlePrepareSelect(stmt *sqlparser.Select, sql string, args []interface{}) error {
	defaultRule := c.schema.rule.DefaultRule
	if len(defaultRule.Nodes) == 0 {
		return errors.ErrNoDefaultNode
	}
	defaultNode := c.proxy.GetNode(c.user)

	//execute in Master DB
	conn, err := c.getBackendConn(defaultNode, false)
	if err != nil {
		return err
	}

	if conn == nil {
		r := c.newEmptyResultset(stmt)
		return c.writeResultset(c.status, r)
	}

	var rs []*mysql.Result
	rs, err = c.executeInNode(conn, sql, args)

	c.closeConn(conn, false)
	if err != nil {
		golog.Error("ClientConn", "handlePrepareSelect", err.Error(), c.connectionId)
		return err
	}

	err = c.mergeSelectResult(rs, stmt)
	if err != nil {
		golog.Error("ClientConn", "handlePrepareSelect", err.Error(), c.connectionId)
	}

	return err
}

func (n *Node) checkMaster() {
	db := n.Master
	if db == nil {
		golog.Error("Node", "checkMaster", "Master is no alive", 0)
		return
	}
	if atomic.LoadInt32(&(db.state)) == Down {
		return
	}

	if err := db.Ping(); err != nil {
		golog.Error("Node", "checkMaster", "Ping", 0, "db.Addr", db.Addr(), "error", err.Error())
	} else {
		n.LastMasterPing = time.Now().Unix()
		atomic.StoreInt32(&(db.state), Up)
		return
	}

	if int64(n.DownAfterNoAlive) > 0 && time.Now().Unix()-n.LastMasterPing > int64(n.DownAfterNoAlive/time.Second) {
		golog.Info("Node", "checkMaster", "Master down", 0,
			"db.Addr", db.Addr(),
			"Master_down_time", int64(n.DownAfterNoAlive/time.Second))
		n.DownMaster(db.addr)
	}
}

func (r *Router) buildDeletePlan(statement sqlparser.Statement) (*Plan, error) {
	plan := &Plan{}
	var where *sqlparser.Where

	stmt := statement.(*sqlparser.Delete)
	plan.Rule = r.GetRule(sqlparser.String(stmt.Table))
	where = stmt.Where

	if where != nil {
		plan.Criteria = where.Expr /*路由条件*/
	} else {
		plan.Rule = r.DefaultRule
	}

	plan.TableIndexs = makeList(0, len(plan.Rule.TableToNode))

	err := plan.calRouteIndexs()
	if err != nil {
		golog.Error("Route", "BuildDeletePlan", err.Error(), 0)
		return nil, err
	}

	if plan.Rule.Type != DefaultRuleType && len(plan.RouteTableIndexs) == 0 {
		golog.Error("Route", "BuildDeletePlan", errors.ErrNoCriteria.Error(), 0)
		return nil, errors.ErrNoCriteria
	}
	//generate sql,如果routeTableindexs为空则表示不分表，不分表则发default node
	err = r.generateDeleteSql(plan, stmt)
	if err != nil {
		return nil, err
	}
	return plan, nil
}

func (c *ClientConn) Handshake() error {
	if err := c.writeInitialHandshake(); err != nil {
		golog.Error("server", "Handshake", err.Error(),
			c.connectionId, "msg", "send initial handshake error")
		return err
	}

	if err := c.readHandshakeResponse(); err != nil {
		golog.Error("server", "readHandshakeResponse",
			err.Error(), c.connectionId,
			"msg", "read Handshake Response error")

		c.writeError(err)

		return err
	}

	if err := c.writeOK(nil); err != nil {
		golog.Error("server", "readHandshakeResponse",
			"write ok fail",
			c.connectionId, "error", err.Error())
		return err
	}

	c.pkg.Sequence = 0

	return nil
}

/*计算表下标和node下标 */
func (plan *Plan) calRouteIndexs() error {
	nodesCount := len(plan.Rule.Nodes)

	if plan.Rule.Type == DefaultRuleType {
		plan.RouteNodeIndexs = []int{0}
		return nil
	}
	if plan.Criteria == nil { //如果没有分表条件，则是全子表扫描
		if plan.Rule.Type != DefaultRuleType {
			golog.Error("Plan", "calRouteIndexs", "plan have no criteria", 0,
				"type", plan.Rule.Type)
			return errors.ErrNoCriteria
		}
	}

	switch criteria := plan.Criteria.(type) {
	case sqlparser.Values: //代表insert中values
		tindex := plan.getInsertTableIndex(criteria)
		plan.RouteTableIndexs = []int{tindex}
		plan.RouteNodeIndexs = plan.TindexsToNindexs([]int{tindex})

		return nil
	case sqlparser.BoolExpr:
		plan.RouteTableIndexs = plan.getTableIndexByBoolExpr(criteria)
		plan.RouteNodeIndexs = plan.TindexsToNindexs(plan.RouteTableIndexs)

		return nil
	default:
		plan.RouteTableIndexs = plan.TableIndexs
		plan.RouteNodeIndexs = makeList(0, nodesCount)
		return nil
	}
}

func (r *Router) buildReplacePlan(statement sqlparser.Statement) (*Plan, error) {
	plan := &Plan{}

	stmt := statement.(*sqlparser.Replace)
	if _, ok := stmt.Rows.(sqlparser.SelectStatement); ok {
		panic(sqlparser.NewParserError("select in replace not allowed"))
	}

	plan.Rule = r.GetRule(sqlparser.String(stmt.Table))
	plan.Criteria = plan.checkValuesType(stmt.Rows.(sqlparser.Values))

	plan.TableIndexs = makeList(0, len(plan.Rule.TableToNode))

	err := plan.calRouteIndexs()
	if err != nil {
		golog.Error("Route", "BuildReplacePlan", err.Error(), 0)
		return nil, err
	}

	err = r.generateReplaceSql(plan, stmt)
	if err != nil {
		return nil, err
	}
	return plan, nil
}

func (c *ClientConn) handleExec(stmt sqlparser.Statement, args []interface{}) error {
	plan, err := c.schema.rule.BuildPlan(stmt)
	conns, err := c.getShardConns(false, plan)
	if err != nil {
		golog.Error("ClientConn", "handleExec", err.Error(), c.connectionId)
		return err
	}
	if conns == nil {
		return c.writeOK(nil)
	}

	var rs []*mysql.Result
	if 1 < len(conns) {
		return errors.ErrExecInMulti
	}
	if 1 < len(plan.RewrittenSqls) {
		nodeIndex := plan.RouteNodeIndexs[0]
		nodeName := plan.Rule.Nodes[nodeIndex]
		txSqls := []string{"begin;"}
		txSqls = append(txSqls, plan.RewrittenSqls[nodeName]...)
		txSqls = append(txSqls, "commit;")
		plan.RewrittenSqls[nodeName] = txSqls
	}

	rs, err = c.executeInMultiNodes(conns, plan.RewrittenSqls, args)
	c.closeShardConns(conns, err != nil)
	if err == nil {
		err = c.mergeExecResult(rs)
	}

	return err
}

func (c *ClientConn) handleAdmin(admin *sqlparser.Admin) error {
	var err error
	var result *mysql.Resultset

	region := sqlparser.String(admin.Region)

	err = c.checkCmdOrder(region, admin.Columns)
	if err != nil {
		return err
	}

	switch strings.ToLower(region) {
	case NodeRegion:
		err = c.handleNodeCmd(admin.Rows)
	case ServerRegion:
		result, err = c.handleServerCmd(admin.Rows)
	default:
		return fmt.Errorf("admin %s not supported now", region)
	}

	if err != nil {
		golog.Error("ClientConn", "handleAdmin", err.Error(),
			c.connectionId, "sql", sqlparser.String(admin))
		return err
	}

	if result != nil {
		return c.writeResultset(c.status, result)
	}

	return c.writeOK(nil)
}

func (n *Node) checkSlave() {
	n.Lock()
	if n.Slave == nil {
		n.Unlock()
		return
	}
	slaves := make([]*DB, len(n.Slave))
	copy(slaves, n.Slave)
	n.Unlock()

	for i := 0; i < len(slaves); i++ {
		if atomic.LoadInt32(&(slaves[i].state)) == Down {
			continue
		}
		if err := slaves[i].Ping(); err != nil {
			golog.Error("Node", "checkSlave", "Ping", 0, "db.Addr", slaves[i].Addr(), "error", err.Error())
		} else {
			n.LastSlavePing = time.Now().Unix()
			atomic.StoreInt32(&(slaves[i].state), Up)
			continue
		}

		if int64(n.DownAfterNoAlive) > 0 && time.Now().Unix()-n.LastSlavePing > int64(n.DownAfterNoAlive/time.Second) {
			golog.Info("Node", "checkMaster", "Master down", 0,
				"db.Addr", slaves[i].Addr(),
				"slave_down_time", int64(n.DownAfterNoAlive/time.Second))
			//If can't ping slave after DownAfterNoAlive, set slave Down
			n.DownSlave(slaves[i].addr)
		}
	}

}

func (r *Router) buildInsertPlan(statement sqlparser.Statement) (*Plan, error) {
	plan := &Plan{}
	stmt := statement.(*sqlparser.Insert)
	if _, ok := stmt.Rows.(sqlparser.SelectStatement); ok {
		return nil, errors.ErrSelectInInsert
	}
	/*根据sql语句的表，获得对应的分片规则*/
	plan.Rule = r.GetRule(sqlparser.String(stmt.Table))

	if stmt.OnDup != nil {
		err := plan.Rule.checkUpdateExprs(sqlparser.UpdateExprs(stmt.OnDup))
		if err != nil {
			return nil, err
		}
	}

	plan.Criteria = plan.checkValuesType(stmt.Rows.(sqlparser.Values))
	plan.TableIndexs = makeList(0, len(plan.Rule.TableToNode))

	err := plan.calRouteIndexs()
	if err != nil {
		golog.Error("Route", "BuildInsertPlan", err.Error(), 0)
		return nil, err
	}

	err = r.generateInsertSql(plan, stmt)
	if err != nil {
		return nil, err
	}
	return plan, nil
}

func (n *Node) UpMaster(addr string) error {
	db, err := n.checkUpDB(addr)
	if err != nil {
		golog.Error("Node", "UpMaster", err.Error(), 0)
	}
	n.Master = db
	return err
}

func (c *ClientConn) readHandshakeResponse() error {
	data, err := c.readPacket()

	if err != nil {
		return err
	}

	pos := 0

	//capability
	c.capability = binary.LittleEndian.Uint32(data[:4])
	pos += 4

	//skip max packet size
	pos += 4

	//charset, skip, if you want to use another charset, use set names
	//c.collation = CollationId(data[pos])
	pos++

	//skip reserved 23[00]
	pos += 23

	//user name
	c.user = string(data[pos : pos+bytes.IndexByte(data[pos:], 0)])
	pos += len(c.user) + 1

	//auth length and auth
	authLen := int(data[pos])
	pos++
	auth := data[pos : pos+authLen]

	checkAuth := mysql.CalcPassword(c.salt, []byte(c.proxy.cfg.Password))
	if !bytes.Equal(auth, checkAuth) {
		golog.Error("ClientConn", "readHandshakeResponse", "error", 0,
			"auth", auth,
			"checkAuth", checkAuth,
			"passworld", c.proxy.cfg.Password)
		return mysql.NewDefaultError(mysql.ER_ACCESS_DENIED_ERROR, c.c.RemoteAddr().String(), c.user, "Yes")
	}

	pos += authLen

	if c.capability&mysql.CLIENT_CONNECT_WITH_DB > 0 {
		if len(data[pos:]) == 0 {
			return nil
		}

		db := string(data[pos : pos+bytes.IndexByte(data[pos:], 0)])
		pos += len(c.db) + 1

		if err := c.useDB(db); err != nil {
			return err
		}
	}

	return nil
}

//返回true表示已经处理，false表示未处理
func (c *ClientConn) preHandleShard(sql string) (bool, error) {
	var rs []*mysql.Result
	var err error

	var execNode *backend.Node
	var fromSlave bool = false

	if len(sql) == 0 {
		return false, errors.ErrCmdUnsupport
	}

	tokens := strings.Fields(sql)
	if len(tokens) == 0 {
		return false, errors.ErrCmdUnsupport
	}

	if c.isInTransaction() {
		execNode, err = c.GetTransExecNode(tokens, sql)
	} else {
		execNode, fromSlave, err = c.GetExecNode(tokens, sql)
	}

	if err != nil {
		return false, err
	}
	//need shard sql
	if execNode == nil {
		return false, nil
	}

	//execute in Master DB
	conn, err := c.getBackendConn(execNode, fromSlave)
	if err != nil {
		return false, err
	}
	rs, err = c.executeInNode(conn, sql, nil)
	if err != nil {
		return false, err
	}
	c.closeConn(conn, false)

	if len(rs) == 0 {
		msg := fmt.Sprintf("result is empty")
		golog.Error("ClientConn", "handleUnsupport", msg, c.connectionId)
		return false, mysql.NewError(mysql.ER_UNKNOWN_ERROR, msg)
	}

	if rs[0].Resultset != nil {
		err = c.writeResultset(c.status, rs[0].Resultset)
	} else {
		err = c.writeOK(rs[0])
	}
	if err != nil {
		return false, err
	}

	return true, nil
}

func (r *Router) buildSelectPlan(statement sqlparser.Statement) (*Plan, error) {
	plan := &Plan{}
	var where *sqlparser.Where
	var tableName string
	stmt := statement.(*sqlparser.Select)
	switch v := (stmt.From[0]).(type) {
	case *sqlparser.AliasedTableExpr:
		tableName = sqlparser.String(v.Expr)
	case *sqlparser.JoinTableExpr:
		if ate, ok := (v.LeftExpr).(*sqlparser.AliasedTableExpr); ok {
			tableName = sqlparser.String(ate.Expr)
		} else {
			tableName = sqlparser.String(v)
		}
	default:
		tableName = sqlparser.String(v)
	}

	plan.Rule = r.GetRule(tableName) //根据表名获得分表规则
	where = stmt.Where

	if where != nil {
		plan.Criteria = where.Expr /*路由条件*/
	} else {
		plan.Rule = r.DefaultRule
	}
	plan.TableIndexs = makeList(0, len(plan.Rule.TableToNode))

	err := plan.calRouteIndexs()
	if err != nil {
		golog.Error("Route", "BuildSelectPlan", err.Error(), 0)
		return nil, err
	}

	if plan.Rule.Type != DefaultRuleType && len(plan.RouteTableIndexs) == 0 {
		golog.Error("Route", "BuildSelectPlan", errors.ErrNoCriteria.Error(), 0)
		return nil, errors.ErrNoCriteria
	}
	//generate sql,如果routeTableindexs为空则表示不分表，不分表则发default node
	err = r.generateSelectSql(plan, stmt)
	if err != nil {
		return nil, err
	}
	return plan, nil
}

func (c *ClientConn) Run() {
	defer func() {
		r := recover()
		if err, ok := r.(error); ok {
			const size = 4096
			buf := make([]byte, size)
			buf = buf[:runtime.Stack(buf, false)]

			golog.Error("ClientConn", "Run",
				err.Error(), 0,
				"stack", string(buf))
		}

		c.Close()
	}()

	for {
		data, err := c.readPacket()

		if err != nil {
			return
		}

		if err := c.dispatch(data); err != nil {
			golog.Error("server", "Run",
				err.Error(), c.connectionId,
			)
			if err != mysql.ErrBadConn {
				c.writeError(err)
			}
		}

		if c.closed {
			return
		}

		c.pkg.Sequence = 0
	}
}

/*处理select语句*/
func (c *ClientConn) handleSelect(stmt *sqlparser.Select, args []interface{}) error {
	var fromSlave bool = true
	plan, err := c.schema.rule.BuildPlan(stmt)
	if err != nil {
		return err
	}
	if 0 < len(stmt.Comments) {
		comment := string(stmt.Comments[0])
		if 0 < len(comment) && strings.ToLower(comment) == MasterComment {
			fromSlave = false
		}
	}

	conns, err := c.getShardConns(fromSlave, plan)
	if err != nil {
		golog.Error("ClientConn", "handleSelect", err.Error(), c.connectionId)
		return err
	}
	if conns == nil {
		r := c.newEmptyResultset(stmt)
		return c.writeResultset(c.status, r)
	}

	var rs []*mysql.Result
	rs, err = c.executeInMultiNodes(conns, plan.RewrittenSqls, args)
	c.closeShardConns(conns, false)
	if err != nil {
		golog.Error("ClientConn", "handleSelect", err.Error(), c.connectionId)
		return err
	}

	err = c.mergeSelectResult(rs, stmt)
	if err != nil {
		golog.Error("ClientConn", "handleSelect", err.Error(), c.connectionId)
	}

	return err
}

func (s *Server) Run() error {
	s.running = true

	for s.running {
		conn, err := s.listener.Accept()
		if err != nil {
			golog.Error("server", "Run", err.Error(), 0)
			continue
		}

		go s.onConn(conn)
	}

	return nil
}

func (r *Router) generateUpdateSql(plan *Plan, stmt sqlparser.Statement) error {
	sqls := make(map[string][]string)
	node, ok := stmt.(*sqlparser.Update)
	if ok == false {
		return errors.ErrStmtConvert
	}
	if len(plan.RouteNodeIndexs) == 0 {
		return errors.ErrNoRouteNode
	}
	if len(plan.RouteTableIndexs) == 0 {
		buf := sqlparser.NewTrackedBuffer(nil)
		stmt.Format(buf)
		nodeName := r.Nodes[0]
		sqls[nodeName] = []string{buf.String()}
	} else {
		nodeCount := len(plan.RouteNodeIndexs)
		if 1 < nodeCount {
			golog.Error("Router", "generateUpdateSql", errors.ErrUpdateInMulti.Error(), 0,
				"RouteNodeIndexs", plan.RouteNodeIndexs)
			return errors.ErrUpdateInMulti
		}
		tableCount := len(plan.RouteTableIndexs)
		for i := 0; i < tableCount; i++ {
			buf := sqlparser.NewTrackedBuffer(nil)
			buf.Fprintf("update %v%v",
				node.Comments,
				node.Table,
			)
			fmt.Fprintf(buf, "_%04d", plan.RouteTableIndexs[i])
			buf.Fprintf(" set %v%v%v%v",
				node.Exprs,
				node.Where,
				node.OrderBy,
				node.Limit,
			)
			tableIndex := plan.RouteTableIndexs[i]
			nodeIndex := plan.Rule.TableToNode[tableIndex]
			nodeName := r.Nodes[nodeIndex]
			if _, ok := sqls[nodeName]; ok == false {
				sqls[nodeName] = make([]string, 0, tableCount)
			}
			sqls[nodeName] = append(sqls[nodeName], buf.String())
		}

	}
	plan.RewrittenSqls = sqls
	return nil
}

func (c *ClientConn) getBackendConn(n *backend.Node, fromSlave bool) (co *backend.BackendConn, err error) {
	if !c.isInTransaction() {
		if fromSlave {
			co, err = n.GetSlaveConn()
			if err != nil {
				co, err = n.GetMasterConn()
			}
		} else {
			co, err = n.GetMasterConn()
		}
		if err != nil {
			golog.Error("server", "getBackendConn", err.Error(), 0)
			return
		}
	} else {
		var ok bool
		c.Lock()
		co, ok = c.txConns[n]
		c.Unlock()

		if !ok {
			if co, err = n.GetMasterConn(); err != nil {
				return
			}

			if err = co.Begin(); err != nil {
				return
			}

			c.Lock()
			c.txConns[n] = co
			c.Unlock()
		}
	}

	//todo, set conn charset, etc...
	if err = co.UseDB(c.db); err != nil {
		return
	}

	if err = co.SetCharset(c.charset); err != nil {
		return
	}

	return
}