func (db *DistDB) lookupMetadata(metadataKey storage.Key, replicas []storage.Replica) (*storage.RangeLocations, error) {
	replica := storage.ChooseRandomReplica(replicas)
	if replica == nil {
		return nil, util.Errorf("No replica to choose for metadata key: %q", metadataKey)
	}

	addr, err := db.nodeIDToAddr(replica.NodeID)
	if err != nil {
		// TODO(harshit): May be retry a different replica.
		return nil, err
	}
	client := rpc.NewClient(addr)
	arg := &storage.InternalRangeLookupRequest{
		RequestHeader: storage.RequestHeader{
			Replica: *replica,
		},
		Key: metadataKey,
	}
	var reply storage.InternalRangeLookupResponse
	err = client.Call("Node.InternalRangeLookup", arg, &reply)
	if err != nil {
		return nil, err
	}
	if reply.Error != nil {
		return nil, reply.Error
	}
	return &reply.Locations, nil
}

// start dials the remote addr and commences gossip once connected.
// Upon exit, signals client is done by pushing it onto the done
// channel. If the client experienced an error, its err field will
// be set. This method starts client processing in a goroutine and
// returns immediately.
func (c *client) start(g *Gossip, done chan *client, context *rpc.Context, stopper *stop.Stopper) {
	stopper.RunWorker(func() {
		var err error

		c.rpcClient = rpc.NewClient(c.addr, context)
		select {
		case <-c.rpcClient.Healthy():
			// Start gossiping and wait for disconnect or error.
			err = c.gossip(g, stopper)
			if context.DisableCache {
				c.rpcClient.Close()
			}
		case <-c.rpcClient.Closed:
			err = util.Errorf("client closed")
		}

		done <- c

		if err != nil {
			if c.peerID != 0 {
				log.Infof("closing client to node %d (%s): %s", c.peerID, c.addr, err)
			} else {
				log.Infof("closing client to %s: %s", c.addr, err)
			}
		}
	})
}

// TestClientNotReady verifies that Send gets an RPC error when a client
// does not become ready.
func TestClientNotReady(t *testing.T) {
	defer leaktest.AfterTest(t)

	stopper := stop.NewStopper()
	defer stopper.Stop()

	nodeContext := newNodeTestContext(nil, stopper)

	// Construct a server that listens but doesn't do anything.
	s, ln := newTestServer(t, nodeContext, true)
	if err := s.RegisterPublic("Heartbeat.Ping", (&Heartbeat{}).Ping, &rpc.PingRequest{}); err != nil {
		t.Fatal(err)
	}

	opts := SendOptions{
		Ordering:        orderStable,
		SendNextTimeout: 100 * time.Nanosecond,
		Timeout:         100 * time.Nanosecond,
	}

	// Send RPC to an address where no server is running.
	if _, err := sendPing(opts, []net.Addr{ln.Addr()}, nodeContext); err != nil {
		retryErr, ok := err.(retry.Retryable)
		if !ok {
			t.Fatalf("Unexpected error type: %v", err)
		}
		if !retryErr.CanRetry() {
			t.Errorf("Expected retryable error: %v", retryErr)
		}
	} else {
		t.Fatalf("Unexpected success")
	}

	// Send the RPC again with no timeout.
	opts.SendNextTimeout = 0
	opts.Timeout = 0
	c := make(chan error)
	go func() {
		if _, err := sendPing(opts, []net.Addr{ln.Addr()}, nodeContext); err == nil {
			c <- util.Errorf("expected error when client is closed")
		} else if !strings.Contains(err.Error(), "failed as client connection was closed") {
			c <- err
		}
		close(c)
	}()

	select {
	case <-c:
		t.Fatalf("Unexpected end of rpc call")
	case <-time.After(1 * time.Millisecond):
	}

	// Grab the client for our invalid address and close it. This will cause the
	// blocked ping RPC to finish.
	rpc.NewClient(ln.Addr(), nodeContext).Close()
	if err := <-c; err != nil {
		t.Fatal(err)
	}
}

// TestRetryableError verifies that Send returns a retryable error
// when it hits an RPC error.
func TestRetryableError(t *testing.T) {
	defer leaktest.AfterTest(t)()

	clientStopper := stop.NewStopper()
	defer clientStopper.Stop()
	clientContext := newNodeTestContext(nil, clientStopper)
	clientContext.HeartbeatTimeout = 10 * clientContext.HeartbeatInterval

	serverStopper := stop.NewStopper()
	serverContext := newNodeTestContext(nil, serverStopper)

	s, ln := newTestServer(t, serverContext)
	registerBatch(t, s, 0)

	c := rpc.NewClient(ln.Addr(), clientContext)
	// Wait until the client becomes healthy and shut down the server.
	<-c.Healthy()
	serverStopper.Stop()
	// Wait until the client becomes unhealthy.
	func() {
		for r := retry.Start(retry.Options{}); r.Next(); {
			select {
			case <-c.Healthy():
			case <-time.After(1 * time.Nanosecond):
				return
			}
		}
	}()

	sp := tracing.NewTracer().StartSpan("node test")
	defer sp.Finish()

	opts := SendOptions{
		Ordering:        orderStable,
		SendNextTimeout: 100 * time.Millisecond,
		Timeout:         100 * time.Millisecond,
		Trace:           sp,
	}
	if _, err := sendBatch(opts, []net.Addr{ln.Addr()}, clientContext); err != nil {
		retryErr, ok := err.(retry.Retryable)
		if !ok {
			t.Fatalf("Unexpected error type: %v", err)
		}
		if !retryErr.CanRetry() {
			t.Errorf("Expected retryable error: %v", retryErr)
		}
	} else {
		t.Fatalf("Unexpected success")
	}
}

// newSender returns a new instance of Sender.
func newSender(server string, context *base.Context, retryOpts retry.Options) (*Sender, error) {
	addr, err := net.ResolveTCPAddr("tcp", server)
	if err != nil {
		return nil, err
	}

	if context.Insecure {
		log.Warning("running in insecure mode, this is strongly discouraged. See --insecure and --certs.")
	}
	ctx := roachrpc.NewContext(context, hlc.NewClock(hlc.UnixNano), nil)
	client := roachrpc.NewClient(addr, &retryOpts, ctx)
	return &Sender{
		client:    client,
		retryOpts: retryOpts,
	}, nil
}

// getNode gets an RPC client to the node where the requested
// key is located. The range cache may be updated. The bi-level range
// metadata for the cluster is consulted in the event that the local
// cache doesn't contain range metadata corresponding to the specified
// key.
func (db *DistDB) getNode(key storage.Key) (*rpc.Client, *storage.Replica, error) {
	meta2Val, err := db.lookupMeta2(key)
	if err != nil {
		return nil, nil, err
	}
	replica := storage.ChooseRandomReplica(meta2Val.Replicas)
	if replica == nil {
		return nil, nil, util.Errorf("No node found for key: %q", key)
	}
	addr, err := db.nodeIDToAddr(replica.NodeID)
	if err != nil {
		// TODO(harshit): May be retry a different replica.
		return nil, nil, err
	}
	return rpc.NewClient(addr), replica, nil
}

// start dials the remote addr and commences gossip once connected.
// Upon exit, signals client is done by pushing it onto the done
// channel. If the client experienced an error, its err field will
// be set. This method blocks and should be invoked via goroutine.
func (c *client) start(g *Gossip, done chan *client) {
	c.rpcClient = rpc.NewClient(c.addr)
	select {
	case <-c.rpcClient.Ready:
		// Start gossip; see below.
	case <-time.After(gossipDialTimeout):
		c.err = util.Errorf("timeout connecting to remote server: %v", c.addr)
		done <- c
		return
	}

	// Start gossipping and wait for disconnect or error.
	c.lastFresh = time.Now().UnixNano()
	err := c.gossip(g)
	if err != nil {
		c.err = util.Errorf("gossip client: %s", err)
	}
	done <- c
}

// start dials the remote addr and commences gossip once connected.
// Upon exit, signals client is done by pushing it onto the done
// channel. If the client experienced an error, its err field will
// be set. This method blocks and should be invoked via goroutine.
func (c *client) start(g *Gossip, done chan *client) {
	c.rpcClient = rpc.NewClient(c.addr, nil)
	select {
	case <-c.rpcClient.Ready:
		// Success!
	case <-c.rpcClient.Closed:
		c.err = util.Errorf("gossip client failed to connect")
		done <- c
		return
	}

	// Start gossipping and wait for disconnect or error.
	c.lastFresh = time.Now().UnixNano()
	err := c.gossip(g)
	if err != nil {
		c.err = util.Errorf("gossip client: %s", err)
	}
	done <- c
}

// TestRetryableError verifies that Send returns a retryable error
// when it hits an RPC error.
func TestRetryableError(t *testing.T) {
	defer leaktest.AfterTest(t)

	stopper := stop.NewStopper()
	defer stopper.Stop()

	nodeContext := newNodeTestContext(nil, stopper)
	nodeContext.HeartbeatTimeout = 10 * nodeContext.HeartbeatInterval
	_, ln := newTestServer(t, nodeContext, false)

	c := rpc.NewClient(ln.Addr(), nodeContext)
	// Wait until the client becomes healthy and shut down the server.
	<-c.Healthy()
	ln.Close()
	// Wait until the client becomes unhealthy.
	func() {
		for r := retry.Start(retry.Options{}); r.Next(); {
			select {
			case <-c.Healthy():
			case <-time.After(1 * time.Nanosecond):
				return
			}
		}
	}()

	opts := SendOptions{
		Ordering:        orderStable,
		SendNextTimeout: 100 * time.Millisecond,
		Timeout:         100 * time.Millisecond,
	}
	if _, err := sendPing(opts, []net.Addr{ln.Addr()}, nodeContext); err != nil {
		retryErr, ok := err.(retry.Retryable)
		if !ok {
			t.Fatalf("Unexpected error type: %v", err)
		}
		if !retryErr.CanRetry() {
			t.Errorf("Expected retryable error: %v", retryErr)
		}
	} else {
		t.Fatalf("Unexpected success")
	}
}

// start dials the remote addr and commences gossip once connected.
// Upon exit, signals client is done by pushing it onto the done
// channel. If the client experienced an error, its err field will
// be set. This method starts client processing in a goroutine and
// returns immediately.
func (c *client) start(g *Gossip, done chan *client, context *rpc.Context, stopper *stop.Stopper) {
	stopper.RunWorker(func() {
		c.rpcClient = rpc.NewClient(c.addr, context)
		select {
		case <-c.rpcClient.Healthy():
			// Success!
		case <-c.rpcClient.Closed:
			c.err = util.Errorf("gossip client was closed")
			done <- c
			return
		}

		// Start gossipping and wait for disconnect or error.
		c.lastFresh = time.Now().UnixNano()
		c.err = c.gossip(g, stopper)
		if context.DisableCache {
			c.rpcClient.Close()
		}
		done <- c
	})
}

// newRPCSender returns a new instance of rpcSender.
func newRPCSender(server string, context *base.Context, retryOpts retry.Options, stopper *stop.Stopper) (*rpcSender, error) {
	addr, err := net.ResolveTCPAddr("tcp", server)
	if err != nil {
		return nil, err
	}

	if context.Insecure {
		log.Warning("running in insecure mode, this is strongly discouraged. See --insecure and --certs.")
	} else {
		if _, err := context.GetClientTLSConfig(); err != nil {
			return nil, err
		}
	}

	ctx := rpc.NewContext(context, hlc.NewClock(hlc.UnixNano), stopper)
	client := rpc.NewClient(addr, ctx)
	return &rpcSender{
		client:    client,
		retryOpts: retryOpts,
	}, nil
}

// start dials the remote addr and commences gossip once connected.
// Upon exit, signals client is done by pushing it onto the done
// channel. If the client experienced an error, its err field will
// be set. This method starts client processing in a goroutine and
// returns immediately.
func (c *client) start(g *Gossip, done chan *client, context *rpc.Context, stopper *util.Stopper) {
	stopper.RunWorker(func() {
		c.rpcClient = rpc.NewClient(c.addr, nil, context)
		select {
		case <-c.rpcClient.Ready:
			// Success!
		case <-c.rpcClient.Closed:
			c.err = util.Errorf("gossip client failed to connect")
			done <- c
			return
		}

		// Start gossipping and wait for disconnect or error.
		c.lastFresh = time.Now().UnixNano()
		c.err = c.gossip(g, stopper)
		if c.err != nil {
			c.rpcClient.Close()
		}
		done <- c
	})
}

// start dials the remote addr and commences gossip once connected.
// Upon exit, signals client is done by pushing it onto the done
// channel. If the client experienced an error, its err field will
// be set. This method starts client processing in a goroutine and
// returns immediately.
func (c *client) start(g *Gossip, done chan *client, context *rpc.Context, stopper *stop.Stopper) {
	stopper.RunWorker(func() {
		var err error

		c.rpcClient = rpc.NewClient(c.addr, context)
		select {
		case <-c.rpcClient.Healthy():
			// Start gossiping and wait for disconnect or error.
			c.lastFresh = time.Now().UnixNano()
			err = c.gossip(g, stopper)
			if context.DisableCache {
				c.rpcClient.Close()
			}
		case <-c.rpcClient.Closed:
			err = util.Errorf("client closed")
		}

		done <- c

		if err != nil {
			log.Infof("gossip client to %s: %s", c.addr, err)
		}
	})
}

// Send sends one or more method RPCs to clients specified by the slice of
// endpoint addrs. Arguments for methods are obtained using the supplied
// getArgs function. Reply structs are obtained through the getReply()
// function. On success, Send returns the first successful reply. Otherwise,
// Send returns an error if and as soon as the number of failed RPCs exceeds
// the available endpoints less the number of required replies.
func send(opts SendOptions, method string, addrs []net.Addr, getArgs func(addr net.Addr) proto.Message,
	getReply func() proto.Message, context *rpc.Context) (proto.Message, error) {
	trace := opts.Trace // not thread safe!

	if len(addrs) < 1 {
		return nil, roachpb.NewSendError(
			fmt.Sprintf("insufficient replicas (%d) to satisfy send request of %d",
				len(addrs), 1), false)
	}

	done := make(chan *netrpc.Call, len(addrs))

	var clients []*rpc.Client
	for _, addr := range addrs {
		clients = append(clients, rpc.NewClient(addr, context))
	}

	var orderedClients []*rpc.Client
	switch opts.Ordering {
	case orderStable:
		orderedClients = clients
	case orderRandom:
		// Randomly permute order, but keep known-unhealthy clients last.
		var healthy, unhealthy []*rpc.Client
		for _, client := range clients {
			select {
			case <-client.Healthy():
				healthy = append(healthy, client)
			default:
				unhealthy = append(unhealthy, client)
			}
		}
		for _, idx := range rand.Perm(len(healthy)) {
			orderedClients = append(orderedClients, healthy[idx])
		}
		for _, idx := range rand.Perm(len(unhealthy)) {
			orderedClients = append(orderedClients, unhealthy[idx])
		}
	}
	// TODO(spencer): going to need to also sort by affinity; closest
	// ping time should win. Makes sense to have the rpc client/server
	// heartbeat measure ping times. With a bit of seasoning, each
	// node will be able to order the healthy replicas based on latency.

	// Send the first request.
	sendOneFn(orderedClients[0], opts.Timeout, method, getArgs, getReply, context, trace, done)
	orderedClients = orderedClients[1:]

	var errors, retryableErrors int

	// Wait for completions.
	for {
		select {
		case call := <-done:
			if call.Error == nil {
				// Verify response data integrity if this is a proto response.
				if req, reqOk := call.Args.(roachpb.Request); reqOk {
					if resp, respOk := call.Reply.(roachpb.Response); respOk {
						if err := resp.Verify(req); err != nil {
							call.Error = err
						}
					} else {
						call.Error = util.Errorf("response to proto request must be a proto")
					}
				}
			}
			err := call.Error
			if err == nil {
				if log.V(2) {
					log.Infof("%s: successful reply: %+v", method, call.Reply)
				}

				return call.Reply.(proto.Message), nil
			}

			// Error handling.
			if log.V(1) {
				log.Warningf("%s: error reply: %s", method, err)
			}

			errors++

			// Since we have a reconnecting client here, disconnect errors are retryable.
			disconnected := err == netrpc.ErrShutdown || err == io.ErrUnexpectedEOF
			if retryErr, ok := err.(retry.Retryable); disconnected || (ok && retryErr.CanRetry()) {
				retryableErrors++
			}

			if remainingNonErrorRPCs := len(addrs) - errors; remainingNonErrorRPCs < 1 {
				return nil, roachpb.NewSendError(
					fmt.Sprintf("too many errors encountered (%d of %d total): %v",
						errors, len(clients), err), remainingNonErrorRPCs+retryableErrors >= 1)
			}
			// Send to additional replicas if available.
//.........这里部分代码省略.........

// processQueue creates a client and sends messages from its designated queue
// via that client, exiting when the client fails or when it idles out. All
// messages remaining in the queue at that point are lost and a new instance of
// processQueue should be started by the next message to be sent.
// TODO(tschottdorf) should let MultiRaft know if the node is down;
// need a feedback mechanism for that. Potentially easiest is to arrange for
// the next call to Send() to fail appropriately.
func (t *rpcTransport) processQueue(raftNodeID proto.RaftNodeID) {
	t.mu.Lock()
	ch, ok := t.queues[raftNodeID]
	t.mu.Unlock()
	if !ok {
		return
	}
	// Clean-up when the loop below shuts down.
	defer func() {
		t.mu.Lock()
		delete(t.queues, raftNodeID)
		t.mu.Unlock()
	}()

	nodeID, _ := proto.DecodeRaftNodeID(raftNodeID)
	addr, err := t.gossip.GetNodeIDAddress(nodeID)
	if err != nil {
		log.Errorf("could not get address for node %d: %s", nodeID, err)
		return
	}
	client := rpc.NewClient(addr, nil, t.rpcContext)
	select {
	case <-t.rpcContext.Stopper.ShouldStop():
		return
	case <-client.Closed:
		log.Warningf("raft client for node %d failed to connect", nodeID)
		return
	case <-time.After(raftIdleTimeout):
		// Should never happen.
		log.Errorf("raft client for node %d stuck connecting", nodeID)
		return
	case <-client.Ready:
	}

	done := make(chan *gorpc.Call, cap(ch))
	var req *multiraft.RaftMessageRequest
	protoReq := &proto.RaftMessageRequest{}
	protoResp := &proto.RaftMessageResponse{}
	for {
		select {
		case <-t.rpcContext.Stopper.ShouldStop():
			return
		case <-time.After(raftIdleTimeout):
			if log.V(1) {
				log.Infof("closing Raft transport to %d due to inactivity", nodeID)
			}
			return
		case <-client.Closed:
			log.Warningf("raft client for node %d closed", nodeID)
			return
		case call := <-done:
			if call.Error != nil {
				log.Errorf("raft message to node %d failed: %s", nodeID, call.Error)
			}
			continue
		case req = <-ch:
		}
		if req == nil {
			return
		}

		// Convert to proto format.
		protoReq.Reset()
		protoReq.GroupID = req.GroupID
		var err error
		if protoReq.Msg, err = req.Message.Marshal(); err != nil {
			log.Errorf("could not marshal message: %s", err)
			continue
		}

		if !client.IsHealthy() {
			log.Warningf("raft client for node %d unhealthy", nodeID)
			return
		}
		client.Go(raftMessageName, protoReq, protoResp, done)

		// TODO(tschottdorf): work around #1176 by wasting just a little
		// bit of time before moving to the next request.
		select {
		case <-done:
		case <-time.After(10 * time.Millisecond):
		}
	}
}

// processQueue creates a client and sends messages from its designated queue
// via that client, exiting when the client fails or when it idles out. All
// messages remaining in the queue at that point are lost and a new instance of
// processQueue should be started by the next message to be sent.
// TODO(tschottdorf) should let MultiRaft know if the node is down;
// need a feedback mechanism for that. Potentially easiest is to arrange for
// the next call to Send() to fail appropriately.
func (t *rpcTransport) processQueue(nodeID roachpb.NodeID, storeID roachpb.StoreID) {
	t.mu.Lock()
	ch, ok := t.queues[storeID]
	t.mu.Unlock()
	if !ok {
		return
	}
	// Clean-up when the loop below shuts down.
	defer func() {
		t.mu.Lock()
		delete(t.queues, storeID)
		t.mu.Unlock()
	}()

	addr, err := t.gossip.GetNodeIDAddress(nodeID)
	if err != nil {
		if log.V(1) {
			log.Errorf("could not get address for node %d: %s", nodeID, err)
		}
		return
	}
	client := rpc.NewClient(addr, t.rpcContext)
	select {
	case <-t.rpcContext.Stopper.ShouldStop():
		return
	case <-client.Closed:
		log.Warningf("raft client for node %d was closed", nodeID)
		return
	case <-time.After(raftIdleTimeout):
		// Should never happen.
		log.Errorf("raft client for node %d stuck connecting", nodeID)
		return
	case <-client.Healthy():
	}

	done := make(chan *gorpc.Call, cap(ch))
	var req *multiraft.RaftMessageRequest
	protoResp := &multiraft.RaftMessageResponse{}
	for {
		select {
		case <-t.rpcContext.Stopper.ShouldStop():
			return
		case <-time.After(raftIdleTimeout):
			if log.V(1) {
				log.Infof("closing Raft transport to %d due to inactivity", nodeID)
			}
			return
		case <-client.Closed:
			log.Warningf("raft client for node %d closed", nodeID)
			return
		case call := <-done:
			if call.Error != nil {
				log.Errorf("raft message to node %d failed: %s", nodeID, call.Error)
			}
			continue
		case req = <-ch:
		}
		if req == nil {
			return
		}

		client.Go(raftMessageName, req, protoResp, done)
	}
}

// Send sends one or more RPCs to clients specified by the slice of
// replicas. On success, Send returns the first successful reply. Otherwise,
// Send returns an error if and as soon as the number of failed RPCs exceeds
// the available endpoints less the number of required replies.
//
// TODO(pmattis): Get rid of the getArgs function which requires the caller to
// maintain a map from address to replica. Instead, pass in the list of
// replicas instead of a list of addresses and use that to populate the
// requests.
func send(opts SendOptions, replicas ReplicaSlice,
	args roachpb.BatchRequest, context *rpc.Context) (proto.Message, error) {
	sp := opts.Trace
	if sp == nil {
		sp = tracing.NilSpan()
	}

	if len(replicas) < 1 {
		return nil, roachpb.NewSendError(
			fmt.Sprintf("insufficient replicas (%d) to satisfy send request of %d",
				len(replicas), 1), false)
	}

	done := make(chan *netrpc.Call, len(replicas))

	clients := make([]batchClient, 0, len(replicas))
	for i, replica := range replicas {
		clients = append(clients, batchClient{
			Client:  rpc.NewClient(&replica.NodeDesc.Address, context),
			replica: &replicas[i],
			args:    args,
		})
	}

	var orderedClients []batchClient
	switch opts.Ordering {
	case orderStable:
		orderedClients = clients
	case orderRandom:
		// Randomly permute order, but keep known-unhealthy clients last.
		var nHealthy int
		for i, client := range clients {
			select {
			case <-client.Healthy():
				clients[i], clients[nHealthy] = clients[nHealthy], clients[i]
				nHealthy++
			default:
			}
		}

		shuffleClients(clients[:nHealthy])
		shuffleClients(clients[nHealthy:])

		orderedClients = clients
	}
	// TODO(spencer): going to need to also sort by affinity; closest
	// ping time should win. Makes sense to have the rpc client/server
	// heartbeat measure ping times. With a bit of seasoning, each
	// node will be able to order the healthy replicas based on latency.

	// Send the first request.
	sendOneFn(&orderedClients[0], opts.Timeout, context, sp, done)
	orderedClients = orderedClients[1:]

	var errors, retryableErrors int

	// Wait for completions.
	var sendNextTimer util.Timer
	defer sendNextTimer.Stop()
	for {
		sendNextTimer.Reset(opts.SendNextTimeout)
		select {
		case <-sendNextTimer.C:
			sendNextTimer.Read = true
			// On successive RPC timeouts, send to additional replicas if available.
			if len(orderedClients) > 0 {
				sp.LogEvent("timeout, trying next peer")
				sendOneFn(&orderedClients[0], opts.Timeout, context, sp, done)
				orderedClients = orderedClients[1:]
			}

		case call := <-done:
			if call.Error == nil {
				// Verify response data integrity if this is a proto response.
				if req, reqOk := call.Args.(roachpb.Request); reqOk {
					if resp, respOk := call.Reply.(roachpb.Response); respOk {
						if err := resp.Verify(req); err != nil {
							call.Error = err
						}
					} else {
						call.Error = util.Errorf("response to proto request must be a proto")
					}
				}
			}
			err := call.Error
			if err == nil {
				if log.V(2) {
					log.Infof("successful reply: %+v", call.Reply)
				}

				return call.Reply.(proto.Message), nil
//.........这里部分代码省略.........