seaweedfs/weed/server/master_grpc_server.go

package weed_server

import (
	"context"
	"errors"
	"fmt"
	"net"
	"sort"
	"time"

	"github.com/google/uuid"
	"github.com/seaweedfs/seaweedfs/weed/cluster"

	"github.com/seaweedfs/seaweedfs/weed/cluster/maintenance"

	"github.com/seaweedfs/seaweedfs/weed/pb"
	"github.com/seaweedfs/seaweedfs/weed/stats"
	"github.com/seaweedfs/seaweedfs/weed/storage/backend"
	"github.com/seaweedfs/seaweedfs/weed/util"

	"github.com/seaweedfs/raft"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/peer"
	"google.golang.org/grpc/status"

	"github.com/seaweedfs/seaweedfs/weed/glog"
	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
	"github.com/seaweedfs/seaweedfs/weed/topology"
)

// A volume moved between the node's disks appears in both lists, and clients
// apply additions before deletions, so passing the removal on would drop a
// location that is still good. Not HasVolumesById, which answers for ec shards
// too: clients hold those separately and prefer the normal location, so a
// replica that became ec shards has to be reported gone.
func shouldBroadcastVolumeRemoval(dn *topology.DataNode, vid needle.VolumeId) bool {
	_, err := dn.GetVolumesById(vid)
	return err != nil
}

// heartbeatResponse carries the options a volume server takes from every
// response it receives. A response that left them out would be read as the
// master turning them off, so anything sent mid-stream has to start here.
func (ms *MasterServer) heartbeatResponse() *master_pb.HeartbeatResponse {
	return &master_pb.HeartbeatResponse{
		VolumeSizeLimit: uint64(ms.option.VolumeSizeLimitMB) * 1024 * 1024,
		Preallocate:     ms.preallocateSize > 0,
	}
}

func (ms *MasterServer) RegisterUuids(heartbeat *master_pb.Heartbeat) (duplicated_uuids []string, err error) {
	ms.Topo.UuidAccessLock.Lock()
	defer ms.Topo.UuidAccessLock.Unlock()
	key := fmt.Sprintf("%s:%d", heartbeat.Ip, heartbeat.Port)
	if ms.Topo.UuidMap == nil {
		ms.Topo.UuidMap = make(map[string][]string)
	}
	// find whether new uuid exists
	for k, v := range ms.Topo.UuidMap {
		sort.Strings(v)
		for _, id := range heartbeat.LocationUuids {
			index := sort.SearchStrings(v, id)
			if index < len(v) && v[index] == id {
				duplicated_uuids = append(duplicated_uuids, id)
				glog.Errorf("directory of %s on %s has been loaded", id, k)
			}
		}
	}
	if len(duplicated_uuids) > 0 {
		return duplicated_uuids, errors.New("volume: Duplicated volume directories were loaded")
	}

	ms.Topo.UuidMap[key] = heartbeat.LocationUuids
	glog.V(0).Infof("found new uuid:%v %v , %v", key, heartbeat.LocationUuids, ms.Topo.UuidMap)
	return nil, nil
}

func (ms *MasterServer) UnRegisterUuids(ip string, port int) {
	ms.Topo.UuidAccessLock.Lock()
	defer ms.Topo.UuidAccessLock.Unlock()
	key := fmt.Sprintf("%s:%d", ip, port)
	delete(ms.Topo.UuidMap, key)
	glog.V(0).Infof("remove volume server %v, online volume server: %v", key, ms.Topo.UuidMap)
}

// announceVolume records vid on the broadcast message. A remote-tier volume
// goes on both lists: RemoteVids carries the classification, and NewVids keeps
// a client too old to read RemoteVids from losing the volume altogether during
// a rolling upgrade.
func announceVolume(message *master_pb.VolumeLocation, vid uint32, isRemote bool) {
	message.NewVids = append(message.NewVids, vid)
	if isRemote {
		message.RemoteVids = append(message.RemoteVids, vid)
	}
}

func (ms *MasterServer) SendHeartbeat(stream master_pb.Seaweed_SendHeartbeatServer) error {
	var dn *topology.DataNode

	defer func() {
		if dn != nil {
			dn.Counter--
			if dn.Counter > 0 {
				glog.V(0).Infof("disconnect phantom volume server %s:%d remaining %d", dn.Ip, dn.Port, dn.Counter)
				return
			}

			message := &master_pb.VolumeLocation{
				DataCenter: dn.GetDataCenterId(),
				Url:        dn.Url(),
				PublicUrl:  dn.PublicUrl,
				GrpcPort:   uint32(dn.GrpcPort),
			}
			for _, v := range dn.GetVolumes() {
				message.DeletedVids = append(message.DeletedVids, uint32(v.Id))
			}
			for _, s := range dn.GetEcShards() {
				message.DeletedEcVids = append(message.DeletedEcVids, uint32(s.VolumeId))
			}

			// if the volume server disconnects and reconnects quickly
			//  the unregister and register can race with each other
			ms.Topo.UnRegisterDataNode(dn)
			glog.V(0).Infof("unregister disconnected volume server %s:%d", dn.Ip, dn.Port)
			ms.UnRegisterUuids(dn.Ip, dn.Port)

			if ms.Topo.IsLeader() && (len(message.DeletedVids) > 0 || len(message.DeletedEcVids) > 0) {
				ms.broadcastToClients(&master_pb.KeepConnectedResponse{VolumeLocation: message})
			}
		}
	}()

	for {
		heartbeat, err := stream.Recv()
		if err != nil {
			// Graceful shutdown on either side cancels the stream; don't warn.
			canceled := errors.Is(err, context.Canceled) || status.Code(err) == codes.Canceled
			switch {
			case canceled && dn != nil:
				glog.V(1).Infof("SendHeartbeat.Recv server %s:%d canceled: %v", dn.Ip, dn.Port, err)
			case canceled:
				glog.V(1).Infof("SendHeartbeat.Recv canceled: %v", err)
			case dn != nil:
				glog.Warningf("SendHeartbeat.Recv server %s:%d : %v", dn.Ip, dn.Port, err)
			default:
				glog.Warningf("SendHeartbeat.Recv: %v", err)
			}
			stats.MasterReceivedHeartbeatCounter.WithLabelValues("error").Inc()
			return err
		}

		if !ms.Topo.IsLeader() {
			// tell the volume servers about the leader we know of right now, so
			// that a follower without one hands the heartbeat back immediately
			// instead of holding it through an election
			newLeader, err := ms.Topo.MaybeLeader()
			if err != nil || newLeader == "" {
				glog.V(1).Infof("SendHeartbeat find leader: %v", err)
				return raft.NotLeaderError
			}
			if err := stream.Send(&master_pb.HeartbeatResponse{
				Leader: string(newLeader),
			}); err != nil {
				if dn != nil {
					glog.Warningf("SendHeartbeat.Send response to %s:%d %v", dn.Ip, dn.Port, err)
				} else {
					glog.Warningf("SendHeartbeat.Send response %v", err)
				}
				return err
			}
			continue
		}

		ms.Topo.Sequence.SetMax(heartbeat.MaxFileKey)
		if dn == nil {
			// Skip delta heartbeat for volume server versions  better than 3.28 https://github.com/seaweedfs/seaweedfs/pull/3630
			if heartbeat.Ip == "" {
				continue
			} // ToDo must be removed after update major version
			dcName, rackName := ms.Topo.Configuration.Locate(heartbeat.Ip, heartbeat.DataCenter, heartbeat.Rack)
			dc := ms.Topo.GetOrCreateDataCenter(dcName)
			rack := dc.GetOrCreateRack(rackName)
			dn = rack.GetOrCreateDataNode(heartbeat.Ip, int(heartbeat.Port), int(heartbeat.GrpcPort), heartbeat.PublicUrl, heartbeat.Id, heartbeat.MaxVolumeCounts)
			glog.V(0).Infof("added volume server %d: %v (id=%s, ip=%v:%d) %v", dn.Counter, dn.Id(), heartbeat.Id, heartbeat.GetIp(), heartbeat.GetPort(), heartbeat.LocationUuids)
			uuidlist, err := ms.RegisterUuids(heartbeat)
			if err != nil {
				if stream_err := stream.Send(&master_pb.HeartbeatResponse{
					DuplicatedUuids: uuidlist,
				}); stream_err != nil {
					glog.Warningf("SendHeartbeat.Send DuplicatedDirectory response to %s:%d %v", dn.Ip, dn.Port, stream_err)
					return stream_err
				}
				return err
			}

			response := ms.heartbeatResponse()
			response.VolumeDigestSupported = true
			if err := stream.Send(response); err != nil {
				glog.Warningf("SendHeartbeat.Send volume size to %s:%d %v", dn.Ip, dn.Port, err)
				return err
			}
			stats.MasterReceivedHeartbeatCounter.WithLabelValues("dataNode").Inc()
			dn.Counter++
		}

		dn.AdjustMaxVolumeCounts(heartbeat.MaxVolumeCounts)
		dn.AdjustDiskUsageBytes(heartbeat.DiskTotalBytes, heartbeat.DiskFreeBytes)
		dn.UpdateDiskTags(heartbeat.DiskTags)

		glog.V(4).Infof("master received heartbeat %s", heartbeat.String())
		stats.MasterReceivedHeartbeatCounter.WithLabelValues("total").Inc()

		// Every heartbeat may carry the state, so a master that just took over
		// learns about a server already in maintenance from the first one.
		if heartbeat.State != nil && ms.Topo.SetDataNodeMaintenanceMode(dn, heartbeat.State.GetMaintenance()) {
			stats.MasterReceivedHeartbeatCounter.WithLabelValues("stateUpdates").Inc()
			glog.V(1).Infof("master sees state update from %s: %v", dn.Url(), heartbeat.State)
		}

		message := &master_pb.VolumeLocation{
			Url:        dn.Url(),
			PublicUrl:  dn.PublicUrl,
			DataCenter: dn.GetDataCenterId(),
			GrpcPort:   uint32(dn.GrpcPort),
		}
		if len(heartbeat.NewVolumes) > 0 {
			stats.MasterReceivedHeartbeatCounter.WithLabelValues("newVolumes").Inc()
		}
		if len(heartbeat.DeletedVolumes) > 0 {
			stats.MasterReceivedHeartbeatCounter.WithLabelValues("deletedVolumes").Inc()
		}
		if len(heartbeat.NewVolumes) > 0 || len(heartbeat.DeletedVolumes) > 0 {
			// first, so the removals below see where the volumes ended up
			ms.Topo.IncrementalSyncDataNodeRegistration(heartbeat.NewVolumes, heartbeat.DeletedVolumes, dn)

			// process delta volume ids if exists for fast volume id updates
			for _, volInfo := range heartbeat.NewVolumes {
				// The short form carries no remote-storage name, so the volume
				// reads as local until a changed or full report names its tier.
				announceVolume(message, volInfo.Id, false)
			}
			for _, volInfo := range heartbeat.DeletedVolumes {
				if !shouldBroadcastVolumeRemoval(dn, needle.VolumeId(volInfo.Id)) {
					continue
				}
				message.DeletedVids = append(message.DeletedVids, volInfo.Id)
			}
		}

		if len(heartbeat.ChangedVolumes) > 0 {
			stats.MasterReceivedHeartbeatCounter.WithLabelValues("changedVolumes").Inc()
			for _, v := range ms.Topo.ApplyVolumeChanges(heartbeat.ChangedVolumes, dn) {
				// Changed volumes include both newly-added replicas and existing
				// replicas whose tier classification flipped, which the client
				// has to be told about to refresh its replica priority.
				announceVolume(message, uint32(v.Id), v.IsRemote())
			}
		}

		if len(heartbeat.Volumes) > 0 || heartbeat.HasNoVolumes {
			if heartbeat.Ip != "" {
				dcName, rackName := ms.Topo.Configuration.Locate(heartbeat.Ip, heartbeat.DataCenter, heartbeat.Rack)
				ms.Topo.DataNodeRegistration(dcName, rackName, dn)
			}

			// process heartbeat.Volumes
			stats.MasterReceivedHeartbeatCounter.WithLabelValues("Volumes").Inc()
			newVolumes, deletedVolumes, changedVolumes := ms.Topo.SyncDataNodeRegistration(heartbeat.Volumes, dn)

			for _, v := range newVolumes {
				glog.V(1).Infof("master see new volume %d from %s", uint32(v.Id), dn.Url())
				announceVolume(message, uint32(v.Id), v.IsRemote())
			}
			// A full reconciliation is the digest mismatch recovery path, and
			// the only way a re-tiered replica reaches the master without a
			// separate ChangedVolumes heartbeat. Announcing the changed set
			// too is what stops the client keeping the old classification.
			for _, v := range changedVolumes {
				glog.V(1).Infof("master see tier/readonly change on volume %d from %s", uint32(v.Id), dn.Url())
				announceVolume(message, uint32(v.Id), v.IsRemote())
			}
			for _, v := range deletedVolumes {
				glog.V(1).Infof("master see deleted volume %d from %s", uint32(v.Id), dn.Url())
				if !shouldBroadcastVolumeRemoval(dn, v.Id) {
					continue
				}
				message.DeletedVids = append(message.DeletedVids, uint32(v.Id))
			}
		}

		if len(heartbeat.NewEcShards) > 0 || len(heartbeat.DeletedEcShards) > 0 {
			stats.MasterReceivedHeartbeatCounter.WithLabelValues("newEcShards").Inc()
			// update master internal volume layouts
			ms.Topo.IncrementalSyncDataNodeEcShards(heartbeat.NewEcShards, heartbeat.DeletedEcShards, dn)

			for _, s := range heartbeat.NewEcShards {
				message.NewEcVids = append(message.NewEcVids, s.Id)
			}
			for _, s := range heartbeat.DeletedEcShards {
				if dn.HasEcShards(needle.VolumeId(s.Id)) {
					continue
				}
				message.DeletedEcVids = append(message.DeletedEcVids, s.Id)
			}

		}

		if len(heartbeat.EcShards) > 0 || heartbeat.HasNoEcShards {
			stats.MasterReceivedHeartbeatCounter.WithLabelValues("ecShards").Inc()
			glog.V(4).Infof("master received ec shards from %s: %+v", dn.Url(), heartbeat.EcShards)
			newShards, deletedShards := ms.Topo.SyncDataNodeEcShards(heartbeat.EcShards, dn)

			// broadcast the ec vid changes to master clients
			for _, s := range newShards {
				message.NewEcVids = append(message.NewEcVids, uint32(s.VolumeId))
			}
			for _, s := range deletedShards {
				if dn.HasVolumesById(s.VolumeId) {
					continue
				}
				message.DeletedEcVids = append(message.DeletedEcVids, uint32(s.VolumeId))
			}

		}
		if len(message.NewVids) > 0 || len(message.DeletedVids) > 0 || len(message.NewEcVids) > 0 || len(message.DeletedEcVids) > 0 {
			ms.broadcastToClients(&master_pb.KeepConnectedResponse{VolumeLocation: message})
		}

		// Checked after everything the heartbeat carried has been applied, so a
		// match means the master is current, not that nothing changed.
		if resend := ms.checkVolumeDigest(heartbeat, dn); resend {
			response := ms.heartbeatResponse()
			response.ResendFullVolumeList = true
			if err := stream.Send(response); err != nil {
				glog.Warningf("SendHeartbeat.Send resend request to %s:%d %v", dn.Ip, dn.Port, err)
				return err
			}
		}
	}
}

// checkVolumeDigest compares the digest a volume server reported against the
// master's own, and reports whether the master needs the full volume list to
// recover. Servers that report no digest are left alone: they still send the
// whole list every time.
func (ms *MasterServer) checkVolumeDigest(heartbeat *master_pb.Heartbeat, dn *topology.DataNode) bool {
	if heartbeat.VolumeDigest == nil {
		return false
	}

	reported := heartbeat.GetVolumeDigest()
	held := dn.VolumeDigest()
	needsFullList, reason := true, ""
	switch {
	case dn.HasDuplicateVolumeIds():
		// Reported twice but stored once, so the digests can never agree. The
		// server has to keep sending its whole list, since nothing else would
		// tell the master what it had stopped holding.
		stats.MasterReceivedHeartbeatCounter.WithLabelValues("volumeDigestNotComparable").Inc()
	case !dn.HasConsistentVolumeIndex():
		// The lookup index has drifted from the disks, which the server cannot
		// see and its digest cannot show. Only a full report re-registers the
		// volumes that stopped being servable.
		stats.MasterReceivedHeartbeatCounter.WithLabelValues("volumeIndexInconsistent").Inc()
		reason = "lookup index disagrees with the volumes held"
	case held != reported:
		stats.MasterReceivedHeartbeatCounter.WithLabelValues("volumeDigestMismatch").Inc()
		reason = fmt.Sprintf("reported digest %d, master holds %d", reported, held)
	default:
		stats.MasterReceivedHeartbeatCounter.WithLabelValues("volumeDigestMatch").Inc()
		needsFullList = false
	}
	if !needsFullList {
		return false
	}

	// A heartbeat that already carried the full list has nothing more to give.
	if len(heartbeat.Volumes) > 0 || heartbeat.HasNoVolumes {
		if reason != "" {
			glog.Warningf("volume server %s still disagrees after a full volume list: %s", dn.Url(), reason)
		}
		return false
	}
	if reason != "" {
		glog.V(0).Infof("volume server %s: %s, requesting the full volume list", dn.Url(), reason)
	}
	return true
}

// KeepConnected keep a stream gRPC call to the master. Used by clients to know the master is up.
// And clients gets the up-to-date list of volume locations
func (ms *MasterServer) KeepConnected(stream master_pb.Seaweed_KeepConnectedServer) error {

	req, recvErr := stream.Recv()
	if recvErr != nil {
		return recvErr
	}

	if !ms.Topo.IsLeader() {
		return ms.informNewLeader(stream)
	}

	clientAddress := req.ClientAddress
	// Ensure that the clientAddress is unique.
	if clientAddress == "" {
		clientAddress = uuid.New().String()
	}
	peerAddress := pb.ServerAddress(clientAddress)

	// buffer by 1 so we don't end up getting stuck writing to stopChan forever
	stopChan := make(chan bool, 1)

	clientName, messageChan := ms.addClient(req.FilerGroup, req.ClientType, peerAddress)
	for _, update := range ms.Cluster.AddClusterNode(req.FilerGroup, req.ClientType, cluster.DataCenter(req.DataCenter), cluster.Rack(req.Rack), peerAddress, req.Version) {
		glog.V(1).Infof("Cluster: %s node %s added to group '%s'", req.ClientType, peerAddress, req.FilerGroup)
		ms.broadcastToClients(update)
	}
	if req.ClientType == cluster.FilerType {
		ms.LockRingManager.AddServer(cluster.FilerGroupName(req.FilerGroup), peerAddress)
	}
	if req.ClientType == cluster.MasterType {
		// Only the leader gets this far, and a master that starts with no raft
		// state cannot campaign its way in, so this registration is where it
		// joins the quorum. The broadcast below is not enough: it only reaches
		// masters already connected to us.
		ms.AdmitRaftPeer(peerAddress)
	}

	defer func() {
		for _, update := range ms.Cluster.RemoveClusterNode(req.FilerGroup, req.ClientType, peerAddress) {
			ms.broadcastToClients(update)
		}
		if req.ClientType == cluster.FilerType {
			ms.LockRingManager.RemoveServer(cluster.FilerGroupName(req.FilerGroup), peerAddress)
		}
		ms.deleteClient(clientName, messageChan)
	}()

	// Send volume locations to the client
	volumeLocations := ms.Topo.ToVolumeLocations()
	if len(volumeLocations) == 0 {
		// Always send at least one message with leader info so the client can unblock
		leader, _ := ms.Topo.Leader()
		if sendErr := stream.Send(&master_pb.KeepConnectedResponse{
			VolumeLocation: &master_pb.VolumeLocation{
				Leader: string(leader),
			},
		}); sendErr != nil {
			return sendErr
		}
	} else {
		for i, message := range volumeLocations {
			if i == 0 {
				if leader, err := ms.Topo.Leader(); err == nil {
					message.Leader = string(leader)
				}
			}
			if sendErr := stream.Send(&master_pb.KeepConnectedResponse{VolumeLocation: message}); sendErr != nil {
				return sendErr
			}
		}
	}

	// Cluster node changes are only broadcast to the clients connected at that
	// moment, so a client that reconnects has to be told who is around now.
	for _, update := range ms.Cluster.ListClusterNodeUpdates(cluster.FilerGroupName(req.FilerGroup), cluster.FilerType) {
		if sendErr := stream.Send(update); sendErr != nil {
			return sendErr
		}
	}

	if initialLockRingUpdate := ms.initialLockRingUpdate(req.ClientType, req.FilerGroup); initialLockRingUpdate != nil {
		if sendErr := stream.Send(initialLockRingUpdate); sendErr != nil {
			return sendErr
		}
	}

	go func() {
		for {
			_, err := stream.Recv()
			if err != nil {
				glog.V(2).Infof("- client %v: %v", clientName, err)
				go func() {
					// consume message chan to avoid deadlock, go routine exit when message chan is closed
					for range messageChan {
						// no op
					}
				}()
				close(stopChan)
				return
			}
		}
	}()

	ticker := time.NewTicker(5 * time.Second)
	defer ticker.Stop()
	for {
		select {
		case message, ok := <-messageChan:
			if !ok {
				// a closed channel receives nil forever; without this check the
				// loop would flood the client with empty messages at wire speed
				return nil
			}
			if err := stream.Send(message); err != nil {
				// The error, not the message: it carries every volume id on a
				// newly connected node, and formatting a proto that size to
				// say a client went away costs more than the send did.
				glog.V(0).Infof("=> client %v: %v", clientName, err)
				return err
			}
		case <-ticker.C:
			if !ms.Topo.IsLeader() {
				stats.MasterRaftIsleader.Set(0)
				stats.MasterAdminLock.Reset()
				stats.MasterReplicaPlacementMismatch.Reset()
				return ms.informNewLeader(stream)
			} else {
				stats.MasterRaftIsleader.Set(1)
			}
		case <-stopChan:
			return nil
		}
	}

}

func (ms *MasterServer) initialLockRingUpdate(clientType string, filerGroup string) *master_pb.KeepConnectedResponse {
	if ms.LockRingManager == nil {
		return nil
	}
	// Filers are ring members; S3 gateways are lock clients that need the same
	// view to dial a key's primary directly. Both get the initial snapshot;
	// later membership changes already broadcast to every connected client.
	if clientType != cluster.FilerType && clientType != cluster.S3Type {
		return nil
	}

	update := ms.LockRingManager.GetLastUpdate(cluster.FilerGroupName(filerGroup))
	if update == nil {
		return nil
	}

	return &master_pb.KeepConnectedResponse{
		LockRingUpdate: update,
	}
}

func (ms *MasterServer) broadcastToClients(message *master_pb.KeepConnectedResponse) {
	ms.clientChansLock.RLock()
	for client, ch := range ms.clientChans {
		select {
		case ch <- message:
			glog.V(4).Infof("send message to %s", client)
		default:
			stats.MasterBroadcastToFullErrorCounter.Inc()
			glog.Errorf("broadcastToClients %s message full", client)
		}
	}
	ms.clientChansLock.RUnlock()
}

// broadcastVolumeLocationsToClients notifies connected clients about newly created volume locations.
func (ms *MasterServer) broadcastVolumeLocationsToClients(locations []*master_pb.VolumeLocation) {
	for _, location := range locations {
		ms.broadcastToClients(&master_pb.KeepConnectedResponse{VolumeLocation: location})
	}
}

func (ms *MasterServer) informNewLeader(stream master_pb.Seaweed_KeepConnectedServer) error {
	// Answer from what raft knows now. Waiting out an election here pins the
	// client to a master that cannot serve it, right when it should be moving
	// on to the next peer to find the one that can.
	leader, err := ms.Topo.MaybeLeader()
	if err != nil || leader == "" {
		glog.V(1).Infof("topo leader: %v", err)
		return raft.NotLeaderError
	}
	if err := stream.Send(&master_pb.KeepConnectedResponse{
		VolumeLocation: &master_pb.VolumeLocation{
			Leader: string(leader),
		},
	}); err != nil {
		return err
	}
	return nil
}

func (ms *MasterServer) addClient(filerGroup, clientType string, clientAddress pb.ServerAddress) (clientName string, messageChan chan *master_pb.KeepConnectedResponse) {
	clientName = filerGroup + "." + clientType + "@" + string(clientAddress)
	glog.V(0).Infof("+ client %v", clientName)

	// we buffer this because otherwise we end up in a potential deadlock where
	// the KeepConnected loop is no longer listening on this channel but we're
	// trying to send to it in SendHeartbeat and so we can't lock the
	// clientChansLock to remove the channel and we're stuck writing to it
	messageChan = make(chan *master_pb.KeepConnectedResponse, 10000)

	ms.clientChansLock.Lock()
	ms.clientChans[clientName] = messageChan
	ms.clientChansLock.Unlock()
	return
}

func (ms *MasterServer) deleteClient(clientName string, messageChan chan *master_pb.KeepConnectedResponse) {
	glog.V(0).Infof("- client %v", clientName)
	ms.clientChansLock.Lock()
	// a client that reconnects before the old handler exits re-registers the
	// same name, so the map may already hold the new stream's channel: close
	// only our own, and leave the entry alone unless it is still ours
	if ms.clientChans[clientName] == messageChan {
		delete(ms.clientChans, clientName)
	}
	// safe under the write lock: broadcasters send while holding the read
	// lock and only to channels found in the map
	close(messageChan)
	ms.clientChansLock.Unlock()
}

func findClientAddress(ctx context.Context, grpcPort uint32) string {
	// fmt.Printf("FromContext %+v\n", ctx)
	pr, ok := peer.FromContext(ctx)
	if !ok {
		glog.Error("failed to get peer from ctx")
		return ""
	}
	if pr.Addr == net.Addr(nil) {
		glog.Error("failed to get peer address")
		return ""
	}
	if grpcPort == 0 {
		return pr.Addr.String()
	}
	if tcpAddr, ok := pr.Addr.(*net.TCPAddr); ok {
		externalIP := tcpAddr.IP
		return util.JoinHostPort(externalIP.String(), int(grpcPort))
	}
	return pr.Addr.String()

}

func (ms *MasterServer) GetMasterConfiguration(ctx context.Context, req *master_pb.GetMasterConfigurationRequest) (*master_pb.GetMasterConfigurationResponse, error) {

	// tell the volume servers about the leader
	leader, _ := ms.Topo.MaybeLeader()

	// MIGRATION: expose maintenance scripts for admin server seeding. Remove after March 2027.
	v := util.GetViper()
	maintenanceScripts := v.GetString("master.maintenance.scripts")
	maintenanceSleepMinutes := v.GetInt("master.maintenance.sleep_minutes")
	if maintenanceSleepMinutes <= 0 {
		maintenanceSleepMinutes = maintenance.DefaultMaintenanceSleepMinutes
	}

	resp := &master_pb.GetMasterConfigurationResponse{
		MetricsAddress:          ms.option.MetricsAddress,
		MetricsIntervalSeconds:  uint32(ms.option.MetricsIntervalSec),
		StorageBackends:         backend.ToPbStorageBackends(),
		DefaultReplication:      ms.option.DefaultReplicaPlacement,
		VolumeSizeLimitMB:       uint32(ms.option.VolumeSizeLimitMB),
		VolumePreallocate:       ms.option.VolumePreallocate,
		Leader:                  string(leader),
		MaintenanceScripts:      maintenanceScripts,
		MaintenanceSleepMinutes: uint32(maintenanceSleepMinutes),
	}

	return resp, nil
}