package peerstream import ( "context" "crypto/subtle" "fmt" "io" "strings" "sync" "time" "github.com/armon/go-metrics" "github.com/golang/protobuf/jsonpb" "github.com/golang/protobuf/proto" "github.com/hashicorp/go-hclog" "google.golang.org/grpc" "google.golang.org/grpc/codes" grpcstatus "google.golang.org/grpc/status" "github.com/hashicorp/consul/agent/connect" external "github.com/hashicorp/consul/agent/grpc-external" "github.com/hashicorp/consul/agent/structs" "github.com/hashicorp/consul/lib" "github.com/hashicorp/consul/proto/pbpeering" "github.com/hashicorp/consul/proto/pbpeerstream" ) type BidirectionalStream interface { Send(*pbpeerstream.ReplicationMessage) error Recv() (*pbpeerstream.ReplicationMessage, error) Context() context.Context } // ExchangeSecret exchanges the one-time secret embedded in a peering token for a // long-lived secret for use with the peering stream handler. This secret exchange // prevents peering tokens from being reused. // // Note that if the peering secret exchange fails, a peering token may need to be // re-generated, since the one-time initiation secret may have been invalidated. func (s *Server) ExchangeSecret(ctx context.Context, req *pbpeerstream.ExchangeSecretRequest) (*pbpeerstream.ExchangeSecretResponse, error) { // For private/internal gRPC handlers, protoc-gen-rpc-glue generates the // requisite methods to satisfy the structs.RPCInfo interface using fields // from the pbcommon package. This service is public, so we can't use those // fields in our proto definition. Instead, we construct our RPCInfo manually. // // Embedding WriteRequest ensures RPCs are forwarded to the leader, embedding // DCSpecificRequest adds the RequestDatacenter method (but as we're not // setting Datacenter it has the effect of *not* doing DC forwarding). var rpcInfo struct { structs.WriteRequest structs.DCSpecificRequest } var resp *pbpeerstream.ExchangeSecretResponse handled, err := s.ForwardRPC(&rpcInfo, func(conn *grpc.ClientConn) error { var err error resp, err = pbpeerstream.NewPeerStreamServiceClient(conn).ExchangeSecret(ctx, req) return err }) if handled || err != nil { return resp, err } defer metrics.MeasureSince([]string{"peering", "exchange_secret"}, time.Now()) // Validate the given establishment secret against the one stored on the server. existing, err := s.GetStore().PeeringSecretsRead(nil, req.PeerID) if err != nil { return nil, grpcstatus.Errorf(codes.Internal, "failed to read peering secret: %v", err) } if existing == nil || subtle.ConstantTimeCompare([]byte(existing.GetEstablishment().GetSecretID()), []byte(req.EstablishmentSecret)) == 0 { return nil, grpcstatus.Error(codes.PermissionDenied, "invalid peering establishment secret") } id, err := s.generateNewStreamSecret() if err != nil { return nil, grpcstatus.Errorf(codes.Internal, "failed to generate peering stream secret: %v", err) } writeReq := &pbpeering.SecretsWriteRequest{ PeerID: req.PeerID, Request: &pbpeering.SecretsWriteRequest_ExchangeSecret{ ExchangeSecret: &pbpeering.SecretsWriteRequest_ExchangeSecretRequest{ // Pass the given establishment secret to that it can be re-validated at the state store. // Validating the establishment secret at the RPC is not enough because there can be // concurrent callers with the same establishment secret. EstablishmentSecret: req.EstablishmentSecret, // Overwrite any existing un-utilized pending stream secret. PendingStreamSecret: id, }, }, } err = s.Backend.PeeringSecretsWrite(writeReq) if err != nil { return nil, grpcstatus.Errorf(codes.Internal, "failed to persist peering secret: %v", err) } return &pbpeerstream.ExchangeSecretResponse{StreamSecret: id}, nil } func (s *Server) generateNewStreamSecret() (string, error) { id, err := lib.GenerateUUID(s.Backend.ValidateProposedPeeringSecret) if err != nil { return "", err } return id, nil } // StreamResources handles incoming streaming connections. func (s *Server) StreamResources(stream pbpeerstream.PeerStreamService_StreamResourcesServer) error { logger := s.Logger.Named("stream-resources").With("request_id", external.TraceID()) logger.Trace("Started processing request") defer logger.Trace("Finished processing request") // NOTE: this code should have similar error handling to the new-request // handling code in HandleStream() if !s.Backend.IsLeader() { // We are not the leader so we will hang up on the dialer. logger.Debug("cannot establish a peering stream on a follower node") st, err := grpcstatus.New(codes.FailedPrecondition, "cannot establish a peering stream on a follower node").WithDetails( &pbpeerstream.LeaderAddress{Address: s.Backend.GetLeaderAddress()}) if err != nil { logger.Error(fmt.Sprintf("failed to marshal the leader address in response; err: %v", err)) return grpcstatus.Error(codes.FailedPrecondition, "cannot establish a peering stream on a follower node") } else { return st.Err() } } // Initial message on a new stream must be a new subscription request. first, err := stream.Recv() if err != nil { logger.Error("failed to establish stream", "error", err) return err } // TODO(peering) Make request contain a list of resources, so that roots and services can be // subscribed to with a single request. See: // https://github.com/envoyproxy/data-plane-api/blob/main/envoy/service/discovery/v3/discovery.proto#L46 req := first.GetOpen() if req == nil { return grpcstatus.Error(codes.InvalidArgument, "first message when initiating a peering must be: Open") } logger.Trace("received initial replication request from peer") logTraceRecv(logger, req) if req.PeerID == "" { return grpcstatus.Error(codes.InvalidArgument, "initial subscription request must specify a PeerID") } _, p, err := s.GetStore().PeeringReadByID(nil, req.PeerID) if err != nil { logger.Error("failed to look up peer", "peer_id", req.PeerID, "error", err) return grpcstatus.Error(codes.Internal, "failed to find PeerID: "+req.PeerID) } if p == nil { return grpcstatus.Error(codes.InvalidArgument, "initial subscription for unknown PeerID: "+req.PeerID) } if !p.IsActive() { // If peering is terminated, then our peer sent the termination message. // For other non-active states, send the termination message. if p.State != pbpeering.PeeringState_TERMINATED { term := &pbpeerstream.ReplicationMessage{ Payload: &pbpeerstream.ReplicationMessage_Terminated_{ Terminated: &pbpeerstream.ReplicationMessage_Terminated{}, }, } logTraceSend(logger, term) // we don't care if send fails; stream will be killed by termination message or grpc error _ = stream.Send(term) } return grpcstatus.Error(codes.Aborted, "peering is marked as deleted: "+req.PeerID) } secrets, err := s.GetStore().PeeringSecretsRead(nil, req.PeerID) if err != nil { logger.Error("failed to look up secrets for peering", "peer_id", req.PeerID, "error", err) return grpcstatus.Error(codes.Internal, "failed to find peering secrets for PeerID: "+req.PeerID) } if secrets == nil { logger.Error("no known secrets for peering", "peer_id", req.PeerID, "error", err) return grpcstatus.Error(codes.Internal, "unable to authorize connection, peering must be re-established") } // Check the given secret ID against the active stream secret. var authorized bool if active := secrets.GetStream().GetActiveSecretID(); active != "" { if subtle.ConstantTimeCompare([]byte(active), []byte(req.StreamSecretID)) == 1 { authorized = true } } // Next check the given stream secret against the locally stored pending stream secret. // A pending stream secret is one that has not been seen by this handler. if pending := secrets.GetStream().GetPendingSecretID(); pending != "" && !authorized { // If the given secret is the currently pending secret, it gets promoted to be the active secret. // This is the case where a server recently exchanged for a stream secret. if subtle.ConstantTimeCompare([]byte(pending), []byte(req.StreamSecretID)) == 0 { return grpcstatus.Error(codes.PermissionDenied, "invalid peering stream secret") } authorized = true promoted := &pbpeering.SecretsWriteRequest{ PeerID: p.ID, Request: &pbpeering.SecretsWriteRequest_PromotePending{ PromotePending: &pbpeering.SecretsWriteRequest_PromotePendingRequest{ // Overwrite any existing un-utilized pending stream secret. ActiveStreamSecret: pending, }, }, } err = s.Backend.PeeringSecretsWrite(promoted) if err != nil { return grpcstatus.Errorf(codes.Internal, "failed to persist peering secret: %v", err) } } if !authorized { return grpcstatus.Error(codes.PermissionDenied, "invalid peering stream secret") } logger.Info("accepted initial replication request from peer", "peer_id", p.ID) if p.PeerID != "" { return grpcstatus.Error(codes.InvalidArgument, "expected PeerID to be empty; the wrong end of peering is being dialed") } streamReq := HandleStreamRequest{ LocalID: p.ID, RemoteID: "", PeerName: p.Name, Partition: p.Partition, Stream: stream, } err = s.HandleStream(streamReq) // A nil error indicates that the peering was deleted and the stream needs to be gracefully shutdown. if err == nil { s.DrainStream(streamReq) return nil } logger.Error("error handling stream", "peer_name", p.Name, "peer_id", req.PeerID, "error", err) return err } type HandleStreamRequest struct { // LocalID is the UUID for the peering in the local Consul datacenter. LocalID string // RemoteID is the UUID for the peering from the perspective of the peer. RemoteID string // PeerName is the name of the peering. PeerName string // Partition is the local partition associated with the peer. Partition string // Stream is the open stream to the peer cluster. Stream BidirectionalStream } func (r HandleStreamRequest) WasDialed() bool { return r.RemoteID == "" } // DrainStream attempts to gracefully drain the stream when the connection is going to be torn down. // Tearing down the connection too quickly can lead our peer receiving a context cancellation error before the stream termination message. // Handling the termination message is important to set the expectation that the peering will not be reestablished unless recreated. func (s *Server) DrainStream(req HandleStreamRequest) { for { // Ensure that we read until an error, or the peer has nothing more to send. if _, err := req.Stream.Recv(); err != nil { if err != io.EOF { s.Logger.Warn("failed to tear down stream gracefully: peer may not have received termination message", "peer_name", req.PeerName, "peer_id", req.LocalID, "error", err) } break } // Since the peering is being torn down we discard all replication messages without an error. // We want to avoid importing new data at this point. } } func (s *Server) HandleStream(streamReq HandleStreamRequest) error { if err := s.realHandleStream(streamReq); err != nil { s.Tracker.DisconnectedDueToError(streamReq.LocalID, err.Error()) return err } // TODO(peering) Also need to clear subscriptions associated with the peer s.Tracker.DisconnectedGracefully(streamReq.LocalID) return nil } // The localID provided is the locally-generated identifier for the peering. // The remoteID is an identifier that the remote peer recognizes for the peering. func (s *Server) realHandleStream(streamReq HandleStreamRequest) error { // TODO: pass logger down from caller? logger := s.Logger.Named("stream"). With("peer_name", streamReq.PeerName). With("peer_id", streamReq.LocalID). With("dialed", streamReq.WasDialed()) logger.Trace("handling stream for peer") // handleStreamCtx is local to this function. handleStreamCtx, cancel := context.WithCancel(streamReq.Stream.Context()) defer cancel() status, err := s.Tracker.Connected(streamReq.LocalID) if err != nil { return fmt.Errorf("failed to register stream: %v", err) } var trustDomain string if s.ConnectEnabled { // Read the TrustDomain up front - we do not allow users to change the ClusterID // so reading it once at the beginning of the stream is sufficient. trustDomain, err = getTrustDomain(s.GetStore(), logger) if err != nil { return err } } remoteSubTracker := newResourceSubscriptionTracker() mgr := newSubscriptionManager( streamReq.Stream.Context(), logger, s.Config, trustDomain, s.Backend, s.GetStore, remoteSubTracker, ) subCh := mgr.subscribe(streamReq.Stream.Context(), streamReq.LocalID, streamReq.PeerName, streamReq.Partition) // We need a mutex to protect against simultaneous sends to the client. var sendMutex sync.Mutex // streamSend is a helper function that sends msg over the stream // respecting the send mutex. It also logs the send and calls status.TrackSendError // on error. streamSend := func(msg *pbpeerstream.ReplicationMessage) error { logTraceSend(logger, msg) sendMutex.Lock() err := streamReq.Stream.Send(msg) sendMutex.Unlock() // We only track send successes and errors for response types because this is meant to track // resources, not request/ack messages. if msg.GetResponse() != nil { if err != nil { status.TrackSendError(err.Error()) } else { status.TrackSendSuccess() } } return err } // Subscribe to all relevant resource types. for _, resourceURL := range []string{ pbpeerstream.TypeURLExportedService, pbpeerstream.TypeURLExportedServiceList, pbpeerstream.TypeURLPeeringTrustBundle, pbpeerstream.TypeURLPeeringServerAddresses, } { sub := makeReplicationRequest(&pbpeerstream.ReplicationMessage_Request{ ResourceURL: resourceURL, PeerID: streamReq.RemoteID, }) if err := streamSend(sub); err != nil { // TODO(peering) Test error handling in calls to Send/Recv return fmt.Errorf("failed to send subscription for %q to stream: %w", resourceURL, err) } } // recvCh sends messages from the gRPC stream. recvCh := make(chan *pbpeerstream.ReplicationMessage) // recvErrCh sends errors received from the gRPC stream. recvErrCh := make(chan error) // Start a goroutine to read from the stream and pass to recvCh and recvErrCh. // Using a separate goroutine allows us to process sends and receives all in the main for{} loop. go func() { for { msg, err := streamReq.Stream.Recv() if err != nil { recvErrCh <- err return } logTraceRecv(logger, msg) select { case recvCh <- msg: case <-handleStreamCtx.Done(): return } } }() // Start a goroutine to send heartbeats at a regular interval. go func() { tick := time.NewTicker(s.outgoingHeartbeatInterval) defer tick.Stop() for { select { case <-handleStreamCtx.Done(): return case <-tick.C: heartbeat := &pbpeerstream.ReplicationMessage{ Payload: &pbpeerstream.ReplicationMessage_Heartbeat_{ Heartbeat: &pbpeerstream.ReplicationMessage_Heartbeat{}, }, } if err := streamSend(heartbeat); err != nil { logger.Warn("error sending heartbeat", "err", err) } } } }() // incomingHeartbeatCtx will complete if incoming heartbeats time out. incomingHeartbeatCtx, incomingHeartbeatCtxCancel := context.WithTimeout(context.Background(), s.incomingHeartbeatTimeout) // NOTE: It's important that we wrap the call to cancel in a wrapper func because during the loop we're // re-assigning the value of incomingHeartbeatCtxCancel and we want the defer to run on the last assigned // value, not the current value. defer func() { incomingHeartbeatCtxCancel() }() // The main loop that processes sends and receives. for { select { // When the doneCh is closed that means that the peering was deleted locally. case <-status.Done(): logger.Info("ending stream") term := &pbpeerstream.ReplicationMessage{ Payload: &pbpeerstream.ReplicationMessage_Terminated_{ Terminated: &pbpeerstream.ReplicationMessage_Terminated{}, }, } if err := streamSend(term); err != nil { // Nolint directive needed due to bug in govet that doesn't see that the cancel // func of the incomingHeartbeatTimer _does_ get called. //nolint:govet return fmt.Errorf("failed to send to stream: %v", err) } logger.Trace("deleting stream status") s.Tracker.DeleteStatus(streamReq.LocalID) return nil // Handle errors received from the stream by shutting down our handler. case err := <-recvErrCh: if err == io.EOF { // NOTE: We don't expect to receive an io.EOF error here when the stream is disconnected gracefully. // When the peering is deleted locally, status.Done() returns which is handled elsewhere and this method // exits. When we receive a Terminated message, that's also handled elsewhere and this method // exits. After the method exits this code here won't receive any recv errors and those will be handled // by DrainStream(). err = fmt.Errorf("stream ended unexpectedly") } else { err = fmt.Errorf("unexpected error receiving from the stream: %w", err) } status.TrackRecvError(err.Error()) return err // We haven't received a heartbeat within the expected interval. Kill the stream. case <-incomingHeartbeatCtx.Done(): return fmt.Errorf("heartbeat timeout") case msg := <-recvCh: // NOTE: this code should have similar error handling to the // initial handling code in StreamResources() if !s.Backend.IsLeader() { // We are not the leader anymore, so we will hang up on the dialer. logger.Info("node is not a leader anymore; cannot continue streaming") st, err := grpcstatus.New(codes.FailedPrecondition, "node is not a leader anymore; cannot continue streaming").WithDetails( &pbpeerstream.LeaderAddress{Address: s.Backend.GetLeaderAddress()}) if err != nil { logger.Error(fmt.Sprintf("failed to marshal the leader address in response; err: %v", err)) return grpcstatus.Error(codes.FailedPrecondition, "node is not a leader anymore; cannot continue streaming") } else { return st.Err() } } if req := msg.GetRequest(); req != nil { if !pbpeerstream.KnownTypeURL(req.ResourceURL) { return grpcstatus.Errorf(codes.InvalidArgument, "subscription request to unknown resource URL: %s", req.ResourceURL) } // There are different formats of requests depending upon where in the stream lifecycle we are. // // 1. Initial Request: This is the first request being received // FROM the establishing peer. This is handled specially in // (*Server).StreamResources BEFORE calling // (*Server).HandleStream. This takes care of determining what // the PeerID is for the stream. // // 2. Subscription Request: This is the first request for a // given ResourceURL within a stream. The Initial Request (1) // is always one of these as well. // // These must contain a valid ResourceURL with no Error or // ResponseNonce set. // // It is valid to subscribe to the same ResourceURL twice // within the lifetime of a stream, but all duplicate // subscriptions are treated as no-ops upon receipt. // // 3. ACK Request: This is the message sent in reaction to an // earlier Response to indicate that the response was processed // by the other side successfully. // // These must contain a ResponseNonce and no Error. // // 4. NACK Request: This is the message sent in reaction to an // earlier Response to indicate that the response was NOT // processed by the other side successfully. // // These must contain a ResponseNonce and an Error. // if !remoteSubTracker.IsSubscribed(req.ResourceURL) { // This must be a new subscription request to add a new // resource type, vet it like a new request. if !streamReq.WasDialed() { if req.PeerID != "" && req.PeerID != streamReq.RemoteID { // Not necessary after the first request from the dialer, // but if provided must match. return grpcstatus.Errorf(codes.InvalidArgument, "initial subscription requests for a resource type must have consistent PeerID values: got=%q expected=%q", req.PeerID, streamReq.RemoteID, ) } } if req.ResponseNonce != "" { return grpcstatus.Error(codes.InvalidArgument, "initial subscription requests for a resource type must not contain a nonce") } if req.Error != nil { return grpcstatus.Error(codes.InvalidArgument, "initial subscription request for a resource type must not contain an error") } if remoteSubTracker.Subscribe(req.ResourceURL) { logger.Info("subscribing to resource type", "resourceURL", req.ResourceURL) } status.TrackAck() continue } // At this point we have a valid ResourceURL and we are subscribed to it. switch { case req.Error == nil: // ACK // TODO(peering): handle ACK fully status.TrackAck() case req.Error != nil: // NACK // TODO(peering): handle NACK fully logger.Warn("client peer was unable to apply resource", "code", req.Error.Code, "error", req.Error.Message) status.TrackNack(fmt.Sprintf("client peer was unable to apply resource: %s", req.Error.Message)) default: // This branch might be dead code, but it could also happen // during a stray 're-subscribe' so just ignore the // message. } continue } if resp := msg.GetResponse(); resp != nil { // TODO(peering): Ensure there's a nonce reply, err := s.processResponse(streamReq.PeerName, streamReq.Partition, status, resp) if err != nil { logger.Error("failed to persist resource", "resourceURL", resp.ResourceURL, "resourceID", resp.ResourceID) status.TrackRecvError(err.Error()) } else { status.TrackRecvResourceSuccess() } // We are replying ACK or NACK depending on whether we successfully processed the response. if err := streamSend(reply); err != nil { return fmt.Errorf("failed to send to stream: %v", err) } continue } if term := msg.GetTerminated(); term != nil { logger.Info("peering was deleted by our peer: marking peering as terminated and cleaning up imported resources") // Once marked as terminated, a separate deferred deletion routine will clean up imported resources. if err := s.Backend.PeeringTerminateByID(&pbpeering.PeeringTerminateByIDRequest{ID: streamReq.LocalID}); err != nil { logger.Error("failed to mark peering as terminated: %w", err) } return nil } if msg.GetHeartbeat() != nil { status.TrackRecvHeartbeat() // Reset the heartbeat timeout by creating a new context. // We first must cancel the old context so there's no leaks. This is safe to do because we're only // reading that context within this for{} loop, and so we won't accidentally trigger the heartbeat // timeout. incomingHeartbeatCtxCancel() // NOTE: IDEs and govet think that the reassigned cancel below never gets // called, but it does by the defer when the heartbeat ctx is first created. // They just can't trace the execution properly for some reason (possibly golang/go#29587). //nolint:govet incomingHeartbeatCtx, incomingHeartbeatCtxCancel = context.WithTimeout(context.Background(), s.incomingHeartbeatTimeout) } case update := <-subCh: var resp *pbpeerstream.ReplicationMessage_Response switch { case strings.HasPrefix(update.CorrelationID, subExportedServiceList): resp, err = makeExportedServiceListResponse(status, update) if err != nil { // Log the error and skip this response to avoid locking up peering due to a bad update event. logger.Error("failed to create exported service list response", "error", err) continue } case strings.HasPrefix(update.CorrelationID, subExportedService): resp, err = makeServiceResponse(status, update) if err != nil { // Log the error and skip this response to avoid locking up peering due to a bad update event. logger.Error("failed to create service response", "error", err) continue } case update.CorrelationID == subCARoot: resp, err = makeCARootsResponse(update) if err != nil { // Log the error and skip this response to avoid locking up peering due to a bad update event. logger.Error("failed to create ca roots response", "error", err) continue } case update.CorrelationID == subServerAddrs: resp, err = makeServerAddrsResponse(update) if err != nil { logger.Error("failed to create server address response", "error", err) continue } default: logger.Warn("unrecognized update type from subscription manager: " + update.CorrelationID) continue } if resp == nil { continue } replResp := makeReplicationResponse(resp) if err := streamSend(replResp); err != nil { // note: govet warns of context leak but it is cleaned up in a defer return fmt.Errorf("failed to push data for %q: %w", update.CorrelationID, err) } } } } func getTrustDomain(store StateStore, logger hclog.Logger) (string, error) { _, cfg, err := store.CAConfig(nil) switch { case err != nil: logger.Error("failed to read Connect CA Config", "error", err) return "", grpcstatus.Error(codes.Internal, "failed to read Connect CA Config") case cfg == nil: logger.Warn("cannot begin stream because Connect CA is not yet initialized") return "", grpcstatus.Error(codes.FailedPrecondition, "Connect CA is not yet initialized") } return connect.SpiffeIDSigningForCluster(cfg.ClusterID).Host(), nil } func (s *Server) StreamStatus(peerID string) (resp Status, found bool) { return s.Tracker.StreamStatus(peerID) } // ConnectedStreams returns a map of connected stream IDs to the corresponding channel for tearing them down. func (s *Server) ConnectedStreams() map[string]chan struct{} { return s.Tracker.ConnectedStreams() } func logTraceRecv(logger hclog.Logger, pb proto.Message) { logTraceProto(logger, pb, true) } func logTraceSend(logger hclog.Logger, pb proto.Message) { logTraceProto(logger, pb, false) } func logTraceProto(logger hclog.Logger, pb proto.Message, received bool) { if !logger.IsTrace() { return } dir := "sent" if received { dir = "received" } // Redact the long-lived stream secret to avoid leaking it in trace logs. pbToLog := pb switch msg := pb.(type) { case *pbpeerstream.ReplicationMessage: clone := &pbpeerstream.ReplicationMessage{} proto.Merge(clone, msg) if clone.GetOpen() != nil { clone.GetOpen().StreamSecretID = "hidden" pbToLog = clone } case *pbpeerstream.ReplicationMessage_Open: clone := &pbpeerstream.ReplicationMessage_Open{} proto.Merge(clone, msg) clone.StreamSecretID = "hidden" pbToLog = clone } m := jsonpb.Marshaler{ Indent: " ", } out, err := m.MarshalToString(pbToLog) if err != nil { out = "" } logger.Trace("replication message", "direction", dir, "protobuf", out) } // resourceSubscriptionTracker is used to keep track of the ResourceURLs that a // stream has subscribed to and can notify you when a subscription comes in by // closing the channels returned by SubscribedChan. type resourceSubscriptionTracker struct { // notifierMap keeps track of a notification channel for each resourceURL. // Keys may exist in here even when they do not exist in 'subscribed' as // calling SubscribedChan has to possibly create and and hand out a // notification channel in advance of any notification. notifierMap map[string]chan struct{} // subscribed is a set that keeps track of resourceURLs that are currently // subscribed to. Keys are never deleted. If a key is present in this map // it is also present in 'notifierMap'. subscribed map[string]struct{} } func newResourceSubscriptionTracker() *resourceSubscriptionTracker { return &resourceSubscriptionTracker{ subscribed: make(map[string]struct{}), notifierMap: make(map[string]chan struct{}), } } // IsSubscribed returns true if the given ResourceURL has an active subscription. func (t *resourceSubscriptionTracker) IsSubscribed(resourceURL string) bool { _, ok := t.subscribed[resourceURL] return ok } // Subscribe subscribes to the given ResourceURL. It will return true if this // was the FIRST time a subscription occurred. It will also close the // notification channel associated with this ResourceURL. func (t *resourceSubscriptionTracker) Subscribe(resourceURL string) bool { if _, ok := t.subscribed[resourceURL]; ok { return false } t.subscribed[resourceURL] = struct{}{} // and notify ch := t.ensureNotifierChan(resourceURL) close(ch) return true } // SubscribedChan returns a channel that will be closed when the ResourceURL is // subscribed using the Subscribe method. func (t *resourceSubscriptionTracker) SubscribedChan(resourceURL string) <-chan struct{} { return t.ensureNotifierChan(resourceURL) } func (t *resourceSubscriptionTracker) ensureNotifierChan(resourceURL string) chan struct{} { if ch, ok := t.notifierMap[resourceURL]; ok { return ch } ch := make(chan struct{}) t.notifierMap[resourceURL] = ch return ch }