Consume pubsub queue and just log

cmd/notification-service/di/inject_pubsub.go

@@ -18,6 +18,7 @@ var pubsubSet = wire.NewSet(
 
 var googlePubsubSet = wire.NewSet(
 	newExternalEventPublisher,
+	newExternalFollowChangeSubscriber,
 )
 
 func newExternalEventPublisher(config config.Config, logger watermill.LoggerAdapter) (app.ExternalEventPublisher, error) {
@@ -31,3 +32,15 @@ func newExternalEventPublisher(config config.Config, logger watermill.LoggerAdap
 		return gcp.NewNoopPublisher(), nil
 	}
 }
+
+func newExternalFollowChangeSubscriber(config config.Config, logger watermill.LoggerAdapter) (app.ExternalFollowChangeSubscriber, error) {
+	if config.GooglePubSubEnabled() {
+		subscriber, err := gcp.NewWatermillSubscriber(config, logger)
+		if err != nil {
+			return nil, errors.Wrap(err, "error creating a watermil subscriber")
+		}
+		return gcp.NewFollowChangeSubscriber(subscriber, logger), nil
+	} else {
+		return gcp.NewNoopSubscriber(), nil
+	}
+}

cmd/notification-service/di/service.go

@@ -13,32 +13,38 @@ import (
 )
 
 type Service struct {
-	app                       app.Application
-	server                    http.Server
-	metricsServer             http.MetricsServer
-	downloader                *app.Downloader
-	receivedEventSubscriber   *memorypubsub.ReceivedEventSubscriber
-	eventSavedSubscriber      *firestorepubsub.EventSavedSubscriber
-	eventWasAlreadySavedCache *adapters.MemoryEventWasAlreadySavedCache
+	app                            app.Application
+	server                         http.Server
+	metricsServer                  http.MetricsServer
+	downloader                     *app.Downloader
+	followChangePuller             *app.FollowChangePuller
+	receivedEventSubscriber        *memorypubsub.ReceivedEventSubscriber
+	externalFollowChangeSubscriber app.ExternalFollowChangeSubscriber
+	eventSavedSubscriber           *firestorepubsub.EventSavedSubscriber
+	eventWasAlreadySavedCache      *adapters.MemoryEventWasAlreadySavedCache
 }
 
 func NewService(
 	app app.Application,
 	server http.Server,
 	metricsServer http.MetricsServer,
 	downloader *app.Downloader,
+	followChangePuller *app.FollowChangePuller,
 	receivedEventSubscriber *memorypubsub.ReceivedEventSubscriber,
+	externalFollowChangeSubscriber app.ExternalFollowChangeSubscriber,
 	eventSavedSubscriber *firestorepubsub.EventSavedSubscriber,
 	eventWasAlreadySavedCache *adapters.MemoryEventWasAlreadySavedCache,
 ) Service {
 	return Service{
-		app:                       app,
-		server:                    server,
-		metricsServer:             metricsServer,
-		downloader:                downloader,
-		receivedEventSubscriber:   receivedEventSubscriber,
-		eventSavedSubscriber:      eventSavedSubscriber,
-		eventWasAlreadySavedCache: eventWasAlreadySavedCache,
+		app:                            app,
+		server:                         server,
+		metricsServer:                  metricsServer,
+		downloader:                     downloader,
+		followChangePuller:             followChangePuller,
+		receivedEventSubscriber:        receivedEventSubscriber,
+		externalFollowChangeSubscriber: externalFollowChangeSubscriber,
+		eventSavedSubscriber:           eventSavedSubscriber,
+		eventWasAlreadySavedCache:      eventWasAlreadySavedCache,
 	}
 }
 
@@ -73,6 +79,10 @@ func (s Service) Run(ctx context.Context) error {
 		errCh <- errors.Wrap(s.receivedEventSubscriber.Run(ctx), "received event subscriber error")
 	}()
 
+	go func() {
+		errCh <- errors.Wrap(s.followChangePuller.Run(ctx), "follow change subscriber error")
+	}()
+
 	runners++
 	go func() {
 		errCh <- errors.Wrap(s.eventSavedSubscriber.Run(ctx), "event saved subscriber error")

cmd/notification-service/di/wire.go

@@ -29,6 +29,7 @@ func BuildService(context.Context, config.Config) (Service, func(), error) {
 		googlePubsubSet,
 		loggingSet,
 		adaptersSet,
+		followChangePullerSet,
 	)
 	return Service{}, nil, nil
 }
@@ -49,13 +50,16 @@ func BuildIntegrationService(context.Context, config.Config) (IntegrationService
 		applicationSet,
 		firestoreAdaptersSet,
 		downloaderSet,
+		followChangePullerSet,
 		generatorSet,
 		pubsubSet,
 		loggingSet,
 		integrationAdaptersSet,
 
 		mocks.NewMockExternalEventPublisher,
+		mocks.NewMockExternalFollowChangeSubscriber,
 		wire.Bind(new(app.ExternalEventPublisher), new(*mocks.MockExternalEventPublisher)),
+		wire.Bind(new(app.ExternalFollowChangeSubscriber), new(*mocks.MockExternalFollowChangeSubscriber)),
 	)
 	return IntegrationService{}, nil, nil
 }
@@ -79,6 +83,10 @@ var downloaderSet = wire.NewSet(
 	app.NewDownloader,
 )
 
+var followChangePullerSet = wire.NewSet(
+	app.NewFollowChangePuller,
+)
+
 var generatorSet = wire.NewSet(
 	notifications.NewGenerator,
 )

go.mod

@@ -14,6 +14,7 @@ require (
 	github.com/gorilla/websocket v1.5.0
 	github.com/hashicorp/go-multierror v1.1.1
 	github.com/nbd-wtf/go-nostr v0.25.7
+	github.com/pkg/errors v0.9.1
 	github.com/prometheus/client_golang v1.16.0
 	github.com/rs/zerolog v1.29.1
 	github.com/sideshow/apns2 v0.23.0
@@ -61,7 +62,6 @@ require (
 	github.com/mattn/go-isatty v0.0.14 // indirect
 	github.com/matttproud/golang_protobuf_extensions v1.0.4 // indirect
 	github.com/oklog/ulid v1.3.1 // indirect
-	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/prometheus/client_model v0.3.0 // indirect
 	github.com/prometheus/common v0.42.0 // indirect

service/adapters/gcp/gcp_follow_change_subscriber.go

@@ -0,0 +1,75 @@
+package gcp
+
+import (
+	"context"
+	"encoding/json"
+
+	"github.com/ThreeDotsLabs/watermill"
+	"github.com/ThreeDotsLabs/watermill-googlecloud/pkg/googlecloud"
+	"github.com/pkg/errors"
+	"github.com/planetary-social/go-notification-service/service/config"
+	"github.com/planetary-social/go-notification-service/service/domain"
+	"google.golang.org/api/option"
+)
+
+const googlePubSubFollowChangeTopic = "follow-changes"
+
+func NewWatermillSubscriber(config config.Config, logger watermill.LoggerAdapter) (*googlecloud.Subscriber, error) {
+	var options []option.ClientOption
+
+	if j := config.GooglePubSubCredentialsJSON(); len(j) > 0 {
+		options = append(options, option.WithCredentialsJSON(config.GooglePubSubCredentialsJSON()))
+	}
+
+	publisherConfig := googlecloud.SubscriberConfig{
+		ProjectID:                 config.GooglePubSubProjectID(),
+		DoNotCreateTopicIfMissing: true,
+		ClientOptions:             options,
+	}
+
+	return googlecloud.NewSubscriber(publisherConfig, logger)
+}
+
+type GCPFollowChangeSubscriber struct {
+	subscriber *googlecloud.Subscriber
+	logger     watermill.LoggerAdapter
+}
+
+func NewFollowChangeSubscriber(subscriber *googlecloud.Subscriber, logger watermill.LoggerAdapter) *GCPFollowChangeSubscriber {
+	return &GCPFollowChangeSubscriber{subscriber: subscriber, logger: logger}
+}
+
+func (p *GCPFollowChangeSubscriber) Subscribe(ctx context.Context) (<-chan *domain.FollowChange, error) {
+	subChan, err := p.subscriber.Subscribe(ctx, googlePubSubFollowChangeTopic)
+	if err != nil {
+		return nil, errors.Wrap(err, "error subscribing")
+	}
+
+	ch := make(chan *domain.FollowChange)
+
+	defer func() {
+		close(ch)
+		p.subscriber.Close()
+	}()
+
+	go func() {
+		var payload domain.FollowChange
+		for message := range subChan {
+			// We never retry messages so we can ACK immediately.
+			message.Ack()
+
+			if err := json.Unmarshal(message.Payload, &payload); err != nil {
+				p.logger.Error("error unmarshaling follow change payload", err, watermill.LogFields{"payload": string(message.Payload)})
+				continue
+			}
+
+			select {
+			case ch <- &payload:
+			case <-ctx.Done():
+				return
+			}
+		}
+	}()
+
+	return ch, nil
+}

service/adapters/gcp/noop_subscriber.go

@@ -0,0 +1,18 @@
+package gcp
+
+import (
+	"context"
+
+	"github.com/planetary-social/go-notification-service/service/domain"
+)
+
+type NoopSubscriber struct {
+}
+
+func NewNoopSubscriber() *NoopSubscriber {
+	return &NoopSubscriber{}
+}
+func (p *NoopSubscriber) Subscribe(ctx context.Context) (<-chan *domain.FollowChange, error) {
+	ch := make(chan *domain.FollowChange)
+	return ch, nil
+}

service/adapters/mocks/external_follow_change_subscriber.go

@@ -0,0 +1,19 @@
+package mocks
+
+import (
+	"context"
+
+	"github.com/planetary-social/go-notification-service/service/domain"
+)
+
+type MockExternalFollowChangeSubscriber struct {
+}
+
+func NewMockExternalFollowChangeSubscriber() *MockExternalFollowChangeSubscriber {
+	return &MockExternalFollowChangeSubscriber{}
+}
+
+func (m MockExternalFollowChangeSubscriber) Subscribe(ctx context.Context) (<-chan *domain.FollowChange, error) {
+	ch := make(chan *domain.FollowChange)
+	return ch, nil
+}

service/adapters/prometheus/prometheus.go

@@ -15,6 +15,7 @@ import (
 const (
 	labelHandlerName          = "handlerName"
 	labelRelayDownloaderState = "state"
+	labelFollowChanges        = "follow changes"
 	labelTopic                = "topic"
 	labelVcsRevision          = "vcsRevision"
 	labelVcsTime              = "vcsTime"
@@ -32,6 +33,7 @@ type Prometheus struct {
 	applicationHandlerCallsCounter          *prometheus.CounterVec
 	applicationHandlerCallDurationHistogram *prometheus.HistogramVec
 	relayDownloaderStateGauge               *prometheus.GaugeVec
+	relayFollowChangeGauge                  prometheus.Counter
 	subscriptionQueueLengthGauge            *prometheus.GaugeVec
 	apnsCallsCounter                        *prometheus.CounterVec
 
@@ -62,6 +64,12 @@ func NewPrometheus(logger logging.Logger) (*Prometheus, error) {
 		},
 		[]string{labelRelayDownloaderState},
 	)
+	relayFollowChangeGauge := prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Name: "follow_change_count",
+			Help: "Number of follow changes.",
+		},
+	)
 	subscriptionQueueLengthGauge := prometheus.NewGaugeVec(
 		prometheus.GaugeOpts{
 			Name: "subscription_queue_length",
@@ -89,6 +97,7 @@ func NewPrometheus(logger logging.Logger) (*Prometheus, error) {
 		applicationHandlerCallsCounter,
 		applicationHandlerCallDurationHistogram,
 		relayDownloaderStateGauge,
+		relayFollowChangeGauge,
 		subscriptionQueueLengthGauge,
 		versionGague,
 		apnsCallsCounter,
@@ -118,6 +127,7 @@ func NewPrometheus(logger logging.Logger) (*Prometheus, error) {
 		applicationHandlerCallsCounter:          applicationHandlerCallsCounter,
 		applicationHandlerCallDurationHistogram: applicationHandlerCallDurationHistogram,
 		relayDownloaderStateGauge:               relayDownloaderStateGauge,
+		relayFollowChangeGauge:                  relayFollowChangeGauge,
 		subscriptionQueueLengthGauge:            subscriptionQueueLengthGauge,
 		apnsCallsCounter:                        apnsCallsCounter,
 
@@ -135,6 +145,10 @@ func (p *Prometheus) MeasureRelayDownloadersState(n int, state app.RelayDownload
 	p.relayDownloaderStateGauge.With(prometheus.Labels{labelRelayDownloaderState: state.String()}).Set(float64(n))
 }
 
+func (p *Prometheus) MeasureFollowChange(n int) {
+	p.relayFollowChangeGauge.Add(float64(n))
+}
+
 func (p *Prometheus) ReportSubscriptionQueueLength(topic string, n int) {
 	p.subscriptionQueueLengthGauge.With(prometheus.Labels{labelTopic: topic}).Set(float64(n))
 }

service/app/app.go

@@ -56,6 +56,10 @@ type ExternalEventPublisher interface {
 	PublishNewEventReceived(ctx context.Context, event domain.Event) error
 }
 
+type ExternalFollowChangeSubscriber interface {
+	Subscribe(ctx context.Context) (<-chan *domain.FollowChange, error)
+}
+
 type Application struct {
 	Commands Commands
 	Queries  Queries
@@ -123,6 +127,7 @@ type ReceivedEventSubscriber interface {
 type Metrics interface {
 	StartApplicationCall(handlerName string) ApplicationCall
 	MeasureRelayDownloadersState(n int, state RelayDownloaderState)
+	MeasureFollowChange(n int)
 }
 
 type ApplicationCall interface {