switch subscriptions to not use events package due to watermill wrapping

internal/pubsub/nats.go

@@ -0,0 +1,131 @@
+package pubsub
+
+import (
+	"bytes"
+	"context"
+	"crypto/md5"
+	"encoding/hex"
+	"encoding/json"
+	"strings"
+
+	"github.com/nats-io/nats.go"
+	"github.com/pkg/errors"
+	"go.infratographer.com/x/events"
+	"go.uber.org/zap"
+)
+
+const subscriptionBufferSize = 10
+
+type changeEvent struct {
+	*nats.Msg
+	events.ChangeMessage
+
+	Error error
+}
+
+type subscriber struct {
+	logger *zap.SugaredLogger
+
+	nats      *nats.Conn
+	jetstream nats.JetStreamContext
+
+	topicPrefix         string
+	queueGroup          string
+	subscriptionOptions []nats.SubOpt
+
+	subscriptions []*nats.Subscription
+
+	context   context.Context
+	cancelCtx func()
+}
+
+func (s *subscriber) durableName(topic string) string {
+	hash := md5.Sum([]byte(topic))
+
+	return s.queueGroup + hex.EncodeToString(hash[:])
+}
+
+// SubscribeChanges subscribes to a topic, returning a channel which change events will be sent to.
+func (s *subscriber) SubscribeChanges(ctx context.Context, topic string) (<-chan *changeEvent, error) {
+	subject := strings.Join([]string{s.topicPrefix, "changes", topic}, ".")
+
+	opts := s.subscriptionOptions
+
+	opts = append(opts, nats.Durable(s.durableName(subject)))
+
+	msgCh := make(chan *changeEvent, subscriptionBufferSize)
+
+	sub, err := s.jetstream.QueueSubscribe(subject, s.queueGroup, func(msg *nats.Msg) {
+		event := &changeEvent{
+			Msg: msg,
+		}
+
+		if err := json.NewDecoder(bytes.NewBuffer(msg.Data)).Decode(&event.ChangeMessage); err != nil {
+			event.Error = err
+		}
+
+		msgCh <- event
+	}, opts...)
+	if err != nil {
+		return nil, err
+	}
+
+	s.subscriptions = append(s.subscriptions, sub)
+
+	go func(subscriber *nats.Subscription) {
+		select {
+		case <-ctx.Done():
+		case <-s.context.Done():
+		}
+
+		if err := sub.Unsubscribe(); err != nil {
+			s.logger.Errorw("unable to unsubscribe", "error", err, "subject", subject)
+		}
+	}(sub)
+
+	return msgCh, nil
+}
+
+// Close closes the underlying nats connection.
+func (s *subscriber) Close() {
+	s.cancelCtx()
+
+	s.nats.Close()
+}
+
+func newSubscriber(ctx context.Context, config events.SubscriberConfig, logger *zap.SugaredLogger, subOptions ...nats.SubOpt) (*subscriber, error) {
+	options := []nats.Option{
+		nats.Timeout(config.Timeout),
+	}
+
+	switch {
+	case config.NATSConfig.CredsFile != "":
+		options = append(options, nats.UserCredentials(config.NATSConfig.CredsFile))
+	case config.NATSConfig.Token != "":
+		options = append(options, nats.Token(config.NATSConfig.Token))
+	}
+
+	conn, err := nats.Connect(config.URL, options...)
+	if err != nil {
+		return nil, errors.Wrap(err, "cannot connect to NATS")
+	}
+
+	js, err := conn.JetStream()
+	if err != nil {
+		conn.Close()
+
+		return nil, errors.Wrap(err, "cannot initialize JetStream")
+	}
+
+	ctx, cancel := context.WithCancel(ctx)
+
+	return &subscriber{
+		logger:              logger,
+		nats:                conn,
+		jetstream:           js,
+		topicPrefix:         config.Prefix,
+		subscriptionOptions: subOptions,
+		context:             ctx,
+		cancelCtx:           cancel,
+	}, nil
+}