Implement notifications service with shared messaging and email drivers (#36)

backend/notifications/bus/dispatch.go

@@ -0,0 +1,108 @@
+// Package bus connects the notification outbox to the shared messaging runtime.
+package bus
+
+import (
+	"context"
+	"strconv"
+	"time"
+
+	"git.sendico.io/tech/sxchnge/notifications/model"
+	merrors "git.sendico.io/tech/sxchnge/shared/errors"
+	mlogger "git.sendico.io/tech/sxchnge/shared/logging"
+	"git.sendico.io/tech/sxchnge/shared/messaging/reliable"
+)
+
+const subject = "sxchnge.notifications.email"
+
+type Outbox interface {
+	Due(context.Context, time.Time) ([]model.Notification, error)
+	Recover(context.Context, time.Time) error
+}
+type Handler interface {
+	Dispatch(context.Context, string) (bool, error)
+}
+type Bus struct {
+	transport    reliable.Transport
+	subscription reliable.Subscription
+	outbox       Outbox
+	handler      Handler
+	logger       mlogger.Logger
+}
+
+func New(ctx context.Context, transport reliable.Transport, admin reliable.Admin, outbox Outbox, handler Handler, logger mlogger.Logger) (*Bus, error) {
+	settings := reliable.DurableSettings{Enabled: true, Stream: reliable.DurableStreamSettings{Name: "SXCHNGE_NOTIFICATIONS", Subjects: []string{subject}, Storage: "file", MaxAgeHours: 48, Replicas: 1}, Provisioning: reliable.DurableProvisioningSettings{Mode: reliable.DurableProvisioningApp, Environment: reliable.DurableEnvironmentNonProduction}}
+	consumer := reliable.DurableConsumerSettings{Durable: "email", Subject: subject, AckWaitSeconds: 60, MaxDeliver: -1, DeliverPolicy: reliable.DurableDeliverAll}
+	if err := admin.EnsureConsumerResources(ctx, settings, consumer); err != nil {
+		return nil, merrors.OpaqueWrap(merrors.ErrServiceUnavailable, err, "configure notification messaging")
+	}
+	subscription, err := transport.OpenConsumer(ctx, settings, consumer)
+	if err != nil {
+		return nil, merrors.OpaqueWrap(merrors.ErrServiceUnavailable, err, "subscribe notification worker")
+	}
+	return &Bus{transport, subscription, outbox, handler, mlogger.Named(logger, "notifications", "bus")}, nil
+}
+func (b *Bus) Close() error { return b.subscription.Close() }
+func (b *Bus) PublishDue(ctx context.Context) error {
+	if err := b.outbox.Recover(ctx, time.Now().UTC()); err != nil {
+		return err
+	}
+	jobs, err := b.outbox.Due(ctx, time.Now().UTC())
+	if err != nil {
+		return err
+	}
+	for _, job := range jobs {
+		err = b.transport.Publish(ctx, reliable.Record{Subject: subject, Payload: []byte(job.ID.Hex()), MessageID: job.ID.Hex() + "-" + strconv.FormatUint(uint64(job.Attempts), 10)})
+		if err != nil {
+			return merrors.OpaqueWrap(merrors.ErrServiceUnavailable, err, "publish notification job")
+		}
+	}
+	return nil
+}
+func (b *Bus) RunPublisher(ctx context.Context) {
+	for ctx.Err() == nil {
+		op, cancel := context.WithTimeout(ctx, 10*time.Second)
+		err := b.PublishDue(op)
+		cancel()
+		if err != nil && ctx.Err() == nil {
+			b.logger.Warn("Notification outbox publication failed")
+		}
+		select {
+		case <-ctx.Done():
+			return
+		case <-time.After(5 * time.Second):
+		}
+	}
+}
+func (b *Bus) RunWorker(ctx context.Context) {
+	for ctx.Err() == nil {
+		deliveries, err := b.subscription.Fetch(ctx, 1, time.Second)
+		if err != nil {
+			if ctx.Err() == nil {
+				b.logger.Warn("Notification job fetch failed")
+			}
+			select {
+			case <-ctx.Done():
+				return
+			case <-time.After(time.Second):
+			}
+			continue
+		}
+		for _, delivery := range deliveries {
+			payload := delivery.Record().Payload
+			if len(payload) == 24 {
+				if _, err = b.handler.Dispatch(ctx, string(payload)); err != nil {
+					b.logger.Warn("Notification job processing failed")
+					continue
+				}
+			} else {
+				b.logger.Warn("Malformed notification job discarded")
+			}
+			ackCtx, cancel := context.WithTimeout(context.WithoutCancel(ctx), 5*time.Second)
+			err = delivery.Ack(ackCtx)
+			cancel()
+			if err != nil {
+				b.logger.Warn("Notification acknowledgement failed")
+			}
+		}
+	}
+}