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subscriber.go
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subscriber.go
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// Copyright (c) Abstract Machines
// SPDX-License-Identifier: Apache-2.0
package nats
import (
"context"
"encoding/json"
"errors"
"fmt"
"log/slog"
"time"
"github.com/absmach/magistrala/pkg/events"
"github.com/absmach/magistrala/pkg/messaging"
broker "github.com/absmach/magistrala/pkg/messaging/nats"
"github.com/nats-io/nats.go"
"github.com/nats-io/nats.go/jetstream"
)
const (
maxReconnects = -1
)
var _ events.Subscriber = (*subEventStore)(nil)
var (
eventsPrefix = "events"
jsStreamConfig = jetstream.StreamConfig{
Name: "events",
Description: "Magistrala stream for sending and receiving messages in between Magistrala events",
Subjects: []string{"events.>"},
Retention: jetstream.LimitsPolicy,
MaxMsgsPerSubject: 1e9,
MaxAge: time.Hour * 24,
MaxMsgSize: 1024 * 1024,
Discard: jetstream.DiscardOld,
Storage: jetstream.FileStorage,
}
// ErrEmptyStream is returned when stream name is empty.
ErrEmptyStream = errors.New("stream name cannot be empty")
// ErrEmptyConsumer is returned when consumer name is empty.
ErrEmptyConsumer = errors.New("consumer name cannot be empty")
)
type subEventStore struct {
conn *nats.Conn
pubsub messaging.PubSub
stream string
consumer string
logger *slog.Logger
}
func NewSubscriber(ctx context.Context, url, stream, consumer string, logger *slog.Logger) (events.Subscriber, error) {
if stream == "" {
return nil, ErrEmptyStream
}
if consumer == "" {
return nil, ErrEmptyConsumer
}
conn, err := nats.Connect(url, nats.MaxReconnects(maxReconnects))
if err != nil {
return nil, err
}
js, err := jetstream.New(conn)
if err != nil {
return nil, err
}
jsStream, err := js.CreateStream(ctx, jsStreamConfig)
if err != nil {
return nil, err
}
pubsub, err := broker.NewPubSub(ctx, url, logger, broker.Stream(jsStream))
if err != nil {
return nil, err
}
return &subEventStore{
conn: conn,
pubsub: pubsub,
stream: stream,
consumer: consumer,
logger: logger,
}, nil
}
func (es *subEventStore) Subscribe(ctx context.Context, handler events.EventHandler) error {
subCfg := messaging.SubscriberConfig{
ID: es.consumer,
Topic: eventsPrefix + "." + es.stream,
Handler: &eventHandler{
handler: handler,
ctx: ctx,
logger: es.logger,
},
DeliveryPolicy: messaging.DeliverNewPolicy,
}
return es.pubsub.Subscribe(ctx, subCfg)
}
func (es *subEventStore) Close() error {
es.conn.Close()
return es.pubsub.Close()
}
type event struct {
Data map[string]interface{}
}
func (re event) Encode() (map[string]interface{}, error) {
return re.Data, nil
}
type eventHandler struct {
handler events.EventHandler
ctx context.Context
logger *slog.Logger
}
func (eh *eventHandler) Handle(msg *messaging.Message) error {
event := event{
Data: make(map[string]interface{}),
}
if err := json.Unmarshal(msg.GetPayload(), &event.Data); err != nil {
return err
}
if err := eh.handler.Handle(eh.ctx, event); err != nil {
eh.logger.Warn(fmt.Sprintf("failed to handle redis event: %s", err))
}
return nil
}
func (eh *eventHandler) Cancel() error {
return nil
}