add events package (#2341)

* add events package

* update go version

events/memory.go

@@ -0,0 +1,244 @@
+package events
+
+import (
+	"encoding/json"
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/pkg/errors"
+	"go-micro.dev/v4/logger"
+	"go-micro.dev/v4/store"
+)
+
+// NewStream returns an initialized memory stream
+func NewStream(opts ...Option) (Stream, error) {
+	// parse the options
+	var options Options
+	for _, o := range opts {
+		o(&options)
+	}
+	return &mem{store: store.NewMemoryStore()}, nil
+}
+
+type subscriber struct {
+	Group   string
+	Topic   string
+	Channel chan Event
+
+	sync.RWMutex
+	retryMap   map[string]int
+	retryLimit int
+	autoAck    bool
+	ackWait    time.Duration
+}
+
+type mem struct {
+	store store.Store
+
+	subs []*subscriber
+	sync.RWMutex
+}
+
+func (m *mem) Publish(topic string, msg interface{}, opts ...PublishOption) error {
+	// validate the topic
+	if len(topic) == 0 {
+		return ErrMissingTopic
+	}
+
+	// parse the options
+	options := PublishOptions{
+		Timestamp: time.Now(),
+	}
+	for _, o := range opts {
+		o(&options)
+	}
+
+	// encode the message if it's not already encoded
+	var payload []byte
+	if p, ok := msg.([]byte); ok {
+		payload = p
+	} else {
+		p, err := json.Marshal(msg)
+		if err != nil {
+			return ErrEncodingMessage
+		}
+		payload = p
+	}
+
+	// construct the event
+	event := &Event{
+		ID:        uuid.New().String(),
+		Topic:     topic,
+		Timestamp: options.Timestamp,
+		Metadata:  options.Metadata,
+		Payload:   payload,
+	}
+
+	// serialize the event to bytes
+	bytes, err := json.Marshal(event)
+	if err != nil {
+		return errors.Wrap(err, "Error encoding event")
+	}
+
+	// write to the store
+	key := fmt.Sprintf("%v/%v", event.Topic, event.ID)
+	if err := m.store.Write(&store.Record{Key: key, Value: bytes}); err != nil {
+		return errors.Wrap(err, "Error writing event to store")
+	}
+
+	// send to the subscribers async
+	go m.handleEvent(event)
+
+	return nil
+}
+
+func (m *mem) Consume(topic string, opts ...ConsumeOption) (<-chan Event, error) {
+	// validate the topic
+	if len(topic) == 0 {
+		return nil, ErrMissingTopic
+	}
+
+	// parse the options
+	options := ConsumeOptions{
+		Group:   uuid.New().String(),
+		AutoAck: true,
+	}
+	for _, o := range opts {
+		o(&options)
+	}
+	// TODO RetryLimit
+
+	// setup the subscriber
+	sub := &subscriber{
+		Channel:    make(chan Event),
+		Topic:      topic,
+		Group:      options.Group,
+		retryMap:   map[string]int{},
+		autoAck:    true,
+		retryLimit: options.GetRetryLimit(),
+	}
+
+	if !options.AutoAck {
+		if options.AckWait == 0 {
+			return nil, fmt.Errorf("invalid AckWait passed, should be positive integer")
+		}
+		sub.autoAck = options.AutoAck
+		sub.ackWait = options.AckWait
+	}
+
+	// register the subscriber
+	m.Lock()
+	m.subs = append(m.subs, sub)
+	m.Unlock()
+
+	// lookup previous events if the start time option was passed
+	if options.Offset.Unix() > 0 {
+		go m.lookupPreviousEvents(sub, options.Offset)
+	}
+
+	// return the channel
+	return sub.Channel, nil
+}
+
+// lookupPreviousEvents finds events for a subscriber which occurred before a given time and sends
+// them into the subscribers channel
+func (m *mem) lookupPreviousEvents(sub *subscriber, startTime time.Time) {
+	// lookup all events which match the topic (a blank topic will return all results)
+	recs, err := m.store.Read(sub.Topic+"/", store.ReadPrefix())
+	if err != nil && logger.V(logger.ErrorLevel, logger.DefaultLogger) {
+		logger.Errorf("Error looking up previous events: %v", err)
+		return
+	} else if err != nil {
+		return
+	}
+
+	// loop through the records and send it to the channel if it matches
+	for _, r := range recs {
+		var ev Event
+		if err := json.Unmarshal(r.Value, &ev); err != nil {
+			continue
+		}
+		if ev.Timestamp.Unix() < startTime.Unix() {
+			continue
+		}
+		sendEvent(&ev, sub)
+	}
+}
+
+// handleEvents sends the event to any registered subscribers.
+func (m *mem) handleEvent(ev *Event) {
+	m.RLock()
+	subs := m.subs
+	m.RUnlock()
+
+	// filteredSubs is a KV map of the queue name and subscribers. This is used to prevent a message
+	// being sent to two subscribers with the same queue.
+	filteredSubs := map[string]*subscriber{}
+
+	// filter down to subscribers who are interested in this topic
+	for _, sub := range subs {
+		if len(sub.Topic) == 0 || sub.Topic == ev.Topic {
+			filteredSubs[sub.Group] = sub
+		}
+	}
+
+	// send the message to each channel async (since one channel might be blocked)
+	for _, sub := range filteredSubs {
+		sendEvent(ev, sub)
+	}
+}
+
+func sendEvent(ev *Event, sub *subscriber) {
+	go func(s *subscriber) {
+		evCopy := *ev
+		if s.autoAck {
+			s.Channel <- evCopy
+			return
+		}
+		evCopy.SetAckFunc(ackFunc(s, evCopy))
+		evCopy.SetNackFunc(nackFunc(s, evCopy))
+		s.retryMap[evCopy.ID] = 0
+		tick := time.NewTicker(s.ackWait)
+		defer tick.Stop()
+		for range tick.C {
+			s.Lock()
+			count, ok := s.retryMap[evCopy.ID]
+			s.Unlock()
+			if !ok {
+				// success
+				break
+			}
+
+			if s.retryLimit > -1 && count > s.retryLimit {
+				if logger.V(logger.ErrorLevel, logger.DefaultLogger) {
+					logger.Errorf("Message retry limit reached, discarding: %v %d %d", evCopy.ID, count, s.retryLimit)
+				}
+				s.Lock()
+				delete(s.retryMap, evCopy.ID)
+				s.Unlock()
+				return
+			}
+			s.Channel <- evCopy
+			s.Lock()
+			s.retryMap[evCopy.ID] = count + 1
+			s.Unlock()
+		}
+	}(sub)
+}
+
+func ackFunc(s *subscriber, evCopy Event) func() error {
+	return func() error {
+		s.Lock()
+		delete(s.retryMap, evCopy.ID)
+		s.Unlock()
+		return nil
+	}
+}
+
+func nackFunc(s *subscriber, evCopy Event) func() error {
+	return func() error {
+		return nil
+	}
+}