/
handler.go
239 lines (195 loc) · 5.91 KB
/
handler.go
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package eventsourcex
import (
"context"
"time"
"github.com/altairsix/eventsource"
nats "github.com/nats-io/go-nats"
"github.com/opentracing/opentracing-go/log"
"github.com/pkg/errors"
)
// Processor performs operations on a stream of events, usually in conjunction with SubscribeStream
type Processor func(ctx context.Context, events ...eventsource.Event) error
// Do is a helper method to invoke the Processor
func (fn Processor) Do(ctx context.Context, events ...eventsource.Event) error {
return fn(ctx, events...)
}
// Handler provides the business end of the MessageHandler struct
type Handler interface {
// Handle receives the inbound message
Receive(offset uint64, data []byte)
}
// HandlerFunc provides a func wrapper for Handler
type HandlerFunc func(offset uint64, data []byte)
// Handle implements the Handle interface
func (fn HandlerFunc) Receive(offset uint64, data []byte) {
fn(offset, data)
}
func WithLogging(h Handler, logger interface {
Info(string, ...log.Field)
}) HandlerFunc {
return func(offset uint64, data []byte) {
logger.Info("handler:received", log.Uint64("offset", offset))
h.Receive(offset, data)
}
}
// WithSendNotices publishes an event to the notices subject if the processor executes successfully
func WithSendNotices(p Processor, nc *nats.Conn, env, boundedContext, source string) Processor {
return func(ctx context.Context, events ...eventsource.Event) error {
if err := p.Do(ctx, events...); err != nil {
return err
}
go func() {
for _, event := range events {
subject := NoticesSubject(env, boundedContext, event.AggregateID())
nc.Publish(subject, []byte(source))
}
}()
return nil
}
}
// Unmarshaler accepts a []byte encoded event and returns an event
type Unmarshaler func([]byte) (eventsource.Event, error)
// Checkpointer persists and retrieves nats streaming offsets
type Checkpointer interface {
// Load retrieves the specified nats streaming offset
Load(ctx context.Context, key string) (uint64, error)
// Save persists the specified nats streaming offset
Save(ctx context.Context, key string, offset uint64) error
}
// MemoryCP provides an in-memory non-thread-safe implementation of a checkpoint
type MemoryCP map[string]uint64
// Load implements Checkpointer.Save
func (m MemoryCP) Load(ctx context.Context, key string) (uint64, error) {
return m[key], nil
}
// Save implements Checkpointer.Save
func (m MemoryCP) Save(ctx context.Context, key string, offset uint64) error {
m[key] = offset
return nil
}
type message struct {
data []byte
offset uint64
}
// MessageHandler encapsulates a nats streaming processor that performs buffered processing
type MessageHandler struct {
ctx context.Context
cancel func()
done chan struct{}
processor Processor
unmarshal Unmarshaler
cp Checkpointer
cpKey string
ch chan *message
interval time.Duration
bufferSize int
}
// MessageHandlerOption allows options to be specified for NewMessageHandler
type MessageHandlerOption func(m *MessageHandler)
// WithBufferSize specifies the max number of messages to be called before callng the Processor
func WithBufferSize(in int) MessageHandlerOption {
return func(m *MessageHandler) {
m.bufferSize = in
}
}
// WithInterval specifies the maximum amount of time that can elapse until we try to flush
// any received events
func WithInterval(d time.Duration) MessageHandlerOption {
return func(m *MessageHandler) {
m.interval = d
}
}
// Done returns a chan that signals when all the resources used by MessageHandler have been released
func (m *MessageHandler) Done() <-chan struct{} {
return m.done
}
func (m *MessageHandler) flush(data ...*message) error {
if len(data) == 0 {
return nil
}
events, sequence, err := bytesToEvents(m.unmarshal, data...)
if err != nil {
return errors.Wrap(err, "unable to convert []byte to events")
}
if err := m.processor.Do(m.ctx, events...); err != nil {
return errors.Wrap(err, "unable to process events")
}
if err := m.cp.Save(m.ctx, m.cpKey, sequence); err != nil {
return errors.Wrapf(err, "unable to save checkpoint, %v %v", m.cpKey, sequence)
}
return nil
}
func (m *MessageHandler) start() {
defer close(m.done)
defer close(m.ch)
defer m.cancel()
t := time.NewTicker(m.interval)
defer t.Stop()
size := m.bufferSize
buffer := make([]*message, size)
offset := 0
for {
select {
case v := <-m.ch:
buffer[offset] = v
offset++
if offset == size {
m.flush(buffer[0:offset]...)
offset = 0
}
case <-t.C:
m.flush(buffer[0:offset]...)
offset = 0
case <-m.ctx.Done():
m.flush(buffer[0:offset]...)
offset = 0
return
}
}
}
// Handle the the specified stream record
func (m *MessageHandler) Receive(offset uint64, data []byte) {
m.ch <- &message{
offset: offset,
data: data,
}
}
// Close releases resources associated with the MessageHandler
func (m *MessageHandler) Close() error {
m.cancel()
<-m.done
return nil
}
// NewMessageHandler constructs a new MessageHandler with the arguments provided
func NewMessageHandler(ctx context.Context, p Processor, u Unmarshaler, cp Checkpointer, cpKey string, opts ...MessageHandlerOption) *MessageHandler {
child, cancel := context.WithCancel(ctx)
h := &MessageHandler{
ctx: child,
cancel: cancel,
done: make(chan struct{}),
processor: p,
unmarshal: u,
cp: cp,
ch: make(chan *message, 256),
interval: time.Millisecond * 250,
bufferSize: 100,
}
for _, opt := range opts {
opt(h)
}
go h.start()
return h
}
func bytesToEvents(unmarshal Unmarshaler, messages ...*message) ([]eventsource.Event, uint64, error) {
events := make([]eventsource.Event, 0, len(messages))
sequence := uint64(0)
for _, m := range messages {
event, err := unmarshal(m.data)
if err != nil {
return nil, 0, errors.Wrapf(err, "unable to unmarshal event at sequence, %v", m.offset)
}
events = append(events, event)
sequence = m.offset
}
return events, sequence, nil
}