Add context to ProducerInterceptor

This change adds a context.Context argument to the ProducerInterceptor
interface, and passes it between the pre- and post-Send interceptor
methods. Having this makes it much easier to write useful
interceptors that can integrate with common tracing SDKs like
OpenTelemetry, as the context is the conventional method for propagating
metadata vertically through a call stack.

For an example of another library using a similar convention, see:
https://github.com/jackc/pgx/blob/9ab9e3c40bbb33c6f37359c87508cbc6a9830ed6/tracer.go#L10

Fixes #443

Author: treuherz

pulsar/internal/pulsartracing/producer_interceptor.go

@@ -29,13 +29,20 @@ const toPrefix = "To__"
 type ProducerInterceptor struct {
 }
 
-func (t *ProducerInterceptor) BeforeSend(producer pulsar.Producer, message *pulsar.ProducerMessage) {
+func (t *ProducerInterceptor) BeforeSend(
+	ctx context.Context,
+	producer pulsar.Producer,
+	message *pulsar.ProducerMessage,
+) context.Context {
 	buildAndInjectSpan(message, producer).Finish()
+	return ctx
 }
 
-func (t *ProducerInterceptor) OnSendAcknowledgement(producer pulsar.Producer,
-	message *pulsar.ProducerMessage,
-	msgID pulsar.MessageID) {
+func (t *ProducerInterceptor) OnSendAcknowledgement(
+	_ context.Context,
+	_ pulsar.Producer,
+	_ *pulsar.ProducerMessage,
+	_ pulsar.MessageID) {
 }
 
 func buildAndInjectSpan(message *pulsar.ProducerMessage, producer pulsar.Producer) opentracing.Span {

pulsar/producer_interceptor.go

@@ -17,27 +17,30 @@
 
 package pulsar
 
+import "context"
+
 type ProducerInterceptor interface {
 	// BeforeSend This is called before send the message to the brokers. This method is allowed to modify the
 	// message.
-	BeforeSend(producer Producer, message *ProducerMessage)
+	BeforeSend(ctx context.Context, producer Producer, message *ProducerMessage) context.Context
 
 	// OnSendAcknowledgement This method is called when the message sent to the broker has been acknowledged,
 	// or when sending the message fails.
-	OnSendAcknowledgement(producer Producer, message *ProducerMessage, msgID MessageID)
+	OnSendAcknowledgement(ctx context.Context, producer Producer, message *ProducerMessage, msgID MessageID)
 }
 
 type ProducerInterceptors []ProducerInterceptor
 
-func (x ProducerInterceptors) BeforeSend(producer Producer, message *ProducerMessage) {
+func (x ProducerInterceptors) BeforeSend(ctx context.Context, producer Producer, message *ProducerMessage) context.Context {
 	for i := range x {
-		x[i].BeforeSend(producer, message)
+		ctx = x[i].BeforeSend(ctx, producer, message)
 	}
+	return ctx
 }
 
-func (x ProducerInterceptors) OnSendAcknowledgement(producer Producer, message *ProducerMessage, msgID MessageID) {
+func (x ProducerInterceptors) OnSendAcknowledgement(ctx context.Context, producer Producer, message *ProducerMessage, msgID MessageID) {
 	for i := range x {
-		x[i].OnSendAcknowledgement(producer, message, msgID)
+		x[i].OnSendAcknowledgement(ctx, producer, message, msgID)
 	}
 }
 

pulsar/producer_partition.go

@@ -994,7 +994,7 @@ func (p *partitionProducer) Send(ctx context.Context, msg *ProducerMessage) (Mes
 	isDone := uAtomic.NewBool(false)
 	doneCh := make(chan struct{})
 
-	p.internalSendAsync(ctx, msg, func(ID MessageID, message *ProducerMessage, e error) {
+	ctx = p.internalSendAsync(ctx, msg, func(ID MessageID, message *ProducerMessage, e error) {
 		if isDone.CAS(false, true) {
 			err = e
 			msgID = ID
@@ -1194,11 +1194,11 @@ func (p *partitionProducer) internalSendAsync(
 	msg *ProducerMessage,
 	callback func(MessageID, *ProducerMessage, error),
 	flushImmediately bool,
-) {
+) context.Context {
 	if err := p.validateMsg(msg); err != nil {
 		p.log.Error(err)
 		runCallback(callback, nil, msg, err)
-		return
+		return ctx
 	}
 
 	sr := sendRequestPool.Get().(*sendRequest)
@@ -1216,43 +1216,46 @@ func (p *partitionProducer) internalSendAsync(
 
 	if err := p.prepareTransaction(sr); err != nil {
 		sr.done(nil, err)
-		return
+		return ctx
 	}
 
 	if p.getProducerState() != producerReady {
 		sr.done(nil, errProducerClosed)
-		return
+		return ctx
 	}
 
-	p.options.Interceptors.BeforeSend(p, msg)
+	ctx = p.options.Interceptors.BeforeSend(ctx, p, msg)
+	sr.ctx = ctx
 
 	if err := p.updateSchema(sr); err != nil {
 		p.log.Error(err)
 		sr.done(nil, err)
-		return
+		return ctx
 	}
 
 	if err := p.updateUncompressedPayload(sr); err != nil {
 		p.log.Error(err)
 		sr.done(nil, err)
-		return
+		return ctx
 	}
 
 	p.updateMetaData(sr)
 
 	if err := p.updateChunkInfo(sr); err != nil {
 		p.log.Error(err)
 		sr.done(nil, err)
-		return
+		return ctx
 	}
 
 	if err := p.reserveResources(sr); err != nil {
 		p.log.Error(err)
 		sr.done(nil, err)
-		return
+		return ctx
 	}
 
 	p.dataChan <- sr
+
+	return ctx
 }
 
 func (p *partitionProducer) ReceivedSendReceipt(response *pb.CommandSendReceipt) {
@@ -1497,7 +1500,7 @@ func (sr *sendRequest) done(msgID MessageID, err error) {
 
 		if sr.totalChunks <= 1 || sr.chunkID == sr.totalChunks-1 {
 			if sr.producer.options.Interceptors != nil {
-				sr.producer.options.Interceptors.OnSendAcknowledgement(sr.producer, sr.msg, msgID)
+				sr.producer.options.Interceptors.OnSendAcknowledgement(sr.ctx, sr.producer, sr.msg, msgID)
 			}
 		}
 	}

pulsar/producer_test.go

@@ -1480,23 +1480,38 @@ func TestProducuerSendFailOnInvalidKey(t *testing.T) {
 
 type noopProduceInterceptor struct{}
 
-func (noopProduceInterceptor) BeforeSend(producer Producer, message *ProducerMessage) {}
+func (noopProduceInterceptor) BeforeSend(ctx context.Context, _ Producer, _ *ProducerMessage) context.Context {
+	return ctx
+}
 
-func (noopProduceInterceptor) OnSendAcknowledgement(producer Producer, message *ProducerMessage, msgID MessageID) {
+func (noopProduceInterceptor) OnSendAcknowledgement(_ context.Context, _ Producer, _ *ProducerMessage, _ MessageID) {
 }
 
-// copyPropertyIntercepotr copy all keys in message properties map and add a suffix
-type metricProduceInterceptor struct {
-	sendn int
-	ackn  int
+type trackingProduceInterceptor struct {
+	sendn       int
+	ackn        int
+	maxDuration time.Duration
 }
 
-func (x *metricProduceInterceptor) BeforeSend(producer Producer, message *ProducerMessage) {
-	x.sendn++
+type beforeSendCtxKey struct{}
+
+func (i *trackingProduceInterceptor) BeforeSend(ctx context.Context, _ Producer, msg *ProducerMessage) context.Context {
+	i.sendn++
+	ctx = context.WithValue(ctx, beforeSendCtxKey{}, time.Now())
+	return ctx
 }
 
-func (x *metricProduceInterceptor) OnSendAcknowledgement(producer Producer, message *ProducerMessage, msgID MessageID) {
-	x.ackn++
+func (i *trackingProduceInterceptor) OnSendAcknowledgement(ctx context.Context, _ Producer, _ *ProducerMessage, _ MessageID) {
+	var dur time.Duration
+	if v := ctx.Value(beforeSendCtxKey{}); v != nil {
+		dur = time.Since(v.(time.Time))
+	}
+
+	if dur > i.maxDuration {
+		i.maxDuration = dur
+	}
+
+	i.ackn++
 }
 
 func TestProducerWithInterceptors(t *testing.T) {
@@ -1519,14 +1534,14 @@ func TestProducerWithInterceptors(t *testing.T) {
 	assert.Nil(t, err)
 	defer consumer.Close()
 
-	metric := &metricProduceInterceptor{}
+	interceptor := &trackingProduceInterceptor{}
 	// create producer
 	producer, err := client.CreateProducer(ProducerOptions{
 		Topic:           topic,
 		DisableBatching: false,
 		Interceptors: ProducerInterceptors{
 			noopProduceInterceptor{},
-			metric,
+			interceptor,
 		},
 	})
 	assert.Nil(t, err)
@@ -1576,8 +1591,9 @@ func TestProducerWithInterceptors(t *testing.T) {
 		consumer.Ack(msg)
 	}
 
-	assert.Equal(t, 10, metric.sendn)
-	assert.Equal(t, 10, metric.ackn)
+	assert.Equal(t, 10, interceptor.sendn)
+	assert.Equal(t, 10, interceptor.ackn)
+	assert.NotZero(t, interceptor.maxDuration)
 }
 
 func TestProducerSendAfterClose(t *testing.T) {
@@ -1720,7 +1736,7 @@ func TestMultipleSchemaOfKeyBasedBatchProducerConsumer(t *testing.T) {
 	}
 	producer.Flush()
 
-	//// create consumer
+	// create consumer
 	consumer, err := client.Subscribe(ConsumerOptions{
 		Topic:                       topic,
 		SubscriptionName:            "my-sub2",
@@ -1811,7 +1827,7 @@ func TestMultipleSchemaProducerConsumer(t *testing.T) {
 	}
 	producer.Flush()
 
-	//// create consumer
+	// create consumer
 	consumer, err := client.Subscribe(ConsumerOptions{
 		Topic:                       topic,
 		SubscriptionName:            "my-sub2",