Allow user to override no-op checkpoint with Option

README.md

@@ -18,11 +18,13 @@ Get the package source:
 
 The consumer leverages a handler func that accepts a Kinesis record. The `Scan` method will consume all shards concurrently and call the callback func as it receives records from the stream.
 
+Important: The default Log, Counter, and Checkpoint are no-op which means no logs, counts, or checkpoints will be emitted when scanning the stream. See the options below to override these defaults.
+
 ```go
 import(
 	// ...
+
 	consumer "github.com/harlow/kinesis-consumer"
-	checkpoint "github.com/harlow/kinesis-consumer/checkpoint/redis"
 )
 
 func main() {
@@ -32,14 +34,8 @@ func main() {
 	)
 	flag.Parse()
 
-	// new checkpoint
+	// consumer
-	ck, err := checkpoint.New(*app, *stream)
+	c, err := consumer.New(*app, *stream)
-	if err != nil {
-		log.Fatalf("checkpoint error: %v", err)
-	}
-
-	// new consumer
-	c, err := consumer.New(ck, *app, *stream)
 	if err != nil {
 		log.Fatalf("consumer error: %v", err)
 	}
@@ -68,7 +64,9 @@ The uniq identifier for a consumer is `[appName, streamName, shardID]`
 
 <img width="722" alt="kinesis-checkpoints" src="https://user-images.githubusercontent.com/739782/33085867-d8336122-ce9a-11e7-8c8a-a8afeb09dff1.png">
 
-There are currently two storage types for checkpoints:
+Note: The default checkpoint is no-op. Which means the scan will not persist any state and the consumer will start from the beginning of the stream each time it is re-started.
+
+To persist scan progress choose one of the following checkpoints:
 
 ### Redis Checkpoint
 
@@ -116,7 +114,7 @@ client := kinesis.New(session.New(aws.NewConfig()))
 
 // consumer
 c, err := consumer.New(
-	consumer,
+	appName,
 	streamName,
 	consumer.WithClient(client),
 )

checkpoint/checkpoint.go

@@ -1,8 +0,0 @@
-package checkpoint
-
-// Checkpoint interface used to allow swappable backends for checkpoining
-// consumer progress in the stream.
-type Checkpoint interface {
-	Get(shardID string) (string, error)
-	Set(shardID string, sequenceNumber string) error
-}

consumer.go

@@ -10,12 +10,11 @@ import (
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/aws/aws-sdk-go/service/kinesis"
-	"github.com/harlow/kinesis-consumer/checkpoint"
 )
 
 type Record = kinesis.Record
 
-// Counter is used for exposing basic metrics from the scanner
+// Counter interface is used for exposing basic metrics from the scanner
 type Counter interface {
 	Add(string, int64)
 }
@@ -24,11 +23,22 @@ type noopCounter struct{}
 
 func (n noopCounter) Add(string, int64) {}
 
+// Checkpoint interface used track consumer progress in the stream
+type Checkpoint interface {
+	Get(shardID string) (string, error)
+	Set(shardID string, sequenceNumber string) error
+}
+
+type noopCheckpoint struct{}
+
+func (n noopCheckpoint) Set(string, string) error { return nil }
+func (n noopCheckpoint) Get(string) (string, error) { return "", nil }
+
 // Option is used to override defaults when creating a new Consumer
 type Option func(*Consumer) error
 
 // WithCheckpoint overrides the default checkpoint
-func WithCheckpoint(checkpoint checkpoint.Checkpoint) Option {
+func WithCheckpoint(checkpoint Checkpoint) Option {
 	return func(c *Consumer) error {
 		c.checkpoint = checkpoint
 		return nil
@@ -53,11 +63,7 @@ func WithCounter(counter Counter) Option {
 
 // New creates a kinesis consumer with default settings. Use Option to override
 // any of the optional attributes.
-func New(checkpoint checkpoint.Checkpoint, app, stream string, opts ...Option) (*Consumer, error) {
+func New(app, stream string, opts ...Option) (*Consumer, error) {
-	if checkpoint == nil {
-		return nil, fmt.Errorf("must provide checkpoint")
-	}
-
 	if app == "" {
 		return nil, fmt.Errorf("must provide app name")
 	}
@@ -67,9 +73,10 @@ func New(checkpoint checkpoint.Checkpoint, app, stream string, opts ...Option) (
 	}
 
 	c := &Consumer{
-		checkpoint: checkpoint,
 		appName:    app,
 		streamName: stream,
+		checkpoint: &noopCheckpoint{},
+		counter: 	&noopCounter{},
 	}
 
 	// set options
@@ -89,11 +96,6 @@ func New(checkpoint checkpoint.Checkpoint, app, stream string, opts ...Option) (
 		c.client = kinesis.New(session.New(aws.NewConfig()))
 	}
 
-	// provide default no-op counter
-	if c.counter == nil {
-		c.counter = &noopCounter{}
-	}
-
 	return c, nil
 }
 
@@ -103,7 +105,7 @@ type Consumer struct {
 	streamName string
 	client     *kinesis.Kinesis
 	logger     *log.Logger
-	checkpoint checkpoint.Checkpoint
+	checkpoint Checkpoint
 	counter    Counter
 }
 

examples/consumer/main.go

@@ -45,7 +45,8 @@ func main() {
 	}
 
 	// consumer
-	c, err := consumer.New(ck, *app, *stream,
+	c, err := consumer.New(*app, *stream,
+		consumer.WithCheckpoint(ck),
 		consumer.WithLogger(logger),
 		consumer.WithCounter(counter),
 	)