fix: handle DynamoDB creation timestamp precision

events/dynamodb.go

@@ -2,6 +2,11 @@
 
 package events
 
+import (
+	"encoding/json"
+	"time"
+)
+
 // The DynamoDBEvent stream event handled to Lambda
 // http://docs.aws.amazon.com/lambda/latest/dg/eventsources.html#eventsources-ddb-update
 type DynamoDBEvent struct {
@@ -84,6 +89,10 @@ type DynamoDBStreamRecord struct {
 	// epoch time (http://www.epochconverter.com/) format.
 	ApproximateCreationDateTime SecondsEpochTime `json:"ApproximateCreationDateTime,omitempty"`
 
+	// The precision of ApproximateCreationDateTime when the timestamp is not in
+	// seconds.
+	ApproximateCreationDateTimePrecision string `json:"ApproximateCreationDateTimePrecision,omitempty"`
+
 	// The primary key attribute(s) for the DynamoDB item that was modified.
 	Keys map[string]DynamoDBAttributeValue `json:"Keys,omitempty"`
 
@@ -104,6 +113,74 @@ type DynamoDBStreamRecord struct {
 	StreamViewType string `json:"StreamViewType"`
 }
 
+const (
+	dynamoDBApproximateCreationDateTimePrecisionMillisecond = "MILLISECOND"
+	dynamoDBApproximateCreationDateTimePrecisionMicrosecond = "MICROSECOND"
+)
+
+func (r DynamoDBStreamRecord) MarshalJSON() ([]byte, error) {
+	type dynamoDBStreamRecord DynamoDBStreamRecord
+	type dynamoDBStreamRecordJSON struct {
+		ApproximateCreationDateTime interface{} `json:"ApproximateCreationDateTime,omitempty"`
+		*dynamoDBStreamRecord
+	}
+
+	record := dynamoDBStreamRecord(r)
+	v := dynamoDBStreamRecordJSON{
+		ApproximateCreationDateTime: r.ApproximateCreationDateTime,
+		dynamoDBStreamRecord:        &record,
+	}
+
+	switch r.ApproximateCreationDateTimePrecision {
+	case dynamoDBApproximateCreationDateTimePrecisionMillisecond:
+		v.ApproximateCreationDateTime = r.ApproximateCreationDateTime.UnixNano() / int64(time.Millisecond)
+	case dynamoDBApproximateCreationDateTimePrecisionMicrosecond:
+		v.ApproximateCreationDateTime = r.ApproximateCreationDateTime.UnixNano() / int64(time.Microsecond)
+	}
+
+	return json.Marshal(v)
+}
+
+func (r *DynamoDBStreamRecord) UnmarshalJSON(data []byte) error {
+	type dynamoDBStreamRecord DynamoDBStreamRecord
+	type dynamoDBStreamRecordJSON struct {
+		ApproximateCreationDateTime json.RawMessage `json:"ApproximateCreationDateTime,omitempty"`
+		*dynamoDBStreamRecord
+	}
+
+	record := dynamoDBStreamRecord(*r)
+	v := dynamoDBStreamRecordJSON{dynamoDBStreamRecord: &record}
+	if err := json.Unmarshal(data, &v); err != nil {
+		return err
+	}
+
+	*r = DynamoDBStreamRecord(record)
+	if len(v.ApproximateCreationDateTime) == 0 {
+		return nil
+	}
+
+	switch r.ApproximateCreationDateTimePrecision {
+	case dynamoDBApproximateCreationDateTimePrecisionMillisecond:
+		var epoch int64
+		if err := json.Unmarshal(v.ApproximateCreationDateTime, &epoch); err != nil {
+			return err
+		}
+		r.ApproximateCreationDateTime = SecondsEpochTime{time.Unix(0, epoch*int64(time.Millisecond))}
+	case dynamoDBApproximateCreationDateTimePrecisionMicrosecond:
+		var epoch int64
+		if err := json.Unmarshal(v.ApproximateCreationDateTime, &epoch); err != nil {
+			return err
+		}
+		r.ApproximateCreationDateTime = SecondsEpochTime{time.Unix(0, epoch*int64(time.Microsecond))}
+	default:
+		if err := r.ApproximateCreationDateTime.UnmarshalJSON(v.ApproximateCreationDateTime); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 type DynamoDBKeyType string
 
 const (

events/dynamodb_test.go

@@ -5,6 +5,7 @@ package events
 import (
 	"encoding/json"
 	"testing"
+	"time"
 
 	"github.com/aws/aws-lambda-go/events/test"
 	"github.com/stretchr/testify/assert"
@@ -35,6 +36,31 @@ func TestDynamoDBEventMarshalingMalformedJson(t *testing.T) {
 	test.TestMalformedJson(t, DynamoDBEvent{})
 }
 
+func TestDynamoDBStreamRecordUnmarshalMicrosecondCreationDateTime(t *testing.T) {
+	inputJSON := []byte(`{
+		"ApproximateCreationDateTime": 1731101300058336,
+		"ApproximateCreationDateTimePrecision": "MICROSECOND",
+		"SequenceNumber": "1",
+		"SizeBytes": 1,
+		"StreamViewType": "NEW_IMAGE"
+	}`)
+
+	var inputRecord DynamoDBStreamRecord
+	if err := json.Unmarshal(inputJSON, &inputRecord); err != nil {
+		t.Errorf("could not unmarshal stream record. details: %v", err)
+	}
+
+	creationDateTime := inputRecord.ApproximateCreationDateTime
+	assert.Equal(t, time.Date(2024, time.November, 8, 21, 28, 20, 58336000, time.UTC), creationDateTime.UTC())
+	assert.Equal(t, "MICROSECOND", inputRecord.ApproximateCreationDateTimePrecision)
+
+	outputJSON, err := json.Marshal(inputRecord)
+	if err != nil {
+		t.Errorf("could not marshal stream record. details: %v", err)
+	}
+	assert.JSONEq(t, string(inputJSON), string(outputJSON))
+}
+
 func TestDynamoDBTimeWindowEventMarshaling(t *testing.T) {
 	// 1. read JSON from file
 	inputJSON := test.ReadJSONFromFile(t, "./testdata/dynamodb-time-window-event.json")