x-pack/filebeat/input/awss3: fix document ID construction when using csv decoder

CHANGELOG.next.asciidoc

@@ -196,6 +196,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 - Redact authorization headers in HTTPJSON debug logs. {pull}41920[41920]
 - Further rate limiting fix in the Okta provider of the Entity Analytics input. {issue}40106[40106] {pull}41977[41977]
 - Fix streaming input handling of invalid or empty websocket messages. {pull}42036[42036]
+- Fix awss3 document ID construction when using the CSV decoder. {pull}42019[42019]
 
 *Heartbeat*
 

x-pack/filebeat/input/awss3/decoding.go

@@ -25,7 +25,10 @@ type decoder interface {
 type valueDecoder interface {
 	decoder
 
-	decodeValue() (any, error)
+	// decodeValue returns the current value, and its offset
+	// in the stream. If the receiver is unable to provide
+	// a unique offset for the value, offset will be negative.
+	decodeValue() (offset int64, val any, _ error)
 }
 
 // newDecoder creates a new decoder based on the codec type.

x-pack/filebeat/input/awss3/decoding_csv.go

@@ -17,6 +17,7 @@
 	r *csv.Reader
 
 	header  []string
+	offset  int64
 	current []string
 
 	err error
@@ -51,14 +52,15 @@
 	if d.err != nil {
 		return false
 	}
+	d.offset = d.r.InputOffset()
 	d.current, d.err = d.r.Read()
 	return d.err == nil
 }
 
 // decode returns the JSON encoded value of the current CSV line. next must
 // have been called before any calls to decode.
 func (d *csvDecoder) decode() ([]byte, error) {
-	v, err := d.decodeValue()
+	_, v, err := d.decodeValue()
 	if err != nil {
 		return nil, err
 	}
@@ -68,12 +70,12 @@
 // decodeValue returns the value of the current CSV line interpreted as
 // an object with fields based on the header held by the receiver. next must
 // have been called before any calls to decode.
-func (d *csvDecoder) decodeValue() (any, error) {
+func (d *csvDecoder) decodeValue() (offset int64, val any, _ error) {
 	if d.err != nil {
-		return nil, d.err
+		return d.offset, nil, d.err
 	}
 	if len(d.current) == 0 {
-		return nil, fmt.Errorf("decode called before next")
+		return d.offset, nil, fmt.Errorf("decode called before next")
 	}
 	m := make(map[string]string, len(d.header))
 	// By the time we are here, current must be the same
@@ -83,12 +85,12 @@
 	for i, n := range d.header {
 		m[n] = d.current[i]
 	}
-	return m, nil
+	return d.offset, m, nil
 }
 
 // close closes the parquet decoder and releases the resources.
 func (d *csvDecoder) close() error {
 	if d.err == io.EOF {
 		return nil
 	}
 	return d.err

x-pack/filebeat/input/awss3/s3_objects.go

@@ -158,13 +158,12 @@ func (p *s3ObjectProcessor) ProcessS3Object(log *logp.Logger, eventCallback func
 	if err != nil {
 		return err
 	}
-	var evtOffset int64
 	switch dec := dec.(type) {
 	case valueDecoder:
 		defer dec.close()
 
 		for dec.next() {
-			val, err := dec.decodeValue()
+			evtOffset, val, err := dec.decodeValue()
 			if err != nil {
 				if errors.Is(err, io.EOF) {
 					return nil
@@ -183,6 +182,7 @@ func (p *s3ObjectProcessor) ProcessS3Object(log *logp.Logger, eventCallback func
 	case decoder:
 		defer dec.close()
 
+		var evtOffset int64
 		for dec.next() {
 			data, err := dec.decode()
 			if err != nil {
@@ -420,13 +420,17 @@ func (p *s3ObjectProcessor) readFile(r io.Reader) error {
 	return nil
 }
 
+// createEvent constructs a beat.Event from message and offset. The value of
+// message populates the event message field, and offset is used to set the
+// log.offset field and, with the object's ARN and key, the @metadata._id field.
+// If offset is negative, it is ignored. No @metadata._id field is added to
+// the event and the log.offset field is not set.
 func (p *s3ObjectProcessor) createEvent(message string, offset int64) beat.Event {
 	event := beat.Event{
 		Timestamp: time.Now().UTC(),
 		Fields: mapstr.M{
 			"message": message,
 			"log": mapstr.M{
-				"offset": offset,
 				"file": mapstr.M{
 					"path": p.s3RequestURL,
 				},
@@ -448,7 +452,10 @@ func (p *s3ObjectProcessor) createEvent(message string, offset int64) beat.Event
 			},
 		},
 	}
-	event.SetID(objectID(p.s3ObjHash, offset))
+	if offset >= 0 {
+		event.Fields.Put("log.offset", offset)
+		event.SetID(objectID(p.s3ObjHash, offset))
+	}
 
 	if len(p.s3Metadata) > 0 {
 		_, _ = event.Fields.Put("aws.s3.metadata", p.s3Metadata)