refactoring to eliminate unnecessary copy && add flag

libbeat/processors/actions/truncate_fields.go

@@ -44,7 +44,7 @@ type truncateFields struct {
 	truncate truncater
 }
 
-type truncater func(*truncateFields, []byte) ([]byte, error)
+type truncater func(*truncateFields, []byte) ([]byte, bool, error)
 
 func init() {
 	processors.RegisterPlugin("truncate_fields",
@@ -99,80 +99,92 @@ func (f *truncateFields) truncateSingleField(field string, event *beat.Event) (*
 		if f.config.IgnoreMissing && errors.Cause(err) == common.ErrKeyNotFound {
 			return event, nil
 		}
-		return event, fmt.Errorf("could not fetch value for key: %s, Error: %+v", field, err)
+		return event, errors.Wrapf(err, "could not fetch value for key: %s", field)
 	}
 
 	switch value := v.(type) {
-	case string:
-		return f.addTruncatedString(field, value, event)
 	case []byte:
 		return f.addTruncatedByte(field, value, event)
+	case string:
+		return f.addTruncatedString(field, value, event)
 	default:
 		return event, fmt.Errorf("value cannot be truncated: %+v", value)
 	}
 
 }
 
 func (f *truncateFields) addTruncatedString(field, value string, event *beat.Event) (*beat.Event, error) {
-	truncated, err := f.truncate(f, []byte(value))
+	truncated, isTruncated, err := f.truncate(f, []byte(value))
 	if err != nil {
 		return event, err
 	}
 	_, err = event.PutValue(field, string(truncated))
 	if err != nil {
 		return event, fmt.Errorf("could not add truncated string value for key: %s, Error: %+v", field, err)
 	}
+
+	if isTruncated {
+		common.AddTagsWithKey(event.Fields, "log.flags", []string{"truncated"})
+	}
+
 	return event, nil
 }
 
 func (f *truncateFields) addTruncatedByte(field string, value []byte, event *beat.Event) (*beat.Event, error) {
-	truncated, err := f.truncate(f, value)
+	truncated, isTruncated, err := f.truncate(f, value)
 	if err != nil {
 		return event, err
 	}
 	_, err = event.PutValue(field, truncated)
 	if err != nil {
 		return event, fmt.Errorf("could not add truncated byte slice value for key: %s, Error: %+v", field, err)
 	}
+
+	if isTruncated {
+		common.AddTagsWithKey(event.Fields, "log.flags", []string{"truncated"})
+	}
+
 	return event, nil
 }
 
-func (f *truncateFields) truncateBytes(value []byte) ([]byte, error) {
+func (f *truncateFields) truncateBytes(value []byte) ([]byte, bool, error) {
 	size := len(value)
-	if size > f.config.MaxBytes {
-		size = f.config.MaxBytes
+	if size <= f.config.MaxBytes {
+		return value, false, nil
 	}
 
+	size = f.config.MaxBytes
 	truncated := make([]byte, size)
 	n := copy(truncated, value[:size])
 	if n != size {
-		return nil, fmt.Errorf("unexpected number of bytes were copied")
+		return nil, false, fmt.Errorf("unexpected number of bytes were copied")
 	}
-	return truncated, nil
+	return truncated, true, nil
 }
 
-func (f *truncateFields) truncateCharacters(value []byte) ([]byte, error) {
+func (f *truncateFields) truncateCharacters(value []byte) ([]byte, bool, error) {
 	count := utf8.RuneCount(value)
-	if count > f.config.MaxChars {
-		count = f.config.MaxChars
+	if count <= f.config.MaxChars {
+		return value, false, nil
 	}
 
+	count = f.config.MaxChars
 	r := bytes.NewReader(value)
 	w := bytes.NewBuffer(nil)
 
 	for i := 0; i < count; i++ {
 		r, _, err := r.ReadRune()
 		if err != nil {
-			return nil, err
+			return nil, false, err
 		}
 
 		_, err = w.WriteRune(r)
 		if err != nil {
-			return nil, err
+			return nil, false, err
 		}
 	}
 
-	return w.Bytes(), nil
+	return w.Bytes(), true, nil
 }
 
 func (f *truncateFields) String() string {

libbeat/processors/actions/truncate_fields_test.go

@@ -30,7 +30,7 @@ func TestTruncateFields(t *testing.T) {
 
 	var tests = map[string]struct {
 		MaxBytes     int
-		MaxCount     int
+		MaxChars     int
 		Input        common.MapStr
 		Output       common.MapStr
 		ShouldError  bool
@@ -43,6 +43,9 @@ func TestTruncateFields(t *testing.T) {
 			},
 			Output: common.MapStr{
 				"message": "too",
+				"log": common.MapStr{
+					"flags": []string{"truncated"},
+				},
 			},
 			ShouldError:  false,
 			TruncateFunc: (*truncateFields).truncateBytes,
@@ -54,6 +57,9 @@ func TestTruncateFields(t *testing.T) {
 			},
 			Output: common.MapStr{
 				"message": []byte("too"),
+				"log": common.MapStr{
+					"flags": []string{"truncated"},
+				},
 			},
 			ShouldError:  false,
 			TruncateFunc: (*truncateFields).truncateBytes,
@@ -92,7 +98,7 @@ func TestTruncateFields(t *testing.T) {
 			TruncateFunc: (*truncateFields).truncateBytes,
 		},
 		"do not truncate characters of short byte line": {
-			MaxCount: 6,
+			MaxChars: 6,
 			Input: common.MapStr{
 				"message": []byte("ez jó"), // this is good (hungarian)
 			},
@@ -114,12 +120,15 @@ func TestTruncateFields(t *testing.T) {
 			TruncateFunc: (*truncateFields).truncateBytes,
 		},
 		"truncate characters of too long byte line": {
-			MaxCount: 10,
+			MaxChars: 10,
 			Input: common.MapStr{
 				"message": []byte("ez egy túl hosszú sor"), // this is a too long line (hungarian)
 			},
 			Output: common.MapStr{
 				"message": []byte("ez egy túl"), // this is a too (hungarian)
+				"log": common.MapStr{
+					"flags": []string{"truncated"},
+				},
 			},
 			ShouldError:  false,
 			TruncateFunc: (*truncateFields).truncateCharacters,
@@ -131,6 +140,9 @@ func TestTruncateFields(t *testing.T) {
 			},
 			Output: common.MapStr{
 				"message": []byte("ez egy tú"), // this is a "to" (hungarian)
+				"log": common.MapStr{
+					"flags": []string{"truncated"},
+				},
 			},
 			ShouldError:  false,
 			TruncateFunc: (*truncateFields).truncateBytes,
@@ -143,7 +155,7 @@ func TestTruncateFields(t *testing.T) {
 				config: truncateFieldsConfig{
 					Fields:      []string{"message"},
 					MaxBytes:    test.MaxBytes,
-					MaxCount:    test.MaxCount,
+					MaxChars:    test.MaxChars,
 					FailOnError: true,
 				},
 				truncate: test.TruncateFunc,