Allow metrics to be unserializable in influx.Reader (#4047)

Metrics that are unserializable will be logged at debug level, but the
rest of the batch will be sent.  Unserializable metrics can occur during
normal operation such as if you remove all fields from a metric or the
metric cannot fit within the line size limit.

plugins/serializers/influx/influx.go

@@ -2,8 +2,9 @@ package influx
 
 import (
 	"bytes"
-	"errors"
+	"fmt"
 	"io"
+	"log"
 	"math"
 	"sort"
 	"strconv"
@@ -26,14 +27,28 @@ const (
 	UintSupport FieldTypeSupport = 1 << iota
 )
 
+// MetricError is an error causing a metric to be unserializable.
+type MetricError struct {
+	s string
+}
+
+func (e MetricError) Error() string {
+	return e.s
+}
+
+// FieldError is an error causing a field to be unserializable.
+type FieldError struct {
+	s string
+}
+
+func (e FieldError) Error() string {
+	return e.s
+}
+
 var (
-	ErrNeedMoreSpace    = errors.New("need more space")
-	ErrInvalidName      = errors.New("invalid name")
-	ErrInvalidFieldKey  = errors.New("invalid field key")
-	ErrInvalidFieldType = errors.New("invalid field type")
-	ErrFieldIsNaN       = errors.New("is NaN")
-	ErrFieldIsInf       = errors.New("is Inf")
-	ErrNoFields         = errors.New("no fields")
+	ErrNeedMoreSpace = &MetricError{"need more space"}
+	ErrInvalidName   = &MetricError{"invalid name"}
+	ErrNoFields      = &MetricError{"no serializable fields"}
 )
 
 // Serializer is a serializer for line protocol.
@@ -148,7 +163,7 @@ func (s *Serializer) buildFieldPair(key string, value interface{}) error {
 	// Some keys are not encodeable as line protocol, such as those with a
 	// trailing '\' or empty strings.
 	if key == "" {
-		return ErrInvalidFieldKey
+		return &FieldError{"invalid field key"}
 	}
 
 	s.pair = append(s.pair, key...)
@@ -182,6 +197,9 @@ func (s *Serializer) writeMetric(w io.Writer, m telegraf.Metric) error {
 	for _, field := range m.FieldList() {
 		err = s.buildFieldPair(field.Key, field.Value)
 		if err != nil {
+			log.Printf(
+				"D! [serializers.influx] could not serialize field %q: %v; discarding field",
+				field.Key, err)
 			continue
 		}
 
@@ -262,11 +280,11 @@ func (s *Serializer) appendFieldValue(buf []byte, value interface{}) ([]byte, er
 		return appendIntField(buf, v), nil
 	case float64:
 		if math.IsNaN(v) {
-			return nil, ErrFieldIsNaN
+			return nil, &FieldError{"is NaN"}
 		}
 
 		if math.IsInf(v, 0) {
-			return nil, ErrFieldIsInf
+			return nil, &FieldError{"is Inf"}
 		}
 
 		return appendFloatField(buf, v), nil
@@ -274,8 +292,9 @@ func (s *Serializer) appendFieldValue(buf []byte, value interface{}) ([]byte, er
 		return appendStringField(buf, v), nil
 	case bool:
 		return appendBoolField(buf, v), nil
+	default:
+		return buf, &FieldError{fmt.Sprintf("invalid value type: %T", v)}
 	}
-	return buf, ErrInvalidFieldType
 }
 
 func appendUintField(buf []byte, value uint64) []byte {

plugins/serializers/influx/reader.go

@@ -2,7 +2,9 @@ package influx
 
 import (
 	"bytes"
+	"fmt"
 	"io"
+	"log"
 
 	"github.com/influxdata/telegraf"
 )
@@ -47,12 +49,26 @@ func (r *reader) Read(p []byte) (int, error) {
 		return 0, io.EOF
 	}
 
-	_, err := r.serializer.Write(r.buf, r.metrics[r.offset])
+	for _, metric := range r.metrics[r.offset:] {
+		_, err := r.serializer.Write(r.buf, metric)
 		r.offset += 1
 		if err != nil {
 			r.buf.Reset()
+			switch err.(type) {
+			case *MetricError:
+				// Since we are serializing an array of metrics, don't fail
+				// the entire batch just because of one unserializable metric.
+				log.Printf(
+					"D! [serializers.influx] could not serialize metric %q: %v; discarding metric",
+					metric.Name(), err)
+				continue
+			default:
+				fmt.Println(err)
 				return 0, err
 			}
+		}
+		break
+	}
 
 	return r.buf.Read(p)
 }

plugins/serializers/influx/reader_test.go

@@ -83,6 +83,62 @@ func TestReader(t *testing.T) {
 			},
 			expected: []byte("cpu value=42 0\n"),
 		},
+		{
+			name:         "continue on failed metrics",
+			maxLineBytes: 4096,
+			bufferSize:   15,
+			input: []telegraf.Metric{
+				MustMetric(
+					metric.New(
+						"",
+						map[string]string{},
+						map[string]interface{}{
+							"value": 42.0,
+						},
+						time.Unix(0, 0),
+					),
+				),
+				MustMetric(
+					metric.New(
+						"cpu",
+						map[string]string{},
+						map[string]interface{}{
+							"value": 42.0,
+						},
+						time.Unix(0, 0),
+					),
+				),
+			},
+			expected: []byte("cpu value=42 0\n"),
+		},
+		{
+			name:         "last metric failed regression",
+			maxLineBytes: 4096,
+			bufferSize:   15,
+			input: []telegraf.Metric{
+				MustMetric(
+					metric.New(
+						"cpu",
+						map[string]string{},
+						map[string]interface{}{
+							"value": 42.0,
+						},
+						time.Unix(0, 0),
+					),
+				),
+				MustMetric(
+					metric.New(
+						"",
+						map[string]string{},
+						map[string]interface{}{
+							"value": 42.0,
+						},
+						time.Unix(0, 0),
+					),
+				),
+			},
+			expected: []byte("cpu value=42 0\n"),
+		},
 	}
 
 	for _, tt := range tests {