feat(serializers.json): Support serializing JSON nested in string fields

config/config.go

@@ -1196,6 +1196,8 @@ func (c *Config) buildSerializer(tbl *ast.Table) (serializers.Serializer, error)
 	c.getFieldDuration(tbl, "json_timestamp_units", &sc.TimestampUnits)
 	c.getFieldString(tbl, "json_timestamp_format", &sc.TimestampFormat)
 	c.getFieldString(tbl, "json_transformation", &sc.Transformation)
+	c.getFieldStringSlice(tbl, "json_nested_fields_include", &sc.JSONNestedFieldInclude)
+	c.getFieldStringSlice(tbl, "json_nested_fields_exclude", &sc.JSONNestedFieldExclude)
 
 	c.getFieldBool(tbl, "splunkmetric_hec_routing", &sc.HecRouting)
 	c.getFieldBool(tbl, "splunkmetric_multimetric", &sc.SplunkmetricMultiMetric)
@@ -1276,6 +1278,7 @@ func (c *Config) missingTomlField(_ reflect.Type, key string) error {
 		"graphite_tag_sanitize_mode", "graphite_tag_support", "graphite_separator",
 		"influx_max_line_bytes", "influx_sort_fields", "influx_uint_support",
 		"json_timestamp_format", "json_timestamp_units", "json_transformation",
+		"json_nested_fields_include", "json_nested_fields_exclude",
 		"prometheus_export_timestamp", "prometheus_sort_metrics", "prometheus_string_as_label",
 		"prometheus_compact_encoding",
 		"splunkmetric_hec_routing", "splunkmetric_multimetric", "splunkmetric_omit_event_tag",

plugins/outputs/azure_data_explorer/azure_data_explorer.go

@@ -323,7 +323,10 @@ func (adx *AzureDataExplorer) Init() error {
 		return fmt.Errorf("unknown ingestion type %q", adx.IngestionType)
 	}
 
-	serializer, err := json.NewSerializer(time.Nanosecond, time.RFC3339Nano, "")
+	serializer, err := json.NewSerializer(json.FormatConfig{
+		TimestampUnits:  time.Nanosecond,
+		TimestampFormat: time.RFC3339Nano,
+	})
 	if err != nil {
 		return err
 	}

plugins/outputs/azure_data_explorer/azure_data_explorer_test.go

@@ -140,7 +140,10 @@ func TestWrite(t *testing.T) {
 
 	for _, tC := range testCases {
 		t.Run(tC.name, func(t *testing.T) {
-			serializer, err := telegrafJson.NewSerializer(time.Second, "", "")
+			serializer, err := telegrafJson.NewSerializer(
+				telegrafJson.FormatConfig{
+					TimestampUnits: time.Second,
+				})
 			require.NoError(t, err)
 
 			plugin := AzureDataExplorer{
@@ -264,7 +267,7 @@ func TestWriteWithType(t *testing.T) {
 	}
 	for _, testCase := range testCases {
 		t.Run(testCase.name, func(t *testing.T) {
-			serializer, err := telegrafJson.NewSerializer(time.Second, "", "")
+			serializer, err := telegrafJson.NewSerializer(telegrafJson.FormatConfig{TimestampUnits: time.Second})
 			require.NoError(t, err)
 			for tableName, jsonValue := range testCase.tableNameToExpectedResult {
 				ingestionType := "queued"

plugins/outputs/event_hubs/event_hubs_test.go

@@ -42,7 +42,7 @@ func (eh *mockEventHub) SendBatch(ctx context.Context, iterator eventhub.BatchIt
 /* End wrapper interface */
 
 func TestInitAndWrite(t *testing.T) {
-	serializer, err := json.NewSerializer(time.Second, "", "")
+	serializer, err := json.NewSerializer(json.FormatConfig{TimestampUnits: time.Second})
 	require.NoError(t, err)
 	mockHub := &mockEventHub{}
 	e := &EventHubs{
@@ -101,7 +101,7 @@ func TestInitAndWriteIntegration(t *testing.T) {
 	testHubCS := os.Getenv("EVENTHUB_CONNECTION_STRING") + ";EntityPath=" + entity.Name
 
 	// Configure the plugin to target the newly created hub
-	serializer, err := json.NewSerializer(time.Second, "", "")
+	serializer, err := json.NewSerializer(json.FormatConfig{TimestampUnits: time.Second})
 	require.NoError(t, err)
 	e := &EventHubs{
 		Hub:              &eventHub{},

plugins/outputs/http/http_test.go

@@ -661,7 +661,7 @@ func TestBatchedUnbatched(t *testing.T) {
 		Method: defaultMethod,
 	}
 
-	jsonSerializer, err := json.NewSerializer(time.Second, "", "")
+	jsonSerializer, err := json.NewSerializer(json.FormatConfig{TimestampUnits: time.Second})
 	require.NoError(t, err)
 	s := map[string]serializers.Serializer{
 		"influx": influx.NewSerializer(),

plugins/outputs/stomp/stomp_test.go

@@ -28,7 +28,11 @@ func TestConnectAndWrite(t *testing.T) {
 	require.NoError(t, err, "failed to start container")
 	defer container.Terminate()
 	var url = fmt.Sprintf("%s:%s", container.Address, container.Ports[servicePort])
-	s, err := serializers.NewJSONSerializer(10*time.Second, "yyy-dd-mmThh:mm:ss", "")
+	s, err := serializers.NewJSONSerializer(
+		&serializers.Config{
+			TimestampUnits:  10 * time.Second,
+			TimestampFormat: "yyy-dd-mmThh:mm:ss",
+		})
 	require.NoError(t, err)
 	st := &STOMP{
 		Host:          url,

plugins/serializers/json/README.md

@@ -33,6 +33,13 @@ The `json` output data format converts metrics into JSON documents.
   ## This allows to generate an arbitrary output form based on the metric(s). Please use
   ## multiline strings (starting and ending with three single-quotes) if needed.
   #json_transformation = ""
+
+  ## Filter for fields that contain nested JSON data.
+  ## The serializer will try to decode matching STRING fields containing
+  ## valid JSON. This is done BEFORE any JSON transformation. The filters
+  ## can contain wildcards.
+  #json_nested_fields_include = []
+  #json_nested_fields_exclude = []
 ```
 
 ## Examples

plugins/serializers/json/json.go

@@ -10,29 +10,47 @@ import (
 	jsonata "github.com/blues/jsonata-go"
 
 	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/filter"
 )
 
+type FormatConfig struct {
+	TimestampUnits      time.Duration
+	TimestampFormat     string
+	Transformation      string
+	NestedFieldsInclude []string
+	NestedFieldsExclude []string
+}
+
 type Serializer struct {
 	TimestampUnits  time.Duration
 	TimestampFormat string
 
 	transformation *jsonata.Expr
+	nestedfields   filter.Filter
 }
 
-func NewSerializer(timestampUnits time.Duration, timestampFormat, transform string) (*Serializer, error) {
+func NewSerializer(cfg FormatConfig) (*Serializer, error) {
 	s := &Serializer{
-		TimestampUnits:  truncateDuration(timestampUnits),
-		TimestampFormat: timestampFormat,
+		TimestampUnits:  truncateDuration(cfg.TimestampUnits),
+		TimestampFormat: cfg.TimestampFormat,
 	}
 
-	if transform != "" {
-		e, err := jsonata.Compile(transform)
+	if cfg.Transformation != "" {
+		e, err := jsonata.Compile(cfg.Transformation)
 		if err != nil {
 			return nil, err
 		}
 		s.transformation = e
 	}
 
+	if len(cfg.NestedFieldsInclude) > 0 || len(cfg.NestedFieldsExclude) > 0 {
+		f, err := filter.NewIncludeExcludeFilter(cfg.NestedFieldsInclude, cfg.NestedFieldsExclude)
+		if err != nil {
+			return nil, err
+		}
+		s.nestedfields = f
+	}
+
 	return s, nil
 }
 
@@ -99,13 +117,26 @@ func (s *Serializer) createObject(metric telegraf.Metric) map[string]interface{}
 
 	fields := make(map[string]interface{}, len(metric.FieldList()))
 	for _, field := range metric.FieldList() {
-		if fv, ok := field.Value.(float64); ok {
+		val := field.Value
+		switch fv := field.Value.(type) {
+		case float64:
 			// JSON does not support these special values
 			if math.IsNaN(fv) || math.IsInf(fv, 0) {
 				continue
 			}
+		case string:
+			// Check for nested fields if any
+			if s.nestedfields != nil && s.nestedfields.Match(field.Key) {
+				bv := []byte(fv)
+				if json.Valid(bv) {
+					var nested interface{}
+					if err := json.Unmarshal(bv, &nested); err == nil {
+						val = nested
+					}
+				}
+			}
 		}
-		fields[field.Key] = field.Value
+		fields[field.Key] = val
 	}
 	m["fields"] = fields
 

plugins/serializers/json/json_test.go

@@ -29,7 +29,7 @@ func TestSerializeMetricFloat(t *testing.T) {
 	}
 	m := metric.New("cpu", tags, fields, now)
 
-	s, err := NewSerializer(0, "", "")
+	s, err := NewSerializer(FormatConfig{})
 	require.NoError(t, err)
 	buf, err := s.Serialize(m)
 	require.NoError(t, err)
@@ -90,7 +90,10 @@ func TestSerialize_TimestampUnits(t *testing.T) {
 				},
 				time.Unix(1525478795, 123456789),
 			)
-			s, err := NewSerializer(tt.timestampUnits, tt.timestampFormat, "")
+			s, err := NewSerializer(FormatConfig{
+				TimestampUnits:  tt.timestampUnits,
+				TimestampFormat: tt.timestampFormat,
+			})
 			require.NoError(t, err)
 			actual, err := s.Serialize(m)
 			require.NoError(t, err)
@@ -109,7 +112,7 @@ func TestSerializeMetricInt(t *testing.T) {
 	}
 	m := metric.New("cpu", tags, fields, now)
 
-	s, err := NewSerializer(0, "", "")
+	s, err := NewSerializer(FormatConfig{})
 	require.NoError(t, err)
 	buf, err := s.Serialize(m)
 	require.NoError(t, err)
@@ -128,7 +131,7 @@ func TestSerializeMetricString(t *testing.T) {
 	}
 	m := metric.New("cpu", tags, fields, now)
 
-	s, err := NewSerializer(0, "", "")
+	s, err := NewSerializer(FormatConfig{})
 	require.NoError(t, err)
 	buf, err := s.Serialize(m)
 	require.NoError(t, err)
@@ -148,7 +151,7 @@ func TestSerializeMultiFields(t *testing.T) {
 	}
 	m := metric.New("cpu", tags, fields, now)
 
-	s, err := NewSerializer(0, "", "")
+	s, err := NewSerializer(FormatConfig{})
 	require.NoError(t, err)
 	buf, err := s.Serialize(m)
 	require.NoError(t, err)
@@ -167,7 +170,7 @@ func TestSerializeMetricWithEscapes(t *testing.T) {
 	}
 	m := metric.New("My CPU", tags, fields, now)
 
-	s, err := NewSerializer(0, "", "")
+	s, err := NewSerializer(FormatConfig{})
 	require.NoError(t, err)
 	buf, err := s.Serialize(m)
 	require.NoError(t, err)
@@ -187,7 +190,7 @@ func TestSerializeBatch(t *testing.T) {
 	)
 
 	metrics := []telegraf.Metric{m, m}
-	s, err := NewSerializer(0, "", "")
+	s, err := NewSerializer(FormatConfig{})
 	require.NoError(t, err)
 	buf, err := s.SerializeBatch(metrics)
 	require.NoError(t, err)
@@ -211,7 +214,7 @@ func TestSerializeBatchSkipInf(t *testing.T) {
 		),
 	}
 
-	s, err := NewSerializer(0, "", "")
+	s, err := NewSerializer(FormatConfig{})
 	require.NoError(t, err)
 	buf, err := s.SerializeBatch(metrics)
 	require.NoError(t, err)
@@ -230,7 +233,7 @@ func TestSerializeBatchSkipInfAllFields(t *testing.T) {
 		),
 	}
 
-	s, err := NewSerializer(0, "", "")
+	s, err := NewSerializer(FormatConfig{})
 	require.NoError(t, err)
 	buf, err := s.SerializeBatch(metrics)
 	require.NoError(t, err)
@@ -266,7 +269,12 @@ func TestSerializeTransformationNonBatch(t *testing.T) {
 			expected := expectedArray.([]interface{})
 
 			// Serialize
-			serializer, err := NewSerializer(cfg.TimestampUnits, cfg.TimestampFormat, cfg.Transformation)
+			serializer, err := NewSerializer(
+				FormatConfig{
+					TimestampUnits:  cfg.TimestampUnits,
+					TimestampFormat: cfg.TimestampFormat,
+					Transformation:  cfg.Transformation,
+				})
 			require.NoError(t, err)
 			for i, m := range metrics {
 				buf, err := serializer.Serialize(m)
@@ -275,8 +283,6 @@ func TestSerializeTransformationNonBatch(t *testing.T) {
 				// Compare
 				var actual interface{}
 				require.NoError(t, json.Unmarshal(buf, &actual))
-				fmt.Printf("actual: %v\n", actual)
-				fmt.Printf("expected: %v\n", expected[i])
 				require.EqualValuesf(t, expected[i], actual, "mismatch in %d", i)
 			}
 		})
@@ -311,7 +317,12 @@ func TestSerializeTransformationBatch(t *testing.T) {
 			require.NoError(t, err)
 
 			// Serialize
-			serializer, err := NewSerializer(cfg.TimestampUnits, cfg.TimestampFormat, cfg.Transformation)
+			serializer, err := NewSerializer(
+				FormatConfig{
+					TimestampUnits:  cfg.TimestampUnits,
+					TimestampFormat: cfg.TimestampFormat,
+					Transformation:  cfg.Transformation,
+				})
 			require.NoError(t, err)
 			buf, err := serializer.SerializeBatch(metrics)
 			require.NoError(t, err)
@@ -324,10 +335,70 @@ func TestSerializeTransformationBatch(t *testing.T) {
 	}
 }
 
+func TestSerializeNesting(t *testing.T) {
+	var tests = []struct {
+		name     string
+		filename string
+		out      string
+	}{
+		{
+			name:     "nested fields include",
+			filename: "testcases/nested_fields_include.conf",
+			out:      "testcases/nested_fields_out.json",
+		},
+		{
+			name:     "nested fields exclude",
+			filename: "testcases/nested_fields_exclude.conf",
+			out:      "testcases/nested_fields_out.json",
+		},
+	}
+	parser := &influx.Parser{}
+	require.NoError(t, parser.Init())
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			filename := filepath.FromSlash(tt.filename)
+			cfg, header, err := loadTestConfiguration(filename)
+			require.NoError(t, err)
+
+			// Get the input metrics
+			metrics, err := testutil.ParseMetricsFrom(header, "Input:", parser)
+			require.NoError(t, err)
+			require.Len(t, metrics, 1)
+
+			// Get the expectations
+			expectedArray, err := loadJSON(tt.out)
+			require.NoError(t, err)
+			expected := expectedArray.(map[string]interface{})
+
+			// Serialize
+			serializer, err := NewSerializer(
+				FormatConfig{
+					TimestampUnits:      cfg.TimestampUnits,
+					TimestampFormat:     cfg.TimestampFormat,
+					Transformation:      cfg.Transformation,
+					NestedFieldsInclude: cfg.JSONNestedFieldsInclude,
+					NestedFieldsExclude: cfg.JSONNestedFieldsExclude,
+				})
+			require.NoError(t, err)
+
+			buf, err := serializer.Serialize(metrics[0])
+			require.NoError(t, err)
+
+			// Compare
+			var actual interface{}
+			require.NoError(t, json.Unmarshal(buf, &actual))
+			require.EqualValues(t, expected, actual)
+		})
+	}
+}
+
 type Config struct {
-	TimestampUnits  time.Duration `toml:"json_timestamp_units"`
-	TimestampFormat string        `toml:"json_timestamp_format"`
-	Transformation  string        `toml:"json_transformation"`
+	TimestampUnits          time.Duration `toml:"json_timestamp_units"`
+	TimestampFormat         string        `toml:"json_timestamp_format"`
+	Transformation          string        `toml:"json_transformation"`
+	JSONNestedFieldsInclude []string      `toml:"json_nested_fields_include"`
+	JSONNestedFieldsExclude []string      `toml:"json_nested_fields_exclude"`
 }
 
 func loadTestConfiguration(filename string) (*Config, []string, error) {

plugins/serializers/json/testcases/nested_fields_exclude.conf

@@ -0,0 +1,6 @@
+# Example for decoding fields that contain nested JSON structures.
+#
+# Input:
+# in,host=myhost,type=diagnostic hops=10,latency=1.23,id-1234="{\"address\": \"AB1A\", \"status\": \"online\"}",id-0000="{\"status\": \"offline\"}",id-5678="{\"address\": \"0000\", \"status\": \"online\"}" 1666006350000000000
+
+json_nested_fields_exclude = ["hops", "latency"]

plugins/serializers/json/testcases/nested_fields_include.conf

@@ -0,0 +1,6 @@
+# Example for decoding fields that contain nested JSON structures.
+#
+# Input:
+# in,host=myhost,type=diagnostic hops=10,latency=1.23,id-1234="{\"address\": \"AB1A\", \"status\": \"online\"}",id-0000="{\"status\": \"offline\"}",id-5678="{\"address\": \"0000\", \"status\": \"online\"}" 1666006350000000000
+
+json_nested_fields_include = ["id-*"]