chore(parser.json_v2): Error out if no config is provided

CHANGELOG.md

@@ -14,6 +14,9 @@
   As a consequence the redunant `logtarget` setting is deprecated, `stderr` is
   used if no `logfile` is provided, otherwise messages are logged to the given
   file. For using the Windows `eventlog` set `logformat = "eventlog"`!
+- This release contains a change in json_v2 parser config parsing -
+  if the config is empty (not define any rules), initialization will fail
+  (see PR [#15844](https://github.com/influxdata/telegraf/pull/15844)).
 
 ## v1.31.3 [2024-08-12]
 

config/config_test.go

@@ -18,6 +18,7 @@ import (
 
 	"github.com/google/go-cmp/cmp"
 	"github.com/google/go-cmp/cmp/cmpopts"
+	"github.com/influxdata/telegraf/plugins/parsers/json_v2"
 	"github.com/stretchr/testify/require"
 
 	"github.com/influxdata/telegraf"
@@ -833,6 +834,18 @@ func TestConfig_ParserInterface(t *testing.T) {
 				"ProtobufMessageType": "addressbook.AddressBook",
 			},
 		},
+		"json_v2": {
+			param: map[string]interface{}{
+				"Configs": []json_v2.Config{{
+					Fields: []json_v2.DataSet{{
+						Path:     "",
+						Type:     "int",
+						Rename:   "",
+						Optional: false,
+					}},
+				}},
+			},
+		},
 	}
 
 	expected := make([]telegraf.Parser, 0, len(formats))
@@ -1039,6 +1052,18 @@ func TestConfig_ProcessorsWithParsers(t *testing.T) {
 				"ProtobufMessageType": "addressbook.AddressBook",
 			},
 		},
+		"json_v2": {
+			param: map[string]interface{}{
+				"Configs": []json_v2.Config{{
+					Fields: []json_v2.DataSet{{
+						Path:     "",
+						Type:     "int",
+						Rename:   "",
+						Optional: false,
+					}},
+				}},
+			},
+		},
 	}
 
 	expected := make([]telegraf.Parser, 0, len(formats))

config/testdata/parsers_new.toml

@@ -26,6 +26,11 @@
 
 [[inputs.parser_test_new]]
   data_format = "json_v2"
+[[inputs.parser_test_new.json_v2]]
+[[inputs.parser_test_new.json_v2.field]]
+  path = ""
+  rename = ""
+  type = "int"
 
 [[inputs.parser_test_new]]
   data_format = "logfmt"

config/testdata/processors_with_parsers.toml

@@ -26,6 +26,11 @@
 
 [[processors.parser_test]]
   data_format = "json_v2"
+[[processors.parser_test.json_v2]]
+[[processors.parser_test.json_v2.field]]
+  path = ""
+  rename = ""
+  type = "int"
 
 [[processors.parser_test]]
   data_format = "logfmt"

plugins/parsers/json_v2/parser.go

@@ -101,6 +101,9 @@ type MetricNode struct {
 }
 
 func (p *Parser) Init() error {
+	if len(p.Configs) == 0 {
+		return errors.New("no configuration provided")
+	}
 	// Propagate the default metric name to the configs in case it is not set there
 	for i, cfg := range p.Configs {
 		if cfg.MeasurementName == "" {

plugins/parsers/json_v2/parser_test.go

@@ -100,6 +100,14 @@ func TestMultipleConfigs(t *testing.T) {
 	}
 }
 
+func TestParserEmptyConfig(t *testing.T) {
+	plugin := &json_v2.Parser{
+		Configs: []json_v2.Config{},
+	}
+
+	require.ErrorContains(t, plugin.Init(), "no configuration provided")
+}
+
 func BenchmarkParsingSequential(b *testing.B) {
 	inputFilename := filepath.Join("testdata", "benchmark", "input.json")