fix(processors.parser): Keep name of original metric if parser doesn't return one (#12116)

plugins/processors/parser/parser.go

@@ -49,7 +49,13 @@ func (p *Parser) Apply(metrics ...telegraf.Metric) []telegraf.Metric {
 						}
 
 						for _, m := range fromFieldMetric {
-							if m.Name() == "" {
+							// The parser get the parent plugin's name as
+							// default measurement name. Thus, in case the
+							// parsed metric does not provide a name itself,
+							// the parser  will return 'parser' as we are in
+							// processors.parser. In those cases we want to
+							// keep the original metric name.
+							if m.Name() == "" || m.Name() == "parser" {
 								m.SetName(metric.Name())
 							}
 						}

plugins/processors/parser/parser_test.go

@@ -10,10 +10,12 @@ import (
 
 	//Blank import to register all new-style parsers
 
+	"github.com/influxdata/telegraf/plugins/parsers"
 	"github.com/influxdata/telegraf/plugins/parsers/grok"
 	"github.com/influxdata/telegraf/plugins/parsers/influx"
 	"github.com/influxdata/telegraf/plugins/parsers/json"
 	"github.com/influxdata/telegraf/plugins/parsers/logfmt"
+	"github.com/influxdata/telegraf/plugins/parsers/value"
 
 	"github.com/influxdata/telegraf/testutil"
 )
@@ -558,6 +560,50 @@ func TestApply(t *testing.T) {
 					time.Unix(0, 0)),
 			},
 		},
+		{
+			name:        "parser without metric name (issue #12115)",
+			parseFields: []string{"value"},
+			merge:       "override",
+			// Create parser the config way with the name of the parent plugin.
+			parser: func() telegraf.Parser {
+				p := parsers.Parsers["value"]("parser")
+				vp := p.(*value.Parser)
+				vp.DataType = "float"
+				vp.FieldName = "value"
+				return vp
+			}(),
+			input: metric.New(
+				"myname",
+				map[string]string{},
+				map[string]interface{}{"value": "7.2"},
+				time.Unix(0, 0)),
+			expected: []telegraf.Metric{
+				metric.New(
+					"myname",
+					map[string]string{},
+					map[string]interface{}{"value": float64(7.2)},
+					time.Unix(0, 0)),
+			},
+		},
+		{
+			name:        "parser with metric name (issue #12115)",
+			parseFields: []string{"value"},
+			merge:       "override",
+			// Create parser the config way with the name of the parent plugin.
+			parser: parsers.Parsers["influx"]("parser"),
+			input: metric.New(
+				"myname",
+				map[string]string{},
+				map[string]interface{}{"value": "test value=7.2"},
+				time.Unix(0, 0)),
+			expected: []telegraf.Metric{
+				metric.New(
+					"test",
+					map[string]string{},
+					map[string]interface{}{"value": float64(7.2)},
+					time.Unix(0, 0)),
+			},
+		},
 	}
 
 	for _, tt := range tests {