fix: Fix panic for non-existing metric names (#9757)

plugins/parsers/registry.go

@@ -395,7 +395,7 @@ func NewXPathParserConfigs(metricName string, cfgs []XPathConfig) []xpath.Config
 	configs := make([]xpath.Config, 0, len(cfgs))
 	for _, cfg := range cfgs {
 		config := xpath.Config(cfg)
-		config.MetricName = metricName
+		config.MetricDefaultName = metricName
 		configs = append(configs, config)
 	}
 	return configs

plugins/parsers/xpath/parser.go

@@ -35,7 +35,7 @@ type Parser struct {
 }
 
 type Config struct {
-	MetricName   string
+	MetricDefaultName string            `toml:"-"`
 	MetricQuery       string            `toml:"metric_name"`
 	Selection         string            `toml:"metric_selection"`
 	Timestamp         string            `toml:"timestamp"`
@@ -160,13 +160,19 @@ func (p *Parser) parseQuery(starttime time.Time, doc, selected dataNode, config
 
 	// Determine the metric name. If a query was specified, use the result of this query and the default metric name
 	// otherwise.
-	metricname = config.MetricName
+	metricname = config.MetricDefaultName
 	if len(config.MetricQuery) > 0 {
 		v, err := p.executeQuery(doc, selected, config.MetricQuery)
 		if err != nil {
 			return nil, fmt.Errorf("failed to query metric name: %v", err)
 		}
-		metricname = v.(string)
+		var ok bool
+		if metricname, ok = v.(string); !ok {
+			if v == nil {
+				p.Log.Infof("Hint: Empty metric-name-node. If you wanted to set a constant please use `metric_name = \"'name'\"`.")
+			}
+			return nil, fmt.Errorf("failed to query metric name: query result is of type %T not 'string'", v)
+		}
 	}
 
 	// By default take the time the parser was invoked and override the value

plugins/parsers/xpath/parser_test.go

@@ -148,7 +148,7 @@ func TestInvalidTypeQueriesFail(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix",
 					FieldsInt: map[string]string{
 						"a": "/Device_1/value_string",
@@ -185,7 +185,7 @@ func TestInvalidTypeQueries(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix",
 					Fields: map[string]string{
 						"a": "number(/Device_1/value_string)",
@@ -207,7 +207,7 @@ func TestInvalidTypeQueries(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix",
 					Fields: map[string]string{
 						"a": "boolean(/Device_1/value_string)",
@@ -252,7 +252,7 @@ func TestParseTimestamps(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix",
 				},
 			},
@@ -269,7 +269,7 @@ func TestParseTimestamps(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName:   "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix",
 					TimestampFmt:      "unix",
 				},
@@ -287,7 +287,7 @@ func TestParseTimestamps(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName:   "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix_ms",
 					TimestampFmt:      "unix_ms",
 				},
@@ -305,7 +305,7 @@ func TestParseTimestamps(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName:   "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix_us",
 					TimestampFmt:      "unix_us",
 				},
@@ -323,7 +323,7 @@ func TestParseTimestamps(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName:   "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix_ns",
 					TimestampFmt:      "unix_ns",
 				},
@@ -341,7 +341,7 @@ func TestParseTimestamps(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName:   "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_iso",
 					TimestampFmt:      "2006-01-02T15:04:05Z",
 				},
@@ -382,7 +382,7 @@ func TestParseSingleValues(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix",
 					Fields: map[string]string{
 						"a": "/Device_1/value_int",
@@ -410,7 +410,7 @@ func TestParseSingleValues(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix",
 					Fields: map[string]string{
 						"a": "number(Device_1/value_int)",
@@ -438,7 +438,7 @@ func TestParseSingleValues(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix",
 					Fields: map[string]string{
 						"b": "number(/Device_1/value_float)",
@@ -468,7 +468,7 @@ func TestParseSingleValues(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix",
 					Fields: map[string]string{
 						"x": "substring-before(/Device_1/value_position, ';')",
@@ -492,7 +492,7 @@ func TestParseSingleValues(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix",
 					Fields: map[string]string{
 						"x": "number(substring-before(/Device_1/value_position, ';'))",
@@ -516,7 +516,7 @@ func TestParseSingleValues(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix",
 					FieldsInt: map[string]string{
 						"x": "substring-before(/Device_1/value_position, ';')",
@@ -540,7 +540,7 @@ func TestParseSingleValues(t *testing.T) {
 			input: singleMetricValuesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix",
 					Tags: map[string]string{
 						"state": "/Device_1/State",
@@ -587,7 +587,7 @@ func TestParseSingleAttributes(t *testing.T) {
 			input: singleMetricAttributesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix/@value",
 				},
 			},
@@ -604,7 +604,7 @@ func TestParseSingleAttributes(t *testing.T) {
 			input: singleMetricAttributesXML,
 			configs: []Config{
 				{
-					MetricName:   "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_iso/@value",
 					TimestampFmt:      "2006-01-02T15:04:05Z",
 				},
@@ -622,7 +622,7 @@ func TestParseSingleAttributes(t *testing.T) {
 			input: singleMetricAttributesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix/@value",
 					Fields: map[string]string{
 						"a": "/Device_1/attr_int/@_",
@@ -650,7 +650,7 @@ func TestParseSingleAttributes(t *testing.T) {
 			input: singleMetricAttributesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix/@value",
 					Fields: map[string]string{
 						"a": "number(/Device_1/attr_int/@_)",
@@ -678,7 +678,7 @@ func TestParseSingleAttributes(t *testing.T) {
 			input: singleMetricAttributesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix/@value",
 					Fields: map[string]string{
 						"b": "number(/Device_1/attr_float/@_)",
@@ -708,7 +708,7 @@ func TestParseSingleAttributes(t *testing.T) {
 			input: singleMetricAttributesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix/@value",
 					Fields: map[string]string{
 						"name": "substring-after(/Device_1/Name/@value, ' ')",
@@ -730,7 +730,7 @@ func TestParseSingleAttributes(t *testing.T) {
 			input: singleMetricAttributesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix/@value",
 					Tags: map[string]string{
 						"state": "/Device_1/State/@_",
@@ -754,7 +754,7 @@ func TestParseSingleAttributes(t *testing.T) {
 			input: singleMetricAttributesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Device_1/Timestamp_unix/@value",
 					Fields: map[string]string{
 						"a": "/Device_1/attr_bool_numeric/@_ = 1",
@@ -799,7 +799,7 @@ func TestParseMultiValues(t *testing.T) {
 			input: singleMetricMultiValuesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Timestamp/@value",
 					Fields: map[string]string{
 						"a": "number(/Device/Value[1])",
@@ -831,7 +831,7 @@ func TestParseMultiValues(t *testing.T) {
 			input: singleMetricMultiValuesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Timestamp:         "/Timestamp/@value",
 					FieldsInt: map[string]string{
 						"a": "/Device/Value[1]",
@@ -886,7 +886,7 @@ func TestParseMultiNodes(t *testing.T) {
 			input: multipleNodesXML,
 			configs: []Config{
 				{
-					MetricName: "test",
+					MetricDefaultName: "test",
 					Selection:         "/Device",
 					Timestamp:         "/Timestamp/@value",
 					Fields: map[string]string{
@@ -999,7 +999,7 @@ func TestParseMetricQuery(t *testing.T) {
 			input: metricNameQueryXML,
 			configs: []Config{
 				{
-					MetricName:  "test",
+					MetricDefaultName: "test",
 					MetricQuery:       "name(/Device_1/Metric/@*[1])",
 					Timestamp:         "/Device_1/Timestamp_unix",
 					Fields: map[string]string{
@@ -1017,6 +1017,29 @@ func TestParseMetricQuery(t *testing.T) {
 				time.Unix(1577923199, 0),
 			),
 		},
+		{
+			name:  "parse metric name constant",
+			input: metricNameQueryXML,
+			configs: []Config{
+				{
+					MetricDefaultName: "test",
+					MetricQuery:       "'the_metric'",
+					Timestamp:         "/Device_1/Timestamp_unix",
+					Fields: map[string]string{
+						"value": "/Device_1/Metric/@*[1]",
+					},
+				},
+			},
+			defaultTags: map[string]string{},
+			expected: testutil.MustMetric(
+				"the_metric",
+				map[string]string{},
+				map[string]interface{}{
+					"value": "ok",
+				},
+				time.Unix(1577923199, 0),
+			),
+		},
 	}
 
 	for _, tt := range tests {
@@ -1032,6 +1055,42 @@ func TestParseMetricQuery(t *testing.T) {
 	}
 }
 
+func TestParseErrors(t *testing.T) {
+	var tests = []struct {
+		name     string
+		input    string
+		configs  []Config
+		expected string
+	}{
+		{
+			name:  "string metric name query",
+			input: metricNameQueryXML,
+			configs: []Config{
+				{
+					MetricDefaultName: "test",
+					MetricQuery:       "arbitrary",
+					Timestamp:         "/Device_1/Timestamp_unix",
+					Fields: map[string]string{
+						"value": "/Device_1/Metric/@*[1]",
+					},
+				},
+			},
+			expected: "failed to query metric name: query result is of type <nil> not 'string'",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			parser := &Parser{Configs: tt.configs, DefaultTags: map[string]string{}, Log: testutil.Logger{Name: "parsers.xml"}}
+			require.NoError(t, parser.Init())
+
+			_, err := parser.ParseLine(tt.input)
+			require.Error(t, err)
+			require.Equal(t, tt.expected, err.Error())
+		})
+	}
+}
+
 func TestEmptySelection(t *testing.T) {
 	var tests = []struct {
 		name    string
@@ -1146,7 +1205,7 @@ func TestTestCases(t *testing.T) {
 			filename := filepath.FromSlash(tt.filename)
 			cfg, header, err := loadTestConfiguration(filename)
 			require.NoError(t, err)
-			cfg.MetricName = "xml"
+			cfg.MetricDefaultName = "xml"
 
 			// Load the xml-content
 			input, err := testutil.ParseRawLinesFrom(header, "File:")