feat: do not error if no nodes found for current config with xpath pa…

…rser (#11102)

plugins/parsers/registry.go

@@ -188,6 +188,7 @@ type Config struct {
 	XPathProtobufFile        string   `toml:"xpath_protobuf_file"`
 	XPathProtobufType        string   `toml:"xpath_protobuf_type"`
 	XPathProtobufImportPaths []string `toml:"xpath_protobuf_import_paths"`
+	XPathAllowEmptySelection bool     `toml:"xpath_allow_empty_selection"`
 	XPathConfig              []XPathConfig
 
 	// JSONPath configuration
@@ -287,6 +288,7 @@ func NewParser(config *Config) (Parser, error) {
 			ProtobufImportPaths: config.XPathProtobufImportPaths,
 			PrintDocument:       config.XPathPrintDocument,
 			DefaultTags:         config.DefaultTags,
+			AllowEmptySelection: config.XPathAllowEmptySelection,
 			Configs:             NewXPathParserConfigs(config.MetricName, config.XPathConfig),
 		}
 	case "json_v2":

plugins/parsers/xpath/README.md

@@ -86,6 +86,10 @@ In this configuration mode, you explicitly specify the field and tags you want t
   ## to get an idea on the expression necessary to derive fields etc.
   # xpath_print_document = false
 
+  ## Allow the results of one of the parsing sections to be empty.
+  ## Useful when not all selected files have the exact same structure.
+  # xpath_allow_empty_selection = false
+
   ## Multiple parsing sections are allowed
   [[inputs.file.xpath]]
     ## Optional: XPath-query to select a subset of nodes from the XML document.
@@ -152,6 +156,10 @@ metric.
   ## to get an idea on the expression necessary to derive fields etc.
   # xpath_print_document = false
 
+  ## Allow the results of one of the parsing sections to be empty.
+  ## Useful when not all selected files have the exact same structure.
+  # xpath_allow_empty_selection = false
+
   ## Multiple parsing sections are allowed
   [[inputs.file.xpath]]
     ## Optional: XPath-query to select a subset of nodes from the XML document.
@@ -201,7 +209,7 @@ metric.
 
 ```
 
-*Please note*: The resulting fields are _always_ of type string!
+**Please note**: The resulting fields are *always* of type string!
 
 It is also possible to specify a mixture of the two alternative ways of specifying fields.
 

plugins/parsers/xpath/parser.go

@@ -29,6 +29,7 @@ type Parser struct {
 	ProtobufMessageType string
 	ProtobufImportPaths []string
 	PrintDocument       bool
+	AllowEmptySelection bool
 	Configs             []Config
 	DefaultTags         map[string]string
 	Log                 telegraf.Logger
@@ -108,7 +109,9 @@ func (p *Parser) Parse(buf []byte) ([]telegraf.Metric, error) {
 		}
 		if len(selectedNodes) < 1 || selectedNodes[0] == nil {
 			p.debugEmptyQuery("metric selection", doc, config.Selection)
-			return nil, fmt.Errorf("cannot parse with empty selection node")
+			if !p.AllowEmptySelection {
+				return metrics, fmt.Errorf("cannot parse with empty selection node")
+			}
 		}
 		p.Log.Debugf("Number of selected metric nodes: %d", len(selectedNodes))
 
@@ -126,37 +129,20 @@ func (p *Parser) Parse(buf []byte) ([]telegraf.Metric, error) {
 }
 
 func (p *Parser) ParseLine(line string) (telegraf.Metric, error) {
-	t := time.Now()
 
-	switch len(p.Configs) {
+	metrics, err := p.Parse([]byte(line))
+	if err != nil {
+		return nil, err
+	}
+
+	switch len(metrics) {
 	case 0:
 		return nil, nil
 	case 1:
-		config := p.Configs[0]
-
-		doc, err := p.document.Parse([]byte(line))
-		if err != nil {
-			return nil, err
-		}
-
-		selected := doc
-		if len(config.Selection) > 0 {
-			selectedNodes, err := p.document.QueryAll(doc, config.Selection)
-			if err != nil {
-				return nil, err
-			}
-			if len(selectedNodes) < 1 || selectedNodes[0] == nil {
-				p.debugEmptyQuery("metric selection", doc, config.Selection)
-				return nil, fmt.Errorf("cannot parse line with empty selection")
-			} else if len(selectedNodes) != 1 {
-				return nil, fmt.Errorf("cannot parse line with multiple selected nodes (%d)", len(selectedNodes))
-			}
-			selected = selectedNodes[0]
-		}
-
-		return p.parseQuery(t, doc, selected, config)
+		return metrics[0], nil
+	default:
+		return metrics[0], fmt.Errorf("cannot parse line with multiple (%d) metrics", len(metrics))
 	}
-	return nil, fmt.Errorf("cannot parse line with multiple (%d) configurations", len(p.Configs))
 }
 
 func (p *Parser) SetDefaultTags(tags map[string]string) {

plugins/parsers/xpath/parser_test.go

@@ -1154,7 +1154,74 @@ func TestEmptySelection(t *testing.T) {
 
 			_, err := parser.Parse([]byte(tt.input))
 			require.Error(t, err)
-			require.Equal(t, err.Error(), "cannot parse with empty selection node")
+			require.Equal(t, "cannot parse with empty selection node", err.Error())
+		})
+	}
+}
+
+func TestEmptySelectionAllowed(t *testing.T) {
+	var tests = []struct {
+		name    string
+		input   string
+		configs []Config
+	}{
+		{
+			name:  "empty path",
+			input: multipleNodesXML,
+			configs: []Config{
+				{
+					Selection: "/Device/NonExisting",
+					Fields:    map[string]string{"value": "number(Value)"},
+					FieldsInt: map[string]string{"mode": "Value/@mode"},
+					Tags:      map[string]string{},
+				},
+			},
+		},
+		{
+			name:  "empty pattern",
+			input: multipleNodesXML,
+			configs: []Config{
+				{
+					Selection: "//NonExisting",
+					Fields:    map[string]string{"value": "number(Value)"},
+					FieldsInt: map[string]string{"mode": "Value/@mode"},
+					Tags:      map[string]string{},
+				},
+			},
+		},
+		{
+			name:  "empty axis",
+			input: multipleNodesXML,
+			configs: []Config{
+				{
+					Selection: "/Device/child::NonExisting",
+					Fields:    map[string]string{"value": "number(Value)"},
+					FieldsInt: map[string]string{"mode": "Value/@mode"},
+					Tags:      map[string]string{},
+				},
+			},
+		},
+		{
+			name:  "empty predicate",
+			input: multipleNodesXML,
+			configs: []Config{
+				{
+					Selection: "/Device[@NonExisting=true]",
+					Fields:    map[string]string{"value": "number(Value)"},
+					FieldsInt: map[string]string{"mode": "Value/@mode"},
+					Tags:      map[string]string{},
+				},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			parser := &Parser{Configs: tt.configs, AllowEmptySelection: true, DefaultTags: map[string]string{}, Log: testutil.Logger{Name: "parsers.xml"}}
+			require.NoError(t, parser.Init())
+
+			_, err := parser.Parse([]byte(tt.input))
+			require.NoError(t, err)
 		})
 	}
 }