fix: tighten reflect usage in pdh and textfile (#2517)

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

internal/collector/performancecounter/performancecounter.go

@@ -323,7 +323,7 @@ func (c *Collector) collectObject(ch chan<- prometheus.Metric, perfDataObject Ob
 				continue
 			}
 
-			if field.Kind() != reflect.TypeFor[prometheus.ValueType]().Kind() {
+			if field.Type() != reflect.TypeFor[prometheus.ValueType]() {
 				errs = append(errs, fmt.Errorf("failed to cast MetricType for %s to prometheus.ValueType", counter.Name))
 
 				continue

internal/collector/textfile/textfile.go

@@ -22,9 +22,9 @@ import (
 	"fmt"
 	"io"
 	"log/slog"
+	"maps"
 	"os"
 	"path/filepath"
-	"reflect"
 	"slices"
 	"sort"
 	"strings"
@@ -140,7 +140,7 @@ func duplicateMetricEntry(metricFamilies []*dto.MetricFamily) bool {
 			_, mapContainsKey := uniqueMetrics[metricName]
 
 			// Duplicate metric found with identical labels & label values
-			if mapContainsKey && reflect.DeepEqual(uniqueMetrics[metricName], labels) {
+			if mapContainsKey && maps.Equal(uniqueMetrics[metricName], labels) {
 				return true
 			}
 

internal/config/flatten_test.go

@@ -18,7 +18,7 @@
 package config
 
 import (
-	"reflect"
+	"maps"
 	"testing"
 
 	"go.yaml.in/yaml/v3"
@@ -49,7 +49,7 @@ func TestConfigFlattening(t *testing.T) {
 	}
 	flattenedValues := flatten(data)
 
-	if !reflect.DeepEqual(expectedResult, flattenedValues) {
+	if !maps.Equal(expectedResult, flattenedValues) {
 		t.Errorf("Flattened values do not match!\nExpected result: %s\nActual result: %s", expectedResult, flattenedValues)
 	}
 }

internal/pdh/collector.go

@@ -110,7 +110,7 @@ func NewCollectorWithReflection(logger *slog.Logger, resultType CounterType, obj
 	}
 
 	if f, ok := valueType.FieldByName("MetricType"); ok {
-		if f.Type.Kind() == reflect.TypeFor[prometheus.ValueType]().Kind() {
+		if f.Type == reflect.TypeFor[prometheus.ValueType]() {
 			collector.metricsTypeIndexValue = f.Index[0]
 		}
 	}

internal/pdh/registry/collector.go

@@ -109,13 +109,13 @@ func (c *Collector) Collect(data any) error {
 
 	dv = dv.Elem()
 
-	elemType := dv.Type().Elem()
-	elemValue := reflect.ValueOf(reflect.New(elemType).Interface()).Elem()
-
-	if dv.Kind() != reflect.Slice || elemType.Kind() != reflect.Struct {
+	if dv.Kind() != reflect.Slice || dv.Type().Elem().Kind() != reflect.Struct {
 		return mi.ErrInvalidEntityType
 	}
 
+	elemType := dv.Type().Elem()
+	elemValue := reflect.ValueOf(reflect.New(elemType).Interface()).Elem()
+
 	perfObjects, err := QueryPerformanceData(c.query, c.object)
 	if err != nil {
 		return fmt.Errorf("QueryPerformanceData: %w", err)

internal/pdh/registry/perflib_test.go

@@ -18,7 +18,10 @@
 package registry
 
 import (
+	"errors"
 	"testing"
+
+	"github.com/prometheus-community/windows_exporter/internal/mi"
 )
 
 // TestNewCollectorStructTypeParam guards against a regression where
@@ -37,6 +40,35 @@ func TestNewCollectorStructTypeParam(t *testing.T) {
 	}
 }
 
+// TestCollectInvalidEntityType guards against a regression where Collect
+// called reflect.Type.Elem() on a non-slice destination and panicked instead
+// of returning mi.ErrInvalidEntityType.
+func TestCollectInvalidEntityType(t *testing.T) {
+	t.Parallel()
+
+	type counterValues struct {
+		Name string
+	}
+
+	c := &Collector{}
+
+	for name, dst := range map[string]any{
+		"nil":                nil,
+		"non-pointer":        []counterValues{},
+		"pointer to struct":  &counterValues{},
+		"pointer to []int":   &[]int{},
+		"pointer to integer": new(int),
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			if err := c.Collect(dst); !errors.Is(err, mi.ErrInvalidEntityType) {
+				t.Errorf("expected %v, got %v", mi.ErrInvalidEntityType, err)
+			}
+		})
+	}
+}
+
 func BenchmarkQueryPerformanceData(b *testing.B) {
 	for b.Loop() {
 		_, _ = QueryPerformanceData("Global", "")