registry: add a multiplier option to convert values to base units (#2774)

Co-authored-by: Claude <noreply@anthropic.com>
Signed-off-by: Claude <noreply@anthropic.com>

internal/collector/registry/registry.go

@@ -31,6 +31,7 @@ import (
 
 	"github.com/alecthomas/kingpin/v2"
 	"github.com/prometheus-community/windows_exporter/internal/mi"
+	"github.com/prometheus-community/windows_exporter/internal/multiplier"
 	"github.com/prometheus-community/windows_exporter/internal/types"
 	"github.com/prometheus/client_golang/prometheus"
 	"go.yaml.in/yaml/v3"
@@ -233,6 +234,15 @@ func (c *Collector) Build(logger *slog.Logger, _ *mi.Session) error {
 				continue
 			}
 
+			m, err := multiplier.New(value.Multiplier)
+			if err != nil {
+				errs = append(errs, fmt.Errorf("value %q of key %s: %w", value.Name, label, err))
+
+				continue
+			}
+
+			value.multiplier = m
+
 			help := value.Help
 			if help == "" {
 				help = "windows_exporter: custom registry metric"
@@ -369,7 +379,7 @@ func (c *Collector) collectKey(ch chan<- prometheus.Metric, key Key) error {
 		ch <- prometheus.MustNewConstMetric(
 			value.desc,
 			value.metricType,
-			float64(val),
+			value.multiplier.Apply(float64(val)),
 		)
 	}
 

internal/collector/registry/registry_output_test.go

@@ -78,6 +78,7 @@ func TestCollectorMetrics(t *testing.T) {
 	// 64-bit handling. Both are well under 2^53, so they convert to float64 exactly.
 	require.NoError(t, k.SetDWordValue("TestDword", 1234))
 	require.NoError(t, k.SetQWordValue("TestQword", 5_000_000_000))
+	require.NoError(t, k.SetDWordValue("TestMilliseconds", 9))
 	require.NoError(t, k.Close())
 
 	t.Cleanup(func() {
@@ -105,6 +106,13 @@ func TestCollectorMetrics(t *testing.T) {
 						Type:   "counter",
 						Labels: map[string]string{"foo": "bar"},
 					},
+					// The multiplier converts milliseconds to seconds; 9 * 0.001
+					// would be 0.009000000000000001.
+					{
+						Name:       "TestMilliseconds",
+						Metric:     "windows_registry_test_scaled_seconds",
+						Multiplier: new(0.001),
+					},
 				},
 			},
 			{
@@ -137,6 +145,9 @@ windows_registry_key_success{key="testgroup"} 1
 # HELP windows_registry_test_custom_metric custom registry help text
 # TYPE windows_registry_test_custom_metric counter
 windows_registry_test_custom_metric{foo="bar"} 5e+09
+# HELP windows_registry_test_scaled_seconds windows_exporter: custom registry metric
+# TYPE windows_registry_test_scaled_seconds gauge
+windows_registry_test_scaled_seconds 0.009
 # HELP windows_registry_testgroup_testdword windows_exporter: custom registry metric
 # TYPE windows_registry_testgroup_testdword gauge
 windows_registry_testgroup_testdword 1234

internal/collector/registry/registry_test.go

@@ -121,6 +121,16 @@ func TestCollectorBuildErrors(t *testing.T) {
 				},
 			}},
 		},
+		{
+			name: "invalid multiplier",
+			config: registry.Config{Keys: []registry.Key{
+				{
+					Name:   "windows_nt",
+					Key:    `HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion`,
+					Values: []registry.Value{{Name: "CurrentMajorVersionNumber", Multiplier: new(0.0)}},
+				},
+			}},
+		},
 		{
 			name: "shared metric name with inconsistent help text",
 			config: registry.Config{Keys: []registry.Key{

internal/collector/registry/types.go

@@ -19,6 +19,7 @@ package registry
 
 import (
 	"github.com/prometheus-community/windows_exporter/internal/config/yamlstring"
+	"github.com/prometheus-community/windows_exporter/internal/multiplier"
 	"github.com/prometheus/client_golang/prometheus"
 	"go.yaml.in/yaml/v3"
 	winregistry "golang.org/x/sys/windows/registry"
@@ -36,15 +37,17 @@ type Key struct {
 }
 
 type Value struct {
-	Name   string            `json:"name"   yaml:"name"`
-	Metric string            `json:"metric" yaml:"metric"`
-	Help   string            `json:"help"   yaml:"help"`
-	Type   string            `json:"type"   yaml:"type"`
-	Labels map[string]string `json:"labels" yaml:"labels"`
+	Name       string            `json:"name"       yaml:"name"`
+	Metric     string            `json:"metric"     yaml:"metric"`
+	Help       string            `json:"help"       yaml:"help"`
+	Type       string            `json:"type"       yaml:"type"`
+	Labels     map[string]string `json:"labels"     yaml:"labels"`
+	Multiplier *float64          `json:"multiplier" yaml:"multiplier"`
 
 	// resolved at Build time
 	desc       *prometheus.Desc
 	metricType prometheus.ValueType
+	multiplier multiplier.Multiplier
 }
 
 // UnmarshalYAML decodes the registry block of the configuration file, where