wmi: add a multiplier option to convert values to base units (#2772)

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

docs/collector.wmi.md

@@ -79,6 +79,7 @@ YAML:
       metric: windows_wmi_logical_disk_free_bytes # optional
       help: Free space on the logical disk in bytes. # optional
       type: gauge # optional
+      multiplier: 1 # optional
       labels: # optional
         source: wmi
 ```
@@ -101,6 +102,7 @@ JSON:
         "metric": "windows_wmi_logical_disk_free_bytes",
         "help": "Free space on the logical disk in bytes.",
         "type": "gauge",
+        "multiplier": 1,
         "labels": { "source": "wmi" }
       }
     ]
@@ -219,6 +221,18 @@ defaults to `gauge`.
 
 This key is optional.
 
+##### multiplier
+
+A factor that the value is multiplied by before it is exported, to convert it to
+the base unit the Prometheus [naming conventions](https://prometheus.io/docs/practices/naming/#base-units)
+ask for. For example, `0.001` converts milliseconds to seconds, `0.01` percent to
+a ratio and `3600` hours to seconds. It must be a positive number, so counters
+keep counting up. If the multiplier is the reciprocal of an integer, like `0.001`,
+the value is divided by that integer instead, which avoids rounding artifacts
+such as `0.009000000000000001`. If not specified, the value is exported as is.
+
+This key is optional.
+
 ##### labels
 
 Labels is a map of key-value pairs that will be added as constant labels to the

internal/collector/wmi/types.go

@@ -20,6 +20,7 @@ package wmi
 import (
 	"github.com/prometheus-community/windows_exporter/internal/config/yamlstring"
 	"github.com/prometheus-community/windows_exporter/internal/mi"
+	"github.com/prometheus-community/windows_exporter/internal/multiplier"
 	"github.com/prometheus/client_golang/prometheus"
 	"go.yaml.in/yaml/v3"
 )
@@ -48,16 +49,18 @@ type LabelProperty struct {
 }
 
 type Property 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.
 	elementName mi.ElementName
 	desc        *prometheus.Desc
 	metricType  prometheus.ValueType
+	multiplier  multiplier.Multiplier
 }
 
 // UnmarshalYAML decodes the wmi block of the configuration file, where the

internal/collector/wmi/wmi.go

@@ -31,6 +31,7 @@ import (
 	"github.com/alecthomas/kingpin/v2"
 	"github.com/prometheus-community/windows_exporter/internal/labelcache"
 	"github.com/prometheus-community/windows_exporter/internal/mi"
+	"github.com/prometheus-community/windows_exporter/internal/multiplier"
 	"github.com/prometheus-community/windows_exporter/internal/scrapecache"
 	"github.com/prometheus-community/windows_exporter/internal/types"
 	"github.com/prometheus/client_golang/prometheus"
@@ -346,6 +347,12 @@ func (c *Collector) Build(logger *slog.Logger, miSession *mi.Session) error {
 				continue
 			}
 
+			if property.multiplier, err = multiplier.New(property.Multiplier); err != nil {
+				errs = append(errs, fmt.Errorf("query %s: property %q: %w", query.Name, property.Name, err))
+
+				continue
+			}
+
 			if label, ok := firstCommonLabel(query.labelNames, property.Labels); ok {
 				errs = append(errs, fmt.Errorf("query %s: property %q: constant label %q is already set by a label property", query.Name, property.Name, label))
 
@@ -588,7 +595,7 @@ func (c *Collector) collectQuery(ch chan<- prometheus.Metric, scrape *labelcache
 			ch <- scrape.MustNewConstMetric(
 				property.desc,
 				property.metricType,
-				value,
+				property.multiplier.Apply(value),
 				labelValues...,
 			)
 		}

internal/collector/wmi/wmi_output_test.go

@@ -167,6 +167,21 @@ func TestCollectorMetrics(t *testing.T) {
 				Class:      "Win32_OperatingSystem",
 				Properties: []wmi.Property{{Name: "Primary", Metric: "windows_wmi_test_shared", Labels: map[string]string{"query": "b"}}},
 			},
+			{
+				// The multiplier converts units, e.g. milliseconds to seconds.
+				Name:  "scaled_down",
+				Class: "Win32_OperatingSystem",
+				Properties: []wmi.Property{
+					{Name: "Primary", Metric: "windows_wmi_test_scaled", Labels: map[string]string{"query": "down"}, Multiplier: new(0.001)},
+				},
+			},
+			{
+				Name:  "scaled_up",
+				Class: "Win32_OperatingSystem",
+				Properties: []wmi.Property{
+					{Name: "Primary", Metric: "windows_wmi_test_scaled", Labels: map[string]string{"query": "up"}, Multiplier: new(3600.0)},
+				},
+			},
 			{
 				Name:       "missing_class",
 				Class:      "Win32_WindowsExporterDoesNotExist",
@@ -205,6 +220,8 @@ windows_wmi_query_success{query="kernel"} 1
 windows_wmi_query_success{query="missing_class"} 0
 windows_wmi_query_success{query="os"} 1
 windows_wmi_query_success{query="partial"} 0
+windows_wmi_query_success{query="scaled_down"} 1
+windows_wmi_query_success{query="scaled_up"} 1
 windows_wmi_query_success{query="shared_a"} 1
 windows_wmi_query_success{query="shared_b"} 1
 windows_wmi_query_success{query="unsupported_label"} 0
@@ -212,6 +229,10 @@ windows_wmi_query_success{query="unsupported_label"} 0
 # TYPE windows_wmi_test_parent_pid counter
 windows_wmi_test_parent_pid{foo="bar",handle="0",path="",pid="0",process="System Idle Process"} 0
 windows_wmi_test_parent_pid{foo="bar",handle="4",path="",pid="4",process="System"} 0
+# HELP windows_wmi_test_scaled windows_exporter: custom WMI metric
+# TYPE windows_wmi_test_scaled gauge
+windows_wmi_test_scaled{query="down"} 0.001
+windows_wmi_test_scaled{query="up"} 3600
 # HELP windows_wmi_test_shared windows_exporter: custom WMI metric
 # TYPE windows_wmi_test_shared gauge
 windows_wmi_test_shared{query="a"} 1
@@ -232,7 +253,7 @@ windows_wmi_test_shared{query="b"} 1
 
 		require.Equal(t, expected, strings.Join(lines, "\n"))
 
-		for _, name := range []string{"kernel", "missing_class", "os", "partial", "shared_a", "shared_b", "unsupported_label"} {
+		for _, name := range []string{"kernel", "missing_class", "os", "partial", "scaled_down", "scaled_up", "shared_a", "shared_b", "unsupported_label"} {
 			require.Regexp(t, `(?m)^windows_wmi_query_duration_seconds\{query="`+name+`"\} \d`, got)
 		}
 	}

internal/collector/wmi/wmi_test.go

@@ -190,6 +190,16 @@ func TestCollectorBuildErrors(t *testing.T) {
 			queries: valid(func(q *wmi.Query) { q.Properties[0].Type = "histogram" }),
 			err:     `invalid type "histogram"`,
 		},
+		{
+			name:    "zero multiplier",
+			queries: valid(func(q *wmi.Query) { q.Properties[0].Multiplier = new(0.0) }),
+			err:     `property "FreeSpace": multiplier must be a positive finite number, got 0`,
+		},
+		{
+			name:    "negative multiplier",
+			queries: valid(func(q *wmi.Query) { q.Properties[0].Multiplier = new(-1.0) }),
+			err:     `multiplier must be a positive finite number, got -1`,
+		},
 		{
 			name:    "invalid label property name",
 			queries: valid(func(q *wmi.Query) { q.LabelProperties = []wmi.LabelProperty{{Name: ""}} }),