fix(cpu_info,diskdrive): stop probing WMI during Build (#2648)

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

internal/collector/cpu_info/cpu_info.go

@@ -151,11 +151,9 @@ func (c *Collector) Build(_ *slog.Logger, miSession *mi.Session) error {
 	c.miQuery = miQuery
 	c.miSession = miSession
 
-	var dst []miProcessor
-	if err := c.miSession.Query(&dst, mi.NamespaceRootCIMv2, c.miQuery, 0); err != nil {
-		return fmt.Errorf("WMI query failed: %w", err)
-	}
-
+	// Win32_Processor exists on every supported Windows version, so Build does not probe it.
+	// WMI can time out shortly after boot. A probe would disable the collector until restart,
+	// while a failing Collect only fails the affected scrapes.
 	return nil
 }
 

internal/collector/cpu_info/cpu_info_test.go

@@ -18,10 +18,15 @@
 package cpu_info_test
 
 import (
+	"log/slog"
 	"testing"
+	"time"
 
 	"github.com/prometheus-community/windows_exporter/internal/collector/cpu_info"
+	"github.com/prometheus-community/windows_exporter/internal/mi"
 	"github.com/prometheus-community/windows_exporter/internal/utils/testutils"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/stretchr/testify/require"
 )
 
 func BenchmarkCollector(b *testing.B) {
@@ -31,3 +36,14 @@ func BenchmarkCollector(b *testing.B) {
 func TestCollector(t *testing.T) {
 	testutils.TestCollector(t, cpu_info.New, nil)
 }
+
+// A WMI failure during Build must not disable the collector until restart, so
+// Build must not query WMI. The uninitialized session fails every query.
+func TestBuildDoesNotQueryWMI(t *testing.T) {
+	c := cpu_info.New(nil)
+
+	t.Cleanup(func() { require.NoError(t, c.Close()) })
+
+	require.NoError(t, c.Build(slog.New(slog.DiscardHandler), &mi.Session{}))
+	require.ErrorIs(t, c.Collect(make(chan prometheus.Metric, 64), time.Second), mi.ErrNotInitialized)
+}

internal/collector/diskdrive/diskdrive.go

@@ -127,11 +127,9 @@ func (c *Collector) Build(logger *slog.Logger, miSession *mi.Session) error {
 	c.miQuery = miQuery
 	c.miSession = miSession
 
-	var dst []diskDrive
-	if err := c.miSession.Query(&dst, mi.NamespaceRootCIMv2, c.miQuery, 0); err != nil {
-		return fmt.Errorf("WMI query failed: %w", err)
-	}
-
+	// Win32_DiskDrive exists on every supported Windows version, so Build does not probe it.
+	// WMI can time out shortly after boot. A probe would disable the collector until restart,
+	// while a failing Collect only fails the affected scrapes.
 	return nil
 }
 

internal/collector/diskdrive/diskdrive_test.go

@@ -18,10 +18,15 @@
 package diskdrive_test
 
 import (
+	"log/slog"
 	"testing"
+	"time"
 
 	"github.com/prometheus-community/windows_exporter/internal/collector/diskdrive"
+	"github.com/prometheus-community/windows_exporter/internal/mi"
 	"github.com/prometheus-community/windows_exporter/internal/utils/testutils"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/stretchr/testify/require"
 )
 
 func BenchmarkCollector(b *testing.B) {
@@ -31,3 +36,14 @@ func BenchmarkCollector(b *testing.B) {
 func TestCollector(t *testing.T) {
 	testutils.TestCollector(t, diskdrive.New, nil)
 }
+
+// A WMI failure during Build must not disable the collector until restart, so
+// Build must not query WMI. The uninitialized session fails every query.
+func TestBuildDoesNotQueryWMI(t *testing.T) {
+	c := diskdrive.New(nil)
+
+	t.Cleanup(func() { require.NoError(t, c.Close()) })
+
+	require.NoError(t, c.Build(slog.New(slog.DiscardHandler), &mi.Session{}))
+	require.ErrorIs(t, c.Collect(make(chan prometheus.Metric, 64), time.Second), mi.ErrNotInitialized)
+}