windows/perfmon fix for `There is more data to return than will fit i…

…n the supplied buffer` (#20630)

* mofidy doc

* fix

* changelog

CHANGELOG.next.asciidoc

@@ -326,6 +326,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Add required option for `metrics` in app_insights. {pull}20406[20406]
 - Groups same timestamp metric values to one event in the app_insights metricset. {pull}20403[20403]
 - Updates vm_compute metricset with more info on guest metrics. {pull}20448[20448]
+- Add fallback for PdhExpandWildCardPathW failing in perfmon metricset. {issue}20139[20139] {pull}20630[20630]
 - Fix resource tags in aws cloudwatch metricset {issue}20326[20326]  {pull}20385[20385]
 - Fix ec2 disk and network metrics to use Sum statistic method. {pull}20680[20680]
 - Fill cloud.account.name with accountID if account alias doesn't exist. {pull}20736[20736]

metricbeat/helper/windows/pdh/pdh_query_windows.go

@@ -212,6 +212,12 @@ func (q *Query) ExpandWildCardPath(wildCardPath string) ([]string, error) {
 		expdPaths, err = PdhExpandCounterPath(utfPath)
 	} else {
 		expdPaths, err = PdhExpandWildCardPath(utfPath)
+		// rarely the PdhExpandWildCardPathW will not retrieve the expanded buffer size initially so the next call will encounter the PDH_MORE_DATA error since the specified size on the input is still less than
+		// the required size. If this is the case we will fallback on the PdhExpandCounterPathW api since it looks to act in a more stable manner. The PdhExpandCounterPathW api does come with some limitations but will
+		// satisfy most cases and return valid paths.
+		if err == PDH_MORE_DATA {
+			expdPaths, err = PdhExpandCounterPath(utfPath)
+		}
 	}
 	if err != nil {
 		return nil, err

metricbeat/module/windows/perfmon/perfmon.go

@@ -61,7 +61,7 @@ func New(base mb.BaseMetricSet) (mb.MetricSet, error) {
 func (m *MetricSet) Fetch(report mb.ReporterV2) error {
 	// if the ignore_non_existent_counters flag is set and no valid counter paths are found the Read func will still execute, a check is done before
 	if len(m.reader.query.Counters) == 0 {
-		return errors.New("no counters to read")
+		m.log.Error("no counter paths were found")
 	}
 
 	// refresh performance counter list

metricbeat/module/windows/perfmon/reader.go

@@ -38,6 +38,7 @@ const (
 	defaultInstanceField  = "instance"
 	defaultObjectField    = "object"
 	replaceUpperCaseRegex = `(?:[^A-Z_\W])([A-Z])[^A-Z]`
+	collectFailedMsg      = "failed collecting counter values"
 )
 
 // Reader will contain the config options
@@ -152,7 +153,13 @@ func (re *Reader) Read() ([]mb.Event, error) {
 	// Some counters, such as rate counters, require two counter values in order to compute a displayable value. In this case we must call PdhCollectQueryData twice before calling PdhGetFormattedCounterValue.
 	// For more information, see Collecting Performance Data (https://docs.microsoft.com/en-us/windows/desktop/PerfCtrs/collecting-performance-data).
 	if err := re.query.CollectData(); err != nil {
-		return nil, errors.Wrap(err, "failed querying counter values")
+		// users can encounter the case no counters are found (services/processes stopped), this should not generate an event with the error message,
+		//could be the case the specific services are started after and picked up by the next RefreshCounterPaths func
+		if err == pdh.PDH_NO_COUNTERS {
+			re.log.Warnf("%s %v", collectFailedMsg, err)
+		} else {
+			return nil, errors.Wrap(err, collectFailedMsg)
+		}
 	}
 
 	// Get the values.