Usage Stats: Allow to add additional metrics to the stats (#29774)

The change allows to add external, additional metrics which will be reported with the rest of hardcoded metrics, allowing to add metrics without a need to change the service itself.

pkg/infra/usagestats/service.go

@@ -21,6 +21,8 @@ func init() {
 	registry.RegisterService(&UsageStatsService{})
 }
 
+type MetricFunc func() (interface{}, error)
+
 type UsageStatsService struct {
 	Cfg                *setting.Cfg               `inject:""`
 	Bus                bus.Bus                    `inject:""`
@@ -30,12 +32,14 @@ type UsageStatsService struct {
 
 	log log.Logger
 
-	oauthProviders map[string]bool
+	oauthProviders  map[string]bool
+	externalMetrics map[string]MetricFunc
 }
 
 func (uss *UsageStatsService) Init() error {
 	uss.log = log.New("infra.usagestats")
 	uss.oauthProviders = social.GetOAuthProviders(uss.Cfg)
+	uss.externalMetrics = make(map[string]MetricFunc)
 	return nil
 }
 

pkg/infra/usagestats/usage_stats.go

@@ -72,6 +72,8 @@ func (uss *UsageStatsService) GetUsageReport() (UsageReport, error) {
 	metrics["stats.edition.oss.count"] = getOssEditionCount()
 	metrics["stats.edition.enterprise.count"] = getEnterpriseEditionCount()
 
+	uss.registerExternalMetrics(metrics)
+
 	userCount := statsQuery.Result.Users
 	avgAuthTokensPerUser := statsQuery.Result.AuthTokens
 	if userCount != 0 {
@@ -186,6 +188,21 @@ func (uss *UsageStatsService) GetUsageReport() (UsageReport, error) {
 	return report, nil
 }
 
+func (uss *UsageStatsService) registerExternalMetrics(metrics map[string]interface{}) {
+	for name, fn := range uss.externalMetrics {
+		result, err := fn()
+		if err != nil {
+			metricsLogger.Error("Failed to fetch external metric", "name", name, "error", err)
+			continue
+		}
+		metrics[name] = result
+	}
+}
+
+func (uss *UsageStatsService) RegisterMetric(name string, fn MetricFunc) {
+	uss.externalMetrics[name] = fn
+}
+
 func (uss *UsageStatsService) sendUsageStats() error {
 	if !setting.ReportingEnabled {
 		return nil