Add HandlerWithAllowlist which can control exposed metrics

prometheus/promhttp/http.go

@@ -45,6 +45,8 @@ import (
 	"github.com/prometheus/common/expfmt"
 
 	"github.com/prometheus/client_golang/prometheus"
+
+	dto "github.com/prometheus/client_model/go"
 )
 
 const (
@@ -90,6 +92,16 @@ func HandlerFor(reg prometheus.Gatherer, opts HandlerOpts) http.Handler {
 	return HandlerForTransactional(prometheus.ToTransactionalGatherer(reg), opts)
 }
 
+func HandlerWithAllowlist(metricNames []string) http.Handler {
+	allowedMetrics := map[string]bool{}
+	for _, m := range metricNames {
+		allowedMetrics[m] = true
+	}
+	return InstrumentMetricHandler(
+		prometheus.DefaultRegisterer, HandlerFor(&FilteredDefaultGatherer{allowedMetrics: allowedMetrics}, HandlerOpts{}),
+	)
+}
+
 // HandlerForTransactional is like HandlerFor, but it uses transactional gather, which
 // can safely change in-place returned *dto.MetricFamily before call to `Gather` and after
 // call to `done` of that `Gather`.
@@ -381,6 +393,35 @@ type HandlerOpts struct {
 	ProcessStartTime time.Time
 }
 
+type FilteredDefaultGatherer struct {
+	allowedMetrics map[string]bool
+}
+
+func (f *FilteredDefaultGatherer) Gather() ([]*dto.MetricFamily, error) {
+	results := []*dto.MetricFamily{}
+	metrics, err := prometheus.DefaultGatherer.Gather()
+	if err != nil {
+		return nil, err
+	}
+	for _, m := range metrics {
+		name := *m.Name
+		keep := false
+
+		if strings.HasPrefix(name, "go_") || strings.HasPrefix(name, "process_") || strings.HasPrefix(name, "promhttp_") {
+			keep = true
+		}
+
+		if f.allowedMetrics[name] {
+			keep = true
+		}
+
+		if keep {
+			results = append(results, m)
+		}
+	}
+	return results, nil
+}
+
 // gzipAccepted returns whether the client will accept gzip-encoded content.
 func gzipAccepted(header http.Header) bool {
 	a := header.Get(acceptEncodingHeader)