core/metrics: improve memory usage (#5364)

internal/telemetry/prometheus/export.go

@@ -0,0 +1,30 @@
+package prometheus
+
+import (
+	"io"
+	"iter"
+
+	dto "github.com/prometheus/client_model/go"
+	"github.com/prometheus/common/expfmt"
+)
+
+// Export writes the metric families to the writer in text format
+func Export(
+	w io.Writer,
+	src iter.Seq2[*dto.MetricFamily, error],
+) error {
+	for mf, err := range src {
+		if err != nil {
+			return err
+		}
+		if err := exportMetricFamily(w, mf); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func exportMetricFamily(w io.Writer, mf *dto.MetricFamily) error {
+	_, err := expfmt.MetricFamilyToText(w, mf)
+	return err
+}