eth/protocols, metrics: use resetting histograms for rare packets

metrics/resetting_sample.go

@@ -0,0 +1,24 @@
+package metrics
+
+// ResettingSample converts an ordinary sample into one that resets whenever its
+// snapshot is retrieved. This will break for multi-monitor systems, but when only
+// a single metric is being pushed out, this ensure that low-frequency events don't
+// skew th charts indefinitely.
+func ResettingSample(sample Sample) Sample {
+	return &resettingSample{
+		Sample: sample,
+	}
+}
+
+// resettingSample is a simple wrapper around a sample that resets it upon the
+// snapshot retrieval.
+type resettingSample struct {
+	Sample
+}
+
+// Snapshot returns a read-only copy of the sample with the original reset.
+func (rs *resettingSample) Snapshot() Sample {
+	s := rs.Sample.Snapshot()
+	rs.Sample.Clear()
+	return s
+}