From 2bb1d5ed233d2d4cdc72baa031b6f7a45a85783a Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Mon, 21 Jul 2025 12:27:41 -0700
Subject: [PATCH 1/2] Add Bandpass Aggregation

Proof-of-concept to allow views to filter measurements.
---
 sdk/metric/aggregation.go | 30 ++++++++++++++++++++++++++++++
 sdk/metric/pipeline.go    | 25 +++++++++++++++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/sdk/metric/aggregation.go b/sdk/metric/aggregation.go
index e6f5cfb2ad9..23c21242afe 100644
--- a/sdk/metric/aggregation.go
+++ b/sdk/metric/aggregation.go
@@ -187,3 +187,33 @@ func (e AggregationBase2ExponentialHistogram) err() error {
 	}
 	return nil
 }
+
+// AggregationBandpass is an [Aggregation] that only records measurements to
+// its Downstream Aggregation if they fall within the specified High and Low
+// bounds. Measurements outside of these bounds are dropped.
+type AggregationBandpass struct {
+	High, Low  float64
+	Downstream Aggregation
+}
+
+var _ Aggregation = AggregationBandpass{}
+
+// copy returns a deep copy of d.
+func (d AggregationBandpass) copy() Aggregation {
+	return AggregationBandpass{
+		High:       d.High,
+		Low:        d.Low,
+		Downstream: d.Downstream.copy(),
+	}
+}
+
+// err returns an error for any misconfiguration.
+func (d AggregationBandpass) err() error {
+	if d.High <= d.Low {
+		return fmt.Errorf("%w: high bound %f is less than or equal to low bound %f", errAgg, d.High, d.Low)
+	}
+	if d.Downstream == nil {
+		return fmt.Errorf("%w: downstream aggregation is nil", errAgg)
+	}
+	return nil
+}
diff --git a/sdk/metric/pipeline.go b/sdk/metric/pipeline.go
index 7bdb699cae0..c31b254d514 100644
--- a/sdk/metric/pipeline.go
+++ b/sdk/metric/pipeline.go
@@ -11,6 +11,7 @@ import (
 	"sync"
 	"sync/atomic"
 
+	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/internal/global"
 	"go.opentelemetry.io/otel/metric/embedded"
 	"go.opentelemetry.io/otel/sdk/instrumentation"
@@ -524,6 +525,20 @@ func (i *inserter[N]) aggregateFunc(
 			noSum = true
 		}
 		meas, comp = b.ExponentialBucketHistogram(a.MaxSize, a.MaxScale, a.NoMinMax, noSum)
+	case AggregationBandpass:
+		d := a.Downstream
+		if d == nil {
+			// This is an error if the downstream is nil, this is a
+			// misconfiguration. However, "fail gracefully" and return nil in
+			// and out to signify the drop aggregator.
+			err = fmt.Errorf(
+				"%w: bandpass aggregation requires a downstream aggregator",
+				errAgg,
+			)
+		} else {
+			meas, comp, err = i.aggregateFunc(b, d, kind)
+			meas = bandpass(meas, a.High, a.Low)
+		}
 
 	default:
 		err = errUnknownAggregation
@@ -532,6 +547,16 @@ func (i *inserter[N]) aggregateFunc(
 	return meas, comp, err
 }
 
+func bandpass[N int64 | float64](m aggregate.Measure[N], high, low float64) aggregate.Measure[N] {
+	return func(ctx context.Context, n N, s attribute.Set) {
+		if n > N(high) || n < N(low) {
+			// Drop the measurement if it is outside of the bandpass.
+			return
+		}
+		m(ctx, n, s)
+	}
+}
+
 // isAggregatorCompatible checks if the aggregation can be used by the instrument.
 // Current compatibility:
 //

From 078a1ff3fc03e47fecb2947b4b975198c70b4a09 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Mon, 21 Jul 2025 12:33:51 -0700
Subject: [PATCH 2/2] Add example

---
 sdk/metric/example_test.go | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/sdk/metric/example_test.go b/sdk/metric/example_test.go
index 234bfd65945..006673e8b90 100644
--- a/sdk/metric/example_test.go
+++ b/sdk/metric/example_test.go
@@ -219,6 +219,30 @@ func ExampleNewView_attributeFilter() {
 	)
 }
 
+func ExampleNewView_filterMeasurements() {
+	// Create a view that restricts values recorded by the "slo" instrument in
+	// the "http" instrumentation library to be within the range of 0 to 100.
+	view := metric.NewView(
+		metric.Instrument{
+			Name:  "slo",
+			Scope: instrumentation.Scope{Name: "http"},
+		},
+		metric.Stream{
+			Aggregation: metric.AggregationBandpass{
+				High:       100,
+				Low:        0,
+				Downstream: metric.AggregationDefault{},
+			},
+		},
+	)
+
+	// The created view can then be registered with the OpenTelemetry metric
+	// SDK using the WithView option.
+	_ = metric.NewMeterProvider(
+		metric.WithView(view),
+	)
+}
+
 func ExampleNewView_exponentialHistogram() {
 	// Create a view that makes the "latency" instrument from the "http"
 	// instrumentation library to be reported as an exponential histogram.