add support for summary metrics in the prometheus bridge

CHANGELOG.md

@@ -15,6 +15,7 @@ The next release will require at least [Go 1.21].
 
 - Add the new `go.opentelemetry.io/contrib/instrgen` package to provide auto-generated source code instrumentation. (#3068, #3108)
 - Support [Go 1.22]. (#5082)
+- Add support for Summary metrics to `go.opentelemetry.io/bridges/prometheus`. (#TODO)
 
 ### Removed
 

bridges/prometheus/doc.go

@@ -19,7 +19,6 @@
 // to be used with OpenTelemetry exporters, including OTLP.
 //
 // Limitations:
-//   - Summary metrics are dropped by the bridge.
 //   - Prometheus histograms are translated to OpenTelemetry fixed-bucket
 //     histograms, rather than exponential histograms.
 //

bridges/prometheus/producer.go

@@ -101,8 +101,10 @@ func convertPrometheusMetricsInto(promMetrics []*dto.MetricFamily, now time.Time
 			newMetric.Data = convertCounter(pm.GetMetric(), now)
 		case dto.MetricType_HISTOGRAM:
 			newMetric.Data = convertHistogram(pm.GetMetric(), now)
+		case dto.MetricType_SUMMARY:
+			newMetric.Data = convertSummary(pm.GetMetric(), now)
 		default:
-			// MetricType_GAUGE_HISTOGRAM, MetricType_SUMMARY, MetricType_UNTYPED
+			// MetricType_GAUGE_HISTOGRAM, MetricType_UNTYPED
 			errs = append(errs, fmt.Errorf("%w: %v for metric %v", errUnsupportedType, pm.GetType(), pm.GetName()))
 			continue
 		}
@@ -204,6 +206,43 @@ func convertBuckets(buckets []*dto.Bucket) ([]float64, []uint64, []metricdata.Ex
 	return bounds, bucketCounts, exemplars
 }
 
+func convertSummary(metrics []*dto.Metric, now time.Time) metricdata.Summary {
+	otelSummary := metricdata.Summary{
+		DataPoints: make([]metricdata.SummaryDataPoint, len(metrics)),
+	}
+	for i, m := range metrics {
+		dp := metricdata.SummaryDataPoint{
+			Attributes:     convertLabels(m.GetLabel()),
+			StartTime:      processStartTime,
+			Time:           now,
+			Count:          m.GetSummary().GetSampleCount(),
+			Sum:            m.GetSummary().GetSampleSum(),
+			QuantileValues: convertQuantiles(m.GetSummary().GetQuantile()),
+		}
+		createdTs := m.GetSummary().GetCreatedTimestamp()
+		if createdTs.IsValid() {
+			dp.StartTime = createdTs.AsTime()
+		}
+		if m.GetTimestampMs() != 0 {
+			dp.Time = time.UnixMilli(m.GetTimestampMs())
+		}
+		otelSummary.DataPoints[i] = dp
+	}
+	return otelSummary
+}
+
+func convertQuantiles(quantiles []*dto.Quantile) []metricdata.QuantileValue {
+	otelQuantiles := make([]metricdata.QuantileValue, len(quantiles))
+	for i, quantile := range quantiles {
+		dp := metricdata.QuantileValue{
+			Quantile: quantile.GetQuantile(),
+			Value:    quantile.GetValue(),
+		}
+		otelQuantiles[i] = dp
+	}
+	return otelQuantiles
+}
+
 func convertLabels(labels []*dto.LabelPair) attribute.Set {
 	kvs := make([]attribute.KeyValue, len(labels))
 	for i, l := range labels {

bridges/prometheus/producer_test.go

@@ -128,19 +128,44 @@ func TestProduce(t *testing.T) {
 			}},
 		},
 		{
-			name: "summary dropped",
+			name: "summary",
 			testFn: func(reg *prometheus.Registry) {
 				metric := prometheus.NewSummary(prometheus.SummaryOpts{
-					Name: "test_summary_metric",
-					Help: "A summary metric for testing",
+					Name:       "test_summary_metric",
+					Help:       "A summary metric for testing",
+					Objectives: map[float64]float64{0.5: 0.05, 0.9: 0.01, 0.99: 0.001},
 					ConstLabels: prometheus.Labels(map[string]string{
 						"foo": "bar",
 					}),
 				})
 				reg.MustRegister(metric)
 				metric.Observe(15.0)
 			},
-			wantErr: errUnsupportedType,
+			expected: []metricdata.ScopeMetrics{{
+				Scope: instrumentation.Scope{
+					Name: scopeName,
+				},
+				Metrics: []metricdata.Metrics{
+					{
+						Name:        "test_summary_metric",
+						Description: "A summary metric for testing",
+						Data: metricdata.Summary{
+							DataPoints: []metricdata.SummaryDataPoint{
+								{
+									Count: 1,
+									Sum:   15.0,
+									QuantileValues: []metricdata.QuantileValue{
+										{Quantile: 0.5, Value: 15},
+										{Quantile: 0.9, Value: 15},
+										{Quantile: 0.99, Value: 15},
+									},
+									Attributes: attribute.NewSet(attribute.String("foo", "bar")),
+								},
+							},
+						},
+					},
+				},
+			}},
 		},
 		{
 			name: "histogram",
@@ -207,12 +232,13 @@ func TestProduce(t *testing.T) {
 				})
 				reg.MustRegister(metric)
 				metric.Set(123.4)
-				unsupportedMetric := prometheus.NewSummary(prometheus.SummaryOpts{
-					Name: "test_summary_metric",
-					Help: "A summary metric for testing",
+				unsupportedMetric := prometheus.NewUntypedFunc(prometheus.UntypedOpts{
+					Name: "test_untyped_metric",
+					Help: "An untyped metric for testing",
+				}, func() float64 {
+					return 135.8
 				})
 				reg.MustRegister(unsupportedMetric)
-				unsupportedMetric.Observe(15.0)
 			},
 			expected: []metricdata.ScopeMetrics{{
 				Scope: instrumentation.Scope{
@@ -315,6 +341,27 @@ func TestProduceForStartTime(t *testing.T) {
 				return sts
 			},
 		},
+		{
+			name: "summary",
+			testFn: func(reg *prometheus.Registry) {
+				metric := prometheus.NewSummary(prometheus.SummaryOpts{
+					Name: "test_summary_metric",
+					Help: "A summary metric for testing",
+					ConstLabels: prometheus.Labels(map[string]string{
+						"foo": "bar",
+					}),
+				})
+				reg.MustRegister(metric)
+			},
+			startTimeFn: func(aggr metricdata.Aggregation) []time.Time {
+				dps := aggr.(metricdata.Summary).DataPoints
+				sts := make([]time.Time, len(dps))
+				for i, dp := range dps {
+					sts[i] = dp.StartTime
+				}
+				return sts
+			},
+		},
 	}
 	for _, tt := range testCases {
 		t.Run(tt.name, func(t *testing.T) {