Sanitize metric names in the prometheus exporter

CHANGELOG.md

@@ -19,6 +19,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - The metric SDK in `go.opentelemetry.io/otel/sdk/metric` is completely refactored to comply with the OpenTelemetry specification.
   Please see the package documentation for how the new SDK is initialized and configured. (#3175)
 - Update the minimum supported go version to go1.18. Removes support for go1.17 (#3179)
+- Instead of dropping metric, the Prometheus exporter will replace any invalid character in metric names with `_`. (#3212)
 
 ### Removed
 

exporters/prometheus/exporter.go

@@ -145,7 +145,7 @@ func getHistogramMetricData(histogram metricdata.Histogram, m metricdata.Metrics
 	dataPoints := make([]*metricData, 0, len(histogram.DataPoints))
 	for _, dp := range histogram.DataPoints {
 		keys, values := getAttrs(dp.Attributes)
-		desc := prometheus.NewDesc(m.Name, m.Description, keys, nil)
+		desc := prometheus.NewDesc(sanitizeName(m.Name), m.Description, keys, nil)
 		buckets := make(map[float64]uint64, len(dp.Bounds))
 		for i, bound := range dp.Bounds {
 			buckets[bound] = dp.BucketCounts[i]
@@ -168,7 +168,7 @@ func getSumMetricData[N int64 | float64](sum metricdata.Sum[N], m metricdata.Met
 	dataPoints := make([]*metricData, 0, len(sum.DataPoints))
 	for _, dp := range sum.DataPoints {
 		keys, values := getAttrs(dp.Attributes)
-		desc := prometheus.NewDesc(m.Name, m.Description, keys, nil)
+		desc := prometheus.NewDesc(sanitizeName(m.Name), m.Description, keys, nil)
 		md := &metricData{
 			name:            m.Name,
 			description:     desc,
@@ -185,7 +185,7 @@ func getGaugeMetricData[N int64 | float64](gauge metricdata.Gauge[N], m metricda
 	dataPoints := make([]*metricData, 0, len(gauge.DataPoints))
 	for _, dp := range gauge.DataPoints {
 		keys, values := getAttrs(dp.Attributes)
-		desc := prometheus.NewDesc(m.Name, m.Description, keys, nil)
+		desc := prometheus.NewDesc(sanitizeName(m.Name), m.Description, keys, nil)
 		md := &metricData{
 			name:            m.Name,
 			description:     desc,
@@ -233,3 +233,19 @@ func sanitizeRune(r rune) rune {
 	}
 	return '_'
 }
+
+func sanitizeName(n string) string {
+	if len(n) == 0 {
+		return n
+	}
+	var sn = make([]string, len(n))
+	for i, b := range n {
+		if !((b >= 'a' && b <= 'z') || (b >= 'A' && b <= 'Z') || b == '_' || b == ':' || (b >= '0' && b <= '9' && i > 0)) {
+			sn[i] = "_"
+		} else {
+			sn[i] = string(b)
+		}
+	}
+
+	return strings.Join(sn, "")
+}

exporters/prometheus/exporter_test.go

@@ -106,8 +106,8 @@ func TestPrometheusExporter(t *testing.T) {
 			},
 		},
 		{
-			name:         "invalid instruments are dropped",
-			expectedFile: "testdata/gauge.txt",
+			name:         "invalid instruments are renamed",
+			expectedFile: "testdata/sanitized_names.txt",
 			recordMetrics: func(ctx context.Context, meter otelmetric.Meter) {
 				attrs := []attribute.KeyValue{
 					attribute.Key("A").String("B"),
@@ -119,16 +119,16 @@ func TestPrometheusExporter(t *testing.T) {
 				gauge.Add(ctx, 100, attrs...)
 				gauge.Add(ctx, -25, attrs...)
 
-				// Invalid, should be dropped.
-				gauge, err = meter.SyncFloat64().UpDownCounter("invalid.gauge.name")
+				// Invalid, will be renamed.
+				gauge, err = meter.SyncFloat64().UpDownCounter("invalid.gauge.name", instrument.WithDescription("a gauge with an invalid name"))
 				require.NoError(t, err)
 				gauge.Add(ctx, 100, attrs...)
 
-				counter, err := meter.SyncFloat64().Counter("invalid.counter.name")
+				counter, err := meter.SyncFloat64().Counter("invalid.counter.name", instrument.WithDescription("a counter with an invalid name"))
 				require.NoError(t, err)
 				counter.Add(ctx, 100, attrs...)
 
-				histogram, err := meter.SyncFloat64().Histogram("invalid.hist.name")
+				histogram, err := meter.SyncFloat64().Histogram("invalid.hist.name", instrument.WithDescription("a histogram with an invalid name"))
 				require.NoError(t, err)
 				histogram.Record(ctx, 23, attrs...)
 			},

exporters/prometheus/testdata/sanitized_names.txt

@@ -0,0 +1,24 @@
+# HELP bar a fun little gauge
+# TYPE bar counter
+bar{A="B",C="D"} 75
+# HELP invalid_counter_name a counter with an invalid name
+# TYPE invalid_counter_name counter
+invalid_counter_name{A="B",C="D"} 100
+# HELP invalid_gauge_name a gauge with an invalid name
+# TYPE invalid_gauge_name counter
+invalid_gauge_name{A="B",C="D"} 100
+# HELP invalid_hist_name a histogram with an invalid name
+# TYPE invalid_hist_name histogram
+invalid_hist_name_bucket{A="B",C="D",le="0"} 0
+invalid_hist_name_bucket{A="B",C="D",le="5"} 0
+invalid_hist_name_bucket{A="B",C="D",le="10"} 0
+invalid_hist_name_bucket{A="B",C="D",le="25"} 1
+invalid_hist_name_bucket{A="B",C="D",le="50"} 0
+invalid_hist_name_bucket{A="B",C="D",le="75"} 0
+invalid_hist_name_bucket{A="B",C="D",le="100"} 0
+invalid_hist_name_bucket{A="B",C="D",le="250"} 0
+invalid_hist_name_bucket{A="B",C="D",le="500"} 0
+invalid_hist_name_bucket{A="B",C="D",le="1000"} 0
+invalid_hist_name_bucket{A="B",C="D",le="+Inf"} 1
+invalid_hist_name_sum{A="B",C="D"} 23
+invalid_hist_name_count{A="B",C="D"} 1