Set bucket bounds as le labels for Prometheus exporter. (#1167)

Closes #1164.

Previously we don't set the bucket bounds for Prometheus Samples,
since bucket bounds is a built-in feature for Prometheus Histogram.
However, as #1164 suggested, we can manually set the bucket bounds
with the same label le that the built-in Histogram uses,
to get the same output as the built-in Prometheus Histogram Samples.

5 files changed, 214 insertions, 53 deletions

diff --git a/exporters/stats/prometheus/README.md b/exporters/stats/prometheus/README.md
index 9a874c29..afe340b4 100644
--- a/exporters/stats/prometheus/README.md
+++ b/exporters/stats/prometheus/README.md
@@ -78,4 +78,4 @@ and [Bridges](https://github.com/prometheus/client_java#bridges).
 
 Java 7 or above is required for using this exporter.
 
-## FAQ
\ No newline at end of file
+## FAQ
diff --git a/exporters/stats/prometheus/src/main/java/io/opencensus/exporter/stats/prometheus/PrometheusExportUtils.java b/exporters/stats/prometheus/src/main/java/io/opencensus/exporter/stats/prometheus/PrometheusExportUtils.java
index e745b594..6999b75b 100644
--- a/exporters/stats/prometheus/src/main/java/io/opencensus/exporter/stats/prometheus/PrometheusExportUtils.java
+++ b/exporters/stats/prometheus/src/main/java/io/opencensus/exporter/stats/prometheus/PrometheusExportUtils.java
@@ -16,6 +16,8 @@
 
 package io.opencensus.exporter.stats.prometheus;
 
+import static io.prometheus.client.Collector.doubleToGoString;
+
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Lists;
@@ -86,6 +88,7 @@ final class PrometheusExportUtils {
   @VisibleForTesting static final String SAMPLE_SUFFIX_BUCKET = "_bucket";
   @VisibleForTesting static final String SAMPLE_SUFFIX_COUNT = "_count";
   @VisibleForTesting static final String SAMPLE_SUFFIX_SUM = "_sum";
+  @VisibleForTesting static final String LABEL_NAME_BUCKET_BOUND = "le";
 
   // Converts a ViewData to a Prometheus MetricFamilySamples.
   static MetricFamilySamples createMetricFamilySamples(ViewData viewData) {
@@ -93,10 +96,12 @@ final class PrometheusExportUtils {
     String name =
         Collector.sanitizeMetricName(OPENCENSUS_NAMESPACE + '_' + view.getName().asString());
     Type type = getType(view.getAggregation(), view.getWindow());
+    List<String> labelNames = convertToLabelNames(view.getColumns());
     List<Sample> samples = Lists.newArrayList();
     for (Entry<List</*@Nullable*/ TagValue>, AggregationData> entry :
         viewData.getAggregationMap().entrySet()) {
-      samples.addAll(getSamples(name, view.getColumns(), entry.getKey(), entry.getValue()));
+      samples.addAll(
+          getSamples(name, labelNames, entry.getKey(), entry.getValue(), view.getAggregation()));
     }
     return new MetricFamilySamples(
         name, type, OPENCENSUS_HELP_MSG + view.getDescription(), samples);
@@ -108,6 +113,13 @@ final class PrometheusExportUtils {
     String name =
         Collector.sanitizeMetricName(OPENCENSUS_NAMESPACE + '_' + view.getName().asString());
     Type type = getType(view.getAggregation(), view.getWindow());
+    List<String> labelNames = convertToLabelNames(view.getColumns());
+    if (containsDisallowedLeLabelForHistogram(labelNames, type)) {
+      throw new IllegalStateException(
+          "Prometheus Histogram cannot have a label named 'le', "
+              + "because it is a reserved label for bucket boundaries. "
+              + "Please remove this tag key from your view.");
+    }
     return new MetricFamilySamples(
         name, type, OPENCENSUS_HELP_MSG + view.getDescription(), Collections.<Sample>emptyList());
   }
@@ -133,20 +145,19 @@ final class PrometheusExportUtils {
         });
   }
 
+  // Converts a row in ViewData (a.k.a Entry<List<TagValue>, AggregationData>) to a list of
+  // Prometheus Samples.
   @VisibleForTesting
   static List<Sample> getSamples(
       final String name,
-      List<TagKey> tagKeys,
+      final List<String> labelNames,
       List</*@Nullable*/ TagValue> tagValues,
-      AggregationData aggregationData) {
+      AggregationData aggregationData,
+      final Aggregation aggregation) {
     Preconditions.checkArgument(
-        tagKeys.size() == tagValues.size(), "Tag keys and tag values have different sizes.");
+        labelNames.size() == tagValues.size(), "Label names and tag values have different sizes.");
     final List<Sample> samples = Lists.newArrayList();
-    final List<String> labelNames = new ArrayList<String>(tagKeys.size());
     final List<String> labelValues = new ArrayList<String>(tagValues.size());
-    for (TagKey tagKey : tagKeys) {
-      labelNames.add(Collector.sanitizeMetricName(tagKey.getName()));
-    }
     for (TagValue tagValue : tagValues) {
       String labelValue = tagValue == null ? "" : tagValue.asString();
       labelValues.add(labelValue);
@@ -177,11 +188,29 @@ final class PrometheusExportUtils {
         new Function<DistributionData, Void>() {
           @Override
           public Void apply(DistributionData arg) {
-            for (long bucketCount : arg.getBucketCounts()) {
+            // For histogram buckets, manually add the bucket boundaries as "le" labels. See
+            // https://github.com/prometheus/client_java/commit/ed184d8e50c82e98bb2706723fff764424840c3a#diff-c505abbde72dd6bf36e89917b3469404R241
+            @SuppressWarnings("unchecked")
+            Distribution distribution = (Distribution) aggregation;
+            List<Double> boundaries = distribution.getBucketBoundaries().getBoundaries();
+            List<String> labelNamesWithLe = new ArrayList<String>(labelNames);
+            labelNamesWithLe.add(LABEL_NAME_BUCKET_BOUND);
+            for (int i = 0; i < arg.getBucketCounts().size(); i++) {
+              List<String> labelValuesWithLe = new ArrayList<String>(labelValues);
+              // The label value of "le" is the upper inclusive bound.
+              // For the last bucket, it should be "+Inf".
+              String bucketBoundary =
+                  doubleToGoString(
+                      i < boundaries.size() ? boundaries.get(i) : Double.POSITIVE_INFINITY);
+              labelValuesWithLe.add(bucketBoundary);
               samples.add(
                   new MetricFamilySamples.Sample(
-                      name + SAMPLE_SUFFIX_BUCKET, labelNames, labelValues, bucketCount));
+                      name + SAMPLE_SUFFIX_BUCKET,
+                      labelNamesWithLe,
+                      labelValuesWithLe,
+                      arg.getBucketCounts().get(i)));
             }
+
             samples.add(
                 new MetricFamilySamples.Sample(
                     name + SAMPLE_SUFFIX_COUNT, labelNames, labelValues, arg.getCount()));
@@ -234,5 +263,30 @@ final class PrometheusExportUtils {
     return samples;
   }
 
+  // Converts the list of tag keys to a list of string label names. Also sanitizes the tag keys.
+  @VisibleForTesting
+  static List<String> convertToLabelNames(List<TagKey> tagKeys) {
+    final List<String> labelNames = new ArrayList<String>(tagKeys.size());
+    for (TagKey tagKey : tagKeys) {
+      labelNames.add(Collector.sanitizeMetricName(tagKey.getName()));
+    }
+    return labelNames;
+  }
+
+  // Returns true if there is an "le" label name in histogram label names, returns false otherwise.
+  // Similar check to
+  // https://github.com/prometheus/client_java/commit/ed184d8e50c82e98bb2706723fff764424840c3a#diff-c505abbde72dd6bf36e89917b3469404R78
+  static boolean containsDisallowedLeLabelForHistogram(List<String> labelNames, Type type) {
+    if (!Type.HISTOGRAM.equals(type)) {
+      return false;
+    }
+    for (String label : labelNames) {
+      if (LABEL_NAME_BUCKET_BOUND.equals(label)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
   private PrometheusExportUtils() {}
 }
diff --git a/exporters/stats/prometheus/src/main/java/io/opencensus/exporter/stats/prometheus/PrometheusStatsCollector.java b/exporters/stats/prometheus/src/main/java/io/opencensus/exporter/stats/prometheus/PrometheusStatsCollector.java
index 884d3ccb..2f4d189d 100644
--- a/exporters/stats/prometheus/src/main/java/io/opencensus/exporter/stats/prometheus/PrometheusStatsCollector.java
+++ b/exporters/stats/prometheus/src/main/java/io/opencensus/exporter/stats/prometheus/PrometheusStatsCollector.java
@@ -16,6 +16,10 @@
 
 package io.opencensus.exporter.stats.prometheus;
 
+import static io.opencensus.exporter.stats.prometheus.PrometheusExportUtils.containsDisallowedLeLabelForHistogram;
+import static io.opencensus.exporter.stats.prometheus.PrometheusExportUtils.convertToLabelNames;
+import static io.opencensus.exporter.stats.prometheus.PrometheusExportUtils.getType;
+
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Lists;
@@ -39,6 +43,7 @@ import java.util.logging.Logger;
  *
  * @since 0.12
  */
+@SuppressWarnings("deprecation")
 public final class PrometheusStatsCollector extends Collector implements Collector.Describable {
 
   private static final Logger logger = Logger.getLogger(PrometheusStatsCollector.class.getName());
@@ -90,20 +95,27 @@ public final class PrometheusStatsCollector extends Collector implements Collect
     span.addAnnotation("Collect Prometheus Metric Samples.");
     try (Scope scope = tracer.withSpan(span)) {
       for (View view : viewManager.getAllExportedViews()) {
-        ViewData viewData = viewManager.getView(view.getName());
-        if (viewData == null) {
-          continue;
-        } else {
-          samples.add(PrometheusExportUtils.createMetricFamilySamples(viewData));
+        if (containsDisallowedLeLabelForHistogram(
+            convertToLabelNames(view.getColumns()),
+            getType(view.getAggregation(), view.getWindow()))) {
+          continue; // silently skip Distribution views with "le" tag key
+        }
+        try {
+          ViewData viewData = viewManager.getView(view.getName());
+          if (viewData == null) {
+            continue;
+          } else {
+            samples.add(PrometheusExportUtils.createMetricFamilySamples(viewData));
+          }
+        } catch (Throwable e) {
+          logger.log(Level.WARNING, "Exception thrown when collecting metric samples.", e);
+          span.setStatus(
+              Status.UNKNOWN.withDescription(
+                  "Exception thrown when collecting Prometheus Metric Samples: "
+                      + exceptionMessage(e)));
         }
       }
       span.addAnnotation("Finish collecting Prometheus Metric Samples.");
-    } catch (Throwable e) {
-      logger.log(Level.WARNING, "Exception thrown when collecting metric samples.", e);
-      span.setStatus(
-          Status.UNKNOWN.withDescription(
-              "Exception thrown when collecting Prometheus Metric Samples: "
-                  + exceptionMessage(e)));
     } finally {
       span.end();
     }
@@ -118,14 +130,16 @@ public final class PrometheusStatsCollector extends Collector implements Collect
     span.addAnnotation("Describe Prometheus Metrics.");
     try (Scope scope = tracer.withSpan(span)) {
       for (View view : viewManager.getAllExportedViews()) {
-        samples.add(PrometheusExportUtils.createDescribableMetricFamilySamples(view));
+        try {
+          samples.add(PrometheusExportUtils.createDescribableMetricFamilySamples(view));
+        } catch (Throwable e) {
+          logger.log(Level.WARNING, "Exception thrown when describing metrics.", e);
+          span.setStatus(
+              Status.UNKNOWN.withDescription(
+                  "Exception thrown when describing Prometheus Metrics: " + exceptionMessage(e)));
+        }
       }
       span.addAnnotation("Finish describing Prometheus Metrics.");
-    } catch (Throwable e) {
-      logger.log(Level.WARNING, "Exception thrown when describing metrics.", e);
-      span.setStatus(
-          Status.UNKNOWN.withDescription(
-              "Exception thrown when describing Prometheus Metrics: " + exceptionMessage(e)));
     } finally {
       span.end();
     }
diff --git a/exporters/stats/prometheus/src/test/java/io/opencensus/exporter/stats/prometheus/PrometheusExportUtilsTest.java b/exporters/stats/prometheus/src/test/java/io/opencensus/exporter/stats/prometheus/PrometheusExportUtilsTest.java
index 507fd3b6..1d112a31 100644
--- a/exporters/stats/prometheus/src/test/java/io/opencensus/exporter/stats/prometheus/PrometheusExportUtilsTest.java
+++ b/exporters/stats/prometheus/src/test/java/io/opencensus/exporter/stats/prometheus/PrometheusExportUtilsTest.java
@@ -17,11 +17,13 @@
 package io.opencensus.exporter.stats.prometheus;
 
 import static com.google.common.truth.Truth.assertThat;
+import static io.opencensus.exporter.stats.prometheus.PrometheusExportUtils.LABEL_NAME_BUCKET_BOUND;
 import static io.opencensus.exporter.stats.prometheus.PrometheusExportUtils.OPENCENSUS_HELP_MSG;
 import static io.opencensus.exporter.stats.prometheus.PrometheusExportUtils.OPENCENSUS_NAMESPACE;
 import static io.opencensus.exporter.stats.prometheus.PrometheusExportUtils.SAMPLE_SUFFIX_BUCKET;
 import static io.opencensus.exporter.stats.prometheus.PrometheusExportUtils.SAMPLE_SUFFIX_COUNT;
 import static io.opencensus.exporter.stats.prometheus.PrometheusExportUtils.SAMPLE_SUFFIX_SUM;
+import static io.opencensus.exporter.stats.prometheus.PrometheusExportUtils.convertToLabelNames;
 
 import com.google.common.collect.ImmutableMap;
 import io.opencensus.common.Duration;
@@ -85,6 +87,7 @@ public class PrometheusExportUtilsTest {
   private static final TagKey K1 = TagKey.create("k1");
   private static final TagKey K2 = TagKey.create("k2");
   private static final TagKey K3 = TagKey.create("k-3");
+  private static final TagKey TAG_KEY_LE = TagKey.create(LABEL_NAME_BUCKET_BOUND);
   private static final TagValue V1 = TagValue.create("v1");
   private static final TagValue V2 = TagValue.create("v2");
   private static final TagValue V3 = TagValue.create("v-3");
@@ -106,6 +109,14 @@ public class PrometheusExportUtilsTest {
           VIEW_NAME_3, DESCRIPTION, MEASURE_DOUBLE, DISTRIBUTION, Arrays.asList(K1), CUMULATIVE);
   private static final View VIEW4 =
       View.create(VIEW_NAME_4, DESCRIPTION, MEASURE_DOUBLE, COUNT, Arrays.asList(K1), INTERVAL);
+  private static final View DISTRIBUTION_VIEW_WITH_LE_KEY =
+      View.create(
+          VIEW_NAME_1,
+          DESCRIPTION,
+          MEASURE_DOUBLE,
+          DISTRIBUTION,
+          Arrays.asList(K1, TAG_KEY_LE),
+          CUMULATIVE);
   private static final CumulativeData CUMULATIVE_DATA =
       CumulativeData.create(Timestamp.fromMillis(1000), Timestamp.fromMillis(2000));
   private static final IntervalData INTERVAL_DATA = IntervalData.create(Timestamp.fromMillis(1000));
@@ -118,6 +129,7 @@ public class PrometheusExportUtilsTest {
     assertThat(SAMPLE_SUFFIX_BUCKET).isEqualTo("_bucket");
     assertThat(SAMPLE_SUFFIX_COUNT).isEqualTo("_count");
     assertThat(SAMPLE_SUFFIX_SUM).isEqualTo("_sum");
+    assertThat(LABEL_NAME_BUCKET_BOUND).isEqualTo("le");
   }
 
   @Test
@@ -166,45 +178,77 @@ public class PrometheusExportUtilsTest {
   public void getSamples() {
     assertThat(
             PrometheusExportUtils.getSamples(
-                SAMPLE_NAME, Arrays.asList(K1, K2), Arrays.asList(V1, V2), SUM_DATA_DOUBLE))
+                SAMPLE_NAME,
+                convertToLabelNames(Arrays.asList(K1, K2)),
+                Arrays.asList(V1, V2),
+                SUM_DATA_DOUBLE,
+                SUM))
         .containsExactly(
             new Sample(SAMPLE_NAME, Arrays.asList("k1", "k2"), Arrays.asList("v1", "v2"), -5.5));
     assertThat(
             PrometheusExportUtils.getSamples(
-                SAMPLE_NAME, Arrays.asList(K3), Arrays.asList(V3), SUM_DATA_LONG))
+                SAMPLE_NAME,
+                convertToLabelNames(Arrays.asList(K3)),
+                Arrays.asList(V3),
+                SUM_DATA_LONG,
+                SUM))
         .containsExactly(
             new Sample(SAMPLE_NAME, Arrays.asList("k_3"), Arrays.asList("v-3"), 123456789));
     assertThat(
             PrometheusExportUtils.getSamples(
-                SAMPLE_NAME, Arrays.asList(K1, K3), Arrays.asList(V1, null), COUNT_DATA))
+                SAMPLE_NAME,
+                convertToLabelNames(Arrays.asList(K1, K3)),
+                Arrays.asList(V1, null),
+                COUNT_DATA,
+                COUNT))
         .containsExactly(
             new Sample(SAMPLE_NAME, Arrays.asList("k1", "k_3"), Arrays.asList("v1", ""), 12345));
     assertThat(
             PrometheusExportUtils.getSamples(
-                SAMPLE_NAME, Arrays.asList(K3), Arrays.asList(V3), MEAN_DATA))
+                SAMPLE_NAME,
+                convertToLabelNames(Arrays.asList(K3)),
+                Arrays.asList(V3),
+                MEAN_DATA,
+                MEAN))
         .containsExactly(
             new Sample(SAMPLE_NAME + "_count", Arrays.asList("k_3"), Arrays.asList("v-3"), 22),
             new Sample(SAMPLE_NAME + "_sum", Arrays.asList("k_3"), Arrays.asList("v-3"), 74.8))
         .inOrder();
     assertThat(
             PrometheusExportUtils.getSamples(
-                SAMPLE_NAME, Arrays.asList(K1), Arrays.asList(V1), DISTRIBUTION_DATA))
+                SAMPLE_NAME,
+                convertToLabelNames(Arrays.asList(K1)),
+                Arrays.asList(V1),
+                DISTRIBUTION_DATA,
+                DISTRIBUTION))
         .containsExactly(
-            new Sample(SAMPLE_NAME + "_bucket", Arrays.asList("k1"), Arrays.asList("v1"), 0),
-            new Sample(SAMPLE_NAME + "_bucket", Arrays.asList("k1"), Arrays.asList("v1"), 2),
-            new Sample(SAMPLE_NAME + "_bucket", Arrays.asList("k1"), Arrays.asList("v1"), 2),
-            new Sample(SAMPLE_NAME + "_bucket", Arrays.asList("k1"), Arrays.asList("v1"), 1),
+            new Sample(
+                SAMPLE_NAME + "_bucket", Arrays.asList("k1", "le"), Arrays.asList("v1", "-5.0"), 0),
+            new Sample(
+                SAMPLE_NAME + "_bucket", Arrays.asList("k1", "le"), Arrays.asList("v1", "0.0"), 2),
+            new Sample(
+                SAMPLE_NAME + "_bucket", Arrays.asList("k1", "le"), Arrays.asList("v1", "5.0"), 2),
+            new Sample(
+                SAMPLE_NAME + "_bucket", Arrays.asList("k1", "le"), Arrays.asList("v1", "+Inf"), 1),
             new Sample(SAMPLE_NAME + "_count", Arrays.asList("k1"), Arrays.asList("v1"), 5),
             new Sample(SAMPLE_NAME + "_sum", Arrays.asList("k1"), Arrays.asList("v1"), 22.0))
         .inOrder();
     assertThat(
             PrometheusExportUtils.getSamples(
-                SAMPLE_NAME, Arrays.asList(K1, K2), Arrays.asList(V1, V2), LAST_VALUE_DATA_DOUBLE))
+                SAMPLE_NAME,
+                convertToLabelNames(Arrays.asList(K1, K2)),
+                Arrays.asList(V1, V2),
+                LAST_VALUE_DATA_DOUBLE,
+                LAST_VALUE))
         .containsExactly(
             new Sample(SAMPLE_NAME, Arrays.asList("k1", "k2"), Arrays.asList("v1", "v2"), 7.9));
     assertThat(
             PrometheusExportUtils.getSamples(
-                SAMPLE_NAME, Arrays.asList(K3), Arrays.asList(V3), LAST_VALUE_DATA_LONG))
+                SAMPLE_NAME,
+                convertToLabelNames(Arrays.asList(K3)),
+                Arrays.asList(V3),
+                LAST_VALUE_DATA_LONG,
+                LAST_VALUE))
         .containsExactly(
             new Sample(SAMPLE_NAME, Arrays.asList("k_3"), Arrays.asList("v-3"), 66666666));
   }
@@ -212,9 +256,23 @@ public class PrometheusExportUtilsTest {
   @Test
   public void getSamples_KeysAndValuesHaveDifferentSizes() {
     thrown.expect(IllegalArgumentException.class);
-    thrown.expectMessage("Tag keys and tag values have different sizes.");
+    thrown.expectMessage("Label names and tag values have different sizes.");
     PrometheusExportUtils.getSamples(
-        SAMPLE_NAME, Arrays.asList(K1, K2, K3), Arrays.asList(V1, V2), DISTRIBUTION_DATA);
+        SAMPLE_NAME,
+        convertToLabelNames(Arrays.asList(K1, K2, K3)),
+        Arrays.asList(V1, V2),
+        DISTRIBUTION_DATA,
+        DISTRIBUTION);
+  }
+
+  @Test
+  public void createDescribableMetricFamilySamples_Histogram_DisallowLeLabelName() {
+    thrown.expect(IllegalStateException.class);
+    thrown.expectMessage(
+        "Prometheus Histogram cannot have a label named 'le', "
+            + "because it is a reserved label for bucket boundaries. "
+            + "Please remove this tag key from your view.");
+    PrometheusExportUtils.createDescribableMetricFamilySamples(DISTRIBUTION_VIEW_WITH_LE_KEY);
   }
 
   @Test
@@ -266,23 +324,23 @@ public class PrometheusExportUtilsTest {
                 Arrays.asList(
                     new Sample(
                         OPENCENSUS_NAMESPACE + "_view_3_bucket",
-                        Arrays.asList("k1"),
-                        Arrays.asList("v-3"),
+                        Arrays.asList("k1", "le"),
+                        Arrays.asList("v-3", "-5.0"),
                         0),
                     new Sample(
                         OPENCENSUS_NAMESPACE + "_view_3_bucket",
-                        Arrays.asList("k1"),
-                        Arrays.asList("v-3"),
+                        Arrays.asList("k1", "le"),
+                        Arrays.asList("v-3", "0.0"),
                         2),
                     new Sample(
                         OPENCENSUS_NAMESPACE + "_view_3_bucket",
-                        Arrays.asList("k1"),
-                        Arrays.asList("v-3"),
+                        Arrays.asList("k1", "le"),
+                        Arrays.asList("v-3", "5.0"),
                         2),
                     new Sample(
                         OPENCENSUS_NAMESPACE + "_view_3_bucket",
-                        Arrays.asList("k1"),
-                        Arrays.asList("v-3"),
+                        Arrays.asList("k1", "le"),
+                        Arrays.asList("v-3", "+Inf"),
                         1),
                     new Sample(
                         OPENCENSUS_NAMESPACE + "_view_3_count",
diff --git a/exporters/stats/prometheus/src/test/java/io/opencensus/exporter/stats/prometheus/PrometheusStatsCollectorTest.java b/exporters/stats/prometheus/src/test/java/io/opencensus/exporter/stats/prometheus/PrometheusStatsCollectorTest.java
index 73f72dba..3f97ac3c 100644
--- a/exporters/stats/prometheus/src/test/java/io/opencensus/exporter/stats/prometheus/PrometheusStatsCollectorTest.java
+++ b/exporters/stats/prometheus/src/test/java/io/opencensus/exporter/stats/prometheus/PrometheusStatsCollectorTest.java
@@ -17,6 +17,7 @@
 package io.opencensus.exporter.stats.prometheus;
 
 import static com.google.common.truth.Truth.assertThat;
+import static io.opencensus.exporter.stats.prometheus.PrometheusExportUtils.LABEL_NAME_BUCKET_BOUND;
 import static org.mockito.Mockito.doReturn;
 
 import com.google.common.collect.ImmutableMap;
@@ -60,6 +61,7 @@ public class PrometheusStatsCollectorTest {
       MeasureDouble.create("measure", "description", "1");
   private static final TagKey K1 = TagKey.create("k1");
   private static final TagKey K2 = TagKey.create("k2");
+  private static final TagKey LE_TAG_KEY = TagKey.create(LABEL_NAME_BUCKET_BOUND);
   private static final TagValue V1 = TagValue.create("v1");
   private static final TagValue V2 = TagValue.create("v2");
   private static final DistributionData DISTRIBUTION_DATA =
@@ -67,11 +69,24 @@ public class PrometheusStatsCollectorTest {
   private static final View VIEW =
       View.create(
           VIEW_NAME, DESCRIPTION, MEASURE_DOUBLE, DISTRIBUTION, Arrays.asList(K1, K2), CUMULATIVE);
+  private static final View VIEW_WITH_LE_TAG_KEY =
+      View.create(
+          VIEW_NAME,
+          DESCRIPTION,
+          MEASURE_DOUBLE,
+          DISTRIBUTION,
+          Arrays.asList(K1, LE_TAG_KEY),
+          CUMULATIVE);
   private static final CumulativeData CUMULATIVE_DATA =
       CumulativeData.create(Timestamp.fromMillis(1000), Timestamp.fromMillis(2000));
   private static final ViewData VIEW_DATA =
       ViewData.create(
           VIEW, ImmutableMap.of(Arrays.asList(V1, V2), DISTRIBUTION_DATA), CUMULATIVE_DATA);
+  private static final ViewData VIEW_DATA_WITH_LE_TAG_KEY =
+      ViewData.create(
+          VIEW_WITH_LE_TAG_KEY,
+          ImmutableMap.of(Arrays.asList(V1, V2), DISTRIBUTION_DATA),
+          CUMULATIVE_DATA);
 
   @Mock private ViewManager mockViewManager;
 
@@ -94,13 +109,25 @@ public class PrometheusStatsCollectorTest {
                 "Opencensus Prometheus metrics: View description",
                 Arrays.asList(
                     new Sample(
-                        name + "_bucket", Arrays.asList("k1", "k2"), Arrays.asList("v1", "v2"), 0),
+                        name + "_bucket",
+                        Arrays.asList("k1", "k2", "le"),
+                        Arrays.asList("v1", "v2", "-5.0"),
+                        0),
                     new Sample(
-                        name + "_bucket", Arrays.asList("k1", "k2"), Arrays.asList("v1", "v2"), 2),
+                        name + "_bucket",
+                        Arrays.asList("k1", "k2", "le"),
+                        Arrays.asList("v1", "v2", "0.0"),
+                        2),
                     new Sample(
-                        name + "_bucket", Arrays.asList("k1", "k2"), Arrays.asList("v1", "v2"), 2),
+                        name + "_bucket",
+                        Arrays.asList("k1", "k2", "le"),
+                        Arrays.asList("v1", "v2", "5.0"),
+                        2),
                     new Sample(
-                        name + "_bucket", Arrays.asList("k1", "k2"), Arrays.asList("v1", "v2"), 1),
+                        name + "_bucket",
+                        Arrays.asList("k1", "k2", "le"),
+                        Arrays.asList("v1", "v2", "+Inf"),
+                        1),
                     new Sample(
                         name + "_count", Arrays.asList("k1", "k2"), Arrays.asList("v1", "v2"), 5),
                     new Sample(
@@ -111,6 +138,14 @@ public class PrometheusStatsCollectorTest {
   }
 
   @Test
+  public void testCollect_SkipDistributionViewWithLeTagKey() {
+    doReturn(ImmutableSet.of(VIEW_WITH_LE_TAG_KEY)).when(mockViewManager).getAllExportedViews();
+    doReturn(VIEW_DATA_WITH_LE_TAG_KEY).when(mockViewManager).getView(VIEW_NAME);
+    PrometheusStatsCollector collector = new PrometheusStatsCollector(mockViewManager);
+    assertThat(collector.collect()).isEmpty();
+  }
+
+  @Test
   public void testDescribe() {
     PrometheusStatsCollector collector = new PrometheusStatsCollector(mockViewManager);
     assertThat(collector.describe())