fix empty histograms from micrometer being sent to the server (#3304)

* fix empty histograms from micrometer being sent to the server * update changelog

Author: jackshirazi

CHANGELOG.asciidoc

@@ -35,7 +35,7 @@ Use subheadings with the "=====" level for adding notes for unreleased changes:
 ===== Bug fixes
 * Prevent bad serialization in edge cases for span compression - {pull}3293[#3293]
 * Allow overriding of transaction type for Servlet-API transactions - {pull}3226[#3226]
-* Fix micrometer histogram serialization - {pull}3290[#3290]
+* Fix micrometer histogram serialization - {pull}3290[#3290], {pull}3304[#3304]
 * Fix transactions not being correctly handled in certain edge cases - {pull}3294[#3294]
 
 [float]

apm-agent-plugins/apm-micrometer-plugin/src/main/java/co/elastic/apm/agent/micrometer/MicrometerMeterRegistrySerializer.java

@@ -201,7 +201,7 @@ private static boolean serializeTimer(JsonWriter jw, HistogramSnapshot histogram
  serializeValue(id, ".count", count, jw, replaceBuilder, dedotMetricName);
  jw.writeByte(JsonWriter.COMMA);
  serializeValue(id, ".sum.us", totalTime, jw, replaceBuilder, dedotMetricName);
- if (histogramSnapshot != null) {
+ if (histogramSnapshot != null && histogramSnapshot.histogramCounts().length > 0) {
  jw.writeByte(JsonWriter.COMMA);
  serializeHistogram(id, histogramSnapshot, jw, replaceBuilder, dedotMetricName);
  }
@@ -229,8 +229,10 @@ private static boolean serializeDistributionSummary(JsonWriter jw, HistogramSnap
  serializeValue(id, ".count", count, jw, replaceBuilder, dedotMetricName);
  jw.writeByte(JsonWriter.COMMA);
  serializeValue(id, ".sum", totalAmount, jw, replaceBuilder, dedotMetricName);
- jw.writeByte(JsonWriter.COMMA);
- serializeHistogram(id, histogramSnapshot, jw, replaceBuilder, dedotMetricName);
+ if (histogramSnapshot != null && histogramSnapshot.histogramCounts().length > 0) {
+ jw.writeByte(JsonWriter.COMMA);
+ serializeHistogram(id, histogramSnapshot, jw, replaceBuilder, dedotMetricName);
+ }
  return true;
  }
  return hasValue;

apm-agent-plugins/apm-micrometer-plugin/src/test/java/co/elastic/apm/agent/micrometer/MicrometerMeterRegistrySerializerTest.java

@@ -80,6 +80,11 @@ void serializeDistributionSummary() {
  serializeOneMeter(new TestSummary());
  }
 
+ @Test
+ void serializeDistributionSummaryWithNoValues() {
+ serializeOneMeter(new TestSummary(false));
+ }
+
  @Test
  void serializeGauge() {
  serializeOneMeter(new TestGauge());
@@ -201,9 +206,18 @@ protected static void checkPathHasValue(JsonNode jsonNode, String[] path, int va
  }
 
  protected static JsonNode getPathNode(JsonNode jsonNode, String[] path) {
+ return getPathNode(jsonNode, path, false);
+ }
+ protected static JsonNode getPathNode(JsonNode jsonNode, String[] path, boolean isNull) {
  assertThat(jsonNode).isNotNull();
- for (String element: path) {
- jsonNode = jsonNode.get(element);
+ for (int i = 0; i < path.length-1; i++) {
+ jsonNode = jsonNode.get(path[i]);
+ assertThat(jsonNode).isNotNull();
+ }
+ jsonNode = jsonNode.get(path[path.length-1]);
+ if (isNull) {
+ assertThat(jsonNode).isNull();
+ } else {
  assertThat(jsonNode).isNotNull();
  }
  return jsonNode;
@@ -261,26 +275,42 @@ public void checkSerialization(JsonNode jsonNode) {
  }
 
  static class TestSummary extends TestMeter {
+ private final boolean setSLOs;
  int sum = 0;
  int count = 0;
  int under5Count = 0;
  int from5To50Count = 0;
  int from50to95Count = 0;
  int[] values = new int[]{22, 55, 66, 98};
 
+ public TestSummary () {
+ this(true);
+ }
+ public TestSummary (boolean setSLOs) {
+ super();
+ this.setSLOs = setSLOs;
+ }
  @Override
  String meternameExtension() {
  return ".count";
  }
 
  @Override
  public void addToMeterRegistry(MeterRegistry registry) {
- meter = DistributionSummary
- .builder(metername())
- .distributionStatisticBufferLength(20)
- .serviceLevelObjectives(5, 50, 95)
- .publishPercentileHistogram()
- .register(registry);
+ if (setSLOs) {
+ meter = DistributionSummary
+ .builder(metername())
+ .distributionStatisticBufferLength(20)
+ .serviceLevelObjectives(5, 50, 95)
+ .publishPercentileHistogram()
+ .register(registry);
+ } else {
+ meter = DistributionSummary
+ .builder(metername())
+ .distributionStatisticBufferLength(20)
+ .publishPercentileHistogram()
+ .register(registry);
+ }
  }
 
  @Override
@@ -303,9 +333,20 @@ public void populateValues() {
  public void checkSerialization(JsonNode jsonNode) {
  checkPathHasValue(jsonNode, path(), count);
  checkPathHasValue(jsonNode, path(".sum"), sum);
- String[] path = path(".histogram");
- path[3] = "values";
- JsonNode histoNode1 = getPathNode(jsonNode, path);
+ String[] temppath = path(".histogram");
+ String[] path;
+ if (!setSLOs) {
+ path = new String[temppath.length-1];
+ System.arraycopy(temppath, 0, path, 0, path.length);
+ } else {
+ path = temppath;
+ path[3] = "values";
+ }
+ JsonNode histoNode1 = getPathNode(jsonNode, path, !setSLOs);
+ if(!setSLOs) {
+ assertThat(histoNode1).isNull();
+ return;
+ }
  assertThat(histoNode1.isArray()).isTrue();
  assertThat(histoNode1.size()).isEqualTo(3); //the 3 bucket boundaries of the SLOs 5,50,95
  assertThat(histoNode1.get(0).asDouble()).isEqualTo(5.0);