fix micrometer invalid double values (#1419)

* fix micrometer invalid double values

Author: SylvainJuge

CHANGELOG.asciidoc

@@ -36,6 +36,7 @@ endif::[]
 * Eliminate `unsupported class version error` messages related to loading the Java 11 HttpClient plugin in pre-Java-11 JVMs {pull}1397[1397]
 * Fix rejected metric events by APM Server with response code 400 due to data validation error - sanitizing Micrometer
 metricset tag keys - {pull}1413[1413]
+* Fix invalid micrometer metrics with non-numeric values {pull}1419[1419]
 * Fix `NoClassDefFoundError` with JDBC instrumentation plugin {pull}1409[1409]
 
 [[release-notes-1.x]]

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

@@ -27,7 +27,6 @@
 import co.elastic.apm.agent.report.serialize.DslJsonSerializer;
 import com.dslplatform.json.DslJson;
 import com.dslplatform.json.JsonWriter;
-import com.dslplatform.json.Nullable;
 import com.dslplatform.json.NumberConverter;
 import io.micrometer.core.instrument.Counter;
 import io.micrometer.core.instrument.DistributionSummary;
@@ -116,10 +115,15 @@ static void serializeMetricSet(List<Tag> tags, List<Meter> meters, long epochMic
                         serializeDistributionSummary(jw, timer.getId(), timer.count(), timer.totalAmount());
                         hasValue = true;
                     } else if (meter instanceof Gauge) {
-                        if (hasValue) jw.writeByte(JsonWriter.COMMA);
                         Gauge gauge = (Gauge) meter;
-                        serializeValue(gauge.getId(), gauge.value(), jw);
-                        hasValue = true;
+
+                        // gauge values can be Double.NaN or +/-Infinite
+                        if (isValidValue(gauge.value())) {
+                            if (hasValue) jw.writeByte(JsonWriter.COMMA);
+                            serializeValue(gauge.getId(), gauge.value(), jw);
+                            hasValue = true;
+                        }
+
                     } else if (meter instanceof Counter) {
                         if (hasValue) jw.writeByte(JsonWriter.COMMA);
                         Counter counter = (Counter) meter;
@@ -198,4 +202,8 @@ private static void serializeValueStart(String key, String suffix, JsonWriter jw
         jw.writeByte(JsonWriter.QUOTE);
         jw.writeByte(JsonWriter.SEMI);
     }
+
+    private static boolean isValidValue(double value) {
+        return !Double.isNaN(value) && !Double.isInfinite(value);
+    }
 }

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

@@ -229,6 +229,23 @@ void testDistributionSummary() {
         assertThat(metricSet.get("metricset").get("samples").get("timer.sum").get("value").longValue()).isEqualTo(3);
     }
 
+    @Test
+    void tryToSerializeInvalidGaugeValues() {
+        for (Double invalidValue : Arrays.asList(Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY, Double.NaN)) {
+            List<Tag> tags = List.of(Tag.of("foo", "bar"));
+            meterRegistry.gauge("gauge1", tags, 42, v -> invalidValue);
+            meterRegistry.gauge("gauge2", tags, 42, v -> 42D);
+            JsonNode metricSet = getSingleMetricSet();
+            assertThat(metricSet.get("metricset").get("samples").get("gauge1"))
+                .describedAs("value of %s is not expected to be written to json", invalidValue)
+                .isNull();
+
+            // serialization should handle ignoring the 1st value
+            assertThat(metricSet.get("metricset").get("samples").get("gauge2").get("value").doubleValue())
+                .isEqualTo(42D);
+        }
+    }
+
     private JsonNode getSingleMetricSet() {
         List<JsonNode> metricSets = getMetricSets();
         assertThat(metricSets).hasSize(1);