Added support for GAUGE_LIST metric type

logstash-core/src/main/java/org/logstash/instrument/metrics/MetricType.java

@@ -68,6 +68,11 @@ public enum MetricType {
      */
     GAUGE_RUBYTIMESTAMP("gauge/rubytimestamp"),
 
+    /**
+     * A gauge backed by a {@link java.util.List} type.
+     */
+    GAUGE_LIST("gauge/list"),
+
     /**
      * A flow-rate {@link FlowMetric}, instantiated with one or more backing {@link Metric}{@code <Number>}.
      */

logstash-core/src/main/java/org/logstash/instrument/metrics/gauge/LazyDelegatingGauge.java

@@ -27,6 +27,7 @@
 import org.logstash.instrument.metrics.AbstractMetric;
 import org.logstash.instrument.metrics.MetricType;
 
+import java.util.List;
 import java.util.Optional;
 
 /**
@@ -117,6 +118,8 @@ private synchronized void wakeMetric(Object value) {
                 lazyMetric = new RubyHashGauge(key, (RubyHash) value);
             } else if (value instanceof RubyTimestamp) {
                 lazyMetric = new RubyTimeStampGauge(key, (RubyTimestamp) value);
+            } else if (value instanceof List<?>) {
+                lazyMetric = new ListGauge(key, (List<?>) value);
             } else {
                 LOGGER.warn("A gauge metric of an unknown type ({}) has been created for key: {}. This may result in invalid serialization.  It is recommended to " +
                         "log an issue to the responsible developer/development team.", value.getClass().getCanonicalName(), key);

logstash-core/src/main/java/org/logstash/instrument/metrics/gauge/ListGauge.java

@@ -0,0 +1,41 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *	http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+
+package org.logstash.instrument.metrics.gauge;
+
+import org.logstash.instrument.metrics.MetricType;
+
+import java.util.List;
+
+public class ListGauge extends AbstractGaugeMetric<List<?>> {
+
+    protected ListGauge(String name) {
+        super(name);
+    }
+
+    protected ListGauge(String name, List<?> initialValue) {
+        super(name, initialValue);
+    }
+
+    public MetricType getType() {
+        return MetricType.GAUGE_LIST;
+    }
+
+}

logstash-core/src/test/java/org/logstash/instrument/metrics/MetricTypeTest.java

@@ -47,6 +47,7 @@ public void ensurePassivity(){
         nameMap.put(MetricType.GAUGE_TEXT, "gauge/text");
         nameMap.put(MetricType.GAUGE_BOOLEAN, "gauge/boolean");
         nameMap.put(MetricType.GAUGE_NUMBER, "gauge/number");
+        nameMap.put(MetricType.GAUGE_LIST, "gauge/list");
         nameMap.put(MetricType.GAUGE_UNKNOWN, "gauge/unknown");
         nameMap.put(MetricType.GAUGE_RUBYHASH, "gauge/rubyhash");
         nameMap.put(MetricType.GAUGE_RUBYTIMESTAMP, "gauge/rubytimestamp");

logstash-core/src/test/java/org/logstash/instrument/metrics/gauge/LazyDelegatingGaugeTest.java

@@ -20,15 +20,17 @@
 
 package org.logstash.instrument.metrics.gauge;
 
-import java.net.URI;
-import java.util.Collections;
 import org.jruby.RubyHash;
 import org.junit.Test;
 import org.logstash.RubyUtil;
 import org.logstash.Timestamp;
 import org.logstash.ext.JrubyTimestampExtLibrary;
 import org.logstash.instrument.metrics.MetricType;
 
+import java.net.URI;
+import java.util.Collections;
+import java.util.List;
+
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
@@ -91,6 +93,11 @@ public void getValue() {
         assertThat(gauge.get()).isNull();
         assertThat(gauge.getType()).isNull();
 
+        //List
+        gauge = new LazyDelegatingGauge("bar", List.of("one", "two"));
+        assertThat(gauge.getValue().toString()).isEqualTo("[one, two]");
+        assertThat(gauge.getType()).isEqualTo(MetricType.GAUGE_LIST);
+
         assertThat(gauge.getName()).isNotEmpty();
     }
 
@@ -169,6 +176,13 @@ public void set() {
         gauge.set(null);
         assertThat(gauge.getValue()).isNull();
         assertThat(gauge.getType()).isEqualTo(MetricType.GAUGE_TEXT);
+
+        // List
+        gauge = new LazyDelegatingGauge("bar");
+        gauge.set(List.of(1,2));
+        assertThat(gauge.getValue().toString()).isEqualTo("[1, 2]");
+        assertThat(gauge.getType()).isEqualTo(MetricType.GAUGE_LIST);
+
     }
 
 }

logstash-core/src/test/java/org/logstash/instrument/metrics/gauge/ListGaugeTest.java

@@ -0,0 +1,82 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *	http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+
+package org.logstash.instrument.metrics.gauge;
+
+import org.jruby.RubyHash;
+import org.jruby.runtime.builtin.IRubyObject;
+import org.junit.Test;
+import org.logstash.RubyUtil;
+import org.logstash.instrument.metrics.MetricType;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Unit tests for {@link TextGauge}
+ */
+public class ListGaugeTest {
+    @Test
+    public void getSetStrings() {
+        ListGauge gauge = new ListGauge("bar");
+        gauge.set(List.of("pipeline_name1", "pipeline_name2"));
+        assertThat(gauge.getValue().toString()).isEqualTo("[pipeline_name1, pipeline_name2]");
+        assertThat(gauge.getType()).isEqualTo(MetricType.GAUGE_LIST);
+    }
+
+    @Test
+    public void getSetNull() {
+        ListGauge gauge = new ListGauge("bar");
+        gauge.set(null);
+        assertThat(gauge.getValue()).isNull();
+        assertThat(gauge.getType()).isEqualTo(MetricType.GAUGE_LIST);
+    }
+
+    @Test
+    public void getSetListOfNull() {
+        List<Object> nullList = new ArrayList<>(Collections.nCopies(2, null));
+        ListGauge gauge = new ListGauge("bar");
+        gauge.set(nullList);
+        assertThat(gauge.getValue().toString()).isEqualTo("[null, null]");
+        assertThat(gauge.getType()).isEqualTo(MetricType.GAUGE_LIST);
+    }
+
+    @Test
+    public void getSetHash() {
+        IRubyObject[] args = {RubyUtil.RUBY.newString("k"), RubyUtil.RUBY.newString("v")};
+        RubyHash rubyHash = RubyHash.newHash(RubyUtil.RUBY, args[0], args[1]);
+
+        ListGauge gauge = new ListGauge("bar");
+        gauge.set(List.of(rubyHash));
+        assertThat(gauge.getValue().toString()).isEqualTo("[{\"k\"=>\"v\"}]");
+        assertThat(gauge.getType()).isEqualTo(MetricType.GAUGE_LIST);
+    }
+
+    @Test
+    public void getSetNumber() {
+        ListGauge gauge = new ListGauge("bar");
+        gauge.set(List.of(123, 456.7));
+        assertThat(gauge.getValue().toString()).isEqualTo("[123, 456.7]");
+        assertThat(gauge.getType()).isEqualTo(MetricType.GAUGE_LIST);
+    }
+}