Add Support for Prometheus Native Histograms

implementations/micrometer-registry-prometheus_native/build.gradle

@@ -0,0 +1,15 @@
+repositories {
+    mavenLocal()
+    mavenCentral()
+}
+
+dependencies {
+    api project(':micrometer-core')
+
+    api 'io.prometheus:prometheus-metrics-core:1.0.0-alpha-2'
+    api 'io.prometheus:prometheus-metrics-model:1.0.0-alpha-2'
+    api 'io.prometheus:prometheus-metrics-exposition-formats:1.0.0-alpha-2'
+    api 'io.prometheus:prometheus-metrics-exporter-servlet-jakarta:1.0.0-alpha-2'
+
+    testImplementation project(':micrometer-test')
+}

implementations/micrometer-registry-prometheus_native/gradle.properties

@@ -0,0 +1 @@
+compatibleVersion=SKIP

implementations/micrometer-registry-prometheus_native/src/main/java/io/micrometer/prometheusnative/Max.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2023 VMware, Inc.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.prometheusnative;
+
+import io.micrometer.core.instrument.distribution.DistributionStatisticConfig;
+import io.prometheus.metrics.core.metrics.SlidingWindow;
+
+/**
+ * Micrometer distributions have a {@code max} value, which is not provided out-of-the-box
+ * by Prometheus histograms or summaries.
+ * <p>
+ * Max is used to track these {@code max} values.
+ */
+public class Max {
+
+    private static class MaxObserver {
+
+        private double current = Double.NaN;
+
+        public void observe(double value) {
+            if (Double.isNaN(current) || current < value) {
+                current = value;
+            }
+        }
+
+        public double get() {
+            return current;
+        }
+
+    }
+
+    private final SlidingWindow<MaxObserver> slidingWindow;
+
+    public Max(DistributionStatisticConfig config) {
+        long maxAgeSeconds = config.getExpiry() != null ? config.getExpiry().toMillis() / 1000L : 60;
+        int ageBuckets = config.getBufferLength() != null ? config.getBufferLength() : 3;
+        slidingWindow = new SlidingWindow<>(MaxObserver.class, MaxObserver::new, MaxObserver::observe, maxAgeSeconds,
+                ageBuckets);
+    }
+
+    public void observe(double value) {
+        slidingWindow.observe(value);
+    }
+
+    public double get() {
+        return slidingWindow.current().get();
+    }
+
+}

implementations/micrometer-registry-prometheus_native/src/main/java/io/micrometer/prometheusnative/PrometheusConfig.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2023 VMware, Inc.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.prometheusnative;
+
+import io.micrometer.core.instrument.config.MeterRegistryConfig;
+import io.prometheus.metrics.config.PrometheusProperties;
+
+public interface PrometheusConfig extends MeterRegistryConfig {
+
+    @Override
+    default String prefix() {
+        return "prometheus";
+    }
+
+    default PrometheusProperties getPrometheusProperties() {
+        // To be discussed: Make Prometheus properties configurable via Spring's
+        // application.properties
+        // under the `management.metrics.export.prometheus` prefix?
+        return PrometheusProperties.get();
+    }
+
+}

implementations/micrometer-registry-prometheus_native/src/main/java/io/micrometer/prometheusnative/PrometheusCounter.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2023 VMware, Inc.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.prometheusnative;
+
+import io.micrometer.common.lang.Nullable;
+import io.prometheus.metrics.core.datapoints.CounterDataPoint;
+import io.prometheus.metrics.core.metrics.Counter;
+import io.prometheus.metrics.model.snapshots.CounterSnapshot.CounterDataPointSnapshot;
+import io.prometheus.metrics.model.snapshots.Exemplar;
+
+public class PrometheusCounter extends PrometheusMeter<Counter, CounterDataPointSnapshot>
+        implements io.micrometer.core.instrument.Counter {
+
+    private final CounterDataPoint dataPoint;
+
+    PrometheusCounter(Id id, Counter counter, CounterDataPoint dataPoint) {
+        super(id, counter);
+        this.dataPoint = dataPoint;
+    }
+
+    @Override
+    public void increment(double amount) {
+        dataPoint.inc(amount);
+    }
+
+    @Override
+    public double count() {
+        return collect().getValue();
+    }
+
+    @Nullable
+    Exemplar exemplar() {
+        return collect().getExemplar();
+    }
+
+}

implementations/micrometer-registry-prometheus_native/src/main/java/io/micrometer/prometheusnative/PrometheusCounterWithCallback.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2023 VMware, Inc.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.prometheusnative;
+
+import io.micrometer.core.instrument.FunctionCounter;
+import io.prometheus.metrics.core.metrics.CounterWithCallback;
+import io.prometheus.metrics.model.snapshots.CounterSnapshot.CounterDataPointSnapshot;
+
+public class PrometheusCounterWithCallback extends PrometheusMeter<CounterWithCallback, CounterDataPointSnapshot>
+        implements FunctionCounter {
+
+    public PrometheusCounterWithCallback(Id id, CounterWithCallback counter) {
+        super(id, counter);
+    }
+
+    @Override
+    public double count() {
+        return collect().getValue();
+    }
+
+}

implementations/micrometer-registry-prometheus_native/src/main/java/io/micrometer/prometheusnative/PrometheusFunctionTimer.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2023 VMware, Inc.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.prometheusnative;
+
+import io.micrometer.core.instrument.FunctionTimer;
+import io.micrometer.core.instrument.Meter;
+import io.prometheus.metrics.core.metrics.SummaryWithCallback;
+import io.prometheus.metrics.model.snapshots.SummarySnapshot.SummaryDataPointSnapshot;
+
+import java.util.concurrent.TimeUnit;
+
+public class PrometheusFunctionTimer extends PrometheusMeter<SummaryWithCallback, SummaryDataPointSnapshot>
+        implements FunctionTimer {
+
+    public PrometheusFunctionTimer(Meter.Id id, SummaryWithCallback summary) {
+        super(id, summary);
+    }
+
+    @Override
+    public double count() {
+        return collect().getCount();
+    }
+
+    @Override
+    public double totalTime(TimeUnit unit) {
+        return toUnit(collect().getSum(), unit);
+    }
+
+    @Override
+    public TimeUnit baseTimeUnit() {
+        return TimeUnit.SECONDS;
+    }
+
+}

implementations/micrometer-registry-prometheus_native/src/main/java/io/micrometer/prometheusnative/PrometheusGaugeWithCallback.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2023 VMware, Inc.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.prometheusnative;
+
+import io.micrometer.core.instrument.Gauge;
+import io.prometheus.metrics.core.metrics.GaugeWithCallback;
+import io.prometheus.metrics.model.snapshots.GaugeSnapshot.GaugeDataPointSnapshot;
+
+public class PrometheusGaugeWithCallback extends PrometheusMeter<GaugeWithCallback, GaugeDataPointSnapshot>
+        implements Gauge {
+
+    public PrometheusGaugeWithCallback(Id id, GaugeWithCallback gauge) {
+        super(id, gauge);
+    }
+
+    @Override
+    public double value() {
+        return collect().getValue();
+    }
+
+}

implementations/micrometer-registry-prometheus_native/src/main/java/io/micrometer/prometheusnative/PrometheusHistogram.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2023 VMware, Inc.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.prometheusnative;
+
+import io.micrometer.core.instrument.DistributionSummary;
+import io.micrometer.core.instrument.distribution.HistogramSnapshot;
+import io.prometheus.metrics.core.datapoints.DistributionDataPoint;
+import io.prometheus.metrics.core.metrics.Histogram;
+import io.prometheus.metrics.model.snapshots.HistogramSnapshot.HistogramDataPointSnapshot;
+
+public class PrometheusHistogram extends PrometheusMeter<Histogram, HistogramDataPointSnapshot>
+        implements DistributionSummary {
+
+    private final Max max;
+
+    private final DistributionDataPoint dataPoint;
+
+    public PrometheusHistogram(Id id, Max max, Histogram histogram, DistributionDataPoint dataPoint) {
+        super(id, histogram);
+        this.max = max;
+        this.dataPoint = dataPoint;
+    }
+
+    @Override
+    public void record(double amount) {
+        dataPoint.observe(amount);
+        max.observe(amount);
+    }
+
+    @Override
+    public long count() {
+        return collect().getCount();
+    }
+
+    @Override
+    public double totalAmount() {
+        return collect().getSum();
+    }
+
+    @Override
+    public double max() {
+        return max.get();
+    }
+
+    @Override
+    public HistogramSnapshot takeSnapshot() {
+        return HistogramSnapshot.empty(count(), totalAmount(), max());
+    }
+
+}

implementations/micrometer-registry-prometheus_native/src/main/java/io/micrometer/prometheusnative/PrometheusInfoGauge.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2023 VMware, Inc.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.prometheusnative;
+
+import io.micrometer.core.instrument.Gauge;
+import io.micrometer.core.instrument.Meter;
+
+/**
+ * Prometheus Info metric.
+ * <p>
+ * Micrometer implements Info metrics as Gauge.
+ */
+public class PrometheusInfoGauge implements Gauge {
+
+    private final Meter.Id id;
+
+    public PrometheusInfoGauge(Id id) {
+        this.id = id;
+    }
+
+    @Override
+    public double value() {
+        return 1.0;
+    }
+
+    @Override
+    public Id getId() {
+        return id;
+    }
+
+}