Make DistributionStatisticConfig extensible

micrometer-core/src/main/java/io/micrometer/core/instrument/distribution/DistributionStatisticConfig.java

@@ -20,6 +20,7 @@
 import io.micrometer.core.instrument.internal.Mergeable;
 
 import java.time.Duration;
+import java.util.Arrays;
 import java.util.NavigableSet;
 import java.util.TreeSet;
 import java.util.stream.LongStream;
@@ -71,6 +72,25 @@ public class DistributionStatisticConfig implements Mergeable<DistributionStatis
     @Nullable
     private Integer bufferLength;
 
+    public DistributionStatisticConfig() {
+    }
+
+    public DistributionStatisticConfig(DistributionStatisticConfig original) {
+        percentileHistogram = original.percentileHistogram;
+        if (original.percentiles != null) {
+            percentiles = Arrays.copyOf(original.percentiles, original.percentiles.length);
+        }
+        percentilePrecision = original.percentilePrecision;
+        if (original.serviceLevelObjectives != null) {
+            serviceLevelObjectives = Arrays.copyOf(original.serviceLevelObjectives,
+                    original.serviceLevelObjectives.length);
+        }
+        minimumExpectedValue = original.minimumExpectedValue;
+        maximumExpectedValue = original.maximumExpectedValue;
+        expiry = original.expiry;
+        bufferLength = original.bufferLength;
+    }
+
     public static Builder builder() {
         return new Builder();
     }
@@ -271,7 +291,15 @@ public double[] getServiceLevelObjectiveBoundaries() {
 
     public static class Builder {
 
-        private final DistributionStatisticConfig config = new DistributionStatisticConfig();
+        protected final DistributionStatisticConfig config;
+
+        public Builder() {
+            config = new DistributionStatisticConfig();
+        }
+
+        protected Builder(DistributionStatisticConfig config) {
+            this.config = config;
+        }
 
         public Builder percentilesHistogram(@Nullable Boolean enabled) {
             config.percentileHistogram = enabled;
@@ -455,11 +483,11 @@ public Builder bufferLength(@Nullable Integer bufferLength) {
          * @return A new immutable distribution configuration.
          */
         public DistributionStatisticConfig build() {
-            validate(config);
+            validate();
             return config;
         }
 
-        private void validate(DistributionStatisticConfig distributionStatisticConfig) {
+        protected void validate() {
             if (config.bufferLength != null && config.bufferLength <= 0) {
                 rejectConfig("bufferLength (" + config.bufferLength + ") must be greater than zero");
             }
@@ -487,8 +515,8 @@ private void validate(DistributionStatisticConfig distributionStatisticConfig) {
                         + ").");
             }
 
-            if (distributionStatisticConfig.getServiceLevelObjectiveBoundaries() != null) {
-                for (double slo : distributionStatisticConfig.getServiceLevelObjectiveBoundaries()) {
+            if (config.getServiceLevelObjectiveBoundaries() != null) {
+                for (double slo : config.getServiceLevelObjectiveBoundaries()) {
                     if (slo <= 0) {
                         rejectConfig("serviceLevelObjectiveBoundaries must contain only the values greater than 0. "
                                 + "Found " + slo);
@@ -497,7 +525,7 @@ private void validate(DistributionStatisticConfig distributionStatisticConfig) {
             }
         }
 
-        private static void rejectConfig(String msg) {
+        protected static void rejectConfig(String msg) {
             throw new InvalidConfigurationException("Invalid distribution configuration: " + msg);
         }
 

micrometer-core/src/test/java/io/micrometer/core/instrument/distribution/DistributionStatisticConfigExtensibilityTest.java

@@ -0,0 +1,155 @@
+/*
+ * 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.core.instrument.distribution;
+
+import io.micrometer.common.lang.Nullable;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class DistributionStatisticConfigExtensibilityTest {
+
+    static class SubDistributionStatisticConfig extends DistributionStatisticConfig {
+
+        public static final SubDistributionStatisticConfig NONE = subBuilder().build();
+
+        @Nullable
+        protected String extraParam;
+
+        @Nullable
+        public String getExtraParam() {
+            return extraParam;
+        }
+
+        SubDistributionStatisticConfig() {
+            super();
+        }
+
+        SubDistributionStatisticConfig(DistributionStatisticConfig original) {
+            super(original);
+            if (original instanceof SubDistributionStatisticConfig) {
+                extraParam = ((SubDistributionStatisticConfig) original).extraParam;
+            }
+        }
+
+        @Override
+        public SubDistributionStatisticConfig merge(DistributionStatisticConfig parent) {
+            DistributionStatisticConfig mergeBySuper = super.merge(parent);
+            SubDistributionStatisticConfig sub = new SubDistributionStatisticConfig(mergeBySuper);
+            if (extraParam == null && parent instanceof SubDistributionStatisticConfig) {
+                sub.extraParam = ((SubDistributionStatisticConfig) parent).extraParam;
+            }
+            else {
+                sub.extraParam = extraParam;
+            }
+            return sub;
+        }
+
+        public static SubBuilder subBuilder() {
+            return new SubBuilder(new SubDistributionStatisticConfig());
+        }
+
+        public static class SubBuilder extends Builder {
+
+            protected SubBuilder(SubDistributionStatisticConfig config) {
+                super(config);
+            }
+
+            public SubBuilder extraParam(@Nullable String extraParam) {
+                ((SubDistributionStatisticConfig) config).extraParam = extraParam;
+                return this;
+            }
+
+            @Override
+            protected void validate() {
+                super.validate();
+                if ("baz".equals(((SubDistributionStatisticConfig) config).extraParam)) {
+                    rejectConfig("No bazzing here");
+                }
+            }
+
+            @Override
+            public SubDistributionStatisticConfig build() {
+                return (SubDistributionStatisticConfig) super.build();
+            }
+
+        }
+
+    }
+
+    @Test
+    void mergeFromSuper() {
+        DistributionStatisticConfig origin = DistributionStatisticConfig.builder()
+            .percentiles(0.5, 0.9)
+            .serviceLevelObjectives(1.5, 2.5)
+            .percentilePrecision(2)
+            .percentilesHistogram(true)
+            .build();
+        SubDistributionStatisticConfig extra = (SubDistributionStatisticConfig) SubDistributionStatisticConfig
+            .subBuilder()
+            .extraParam("foo")
+            .percentiles(0.5, 0.9, 0.99)
+            .build();
+        DistributionStatisticConfig merged = origin.merge(extra);
+        assertEquals(2, merged.getPercentilePrecision());
+        assertEquals(Boolean.TRUE, merged.isPercentileHistogram());
+        assertArrayEquals(new double[] { 0.5, 0.9 }, merged.getPercentiles());
+        assertFalse(merged instanceof SubDistributionStatisticConfig);
+    }
+
+    @Test
+    void mergeFromSub() {
+        DistributionStatisticConfig origin = DistributionStatisticConfig.builder()
+            .percentiles(0.5, 0.9)
+            .serviceLevelObjectives(1.5, 2.5)
+            .percentilePrecision(2)
+            .percentilesHistogram(true)
+            .build();
+        SubDistributionStatisticConfig extra = (SubDistributionStatisticConfig) SubDistributionStatisticConfig
+            .subBuilder()
+            .extraParam("foo")
+            .percentiles(0.5, 0.9, 0.99)
+            .build();
+        SubDistributionStatisticConfig merged = extra.merge(origin);
+        assertEquals(2, merged.getPercentilePrecision());
+        assertEquals(Boolean.TRUE, merged.isPercentileHistogram());
+        assertArrayEquals(new double[] { 0.5, 0.9, 0.99 }, merged.getPercentiles());
+        assertEquals("foo", merged.getExtraParam());
+    }
+
+    @Test
+    void mergeSubsTogether() {
+        SubDistributionStatisticConfig origin = (SubDistributionStatisticConfig) SubDistributionStatisticConfig
+            .subBuilder()
+            .extraParam("bar")
+            .percentiles(0.5, 0.9)
+            .serviceLevelObjectives(1.5, 2.5)
+            .percentilePrecision(2)
+            .percentilesHistogram(true)
+            .build();
+        SubDistributionStatisticConfig extra = (SubDistributionStatisticConfig) SubDistributionStatisticConfig
+            .subBuilder()
+            .extraParam("foo")
+            .percentiles(0.5, 0.9, 0.99)
+            .build();
+        SubDistributionStatisticConfig merged = origin.merge(extra);
+        assertEquals(2, merged.getPercentilePrecision());
+        assertEquals(Boolean.TRUE, merged.isPercentileHistogram());
+        assertArrayEquals(new double[] { 0.5, 0.9 }, merged.getPercentiles());
+        assertEquals("bar", merged.getExtraParam());
+    }
+
+}