Make per-meter OTLP configuration more flexible

Allow users to configure in more ways than an exact match on the meter name.

Author: shakuzen

Diff for: implementations/micrometer-registry-otlp/src/main/java/io/micrometer/registry/otlp/OtlpConfig.java

@@ -15,6 +15,7 @@
  */
 package io.micrometer.registry.otlp;
 
+import io.micrometer.core.instrument.Meter;
 import io.micrometer.core.instrument.config.InvalidConfigurationException;
 import io.micrometer.core.instrument.config.validate.Validated;
 import io.micrometer.core.instrument.push.PushRegistryConfig;
@@ -23,6 +24,7 @@
 import java.net.URLDecoder;
 import java.util.*;
 import java.util.concurrent.TimeUnit;
+import java.util.function.Function;
 import java.util.stream.Collectors;
 
 import static io.micrometer.core.instrument.config.MeterRegistryConfigValidator.*;
@@ -229,15 +231,16 @@ default HistogramFlavor histogramFlavor() {
 
     /**
      * Configures the histogram flavor to use on a per-meter level. This will override the
-     * {@link #histogramFlavor()} configuration for matching Meters. The key is used to do
-     * an exact match on the Meter's name.
-     * @return mapping of meter name to histogram flavor
+     * {@link #histogramFlavor()} configuration for matching Meters. By default, the key
+     * is used to do an exact match on the Meter's name.
+     * @return mapping of meter ID to histogram flavor
      * @since 1.15.0
      * @see #histogramFlavor()
      */
-    default Map<String, HistogramFlavor> histogramFlavorPerMeter() {
-        return getStringMap(this, "histogramFlavorPerMeter", HistogramFlavor::fromString)
-            .orElse(Collections.emptyMap());
+    default Function<Meter.Id, HistogramFlavor> histogramFlavorPerMeter() {
+        return id -> getStringMap(this, "histogramFlavorPerMeter", HistogramFlavor::fromString)
+            .orElse(Collections.emptyMap())
+            .getOrDefault(id.getName(), histogramFlavor());
     }
 
     /**
@@ -267,15 +270,16 @@ default int maxBucketCount() {
 
     /**
      * Configures the max bucket count to use on a per-meter level. This will override the
-     * {@link #maxBucketCount()} configuration for matching Meters. The key is used to do
-     * an exact match on the Meter's name. This has no effect on a meter if it does not
-     * have an exponential bucket histogram configured.
-     * @return mapping of meter name to max bucket count
+     * {@link #maxBucketCount()} configuration for matching Meters. By default, the key is
+     * used to do an exact match on the Meter's name. This has no effect on a meter if it
+     * does not have an exponential bucket histogram configured.
+     * @return mapping of meter ID to max bucket count
      * @since 1.15.0
      * @see #maxBucketCount()
      */
-    default Map<String, Integer> maxBucketsPerMeter() {
-        return getStringMap(this, "maxBucketsPerMeter", Integer::parseInt).orElse(Collections.emptyMap());
+    default Function<Meter.Id, Integer> maxBucketsPerMeter() {
+        return id -> getStringMap(this, "maxBucketsPerMeter", Integer::parseInt).orElse(Collections.emptyMap())
+            .getOrDefault(id.getName(), maxBucketCount());
     }
 
     @Override

Diff for: implementations/micrometer-registry-otlp/src/main/java/io/micrometer/registry/otlp/OtlpMeterRegistry.java

@@ -430,13 +430,12 @@ private Histogram getHistogram(Meter.Id id, DistributionStatisticConfig distribu
     }
 
     private int getMaxBuckets(Meter.Id id) {
-        return config.maxBucketsPerMeter().getOrDefault(id.getName(), config.maxBucketCount());
+        return config.maxBucketsPerMeter().apply(id);
     }
 
     private HistogramFlavor histogramFlavor(Meter.Id id, OtlpConfig otlpConfig,
             DistributionStatisticConfig distributionStatisticConfig) {
-        HistogramFlavor preferredHistogramFlavor = otlpConfig.histogramFlavorPerMeter()
-            .getOrDefault(id.getName(), otlpConfig.histogramFlavor());
+        HistogramFlavor preferredHistogramFlavor = otlpConfig.histogramFlavorPerMeter().apply(id);
 
         final double[] serviceLevelObjectiveBoundaries = distributionStatisticConfig
             .getServiceLevelObjectiveBoundaries();

Diff for: implementations/micrometer-registry-otlp/src/test/java/io/micrometer/registry/otlp/OtlpConfigTest.java

@@ -15,6 +15,8 @@
  */
 package io.micrometer.registry.otlp;
 
+import io.micrometer.core.instrument.Meter;
+import io.micrometer.core.instrument.Tags;
 import io.micrometer.core.instrument.config.InvalidConfigurationException;
 import org.junit.jupiter.api.Test;
 
@@ -23,9 +25,10 @@
 import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
+import java.util.function.Function;
 import java.util.stream.Stream;
 
-import static java.util.Map.entry;
+import static io.micrometer.core.instrument.config.validate.PropertyValidator.getStringMap;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static uk.org.webcompere.systemstubs.SystemStubs.withEnvironmentVariable;
@@ -284,9 +287,47 @@ void histogramFlavorPerMeter() {
                 "a.b.c=explicit_bucket_histogram ,expo =base2_exponential_bucket_histogram");
         OtlpConfig otlpConfig = properties::get;
         assertThat(otlpConfig.validate().isValid()).isTrue();
-        assertThat(otlpConfig.histogramFlavorPerMeter()).containsExactly(
-                entry("a.b.c", HistogramFlavor.EXPLICIT_BUCKET_HISTOGRAM),
-                entry("expo", HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM));
+        assertThat(otlpConfig.histogramFlavorPerMeter().apply(idWithName("a.b.c")))
+            .isEqualTo(HistogramFlavor.EXPLICIT_BUCKET_HISTOGRAM);
+        assertThat(otlpConfig.histogramFlavorPerMeter().apply(idWithName("expo")))
+            .isEqualTo(HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM);
+    }
+
+    @Test
+    void customHistogramFlavorPerMeterFunction() {
+        Map<String, String> properties = new HashMap<>();
+        properties.put("otlp.histogramFlavorPerMeter",
+                "a.b.c=explicit_bucket_histogram,expo=base2_exponential_bucket_histogram");
+        OtlpConfig otlpConfig = new OtlpConfig() {
+            @Override
+            public String get(String key) {
+                return properties.get(key);
+            }
+
+            @Override
+            public Function<Meter.Id, HistogramFlavor> histogramFlavorPerMeter() {
+                return id -> {
+                    Map<String, HistogramFlavor> histogramFlavorPerMeter = getStringMap(this, "histogramFlavorPerMeter",
+                            HistogramFlavor::fromString)
+                        .orElse(Collections.emptyMap());
+                    for (Map.Entry<String, HistogramFlavor> entry : histogramFlavorPerMeter.entrySet()) {
+                        if (id.getName().startsWith(entry.getKey())) {
+                            return entry.getValue();
+                        }
+                    }
+                    return histogramFlavor();
+                };
+            }
+        };
+        assertThat(otlpConfig.validate().isValid()).isTrue();
+        assertThat(otlpConfig.histogramFlavorPerMeter().apply(idWithName("something")))
+            .isEqualTo(otlpConfig.histogramFlavor());
+        assertThat(otlpConfig.histogramFlavorPerMeter().apply(idWithName("a.b.c")))
+            .isEqualTo(HistogramFlavor.EXPLICIT_BUCKET_HISTOGRAM);
+        assertThat(otlpConfig.histogramFlavorPerMeter().apply(idWithName("expo")))
+            .isEqualTo(HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM);
+        assertThat(otlpConfig.histogramFlavorPerMeter().apply(idWithName("expo.other")))
+            .isEqualTo(HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM);
     }
 
     @Test
@@ -295,7 +336,11 @@ void maxBucketsPerMeter() {
         properties.put("otlp.maxBucketsPerMeter", "a.b.c = 10");
         OtlpConfig otlpConfig = properties::get;
         assertThat(otlpConfig.validate().isValid()).isTrue();
-        assertThat(otlpConfig.maxBucketsPerMeter()).containsExactly(entry("a.b.c", 10));
+        assertThat(otlpConfig.maxBucketsPerMeter().apply(idWithName("a.b.c"))).isEqualTo(10);
+    }
+
+    Meter.Id idWithName(String name) {
+        return new Meter.Id(name, Tags.empty(), null, null, Meter.Type.OTHER);
     }
 
 }

Diff for: implementations/micrometer-registry-otlp/src/test/java/io/micrometer/registry/otlp/OtlpMeterRegistryTest.java

@@ -31,6 +31,7 @@
 import java.time.Duration;
 import java.util.*;
 import java.util.concurrent.TimeUnit;
+import java.util.function.Function;
 import java.util.stream.IntStream;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -427,8 +428,9 @@ public HistogramFlavor histogramFlavor() {
             }
 
             @Override
-            public Map<String, HistogramFlavor> histogramFlavorPerMeter() {
-                return Collections.singletonMap("expo", HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM);
+            public Function<Meter.Id, HistogramFlavor> histogramFlavorPerMeter() {
+                return id -> id.getName().equals("expo") ? HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM
+                        : histogramFlavor();
             }
         };
         OtlpMeterRegistry meterRegistry = new OtlpMeterRegistry(config, clock);
@@ -477,8 +479,8 @@ public int maxBucketCount() {
             }
 
             @Override
-            public Map<String, Integer> maxBucketsPerMeter() {
-                return Collections.singletonMap("low.variation", 15);
+            public Function<Meter.Id, Integer> maxBucketsPerMeter() {
+                return id -> id.getName().equals("low.variation") ? 15 : maxBucketCount();
             }
         };
         OtlpMeterRegistry meterRegistry = new OtlpMeterRegistry(config, clock);