Make per-meter OTLP configuration more flexible

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

@@ -15,12 +15,13 @@
  */
 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;
 
-import java.time.Duration;
 import java.net.URLDecoder;
+import java.time.Duration;
 import java.util.*;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
@@ -228,18 +229,40 @@ 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.
+     * Configures the histogram flavor mapping to use on a per-meter level. This can
+     * override the {@link #histogramFlavor()} configuration for matching Meters. By
+     * default, {@link #histogramFlavorPerMeter(Meter.Id)} uses the result of this method
+     * to look up the {@link HistogramFlavor} by {@link Meter.Id} (exact match on the
+     * Meter's name by default). This means that this method provides the data while
+     * {@link #histogramFlavorPerMeter(Meter.Id)} provides the logic for the lookup, and
+     * you can override them independently.
      * @return mapping of meter name to histogram flavor
      * @since 1.15.0
+     * @see #histogramFlavorPerMeter(Meter.Id)
      * @see #histogramFlavor()
      */
     default Map<String, HistogramFlavor> histogramFlavorPerMeter() {
         return getStringMap(this, "histogramFlavorPerMeter", HistogramFlavor::fromString)
             .orElse(Collections.emptyMap());
     }
 
+    /**
+     * Looks up the histogram flavor to use on a per-meter level. This will override the
+     * {@link #histogramFlavor()} lookup behavior for matching Meters. By default, the key
+     * is used to do an exact match on the Meter's name in the map that
+     * {@link #histogramFlavorPerMeter()} returns. This means that
+     * {@link #histogramFlavorPerMeter()} provides the data while this method provides the
+     * logic for the lookup, and you can override them independently.
+     * @param id the {@link Meter.Id} the {@link HistogramFlavor} is configured for
+     * @return the histogram flavor mapped to the {@link Meter.Id}
+     * @since 1.15.0
+     * @see #histogramFlavorPerMeter()
+     * @see #histogramFlavor()
+     */
+    default HistogramFlavor histogramFlavorPerMeter(Meter.Id id) {
+        return histogramFlavorPerMeter().getOrDefault(id.getName(), histogramFlavor());
+    }
+
     /**
      * Max scale to use for exponential histograms, if configured.
      * @return maxScale
@@ -266,18 +289,41 @@ 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.
+     * Configures the max bucket count mapping to use on a per-meter level. This can
+     * override the {@link #maxBucketCount()} configuration for matching Meters. By
+     * default {@link #maxBucketsPerMeter(Meter.Id)} uses the result of this method to
+     * look up the max bucket count by {@link Meter.Id} (exact match on the Meter's name
+     * by default). This means that this method provides the data while
+     * {@link #maxBucketsPerMeter(Meter.Id)} provides the logic for the lookup, and you
+     * can override them independently. 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
      * @since 1.15.0
+     * @see #maxBucketsPerMeter(Meter.Id)
      * @see #maxBucketCount()
      */
     default Map<String, Integer> maxBucketsPerMeter() {
         return getStringMap(this, "maxBucketsPerMeter", Integer::parseInt).orElse(Collections.emptyMap());
     }
 
+    /**
+     * Looks up the max bucket count to use on a per-meter level. This will override the
+     * {@link #maxBucketCount()} lookup behavior for matching Meters. By default, the key
+     * is used to do an exact match on the Meter's name in the map that
+     * {@link #maxBucketsPerMeter()} returns. This means that
+     * {@link #maxBucketsPerMeter()} provides the data while this method provides the
+     * logic for the lookup, and you can override them independently. This has no effect
+     * on a meter if it does not have an exponential bucket histogram configured.
+     * @param id the {@link Meter.Id} the max bucket count is configured for
+     * @return the max bucket count mapped to the {@link Meter.Id}
+     * @since 1.15.0
+     * @see #maxBucketsPerMeter()
+     * @see #maxBucketCount()
+     */
+    default Integer maxBucketsPerMeter(Meter.Id id) {
+        return maxBucketsPerMeter().getOrDefault(id.getName(), maxBucketCount());
+    }
+
     @Override
     default Validated<?> validate() {
         return checkAll(this, c -> PushRegistryConfig.validate(c), checkRequired("url", OtlpConfig::url),

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

@@ -18,8 +18,8 @@
 import io.micrometer.common.lang.Nullable;
 import io.micrometer.common.util.internal.logging.InternalLogger;
 import io.micrometer.common.util.internal.logging.InternalLoggerFactory;
-import io.micrometer.core.instrument.Timer;
 import io.micrometer.core.instrument.*;
+import io.micrometer.core.instrument.Timer;
 import io.micrometer.core.instrument.config.NamingConvention;
 import io.micrometer.core.instrument.distribution.*;
 import io.micrometer.core.instrument.distribution.pause.PauseDetector;
@@ -430,13 +430,15 @@ private Histogram getHistogram(Meter.Id id, DistributionStatisticConfig distribu
     }
 
     private int getMaxBuckets(Meter.Id id) {
-        return config.maxBucketsPerMeter().getOrDefault(id.getName(), config.maxBucketCount());
+        Integer perMeterMaxBuckets = config.maxBucketsPerMeter(id);
+        return perMeterMaxBuckets == null ? config.maxBucketCount() : perMeterMaxBuckets;
     }
 
     private HistogramFlavor histogramFlavor(Meter.Id id, OtlpConfig otlpConfig,
             DistributionStatisticConfig distributionStatisticConfig) {
-        HistogramFlavor preferredHistogramFlavor = otlpConfig.histogramFlavorPerMeter()
-            .getOrDefault(id.getName(), otlpConfig.histogramFlavor());
+        HistogramFlavor preferredHistogramFlavor = otlpConfig.histogramFlavorPerMeter(id);
+        preferredHistogramFlavor = preferredHistogramFlavor == null ? otlpConfig.histogramFlavor()
+                : preferredHistogramFlavor;
 
         final double[] serviceLevelObjectiveBoundaries = distributionStatisticConfig
             .getServiceLevelObjectiveBoundaries();

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;
 
@@ -25,7 +27,6 @@
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Stream;
 
-import static java.util.Map.entry;
 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 +285,41 @@ 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(idWithName("a.b.c")))
+            .isEqualTo(HistogramFlavor.EXPLICIT_BUCKET_HISTOGRAM);
+        assertThat(otlpConfig.histogramFlavorPerMeter(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 HistogramFlavor histogramFlavorPerMeter(Meter.Id id) {
+                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(idWithName("something"))).isEqualTo(otlpConfig.histogramFlavor());
+        assertThat(otlpConfig.histogramFlavorPerMeter(idWithName("a.b.c")))
+            .isEqualTo(HistogramFlavor.EXPLICIT_BUCKET_HISTOGRAM);
+        assertThat(otlpConfig.histogramFlavorPerMeter(idWithName("expo")))
+            .isEqualTo(HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM);
+        assertThat(otlpConfig.histogramFlavorPerMeter(idWithName("expo.other")))
+            .isEqualTo(HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM);
     }
 
     @Test
@@ -295,7 +328,11 @@ 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(idWithName("a.b.c"))).isEqualTo(10);
+    }
+
+    Meter.Id idWithName(String name) {
+        return new Meter.Id(name, Tags.empty(), null, null, Meter.Type.OTHER);
     }
 
 }

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

@@ -16,8 +16,8 @@
 package io.micrometer.registry.otlp;
 
 import io.micrometer.core.Issue;
-import io.micrometer.core.instrument.Timer;
 import io.micrometer.core.instrument.*;
+import io.micrometer.core.instrument.Timer;
 import io.micrometer.core.instrument.distribution.DistributionStatisticConfig;
 import io.micrometer.core.ipc.http.HttpSender;
 import io.opentelemetry.proto.metrics.v1.ExponentialHistogramDataPoint;
@@ -427,8 +427,9 @@ public HistogramFlavor histogramFlavor() {
             }
 
             @Override
-            public Map<String, HistogramFlavor> histogramFlavorPerMeter() {
-                return Collections.singletonMap("expo", HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM);
+            public HistogramFlavor histogramFlavorPerMeter(Meter.Id id) {
+                return id.getName().equals("expo") ? HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM
+                        : histogramFlavor();
             }
         };
         OtlpMeterRegistry meterRegistry = new OtlpMeterRegistry(config, clock);
@@ -477,8 +478,8 @@ public int maxBucketCount() {
             }
 
             @Override
-            public Map<String, Integer> maxBucketsPerMeter() {
-                return Collections.singletonMap("low.variation", 15);
+            public Integer maxBucketsPerMeter(Meter.Id id) {
+                return id.getName().equals("low.variation") ? 15 : maxBucketCount();
             }
         };
         OtlpMeterRegistry meterRegistry = new OtlpMeterRegistry(config, clock);