Added an option to have baggage through Observation API

docs/modules/ROOT/pages/api.adoc

@@ -65,6 +65,21 @@ IMPORTANT: For Brave, remember to set up the `PropagationFactory` so that it con
 include::{include-java}/tracing/TracingApiTests.java[tags=baggage_brave_setup,indent=0]
 -----
 
+=== Baggage with Micrometer Observation API
+
+If you're using Micrometer Observation API, there's no notion of baggage. If you set up a `BaggageManager` to have the baggage fields configured, we will assume that when the Observation gets put in scope, whatever low and high cardinality keys are set on the Observation will be put in scope as baggage (assuming that their names match with the configuration on the `BaggageManager`). Below you can find example of such setup with OpenTelemetry `BaggageManager`.
+
+[source,java,subs=+attributes]
+-----
+include::{include-bridges-java}/micrometer-tracing-bridge-otel/src/test/java/io/micrometer/tracing/otel/bridge/BaggageTests.java[tags=baggageManager,indent=0]
+
+include::{include-bridges-java}/micrometer-tracing-bridge-otel/src/test/java/io/micrometer/tracing/otel/bridge/BaggageTests.java[tags=observationRegistrySetup,indent=0]
+
+include::{include-bridges-java}/micrometer-tracing-bridge-otel/src/test/java/io/micrometer/tracing/otel/bridge/BaggageTests.java[tags=observation,indent=0]
+
+include::{include-bridges-java}/micrometer-tracing-bridge-otel/src/test/java/io/micrometer/tracing/otel/bridge/BaggageTests.java[tags=observationScope,indent=0]
+-----
+
 == Aspect Oriented Programming
 
 Micrometer Tracing contains `@NewSpan`, `@ContinueSpan`, and `@SpanTag` annotations that frameworks can use to create or customize spans for either specific types of methods such as those serving web request endpoints or, more generally, to all methods.

micrometer-tracing-bridges/micrometer-tracing-bridge-brave/src/main/java/io/micrometer/tracing/brave/bridge/BraveBaggageManager.java

@@ -1,5 +1,5 @@
 /**
- * Copyright 2022 the original author or authors.
+ * Copyright 2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,6 +22,7 @@
 import io.micrometer.tracing.*;
 
 import java.io.Closeable;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -36,15 +37,25 @@ public class BraveBaggageManager implements Closeable, BaggageManager {
 
     private final List<String> tagFields;
 
+    private final List<String> remoteFields;
+
     @Nullable
     private Tracer tracer;
 
     /**
      * Create an instance of {@link BraveBaggageManager}.
      * @param tagFields fields of baggage keys that should become tags on a span
+     * @param remoteFields fields of baggage keys that should be propagated over the wire
      */
-    public BraveBaggageManager(List<String> tagFields) {
+    public BraveBaggageManager(List<String> tagFields, List<String> remoteFields) {
         this.tagFields = tagFields;
+        this.remoteFields = remoteFields(tagFields, remoteFields);
+    }
+
+    private static List<String> remoteFields(List<String> tagFields, List<String> remoteFields) {
+        List<String> combined = new ArrayList<>(tagFields);
+        combined.addAll(remoteFields);
+        return combined;
     }
 
     /**
@@ -53,6 +64,16 @@ public BraveBaggageManager(List<String> tagFields) {
      */
     public BraveBaggageManager() {
         this.tagFields = Collections.emptyList();
+        this.remoteFields = Collections.emptyList();
+    }
+
+    /**
+     * Create an instance of {@link BraveBaggageManager}.
+     * @param tagFields fields of baggage keys that should become tags on a span
+     */
+    public BraveBaggageManager(List<String> tagFields) {
+        this.tagFields = tagFields;
+        this.remoteFields = new ArrayList<>(tagFields);
     }
 
     @Override
@@ -136,4 +157,9 @@ void setTracer(Tracer tracer) {
         this.tracer = tracer;
     }
 
+    @Override
+    public List<String> getRemoteFields() {
+        return this.remoteFields;
+    }
+
 }

micrometer-tracing-bridges/micrometer-tracing-bridge-brave/src/main/java/io/micrometer/tracing/brave/bridge/BraveTracer.java

@@ -18,6 +18,7 @@
 import brave.propagation.TraceContextOrSamplingFlags;
 import io.micrometer.tracing.*;
 
+import java.util.List;
 import java.util.Map;
 
 /**
@@ -156,6 +157,11 @@ public CurrentTraceContext currentTraceContext() {
         return this.currentTraceContext;
     }
 
+    @Override
+    public List<String> getRemoteFields() {
+        return this.braveBaggageManager.getRemoteFields();
+    }
+
 }
 
 class BraveSpanInScope implements Tracer.SpanInScope {

micrometer-tracing-bridges/micrometer-tracing-bridge-brave/src/test/java/io/micrometer/tracing/brave/bridge/BaggageTests.java

@@ -1,5 +1,5 @@
 /**
- * Copyright 2022 the original author or authors.
+ * Copyright 2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,13 +27,17 @@
 import io.micrometer.common.util.internal.logging.InternalLogger;
 import io.micrometer.common.util.internal.logging.InternalLoggerFactory;
 import io.micrometer.context.ContextRegistry;
+import io.micrometer.observation.Observation;
+import io.micrometer.observation.Observation.Scope;
 import io.micrometer.observation.ObservationRegistry;
 import io.micrometer.observation.contextpropagation.ObservationThreadLocalAccessor;
 import io.micrometer.tracing.*;
 import io.micrometer.tracing.contextpropagation.ObservationAwareSpanThreadLocalAccessor;
+import io.micrometer.tracing.handler.DefaultTracingObservationHandler;
 import org.assertj.core.api.Assertions;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import reactor.core.observability.micrometer.Micrometer;
 import reactor.core.publisher.Hooks;
@@ -42,6 +46,7 @@
 import reactor.core.scheduler.Schedulers;
 
 import java.time.Duration;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
@@ -61,6 +66,10 @@ class BaggageTests {
 
     public static final String TAG_VALUE = "tagValue";
 
+    public static final String OBSERVATION_BAGGAGE_KEY = "observationKey";
+
+    public static final String OBSERVATION_BAGGAGE_VALUE = "observationValue";
+
     TestSpanHandler spanHandler = new TestSpanHandler();
 
     StrictCurrentTraceContext braveCurrentTraceContext = StrictCurrentTraceContext.create();
@@ -73,6 +82,7 @@ class BaggageTests {
         .traceId128Bit(true)
         .propagationFactory(BaggagePropagation.newFactoryBuilder(B3Propagation.FACTORY)
             .add(BaggagePropagationConfig.SingleBaggageField.remote(BaggageField.create(KEY_1)))
+            .add(BaggagePropagationConfig.SingleBaggageField.remote(BaggageField.create(OBSERVATION_BAGGAGE_KEY)))
             .add(BaggagePropagationConfig.SingleBaggageField.local(BaggageField.create(TAG_KEY)))
             .build())
         .sampler(Sampler.ALWAYS_SAMPLE)
@@ -84,10 +94,15 @@ class BaggageTests {
     BravePropagator propagator = new BravePropagator(tracing);
 
     Tracer tracer = new BraveTracer(this.braveTracer, this.bridgeContext,
-            new BraveBaggageManager(Collections.singletonList(TAG_KEY)));
+            new BraveBaggageManager(Collections.singletonList(TAG_KEY), Arrays.asList(KEY_1, OBSERVATION_BAGGAGE_KEY)));
 
     ObservationRegistry observationRegistry = ObservationThreadLocalAccessor.getInstance().getObservationRegistry();
 
+    @BeforeEach
+    void setupHandler() {
+        observationRegistry.observationConfig().observationHandler(new DefaultTracingObservationHandler(tracer));
+    }
+
     @AfterEach
     void cleanup() {
         tracing.close();
@@ -258,6 +273,30 @@ void baggageTagKey() {
         then(mutableSpan.tags().get(TAG_KEY)).isEqualTo(TAG_VALUE);
     }
 
+    @Test
+    void baggageWithObservationApiWithRemoteFields() {
+        Observation observation = Observation.start("foo", observationRegistry)
+            .lowCardinalityKeyValue(KEY_1, TAG_VALUE)
+            .highCardinalityKeyValue(OBSERVATION_BAGGAGE_KEY, OBSERVATION_BAGGAGE_VALUE);
+        then(tracer.getBaggage(KEY_1).get()).isNull();
+        then(tracer.getBaggage(OBSERVATION_BAGGAGE_KEY).get()).isNull();
+
+        try (Scope scope = observation.openScope()) {
+            then(tracer.getBaggage(KEY_1).get()).isEqualTo(TAG_VALUE);
+            then(tracer.getBaggage(OBSERVATION_BAGGAGE_KEY).get()).isEqualTo(OBSERVATION_BAGGAGE_VALUE);
+        }
+
+        then(tracer.currentSpan()).isNull();
+        then(tracer.getBaggage(KEY_1).get()).isNull();
+        then(tracer.getBaggage(OBSERVATION_BAGGAGE_KEY).get()).isNull();
+        observation.stop();
+
+        then(spanHandler.spans()).hasSize(1);
+        MutableSpan mutableSpan = spanHandler.spans().get(0);
+        then(mutableSpan.tags().get(KEY_1)).isEqualTo(TAG_VALUE);
+        then(mutableSpan.tags().get(OBSERVATION_BAGGAGE_KEY)).isEqualTo(OBSERVATION_BAGGAGE_VALUE);
+    }
+
     @Test
     void baggageTagKeyWithLegacyApi() {
         ScopedSpan span = this.tracer.startScopedSpan("call1");

micrometer-tracing-bridges/micrometer-tracing-bridge-otel/src/main/java/io/micrometer/tracing/otel/bridge/OtelBaggageManager.java

@@ -15,18 +15,6 @@
  */
 package io.micrometer.tracing.otel.bridge;
 
-import java.util.ArrayDeque;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Deque;
-import java.util.HashMap;
-import java.util.Iterator;
-import java.util.LinkedList;
-import java.util.List;
-import java.util.Map;
-import java.util.Objects;
-import java.util.function.BiConsumer;
-
 import io.micrometer.common.lang.Nullable;
 import io.micrometer.tracing.BaggageInScope;
 import io.micrometer.tracing.BaggageManager;
@@ -38,6 +26,9 @@
 import io.opentelemetry.api.baggage.BaggageEntryMetadata;
 import io.opentelemetry.context.Context;
 
+import java.util.*;
+import java.util.function.BiConsumer;
+
 import static java.util.Collections.unmodifiableCollection;
 import static java.util.Collections.unmodifiableMap;
 import static java.util.function.Function.identity;
@@ -71,10 +62,16 @@ public class OtelBaggageManager implements BaggageManager {
     public OtelBaggageManager(CurrentTraceContext currentTraceContext, List<String> remoteFields,
             List<String> tagFields) {
         this.currentTraceContext = currentTraceContext;
-        this.remoteFields = remoteFields;
+        this.remoteFields = remoteFields(tagFields, remoteFields);
         this.tagFields = tagFields;
     }
 
+    private static List<String> remoteFields(List<String> tagFields, List<String> remoteFields) {
+        List<String> combined = new ArrayList<>(tagFields);
+        combined.addAll(remoteFields);
+        return combined;
+    }
+
     @Override
     public Map<String, String> getAllBaggage() {
         return toMap(currentBaggage());
@@ -213,6 +210,11 @@ private String propagationString(boolean remoteField) {
         return propagation;
     }
 
+    @Override
+    public List<String> getRemoteFields() {
+        return this.remoteFields;
+    }
+
 }
 
 class CompositeBaggage implements io.opentelemetry.api.baggage.Baggage {

micrometer-tracing-bridges/micrometer-tracing-bridge-otel/src/main/java/io/micrometer/tracing/otel/bridge/OtelTracer.java

@@ -1,5 +1,5 @@
 /**
- * Copyright 2022 the original author or authors.
+ * Copyright 2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@
 import io.opentelemetry.context.Context;
 import io.opentelemetry.context.Scope;
 
+import java.util.List;
 import java.util.Map;
 
 /**
@@ -196,6 +197,11 @@ public BaggageInScope createBaggageInScope(TraceContext traceContext, String nam
         return this.otelBaggageManager.createBaggageInScope(traceContext, name, value);
     }
 
+    @Override
+    public List<String> getRemoteFields() {
+        return this.otelBaggageManager.getRemoteFields();
+    }
+
     /**
      * Publisher of events.
      */