Support adding W3C baggage as span tags

dd-java-agent/instrumentation/okhttp-3/src/test/groovy/OkHttp3Test.groovy

@@ -78,6 +78,65 @@ abstract class OkHttp3Test extends HttpClientTest {
     method = "GET"
     url = server.address.resolve(path)
   }
+
+  def "baggage span tags are properly added"() {
+    setup:
+    // W3C Baggage header format: key1=value1,key2=value2,key3=value3
+    def baggageHeader = "user.id=bark,session.id=test-sess1,account.id=fetch,language=en"
+    def sentHeaders = [:]
+
+    when:
+    def status
+    // Capture the headers that OkHttp3 sends
+    def interceptor = new Interceptor() {
+        @Override
+        Response intercept(Chain chain) throws IOException {
+          def request = chain.request()
+          // Capture all headers sent
+          request.headers().names().each { headerName ->
+            sentHeaders[headerName] = request.header(headerName)
+          }
+          return chain.proceed(request)
+        }
+      }
+
+    def testClient = new OkHttpClient.Builder()
+      .connectTimeout(CONNECT_TIMEOUT_MS, TimeUnit.MILLISECONDS)
+      .readTimeout(READ_TIMEOUT_MS, TimeUnit.MILLISECONDS)
+      .writeTimeout(READ_TIMEOUT_MS, TimeUnit.MILLISECONDS)
+      .addInterceptor(interceptor)
+      .build()
+
+    def request = new Request.Builder()
+      .url(server.address.resolve("/success").toURL())
+      .header("baggage", baggageHeader)  // Pass baggage directly in header
+      .get()
+      .build()
+    def response = testClient.newCall(request).execute()
+    status = response.code()
+
+    then:
+    status == 200
+    // Verify baggage header was sent
+    sentHeaders["baggage"] == baggageHeader
+    sentHeaders["baggage"].contains("user.id=bark")
+    sentHeaders["baggage"].contains("session.id=test-sess1")
+    sentHeaders["baggage"].contains("account.id=fetch")
+    sentHeaders["baggage"].contains("language=en")
+
+    // Verify the resulting span has the correct baggage tags (only default configured keys)
+    assertTraces(1) {
+      trace(1) {
+        clientSpan(it, null, "GET", false, false, server.address.resolve("/success"), 200, false, null, false, [
+          // Should have baggage tags for keys in default configuration
+          "baggage.user.id": "bark",
+          "baggage.session.id": "test-sess1",
+          "baggage.account.id": "fetch",
+          // "baggage.language" should NOT be present since it's not in default config
+        ])
+      }
+    }
+  }
 }
 
 @Timeout(5)

dd-trace-api/src/main/java/datadog/trace/api/ConfigDefaults.java

@@ -84,6 +84,8 @@ public final class ConfigDefaults {
       new LinkedHashSet<>(asList(PropagationStyle.DATADOG));
   static final int DEFAULT_TRACE_BAGGAGE_MAX_ITEMS = 64;
   static final int DEFAULT_TRACE_BAGGAGE_MAX_BYTES = 8192;
+  static final List<String> DEFAULT_TRACE_BAGGAGE_TAG_KEYS =
+      Arrays.asList("user.id", "session.id", "account.id");
   static final boolean DEFAULT_JMX_FETCH_ENABLED = true;
   static final boolean DEFAULT_TRACE_AGENT_V05_ENABLED = false;
 

dd-trace-api/src/main/java/datadog/trace/api/config/TracerConfig.java

@@ -98,6 +98,7 @@ public final class TracerConfig {
   public static final String TRACE_PROPAGATION_EXTRACT_FIRST = "trace.propagation.extract.first";
   public static final String TRACE_BAGGAGE_MAX_ITEMS = "trace.baggage.max.items";
   public static final String TRACE_BAGGAGE_MAX_BYTES = "trace.baggage.max.bytes";
+  public static final String TRACE_BAGGAGE_TAG_KEYS = "trace.baggage.tag.keys";
 
   public static final String ENABLE_TRACE_AGENT_V05 = "trace.agent.v0.5.enabled";
 

dd-trace-core/src/main/java/datadog/trace/core/CoreTracer.java

@@ -1604,6 +1604,7 @@ private DDSpanContext buildSpanContext() {
       Object ciVisibilityContextData;
       final PathwayContext pathwayContext;
       final PropagationTags propagationTags;
+      final Map<String, String> baggageTags;
 
       if (this.spanId == 0) {
         spanId = tracer.idGenerationStrategy.generateSpanId();
@@ -1651,6 +1652,7 @@ private DDSpanContext buildSpanContext() {
         coreTags = null;
         coreTagsNeedsIntercept = false;
         rootSpanTags = null;
+        baggageTags = null;
         rootSpanTagsNeedsIntercept = false;
         parentServiceName = ddsc.getServiceName();
         if (serviceName == null) {
@@ -1706,6 +1708,7 @@ private DDSpanContext buildSpanContext() {
           coreTagsNeedsIntercept = true; // maybe intercept isn't needed?
           origin = tc.getOrigin();
           baggage = tc.getBaggage();
+          baggageTags = mapBaggageTags(baggage);
           requestContextDataAppSec = tc.getRequestContextDataAppSec();
           requestContextDataIast = tc.getRequestContextDataIast();
           ciVisibilityContextData = tc.getCiVisibilityContextData();
@@ -1718,6 +1721,7 @@ private DDSpanContext buildSpanContext() {
           requestContextDataAppSec = null;
           requestContextDataIast = null;
           ciVisibilityContextData = null;
+          baggageTags = null;
         }
 
         rootSpanTags = tracer.localRootSpanTags;
@@ -1826,6 +1830,7 @@ private DDSpanContext buildSpanContext() {
       context.setAllTags(coreTags, coreTagsNeedsIntercept);
       context.setAllTags(rootSpanTags, rootSpanTagsNeedsIntercept);
       context.setAllTags(contextualTags);
+      context.setAllTags(baggageTags);
       return context;
     }
   }
@@ -1910,4 +1915,26 @@ static TagMap withTracerTags(
     }
     return result.freeze();
   }
+
+  static Map<String, String> mapBaggageTags(Map<String, String> baggage) {
+    List<String> baggageTagKeys = Config.get().getTraceBaggageTagKeys();
+    if (baggageTagKeys.isEmpty()) {
+      return Collections.emptyMap();
+    }
+    Map<String, String> baggageTags = new HashMap<>(baggageTagKeys.size());
+    for (String key : baggageTagKeys) {
+      if (key == "*") {
+        // If the key is "*", we add all baggage items
+        for (Map.Entry<String, String> entry : baggage.entrySet()) {
+          baggageTags.put("baggage." + entry.getKey(), entry.getValue());
+        }
+        break;
+      }
+      String value = baggage.get(key);
+      if (value != null) {
+        baggageTags.put("baggage." + key, value);
+      }
+    }
+    return Collections.unmodifiableMap(baggageTags);
+  }
 }

dd-trace-core/src/test/groovy/datadog/trace/core/CoreSpanBuilderTest.groovy

@@ -4,12 +4,14 @@ import static datadog.trace.api.DDTags.DJM_ENABLED
 import static datadog.trace.api.DDTags.DSM_ENABLED
 import static datadog.trace.api.DDTags.PROFILING_ENABLED
 import static datadog.trace.api.DDTags.SCHEMA_VERSION_TAG_KEY
+import static datadog.trace.api.config.TracerConfig.TRACE_BAGGAGE_TAG_KEYS
 
 import datadog.trace.api.Config
 import datadog.trace.api.DDSpanId
 import datadog.trace.api.DDTraceId
 import datadog.trace.api.TagMap
 import datadog.trace.api.gateway.RequestContextSlot
+import datadog.trace.api.sampling.PrioritySampling
 import datadog.trace.api.naming.SpanNaming
 import datadog.trace.api.sampling.PrioritySampling
 import datadog.trace.bootstrap.instrumentation.api.AgentScope
@@ -492,6 +494,31 @@ class CoreSpanBuilderTest extends DDCoreSpecification {
     span1.finish()
   }
 
+  def "buildSpan should add baggage tags with different configurations"() {
+    setup:
+    injectSysConfig(TRACE_BAGGAGE_TAG_KEYS, baggageTagKeysConfig)
+    def baggage = ["user.id": "alice", "session.id": "123", "region": "us-west-1", "env": "production"]
+    def tagContext = new TagContext(null, null, null, baggage, PrioritySampling.UNSET, null, DATADOG, DDTraceId.ZERO)
+
+    when:
+    def span = tracer.buildSpan("test", "test-op")
+      .asChildOf(tagContext)
+      .start()
+
+    then:
+    // Filter span tags to only check baggage tags (those starting with "baggage.")
+    def actualBaggageTags = span.tags.findAll { key, value -> key.startsWith("baggage.") }
+    actualBaggageTags == expectedBaggageTags
+
+    cleanup:
+    span.finish()
+
+    where:
+    baggageTagKeysConfig | expectedBaggageTags
+    "user.id"            | ["baggage.user.id": "alice"]
+    "user.id,session.id" | ["baggage.user.id": "alice", "baggage.session.id": "123"]
+  }
+
   def productTags() {
     def productTags = [
       (PROFILING_ENABLED) : Config.get().isProfilingEnabled() ? 1 : 0

dd-trace-core/src/test/groovy/datadog/trace/core/CoreTracerTest.groovy

@@ -38,6 +38,7 @@ import static datadog.trace.api.config.TracerConfig.HEADER_TAGS
 import static datadog.trace.api.config.TracerConfig.PRIORITY_SAMPLING
 import static datadog.trace.api.config.TracerConfig.SERVICE_MAPPING
 import static datadog.trace.api.config.TracerConfig.SPAN_TAGS
+import static datadog.trace.api.config.TracerConfig.TRACE_BAGGAGE_TAG_KEYS
 import static datadog.trace.api.config.TracerConfig.WRITER_TYPE
 
 @Timeout(10)
@@ -639,6 +640,33 @@ class CoreTracerTest extends DDCoreSpecification {
     "service" | "env"  | "service"     | "env_1"
     "service" | "env"  | "service_2"   | "env_2"
   }
+
+  def "test mapBaggageTags default"() {
+    when:
+    def tags = CoreTracer.mapBaggageTags(["user.id": "doggo", "account.id": "test", "session.id":"1234", "region":"us-east-1"])
+    then:
+    tags == ["baggage.user.id": "doggo", "baggage.account.id": "test", "baggage.session.id": "1234"]
+  }
+
+  def "test mapBaggageTags with different configurations"() {
+    setup:
+    injectSysConfig(TRACE_BAGGAGE_TAG_KEYS, baggageTagKeysConfig)
+
+    when:
+    def tags = CoreTracer.mapBaggageTags(["user.id": "doggo", "foo": "bar", "language":"en"])
+
+    then:
+    tags == expectedTags
+
+    where:
+    baggageTagKeysConfig | expectedTags
+    "*"                  | ["baggage.user.id": "doggo", "baggage.foo": "bar", "baggage.language": "en"]
+    " "                  | [:]
+    "system.id"          | [:]
+    "user.id"            | ["baggage.user.id": "doggo"]
+    "foo"                | ["baggage.foo": "bar"]
+    "user.id,foo"        | ["baggage.user.id": "doggo", "baggage.foo": "bar"]
+  }
 }
 
 class WriterWithExplicitFlush implements datadog.trace.common.writer.Writer {

internal-api/src/main/java/datadog/trace/api/Config.java

@@ -151,6 +151,7 @@
 import static datadog.trace.api.ConfigDefaults.DEFAULT_TRACE_ANALYTICS_ENABLED;
 import static datadog.trace.api.ConfigDefaults.DEFAULT_TRACE_BAGGAGE_MAX_BYTES;
 import static datadog.trace.api.ConfigDefaults.DEFAULT_TRACE_BAGGAGE_MAX_ITEMS;
+import static datadog.trace.api.ConfigDefaults.DEFAULT_TRACE_BAGGAGE_TAG_KEYS;
 import static datadog.trace.api.ConfigDefaults.DEFAULT_TRACE_CLOUD_PAYLOAD_TAGGING_SERVICES;
 import static datadog.trace.api.ConfigDefaults.DEFAULT_TRACE_EXPERIMENTAL_FEATURES_ENABLED;
 import static datadog.trace.api.ConfigDefaults.DEFAULT_TRACE_HTTP_RESOURCE_REMOVE_TRAILING_SLASH;
@@ -583,6 +584,7 @@
 import static datadog.trace.api.config.TracerConfig.TRACE_ANALYTICS_ENABLED;
 import static datadog.trace.api.config.TracerConfig.TRACE_BAGGAGE_MAX_BYTES;
 import static datadog.trace.api.config.TracerConfig.TRACE_BAGGAGE_MAX_ITEMS;
+import static datadog.trace.api.config.TracerConfig.TRACE_BAGGAGE_TAG_KEYS;
 import static datadog.trace.api.config.TracerConfig.TRACE_CLIENT_IP_HEADER;
 import static datadog.trace.api.config.TracerConfig.TRACE_CLIENT_IP_RESOLVER_ENABLED;
 import static datadog.trace.api.config.TracerConfig.TRACE_CLOUD_PAYLOAD_TAGGING_MAX_DEPTH;
@@ -823,6 +825,7 @@ public static String getHostName() {
   private final boolean tracePropagationExtractFirst;
   private final int traceBaggageMaxItems;
   private final int traceBaggageMaxBytes;
+  private final List<String> traceBaggageTagKeys;
   private final int clockSyncPeriod;
   private final boolean logsInjectionEnabled;
 
@@ -1695,6 +1698,11 @@ private Config(final ConfigProvider configProvider, final InstrumenterConfig ins
         // If we have a new setting, we log a warning
         logOverriddenDeprecatedSettingWarning(PROPAGATION_STYLE_INJECT, injectOrigin, inject);
       }
+
+      // Parse the baggage tag keys configuration
+      traceBaggageTagKeys =
+          configProvider.getList(TRACE_BAGGAGE_TAG_KEYS, DEFAULT_TRACE_BAGGAGE_TAG_KEYS);
+
       // Now we can check if we should pick the default injection/extraction
 
       tracePropagationStylesToExtract =
@@ -2966,6 +2974,10 @@ public Map<String, String> getBaggageMapping() {
     return baggageMapping;
   }
 
+  public List<String> getTraceBaggageTagKeys() {
+    return traceBaggageTagKeys;
+  }
+
   public Map<String, String> getHttpServerPathResourceNameMapping() {
     return httpServerPathResourceNameMapping;
   }
@@ -5374,6 +5386,8 @@ public String toString() {
         + traceKeepLatencyThreshold
         + ", traceStrictWritesEnabled="
         + traceStrictWritesEnabled
+        + ", traceBaggageTagKeys="
+        + traceBaggageTagKeys
         + ", tracePropagationStylesToExtract="
         + tracePropagationStylesToExtract
         + ", tracePropagationStylesToInject="