propagating baggage, redux

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

@@ -74,6 +74,8 @@
 import datadog.trace.common.writer.WriterFactory;
 import datadog.trace.common.writer.ddintake.DDIntakeTraceInterceptor;
 import datadog.trace.context.TraceScope;
+import datadog.trace.core.propagation.W3CBaggageExtractor;
+import datadog.trace.core.propagation.W3CBaggageInjector;
 import datadog.trace.core.datastreams.DataStreamContextInjector;
 import datadog.trace.core.datastreams.DataStreamsMonitoring;
 import datadog.trace.core.datastreams.DefaultDataStreamsMonitoring;
@@ -707,17 +709,19 @@ private CoreTracer(
 
     sharedCommunicationObjects.whenReady(this.dataStreamsMonitoring::start);
 
-    // Create default extractor from config if not provided and decorate it with DSM extractor
+    // Create default extractor from config if not provided and decorate it with DSM and baggage extractors
     HttpCodec.Extractor builtExtractor =
         extractor == null ? HttpCodec.createExtractor(config, this::captureTraceConfig) : extractor;
     builtExtractor = this.dataStreamsMonitoring.extractor(builtExtractor);
-    // Create all HTTP injectors plus the DSM one
+    builtExtractor = new W3CBaggageExtractor(builtExtractor);
+    // Create all HTTP injectors plus the DSM and baggage injectors
     Map<TracePropagationStyle, HttpCodec.Injector> injectors =
         HttpCodec.allInjectorsFor(config, invertMap(baggageMapping));
     DataStreamContextInjector dataStreamContextInjector = this.dataStreamsMonitoring.injector();
+    W3CBaggageInjector baggageInjector = new W3CBaggageInjector();
     // Store all propagators to propagation
     this.propagation =
-        new CorePropagation(builtExtractor, injector, injectors, dataStreamContextInjector);
+        new CorePropagation(builtExtractor, injector, injectors, dataStreamContextInjector, baggageInjector);
 
     this.tagInterceptor =
         null == tagInterceptor ? new TagInterceptor(new RuleFlags(config)) : tagInterceptor;

dd-trace-core/src/main/java/datadog/trace/core/propagation/CorePropagation.java

@@ -14,6 +14,7 @@ public class CorePropagation implements AgentPropagation {
   private final HttpCodec.Injector injector;
   private final Map<TracePropagationStyle, HttpCodec.Injector> injectors;
   private final DataStreamContextInjector dataStreamContextInjector;
+  private final W3CBaggageInjector baggageInjector;
   private final HttpCodec.Extractor extractor;
 
   /**
@@ -29,11 +30,13 @@ public CorePropagation(
       HttpCodec.Extractor extractor,
       HttpCodec.Injector defaultInjector,
       Map<TracePropagationStyle, HttpCodec.Injector> injectors,
-      DataStreamContextInjector dataStreamContextInjector) {
+      DataStreamContextInjector dataStreamContextInjector,
+      W3CBaggageInjector baggageInjector) {
     this.extractor = extractor;
     this.injector = defaultInjector;
     this.injectors = injectors;
     this.dataStreamContextInjector = dataStreamContextInjector;
+    this.baggageInjector = baggageInjector;
   }
 
   @Override

dd-trace-core/src/main/java/datadog/trace/core/propagation/W3CBaggageExtractor.java

@@ -0,0 +1,25 @@
+package datadog.trace.core.propagation;
+
+import datadog.trace.bootstrap.instrumentation.api.AgentPropagation;
+import datadog.trace.bootstrap.instrumentation.api.TagContext;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class W3CBaggageExtractor implements HttpCodec.Extractor {
+  private static final Logger LOGGER = LoggerFactory.getLogger(W3CBaggageExtractor.class);
+  private final HttpCodec.Extractor delegate;
+
+  public W3CBaggageExtractor(HttpCodec.Extractor delegate) {
+    this.delegate = delegate;
+  }
+
+  @Override
+  public <C> TagContext extract(C carrier, AgentPropagation.ContextVisitor<C> getter) {
+    // delegate to the default HTTP extraction
+    TagContext context = this.delegate.extract(carrier, getter);
+
+    // TODO: extract baggage from carrier and add it to context
+
+    return context;
+  }
+}

dd-trace-core/src/main/java/datadog/trace/core/propagation/W3CBaggageInjector.java

@@ -0,0 +1,31 @@
+package datadog.trace.core.propagation;
+
+import datadog.trace.bootstrap.instrumentation.api.AgentPropagation;
+import datadog.trace.bootstrap.instrumentation.api.AgentSpan;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.Map;
+
+public class W3CBaggageInjector {
+  private static final Logger LOGGER = LoggerFactory.getLogger(W3CBaggageInjector.class);
+
+  public <C> void inject(AgentSpan span, C carrier, AgentPropagation.Setter<C> setter) {
+    StringBuilder builder = new StringBuilder();
+
+    for (final Map.Entry<String, String> baggageItem : span.context().baggageItems()) {
+      // quick and dirty implementation for now
+      if (builder.length() > 0) {
+        builder.append(",");
+      }
+
+      // TODO: encode baggageItem.getValue() to be W3C compliant
+      builder.append(baggageItem.getKey())
+          .append('=')
+          .append(HttpCodec.encodeBaggage(baggageItem.getValue()));
+    }
+
+    setter.set(carrier, "baggage", builder.toString());
+  }
+}
+