Add support for B3 multi header propagation

- Order propagation extractors by priority (W3C, B3, B3 multi)

Author: mhalbritter

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/BraveAutoConfiguration.java

@@ -176,7 +176,8 @@ static class BraveNoBaggageConfiguration {
 		Factory propagationFactory(TracingProperties properties) {
 			Iterable<Factory> injectorFactories = PropagationFactoryFactory
 				.factoriesFor(properties.getPropagation().getType());
-			Iterable<Factory> extractorFactories = PropagationFactoryFactory.factoriesFor(PropagationType.values());
+			Iterable<Factory> extractorFactories = PropagationFactoryFactory
+				.factoriesFor(PropagationType.orderedValues());
 			return new CompositePropagationFactory(injectorFactories, extractorFactories);
 		}
 
@@ -199,7 +200,7 @@ BaggagePropagation.FactoryBuilder propagationFactoryBuilder(
 			Iterable<Factory> injectorFactories = PropagationFactoryFactory.factoriesFor(BRAVE_BAGGAGE_MANAGER,
 					this.tracingProperties.getPropagation().getType());
 			Iterable<Factory> extractorFactories = PropagationFactoryFactory.factoriesFor(BRAVE_BAGGAGE_MANAGER,
-					PropagationType.values());
+					PropagationType.orderedValues());
 			Factory delegate = new CompositePropagationFactory(injectorFactories, extractorFactories);
 			FactoryBuilder builder = BaggagePropagation.newFactoryBuilder(delegate);
 			baggagePropagationCustomizers.orderedStream().forEach((customizer) -> customizer.customize(builder));
@@ -258,23 +259,31 @@ ScopeDecorator correlationScopeDecorator(CorrelationScopeDecorator.Builder build
 	/**
 	 * Factory for {@link Factory propagation factories}.
 	 */
-	private static class PropagationFactoryFactory {
+	private static final class PropagationFactoryFactory {
 
 		private PropagationFactoryFactory() {
 		}
 
 		/**
-		 * Creates a new B3 propagation factory.
-		 * @return B3 propagation factory.
+		 * Creates a new B3 propagation factory using a single B3 header.
+		 * @return the B3 propagation factory
 		 */
-		private static Factory b3() {
+		private static Factory b3Single() {
 			return B3Propagation.newFactoryBuilder().injectFormat(B3Propagation.Format.SINGLE_NO_PARENT).build();
 		}
 
+		/**
+		 * Creates a new B3 propagation factory using multiple B3 headers.
+		 * @return the B3 propagation factory
+		 */
+		private static Factory b3Multi() {
+			return B3Propagation.newFactoryBuilder().injectFormat(B3Propagation.Format.MULTI).build();
+		}
+
 		/**
 		 * Creates a new W3C propagation factory.
 		 * @param baggageManager baggage manager to use, or {@code null}
-		 * @return W3C Propagation propagation factory
+		 * @return the W3C propagation factory
 		 */
 		private static W3CPropagation w3c(BaggageManager baggageManager) {
 			return (baggageManager != null) ? new W3CPropagation(baggageManager, Collections.emptyList())
@@ -283,25 +292,18 @@ private static W3CPropagation w3c(BaggageManager baggageManager) {
 
 		private static Factory forType(BaggageManager baggageManager, PropagationType type) {
 			return switch (type) {
-				case B3 -> PropagationFactoryFactory.b3();
+				case B3 -> PropagationFactoryFactory.b3Single();
+				case B3_MULTI -> PropagationFactoryFactory.b3Multi();
 				case W3C -> PropagationFactoryFactory.w3c(baggageManager);
 			};
 		}
 
 		private static List<Factory> factoriesFor(Collection<PropagationType> types) {
-			return factoriesFor(null, types.toArray(PropagationType[]::new));
-		}
-
-		private static List<Factory> factoriesFor(PropagationType... types) {
 			return factoriesFor(null, types);
 		}
 
 		private static List<Factory> factoriesFor(BaggageManager baggageManager, Collection<PropagationType> types) {
-			return factoriesFor(baggageManager, types.toArray(PropagationType[]::new));
-		}
-
-		private static List<Factory> factoriesFor(BaggageManager baggageManager, PropagationType... types) {
-			List<Factory> result = new ArrayList<>(types.length);
+			List<Factory> result = new ArrayList<>(types.size());
 			for (PropagationType type : types) {
 				result.add(forType(baggageManager, type));
 			}

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/CompositePropagationFactory.java

@@ -68,7 +68,7 @@ public <R> TraceContext.Injector<R> injector(Setter<R, String> setter) {
 
 	@Override
 	public <R> TraceContext.Extractor<R> extractor(Getter<R, String> getter) {
-		return request -> {
+		return (request) -> {
 			for (Propagation<String> extractor : this.extractors) {
 				TraceContextOrSamplingFlags extract = extractor.extractor(getter).extract(request);
 				if (extract != TraceContextOrSamplingFlags.EMPTY) {

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/TracingProperties.java

@@ -17,8 +17,9 @@
 package org.springframework.boot.actuate.autoconfigure.tracing;
 
 import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Comparator;
 import java.util.List;
-import java.util.Set;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
 
@@ -167,29 +168,54 @@ public void setFields(List<String> fields) {
 	public static class Propagation {
 
 		/**
-		 * Tracing context propagation types.
+		 * Tracing context propagation types produced by the application.
 		 */
-		private Set<PropagationType> type = Set.of(PropagationType.W3C);
+		private List<PropagationType> type = List.of(PropagationType.W3C);
 
-		public Set<PropagationType> getType() {
+		public List<PropagationType> getType() {
 			return this.type;
 		}
 
-		public void setType(Set<PropagationType> type) {
+		public void setType(List<PropagationType> type) {
 			this.type = type;
 		}
 
 		enum PropagationType {
 
 			/**
-			 * B3 propagation type.
+			 * <a href="https://github.com/openzipkin/b3-propagation#single-header">B3
+			 * single header</a> propagation.
 			 */
-			B3,
+			B3(1),
 
 			/**
-			 * W3C propagation type.
+			 * <a href="https://github.com/openzipkin/b3-propagation#multiple-headers">B3
+			 * multiple headers</a> propagation.
 			 */
-			W3C
+			B3_MULTI(2),
+
+			/**
+			 * W3C propagation.
+			 */
+			W3C(0);
+
+			/**
+			 * Order of the enum value. The {@link #orderedValues()} method returns the
+			 * enum values in ascending order.
+			 */
+			private final int order;
+
+			PropagationType(int order) {
+				this.order = order;
+			}
+
+			/**
+			 * Returns the ordered values.
+			 * @return the ordered values
+			 */
+			static List<PropagationType> orderedValues() {
+				return Arrays.stream(values()).sorted(Comparator.comparing((value) -> value.order)).toList();
+			}
 
 		}