Fixed custom propagation mode option

with this change when CUSTOM mode is turned on we will search for user provided Propagation bean or else noop

fixes gh-1836

spring-cloud-sleuth-brave/src/main/java/org/springframework/cloud/sleuth/brave/bridge/CompositePropagationFactorySupplier.java

@@ -30,6 +30,7 @@ import brave.propagation.TraceContextOrSamplingFlags;
 import brave.propagation.aws.AWSPropagation;
 
 import org.springframework.beans.factory.BeanFactory;
+import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.cloud.sleuth.brave.propagation.PropagationFactorySupplier;
 import org.springframework.cloud.sleuth.brave.propagation.PropagationType;
 
@@ -56,7 +57,7 @@ public class CompositePropagationFactorySupplier implements PropagationFactorySu
 
 	@Override
 	public Propagation.Factory get() {
-		return new CompositePropagationFactory(
+		return new CompositePropagationFactory(this.beanFactory,
 				this.beanFactory.getBeanProvider(BraveBaggageManager.class).getIfAvailable(BraveBaggageManager::new),
 				this.localFields, this.types);
 	}
@@ -69,8 +70,8 @@ class CompositePropagationFactory extends Propagation.Factory implements Propaga
 
 	private final List<PropagationType> types;
 
-	CompositePropagationFactory(BraveBaggageManager braveBaggageManager, List<String> localFields,
+	CompositePropagationFactory(BeanFactory beanFactory, BraveBaggageManager braveBaggageManager,
-			List<PropagationType> types) {
+			List<String> localFields, List<PropagationType> types) {
 		this.types = types;
 		this.mapping.put(PropagationType.AWS, AWSPropagation.FACTORY.get());
 		// Note: Versions <2.2.3 use injectFormat(MULTI) for non-remote (ex
@@ -79,7 +80,7 @@ class CompositePropagationFactory extends Propagation.Factory implements Propaga
 		this.mapping.put(PropagationType.B3,
 				B3Propagation.newFactoryBuilder().injectFormat(B3Propagation.Format.SINGLE_NO_PARENT).build().get());
 		this.mapping.put(PropagationType.W3C, new W3CPropagation(braveBaggageManager, localFields));
-		this.mapping.put(PropagationType.CUSTOM, NoOpPropagation.INSTANCE);
+		this.mapping.put(PropagationType.CUSTOM, new LazyPropagation(beanFactory.getBeanProvider(Propagation.class)));
 	}
 
 	@Override
@@ -116,6 +117,32 @@ class CompositePropagationFactory extends Propagation.Factory implements Propaga
 		return StringPropagationAdapter.create(this, keyFactory);
 	}
 
+	@SuppressWarnings("unchecked")
+	private static final class LazyPropagation implements Propagation<String> {
+
+		private final ObjectProvider<Propagation> delegate;
+
+		private LazyPropagation(ObjectProvider<Propagation> delegate) {
+			this.delegate = delegate;
+		}
+
+		@Override
+		public List<String> keys() {
+			return this.delegate.getIfAvailable(() -> NoOpPropagation.INSTANCE).keys();
+		}
+
+		@Override
+		public <R> TraceContext.Injector<R> injector(Setter<R, String> setter) {
+			return this.delegate.getIfAvailable(() -> NoOpPropagation.INSTANCE).injector(setter);
+		}
+
+		@Override
+		public <R> TraceContext.Extractor<R> extractor(Getter<R, String> getter) {
+			return this.delegate.getIfAvailable(() -> NoOpPropagation.INSTANCE).extractor(getter);
+		}
+
+	}
+
 	private static class NoOpPropagation implements Propagation<String> {
 
 		static final NoOpPropagation INSTANCE = new NoOpPropagation();

spring-cloud-sleuth-brave/src/test/java/org/springframework/cloud/sleuth/brave/bridge/CompositePropagationFactorySupplierTests.java

@@ -0,0 +1,118 @@
+/*
+ * Copyright 2013-2021 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.sleuth.brave.bridge;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Objects;
+
+import brave.internal.codec.HexCodec;
+import brave.internal.propagation.StringPropagationAdapter;
+import brave.propagation.Propagation;
+import brave.propagation.TraceContext;
+import brave.propagation.TraceContextOrSamplingFlags;
+import org.assertj.core.api.BDDAssertions;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+
+import org.springframework.beans.factory.BeanFactory;
+import org.springframework.cloud.loadbalancer.support.SimpleObjectProvider;
+import org.springframework.cloud.sleuth.brave.propagation.PropagationType;
+import org.springframework.util.StringUtils;
+
+class CompositePropagationFactorySupplierTests {
+
+	@Test
+	void should_pick_custom_registered_propagation_when_custom_mode_picked() {
+		BeanFactory beanFactory = Mockito.mock(BeanFactory.class);
+		Mockito.when(beanFactory.getBeanProvider(BraveBaggageManager.class))
+				.thenReturn(new SimpleObjectProvider(new BraveBaggageManager()));
+		Mockito.when(beanFactory.getBeanProvider(Propagation.class))
+				.thenReturn(new SimpleObjectProvider(new CustomTracePropagation()));
+
+		CompositePropagationFactorySupplier supplier = new CompositePropagationFactorySupplier(beanFactory,
+				Collections.emptyList(), Collections.singletonList(PropagationType.CUSTOM));
+
+		BDDAssertions.then(supplier.get().get().keys()).containsExactly(CustomTraceExtractor.CUSTOM_TRACE_HEADER);
+	}
+
+}
+
+class CustomTracePropagation extends Propagation.Factory implements Propagation<String> {
+
+	public static final List<String> KEYS = Collections.singletonList(CustomTraceExtractor.CUSTOM_TRACE_HEADER);
+
+	@Override
+	public List<String> keys() {
+		return KEYS;
+	}
+
+	@Override
+	public <R> TraceContext.Injector<R> injector(Setter<R, String> setter) {
+		return (traceContext, request) -> {
+			String trace = traceContext.traceIdString() + ":" + traceContext.spanIdString();
+			setter.put(request, CustomTraceExtractor.CUSTOM_TRACE_HEADER, trace);
+		};
+	}
+
+	@Override
+	public <R> TraceContext.Extractor<R> extractor(Getter<R, String> getter) {
+		Objects.requireNonNull(getter);
+		return new CustomTraceExtractor<>(getter);
+	}
+
+	@Override
+	public <K> Propagation<K> create(KeyFactory<K> keyFactory) {
+		return StringPropagationAdapter.create(this, keyFactory);
+	}
+
+}
+
+class CustomTraceExtractor<R> implements TraceContext.Extractor<R> {
+
+	static final String CUSTOM_TRACE_HEADER = "x-custom-trace";
+
+	final Propagation.Getter<R, String> getter;
+
+	CustomTraceExtractor(Propagation.Getter<R, String> getter) {
+		this.getter = getter;
+	}
+
+	@Override
+	@SuppressWarnings("ReturnCount")
+	public TraceContextOrSamplingFlags extract(R request) {
+		String traceString = getter.get(request, CUSTOM_TRACE_HEADER);
+		if (!StringUtils.hasText(traceString)) {
+			return TraceContextOrSamplingFlags.EMPTY;
+		}
+		String[] trace = traceString.split(":");
+		if (trace.length != 2) {
+			return TraceContextOrSamplingFlags.EMPTY;
+		}
+
+		try {
+			TraceContext traceContext = TraceContext.newBuilder().traceId(HexCodec.lowerHexToUnsignedLong(trace[0]))
+					.spanId(HexCodec.lowerHexToUnsignedLong(trace[1])).build();
+
+			return TraceContextOrSamplingFlags.create(traceContext);
+		}
+		catch (NumberFormatException ex) {
+			return TraceContextOrSamplingFlags.EMPTY;
+		}
+	}
+
+}

spring-cloud-sleuth-instrumentation/src/main/java/org/springframework/cloud/sleuth/instrument/web/client/TraceWebClientBeanPostProcessor.java

@@ -80,4 +80,3 @@ public class TraceWebClientBeanPostProcessor implements BeanPostProcessor {
 	}
 
 }
-

spring-cloud-sleuth-instrumentation/src/main/java/org/springframework/cloud/sleuth/instrument/web/client/feign/TraceFeignBuilderBeanPostProcessor.java

@@ -27,8 +27,8 @@ import org.springframework.beans.factory.config.BeanPostProcessor;
 import org.springframework.util.ReflectionUtils;
 
 /**
- * {@link BeanPostProcessor} that ensures that each {@link Feign.Builder} has
+ * {@link BeanPostProcessor} that ensures that each {@link Feign.Builder} has a trace
- * a trace representation of a {@link Client}.
+ * representation of a {@link Client}.
  *
  * @author Marcin Grzejszczak
  * @since 3.0.2