Inserts filter function only once; fixes gh-863

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

@@ -16,6 +16,9 @@
 
 package org.springframework.cloud.sleuth.instrument.web.client;
 
+import java.util.List;
+import java.util.function.Consumer;
+
 import brave.Span;
 import brave.Tracer;
 import brave.http.HttpClientHandler;
@@ -61,14 +64,24 @@ class TraceWebClientBeanPostProcessor implements BeanPostProcessor {
 			WebClient webClient = (WebClient) bean;
 			return webClient
 					.mutate()
-					.filter(new TraceExchangeFilterFunction(this.beanFactory))
+					.filters(addTraceExchangeFilterFunctionIfNotPresent())
 					.build();
 		} else if (bean instanceof WebClient.Builder) {
 			WebClient.Builder webClientBuilder = (WebClient.Builder) bean;
-			return webClientBuilder.filter(new TraceExchangeFilterFunction(this.beanFactory));
+			return webClientBuilder.filters(addTraceExchangeFilterFunctionIfNotPresent());
 		}
 		return bean;
 	}
+
+	private Consumer<List<ExchangeFilterFunction>> addTraceExchangeFilterFunctionIfNotPresent() {
+		return functions -> {
+			if (functions
+					.stream()
+					.noneMatch(f -> f instanceof TraceExchangeFilterFunction)) {
+				functions.add(new TraceExchangeFilterFunction(this.beanFactory));
+			}
+		};
+	}
 }
 
 class TraceExchangeFilterFunction implements ExchangeFilterFunction {

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/web/client/TraceWebClientBeanPostProcessorTest.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2013-2018 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
+ *
+ *      http://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.instrument.web.client;
+
+import org.assertj.core.api.BDDAssertions;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnitRunner;
+import org.springframework.beans.factory.BeanFactory;
+import org.springframework.web.reactive.function.client.WebClient;
+
+/**
+ * @author Marcin Grzejszczak
+ */
+@RunWith(MockitoJUnitRunner.class)
+public class TraceWebClientBeanPostProcessorTest {
+
+	@Mock BeanFactory beanFactory;
+
+	@Test public void should_add_filter_only_once_to_web_client() {
+		TraceWebClientBeanPostProcessor processor = new TraceWebClientBeanPostProcessor(this.beanFactory);
+		WebClient client = WebClient.create();
+
+		client = (WebClient) processor.postProcessAfterInitialization(client, "foo");
+		client = (WebClient) processor.postProcessAfterInitialization(client, "foo");
+
+		client.mutate().filters(filters -> {
+			BDDAssertions.then(filters).hasSize(1);
+			BDDAssertions.then(filters.get(0)).isInstanceOf(TraceExchangeFilterFunction.class);
+		});
+	}
+
+	@Test public void should_add_filter_only_once_to_web_client_via_builder() {
+		TraceWebClientBeanPostProcessor processor = new TraceWebClientBeanPostProcessor(this.beanFactory);
+		WebClient.Builder builder = WebClient.builder();
+
+		builder = (WebClient.Builder) processor.postProcessAfterInitialization(builder, "foo");
+		builder = (WebClient.Builder) processor.postProcessAfterInitialization(builder, "foo");
+
+		builder.build().mutate().filters(filters -> {
+			BDDAssertions.then(filters).hasSize(1);
+			BDDAssertions.then(filters.get(0)).isInstanceOf(TraceExchangeFilterFunction.class);
+		});
+	}
+}