Break cycles between Zipkin senders and HTTP client observation

Previously, RestTemplateBuilder and WebClient.Builder beans were used
to create the HTTP client for sending out spans. Those same beans are
also instrumented for observability which results in a cycle.

This commit breaks the cycle by not using the application-web
builders to create the RestTemplate and WebClient's used by the Zipkin
senders. Instead, builders are created inline, with new callbacks
being introduced to allow the user to customize these Zipkin-specific
builders.

See gh-32528

Author: marcingrzejszczak

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

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.actuate.autoconfigure.tracing.zipkin;
 
+import java.util.List;
+
 import io.opentelemetry.exporter.zipkin.ZipkinSpanExporter;
 import zipkin2.Span;
 import zipkin2.codec.BytesEncoder;
@@ -73,12 +75,12 @@ static class RestTemplateSenderConfiguration {
 
 		@Bean
 		@ConditionalOnMissingBean(Sender.class)
-		@ConditionalOnBean(RestTemplateBuilder.class)
 		ZipkinRestTemplateSender restTemplateSender(ZipkinProperties properties,
-				RestTemplateBuilder restTemplateBuilder) {
-			RestTemplate restTemplate = restTemplateBuilder.setConnectTimeout(properties.getConnectTimeout())
-					.setReadTimeout(properties.getReadTimeout()).build();
-			return new ZipkinRestTemplateSender(properties.getEndpoint(), restTemplate);
+				List<ZipkinRestTemplateBuilderCustomizer> customizers) {
+			RestTemplateBuilder restTemplateBuilder = new RestTemplateBuilder()
+					.setConnectTimeout(properties.getConnectTimeout()).setReadTimeout(properties.getReadTimeout());
+			customizers.forEach((c) -> c.customize(restTemplateBuilder));
+			return new ZipkinRestTemplateSender(properties.getEndpoint(), restTemplateBuilder.build());
 		}
 
 	}
@@ -90,10 +92,11 @@ static class WebClientSenderConfiguration {
 
 		@Bean
 		@ConditionalOnMissingBean(Sender.class)
-		@ConditionalOnBean(WebClient.Builder.class)
-		ZipkinWebClientSender webClientSender(ZipkinProperties properties, WebClient.Builder webClientBuilder) {
-			WebClient webClient = webClientBuilder.build();
-			return new ZipkinWebClientSender(properties.getEndpoint(), webClient);
+		ZipkinWebClientSender webClientSender(ZipkinProperties properties,
+				List<ZipkinWebClientBuilderCustomizer> customizers) {
+			WebClient.Builder builder = WebClient.builder();
+			customizers.forEach((c) -> c.customize(builder));
+			return new ZipkinWebClientSender(properties.getEndpoint(), builder.build());
 		}
 
 	}

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/tracing/zipkin/ZipkinConfigurationsSenderConfigurationTests.java

@@ -17,6 +17,7 @@
 package org.springframework.boot.actuate.autoconfigure.tracing.zipkin;
 
 import org.junit.jupiter.api.Test;
+import org.mockito.ArgumentMatchers;
 import zipkin2.reporter.Sender;
 import zipkin2.reporter.urlconnection.URLConnectionSender;
 
@@ -26,12 +27,12 @@
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.boot.test.context.runner.ReactiveWebApplicationContextRunner;
 import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
-import org.springframework.boot.web.client.RestTemplateBuilder;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.web.reactive.function.client.WebClient;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.BDDMockito.then;
 import static org.mockito.Mockito.mock;
 
 /**
@@ -66,6 +67,8 @@ void shouldPreferWebClientSenderIfWebApplicationIsReactiveAndUrlSenderIsNotAvail
 					assertThat(context).doesNotHaveBean(URLConnectionSender.class);
 					assertThat(context).hasSingleBean(Sender.class);
 					assertThat(context).hasSingleBean(ZipkinWebClientSender.class);
+					then(context.getBean(ZipkinWebClientBuilderCustomizer.class)).should()
+							.customize(ArgumentMatchers.any());
 				});
 	}
 
@@ -90,29 +93,29 @@ void shouldPreferWebClientInNonWebApplicationAndUrlConnectionSenderIsNotAvailabl
 	}
 
 	@Test
-	void willUseRestTemplateInNonWebApplicationIfUrlConnectionSenderIsNotAvailable() {
+	void willUseRestTemplateInNonWebApplicationIfUrlConnectionSenderAndWebclientAreNotAvailable() {
 		this.contextRunner.withUserConfiguration(RestTemplateConfiguration.class)
-				.withClassLoader(new FilteredClassLoader("zipkin2.reporter.urlconnection")).run((context) -> {
+				.withClassLoader(new FilteredClassLoader(URLConnectionSender.class, WebClient.class)).run((context) -> {
 					assertThat(context).doesNotHaveBean(URLConnectionSender.class);
 					assertThat(context).hasSingleBean(Sender.class);
 					assertThat(context).hasSingleBean(ZipkinRestTemplateSender.class);
 				});
 	}
 
 	@Test
-	void willUseRestTemplateInServletWebApplicationIfUrlConnectionSenderIsNotAvailable() {
+	void willUseRestTemplateInServletWebApplicationIfUrlConnectionSenderAndWebClientNotAvailable() {
 		this.servletContextRunner.withUserConfiguration(RestTemplateConfiguration.class)
-				.withClassLoader(new FilteredClassLoader("zipkin2.reporter.urlconnection")).run((context) -> {
+				.withClassLoader(new FilteredClassLoader(URLConnectionSender.class, WebClient.class)).run((context) -> {
 					assertThat(context).doesNotHaveBean(URLConnectionSender.class);
 					assertThat(context).hasSingleBean(Sender.class);
 					assertThat(context).hasSingleBean(ZipkinRestTemplateSender.class);
 				});
 	}
 
 	@Test
-	void willUseRestTemplateInReactiveWebApplicationIfUrlConnectionSenderIsNotAvailable() {
+	void willUseRestTemplateInReactiveWebApplicationIfUrlConnectionSenderAndWebClientAreNotAvailable() {
 		this.reactiveContextRunner.withUserConfiguration(RestTemplateConfiguration.class)
-				.withClassLoader(new FilteredClassLoader("zipkin2.reporter.urlconnection")).run((context) -> {
+				.withClassLoader(new FilteredClassLoader(URLConnectionSender.class, WebClient.class)).run((context) -> {
 					assertThat(context).doesNotHaveBean(URLConnectionSender.class);
 					assertThat(context).hasSingleBean(Sender.class);
 					assertThat(context).hasSingleBean(ZipkinRestTemplateSender.class);
@@ -140,8 +143,8 @@ void shouldBackOffOnCustomBeans() {
 	private static class RestTemplateConfiguration {
 
 		@Bean
-		RestTemplateBuilder restTemplateBuilder() {
-			return new RestTemplateBuilder();
+		ZipkinRestTemplateBuilderCustomizer restTemplateBuilder() {
+			return mock(ZipkinRestTemplateBuilderCustomizer.class);
 		}
 
 	}
@@ -150,8 +153,8 @@ RestTemplateBuilder restTemplateBuilder() {
 	private static class WebClientConfiguration {
 
 		@Bean
-		WebClient.Builder webClientBuilder() {
-			return WebClient.builder();
+		ZipkinWebClientBuilderCustomizer webClientBuilder() {
+			return mock(ZipkinWebClientBuilderCustomizer.class);
 		}
 
 	}