Forwarded header auto-config should be conditional on missing bean

See gh-5677

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/reactive/ReactiveWebServerFactoryAutoConfiguration.java

@@ -25,6 +25,7 @@ import org.springframework.beans.factory.support.RootBeanDefinition;
 import org.springframework.boot.autoconfigure.AutoConfigureOrder;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
 import org.springframework.boot.autoconfigure.web.ServerProperties;
@@ -65,6 +66,7 @@ public class ReactiveWebServerFactoryAutoConfiguration {
 	}
 
 	@Bean
+	@ConditionalOnMissingBean
 	@ConditionalOnProperty(value = "server.forward-headers-strategy",
 			havingValue = "framework")
 	public ForwardedHeaderTransformer forwardedHeaderTransformer() {

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/ServletWebServerFactoryAutoConfiguration.java

@@ -79,6 +79,7 @@ public class ServletWebServerFactoryAutoConfiguration {
 	}
 
 	@Bean
+	@ConditionalOnMissingFilterBean(ForwardedHeaderFilter.class)
 	@ConditionalOnProperty(value = "server.forward-headers-strategy",
 			havingValue = "framework")
 	public FilterRegistrationBean<ForwardedHeaderFilter> forwardedHeaderFilter() {

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/ReactiveWebServerFactoryAutoConfigurationTests.java

@@ -165,6 +165,16 @@ public class ReactiveWebServerFactoryAutoConfigurationTests {
 						.doesNotHaveBean(ForwardedHeaderTransformer.class));
 	}
 
+	@Test
+	public void forwardedHeaderTransformerWhenAlreadyRegisteredShouldBackOff() {
+		this.contextRunner
+				.withUserConfiguration(ForwardedHeaderTransformerConfiguration.class,
+						HttpHandlerConfiguration.class)
+				.withPropertyValues("server.forward-headers-strategy=framework")
+				.run((context) -> assertThat(context)
+						.hasSingleBean(ForwardedHeaderTransformer.class));
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	protected static class HttpHandlerConfiguration {
 
@@ -238,4 +248,14 @@ public class ReactiveWebServerFactoryAutoConfigurationTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class ForwardedHeaderTransformerConfiguration {
+
+		@Bean
+		public ForwardedHeaderTransformer testForwardedHeaderTransformer() {
+			return new ForwardedHeaderTransformer();
+		}
+
+	}
+
 }

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/ServletWebServerFactoryAutoConfigurationTests.java

@@ -208,6 +208,14 @@ public class ServletWebServerFactoryAutoConfigurationTests {
 						.doesNotHaveBean(FilterRegistrationBean.class));
 	}
 
+	@Test
+	public void forwardedHeaderFilterWhenFilterAlreadyRegisteredShouldBackOff() {
+		this.contextRunner.withUserConfiguration(ForwardedHeaderFilterConfiguration.class)
+				.withPropertyValues("server.forward-headers-strategy=framework")
+				.run((context) -> assertThat(context)
+						.hasSingleBean(FilterRegistrationBean.class));
+	}
+
 	private ContextConsumer<AssertableWebApplicationContext> verifyContext() {
 		return this::verifyContext;
 	}
@@ -357,4 +365,15 @@ public class ServletWebServerFactoryAutoConfigurationTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class ForwardedHeaderFilterConfiguration {
+
+		@Bean
+		public FilterRegistrationBean<ForwardedHeaderFilter> testForwardedHeaderFilter() {
+			ForwardedHeaderFilter filter = new ForwardedHeaderFilter();
+			return new FilterRegistrationBean<>(filter);
+		}
+
+	}
+
 }