Revert "Temporarily remove auto-config for Reactor context propagation"

This reverts commit 88de3cc089.

See gh-34201

spring-boot-project/spring-boot-autoconfigure/build.gradle

@@ -220,6 +220,7 @@ dependencies {
 	testImplementation("com.mysql:mysql-connector-j")
 	testImplementation("com.squareup.okhttp3:mockwebserver")
 	testImplementation("com.sun.xml.messaging.saaj:saaj-impl")
+	testImplementation("io.micrometer:context-propagation")
 	testImplementation("io.projectreactor:reactor-test")
 	testImplementation("io.r2dbc:r2dbc-h2")
 	testImplementation("jakarta.json:jakarta.json-api")

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/reactor/ReactorAutoConfiguration.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2012-2023 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.boot.autoconfigure.reactor;
+
+import reactor.core.publisher.Hooks;
+
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * {@link EnableAutoConfiguration Auto-configuration} for Reactor.
+ *
+ * @author Brian Clozel
+ * @since 3.0.2
+ */
+@Configuration(proxyBeanMethods = false)
+@ConditionalOnClass(Hooks.class)
+@EnableConfigurationProperties(ReactorProperties.class)
+public class ReactorAutoConfiguration {
+
+	public ReactorAutoConfiguration(ReactorProperties properties) {
+		if (properties.getContextPropagation() == ReactorProperties.ContextPropagationMode.AUTO) {
+			Hooks.enableAutomaticContextPropagation();
+		}
+	}
+
+}

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/reactor/ReactorProperties.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2012-2023 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.boot.autoconfigure.reactor;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+
+/**
+ * Configuration properties for Reactor.
+ *
+ * @author Brian Clozel
+ * @since 3.0.3
+ */
+@ConfigurationProperties(prefix = "spring.reactor")
+public class ReactorProperties {
+
+	/**
+	 * Context Propagation support mode for Reactor operators.
+	 */
+	private ContextPropagationMode contextPropagation = ContextPropagationMode.AUTO;
+
+	public ContextPropagationMode getContextPropagation() {
+		return this.contextPropagation;
+	}
+
+	public void setContextPropagation(ContextPropagationMode contextPropagation) {
+		this.contextPropagation = contextPropagation;
+	}
+
+	public enum ContextPropagationMode {
+
+		/**
+		 * Context Propagation is applied to all Reactor operators.
+		 */
+		AUTO,
+
+		/**
+		 * Context Propagation is only applied to "tap" and "handle" Reactor operators.
+		 */
+		LIMITED
+
+	}
+
+}

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/reactor/package-info.java

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2023 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.
+ */
+
+/**
+ * Auto-configuration for Reactor.
+ */
+package org.springframework.boot.autoconfigure.reactor;

spring-boot-project/spring-boot-autoconfigure/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -2090,6 +2090,10 @@
         "level": "error"
       }
     },
+    {
+      "name": "spring.reactor.context-propagation",
+      "defaultValue": "auto"
+    },
     {
       "name": "spring.reactor.stacktrace-mode.enabled",
       "description": "Whether Reactor should collect stacktrace information at runtime.",

spring-boot-project/spring-boot-autoconfigure/src/main/resources/META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports

@@ -97,6 +97,7 @@ org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration
 org.springframework.boot.autoconfigure.pulsar.PulsarAutoConfiguration
 org.springframework.boot.autoconfigure.pulsar.PulsarReactiveAutoConfiguration
 org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration
+org.springframework.boot.autoconfigure.reactor.ReactorAutoConfiguration
 org.springframework.boot.autoconfigure.r2dbc.R2dbcAutoConfiguration
 org.springframework.boot.autoconfigure.r2dbc.R2dbcTransactionManagerAutoConfiguration
 org.springframework.boot.autoconfigure.rsocket.RSocketMessagingAutoConfiguration

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/reactor/ReactorAutoConfigurationTests.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright 2012-2023 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.boot.autoconfigure.reactor;
+
+import java.util.concurrent.atomic.AtomicReference;
+
+import io.micrometer.context.ContextRegistry;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import reactor.core.publisher.Mono;
+import reactor.util.context.Context;
+
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link ReactorAutoConfiguration}.
+ *
+ * @author Brian Clozel
+ */
+class ReactorAutoConfigurationTests {
+
+	private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
+		.withConfiguration(AutoConfigurations.of(ReactorAutoConfiguration.class));
+
+	private static final String THREADLOCAL_KEY = "ReactorAutoConfigurationTests";
+
+	private static final ThreadLocal<String> THREADLOCAL_VALUE = ThreadLocal.withInitial(() -> "failure");
+
+	@BeforeAll
+	static void initializeThreadLocalAccessors() {
+		ContextRegistry globalRegistry = ContextRegistry.getInstance();
+		globalRegistry.registerThreadLocalAccessor(THREADLOCAL_KEY, THREADLOCAL_VALUE);
+	}
+
+	@Test
+	void shouldConfigureAutomaticContextPropagation() {
+		AtomicReference<String> threadLocalValue = new AtomicReference<>();
+		this.contextRunner.run((applicationContext) -> {
+			Mono.just("test")
+				.doOnNext((element) -> threadLocalValue.set(THREADLOCAL_VALUE.get()))
+				.contextWrite(Context.of(THREADLOCAL_KEY, "success"))
+				.block();
+			assertThat(threadLocalValue.get()).isEqualTo("success");
+		});
+	}
+
+}

spring-boot-project/spring-boot-docs/src/docs/asciidoc/actuator/observability.adoc

@@ -80,4 +80,7 @@ The attributes of the `Resource` can be configured via the configprop:management
 NOTE: Spring Boot does not provide auto-configuration for OpenTelemetry metrics or logging.
 OpenTelemetry tracing is only auto-configured when used together with <<actuator#actuator.micrometer-tracing, Micrometer Tracing>>.
 
+Observability support relies on the https://github.com/micrometer-metrics/context-propagation[Context Propagation library] for forwarding the current observation across threads and reactive pipelines.
+`ThreadLocal` values are automatically reinstated in reactive operators, this behavior is controlled with the configprop:spring.reactor.context-propagation[] property.
+
 The next sections will provide more details about logging, metrics and traces.

spring-boot-project/spring-boot-parent/build.gradle

@@ -138,6 +138,13 @@ bom {
 			]
 		}
 	}
+	library("Micrometer Context Propagation", "1.0.2") {
+		group("io.micrometer") {
+			modules = [
+					"context-propagation"
+			]
+		}
+	}
 	library("MockK", "1.13.5") {
 		group("io.mockk") {
 			modules = [