Auto-configure Micrometer Observations

This commit auto-configures in the Micrometer Observations
API and its Observation server interceptor.

Resolves #1

Signed-off-by: Sunny <hmtang@gmail.com>

spring-grpc-dependencies/pom.xml

@@ -54,6 +54,7 @@
 		<grpc.version>1.63.2</grpc.version>
 		<protobuf-java.version>3.25.5</protobuf-java.version>
 		<google-common-protos.version>2.46.0</google-common-protos.version>
+		<micrometer.version>1.13.6</micrometer.version>
 	</properties>
 
 	<dependencyManagement>
@@ -112,6 +113,13 @@
 				<artifactId>proto-google-common-protos</artifactId>
 				<version>${google-common-protos.version}</version>
 			</dependency>
+			<dependency>
+				<groupId>io.micrometer</groupId>
+				<artifactId>micrometer-bom</artifactId>
+				<version>${micrometer.version}</version>
+				<type>pom</type>
+				<scope>import</scope>
+			</dependency>
 		</dependencies>
 	</dependencyManagement>
 

spring-grpc-spring-boot-autoconfigure/pom.xml

@@ -75,6 +75,16 @@
 			<artifactId>spring-boot-starter</artifactId>
 			<scope>provided</scope>
 		</dependency>
+		<dependency>
+			<groupId>io.micrometer</groupId>
+			<artifactId>micrometer-observation</artifactId>
+			<optional>true</optional>
+		</dependency>
+		<dependency>
+			<groupId>io.micrometer</groupId>
+			<artifactId>micrometer-core</artifactId>
+			<optional>true</optional>
+		</dependency>
 
 		<!-- test dependencies -->
 		<dependency>

spring-grpc-spring-boot-autoconfigure/src/main/java/org/springframework/grpc/autoconfigure/server/GrpcServerObservationAutoConfiguration.java

@@ -0,0 +1,32 @@
+package org.springframework.grpc.autoconfigure.server;
+
+import io.grpc.ServerBuilder;
+import io.grpc.ServerInterceptor;
+import io.micrometer.core.instrument.binder.grpc.ObservationGrpcServerInterceptor;
+import io.micrometer.observation.ObservationRegistry;
+import org.springframework.boot.autoconfigure.AutoConfiguration;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.context.annotation.Bean;
+import org.springframework.grpc.server.ServerBuilderCustomizer;
+
+@AutoConfiguration(
+		afterName = "org.springframework.boot.actuate.autoconfigure.observation.ObservationAutoConfiguration")
+@ConditionalOnClass(value = { ObservationRegistry.class, ObservationGrpcServerInterceptor.class })
+@ConditionalOnBean(ObservationRegistry.class)
+@ConditionalOnProperty(value = "spring.grpc.server.observation.enabled", matchIfMissing = true)
+public class GrpcServerObservationAutoConfiguration {
+
+	@Bean
+	public ServerInterceptor observationGrpcServerInterceptor(ObservationRegistry observationRegistry) {
+		return new ObservationGrpcServerInterceptor(observationRegistry);
+	}
+
+	@Bean
+	<T extends ServerBuilder<T>> ServerBuilderCustomizer<T> metricsInterceptor(
+			ServerInterceptor observationGrpcServerInterceptor) {
+		return (serverBuilder) -> serverBuilder.intercept(observationGrpcServerInterceptor);
+	}
+
+}

spring-grpc-spring-boot-autoconfigure/src/test/java/org/springframework/grpc/autoconfigure/server/GrpcServerObservationAutoConfigurationTests.java

@@ -0,0 +1,48 @@
+package org.springframework.grpc.autoconfigure.server;
+
+import io.grpc.ServerBuilder;
+import io.grpc.ServerInterceptor;
+import io.micrometer.observation.ObservationRegistry;
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.grpc.server.ServerBuilderCustomizer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class GrpcServerObservationAutoConfigurationTests {
+
+	private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
+		.withConfiguration(AutoConfigurations.of(GrpcServerObservationAutoConfiguration.class));
+
+	@Test
+	void whenObservationRegistryNotProvided_thenObservationInterceptorNotConfigured() {
+		this.contextRunner.run(context -> {
+			assertThat(context).doesNotHaveBean(ServerBuilderCustomizer.class);
+		});
+	}
+
+	@Test
+	void whenObservationInterceptorConfigured_thenServerBuilderCustomizerConfigured() {
+		this.contextRunner.withBean(ObservationRegistry.class, ObservationRegistry::create).run(context -> {
+			assertThat(context).hasSingleBean(ServerBuilderCustomizer.class);
+			assertThat(context).hasSingleBean(ServerInterceptor.class);
+			ServerInterceptor interceptor = context.getBean(ServerInterceptor.class);
+			ServerBuilderCustomizer customizer = context.getBean(ServerBuilderCustomizer.class);
+			ServerBuilder<?> builder = org.mockito.Mockito.mock(ServerBuilder.class);
+			customizer.customize(builder);
+			org.mockito.Mockito.verify(builder, org.mockito.Mockito.times(1)).intercept(interceptor);
+		});
+	}
+
+	@Test
+	void whenObservationPropertyDisabled_thenServerBuilderCustomizerNotConfigured() {
+		this.contextRunner.withPropertyValues("spring.grpc.server.observation.enabled=false")
+			.withBean(ObservationRegistry.class, ObservationRegistry::create)
+			.run(context -> {
+				assertThat(context).doesNotHaveBean(ServerBuilderCustomizer.class);
+				assertThat(context).doesNotHaveBean(ServerInterceptor.class);
+			});
+	}
+
+}