Add GrpcServiceDiscoverer to prepare for interceptors

This commit re-introduces the service discoverer concept from the
gRPC ecosystem. We previously removed it but realized that the
abstraction is helpful to provide fully configured service
definitions with features like server interceptors. The next
commit will take advantage of this commit to add interceptors.

See #4

Author: onobc

spring-grpc-core/src/main/java/org/springframework/grpc/server/GrpcServiceDiscoverer.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2024-2024 The gRPC-Spring 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.grpc.server;
+
+import java.util.List;
+
+import io.grpc.ServerServiceDefinition;
+
+/**
+ * Discovers {@link ServerServiceDefinition gRPC services} to be provided by the server.
+ *
+ * @author Michael (yidongnan@gmail.com)
+ * @author Chris Bono
+ */
+@FunctionalInterface
+public interface GrpcServiceDiscoverer {
+
+	/**
+	 * Find gRPC services for the server to provide.
+	 * @return list of services to add to the server - empty when no services available
+	 */
+	List<ServerServiceDefinition> findServices();
+
+}

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

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2016-2023 The gRPC-Spring 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.grpc.autoconfigure.server;
+
+import java.util.List;
+
+import io.grpc.BindableService;
+import io.grpc.ServerServiceDefinition;
+
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.grpc.server.GrpcServiceDiscoverer;
+
+/**
+ * The default {@link GrpcServiceDiscoverer} that finds all {@link BindableService} beans
+ * and configures and binds them.
+ *
+ * @author Michael (yidongnan@gmail.com)
+ * @author Chris Bono
+ */
+class DefaultGrpcServiceDiscoverer implements GrpcServiceDiscoverer {
+
+	private final ObjectProvider<BindableService> grpcServicesProvider;
+
+	DefaultGrpcServiceDiscoverer(ObjectProvider<BindableService> grpcServicesProvider) {
+		this.grpcServicesProvider = grpcServicesProvider;
+	}
+
+	@Override
+	public List<ServerServiceDefinition> findServices() {
+		return grpcServicesProvider.orderedStream().map(BindableService::bindService).toList();
+	}
+
+}

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

@@ -28,6 +28,7 @@
 import org.springframework.context.annotation.Import;
 import org.springframework.grpc.autoconfigure.common.codec.GrpcCodecConfiguration;
 import org.springframework.grpc.server.GrpcServerFactory;
+import org.springframework.grpc.server.GrpcServiceDiscoverer;
 import org.springframework.grpc.server.ServerBuilderCustomizer;
 import org.springframework.grpc.server.lifecycle.GrpcServerLifecycle;
 
@@ -69,4 +70,10 @@ ServerBuilderCustomizers serverBuilderCustomizers(ObjectProvider<ServerBuilderCu
 		return new ServerBuilderCustomizers(customizers.orderedStream().toList());
 	}
 
+	@ConditionalOnMissingBean
+	@Bean
+	GrpcServiceDiscoverer grpcServiceDiscoverer(ObjectProvider<BindableService> bindableServicesProvider) {
+		return new DefaultGrpcServiceDiscoverer(bindableServicesProvider);
+	}
+
 }

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

@@ -20,7 +20,6 @@
 
 import javax.net.ssl.KeyManagerFactory;
 
-import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
@@ -30,11 +29,11 @@
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.grpc.server.GrpcServerFactory;
+import org.springframework.grpc.server.GrpcServiceDiscoverer;
 import org.springframework.grpc.server.NettyGrpcServerFactory;
 import org.springframework.grpc.server.ServerBuilderCustomizer;
 import org.springframework.grpc.server.ShadedNettyGrpcServerFactory;
 
-import io.grpc.BindableService;
 import io.grpc.CompressorRegistry;
 import io.grpc.DecompressorRegistry;
 import io.grpc.netty.NettyServerBuilder;
@@ -54,7 +53,7 @@ static class ShadedNettyServerFactoryConfiguration {
 
 		@Bean
 		ShadedNettyGrpcServerFactory shadedNettyGrpcServerFactory(GrpcServerProperties properties,
-				ObjectProvider<BindableService> grpcServicesProvider, ServerBuilderCustomizers serverBuilderCustomizers,
+				GrpcServiceDiscoverer grpcServicesDiscoverer, ServerBuilderCustomizers serverBuilderCustomizers,
 				SslBundles bundles) {
 			ShadedNettyServerFactoryPropertyMapper mapper = new ShadedNettyServerFactoryPropertyMapper(properties);
 			List<ServerBuilderCustomizer<io.grpc.netty.shaded.io.grpc.netty.NettyServerBuilder>> builderCustomizers = List
@@ -66,7 +65,7 @@ ShadedNettyGrpcServerFactory shadedNettyGrpcServerFactory(GrpcServerProperties p
 			}
 			ShadedNettyGrpcServerFactory factory = new ShadedNettyGrpcServerFactory(properties.getAddress(), keyManager,
 					builderCustomizers);
-			grpcServicesProvider.orderedStream().map(BindableService::bindService).forEach(factory::addService);
+			grpcServicesDiscoverer.findServices().forEach(factory::addService);
 			return factory;
 		}
 
@@ -94,7 +93,7 @@ static class NettyServerFactoryConfiguration {
 
 		@Bean
 		NettyGrpcServerFactory nettyGrpcServerFactory(GrpcServerProperties properties,
-				ObjectProvider<BindableService> grpcServicesProvider, ServerBuilderCustomizers serverBuilderCustomizers,
+				GrpcServiceDiscoverer grpcServicesDiscoverer, ServerBuilderCustomizers serverBuilderCustomizers,
 				SslBundles bundles) {
 			NettyServerFactoryPropertyMapper mapper = new NettyServerFactoryPropertyMapper(properties);
 			List<ServerBuilderCustomizer<NettyServerBuilder>> builderCustomizers = List
@@ -106,7 +105,7 @@ NettyGrpcServerFactory nettyGrpcServerFactory(GrpcServerProperties properties,
 			}
 			NettyGrpcServerFactory factory = new NettyGrpcServerFactory(properties.getAddress(), keyManager,
 					builderCustomizers);
-			grpcServicesProvider.orderedStream().map(BindableService::bindService).forEach(factory::addService);
+			grpcServicesDiscoverer.findServices().forEach(factory::addService);
 			return factory;
 		}
 

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

@@ -28,6 +28,7 @@
 import java.util.concurrent.TimeUnit;
 
 import org.assertj.core.api.InstanceOfAssertFactories;
+import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.mockito.InOrder;
 import org.mockito.MockedStatic;
@@ -41,6 +42,7 @@
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.annotation.Order;
 import org.springframework.grpc.server.GrpcServerFactory;
+import org.springframework.grpc.server.GrpcServiceDiscoverer;
 import org.springframework.grpc.server.NettyGrpcServerFactory;
 import org.springframework.grpc.server.ServerBuilderCustomizer;
 import org.springframework.grpc.server.ShadedNettyGrpcServerFactory;
@@ -60,10 +62,16 @@
  */
 class GrpcServerAutoConfigurationTests {
 
-	private ApplicationContextRunner contextRunner() {
-		BindableService service = mock();
-		ServerServiceDefinition serviceDefinition = ServerServiceDefinition.builder("my-service").build();
+	private final BindableService service = mock();
+
+	private final ServerServiceDefinition serviceDefinition = ServerServiceDefinition.builder("my-service").build();
+
+	@BeforeEach
+	void prepareForTest() {
 		when(service.bindService()).thenReturn(serviceDefinition);
+	}
+
+	private ApplicationContextRunner contextRunner() {
 		// NOTE: we use noop server lifecycle to avoid startup
 		return new ApplicationContextRunner()
 			.withConfiguration(AutoConfigurations.of(GrpcServerAutoConfiguration.class,
@@ -73,9 +81,6 @@ private ApplicationContextRunner contextRunner() {
 	}
 
 	private ApplicationContextRunner contextRunnerWithLifecyle() {
-		BindableService service = mock();
-		ServerServiceDefinition serviceDefinition = ServerServiceDefinition.builder("my-service").build();
-		when(service.bindService()).thenReturn(serviceDefinition);
 		// NOTE: we use noop server lifecycle to avoid startup
 		return new ApplicationContextRunner()
 			.withConfiguration(AutoConfigurations.of(GrpcServerAutoConfiguration.class,
@@ -111,6 +116,24 @@ void serverLifecycleAutoConfiguredAsExpected() {
 				.hasFieldOrPropertyWithValue("factory", context.getBean(GrpcServerFactory.class)));
 	}
 
+	@Test
+	void whenHasUserDefinedGrpcServiceDiscovererDoesNotAutoConfigureBean() {
+		GrpcServiceDiscoverer customGrpcServiceDiscoverer = mock(GrpcServiceDiscoverer.class);
+		this.contextRunnerWithLifecyle()
+			.withBean("customGrpcServiceDiscoverer", GrpcServiceDiscoverer.class, () -> customGrpcServiceDiscoverer)
+			.run((context) -> assertThat(context).getBean(GrpcServiceDiscoverer.class)
+				.isSameAs(customGrpcServiceDiscoverer));
+	}
+
+	@Test
+	void grpcServiceDiscovererAutoConfiguredAsExpected() {
+		this.contextRunnerWithLifecyle()
+			.run((context) -> assertThat(context).getBean(GrpcServiceDiscoverer.class)
+				.extracting(GrpcServiceDiscoverer::findServices,
+						InstanceOfAssertFactories.list(ServerServiceDefinition.class))
+				.containsExactly(this.serviceDefinition));
+	}
+
 	@Test
 	void whenHasUserDefinedServerBuilderCustomizersDoesNotAutoConfigureBean() {
 		ServerBuilderCustomizers customCustomizers = mock(ServerBuilderCustomizers.class);