Add NettyServerCustomizer for Reactor Netty support

This commit adds a new customizer interface, `NettyServerCustomizer` for
customizing Reactor Netty server instances while they're being built.

Closes gh-10418

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/netty/NettyReactiveWebServerFactory.java

@@ -16,6 +16,12 @@
 
 package org.springframework.boot.web.embedded.netty;
 
+import java.net.InetSocketAddress;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+
 import reactor.ipc.netty.http.server.HttpServer;
 
 import org.springframework.boot.web.reactive.server.AbstractReactiveWebServerFactory;
@@ -23,6 +29,7 @@ import org.springframework.boot.web.reactive.server.ReactiveWebServerFactory;
 import org.springframework.boot.web.server.WebServer;
 import org.springframework.http.server.reactive.HttpHandler;
 import org.springframework.http.server.reactive.ReactorHttpHandlerAdapter;
+import org.springframework.util.Assert;
 
 /**
  * {@link ReactiveWebServerFactory} that can be used to create {@link NettyWebServer}s.
@@ -32,6 +39,8 @@ import org.springframework.http.server.reactive.ReactorHttpHandlerAdapter;
  */
 public class NettyReactiveWebServerFactory extends AbstractReactiveWebServerFactory {
 
+	private List<NettyServerCustomizer> nettyServerCustomizers = new ArrayList<>();
+
 	public NettyReactiveWebServerFactory() {
 	}
 
@@ -47,15 +56,53 @@ public class NettyReactiveWebServerFactory extends AbstractReactiveWebServerFact
 		return new NettyWebServer(server, handlerAdapter);
 	}
 
+	/**
+	 * Returns a mutable collection of the {@link NettyServerCustomizer}s that will be
+	 * applied to the Netty server builder.
+	 * @return the customizers that will be applied
+	 */
+	public Collection<NettyServerCustomizer> getNettyServerCustomizers() {
+		return this.nettyServerCustomizers;
+	}
+
+	/**
+	 * Set {@link NettyServerCustomizer}s that should be applied to the Netty
+	 * server builder. Calling this method will replace any existing customizers.
+	 * @param nettyServerCustomizers the customizers to set
+	 */
+	public void setNettyServerCustomizers(
+			Collection<? extends NettyServerCustomizer> nettyServerCustomizers) {
+		Assert.notNull(nettyServerCustomizers,
+				"NettyServerCustomizers must not be null");
+		this.nettyServerCustomizers = new ArrayList<>(nettyServerCustomizers);
+	}
+
+
+	/**
+	 * Add {@link NettyServerCustomizer}s that should applied while building the server.
+	 * @param nettyServerCustomizer the customizers to add
+	 */
+	public void addContextCustomizers(
+			NettyServerCustomizer... nettyServerCustomizer) {
+		Assert.notNull(nettyServerCustomizer,
+				"NettyWebServerCustomizer must not be null");
+		this.nettyServerCustomizers.addAll(Arrays.asList(nettyServerCustomizer));
+	}
+
 	private HttpServer createHttpServer() {
-		HttpServer server;
+		return HttpServer.builder().options(options -> {
+			options.listenAddress(getListenAddress());
+			this.nettyServerCustomizers.forEach(customizer -> customizer.customize(options));
+		}).build();
+	}
+
+	private InetSocketAddress getListenAddress() {
 		if (getAddress() != null) {
-			server = HttpServer.create(getAddress().getHostAddress(), getPort());
+			return new InetSocketAddress(getAddress().getHostAddress(), getPort());
 		}
 		else {
-			server = HttpServer.create(getPort());
+			return new InetSocketAddress(getPort());
 		}
-		return server;
 	}
 
 }

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/netty/NettyServerCustomizer.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2012-2017 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
+ *
+ *      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.boot.web.embedded.netty;
+
+import reactor.ipc.netty.http.server.HttpServerOptions;
+
+/**
+ * Callback interface that can be used to customize a Reactor Netty server builder.
+ *
+ * @author Brian Clozel
+ * @see NettyReactiveWebServerFactory
+ * @since 2.0.0
+ */
+@FunctionalInterface
+public interface NettyServerCustomizer {
+
+	/**
+	 * Customize the Netty web server.
+	 * @param builder the server options builder to customize
+	 */
+	void customize(HttpServerOptions.Builder builder);
+}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/embedded/netty/NettyReactiveWebServerFactoryTests.java

@@ -16,13 +16,20 @@
 
 package org.springframework.boot.web.embedded.netty;
 
+import java.util.Arrays;
+
 import org.junit.Test;
+import org.mockito.InOrder;
+import reactor.ipc.netty.http.server.HttpServerOptions;
 
 import org.springframework.boot.web.reactive.server.AbstractReactiveWebServerFactory;
 import org.springframework.boot.web.reactive.server.AbstractReactiveWebServerFactoryTests;
 import org.springframework.boot.web.server.PortInUseException;
 
 import static org.hamcrest.Matchers.equalTo;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.inOrder;
+import static org.mockito.Mockito.mock;
 
 /**
  * Tests for {@link NettyReactiveWebServerFactory}.
@@ -33,7 +40,7 @@ public class NettyReactiveWebServerFactoryTests
 		extends AbstractReactiveWebServerFactoryTests {
 
 	@Override
-	protected AbstractReactiveWebServerFactory getFactory() {
+	protected NettyReactiveWebServerFactory getFactory() {
 		return new NettyReactiveWebServerFactory(0);
 	}
 
@@ -50,4 +57,20 @@ public class NettyReactiveWebServerFactoryTests
 		factory.getWebServer(new EchoHandler()).start();
 	}
 
+	@Test
+	public void nettyCustomizers() throws Exception {
+		NettyReactiveWebServerFactory factory = getFactory();
+		NettyServerCustomizer[] customizers = new NettyServerCustomizer[2];
+		for (int i = 0; i < customizers.length; i++) {
+			customizers[i] = mock(NettyServerCustomizer.class);
+		}
+		factory.setNettyServerCustomizers(Arrays.asList(customizers[0], customizers[1]));
+		this.webServer = factory.getWebServer(new EchoHandler());
+
+		InOrder ordered = inOrder((Object[]) customizers);
+		for (NettyServerCustomizer customizer : customizers) {
+			ordered.verify(customizer).customize(any(HttpServerOptions.Builder.class));
+		}
+	}
+
 }