Add @FunctionalSpringBootTest and mini web server

User can run a minimal HTTP app using an app that is a Function
or an ApplicationContextInitializer. Can also test using
@FunctionalSpringBootTest in place of @SpringBootTest.

Add some tests and documentation for functional beans

Make server.address configurable

spring-cloud-function-web/src/main/java/org/springframework/cloud/function/web/function/FunctionEndpointInitializer.java

@@ -0,0 +1,202 @@
+package org.springframework.cloud.function.web.function;
+
+import java.lang.management.ManagementFactory;
+import java.time.Duration;
+import java.util.Set;
+import java.util.function.Function;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import org.springframework.boot.autoconfigure.web.ErrorProperties;
+import org.springframework.boot.autoconfigure.web.ResourceProperties;
+import org.springframework.boot.autoconfigure.web.reactive.error.DefaultErrorWebExceptionHandler;
+import org.springframework.boot.web.reactive.error.DefaultErrorAttributes;
+import org.springframework.boot.web.reactive.error.ErrorAttributes;
+import org.springframework.cloud.function.context.FunctionCatalog;
+import org.springframework.cloud.function.context.catalog.FunctionInspector;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.ApplicationContextInitializer;
+import org.springframework.context.ApplicationEvent;
+import org.springframework.context.event.ContextRefreshedEvent;
+import org.springframework.context.event.SmartApplicationListener;
+import org.springframework.context.support.GenericApplicationContext;
+import org.springframework.core.env.Environment;
+import org.springframework.http.codec.ServerCodecConfigurer;
+import org.springframework.http.server.reactive.HttpHandler;
+import org.springframework.http.server.reactive.ReactorHttpHandlerAdapter;
+import org.springframework.util.ClassUtils;
+import org.springframework.web.reactive.function.server.HandlerStrategies;
+import org.springframework.web.reactive.function.server.RouterFunction;
+import org.springframework.web.reactive.function.server.RouterFunctions;
+import org.springframework.web.server.WebExceptionHandler;
+import org.springframework.web.server.adapter.HttpWebHandlerAdapter;
+import org.springframework.web.server.adapter.WebHttpHandlerBuilder;
+
+import static org.springframework.web.reactive.function.server.RequestPredicates.POST;
+import static org.springframework.web.reactive.function.server.RouterFunctions.route;
+import static org.springframework.web.reactive.function.server.ServerResponse.ok;
+
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import reactor.netty.DisposableServer;
+import reactor.netty.http.server.HttpServer;
+
+public class FunctionEndpointInitializer
+		implements ApplicationContextInitializer<GenericApplicationContext> {
+
+	@Override
+	public void initialize(GenericApplicationContext context) {
+		if (context.getEnvironment().getProperty("spring.functional.enabled",
+				Boolean.class, false) && ClassUtils.isPresent("org.springframework.http.server.reactive.HttpHandler", null)) {
+			registerEndpoint(context);
+			registerWebFluxAutoConfiguration(context);
+		}
+	}
+
+	private void registerWebFluxAutoConfiguration(GenericApplicationContext context) {
+		context.registerBean(DefaultErrorWebExceptionHandler.class,
+				() -> errorHandler(context));
+		context.registerBean(WebHttpHandlerBuilder.WEB_HANDLER_BEAN_NAME,
+				HttpWebHandlerAdapter.class, () -> httpHandler(context));
+		context.addApplicationListener(new ServerListener(context));
+	}
+
+	private void registerEndpoint(GenericApplicationContext context) {
+		context.registerBean(FunctionEndpointFactory.class,
+				() -> new FunctionEndpointFactory(context.getBean(FunctionCatalog.class),
+						context.getBean(FunctionInspector.class),
+						context.getEnvironment()));
+		context.registerBean(RouterFunction.class,
+				() -> context.getBean(FunctionEndpointFactory.class).functionEndpoints());
+	}
+
+	private HttpWebHandlerAdapter httpHandler(GenericApplicationContext context) {
+		return (HttpWebHandlerAdapter) RouterFunctions.toHttpHandler(
+				context.getBean(RouterFunction.class),
+				HandlerStrategies.empty()
+						.exceptionHandler(context.getBean(WebExceptionHandler.class))
+						.codecs(config -> config.registerDefaults(true)).build());
+	}
+
+	private DefaultErrorWebExceptionHandler errorHandler(
+			GenericApplicationContext context) {
+		context.registerBean(ErrorAttributes.class, () -> new DefaultErrorAttributes());
+		context.registerBean(ErrorProperties.class, () -> new ErrorProperties());
+		context.registerBean(ResourceProperties.class, () -> new ResourceProperties());
+		DefaultErrorWebExceptionHandler handler = new DefaultErrorWebExceptionHandler(
+				context.getBean(ErrorAttributes.class),
+				context.getBean(ResourceProperties.class),
+				context.getBean(ErrorProperties.class), context);
+		ServerCodecConfigurer codecs = ServerCodecConfigurer.create();
+		handler.setMessageWriters(codecs.getWriters());
+		handler.setMessageReaders(codecs.getReaders());
+		return handler;
+	}
+
+	private static class ServerListener implements SmartApplicationListener {
+
+		private static Log logger = LogFactory.getLog(ServerListener.class);
+
+		private GenericApplicationContext context;
+
+		public ServerListener(GenericApplicationContext context) {
+			this.context = context;
+		}
+
+		@Override
+		public void onApplicationEvent(ApplicationEvent event) {
+			ApplicationContext context = ((ContextRefreshedEvent) event)
+					.getApplicationContext();
+			if (context != this.context) {
+				return;
+			}
+			if (!ClassUtils.isPresent(
+					"org.springframework.http.server.reactive.HttpHandler", null)) {
+				logger.info("No web server classes found so no server to start");
+				return;
+			}
+			Integer port = Integer.valueOf(context.getEnvironment()
+					.resolvePlaceholders("${server.port:${PORT:8080}}"));
+			String address = context.getEnvironment()
+					.resolvePlaceholders("${server.address:0.0.0.0}");
+			if (port >= 0) {
+				HttpHandler handler = context.getBean(HttpHandler.class);
+				ReactorHttpHandlerAdapter adapter = new ReactorHttpHandlerAdapter(
+						handler);
+				HttpServer httpServer = HttpServer.create().host(address).port(port)
+						.handle(adapter);
+				Thread thread = new Thread(() -> httpServer
+						.bindUntilJavaShutdown(Duration.ofSeconds(60), this::callback),
+						"server-startup");
+				thread.setDaemon(false);
+				thread.start();
+			}
+		}
+
+		private void callback(DisposableServer server) {
+			logger.info("Server started");
+			try {
+				double uptime = ManagementFactory.getRuntimeMXBean().getUptime();
+				System.err.println("JVM running for " + uptime + "ms");
+			}
+			catch (Throwable e) {
+			}
+		}
+
+		@Override
+		public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
+			return eventType.isAssignableFrom(ContextRefreshedEvent.class);
+		}
+
+	}
+
+}
+
+class FunctionEndpointFactory {
+
+	private static Log logger = LogFactory.getLog(FunctionEndpointFactory.class);
+
+	private Function<Flux<?>, Flux<?>> function;
+
+	private FunctionInspector inspector;
+
+	public FunctionEndpointFactory(FunctionCatalog catalog, FunctionInspector inspector,
+			Environment environment) {
+		String handler = environment.resolvePlaceholders("${function.handler}");
+		if (handler.startsWith("$")) {
+			handler = null;
+		}
+		this.inspector = inspector;
+		this.function = extract(catalog, handler);
+	}
+
+	private Function<Flux<?>, Flux<?>> extract(FunctionCatalog catalog, String handler) {
+		Set<String> names = catalog.getNames(Function.class);
+		if (!names.isEmpty()) {
+			logger.info("Found functions: " + names);
+			if (handler != null) {
+				logger.info("Configured function: " + handler);
+				if (!names.contains(handler)) {
+					throw new IllegalStateException("Cannot locate function: " + handler);
+				}
+				return catalog.lookup(Function.class, handler);
+			}
+			return catalog.lookup(Function.class, names.iterator().next());
+		}
+		throw new IllegalStateException("No function defined");
+	}
+
+	@SuppressWarnings({ "unchecked" })
+	public <T> RouterFunction<?> functionEndpoints() {
+		return route(POST("/"), request -> {
+			Class<?> inputType = this.inspector.getInputType(this.function);
+			Class<T> outputType = (Class<T>) this.inspector.getOutputType(this.function);
+			return ok().body(
+					Mono.from(
+							(Flux<T>) this.function.apply(request.bodyToFlux(inputType))),
+					outputType);
+		});
+	}
+
+}

spring-cloud-function-web/src/main/resources/META-INF/spring.factories

@@ -6,3 +6,6 @@ org.springframework.cloud.function.web.source.SupplierAutoConfiguration
 org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc=\
 org.springframework.cloud.function.web.flux.ReactorAutoConfiguration,\
 org.springframework.cloud.function.context.config.ContextFunctionCatalogAutoConfiguration
+
+org.springframework.context.ApplicationContextInitializer=\
+org.springframework.cloud.function.web.function.FunctionEndpointInitializer