Add multipart support to WebFlux functional API

Issue: SPR-14546

spring-webflux/src/test/java/org/springframework/web/reactive/config/DelegatingWebFluxConfigurationTests.java

@@ -103,7 +103,7 @@ public class DelegatingWebFluxConfigurationTests {
 		verify(webFluxConfigurer).configureArgumentResolvers(any());
 
 		assertSame(formatterRegistry.getValue(), initializerConversionService);
-		assertEquals(9, codecsConfigurer.getValue().getReaders().size());
+		assertEquals(10, codecsConfigurer.getValue().getReaders().size());
 	}
 
 	@Test

spring-webflux/src/test/java/org/springframework/web/reactive/config/WebFluxConfigurationSupportTests.java

@@ -127,7 +127,7 @@ public class WebFluxConfigurationSupportTests {
 		assertNotNull(adapter);
 
 		List<HttpMessageReader<?>> readers = adapter.getMessageCodecConfigurer().getReaders();
-		assertEquals(9, readers.size());
+		assertEquals(10, readers.size());
 
 		assertHasMessageReader(readers, forClass(byte[].class), APPLICATION_OCTET_STREAM);
 		assertHasMessageReader(readers, forClass(ByteBuffer.class), APPLICATION_OCTET_STREAM);

spring-webflux/src/test/java/org/springframework/web/reactive/function/MultipartIntegrationTests.java

@@ -0,0 +1,104 @@
+/*
+ * Copyright 2002-2017 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.web.reactive.function;
+
+import java.util.Map;
+
+import org.junit.Test;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.MediaType;
+import org.springframework.http.codec.multipart.Part;
+import org.springframework.util.LinkedMultiValueMap;
+import org.springframework.util.MultiValueMap;
+import org.springframework.web.reactive.function.client.ClientResponse;
+import org.springframework.web.reactive.function.client.WebClient;
+import org.springframework.web.reactive.function.server.AbstractRouterFunctionIntegrationTests;
+import org.springframework.web.reactive.function.server.RouterFunction;
+import org.springframework.web.reactive.function.server.ServerRequest;
+import org.springframework.web.reactive.function.server.ServerResponse;
+
+import static org.junit.Assert.assertEquals;
+
+import static org.springframework.web.reactive.function.server.RequestPredicates.POST;
+import static org.springframework.web.reactive.function.server.RouterFunctions.route;
+
+public class MultipartIntegrationTests extends AbstractRouterFunctionIntegrationTests {
+
+	private final WebClient webClient = WebClient.create();
+
+	@Test
+	public void multipart() {
+		Mono<ClientResponse> result = webClient
+				.post()
+				.uri("http://localhost:" + this.port + "/")
+				.contentType(MediaType.MULTIPART_FORM_DATA)
+				.body(BodyInserters.fromMultipartData(generateBody()))
+				.exchange();
+
+		StepVerifier
+				.create(result)
+				.consumeNextWith(response -> {
+					assertEquals(HttpStatus.OK, response.statusCode());
+				})
+				.verifyComplete();
+	}
+
+	private MultiValueMap<String, Object> generateBody() {
+		HttpHeaders fooHeaders = new HttpHeaders();
+		fooHeaders.setContentType(MediaType.TEXT_PLAIN);
+		ClassPathResource fooResource = new ClassPathResource("org/springframework/http/codec/multipart/foo.txt");
+		HttpEntity<ClassPathResource> fooPart = new HttpEntity<>(fooResource, fooHeaders);
+		HttpEntity<String> barPart = new HttpEntity<>("bar");
+		MultiValueMap<String, Object> parts = new LinkedMultiValueMap<>();
+		parts.add("fooPart", fooPart);
+		parts.add("barPart", barPart);
+		return parts;
+	}
+
+	@Override
+	protected RouterFunction<ServerResponse> routerFunction() {
+		MultipartHandler multipartHandler = new MultipartHandler();
+		return route(POST("/"), multipartHandler::handle);
+	}
+
+	private static class MultipartHandler {
+
+		public Mono<ServerResponse> handle(ServerRequest request) {
+			return request
+					.body(BodyExtractors.toMultipartData())
+					.flatMap(map -> {
+						Map<String, Part> parts = map.toSingleValueMap();
+						try {
+							assertEquals(2, parts.size());
+							assertEquals("foo.txt", parts.get("fooPart").getFilename().get());
+							assertEquals("bar", parts.get("barPart").getContentAsString().block());
+						}
+						catch(Exception e) {
+							return Mono.error(e);
+						}
+						return ServerResponse.ok().build();
+					});
+		}
+	}
+
+}