Implement reactive HiddenHttpMethodFilter

Provides the ability to embed an HTTP verb inside a hidden form field
(like Thymeleaf's th:method operator).

Issue: SPR-15206

spring-web/src/main/java/org/springframework/web/filter/reactive/HiddenHttpMethodFilter.java

@@ -0,0 +1,97 @@
+/*
+ * Copyright 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.filter.reactive;
+
+import org.springframework.http.HttpMethod;
+import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.util.Assert;
+import org.springframework.web.server.ServerWebExchange;
+import org.springframework.web.server.WebFilter;
+import org.springframework.web.server.WebFilterChain;
+import reactor.core.publisher.Mono;
+
+import java.util.Locale;
+import java.util.Optional;
+
+/**
+ * Reactive {@link WebFilter} that converts posted method parameters into HTTP methods,
+ * retrievable via {@link ServerHttpRequest#getMethod()}. Since browsers currently only
+ * support GET and POST, a common technique - used by the Prototype library, for instance -
+ * is to use a normal POST with an additional hidden form field ({@code _method})
+ * to pass the "real" HTTP method along. This filter reads that parameter and changes
+ * the {@link ServerHttpRequest#getMethod()} return value using {@link ServerWebExchange#mutate()}.
+ *
+ * <p>The name of the request parameter defaults to {@code _method}, but can be
+ * adapted via the {@link #setMethodParam(String) methodParam} property.
+ *
+ * @author Greg Turnquist
+ * @since 5.0
+ */
+public class HiddenHttpMethodFilter implements WebFilter {
+
+	/** Default method parameter: {@code _method} */
+	public static final String DEFAULT_METHOD_PARAM = "_method";
+
+	private String methodParam = DEFAULT_METHOD_PARAM;
+
+	/**
+	 * Set the parameter name to look for HTTP methods.
+	 * @see #DEFAULT_METHOD_PARAM
+	 */
+	public void setMethodParam(String methodParam) {
+		Assert.hasText(methodParam, "'methodParam' must not be empty");
+		this.methodParam = methodParam;
+	}
+
+	/**
+	 * Transform an HTTP POST into another method based on {@code methodParam}
+	 *
+	 * @param exchange the current server exchange
+	 * @param chain provides a way to delegate to the next filter
+	 * @return
+	 */
+	@Override
+	public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
+
+		if (exchange.getRequest().getMethod() == HttpMethod.POST) {
+			return exchange.getFormData()
+				.map(map -> Optional.ofNullable(map.getFirst(methodParam)))
+				.map(method -> convertedRequest(exchange, method))
+				.then(convertedExchange -> chain.filter(convertedExchange));
+		} else {
+			return chain.filter(exchange);
+		}
+	}
+
+	/**
+	 * Mutate exchange into a new HTTP method.
+	 *
+	 * @param exchange - original request
+	 * @param method - request HTTP method based on form data
+	 * @return a mutated {@link ServerWebExchange}
+	 */
+	private ServerWebExchange convertedRequest(ServerWebExchange exchange, Optional<String> method) {
+
+		String upperMethod = method
+			.map(String::toString)
+			.orElse(HttpMethod.POST.toString())
+			.toUpperCase(Locale.ENGLISH);
+
+		return exchange.mutate()
+			.request(builder -> builder.method(HttpMethod.resolve(upperMethod)))
+			.build();
+	}
+}

spring-web/src/test/java/org/springframework/web/filter/reactive/HiddenHttpMethodFilterTests.java

@@ -0,0 +1,119 @@
+/*
+ * Copyright 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.filter.reactive;
+
+import org.junit.Test;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.MediaType;
+import org.springframework.mock.http.server.reactive.test.MockServerHttpRequest;
+import org.springframework.mock.http.server.reactive.test.MockServerHttpResponse;
+import org.springframework.web.server.ServerWebExchange;
+import org.springframework.web.server.WebFilterChain;
+import org.springframework.web.server.adapter.DefaultServerWebExchange;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+
+import java.util.Optional;
+
+import static org.junit.Assert.*;
+
+/**
+ * @author Greg Turnquist
+ */
+public class HiddenHttpMethodFilterTests {
+
+	private final HiddenHttpMethodFilter filter = new HiddenHttpMethodFilter();
+
+	@Test
+	public void filterWithParameter() {
+		ServerWebExchange mockExchange = createExchange(Optional.of("DELETE"));
+
+		WebFilterChain filterChain = exchange -> {
+			assertEquals("Invalid method", HttpMethod.DELETE, exchange.getRequest().getMethod());
+			return Mono.empty();
+		};
+
+		StepVerifier.create(filter.filter(mockExchange, filterChain))
+			.expectComplete()
+			.verify();
+	}
+
+	@Test
+	public void filterWithNoParameter() {
+		ServerWebExchange mockExchange = createExchange(Optional.empty());
+
+		WebFilterChain filterChain = exchange -> {
+			assertEquals("Invalid method", HttpMethod.POST, exchange.getRequest().getMethod());
+			return Mono.empty();
+		};
+
+		StepVerifier.create(filter.filter(mockExchange, filterChain))
+			.expectComplete()
+			.verify();
+	}
+
+	@Test
+	public void filterWithDifferentMethodParam() {
+		ServerWebExchange mockExchange = createExchange("_foo", Optional.of("DELETE"));
+
+		WebFilterChain filterChain = exchange -> {
+			assertEquals("Invalid method", HttpMethod.DELETE, exchange.getRequest().getMethod());
+			return Mono.empty();
+		};
+
+		filter.setMethodParam("_foo");
+
+		StepVerifier.create(filter.filter(mockExchange, filterChain))
+			.expectComplete()
+			.verify();
+	}
+
+	@Test
+	public void filterWithoutPost() {
+		ServerWebExchange mockExchange = createExchange(Optional.of("DELETE")).mutate()
+			.request(builder -> builder.method(HttpMethod.PUT))
+			.build();
+
+		WebFilterChain filterChain = exchange -> {
+			assertEquals("Invalid method", HttpMethod.PUT, exchange.getRequest().getMethod());
+			return Mono.empty();
+		};
+
+		StepVerifier.create(filter.filter(mockExchange, filterChain))
+			.expectComplete()
+			.verify();
+	}
+
+	private ServerWebExchange createExchange(Optional<String> optionalMethod) {
+		return createExchange("_method", optionalMethod);
+	}
+
+	private ServerWebExchange createExchange(String methodName, Optional<String> optionalBody) {
+		MockServerHttpRequest.BodyBuilder builder = MockServerHttpRequest
+			.post("/hotels")
+			.header(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_FORM_URLENCODED_VALUE);
+
+		MockServerHttpRequest request = optionalBody
+			.map(method -> builder.body(methodName + "=" + method))
+			.orElse(builder.build());
+
+		MockServerHttpResponse response = new MockServerHttpResponse();
+
+		return new DefaultServerWebExchange(request, response);
+	}
+
+}