Add PreFlightRequestWebFilter

Closes gh-26885

spring-web/src/main/java/org/springframework/web/cors/reactive/PreFlightRequestHandler.java

@@ -25,6 +25,7 @@ import org.springframework.web.server.ServerWebExchange;
  *
  * @author Rossen Stoyanchev
  * @since 5.3.4
+ * @see PreFlightRequestWebFilter
  */
 public interface PreFlightRequestHandler {
 

spring-web/src/main/java/org/springframework/web/cors/reactive/PreFlightRequestWebFilter.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2002-2021 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
+ *
+ *      https://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.cors.reactive;
+
+import reactor.core.publisher.Mono;
+
+import org.springframework.util.Assert;
+import org.springframework.web.server.ServerWebExchange;
+import org.springframework.web.server.WebFilter;
+import org.springframework.web.server.WebFilterChain;
+
+/**
+ * WebFilter that handles pre-flight requests through a
+ * {@link PreFlightRequestHandler} and bypasses the rest of the chain.
+ *
+ * <p>A WebFlux application can simply inject PreFlightRequestHandler and use
+ * it to create an instance of this WebFilter since {@code @EnableWebFlux}
+ * declares {@code DispatcherHandler} as a bean and that is a
+ * PreFlightRequestHandler.
+ *
+ * @author Rossen Stoyanchev
+ * @since 5.3.7
+ */
+public class PreFlightRequestWebFilter implements WebFilter {
+
+	private final PreFlightRequestHandler handler;
+
+
+	/**
+	 * Create an instance that will delegate to the given handler.
+	 */
+	public PreFlightRequestWebFilter(PreFlightRequestHandler handler) {
+		Assert.notNull(handler, "PreFlightRequestHandler is required");
+		this.handler = handler;
+	}
+
+
+	@Override
+	public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
+		return (CorsUtils.isPreFlightRequest(exchange.getRequest()) ?
+				this.handler.handlePreFlight(exchange) : chain.filter(exchange));
+	}
+
+}