Add UrlHandlerFilter for WebFlux

Closes gh-32830

Author: rstoyanchev

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

@@ -0,0 +1,318 @@
+/*
+ * Copyright 2002-2024 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.filter.reactive;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatusCode;
+import org.springframework.http.server.PathContainer;
+import org.springframework.http.server.RequestPath;
+import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.http.server.reactive.ServerHttpResponse;
+import org.springframework.lang.Nullable;
+import org.springframework.util.LinkedMultiValueMap;
+import org.springframework.util.MultiValueMap;
+import org.springframework.util.StringUtils;
+import org.springframework.web.server.ServerWebExchange;
+import org.springframework.web.server.WebFilter;
+import org.springframework.web.server.WebFilterChain;
+import org.springframework.web.util.pattern.PathPattern;
+import org.springframework.web.util.pattern.PathPatternParser;
+
+/**
+ * {@link org.springframework.web.server.WebFilter} that modifies the URL, and
+ * then redirects or wraps the request to apply the change.
+ *
+ * <p>To create an instance, you can use the following:
+ *
+ * <pre>
+ * UrlHandlerFilter filter = UrlHandlerFilter
+ *    .trailingSlashHandler("/path1/**").redirect(HttpStatus.PERMANENT_REDIRECT)
+ *    .trailingSlashHandler("/path2/**").mutateRequest()
+ *    .build();
+ * </pre>
+ *
+ * <p>This {@code WebFilter} should be ordered ahead of security filters.
+ *
+ * @author Rossen Stoyanchev
+ * @since 6.2
+ */
+public final class UrlHandlerFilter implements WebFilter {
+
+	private static final Log logger = LogFactory.getLog(UrlHandlerFilter.class);
+
+
+	private final MultiValueMap<Handler, PathPattern> handlers;
+
+
+	private UrlHandlerFilter(MultiValueMap<Handler, PathPattern> handlers) {
+		this.handlers = new LinkedMultiValueMap<>(handlers);
+	}
+
+
+	@Override
+	public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
+		RequestPath path = exchange.getRequest().getPath();
+		for (Map.Entry<Handler, List<PathPattern>> entry : this.handlers.entrySet()) {
+			if (!entry.getKey().canHandle(exchange)) {
+				continue;
+			}
+			for (PathPattern pattern : entry.getValue()) {
+				if (pattern.matches(path)) {
+					return entry.getKey().handle(exchange, chain);
+				}
+			}
+		}
+		return chain.filter(exchange);
+	}
+
+	/**
+	 * Create a builder by adding a handler for URL's with a trailing slash.
+	 * @param pathPatterns path patterns to map the handler to, e.g.
+	 * <code>"/path/&#42;"</code>, <code>"/path/&#42;&#42;"</code>,
+	 * <code>"/path/foo/"</code>.
+	 * @return a spec to configure the trailing slash handler with
+	 * @see Builder#trailingSlashHandler(String...)
+	 */
+	public static Builder.TrailingSlashSpec trailingSlashHandler(String... pathPatterns) {
+		return new DefaultBuilder().trailingSlashHandler(pathPatterns);
+	}
+
+
+	/**
+	 * Builder for {@link UrlHandlerFilter}.
+	 */
+	public interface Builder {
+
+		/**
+		 * Add a handler for URL's with a trailing slash.
+		 * @param pathPatterns path patterns to map the handler to, e.g.
+		 * <code>"/path/&#42;"</code>, <code>"/path/&#42;&#42;"</code>,
+		 * <code>"/path/foo/"</code>.
+		 * @return a spec to configure the handler with
+		 */
+		TrailingSlashSpec trailingSlashHandler(String... pathPatterns);
+
+		/**
+		 * Build the {@link UrlHandlerFilter} instance.
+		 */
+		UrlHandlerFilter build();
+
+
+		/**
+		 * A spec to configure a trailing slash handler.
+		 */
+		interface TrailingSlashSpec {
+
+			/**
+			 * Configure a request interceptor to be called just before the handler
+			 * is invoked when a URL with a trailing slash is matched.
+			 */
+			TrailingSlashSpec intercept(Function<ServerHttpRequest, Mono<Void>> interceptor);
+
+			/**
+			 * Handle requests by sending a redirect to the same URL but the
+			 * trailing slash trimmed.
+			 * @param statusCode the redirect status to use
+			 * @return the top level {@link Builder}, which allows adding more
+			 * handlers and then building the Filter instance.
+			 */
+			Builder redirect(HttpStatusCode statusCode);
+
+			/**
+			 * Handle the request by wrapping it in order to trim the trailing
+			 * slash, and delegating to the rest of the filter chain.
+			 * @return the top level {@link Builder}, which allows adding more
+			 * handlers and then building the Filter instance.
+			 */
+			Builder mutateRequest();
+		}
+	}
+
+
+	/**
+	 * Default {@link Builder} implementation.
+	 */
+	private static final class DefaultBuilder implements Builder {
+
+		private final PathPatternParser patternParser = new PathPatternParser();
+
+		private final MultiValueMap<Handler, PathPattern> handlers = new LinkedMultiValueMap<>();
+
+		@Override
+		public TrailingSlashSpec trailingSlashHandler(String... patterns) {
+			return new DefaultTrailingSlashSpec(patterns);
+		}
+
+		private DefaultBuilder addHandler(List<PathPattern> pathPatterns, Handler handler) {
+			pathPatterns.forEach(pattern -> this.handlers.add(handler, pattern));
+			return this;
+		}
+
+		@Override
+		public UrlHandlerFilter build() {
+			return new UrlHandlerFilter(this.handlers);
+		}
+
+
+		private final class DefaultTrailingSlashSpec implements TrailingSlashSpec {
+
+			private final List<PathPattern> pathPatterns;
+
+			@Nullable
+			private List<Function<ServerHttpRequest, Mono<Void>>> interceptors;
+
+			private DefaultTrailingSlashSpec(String[] patterns) {
+				this.pathPatterns = Arrays.stream(patterns)
+						.map(pattern -> pattern.endsWith("**") || pattern.endsWith("/") ? pattern : pattern + "/")
+						.map(patternParser::parse)
+						.toList();
+			}
+
+			@Override
+			public TrailingSlashSpec intercept(Function<ServerHttpRequest, Mono<Void>> interceptor) {
+				this.interceptors = (this.interceptors != null ? this.interceptors : new ArrayList<>());
+				this.interceptors.add(interceptor);
+				return this;
+			}
+
+			@Override
+			public Builder redirect(HttpStatusCode statusCode) {
+				Handler handler = new RedirectTrailingSlashHandler(statusCode, this.interceptors);
+				return DefaultBuilder.this.addHandler(this.pathPatterns, handler);
+			}
+
+			@Override
+			public Builder mutateRequest() {
+				Handler handler = new RequestWrappingTrailingSlashHandler(this.interceptors);
+				return DefaultBuilder.this.addHandler(this.pathPatterns, handler);
+			}
+		}
+	}
+
+
+	/**
+	 * Internal handler to encapsulate different ways to handle a request.
+	 */
+	private interface Handler {
+
+		/**
+		 * Whether the handler handles the given request.
+		 */
+		boolean canHandle(ServerWebExchange exchange);
+
+		/**
+		 * Handle the request, possibly delegating to the rest of the filter chain.
+		 */
+		Mono<Void> handle(ServerWebExchange exchange, WebFilterChain chain);
+	}
+
+
+	/**
+	 * Base class for trailing slash {@link Handler} implementations.
+	 */
+	private abstract static class AbstractTrailingSlashHandler implements Handler {
+
+		private static final List<Function<ServerHttpRequest, Mono<Void>>> defaultInterceptors =
+				List.of(request -> {
+					if (logger.isTraceEnabled()) {
+						logger.trace("Handling trailing slash URL: " + request.getMethod() + " " + request.getURI());
+					}
+					return Mono.empty();
+				});
+
+		private final List<Function<ServerHttpRequest, Mono<Void>>> interceptors;
+
+		protected AbstractTrailingSlashHandler(@Nullable List<Function<ServerHttpRequest, Mono<Void>>> interceptors) {
+			this.interceptors = (interceptors != null ? new ArrayList<>(interceptors) : defaultInterceptors);
+		}
+
+		@Override
+		public boolean canHandle(ServerWebExchange exchange) {
+			List<PathContainer.Element> elements = exchange.getRequest().getPath().elements();
+			return (elements.size() > 1 && elements.get(elements.size() - 1).value().equals("/"));
+		}
+
+		@Override
+		public Mono<Void> handle(ServerWebExchange exchange, WebFilterChain chain) {
+			List<Mono<Void>> monos = new ArrayList<>(this.interceptors.size());
+			this.interceptors.forEach(interceptor -> monos.add(interceptor.apply(exchange.getRequest())));
+			return Flux.concat(monos).then(Mono.defer(() -> handleInternal(exchange, chain)));
+		}
+
+		protected abstract Mono<Void> handleInternal(ServerWebExchange exchange, WebFilterChain chain);
+
+		protected String trimTrailingSlash(ServerHttpRequest request) {
+			String path = request.getURI().getRawPath();
+			int index = (StringUtils.hasLength(path) ? path.lastIndexOf('/') : -1);
+			return (index != -1 ? path.substring(0, index) : path);
+		}
+	}
+
+
+	/**
+	 * Path handler that sends a redirect.
+	 */
+	private static final class RedirectTrailingSlashHandler extends AbstractTrailingSlashHandler {
+
+		private final HttpStatusCode statusCode;
+
+		RedirectTrailingSlashHandler(
+				HttpStatusCode statusCode, @Nullable List<Function<ServerHttpRequest, Mono<Void>>> interceptors) {
+
+			super(interceptors);
+			this.statusCode = statusCode;
+		}
+
+		@Override
+		public Mono<Void> handleInternal(ServerWebExchange exchange, WebFilterChain chain) {
+			ServerHttpResponse response = exchange.getResponse();
+			response.setStatusCode(this.statusCode);
+			response.getHeaders().set(HttpHeaders.LOCATION, trimTrailingSlash(exchange.getRequest()));
+			return Mono.empty();
+		}
+	}
+
+
+	/**
+	 * Path handler that mutates the request and continues processing.
+	 */
+	private static final class RequestWrappingTrailingSlashHandler extends AbstractTrailingSlashHandler {
+
+		RequestWrappingTrailingSlashHandler(@Nullable List<Function<ServerHttpRequest, Mono<Void>>> interceptors) {
+			super(interceptors);
+		}
+
+		@Override
+		public Mono<Void> handleInternal(ServerWebExchange exchange, WebFilterChain chain) {
+			ServerHttpRequest request = exchange.getRequest();
+			ServerHttpRequest mutatedRequest = request.mutate().path(trimTrailingSlash(request)).build();
+			return chain.filter(exchange.mutate().request(mutatedRequest).build());
+		}
+	}
+
+}