Add ForwardedHeaderFilter

The new Filter is simply a new way of packaging the ability to extract
X-Forwarded-* headers already available via UriComponentsBuilder.

The Filter wraps the request and the effect is that anything using the
request will see the original schem, host, and port.

Issue: SPR-13614

spring-web/src/main/java/org/springframework/web/filter/ForwardedHeaderFilter.java

@@ -0,0 +1,193 @@
+/*
+ * Copyright 2002-2016 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;
+
+import java.io.IOException;
+import java.util.Collections;
+import java.util.Enumeration;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import javax.servlet.FilterChain;
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletRequestWrapper;
+import javax.servlet.http.HttpServletResponse;
+
+import org.springframework.http.HttpRequest;
+import org.springframework.http.server.ServletServerHttpRequest;
+import org.springframework.web.util.UriComponents;
+import org.springframework.web.util.UriComponentsBuilder;
+
+
+/**
+ * Filter that wraps the request in order to override its
+ * {@link HttpServletRequest#getServerName() getServerName()},
+ * {@link HttpServletRequest#getServerPort() getServerPort()},
+ * {@link HttpServletRequest#getScheme() getScheme()}, and
+ * {@link HttpServletRequest#isSecure() isSecure()} methods with values derived
+ * from "Fowarded" or "X-Forwarded-*" headers. In effect the wrapped request
+ * reflects the client-originated protocol and address.
+ *
+ * @author Rossen Stoyanchev
+ * @since 4.3
+ */
+public class ForwardedHeaderFilter extends OncePerRequestFilter {
+
+	private static final Set<String> FORWARDED_HEADER_NAMES;
+
+	static {
+		FORWARDED_HEADER_NAMES = new HashSet<String>(4);
+		FORWARDED_HEADER_NAMES.add("Forwarded");
+		FORWARDED_HEADER_NAMES.add("X-Forwarded-Host");
+		FORWARDED_HEADER_NAMES.add("X-Forwarded-Port");
+		FORWARDED_HEADER_NAMES.add("X-Forwarded-Proto");
+	}
+
+
+	@Override
+	protected boolean shouldNotFilter(HttpServletRequest request) throws ServletException {
+		Enumeration<String> headerNames = request.getHeaderNames();
+		while (headerNames.hasMoreElements()) {
+			String name = headerNames.nextElement();
+			if (FORWARDED_HEADER_NAMES.contains(name)) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	@Override
+	protected boolean shouldNotFilterAsyncDispatch() {
+		return false;
+	}
+
+	@Override
+	protected boolean shouldNotFilterErrorDispatch() {
+		return false;
+	}
+
+	@Override
+	protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response,
+			FilterChain filterChain) throws ServletException, IOException {
+
+		filterChain.doFilter(new ForwardedHeaderRequestWrapper(request), response);
+	}
+
+
+	private static class ForwardedHeaderRequestWrapper extends HttpServletRequestWrapper {
+
+		private final String scheme;
+
+		private final boolean secure;
+
+		private final String host;
+
+		private final int port;
+
+		private final String portInUrl;
+
+		private final Map<String, List<String>> headers = new LinkedHashMap<String, List<String>>();
+
+
+		public ForwardedHeaderRequestWrapper(HttpServletRequest request) {
+			super(request);
+
+			HttpRequest httpRequest = new ServletServerHttpRequest(request);
+			UriComponents uriComponents = UriComponentsBuilder.fromHttpRequest(httpRequest).build();
+			int port = uriComponents.getPort();
+
+			this.scheme = uriComponents.getScheme();
+			this.secure = "https".equals(scheme);
+			this.host = uriComponents.getHost();
+			this.port = (port == -1 ? (this.secure ? 443 : 80) : port);
+			this.portInUrl = (port == -1 ? "" : ":" + port);
+
+			Enumeration<String> headerNames = request.getHeaderNames();
+			while (headerNames.hasMoreElements()) {
+				String name = headerNames.nextElement();
+				this.headers.put(name, Collections.list(request.getHeaders(name)));
+			}
+			for (String name : FORWARDED_HEADER_NAMES) {
+				this.headers.remove(name);
+			}
+		}
+
+
+		@Override
+		public String getHeader(String name) {
+			Map.Entry<String, List<String>> header = getHeaderEntry(name);
+			if (header == null || header.getValue() == null || header.getValue().isEmpty()) {
+				return null;
+			}
+			return header.getValue().get(0);
+		}
+
+		protected Map.Entry<String, List<String>> getHeaderEntry(String name) {
+			for (Map.Entry<String, List<String>> entry : this.headers.entrySet()) {
+				if (entry.getKey().equalsIgnoreCase(name)) {
+					return entry;
+				}
+			}
+			return null;
+		}
+
+		@Override
+		public Enumeration<String> getHeaderNames() {
+			return Collections.enumeration(this.headers.keySet());
+		}
+
+		@Override
+		public Enumeration<String> getHeaders(String name) {
+			Map.Entry<String, List<String>> header = getHeaderEntry(name);
+			if (header == null || header.getValue() == null) {
+				return Collections.enumeration(Collections.<String>emptyList());
+			}
+			return Collections.enumeration(header.getValue());
+		}
+
+		@Override
+		public String getScheme() {
+			return this.scheme;
+		}
+
+		@Override
+		public String getServerName() {
+			return this.host;
+		}
+
+		@Override
+		public int getServerPort() {
+			return this.port;
+		}
+
+		@Override
+		public boolean isSecure() {
+			return this.secure;
+		}
+
+		@Override
+		public StringBuffer getRequestURL() {
+			StringBuffer sb = new StringBuffer();
+			sb.append(this.scheme).append("://").append(this.host).append(this.portInUrl);
+			sb.append(getRequestURI());
+			return sb;
+		}
+	}
+
+}