Improve docs on forwarded headers

Issue: SPR-15612

Author: rstoyanchev

spring-web/src/main/java/org/springframework/web/util/UriComponentsBuilder.java

@@ -274,7 +274,7 @@ public static UriComponentsBuilder fromHttpUrl(String httpUrl) {
 	/**
 	 * Create a new {@code UriComponents} object from the URI associated with
 	 * the given HttpRequest while also overlaying with values from the headers
-	 * "Forwarded" (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>,
+	 * "Forwarded" (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
 	 * or "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" if
 	 * "Forwarded" is not found.
 	 * @param request the source request

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/MvcUriComponentsBuilder.java

@@ -68,18 +68,28 @@
 
 /**
  * Creates instances of {@link org.springframework.web.util.UriComponentsBuilder}
- * by pointing to Spring MVC controllers and {@code @RequestMapping} methods.
+ * by pointing to {@code @RequestMapping} methods on Spring MVC controllers.
  *
- * <p>The static {@code fromXxx(...)} methods prepare links relative to the
- * current request as determined by a call to
+ * <p>There are several groups of methods:
+ * <ul>
+ * <li>Static {@code fromXxx(...)} methods to prepare links using information
+ * from the current request as determined by a call to
  * {@link org.springframework.web.servlet.support.ServletUriComponentsBuilder#fromCurrentServletMapping()}.
+ * <li>Static {@code fromXxx(UriComponentsBuilder,...)} methods can be given
+ * a baseUrl when operating outside the context of a request.
+ * <li>Instance-based {@code withXxx(...)} methods where an instance of
+ * MvcUriComponentsBuilder is created with a baseUrl via
+ * {@link #relativeTo(org.springframework.web.util.UriComponentsBuilder)}.
+ * </ul>
  *
- * <p>The static {@code fromXxx(UriComponentsBuilder,...)} methods can be given
- * the baseUrl when operating outside the context of a request.
- *
- * <p>You can also create an MvcUriComponentsBuilder instance with a baseUrl
- * via {@link #relativeTo(org.springframework.web.util.UriComponentsBuilder)}
- * and then use the non-static {@code withXxx(...)} method variants.
+ * <p><strong>Note:</strong> This class extracts and uses values from the headers
+ * "Forwarded" (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
+ * or "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" if
+ * "Forwarded" is not found, in order to reflect the client-originated protocol
+ * and address. As an alternative consider using the
+ * {@link org.springframework.web.filter.ForwardedHeaderFilter} to have such
+ * headers extracted once and removed, or removed only (without being used).
+ * See the reference for further information including security considerations.
  *
  * @author Oliver Gierke
  * @author Rossen Stoyanchev
@@ -140,6 +150,8 @@ public static MvcUriComponentsBuilder relativeTo(UriComponentsBuilder baseUrl) {
 	 * Create a {@link UriComponentsBuilder} from the mapping of a controller class
 	 * and current request information including Servlet mapping. If the controller
 	 * contains multiple mappings, only the first one is used.
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @param controllerType the controller to build a URI for
 	 * @return a UriComponentsBuilder instance (never {@code null})
 	 */
@@ -152,6 +164,8 @@ public static UriComponentsBuilder fromController(Class<?> controllerType) {
 	 * {@code UriComponentsBuilder} representing the base URL. This is useful
 	 * when using MvcUriComponentsBuilder outside the context of processing a
 	 * request or to apply a custom baseUrl not matching the current request.
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @param builder the builder for the base URL; the builder will be cloned
 	 * and therefore not modified and may be re-used for further calls.
 	 * @param controllerType the controller to build a URI for
@@ -169,6 +183,8 @@ public static UriComponentsBuilder fromController(UriComponentsBuilder builder,
 	 * Create a {@link UriComponentsBuilder} from the mapping of a controller
 	 * method and an array of method argument values. This method delegates
 	 * to {@link #fromMethod(Class, Method, Object...)}.
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @param controllerType the controller
 	 * @param methodName the method name
 	 * @param args the argument values
@@ -188,6 +204,8 @@ public static UriComponentsBuilder fromMethodName(Class<?> controllerType,
 	 * accepts a {@code UriComponentsBuilder} representing the base URL. This is
 	 * useful when using MvcUriComponentsBuilder outside the context of processing
 	 * a request or to apply a custom baseUrl not matching the current request.
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @param builder the builder for the base URL; the builder will be cloned
 	 * and therefore not modified and may be re-used for further calls.
 	 * @param controllerType the controller
@@ -235,6 +253,10 @@ public static UriComponentsBuilder fromMethodName(UriComponentsBuilder builder,
 	 * controller.getAddressesForCountry("US")
 	 * builder = MvcUriComponentsBuilder.fromMethodCall(controller);
 	 * </pre>
+	 *
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
+	 *
 	 * @param info either the value returned from a "mock" controller
 	 * invocation or the "mock" controller itself after an invocation
 	 * @return a UriComponents instance
@@ -253,6 +275,8 @@ public static UriComponentsBuilder fromMethodCall(Object info) {
 	 * {@code UriComponentsBuilder} representing the base URL. This is useful
 	 * when using MvcUriComponentsBuilder outside the context of processing a
 	 * request or to apply a custom baseUrl not matching the current request.
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @param builder the builder for the base URL; the builder will be cloned
 	 * and therefore not modified and may be re-used for further calls.
 	 * @param info either the value returned from a "mock" controller
@@ -303,6 +327,10 @@ public static UriComponentsBuilder fromMethodCall(UriComponentsBuilder builder,
 	 * </pre>
 	 * <p>Note that it's not necessary to specify all arguments. Only the ones
 	 * required to prepare the URL, mainly {@code @RequestParam} and {@code @PathVariable}).
+	 *
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
+	 *
 	 * @param mappingName the mapping name
 	 * @return a builder to prepare the URI String
 	 * @throws IllegalArgumentException if the mapping name is not found or
@@ -318,6 +346,8 @@ public static MethodArgumentBuilder fromMappingName(String mappingName) {
 	 * {@code UriComponentsBuilder} representing the base URL. This is useful
 	 * when using MvcUriComponentsBuilder outside the context of processing a
 	 * request or to apply a custom baseUrl not matching the current request.
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @param builder the builder for the base URL; the builder will be cloned
 	 * and therefore not modified and may be re-used for further calls.
 	 * @param name the mapping name
@@ -350,6 +380,8 @@ public static MethodArgumentBuilder fromMappingName(UriComponentsBuilder builder
 	 * {@link org.springframework.web.method.support.UriComponentsContributor
 	 * UriComponentsContributor}) while remaining argument values are ignored and
 	 * can be {@code null}.
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @param controllerType the controller type
 	 * @param method the controller method
 	 * @param args argument values for the controller method
@@ -366,6 +398,8 @@ public static UriComponentsBuilder fromMethod(Class<?> controllerType, Method me
 	 * This is useful when using MvcUriComponentsBuilder outside the context of
 	 * processing a request or to apply a custom baseUrl not matching the
 	 * current request.
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @param baseUrl the builder for the base URL; the builder will be cloned
 	 * and therefore not modified and may be re-used for further calls.
 	 * @param controllerType the controller type
@@ -557,6 +591,9 @@ private static WebApplicationContext getWebApplicationContext() {
 	 * <pre class="code">
 	 * MvcUriComponentsBuilder.fromMethodCall(on(FooController.class).getFoo(1)).build();
 	 * </pre>
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
+	 *
 	 * @param controllerType the target controller
 	 */
 	public static <T> T on(Class<T> controllerType) {
@@ -579,6 +616,8 @@ public static <T> T on(Class<T> controllerType) {
 	 * fooController.saveFoo(2, null);
 	 * builder = MvcUriComponentsBuilder.fromMethodCall(fooController);
 	 * </pre>
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @param controllerType the target controller
 	 */
 	public static <T> T controller(Class<T> controllerType) {
@@ -634,6 +673,8 @@ private static <T> T initProxy(Class<?> type, ControllerMethodInvocationIntercep
 	/**
 	 * An alternative to {@link #fromController(Class)} for use with an instance
 	 * of this class created via a call to {@link #relativeTo}.
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @since 4.2
 	 */
 	public UriComponentsBuilder withController(Class<?> controllerType) {
@@ -643,6 +684,8 @@ public UriComponentsBuilder withController(Class<?> controllerType) {
 	/**
 	 * An alternative to {@link #fromMethodName(Class, String, Object...)}} for
 	 * use with an instance of this class created via {@link #relativeTo}.
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @since 4.2
 	 */
 	public UriComponentsBuilder withMethodName(Class<?> controllerType, String methodName, Object... args) {
@@ -652,6 +695,8 @@ public UriComponentsBuilder withMethodName(Class<?> controllerType, String metho
 	/**
 	 * An alternative to {@link #fromMethodCall(Object)} for use with an instance
 	 * of this class created via {@link #relativeTo}.
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @since 4.2
 	 */
 	public UriComponentsBuilder withMethodCall(Object invocationInfo) {
@@ -661,6 +706,8 @@ public UriComponentsBuilder withMethodCall(Object invocationInfo) {
 	/**
 	 * An alternative to {@link #fromMappingName(String)} for use with an instance
 	 * of this class created via {@link #relativeTo}.
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @since 4.2
 	 */
 	public MethodArgumentBuilder withMappingName(String mappingName) {
@@ -670,6 +717,8 @@ public MethodArgumentBuilder withMappingName(String mappingName) {
 	/**
 	 * An alternative to {@link #fromMethod(Class, Method, Object...)}
 	 * for use with an instance of this class created via {@link #relativeTo}.
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 * @since 4.2
 	 */
 	public UriComponentsBuilder withMethod(Class<?> controllerType, Method method, Object... args) {

spring-webmvc/src/main/java/org/springframework/web/servlet/support/ServletUriComponentsBuilder.java

@@ -32,7 +32,17 @@
 import org.springframework.web.util.UrlPathHelper;
 
 /**
- * A UriComponentsBuilder that extracts information from the HttpServletRequest.
+ * UriComponentsBuilder with additional static factory methods to create links
+ * based on the current HttpServletRequest.
+ *
+ * <p><strong>Note:</strong> This class extracts and uses values from the headers
+ * "Forwarded" (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>),
+ * or "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" if
+ * "Forwarded" is not found, in order to reflect the client-originated protocol
+ * and address. As an alternative consider using the
+ * {@link org.springframework.web.filter.ForwardedHeaderFilter} to have such
+ * headers extracted once and removed, or removed only (without being used).
+ * See the reference for further information including security considerations.
  *
  * @author Rossen Stoyanchev
  * @since 3.1
@@ -69,6 +79,9 @@ protected ServletUriComponentsBuilder(ServletUriComponentsBuilder other) {
 	/**
 	 * Prepare a builder from the host, port, scheme, and context path of the
 	 * given HttpServletRequest.
+	 *
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 */
 	public static ServletUriComponentsBuilder fromContextPath(HttpServletRequest request) {
 		ServletUriComponentsBuilder builder = initFromRequest(request);
@@ -83,6 +96,9 @@ public static ServletUriComponentsBuilder fromContextPath(HttpServletRequest req
 	 * will end with "/main". If the servlet is mapped otherwise, e.g.
 	 * {@code "/"} or {@code "*.do"}, the result will be the same as
 	 * if calling {@link #fromContextPath(HttpServletRequest)}.
+	 *
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 */
 	public static ServletUriComponentsBuilder fromServletMapping(HttpServletRequest request) {
 		ServletUriComponentsBuilder builder = fromContextPath(request);
@@ -95,6 +111,9 @@ public static ServletUriComponentsBuilder fromServletMapping(HttpServletRequest
 	/**
 	 * Prepare a builder from the host, port, scheme, and path (but not the query)
 	 * of the HttpServletRequest.
+	 *
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 */
 	public static ServletUriComponentsBuilder fromRequestUri(HttpServletRequest request) {
 		ServletUriComponentsBuilder builder = initFromRequest(request);
@@ -105,6 +124,9 @@ public static ServletUriComponentsBuilder fromRequestUri(HttpServletRequest requ
 	/**
 	 * Prepare a builder by copying the scheme, host, port, path, and
 	 * query string of an HttpServletRequest.
+	 *
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 */
 	public static ServletUriComponentsBuilder fromRequest(HttpServletRequest request) {
 		ServletUriComponentsBuilder builder = initFromRequest(request);
@@ -153,6 +175,9 @@ private static String prependForwardedPrefix(HttpServletRequest request, String
 	/**
 	 * Same as {@link #fromContextPath(HttpServletRequest)} except the
 	 * request is obtained through {@link RequestContextHolder}.
+	 *
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 */
 	public static ServletUriComponentsBuilder fromCurrentContextPath() {
 		return fromContextPath(getCurrentRequest());
@@ -161,6 +186,9 @@ public static ServletUriComponentsBuilder fromCurrentContextPath() {
 	/**
 	 * Same as {@link #fromServletMapping(HttpServletRequest)} except the
 	 * request is obtained through {@link RequestContextHolder}.
+	 *
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 */
 	public static ServletUriComponentsBuilder fromCurrentServletMapping() {
 		return fromServletMapping(getCurrentRequest());
@@ -169,6 +197,9 @@ public static ServletUriComponentsBuilder fromCurrentServletMapping() {
 	/**
 	 * Same as {@link #fromRequestUri(HttpServletRequest)} except the
 	 * request is obtained through {@link RequestContextHolder}.
+	 *
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 */
 	public static ServletUriComponentsBuilder fromCurrentRequestUri() {
 		return fromRequestUri(getCurrentRequest());
@@ -177,6 +208,9 @@ public static ServletUriComponentsBuilder fromCurrentRequestUri() {
 	/**
 	 * Same as {@link #fromRequest(HttpServletRequest)} except the
 	 * request is obtained through {@link RequestContextHolder}.
+	 *
+	 * <p><strong>Note:</strong> This method extracts values from "Forwarded"
+	 * and "X-Forwarded-*" headers if found. See class-level docs.
 	 */
 	public static ServletUriComponentsBuilder fromCurrentRequest() {
 		return fromRequest(getCurrentRequest());

src/asciidoc/web-mvc.adoc

@@ -3389,6 +3389,38 @@ with a base URL and then use the instance-based "withXxx" methods. For example:
 ----
 
 
+[[mvc-links-to-controllers-forwarded-headers]]
+=== Working with "Forwarded" and "X-Forwarded-*" Headers
+
+As a request goes through proxies such as load balancers the host, port, and
+scheme may change presenting a challenge for applications that need to create links
+to resources since the links should reflect the host, port, and scheme of the
+original request as seen from a client perspective.
+
+https://tools.ietf.org/html/rfc7239[RFC 7239] defines the "Forwarded" HTTP header
+for proxies to use to provide information about the original request. There are also
+other non-standard headers in use such as "X-Forwarded-Host", "X-Forwarded-Port",
+and "X-Forwarded-Proto".
+
+Both `ServletUriComponentsBuilder` and `MvcUriComponentsBuilder` detect, extract, and use
+information from the "Forwarded" header, or from "X-Forwarded-Host", "X-Forwarded-Port",
+and "X-Forwarded-Proto" if "Forwarded" is not present, so that the resulting links reflect
+the original request.
+
+The `ForwardedHeaderFilter` provides an alternative to do the same once and globally for
+the entire application. The filter wraps the request in order to overlay host, port, and
+scheme information and also "hides" any forwarded headers for subsequent processing.
+
+Note that there are security considerations when using forwarded headers as explained
+in Section 8 of RFC 7239. At the application level it is difficult to determine whether
+forwarded headers can be trusted or not. This is why the network upstream should be
+configured correctly to filter out untrusted forwarded headers from the outside.
+
+Applications that don't have a proxy and don't need to use forwarded headers can
+configure the `ForwardedHeaderFilter` to remove and ignore such headers.
+
+
+
 [[mvc-links-to-controllers-from-views]]
 === Building URIs to Controllers and methods from views