Add X-Forwarded-For header support to Undertow

Add a `useForwardHeaders` property to allow embedded Undertow
containers to respect X-Forwarded-For headers.

Fixes gh-3881

spring-boot/src/main/java/org/springframework/boot/context/embedded/undertow/UndertowEmbeddedServletContainer.java

@@ -71,6 +71,8 @@ public class UndertowEmbeddedServletContainer implements EmbeddedServletContaine
 
 	private final String contextPath;
 
+	private final boolean useForwardHeaders;
+
 	private final boolean autoStart;
 
 	private final Compression compression;
@@ -81,9 +83,16 @@ public class UndertowEmbeddedServletContainer implements EmbeddedServletContaine
 
 	public UndertowEmbeddedServletContainer(Builder builder, DeploymentManager manager,
 			String contextPath, int port, boolean autoStart, Compression compression) {
+		this(builder, manager, contextPath, port, false, autoStart, compression);
+	}
+
+	public UndertowEmbeddedServletContainer(Builder builder, DeploymentManager manager,
+			String contextPath, int port, boolean useForwardHeaders, boolean autoStart,
+			Compression compression) {
 		this.builder = builder;
 		this.manager = manager;
 		this.contextPath = contextPath;
+		this.useForwardHeaders = useForwardHeaders;
 		this.autoStart = autoStart;
 		this.compression = compression;
 	}
@@ -105,7 +114,11 @@ public class UndertowEmbeddedServletContainer implements EmbeddedServletContaine
 	private Undertow createUndertowServer() {
 		try {
 			HttpHandler httpHandler = this.manager.start();
-			this.builder.setHandler(getContextHandler(httpHandler));
+			httpHandler = getContextHandler(httpHandler);
+			if (this.useForwardHeaders) {
+				httpHandler = Handlers.proxyPeerAddress(httpHandler);
+			}
+			this.builder.setHandler(httpHandler);
 			return this.builder.build();
 		}
 		catch (ServletException ex) {

spring-boot/src/main/java/org/springframework/boot/context/embedded/undertow/UndertowEmbeddedServletContainerFactory.java

@@ -121,6 +121,8 @@ public class UndertowEmbeddedServletContainerFactory extends
 
 	private boolean accessLogEnabled = false;
 
+	private boolean useForwardHeaders;
+
 	/**
 	 * Create a new {@link UndertowEmbeddedServletContainerFactory} instance.
 	 */
@@ -220,7 +222,7 @@ public class UndertowEmbeddedServletContainerFactory extends
 		int port = getPort();
 		Builder builder = createBuilder(port);
 		return new UndertowEmbeddedServletContainer(builder, manager, getContextPath(),
-				port, port >= 0, getCompression());
+				port, this.useForwardHeaders, port >= 0, getCompression());
 	}
 
 	private Builder createBuilder(int port) {
@@ -519,6 +521,15 @@ public class UndertowEmbeddedServletContainerFactory extends
 		return this.accessLogEnabled;
 	}
 
+	/**
+	 * Set if x-forward-* headers should be processed.
+	 * @param useForwardHeaders if x-forward headers should be used
+	 * @since 1.3.0
+	 */
+	public void setUseForwardHeaders(boolean useForwardHeaders) {
+		this.useForwardHeaders = useForwardHeaders;
+	}
+
 	/**
 	 * Undertow {@link ResourceManager} for JAR resources.
 	 */

spring-boot/src/test/java/org/springframework/boot/context/embedded/undertow/UndertowEmbeddedServletContainerFactoryTests.java

@@ -149,6 +149,13 @@ public class UndertowEmbeddedServletContainerFactoryTests extends
 		assertEquals("/", contextPath.get());
 	}
 
+	@Test
+	public void useForwardHeaders() throws Exception {
+		UndertowEmbeddedServletContainerFactory factory = getFactory();
+		factory.setUseForwardHeaders(true);
+		assertForwardHeaderIsUsed(factory);
+	}
+
 	@Override
 	protected Object getJspServlet() {
 		return null; // Undertow does not support JSPs