Support encodeUrl mechanism via ServerHttpResponse

Issue: SPR-14529

spring-web/src/main/java/org/springframework/http/server/reactive/AbstractServerHttpResponse.java

@@ -19,6 +19,7 @@ package org.springframework.http.server.reactive;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Function;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
@@ -66,6 +67,8 @@ public abstract class AbstractServerHttpResponse implements ServerHttpResponse {
 
 	private final MultiValueMap<String, ResponseCookie> cookies;
 
+	private Function<String, String> urlEncoder = url -> url;
+
 	private final AtomicReference<State> state = new AtomicReference<>(State.NEW);
 
 	private final List<Supplier<? extends Mono<Void>>> commitActions = new ArrayList<>(4);
@@ -117,6 +120,16 @@ public abstract class AbstractServerHttpResponse implements ServerHttpResponse {
 				CollectionUtils.unmodifiableMultiValueMap(this.cookies) : this.cookies);
 	}
 
+	@Override
+	public String encodeUrl(String url) {
+		return (this.urlEncoder != null ? this.urlEncoder.apply(url) : url);
+	}
+
+	@Override
+	public void registerUrlEncoder(Function<String, String> encoder) {
+		this.urlEncoder = (this.urlEncoder != null ? this.urlEncoder.andThen(encoder) : encoder);
+	}
+
 	@Override
 	public void beforeCommit(Supplier<? extends Mono<Void>> action) {
 		if (action != null) {

spring-web/src/main/java/org/springframework/http/server/reactive/ServerHttpResponse.java

@@ -16,6 +16,8 @@
 
 package org.springframework.http.server.reactive;
 
+import java.util.function.Function;
+
 import reactor.core.publisher.Mono;
 
 import org.springframework.http.HttpStatus;
@@ -50,6 +52,24 @@ public interface ServerHttpResponse extends ReactiveHttpOutputMessage {
 	 */
 	MultiValueMap<String, ResponseCookie> getCookies();
 
+	/**
+	 * A mechanism for URL rewriting that applications and libraries such as
+	 * HTML template libraries to use consistently for all URLs emitted by
+	 * the application. Doing so enables the registration of URL encoders via
+	 * {@link #registerUrlEncoder} that can insert an id for authentication,
+	 * a nonce for CSRF protection, a version for a static resource, etc.
+	 * @param url the URL to encode
+	 * @return the encoded URL or the same
+	 */
+	String encodeUrl(String url);
+
+	/**
+	 * Register a URL rewriting function for use with {@link #encodeUrl}.
+	 * The function must return an encoded URL or the same URL.
+	 * @param encoder a URL encoding function to use
+	 */
+	void registerUrlEncoder(Function<String, String> encoder);
+
 	/**
 	 * Indicate that request handling is complete, allowing for any cleanup or
 	 * end-of-processing tasks to be performed such as applying header changes

spring-web/src/test/java/org/springframework/http/server/reactive/ServerHttpResponseTests.java

@@ -42,6 +42,27 @@ import static org.junit.Assert.assertSame;
  */
 public class ServerHttpResponseTests {
 
+	@Test
+	public void encodeUrlDefault() throws Exception {
+		TestServerHttpResponse response = new TestServerHttpResponse();
+		assertEquals("/foo", response.encodeUrl("/foo"));
+	}
+
+	@Test
+	public void encodeUrlWithEncoder() throws Exception {
+		TestServerHttpResponse response = new TestServerHttpResponse();
+		response.registerUrlEncoder(s -> s + "?nonce=123");
+		assertEquals("/foo?nonce=123", response.encodeUrl("/foo"));
+	}
+
+	@Test
+	public void encodeUrlWithMultipleEncoders() throws Exception {
+		TestServerHttpResponse response = new TestServerHttpResponse();
+		response.registerUrlEncoder(s -> s + ";p=abc");
+		response.registerUrlEncoder(s -> s + "?q=123");
+		assertEquals("/foo;p=abc?q=123", response.encodeUrl("/foo"));
+	}
+
 	@Test
 	public void writeWith() throws Exception {
 		TestServerHttpResponse response = new TestServerHttpResponse();

spring-web/src/test/java/org/springframework/mock/http/server/reactive/test/MockServerHttpResponse.java

@@ -18,6 +18,7 @@ package org.springframework.mock.http.server.reactive.test;
 
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
+import java.util.function.Function;
 import java.util.function.Supplier;
 
 import org.reactivestreams.Publisher;
@@ -49,6 +50,8 @@ public class MockServerHttpResponse implements ServerHttpResponse {
 
 	private final MultiValueMap<String, ResponseCookie> cookies = new LinkedMultiValueMap<>();
 
+	private Function<String, String> urlEncoder = url -> url;
+
 	private Flux<DataBuffer> body;
 
 	private Flux<Publisher<DataBuffer>> bodyWithFlushes;
@@ -77,6 +80,16 @@ public class MockServerHttpResponse implements ServerHttpResponse {
 		return this.cookies;
 	}
 
+	@Override
+	public String encodeUrl(String url) {
+		return (this.urlEncoder != null ? this.urlEncoder.apply(url) : url);
+	}
+
+	@Override
+	public void registerUrlEncoder(Function<String, String> encoder) {
+		this.urlEncoder = (this.urlEncoder != null ? this.urlEncoder.andThen(encoder) : encoder);
+	}
+
 	public Publisher<DataBuffer> getBody() {
 		return this.body;
 	}