Adds AfterFilterFunctions.dedupeResponseHeader()

See gh-2949

spring-cloud-gateway-server-mvc/src/main/java/org/springframework/cloud/gateway/server/mvc/filter/AfterFilterFunctions.java

@@ -18,6 +18,7 @@ package org.springframework.cloud.gateway.server.mvc.filter;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.function.BiFunction;
 import java.util.regex.Pattern;
@@ -25,7 +26,10 @@ import java.util.regex.Pattern;
 import org.springframework.cloud.gateway.server.mvc.common.HttpStatusHolder;
 import org.springframework.cloud.gateway.server.mvc.common.MvcUtils;
 import org.springframework.cloud.gateway.server.mvc.handler.GatewayServerResponse;
+import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatusCode;
+import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
 import org.springframework.web.servlet.function.ServerRequest;
 import org.springframework.web.servlet.function.ServerResponse;
 
@@ -43,6 +47,50 @@ public abstract class AfterFilterFunctions {
 		};
 	}
 
+	public static BiFunction<ServerRequest, ServerResponse, ServerResponse> dedupeResponseHeader(String name) {
+		return dedupeResponseHeader(name, DedupeStrategy.RETAIN_FIRST);
+	}
+
+	public static BiFunction<ServerRequest, ServerResponse, ServerResponse> dedupeResponseHeader(String name,
+			DedupeStrategy strategy) {
+		Assert.hasText(name, "name must not be null or empty");
+		Assert.notNull(strategy, "strategy must not be null");
+		return (request, response) -> {
+			dedupeHeaders(response.headers(), name, strategy);
+			return response;
+		};
+	}
+
+	private static void dedupeHeaders(HttpHeaders headers, String names, DedupeStrategy strategy) {
+		if (headers == null || names == null || strategy == null) {
+			return;
+		}
+		String[] tokens = StringUtils.tokenizeToStringArray(names, " ", true, true);
+		for (String name : tokens) {
+			dedupeHeader(headers, name.trim(), strategy);
+		}
+	}
+
+	private static void dedupeHeader(HttpHeaders headers, String name, DedupeStrategy strategy) {
+		List<String> values = headers.get(name);
+		if (values == null || values.size() <= 1) {
+			return;
+		}
+		switch (strategy) {
+			case RETAIN_FIRST:
+				headers.set(name, values.get(0));
+				break;
+			case RETAIN_LAST:
+				headers.set(name, values.get(values.size() - 1));
+				break;
+			case RETAIN_UNIQUE:
+				headers.put(name, new ArrayList<>(new LinkedHashSet<>(values)));
+				break;
+			default:
+				break;
+		}
+	}
+
 	public static BiFunction<ServerRequest, ServerResponse, ServerResponse> removeResponseHeader(String name) {
 		return (request, response) -> {
 			response.headers().remove(name);
@@ -90,4 +138,23 @@ public abstract class AfterFilterFunctions {
 		};
 	}
 
+	public enum DedupeStrategy {
+
+		/**
+		 * Default: Retain the first value only.
+		 */
+		RETAIN_FIRST,
+
+		/**
+		 * Retain the last value only.
+		 */
+		RETAIN_LAST,
+
+		/**
+		 * Retain all unique values in the order of their first encounter.
+		 */
+		RETAIN_UNIQUE
+
+	}
+
 }

spring-cloud-gateway-server-mvc/src/main/java/org/springframework/cloud/gateway/server/mvc/filter/FilterFunctions.java

@@ -24,6 +24,7 @@ import java.util.Collection;
 import org.springframework.cloud.gateway.server.mvc.common.HttpStatusHolder;
 import org.springframework.cloud.gateway.server.mvc.common.KeyValues;
 import org.springframework.cloud.gateway.server.mvc.common.Shortcut;
+import org.springframework.cloud.gateway.server.mvc.filter.AfterFilterFunctions.DedupeStrategy;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatusCode;
 import org.springframework.util.Assert;
@@ -60,6 +61,16 @@ public interface FilterFunctions {
 		return ofResponseProcessor(AfterFilterFunctions.addResponseHeader(name, values));
 	}
 
+	static HandlerFilterFunction<ServerResponse, ServerResponse> dedupeResponseHeader(String name) {
+		return ofResponseProcessor(AfterFilterFunctions.dedupeResponseHeader(name));
+	}
+
+	@Shortcut
+	static HandlerFilterFunction<ServerResponse, ServerResponse> dedupeResponseHeader(String name,
+			DedupeStrategy strategy) {
+		return ofResponseProcessor(AfterFilterFunctions.dedupeResponseHeader(name, strategy));
+	}
+
 	@Shortcut
 	static HandlerFilterFunction<ServerResponse, ServerResponse> mapRequestHeader(String fromHeader, String toHeader) {
 		return ofRequestProcessor(BeforeFilterFunctions.mapRequestHeader(fromHeader, toHeader));

spring-cloud-gateway-server-mvc/src/test/java/org/springframework/cloud/gateway/server/mvc/ServerMvcIntegrationTests.java

@@ -69,7 +69,11 @@ import org.springframework.web.servlet.function.ServerRequest;
 import org.springframework.web.servlet.function.ServerResponse;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.cloud.gateway.server.mvc.filter.AfterFilterFunctions.DedupeStrategy.RETAIN_FIRST;
+import static org.springframework.cloud.gateway.server.mvc.filter.AfterFilterFunctions.DedupeStrategy.RETAIN_LAST;
+import static org.springframework.cloud.gateway.server.mvc.filter.AfterFilterFunctions.DedupeStrategy.RETAIN_UNIQUE;
 import static org.springframework.cloud.gateway.server.mvc.filter.AfterFilterFunctions.addResponseHeader;
+import static org.springframework.cloud.gateway.server.mvc.filter.AfterFilterFunctions.dedupeResponseHeader;
 import static org.springframework.cloud.gateway.server.mvc.filter.AfterFilterFunctions.removeResponseHeader;
 import static org.springframework.cloud.gateway.server.mvc.filter.AfterFilterFunctions.rewriteResponseHeader;
 import static org.springframework.cloud.gateway.server.mvc.filter.AfterFilterFunctions.setResponseHeader;
@@ -476,6 +480,15 @@ public class ServerMvcIntegrationTests {
 				});
 	}
 
+	@Test
+	public void dedupeResponseHeaderWorks() {
+		restClient.get().uri("/headers").header("Host", "www.deduperesponseheader.org").exchange().expectStatus().isOk()
+				.expectHeader().valueEquals("Access-Control-Allow-Credentials", "true").expectHeader()
+				.valueEquals("Access-Control-Allow-Origin", "https://example.org").expectHeader()
+				.valueEquals("Scout-Cookie", "S'mores").expectHeader()
+				.valueEquals("Next-Week-Lottery-Numbers", "4", "2", "42");
+	}
+
 	@Test
 	public void addRequestHeadersIfNotPresentWorks() {
 		restClient.get().uri("/headers").header("Host", "www.addrequestheadersifnotpresent.org")
@@ -881,6 +894,29 @@ public class ServerMvcIntegrationTests {
 			// @formatter:on
 		}
 
+		@Bean
+		public RouterFunction<ServerResponse> gatewayRouterFunctionsDedupeResponseHeader() {
+			// @formatter:off
+			return route("testdeduperesponseheader")
+					.route(GET("/headers").and(host("{sub}.deduperesponseheader.org")), http())
+					.filter(new HttpbinUriResolver())
+					.after(dedupeResponseHeader("Access-Control-Allow-Credentials Access-Control-Allow-Origin", RETAIN_FIRST))
+					.after(dedupeResponseHeader("Scout-Cookie", RETAIN_LAST))
+					.after(dedupeResponseHeader("Next-Week-Lottery-Numbers", RETAIN_UNIQUE))
+					.after(addResponseHeader("Access-Control-Allow-Credentials", "false"))
+					.after(setResponseHeader("Access-Control-Allow-Credentials", "true"))
+					.after(addResponseHeader("Access-Control-Allow-Origin", "*"))
+					.after(setResponseHeader("Access-Control-Allow-Origin", "https://example.org"))
+					.after(addResponseHeader("Scout-Cookie", "S'mores"))
+					.after(setResponseHeader("Scout-Cookie", "Thin Mints"))
+					.after(addResponseHeader("Next-Week-Lottery-Numbers", "42"))
+					.after(addResponseHeader("Next-Week-Lottery-Numbers", "2"))
+					.after(addResponseHeader("Next-Week-Lottery-Numbers", "2"))
+					.after(setResponseHeader("Next-Week-Lottery-Numbers", "4"))
+					.build();
+			// @formatter:on
+		}
+
 	}
 
 	@RestController