AddResponseHeaderGatewayFilterFactory support override option

docs/modules/ROOT/pages/spring-cloud-gateway/gatewayfilter-factories/addresponseheader-factory.adoc

@@ -1,7 +1,7 @@
 [[addresponseheader-gatewayfilter-factory]]
 = `AddResponseHeader` `GatewayFilter` Factory
 
-The `AddResponseHeader` `GatewayFilter` Factory takes a `name` and `value` parameter.
+The `AddResponseHeader` `GatewayFilter` Factory takes three parameters: `name`, `value` and `override`(default value is `true`) .
 The following example configures an `AddResponseHeader` `GatewayFilter`:
 
 .application.yml
@@ -15,9 +15,12 @@ spring:
         uri: https://example.org
         filters:
         - AddResponseHeader=X-Response-Red, Blue
+        - AddResponseHeader=X-Response-Black, White, false
 ----
 
 This adds `X-Response-Red:Blue` header to the downstream response's headers for all matching requests.
+and if the response already contains the `X-Response-Black` header, this will not add the `X-Response-Black: White`
+header to the downstream response's headers for all matching requests.
 
 `AddResponseHeader` is aware of URI variables used to match a path or host.
 URI variables may be used in the value and are expanded at runtime.

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/filter/factory/AddResponseHeaderGatewayFilterFactory.java

@@ -16,12 +16,17 @@
 
 package org.springframework.cloud.gateway.filter.factory;
 
+import java.util.Arrays;
+import java.util.List;
+
 import reactor.core.publisher.Mono;
 
 import org.springframework.cloud.gateway.filter.GatewayFilter;
 import org.springframework.cloud.gateway.filter.GatewayFilterChain;
 import org.springframework.cloud.gateway.support.ServerWebExchangeUtils;
+import org.springframework.core.style.ToStringCreator;
 import org.springframework.http.HttpHeaders;
+import org.springframework.util.StringUtils;
 import org.springframework.web.server.ServerWebExchange;
 
 import static org.springframework.cloud.gateway.support.GatewayToStringStyler.filterToStringCreator;
@@ -31,6 +36,23 @@
  */
 public class AddResponseHeaderGatewayFilterFactory extends AbstractNameValueGatewayFilterFactory {
 
+	private static final String OVERRIDE_KEY = "override";
+
+	@Override
+	public Class getConfigClass() {
+		return Config.class;
+	}
+
+	@Override
+	public NameValueConfig newConfig() {
+		return new Config();
+	}
+
+	@Override
+	public List<String> shortcutFieldOrder() {
+		return Arrays.asList(GatewayFilter.NAME_KEY, GatewayFilter.VALUE_KEY, OVERRIDE_KEY);
+	}
+
 	@Override
 	public GatewayFilter apply(NameValueConfig config) {
 		return new GatewayFilter() {
@@ -41,6 +63,13 @@ public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
 
 			@Override
 			public String toString() {
+				if (config instanceof Config) {
+					return filterToStringCreator(AddResponseHeaderGatewayFilterFactory.this)
+						.append(GatewayFilter.NAME_KEY, config.getName())
+						.append(GatewayFilter.VALUE_KEY, config.getValue())
+						.append(OVERRIDE_KEY, ((Config) config).isOverride())
+						.toString();
+				}
 				return filterToStringCreator(AddResponseHeaderGatewayFilterFactory.this)
 					.append(config.getName(), config.getValue())
 					.toString();
@@ -49,12 +78,51 @@ public String toString() {
 	}
 
 	void addHeader(ServerWebExchange exchange, NameValueConfig config) {
-		final String value = ServerWebExchangeUtils.expand(exchange, config.getValue());
-		HttpHeaders headers = exchange.getResponse().getHeaders();
 		// if response has been commited, no more response headers will bee added.
 		if (!exchange.getResponse().isCommitted()) {
-			headers.add(config.getName(), value);
+			final String value = ServerWebExchangeUtils.expand(exchange, config.getValue());
+			HttpHeaders headers = exchange.getResponse().getHeaders();
+
+			boolean override = true; // default is true
+			if (config instanceof Config) {
+				override = ((Config) config).isOverride();
+			}
+
+			if (override) {
+				headers.add(config.getName(), value);
+			}
+			else {
+				boolean headerIsMissingOrBlank = headers.getOrEmpty(config.getName())
+					.stream()
+					.allMatch(h -> !StringUtils.hasText(h));
+				if (headerIsMissingOrBlank) {
+					headers.add(config.getName(), value);
+				}
+			}
 		}
 	}
 
+	public static class Config extends AbstractNameValueGatewayFilterFactory.NameValueConfig {
+
+		private boolean override = true;
+
+		public boolean isOverride() {
+			return override;
+		}
+
+		public Config setOverride(boolean override) {
+			this.override = override;
+			return this;
+		}
+
+		@Override
+		public String toString() {
+			return new ToStringCreator(this).append(NAME_KEY, name)
+				.append(VALUE_KEY, value)
+				.append(OVERRIDE_KEY, override)
+				.toString();
+		}
+
+	}
+
 }

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/route/builder/GatewayFilterSpec.java

@@ -225,6 +225,22 @@ public GatewayFilterSpec addResponseHeader(String headerName, String headerValue
 			.apply(c -> c.setName(headerName).setValue(headerValue)));
 	}
 
+	/**
+	 * Adds a header to the response returned to the Gateway from the route.
+	 * @param headerName the header name
+	 * @param headerValue the header value
+	 * @param override override or not
+	 * @return a {@link GatewayFilterSpec} that can be used to apply additional filters
+	 */
+	public GatewayFilterSpec addResponseHeader(String headerName, String headerValue, boolean override) {
+		AddResponseHeaderGatewayFilterFactory.Config config = new AddResponseHeaderGatewayFilterFactory.Config();
+		config.setName(headerName);
+		config.setValue(headerValue);
+		config.setOverride(override);
+
+		return filter(getBean(AddResponseHeaderGatewayFilterFactory.class).apply(config));
+	}
+
 	/**
 	 * A filter that adds a local cache for storing response body for repeated requests.
 	 * <p>

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/filter/factory/AddResponseHeaderGatewayFilterFactoryTests.java

@@ -17,6 +17,8 @@
 package org.springframework.cloud.gateway.filter.factory;
 
 import java.net.URI;
+import java.util.HashMap;
+import java.util.Map;
 
 import org.junit.jupiter.api.Test;
 
@@ -51,15 +53,64 @@ void testResponseHeaderFilter() {
 			.header("Host", host)
 			.exchange()
 			.expectHeader()
-			.valueEquals("X-Request-Foo", expectedValue);
+			.valueEquals("X-Request-Foo", expectedValue)
+			.expectHeader()
+			.valueEquals("X-Request-Example", "ValueA");
+	}
+
+	@Test
+	void testResponseHeaderFilterHeaderPresent() {
+		URI uri = UriComponentsBuilder.fromUriString(this.baseUri + "/headers").build(true).toUri();
+		String host = "www.addresponseheader.org";
+		String expectedValue = "Bar";
+
+		Map<String, String> body = new HashMap<>();
+		body.put("X-Request-Example", "ValueB");
+
+		testClient.patch()
+			.uri(uri)
+			.header("Host", host)
+			.bodyValue(body)
+			.exchange()
+			.expectHeader()
+			.valueEquals("X-Request-Foo", expectedValue)
+			.expectHeader()
+			.valueEquals("X-Request-Example", "ValueB");
 	}
 
 	@Test
 	void testResponseHeaderFilterJavaDsl() {
-		URI uri = UriComponentsBuilder.fromUriString(this.baseUri + "/get").build(true).toUri();
+		URI uri = UriComponentsBuilder.fromUriString(this.baseUri + "/headers").build(true).toUri();
+		String host = "www.addresponseheaderjava.org";
+		String expectedValue = "myresponsevalue-www";
+		testClient.get()
+			.uri(uri)
+			.header("Host", host)
+			.exchange()
+			.expectHeader()
+			.valueEquals("example", expectedValue)
+			.expectHeader()
+			.valueEquals("example2", "myresponsevalue2-www");
+	}
+
+	@Test
+	void testResponseHeaderFilterHeaderPresentJavaDsl() {
+		URI uri = UriComponentsBuilder.fromUriString(this.baseUri + "/headers").build(true).toUri();
 		String host = "www.addresponseheaderjava.org";
 		String expectedValue = "myresponsevalue-www";
-		testClient.get().uri(uri).header("Host", host).exchange().expectHeader().valueEquals("example", expectedValue);
+
+		Map<String, String> body = new HashMap<>();
+		body.put("example2", "myresponsevalue2");
+
+		testClient.patch()
+			.uri(uri)
+			.header("Host", host)
+			.bodyValue(body)
+			.exchange()
+			.expectHeader()
+			.valueEquals("example", expectedValue)
+			.expectHeader()
+			.valueEquals("example2", "myresponsevalue2");
 	}
 
 	@Test
@@ -81,11 +132,11 @@ static class TestConfig {
 		public RouteLocator testRouteLocator(RouteLocatorBuilder builder) {
 			return builder.routes()
 				.route("add_response_header_java_test",
-						r -> r.path("/get")
+						r -> r.path("/headers")
 							.and()
 							.host("{sub}.addresponseheaderjava.org")
-							.filters(
-									f -> f.prefixPath("/httpbin").addResponseHeader("example", "myresponsevalue-{sub}"))
+							.filters(f -> f.addResponseHeader("example", "myresponsevalue-{sub}")
+								.addResponseHeader("example2", "myresponsevalue2-{sub}", false))
 							.uri(uri))
 				.build();
 		}

spring-cloud-gateway-server/src/test/resources/application.yml

@@ -72,6 +72,7 @@ spring:
         - Path=/headers
         filters:
         - AddResponseHeader=X-Request-Foo, Bar
+        - AddResponseHeader=X-Request-Example, ValueA, false
 
       - id: cache_request_body_test
         uri: ${test.uri}