Merge branch '3.1.x'

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

@@ -181,7 +181,7 @@ public class NettyRoutingFilter implements GlobalFilter, Ordered {
 
 			exchange.getAttributes().put(CLIENT_RESPONSE_HEADER_NAMES, filteredResponseHeaders.keySet());
 
-			response.getHeaders().putAll(filteredResponseHeaders);
+			response.getHeaders().addAll(filteredResponseHeaders);
 
 			return Mono.just(res);
 		});

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

@@ -132,6 +132,16 @@ public class NettyRoutingFilterIntegrationTests extends BaseWebClientTests {
 		testClient.get().uri("/delay/2").exchange().expectStatus().isEqualTo(HttpStatus.OK);
 	}
 
+	@Test
+	public void testHeadersAreClearedOnFallback() {
+		String header = "X-Test-SHOULD-MERGED-HEADER";
+		String gatewayHeaderValue = "value-from-gateway";
+		String upstreamHeaderValue = "value-from-upstream";
+		testClient.post().uri("/responseheaders/200").header("Host", "www.mergeresponseheader.org")
+				.header(header, upstreamHeaderValue).exchange().expectHeader()
+				.valueEquals(header, gatewayHeaderValue, upstreamHeaderValue);
+	}
+
 	@EnableAutoConfiguration
 	@SpringBootConfiguration
 	@Import(DefaultTestConfig.class)

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

@@ -60,6 +60,17 @@ spring:
           metadata:
             response-timeout: notANumber
 
+        # =====================================
+        - id: per_route_merge_response_headers
+          uri: ${test.uri}
+          predicates:
+            - Host=**.mergeresponseheader.org
+            - Path=/responseheaders/**
+          filters:
+            - AddResponseHeader=X-Test-SHOULD-MERGED-HEADER, value-from-gateway
+          metadata:
+            response-timeout: 1000
+
         # =====================================
         # should be last and not follow alphabetical order
         - id: default_path_to_httpbin