Customize load balanced requests according to the chosen ServiceInstance

docs/src/main/asciidoc/spring-cloud-openfeign.adoc

@@ -815,6 +815,33 @@ Sometimes, when load balancing is enabled for Feign clients, you may want to use
 spring.cloud.openfeign.oauth2.load-balanced=true
 ----
 
+=== Transform the load-balanced HTTP request
+
+You can use the selected `ServiceInstance` to transform the load-balanced HTTP Request.
+
+For `Request`, you need to implement and define `LoadBalancerFeignRequestTransformer`, as follows:
+
+[source,java,indent=0]
+----
+	@Bean
+	public LoadBalancerFeignRequestTransformer transformer() {
+		return new LoadBalancerFeignRequestTransformer() {
+
+			@Override
+			public Request transformRequest(Request request, ServiceInstance instance) {
+				Map<String, Collection<String>> headers = new HashMap<>(request.headers());
+				headers.put("X-ServiceId", Collections.singletonList(instance.getServiceId()));
+				headers.put("X-InstanceId", Collections.singletonList(instance.getInstanceId()));
+				return Request.create(request.httpMethod(), request.url(), headers, request.body(), request.charset(),
+						request.requestTemplate());
+			}
+		};
+	}
+----
+
+If multiple transformers are defined, they are applied in the order in which beans are defined.
+Alternatively, you can use `LoadBalancerFeignRequestTransformer.DEFAULT_ORDER` to specify the order.
+
 == Configuration properties
 
 To see the list of all Spring Cloud OpenFeign related configuration properties please check link:appendix.html[the Appendix page].

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/loadbalancer/DefaultFeignLoadBalancerConfiguration.java

@@ -16,6 +16,8 @@
 
 package org.springframework.cloud.openfeign.loadbalancer;
 
+import java.util.List;
+
 import feign.Client;
 
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
@@ -36,6 +38,7 @@
  * that uses {@link Client.Default} under the hood.
  *
  * @author Olga Maciaszek-Sharma
+ * @author changjin wei(魏昌进)
  * @since 2.2.0
  */
 @Configuration(proxyBeanMethods = false)
@@ -46,9 +49,10 @@ class DefaultFeignLoadBalancerConfiguration {
 	@ConditionalOnMissingBean
 	@Conditional(OnRetryNotEnabledCondition.class)
 	public Client feignClient(LoadBalancerClient loadBalancerClient,
-			LoadBalancerClientFactory loadBalancerClientFactory) {
+			LoadBalancerClientFactory loadBalancerClientFactory,
+			List<LoadBalancerFeignRequestTransformer> transformers) {
 		return new FeignBlockingLoadBalancerClient(new Client.Default(null, null), loadBalancerClient,
-				loadBalancerClientFactory);
+				loadBalancerClientFactory, transformers);
 	}
 
 	@Bean
@@ -58,9 +62,10 @@ public Client feignClient(LoadBalancerClient loadBalancerClient,
 	@ConditionalOnProperty(value = "spring.cloud.loadbalancer.retry.enabled", havingValue = "true",
 			matchIfMissing = true)
 	public Client feignRetryClient(LoadBalancerClient loadBalancerClient,
-			LoadBalancedRetryFactory loadBalancedRetryFactory, LoadBalancerClientFactory loadBalancerClientFactory) {
+			LoadBalancedRetryFactory loadBalancedRetryFactory, LoadBalancerClientFactory loadBalancerClientFactory,
+			List<LoadBalancerFeignRequestTransformer> transformers) {
 		return new RetryableFeignBlockingLoadBalancerClient(new Client.Default(null, null), loadBalancerClient,
-				loadBalancedRetryFactory, loadBalancerClientFactory);
+				loadBalancedRetryFactory, loadBalancerClientFactory, transformers);
 	}
 
 }

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/loadbalancer/FeignBlockingLoadBalancerClient.java

@@ -19,6 +19,8 @@
 import java.io.IOException;
 import java.net.URI;
 import java.nio.charset.StandardCharsets;
+import java.util.Collections;
+import java.util.List;
 import java.util.Set;
 
 import feign.Client;
@@ -49,6 +51,7 @@
  * {@link ServiceInstance} to use while resolving the request host.
  *
  * @author Olga Maciaszek-Sharma
+ * @author changjin wei(魏昌进)
  * @since 2.2.0
  */
 @SuppressWarnings({ "unchecked", "rawtypes" })
@@ -62,23 +65,41 @@ public class FeignBlockingLoadBalancerClient implements Client {
 
 	private final LoadBalancerClientFactory loadBalancerClientFactory;
 
+	private final List<LoadBalancerFeignRequestTransformer> transformers;
+
 	/**
 	 * @deprecated in favour of
-	 * {@link FeignBlockingLoadBalancerClient#FeignBlockingLoadBalancerClient(Client, LoadBalancerClient, LoadBalancerClientFactory)}
+	 * {@link FeignBlockingLoadBalancerClient#FeignBlockingLoadBalancerClient(Client, LoadBalancerClient, LoadBalancerClientFactory, List)}
 	 */
 	@Deprecated
 	public FeignBlockingLoadBalancerClient(Client delegate, LoadBalancerClient loadBalancerClient,
 			LoadBalancerProperties properties, LoadBalancerClientFactory loadBalancerClientFactory) {
 		this.delegate = delegate;
 		this.loadBalancerClient = loadBalancerClient;
 		this.loadBalancerClientFactory = loadBalancerClientFactory;
+		this.transformers = Collections.emptyList();
 	}
 
+	/**
+	 * @deprecated in favour of
+	 * {@link FeignBlockingLoadBalancerClient#FeignBlockingLoadBalancerClient(Client, LoadBalancerClient, LoadBalancerClientFactory, List)}
+	 */
+	@Deprecated
 	public FeignBlockingLoadBalancerClient(Client delegate, LoadBalancerClient loadBalancerClient,
 			LoadBalancerClientFactory loadBalancerClientFactory) {
 		this.delegate = delegate;
 		this.loadBalancerClient = loadBalancerClient;
 		this.loadBalancerClientFactory = loadBalancerClientFactory;
+		this.transformers = Collections.emptyList();
+	}
+
+	public FeignBlockingLoadBalancerClient(Client delegate, LoadBalancerClient loadBalancerClient,
+			LoadBalancerClientFactory loadBalancerClientFactory,
+			List<LoadBalancerFeignRequestTransformer> transformers) {
+		this.delegate = delegate;
+		this.loadBalancerClient = loadBalancerClient;
+		this.loadBalancerClientFactory = loadBalancerClientFactory;
+		this.transformers = transformers;
 	}
 
 	@Override
@@ -109,7 +130,7 @@ public Response execute(Request request, Request.Options options) throws IOExcep
 					.body(message, StandardCharsets.UTF_8).build();
 		}
 		String reconstructedUrl = loadBalancerClient.reconstructURI(instance, originalUri).toString();
-		Request newRequest = buildRequest(request, reconstructedUrl);
+		Request newRequest = buildRequest(request, reconstructedUrl, instance);
 		return executeWithLoadBalancerLifecycleProcessing(delegate, options, newRequest, lbRequest, lbResponse,
 				supportedLifecycleProcessors);
 	}
@@ -119,6 +140,16 @@ protected Request buildRequest(Request request, String reconstructedUrl) {
 				request.charset(), request.requestTemplate());
 	}
 
+	protected Request buildRequest(Request request, String reconstructedUrl, ServiceInstance instance) {
+		Request newRequest = buildRequest(request, reconstructedUrl);
+		if (transformers != null) {
+			for (LoadBalancerFeignRequestTransformer transformer : transformers) {
+				newRequest = transformer.transformRequest(newRequest, instance);
+			}
+		}
+		return newRequest;
+	}
+
 	// Visible for Sleuth instrumentation
 	public Client getDelegate() {
 		return delegate;

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/loadbalancer/HttpClient5FeignLoadBalancerConfiguration.java

@@ -16,6 +16,8 @@
 
 package org.springframework.cloud.openfeign.loadbalancer;
 
+import java.util.List;
+
 import feign.Client;
 import feign.hc5.ApacheHttp5Client;
 import org.apache.hc.client5.http.classic.HttpClient;
@@ -40,6 +42,7 @@
  * that uses {@link ApacheHttp5Client} under the hood.
  *
  * @author Nguyen Ky Thanh
+ * @author changjin wei(魏昌进)
  */
 @Configuration(proxyBeanMethods = false)
 @ConditionalOnClass(ApacheHttp5Client.class)
@@ -53,9 +56,11 @@ class HttpClient5FeignLoadBalancerConfiguration {
 	@ConditionalOnMissingBean
 	@Conditional(OnRetryNotEnabledCondition.class)
 	public Client feignClient(LoadBalancerClient loadBalancerClient, HttpClient httpClient5,
-			LoadBalancerClientFactory loadBalancerClientFactory) {
+			LoadBalancerClientFactory loadBalancerClientFactory,
+			List<LoadBalancerFeignRequestTransformer> transformers) {
 		Client delegate = new ApacheHttp5Client(httpClient5);
-		return new FeignBlockingLoadBalancerClient(delegate, loadBalancerClient, loadBalancerClientFactory);
+		return new FeignBlockingLoadBalancerClient(delegate, loadBalancerClient, loadBalancerClientFactory,
+				transformers);
 	}
 
 	@Bean
@@ -65,10 +70,11 @@ public Client feignClient(LoadBalancerClient loadBalancerClient, HttpClient http
 	@ConditionalOnProperty(value = "spring.cloud.loadbalancer.retry.enabled", havingValue = "true",
 			matchIfMissing = true)
 	public Client feignRetryClient(LoadBalancerClient loadBalancerClient, HttpClient httpClient5,
-			LoadBalancedRetryFactory loadBalancedRetryFactory, LoadBalancerClientFactory loadBalancerClientFactory) {
+			LoadBalancedRetryFactory loadBalancedRetryFactory, LoadBalancerClientFactory loadBalancerClientFactory,
+			List<LoadBalancerFeignRequestTransformer> transformers) {
 		Client delegate = new ApacheHttp5Client(httpClient5);
 		return new RetryableFeignBlockingLoadBalancerClient(delegate, loadBalancerClient, loadBalancedRetryFactory,
-				loadBalancerClientFactory);
+				loadBalancerClientFactory, transformers);
 	}
 
 }

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/loadbalancer/HttpClientFeignLoadBalancerConfiguration.java

@@ -16,6 +16,8 @@
 
 package org.springframework.cloud.openfeign.loadbalancer;
 
+import java.util.List;
+
 import feign.Client;
 import feign.httpclient.ApacheHttpClient;
 import org.apache.http.client.HttpClient;
@@ -42,6 +44,7 @@
  *
  * @author Olga Maciaszek-Sharma
  * @author Nguyen Ky Thanh
+ * @author changjin wei(魏昌进)
  * @since 2.2.0
  */
 @Configuration(proxyBeanMethods = false)
@@ -57,9 +60,11 @@ class HttpClientFeignLoadBalancerConfiguration {
 	@ConditionalOnMissingBean
 	@Conditional(OnRetryNotEnabledCondition.class)
 	public Client feignClient(LoadBalancerClient loadBalancerClient, HttpClient httpClient,
-			LoadBalancerClientFactory loadBalancerClientFactory) {
+			LoadBalancerClientFactory loadBalancerClientFactory,
+			List<LoadBalancerFeignRequestTransformer> transformers) {
 		ApacheHttpClient delegate = new ApacheHttpClient(httpClient);
-		return new FeignBlockingLoadBalancerClient(delegate, loadBalancerClient, loadBalancerClientFactory);
+		return new FeignBlockingLoadBalancerClient(delegate, loadBalancerClient, loadBalancerClientFactory,
+				transformers);
 	}
 
 	@Bean
@@ -69,10 +74,11 @@ public Client feignClient(LoadBalancerClient loadBalancerClient, HttpClient http
 	@ConditionalOnProperty(value = "spring.cloud.loadbalancer.retry.enabled", havingValue = "true",
 			matchIfMissing = true)
 	public Client feignRetryClient(LoadBalancerClient loadBalancerClient, HttpClient httpClient,
-			LoadBalancedRetryFactory loadBalancedRetryFactory, LoadBalancerClientFactory loadBalancerClientFactory) {
+			LoadBalancedRetryFactory loadBalancedRetryFactory, LoadBalancerClientFactory loadBalancerClientFactory,
+			List<LoadBalancerFeignRequestTransformer> transformers) {
 		ApacheHttpClient delegate = new ApacheHttpClient(httpClient);
 		return new RetryableFeignBlockingLoadBalancerClient(delegate, loadBalancerClient, loadBalancedRetryFactory,
-				loadBalancerClientFactory);
+				loadBalancerClientFactory, transformers);
 	}
 
 }

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/loadbalancer/LoadBalancerFeignRequestTransformer.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2013-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.openfeign.loadbalancer;
+
+import feign.Request;
+
+import org.springframework.cloud.client.ServiceInstance;
+import org.springframework.core.annotation.Order;
+
+/**
+ * Allows applications to transform the load-balanced {@link Request} given the chosen
+ * {@link org.springframework.cloud.client.ServiceInstance}.
+ *
+ * @author changjin wei(魏昌进)
+ */
+@Order(LoadBalancerFeignRequestTransformer.DEFAULT_ORDER)
+public interface LoadBalancerFeignRequestTransformer {
+
+	/**
+	 * Order for the {@link LoadBalancerFeignRequestTransformer}.
+	 */
+	int DEFAULT_ORDER = 0;
+
+	/**
+	 * Allows transforming load-balanced requests based on the provided {@link ServiceInstance}.
+	 * @param request Original request.
+	 * @param instance ServiceInstance returned from LoadBalancer.
+	 * @return New request or original request
+	 */
+	Request transformRequest(Request request, ServiceInstance instance);
+
+}

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/loadbalancer/OkHttpFeignLoadBalancerConfiguration.java

@@ -16,6 +16,8 @@
 
 package org.springframework.cloud.openfeign.loadbalancer;
 
+import java.util.List;
+
 import feign.Client;
 import feign.okhttp.OkHttpClient;
 
@@ -39,6 +41,7 @@
  * that uses {@link OkHttpClient} under the hood.
  *
  * @author Olga Maciaszek-Sharma
+ * @author changjin wei(魏昌进)
  * @since 2.2.0
  */
 @Configuration(proxyBeanMethods = false)
@@ -53,9 +56,11 @@ class OkHttpFeignLoadBalancerConfiguration {
 	@ConditionalOnMissingBean
 	@Conditional(OnRetryNotEnabledCondition.class)
 	public Client feignClient(okhttp3.OkHttpClient okHttpClient, LoadBalancerClient loadBalancerClient,
-			LoadBalancerClientFactory loadBalancerClientFactory) {
+			LoadBalancerClientFactory loadBalancerClientFactory,
+			List<LoadBalancerFeignRequestTransformer> transformers) {
 		OkHttpClient delegate = new OkHttpClient(okHttpClient);
-		return new FeignBlockingLoadBalancerClient(delegate, loadBalancerClient, loadBalancerClientFactory);
+		return new FeignBlockingLoadBalancerClient(delegate, loadBalancerClient, loadBalancerClientFactory,
+				transformers);
 	}
 
 	@Bean
@@ -65,10 +70,11 @@ public Client feignClient(okhttp3.OkHttpClient okHttpClient, LoadBalancerClient
 	@ConditionalOnProperty(value = "spring.cloud.loadbalancer.retry.enabled", havingValue = "true",
 			matchIfMissing = true)
 	public Client feignRetryClient(LoadBalancerClient loadBalancerClient, okhttp3.OkHttpClient okHttpClient,
-			LoadBalancedRetryFactory loadBalancedRetryFactory, LoadBalancerClientFactory loadBalancerClientFactory) {
+			LoadBalancedRetryFactory loadBalancedRetryFactory, LoadBalancerClientFactory loadBalancerClientFactory,
+			List<LoadBalancerFeignRequestTransformer> transformers) {
 		OkHttpClient delegate = new OkHttpClient(okHttpClient);
 		return new RetryableFeignBlockingLoadBalancerClient(delegate, loadBalancerClient, loadBalancedRetryFactory,
-				loadBalancerClientFactory);
+				loadBalancerClientFactory, transformers);
 	}
 
 }