Add hints to API via the Request interface. Fixes gh-647. (#669)

* Add hints to API via the Request interface. Fixes gh-647.

* Switch to generic context.

spring-cloud-commons/src/main/java/org/springframework/cloud/client/loadbalancer/reactive/DefaultRequest.java

@@ -17,8 +17,30 @@
 package org.springframework.cloud.client.loadbalancer.reactive;
 
 /**
+ * A default implementation of {@link Request}.
+ *
  * @author Spencer Gibb
+ * @author Olga Maciaszek-Sharma
  */
-public class DefaultRequest implements Request {
+public class DefaultRequest<T> implements Request<T> {
+
+	private T context;
+
+	public DefaultRequest() {
+		new DefaultRequestContext();
+	}
+
+	public DefaultRequest(T context) {
+		this.context = context;
+	}
+
+	@Override
+	public T getContext() {
+		return context;
+	}
+
+	public void setContext(T context) {
+		this.context = context;
+	}
 
 }

spring-cloud-commons/src/main/java/org/springframework/cloud/client/loadbalancer/reactive/DefaultRequestContext.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2012-2019 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.client.loadbalancer.reactive;
+
+/**
+ * Contains information relevant to the request.
+ *
+ * @author Olga Maciaszek-Sharma
+ */
+public class DefaultRequestContext {
+
+	/**
+	 * A {@link String} value of hint that can be used to choose the correct service
+	 * instance.
+	 */
+	private String hint = "default";
+
+	public DefaultRequestContext() {
+	}
+
+	public DefaultRequestContext(String hint) {
+		this.hint = hint;
+	}
+
+	public String getHint() {
+		return hint;
+	}
+
+	public void setHint(String hint) {
+		this.hint = hint;
+	}
+
+}

spring-cloud-commons/src/main/java/org/springframework/cloud/client/loadbalancer/reactive/ReactiveLoadBalancer.java

@@ -30,13 +30,14 @@ public interface ReactiveLoadBalancer<T> {
 	/**
 	 * Default implementation of a request.
 	 */
-	Request REQUEST = new DefaultRequest();
+	Request<DefaultRequestContext> REQUEST = new DefaultRequest();
 
 	/**
 	 * Choose the next server based on the load balancing algorithm.
 	 * @param request - incoming request
 	 * @return publisher for the response
 	 */
+	@SuppressWarnings("rawtypes")
 	Publisher<Response<T>> choose(Request request);
 
 	default Publisher<Response<T>> choose() { // conflicting name

spring-cloud-commons/src/main/java/org/springframework/cloud/client/loadbalancer/reactive/Request.java

@@ -20,8 +20,14 @@ package org.springframework.cloud.client.loadbalancer.reactive;
  * Marker interface for a request.
  *
  * @author Spencer Gibb
+ * @author Olga Maciaszek-Sharma
  */
-public interface Request {
+public interface Request<C> {
+
+	// Avoid breaking backward compatibility
+	default C getContext() {
+		return null;
+	}
 
 	// TODO: define contents
 

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

@@ -35,6 +35,7 @@ public interface ReactorLoadBalancer<T> extends ReactiveLoadBalancer<T> {
 	 * @param request - an input request
 	 * @return - mono of response
 	 */
+	@SuppressWarnings("rawtypes")
 	Mono<Response<T>> choose(Request request);
 
 	default Mono<Response<T>> choose() {

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

@@ -104,6 +104,7 @@ public class RoundRobinLoadBalancer implements ReactorServiceInstanceLoadBalance
 		this.position = new AtomicInteger(seedPosition);
 	}
 
+	@SuppressWarnings("rawtypes")
 	@Override
 	// see original
 	// https://github.com/Netflix/ocelli/blob/master/ocelli-core/

spring-cloud-loadbalancer/src/test/java/org/springframework/cloud/loadbalancer/core/LoadBalancerTests.java

@@ -24,6 +24,7 @@ import org.junit.runner.RunWith;
 import reactor.core.publisher.Mono;
 import reactor.test.StepVerifier;
 
+import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.SpringBootConfiguration;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
@@ -33,7 +34,11 @@ import org.springframework.cloud.client.DefaultServiceInstance;
 import org.springframework.cloud.client.ServiceInstance;
 import org.springframework.cloud.client.loadbalancer.reactive.CompletionContext;
 import org.springframework.cloud.client.loadbalancer.reactive.CompletionContext.Status;
+import org.springframework.cloud.client.loadbalancer.reactive.DefaultRequest;
+import org.springframework.cloud.client.loadbalancer.reactive.DefaultRequestContext;
+import org.springframework.cloud.client.loadbalancer.reactive.DefaultResponse;
 import org.springframework.cloud.client.loadbalancer.reactive.ReactiveLoadBalancer;
+import org.springframework.cloud.client.loadbalancer.reactive.Request;
 import org.springframework.cloud.client.loadbalancer.reactive.Response;
 import org.springframework.cloud.loadbalancer.annotation.LoadBalancerClient;
 import org.springframework.cloud.loadbalancer.annotation.LoadBalancerClients;
@@ -45,6 +50,7 @@ import org.springframework.core.ResolvableType;
 import org.springframework.core.env.Environment;
 import org.springframework.test.context.junit4.SpringRunner;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.BDDAssertions.then;
 
 /**
@@ -125,6 +131,11 @@ public class LoadBalancerTests {
 		assertLoadBalancer(loadBalancer, Arrays.asList("1host", "2host-secure"));
 	}
 
+	private static DefaultServiceInstance instance(String serviceId, String host,
+			boolean secure) {
+		return new DefaultServiceInstance(serviceId, serviceId, host, 80, secure);
+	}
+
 	@Test
 	public void staticConfigurationWorksWithServiceInstanceListSupplier() {
 		String serviceId = "test1";
@@ -136,9 +147,44 @@ public class LoadBalancerTests {
 		assertLoadBalancer(loadBalancer, Arrays.asList("1host", "2host-secure"));
 	}
 
-	private DefaultServiceInstance instance(String serviceId, String host,
-			boolean secure) {
-		return new DefaultServiceInstance(serviceId, serviceId, host, 80, secure);
+	@SuppressWarnings("ConstantConditions")
+	@Test
+	public void canPassHintViaRequest() {
+		String serviceId = "test1";
+		RoundRobinLoadBalancer loadBalancer = new TestHintLoadBalancer(
+				ServiceInstanceListSuppliers.toProvider(serviceId,
+						instance(serviceId, "1host", false),
+						instance(serviceId, "2host-secure", true)),
+				serviceId);
+		Request<DefaultRequestContext> request = new DefaultRequest<>(
+				new DefaultRequestContext("test2"));
+
+		ServiceInstance serviceInstance = loadBalancer.choose(request).block()
+				.getServer();
+
+		assertThat(serviceInstance.getServiceId()).isEqualTo("test2");
+	}
+
+	private static class TestHintLoadBalancer extends RoundRobinLoadBalancer {
+
+		TestHintLoadBalancer(
+				ObjectProvider<ServiceInstanceListSupplier> serviceInstanceListSupplierProvider,
+				String serviceId) {
+			super(serviceInstanceListSupplierProvider, serviceId);
+		}
+
+		@SuppressWarnings("rawtypes")
+		@Override
+		public Mono<Response<ServiceInstance>> choose(Request request) {
+			if (request.getContext() instanceof DefaultRequestContext) {
+				DefaultRequestContext requestContext = (DefaultRequestContext) request
+						.getContext();
+				return Mono.just(new DefaultResponse(
+						instance(requestContext.getHint(), "host", false)));
+			}
+			return Mono.empty();
+		}
+
 	}
 
 	@EnableAutoConfiguration