[Test] Add test for custom requests in High Level Rest Client (#25106)

This commit adds a test that tests and demonstrates how
{@link RestHighLevelClient} can be extended to support
custom endpoint.

client/rest-high-level/src/main/java/org/elasticsearch/client/RestHighLevelClient.java

@@ -371,14 +371,14 @@ public void clearScrollAsync(ClearScrollRequest clearScrollRequest, ActionListen
                 listener, emptySet(), headers);
     }
 
-    private <Req extends ActionRequest, Resp> Resp performRequestAndParseEntity(Req request,
+    protected <Req extends ActionRequest, Resp> Resp performRequestAndParseEntity(Req request,
                                                                             CheckedFunction<Req, Request, IOException> requestConverter,
                                                                             CheckedFunction<XContentParser, Resp, IOException> entityParser,
                                                                             Set<Integer> ignores, Header... headers) throws IOException {
         return performRequest(request, requestConverter, (response) -> parseEntity(response.getEntity(), entityParser), ignores, headers);
     }
 
-    <Req extends ActionRequest, Resp> Resp performRequest(Req request,
+    protected <Req extends ActionRequest, Resp> Resp performRequest(Req request,
                                                           CheckedFunction<Req, Request, IOException> requestConverter,
                                                           CheckedFunction<Response, Resp, IOException> responseConverter,
                                                           Set<Integer> ignores, Header... headers) throws IOException {
@@ -408,15 +408,15 @@ <Req extends ActionRequest, Resp> Resp performRequest(Req request,
         }
     }
 
-    private <Req extends ActionRequest, Resp> void performRequestAsyncAndParseEntity(Req request,
+    protected <Req extends ActionRequest, Resp> void performRequestAsyncAndParseEntity(Req request,
                                                                  CheckedFunction<Req, Request, IOException> requestConverter,
                                                                  CheckedFunction<XContentParser, Resp, IOException> entityParser,
                                                                  ActionListener<Resp> listener, Set<Integer> ignores, Header... headers) {
         performRequestAsync(request, requestConverter, (response) -> parseEntity(response.getEntity(), entityParser),
                 listener, ignores, headers);
     }
 
-    <Req extends ActionRequest, Resp> void performRequestAsync(Req request,
+    protected <Req extends ActionRequest, Resp> void performRequestAsync(Req request,
                                                                CheckedFunction<Req, Request, IOException> requestConverter,
                                                                CheckedFunction<Response, Resp, IOException> responseConverter,
                                                                ActionListener<Resp> listener, Set<Integer> ignores, Header... headers) {

client/rest-high-level/src/test/java/org/elasticsearch/client/CustomRestHighLevelClientTests.java

@@ -0,0 +1,181 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you 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
+ *
+ *    http://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.elasticsearch.client;
+
+import org.apache.http.Header;
+import org.apache.http.HttpEntity;
+import org.apache.http.HttpHost;
+import org.apache.http.HttpResponse;
+import org.apache.http.ProtocolVersion;
+import org.apache.http.RequestLine;
+import org.apache.http.client.methods.HttpGet;
+import org.apache.http.entity.ByteArrayEntity;
+import org.apache.http.entity.ContentType;
+import org.apache.http.message.BasicHeader;
+import org.apache.http.message.BasicHttpResponse;
+import org.apache.http.message.BasicRequestLine;
+import org.apache.http.message.BasicStatusLine;
+import org.apache.lucene.util.BytesRef;
+import org.elasticsearch.Build;
+import org.elasticsearch.Version;
+import org.elasticsearch.action.ActionListener;
+import org.elasticsearch.action.main.MainRequest;
+import org.elasticsearch.action.main.MainResponse;
+import org.elasticsearch.cluster.ClusterName;
+import org.elasticsearch.common.SuppressForbidden;
+import org.elasticsearch.common.xcontent.XContentHelper;
+import org.elasticsearch.common.xcontent.XContentType;
+import org.elasticsearch.test.ESTestCase;
+import org.junit.Before;
+
+import java.io.IOException;
+import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
+
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.emptySet;
+import static org.elasticsearch.client.ESRestHighLevelClientTestCase.execute;
+import static org.mockito.Matchers.any;
+import static org.mockito.Matchers.anyMapOf;
+import static org.mockito.Matchers.anyObject;
+import static org.mockito.Matchers.anyVararg;
+import static org.mockito.Matchers.eq;
+import static org.mockito.Mockito.doAnswer;
+import static org.mockito.Mockito.mock;
+
+/**
+ * Test and demonstrates how {@link RestHighLevelClient} can be extended to support custom endpoints.
+ */
+public class CustomRestHighLevelClientTests extends ESTestCase {
+
+    private static final String ENDPOINT = "/_custom";
+
+    private CustomRestClient restHighLevelClient;
+
+    @Before
+    @SuppressWarnings("unchecked")
+    public void initClients() throws IOException {
+        if (restHighLevelClient == null) {
+            final RestClient restClient = mock(RestClient.class);
+            restHighLevelClient = new CustomRestClient(restClient);
+
+            doAnswer(mock -> mockPerformRequest((Header) mock.getArguments()[4]))
+                    .when(restClient)
+                    .performRequest(eq(HttpGet.METHOD_NAME), eq(ENDPOINT), anyMapOf(String.class, String.class), anyObject(), anyVararg());
+
+            doAnswer(mock -> mockPerformRequestAsync((Header) mock.getArguments()[5], (ResponseListener) mock.getArguments()[4]))
+                    .when(restClient)
+                    .performRequestAsync(eq(HttpGet.METHOD_NAME), eq(ENDPOINT), anyMapOf(String.class, String.class),
+                            any(HttpEntity.class), any(ResponseListener.class), anyVararg());
+        }
+    }
+
+    public void testCustomEndpoint() throws IOException {
+        final MainRequest request = new MainRequest();
+        final Header header = new BasicHeader("node_name", randomAlphaOfLengthBetween(1, 10));
+
+        MainResponse response = execute(request, restHighLevelClient::custom, restHighLevelClient::customAsync, header);
+        assertEquals(header.getValue(), response.getNodeName());
+
+        response = execute(request, restHighLevelClient::customAndParse, restHighLevelClient::customAndParseAsync, header);
+        assertEquals(header.getValue(), response.getNodeName());
+    }
+
+    /**
+     * The {@link RestHighLevelClient} must declare the following execution methods using the <code>protected</code> modifier
+     * so that they can be used by subclasses to implement custom logic.
+     */
+    @SuppressForbidden(reason = "We're forced to uses Class#getDeclaredMethods() here because this test checks protected methods")
+    public void testMethodsVisibility() throws ClassNotFoundException {
+        String[] methodNames = new String[]{"performRequest", "performRequestAndParseEntity", "performRequestAsync",
+                "performRequestAsyncAndParseEntity"};
+        for (String methodName : methodNames) {
+            boolean found = false;
+            for (Method method : RestHighLevelClient.class.getDeclaredMethods()) {
+                if (method.getName().equals(methodName)) {
+                    assertTrue("Method " + methodName + " must be protected", Modifier.isProtected(method.getModifiers()));
+                    found = true;
+                }
+            }
+            assertTrue("Failed to find method " + methodName, found);
+        }
+    }
+
+    /**
+     * Mocks the asynchronous request execution by calling the {@link #mockPerformRequest(Header)} method.
+     */
+    private Void mockPerformRequestAsync(Header httpHeader, ResponseListener responseListener) {
+        try {
+            responseListener.onSuccess(mockPerformRequest(httpHeader));
+        } catch (IOException e) {
+            responseListener.onFailure(e);
+        }
+        return null;
+    }
+
+    /**
+     * Mocks the synchronous request execution like if it was executed by Elasticsearch.
+     */
+    private Response mockPerformRequest(Header httpHeader) throws IOException {
+        ProtocolVersion protocol = new ProtocolVersion("HTTP", 1, 1);
+        HttpResponse httpResponse = new BasicHttpResponse(new BasicStatusLine(protocol, 200, "OK"));
+
+        MainResponse response = new MainResponse(httpHeader.getValue(), Version.CURRENT, ClusterName.DEFAULT, "_na", Build.CURRENT, true);
+        BytesRef bytesRef = XContentHelper.toXContent(response, XContentType.JSON, false).toBytesRef();
+        httpResponse.setEntity(new ByteArrayEntity(bytesRef.bytes, ContentType.APPLICATION_JSON));
+
+        RequestLine requestLine = new BasicRequestLine(HttpGet.METHOD_NAME, ENDPOINT, protocol);
+        return new Response(requestLine, new HttpHost("localhost", 9200), httpResponse);
+    }
+
+    /**
+     * A custom high level client that provides custom methods to execute a request and get its associate response back.
+     */
+    static class CustomRestClient extends RestHighLevelClient {
+
+        private CustomRestClient(RestClient restClient) {
+            super(restClient);
+        }
+
+        MainResponse custom(MainRequest mainRequest, Header... headers) throws IOException {
+            return performRequest(mainRequest, this::toRequest, this::toResponse, emptySet(), headers);
+        }
+
+        MainResponse customAndParse(MainRequest mainRequest, Header... headers) throws IOException {
+            return performRequestAndParseEntity(mainRequest, this::toRequest, MainResponse::fromXContent, emptySet(), headers);
+        }
+
+        void customAsync(MainRequest mainRequest, ActionListener<MainResponse> listener, Header... headers) {
+            performRequestAsync(mainRequest, this::toRequest, this::toResponse, listener, emptySet(), headers);
+        }
+
+        void customAndParseAsync(MainRequest mainRequest, ActionListener<MainResponse> listener, Header... headers) {
+            performRequestAsyncAndParseEntity(mainRequest, this::toRequest, MainResponse::fromXContent, listener, emptySet(), headers);
+        }
+
+        Request toRequest(MainRequest mainRequest) throws IOException {
+            return new Request(HttpGet.METHOD_NAME, ENDPOINT, emptyMap(), null);
+        }
+
+        MainResponse toResponse(Response response) throws IOException {
+            return parseEntity(response.getEntity(), MainResponse::fromXContent);
+        }
+    }
+}