Created SDK Client to interact with OpenSearch

build.gradle

@@ -59,6 +59,8 @@ dependencies {
     implementation "org.opensearch.plugin:transport-netty4-client:3.0.0-SNAPSHOT"
     implementation group: 'org.apache.logging.log4j', name: 'log4j-api', version: '2.17.1'
     implementation group: 'org.apache.logging.log4j', name: 'log4j-core', version: '2.17.1'
+    implementation 'org.opensearch.client:opensearch-rest-client:2.0.0'
+    implementation 'org.opensearch.client:opensearch-java:2.0.0'
     implementation "io.netty:netty-all:4.1.73.Final"
     testCompileOnly ("junit:junit:4.13.2") {
         exclude module : 'hamcrest'

src/main/java/org/opensearch/sdk/ExtensionsRunner.java

@@ -71,6 +71,8 @@ public class ExtensionsRunner {
     private String uniqueId;
     private DiscoveryNode opensearchNode;
     private TransportService extensionTransportService = null;
+    private int port;
+    private String hostAddress;
 
     private final Settings settings = Settings.builder()
         .put("node.name", extensionSettings.getExtensionName())
@@ -143,6 +145,8 @@ InitializeExtensionsResponse handleExtensionInitRequest(InitializeExtensionsRequ
             return initializeExtensionsResponse;
         } finally {
             // After sending successful response to initialization, send the REST API
+            port = opensearchNode.getAddress().getPort();
+            hostAddress = opensearchNode.getAddress().getAddress();
             setOpensearchNode(opensearchNode);
             extensionTransportService.connectToNode(opensearchNode);
             sendRegisterRestActionsRequest(extensionTransportService);

src/main/java/org/opensearch/sdk/SDKClient.java

@@ -0,0 +1,67 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+package org.opensearch.sdk;
+
+import java.io.IOException;
+
+import org.apache.http.HttpHost;
+
+import org.apache.http.conn.ssl.NoopHostnameVerifier;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.opensearch.client.RestClient;
+import org.opensearch.client.RestClientBuilder;
+import org.opensearch.client.json.jackson.JacksonJsonpMapper;
+import org.opensearch.client.opensearch.OpenSearchClient;
+import org.opensearch.client.transport.OpenSearchTransport;
+import org.opensearch.client.transport.rest_client.RestClientTransport;
+
+/**
+ * This class creates SDKClient for an extension to make requests to OpenSearch
+ */
+public class SDKClient {
+    private final Logger logger = LogManager.getLogger(SDKClient.class);
+    private OpenSearchClient javaClient;
+    private RestClient restClient = null;
+
+    /**
+     * Creates OpenSearchClient for SDK. It also creates a restClient as a wrapper around Java OpenSearchClient
+     * @param hostAddress The address of OpenSearch cluster, client can connect to
+     * @param port The port of OpenSearch cluster
+     * @throws IOException if client failed
+     * @return SDKClient which is internally an OpenSearchClient. The user is responsible for calling {@link #doCloseRestClient()} when finished with the client
+     */
+    public OpenSearchClient initializeClient(String hostAddress, int port) throws IOException {
+        RestClientBuilder builder = RestClient.builder(new HttpHost(hostAddress, port));
+        builder.setStrictDeprecationMode(true);
+        builder.setHttpClientConfigCallback(httpClientBuilder -> {
+            try {
+                return httpClientBuilder.setSSLHostnameVerifier(NoopHostnameVerifier.INSTANCE);
+            } catch (Exception e) {
+                throw new RuntimeException(e);
+            }
+        });
+
+        restClient = builder.build();
+
+        // Create Client
+        OpenSearchTransport transport = new RestClientTransport(restClient, new JacksonJsonpMapper());
+        javaClient = new OpenSearchClient(transport);
+        return javaClient;
+    }
+
+    /**
+     *
+     * @throws IOException if closing the restClient fails
+     */
+    public void doCloseRestClient() throws IOException {
+        if (restClient != null) {
+            restClient.close();
+        }
+    }
+}

src/test/java/org/opensearch/sdk/TestSDKClient.java

@@ -0,0 +1,43 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.sdk;
+
+import org.junit.jupiter.api.Test;
+import org.opensearch.client.opensearch.OpenSearchClient;
+import org.opensearch.client.opensearch.indices.Alias;
+import org.opensearch.client.opensearch.indices.CreateIndexRequest;
+import org.opensearch.test.OpenSearchTestCase;
+
+import java.net.ConnectException;
+
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+
+public class TestSDKClient extends OpenSearchTestCase {
+    SDKClient sdkClient = new SDKClient();
+
+    @Test
+    public void testCreateClient() throws Exception {
+
+        OpenSearchClient testClient = sdkClient.initializeClient("localhost", 9200);
+        assertInstanceOf(OpenSearchClient.class, testClient);
+
+        assertThrows(
+            ConnectException.class,
+            () -> testClient.indices()
+                .create(
+                    new CreateIndexRequest.Builder().index("my-index")
+                        .aliases("foo", new Alias.Builder().isWriteIndex(true).build())
+                        .build()
+                )
+        );
+
+        sdkClient.doCloseRestClient();
+    }
+
+}