Rest High Level client: Add List Tasks (#29546)

This change adds a `listTasks` method to the high level java
ClusterClient which allows listing running tasks through the 
task management API.

Related to #27205

Author: Van0SS

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

@@ -21,6 +21,8 @@
 
 import org.apache.http.Header;
 import org.elasticsearch.action.ActionListener;
+import org.elasticsearch.action.admin.cluster.node.tasks.list.ListTasksRequest;
+import org.elasticsearch.action.admin.cluster.node.tasks.list.ListTasksResponse;
 import org.elasticsearch.action.admin.cluster.settings.ClusterUpdateSettingsRequest;
 import org.elasticsearch.action.admin.cluster.settings.ClusterUpdateSettingsResponse;
 
@@ -63,4 +65,26 @@ public void putSettingsAsync(ClusterUpdateSettingsRequest clusterUpdateSettingsR
         restHighLevelClient.performRequestAsyncAndParseEntity(clusterUpdateSettingsRequest, RequestConverters::clusterPutSettings,
                 ClusterUpdateSettingsResponse::fromXContent, listener, emptySet(), headers);
     }
+
+    /**
+     * Get current tasks using the Task Management API
+     * <p>
+     * See
+     * <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/tasks.html"> Task Management API on elastic.co</a>
+     */
+    public ListTasksResponse listTasks(ListTasksRequest request, Header... headers) throws IOException {
+        return restHighLevelClient.performRequestAndParseEntity(request, RequestConverters::listTasks, ListTasksResponse::fromXContent,
+                emptySet(), headers);
+    }
+
+    /**
+     * Asynchronously get current tasks using the Task Management API
+     * <p>
+     * See
+     * <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/tasks.html"> Task Management API on elastic.co</a>
+     */
+    public void listTasksAsync(ListTasksRequest request, ActionListener<ListTasksResponse> listener, Header... headers) {
+        restHighLevelClient.performRequestAsyncAndParseEntity(request, RequestConverters::listTasks, ListTasksResponse::fromXContent,
+                listener, emptySet(), headers);
+    }
 }

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

@@ -29,6 +29,7 @@
 import org.apache.http.entity.ContentType;
 import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.action.DocWriteRequest;
+import org.elasticsearch.action.admin.cluster.node.tasks.list.ListTasksRequest;
 import org.elasticsearch.action.admin.cluster.repositories.get.GetRepositoriesRequest;
 import org.elasticsearch.action.admin.cluster.repositories.put.PutRepositoryRequest;
 import org.elasticsearch.action.admin.cluster.settings.ClusterUpdateSettingsRequest;
@@ -45,8 +46,8 @@
 import org.elasticsearch.action.admin.indices.open.OpenIndexRequest;
 import org.elasticsearch.action.admin.indices.refresh.RefreshRequest;
 import org.elasticsearch.action.admin.indices.rollover.RolloverRequest;
-import org.elasticsearch.action.admin.indices.settings.put.UpdateSettingsRequest;
 import org.elasticsearch.action.admin.indices.settings.get.GetSettingsRequest;
+import org.elasticsearch.action.admin.indices.settings.put.UpdateSettingsRequest;
 import org.elasticsearch.action.admin.indices.shrink.ResizeRequest;
 import org.elasticsearch.action.admin.indices.shrink.ResizeType;
 import org.elasticsearch.action.admin.indices.template.put.PutIndexTemplateRequest;
@@ -83,6 +84,7 @@
 import org.elasticsearch.rest.action.search.RestSearchAction;
 import org.elasticsearch.script.mustache.SearchTemplateRequest;
 import org.elasticsearch.search.fetch.subphase.FetchSourceContext;
+import org.elasticsearch.tasks.TaskId;
 
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
@@ -606,6 +608,22 @@ static Request clusterPutSettings(ClusterUpdateSettingsRequest clusterUpdateSett
         return request;
     }
 
+    static Request listTasks(ListTasksRequest listTaskRequest) {
+        if (listTaskRequest.getTaskId() != null && listTaskRequest.getTaskId().isSet()) {
+            throw new IllegalArgumentException("TaskId cannot be used for list tasks request");
+        }
+        Request request  = new Request(HttpGet.METHOD_NAME, "/_tasks");
+        Params params = new Params(request);
+        params.withTimeout(listTaskRequest.getTimeout())
+            .withDetailed(listTaskRequest.getDetailed())
+            .withWaitForCompletion(listTaskRequest.getWaitForCompletion())
+            .withParentTaskId(listTaskRequest.getParentTaskId())
+            .withNodes(listTaskRequest.getNodes())
+            .withActions(listTaskRequest.getActions())
+            .putParam("group_by", "none");
+        return request;
+    }
+
     static Request rollover(RolloverRequest rolloverRequest) throws IOException {
         String endpoint = new EndpointBuilder().addPathPart(rolloverRequest.getAlias()).addPathPartAsIs("_rollover")
                 .addPathPart(rolloverRequest.getNewIndexName()).build();
@@ -932,6 +950,41 @@ Params withPreserveExisting(boolean preserveExisting) {
             return this;
         }
 
+        Params withDetailed(boolean detailed) {
+            if (detailed) {
+                return putParam("detailed", Boolean.TRUE.toString());
+            }
+            return this;
+        }
+
+        Params withWaitForCompletion(boolean waitForCompletion) {
+            if (waitForCompletion) {
+                return putParam("wait_for_completion", Boolean.TRUE.toString());
+            }
+            return this;
+        }
+
+        Params withNodes(String[] nodes) {
+            if (nodes != null && nodes.length > 0) {
+                return putParam("nodes", String.join(",", nodes));
+            }
+            return this;
+        }
+
+        Params withActions(String[] actions) {
+            if (actions != null && actions.length > 0) {
+                return putParam("actions", String.join(",", actions));
+            }
+            return this;
+        }
+
+        Params withParentTaskId(TaskId parentTaskId) {
+            if (parentTaskId != null && parentTaskId.isSet()) {
+                return putParam("parent_task_id", parentTaskId.toString());
+            }
+            return this;
+        }
+
         Params withVerify(boolean verify) {
             if (verify) {
                 return putParam("verify", Boolean.TRUE.toString());

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

@@ -20,6 +20,9 @@
 package org.elasticsearch.client;
 
 import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.action.admin.cluster.node.tasks.list.ListTasksRequest;
+import org.elasticsearch.action.admin.cluster.node.tasks.list.ListTasksResponse;
+import org.elasticsearch.action.admin.cluster.node.tasks.list.TaskGroup;
 import org.elasticsearch.action.admin.cluster.settings.ClusterUpdateSettingsRequest;
 import org.elasticsearch.action.admin.cluster.settings.ClusterUpdateSettingsResponse;
 import org.elasticsearch.cluster.routing.allocation.decider.EnableAllocationDecider;
@@ -29,13 +32,16 @@
 import org.elasticsearch.common.xcontent.support.XContentMapValues;
 import org.elasticsearch.indices.recovery.RecoverySettings;
 import org.elasticsearch.rest.RestStatus;
+import org.elasticsearch.tasks.TaskInfo;
 
 import java.io.IOException;
 import java.util.HashMap;
 import java.util.Map;
 
+import static java.util.Collections.emptyList;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcked;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.greaterThanOrEqualTo;
 import static org.hamcrest.Matchers.notNullValue;
 import static org.hamcrest.Matchers.nullValue;
 
@@ -105,4 +111,29 @@ public void testClusterUpdateSettingNonExistent() {
         assertThat(exception.getMessage(), equalTo(
                 "Elasticsearch exception [type=illegal_argument_exception, reason=transient setting [" + setting + "], not recognized]"));
     }
+
+    public void testListTasks() throws IOException {
+        ListTasksRequest request = new ListTasksRequest();
+        ListTasksResponse response = execute(request, highLevelClient().cluster()::listTasks, highLevelClient().cluster()::listTasksAsync);
+
+        assertThat(response, notNullValue());
+        assertThat(response.getNodeFailures(), equalTo(emptyList()));
+        assertThat(response.getTaskFailures(), equalTo(emptyList()));
+        // It's possible that there are other tasks except 'cluster:monitor/tasks/lists[n]' and 'action":"cluster:monitor/tasks/lists'
+        assertThat(response.getTasks().size(), greaterThanOrEqualTo(2));
+        boolean listTasksFound = false;
+        for (TaskGroup taskGroup : response.getTaskGroups()) {
+            TaskInfo parent = taskGroup.getTaskInfo();
+            if ("cluster:monitor/tasks/lists".equals(parent.getAction())) {
+                assertThat(taskGroup.getChildTasks().size(), equalTo(1));
+                TaskGroup childGroup = taskGroup.getChildTasks().iterator().next();
+                assertThat(childGroup.getChildTasks().isEmpty(), equalTo(true));
+                TaskInfo child = childGroup.getTaskInfo();
+                assertThat(child.getAction(), equalTo("cluster:monitor/tasks/lists[n]"));
+                assertThat(child.getParentTaskId(), equalTo(parent.getTaskId()));
+                listTasksFound = true;
+            }
+        }
+        assertTrue("List tasks were not found", listTasksFound);
+    }
 }