REST : Add ACK Rest Action

This commit adds the alert ack rest action.

Original commit: elastic/x-pack-elasticsearch@73a0286863

src/main/java/org/elasticsearch/alerts/rest/RestAckAlertAction.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+package org.elasticsearch.alerts.rest;
+
+import org.elasticsearch.alerts.AlertsStore;
+import org.elasticsearch.alerts.client.AlertsClient;
+import org.elasticsearch.alerts.transport.actions.ack.AckAlertRequest;
+import org.elasticsearch.alerts.transport.actions.ack.AckAlertResponse;
+import org.elasticsearch.client.Client;
+import org.elasticsearch.common.inject.Inject;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.rest.*;
+import org.elasticsearch.rest.action.support.RestBuilderListener;
+
+/**
+ * The rest action to ack an alert
+ */
+public class RestAckAlertAction extends BaseRestHandler {
+
+    private final AlertsClient alertsClient;
+
+    @Inject
+    protected RestAckAlertAction(Settings settings, RestController controller, Client client, AlertsClient alertsClient) {
+        super(settings, controller, client);
+        this.alertsClient = alertsClient;
+        controller.registerHandler(RestRequest.Method.PUT, AlertsStore.ALERT_INDEX + "/{name}/_ack", this);
+    }
+
+    @Override
+    protected void handleRequest(RestRequest request, RestChannel restChannel, Client client) throws Exception {
+        final AckAlertRequest ackAlertRequest = new AckAlertRequest();
+        ackAlertRequest.setAlertName(request.param("name"));
+        alertsClient.ackAlert(ackAlertRequest, new RestBuilderListener<AckAlertResponse>(restChannel) {
+
+            @Override
+            public RestResponse buildResponse(AckAlertResponse ackAlertResponse, XContentBuilder builder) throws Exception {
+                builder.startObject();
+                builder.field(AlertsStore.ACK_STATE_FIELD.getPreferredName(), ackAlertResponse.getAlertAckState().toString());
+                builder.endObject();
+                return new BytesRestResponse(RestStatus.OK, builder);
+            }
+        });
+    }
+    
+}