HLRC: Add get rollup job (#33921)

Adds support for the get rollup job to the High Level REST Client. I had
to do three interesting and unexpected things:
1. I ported the rollup state wiping code into the high level client
tests. I'll move this into the test framework in a followup and remove
the x-pack version.
2. The `timeout` in the rollup config was serialized using the
`toString` representation of `TimeValue` which produces fractional time
values which are more human readable but aren't supported by parsing. So
I switched it to `getStringRep`.
3. Refactor the xcontent round trip testing utilities so we can test
parsing of classes that don't implements `ToXContent`.

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

@@ -20,6 +20,8 @@
 package org.elasticsearch.client;
 
 import org.elasticsearch.action.ActionListener;
+import org.elasticsearch.client.rollup.GetRollupJobRequest;
+import org.elasticsearch.client.rollup.GetRollupJobResponse;
 import org.elasticsearch.client.rollup.PutRollupJobRequest;
 import org.elasticsearch.client.rollup.PutRollupJobResponse;
 
@@ -73,4 +75,37 @@ public void putRollupJobAsync(PutRollupJobRequest request, RequestOptions option
             PutRollupJobResponse::fromXContent,
             listener, Collections.emptySet());
     }
+
+    /**
+     * Get a rollup job from the cluster.
+     * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/rollup-put-job.html">
+     * the docs</a> for more.
+     * @param request the request
+     * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
+     * @return the response
+     * @throws IOException in case there is a problem sending the request or parsing back the response
+     */
+    public GetRollupJobResponse getRollupJob(GetRollupJobRequest request, RequestOptions options) throws IOException {
+        return restHighLevelClient.performRequestAndParseEntity(request,
+            RollupRequestConverters::getJob,
+            options,
+            GetRollupJobResponse::fromXContent,
+            Collections.emptySet());
+    }
+
+    /**
+     * Asynchronously get a rollup job from the cluster.
+     * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/rollup-put-job.html">
+     * the docs</a> for more.
+     * @param request the request
+     * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
+     * @param listener the listener to be notified upon request completion
+     */
+    public void getRollupJobAsync(GetRollupJobRequest request, RequestOptions options, ActionListener<GetRollupJobResponse> listener) {
+        restHighLevelClient.performRequestAsyncAndParseEntity(request,
+            RollupRequestConverters::getJob,
+            options,
+            GetRollupJobResponse::fromXContent,
+            listener, Collections.emptySet());
+    }
 }

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

@@ -18,7 +18,9 @@
  */
 package org.elasticsearch.client;
 
+import org.apache.http.client.methods.HttpGet;
 import org.apache.http.client.methods.HttpPut;
+import org.elasticsearch.client.rollup.GetRollupJobRequest;
 import org.elasticsearch.client.rollup.PutRollupJobRequest;
 
 import java.io.IOException;
@@ -42,4 +44,14 @@ static Request putJob(final PutRollupJobRequest putRollupJobRequest) throws IOEx
         request.setEntity(createEntity(putRollupJobRequest, REQUEST_BODY_CONTENT_TYPE));
         return request;
     }
+
+    static Request getJob(final GetRollupJobRequest getRollupJobRequest) {
+        String endpoint = new RequestConverters.EndpointBuilder()
+            .addPathPartAsIs("_xpack")
+            .addPathPartAsIs("rollup")
+            .addPathPartAsIs("job")
+            .addPathPart(getRollupJobRequest.getJobId())
+            .build();
+        return new Request(HttpGet.METHOD_NAME, endpoint);
+    }
 }

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

@@ -0,0 +1,77 @@
+/*
+ * 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.rollup;
+
+import org.elasticsearch.client.Validatable;
+import org.elasticsearch.client.ValidationException;
+
+import java.util.Objects;
+import java.util.Optional;
+
+/**
+ * Request to fetch rollup jobs.
+ */
+public class GetRollupJobRequest implements Validatable {
+    private final String jobId;
+
+    /**
+     * Create a requets .
+     * @param jobId id of the job to return or {@code _all} to return all jobs
+     */
+    public GetRollupJobRequest(final String jobId) {
+        Objects.requireNonNull(jobId, "jobId is required");
+        if ("_all".equals(jobId)) {
+            throw new IllegalArgumentException("use the default ctor to ask for all jobs");
+        }
+        this.jobId = jobId;
+    }
+
+    /**
+     * Create a request to load all rollup jobs.
+     */
+    public GetRollupJobRequest() {
+        this.jobId = "_all";
+    }
+
+    /**
+     * ID of the job to return.
+     */
+    public String getJobId() {
+        return jobId;
+    }
+
+    @Override
+    public Optional<ValidationException> validate() {
+        return Optional.empty();
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        final GetRollupJobRequest that = (GetRollupJobRequest) o;
+        return jobId.equals(that.jobId);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(jobId);
+    }
+}