Fix AbstractBulkByScrollRequest slices parameter via Rest

Currently the AbstractBulkByScrollRequest accepts slice values of 0 via its
`setSlices` method, denoting the "auto" slicing behaviour that is usable by
settting the "slices=auto" parameter on rest requests. When using the High Level
Rest Client, however, we send the 0 value as an integer, which is then rejected
as invalid by `AbstractBulkByScrollRequest#parseSlices`. Instead of making
parsing of the rest request more lenient, this PR opts for changing the
RequestConverter logic in the client to translate 0 values to "auto" on the rest
requests.

Closes elastic#53044

Author: Christoph Büscher

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

@@ -557,8 +557,13 @@ private static Request prepareReindexRequest(ReindexRequest reindexRequest, bool
             .withRefresh(reindexRequest.isRefresh())
             .withTimeout(reindexRequest.getTimeout())
             .withWaitForActiveShards(reindexRequest.getWaitForActiveShards())
-            .withRequestsPerSecond(reindexRequest.getRequestsPerSecond())
-            .withSlices(reindexRequest.getSlices());
+            .withRequestsPerSecond(reindexRequest.getRequestsPerSecond());
+        if (reindexRequest.getSlices() == 0) {
+            // translate to "auto" value
+            params.withAutoSlices();
+        } else {
+            params.withSlices(reindexRequest.getSlices());
+        }
 
         if (reindexRequest.getScrollTime() != null) {
             params.putParam("scroll", reindexRequest.getScrollTime());
@@ -579,8 +584,13 @@ private static Request prepareDeleteByQueryRequest(DeleteByQueryRequest deleteBy
             .withWaitForActiveShards(deleteByQueryRequest.getWaitForActiveShards())
             .withRequestsPerSecond(deleteByQueryRequest.getRequestsPerSecond())
             .withIndicesOptions(deleteByQueryRequest.indicesOptions())
-            .withWaitForCompletion(waitForCompletion)
-            .withSlices(deleteByQueryRequest.getSlices());
+            .withWaitForCompletion(waitForCompletion);
+        if (deleteByQueryRequest.getSlices() == 0) {
+            // translate to "auto" value
+            params.withAutoSlices();
+        } else {
+            params.withSlices(deleteByQueryRequest.getSlices());
+        }
         if (deleteByQueryRequest.isAbortOnVersionConflict() == false) {
             params.putParam("conflicts", "proceed");
         }
@@ -608,8 +618,13 @@ static Request updateByQuery(UpdateByQueryRequest updateByQueryRequest) throws I
             .withTimeout(updateByQueryRequest.getTimeout())
             .withWaitForActiveShards(updateByQueryRequest.getWaitForActiveShards())
             .withRequestsPerSecond(updateByQueryRequest.getRequestsPerSecond())
-            .withIndicesOptions(updateByQueryRequest.indicesOptions())
-            .withSlices(updateByQueryRequest.getSlices());
+            .withIndicesOptions(updateByQueryRequest.indicesOptions());
+        if (updateByQueryRequest.getSlices() == 0) {
+            // translate to "auto" value
+            params.withAutoSlices();
+        } else {
+            params.withSlices(updateByQueryRequest.getSlices());
+        }
         if (updateByQueryRequest.isAbortOnVersionConflict() == false) {
             params.putParam("conflicts", "proceed");
         }
@@ -916,6 +931,10 @@ Params withSlices(int slices) {
             return putParam("slices", String.valueOf(slices));
         }
 
+        Params withAutoSlices() {
+            return putParam("slices", AbstractBulkByScrollRequest.AUTO_SLICES_VALUE);
+        }
+
         Params withStoredFields(String[] storedFields) {
             if (storedFields != null && storedFields.length > 0) {
                 return putParam("stored_fields", String.join(",", storedFields));

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

@@ -19,6 +19,8 @@
 
 package org.elasticsearch.client;
 
+import com.carrotsearch.randomizedtesting.annotations.Repeat;
+
 import org.apache.http.HttpEntity;
 import org.apache.http.client.methods.HttpDelete;
 import org.apache.http.client.methods.HttpGet;
@@ -80,6 +82,7 @@
 import org.elasticsearch.index.rankeval.RankEvalSpec;
 import org.elasticsearch.index.rankeval.RatedRequest;
 import org.elasticsearch.index.rankeval.RestRankEvalAction;
+import org.elasticsearch.index.reindex.AbstractBulkByScrollRequest;
 import org.elasticsearch.index.reindex.DeleteByQueryRequest;
 import org.elasticsearch.index.reindex.ReindexRequest;
 import org.elasticsearch.index.reindex.RemoteInfo;
@@ -132,6 +135,7 @@
 import static org.hamcrest.Matchers.hasKey;
 import static org.hamcrest.Matchers.nullValue;
 
+@Repeat(iterations = 100)
 public class RequestConvertersTests extends ESTestCase {
     public void testPing() {
         Request request = RequestConverters.ping();
@@ -437,9 +441,13 @@ public void testReindex() throws IOException {
             reindexRequest.setSourceQuery(new TermQueryBuilder("foo", "fooval"));
         }
         if (randomBoolean()) {
-            int slices = randomInt(100);
+            int slices = randomIntBetween(0,4);
             reindexRequest.setSlices(slices);
-            expectedParams.put("slices", String.valueOf(slices));
+            if (slices == 0) {
+                expectedParams.put("slices", AbstractBulkByScrollRequest.AUTO_SLICES_VALUE);
+            } else {
+                expectedParams.put("slices", Integer.toString(slices));
+            }
         } else {
             expectedParams.put("slices", "1");
         }
@@ -500,7 +508,11 @@ public void testUpdateByQuery() throws IOException {
         }
         if (randomBoolean()) {
             int slices = randomIntBetween(0, 4);
-            expectedParams.put("slices", Integer.toString(slices));
+            if (slices == 0) {
+                expectedParams.put("slices", AbstractBulkByScrollRequest.AUTO_SLICES_VALUE);
+            } else {
+                expectedParams.put("slices", Integer.toString(slices));
+            }
             updateByQueryRequest.setSlices(slices);
         } else {
             expectedParams.put("slices", "1");
@@ -556,7 +568,11 @@ public void testDeleteByQuery() throws IOException {
         }
         if (randomBoolean()) {
             int slices = randomIntBetween(0, 4);
-            expectedParams.put("slices", Integer.toString(slices));
+            if (slices == 0) {
+                expectedParams.put("slices", AbstractBulkByScrollRequest.AUTO_SLICES_VALUE);
+            } else {
+                expectedParams.put("slices", Integer.toString(slices));
+            }
             deleteByQueryRequest.setSlices(slices);
         } else {
             expectedParams.put("slices", "1");

server/src/main/java/org/elasticsearch/index/reindex/AbstractBulkByScrollRequest.java

@@ -375,6 +375,7 @@ public TimeValue getScrollTime() {
 
     /**
      * The number of slices this task should be divided into. Defaults to 1 meaning the task isn't sliced into subtasks.
+     * A value of 0 is equivalent to the "auto" slices parameter of the Rest API.
      */
     public Self setSlices(int slices) {
         if (slices < 0) {