Place the errors field first in bulk response (#98303)

The bulk response is a map of fields that is inherently unordered.
However, we have some control over the order in which fields are
serialized. This commit places the errors field first to allow clients
who want to incrementally parse the response until the errors field is
encountered potentially encounter the field earlier.

There is also a test added to inform us if a future version of jackson
were to change the order of serialization.

server/src/main/java/org/elasticsearch/action/bulk/BulkResponse.java

@@ -142,11 +142,11 @@ public class BulkResponse extends ActionResponse implements Iterable<BulkItemRes
     @Override
     public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
         builder.startObject();
+        builder.field(ERRORS, hasFailures());
         builder.field(TOOK, tookInMillis);
         if (ingestTookInMillis != BulkResponse.NO_INGEST_TOOK) {
             builder.field(INGEST_TOOK, ingestTookInMillis);
         }
-        builder.field(ERRORS, hasFailures());
         builder.startArray(ITEMS);
         for (BulkItemResponse item : this) {
             item.toXContent(builder, params);

server/src/test/java/org/elasticsearch/action/bulk/BulkResponseTests.java

@@ -29,6 +29,7 @@ import static org.elasticsearch.action.bulk.BulkItemResponseTests.assertBulkItem
 import static org.elasticsearch.action.bulk.BulkResponse.NO_INGEST_TOOK;
 import static org.elasticsearch.common.xcontent.XContentHelper.toXContent;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertToXContentEquivalent;
+import static org.hamcrest.Matchers.equalTo;
 
 public class BulkResponseTests extends ESTestCase {
 
@@ -47,17 +48,7 @@ public class BulkResponseTests extends ESTestCase {
             DocWriteRequest.OpType opType = randomFrom(DocWriteRequest.OpType.values());
 
             if (frequently()) {
-                Tuple<? extends DocWriteResponse, ? extends DocWriteResponse> randomDocWriteResponses = null;
-                if (opType == DocWriteRequest.OpType.INDEX || opType == DocWriteRequest.OpType.CREATE) {
-                    randomDocWriteResponses = IndexResponseTests.randomIndexResponse();
-                } else if (opType == DocWriteRequest.OpType.DELETE) {
-                    randomDocWriteResponses = DeleteResponseTests.randomDeleteResponse();
-                } else if (opType == DocWriteRequest.OpType.UPDATE) {
-                    randomDocWriteResponses = UpdateResponseTests.randomUpdateResponse(xContentType);
-                } else {
-                    fail("Test does not support opType [" + opType + "]");
-                }
-
+                Tuple<? extends DocWriteResponse, ? extends DocWriteResponse> randomDocWriteResponses = success(opType, xContentType);
                 bulkItems[i] = BulkItemResponse.success(i, opType, randomDocWriteResponses.v1());
                 expectedBulkItems[i] = BulkItemResponse.success(i, opType, randomDocWriteResponses.v2());
             } else {
@@ -97,4 +88,64 @@ public class BulkResponseTests extends ESTestCase {
         BytesReference expectedFinalBytes = toXContent(parsedBulkResponse, xContentType, humanReadable);
         assertToXContentEquivalent(expectedFinalBytes, finalBytes, xContentType);
     }
+
+    public void testToXContentPlacesErrorsFirst() throws IOException {
+        XContentType xContentType = randomFrom(XContentType.values());
+        boolean humanReadable = randomBoolean();
+
+        boolean errors = false;
+        long took = randomFrom(randomNonNegativeLong(), -1L);
+        long ingestTook = randomFrom(randomNonNegativeLong(), NO_INGEST_TOOK);
+        int nbBulkItems = randomIntBetween(1, 10);
+
+        BulkItemResponse[] bulkItems = new BulkItemResponse[nbBulkItems];
+
+        for (int i = 0; i < nbBulkItems; i++) {
+            DocWriteRequest.OpType opType = randomFrom(DocWriteRequest.OpType.values());
+            if (frequently()) {
+                Tuple<? extends DocWriteResponse, ? extends DocWriteResponse> randomDocWriteResponses = success(opType, xContentType);
+
+                BulkItemResponse success = BulkItemResponse.success(i, opType, randomDocWriteResponses.v1());
+                bulkItems[i] = success;
+            } else {
+                errors = true;
+                String index = randomAlphaOfLength(5);
+                String id = randomAlphaOfLength(5);
+
+                Tuple<Throwable, ElasticsearchException> failures = randomExceptions();
+
+                Exception bulkItemCause = (Exception) failures.v1();
+                bulkItems[i] = BulkItemResponse.failure(i, opType, new BulkItemResponse.Failure(index, id, bulkItemCause));
+            }
+        }
+
+        BulkResponse bulkResponse = new BulkResponse(bulkItems, took, ingestTook);
+        BytesReference originalBytes = toXContent(bulkResponse, xContentType, ToXContent.EMPTY_PARAMS, humanReadable);
+
+        try (XContentParser parser = createParser(xContentType.xContent(), originalBytes)) {
+            assertThat(parser.nextToken(), equalTo(XContentParser.Token.START_OBJECT));
+            XContentParser.Token firstField = parser.nextToken();
+            assertThat(firstField, equalTo(XContentParser.Token.FIELD_NAME));
+            assertThat(parser.currentName(), equalTo("errors"));
+            assertThat(parser.nextToken(), equalTo(XContentParser.Token.VALUE_BOOLEAN));
+            assertThat(parser.booleanValue(), equalTo(errors));
+        }
+    }
+
+    private static Tuple<? extends DocWriteResponse, ? extends DocWriteResponse> success(
+        DocWriteRequest.OpType opType,
+        XContentType xContentType
+    ) {
+        Tuple<? extends DocWriteResponse, ? extends DocWriteResponse> randomDocWriteResponses = null;
+        if (opType == DocWriteRequest.OpType.INDEX || opType == DocWriteRequest.OpType.CREATE) {
+            randomDocWriteResponses = IndexResponseTests.randomIndexResponse();
+        } else if (opType == DocWriteRequest.OpType.DELETE) {
+            randomDocWriteResponses = DeleteResponseTests.randomDeleteResponse();
+        } else if (opType == DocWriteRequest.OpType.UPDATE) {
+            randomDocWriteResponses = UpdateResponseTests.randomUpdateResponse(xContentType);
+        } else {
+            fail("Test does not support opType [" + opType + "]");
+        }
+        return randomDocWriteResponses;
+    }
 }