SearchResponse#fromXContent to not require START_OBJECT as current token (#24794)

The method should rather advance one token and only then require a START_OBJECT as the current token. This allows to parse given a parser that's at the beginning of the response, where the initial/current token is null.

Author: javanna

core/src/main/java/org/elasticsearch/action/search/SearchResponse.java

@@ -222,7 +222,7 @@ public XContentBuilder innerToXContent(XContentBuilder builder, Params params) t
     }
 
     public static SearchResponse fromXContent(XContentParser parser) throws IOException {
-        ensureExpectedToken(XContentParser.Token.START_OBJECT, parser.currentToken(), parser::getTokenLocation);
+        ensureExpectedToken(XContentParser.Token.START_OBJECT, parser.nextToken(), parser::getTokenLocation);
         XContentParser.Token token;
         String currentFieldName = null;
         SearchHits hits = null;

core/src/test/java/org/elasticsearch/action/search/SearchResponseTests.java

@@ -49,7 +49,6 @@
 import java.util.List;
 
 import static java.util.Collections.singletonMap;
-import static org.elasticsearch.common.xcontent.XContentParserUtils.ensureExpectedToken;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertToXContentEquivalent;
 
 public class SearchResponseTests extends ESTestCase {
@@ -104,7 +103,6 @@ public void testFromXContent() throws IOException {
         final ToXContent.Params params = new ToXContent.MapParams(singletonMap(RestSearchAction.TYPED_KEYS_PARAM, "true"));
         BytesReference originalBytes = toShuffledXContent(response, xcontentType, params, humanReadable);
         try (XContentParser parser = createParser(xcontentType.xContent(), originalBytes)) {
-            ensureExpectedToken(XContentParser.Token.START_OBJECT, parser.nextToken(), parser::getTokenLocation);
             SearchResponse parsed = SearchResponse.fromXContent(parser);
             assertToXContentEquivalent(originalBytes, XContentHelper.toXContent(parsed, xcontentType, params, humanReadable), xcontentType);
             assertEquals(XContentParser.Token.END_OBJECT, parser.currentToken());
@@ -129,7 +127,6 @@ public void testFromXContentWithFailures() throws IOException {
         final ToXContent.Params params = new ToXContent.MapParams(singletonMap(RestSearchAction.TYPED_KEYS_PARAM, "true"));
         BytesReference originalBytes = toShuffledXContent(response, xcontentType, params, randomBoolean());
         try (XContentParser parser = createParser(xcontentType.xContent(), originalBytes)) {
-            ensureExpectedToken(XContentParser.Token.START_OBJECT, parser.nextToken(), parser::getTokenLocation);
             SearchResponse parsed = SearchResponse.fromXContent(parser);
             for (int i = 0; i < parsed.getShardFailures().length; i++) {
                 ShardSearchFailure parsedFailure = parsed.getShardFailures()[i];