[8.16] [Test] Flush response body for progress (elastic#115177) (elastic#115613)

* [Test] Flush response body for progress (elastic#115177)

In JDK23, response headers are no longer always immediately sent. See
also https://bugs.openjdk.org/browse/JDK-8331847 This PR adds flush call
for the response body to make progress.

Resolves: elastic#115145 Resolves: elastic#115164
(cherry picked from commit 8c23fd7)

* unmute

Author: ywangd

modules/repository-s3/src/test/java/org/elasticsearch/repositories/s3/S3BlobContainerRetriesTests.java

@@ -573,16 +573,16 @@ public void handle(HttpExchange exchange) throws IOException {
                         ),
                         -1
                     );
+                    exchange.getResponseBody().flush();
                 } else if (randomBoolean()) {
                     final var bytesSent = sendIncompleteContent(exchange, bytes);
                     if (bytesSent < meaningfulProgressBytes) {
                         failuresWithoutProgress += 1;
-                    } else {
-                        exchange.getResponseBody().flush();
                     }
                 } else {
                     failuresWithoutProgress += 1;
                 }
+                exchange.getResponseBody().flush();
                 exchange.close();
             }
         }
@@ -627,6 +627,7 @@ public void handle(HttpExchange exchange) throws IOException {
                 failureCount += 1;
                 Streams.readFully(exchange.getRequestBody());
                 sendIncompleteContent(exchange, bytes);
+                exchange.getResponseBody().flush();
                 exchange.close();
             }
         }

muted-tests.yml

@@ -355,9 +355,6 @@ tests:
 - class: org.elasticsearch.xpack.inference.DefaultEndPointsIT
   method: testInferDeploysDefaultE5
   issue: https://github.com/elastic/elasticsearch/issues/115361
-- class: org.elasticsearch.repositories.s3.S3BlobContainerRetriesTests
-  method: testReadRetriesAfterMeaningfulProgress
-  issue: https://github.com/elastic/elasticsearch/issues/115583
 
 # Examples:
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