Improve comments

Author: alextwoods

services-custom/s3-transfer-manager/src/test/java/software/amazon/awssdk/transfer/s3/internal/S3JavaMultipartTransferProgressListenerTest.java

@@ -367,9 +367,6 @@ void copyWithJavaBasedClient_listeners_reports_ProgressWhenSuccess_copy() {
     /**
      * Verifies that TransferListener callbacks fire for unknown-content-length uploads that fit in a single chunk.
      * This is the scenario where UploadWithUnknownContentLengthHelper routes to uploadInOneChunk.
-     * Before the fix, only transferInitiated fired; transferComplete never fired because endOfStreamFuture
-     * was never completed (the wrapper body was bypassed by splitCloseable and uploadInOneChunk did not
-     * signal the progress listener).
      */
     @Test
     void unknownContentLength_singleChunk_transferCompleteFires() {
@@ -410,8 +407,7 @@ void unknownContentLength_singleChunk_transferCompleteFires() {
 
     /**
      * Verifies that TransferListener callbacks fire for unknown-content-length uploads that exceed the part size
-     * and go through the multipart upload path. This path was already working before the fix because
-     * multipartClientProgressListener compensates for the wrapper body being bypassed by splitCloseable.
+     * and go through the multipart upload path. 
      */
     @Test
     void unknownContentLength_multiChunk_allCallbacksFire() {

services/s3/src/main/java/software/amazon/awssdk/services/s3/internal/multipart/MultipartUploadHelper.java

@@ -173,9 +173,9 @@ void uploadInOneChunk(PutObjectRequest putObjectRequest,
                 asyncRequestBody.contentLength().ifPresent(progressListener::subscriberOnNext);
             }
             // Always signal completion so that TransferProgressUpdater's endOfStreamFuture completes
-            // and the TransferListener's transferComplete callback fires. This is critical for the
-            // unknown-content-length single-chunk path where splitCloseable() bypasses the wrapper body
-            // that would normally complete endOfStreamFuture via subscriberOnComplete.
+            // and the TransferListener's transferComplete callback fires.
+            // For unknown content length we don't know if it wil lbe one chunk or not ahead of time
+            // and so don't set REPORT_PROGRESS_IN_SINGLE_CHUNK attribute.
             progressListener.subscriberOnComplete();
             returnFuture.complete(response);
         });