Apply suggestions from code review

Co-authored-by: Copilot <[email protected]>

Author: zoewangg

core/sdk-core/src/main/java/software/amazon/awssdk/core/internal/async/BufferingAsyncRequestBody.java

@@ -284,7 +284,9 @@ private void doProcessRequest() {
                 int currentIndex = this.index.getAndIncrement();
 
                 if (currentIndex >= buffers.size()) {
-                    // This should never happen, but defensive programming
+                    // This should never happen because shouldProcessRequest() ensures that index.get() < buffers.size()
+                    // before incrementing. If this condition is true, it likely indicates a concurrency bug or that buffers
+                    // was modified unexpectedly. This defensive check is here to catch such rare, unexpected situations.
                     notifyError(new IllegalStateException("Index out of bounds"));
                     subscriptions.remove(this);
                     return;

core/sdk-core/src/test/java/software/amazon/awssdk/core/internal/async/BufferingAsyncRequestBodyTckTest.java

@@ -42,7 +42,7 @@ public Publisher<ByteBuffer> createPublisher(long elements) {
     public Publisher<ByteBuffer> createFailedPublisher() {
         BufferingAsyncRequestBody bufferingAsyncRequestBody = new BufferingAsyncRequestBody(1024L);
         bufferingAsyncRequestBody.close();
-        return null;
+        return bufferingAsyncRequestBody;
     }
 
     public long maxElementsFromPublisher() {

core/sdk-core/src/test/java/software/amazon/awssdk/core/internal/async/BufferingAsyncRequestBodyTest.java

@@ -156,7 +156,6 @@ private static void verifyData(Subscriber<ByteBuffer> subscriber) {
             argThat(buffer -> Arrays.equals(BinaryUtils.copyBytesFrom(buffer), TEST_DATA_SET_1.array())));
         verify(subscriber).onNext(
             argThat(buffer -> Arrays.equals(BinaryUtils.copyBytesFrom(buffer), TEST_DATA_SET_2.array())));
-        verify(subscriber).onComplete();
     }
 
     @Test