Remove EmptyObjectRangeNotSatisfiableException, add presigned URL Javadoc and checksum test

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

@@ -148,8 +148,7 @@ private void sendFirstRequest(AsyncResponseTransformer<GetObjectResponse, GetObj
 
             if (error != null) {
                 if (PresignedUrlDownloadHelper.isRangeNotSatisfiable(error)) {
-                    resultFuture.completeExceptionally(
-                        new PresignedUrlDownloadHelper.EmptyObjectRangeNotSatisfiableException(error));
+                    resultFuture.completeExceptionally(error);
                     synchronized (subscriptionLock) {
                         subscription.cancel();
                     }

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

@@ -67,10 +67,7 @@ public <T> CompletableFuture<T> downloadObject(
         doMultipartDownload(presignedRequest, asyncResponseTransformer)
             .whenComplete((result, error) -> {
                 Throwable cause = error instanceof CompletionException ? error.getCause() : error;
-                // Parallel path wraps it as EmptyObjectRangeNotSatisfiableException;
-                // serial path (toBytes, custom transformers) surfaces raw S3Exception.
-                if (cause instanceof EmptyObjectRangeNotSatisfiableException
-                    || isRangeNotSatisfiable(cause)) {
+                if (isRangeNotSatisfiable(cause)) {
                     log.debug(() -> "Received 416 on first request, falling back to non-range GET for empty object");
                     asyncPresignedUrlExtension.getObject(presignedRequest, asyncResponseTransformer)
                                               .whenComplete((r, e) -> {
@@ -242,14 +239,4 @@ static boolean isRangeNotSatisfiable(Throwable error) {
         Throwable cause = error instanceof CompletionException ? error.getCause() : error;
         return cause instanceof S3Exception && ((S3Exception) cause).statusCode() == 416;
     }
-
-    /**
-     * Marker exception wrapping a 416 on the first range request, signaling an empty object.
-     * Used to distinguish from 416 errors on subsequent requests which should propagate as failures.
-     */
-    static class EmptyObjectRangeNotSatisfiableException extends RuntimeException {
-        EmptyObjectRangeNotSatisfiableException(Throwable cause) {
-            super("Object is empty (416 on first range request)", cause);
-        }
-    }
 }

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

@@ -137,8 +137,7 @@ private void makeRangeRequest(long partIndex,
             if (error != null) {
                 if (partIndex == 0 && PresignedUrlDownloadHelper.isRangeNotSatisfiable(error)) {
                     log.debug(() -> "Received 416 on first range request, object is empty");
-                    resultFuture.completeExceptionally(
-                        new PresignedUrlDownloadHelper.EmptyObjectRangeNotSatisfiableException(error));
+                    resultFuture.completeExceptionally(error);
                     synchronized (lock) {
                         subscription.cancel();
                     }

services/s3/src/main/java/software/amazon/awssdk/services/s3/presignedurl/model/PresignedUrlDownloadRequest.java

@@ -25,6 +25,13 @@
 
 /**
  * Request object for performing download operations using a presigned URL.
+ *
+ * <p>Presigned URLs with additional signed headers (beyond {@code Range}, {@code If-Match}, and
+ * {@code x-amz-checksum-mode}) are not supported. If the presigned URL was signed with {@code Range} or
+ * {@code If-Match}, those values must be set on this request via {@link Builder#range(String)} or
+ * {@link Builder#ifMatch(String)} — otherwise S3 will return a {@code SignatureDoesNotMatch} error.
+ * The {@code x-amz-checksum-mode} header is replayed automatically by the SDK and requires no
+ * additional configuration.
  */
 @SdkPublicApi
 public final class PresignedUrlDownloadRequest implements ToCopyableBuilder<PresignedUrlDownloadRequest.Builder,