Add DownloadDirectoryWithResponse

generator/.DevConfigs/55fe9e14-c79e-4426-9828-deae0451d4f6.json

@@ -0,0 +1,11 @@
+{
+  "services": [
+    {
+      "serviceName": "S3",
+      "type": "minor",
+      "changeLogMessages": [
+        "Created new DownloadDirectoryWithResponseAsync methods on the Amazon.S3.Transfer.TransferUtility class. The new operations support downloading directories using multipart download for files and return response metadata."
+      ]
+    }
+  ]
+}

sdk/src/Services/S3/Custom/Transfer/Internal/DownloadDirectoryCommand.cs

@@ -42,16 +42,24 @@ internal partial class DownloadDirectoryCommand : BaseCommand<TransferUtilityDow
         private readonly IAmazonS3 _s3Client;
         private readonly TransferUtilityDownloadDirectoryRequest _request;
         private readonly bool _skipEncryptionInstructionFiles;
+        private readonly bool _useMultipartDownload;
         int _totalNumberOfFilesToDownload;
         int _numberOfFilesDownloaded;
         long _totalBytes;
         long _transferredBytes;        
         string _currentFile;
 
         internal DownloadDirectoryCommand(IAmazonS3 s3Client, TransferUtilityDownloadDirectoryRequest request)
+            : this(s3Client, request, useMultipartDownload: false)
+        {
+        }
+
+        internal DownloadDirectoryCommand(IAmazonS3 s3Client, TransferUtilityDownloadDirectoryRequest request, bool useMultipartDownload)
         {
             if (s3Client == null)
-                throw new ArgumentNullException("s3Client");
+                throw new ArgumentNullException(nameof(s3Client));
+            if (request == null)
+                throw new ArgumentNullException(nameof(request));
 
             this._s3Client = s3Client;
             this._request = request;
@@ -60,6 +68,13 @@ internal DownloadDirectoryCommand(IAmazonS3 s3Client, TransferUtilityDownloadDir
                 request.FailurePolicy == FailurePolicy.AbortOnFailure
                     ? new AbortOnFailurePolicy()
                     : new ContinueOnFailurePolicy(_errors);
+            this._useMultipartDownload = useMultipartDownload;
+        }
+
+        internal DownloadDirectoryCommand(IAmazonS3 s3Client, TransferUtilityDownloadDirectoryRequest request, TransferUtilityConfig config, bool useMultipartDownload)
+            : this(s3Client, request, useMultipartDownload)
+        {
+            this._config = config;
         }
 
         private void downloadedProgressEventCallback(object sender, WriteObjectProgressArgs e)

sdk/src/Services/S3/Custom/Transfer/Internal/FilePartDataHandler.cs

@@ -47,6 +47,10 @@ private Logger Logger
             get { return Logger.GetLogger(typeof(TransferUtility)); }
         }
 
+        /// <summary>
+        /// Initializes a new instance for file downloads.
+        /// Writes parts directly to disk without memory buffering.
+        /// </summary>
         public FilePartDataHandler(FileDownloadConfiguration config)
         {
             _config = config ?? throw new ArgumentNullException(nameof(config));
@@ -90,14 +94,16 @@ await WritePartToFileAsync(offset, response, cancellationToken)
         /// <inheritdoc/>
         public Task WaitForCapacityAsync(CancellationToken cancellationToken)
         {
-            // No backpressure needed - OS handles concurrent file access
+            // No-op: FilePartDataHandler writes directly to disk without buffering parts in memory.
+            // Memory throttling is only needed for BufferedPartDataHandler which keeps parts in memory.
             return Task.CompletedTask;
         }
 
         /// <inheritdoc/>
         public void ReleaseCapacity()
         {
-            // No-op
+            // No-op: FilePartDataHandler writes directly to disk without buffering parts in memory.
+            // Memory throttling is only needed for BufferedPartDataHandler which keeps parts in memory.
         }
 
         /// <inheritdoc/>

sdk/src/Services/S3/Custom/Transfer/Internal/MultipartDownloadCommand.cs

@@ -20,6 +20,7 @@
  *
  */
 using System;
+using System.Threading;
 using Amazon.Runtime.Internal.Util;
 using Amazon.S3.Model;
 using Amazon.S3.Util;
@@ -36,6 +37,7 @@ internal partial class MultipartDownloadCommand : BaseCommand<TransferUtilityDow
         private readonly IAmazonS3 _s3Client;
         private readonly TransferUtilityDownloadRequest _request;
         private readonly TransferUtilityConfig _config;
+        private readonly SemaphoreSlim _sharedHttpThrottler;
 
         // Track last known transferred bytes from coordinator's progress events
         private long _lastKnownTransferredBytes;
@@ -49,16 +51,29 @@ private static Logger Logger
         }
 
         /// <summary>
-        /// Initializes a new instance of the MultipartDownloadCommand class.
+        /// Initializes a new instance of the MultipartDownloadCommand class for single file downloads.
         /// </summary>
         /// <param name="s3Client">The S3 client to use for downloads.</param>
         /// <param name="request">The download request containing configuration.</param>
         /// <param name="config">The TransferUtility configuration.</param>
         internal MultipartDownloadCommand(IAmazonS3 s3Client, TransferUtilityDownloadRequest request, TransferUtilityConfig config)
+            : this(s3Client, request, config, null)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the MultipartDownloadCommand class for directory downloads.
+        /// </summary>
+        /// <param name="s3Client">The S3 client to use for downloads.</param>
+        /// <param name="request">The download request containing configuration.</param>
+        /// <param name="config">The TransferUtility configuration.</param>
+        /// <param name="sharedHttpThrottler">Shared HTTP concurrency throttler for directory operations, or null for single file downloads.</param>
+        internal MultipartDownloadCommand(IAmazonS3 s3Client, TransferUtilityDownloadRequest request, TransferUtilityConfig config, SemaphoreSlim sharedHttpThrottler)
         {
             _s3Client = s3Client ?? throw new ArgumentNullException(nameof(s3Client));
             _request = request ?? throw new ArgumentNullException(nameof(request));
             _config = config ?? throw new ArgumentNullException(nameof(config));
+            _sharedHttpThrottler = sharedHttpThrottler; // Can be null for single file downloads
         }
 
         /// <summary>

sdk/src/Services/S3/Custom/Transfer/Internal/MultipartDownloadManager.cs

@@ -44,6 +44,7 @@ internal class MultipartDownloadManager : IDownloadManager
         private readonly DownloadManagerConfiguration _config;
         private readonly IPartDataHandler _dataHandler;
         private readonly SemaphoreSlim _httpConcurrencySlots;
+        private readonly bool _ownsHttpThrottler;
         private readonly RequestEventHandler _requestEventHandler;
 
         private Exception _downloadException;
@@ -79,23 +80,82 @@ private Logger Logger
         public Task DownloadCompletionTask => _downloadCompletionTask ?? Task.CompletedTask;
 
         /// <summary>
-        /// Initializes a new instance of the <see cref="MultipartDownloadManager"/> class.
+        /// Initializes a new instance of the <see cref="MultipartDownloadManager"/> for single file downloads.
+        /// This constructor creates and owns its own HTTP concurrency throttler based on the configuration.
         /// </summary>
-        /// <param name="s3Client">The <see cref="IAmazonS3"/> client for making S3 requests.</param>
-        /// <param name="request">The <see cref="BaseDownloadRequest"/> containing download parameters.</param>
-        /// <param name="config">The <see cref="DownloadManagerConfiguration"/> with download settings.</param>
-        /// <param name="dataHandler">The <see cref="IPartDataHandler"/> for processing downloaded parts.</param>
-        /// <param name="requestEventHandler">Optional <see cref="RequestEventHandler"/> for user agent tracking.</param>
-        /// <exception cref="ArgumentNullException">Thrown when any required parameter is null.</exception>
+        /// <param name="s3Client">The <see cref="IAmazonS3"/> client used to make GetObject requests to S3.</param>
+        /// <param name="request">The <see cref="BaseDownloadRequest"/> containing bucket, key, version, and download strategy configuration.</param>
+        /// <param name="config">The <see cref="DownloadManagerConfiguration"/> specifying concurrency limits and part size settings.</param>
+        /// <param name="dataHandler">The <see cref="IPartDataHandler"/> responsible for buffering and processing downloaded part data.</param>
+        /// <param name="requestEventHandler">Optional request event handler for adding custom headers or tracking requests. May be null.</param>
+        /// <exception cref="ArgumentNullException">
+        /// Thrown when <paramref name="s3Client"/>, <paramref name="request"/>, <paramref name="config"/>, or <paramref name="dataHandler"/> is null.
+        /// </exception>
+        /// <remarks>
+        /// This constructor is used for single file downloads where each download manages its own HTTP concurrency.
+        /// The created <see cref="SemaphoreSlim"/> throttler will be disposed when this instance is disposed.
+        /// For directory downloads with shared concurrency management, use the overload that accepts a shared throttler.
+        /// </remarks>
+        /// <seealso cref="DownloadManagerConfiguration"/>
+        /// <seealso cref="IPartDataHandler"/>
+        /// <seealso cref="MultipartDownloadType"/>
         public MultipartDownloadManager(IAmazonS3 s3Client, BaseDownloadRequest request, DownloadManagerConfiguration config, IPartDataHandler dataHandler, RequestEventHandler requestEventHandler = null)
+            : this(s3Client, request, config, dataHandler, requestEventHandler, null)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="MultipartDownloadManager"/> for directory downloads or scenarios requiring shared concurrency control.
+        /// This constructor allows using a shared HTTP concurrency throttler across multiple concurrent file downloads.
+        /// </summary>
+        /// <param name="s3Client">The <see cref="IAmazonS3"/> client used to make GetObject requests to S3.</param>
+        /// <param name="request">The <see cref="BaseDownloadRequest"/> containing bucket, key, version, and download strategy configuration.</param>
+        /// <param name="config">The <see cref="DownloadManagerConfiguration"/> specifying concurrency limits and part size settings.</param>
+        /// <param name="dataHandler">The <see cref="IPartDataHandler"/> responsible for buffering and processing downloaded part data.</param>
+        /// <param name="requestEventHandler">Optional request event handler for adding custom headers or tracking requests. May be null.</param>
+        /// <param name="sharedHttpThrottler">
+        /// Optional shared <see cref="SemaphoreSlim"/> for coordinating HTTP concurrency across multiple downloads.
+        /// If null, a new throttler will be created and owned by this instance.
+        /// If provided, the caller retains ownership and responsibility for disposal.
+        /// </param>
+        /// <exception cref="ArgumentNullException">
+        /// Thrown when <paramref name="s3Client"/>, <paramref name="request"/>, <paramref name="config"/>, or <paramref name="dataHandler"/> is null.
+        /// </exception>
+        /// <remarks>
+        /// <para>
+        /// This constructor is typically used by directory download operations where multiple files are being downloaded
+        /// concurrently and need to share a global HTTP concurrency limit.
+        /// </para>
+        /// <para>
+        /// <strong>Resource Ownership:</strong>
+        /// If <paramref name="sharedHttpThrottler"/> is provided, this instance does NOT take ownership and will NOT dispose it.
+        /// If <paramref name="sharedHttpThrottler"/> is null, this instance creates and owns the throttler and will dispose it.
+        /// </para>
+        /// </remarks>
+        /// <seealso cref="DownloadManagerConfiguration"/>
+        /// <seealso cref="IPartDataHandler"/>
+        /// <seealso cref="MultipartDownloadType"/>
+        /// <seealso cref="DiscoverDownloadStrategyAsync"/>
+        /// <seealso cref="StartDownloadsAsync"/>
+        public MultipartDownloadManager(IAmazonS3 s3Client, BaseDownloadRequest request, DownloadManagerConfiguration config, IPartDataHandler dataHandler, RequestEventHandler requestEventHandler, SemaphoreSlim sharedHttpThrottler)
         {
             _s3Client = s3Client ?? throw new ArgumentNullException(nameof(s3Client));
             _request = request ?? throw new ArgumentNullException(nameof(request));
             _config = config ?? throw new ArgumentNullException(nameof(config));
             _dataHandler = dataHandler ?? throw new ArgumentNullException(nameof(dataHandler));
             _requestEventHandler = requestEventHandler;
 
-            _httpConcurrencySlots = new SemaphoreSlim(_config.ConcurrentServiceRequests);
+            // Use shared throttler if provided, otherwise create our own
+            if (sharedHttpThrottler != null)
+            {
+                _httpConcurrencySlots = sharedHttpThrottler;
+                _ownsHttpThrottler = false; // Don't dispose - directory command owns it
+            }
+            else
+            {
+                _httpConcurrencySlots = new SemaphoreSlim(_config.ConcurrentServiceRequests);
+                _ownsHttpThrottler = true; // We own it, so we dispose it
+            }
         }
 
         /// <inheritdoc/>
@@ -654,7 +714,11 @@ public void Dispose()
             {
                 try
                 {
-                    _httpConcurrencySlots?.Dispose();
+                    // Only dispose HTTP throttler if we own it
+                    if (_ownsHttpThrottler)
+                    {
+                        _httpConcurrencySlots?.Dispose();
+                    }
                     _dataHandler?.Dispose();
                 }
                 catch (Exception)

sdk/src/Services/S3/Custom/Transfer/Internal/_async/MultipartDownloadCommand.async.cs

@@ -50,12 +50,14 @@ public override async Task<TransferUtilityDownloadResponse> ExecuteAsync(Cancell
             using (var dataHandler = new FilePartDataHandler(config))
             {
                 // Create coordinator to manage the download process
+                // Pass shared HTTP throttler to control concurrency across files
                 using (var coordinator = new MultipartDownloadManager(
                     _s3Client,
                     _request,
                     config,
                     dataHandler,
-                    RequestEventHandler))
+                    RequestEventHandler,
+                    _sharedHttpThrottler))
                 {
                     long totalBytes = -1;
                     try

sdk/src/Services/S3/Custom/Transfer/Internal/_bcl+netstandard/DownloadDirectoryCommand.cs

@@ -66,23 +66,43 @@ public override async Task<TransferUtilityDownloadDirectoryResponse> ExecuteAsyn
 
             this._totalNumberOfFilesToDownload = objs.Count;
 
-            SemaphoreSlim asyncThrottler = null;
+            // Two-level throttling architecture:
+            // 1. File-level throttler: Controls how many files are downloaded concurrently
+            // 2. HTTP-level throttler: Controls total HTTP requests across ALL file downloads
+            //
+            // Example with ConcurrentServiceRequests = 10:
+            //   - fileOperationThrottler = 10: Up to 10 files can download simultaneously
+            //   - sharedHttpRequestThrottler = 10: All 10 files share 10 total HTTP request slots
+            //   - Without HTTP throttler: Would result in 10 files × 10 parts = 100 concurrent HTTP requests
+            //   - With HTTP throttler: Enforces 10 total concurrent HTTP requests across all files
+            //
+            // This prevents resource exhaustion when downloading many large files with multipart downloads.
+            SemaphoreSlim fileOperationThrottler = null;
+            SemaphoreSlim sharedHttpRequestThrottler = null;
             CancellationTokenSource internalCts = null;
 
             try
             {
-                asyncThrottler = DownloadFilesConcurrently ?
+                // File-level throttler: Controls concurrent file operations
+                fileOperationThrottler = DownloadFilesConcurrently ?
                     new SemaphoreSlim(this._config.ConcurrentServiceRequests) :
                     new SemaphoreSlim(1);
 
+                // HTTP-level throttler: Shared across all downloads to control total HTTP concurrency
+                // Only needed for multipart downloads where each file makes multiple HTTP requests
+                if (this._useMultipartDownload)
+                {
+                    sharedHttpRequestThrottler = new SemaphoreSlim(this._config.ConcurrentServiceRequests);
+                }
+
                 internalCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
                 var pendingTasks = new List<Task>();
                 foreach (S3Object s3o in objs)
                 {
                     if (s3o.Key.EndsWith("/", StringComparison.Ordinal))
                         continue;
 
-                    await asyncThrottler.WaitAsync(cancellationToken)
+                    await fileOperationThrottler.WaitAsync(cancellationToken)
                         .ConfigureAwait(continueOnCapturedContext: false);
 
                     try
@@ -137,7 +157,15 @@ await asyncThrottler.WaitAsync(cancellationToken)
 
                         var task = _failurePolicy.ExecuteAsync(
                             async () => {
-                                var command = new DownloadCommand(this._s3Client, downloadRequest);
+                                BaseCommand<TransferUtilityDownloadResponse> command;
+                                if (this._useMultipartDownload)
+                                {
+                                    command = new MultipartDownloadCommand(this._s3Client, downloadRequest, this._config, sharedHttpRequestThrottler);
+                                }
+                                else
+                                {
+                                    command = new DownloadCommand(this._s3Client, downloadRequest);
+                                }
                                 await command.ExecuteAsync(internalCts.Token)
                                     .ConfigureAwait(false);
                             },
@@ -149,7 +177,7 @@ await command.ExecuteAsync(internalCts.Token)
                     }
                     finally
                     {
-                        asyncThrottler.Release();
+                        fileOperationThrottler.Release();
                     }
                 }
                 await TaskHelpers.WhenAllOrFirstExceptionAsync(pendingTasks, cancellationToken)
@@ -170,7 +198,8 @@ await TaskHelpers.WhenAllOrFirstExceptionAsync(pendingTasks, cancellationToken)
             finally
             {
                 internalCts.Dispose();
-                asyncThrottler.Dispose();
+                fileOperationThrottler.Dispose();
+                sharedHttpRequestThrottler?.Dispose();
             }
         }