Update TransferUtilityConfig and BaseDownloadRequest to add multi part download config options

Author: GarrettBeatty

generator/.DevConfigs/19ed68ce-9f46-4e1e-a0ff-45a2b3641946.json

@@ -0,0 +1,13 @@
+{
+  "services": [
+    {
+      "serviceName": "S3",
+      "type": "patch",
+      "changeLogMessages": [
+        "Added MaxInMemoryParts property to TransferUtilityConfig for controlling memory usage during multipart downloads",
+        "Added PartSize property to BaseDownloadRequest for configuring multipart download part sizes",
+        "Added MultipartDownloadType enum and property to BaseDownloadRequest for selecting download strategy"
+      ]
+    }
+  ]
+}

sdk/src/Services/S3/Custom/Transfer/BaseDownloadRequest.cs

@@ -28,6 +28,22 @@
 
 namespace Amazon.S3.Transfer
 {
+    /// <summary>
+    /// Specifies the strategy for multipart downloads
+    /// </summary>
+    public enum MultipartDownloadType
+    {
+        /// <summary>
+        /// Use part-based downloads with original upload part boundaries
+        /// </summary>
+        PART,
+        
+        /// <summary>
+        /// Use range-based downloads with configurable part sizes
+        /// </summary>
+        RANGE
+    }
+
     /// <summary>
     /// The base class for requests that return Amazon S3 objects.
     /// </summary>
@@ -51,6 +67,10 @@ public abstract class BaseDownloadRequest
         private string ifNoneMatch;
         private ResponseHeaderOverrides responseHeaders;
 
+        // Optional part size override (defaults to 8MB per SEP recommendations)
+        private long? partSize;
+        private MultipartDownloadType multipartDownloadType = MultipartDownloadType.PART;
+        
         /// <summary>
         /// 	Gets or sets the name of the bucket.
         /// </summary>
@@ -330,5 +350,46 @@ public ResponseHeaderOverrides ResponseHeaderOverrides
                 this.responseHeaders = value;
             }
         }
+
+        /// <summary>
+        /// Gets or sets the part size of the download in bytes.
+        /// The downloaded file will be divided into 
+        /// parts the size specified and
+        /// downloaded from Amazon S3 individually.
+        /// This is used when MultipartDownloadType is set to RANGE.
+        /// Default is 8MB per SEP recommendations.
+        /// </summary>
+        /// <value>
+        /// The part size of the download.
+        /// </value>
+        public long PartSize
+        {
+            get { return this.partSize.GetValueOrDefault(); }
+            set { this.partSize = value; }
+        }
+
+        /// <summary>
+        /// Checks if PartSize property is set.
+        /// </summary>
+        /// <returns>true if PartSize property is set.</returns>
+        internal bool IsSetPartSize()
+        {
+            return this.partSize.HasValue;
+        }
+
+        /// <summary>
+        /// Gets or sets the type of multipart download to use.
+        /// PART: Uses part GET with original part sizes from upload (ignores PartSize)
+        /// RANGE: Uses ranged GET with PartSize to determine ranges
+        /// Default is PART
+        /// </summary>
+        /// <value>
+        /// The multipart download type.
+        /// </value>
+        public MultipartDownloadType MultipartDownloadType
+        {
+            get { return this.multipartDownloadType; }
+            set { this.multipartDownloadType = value; }
+        }
     }
-}
+}

sdk/src/Services/S3/Custom/Transfer/TransferUtilityConfig.cs

@@ -42,6 +42,7 @@ public partial class TransferUtilityConfig
     {
         long _minSizeBeforePartUpload = 16 * (long)Math.Pow(2, 20);
         int _concurrentServiceRequests;
+        int _maxInMemoryParts = 1024; // When combined with the default part size of 8MB, we get 8GB of memory being utilized as the default.
 
         /// <summary>
         /// Default constructor.
@@ -81,5 +82,21 @@ public int ConcurrentServiceRequests
                 this._concurrentServiceRequests = value;
             }
         }
+
+        /// <summary>
+        /// Gets or sets the maximum number of parts to buffer in memory during multipart downloads.
+        /// The default value is 1024.
+        /// </summary>
+        public int MaxInMemoryParts
+        {
+            get { return this._maxInMemoryParts; }
+            set
+            {
+                if (value < 1)
+                    value = 1;
+
+                this._maxInMemoryParts = value;
+            }
+        }
     }
 }