1 files changed, 84 insertions, 0 deletions
diff --git a/Jellyfin.Api/Helpers/ProgressiveFileCopier.cs b/Jellyfin.Api/Helpers/ProgressiveFileCopier.cs
new file mode 100644
index 000000000..e8e6966f4
--- /dev/null
+++ b/Jellyfin.Api/Helpers/ProgressiveFileCopier.cs
@@ -0,0 +1,84 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using MediaBrowser.Controller.Library;
+using MediaBrowser.Model.IO;
+
+namespace Jellyfin.Api.Helpers
+{
+    /// <summary>
+    /// Progressive file copier.
+    /// </summary>
+    public class ProgressiveFileCopier
+    {
+        private readonly string? _path;
+        private readonly IDirectStreamProvider? _directStreamProvider;
+        private readonly IStreamHelper _streamHelper;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ProgressiveFileCopier"/> class.
+        /// </summary>
+        /// <param name="streamHelper">Instance of the <see cref="IStreamHelper"/> interface.</param>
+        /// <param name="path">Filepath to stream from.</param>
+        public ProgressiveFileCopier(IStreamHelper streamHelper, string path)
+        {
+            _path = path;
+            _streamHelper = streamHelper;
+            _directStreamProvider = null;
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ProgressiveFileCopier"/> class.
+        /// </summary>
+        /// <param name="streamHelper">Instance of the <see cref="IStreamHelper"/> interface.</param>
+        /// <param name="directStreamProvider">Instance of the <see cref="IDirectStreamProvider"/> interface.</param>
+        public ProgressiveFileCopier(IStreamHelper streamHelper, IDirectStreamProvider directStreamProvider)
+        {
+            _directStreamProvider = directStreamProvider;
+            _streamHelper = streamHelper;
+            _path = null;
+        }
+
+        /// <summary>
+        /// Write source stream to output.
+        /// </summary>
+        /// <param name="outputStream">Output stream.</param>
+        /// <param name="cancellationToken">Cancellation token.</param>
+        /// <returns>A <see cref="Task"/>.</returns>
+        public async Task WriteToAsync(Stream outputStream, CancellationToken cancellationToken)
+        {
+            if (_directStreamProvider != null)
+            {
+                await _directStreamProvider.CopyToAsync(outputStream, cancellationToken).ConfigureAwait(false);
+                return;
+            }
+
+            var fileOptions = FileOptions.SequentialScan;
+
+            // use non-async filestream along with read due to https://github.com/dotnet/corefx/issues/6039
+            if (Environment.OSVersion.Platform != PlatformID.Win32NT)
+            {
+                fileOptions |= FileOptions.Asynchronous;
+            }
+
+            await using var inputStream = new FileStream(_path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite, 4096, fileOptions);
+            const int emptyReadLimit = 100;
+            var eofCount = 0;
+            while (eofCount < emptyReadLimit)
+            {
+                var bytesRead = await _streamHelper.CopyToAsync(inputStream, outputStream, cancellationToken).ConfigureAwait(false);
+
+                if (bytesRead == 0)
+                {
+                    eofCount++;
+                    await Task.Delay(100, cancellationToken).ConfigureAwait(false);
+                }
+                else
+                {
+                    eofCount = 0;
+                }
+            }
+        }
+    }
+}