Address PR review issues - cancellable retry delay, async file I/O, stream leak, and race guards in Resume/Start

Author: NeuralFault

StabilityMatrix.Core/Models/TrackedDownload.cs

@@ -79,6 +79,7 @@ public class TrackedDownload
     public Exception? Exception { get; private set; }
 
     private int attempts;
+    private CancellationTokenSource? retryDelayCancellationTokenSource;
 
     #region Events
     public event EventHandler<ProgressReport>? ProgressUpdate;
@@ -185,6 +186,11 @@ internal void Start()
                 $"Download state must be inactive or pending to start, not {ProgressState}"
             );
         }
+        // Cancel any pending auto-retry delay (defensive: Start() accepts Inactive state).
+        retryDelayCancellationTokenSource?.Cancel();
+        retryDelayCancellationTokenSource?.Dispose();
+        retryDelayCancellationTokenSource = null;
+
         Logger.Debug("Starting download {Download}", FileName);
 
         EnsureDownloadService();
@@ -202,13 +208,19 @@ internal void Start()
 
     internal void Resume()
     {
+        // Cancel any pending auto-retry delay since we're resuming now.
+        retryDelayCancellationTokenSource?.Cancel();
+        retryDelayCancellationTokenSource?.Dispose();
+        retryDelayCancellationTokenSource = null;
+
         if (ProgressState != ProgressState.Inactive && ProgressState != ProgressState.Paused)
         {
             Logger.Warn(
                 "Attempted to resume download {Download} but it is not paused ({State})",
                 FileName,
                 ProgressState
             );
+            return;
         }
         Logger.Debug("Resuming download {Download}", FileName);
 
@@ -236,6 +248,11 @@ internal void Resume()
 
     public void Pause()
     {
+        // Cancel any pending auto-retry delay.
+        retryDelayCancellationTokenSource?.Cancel();
+        retryDelayCancellationTokenSource?.Dispose();
+        retryDelayCancellationTokenSource = null;
+
         if (ProgressState != ProgressState.Working)
         {
             Logger.Warn(
@@ -265,6 +282,11 @@ public void Cancel()
             return;
         }
 
+        // Cancel any pending auto-retry delay.
+        retryDelayCancellationTokenSource?.Cancel();
+        retryDelayCancellationTokenSource?.Dispose();
+        retryDelayCancellationTokenSource = null;
+
         Logger.Debug("Cancelling download {Download}", FileName);
 
         // Cancel token if it exists
@@ -387,8 +409,21 @@ private void OnDownloadTaskCompleted(Task task)
                 ProgressState = ProgressState.Inactive;
                 OnProgressStateChanged(ProgressState.Inactive);
 
-                // Fire-and-forget the delayed resume to avoid blocking the task continuation thread.
-                Task.Delay(Math.Max(delayMs, 0)).ContinueWith(_ => Resume()).SafeFireAndForget();
+                // Clean up the completed task resources; Resume() will create new ones.
+                downloadTask = null;
+                downloadCancellationTokenSource = null;
+                downloadPauseTokenSource = null;
+
+                // Schedule the retry with a cancellation token so Cancel/Pause can abort the delay.
+                retryDelayCancellationTokenSource?.Dispose();
+                retryDelayCancellationTokenSource = new CancellationTokenSource();
+                Task.Delay(Math.Max(delayMs, 0), retryDelayCancellationTokenSource.Token)
+                    .ContinueWith(t =>
+                    {
+                        if (t.IsCompletedSuccessfully)
+                            Resume();
+                    })
+                    .SafeFireAndForget();
                 return;
             }
 

StabilityMatrix.Core/Services/TrackedDownloadService.cs

@@ -138,13 +138,33 @@ public async Task TryRestartDownload(TrackedDownload download)
         downloadsDir.Create();
         var jsonFile = downloadsDir.JoinFile($"{download.Id}.json");
 
-        var jsonFileStream = jsonFile.Info.Open(FileMode.Create, FileAccess.ReadWrite, FileShare.Read);
-        var json = JsonSerializer.Serialize(download);
-        jsonFileStream.Write(Encoding.UTF8.GetBytes(json));
-        jsonFileStream.Flush();
+        var jsonFileStream = new FileStream(
+            jsonFile.Info.FullName,
+            FileMode.Create,
+            FileAccess.ReadWrite,
+            FileShare.Read,
+            bufferSize: 4096,
+            useAsync: true
+        );
+        var jsonBytes = JsonSerializer.SerializeToUtf8Bytes(download);
+
+        try
+        {
+            await jsonFileStream.WriteAsync(jsonBytes).ConfigureAwait(false);
+            await jsonFileStream.FlushAsync().ConfigureAwait(false);
 
-        // Handlers are already attached from the original AddDownload call.
-        downloads.TryAdd(download.Id, (download, jsonFileStream));
+            // Handlers are already attached from the original AddDownload call.
+            if (!downloads.TryAdd(download.Id, (download, jsonFileStream)))
+            {
+                // Already tracked; discard the newly opened stream.
+                await jsonFileStream.DisposeAsync().ConfigureAwait(false);
+            }
+        }
+        catch
+        {
+            await jsonFileStream.DisposeAsync().ConfigureAwait(false);
+            throw;
+        }
 
         await TryResumeDownload(download).ConfigureAwait(false);
     }