🐛 AsyncResult contains invalid value

- AsyncResult should contain invalid value immediately after async operation is marked as completed
- there was race condition problems with callback method which is invoked on different thread so updating of value is done without any synchronization. So in some cases async operation is marked as completed but async result value is not yet updated and contains invalid value

src/Renci.SshNet/SftpClient.cs

@@ -584,7 +584,7 @@ public IEnumerable<ISftpFile> ListDirectory(string path, Action<int> listCallbac
         {
             CheckDisposed();
 
-            return InternalListDirectory(path, listCallback);
+            return InternalListDirectory(path, asyncResult: null, listCallback);
         }
 
 #if FEATURE_ASYNC_ENUMERABLE
@@ -669,12 +669,7 @@ public IAsyncResult BeginListDirectory(string path, AsyncCallback asyncCallback,
             {
                 try
                 {
-                    var result = InternalListDirectory(path, count =>
-                    {
-                        asyncResult.Update(count);
-
-                        listCallback?.Invoke(count);
-                    });
+                    var result = InternalListDirectory(path, asyncResult, listCallback);
 
                     asyncResult.SetAsCompleted(result, completedSynchronously: false);
                 }
@@ -899,12 +894,7 @@ public IAsyncResult BeginDownloadFile(string path, Stream output, AsyncCallback
             {
                 try
                 {
-                    InternalDownloadFile(path, output, asyncResult, offset =>
-                    {
-                        asyncResult.Update(offset);
-
-                        downloadCallback?.Invoke(offset);
-                    });
+                    InternalDownloadFile(path, output, asyncResult, downloadCallback);
 
                     asyncResult.SetAsCompleted(exception: null, completedSynchronously: false);
                 }
@@ -1132,11 +1122,7 @@ public IAsyncResult BeginUploadFile(Stream input, string path, bool canOverride,
             {
                 try
                 {
-                    InternalUploadFile(input, path, flags, asyncResult, offset =>
-                        {
-                            asyncResult.Update(offset);
-                            uploadCallback?.Invoke(offset);
-                        });
+                    InternalUploadFile(input, path, flags, asyncResult, uploadCallback);
 
                     asyncResult.SetAsCompleted(exception: null, completedSynchronously: false);
                 }
@@ -2200,7 +2186,7 @@ private IEnumerable<FileInfo> InternalSynchronizeDirectories(string sourcePath,
 
                 #region Existing Files at The Destination
 
-                var destFiles = InternalListDirectory(destinationPath, listCallback: null);
+                var destFiles = InternalListDirectory(destinationPath, asyncResult: null, listCallback: null);
                 var destDict = new Dictionary<string, ISftpFile>();
                 foreach (var destFile in destFiles)
                 {
@@ -2267,13 +2253,14 @@ private IEnumerable<FileInfo> InternalSynchronizeDirectories(string sourcePath,
         /// Internals the list directory.
         /// </summary>
         /// <param name="path">The path.</param>
+        /// <param name="asyncResult">An <see cref="IAsyncResult"/> that references the asynchronous request.</param>
         /// <param name="listCallback">The list callback.</param>
         /// <returns>
         /// A list of files in the specfied directory.
         /// </returns>
         /// <exception cref="ArgumentNullException"><paramref name="path" /> is <b>null</b>.</exception>
         /// <exception cref="SshConnectionException">Client not connected.</exception>
-        private IEnumerable<ISftpFile> InternalListDirectory(string path, Action<int> listCallback)
+        private IEnumerable<ISftpFile> InternalListDirectory(string path, SftpListDirectoryAsyncResult asyncResult, Action<int> listCallback)
         {
             if (path is null)
             {
@@ -2309,6 +2296,8 @@ private IEnumerable<ISftpFile> InternalListDirectory(string path, Action<int> li
                                             f.Value));
                 }
 
+                asyncResult?.Update(result.Count);
+
                 //  Call callback to report number of files read
                 if (listCallback is not null)
                 {
@@ -2375,6 +2364,8 @@ private void InternalDownloadFile(string path, Stream output, SftpDownloadAsyncR
 
                     totalBytesRead += (ulong) data.Length;
 
+                    asyncResult?.Update(totalBytesRead);
+
                     if (downloadCallback is not null)
                     {
                         // copy offset to ensure it's not modified between now and execution of callback
@@ -2447,6 +2438,8 @@ private void InternalUploadFile(Stream input, string path, Flags flags, SftpUplo
                                 _ = Interlocked.Decrement(ref expectedResponses);
                                 _ = responseReceivedWaitHandle.Set();
 
+                                asyncResult?.Update(writtenBytes);
+
                                 //  Call callback to report number of bytes written
                                 if (uploadCallback is not null)
                                 {