feat(storage): Complete removal of direct file system access in FileIO

src/Uno.UWP/Storage/FileIO.cs

@@ -5,6 +5,7 @@
 using Windows.Foundation;
 using Windows.Storage.Streams;
 using System.Collections.Generic;
+using System.Threading;
 using Uno.Extensions;
 using UwpUnicodeEncoding = Windows.Storage.Streams.UnicodeEncoding;
 using UwpBuffer = Windows.Storage.Streams.Buffer;
@@ -256,14 +257,15 @@ private static async Task WriteBytesTaskAsync(IStorageFile file, byte[] buffer,
 				throw new ArgumentNullException(nameof(file));
 			}
 
-			using var fs = File.Create(file.Path);
+			using var fs = await file.OpenStreamForWriteAsync();
 			await fs.WriteAsync(buffer, 0, buffer.Length);
 		}
 
 		private static async Task<IBuffer> ReadBufferTaskAsync(IStorageFile file)
 		{
-			using var fs = File.OpenRead(file.Path);
+			using var fs = await file.OpenStreamForReadAsync();
 			var bytes = await fs.ReadBytesAsync();
+
 			return new UwpBuffer(bytes);
 		}
 
@@ -275,22 +277,26 @@ private static async Task WriteBufferTaskAsync(IStorageFile file, IBuffer buffer
 
 		private static async Task<Encoding> GetEncodingFromFileAsync(IStorageFile file)
 		{
-			if (File.Exists(file.Path))
+			// If the file has a local path, try to not create it
+			if (file.Path is {} path && !string.IsNullOrWhiteSpace(path) && !File.Exists(path))
+			{
+				return Encoding.UTF8;
+			}
+
+			using Stream fileStream = await file.OpenStreamForReadAsync();
+			var bytes = new byte[2];
+			if (await fileStream.ReadAsync(bytes, 0, bytes.Length) == 2)
 			{
-				using Stream fileStream = await file.OpenStreamForReadAsync();
-				var bytes = new byte[2];
-				if (await fileStream.ReadAsync(bytes, 0, bytes.Length) == 2)
+				if (bytes[0] == 0xff && bytes[1] == 0xfe)
 				{
-					if (bytes[0] == 0xff && bytes[1] == 0xfe)
-					{
-						return Encoding.Unicode;
-					}
-					else if (bytes[0] == 0xfe && bytes[1] == 0xff)
-					{
-						return Encoding.BigEndianUnicode;
-					}
+					return Encoding.Unicode;
+				}
+				else if (bytes[0] == 0xfe && bytes[1] == 0xff)
+				{
+					return Encoding.BigEndianUnicode;
 				}
 			}
+
 			return Encoding.UTF8;
 		}
 

src/Uno.UWP/System.IO/WindowsRuntimeStorageExtensions.cs

@@ -36,8 +36,8 @@ public static async Task<Stream> OpenStreamForWriteAsync(this IStorageFile windo
 			}
 			else
 			{
-				var writeTransaction = await windowsRuntimeFile.OpenTransactedWriteAsync();
-				return writeTransaction.AsAutoCommitStream();
+				var raStream = await windowsRuntimeFile.OpenAsync(FileAccessMode.ReadWrite);
+				return raStream.AsStreamForWrite();
 			}
 		}