Wasm: FileOpenPicker's StorageFile throws exception when calling Flush on the read stream

[alove-kahua]

Current behavior

Calling Flush after opening a read stream from a StorageFile throws exception. This is different than UWP and the documentation states it should be acceptable.

Documentation:
Because a buffer can be used for either reading or writing, Flush() performs the following two functions:

Any data previously written to the buffer is copied to the file and the buffer is cleared except for its encoder state.

If BufferedStream.CanSeek is true and data was previously copied from the file to the buffer for reading, the current position within the file is decremented by the number of unread bytes in the buffer. The buffer is then cleared.

Expected behavior

No exception is thrown.

How to reproduce it (as minimally and precisely as possible)

StreamReadAsyncException.zip

Workaround

Either don't call Flush, or temporarily catch the exception and swallow it.

Environment

Nuget Package:

• Uno.UI / Uno.UI.WebAssembly / Uno.UI.Skia
• Uno.WinUI / Uno.WinUI.WebAssembly / Uno.WinUI.Skia
• Uno.SourceGenerationTasks
• Uno.UI.RemoteControl / Uno.WinUI.RemoteControl
• Other:

Nuget Package Version(s):

Affected platform(s):

• iOS
• Android
• WebAssembly
• WebAssembly renderers for Xamarin.Forms
• macOS
• Skia
  • WPF
  • GTK (Linux)
  • Tizen
• Windows
• Build tasks
• Solution Templates

IDE:

• Visual Studio 2017 (version: )
• Visual Studio 2019 (version: )
• Visual Studio for Mac (version: )
• Rider Windows (version: )
• Rider macOS (version: )
• Visual Studio Code (version: )

Relevant plugins:

• Resharper (version: )

Anything else we need to know?