Cannot catch exception thrown by File.WriteAllBytesAsync

[JerrettDavis]

When attempting to use IFile.WriteAllBytesAsync, all underlying exceptions from File.WriteAllBytesAsync are quietly disregarded. I can see the exceptions being thrown, but a try/catch fails to catch the exceptions. Instead, the program continues execution on the next line. I believe this is due to the FileWrapper not awaiting the response from File.WriteAllBytes, and instead it's always returning a Task.Completed task.

[robkeim]

@JerrettDavis in order to catch exceptions thrown by async methods you need to await their results like this:

Task<Result> resultTask = someMethodThatReturnsAResultByThrowsAnException();
// No exception is thrown at this point
// Continue doing other work...
try
{
    Result result = await resultTask; // this will now throw an exception
}
catch (Exception e)
{
    // Handle your exception here
}

Here you can see a quick fiddle that I threw together showing this behavior:
https://dotnetfiddle.net/7jj6lJ

[JerrettDavis]

@robkeim Ordinarily, that would work, but it doesn't appear to work properly for WriteAllBytesAsync.

Here is an example method:

public async Task<string> SaveFileAsync(string path, byte[] file, string fileType, CancellationToken cancellationToken = default)
{
    var filename = _filenameProvider.GetFilename(path, fileType);
    var fullPath = _fileSystem.Path.Combine(path, filename)?.Replace('/', '\\');

    _fileSystem.Directory.CreateDirectory(path);
    try
    {
        await _fileSystem.File.WriteAllBytesAsync(fullPath, file, cancellationToken);
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex);
    }

    return filename;
}

The catch block is never triggered, but if I switch the method over to WriteAllBytes it works as desired.

You can also see the exception being thrown in the Debug output window.

And here is an example fiddle.

[fgreinacher]

This is fixed with https://github.com/System-IO-Abstractions/System.IO.Abstractions/releases/tag/v6.0.15, should be on NuGet.org soon

[JerrettDavis]

It's live on nuget, and the fix is confirmed working in my original use-case.