How to return an office document to OfficeOnline from WOPI API?

I am trying to use C# minimal API to develop a WOPI API for office online and on returning file to client i am always getting this error messages:

"Timeout are not supported on this stream".

I am using 'application/octet-stream' HTTP Header.

As you may know it is not possible for JsonSerializer to serialize a stream to return it as response, you have to load your file into byte[] afterward you put it in response body using code like this:

    FileInfo fileInfo = new FileInfo(filePath);
    FileStream fs = fileInfo.OpenRead();
    byte[] content = fs.ReadBytesAsync();

and then in returning part:

    httpContext.Response.ContentType = MediaTypeNames.Application.Octet;
    return HttpContext.Response.Body.Write(content,0,content.Lenght)

of course second part of code should take place in an extension method for Result.Extension somthing like this:

static class FileResultExtension
{
    public static IResult File(this IResultExtensions resultExtensions, byte[] fileResult)
    {
        ArgumentNullException.ThrowIfNull(resultExtensions);

        return new FileResult(fileResult);
    }
}

class FileResult : IResult
{
    private readonly byte[] _fileResult;

    public FileResult(byte[] fileResult)
    {
        _fileResult = fileResult;
    }

    public Task ExecuteAsync(HttpContext httpContext)
    {
        httpContext.Response.ContentType = MediaTypeNames.Application.Octet;
        return httpContext.Response.Body.WriteAsync(_fileResult,0,_fileResult.Length);
    }
}

and use it in Program.cs like this:

app.MapGet("/wopi/files/{id}/contents", (FilesService fileService, string id) =>
{
    var result = fileService.GetFile(id).Result;
    MemoryStream memoryStream = new MemoryStream();
    memoryStream.Write(result, 0, result.Length);
    return Results.Extensions.File(result);
}).WithName("GetFile");