.NET怎么实现文件的上传和下载功能

[HttpPost("upload")]
public async Task<IActionResult> UploadFile(IFormFile file)
{
    if (file == null || file.Length == 0)
        return BadRequest("没有选择文件");

    var uploadDir = Path.Combine(Directory.GetCurrentDirectory(), "uploads");
    var filePath = Path.Combine(uploadDir, file.FileName);

    // 确保目录存在
    if (!Directory.Exists(uploadDir))
        Directory.CreateDirectory(uploadDir);

    using (var stream = new FileStream(filePath, FileMode.Create))
    {
        await file.CopyToAsync(stream);
    }

    return Ok(new { message = "文件上传成功", fileName = file.FileName });
}

<form asp-action="UploadFile" method="post" enctype="multipart/form-data">
    <input type="file" name="file" />
    <button type="submit">上传</button>
</form>

[HttpGet("download/{fileName}")]
public IActionResult DownloadFile(string fileName)
{
    var filePath = Path.Combine(Directory.GetCurrentDirectory(), "uploads", fileName);

    if (!System.IO.File.Exists(filePath))
        return NotFound("文件不存在");

    var fileBytes = System.IO.File.ReadAllBytes(filePath);
    return File(fileBytes, "application/octet-stream", fileName);
}

return PhysicalFile(filePath, "application/octet-stream", fileName);