c# - 如何在 ASP.Net Core 中验证上传的文件

Question

我正在使用 ASP.NET Core 2.2 并且我正在使用模型绑定(bind)来上传文件。

这是我的UserViewModel

public class UserViewModel
{
    [Required(ErrorMessage = "Please select a file.")]
    [DataType(DataType.Upload)]
    public IFormFile Photo { get; set; }
}

这是MyView

@model UserViewModel

<form method="post"
      asp-action="UploadPhoto"
      asp-controller="TestFileUpload"
      enctype="multipart/form-data">
    <div asp-validation-summary="ModelOnly" class="text-danger"></div>

    <input asp-for="Photo" />
    <span asp-validation-for="Photo" class="text-danger"></span>
    <input type="submit" value="Upload"/>
</form>

最后这是 MyController

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> UploadPhoto(UserViewModel userViewModel)
{
    if (ModelState.IsValid)
    {
        var formFile = userViewModel.Photo;
        if (formFile == null || formFile.Length == 0)
        {
            ModelState.AddModelError("", "Uploaded file is empty or null.");
            return View(viewName: "Index");
        }

        var uploadsRootFolder = Path.Combine(_environment.WebRootPath, "uploads");
        if (!Directory.Exists(uploadsRootFolder))
        {
            Directory.CreateDirectory(uploadsRootFolder);
        }

        var filePath = Path.Combine(uploadsRootFolder, formFile.FileName);
        using (var fileStream = new FileStream(filePath, FileMode.Create))
        {
            await formFile.CopyToAsync(fileStream).ConfigureAwait(false);
        }

        RedirectToAction("Index");
    }
    return View(viewName: "Index");
}

如何将上传的文件限制为小于 5MB，并带有 .jpeg 和 .png 等特定扩展名？我认为这两个验证都是在 ViewModel 中完成的。但我不知道该怎么做。

Answer 1

您可以自定义验证属性 MaxFileSizeAttribute，如下所示

最大文件大小属性

public class MaxFileSizeAttribute : ValidationAttribute
{
    private readonly int _maxFileSize;
    public MaxFileSizeAttribute(int maxFileSize)
    {
        _maxFileSize = maxFileSize;
    }

    protected override ValidationResult IsValid(
    object value, ValidationContext validationContext)
    {
        var file = value as IFormFile;
        if (file != null)
        {
           if (file.Length > _maxFileSize)
            {
                return new ValidationResult(GetErrorMessage());
            }
        }

        return ValidationResult.Success;
    }

    public string GetErrorMessage()
    {
        return $"Maximum allowed file size is { _maxFileSize} bytes.";
    }
}

AllowedExtensionsAttribute

public class AllowedExtensionsAttribute : ValidationAttribute
{
    private readonly string[] _extensions;
    public AllowedExtensionsAttribute(string[] extensions)
    {
        _extensions = extensions;
    }
    
    protected override ValidationResult IsValid(
    object value, ValidationContext validationContext)
    {
        var file = value as IFormFile;
        if (file != null)
        {
            var extension = Path.GetExtension(file.FileName);
            if (!_extensions.Contains(extension.ToLower()))
            {
                return new ValidationResult(GetErrorMessage());
            }
        }
        
        return ValidationResult.Success;
    }

    public string GetErrorMessage()
    {
        return $"This photo extension is not allowed!";
    }
}

将MaxFileSize 属性和AllowedExtensions 属性添加到Photo 属性

public class UserViewModel
{
        [Required(ErrorMessage = "Please select a file.")]
        [DataType(DataType.Upload)]
        [MaxFileSize(5* 1024 * 1024)]
        [AllowedExtensions(new string[] { ".jpg", ".png" })]
        public IFormFile Photo { get; set; }
 }