Question

我需要将文件从客户端上传到服务器。但是我发现了一个问题，我无法过滤文件。我需要丢弃没有合适扩展名的文件。如果文件没有正确的扩展名，那么我将不会将其加载到服务器。

我尝试过滤，但是我不知道该如何写。有人可以帮我这部分吗？

public enum FileExtension 
    {
    Unknown = 0,
    Doc = 1,
    Rtf = 2,
    Html = 3
}

public static class FileExtensionExtensions {
    public static string GetExtension(this FileExtension ext) {
        switch (ext) {
        case FileExtension.Doc:
            return ".doc";
        case FileExtension.Html:
            return ".html";
        case FileExtension.Rtf:
            return ".rtf";
        default:
            throw new ArgumentException();
        }
    }

    public static FileExtension GetFileExtension(string ext) {
        if (string.IsNullOrWhiteSpace(ext)) throw new ArgumentException("message", nameof(ext));
        ext = ext.Trim('.').ToLower();

        switch (ext) {
        case ".doc":
            return FileExtension.Doc;
        case ".html":
            return FileExtension.Html;
        case ".rtf":
            return FileExtension.Rtf;
        default:
            throw new ArgumentException();
        }
    }
}

[Route("api")][ApiController]
public class UploadDownloadController:
ControllerBase {
    private IHostingEnvironment _hostingEnvironment;

    public UploadDownloadController(IHostingEnvironment environment) {

        _hostingEnvironment = environment;
    }

    [HttpPost][Route("upload")]
    public async Task < IActionResult > Upload(IFormFile file) {
        string fileExtension = Path.GetExtension(file.FileName).Trim('.');

        if (file.Length > 0) {
            string dir = Folder.GetAllPath(Path.Combine(Folder.GetAllPath, fileExtension));
            string filePath = Path.Combine(dir, file.FileName);
            using(var fileStream = new FileStream(filePath, FileMode.Create)) {
                await file.CopyToAsync(fileStream);
            }
        }
        return Ok();
    }

    [HttpGet][Route("download")]
    public async Task < IActionResult > Download([FromQuery] string file) {
        string fileExtension = Path.GetExtension(file).Trim('.');
        string dir = Folder.GetAllPath(Path.Combine(Folder.GetAllPath, fileExtension));
        string filePath = Path.Combine(dir, file);
        if (!System.IO.File.Exists(filePath)) return NotFound();

        var memory = new MemoryStream();
        using(var stream = new FileStream(filePath, FileMode.Open)) {
            await stream.CopyToAsync(memory);
        }
        memory.Position = 0;
        return File(memory, GetContentType(filePath), file);
    }

    [HttpGet][Route("files")]
    public IActionResult Files() {
        var result = new List < string > ();

        if (Directory.Exists(Folder.GetAllPath("txt"))) {
            var files = Directory.GetFiles(Folder.GetAllPath("txt")).Select(fn = >Path.GetFileName(fn));
            result.AddRange(files);
        }
        return Ok(result);
    }

    private string GetContentType(string path) {
        var provider = new FileExtensionContentTypeProvider();
        string contentType;
        if (!provider.TryGetContentType(path, out contentType)) {
            contentType = "application/octet-stream";
        }
        return contentType;
    }
}

}

Answer 1

您的第一个问题是，您显示的代码是服务器端代码。这意味着您只能在文件（IFormFile）上载后检测文件类型。我假设您要在文件上传之前停止文件选择和文件上传。您将必须在客户端使用JavaScript或Angular等客户端框架进行此操作。

指针：在HTML DOM中定义文件输入时，您可以指定允许的扩展名。例如。 .txt，.csv您也可以将其扩展为mime类型。例如。图片/ jpg，图片/ gif。请注意，这并非万无一失，只能描述为尽力而为。仍然需要客户端验证。

<input type="file" accept=".txt, .csv" />
<input type="file" accept="image/jpg, image/gif">
<input type="file" accept=".txt, .csv, image/jpg, image/gif">

我需要丢弃不适合扩展名的文件

1 个答案: