c# - ReadAsMultipartAsync 和 MultiPartFormDataStreamProvider 出错

Question

我正在尝试将文件异步上传到我的网络服务器 (ASP.NET MVC)。专门针对我的 web api 端点。我遵循了几个教程，但我不断收到空参数错误。

当我继承 MultipartFormDataStreamProvider 时会发生这种情况。 GetLocalFileName 方法首先使用正确的 HttpContentHeaders 正确调用，但随后使用 null header 进行第二次调用。

文件以我设置的文件名成功保存，但出现异常时，我无法知道生成的文件名是什么。

但是，如果我只使用基础 MultipartFormDataStreamProvider 类，文件会完美保存，没有错误，但在这种情况下我无法控制文件名。

这是 api 方法:

[HttpPost]
    public async Task<FilesUploadResult> Save()
    {
        // Check if the request contains multipart/form-data.
        if (!Request.Content.IsMimeMultipartContent())
        {
            var ret = new FilesUploadResult(HttpStatusCode.UnsupportedMediaType, null);
            ret.Message = "Unsupported Media Type. Request must contain multipart/form-data form.";
            return ret;
        }

        var path = UploadsFolderPath;

        // to-do: this works but for some reason makes a call with empty headers.
        var provider = new SimpleMultipartFormDataStreamProvider(path);

        // this provider saves the file with an arbritrary name
        //var provider = new MultipartFormDataStreamProvider(path);

        try
        {
            // Read the form data.
            await Request.Content.ReadAsMultipartAsync(provider as MultipartFormDataStreamProvider);

            var files = from f in provider.FileData
                        let info = new FileInfo(f.LocalFileName)
                        select new FileUploadDescription(info.Name, path + "\\" + info.Name, info.Length, HttpStatusCode.Created);

            var ret = new FilesUploadResult(HttpStatusCode.OK, files);
            return ret;
        }
        catch (Exception ex)
        {
            var ret = new FilesUploadResult(HttpStatusCode.InternalServerError, null);
            ret.Message = ex.Message;
            return ret;
        }
    }

这是我的 SimpleMultipartFormDataStreamProvider 的代码:

public class SimpleMultipartFormDataStreamProvider : MultipartFormDataStreamProvider
{
    public SimpleMultipartFormDataStreamProvider(string path) : base(path) { }

    public override string GetLocalFileName(HttpContentHeaders headers)
    {

        // make sure the headers are valid
        if (headers == null)
        {

            throw new ArgumentNullException("headers");
        }

        // filename
        var filename = CleanString(headers.ContentDisposition.FileName); ;

        // create the local file name
        var localFileName = string.Format("_{0}_{1}", GetRandomName(), filename);

        //this is here because Chrome submits files in quotation marks which get treated as part of the filename and get escaped
        return localFileName.Replace("\"", string.Empty);
    }

    private string GetRandomName()
    {
        return GuidHelper.ShortUniqueId(16);
    }

    private static string CleanString(string str)
    {
        if (string.IsNullOrWhiteSpace(str))
            return string.Empty;

        var sb = new StringBuilder();
        foreach (char c in str)
        {
            if ((c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || c == '.' || c == '_')
            {
                sb.Append(c);
            }
        }
        return sb.ToString();
    }
}

谁能告诉我为什么 GetLocalFileName 被调用了两次，而第二次调用时 header 为空？

Answer 1

即使我在 MVC4 中遇到过这种行为，它也提交了 2 个文件，其中一个是空的，所以最好检查文件是否有任何内容，然后继续保存文件。 可以有多种方法: 其中之一是从 Request.Files 中获取所有文件的列表(这是一个字符串数组)

      foreach (string fileName in Request.Files)
            {
                HttpPostedFileBase file = Request.Files[fileName];
                //Save file content goes here
                if (file != null && file.ContentLength > 0)
                 {
                     //logic to save the content
                 }
             }