ASP.NET WebApi file upload using guid and file extension

Question

I currently am able to save a file being uploaded to a WebAPI controller, but I'd like to be able to save the file as a guid with the correct file name extension so it can be viewed correctly.

Code:

 [ValidationFilter]
    public HttpResponseMessage UploadFile([FromUri]string AdditionalInformation)
    {
        var task = this.Request.Content.ReadAsStreamAsync();
        task.Wait();

        using (var requestStream = task.Result)
        {
            try
            {
                // how can I get the file extension of the content and append this to the file path below?

                using (var fileStream = File.Create(HttpContext.Current.Server.MapPath("~/" + Guid.NewGuid().ToString())))
                {
                    requestStream.CopyTo(fileStream);
                }
            }
            catch (IOException)
            {                    
                throw new HttpResponseException(HttpStatusCode.InternalServerError);
            }
        }

        HttpResponseMessage response = new HttpResponseMessage();
        response.StatusCode = HttpStatusCode.Created;
        return response;
    }

I can't seem to get a handle on the actual filename of the content. I thought headers.ContentDisposition.FileName might be a candidate but that doesn't seem to get populated.

Answer 1

Thanks for the comments above which pointed me in the right direction.

To clarify the final solution, I used a MultipartFormDataStreamProvider which streams the file automatically. The code is in another question I posted to a different problem here: MultipartFormDataStreamProvider and preserving current HttpContext

My full provider code is listed below. The key to generating the guid file name is to override the GetLocalFileName function and use the headers.ContentDisposition property. The provider handles the streaming of the content to file.

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

    public override Stream GetStream(HttpContent parent, HttpContentHeaders headers)
    {
        // restrict what images can be selected
        var extensions = new[] { "png", "gif", "jpg" };
        var filename = headers.ContentDisposition.FileName.Replace("\"", string.Empty);

        if (filename.IndexOf('.') < 0)
            return Stream.Null;

        var extension = filename.Split('.').Last();

        return extensions.Any(i => i.Equals(extension, StringComparison.InvariantCultureIgnoreCase))
                   ? base.GetStream(parent, headers)
                   : Stream.Null;

    }

    public override string GetLocalFileName(System.Net.Http.Headers.HttpContentHeaders headers)
    {
        // override the filename which is stored by the provider (by default is bodypart_x)
        string oldfileName = headers.ContentDisposition.FileName.Replace("\"", string.Empty);
        string newFileName = Guid.NewGuid().ToString() + Path.GetExtension(oldfileName);

        return newFileName;       
    }
}