Check file extension before uploading file in asp.net web api

asp.net, asp.net-web-api, c#

Solution

I don't know how to check file extension as I can't override method GetStream

And why is that? Nothing stops you from overriding `GetStream`

For example:

public class ImageOnlyMultipartMemoryStreamProvider : MultipartMemoryStreamProvider
{
    public override Stream GetStream(HttpContent parent, HttpContentHeaders headers)
    {

         var fileExtension = CommonUtils.GetFileExtension(headers.ContentDisposition.FileName);

         return _allowedExtensions == null || _allowedExtensions.Any(i => i.Equals(fileExtension , StringComparison.InvariantCultureIgnoreCase)) ? base.GetStream(parent, headers) : Stream.Null;
    }
}

Problem

Here is my task: I need to upload immages to a server using Asp.Net web api. I need to check file's extension before uploading it (I want to allow uploading only immages). I need to get the file as a Stream or Base64String as I want to resize it before saving to server. Here is what I've tried. I am able to upload file to server, using `MultipartFormDataStreamProvider`, and after I've inhereted my `CustomMultipartFormDataStreamProvider` from that `MultipartFormDataStreamProvider`, I was able to check file-extension in the GetStream method like: ``` public override Stream GetStream(HttpContent parent, System.Net.Http.Headers.HttpContentHeaders headers) { if (!String.IsNullOrEmpty(headers.ContentDisposition.FileName)) { var fileExtension = CommonUtils.GetFileExtension(headers.ContentDisposition.FileName); if (_allowedExtensions != null && !_allowedExtensions.Contains(fileExtension.ToLower())) { return Stream.Null; } } return base.GetStream(parent, headers); } ``` But `MultipartFormDataStreamProvider` saves file to the specified folder and not returning a Stream, and if I want to resize it, I need to read it from the HDD, resize, save as new file and delete the old one. The other variant is to use `MultipartMemoryStreamProvider` - here I can get a Stream: ``` var task = Request.Content.ReadAsMultipartAsync<MultipartMemoryStreamProvider>(new MultipartMemoryStreamProvider()) .ContinueWith<HttpResponseMessage>((tsk) => { MultipartMemoryStreamProvider provider = tsk.Result; Stream stream = provider.Contents[0].ReadAsStreamAsync().Result; String imageBase64 = Convert.ToBase64String(CommonUtils.StreamToByteArray(stream)); ...... } ``` But with `MultipartMemoryStreamProvider` I don't know how to check file extension as I can't override method GetStream Is there a way to both check file extension before uploading file and get a file as a Stream instead of saving it to the disc. Or the only way is to `save->resize->save new->delete` old?

Original source