File Name from HttpRequestMessage Content - asp.net-mvc

Question

I implemented a POST Rest service to upload files to my server. the problem i have right now is that i want to restrict the uploaded files by its type. lets say for example i only want to allow .pdf files to be uploaded.
What I tried to do was
Task<Stream> task = this.Request.Content.ReadAsStreamAsync();
task.Wait();
FileStream requestStream = (FileStream)task.Result;
but unfortunately its not possible to cast the Stream to a FileStream and access the type via requestStream.Name.
is there an easy way (except writing the stream to the disk and check then the type) to get the filetype?

Answer 1

If you upload file to Web API and you want to get access to file data (Content-Disposition) you should upload the file as MIME multipart (multipart/form-data).
Here I showed some examples on how to upload from HTML form, Javascript and from .NET.
You can then do something like this, this example checks for pdf/doc files only:
public async Task<HttpResponseMessage> Post()
{
if (!Request.Content.IsMimeMultipartContent())
{
throw new HttpResponseException(Request.CreateResponse(HttpStatusCode.NotAcceptable,
"This request is not properly formatted - not multipart."));
}
var provider = new RestrictiveMultipartMemoryStreamProvider();
//READ CONTENTS OF REQUEST TO MEMORY WITHOUT FLUSHING TO DISK
await Request.Content.ReadAsMultipartAsync(provider);
foreach (HttpContent ctnt in provider.Contents)
{
//now read individual part into STREAM
var stream = await ctnt.ReadAsStreamAsync();
if (stream.Length != 0)
{
using (var ms = new MemoryStream())
{
//do something with the file memorystream
}
}
}
return Request.CreateResponse(HttpStatusCode.OK);
}
}
public class RestrictiveMultipartMemoryStreamProvider : MultipartMemoryStreamProvider
{
public override Stream GetStream(HttpContent parent, HttpContentHeaders headers)
{
var extensions = new[] {"pdf", "doc"};
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;
}
}