How to post and receive a file with web api

Question

I have a Api Post method that I want to be able to accept any file type and that looks like this:

[HttpPost]
    public async Task<IHttpActionResult> Post()
    {
        if (!Request.Content.IsMimeMultipartContent())
        {
            throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);
        }

        var provider = new MultipartMemoryStreamProvider();
        await Request.Content.ReadAsMultipartAsync(provider);

        if (provider.Contents.Count != 1)
        {
            throw new HttpResponseException(Request.CreateResponse(HttpStatusCode.BadRequest,
                "You must include exactly one file per request."));
        }

        var file = provider.Contents[0];
        var filename = file.Headers.ContentDisposition.FileName.Trim('\"');
        var buffer = await file.ReadAsByteArrayAsync();
  }

This works in fiddler when I try to post an image to it. However, I'm writing a client library and I have a method that looks like this:

        public string PostAttachment(byte[] data, Uri endpoint, string contentType)
    {
        var request = (HttpWebRequest)WebRequest.Create(endpoint);
        request.Method = "POST";
        request.ContentType = contentType;
        request.ContentLength = data.Length;

        var stream = request.GetRequestStream();
        stream.Write(data, 0, data.Length);
        stream.Close();

        var response = (HttpWebResponse) request.GetResponse();
        using (var reader = new StreamReader(response.GetResponseStream()))
        {
           return reader.ReadToEnd();
        }            
    }

Whenever I try to post an image using this, I'm getting a UnsuportedMediaType error. I'm assuming it's because my image isn't Multi Part Content? Is there an easy way to make my request of the correct type?

If I have to change my web api post method, is there an easy way of doing that without writing files to the server and keeping it in memory?

Answer 1

The MultipartFormDataContent from the System.Net.Http namespace will allow you to post multipart form data.

private async Task<string> PostAttachment(byte[] data, Uri url, string contentType)
{
  HttpContent content = new ByteArrayContent(data);

  content.Headers.ContentType = new MediaTypeHeaderValue(contentType); 

  using (var form = new MultipartFormDataContent())
  {
    form.Add(content);

    using(var client = new HttpClient())
    {
      var response = await client.PostAsync(url, form);
      return await response.Content.ReadAsStringAsync();
    }
  }
}