WebAPI cannot parse multipart/form-data post

[Origin]: http://education-eco.blogspot.ca/2014/01/webapi-cannot-parse-multipartform-data.html

I’m trying to accept a post from a client (iOS app) and my code keeps failing on reading the stream. Says the message is not complete. I’ve been trying to get this working for hours it seems like something is wrong in my message format or something. All I’m trying to do is read a string but the developer I’m working with who is doing the iOS part only knows how to send multipart/form-data not content-type json.

Here is exact error: Unexpected end of MIME multipart stream. MIME multipart message is not complete.”

It fails here: await Request.Content.ReadAsMultipartAsync(provider);

Headers:

POST http://localhost:8603/api/login HTTP/1.1
Host: localhost:8603
Accept-Encoding: gzip,deflate
Content-Type: multipart/form-data; boundary=------------nx-oauth216807
Content-Length: 364
Accept-Language: en-us
Accept: */*
Connection: keep-alive

Body:

--------------nx-oauth216807
Content-Disposition: form-data; name="token"

CAAH5su8bZC1IBAC3Qk4aztKzisZCd2Muc3no4BqVUycnZAFSKuleRU7V9uZCbc8DZCedYQTIFKwJbVZCANJCs4ZCZA654PgA22Nei9KiIMLsGbZBaNQugouuLNafNqIOTs9wDvD61ZA6WSTd73AVtFp9tQ1PmFGz601apUGHSimYZCjLfGBo40EBQ5z6eSMNiFeSylym1pK4PCvI17fXCmOcRix4cs96EBl8ZA1opGKVuWizOsS0WZCMiVGvT
--------------nx-oauth216807

Here is the WebAPI code:

    public async Task<HttpResponseMessage> PostFormData()
    {
        // Check if the request contains multipart/form-data.
        if (!Request.Content.IsMimeMultipartContent())
        {
            throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);
        }
        try
        {
        string root = HttpContext.Current.Server.MapPath("~/App_Data");
        var provider = new MultipartFormDataStreamProvider(root);

        // Read the form data and return an async task.
        await Request.Content.ReadAsMultipartAsync(provider);

        // This illustrates how to get the file names.
        foreach (MultipartFileData file in provider.FileData)
        {
            Trace.WriteLine(file.Headers.ContentDisposition.FileName);
            Trace.WriteLine("Server file path: " + file.LocalFileName);
        }
        return Request.CreateResponse(HttpStatusCode.OK);

        }
        catch (System.Exception e)
        {
            return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, e);
        }
    }

A \r\n needs to be appended at the end of request content stream.

Instead of using this line to read the data: await Request.Content.ReadAsMultipartAsync(provider);

You will need to:
1. load the request stream to memory
2. append the \r\n string that is required
3. create a stream content from the memory content
4. manually add the request headers to the stream content
5. Finally use this instead: streamContent.ReadAsMultipartAsync(provider);

Check the answer of Landuber Kassa here for the complete code: http://stackoverflow.com/questions/13770536/asp-net-web-api-unexpected-end-of-mime-multi-part-stream-when-uploading-from-fl/17290999#comment42617381_17290999

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