WebAPI cannot parse multipart/form-data post

Question

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);
        }
    }

Answer 1

My application was experiencing this error periodically too. Upgrading to WEB API 2.1 did nothing and the exception message is completely useless.

I think what was actually happening though is it was choking on large files. Increasing my max request limits in web.config seemed to fix it right up.

<system.web>
    <httpRuntime maxRequestLength="30000" />
</system.web>

<system.webServer>
    <security>
      <requestFiltering>
        <requestLimits maxAllowedContentLength="30000" />
      </requestFiltering>
    </security>
</system.webServer>

(This sets the ceiling to 30 megs. Set it to whatever you need. More info here)

Answer 2

I encountered this error too. The InnerException is Cannot access a disposed object. This means that something is reading your stream before your call to ReadAsMultipartAsync.
Somewhere before this call Request.Content.ReadAsMultipartAsync(provider), you can call Request.Content.LoadIntoBufferAsync().Wait(), which will load this tream into a buffer and allow you to read it more than once.
This is not an optimal solution, but it works.

Answer 3

I am leaving this here since it took me quite some time trying other workarounds until I bumped onto the following helpful answer and some people having this issue may end up on this post.

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: ASP.NET Web API, unexpected end of MIME multi-part stream when uploading from Flex FileReference

Answer 4

Just a modification for Shaw Levin answer in case anyone wants to use it.

boundary = value.Substring(0, value.IndexOf("\r\n")); will find the first occurance of the CRLF, you should change it to boundary = value.Substring(0, value.LastIndexOf("\r\n")); so it looks for the last occurance. Otherwise if the content includes a CRLF somewhere in the middle you will lose part of the data in the request.

Answer 5

There were similar error posts, for some, the solution worked is: to mention Id="", name="" attribute to file upload html control, thanks to WebAPI upload error. Expected end of MIME multipart stream. MIME multipart message is not complete

But in my case, it did not resolve with above simple tweak :(

Answer 6

I would not recommend this answer - hopefully there is a better way available now.

Someone asked so here is my custom parser which has been working fine:

Boundary comes from here:

        string value;
        using (var reader = new StreamReader(tempStream, Encoding.UTF8))
        {
            value = reader.ReadToEnd();
            // Do something with the value
        }

        boundary = value.Substring(0, value.IndexOf("\r\n"));

And then we parse the content of the request here:

   public Dictionary<string, BodyContent> ParseContent(string content)
    {
        string[] list = content.Split(new string[] { boundary }, StringSplitOptions.RemoveEmptyEntries);
        string name="", val="";
        Dictionary<string, BodyContent> temp = new Dictionary<string, BodyContent>();
        foreach (String s in list)
        {
            if (s == "--" || s == "--\r\n")
            {
                //Do nothing.
            }
            else
            {
                string[] token = s.Split(new string[] { "\r\n" }, StringSplitOptions.RemoveEmptyEntries);
                val = "";
                name = "";
                foreach (string x in token)
                {

                    if(x.StartsWith("Content-Disposition"))
                    {
                        //Name
                        name = x.Substring(x.IndexOf("name=")+5, x.Length - x.IndexOf("name=")-5);
                        name = name.Replace(@"\","");
                        name = name.Replace("\"","");
                    }
                    if (x.StartsWith("--"))
                    {
                        break;
                    }
                    if (!x.StartsWith("--") && !x.StartsWith("Content-Disposition"))
                    {
                        val = x;
                    }

                }
                if (name.Length > 0)
                {
                    BodyContent b = new BodyContent();
                    b.content = name;
                    if (val.Length == 0)
                    {
                        b.value = "";
                    }
                    else
                    {
                        b.value = val;
                    }
                    temp.Add(name, b);
                }
            }

        }
        return temp;        
    }