Reading HTTP File AND Form data without writing to disk using Web API

Question

My question is similar to this one: webapi-file-uploading-without-writing-files-to-disk

However, this and most of the other similar questions stop at reading the file data. I have made that bit work fine, but I am also wanting to read the rest of the form data in the form which has other elements for the upload such as 'Title' etc. This comes from the solution in the aforementioned question:

            var filesToReadProvider = await Request.Content.ReadAsMultipartAsync();

The filesToReadProvider is a collection of HTTPContent objects, so I tried:

        List<HttpContent> uploadedstuff = filesToReadProvider.Contents.ToList();
        Image image = new Image(); ;        // The image object we will create
        Stream filestream;  // The file stream object to use with the image
        foreach (var thing in uploadedstuff)
        {
            try
            {
                string name = thing.Headers.ContentDisposition.Name.Replace("\"", ""); // String is quoted "\""namestring"\"" so need it stripped out
                List<NameValueHeaderValue> parameters = thing.Headers.ContentDisposition.Parameters.ToList();
                if (name == "file")
                {
                    image.LocalFileName = thing.Headers.ContentDisposition.FileName;
                    filestream = await thing.ReadAsStreamAsync();
                }
                if (name == "Title")
                {
                    // vvv- this line causes an exception.
                    NameValueCollection titleData = await thing.ReadAsFormDataAsync();
                }
            }
            catch (System.Exception e)
            {
                var message = "Something went wrong";
                HttpResponseMessage err = new HttpResponseMessage() { StatusCode = HttpStatusCode.ExpectationFailed, ReasonPhrase = message };
                return ResponseMessage(err);
            }
        }

Any ideas what I should be doing to get to eg: the 'Title' form data? I feel I am close, but may be taking the wrong approach? Many thanks.

Answer 1

Now that it is sorted out in the comments I shall post this answer to help others maybe.

form multipart content sends a data back to server like this"

---------------------------acebdf13572468
Content-Disposition: form-data; name="file"; 
Content-Type: image/*

<@INCLUDE *App.jpg*@>
---------------------------acebdf13572468
Content-Disposition: form-data; name="TextField";
Content-Type: application/octet-stream

Text Value
---------------------------acebdf13572468
Content-Disposition: form-data; name="JsonField";
Content-Type: application/json

{
"Json" : "Object"
}
---------------------------acebdf13572468--

Each part that is separated with the separator line (i.e. ---------------------------acebdf13572468) is a content of it's own, hence, multipart.

You can send data as json in one field as shown above or send text or anything. Usually browsers send each control in a single part of it's own. You can read this kind of data via ASP.Net model binder by specifying [FromForm] in controller arguments.

Or in this particular case you might read it with thing.ReadAsStreamAsync(); and thing.ReadAsStringAsync();

--Edit--

So the aforementioned method is useful when directly reading data or otherwise not MVC projects. If you are using MVC you can easily read the like this.

Let's imagine you have a model like

public class Model
{
    public string Title { get; set; }
}

then you would create a controller and action like this:

public class MainController : Controller
{
    [HttpPost]
    public async Task<IActionResult> UploadImage([FromForm]Model model)
    {
        var files = Request.Files;
        var title = model.Title
        //And you can save or use files and content at the same time.
    }
}

This is usually what you would do in an MVC scenario and if you use Razor or Pages in the client side you wouldn't even need to specify the [FromForm] attribute.

I hope this helps you.

Disclaimer. I have written all this in browser. May contain syntax and other errors.