public Task<HttpResponseMessage> PostFormData()
{
// Check if the request contains multipart/form-data.
if (!Request.Content.IsMimeMultipartContent())
{
throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);
}

string root = HttpContext.Current.Server.MapPath("~/App_Data");
var provider = new MultipartFormDataStreamProvider(root);

// Read the form data and return an async task.
var task = Request.Content.ReadAsMultipartAsync(provider).
ContinueWith<HttpResponseMessage>(t =>
{
if (t.IsFaulted || t.IsCanceled)
{
Request.CreateErrorResponse(HttpStatusCode.InternalServerError, t.Exception);
}

// 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);
});

return task;
}
Reading Form Control Data

The HTML form that I showed earlier had a text input control.

<div>
<label for="caption">Image Caption</label>
<input name="caption" type="text" />
</div>
You can get the value of the control from the FormData property of the MultipartFormDataStreamProvider.

public async Task<HttpResponseMessage> PostFormData()
{
if (!Request.Content.IsMimeMultipartContent())
{
throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);
}

string root = HttpContext.Current.Server.MapPath("~/App_Data");
var provider = new MultipartFormDataStreamProvider(root);

try
{
await Request.Content.ReadAsMultipartAsync(provider);

// Show all the key-value pairs.
foreach (var key in provider.FormData.AllKeys)
{
foreach (var val in provider.FormData.GetValues(key))
{
Trace.WriteLine(string.Format("{0}: {1}", key, val));
}
}

return Request.CreateResponse(HttpStatusCode.OK);
}
catch (System.Exception e)
{
return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, e);
}
}
FormData is a NameValueCollection that contains name/value pairs for the form controls. The collection can contain duplicate keys. Consider this form:

<form name="trip_search" method="post" enctype="multipart/form-data" action="/www.asp.net/web-api/overview/working-with-http/api/upload">
<div>
<input type="radio" name="trip" value="round-trip"/>
Round-Trip
</div>
<div>
<input type="radio" name="trip" value="one-way"/>
One-Way
</div>

<div>
<input type="checkbox" name="options" value="nonstop" />
Only show non-stop flights
</div>
<div>
<input type="checkbox" name="options" value="airports" />
Compare nearby airports
</div>
<div>
<input type="checkbox" name="options" value="dates" />
My travel dates are flexible
</div>

<div>
<label for="seat">Seating Preference</label>
<select name="seat">
<option value="aisle">Aisle</option>
<option value="window">Window</option>
<option value="center">Center</option>
<option value="none">No Preference</option>
</select>
</div>
</form>