How to send a file and form data with HttpClient in C#

Question

How can I send a file and form data with the HttpClient?

I have two ways to send a file or form data. But I want to send both like an HTML form. How can

Answer 1

Here's code I'm using to post form information and a csv file

using (var httpClient = new HttpClient())
{
    var surveyBytes = ConvertToByteArray(surveyResponse);

    httpClient.DefaultRequestHeaders.Add("X-API-TOKEN", _apiToken);
    httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

    var byteArrayContent =   new ByteArrayContent(surveyBytes);
    byteArrayContent.Headers.ContentType = MediaTypeHeaderValue.Parse("text/csv");

    var response = await httpClient.PostAsync(_importUrl, new MultipartFormDataContent
    {
        {new StringContent(surveyId), "\"surveyId\""},
        {byteArrayContent, "\"file\"", "\"feedback.csv\""}
    });

    return response;
}

This is for .net 4.5.

Note the \" in the MultipartFormDataContent. There is a bug in MultipartFormDataContent.

In 4.5.1 MultipartFormDataContent wraps the data with the correct quotes.

Update: This link to the bug no longer works since the have retired Microsoft Connect.