How to post form-data IFormFile with HttpClient?

Question

I have backend endpoint Task<ActionResult> Post(IFormFile csvFile) and I need to call this endpoint from HttpClient. Currently I am getting Unsupported media type error. Here is my code:

var filePath = Path.Combine("IntegrationTests", "file.csv");
var gg = File.ReadAllBytes(filePath);
var byteArrayContent = new ByteArrayContent(gg);
var postResponse = await _client.PostAsync("offers", new MultipartFormDataContent
{
    {byteArrayContent }
});

Answer 1

You need to specify parameter name in MultipartFormDataContent collection matching action parameter name (csvFile) and a random file name

var multipartContent = new MultipartFormDataContent();
multipartContent.Add(byteArrayContent, "csvFile", "filename");
var postResponse = await _client.PostAsync("offers", multipartContent);

or equivalent

var postResponse = await _client.PostAsync("offers", new MultipartFormDataContent {
    { byteArrayContent, "csvFile", "filename" }
});

Answer 2

Use this snippet:

const string url = "https://localhost:5001/api/Upload";
const string filePath = @"C:\Path\To\File.png";

using (var httpClient = new HttpClient())
{
    using (var form = new MultipartFormDataContent())
    {
        using (var fs = File.OpenRead(filePath))
        {
            using (var streamContent = new StreamContent(fs))
            {
                using (var fileContent = new ByteArrayContent(await streamContent.ReadAsByteArrayAsync()))
                {
                    fileContent.Headers.ContentType = MediaTypeHeaderValue.Parse("multipart/form-data");

                    // "file" parameter name should be the same as the server side input parameter name
                    form.Add(fileContent, "file", Path.GetFileName(filePath));
                    HttpResponseMessage response = await httpClient.PostAsync(url, form);
                }
            }
        }
    }
}