Estou tentando fazer upload de vários arquivos usandoSystem.Net.Http.HttpClient.

using (var content = new MultipartFormDataContent())
{
   content.Add(new StreamContent(imageStream), "image", "image.jpg");
   content.Add(new StreamContent(signatureStream), "signature", "image.jpg.sig");

   var response = await httpClient.PostAsync(_profileImageUploadUri, content);
   response.EnsureSuccessStatusCode();
}

isso envia somente mulipart / form-data, mas eu esperava multipart / mixed em algum lugar no post.

UPDATE: Ok, eu tenho por perto.

using (var content = new MultipartFormDataContent())
{
    var mixed = new MultipartContent("mixed")
    {
        CreateFileContent(imageStream, "image.jpg", "image/jpeg"),
        CreateFileContent(signatureStream, "image.jpg.sig", "application/octet-stream")
    };

    content.Add(mixed, "files");

    var response = await httpClient.PostAsync(_profileImageUploadUri, content);
    response.EnsureSuccessStatusCode();
}

private StreamContent CreateFileContent(Stream stream, string fileName, string contentType)
{
    var fileContent = new StreamContent(stream);
    fileContent.Headers.ContentDisposition = new ContentDispositionHeaderValue("file") {FileName = fileName};
    fileContent.Headers.ContentType = new MediaTypeHeaderValue(contentType);
    return fileContent;
}

Isso parece correto no tubarão. mas eu não vejo os arquivos no meu controlador.

[HttpPost]
public ActionResult UploadProfileImage(IEnumerable<HttpPostedFileBase> postedFiles)
{
    if(postedFiles == null)
        return new HttpStatusCodeResult(HttpStatusCode.BadRequest);

    // more code here
}

postedFiles ainda é nulo. Alguma ideia?