MultiPartFormData Streaming

DisableFormValueModelBindingAttribute.cs

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
public class DisableFormValueModelBindingAttribute : Attribute, IResourceFilter
{
    public void OnResourceExecuting(ResourceExecutingContext context)
    {
        var factories = context.ValueProviderFactories;
        factories.RemoveType<FormValueProviderFactory>();
        factories.RemoveType<JQueryFormValueProviderFactory>();
    }

    public void OnResourceExecuted(ResourceExecutedContext context)
    {
    }
}

MultipartRequestHelper.cs

public static class MultipartRequestHelper
  {
      // Content-Type: multipart/form-data; boundary="----WebKitFormBoundarymx2fSWqWSd0OxQqq"
      // The spec says 70 characters is a reasonable limit.
      public static string GetBoundary(MediaTypeHeaderValue contentType, int lengthLimit)
      {
          var boundary = HeaderUtilities.RemoveQuotes(contentType.Boundary).ToString();

          if (string.IsNullOrWhiteSpace(boundary))
          {
              throw new InvalidDataException("Missing content-type boundary.");
          }

          if (boundary.Length > lengthLimit)
          {
              throw new InvalidDataException(
                  $"Multipart boundary length limit {lengthLimit} exceeded.");
          }

          return boundary;
      }

      public static bool IsMultipartContentType(string contentType)
      {
          return !string.IsNullOrEmpty(contentType)
                 && contentType.IndexOf("multipart/", StringComparison.OrdinalIgnoreCase) >= 0;
      }

      public static bool HasFormDataContentDisposition(ContentDispositionHeaderValue contentDisposition)
      {
          // Content-Disposition: form-data; name="key";
          return contentDisposition != null
                 && contentDisposition.DispositionType.Equals("form-data")
                 && string.IsNullOrEmpty(contentDisposition.FileName.Value)
                 && string.IsNullOrEmpty(contentDisposition.FileNameStar.Value);
      }

      public static bool HasFileContentDisposition(ContentDispositionHeaderValue contentDisposition)
      {
          // Content-Disposition: form-data; name="myfile1"; filename="Misc 002.jpg"
          return contentDisposition != null
                 && contentDisposition.DispositionType.Equals("form-data")
                 && (!string.IsNullOrEmpty(contentDisposition.FileName.Value)
                     || !string.IsNullOrEmpty(contentDisposition.FileNameStar.Value));
      }

      public static Encoding GetEncoding(MultipartSection section)
      {
          var hasMediaTypeHeader = MediaTypeHeaderValue.TryParse(section.ContentType, out var mediaType);
          // UTF-7 is insecure and should not be honored. UTF-8 will succeed in 
          // most cases.
          if (!hasMediaTypeHeader || Encoding.UTF7.Equals(mediaType.Encoding))
          {
              return Encoding.UTF8;
          }

          return mediaType.Encoding;
      }
  }

MultiStreamSample.cs

var boundary = MultipartRequestHelper.GetBoundary(
                    MediaTypeHeaderValue.Parse(Request.ContentType),
                    DefaultFormOptions.MultipartBoundaryLengthLimit);
var reader = new MultipartReader(boundary, HttpContext.Request.Body);

var section = await reader.ReadNextSectionAsync(cancellationToken);

while (section != null)
{
    var hasContentDispositionHeader =
        ContentDispositionHeaderValue.TryParse(section.ContentDisposition, out var contentDisposition);

    if (hasContentDispositionHeader)
    {
        if (MultipartRequestHelper.HasFileContentDisposition(contentDisposition))
        {
            // await section.Body.CopyToAsync(storageStream, cancellationToken);
        }
        else if (MultipartRequestHelper.HasFormDataContentDisposition(contentDisposition))
        {
            var key = HeaderUtilities.RemoveQuotes(contentDisposition.Name);
            var encoding = MultipartRequestHelper.GetEncoding(section);

            using (var streamReader = new StreamReader(section.Body, encoding, true, 1024, true))
            {
                var value = await streamReader.ReadToEndAsync();

                form.Add(key.Value, value);
            }
        }
    }

    section = await reader.ReadNextSectionAsync(cancellationToken);
}