Resolving 'Malformed FormData Request' errors in C#

Created by Kesh Bhamidipaty, Modified on Thu, 13 Jun at 11:50 PM by Kesh Bhamidipaty

This article outlines likely causes for 'Malformed FormData Request' errors when using the Stability API in C#, and gives example approaches for resolving them.

Symptoms

The following shows the relevant bit of the HTTP response seen when making a request to a Stability API endpoint in C#:

{"success":false,"message":"Malformed FormData request. Content-Disposition header in FormData part is missing a name."}

Possible Root Cause & Solution

C# may not quote the Content-Disposition header by default. In this case, the following helper functions can be used as a workaround:

private static StringContent stringFormField(string name, string value) {
  var formField = new StringContent(value);
  formField.Headers.ContentDisposition = new ContentDispositionHeaderValue("form-data")
  {
    Name = $"\"{name}\""
  };
  return formField;
}

private static async Task<ByteArrayContent> imageFormField(string name, string imagePath, string mimeType) {
  var filename = Path.GetFileName(imagePath);
  var imageBytes = await File.ReadAllBytesAsync(imagePath);
  var formField = new ByteArrayContent(imageBytes);
  formField.Headers.ContentType = new MediaTypeHeaderValue(mimeType);
  formField.Headers.ContentDisposition = new ContentDispositionHeaderValue("form-data")
  {
    Name = $"\"{name}\"",
    FileName = $"\"{filename}\""
  };
  return formField;
}

Which can be used like so:

using var formData = new MultipartFormDataContent
{
    stringFormField("prompt", "large nebula full for stars both near and far"),
    stringFormField("right", "500"),
    await imageFormField("image", imagePath, "image/png")
};