This is a quick repo that demonstrates an issue that I'm having with file uploads to Stripe

Our servers do not have a read only file system so I cannot pass a file path to hackney, I can only pass in the contents of the file.

When doing so I receive an "invalid_request_error", with an "Invalid Hash" message

You can reproduce this issue by doing the following

  $: mix deps.get
  $: mix deps.compile
  $: iex -S mix

  $: {:ok, path} = File.cwd()
  $: secret_key = __REPLACE_WITH_STRIPE_SECRET_KEY__
  $: phoenix_img = "#{path}/assets/images/phoenix.png"
  $: {:ok, file} = File.read(phoenix_img)
  $: bad_body = [{"purpose", "dispute_evidence"}, {"file", file, [{"content-type", "image/png"}, {"filename", "phoenix.png"}]}]
  $: {:ok, fail_response} = Stripe.File.create(body, secret_key)

Everything else works if I follow the traditional method of just passing in a file path as described in the docs of hackney

  $: iex -S mix

  $: {:ok, path} = File.cwd()
  $: secret_key = __REPLACE_WITH_STRIPE_SECRET_KEY__
  $: phoenix_img = "#{path}/assets/images/phoenix.png"
  $: good_body = [{"purpose", "dispute_evidence"}, {:file, phoenix_img}]
  $: {:ok, response} = Stripe.File.create(body, secret_key)

Here is the relevant code for hackney's multipart handling

https://github.com/benoitc/hackney/blob/master/src/hackney_multipart.erl#L56

I am attempting to fake the form encoding that works via pattern matching on line 58 by duplicating the params and going through the path on line 100. The resulting value looks good to me but obviously fails when attempting to upload to stripe.

You can check the resulting encodings against one another by using the following function:

$: Stripe.File.body_to_utf8(bad_body)
$: Stripe.File.body_to_utf8(good_body)

Is there something that I'm missing? I think this should work but I could be missing a step.