Seperate store_filename from url_filename in definition

[coop]

The documentation states that it's possible to change the filename with the filename function:

It may be undesirable to retain original filenames (eg, it may contain personally identifiable information, vulgarity, vulnerabilities with Unicode characters, etc).

You may specify the destination filename for uploaded versions through your definition module.

For our use case we want to replace the uploaded filename with something randomly generated (not derived from the original filename). I have noticed that that the filename function is used to both generate new filenames and create publicly accessible urls... From what I can see this is problematic when the filename function contains data that is not derivable from the original filename. For example this is the implementation of our filename function:

defmodule MyDefinition do
  def filename(_version, {_file, _scope}) do
    now = DateTime.to_unix(DateTime.utc_now(), :millisecond)
    token = 16 |> :crypto.strong_rand_bytes() |> Base.url_encode64()

    "#{now}_#{token}"
  end
end

This correctly creates a filename with now + token but when I ask for the url I get something completely random because it invokes filename again.

Am I doing this correctly? Is there a different API I should be using? Have I misunderstood the documentation?

I am using ecto-arc so I know the correct filename - I am thinking of reimplementing this functionality by only calling filename when storing the image and passing through for url or separating store_filename vs url_filename.

It's possible that this functionality already exists and I'm just missing it somewhere.

Thanks

[achempion]

You can check if the scope already has the defined filename and use the old instead of generating new one.

[coop]

@achempion do you have an example of how to do that?