A plugin refused the content. Send other content.

Plugins return or raise it for content that breaks the disk's rules, such as Fil.Plugin.Validation for a file that's too large or of a type the disk doesn't take. :reason says which rule, in the form the plugin documents. Raised while the content of a write is read (from a function given to Fil.Op.scan_content/4, say), it's the write's result, and nothing is written. Fil.Plug answers an upload that fails with it with a 413 for {:too_large, _}, a 415 for {:content_type, _}, {:content_type_mismatch, _, _} and {:extension, _}, and a 422 for anything else, without the reason.

iex> disk =
...>   Fil.disk(adapter: Fil.Adapter.Memory)
...>   |> Fil.attach(:no_html, fn op, next, _opts ->
...>     op
...>     |> Fil.Op.scan_content(nil, fn chunk, acc ->
...>       if chunk =~ "<script", do: raise(%Fil.InvalidContentError{reason: :html}), else: acc
...>     end)
...>     |> next.()
...>   end)
iex> {:error, error} = Fil.write(disk, "notes.txt", "<script>alert(1)</script>")
iex> Exception.message(error)
~s|could not write "notes.txt" on #Fil.Disk<memory>: the content was rejected (:html)|
iex> Fil.exists?(disk, "notes.txt")
false