Add mix task for decrypting uploads

lib/mix/tasks/wiki/upload.ex

@@ -0,0 +1,23 @@
+defmodule Mix.Tasks.Wiki.Upload do
+  use Mix.Task
+  alias Wiki.{Repo, Accounts, Accounts.User, Content.Upload}
+
+  @shortdoc "Decrypts an upload into the given file"
+  def run(["decrypt", id, output_file]) do
+    email = IO.gets("Email: ") |> String.trim()
+    password = IO.gets("Password: ") |> String.trim()
+
+    Mix.Task.run("app.start")
+
+    user = Repo.get_by!(User, email: email)
+    upload = Repo.get!(Upload, String.to_integer(id)) |> Repo.preload(:page)
+
+    if upload.page.user_id != user.id do
+      raise "upload owner does not match provided user"
+    else
+      key = Accounts.generate_content_encryption_key(user, %{"password" => password})
+      key = Base.decode16!(key, case: :lower)
+      Upload.decrypt_to_file(upload, key, output_file)
+    end
+  end
+end

lib/wiki/content/upload.ex

@@ -80,7 +80,7 @@ defmodule Wiki.Content.Upload do
   end
 
   @spec upload_dir() :: String.t()
-  defp upload_dir() do
+  def upload_dir() do
     dir = Application.get_env(:wiki, :upload_dir)
 
     if is_nil(dir) do
@@ -98,6 +98,25 @@ defmodule Wiki.Content.Upload do
     :crypto.crypto_one_time(:aes_256_ctr, key, iv, encrypted_data, false)
   end
 
+  @spec decrypt_to_file(t(), binary(), String.t()) :: File.t()
+  def decrypt_to_file(upload, key, path) when is_binary(path) do
+    {:ok, output} = File.open(path, [:write, :binary])
+
+    :ok = decrypt_to_file(upload, key, output)
+
+    File.close(output)
+  end
+
+  @spec decrypt_to_file(t(), binary(), File.io_device()) :: File.t()
+  def decrypt_to_file(upload, key, output) do
+    decrypt_stream(upload, key)
+    |> Enum.each(fn data ->
+      IO.binwrite(output, data)
+    end)
+
+    :ok
+  end
+
   @spec decrypt_stream(t(), binary()) :: Enumerable.t()
   def decrypt_stream(%__MODULE__{relative_path: filename, encryption_iv: iv}, key) do
     start_fun = fn ->
@@ -125,7 +144,7 @@ defmodule Wiki.Content.Upload do
       end
     end
 
-    after_fun = fn {state, input_dev} ->
+    after_fun = fn {_state, input_dev} ->
       File.close(input_dev)
     end