Implement deleting an uploaded file

If we want to clean memory within a very long-lived process, we
currently have no way to do so. This attempts to offer a way to delete a
file earlier when we know it won't be needed anymore but it's process
owner will.

Author: NelsonVides

lib/plug/upload.ex

@@ -59,6 +59,19 @@ defmodule Plug.Upload do
     end
   end
 
+  @doc """
+  Deletes the given upload file.
+  """
+  @spec delete(t | binary) :: :ok | {:error, term}
+  def delete(%__MODULE__{path: path}), do: delete(path)
+
+  def delete(path) when is_binary(path) do
+    with :ok <- :file.delete(path, [:raw]) do
+      :ets.delete_object(@path_table, {self(), path})
+      :ok
+    end
+  end
+
   @doc """
   Assign ownership of the given upload file to another process.
 

test/plug/upload_test.exs

@@ -24,6 +24,13 @@ defmodule Plug.UploadTest do
     end
   end
 
+  test "removes the random file on request" do
+    {:ok, path} = Plug.Upload.random_file("sample")
+    File.open!(path)
+    :ok = Plug.Upload.delete(path)
+    wait_until(fn -> not File.exists?(path) end)
+  end
+
   defp wait_until(fun) do
     if fun.() do
       :ok