Add known_types/0 function that lists all known types (#79)

lib/mime.ex

@@ -164,6 +164,22 @@ defmodule MIME do
     unquote(Macro.escape(custom_types))
   end
 
+  @doc """
+  Returns a mapping of all known types to their extensions,
+  including custom types compiled into the MIME module.
+  
+  ## Examples
+  
+      known_types()
+      #=> %{"application/json" => ["json"], ...}
+
+  """
+  @doc since: "2.1.0"
+  @spec known_types() :: %{required(String.t()) => [String.t()]}
+  def known_types do
+    unquote(Macro.escape(all_types))
+  end
+
   @doc """
   Returns the extensions associated with a given MIME type.
 

test/mime_test.exs

@@ -49,6 +49,19 @@ defmodule MIMETest do
     assert from_path("image.psd") == "image/vnd.adobe.photoshop"
   end
 
+  test "known_types/0" do
+    Application.put_env(:mime, :types, %{"application/dicom" => ["dcm"]})
+    recompile!()
+
+    assert is_map(known_types())
+
+    assert Map.has_key?(known_types(), "application/json")
+    assert Map.has_key?(known_types(), "application/dicom")
+
+    assert Map.get(known_types(), "application/json") == ["json"]
+    assert Map.get(known_types(), "application/dicom") == ["dcm"]
+  end
+
   test "types map is sorted" do
     quoted = Code.string_to_quoted!(File.read!("lib/mime.ex"))