Ignore params and detect subtype suffix in extensions/1 (#45)

* Ignore media type params

* Detect subtype suffix in extensions/1

See: https://tools.ietf.org/html/rfc6838#section-4.2.8

lib/mime/application.ex

@@ -96,13 +96,28 @@ defmodule MIME.Application do
           iex> MIME.extensions("application/json")
           ["json"]
 
+          iex> MIME.extensions("application/vnd.custom+xml")
+          ["xml"]
+
           iex> MIME.extensions("foo/bar")
           []
 
       """
       @spec extensions(String.t()) :: [String.t()]
       def extensions(type) do
-        mime_to_ext(downcase(type, "")) || []
+        mime =
+          type
+          |> strip_params()
+          |> downcase("")
+
+        mime_to_ext(mime) || suffix(mime) || []
+      end
+
+      defp suffix(type) do
+        case String.split(type, "+") do
+          [type_subtype_without_suffix, suffix] -> [suffix]
+          _ -> nil
+        end
       end
 
       @default_type "application/octet-stream"
@@ -161,6 +176,10 @@ defmodule MIME.Application do
         end
       end
 
+      defp strip_params(string) do
+        string |> :binary.split(";") |> hd()
+      end
+
       defp downcase(<<h, t::binary>>, acc) when h in ?A..?Z,
         do: downcase(t, <<acc::binary, h + 32>>)
 

test/mime_test.exs

@@ -10,10 +10,15 @@ defmodule MIMETest do
   end
 
   test "extensions/1" do
-    assert "json" in extensions("application/json")
+    assert extensions("application/json") == ["json"]
     assert extensions("application/vnd.api+json") == ["json-api"]
     assert extensions("audio/amr") == ["amr"]
     assert extensions("IMAGE/PNG") == ["png"]
+
+    assert extensions("application/json; charset=utf-8") == ["json"]
+
+    assert extensions("application/vnd.custom+xml") == ["xml"]
+    assert extensions("application/vnd.custom+xml+xml") == []
   end
 
   test "type/1" do