Implement Xgit.Util.ParseCharlist.decode_ambiguous_charlist/1. (#196)

* Implement Xgit.Util.ParseCharlist.decode_ambiguous_charlist/1.

* Replace uses of RawParseUtils.decode/1 with ParseCharlist.decode_ambiguous_charlist/1.

* A few small fixes.

lib/xgit/core/object.ex

@@ -58,6 +58,7 @@ defmodule Xgit.Core.Object do
   alias Xgit.Core.FileMode
   alias Xgit.Core.FilePath
   alias Xgit.Core.ObjectId
+  alias Xgit.Util.ParseCharlist
   alias Xgit.Util.ParseDecimal
   alias Xgit.Util.RawParseUtils
 
@@ -424,7 +425,7 @@ defmodule Xgit.Core.Object do
 
   defp normalize(name, true = _mac?) when is_list(name) do
     name
-    |> RawParseUtils.decode()
+    |> ParseCharlist.decode_ambiguous_charlist()
     |> String.downcase()
     |> :unicode.characters_to_nfc_binary()
   end

lib/xgit/core/person_ident.ex

@@ -51,6 +51,7 @@ defmodule Xgit.Core.PersonIdent do
   A combination of a person identity and time in git.
   """
 
+  alias Xgit.Util.ParseCharlist
   alias Xgit.Util.ParseDecimal
   alias Xgit.Util.RawParseUtils
 
@@ -104,8 +105,8 @@ defmodule Xgit.Core.PersonIdent do
          name <- parse_name(b),
          {time, tz} <- parse_tz(email_start) do
       %__MODULE__{
-        name: RawParseUtils.decode(name),
-        email: RawParseUtils.decode(email),
+        name: ParseCharlist.decode_ambiguous_charlist(name),
+        email: ParseCharlist.decode_ambiguous_charlist(email),
         when: time,
         tz_offset: tz
       }

lib/xgit/util/parse_charlist.ex

@@ -0,0 +1,20 @@
+defmodule Xgit.Util.ParseCharlist do
+  @moduledoc false
+  # Internal utility for parsing charlists with ambiguous encodings.
+
+  import Xgit.Util.ForceCoverage
+
+  @doc ~S"""
+  Convert a list of bytes to an Elixir (UTF-8) string when the encoding is not
+  definitively known. Try parsing as a UTF-8 byte array first, then try ISO-8859-1.
+  """
+  @spec decode_ambiguous_charlist(b :: [byte]) :: String.t()
+  def decode_ambiguous_charlist(b) when is_list(b) do
+    raw = :erlang.list_to_binary(b)
+
+    case :unicode.characters_to_binary(raw) do
+      utf8 when is_binary(utf8) -> cover(utf8)
+      _ -> :unicode.characters_to_binary(raw, :latin1)
+    end
+  end
+end

test/xgit/util/parse_charlist_test.exs

@@ -0,0 +1,13 @@
+defmodule Xgit.Util.ParseCharlistTest do
+  use ExUnit.Case, async: true
+
+  alias Xgit.Util.ParseCharlist
+
+  test "decode/1" do
+    assert ParseCharlist.decode_ambiguous_charlist([64, 65, 66]) == "@AB"
+    assert ParseCharlist.decode_ambiguous_charlist([228, 105, 116, 105]) == "äiti"
+    assert ParseCharlist.decode_ambiguous_charlist([195, 164, 105, 116, 105]) == "äiti"
+    assert ParseCharlist.decode_ambiguous_charlist([66, 106, 246, 114, 110]) == "Björn"
+    assert ParseCharlist.decode_ambiguous_charlist([66, 106, 195, 182, 114, 110]) == "Björn"
+  end
+end