Issue #82 (#83)

* Erlang/Elixir nil/null issue addressed similar to jiffy use_nil approach.

* README updated.

* use_nil additionality implemented for unpack method.

README.md

@@ -88,6 +88,10 @@ bin         binary()     binary()
 str         binary()     string()
 ```
 
+### `{use_nil, boolean()}`
+
+Handles Elixir `nil` as `null` Erlang atom. Default value is `false`.
+
 ### `{validate_string, boolean()}`
 
 Only in unpacking, UTF-8 validation at unpacking from `str` type will

src/msgpack.erl

@@ -53,6 +53,7 @@
          {allow_atom, none|pack} |
          {known_atoms, [atom()]} |
          {unpack_str, as_binary|as_list|as_tagged_list} |
+         {use_nil, boolean()} |
          {validate_string, boolean()} |
          {pack_str, from_binary|from_list|from_tagged_list|none} |
          {map_format, map|jiffy|jsx} |
@@ -171,6 +172,9 @@ parse_options([{known_atoms, Atoms}|T], Opt0) when is_list(Atoms) ->
 parse_options([{unpack_str, As}|T], Opt0) when As =:= as_binary orelse As =:= as_list orelse As =:= as_tagged_list ->
     parse_options(T, Opt0?OPTION{unpack_str=As});
 
+parse_options([{use_nil, Bool}|T], Opt) when is_boolean(Bool) ->
+    parse_options(T, Opt?OPTION{use_nil=Bool});
+
 parse_options([{validate_string, Bool}|T], Opt) when is_boolean(Bool) ->
     parse_options(T, Opt?OPTION{validate_string=Bool});
 

src/msgpack.hrl

@@ -38,6 +38,7 @@
           allow_atom = pack  :: none | pack, %% allows atom when packing
           known_atoms = [] :: [atom()|binary()],
           unpack_str = as_list :: as_binary | as_list | as_tagged_list,
+          use_nil = false :: boolean(),
           validate_string = false :: boolean(),
           pack_str = from_list :: from_binary | from_list | from_tagged_list | none,
           map_format = ?DEFAULT_MAP_FORMAT :: format_type(),

src/msgpack_packer.erl

@@ -33,6 +33,8 @@ pack(F, _) when is_float(F) ->
     pack_double(F);
 pack(null, _Opt) ->
     << 16#C0:8 >>;
+pack(nil, ?OPTION{use_nil = true}) ->
+    << 16#C0:8 >>;
 pack(false, _) ->
     << 16#C2:8 >>;
 pack(true, _) ->

src/msgpack_unpacker.erl

@@ -29,6 +29,8 @@
 %% unpack them all
 -spec unpack_stream(Bin::binary(), ?OPTION{}) -> {msgpack:object(), binary()} | {error, any()} | no_return().
 %% ATOMS
+unpack_stream(<<16#C0, Rest/binary>>, ?OPTION{use_nil = true}) ->
+    {nil, Rest};
 unpack_stream(<<16#C0, Rest/binary>>, _) ->
     {null, Rest};
 unpack_stream(<<16#C2, Rest/binary>>, _) ->

test/msgpack_tests.erl

@@ -646,6 +646,27 @@ unpack_str_validation_test_() ->
                                     [{spec,new},{unpack_str,from_list},{validate_string,true}]))]}
     ].
 
+pack_nil_test_() ->
+    ElixirStyleNil = nil,
+    NilConversionOpt = [{use_nil, true}],
+    UseNilDefaultResult = msgpack:pack(ElixirStyleNil),
+    UseNilTrueResult = msgpack:pack(ElixirStyleNil, NilConversionOpt),
+    [{"use_nil default false",
+      [?_assertEqual({ok, <<"nil">>}, msgpack:unpack(UseNilDefaultResult))]},
+     {"use_nil explicitly set to true",
+      [?_assertEqual({ok, null}, msgpack:unpack(UseNilTrueResult))]}
+    ].
+
+unpack_nil_test_() ->
+    NullPacked = <<16#C0>>,
+    NilConversionOpt = [{use_nil, true}],
+    UseNilDefaultResult = msgpack:unpack(NullPacked),
+    UseNilTrueResult = msgpack:unpack(NullPacked, NilConversionOpt),
+    [{"use_nil default false",
+      [?_assertEqual({ok, null}, UseNilDefaultResult)]},
+     {"use_nil explicitly set to true",
+      [?_assertEqual({ok, nil}, UseNilTrueResult)]}
+    ].
 
 float_unpacking_test_() ->
     %% float 32