Make config file parsers pluggable (#1)

In order to simplify deps, this PR makes config file formats pluggable. The extensions supported by default are "json" and "eterm".
The default json decoder is the one from OTP, but if one prefers another (e.g. `zj`), it's possible to choose that when installing the gmconfig env.

Example of adding a yaml decoder:
```erlang
instrument_gmconfig() ->
    gmconfig:set_gmconfig_env(gmconfig_env()).

-spec gmconfig_env() -> gmconfig:gmconfig().
gmconfig_env() ->
    #{ ...
     , config_formats => add_yamerl() }.

add_yamerl() ->
    Default = maps:get(config_formats, gmconfig:default_gmconfig_env()),
    case maps:is_key("yaml", Default) of
        true ->
            Default;
        false ->
            Default#{"yaml" => fun yamerl_decode/1}
    end.

yamerl_decode(Bin) ->
    yamerl:decode(Bin, [{str_node_as_binary, true},
                        {map_node_format, map}]).
```

Co-authored-by: Ulf Wiger <ulf@wiger.net>
Reviewed-on: #1

rebar.config

@@ -3,9 +3,7 @@
 {plugins, [rebar3_hex]}.
 
 {deps, [
-         {zj, {git, "https://gitlab.com/zxq9/zj.git", {tag, "1.1.2"}}}
-       , {yamerl, "0.10.0"}
-       , {setup, "2.1.2"}
+        {setup, "2.2.1"}
        ]}.
 
 {profiles, [
@@ -17,5 +15,5 @@
                deprecated_function_calls, deprecated_functions]}.
 
 {dialyzer, [ {warnings, [unknown]}
-           , {base_plt_apps, [erts, kernel, stdlib, yamerl, zj, setup]}
+           , {base_plt_apps, [erts, kernel, stdlib, setup]}
            ]}.

rebar.lock

@@ -1,15 +1,4 @@
-{"1.2.0",
-[{<<"setup">>,{pkg,<<"setup">>,<<"2.1.2">>},0},
- {<<"yamerl">>,{pkg,<<"yamerl">>,<<"0.10.0">>},0},
- {<<"zj">>,
-  {git,"https://gitlab.com/zxq9/zj.git",
-       {ref,"090a43d23edc481695664f16763f147a78c45afc"}},
-  0}]}.
-[
-{pkg_hash,[
- {<<"setup">>, <<"43C0BBFE9160DE7925BF2FC2FE4396A99DC4EE1B73F0DC46ACC3F10E27B07A9C">>},
- {<<"yamerl">>, <<"4FF81FEE2F1F6A46F1700C0D880B24D193DDB74BD14EF42CB0BCF46E81EF2F8E">>}]},
-{pkg_hash_ext,[
- {<<"setup">>, <<"596713D48D8241DF31821C08A9F7BAAF3E7CDD042C8396BC956CC7AE056925DC">>},
- {<<"yamerl">>, <<"346ADB2963F1051DC837A2364E4ACF6EB7D80097C0F53CBDC3046EC8EC4B4E6E">>}]}
-].
+[{<<"setup">>,
+  {git,"https://github.com/uwiger/setup.git",
+       {ref,"9675f9a25c2087e676660911987935caeff9fef8"}},
+  0}].

src/gmconfig.app.src

@@ -7,7 +7,7 @@
    [
      kernel
    , stdlib
-   , zj
+   , setup
    ]},
   {env, []},
   {modules, []},

src/gmconfig.erl

@@ -48,6 +48,7 @@
         , gmconfig_env/1
         , gmconfig_env/2
         , set_gmconfig_env/1
+        , default_gmconfig_env/0
         ]).
 
 -ifdef(TEST).
@@ -62,11 +63,19 @@
 
 -include_lib("kernel/include/logger.hrl").
 
+-type extension() :: string().   %% file extension (without leading dot)
+
+-type decoder_return() :: config_tree()
+                        | {ok, config_tree()}
+                        | {error, any()}.
+-type decoder_fun() :: fun( (binary()) -> decoder_return() ).
+
 -type gmconfig() :: #{ os_env_prefix => string()
                      , config_file_basename => string() | 'undefined'
                      , config_file_os_env => string() | 'undefined'
                      , config_file_search_path => [string() | fun(() -> string())]
-                     , system_suffix => string()
+                     , system_suffix  => string()
+                     , config_formats => #{ extension() => decoder_fun() }
                      , schema => string() | map() | fun(() -> map())}.
 
 -type basic_type() :: number() | binary() | boolean().
@@ -110,12 +119,13 @@ mock_system_defaults(Config) ->
 -endif.
 
 -spec set_gmconfig_env(gmconfig()) -> ok.
-set_gmconfig_env(Env) when is_map(Env) ->
+set_gmconfig_env(Env0) when is_map(Env0) ->
+    Env = maps:merge(default_gmconfig_env(), Env0),
     persistent_term:put({?MODULE, gmconfig_env}, Env).
 
 -spec gmconfig_env() -> gmconfig().
 gmconfig_env() ->
-    persistent_term:get({?MODULE, gmconfig_env}, default_gmconfig()).
+    persistent_term:get({?MODULE, gmconfig_env}, default_gmconfig_env()).
 
 -spec gmconfig_env(atom()) -> any().
 gmconfig_env(Key) ->
@@ -142,11 +152,13 @@ search_path(Kind) ->
               end, Path0)
     end.
 
-default_gmconfig() ->
+default_gmconfig_env() ->
     #{ os_env_prefix => "GM"
      , config_file_basename => "gmconfig"
      , config_file_os_env => undefined
      , config_file_search_path => ["."]
+     , config_formats => #{ "json"  => fun json_decode/1
+                          , "eterm" => fun eterm_consult/1 }
      , system_defaults_search_path => [fun setup:data_dir/0]
      , system_suffix => "" }.
 
@@ -552,8 +564,8 @@ coerce_type(Key, Value, Schema) ->
                 <<"integer">> -> to_integer(Value);
                 <<"string">>  -> to_string(Value);
                 <<"boolean">> -> to_bool(Value);
-                <<"array">>   -> json_decode(list_to_binary(Value));
-                <<"object">>  -> json_decode(list_to_binary(Value))
+                <<"array">>   -> json:decode(list_to_binary(Value));
+                <<"object">>  -> json:decode(list_to_binary(Value))
             end;
         _ ->
             error({unknown_key, Key})
@@ -642,10 +654,21 @@ search_default_config() ->
         Basename ->
             Dirs = search_path(),
             SystemSuffix = get_system_suffix(),
-            Fname = Basename ++ SystemSuffix ++ ".{json,yaml}",
+            ExtPattern = extension_pattern(),
+            Fname = Basename ++ SystemSuffix ++ ExtPattern,
             search_for_config_file(Dirs, Fname)
     end.
 
+config_formats() ->
+    gmconfig_env(config_formats).
+
+extension_pattern() ->
+    Exts = maps:keys(config_formats()),
+    lists:flatten([".{", intersperse(Exts),"}"]).
+
+intersperse([H|T]) ->
+    [H | [[",", X] || X <- T]].
+
 search_for_config_file(Dirs, FileWildcard) ->
     lists:foldl(
       fun(D0, undefined) ->
@@ -665,13 +688,16 @@ to_list_string(S) when is_list(S) ->
     binary_to_list(iolist_to_binary(S)).
 
 do_load_user_config(F, Action, Mode) ->
-    case {filename:extension(F), Action} of
-        {".json", store} -> store(read_json(F, Mode), Mode);
-        {".yaml", store} -> store(read_yaml(F, Mode), Mode);
-        {".json", check} -> check_config_(catch read_json(F, Mode));
-        {".yaml", check} -> check_config_(catch read_yaml(F, Mode))
+    {Ext, Decoder} = pick_decoder(F),
+    case Action of
+        store -> store(read_file(F, Ext, Decoder, Mode), Mode);
+        check -> check_config_(catch read_file(F, Ext, Decoder, Mode))
     end.
 
+pick_decoder(F) ->
+    "." ++ Ext = filename:extension(F),
+    {Ext, maps:get(Ext, config_formats())}.
+
 store(Vars, Mode) when is_map(Vars) ->
     case pt_get_config() of
         Map when map_size(Map) == 0 ->
@@ -726,12 +752,15 @@ silent_as_report(silent) -> report;
 silent_as_report(Mode  ) -> Mode.
 
 schema_string(Schema, Mode) ->
-    JSONSchema = json:encode(Schema),
+    JSONSchema = json_encode(Schema),
     case Mode of
         check  -> json:format(JSONSchema, #{indent => 2});
         report -> JSONSchema
     end.
 
+json_encode(J) ->
+    iolist_to_binary(json:encode(J)).
+
 error_format(Fmt, Args, check) ->
     io:format(Fmt, Args);
 error_format(Fmt, Args, report) ->
@@ -906,70 +935,64 @@ update_map(With, Map) when is_map(With), is_map(Map) ->
               end
       end, Map, With).
 
-read_json(F, Mode) ->
-    validate(
-      try_decode(F, fun(F1) ->
-                            json_consult(F1)
-                    end, "JSON", Mode), F, Mode).
-
-json_consult(F) ->
+read_file(F, Type, Decoder, Mode) ->
     case setup_file:read_file(F) of
         {ok, Bin} ->
-            [json_decode(Bin)];
+            validate(
+              try_decode_bin(Bin, Decoder, Type, Mode),
+              F, Mode);
         {error, Reason} ->
-            ?LOG_ERROR("Read error ~s - ~p", [F, Reason]),
+            error_msg(Mode, "Read error ~s - ~p", [F, Reason]),
             error({read_error, F, Reason})
     end.
 
-json_decode(Bin) ->
-    case json_decode_(Bin) of
-        {ok, Value} ->
-            Value;
-        {error, Reason} ->
-            ?LOG_ERROR("CAUGHT: ~p", [Reason]),
-            error(Reason)
+json_decode(Str) when is_list(Str) ->
+    json:decode(iolist_to_binary(Str));
+json_decode(Bin) when is_binary(Bin) ->
+    json:decode(Bin).
+
+eterm_consult(Bin) ->
+    case setup_file:consult_binary(Bin) of
+        {ok, [Map]} when is_map(Map) ->
+            {ok, normalize_config(Map)};
+        {ok, Other} ->
+            error({unknown_data, Other});
+        {error, _} = Error ->
+            Error
     end.
 
-json_decode_(Bin) ->
-    case zj:binary_decode(Bin) of
-        {ok, _} = Ok ->
-            Ok;
-        {error, _Parsed, Remainder} ->
-            {error, {json_decode_error, string_slice(Remainder)}}
-    end.
-
--define(SliceSz, 80).
-string_slice(B) ->
-    case size(B) of
-        Sz when Sz > ?SliceSz ->
-            Sl = string:slice(B, 0, ?SliceSz - 4),
-            <<Sl/binary, " ...">>;
-        _ ->
-            B
-    end.
-
-read_yaml(F, Mode) ->
-    validate(
-      try_decode(
-        F,
-        fun(F1) ->
-                yamerl:decode_file(F1, [{str_node_as_binary, true},
-                                        {map_node_format, map}])
-        end, "YAML", Mode),
-      F, Mode).
-
-try_decode(F, DecF, Fmt, Mode) ->
-    try DecF(F)
+normalize_config(Map) when is_map(Map) ->
+    try
+        json:decode(iolist_to_binary(json:encode(Map)))
     catch
         error:E ->
-            error_msg(Mode, "Error reading ~s file: ~s~n", [Fmt, F]),
-            erlang:error(E)
+            error({cannot_normalize, E, Map})
     end.
 
-validate(JSON, F, Mode) when is_list(JSON) ->
-    check_validation([validate_(J) || J <- JSON], JSON, F, Mode).
-%% validate(JSON, F, Mode) when is_map(JSON) ->
-%%     validate([JSON], F, Mode).
+try_decode_bin(Bin, Decoder, Fmt, Mode) ->
+    try decode_bin(Bin, Decoder)
+    catch
+        error:E:T ->
+            error_msg(Mode, "CAUGHT for ~p: ~p / ~p", [Fmt, E, T]),
+            error(E)
+    end.
+
+decode_bin(Str, Decoder) when is_list(Str) ->
+    decode_bin(iolist_to_binary(Str), Decoder);
+decode_bin(Bin, Decoder) when is_binary(Bin), is_function(Decoder, 1) ->
+    case Decoder(Bin) of
+        {ok, Map} when is_map(Map) ->
+            Map;
+        Map when is_map(Map) ->
+            Map;
+        {error, E} ->
+            error(E);
+        Other ->
+            error({bad_decoder_return, Other})
+    end.
+
+validate(JSON, F, Mode) when is_map(JSON) ->
+    check_validation([validate_(JSON)], JSON, F, Mode).
 
 vinfo(Mode, Res, F) ->
     case Res of
@@ -1071,7 +1094,8 @@ ensure_schema_loaded() ->
 
 load_schema() ->
     JSON = gmconfig_schema(),
-    Schema = json_decode(JSON),
+    Decode = maps:get("json", config_formats()),
+    Schema = decode_bin(JSON, Decode),
     pt_set_schema(Schema),
     Schema.
 
@@ -1084,3 +1108,13 @@ gmconfig_schema() ->
         F when is_function(F, 0) ->
             F()
     end.
+
+json_consult(F) ->
+    Decode = maps:get("json", config_formats()),
+    case setup_file:read_file(F) of
+        {ok, Bin} ->
+            decode_bin(Bin, Decode);
+        {error, Reason} ->
+            ?LOG_ERROR("Read error ~s - ~p", [F, Reason]),
+            error({read_error, F, Reason})
+    end.