Added float_as_string option to prevent losing of precision of float …

README.md

@@ -318,6 +318,7 @@ option() = dirty_strings
     | return_tail
     | uescape
     | unescaped_jsonp
+    | float_as_string
 
 strict_option() = comments
     | trailing_commas
@@ -415,6 +416,13 @@ additional options beyond these. see
     these codepoints are escaped (to `\u2028` and `\u2029`, respectively) to 
     retain compatibility. this option simply removes that escaping
 
+- `float_as_string`
+
+  the precision of float values in jsons are not restricted by the IEEE 754 standard.
+  in some cases it is not allowed to lose precision during the decoding of a json structure,
+  this option decodes the float values as strings. this way it possible to handle these values with
+  solutions that preserve precision, like the decimal library.
+
 
 ## exports ##
 

src/jsx.erl

@@ -194,6 +194,9 @@ test_cases() ->
     ++ floats()
     ++ compound_object().
 
+float_as_string_test_cases() ->
+    string_floats().
+
 %% segregate these so we can skip them in `jsx_to_term`
 special_test_cases() -> special_objects() ++ special_array().
 
@@ -303,6 +306,34 @@ naked_floats() ->
         || X <- Raw ++ [ -1 * Y || Y <- Raw ]
     ].
 
+floats_as_string() ->
+    Raw = [
+              "0.0", "0.1", "0.2", "0.3", "0.4", "0.5", "0.6", "0.7", "0.8", "0.9",
+              "1.0", "1.1", "1.2", "1.3", "1.4", "1.5", "1.6", "1.7", "1.8", "1.9",
+              "1234567890.0987654321",
+              "0.0e0",
+              "1234567890.0987654321e16",
+              "0.1e0", "0.1e1", "0.1e2", "0.1e4", "0.1e8", "0.1e16", "0.1e308",
+              "1.0e0", "1.0e1", "1.0e2", "1.0e4", "1.0e8", "1.0e16", "1.0e308",
+              "2.2250738585072014e-308",    %% min normalized float
+              "1.7976931348623157e308",     %% max normalized float
+              "5.0e-324",                   %% min denormalized float
+              "2.225073858507201e-308"      %% max denormalized float
+          ],
+    [
+        {
+            X,
+            list_to_binary(X),
+            X,
+            [{string, list_to_binary(X)}]
+        }
+        || X <- Raw
+    ].
+
+string_floats() ->
+    floats_as_string()
+    ++ [ wrap_with_array(Test) || Test <- floats_as_string() ]
+    ++ [ wrap_with_object(Test) || Test <- floats_as_string() ].
 
 floats() ->
     naked_floats()
@@ -425,6 +456,14 @@ incremental_decode(JSON) ->
     ),
     Final(end_stream).
 
+incremental_decode_float_as_string(JSON) ->
+    Final = lists:foldl(
+        fun(Byte, Decoder) -> {incomplete, F} = Decoder(Byte), F end,
+        decoder(jsx, [], [stream, float_as_string]),
+        json_to_bytes(JSON)
+    ),
+    Final(end_stream).
+
 
 incremental_parse(Events) ->
     Final = lists:foldl(
@@ -453,6 +492,14 @@ decode_test_() ->
         || {Title, JSON, _, Events} <- Data
     ].
 
+decode_float_as_string_test_() ->
+    Data = float_as_string_test_cases(),
+    [{Title, ?_assertEqual(Events ++ [end_json], (decoder(?MODULE, [], [float_as_string]))(JSON))}
+     || {Title, JSON, _, Events} <- Data
+    ] ++
+        [{Title ++ " (incremental)", ?_assertEqual(Events ++ [end_json], incremental_decode_float_as_string(JSON))}
+         || {Title, JSON, _, Events} <- Data
+        ].
 
 parse_test_() ->
     Data = test_cases(),

src/jsx_config.erl

@@ -60,6 +60,7 @@
                 | {indent, non_neg_integer()}
                 | {depth, non_neg_integer()}
                 | {newline, binary()}
+                | {float_as_string, boolean()}
                 | legacy_option()
                 | {legacy_option(), boolean()}.
 -type legacy_option() :: strict_comments
@@ -114,6 +115,8 @@ parse_config([multi_term|Rest], Config) ->
     parse_config(Rest, Config#config{multi_term=true});
 parse_config([return_tail|Rest], Config) ->
     parse_config(Rest, Config#config{return_tail=true});
+parse_config([float_as_string|Rest], Config) ->
+    parse_config(Rest, Config#config{float_as_string=true});
 %% retained for backwards compat, now does nothing however
 parse_config([repeat_keys|Rest], Config) ->
     parse_config(Rest, Config);
@@ -215,7 +218,8 @@ valid_flags() ->
         stream,
         uescape,
         error_handler,
-        incomplete_handler
+        incomplete_handler,
+        float_as_string
     ].
 
 
@@ -259,7 +263,8 @@ config_test_() ->
                     strict_escapes = true,
                     strict_control_codes = true,
                     stream = true,
-                    uescape = true
+                    uescape = true,
+                    float_as_string = true
                 },
                 parse_config([dirty_strings,
                     escaped_forward_slashes,
@@ -270,7 +275,8 @@ config_test_() ->
                     repeat_keys,
                     strict,
                     stream,
-                    uescape
+                    uescape,
+                    float_as_string
                 ])
             )
         },
@@ -342,6 +348,7 @@ config_to_list_test_() ->
                 stream,
                 uescape,
                 unescaped_jsonp,
+                float_as_string,
                 strict
             ],
             config_to_list(
@@ -356,7 +363,8 @@ config_to_list_test_() ->
                     strict_escapes = true,
                     strict_control_codes = true,
                     stream = true,
-                    uescape = true
+                    uescape = true,
+                    float_as_string = true
                 }
             )
         )},

src/jsx_config.hrl

@@ -13,6 +13,7 @@
     return_tail = false                 :: boolean(),
     uescape = false                     :: boolean(),
     unescaped_jsonp = false             :: boolean(),
+    float_as_string = false             :: boolean(),
     error_handler = false               :: false | jsx_config:handler(),
     incomplete_handler = false          :: false | jsx_config:handler()
 }).

src/jsx_decoder.erl

@@ -25,7 +25,7 @@
 
 %% inline handle_event, format_number and maybe_replace
 -compile({inline, [handle_event/3]}).
--compile({inline, [format_number/1]}).
+-compile({inline, [format_number/2]}).
 -compile({inline, [maybe_replace/2]}).
 -compile({inline, [doublequote/5, singlequote/5]}).
 
@@ -944,10 +944,14 @@ exp(_, N) -> {finish_float, N}.
 
 
 finish_number(Rest, Handler, Acc, Stack, Config) ->
-    maybe_done(Rest, handle_event(format_number(Acc), Handler, Config), Stack, Config).
+    maybe_done(Rest, handle_event(format_number(Acc, Config), Handler, Config), Stack, Config).
 
-format_number({integer, Acc}) -> {integer, binary_to_integer(Acc)};
-format_number({float, Acc}) -> {float, binary_to_float(Acc)}.
+format_number({integer, Acc}, _Config) -> {integer, binary_to_integer(Acc)};
+format_number({float, Acc}, Config) ->
+    case Config#config.float_as_string of
+        false -> {float, binary_to_float(Acc)};
+        _ -> {string, Acc}
+    end.
 
 true(<<$r, $u, $e, Rest/binary>>, Handler, Stack, Config) ->
     maybe_done(Rest, handle_event({literal, true}, Handler, Config), Stack, Config);
@@ -1906,4 +1910,16 @@ return_tail_test_() ->
         )}
     ].
 
+decode_float_as_string_test_() ->
+    [
+        {"simple_float_as_string", ?_assertEqual(
+            <<"3.13">>,
+            jsx:decode(<<"3.13">>, [float_as_string])
+        )},
+        {"float_as_string_in_object", ?_assertEqual(
+            #{<<"a">> => <<"1000000000.5549999">>},
+            jsx:decode(<<"{\"a\":\"1000000000.5549999\"}">>, [float_as_string])
+        )}
+    ].
+
 -endif.