jsone

jsone (1.0.0)

An Erlang library for encoding, decoding JSON data.

Features

• Provides simple encode/decode function only
• RFC4627-compliant
• Supports UTF-8 encoded binary
• Pure Erlang
• Highly Efficient
  • Maybe one of the fastest JSON library (except those which are implemented in NIF)
    • See Benchmark
  • Decode function is written in continuation-passing style(CPS)
    • CPS facilitates application of 'creation of sub binary delayed' optimization
    • See also Erlang Efficiency Guide

QuickStart

# clone
$ git clone git://github.com/sile/jsone.git
$ cd jsone

# If you want to use HiPE enabled version, please execute following command.
# $ git checkout hipe

# compile
$ make compile

# run tests
$ make eunit

# dialyze
$ make dialyze

# Erlang shell
$ make start
1> jsone:decode(<<"[1,2,3]">>).
[1,2,3]

Usage Example

%% Decode
> jsone:decode(<<"[1,2,3]">>).
[1,2,3]

> jsone:decode(<<"{\"1\":2}">>).
#{<<"1">> => 2}

> jsone:decode(<<"{\"1\":2}">>, [{object_format, tuple}]). % tuple format
{[{<<"1">>, 2}]}

> jsone:decode(<<"{\"1\":2}">>, [{object_format, proplist}]). % proplist format
[{<<"1">>, 2}]

> jsone:try_decode(<<"[1,2,3] \"next value\"">>). % try_decode/1 returns remaining (unconsumed binary)
{ok,[1,2,3],<<" \"next value\"">>}

% error: raises exception
> jsone:decode(<<"1.x">>).
** exception error: bad argument
     in function  jsone_decode:number_fraction_part_rest/6
        called as jsone_decode:number_fraction_part_rest(<<"x">>,1,1,0,[],<<>>)
     in call from jsone:decode/1 (src/jsone.erl, line 71)

% error: returns {error, Reason}
> jsone:try_decode(<<"1.x">>).
{error,{badarg,[{jsone_decode,number_fraction_part_rest,
                              [<<"x">>,1,1,0,[],<<>>],
                              [{line,228}]}]}}


%% Encode
> jsone:encode([1,2,3]).
<<"[1,2,3]">>

> jsone:encode(#{<<"key">> => <<"value">>}).  % map format
> jsone:encode({[{<<"key">>, <<"value">>}]}). % tuple format
> jsone:encode([{<<"key">>, <<"value">>}]).  % proplist format
<<"{\"key\":\"value\"}">>

> jsone:encode(#{key => <<"value">>}). % atom key is allowed
<<"{\"key\":\"value\"}">>

% error: raises exception
> jsone:encode(#{123 => <<"value">>}). % non binary|atom key is not allowed
** exception error: bad argument
     in function  jsone_encode:object_members/3
        called as jsone_encode:object_members([{123,<<"value">>}],[],<<"{">>)
     in call from jsone:encode/1 (src/jsone.erl, line 97)

% error: returns {error, Reason}
> jsone:try_encode({[{123, <<"value">>}]}).
{error,{badarg,[{jsone_encode,object_members,
                              [[{123,<<"value">>}],[],<<"{">>],
                              [{line,138}]}]}}

% 'object_key_type' option allows non-string object key
> jsone:encode({[{123, <<"value">>}]}, [{object_key_type, scalar}]).
<<"{\"123\":\"value\"}">>

%% Pretty Print
> Data = [true, #{<<"1">> => 2, <<"array">> => [[[[1]]], #{<<"ab">> => <<"cd">>}, false]}, null].
> io:format("~s\n", [jsone:encode(Data, [{indent, 1}, {space, 2}])]).
[
  true,
  {
    "1": 2,
    "array": [
      [
        [
          [
            1
          ]
        ]
      ],
      {
        "ab": "cd"
      },
      false
    ]
  },
  null
]
ok

%% Number Format
> jsone:encode(1). % integer
<<"1">>

> jsone:encode(1.23). % float
<<"1.22999999999999998224e+00">> % default: scientific notation

> jsone:encode(1.23, [{float_format, [{decimals, 4}]}]). % decimal notation
<<"1.2300">>

> jsone:encode(1.23, [{float_format, [{decimals, 4}, compact]}]). % compact decimal notation
<<"1.23">>

Data Mapping (Erlang <=> JSON)

Erlang                  JSON             Erlang
=================================================================================================

null                 -> null          -> null
true                 -> true          -> true
false                -> false         -> false
<<"abc">>            -> "abc"         -> <<"abc">>
abc                  -> "abc"         -> <<"abc">> % non-special atom is regarded as a binary
123                  -> 123           -> 123
123.4                -> 123.4         -> 123.4
[1,2,3]              -> [1,2,3]       -> [1,2,3]
{[]}                 -> {}            -> {[]}                       % object_format=tuple
{[{key, <<"val">>}]} -> {"key":"val"} -> {[{<<"key">>, <<"val">>}]} % object_format=tuple
[{}]                 -> {}            -> [{}]                       % object_format=proplist
[{<<"key">>, val}]   -> {"key":"val"} -> [{<<"key">>, <<"val">>}]   % object_format=proplist
#{}                  -> {}            -> #{}                        % object_format=map
#{key => val}        -> {"key":"val"} -> #{<<"key">> => <<"val">>}  % object_format=map

API

See EDoc Document

Benchmark

Environment/Method

• OS: CentOS 6.5
• CPU: Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz (x8)
• Erlang/OTP: R17.1
• Benchmark Tool: erl_json_test
• CompileOption: [native, {hipe, [o3]}]

Target

• jiffy-0.11.3 (NIF)
• jsone-v0.2.3 (HiPE)
• jsonerl (HiPE)
• jsonx (NIF)
• jsx-v2.0.1 (HiPE)
• mochijson2 (HiPE)
• yawsjson2 (HiPE)

Decode Result

• column: module name
• row: data size (bytes)
• cell: elapsed time (micro seconds)

	jiffy	jsone	jsonerl	jsonx	jsx	mochijson2	yawsjson2
559 (1x)	12	11	61	7	50	28	37
1583 (3x)	24	25	66	15	134	68	84
4637 (9x)	65	86	178	36	410	186	311
13914 (27x)	189	271	533	109	1466	550	582
41542 (81x)	525	813	1578	299	4684	1599	1939
124726 (243x)	1549	2406	4709	852	14562	4799	6123

Encode Result

• column: module name
• row: data size (bytes)
• cell: elapsed time (micro seconds)

	jiffy	jsone	jsonerl	jsonx	jsx	mochijson2	yawsjson2
559 (1x)	14	19	21	8	83	19	15
1583 (3x)	29	49	65	14	228	61	42
4637 (9x)	77	133	229	36	638	225	161
13914 (27x)	215	393	737	101	1993	664	435
41542 (81x)	621	1172	2058	300	6237	2310	1192
124726 (243x)	1830	3968	5842	828	17032	6979	5266