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jsx (v3.0.0)

an erlang application for consuming, producing and manipulating json. inspired by yajl

jsx is built via rebar3

current status:

jsx is released under the terms of the MIT license

copyright 2010-2016 alisdair sullivan

index

quickstart

to add to a rebar3 project

Add to rebar.config

...
{erl_opts, [debug_info]}.
{deps, [
       ...
       {jsx, "~> 3.0"}
]}.
...

to build the library and run tests

$ rebar3 compile
$ rebar3 eunit

to convert a utf8 binary containing a json string into an erlang term

1> jsx:decode(<<"{\"library\": \"jsx\", \"awesome\": true}">>, []).
#{<<"awesome">> => true,<<"library">> => <<"jsx">>}
2> jsx:decode(<<"{\"library\": \"jsx\", \"awesome\": true}">>, [{return_maps, false}]).
[{<<"library">>,<<"jsx">>},{<<"awesome">>,true}]
3> jsx:decode(<<"[\"a\",\"list\",\"of\",\"words\"]">>).
[<<"a">>, <<"list">>, <<"of">>, <<"words">>]

to convert an erlang term into a utf8 binary containing a json string

1> jsx:encode(#{<<"library">> => <<"jsx">>, <<"awesome">> => true}).
<<"{\"awesome\":true,\"library\":\"jsx\"}">>
2> jsx:encode([{<<"library">>,<<"jsx">>},{<<"awesome">>,true}]).
<<"{\"library\": \"jsx\", \"awesome\": true}">>
3> jsx:encode([<<"a">>, <<"list">>, <<"of">>, <<"words">>]).
<<"[\"a\",\"list\",\"of\",\"words\"]">>

to check if a binary or a term is valid json

1> jsx:is_json(<<"[\"this is json\"]">>).
true
2> jsx:is_json("[\"this is not\"]").
false
3> jsx:is_term([<<"this is a term">>]).
true
4> jsx:is_term([this, is, not]).
false

to minify some json

1> jsx:minify(<<"{
  \"a list\": [
    1,
    2,
    3
  ]
}">>).
<<"{\"a list\":[1,2,3]}">>

to prettify some json

1> jsx:prettify(<<"{\"a list\":[1,2,3]}">>).
<<"{
  \"a list\": [
    1,
    2,
    3
  ]
}">>

description

jsx is an erlang application for consuming, producing and manipulating json

jsx follows the json spec as closely as possible with allowances for real world usage

jsx is pragmatic. the json spec allows extensions so jsx extends the spec in a number of ways. see the section on strict in options below though

json has no official comments but this parser allows c/c++ style comments. anywhere whitespace is allowed you can insert comments (both // ... and /* ... */)

some particularly irresponsible json emitters leave trailing commas at the end of objects or arrays. jsx allows a single trailing comma in input. multiple commas in any position or a preceding comma are still errors

all jsx decoder input should be utf8 encoded binaries. sometimes you get binaries that are almost but not quite valid utf8 whether due to improper escaping or poor encoding. jsx replaces invalid codepoints and poorly formed sequences with the unicode replacement character (u+FFFD) but does it's best to return something comprehensible

json only allows keys and strings to be delimited by double quotes (u+0022) but javascript allows them to be delimited by single quotes (u+0027) as well. jsx follows javascript in this. strings that start with single quotes can contain double quotes but must end with single quotes and must escape any single quotes they contain

json and jsx only recognize escape sequences as outlined in the json spec. it just ignores bad escape sequences leaving them in strings unaltered

json <-> erlang mapping

jsonerlang
numberinteger() and float()
stringbinary() and atom()
true, false and nulltrue, false and null
array[] and [JSON]
object#{}, [{}] and [{binary() OR atom() OR integer(), JSON}]
see belowdatetime()

incomplete input

jsx can handle incomplete json texts. if the option stream is passed to the decoder or parser and if a partial json text is parsed, rather than returning a term from your callback handler, jsx returns {incomplete, F} where F is a function with an identical API to the anonymous fun returned from decoder/3, encoder/3 or parser/3. it retains the internal state of the parser at the point where input was exhausted. this allows you to parse as you stream json over a socket or file descriptor, or to parse large json texts without needing to keep them entirely in memory

however, it is important to recognize that jsx is conservative by default. jsx will not consider the parsing complete even when input is exhausted and the json text is unambiguously incomplete. to end parsing call the incomplete function with the argument end_stream (or end_json) like:

1> {incomplete, F} = jsx:decode(<<"[">>, [stream]).
{incomplete,#Fun<jsx_decoder.1.122947756>}
2> F(end_stream).  % can also be `F(end_json)`
** exception error: bad argument
3> {incomplete, G} = F(<<"]">>).
{incomplete,#Fun<jsx_decoder.1.122947756>}
4> G(end_stream).  % can also be `G(end_json)`
[]

data types

json_term()

json_term() = [json_term()]
    | [{binary() | atom() | integer(), json_term()}]
    | #{} % map of any size, not just the empty map
    | true
    | false
    | null
    | integer()
    | float()
    | binary()
    | atom()
		| datetime()

the erlang representation of json. binaries should be utf8 encoded, or close at least

json_text()

json_text() = binary()

a utf8 encoded binary containing a json string

event()

event() = start_object
    | end_object
    | start_array
    | end_array
    | {key, binary()}
    | {string, binary()}
    | {integer, integer()}
    | {float, float()}
    | {literal, true}
    | {literal, false}
    | {literal, null}
    | end_json

the subset of token() emitted by the decoder and encoder to handlers

option()

option() = dirty_strings
    | escaped_forward_slashes
    | escaped_strings
    | repeat_keys
    | stream
    | strict
    | {strict, [strict_option()]}
    | return_tail
    | uescape
    | unescaped_jsonp

strict_option() = comments
    | trailing_commas
    | utf8
    | single_quotes
    | escapes

jsx functions all take a common set of options. not all flags have meaning in all contexts, but they are always valid options. functions may have additional options beyond these. see individual function documentation for details

exports

encoder/3, decoder/3 & parser/3

decoder(Module, Args, Opts) -> Fun((JSONText) -> any())
encoder(Module, Args, Opts) -> Fun((JSONTerm) -> any())
parser(Module, Args, Opts) -> Fun((Tokens) -> any())

  Module = atom()
  Args = any()
  Opts = [option()]
  JSONText = json_text()
  JSONTerm = json_term()
  Tokens = event() | [event()]

jsx is a json compiler with interleaved tokenizing, syntactic analysis and semantic analysis stages. included are two tokenizers; one that handles json texts (decoder/3) and one that handles erlang terms (encoder/3). there is also an entry point to the syntactic analysis stage for use with user-defined tokenizers (parser/3)

all three functions return an anonymous function that takes the appropriate type of input and returns the result of performing semantic analysis, the tuple {incomplete, F} where F is a new anonymous function (see incomplete input) or a badarg error exception if syntactic analysis fails

Module is the name of the callback module

Args is any term that will be passed to Module:init/1 prior to syntactic analysis to produce an initial state

Opts are detailed here

check out callback module documentation for details of the callback module interface

decode/1,2

decode(JSON) -> Term
decode(JSON, Opts) -> Term

  JSON = json_text()
  Term = json_term()
  Opts = [option() | labels | {labels, Label} | return_maps]
    Label = binary | atom | existing_atom | attempt_atom
    F = fun((any()) -> any())

decode parses a json text (a utf8 encoded binary) and produces an erlang term

the option labels controls how keys are converted from json to erlang terms. binary (the default behavior) does no conversion beyond normal escaping. atom converts keys to erlang atoms and results in a badarg error if the keys fall outside the range of erlang atoms. existing_atom is identical to atom except it will not add new atoms to the atom table and will result in a badarg error if the atom does not exist. attempt_atom will convert keys to atoms when they exist, and leave them as binary otherwise

the option {return_maps, false} will return objects as proplists instead of maps.

raises a badarg error exception if input is not valid json

encode/1,2

encode(Term) -> JSON
encode(Term, Opts) -> JSON

  Term = json_term()
  JSON = json_text()
  Opts = [option() | space | {space, N} | indent | {indent, N}]
    N = pos_integer()

encode converts an erlang term into json text (a utf8 encoded binary)

the option {space, N} inserts N spaces after every comma and colon in your json output. space is an alias for {space, 1}. the default is {space, 0}

the option {indent, N} inserts a newline and N spaces for each level of indentation in your json output. note that this overrides spaces inserted after a comma. indent is an alias for {indent, 1}. the default is {indent, 0}

raises a badarg error exception if input is not a valid erlang representation of json

format/1,2

format(JSON) -> JSON
format(JSON, Opts) -> JSON

  JSON = json_text()
  Opts = [option() | space | {space, N} | indent | {indent, N} | {newline, LF}]
     N = pos_integer()
    LF = binary()

format parses a json text (a utf8 encoded binary) and produces a new json text according to the format rules specified by Opts

the option {space, N} inserts N spaces after every comma and colon in your json output. space is an alias for {space, 1}. the default is {space, 0}

the option {indent, N} inserts a newline and N spaces for each level of indentation in your json output. note that this overrides spaces inserted after a comma. indent is an alias for {indent, 1}. the default is {indent, 0}

the option {newline, LF} defines a custom newline symbol(s). the default is {newline, <<$\n>>}

raises a badarg error exception if input is not valid json

minify/1

minify(JSON) -> JSON

  JSON = json_text()

minify parses a json text (a utf8 encoded binary) and produces a new json text stripped of whitespace

raises a badarg error exception if input is not valid json

prettify/1

prettify(JSON) -> JSON

  JSON = json_text()

prettify parses a json text (a utf8 encoded binary) and produces a new json text equivalent to format(JSON, [{space, 1}, {indent, 2}])

raises a badarg error exception if input is not valid json

is_json/1,2

is_json(MaybeJSON) -> true | false
is_json(MaybeJSON, Opts) -> true | false

  MaybeJSON = any()
  Opts = options()

returns true if input is a valid json text, false if not

what exactly constitutes valid json may be altered

is_term/1,2

is_term(MaybeJSON) -> true | false
is_term(MaybeJSON, Opts) -> true | false

  MaybeJSON = any()
  Opts = options()

returns true if input is a valid erlang representation of json, false if not

what exactly constitutes valid json may be altered via options

callback exports

the following functions should be exported from a jsx callback module

Module:init/1

Module:init(Args) -> InitialState

  Args = any()
  InitialState = any()

whenever any of encoder/3, decoder/3 or parser/3 are called, this function is called with the Args argument provided in the calling function to obtain InitialState

Module:handle_event/2

Module:handle_event(Event, State) -> NewState

  Event = [event()]
  State = any()
  NewState = any()

semantic analysis is performed by repeatedly calling handle_event/2 with a stream of events emitted by the tokenizer and the current state. the new state returned is used as the input to the next call to handle_event/2. the following events must be handled:

acknowledgements

jsx wouldn't be what it is without the contributions of Paul J. Davis, Lloyd Hilaiel, John Engelhart, Bob Ippolito, Brujo Benavides, Alex Kropivny, Steve Strong, Michael Truog, Devin Torres, fogfish, emptytea, John Daily, Ola Bäckström, Joseph Crowe, Patrick Gombert, Eshengazin S. Kuat, Max Lapshin, Bikram Chatterjee, Michael Uvarov, Led and tvv