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
Add to rebar.config
...
{erl_opts, [debug_info]}.
{deps, [
...
{jsx, "~> 3.0"}
]}.
...$ rebar3 compile
$ rebar3 eunit1> 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">>]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\"]">>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]).
false1> jsx:minify(<<"{
\"a list\": [
1,
2,
3
]
}">>).
<<"{\"a list\":[1,2,3]}">>1> jsx:prettify(<<"{\"a list\":[1,2,3]}">>).
<<"{
\"a list\": [
1,
2,
3
]
}">>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 |
|---|---|
number |
integer() and float() |
string |
binary() and atom() |
true, false and null |
true, false and null |
array |
[] and [JSON] |
object |
#{}, [{}] and [{binary() OR atom() OR integer(), JSON}] |
| see below | datetime() |
-
numbers
javascript and thus json represent all numeric values with floats. there's no reason for erlang -- a language that supports arbitrarily large integers -- to restrict all numbers to the ieee754 range
whenever possible, jsx will interpret json numbers that look like integers as integers. other numbers will be converted to erlang's floating point type, which is nearly but not quite iee754. negative zero is not representable in erlang (zero is unsigned in erlang and
0is equivalent to-0) and will be interpreted as regular zero. numbers not representable are beyond the concern of this implementation, and will result in parsing errorswhen converting from erlang to json, floats are represented with their shortest representation that will round trip without loss of precision. this means that some floats may be superficially dissimilar (although functionally equivalent). for example,
1.0000000000000001will be represented by1.0 -
strings
json strings must be unicode encoded binaries or erlang atoms. in practice, because jsx only accepts
utf8binaries all binary strings must beutf8. in addition to being unicode json strings restrict a number of codepoints and define a number of escape sequencesjson string escapes of the form
\uXXXXwill be converted to their equivalent codepoints during parsing. this means control characters and other codepoints disallowed by the json spec may be encountered in resulting strings. the utf8 restriction means the surrogates are explicitly disallowed. if a string contains escaped surrogates (u+d800tou+dfff) they are interpreted but only when they form valid surrogate pairs. surrogates encountered otherwise are replaced with the replacement codepoint (u+fffd)all erlang strings are represented by valid
utf8encoded binaries. the encoder will check strings for conformance. badly formedutf8sequences may be replaced with the replacement codepoint (u+fffd) according to the unicode specthis implementation performs no normalization on strings beyond that detailed here. be careful when comparing strings as equivalent strings may have different
utf8encodings -
true, false and null
the json primitives
true,falseandnullare represented by the erlang atomstrue,falseandnull. surprise -
arrays
json arrays are represented with erlang lists of json values as described in this section
-
objects
json objects are represented by erlang maps.
-
datetime
erlang datetime tuples (
{{Year, Month, Day}, {Hour, Min, Sec}}) as returned fromerlang:localtime/0are automatically encoded as iso8601 strings and are assumed to be UTC time. no conversion is attempted of json iso8601 strings in decoded json
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)`
[]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() = binary()a utf8 encoded binary containing a json string
event() = start_object
| end_object
| start_array
| end_array
| {key, binary()}
| {string, binary()}
| {integer, integer()}
| {float, float()}
| {literal, true}
| {literal, false}
| {literal, null}
| end_jsonthe subset of token() emitted by the decoder and encoder to handlers
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
| escapesjsx 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
-
dirty_stringsjson escaping is lossy; it mutates the json string and repeated application can result in unwanted behaviour. if your strings are already escaped (or you'd like to force invalid strings into "json" you monster) use this flag to bypass escaping. this can also be used to read in really invalid json strings. everything between unescaped quotes are passed as is to the resulting string term. note that this takes precedence over any other options
-
escaped_forward_slashesjson strings are escaped according to the json spec. this means forward slashes (solidus) are only escaped when this flag is present. otherwise they are left unescaped. you may want to use this if you are embedding json directly into a html or xml document
-
escaped_stringsby default both the encoder and decoder return strings as utf8 binaries appropriate for use in erlang. escape sequences that were present in decoded terms are converted into the appropriate codepoint while encoded terms are unaltered. this flag escapes strings as if for output in json, removing control codes and problematic codepoints and replacing them with the appropriate escapes
-
streamsee incomplete input
-
strictas mentioned earlier, jsx is pragmatic. if you're more of a json purist or you're really into bdsm stricter adherence to the spec is possible. the following restrictions are available
-
commentscomments are disabled and result in a
badargerror -
trailing_commastrailing commas in an object or list result in
badargerrors -
utf8invalid codepoints and malformed unicode result in
badargerrors -
single_quotesonly keys and strings delimited by double quotes (
u+0022) are allowed. the single quote (u+0027) results in abadargerror -
escapesescape sequences not adhering to the json spec result in a
badargerror -
control_codescontrol codes in strings result in
badargerrors
any combination of these can be passed to jsx by using
{strict, [strict_option()]}.strictis equivalent to{strict, [comments, trailing_commas, utf8, single_quotes, escapes, control_codes]} -
-
return_tailupon reaching the end of a valid json term in an input stream return the term and any remaining bytes in the input stream as
{with_tail, term(), binary()}where the second member of the tuple is the json term and the third is any remaining bytes. note that leading whitespace will be stripped from the tail -
uescapeescape all codepoints outside the ascii range for 7 bit clean output. note this escaping takes place even if no other string escaping is requested (via
escaped_strings) -
unescaped_jsonpjavascript interpreters treat the codepoints
u+2028andu+2029as significant whitespace. json strings that contain either of these codepoints will be parsed incorrectly by some javascript interpreters. by default, these codepoints are escaped (to\u2028and\u2029, respectively) to retain compatibility. this option simply removes that escaping
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(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(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(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(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(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(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(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
the following functions should be exported from a jsx callback module
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(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:
-
start_objectthe start of a json object
-
'{key, binary()}'
the key of an entry in a json object
-
end_objectthe end of a json object
-
start_arraythe start of a json array
-
end_arraythe end of a json array
-
{string, binary()}a json string. it will usually be a
utf8encoded binary. see the options for possible exceptions. note that keys are also json strings -
{integer, integer()}an erlang integer (bignum)
-
{float, float()}an erlang float
-
{literal, true}the atom
true -
{literal, false}the atom
false -
{literal, null}the atom
null -
end_jsonthis event is emitted when syntactic analysis is completed. you should do any cleanup and return the result of your semantic analysis
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
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