jsx/README.markdown

jsx (v0.10.0)

a sane json implementation for erlang, inspired by yajl

copyright 2011 alisdair sullivan

jsx is released under the terms of the MIT license

quickstart

to build jsx, make or ./rebar compile

converting json to erlang terms

parses a JSON text (a utf8 encoded binary) and produces an erlang term (see json <-> erlang mapping details below)

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

types:

• JSON = binary()
• Term = [] | [{}] | [any()]
• Opts = [] | [loose_unicode]

if the option loose_unicode is present invalid codepoints are replaced with u+FFFD. default behaviour is a badarg error

converting erlang terms to json

produces a JSON text from an erlang term (see json <-> erlang mapping details below)

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

types:

• JSON = binary()
• Term = [] | [{}] | [any()]
• Opts = [] | [Opt]
• Opt =
  • space
  • {space, N}
  • indent
  • {indent, N}
  • escape_forward_slash

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}

if the option escape_forward_slash is enabled, $/ is escaped. this is not normally required but is necessary for compatibility with microsoft's json date format

formatting json texts

produces a JSON text from JSON text, reformatted

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

see term_to_json/1,2 for types and options

json <-> erlang

json	erlang
number	integer()
string	binary()
true	true
false	false
null	null
array	list()
object	[{}]

json

json must be encoded in utf8. if it's invalid utf8, it probably won't parse without errors. one optional exception is made for json strings that are otherwise utf8, see under strings below.

numbers

javascript and thus json represents all numeric values with floats. as this is woefully insufficient for many uses, jsx, just like erlang, supports bigints. whenever possible, this library 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. numbers not representable with either type are beyond the concern of this implementation, and will result in parsing errors (with the exception of negative zero, which is converted into plain old zero)

when converting from erlang to json, numbers 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, 1.0000000000000001 will be represented by 1.0

strings

the json spec is frustratingly vague on the exact details of json strings. json must be unicode, but no encoding is specified. javascript explicitly allows strings containing codepoints explicitly disallowed by unicode. json allows implementations to set limits on the content of strings and other implementations attempt to resolve this in various ways. this implementation, in default operation, only accepts strings that meet the constraints set out in the json spec (properly escaped control characters and quotes) and that are encoded in utf8. in the interests of pragmatism, however, the parser option loose_unicode attempts to replace invalid utf8 sequences with the replacement codepoint u+fffd when possible

all erlang strings are represented by valid utf8 encoded binaries

this implementation performs no normalization on strings beyond that detailed here. be careful when comparing strings

keys

keys are functionally identical to strings. see string above

true, false and null

the json primitives true, false and null are represented by the erlang atoms true, false and null. suprise

arrays

json arrays are represented with erlang lists of json values as described in this document

objects

json objects are represented by erlang proplists. the empty object has the special representation [{}] to differentiate it from the empty list. ambiguities like [true, false] prevent using the shorthand form of property lists using atoms as properties. all properties must be tuples. all keys must be encoded as in string, above

acknowledgements

paul davis, lloyd hilaiel, john engelhart, bob ippolito, fernando benavides and alex kropivny have all contributed to the development of jsx, whether they know it or not