ref: 2459e34d77e2e21ef829c0dfaafd99433899494f
dir: /man/2/json/
.TH JSON 2
.SH NAME
json: readjson, writejson, JValue \- read, write and represent values in JavaScript Object Notation
.SH SYNOPSIS
.EX
include "json.m";
json := load JSON JSON->PATH;
JValue: adt {
pick{
Object =>
mem: cyclic list of (string, ref JValue);
Array =>
a: cyclic array of ref JValue;
String =>
s: string;
Int =>
value: big;
Real =>
value: real;
True or
False or
Null =>
}
isarray: fn(v: self ref JValue): int;
isfalse: fn(v: self ref JValue): int;
isint: fn(v: self ref JValue): int;
isnull: fn(v: self ref JValue): int;
isnumber: fn(v: self ref JValue): int;
isobject: fn(v: self ref JValue): int;
isreal: fn(v: self ref JValue): int;
isstring: fn(v: self ref JValue): int;
istrue: fn(v: self ref JValue): int;
copy: fn(v: self ref JValue): ref Jvalue;
eq: fn(v: self ref JValue, v: ref JValue): int;
get: fn(v: self ref JValue, mem: string): ref JValue;
set: fn(v: self ref JValue, mem: string, value: ref JValue);
text: fn(v: self ref JValue): string;
};
init: fn(bufio: Bufio);
readjson: fn(input: ref Bufio->Iobuf): (ref JValue, string);
writejson: fn(output: ref Bufio->Iobuf, val: ref JValue): int;
jvarray: fn(a: array of ref JValue): ref JValue.Array;
jvbig: fn(b: big): ref JValue.Int;
jvfalse: fn(): ref JValue.False;
jvint: fn(i: int): ref JValue.Int;
jvnull: fn(): ref JValue.Null;
jvobject: fn(m: list of (string, ref JValue)): ref JValue.Object;
jvreal: fn(r: real): ref JValue.Real;
jvstring: fn(s: string): ref JValue.String;
jvtrue: fn(): ref JValue.True;
.EE
.SH DESCRIPTION
.B JSON
provides value representations, and encoding and decoding operations for the JavaScript Object Notation (JSON)
described by Internet RFC4627
and summarised in
.IR json (6).
.PP
.B Init
must be called before invoking any other operation of the module.
The
.I bufio
parameter must refer to the instance of
.IR bufio (2)
that provides the
.B Iobuf
parameters used for input and output.
.PP
.B JValue
is the internal representation of values transmitted by the JSON encoding.
They are distinguished in a pick adt:
.TP
.B JValue.False
Represents the value
.BR false .
.TP
.B JValue.Null
Represents a null value of any type.
.TP
.B JValue.True
Represents the value
.BR true .
.TP
.B JValue.Int
Represents as a Limbo
.B big
a JavaScript number with no fractional part.
.TP
.B JValue.Real
Represents as a Limbo
.B real
a JavaScript number with a fractional part.
.TP
.B JValue.String
Represents a JavaScript string of Unicode characters from
.B +U'0000'
to
.BR +U'FFFF' .
.TP
.B JValue.Array
Represents a JavaScript array of values of any type.
.TP
.B JValue.Object
Represents a tuple of (member/property name, value) pairs corresponding to the value of a JavaScript object,
or an associative array or table, indexed by strings.
The member names must be unique within a value.
.PP
.B Readjson
reads a single value in JSON
format from the
.I input
stream and returns a tuple
.BI ( val,\ err ).
On success,
.I val
is a
.B JValue
that represents the value successfully read.
If an error occurs,
.I val
is nil and
.I err
contains a diagnostic.
.PP
.B Writejson
writes to the
.I output
stream in JSON format a
representation of the value
.IR v .
It returns 0 on success and -1 on error (setting the system error string).
.PP
The easiest way to create a new
.B JValue
for subsequent output is with one of the module-level functions
.BR jvarray ,
.BR jvint ,
.BR jvobject ,
.BR jvstring ,
and so on.
As values of a pick adt, a
.B JValue
can be inspected using Limbo's
.B tagof
operator and the appropriate variant accessed using a
.B pick
statement.
.B JValue
also supports several groups of common operations, for smaller, tidier code.
First, the set of enquiry functions
.IB v .is X ()
return true if the value
.I v
is an instance of the JavaScript type
.I X
.RI ( array ,
.IR int ,
.IR object ,
.IR real ,
.IR string ,
etc).
A
.I numeric
value is either
.I int
or
.IR real .
The other operations are:
.TP
.IB v .copy()
Return a (reference to) a copy of value
.IR v .
The copying is not recursive.
.TP
.IB v .eq( w )
Return true if the values of
.I v
and
.I w
are equal, including the values of corresponding subcomponents, recursively
.TP
.IB v .get( mem )
Return the value associated with the member named
.I mem
in
.IR v ;
return null if there is none.
.TP
.IB v .set( mem,\ value )
Adds or changes the
.I value
associated with the member named
.I mem
in
.IR v ,
which must be a
.BR JValue.Object (
raises exception
.B "json: set non-object"
otherwise).
.TP
.IB v .text()
Return a string containing the JSON representation of
.IR v .
.SH SOURCE
.B /appl/lib/json.b
.SH SEE ALSO
.IR sexprs (2),
.IR ubfa (2) ,
.IR json (6),
.IR sexprs (6),
.IR ubfa (6)
.br
D Crockford, ``The application/json Media Type for JavaScript Object Notation (JSON)'',
.IR RFC4627 .