1JSON(3)               User Contributed Perl Documentation              JSON(3)
2
3
4

NAME

6       JSON - JSON (JavaScript Object Notation) encoder/decoder
7

SYNOPSIS

9        use JSON; # imports encode_json, decode_json, to_json and from_json.
10
11        # simple and fast interfaces (expect/generate UTF-8)
12
13        $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
14        $perl_hash_or_arrayref  = decode_json $utf8_encoded_json_text;
15
16        # OO-interface
17
18        $json = JSON->new->allow_nonref;
19
20        $json_text   = $json->encode( $perl_scalar );
21        $perl_scalar = $json->decode( $json_text );
22
23        $pretty_printed = $json->pretty->encode( $perl_scalar ); # pretty-printing
24

VERSION

26           2.97001
27

DESCRIPTION

29       This module is a thin wrapper for JSON::XS-compatible modules with a
30       few additional features. All the backend modules convert a Perl data
31       structure to a JSON text as of RFC4627 (which we know is obsolete but
32       we still stick to; see below for an option to support part of RFC7159)
33       and vice versa.  This module uses JSON::XS by default, and when
34       JSON::XS is not available, this module falls back on JSON::PP, which is
35       in the Perl core since 5.14.  If JSON::PP is not available either, this
36       module then falls back on JSON::backportPP (which is actually JSON::PP
37       in a different .pm file) bundled in the same distribution as this
38       module. You can also explicitly specify to use Cpanel::JSON::XS, a fork
39       of JSON::XS by Reini Urban.
40
41       All these backend modules have slight incompatibilities between them,
42       including extra features that other modules don't support, but as long
43       as you use only common features (most important ones are described
44       below), migration from backend to backend should be reasonably easy.
45       For details, see each backend module you use.
46

CHOOSING BACKEND

48       This module respects an environmental variable called
49       "PERL_JSON_BACKEND" when it decides a backend module to use. If this
50       environmental variable is not set, it tries to load JSON::XS, and if
51       JSON::XS is not available, it falls back on JSON::PP, and then
52       JSON::backportPP if JSON::PP is not available either.
53
54       If you always don't want it to fall back on pure perl modules, set the
55       variable like this ("export" may be "setenv", "set" and the likes,
56       depending on your environment):
57
58         > export PERL_JSON_BACKEND=JSON::XS
59
60       If you prefer Cpanel::JSON::XS to JSON::XS, then:
61
62         > export PERL_JSON_BACKEND=Cpanel::JSON::XS,JSON::XS,JSON::PP
63
64       You may also want to set this variable at the top of your test files,
65       in order not to be bothered with incompatibilities between backends
66       (you need to wrap this in "BEGIN", and set before actually "use"-ing
67       JSON module, as it decides its backend as soon as it's loaded):
68
69         BEGIN { $ENV{PERL_JSON_BACKEND}='JSON::backportPP'; }
70         use JSON;
71

USING OPTIONAL FEATURES

73       There are a few options you can set when you "use" this module:
74
75       -support_by_pp
76              BEGIN { $ENV{PERL_JSON_BACKEND} = 'JSON::XS' }
77
78              use JSON -support_by_pp;
79
80              my $json = JSON->new;
81              # escape_slash is for JSON::PP only.
82              $json->allow_nonref->escape_slash->encode("/");
83
84           With this option, this module loads its pure perl backend along
85           with its XS backend (if available), and lets the XS backend to
86           watch if you set a flag only JSON::PP supports. When you do, the
87           internal JSON::XS object is replaced with a newly created JSON::PP
88           object with the setting copied from the XS object, so that you can
89           use JSON::PP flags (and its slower "decode"/"encode" methods) from
90           then on. In other words, this is not something that allows you to
91           hook JSON::XS to change its behavior while keeping its speed.
92           JSON::XS and JSON::PP objects are quite different (JSON::XS object
93           is a blessed scalar reference, while JSON::PP object is a blessed
94           hash reference), and can't share their internals.
95
96           To avoid needless overhead (by copying settings), you are advised
97           not to use this option and just to use JSON::PP explicitly when you
98           need JSON::PP features.
99
100       -convert_blessed_universally
101              use JSON -convert_blessed_universally;
102
103              my $json = JSON->new->allow_nonref->convert_blessed;
104              my $object = bless {foo => 'bar'}, 'Foo';
105              $json->encode($object); # => {"foo":"bar"}
106
107           JSON::XS-compatible backend modules don't encode blessed objects by
108           default (except for their boolean values, which are typically
109           blessed JSON::PP::Boolean objects). If you need to encode a data
110           structure that may contain objects, you usually need to look into
111           the structure and replace objects with alternative non-blessed
112           values, or enable "convert_blessed" and provide a "TO_JSON" method
113           for each object's (base) class that may be found in the structure,
114           in order to let the methods replace the objects with whatever
115           scalar values the methods return.
116
117           If you need to serialise data structures that may contain arbitrary
118           objects, it's probably better to use other serialisers (such as
119           Sereal or Storable for example), but if you do want to use this
120           module for that purpose, "-convert_blessed_universally" option may
121           help, which tweaks "encode" method of the backend to install
122           "UNIVERSAL::TO_JSON" method (locally) before encoding, so that all
123           the objects that don't have their own "TO_JSON" method can fall
124           back on the method in the "UNIVERSAL" namespace. Note that you
125           still need to enable "convert_blessed" flag to actually encode
126           objects in a data structure, and "UNIVERSAL::TO_JSON" method
127           installed by this option only converts blessed hash/array
128           references into their unblessed clone (including private
129           keys/values that are not supposed to be exposed). Other blessed
130           references will be converted into null.
131
132           This feature is experimental and may be removed in the future.
133
134       -no_export
135           When you don't want to import functional interfaces from a module,
136           you usually supply "()" to its "use" statement.
137
138               use JSON (); # no functional interfaces
139
140           If you don't want to import functional interfaces, but you also
141           want to use any of the above options, add "-no_export" to the
142           option list.
143
144              # no functional interfaces, while JSON::PP support is enabled.
145              use JSON -support_by_pp, -no_export;
146

FUNCTIONAL INTERFACE

148       This section is taken from JSON::XS. "encode_json" and "decode_json"
149       are exported by default.
150
151       This module also exports "to_json" and "from_json" for backward
152       compatibility. These are slower, and may expect/generate different
153       stuff from what "encode_json" and "decode_json" do, depending on their
154       options. It's better just to use Object-Oriented interfaces than using
155       these two functions.
156
157   encode_json
158           $json_text = encode_json $perl_scalar
159
160       Converts the given Perl data structure to a UTF-8 encoded, binary
161       string (that is, the string contains octets only). Croaks on error.
162
163       This function call is functionally identical to:
164
165           $json_text = JSON->new->utf8->encode($perl_scalar)
166
167       Except being faster.
168
169   decode_json
170           $perl_scalar = decode_json $json_text
171
172       The opposite of "encode_json": expects an UTF-8 (binary) string and
173       tries to parse that as an UTF-8 encoded JSON text, returning the
174       resulting reference. Croaks on error.
175
176       This function call is functionally identical to:
177
178           $perl_scalar = JSON->new->utf8->decode($json_text)
179
180       Except being faster.
181
182   to_json
183          $json_text = to_json($perl_scalar[, $optional_hashref])
184
185       Converts the given Perl data structure to a Unicode string by default.
186       Croaks on error.
187
188       Basically, this function call is functionally identical to:
189
190          $json_text = JSON->new->encode($perl_scalar)
191
192       Except being slower.
193
194       You can pass an optional hash reference to modify its behavior, but
195       that may change what "to_json" expects/generates (see "ENCODING/CODESET
196       FLAG NOTES" for details).
197
198          $json_text = to_json($perl_scalar, {utf8 => 1, pretty => 1})
199          # => JSON->new->utf8(1)->pretty(1)->encode($perl_scalar)
200
201   from_json
202          $perl_scalar = from_json($json_text[, $optional_hashref])
203
204       The opposite of "to_json": expects a Unicode string and tries to parse
205       it, returning the resulting reference. Croaks on error.
206
207       Basically, this function call is functionally identical to:
208
209           $perl_scalar = JSON->new->decode($json_text)
210
211       You can pass an optional hash reference to modify its behavior, but
212       that may change what "from_json" expects/generates (see
213       "ENCODING/CODESET FLAG NOTES" for details).
214
215           $perl_scalar = from_json($json_text, {utf8 => 1})
216           # => JSON->new->utf8(1)->decode($json_text)
217
218   JSON::is_bool
219           $is_boolean = JSON::is_bool($scalar)
220
221       Returns true if the passed scalar represents either JSON::true or
222       JSON::false, two constants that act like 1 and 0 respectively and are
223       also used to represent JSON "true" and "false" in Perl strings.
224
225       See MAPPING, below, for more information on how JSON values are mapped
226       to Perl.
227

COMMON OBJECT-ORIENTED INTERFACE

229       This section is also taken from JSON::XS.
230
231       The object oriented interface lets you configure your own encoding or
232       decoding style, within the limits of supported formats.
233
234   new
235           $json = JSON->new
236
237       Creates a new JSON::XS-compatible backend object that can be used to
238       de/encode JSON strings. All boolean flags described below are by
239       default disabled.
240
241       The mutators for flags all return the backend object again and thus
242       calls can be chained:
243
244          my $json = JSON->new->utf8->space_after->encode({a => [1,2]})
245          => {"a": [1, 2]}
246
247   ascii
248           $json = $json->ascii([$enable])
249
250           $enabled = $json->get_ascii
251
252       If $enable is true (or missing), then the "encode" method will not
253       generate characters outside the code range 0..127 (which is ASCII). Any
254       Unicode characters outside that range will be escaped using either a
255       single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape
256       sequence, as per RFC4627. The resulting encoded JSON text can be
257       treated as a native Unicode string, an ascii-encoded, latin1-encoded or
258       UTF-8 encoded string, or any other superset of ASCII.
259
260       If $enable is false, then the "encode" method will not escape Unicode
261       characters unless required by the JSON syntax or other flags. This
262       results in a faster and more compact format.
263
264       See also the section ENCODING/CODESET FLAG NOTES later in this
265       document.
266
267       The main use for this flag is to produce JSON texts that can be
268       transmitted over a 7-bit channel, as the encoded JSON texts will not
269       contain any 8 bit characters.
270
271         JSON->new->ascii(1)->encode([chr 0x10401])
272         => ["\ud801\udc01"]
273
274   latin1
275           $json = $json->latin1([$enable])
276
277           $enabled = $json->get_latin1
278
279       If $enable is true (or missing), then the "encode" method will encode
280       the resulting JSON text as latin1 (or iso-8859-1), escaping any
281       characters outside the code range 0..255. The resulting string can be
282       treated as a latin1-encoded JSON text or a native Unicode string. The
283       "decode" method will not be affected in any way by this flag, as
284       "decode" by default expects Unicode, which is a strict superset of
285       latin1.
286
287       If $enable is false, then the "encode" method will not escape Unicode
288       characters unless required by the JSON syntax or other flags.
289
290       See also the section ENCODING/CODESET FLAG NOTES later in this
291       document.
292
293       The main use for this flag is efficiently encoding binary data as JSON
294       text, as most octets will not be escaped, resulting in a smaller
295       encoded size. The disadvantage is that the resulting JSON text is
296       encoded in latin1 (and must correctly be treated as such when storing
297       and transferring), a rare encoding for JSON. It is therefore most
298       useful when you want to store data structures known to contain binary
299       data efficiently in files or databases, not when talking to other JSON
300       encoders/decoders.
301
302         JSON->new->latin1->encode (["\x{89}\x{abc}"]
303         => ["\x{89}\\u0abc"]    # (perl syntax, U+abc escaped, U+89 not)
304
305   utf8
306           $json = $json->utf8([$enable])
307
308           $enabled = $json->get_utf8
309
310       If $enable is true (or missing), then the "encode" method will encode
311       the JSON result into UTF-8, as required by many protocols, while the
312       "decode" method expects to be handled an UTF-8-encoded string.  Please
313       note that UTF-8-encoded strings do not contain any characters outside
314       the range 0..255, they are thus useful for bytewise/binary I/O. In
315       future versions, enabling this option might enable autodetection of the
316       UTF-16 and UTF-32 encoding families, as described in RFC4627.
317
318       If $enable is false, then the "encode" method will return the JSON
319       string as a (non-encoded) Unicode string, while "decode" expects thus a
320       Unicode string.  Any decoding or encoding (e.g. to UTF-8 or UTF-16)
321       needs to be done yourself, e.g. using the Encode module.
322
323       See also the section ENCODING/CODESET FLAG NOTES later in this
324       document.
325
326       Example, output UTF-16BE-encoded JSON:
327
328         use Encode;
329         $jsontext = encode "UTF-16BE", JSON->new->encode ($object);
330
331       Example, decode UTF-32LE-encoded JSON:
332
333         use Encode;
334         $object = JSON->new->decode (decode "UTF-32LE", $jsontext);
335
336   pretty
337           $json = $json->pretty([$enable])
338
339       This enables (or disables) all of the "indent", "space_before" and
340       "space_after" (and in the future possibly more) flags in one call to
341       generate the most readable (or most compact) form possible.
342
343   indent
344           $json = $json->indent([$enable])
345
346           $enabled = $json->get_indent
347
348       If $enable is true (or missing), then the "encode" method will use a
349       multiline format as output, putting every array member or object/hash
350       key-value pair into its own line, indenting them properly.
351
352       If $enable is false, no newlines or indenting will be produced, and the
353       resulting JSON text is guaranteed not to contain any "newlines".
354
355       This setting has no effect when decoding JSON texts.
356
357   space_before
358           $json = $json->space_before([$enable])
359
360           $enabled = $json->get_space_before
361
362       If $enable is true (or missing), then the "encode" method will add an
363       extra optional space before the ":" separating keys from values in JSON
364       objects.
365
366       If $enable is false, then the "encode" method will not add any extra
367       space at those places.
368
369       This setting has no effect when decoding JSON texts. You will also most
370       likely combine this setting with "space_after".
371
372       Example, space_before enabled, space_after and indent disabled:
373
374          {"key" :"value"}
375
376   space_after
377           $json = $json->space_after([$enable])
378
379           $enabled = $json->get_space_after
380
381       If $enable is true (or missing), then the "encode" method will add an
382       extra optional space after the ":" separating keys from values in JSON
383       objects and extra whitespace after the "," separating key-value pairs
384       and array members.
385
386       If $enable is false, then the "encode" method will not add any extra
387       space at those places.
388
389       This setting has no effect when decoding JSON texts.
390
391       Example, space_before and indent disabled, space_after enabled:
392
393          {"key": "value"}
394
395   relaxed
396           $json = $json->relaxed([$enable])
397
398           $enabled = $json->get_relaxed
399
400       If $enable is true (or missing), then "decode" will accept some
401       extensions to normal JSON syntax (see below). "encode" will not be
402       affected in anyway. Be aware that this option makes you accept invalid
403       JSON texts as if they were valid!. I suggest only to use this option to
404       parse application-specific files written by humans (configuration
405       files, resource files etc.)
406
407       If $enable is false (the default), then "decode" will only accept valid
408       JSON texts.
409
410       Currently accepted extensions are:
411
412       ·   list items can have an end-comma
413
414           JSON separates array elements and key-value pairs with commas. This
415           can be annoying if you write JSON texts manually and want to be
416           able to quickly append elements, so this extension accepts comma at
417           the end of such items not just between them:
418
419              [
420                 1,
421                 2, <- this comma not normally allowed
422              ]
423              {
424                 "k1": "v1",
425                 "k2": "v2", <- this comma not normally allowed
426              }
427
428       ·   shell-style '#'-comments
429
430           Whenever JSON allows whitespace, shell-style comments are
431           additionally allowed. They are terminated by the first carriage-
432           return or line-feed character, after which more white-space and
433           comments are allowed.
434
435             [
436                1, # this comment not allowed in JSON
437                   # neither this one...
438             ]
439
440   canonical
441           $json = $json->canonical([$enable])
442
443           $enabled = $json->get_canonical
444
445       If $enable is true (or missing), then the "encode" method will output
446       JSON objects by sorting their keys. This is adding a comparatively high
447       overhead.
448
449       If $enable is false, then the "encode" method will output key-value
450       pairs in the order Perl stores them (which will likely change between
451       runs of the same script, and can change even within the same run from
452       5.18 onwards).
453
454       This option is useful if you want the same data structure to be encoded
455       as the same JSON text (given the same overall settings). If it is
456       disabled, the same hash might be encoded differently even if contains
457       the same data, as key-value pairs have no inherent ordering in Perl.
458
459       This setting has no effect when decoding JSON texts.
460
461       This setting has currently no effect on tied hashes.
462
463   allow_nonref
464           $json = $json->allow_nonref([$enable])
465
466           $enabled = $json->get_allow_nonref
467
468       If $enable is true (or missing), then the "encode" method can convert a
469       non-reference into its corresponding string, number or null JSON value,
470       which is an extension to RFC4627. Likewise, "decode" will accept those
471       JSON values instead of croaking.
472
473       If $enable is false, then the "encode" method will croak if it isn't
474       passed an arrayref or hashref, as JSON texts must either be an object
475       or array. Likewise, "decode" will croak if given something that is not
476       a JSON object or array.
477
478       Example, encode a Perl scalar as JSON value with enabled
479       "allow_nonref", resulting in an invalid JSON text:
480
481          JSON->new->allow_nonref->encode ("Hello, World!")
482          => "Hello, World!"
483
484   allow_unknown
485           $json = $json->allow_unknown ([$enable])
486
487           $enabled = $json->get_allow_unknown
488
489       If $enable is true (or missing), then "encode" will not throw an
490       exception when it encounters values it cannot represent in JSON (for
491       example, filehandles) but instead will encode a JSON "null" value. Note
492       that blessed objects are not included here and are handled separately
493       by c<allow_nonref>.
494
495       If $enable is false (the default), then "encode" will throw an
496       exception when it encounters anything it cannot encode as JSON.
497
498       This option does not affect "decode" in any way, and it is recommended
499       to leave it off unless you know your communications partner.
500
501   allow_blessed
502           $json = $json->allow_blessed([$enable])
503
504           $enabled = $json->get_allow_blessed
505
506       See "OBJECT SERIALISATION" for details.
507
508       If $enable is true (or missing), then the "encode" method will not barf
509       when it encounters a blessed reference that it cannot convert
510       otherwise. Instead, a JSON "null" value is encoded instead of the
511       object.
512
513       If $enable is false (the default), then "encode" will throw an
514       exception when it encounters a blessed object that it cannot convert
515       otherwise.
516
517       This setting has no effect on "decode".
518
519   convert_blessed
520           $json = $json->convert_blessed([$enable])
521
522           $enabled = $json->get_convert_blessed
523
524       See "OBJECT SERIALISATION" for details.
525
526       If $enable is true (or missing), then "encode", upon encountering a
527       blessed object, will check for the availability of the "TO_JSON" method
528       on the object's class. If found, it will be called in scalar context
529       and the resulting scalar will be encoded instead of the object.
530
531       The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
532       returns other blessed objects, those will be handled in the same way.
533       "TO_JSON" must take care of not causing an endless recursion cycle (==
534       crash) in this case. The name of "TO_JSON" was chosen because other
535       methods called by the Perl core (== not by the user of the object) are
536       usually in upper case letters and to avoid collisions with any
537       "to_json" function or method.
538
539       If $enable is false (the default), then "encode" will not consider this
540       type of conversion.
541
542       This setting has no effect on "decode".
543
544   filter_json_object
545           $json = $json->filter_json_object([$coderef])
546
547       When $coderef is specified, it will be called from "decode" each time
548       it decodes a JSON object. The only argument is a reference to the
549       newly-created hash. If the code references returns a single scalar
550       (which need not be a reference), this value (i.e. a copy of that scalar
551       to avoid aliasing) is inserted into the deserialised data structure. If
552       it returns an empty list (NOTE: not "undef", which is a valid scalar),
553       the original deserialised hash will be inserted. This setting can slow
554       down decoding considerably.
555
556       When $coderef is omitted or undefined, any existing callback will be
557       removed and "decode" will not change the deserialised hash in any way.
558
559       Example, convert all JSON objects into the integer 5:
560
561          my $js = JSON->new->filter_json_object (sub { 5 });
562          # returns [5]
563          $js->decode ('[{}]'); # the given subroutine takes a hash reference.
564          # throw an exception because allow_nonref is not enabled
565          # so a lone 5 is not allowed.
566          $js->decode ('{"a":1, "b":2}');
567
568   filter_json_single_key_object
569           $json = $json->filter_json_single_key_object($key [=> $coderef])
570
571       Works remotely similar to "filter_json_object", but is only called for
572       JSON objects having a single key named $key.
573
574       This $coderef is called before the one specified via
575       "filter_json_object", if any. It gets passed the single value in the
576       JSON object. If it returns a single value, it will be inserted into the
577       data structure. If it returns nothing (not even "undef" but the empty
578       list), the callback from "filter_json_object" will be called next, as
579       if no single-key callback were specified.
580
581       If $coderef is omitted or undefined, the corresponding callback will be
582       disabled. There can only ever be one callback for a given key.
583
584       As this callback gets called less often then the "filter_json_object"
585       one, decoding speed will not usually suffer as much. Therefore, single-
586       key objects make excellent targets to serialise Perl objects into,
587       especially as single-key JSON objects are as close to the type-tagged
588       value concept as JSON gets (it's basically an ID/VALUE tuple). Of
589       course, JSON does not support this in any way, so you need to make sure
590       your data never looks like a serialised Perl hash.
591
592       Typical names for the single object key are "__class_whatever__", or
593       "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
594       things like "__class_md5sum(classname)__", to reduce the risk of
595       clashing with real hashes.
596
597       Example, decode JSON objects of the form "{ "__widget__" => <id> }"
598       into the corresponding $WIDGET{<id>} object:
599
600          # return whatever is in $WIDGET{5}:
601          JSON
602             ->new
603             ->filter_json_single_key_object (__widget__ => sub {
604                   $WIDGET{ $_[0] }
605                })
606             ->decode ('{"__widget__": 5')
607
608          # this can be used with a TO_JSON method in some "widget" class
609          # for serialisation to json:
610          sub WidgetBase::TO_JSON {
611             my ($self) = @_;
612
613             unless ($self->{id}) {
614                $self->{id} = ..get..some..id..;
615                $WIDGET{$self->{id}} = $self;
616             }
617
618             { __widget__ => $self->{id} }
619          }
620
621   max_depth
622           $json = $json->max_depth([$maximum_nesting_depth])
623
624           $max_depth = $json->get_max_depth
625
626       Sets the maximum nesting level (default 512) accepted while encoding or
627       decoding. If a higher nesting level is detected in JSON text or a Perl
628       data structure, then the encoder and decoder will stop and croak at
629       that point.
630
631       Nesting level is defined by number of hash- or arrayrefs that the
632       encoder needs to traverse to reach a given point or the number of "{"
633       or "[" characters without their matching closing parenthesis crossed to
634       reach a given character in a string.
635
636       Setting the maximum depth to one disallows any nesting, so that ensures
637       that the object is only a single hash/object or array.
638
639       If no argument is given, the highest possible setting will be used,
640       which is rarely useful.
641
642   max_size
643           $json = $json->max_size([$maximum_string_size])
644
645           $max_size = $json->get_max_size
646
647       Set the maximum length a JSON text may have (in bytes) where decoding
648       is being attempted. The default is 0, meaning no limit. When "decode"
649       is called on a string that is longer then this many bytes, it will not
650       attempt to decode the string but throw an exception. This setting has
651       no effect on "encode" (yet).
652
653       If no argument is given, the limit check will be deactivated (same as
654       when 0 is specified).
655
656   encode
657           $json_text = $json->encode($perl_scalar)
658
659       Converts the given Perl value or data structure to its JSON
660       representation. Croaks on error.
661
662   decode
663           $perl_scalar = $json->decode($json_text)
664
665       The opposite of "encode": expects a JSON text and tries to parse it,
666       returning the resulting simple scalar or reference. Croaks on error.
667
668   decode_prefix
669           ($perl_scalar, $characters) = $json->decode_prefix($json_text)
670
671       This works like the "decode" method, but instead of raising an
672       exception when there is trailing garbage after the first JSON object,
673       it will silently stop parsing there and return the number of characters
674       consumed so far.
675
676       This is useful if your JSON texts are not delimited by an outer
677       protocol and you need to know where the JSON text ends.
678
679          JSON->new->decode_prefix ("[1] the tail")
680          => ([1], 3)
681

ADDITIONAL METHODS

683       The following methods are for this module only.
684
685   backend
686           $backend = $json->backend
687
688       Since 2.92, "backend" method returns an abstract backend module used
689       currently, which should be JSON::Backend::XS (which inherits JSON::XS
690       or Cpanel::JSON::XS), or JSON::Backend::PP (which inherits JSON::PP),
691       not to monkey-patch the actual backend module globally.
692
693       If you need to know what is used actually, use "isa", instead of string
694       comparison.
695
696   is_xs
697           $boolean = $json->is_xs
698
699       Returns true if the backend inherits JSON::XS or Cpanel::JSON::XS.
700
701   is_pp
702           $boolean = $json->is_pp
703
704       Returns true if the backend inherits JSON::PP.
705
706   property
707           $settings = $json->property()
708
709       Returns a reference to a hash that holds all the common flag settings.
710
711           $json = $json->property('utf8' => 1)
712           $value = $json->property('utf8') # 1
713
714       You can use this to get/set a value of a particular flag.
715

INCREMENTAL PARSING

717       This section is also taken from JSON::XS.
718
719       In some cases, there is the need for incremental parsing of JSON texts.
720       While this module always has to keep both JSON text and resulting Perl
721       data structure in memory at one time, it does allow you to parse a JSON
722       stream incrementally. It does so by accumulating text until it has a
723       full JSON object, which it then can decode. This process is similar to
724       using "decode_prefix" to see if a full JSON object is available, but is
725       much more efficient (and can be implemented with a minimum of method
726       calls).
727
728       This module will only attempt to parse the JSON text once it is sure it
729       has enough text to get a decisive result, using a very simple but truly
730       incremental parser. This means that it sometimes won't stop as early as
731       the full parser, for example, it doesn't detect mismatched parentheses.
732       The only thing it guarantees is that it starts decoding as soon as a
733       syntactically valid JSON text has been seen. This means you need to set
734       resource limits (e.g. "max_size") to ensure the parser will stop
735       parsing in the presence if syntax errors.
736
737       The following methods implement this incremental parser.
738
739   incr_parse
740           $json->incr_parse( [$string] ) # void context
741
742           $obj_or_undef = $json->incr_parse( [$string] ) # scalar context
743
744           @obj_or_empty = $json->incr_parse( [$string] ) # list context
745
746       This is the central parsing function. It can both append new text and
747       extract objects from the stream accumulated so far (both of these
748       functions are optional).
749
750       If $string is given, then this string is appended to the already
751       existing JSON fragment stored in the $json object.
752
753       After that, if the function is called in void context, it will simply
754       return without doing anything further. This can be used to add more
755       text in as many chunks as you want.
756
757       If the method is called in scalar context, then it will try to extract
758       exactly one JSON object. If that is successful, it will return this
759       object, otherwise it will return "undef". If there is a parse error,
760       this method will croak just as "decode" would do (one can then use
761       "incr_skip" to skip the erroneous part). This is the most common way of
762       using the method.
763
764       And finally, in list context, it will try to extract as many objects
765       from the stream as it can find and return them, or the empty list
766       otherwise. For this to work, there must be no separators (other than
767       whitespace) between the JSON objects or arrays, instead they must be
768       concatenated back-to-back. If an error occurs, an exception will be
769       raised as in the scalar context case. Note that in this case, any
770       previously-parsed JSON texts will be lost.
771
772       Example: Parse some JSON arrays/objects in a given string and return
773       them.
774
775           my @objs = JSON->new->incr_parse ("[5][7][1,2]");
776
777   incr_text
778           $lvalue_string = $json->incr_text
779
780       This method returns the currently stored JSON fragment as an lvalue,
781       that is, you can manipulate it. This only works when a preceding call
782       to "incr_parse" in scalar context successfully returned an object.
783       Under all other circumstances you must not call this function (I mean
784       it.  although in simple tests it might actually work, it will fail
785       under real world conditions). As a special exception, you can also call
786       this method before having parsed anything.
787
788       That means you can only use this function to look at or manipulate text
789       before or after complete JSON objects, not while the parser is in the
790       middle of parsing a JSON object.
791
792       This function is useful in two cases: a) finding the trailing text
793       after a JSON object or b) parsing multiple JSON objects separated by
794       non-JSON text (such as commas).
795
796   incr_skip
797           $json->incr_skip
798
799       This will reset the state of the incremental parser and will remove the
800       parsed text from the input buffer so far. This is useful after
801       "incr_parse" died, in which case the input buffer and incremental
802       parser state is left unchanged, to skip the text parsed so far and to
803       reset the parse state.
804
805       The difference to "incr_reset" is that only text until the parse error
806       occurred is removed.
807
808   incr_reset
809           $json->incr_reset
810
811       This completely resets the incremental parser, that is, after this
812       call, it will be as if the parser had never parsed anything.
813
814       This is useful if you want to repeatedly parse JSON objects and want to
815       ignore any trailing data, which means you have to reset the parser
816       after each successful decode.
817

MAPPING

819       Most of this section is also taken from JSON::XS.
820
821       This section describes how the backend modules map Perl values to JSON
822       values and vice versa. These mappings are designed to "do the right
823       thing" in most circumstances automatically, preserving round-tripping
824       characteristics (what you put in comes out as something equivalent).
825
826       For the more enlightened: note that in the following descriptions,
827       lowercase perl refers to the Perl interpreter, while uppercase Perl
828       refers to the abstract Perl language itself.
829
830   JSON -> PERL
831       object
832           A JSON object becomes a reference to a hash in Perl. No ordering of
833           object keys is preserved (JSON does not preserver object key
834           ordering itself).
835
836       array
837           A JSON array becomes a reference to an array in Perl.
838
839       string
840           A JSON string becomes a string scalar in Perl - Unicode codepoints
841           in JSON are represented by the same codepoints in the Perl string,
842           so no manual decoding is necessary.
843
844       number
845           A JSON number becomes either an integer, numeric (floating point)
846           or string scalar in perl, depending on its range and any fractional
847           parts. On the Perl level, there is no difference between those as
848           Perl handles all the conversion details, but an integer may take
849           slightly less memory and might represent more values exactly than
850           floating point numbers.
851
852           If the number consists of digits only, this module will try to
853           represent it as an integer value. If that fails, it will try to
854           represent it as a numeric (floating point) value if that is
855           possible without loss of precision. Otherwise it will preserve the
856           number as a string value (in which case you lose roundtripping
857           ability, as the JSON number will be re-encoded to a JSON string).
858
859           Numbers containing a fractional or exponential part will always be
860           represented as numeric (floating point) values, possibly at a loss
861           of precision (in which case you might lose perfect roundtripping
862           ability, but the JSON number will still be re-encoded as a JSON
863           number).
864
865           Note that precision is not accuracy - binary floating point values
866           cannot represent most decimal fractions exactly, and when
867           converting from and to floating point, this module only guarantees
868           precision up to but not including the least significant bit.
869
870       true, false
871           These JSON atoms become "JSON::true" and "JSON::false",
872           respectively. They are overloaded to act almost exactly like the
873           numbers 1 and 0. You can check whether a scalar is a JSON boolean
874           by using the "JSON::is_bool" function.
875
876       null
877           A JSON null atom becomes "undef" in Perl.
878
879       shell-style comments ("# text")
880           As a nonstandard extension to the JSON syntax that is enabled by
881           the "relaxed" setting, shell-style comments are allowed. They can
882           start anywhere outside strings and go till the end of the line.
883
884   PERL -> JSON
885       The mapping from Perl to JSON is slightly more difficult, as Perl is a
886       truly typeless language, so we can only guess which JSON type is meant
887       by a Perl value.
888
889       hash references
890           Perl hash references become JSON objects. As there is no inherent
891           ordering in hash keys (or JSON objects), they will usually be
892           encoded in a pseudo-random order. This module can optionally sort
893           the hash keys (determined by the canonical flag), so the same data
894           structure will serialise to the same JSON text (given same settings
895           and version of the same backend), but this incurs a runtime
896           overhead and is only rarely useful, e.g. when you want to compare
897           some JSON text against another for equality.
898
899       array references
900           Perl array references become JSON arrays.
901
902       other references
903           Other unblessed references are generally not allowed and will cause
904           an exception to be thrown, except for references to the integers 0
905           and 1, which get turned into "false" and "true" atoms in JSON. You
906           can also use "JSON::false" and "JSON::true" to improve readability.
907
908              encode_json [\0,JSON::true]      # yields [false,true]
909
910       JSON::true, JSON::false, JSON::null
911           These special values become JSON true and JSON false values,
912           respectively. You can also use "\1" and "\0" directly if you want.
913
914       blessed objects
915           Blessed objects are not directly representable in JSON, but
916           "JSON::XS" allows various ways of handling objects. See "OBJECT
917           SERIALISATION", below, for details.
918
919       simple scalars
920           Simple Perl scalars (any scalar that is not a reference) are the
921           most difficult objects to encode: this module will encode undefined
922           scalars as JSON "null" values, scalars that have last been used in
923           a string context before encoding as JSON strings, and anything else
924           as number value:
925
926              # dump as number
927              encode_json [2]                      # yields [2]
928              encode_json [-3.0e17]                # yields [-3e+17]
929              my $value = 5; encode_json [$value]  # yields [5]
930
931              # used as string, so dump as string
932              print $value;
933              encode_json [$value]                 # yields ["5"]
934
935              # undef becomes null
936              encode_json [undef]                  # yields [null]
937
938           You can force the type to be a string by stringifying it:
939
940              my $x = 3.1; # some variable containing a number
941              "$x";        # stringified
942              $x .= "";    # another, more awkward way to stringify
943              print $x;    # perl does it for you, too, quite often
944
945           You can force the type to be a number by numifying it:
946
947              my $x = "3"; # some variable containing a string
948              $x += 0;     # numify it, ensuring it will be dumped as a number
949              $x *= 1;     # same thing, the choice is yours.
950
951           You can not currently force the type in other, less obscure, ways.
952           Tell me if you need this capability (but don't forget to explain
953           why it's needed :).
954
955           Note that numerical precision has the same meaning as under Perl
956           (so binary to decimal conversion follows the same rules as in Perl,
957           which can differ to other languages). Also, your perl interpreter
958           might expose extensions to the floating point numbers of your
959           platform, such as infinities or NaN's - these cannot be represented
960           in JSON, and it is an error to pass those in.
961
962   OBJECT SERIALISATION
963       As for Perl objects, this module only supports a pure JSON
964       representation (without the ability to deserialise the object
965       automatically again).
966
967       SERIALISATION
968
969       What happens when this module encounters a Perl object depends on the
970       "allow_blessed" and "convert_blessed" settings, which are used in this
971       order:
972
973       1. "convert_blessed" is enabled and the object has a "TO_JSON" method.
974           In this case, the "TO_JSON" method of the object is invoked in
975           scalar context. It must return a single scalar that can be directly
976           encoded into JSON. This scalar replaces the object in the JSON
977           text.
978
979           For example, the following "TO_JSON" method will convert all URI
980           objects to JSON strings when serialised. The fact that these values
981           originally were URI objects is lost.
982
983              sub URI::TO_JSON {
984                 my ($uri) = @_;
985                 $uri->as_string
986              }
987
988       2. "allow_blessed" is enabled.
989           The object will be serialised as a JSON null value.
990
991       3. none of the above
992           If none of the settings are enabled or the respective methods are
993           missing, this module throws an exception.
994

ENCODING/CODESET FLAG NOTES

996       This section is taken from JSON::XS.
997
998       The interested reader might have seen a number of flags that signify
999       encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
1000       some confusion on what these do, so here is a short comparison:
1001
1002       "utf8" controls whether the JSON text created by "encode" (and expected
1003       by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
1004       control whether "encode" escapes character values outside their
1005       respective codeset range. Neither of these flags conflict with each
1006       other, although some combinations make less sense than others.
1007
1008       Care has been taken to make all flags symmetrical with respect to
1009       "encode" and "decode", that is, texts encoded with any combination of
1010       these flag values will be correctly decoded when the same flags are
1011       used - in general, if you use different flag settings while encoding
1012       vs. when decoding you likely have a bug somewhere.
1013
1014       Below comes a verbose discussion of these flags. Note that a "codeset"
1015       is simply an abstract set of character-codepoint pairs, while an
1016       encoding takes those codepoint numbers and encodes them, in our case
1017       into octets. Unicode is (among other things) a codeset, UTF-8 is an
1018       encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
1019       encodings at the same time, which can be confusing.
1020
1021       "utf8" flag disabled
1022           When "utf8" is disabled (the default), then "encode"/"decode"
1023           generate and expect Unicode strings, that is, characters with high
1024           ordinal Unicode values (> 255) will be encoded as such characters,
1025           and likewise such characters are decoded as-is, no changes to them
1026           will be done, except "(re-)interpreting" them as Unicode codepoints
1027           or Unicode characters, respectively (to Perl, these are the same
1028           thing in strings unless you do funny/weird/dumb stuff).
1029
1030           This is useful when you want to do the encoding yourself (e.g. when
1031           you want to have UTF-16 encoded JSON texts) or when some other
1032           layer does the encoding for you (for example, when printing to a
1033           terminal using a filehandle that transparently encodes to UTF-8 you
1034           certainly do NOT want to UTF-8 encode your data first and have Perl
1035           encode it another time).
1036
1037       "utf8" flag enabled
1038           If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1039           characters using the corresponding UTF-8 multi-byte sequence, and
1040           will expect your input strings to be encoded as UTF-8, that is, no
1041           "character" of the input string must have any value > 255, as UTF-8
1042           does not allow that.
1043
1044           The "utf8" flag therefore switches between two modes: disabled
1045           means you will get a Unicode string in Perl, enabled means you get
1046           an UTF-8 encoded octet/binary string in Perl.
1047
1048       "latin1" or "ascii" flags enabled
1049           With "latin1" (or "ascii") enabled, "encode" will escape characters
1050           with ordinal values > 255 (> 127 with "ascii") and encode the
1051           remaining characters as specified by the "utf8" flag.
1052
1053           If "utf8" is disabled, then the result is also correctly encoded in
1054           those character sets (as both are proper subsets of Unicode,
1055           meaning that a Unicode string with all character values < 256 is
1056           the same thing as a ISO-8859-1 string, and a Unicode string with
1057           all character values < 128 is the same thing as an ASCII string in
1058           Perl).
1059
1060           If "utf8" is enabled, you still get a correct UTF-8-encoded string,
1061           regardless of these flags, just some more characters will be
1062           escaped using "\uXXXX" then before.
1063
1064           Note that ISO-8859-1-encoded strings are not compatible with UTF-8
1065           encoding, while ASCII-encoded strings are. That is because the
1066           ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the
1067           ISO-8859-1 codeset being a subset of Unicode), while ASCII is.
1068
1069           Surprisingly, "decode" will ignore these flags and so treat all
1070           input values as governed by the "utf8" flag. If it is disabled,
1071           this allows you to decode ISO-8859-1- and ASCII-encoded strings, as
1072           both strict subsets of Unicode. If it is enabled, you can correctly
1073           decode UTF-8 encoded strings.
1074
1075           So neither "latin1" nor "ascii" are incompatible with the "utf8"
1076           flag - they only govern when the JSON output engine escapes a
1077           character or not.
1078
1079           The main use for "latin1" is to relatively efficiently store binary
1080           data as JSON, at the expense of breaking compatibility with most
1081           JSON decoders.
1082
1083           The main use for "ascii" is to force the output to not contain
1084           characters with values > 127, which means you can interpret the
1085           resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
1086           any character set and 8-bit-encoding, and still get the same data
1087           structure back. This is useful when your channel for JSON transfer
1088           is not 8-bit clean or the encoding might be mangled in between
1089           (e.g. in mail), and works because ASCII is a proper subset of most
1090           8-bit and multibyte encodings in use in the world.
1091

BACKWARD INCOMPATIBILITY

1093       Since version 2.90, stringification (and string comparison) for
1094       "JSON::true" and "JSON::false" has not been overloaded. It shouldn't
1095       matter as long as you treat them as boolean values, but a code that
1096       expects they are stringified as "true" or "false" doesn't work as you
1097       have expected any more.
1098
1099           if (JSON::true eq 'true') {  # now fails
1100
1101           print "The result is $JSON::true now."; # => The result is 1 now.
1102
1103       And now these boolean values don't inherit JSON::Boolean, either.  When
1104       you need to test a value is a JSON boolean value or not, use
1105       "JSON::is_bool" function, instead of testing the value inherits a
1106       particular boolean class or not.
1107

BUGS

1109       Please report bugs on backend selection and additional features this
1110       module provides to RT or GitHub issues for this module:
1111
1112       https://rt.cpan.org/Public/Dist/Display.html?Queue=JSON
1113       https://github.com/makamaka/JSON/issues
1114
1115       Please report bugs and feature requests on decoding/encoding and
1116       boolean behaviors to the author of the backend module you are using.
1117

SEE ALSO

1119       JSON::XS, Cpanel::JSON::XS, JSON::PP for backends.
1120
1121       JSON::MaybeXS, an alternative that prefers Cpanel::JSON::XS.
1122
1123       "RFC4627"(<http://www.ietf.org/rfc/rfc4627.txt>)
1124

AUTHOR

1126       Makamaka Hannyaharamitu, <makamaka[at]cpan.org>
1127
1128       JSON::XS was written by  Marc Lehmann <schmorp[at]schmorp.de>
1129
1130       The release of this new version owes to the courtesy of Marc Lehmann.
1131
1133       Copyright 2005-2013 by Makamaka Hannyaharamitu
1134
1135       This library is free software; you can redistribute it and/or modify it
1136       under the same terms as Perl itself.
1137
1138
1139
1140perl v5.28.0                      2017-12-21                           JSON(3)
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