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Revision 1.82 by root, Sun Dec 30 21:24:57 2007 UTC vs.
Revision 1.152 by root, Wed Oct 30 22:11:01 2013 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
		5	=encoding utf-8
4		6
5	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ	7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
6	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)	8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7		9
8	=head1 SYNOPSIS	10	=head1 SYNOPSIS
…		…
35	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
36	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
37		39
38	Beginning with version 2.0 of the JSON module, when both JSON and	40	Beginning with version 2.0 of the JSON module, when both JSON and
39	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be	41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
40	overriden) with no overhead due to emulation (by inheritign constructor	42	overridden) with no overhead due to emulation (by inheriting constructor
41	and methods). If JSON::XS is not available, it will fall back to the	43	and methods). If JSON::XS is not available, it will fall back to the
42	compatible JSON::PP module as backend, so using JSON instead of JSON::XS	44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
43	gives you a portable JSON API that can be fast when you need and doesn't	45	gives you a portable JSON API that can be fast when you need and doesn't
44	require a C compiler when that is a problem.	46	require a C compiler when that is a problem.
45		47
…		…
47	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
48	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
49	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
50	reports for other reasons.	52	reports for other reasons.
51		53
52	See COMPARISON, below, for a comparison to some other JSON modules.
53
54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
55	vice versa.	55	vice versa.
56		56
57	=head2 FEATURES	57	=head2 FEATURES
58		58
59	=over 4	59	=over 4
60		60
61	=item * correct Unicode handling	61	=item * correct Unicode handling
62		62
63	This module knows how to handle Unicode, and even documents how and when	63	This module knows how to handle Unicode, documents how and when it does
64	it does so.	64	so, and even documents what "correct" means.
65		65
66	=item * round-trip integrity	66	=item * round-trip integrity
67		67
68	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
69	by JSON, the deserialised data structure is identical on the Perl level.	69	by JSON and Perl, the deserialised data structure is identical on the Perl
70	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
71	like a number).	71	it looks like a number). There I<are> minor exceptions to this, read the
		72	MAPPING section below to learn about those.
72		73
73	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
74		75
75	There is no guessing, no generating of illegal JSON texts by default,	76	There is no guessing, no generating of illegal JSON texts by default,
76	and only JSON is accepted as input by default (the latter is a security	77	and only JSON is accepted as input by default (the latter is a security
77	feature).	78	feature).
78		79
79	=item * fast	80	=item * fast
80		81
81	Compared to other JSON modules, this module compares favourably in terms	82	Compared to other JSON modules and other serialisers such as Storable,
82	of speed, too.	83	this module usually compares favourably in terms of speed, too.
83		84
84	=item * simple to use	85	=item * simple to use
85		86
86	This module has both a simple functional interface as well as an OO	87	This module has both a simple functional interface as well as an object
87	interface.	88	oriented interface.
88		89
89	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
90		91
91	You can choose between the most compact guaranteed single-line format	92	You can choose between the most compact guaranteed-single-line format
92	possible (nice for simple line-based protocols), a pure-ascii format	93	possible (nice for simple line-based protocols), a pure-ASCII format
93	(for when your transport is not 8-bit clean, still supports the whole	94	(for when your transport is not 8-bit clean, still supports the whole
94	Unicode range), or a pretty-printed format (for when you want to read that	95	Unicode range), or a pretty-printed format (for when you want to read that
95	stuff). Or you can combine those features in whatever way you like.	96	stuff). Or you can combine those features in whatever way you like.
96		97
97	=back	98	=back
98		99
99	=cut	100	=cut
100		101
101	package JSON::XS;	102	package JSON::XS;
102		103
103	use strict;	104	use common::sense;
104		105
105	our $VERSION = '2.01';	106	our $VERSION = 3.01;
106	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
107		108
108	our @EXPORT = qw(encode_json decode_json to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
109
110	sub to_json($) {
111	require Carp;
112	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
113	}
114
115	sub from_json($) {
116	require Carp;
117	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
118	}
119		110
120	use Exporter;	111	use Exporter;
121	use XSLoader;	112	use XSLoader;
122		113
		114	use Types::Serialiser ();
		115
123	=head1 FUNCTIONAL INTERFACE	116	=head1 FUNCTIONAL INTERFACE
124		117
125	The following convenience methods are provided by this module. They are	118	The following convenience methods are provided by this module. They are
126	exported by default:	119	exported by default:
127		120
…		…
134		127
135	This function call is functionally identical to:	128	This function call is functionally identical to:
136		129
137	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	130	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
138		131
139	except being faster.	132	Except being faster.
140		133
141	=item $perl_scalar = decode_json $json_text	134	=item $perl_scalar = decode_json $json_text
142		135
143	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries	136	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
144	to parse that as an UTF-8 encoded JSON text, returning the resulting	137	to parse that as an UTF-8 encoded JSON text, returning the resulting
…		…
146		139
147	This function call is functionally identical to:	140	This function call is functionally identical to:
148		141
149	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	142	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
150		143
151	except being faster.	144	Except being faster.
152
153	=item $is_boolean = JSON::XS::is_bool $scalar
154
155	Returns true if the passed scalar represents either JSON::XS::true or
156	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
157	and are used to represent JSON C<true> and C<false> values in Perl.
158
159	See MAPPING, below, for more information on how JSON values are mapped to
160	Perl.
161		145
162	=back	146	=back
163		147
164		148
165	=head1 A FEW NOTES ON UNICODE AND PERL	149	=head1 A FEW NOTES ON UNICODE AND PERL
…		…
174	This enables you to store Unicode characters as single characters in a	158	This enables you to store Unicode characters as single characters in a
175	Perl string - very natural.	159	Perl string - very natural.
176		160
177	=item 2. Perl does I<not> associate an encoding with your strings.	161	=item 2. Perl does I<not> associate an encoding with your strings.
178		162
179	Unless you force it to, e.g. when matching it against a regex, or printing	163	... until you force it to, e.g. when matching it against a regex, or
180	the scalar to a file, in which case Perl either interprets your string as	164	printing the scalar to a file, in which case Perl either interprets your
181	locale-encoded text, octets/binary, or as Unicode, depending on various	165	string as locale-encoded text, octets/binary, or as Unicode, depending
182	settings. In no case is an encoding stored together with your data, it is	166	on various settings. In no case is an encoding stored together with your
183	I<use> that decides encoding, not any magical metadata.	167	data, it is I<use> that decides encoding, not any magical meta data.
184		168
185	=item 3. The internal utf-8 flag has no meaning with regards to the	169	=item 3. The internal utf-8 flag has no meaning with regards to the
186	encoding of your string.	170	encoding of your string.
187		171
188	Just ignore that flag unless you debug a Perl bug, a module written in	172	Just ignore that flag unless you debug a Perl bug, a module written in
…		…
194		178
195	If you didn't know about that flag, just the better, pretend it doesn't	179	If you didn't know about that flag, just the better, pretend it doesn't
196	exist.	180	exist.
197		181
198	=item 4. A "Unicode String" is simply a string where each character can be	182	=item 4. A "Unicode String" is simply a string where each character can be
199	validly interpreted as a Unicode codepoint.	183	validly interpreted as a Unicode code point.
200		184
201	If you have UTF-8 encoded data, it is no longer a Unicode string, but a	185	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
202	Unicode string encoded in UTF-8, giving you a binary string.	186	Unicode string encoded in UTF-8, giving you a binary string.
203		187
204	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.	188	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
…		…
242		226
243	If C<$enable> is false, then the C<encode> method will not escape Unicode	227	If C<$enable> is false, then the C<encode> method will not escape Unicode
244	characters unless required by the JSON syntax or other flags. This results	228	characters unless required by the JSON syntax or other flags. This results
245	in a faster and more compact format.	229	in a faster and more compact format.
246		230
		231	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		232	document.
		233
247	The main use for this flag is to produce JSON texts that can be	234	The main use for this flag is to produce JSON texts that can be
248	transmitted over a 7-bit channel, as the encoded JSON texts will not	235	transmitted over a 7-bit channel, as the encoded JSON texts will not
249	contain any 8 bit characters.	236	contain any 8 bit characters.
250		237
251	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	238	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
262	will not be affected in any way by this flag, as C<decode> by default	249	will not be affected in any way by this flag, as C<decode> by default
263	expects Unicode, which is a strict superset of latin1.	250	expects Unicode, which is a strict superset of latin1.
264		251
265	If C<$enable> is false, then the C<encode> method will not escape Unicode	252	If C<$enable> is false, then the C<encode> method will not escape Unicode
266	characters unless required by the JSON syntax or other flags.	253	characters unless required by the JSON syntax or other flags.
		254
		255	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		256	document.
267		257
268	The main use for this flag is efficiently encoding binary data as JSON	258	The main use for this flag is efficiently encoding binary data as JSON
269	text, as most octets will not be escaped, resulting in a smaller encoded	259	text, as most octets will not be escaped, resulting in a smaller encoded
270	size. The disadvantage is that the resulting JSON text is encoded	260	size. The disadvantage is that the resulting JSON text is encoded
271	in latin1 (and must correctly be treated as such when storing and	261	in latin1 (and must correctly be treated as such when storing and
…		…
290		280
291	If C<$enable> is false, then the C<encode> method will return the JSON	281	If C<$enable> is false, then the C<encode> method will return the JSON
292	string as a (non-encoded) Unicode string, while C<decode> expects thus a	282	string as a (non-encoded) Unicode string, while C<decode> expects thus a
293	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	283	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
294	to be done yourself, e.g. using the Encode module.	284	to be done yourself, e.g. using the Encode module.
		285
		286	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		287	document.
295		288
296	Example, output UTF-16BE-encoded JSON:	289	Example, output UTF-16BE-encoded JSON:
297		290
298	use Encode;	291	use Encode;
299	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	292	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
422	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	415	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
423	by sorting their keys. This is adding a comparatively high overhead.	416	by sorting their keys. This is adding a comparatively high overhead.
424		417
425	If C<$enable> is false, then the C<encode> method will output key-value	418	If C<$enable> is false, then the C<encode> method will output key-value
426	pairs in the order Perl stores them (which will likely change between runs	419	pairs in the order Perl stores them (which will likely change between runs
427	of the same script).	420	of the same script, and can change even within the same run from 5.18
		421	onwards).
428		422
429	This option is useful if you want the same data structure to be encoded as	423	This option is useful if you want the same data structure to be encoded as
430	the same JSON text (given the same overall settings). If it is disabled,	424	the same JSON text (given the same overall settings). If it is disabled,
431	the same hash might be encoded differently even if contains the same data,	425	the same hash might be encoded differently even if contains the same data,
432	as key-value pairs have no inherent ordering in Perl.	426	as key-value pairs have no inherent ordering in Perl.
433		427
434	This setting has no effect when decoding JSON texts.	428	This setting has no effect when decoding JSON texts.
435		429
		430	This setting has currently no effect on tied hashes.
		431
436	=item $json = $json->allow_nonref ([$enable])	432	=item $json = $json->allow_nonref ([$enable])
437		433
438	=item $enabled = $json->get_allow_nonref	434	=item $enabled = $json->get_allow_nonref
439		435
440	If C<$enable> is true (or missing), then the C<encode> method can convert a	436	If C<$enable> is true (or missing), then the C<encode> method can convert a
…		…
451	resulting in an invalid JSON text:	447	resulting in an invalid JSON text:
452		448
453	JSON::XS->new->allow_nonref->encode ("Hello, World!")	449	JSON::XS->new->allow_nonref->encode ("Hello, World!")
454	=> "Hello, World!"	450	=> "Hello, World!"
455		451
		452	=item $json = $json->allow_unknown ([$enable])
		453
		454	=item $enabled = $json->get_allow_unknown
		455
		456	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		457	exception when it encounters values it cannot represent in JSON (for
		458	example, filehandles) but instead will encode a JSON C<null> value. Note
		459	that blessed objects are not included here and are handled separately by
		460	c<allow_nonref>.
		461
		462	If C<$enable> is false (the default), then C<encode> will throw an
		463	exception when it encounters anything it cannot encode as JSON.
		464
		465	This option does not affect C<decode> in any way, and it is recommended to
		466	leave it off unless you know your communications partner.
		467
456	=item $json = $json->allow_blessed ([$enable])	468	=item $json = $json->allow_blessed ([$enable])
457		469
458	=item $enabled = $json->get_allow_blessed	470	=item $enabled = $json->get_allow_blessed
459		471
		472	See L<OBJECT SERIALISATION> for details.
		473
460	If C<$enable> is true (or missing), then the C<encode> method will not	474	If C<$enable> is true (or missing), then the C<encode> method will not
461	barf when it encounters a blessed reference. Instead, the value of the	475	barf when it encounters a blessed reference that it cannot convert
462	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>	476	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
463	disabled or no C<TO_JSON> method found) or a representation of the
464	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
465	encoded. Has no effect on C<decode>.
466		477
467	If C<$enable> is false (the default), then C<encode> will throw an	478	If C<$enable> is false (the default), then C<encode> will throw an
468	exception when it encounters a blessed object.	479	exception when it encounters a blessed object that it cannot convert
		480	otherwise.
		481
		482	This setting has no effect on C<decode>.
469		483
470	=item $json = $json->convert_blessed ([$enable])	484	=item $json = $json->convert_blessed ([$enable])
471		485
472	=item $enabled = $json->get_convert_blessed	486	=item $enabled = $json->get_convert_blessed
		487
		488	See L<OBJECT SERIALISATION> for details.
473		489
474	If C<$enable> is true (or missing), then C<encode>, upon encountering a	490	If C<$enable> is true (or missing), then C<encode>, upon encountering a
475	blessed object, will check for the availability of the C<TO_JSON> method	491	blessed object, will check for the availability of the C<TO_JSON> method
476	on the object's class. If found, it will be called in scalar context	492	on the object's class. If found, it will be called in scalar context and
477	and the resulting scalar will be encoded instead of the object. If no	493	the resulting scalar will be encoded instead of the object.
478	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
479	to do.
480		494
481	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	495	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
482	returns other blessed objects, those will be handled in the same	496	returns other blessed objects, those will be handled in the same
483	way. C<TO_JSON> must take care of not causing an endless recursion cycle	497	way. C<TO_JSON> must take care of not causing an endless recursion cycle
484	(== crash) in this case. The name of C<TO_JSON> was chosen because other	498	(== crash) in this case. The name of C<TO_JSON> was chosen because other
485	methods called by the Perl core (== not by the user of the object) are	499	methods called by the Perl core (== not by the user of the object) are
486	usually in upper case letters and to avoid collisions with any C<to_json>	500	usually in upper case letters and to avoid collisions with any C<to_json>
487	function or method.	501	function or method.
488		502
489	This setting does not yet influence C<decode> in any way, but in the	503	If C<$enable> is false (the default), then C<encode> will not consider
490	future, global hooks might get installed that influence C<decode> and are	504	this type of conversion.
491	enabled by this setting.
492		505
493	If C<$enable> is false, then the C<allow_blessed> setting will decide what	506	This setting has no effect on C<decode>.
494	to do when a blessed object is found.	507
		508	=item $json = $json->allow_tags ([$enable])
		509
		510	=item $enabled = $json->allow_tags
		511
		512	See L<OBJECT SERIALISATION> for details.
		513
		514	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		515	blessed object, will check for the availability of the C<FREEZE> method on
		516	the object's class. If found, it will be used to serialise the object into
		517	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		518
		519	It also causes C<decode> to parse such tagged JSON values and deserialise
		520	them via a call to the C<THAW> method.
		521
		522	If C<$enable> is false (the default), then C<encode> will not consider
		523	this type of conversion, and tagged JSON values will cause a parse error
		524	in C<decode>, as if tags were not part of the grammar.
495		525
496	=item $json = $json->filter_json_object ([$coderef->($hashref)])	526	=item $json = $json->filter_json_object ([$coderef->($hashref)])
497		527
498	When C<$coderef> is specified, it will be called from C<decode> each	528	When C<$coderef> is specified, it will be called from C<decode> each
499	time it decodes a JSON object. The only argument is a reference to the	529	time it decodes a JSON object. The only argument is a reference to the
…		…
600	=item $json = $json->max_depth ([$maximum_nesting_depth])	630	=item $json = $json->max_depth ([$maximum_nesting_depth])
601		631
602	=item $max_depth = $json->get_max_depth	632	=item $max_depth = $json->get_max_depth
603		633
604	Sets the maximum nesting level (default C<512>) accepted while encoding	634	Sets the maximum nesting level (default C<512>) accepted while encoding
605	or decoding. If the JSON text or Perl data structure has an equal or	635	or decoding. If a higher nesting level is detected in JSON text or a Perl
606	higher nesting level then this limit, then the encoder and decoder will	636	data structure, then the encoder and decoder will stop and croak at that
607	stop and croak at that point.	637	point.
608		638
609	Nesting level is defined by number of hash- or arrayrefs that the encoder	639	Nesting level is defined by number of hash- or arrayrefs that the encoder
610	needs to traverse to reach a given point or the number of C<{> or C<[>	640	needs to traverse to reach a given point or the number of C<{> or C<[>
611	characters without their matching closing parenthesis crossed to reach a	641	characters without their matching closing parenthesis crossed to reach a
612	given character in a string.	642	given character in a string.
613		643
614	Setting the maximum depth to one disallows any nesting, so that ensures	644	Setting the maximum depth to one disallows any nesting, so that ensures
615	that the object is only a single hash/object or array.	645	that the object is only a single hash/object or array.
616		646
617	The argument to C<max_depth> will be rounded up to the next highest power
618	of two. If no argument is given, the highest possible setting will be	647	If no argument is given, the highest possible setting will be used, which
619	used, which is rarely useful.	648	is rarely useful.
		649
		650	Note that nesting is implemented by recursion in C. The default value has
		651	been chosen to be as large as typical operating systems allow without
		652	crashing.
620		653
621	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	654	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
622		655
623	=item $json = $json->max_size ([$maximum_string_size])	656	=item $json = $json->max_size ([$maximum_string_size])
624		657
625	=item $max_size = $json->get_max_size	658	=item $max_size = $json->get_max_size
626		659
627	Set the maximum length a JSON text may have (in bytes) where decoding is	660	Set the maximum length a JSON text may have (in bytes) where decoding is
628	being attempted. The default is C<0>, meaning no limit. When C<decode>	661	being attempted. The default is C<0>, meaning no limit. When C<decode>
629	is called on a string longer then this number of characters it will not	662	is called on a string that is longer then this many bytes, it will not
630	attempt to decode the string but throw an exception. This setting has no	663	attempt to decode the string but throw an exception. This setting has no
631	effect on C<encode> (yet).	664	effect on C<encode> (yet).
632		665
633	The argument to C<max_size> will be rounded up to the next B<highest>	666	If no argument is given, the limit check will be deactivated (same as when
634	power of two (so may be more than requested). If no argument is given, the	667	C<0> is specified).
635	limit check will be deactivated (same as when C<0> is specified).
636		668
637	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	669	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
638		670
639	=item $json_text = $json->encode ($perl_scalar)	671	=item $json_text = $json->encode ($perl_scalar)
640		672
641	Converts the given Perl data structure (a simple scalar or a reference	673	Converts the given Perl value or data structure to its JSON
642	to a hash or array) to its JSON representation. Simple scalars will be	674	representation. Croaks on error.
643	converted into JSON string or number sequences, while references to arrays
644	become JSON arrays and references to hashes become JSON objects. Undefined
645	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
646	nor C<false> values will be generated.
647		675
648	=item $perl_scalar = $json->decode ($json_text)	676	=item $perl_scalar = $json->decode ($json_text)
649		677
650	The opposite of C<encode>: expects a JSON text and tries to parse it,	678	The opposite of C<encode>: expects a JSON text and tries to parse it,
651	returning the resulting simple scalar or reference. Croaks on error.	679	returning the resulting simple scalar or reference. Croaks on error.
652
653	JSON numbers and strings become simple Perl scalars. JSON arrays become
654	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
655	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
656		680
657	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	681	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
658		682
659	This works like the C<decode> method, but instead of raising an exception	683	This works like the C<decode> method, but instead of raising an exception
660	when there is trailing garbage after the first JSON object, it will	684	when there is trailing garbage after the first JSON object, it will
661	silently stop parsing there and return the number of characters consumed	685	silently stop parsing there and return the number of characters consumed
662	so far.	686	so far.
663		687
664	This is useful if your JSON texts are not delimited by an outer protocol	688	This is useful if your JSON texts are not delimited by an outer protocol
665	(which is not the brightest thing to do in the first place) and you need
666	to know where the JSON text ends.	689	and you need to know where the JSON text ends.
667		690
668	JSON::XS->new->decode_prefix ("[1] the tail")	691	JSON::XS->new->decode_prefix ("[1] the tail")
669	=> ([], 3)	692	=> ([], 3)
670		693
671	=back	694	=back
		695
		696
		697	=head1 INCREMENTAL PARSING
		698
		699	In some cases, there is the need for incremental parsing of JSON
		700	texts. While this module always has to keep both JSON text and resulting
		701	Perl data structure in memory at one time, it does allow you to parse a
		702	JSON stream incrementally. It does so by accumulating text until it has
		703	a full JSON object, which it then can decode. This process is similar to
		704	using C<decode_prefix> to see if a full JSON object is available, but
		705	is much more efficient (and can be implemented with a minimum of method
		706	calls).
		707
		708	JSON::XS will only attempt to parse the JSON text once it is sure it
		709	has enough text to get a decisive result, using a very simple but
		710	truly incremental parser. This means that it sometimes won't stop as
		711	early as the full parser, for example, it doesn't detect mismatched
		712	parentheses. The only thing it guarantees is that it starts decoding as
		713	soon as a syntactically valid JSON text has been seen. This means you need
		714	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		715	parsing in the presence if syntax errors.
		716
		717	The following methods implement this incremental parser.
		718
		719	=over 4
		720
		721	=item [void, scalar or list context] = $json->incr_parse ([$string])
		722
		723	This is the central parsing function. It can both append new text and
		724	extract objects from the stream accumulated so far (both of these
		725	functions are optional).
		726
		727	If C<$string> is given, then this string is appended to the already
		728	existing JSON fragment stored in the C<$json> object.
		729
		730	After that, if the function is called in void context, it will simply
		731	return without doing anything further. This can be used to add more text
		732	in as many chunks as you want.
		733
		734	If the method is called in scalar context, then it will try to extract
		735	exactly I<one> JSON object. If that is successful, it will return this
		736	object, otherwise it will return C<undef>. If there is a parse error,
		737	this method will croak just as C<decode> would do (one can then use
		738	C<incr_skip> to skip the erroneous part). This is the most common way of
		739	using the method.
		740
		741	And finally, in list context, it will try to extract as many objects
		742	from the stream as it can find and return them, or the empty list
		743	otherwise. For this to work, there must be no separators between the JSON
		744	objects or arrays, instead they must be concatenated back-to-back. If
		745	an error occurs, an exception will be raised as in the scalar context
		746	case. Note that in this case, any previously-parsed JSON texts will be
		747	lost.
		748
		749	Example: Parse some JSON arrays/objects in a given string and return
		750	them.
		751
		752	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		753
		754	=item $lvalue_string = $json->incr_text
		755
		756	This method returns the currently stored JSON fragment as an lvalue, that
		757	is, you can manipulate it. This I<only> works when a preceding call to
		758	C<incr_parse> in I<scalar context> successfully returned an object. Under
		759	all other circumstances you must not call this function (I mean it.
		760	although in simple tests it might actually work, it I<will> fail under
		761	real world conditions). As a special exception, you can also call this
		762	method before having parsed anything.
		763
		764	This function is useful in two cases: a) finding the trailing text after a
		765	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		766	(such as commas).
		767
		768	=item $json->incr_skip
		769
		770	This will reset the state of the incremental parser and will remove
		771	the parsed text from the input buffer so far. This is useful after
		772	C<incr_parse> died, in which case the input buffer and incremental parser
		773	state is left unchanged, to skip the text parsed so far and to reset the
		774	parse state.
		775
		776	The difference to C<incr_reset> is that only text until the parse error
		777	occurred is removed.
		778
		779	=item $json->incr_reset
		780
		781	This completely resets the incremental parser, that is, after this call,
		782	it will be as if the parser had never parsed anything.
		783
		784	This is useful if you want to repeatedly parse JSON objects and want to
		785	ignore any trailing data, which means you have to reset the parser after
		786	each successful decode.
		787
		788	=back
		789
		790	=head2 LIMITATIONS
		791
		792	All options that affect decoding are supported, except
		793	C<allow_nonref>. The reason for this is that it cannot be made to work
		794	sensibly: JSON objects and arrays are self-delimited, i.e. you can
		795	concatenate them back to back and still decode them perfectly. This does
		796	not hold true for JSON numbers, however.
		797
		798	For example, is the string C<1> a single JSON number, or is it simply the
		799	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		800	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		801	takes the conservative route and disallows this case.
		802
		803	=head2 EXAMPLES
		804
		805	Some examples will make all this clearer. First, a simple example that
		806	works similarly to C<decode_prefix>: We want to decode the JSON object at
		807	the start of a string and identify the portion after the JSON object:
		808
		809	my $text = "[1,2,3] hello";
		810
		811	my $json = new JSON::XS;
		812
		813	my $obj = $json->incr_parse ($text)
		814	or die "expected JSON object or array at beginning of string";
		815
		816	my $tail = $json->incr_text;
		817	# $tail now contains " hello"
		818
		819	Easy, isn't it?
		820
		821	Now for a more complicated example: Imagine a hypothetical protocol where
		822	you read some requests from a TCP stream, and each request is a JSON
		823	array, without any separation between them (in fact, it is often useful to
		824	use newlines as "separators", as these get interpreted as whitespace at
		825	the start of the JSON text, which makes it possible to test said protocol
		826	with C<telnet>...).
		827
		828	Here is how you'd do it (it is trivial to write this in an event-based
		829	manner):
		830
		831	my $json = new JSON::XS;
		832
		833	# read some data from the socket
		834	while (sysread $socket, my $buf, 4096) {
		835
		836	# split and decode as many requests as possible
		837	for my $request ($json->incr_parse ($buf)) {
		838	# act on the $request
		839	}
		840	}
		841
		842	Another complicated example: Assume you have a string with JSON objects
		843	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		844	[3]>). To parse them, we have to skip the commas between the JSON texts,
		845	and here is where the lvalue-ness of C<incr_text> comes in useful:
		846
		847	my $text = "[1],[2], [3]";
		848	my $json = new JSON::XS;
		849
		850	# void context, so no parsing done
		851	$json->incr_parse ($text);
		852
		853	# now extract as many objects as possible. note the
		854	# use of scalar context so incr_text can be called.
		855	while (my $obj = $json->incr_parse) {
		856	# do something with $obj
		857
		858	# now skip the optional comma
		859	$json->incr_text =~ s/^ \s* , //x;
		860	}
		861
		862	Now lets go for a very complex example: Assume that you have a gigantic
		863	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		864	but you cannot load it into memory fully (this has actually happened in
		865	the real world :).
		866
		867	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		868	can still help you: You implement a (very simple) array parser and let
		869	JSON decode the array elements, which are all full JSON objects on their
		870	own (this wouldn't work if the array elements could be JSON numbers, for
		871	example):
		872
		873	my $json = new JSON::XS;
		874
		875	# open the monster
		876	open my $fh, "<bigfile.json"
		877	or die "bigfile: $!";
		878
		879	# first parse the initial "["
		880	for (;;) {
		881	sysread $fh, my $buf, 65536
		882	or die "read error: $!";
		883	$json->incr_parse ($buf); # void context, so no parsing
		884
		885	# Exit the loop once we found and removed(!) the initial "[".
		886	# In essence, we are (ab-)using the $json object as a simple scalar
		887	# we append data to.
		888	last if $json->incr_text =~ s/^ \s* \[ //x;
		889	}
		890
		891	# now we have the skipped the initial "[", so continue
		892	# parsing all the elements.
		893	for (;;) {
		894	# in this loop we read data until we got a single JSON object
		895	for (;;) {
		896	if (my $obj = $json->incr_parse) {
		897	# do something with $obj
		898	last;
		899	}
		900
		901	# add more data
		902	sysread $fh, my $buf, 65536
		903	or die "read error: $!";
		904	$json->incr_parse ($buf); # void context, so no parsing
		905	}
		906
		907	# in this loop we read data until we either found and parsed the
		908	# separating "," between elements, or the final "]"
		909	for (;;) {
		910	# first skip whitespace
		911	$json->incr_text =~ s/^\s*//;
		912
		913	# if we find "]", we are done
		914	if ($json->incr_text =~ s/^\]//) {
		915	print "finished.\n";
		916	exit;
		917	}
		918
		919	# if we find ",", we can continue with the next element
		920	if ($json->incr_text =~ s/^,//) {
		921	last;
		922	}
		923
		924	# if we find anything else, we have a parse error!
		925	if (length $json->incr_text) {
		926	die "parse error near ", $json->incr_text;
		927	}
		928
		929	# else add more data
		930	sysread $fh, my $buf, 65536
		931	or die "read error: $!";
		932	$json->incr_parse ($buf); # void context, so no parsing
		933	}
		934
		935	This is a complex example, but most of the complexity comes from the fact
		936	that we are trying to be correct (bear with me if I am wrong, I never ran
		937	the above example :).
		938
672		939
673		940
674	=head1 MAPPING	941	=head1 MAPPING
675		942
676	This section describes how JSON::XS maps Perl values to JSON values and	943	This section describes how JSON::XS maps Perl values to JSON values and
…		…
706		973
707	A JSON number becomes either an integer, numeric (floating point) or	974	A JSON number becomes either an integer, numeric (floating point) or
708	string scalar in perl, depending on its range and any fractional parts. On	975	string scalar in perl, depending on its range and any fractional parts. On
709	the Perl level, there is no difference between those as Perl handles all	976	the Perl level, there is no difference between those as Perl handles all
710	the conversion details, but an integer may take slightly less memory and	977	the conversion details, but an integer may take slightly less memory and
711	might represent more values exactly than (floating point) numbers.	978	might represent more values exactly than floating point numbers.
712		979
713	If the number consists of digits only, JSON::XS will try to represent	980	If the number consists of digits only, JSON::XS will try to represent
714	it as an integer value. If that fails, it will try to represent it as	981	it as an integer value. If that fails, it will try to represent it as
715	a numeric (floating point) value if that is possible without loss of	982	a numeric (floating point) value if that is possible without loss of
716	precision. Otherwise it will preserve the number as a string value.	983	precision. Otherwise it will preserve the number as a string value (in
		984	which case you lose roundtripping ability, as the JSON number will be
		985	re-encoded to a JSON string).
717		986
718	Numbers containing a fractional or exponential part will always be	987	Numbers containing a fractional or exponential part will always be
719	represented as numeric (floating point) values, possibly at a loss of	988	represented as numeric (floating point) values, possibly at a loss of
720	precision.	989	precision (in which case you might lose perfect roundtripping ability, but
		990	the JSON number will still be re-encoded as a JSON number).
721		991
722	This might create round-tripping problems as numbers might become strings,	992	Note that precision is not accuracy - binary floating point values cannot
723	but as Perl is typeless there is no other way to do it.	993	represent most decimal fractions exactly, and when converting from and to
		994	floating point, JSON::XS only guarantees precision up to but not including
		995	the least significant bit.
724		996
725	=item true, false	997	=item true, false
726		998
727	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	999	These JSON atoms become C<Types::Serialiser::true> and
728	respectively. They are overloaded to act almost exactly like the numbers	1000	C<Types::Serialiser::false>, respectively. They are overloaded to act
729	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using	1001	almost exactly like the numbers C<1> and C<0>. You can check whether
730	the C<JSON::XS::is_bool> function.	1002	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1003	function (after C<use Types::Serialier>, of course).
731		1004
732	=item null	1005	=item null
733		1006
734	A JSON null atom becomes C<undef> in Perl.	1007	A JSON null atom becomes C<undef> in Perl.
		1008
		1009	=item shell-style comments (C<< # I<text> >>)
		1010
		1011	As a nonstandard extension to the JSON syntax that is enabled by the
		1012	C<relaxed> setting, shell-style comments are allowed. They can start
		1013	anywhere outside strings and go till the end of the line.
		1014
		1015	=item tagged values (C<< (I<tag>)I<value> >>).
		1016
		1017	Another nonstandard extension to the JSON syntax, enabled with the
		1018	C<allow_tags> setting, are tagged values. In this implementation, the
		1019	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1020	I<value> must be a JSON array encoding optional constructor arguments.
		1021
		1022	See L<OBJECT SERIALISATION>, below, for details.
735		1023
736	=back	1024	=back
737		1025
738		1026
739	=head2 PERL -> JSON	1027	=head2 PERL -> JSON
…		…
744		1032
745	=over 4	1033	=over 4
746		1034
747	=item hash references	1035	=item hash references
748		1036
749	Perl hash references become JSON objects. As there is no inherent ordering	1037	Perl hash references become JSON objects. As there is no inherent
750	in hash keys (or JSON objects), they will usually be encoded in a	1038	ordering in hash keys (or JSON objects), they will usually be encoded
751	pseudo-random order that can change between runs of the same program but	1039	in a pseudo-random order. JSON::XS can optionally sort the hash keys
752	stays generally the same within a single run of a program. JSON::XS can	1040	(determined by the I<canonical> flag), so the same datastructure will
753	optionally sort the hash keys (determined by the I<canonical> flag), so	1041	serialise to the same JSON text (given same settings and version of
754	the same datastructure will serialise to the same JSON text (given same	1042	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
755	settings and version of JSON::XS), but this incurs a runtime overhead	1043	e.g. when you want to compare some JSON text against another for equality.
756	and is only rarely useful, e.g. when you want to compare some JSON text
757	against another for equality.
758		1044
759	=item array references	1045	=item array references
760		1046
761	Perl array references become JSON arrays.	1047	Perl array references become JSON arrays.
762		1048
763	=item other references	1049	=item other references
764		1050
765	Other unblessed references are generally not allowed and will cause an	1051	Other unblessed references are generally not allowed and will cause an
766	exception to be thrown, except for references to the integers C<0> and	1052	exception to be thrown, except for references to the integers C<0> and
767	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1053	C<1>, which get turned into C<false> and C<true> atoms in JSON.
768	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
769		1054
		1055	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1056	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1057	and C<Types::Serialiser::true> to improve readability.
		1058
		1059	use Types::Serialiser;
770	encode_json [\0,JSON::XS::true] # yields [false,true]	1060	encode_json [\0, Types::Serialiser::true] # yields [false,true]
771		1061
772	=item JSON::XS::true, JSON::XS::false	1062	=item Types::Serialiser::true, Types::Serialiser::false
773		1063
774	These special values become JSON true and JSON false values,	1064	These special values from the L<Types::Serialiser> module become JSON true
775	respectively. You can also use C<\1> and C<\0> directly if you want.	1065	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1066	directly if you want.
776		1067
777	=item blessed objects	1068	=item blessed objects
778		1069
779	Blessed objects are not allowed. JSON::XS currently tries to encode their	1070	Blessed objects are not directly representable in JSON, but C<JSON::XS>
780	underlying representation (hash- or arrayref), but this behaviour might	1071	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
781	change in future versions.	1072	below, for details.
782		1073
783	=item simple scalars	1074	=item simple scalars
784		1075
785	Simple Perl scalars (any scalar that is not a reference) are the most	1076	Simple Perl scalars (any scalar that is not a reference) are the most
786	difficult objects to encode: JSON::XS will encode undefined scalars as	1077	difficult objects to encode: JSON::XS will encode undefined scalars as
787	JSON null value, scalars that have last been used in a string context	1078	JSON C<null> values, scalars that have last been used in a string context
788	before encoding as JSON strings and anything else as number value:	1079	before encoding as JSON strings, and anything else as number value:
789		1080
790	# dump as number	1081	# dump as number
791	encode_json [2] # yields [2]	1082	encode_json [2] # yields [2]
792	encode_json [-3.0e17] # yields [-3e+17]	1083	encode_json [-3.0e17] # yields [-3e+17]
793	my $value = 5; encode_json [$value] # yields [5]	1084	my $value = 5; encode_json [$value] # yields [5]
…		…
811	my $x = "3"; # some variable containing a string	1102	my $x = "3"; # some variable containing a string
812	$x += 0; # numify it, ensuring it will be dumped as a number	1103	$x += 0; # numify it, ensuring it will be dumped as a number
813	$x *= 1; # same thing, the choice is yours.	1104	$x *= 1; # same thing, the choice is yours.
814		1105
815	You can not currently force the type in other, less obscure, ways. Tell me	1106	You can not currently force the type in other, less obscure, ways. Tell me
816	if you need this capability.	1107	if you need this capability (but don't forget to explain why it's needed
		1108	:).
		1109
		1110	Note that numerical precision has the same meaning as under Perl (so
		1111	binary to decimal conversion follows the same rules as in Perl, which
		1112	can differ to other languages). Also, your perl interpreter might expose
		1113	extensions to the floating point numbers of your platform, such as
		1114	infinities or NaN's - these cannot be represented in JSON, and it is an
		1115	error to pass those in.
817		1116
818	=back	1117	=back
819		1118
		1119	=head2 OBJECT SERIALISATION
820		1120
821	=head1 COMPARISON	1121	As JSON cannot directly represent Perl objects, you have to choose between
		1122	a pure JSON representation (without the ability to deserialise the object
		1123	automatically again), and a nonstandard extension to the JSON syntax,
		1124	tagged values.
822		1125
823	As already mentioned, this module was created because none of the existing	1126	=head3 SERIALISATION
824	JSON modules could be made to work correctly. First I will describe the	1127
825	problems (or pleasures) I encountered with various existing JSON modules,	1128	What happens when C<JSON::XS> encounters a Perl object depends on the
826	followed by some benchmark values. JSON::XS was designed not to suffer	1129	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
827	from any of these problems or limitations.	1130	used in this order:
828		1131
829	=over 4	1132	=over 4
830		1133
831	=item JSON 1.07	1134	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
832		1135
833	Slow (but very portable, as it is written in pure Perl).	1136	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1137	serialisation protocol to create a tagged JSON value, using a nonstandard
		1138	extension to the JSON syntax.
834		1139
835	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1140	This works by invoking the C<FREEZE> method on the object, with the first
836	undocumented. One can get far by feeding it Unicode strings and doing	1141	argument being the object to serialise, and the second argument being the
837	en-/decoding oneself, but Unicode escapes are not working properly).	1142	constant string C<JSON> to distinguish it from other serialisers.
838		1143
839	No round-tripping (strings get clobbered if they look like numbers, e.g.	1144	The C<FREEZE> method can return any number of values (i.e. zero or
840	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	1145	more). These values and the paclkage/classname of the object will then be
841	decode into the number 2.	1146	encoded as a tagged JSON value in the following format:
842		1147
843	=item JSON::PC 0.01	1148	("classname")[FREEZE return values...]
844		1149
845	Very fast.	1150	e.g.:
846		1151
847	Undocumented/buggy Unicode handling.	1152	("URI")["http://www.google.com/"]
		1153	("MyDate")[2013,10,29]
		1154	("ImageData::JPEG")["Z3...VlCg=="]
848		1155
849	No round-tripping.	1156	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1157	objects C<type> and C<id> members to encode the object:
850		1158
851	Has problems handling many Perl values (e.g. regex results and other magic	1159	sub My::Object::FREEZE {
852	values will make it croak).	1160	my ($self, $serialiser) = @_;
853		1161
854	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1162	($self->{type}, $self->{id})
855	which is not a valid JSON text.	1163	}
856		1164
857	Unmaintained (maintainer unresponsive for many months, bugs are not	1165	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
858	getting fixed).
859		1166
860	=item JSON::Syck 0.21	1167	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1168	context. It must return a single scalar that can be directly encoded into
		1169	JSON. This scalar replaces the object in the JSON text.
861		1170
862	Very buggy (often crashes).	1171	For example, the following C<TO_JSON> method will convert all L<URI>
		1172	objects to JSON strings when serialised. The fatc that these values
		1173	originally were L<URI> objects is lost.
863		1174
864	Very inflexible (no human-readable format supported, format pretty much	1175	sub URI::TO_JSON {
865	undocumented. I need at least a format for easy reading by humans and a	1176	my ($uri) = @_;
866	single-line compact format for use in a protocol, and preferably a way to	1177	$uri->as_string
867	generate ASCII-only JSON texts).	1178	}
868		1179
869	Completely broken (and confusingly documented) Unicode handling (Unicode	1180	=item 3. C<allow_blessed> is enabled.
870	escapes are not working properly, you need to set ImplicitUnicode to
871	I<different> values on en- and decoding to get symmetric behaviour).
872		1181
873	No round-tripping (simple cases work, but this depends on whether the scalar	1182	The object will be serialised as a JSON null value.
874	value was used in a numeric context or not).
875		1183
876	Dumping hashes may skip hash values depending on iterator state.	1184	=item 4. none of the above
877		1185
878	Unmaintained (maintainer unresponsive for many months, bugs are not	1186	If none of the settings are enabled or the respective methods are missing,
879	getting fixed).	1187	C<JSON::XS> throws an exception.
880
881	Does not check input for validity (i.e. will accept non-JSON input and
882	return "something" instead of raising an exception. This is a security
883	issue: imagine two banks transferring money between each other using
884	JSON. One bank might parse a given non-JSON request and deduct money,
885	while the other might reject the transaction with a syntax error. While a
886	good protocol will at least recover, that is extra unnecessary work and
887	the transaction will still not succeed).
888
889	=item JSON::DWIW 0.04
890
891	Very fast. Very natural. Very nice.
892
893	Undocumented Unicode handling (but the best of the pack. Unicode escapes
894	still don't get parsed properly).
895
896	Very inflexible.
897
898	No round-tripping.
899
900	Does not generate valid JSON texts (key strings are often unquoted, empty keys
901	result in nothing being output)
902
903	Does not check input for validity.
904		1188
905	=back	1189	=back
906		1190
		1191	=head3 DESERIALISATION
		1192
		1193	For deserialisation there are only two cases to consider: either
		1194	nonstandard tagging was used, in which case C<allow_tags> decides,
		1195	or objects cannot be automatically be deserialised, in which
		1196	case you can use postprocessing or the C<filter_json_object> or
		1197	C<filter_json_single_key_object> callbacks to get some real objects our of
		1198	your JSON.
		1199
		1200	This section only considers the tagged value case: I a tagged JSON object
		1201	is encountered during decoding and C<allow_tags> is disabled, a parse
		1202	error will result (as if tagged values were not part of the grammar).
		1203
		1204	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1205	of the package/classname used during serialisation (it will not attempt
		1206	to load the package as a Perl module). If there is no such method, the
		1207	decoding will fail with an error.
		1208
		1209	Otherwise, the C<THAW> method is invoked with the classname as first
		1210	argument, the constant string C<JSON> as second argument, and all the
		1211	values from the JSON array (the values originally returned by the
		1212	C<FREEZE> method) as remaining arguments.
		1213
		1214	The method must then return the object. While technically you can return
		1215	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1216	make that work in all cases, so better return an actual blessed reference.
		1217
		1218	As an example, let's implement a C<THAW> function that regenerates the
		1219	C<My::Object> from the C<FREEZE> example earlier:
		1220
		1221	sub My::Object::THAW {
		1222	my ($class, $serialiser, $type, $id) = @_;
		1223
		1224	$class->new (type => $type, id => $id)
		1225	}
		1226
		1227
		1228	=head1 ENCODING/CODESET FLAG NOTES
		1229
		1230	The interested reader might have seen a number of flags that signify
		1231	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1232	some confusion on what these do, so here is a short comparison:
		1233
		1234	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1235	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1236	control whether C<encode> escapes character values outside their respective
		1237	codeset range. Neither of these flags conflict with each other, although
		1238	some combinations make less sense than others.
		1239
		1240	Care has been taken to make all flags symmetrical with respect to
		1241	C<encode> and C<decode>, that is, texts encoded with any combination of
		1242	these flag values will be correctly decoded when the same flags are used
		1243	- in general, if you use different flag settings while encoding vs. when
		1244	decoding you likely have a bug somewhere.
		1245
		1246	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1247	simply an abstract set of character-codepoint pairs, while an encoding
		1248	takes those codepoint numbers and I<encodes> them, in our case into
		1249	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1250	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1251	the same time, which can be confusing.
		1252
		1253	=over 4
		1254
		1255	=item C<utf8> flag disabled
		1256
		1257	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1258	and expect Unicode strings, that is, characters with high ordinal Unicode
		1259	values (> 255) will be encoded as such characters, and likewise such
		1260	characters are decoded as-is, no changes to them will be done, except
		1261	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1262	respectively (to Perl, these are the same thing in strings unless you do
		1263	funny/weird/dumb stuff).
		1264
		1265	This is useful when you want to do the encoding yourself (e.g. when you
		1266	want to have UTF-16 encoded JSON texts) or when some other layer does
		1267	the encoding for you (for example, when printing to a terminal using a
		1268	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1269	to UTF-8 encode your data first and have Perl encode it another time).
		1270
		1271	=item C<utf8> flag enabled
		1272
		1273	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1274	characters using the corresponding UTF-8 multi-byte sequence, and will
		1275	expect your input strings to be encoded as UTF-8, that is, no "character"
		1276	of the input string must have any value > 255, as UTF-8 does not allow
		1277	that.
		1278
		1279	The C<utf8> flag therefore switches between two modes: disabled means you
		1280	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1281	octet/binary string in Perl.
		1282
		1283	=item C<latin1> or C<ascii> flags enabled
		1284
		1285	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1286	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1287	characters as specified by the C<utf8> flag.
		1288
		1289	If C<utf8> is disabled, then the result is also correctly encoded in those
		1290	character sets (as both are proper subsets of Unicode, meaning that a
		1291	Unicode string with all character values < 256 is the same thing as a
		1292	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1293	the same thing as an ASCII string in Perl).
		1294
		1295	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1296	regardless of these flags, just some more characters will be escaped using
		1297	C<\uXXXX> then before.
		1298
		1299	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1300	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1301	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1302	a subset of Unicode), while ASCII is.
		1303
		1304	Surprisingly, C<decode> will ignore these flags and so treat all input
		1305	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1306	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1307	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1308
		1309	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1310	they only govern when the JSON output engine escapes a character or not.
		1311
		1312	The main use for C<latin1> is to relatively efficiently store binary data
		1313	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1314
		1315	The main use for C<ascii> is to force the output to not contain characters
		1316	with values > 127, which means you can interpret the resulting string
		1317	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1318	8-bit-encoding, and still get the same data structure back. This is useful
		1319	when your channel for JSON transfer is not 8-bit clean or the encoding
		1320	might be mangled in between (e.g. in mail), and works because ASCII is a
		1321	proper subset of most 8-bit and multibyte encodings in use in the world.
		1322
		1323	=back
		1324
		1325
		1326	=head2 JSON and ECMAscript
		1327
		1328	JSON syntax is based on how literals are represented in javascript (the
		1329	not-standardised predecessor of ECMAscript) which is presumably why it is
		1330	called "JavaScript Object Notation".
		1331
		1332	However, JSON is not a subset (and also not a superset of course) of
		1333	ECMAscript (the standard) or javascript (whatever browsers actually
		1334	implement).
		1335
		1336	If you want to use javascript's C<eval> function to "parse" JSON, you
		1337	might run into parse errors for valid JSON texts, or the resulting data
		1338	structure might not be queryable:
		1339
		1340	One of the problems is that U+2028 and U+2029 are valid characters inside
		1341	JSON strings, but are not allowed in ECMAscript string literals, so the
		1342	following Perl fragment will not output something that can be guaranteed
		1343	to be parsable by javascript's C<eval>:
		1344
		1345	use JSON::XS;
		1346
		1347	print encode_json [chr 0x2028];
		1348
		1349	The right fix for this is to use a proper JSON parser in your javascript
		1350	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1351	F<json2.js> parser).
		1352
		1353	If this is not an option, you can, as a stop-gap measure, simply encode to
		1354	ASCII-only JSON:
		1355
		1356	use JSON::XS;
		1357
		1358	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1359
		1360	Note that this will enlarge the resulting JSON text quite a bit if you
		1361	have many non-ASCII characters. You might be tempted to run some regexes
		1362	to only escape U+2028 and U+2029, e.g.:
		1363
		1364	# DO NOT USE THIS!
		1365	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1366	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1367	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1368	print $json;
		1369
		1370	Note that I<this is a bad idea>: the above only works for U+2028 and
		1371	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1372	javascript implementations, however, have issues with other characters as
		1373	well - using C<eval> naively simply I<will> cause problems.
		1374
		1375	Another problem is that some javascript implementations reserve
		1376	some property names for their own purposes (which probably makes
		1377	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1378	C<__proto__> property name for its own purposes.
		1379
		1380	If that is a problem, you could parse try to filter the resulting JSON
		1381	output for these property strings, e.g.:
		1382
		1383	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1384
		1385	This works because C<__proto__> is not valid outside of strings, so every
		1386	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1387
		1388	If you know of other incompatibilities, please let me know.
		1389
907		1390
908	=head2 JSON and YAML	1391	=head2 JSON and YAML
909		1392
910	You often hear that JSON is a subset of YAML. This is, however, a mass	1393	You often hear that JSON is a subset of YAML. This is, however, a mass
911	hysteria(*) and very far from the truth. In general, there is no way to	1394	hysteria(*) and very far from the truth (as of the time of this writing),
		1395	so let me state it clearly: I<in general, there is no way to configure
912	configure JSON::XS to output a data structure as valid YAML that works for	1396	JSON::XS to output a data structure as valid YAML> that works in all
913	all cases.	1397	cases.
914		1398
915	If you really must use JSON::XS to generate YAML, you should use this	1399	If you really must use JSON::XS to generate YAML, you should use this
916	algorithm (subject to change in future versions):	1400	algorithm (subject to change in future versions):
917		1401
918	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1402	my $to_yaml = JSON::XS->new->utf8->space_after (1);
919	my $yaml = $to_yaml->encode ($ref) . "\n";	1403	my $yaml = $to_yaml->encode ($ref) . "\n";
920		1404
921	This will usually generate JSON texts that also parse as valid	1405	This will I<usually> generate JSON texts that also parse as valid
922	YAML. Please note that YAML has hardcoded limits on (simple) object key	1406	YAML. Please note that YAML has hardcoded limits on (simple) object key
923	lengths that JSON doesn't have and also has different and incompatible	1407	lengths that JSON doesn't have and also has different and incompatible
924	unicode handling, so you should make sure that your hash keys are	1408	unicode character escape syntax, so you should make sure that your hash
925	noticeably shorter than the 1024 "stream characters" YAML allows and that	1409	keys are noticeably shorter than the 1024 "stream characters" YAML allows
926	you do not have codepoints with values outside the Unicode BMP (basic	1410	and that you do not have characters with codepoint values outside the
927	multilingual page). YAML also does not allow C<\/> sequences in strings	1411	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
928	(which JSON::XS does not I<currently> generate).	1412	sequences in strings (which JSON::XS does not I<currently> generate, but
		1413	other JSON generators might).
929		1414
930	There might be other incompatibilities that I am not aware of. In general	1415	There might be other incompatibilities that I am not aware of (or the YAML
		1416	specification has been changed yet again - it does so quite often). In
931	you should not try to generate YAML with a JSON generator or vice versa,	1417	general you should not try to generate YAML with a JSON generator or vice
932	or try to parse JSON with a YAML parser or vice versa: chances are high	1418	versa, or try to parse JSON with a YAML parser or vice versa: chances are
933	that you will run into severe interoperability problems when you least	1419	high that you will run into severe interoperability problems when you
934	expect it.	1420	least expect it.
935		1421
936	=over 4	1422	=over 4
937		1423
938	=item (*)	1424	=item (*)
939		1425
940	This is spread actively by the YAML team, however. For many years now they	1426	I have been pressured multiple times by Brian Ingerson (one of the
941	claim YAML were a superset of JSON, even when proven otherwise.	1427	authors of the YAML specification) to remove this paragraph, despite him
		1428	acknowledging that the actual incompatibilities exist. As I was personally
		1429	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1430	educate people about these issues, so others do not run into the same
		1431	problem again and again. After this, Brian called me a (quote)I<complete
		1432	and worthless idiot>(unquote).
942		1433
943	Even the author of this manpage was at some point accused of providing	1434	In my opinion, instead of pressuring and insulting people who actually
944	"incorrect" information, despite the evidence presented (claims ranged	1435	clarify issues with YAML and the wrong statements of some of its
945	from "your documentation contains inaccurate and negative statements about	1436	proponents, I would kindly suggest reading the JSON spec (which is not
946	YAML" (the only negative comment is this footnote, and it didn't exist	1437	that difficult or long) and finally make YAML compatible to it, and
947	back then; the question on which claims were inaccurate was never answered	1438	educating users about the changes, instead of spreading lies about the
948	etc.) to "the YAML spec is not up-to-date" (the *real* and suppsedly	1439	real compatibility for many I<years> and trying to silence people who
949	JSON-compatible spec is apparently not currently publicly available)	1440	point out that it isn't true.
950	to actual requests to replace this section by *incorrect* information,
951	suppressing information about the real problem).
952		1441
953	So whenever you are told that YAML was a superset of JSON, first check	1442	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
954	wether it is really true (it might be when you check it, but it cetrainly	1443	though the incompatibilities have been documented (and are known to Brian)
955	is not true when this was written). I would much prefer if the YAML team	1444	for many years and the spec makes explicit claims that YAML is a superset
956	would spent their time on actually making JSON compatibility a truth	1445	of JSON. It would be so easy to fix, but apparently, bullying people and
957	(JSON, after all, has a very small and simple specification) instead of	1446	corrupting userdata is so much easier.
958	trying to lobby/force people into reporting untruths.
959		1447
960	=back	1448	=back
961		1449
962		1450
963	=head2 SPEED	1451	=head2 SPEED
…		…
965	It seems that JSON::XS is surprisingly fast, as shown in the following	1453	It seems that JSON::XS is surprisingly fast, as shown in the following
966	tables. They have been generated with the help of the C<eg/bench> program	1454	tables. They have been generated with the help of the C<eg/bench> program
967	in the JSON::XS distribution, to make it easy to compare on your own	1455	in the JSON::XS distribution, to make it easy to compare on your own
968	system.	1456	system.
969		1457
970	First comes a comparison between various modules using a very short	1458	First comes a comparison between various modules using
971	single-line JSON string:	1459	a very short single-line JSON string (also available at
		1460	L<http://dist.schmorp.de/misc/json/short.json>).
972		1461
973	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1462	{"method": "handleMessage", "params": ["user1",
974	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1463	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1464	1, 0]}
975		1465
976	It shows the number of encodes/decodes per second (JSON::XS uses	1466	It shows the number of encodes/decodes per second (JSON::XS uses
977	the functional interface, while JSON::XS/2 uses the OO interface	1467	the functional interface, while JSON::XS/2 uses the OO interface
978	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1468	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
979	shrink). Higher is better:	1469	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1470	uses the from_json method). Higher is better:
980		1471
981	module | encode | decode |	1472	module | encode | decode |
982	-----------|------------|------------|	1473	--------------|------------|------------|
983	JSON 1.x | 4990.842 | 4088.813 |	1474	JSON::DWIW/DS | 86302.551 | 102300.098 |
984	JSON::DWIW | 51653.990 | 71575.154 |	1475	JSON::DWIW/FJ | 86302.551 | 75983.768 |
985	JSON::PC | 65948.176 | 74631.744 |	1476	JSON::PP | 15827.562 | 6638.658 |
986	JSON::PP | 8931.652 | 3817.168 |	1477	JSON::Syck | 63358.066 | 47662.545 |
987	JSON::Syck | 24877.248 | 27776.848 |	1478	JSON::XS | 511500.488 | 511500.488 |
988	JSON::XS | 388361.481 | 227951.304 |	1479	JSON::XS/2 | 291271.111 | 388361.481 |
989	JSON::XS/2 | 227951.304 | 218453.333 |	1480	JSON::XS/3 | 361577.931 | 361577.931 |
990	JSON::XS/3 | 338250.323 | 218453.333 |	1481	Storable | 66788.280 | 265462.278 |
991	Storable | 16500.016 | 135300.129 |
992	-----------+------------+------------+	1482	--------------+------------+------------+
993		1483
994	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1484	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
995	about three times faster on decoding, and over forty times faster	1485	about five times faster on decoding, and over thirty to seventy times
996	than JSON, even with pretty-printing and key sorting. It also compares	1486	faster than JSON's pure perl implementation. It also compares favourably
997	favourably to Storable for small amounts of data.	1487	to Storable for small amounts of data.
998		1488
999	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1489	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1000	search API (http://nanoref.com/yahooapis/mgPdGg):	1490	search API (L<http://dist.schmorp.de/misc/json/long.json>).
1001		1491
1002	module | encode | decode |	1492	module | encode | decode |
1003	-----------|------------|------------|	1493	--------------|------------|------------|
1004	JSON 1.x | 55.260 | 34.971 |	1494	JSON::DWIW/DS | 1647.927 | 2673.916 |
1005	JSON::DWIW | 825.228 | 1082.513 |	1495	JSON::DWIW/FJ | 1630.249 | 2596.128 |
1006	JSON::PC | 3571.444 | 2394.829 |
1007	JSON::PP | 210.987 | 32.574 |	1496	JSON::PP | 400.640 | 62.311 |
1008	JSON::Syck | 552.551 | 787.544 |	1497	JSON::Syck | 1481.040 | 1524.869 |
1009	JSON::XS | 5780.463 | 4854.519 |	1498	JSON::XS | 20661.596 | 9541.183 |
1010	JSON::XS/2 | 3869.998 | 4798.975 |	1499	JSON::XS/2 | 10683.403 | 9416.938 |
1011	JSON::XS/3 | 5862.880 | 4798.975 |	1500	JSON::XS/3 | 20661.596 | 9400.054 |
1012	Storable | 4445.002 | 5235.027 |	1501	Storable | 19765.806 | 10000.725 |
1013	-----------+------------+------------+	1502	--------------+------------+------------+
1014		1503
1015	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1504	Again, JSON::XS leads by far (except for Storable which non-surprisingly
1016	decodes faster).	1505	decodes a bit faster).
1017		1506
1018	On large strings containing lots of high Unicode characters, some modules	1507	On large strings containing lots of high Unicode characters, some modules
1019	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1508	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
1020	will be broken due to missing (or wrong) Unicode handling. Others refuse	1509	will be broken due to missing (or wrong) Unicode handling. Others refuse
1021	to decode or encode properly, so it was impossible to prepare a fair	1510	to decode or encode properly, so it was impossible to prepare a fair
…		…
1047	to free the temporary). If that is exceeded, the program crashes. To be	1536	to free the temporary). If that is exceeded, the program crashes. To be
1048	conservative, the default nesting limit is set to 512. If your process	1537	conservative, the default nesting limit is set to 512. If your process
1049	has a smaller stack, you should adjust this setting accordingly with the	1538	has a smaller stack, you should adjust this setting accordingly with the
1050	C<max_depth> method.	1539	C<max_depth> method.
1051		1540
1052	And last but least, something else could bomb you that I forgot to think	1541	Something else could bomb you, too, that I forgot to think of. In that
1053	of. In that case, you get to keep the pieces. I am always open for hints,	1542	case, you get to keep the pieces. I am always open for hints, though...
1054	though...	1543
		1544	Also keep in mind that JSON::XS might leak contents of your Perl data
		1545	structures in its error messages, so when you serialise sensitive
		1546	information you might want to make sure that exceptions thrown by JSON::XS
		1547	will not end up in front of untrusted eyes.
1055		1548
1056	If you are using JSON::XS to return packets to consumption	1549	If you are using JSON::XS to return packets to consumption
1057	by JavaScript scripts in a browser you should have a look at	1550	by JavaScript scripts in a browser you should have a look at
1058	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1551	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
1059	you are vulnerable to some common attack vectors (which really are browser	1552	see whether you are vulnerable to some common attack vectors (which really
1060	design bugs, but it is still you who will have to deal with it, as major	1553	are browser design bugs, but it is still you who will have to deal with
1061	browser developers care only for features, not about getting security	1554	it, as major browser developers care only for features, not about getting
1062	right).	1555	security right).
1063		1556
		1557
		1558	=head1 INTEROPERABILITY WITH OTHER MODULES
		1559
		1560	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1561	constants. That means that the JSON true and false values will be
		1562	comaptible to true and false values of iother modules that do the same,
		1563	such as L<JSON::PP> and L<CBOR::XS>.
		1564
		1565
		1566	=head1 INTEROPERABILITY WITH OTHER JSON DECODERS
		1567
		1568	As long as you only serialise data that can be directly expressed in JSON,
		1569	C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs,
		1570	but C<JSON::XS> has found more bugs in the official JSON testsuite (1)
		1571	than the official JSON testsuite has found in C<JSON::XS> (0)).
		1572
		1573	When you have trouble decoding JSON generated by this module using other
		1574	decoders, then it is very likely that you have an encoding mismatch or the
		1575	other decoder is broken.
		1576
		1577	When decoding, C<JSON::XS> is strict by default and will likely catch all
		1578	errors. There are currently two settings that change this: C<relaxed>
		1579	makes C<JSON::XS> accept (but not generate) some non-standard extensions,
		1580	and C<allow_tags> will allow you to encode and decode Perl objects, at the
		1581	cost of not outputting valid JSON anymore.
		1582
		1583	=head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
		1584
		1585	When you use C<allow_tags> to use the extended (and also nonstandard and
		1586	invalid) JSON syntax for serialised objects, and you still want to decode
		1587	the generated When you want to serialise objects, you can run a regex
		1588	to replace the tagged syntax by standard JSON arrays (it only works for
		1589	"normal" packagesnames without comma, newlines or single colons). First,
		1590	the readable Perl version:
		1591
		1592	# if your FREEZE methods return no values, you need this replace first:
		1593	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
		1594
		1595	# this works for non-empty constructor arg lists:
		1596	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
		1597
		1598	And here is a less readable version that is easy to adapt to other
		1599	languages:
		1600
		1601	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
		1602
		1603	Here is an ECMAScript version (same regex):
		1604
		1605	json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
		1606
		1607	Since this syntax converts to standard JSON arrays, it might be hard to
		1608	distinguish serialised objects from normal arrays. You can prepend a
		1609	"magic number" as first array element to reduce chances of a collision:
		1610
		1611	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
		1612
		1613	And after decoding the JSON text, you could walk the data
		1614	structure looking for arrays with a first element of
		1615	C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>.
		1616
		1617	The same approach cna be used to create the tagged format with another
		1618	encoder. First, you create an array with the magic string as first member,
		1619	the classname as second, and constructor arguments last, encode it as part
		1620	of your JSON structure, and then:
		1621
		1622	$json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
		1623
		1624	Again, this has some limitations - the magic string must not be encoded
		1625	with character escapes, and the constructor arguments must be non-empty.
1064		1626
1065	=head1 THREADS	1627	=head1 THREADS
1066		1628
1067	This module is I<not> guaranteed to be thread safe and there are no	1629	This module is I<not> guaranteed to be thread safe and there are no
1068	plans to change this until Perl gets thread support (as opposed to the	1630	plans to change this until Perl gets thread support (as opposed to the
1069	horribly slow so-called "threads" which are simply slow and bloated	1631	horribly slow so-called "threads" which are simply slow and bloated
1070	process simulations - use fork, its I<much> faster, cheaper, better).	1632	process simulations - use fork, it's I<much> faster, cheaper, better).
1071		1633
1072	(It might actually work, but you have been warned).	1634	(It might actually work, but you have been warned).
1073		1635
1074		1636
		1637	=head1 THE PERILS OF SETLOCALE
		1638
		1639	Sometimes people avoid the Perl locale support and directly call the
		1640	system's setlocale function with C<LC_ALL>.
		1641
		1642	This breaks both perl and modules such as JSON::XS, as stringification of
		1643	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1644	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1645	perl to stringify numbers).
		1646
		1647	The solution is simple: don't call C<setlocale>, or use it for only those
		1648	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1649
		1650	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1651	actually needs it (avoiding stringification of numbers), and restore it
		1652	afterwards.
		1653
		1654
1075	=head1 BUGS	1655	=head1 BUGS
1076		1656
1077	While the goal of this module is to be correct, that unfortunately does	1657	While the goal of this module is to be correct, that unfortunately does
1078	not mean its bug-free, only that I think its design is bug-free. It is	1658	not mean it's bug-free, only that I think its design is bug-free. If you
1079	still relatively early in its development. If you keep reporting bugs they	1659	keep reporting bugs they will be fixed swiftly, though.
1080	will be fixed swiftly, though.
1081		1660
1082	Please refrain from using rt.cpan.org or any other bug reporting	1661	Please refrain from using rt.cpan.org or any other bug reporting
1083	service. I put the contact address into my modules for a reason.	1662	service. I put the contact address into my modules for a reason.
1084		1663
1085	=cut	1664	=cut
1086		1665
1087	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1666	BEGIN {
1088	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };	1667	*true = \$Types::Serialiser::true;
		1668	*true = \&Types::Serialiser::true;
		1669	*false = \$Types::Serialiser::false;
		1670	*false = \&Types::Serialiser::false;
		1671	*is_bool = \&Types::Serialiser::is_bool;
1089		1672
1090	sub true() { $true }	1673	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
1091	sub false() { $false }
1092
1093	sub is_bool($) {
1094	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1095	# or UNIVERSAL::isa $_[0], "JSON::Literal"
1096	}	1674	}
1097		1675
1098	XSLoader::load "JSON::XS", $VERSION;	1676	XSLoader::load "JSON::XS", $VERSION;
1099		1677
1100	package JSON::XS::Boolean;	1678	=head1 SEE ALSO
1101		1679
1102	use overload	1680	The F<json_xs> command line utility for quick experiments.
1103	"0+" => sub { ${$_[0]} },
1104	"++" => sub { $_[0] = ${$_[0]} + 1 },
1105	"--" => sub { $_[0] = ${$_[0]} - 1 },
1106	fallback => 1;
1107
1108	1;
1109		1681
1110	=head1 AUTHOR	1682	=head1 AUTHOR
1111		1683
1112	Marc Lehmann <schmorp@schmorp.de>	1684	Marc Lehmann <schmorp@schmorp.de>
1113	http://home.schmorp.de/	1685	http://home.schmorp.de/
1114		1686
1115	=cut	1687	=cut
1116		1688
		1689	1
		1690

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