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Revision 1.93 by root, Sat Mar 22 22:21:33 2008 UTC vs.
Revision 1.170 by root, Thu Nov 15 22:35:35 2018 UTC

1	=head1 NAME	1	=head1 NAME
2		2
		3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
3	=encoding utf-8	5	=encoding utf-8
4
5	JSON::XS - JSON serialising/deserialising, done correctly and fast
6		6
7	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
8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)	8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
9		9
10	=head1 SYNOPSIS	10	=head1 SYNOPSIS
…		…
35		35
36	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
37	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
38	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.
39		39
40	Beginning with version 2.0 of the JSON module, when both JSON and
41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
42	overriden) with no overhead due to emulation (by inheritign constructor
43	and methods). If JSON::XS is not available, it will fall back to the
44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
45	gives you a portable JSON API that can be fast when you need and doesn't
46	require a C compiler when that is a problem.
47
48	As this is the n-th-something JSON module on CPAN, what was the reason
49	to write yet another JSON module? While it seems there are many JSON
50	modules, none of them correctly handle all corner cases, and in most cases
51	their maintainers are unresponsive, gone missing, or not listening to bug
52	reports for other reasons.
53
54	See COMPARISON, below, for a comparison to some other JSON modules.
55
56	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	40	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
57	vice versa.	41	vice versa.
58		42
59	=head2 FEATURES	43	=head2 FEATURES
60		44
61	=over 4	45	=over
62		46
63	=item * correct Unicode handling	47	=item * correct Unicode handling
64		48
65	This module knows how to handle Unicode, documents how and when it does	49	This module knows how to handle Unicode, documents how and when it does
66	so, and even documents what "correct" means.	50	so, and even documents what "correct" means.
67		51
68	=item * round-trip integrity	52	=item * round-trip integrity
69		53
70	When you serialise a perl data structure using only datatypes supported	54	When you serialise a perl data structure using only data types supported
71	by JSON, the deserialised data structure is identical on the Perl level.	55	by JSON and Perl, the deserialised data structure is identical on the Perl
72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	56	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
73	like a number). There minor I<are> exceptions to this, read the MAPPING	57	it looks like a number). There I<are> minor exceptions to this, read the
74	section below to learn about those.	58	MAPPING section below to learn about those.
75		59
76	=item * strict checking of JSON correctness	60	=item * strict checking of JSON correctness
77		61
78	There is no guessing, no generating of illegal JSON texts by default,	62	There is no guessing, no generating of illegal JSON texts by default,
79	and only JSON is accepted as input by default (the latter is a security	63	and only JSON is accepted as input by default (the latter is a security
…		…
84	Compared to other JSON modules and other serialisers such as Storable,	68	Compared to other JSON modules and other serialisers such as Storable,
85	this module usually compares favourably in terms of speed, too.	69	this module usually compares favourably in terms of speed, too.
86		70
87	=item * simple to use	71	=item * simple to use
88		72
89	This module has both a simple functional interface as well as an objetc	73	This module has both a simple functional interface as well as an object
90	oriented interface interface.	74	oriented interface.
91		75
92	=item * reasonably versatile output formats	76	=item * reasonably versatile output formats
93		77
94	You can choose between the most compact guaranteed-single-line format	78	You can choose between the most compact guaranteed-single-line format
95	possible (nice for simple line-based protocols), a pure-ascii format	79	possible (nice for simple line-based protocols), a pure-ASCII format
96	(for when your transport is not 8-bit clean, still supports the whole	80	(for when your transport is not 8-bit clean, still supports the whole
97	Unicode range), or a pretty-printed format (for when you want to read that	81	Unicode range), or a pretty-printed format (for when you want to read that
98	stuff). Or you can combine those features in whatever way you like.	82	stuff). Or you can combine those features in whatever way you like.
99		83
100	=back	84	=back
101		85
102	=cut	86	=cut
103		87
104	package JSON::XS;	88	package JSON::XS;
105		89
106	use strict;	90	use common::sense;
107		91
108	our $VERSION = '2.1';	92	our $VERSION = '4.0';
109	our @ISA = qw(Exporter);	93	our @ISA = qw(Exporter);
110		94
111	our @EXPORT = qw(encode_json decode_json to_json from_json);	95	our @EXPORT = qw(encode_json decode_json);
112
113	sub to_json($) {
114	require Carp;
115	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");
116	}
117
118	sub from_json($) {
119	require Carp;
120	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");
121	}
122		96
123	use Exporter;	97	use Exporter;
124	use XSLoader;	98	use XSLoader;
125		99
		100	use Types::Serialiser ();
		101
126	=head1 FUNCTIONAL INTERFACE	102	=head1 FUNCTIONAL INTERFACE
127		103
128	The following convenience methods are provided by this module. They are	104	The following convenience methods are provided by this module. They are
129	exported by default:	105	exported by default:
130		106
131	=over 4	107	=over
132		108
133	=item $json_text = encode_json $perl_scalar	109	=item $json_text = encode_json $perl_scalar
134		110
135	Converts the given Perl data structure to a UTF-8 encoded, binary string	111	Converts the given Perl data structure to a UTF-8 encoded, binary string
136	(that is, the string contains octets only). Croaks on error.	112	(that is, the string contains octets only). Croaks on error.
137		113
138	This function call is functionally identical to:	114	This function call is functionally identical to:
139		115
140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	116	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
141		117
142	except being faster.	118	Except being faster.
143		119
144	=item $perl_scalar = decode_json $json_text	120	=item $perl_scalar = decode_json $json_text
145		121
146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries	122	The opposite of C<encode_json>: expects a UTF-8 (binary) string and tries
147	to parse that as an UTF-8 encoded JSON text, returning the resulting	123	to parse that as a UTF-8 encoded JSON text, returning the resulting
148	reference. Croaks on error.	124	reference. Croaks on error.
149		125
150	This function call is functionally identical to:	126	This function call is functionally identical to:
151		127
152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	128	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
153		129
154	except being faster.	130	Except being faster.
155
156	=item $is_boolean = JSON::XS::is_bool $scalar
157
158	Returns true if the passed scalar represents either JSON::XS::true or
159	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
160	and are used to represent JSON C<true> and C<false> values in Perl.
161
162	See MAPPING, below, for more information on how JSON values are mapped to
163	Perl.
164		131
165	=back	132	=back
166		133
167		134
168	=head1 A FEW NOTES ON UNICODE AND PERL	135	=head1 A FEW NOTES ON UNICODE AND PERL
169		136
170	Since this often leads to confusion, here are a few very clear words on	137	Since this often leads to confusion, here are a few very clear words on
171	how Unicode works in Perl, modulo bugs.	138	how Unicode works in Perl, modulo bugs.
172		139
173	=over 4	140	=over
174		141
175	=item 1. Perl strings can store characters with ordinal values > 255.	142	=item 1. Perl strings can store characters with ordinal values > 255.
176		143
177	This enables you to store Unicode characters as single characters in a	144	This enables you to store Unicode characters as single characters in a
178	Perl string - very natural.	145	Perl string - very natural.
…		…
197		164
198	If you didn't know about that flag, just the better, pretend it doesn't	165	If you didn't know about that flag, just the better, pretend it doesn't
199	exist.	166	exist.
200		167
201	=item 4. A "Unicode String" is simply a string where each character can be	168	=item 4. A "Unicode String" is simply a string where each character can be
202	validly interpreted as a Unicode codepoint.	169	validly interpreted as a Unicode code point.
203		170
204	If you have UTF-8 encoded data, it is no longer a Unicode string, but a	171	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
205	Unicode string encoded in UTF-8, giving you a binary string.	172	Unicode string encoded in UTF-8, giving you a binary string.
206		173
207	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.	174	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
…		…
216	=head1 OBJECT-ORIENTED INTERFACE	183	=head1 OBJECT-ORIENTED INTERFACE
217		184
218	The object oriented interface lets you configure your own encoding or	185	The object oriented interface lets you configure your own encoding or
219	decoding style, within the limits of supported formats.	186	decoding style, within the limits of supported formats.
220		187
221	=over 4	188	=over
222		189
223	=item $json = new JSON::XS	190	=item $json = new JSON::XS
224		191
225	Creates a new JSON::XS object that can be used to de/encode JSON	192	Creates a new JSON::XS object that can be used to de/encode JSON
226	strings. All boolean flags described below are by default I<disabled>.	193	strings. All boolean flags described below are by default I<disabled>
		194	(with the exception of C<allow_nonref>, which defaults to I<enabled> since
		195	version C<4.0>).
227		196
228	The mutators for flags all return the JSON object again and thus calls can	197	The mutators for flags all return the JSON object again and thus calls can
229	be chained:	198	be chained:
230		199
231	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	200	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
…		…
289		258
290	=item $enabled = $json->get_utf8	259	=item $enabled = $json->get_utf8
291		260
292	If C<$enable> is true (or missing), then the C<encode> method will encode	261	If C<$enable> is true (or missing), then the C<encode> method will encode
293	the JSON result into UTF-8, as required by many protocols, while the	262	the JSON result into UTF-8, as required by many protocols, while the
294	C<decode> method expects to be handled an UTF-8-encoded string. Please	263	C<decode> method expects to be handed a UTF-8-encoded string. Please
295	note that UTF-8-encoded strings do not contain any characters outside the	264	note that UTF-8-encoded strings do not contain any characters outside the
296	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	265	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
297	versions, enabling this option might enable autodetection of the UTF-16	266	versions, enabling this option might enable autodetection of the UTF-16
298	and UTF-32 encoding families, as described in RFC4627.	267	and UTF-32 encoding families, as described in RFC4627.
299		268
…		…
384		353
385	=item $enabled = $json->get_relaxed	354	=item $enabled = $json->get_relaxed
386		355
387	If C<$enable> is true (or missing), then C<decode> will accept some	356	If C<$enable> is true (or missing), then C<decode> will accept some
388	extensions to normal JSON syntax (see below). C<encode> will not be	357	extensions to normal JSON syntax (see below). C<encode> will not be
389	affected in anyway. I<Be aware that this option makes you accept invalid	358	affected in any way. I<Be aware that this option makes you accept invalid
390	JSON texts as if they were valid!>. I suggest only to use this option to	359	JSON texts as if they were valid!>. I suggest only to use this option to
391	parse application-specific files written by humans (configuration files,	360	parse application-specific files written by humans (configuration files,
392	resource files etc.)	361	resource files etc.)
393		362
394	If C<$enable> is false (the default), then C<decode> will only accept	363	If C<$enable> is false (the default), then C<decode> will only accept
395	valid JSON texts.	364	valid JSON texts.
396		365
397	Currently accepted extensions are:	366	Currently accepted extensions are:
398		367
399	=over 4	368	=over
400		369
401	=item * list items can have an end-comma	370	=item * list items can have an end-comma
402		371
403	JSON I<separates> array elements and key-value pairs with commas. This	372	JSON I<separates> array elements and key-value pairs with commas. This
404	can be annoying if you write JSON texts manually and want to be able to	373	can be annoying if you write JSON texts manually and want to be able to
…		…
423	[	392	[
424	1, # this comment not allowed in JSON	393	1, # this comment not allowed in JSON
425	# neither this one...	394	# neither this one...
426	]	395	]
427		396
		397	=item * literal ASCII TAB characters in strings
		398
		399	Literal ASCII TAB characters are now allowed in strings (and treated as
		400	C<\t>).
		401
		402	[
		403	"Hello\tWorld",
		404	"Hello<TAB>World", # literal <TAB> would not normally be allowed
		405	]
		406
428	=back	407	=back
429		408
430	=item $json = $json->canonical ([$enable])	409	=item $json = $json->canonical ([$enable])
431		410
432	=item $enabled = $json->get_canonical	411	=item $enabled = $json->get_canonical
…		…
434	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	413	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
435	by sorting their keys. This is adding a comparatively high overhead.	414	by sorting their keys. This is adding a comparatively high overhead.
436		415
437	If C<$enable> is false, then the C<encode> method will output key-value	416	If C<$enable> is false, then the C<encode> method will output key-value
438	pairs in the order Perl stores them (which will likely change between runs	417	pairs in the order Perl stores them (which will likely change between runs
439	of the same script).	418	of the same script, and can change even within the same run from 5.18
		419	onwards).
440		420
441	This option is useful if you want the same data structure to be encoded as	421	This option is useful if you want the same data structure to be encoded as
442	the same JSON text (given the same overall settings). If it is disabled,	422	the same JSON text (given the same overall settings). If it is disabled,
443	the same hash might be encoded differently even if contains the same data,	423	the same hash might be encoded differently even if contains the same data,
444	as key-value pairs have no inherent ordering in Perl.	424	as key-value pairs have no inherent ordering in Perl.
445		425
446	This setting has no effect when decoding JSON texts.	426	This setting has no effect when decoding JSON texts.
447		427
		428	This setting has currently no effect on tied hashes.
		429
448	=item $json = $json->allow_nonref ([$enable])	430	=item $json = $json->allow_nonref ([$enable])
449		431
450	=item $enabled = $json->get_allow_nonref	432	=item $enabled = $json->get_allow_nonref
		433
		434	Unlike other boolean options, this opotion is enabled by default beginning
		435	with version C<4.0>. See L<SECURITY CONSIDERATIONS> for the gory details.
451		436
452	If C<$enable> is true (or missing), then the C<encode> method can convert a	437	If C<$enable> is true (or missing), then the C<encode> method can convert a
453	non-reference into its corresponding string, number or null JSON value,	438	non-reference into its corresponding string, number or null JSON value,
454	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	439	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
455	values instead of croaking.	440	values instead of croaking.
…		…
457	If C<$enable> is false, then the C<encode> method will croak if it isn't	442	If C<$enable> is false, then the C<encode> method will croak if it isn't
458	passed an arrayref or hashref, as JSON texts must either be an object	443	passed an arrayref or hashref, as JSON texts must either be an object
459	or array. Likewise, C<decode> will croak if given something that is not a	444	or array. Likewise, C<decode> will croak if given something that is not a
460	JSON object or array.	445	JSON object or array.
461		446
462	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,	447	Example, encode a Perl scalar as JSON value without enabled C<allow_nonref>,
463	resulting in an invalid JSON text:	448	resulting in an error:
464		449
465	JSON::XS->new->allow_nonref->encode ("Hello, World!")	450	JSON::XS->new->allow_nonref (0)->encode ("Hello, World!")
466	=> "Hello, World!"	451	=> hash- or arrayref expected...
		452
		453	=item $json = $json->allow_unknown ([$enable])
		454
		455	=item $enabled = $json->get_allow_unknown
		456
		457	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		458	exception when it encounters values it cannot represent in JSON (for
		459	example, filehandles) but instead will encode a JSON C<null> value. Note
		460	that blessed objects are not included here and are handled separately by
		461	c<allow_nonref>.
		462
		463	If C<$enable> is false (the default), then C<encode> will throw an
		464	exception when it encounters anything it cannot encode as JSON.
		465
		466	This option does not affect C<decode> in any way, and it is recommended to
		467	leave it off unless you know your communications partner.
467		468
468	=item $json = $json->allow_blessed ([$enable])	469	=item $json = $json->allow_blessed ([$enable])
469		470
470	=item $enabled = $json->get_allow_blessed	471	=item $enabled = $json->get_allow_blessed
471		472
		473	See L<OBJECT SERIALISATION> for details.
		474
472	If C<$enable> is true (or missing), then the C<encode> method will not	475	If C<$enable> is true (or missing), then the C<encode> method will not
473	barf when it encounters a blessed reference. Instead, the value of the	476	barf when it encounters a blessed reference that it cannot convert
474	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>	477	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
475	disabled or no C<TO_JSON> method found) or a representation of the
476	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
477	encoded. Has no effect on C<decode>.
478		478
479	If C<$enable> is false (the default), then C<encode> will throw an	479	If C<$enable> is false (the default), then C<encode> will throw an
480	exception when it encounters a blessed object.	480	exception when it encounters a blessed object that it cannot convert
		481	otherwise.
		482
		483	This setting has no effect on C<decode>.
481		484
482	=item $json = $json->convert_blessed ([$enable])	485	=item $json = $json->convert_blessed ([$enable])
483		486
484	=item $enabled = $json->get_convert_blessed	487	=item $enabled = $json->get_convert_blessed
		488
		489	See L<OBJECT SERIALISATION> for details.
485		490
486	If C<$enable> is true (or missing), then C<encode>, upon encountering a	491	If C<$enable> is true (or missing), then C<encode>, upon encountering a
487	blessed object, will check for the availability of the C<TO_JSON> method	492	blessed object, will check for the availability of the C<TO_JSON> method
488	on the object's class. If found, it will be called in scalar context	493	on the object's class. If found, it will be called in scalar context and
489	and the resulting scalar will be encoded instead of the object. If no	494	the resulting scalar will be encoded instead of the object.
490	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
491	to do.
492		495
493	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	496	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
494	returns other blessed objects, those will be handled in the same	497	returns other blessed objects, those will be handled in the same
495	way. C<TO_JSON> must take care of not causing an endless recursion cycle	498	way. C<TO_JSON> must take care of not causing an endless recursion cycle
496	(== crash) in this case. The name of C<TO_JSON> was chosen because other	499	(== crash) in this case. The name of C<TO_JSON> was chosen because other
497	methods called by the Perl core (== not by the user of the object) are	500	methods called by the Perl core (== not by the user of the object) are
498	usually in upper case letters and to avoid collisions with any C<to_json>	501	usually in upper case letters and to avoid collisions with any C<to_json>
499	function or method.	502	function or method.
500		503
501	This setting does not yet influence C<decode> in any way, but in the	504	If C<$enable> is false (the default), then C<encode> will not consider
502	future, global hooks might get installed that influence C<decode> and are	505	this type of conversion.
503	enabled by this setting.
504		506
505	If C<$enable> is false, then the C<allow_blessed> setting will decide what	507	This setting has no effect on C<decode>.
506	to do when a blessed object is found.	508
		509	=item $json = $json->allow_tags ([$enable])
		510
		511	=item $enabled = $json->get_allow_tags
		512
		513	See L<OBJECT SERIALISATION> for details.
		514
		515	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		516	blessed object, will check for the availability of the C<FREEZE> method on
		517	the object's class. If found, it will be used to serialise the object into
		518	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		519
		520	It also causes C<decode> to parse such tagged JSON values and deserialise
		521	them via a call to the C<THAW> method.
		522
		523	If C<$enable> is false (the default), then C<encode> will not consider
		524	this type of conversion, and tagged JSON values will cause a parse error
		525	in C<decode>, as if tags were not part of the grammar.
507		526
508	=item $json = $json->filter_json_object ([$coderef->($hashref)])	527	=item $json = $json->filter_json_object ([$coderef->($hashref)])
509		528
510	When C<$coderef> is specified, it will be called from C<decode> each	529	When C<$coderef> is specified, it will be called from C<decode> each
511	time it decodes a JSON object. The only argument is a reference to the	530	time it decodes a JSON object. The only argument is a reference to
512	newly-created hash. If the code references returns a single scalar (which	531	the newly-created hash. If the code reference returns a single scalar
513	need not be a reference), this value (i.e. a copy of that scalar to avoid	532	(which need not be a reference), this value (or rather a copy of it) is
514	aliasing) is inserted into the deserialised data structure. If it returns	533	inserted into the deserialised data structure. If it returns an empty
515	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the	534	list (NOTE: I<not> C<undef>, which is a valid scalar), the original
516	original deserialised hash will be inserted. This setting can slow down	535	deserialised hash will be inserted. This setting can slow down decoding
517	decoding considerably.	536	considerably.
518		537
519	When C<$coderef> is omitted or undefined, any existing callback will	538	When C<$coderef> is omitted or undefined, any existing callback will
520	be removed and C<decode> will not change the deserialised hash in any	539	be removed and C<decode> will not change the deserialised hash in any
521	way.	540	way.
522		541
…		…
612	=item $json = $json->max_depth ([$maximum_nesting_depth])	631	=item $json = $json->max_depth ([$maximum_nesting_depth])
613		632
614	=item $max_depth = $json->get_max_depth	633	=item $max_depth = $json->get_max_depth
615		634
616	Sets the maximum nesting level (default C<512>) accepted while encoding	635	Sets the maximum nesting level (default C<512>) accepted while encoding
617	or decoding. If the JSON text or Perl data structure has an equal or	636	or decoding. If a higher nesting level is detected in JSON text or a Perl
618	higher nesting level then this limit, then the encoder and decoder will	637	data structure, then the encoder and decoder will stop and croak at that
619	stop and croak at that point.	638	point.
620		639
621	Nesting level is defined by number of hash- or arrayrefs that the encoder	640	Nesting level is defined by number of hash- or arrayrefs that the encoder
622	needs to traverse to reach a given point or the number of C<{> or C<[>	641	needs to traverse to reach a given point or the number of C<{> or C<[>
623	characters without their matching closing parenthesis crossed to reach a	642	characters without their matching closing parenthesis crossed to reach a
624	given character in a string.	643	given character in a string.
625		644
626	Setting the maximum depth to one disallows any nesting, so that ensures	645	Setting the maximum depth to one disallows any nesting, so that ensures
627	that the object is only a single hash/object or array.	646	that the object is only a single hash/object or array.
628		647
629	The argument to C<max_depth> will be rounded up to the next highest power
630	of two. If no argument is given, the highest possible setting will be	648	If no argument is given, the highest possible setting will be used, which
631	used, which is rarely useful.	649	is rarely useful.
		650
		651	Note that nesting is implemented by recursion in C. The default value has
		652	been chosen to be as large as typical operating systems allow without
		653	crashing.
632		654
633	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	655	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
634		656
635	=item $json = $json->max_size ([$maximum_string_size])	657	=item $json = $json->max_size ([$maximum_string_size])
636		658
637	=item $max_size = $json->get_max_size	659	=item $max_size = $json->get_max_size
638		660
639	Set the maximum length a JSON text may have (in bytes) where decoding is	661	Set the maximum length a JSON text may have (in bytes) where decoding is
640	being attempted. The default is C<0>, meaning no limit. When C<decode>	662	being attempted. The default is C<0>, meaning no limit. When C<decode>
641	is called on a string longer then this number of characters it will not	663	is called on a string that is longer then this many bytes, it will not
642	attempt to decode the string but throw an exception. This setting has no	664	attempt to decode the string but throw an exception. This setting has no
643	effect on C<encode> (yet).	665	effect on C<encode> (yet).
644		666
645	The argument to C<max_size> will be rounded up to the next B<highest>	667	If no argument is given, the limit check will be deactivated (same as when
646	power of two (so may be more than requested). If no argument is given, the	668	C<0> is specified).
647	limit check will be deactivated (same as when C<0> is specified).
648		669
649	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	670	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
650		671
651	=item $json_text = $json->encode ($perl_scalar)	672	=item $json_text = $json->encode ($perl_scalar)
652		673
653	Converts the given Perl data structure (a simple scalar or a reference	674	Converts the given Perl value or data structure to its JSON
654	to a hash or array) to its JSON representation. Simple scalars will be	675	representation. Croaks on error.
655	converted into JSON string or number sequences, while references to arrays
656	become JSON arrays and references to hashes become JSON objects. Undefined
657	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
658	nor C<false> values will be generated.
659		676
660	=item $perl_scalar = $json->decode ($json_text)	677	=item $perl_scalar = $json->decode ($json_text)
661		678
662	The opposite of C<encode>: expects a JSON text and tries to parse it,	679	The opposite of C<encode>: expects a JSON text and tries to parse it,
663	returning the resulting simple scalar or reference. Croaks on error.	680	returning the resulting simple scalar or reference. Croaks on error.
664
665	JSON numbers and strings become simple Perl scalars. JSON arrays become
666	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
667	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
668		681
669	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	682	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
670		683
671	This works like the C<decode> method, but instead of raising an exception	684	This works like the C<decode> method, but instead of raising an exception
672	when there is trailing garbage after the first JSON object, it will	685	when there is trailing garbage after the first JSON object, it will
673	silently stop parsing there and return the number of characters consumed	686	silently stop parsing there and return the number of characters consumed
674	so far.	687	so far.
675		688
676	This is useful if your JSON texts are not delimited by an outer protocol	689	This is useful if your JSON texts are not delimited by an outer protocol
677	(which is not the brightest thing to do in the first place) and you need
678	to know where the JSON text ends.	690	and you need to know where the JSON text ends.
679		691
680	JSON::XS->new->decode_prefix ("[1] the tail")	692	JSON::XS->new->decode_prefix ("[1] the tail")
681	=> ([], 3)	693	=> ([1], 3)
682		694
683	=back	695	=back
		696
		697
		698	=head1 INCREMENTAL PARSING
		699
		700	In some cases, there is the need for incremental parsing of JSON
		701	texts. While this module always has to keep both JSON text and resulting
		702	Perl data structure in memory at one time, it does allow you to parse a
		703	JSON stream incrementally. It does so by accumulating text until it has
		704	a full JSON object, which it then can decode. This process is similar to
		705	using C<decode_prefix> to see if a full JSON object is available, but
		706	is much more efficient (and can be implemented with a minimum of method
		707	calls).
		708
		709	JSON::XS will only attempt to parse the JSON text once it is sure it
		710	has enough text to get a decisive result, using a very simple but
		711	truly incremental parser. This means that it sometimes won't stop as
		712	early as the full parser, for example, it doesn't detect mismatched
		713	parentheses. The only thing it guarantees is that it starts decoding as
		714	soon as a syntactically valid JSON text has been seen. This means you need
		715	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		716	parsing in the presence if syntax errors.
		717
		718	The following methods implement this incremental parser.
		719
		720	=over
		721
		722	=item [void, scalar or list context] = $json->incr_parse ([$string])
		723
		724	This is the central parsing function. It can both append new text and
		725	extract objects from the stream accumulated so far (both of these
		726	functions are optional).
		727
		728	If C<$string> is given, then this string is appended to the already
		729	existing JSON fragment stored in the C<$json> object.
		730
		731	After that, if the function is called in void context, it will simply
		732	return without doing anything further. This can be used to add more text
		733	in as many chunks as you want.
		734
		735	If the method is called in scalar context, then it will try to extract
		736	exactly I<one> JSON object. If that is successful, it will return this
		737	object, otherwise it will return C<undef>. If there is a parse error,
		738	this method will croak just as C<decode> would do (one can then use
		739	C<incr_skip> to skip the erroneous part). This is the most common way of
		740	using the method.
		741
		742	And finally, in list context, it will try to extract as many objects
		743	from the stream as it can find and return them, or the empty list
		744	otherwise. For this to work, there must be no separators (other than
		745	whitespace) between the JSON objects or arrays, instead they must be
		746	concatenated back-to-back. If an error occurs, an exception will be
		747	raised as in the scalar context case. Note that in this case, any
		748	previously-parsed JSON texts will be lost.
		749
		750	Example: Parse some JSON arrays/objects in a given string and return
		751	them.
		752
		753	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		754
		755	=item $lvalue_string = $json->incr_text
		756
		757	This method returns the currently stored JSON fragment as an lvalue, that
		758	is, you can manipulate it. This I<only> works when a preceding call to
		759	C<incr_parse> in I<scalar context> successfully returned an object. Under
		760	all other circumstances you must not call this function (I mean it.
		761	although in simple tests it might actually work, it I<will> fail under
		762	real world conditions). As a special exception, you can also call this
		763	method before having parsed anything.
		764
		765	That means you can only use this function to look at or manipulate text
		766	before or after complete JSON objects, not while the parser is in the
		767	middle of parsing a JSON object.
		768
		769	This function is useful in two cases: a) finding the trailing text after a
		770	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		771	(such as commas).
		772
		773	=item $json->incr_skip
		774
		775	This will reset the state of the incremental parser and will remove
		776	the parsed text from the input buffer so far. This is useful after
		777	C<incr_parse> died, in which case the input buffer and incremental parser
		778	state is left unchanged, to skip the text parsed so far and to reset the
		779	parse state.
		780
		781	The difference to C<incr_reset> is that only text until the parse error
		782	occurred is removed.
		783
		784	=item $json->incr_reset
		785
		786	This completely resets the incremental parser, that is, after this call,
		787	it will be as if the parser had never parsed anything.
		788
		789	This is useful if you want to repeatedly parse JSON objects and want to
		790	ignore any trailing data, which means you have to reset the parser after
		791	each successful decode.
		792
		793	=back
		794
		795	=head2 LIMITATIONS
		796
		797	The incremental parser is a non-exact parser: it works by gathering as
		798	much text as possible that I<could> be a valid JSON text, followed by
		799	trying to decode it.
		800
		801	That means it sometimes needs to read more data than strictly necessary to
		802	diagnose an invalid JSON text. For example, after parsing the following
		803	fragment, the parser I<could> stop with an error, as this fragment
		804	I<cannot> be the beginning of a valid JSON text:
		805
		806	[,
		807
		808	In reality, hopwever, the parser might continue to read data until a
		809	length limit is exceeded or it finds a closing bracket.
		810
		811	=head2 EXAMPLES
		812
		813	Some examples will make all this clearer. First, a simple example that
		814	works similarly to C<decode_prefix>: We want to decode the JSON object at
		815	the start of a string and identify the portion after the JSON object:
		816
		817	my $text = "[1,2,3] hello";
		818
		819	my $json = new JSON::XS;
		820
		821	my $obj = $json->incr_parse ($text)
		822	or die "expected JSON object or array at beginning of string";
		823
		824	my $tail = $json->incr_text;
		825	# $tail now contains " hello"
		826
		827	Easy, isn't it?
		828
		829	Now for a more complicated example: Imagine a hypothetical protocol where
		830	you read some requests from a TCP stream, and each request is a JSON
		831	array, without any separation between them (in fact, it is often useful to
		832	use newlines as "separators", as these get interpreted as whitespace at
		833	the start of the JSON text, which makes it possible to test said protocol
		834	with C<telnet>...).
		835
		836	Here is how you'd do it (it is trivial to write this in an event-based
		837	manner):
		838
		839	my $json = new JSON::XS;
		840
		841	# read some data from the socket
		842	while (sysread $socket, my $buf, 4096) {
		843
		844	# split and decode as many requests as possible
		845	for my $request ($json->incr_parse ($buf)) {
		846	# act on the $request
		847	}
		848	}
		849
		850	Another complicated example: Assume you have a string with JSON objects
		851	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		852	[3]>). To parse them, we have to skip the commas between the JSON texts,
		853	and here is where the lvalue-ness of C<incr_text> comes in useful:
		854
		855	my $text = "[1],[2], [3]";
		856	my $json = new JSON::XS;
		857
		858	# void context, so no parsing done
		859	$json->incr_parse ($text);
		860
		861	# now extract as many objects as possible. note the
		862	# use of scalar context so incr_text can be called.
		863	while (my $obj = $json->incr_parse) {
		864	# do something with $obj
		865
		866	# now skip the optional comma
		867	$json->incr_text =~ s/^ \s* , //x;
		868	}
		869
		870	Now lets go for a very complex example: Assume that you have a gigantic
		871	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		872	but you cannot load it into memory fully (this has actually happened in
		873	the real world :).
		874
		875	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		876	can still help you: You implement a (very simple) array parser and let
		877	JSON decode the array elements, which are all full JSON objects on their
		878	own (this wouldn't work if the array elements could be JSON numbers, for
		879	example):
		880
		881	my $json = new JSON::XS;
		882
		883	# open the monster
		884	open my $fh, "<bigfile.json"
		885	or die "bigfile: $!";
		886
		887	# first parse the initial "["
		888	for (;;) {
		889	sysread $fh, my $buf, 65536
		890	or die "read error: $!";
		891	$json->incr_parse ($buf); # void context, so no parsing
		892
		893	# Exit the loop once we found and removed(!) the initial "[".
		894	# In essence, we are (ab-)using the $json object as a simple scalar
		895	# we append data to.
		896	last if $json->incr_text =~ s/^ \s* \[ //x;
		897	}
		898
		899	# now we have the skipped the initial "[", so continue
		900	# parsing all the elements.
		901	for (;;) {
		902	# in this loop we read data until we got a single JSON object
		903	for (;;) {
		904	if (my $obj = $json->incr_parse) {
		905	# do something with $obj
		906	last;
		907	}
		908
		909	# add more data
		910	sysread $fh, my $buf, 65536
		911	or die "read error: $!";
		912	$json->incr_parse ($buf); # void context, so no parsing
		913	}
		914
		915	# in this loop we read data until we either found and parsed the
		916	# separating "," between elements, or the final "]"
		917	for (;;) {
		918	# first skip whitespace
		919	$json->incr_text =~ s/^\s*//;
		920
		921	# if we find "]", we are done
		922	if ($json->incr_text =~ s/^\]//) {
		923	print "finished.\n";
		924	exit;
		925	}
		926
		927	# if we find ",", we can continue with the next element
		928	if ($json->incr_text =~ s/^,//) {
		929	last;
		930	}
		931
		932	# if we find anything else, we have a parse error!
		933	if (length $json->incr_text) {
		934	die "parse error near ", $json->incr_text;
		935	}
		936
		937	# else add more data
		938	sysread $fh, my $buf, 65536
		939	or die "read error: $!";
		940	$json->incr_parse ($buf); # void context, so no parsing
		941	}
		942
		943	This is a complex example, but most of the complexity comes from the fact
		944	that we are trying to be correct (bear with me if I am wrong, I never ran
		945	the above example :).
		946
684		947
685		948
686	=head1 MAPPING	949	=head1 MAPPING
687		950
688	This section describes how JSON::XS maps Perl values to JSON values and	951	This section describes how JSON::XS maps Perl values to JSON values and
…		…
695	refers to the abstract Perl language itself.	958	refers to the abstract Perl language itself.
696		959
697		960
698	=head2 JSON -> PERL	961	=head2 JSON -> PERL
699		962
700	=over 4	963	=over
701		964
702	=item object	965	=item object
703		966
704	A JSON object becomes a reference to a hash in Perl. No ordering of object	967	A JSON object becomes a reference to a hash in Perl. No ordering of object
705	keys is preserved (JSON does not preserve object key ordering itself).	968	keys is preserved (JSON does not preserve object key ordering itself).
…		…
725	If the number consists of digits only, JSON::XS will try to represent	988	If the number consists of digits only, JSON::XS will try to represent
726	it as an integer value. If that fails, it will try to represent it as	989	it as an integer value. If that fails, it will try to represent it as
727	a numeric (floating point) value if that is possible without loss of	990	a numeric (floating point) value if that is possible without loss of
728	precision. Otherwise it will preserve the number as a string value (in	991	precision. Otherwise it will preserve the number as a string value (in
729	which case you lose roundtripping ability, as the JSON number will be	992	which case you lose roundtripping ability, as the JSON number will be
730	re-encoded toa JSON string).	993	re-encoded to a JSON string).
731		994
732	Numbers containing a fractional or exponential part will always be	995	Numbers containing a fractional or exponential part will always be
733	represented as numeric (floating point) values, possibly at a loss of	996	represented as numeric (floating point) values, possibly at a loss of
734	precision (in which case you might lose perfect roundtripping ability, but	997	precision (in which case you might lose perfect roundtripping ability, but
735	the JSON number will still be re-encoded as a JSON number).	998	the JSON number will still be re-encoded as a JSON number).
736		999
		1000	Note that precision is not accuracy - binary floating point values cannot
		1001	represent most decimal fractions exactly, and when converting from and to
		1002	floating point, JSON::XS only guarantees precision up to but not including
		1003	the least significant bit.
		1004
737	=item true, false	1005	=item true, false
738		1006
739	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	1007	These JSON atoms become C<Types::Serialiser::true> and
740	respectively. They are overloaded to act almost exactly like the numbers	1008	C<Types::Serialiser::false>, respectively. They are overloaded to act
741	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using	1009	almost exactly like the numbers C<1> and C<0>. You can check whether
742	the C<JSON::XS::is_bool> function.	1010	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1011	function (after C<use Types::Serialier>, of course).
743		1012
744	=item null	1013	=item null
745		1014
746	A JSON null atom becomes C<undef> in Perl.	1015	A JSON null atom becomes C<undef> in Perl.
		1016
		1017	=item shell-style comments (C<< # I<text> >>)
		1018
		1019	As a nonstandard extension to the JSON syntax that is enabled by the
		1020	C<relaxed> setting, shell-style comments are allowed. They can start
		1021	anywhere outside strings and go till the end of the line.
		1022
		1023	=item tagged values (C<< (I<tag>)I<value> >>).
		1024
		1025	Another nonstandard extension to the JSON syntax, enabled with the
		1026	C<allow_tags> setting, are tagged values. In this implementation, the
		1027	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1028	I<value> must be a JSON array encoding optional constructor arguments.
		1029
		1030	See L<OBJECT SERIALISATION>, below, for details.
747		1031
748	=back	1032	=back
749		1033
750		1034
751	=head2 PERL -> JSON	1035	=head2 PERL -> JSON
752		1036
753	The mapping from Perl to JSON is slightly more difficult, as Perl is a	1037	The mapping from Perl to JSON is slightly more difficult, as Perl is a
754	truly typeless language, so we can only guess which JSON type is meant by	1038	truly typeless language, so we can only guess which JSON type is meant by
755	a Perl value.	1039	a Perl value.
756		1040
757	=over 4	1041	=over
758		1042
759	=item hash references	1043	=item hash references
760		1044
761	Perl hash references become JSON objects. As there is no inherent ordering	1045	Perl hash references become JSON objects. As there is no inherent
762	in hash keys (or JSON objects), they will usually be encoded in a	1046	ordering in hash keys (or JSON objects), they will usually be encoded
763	pseudo-random order that can change between runs of the same program but	1047	in a pseudo-random order. JSON::XS can optionally sort the hash keys
764	stays generally the same within a single run of a program. JSON::XS can	1048	(determined by the I<canonical> flag), so the same datastructure will
765	optionally sort the hash keys (determined by the I<canonical> flag), so	1049	serialise to the same JSON text (given same settings and version of
766	the same datastructure will serialise to the same JSON text (given same	1050	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
767	settings and version of JSON::XS), but this incurs a runtime overhead	1051	e.g. when you want to compare some JSON text against another for equality.
768	and is only rarely useful, e.g. when you want to compare some JSON text
769	against another for equality.
770		1052
771	=item array references	1053	=item array references
772		1054
773	Perl array references become JSON arrays.	1055	Perl array references become JSON arrays.
774		1056
775	=item other references	1057	=item other references
776		1058
777	Other unblessed references are generally not allowed and will cause an	1059	Other unblessed references are generally not allowed and will cause an
778	exception to be thrown, except for references to the integers C<0> and	1060	exception to be thrown, except for references to the integers C<0> and
779	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1061	C<1>, which get turned into C<false> and C<true> atoms in JSON.
780	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
781		1062
		1063	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1064	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1065	and C<Types::Serialiser::true> to improve readability.
		1066
		1067	use Types::Serialiser;
782	encode_json [\0,JSON::XS::true] # yields [false,true]	1068	encode_json [\0, Types::Serialiser::true] # yields [false,true]
783		1069
784	=item JSON::XS::true, JSON::XS::false	1070	=item Types::Serialiser::true, Types::Serialiser::false
785		1071
786	These special values become JSON true and JSON false values,	1072	These special values from the L<Types::Serialiser> module become JSON true
787	respectively. You can also use C<\1> and C<\0> directly if you want.	1073	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1074	directly if you want.
788		1075
789	=item blessed objects	1076	=item blessed objects
790		1077
791	Blessed objects are not directly representable in JSON. See the	1078	Blessed objects are not directly representable in JSON, but C<JSON::XS>
792	C<allow_blessed> and C<convert_blessed> methods on various options on	1079	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
793	how to deal with this: basically, you can choose between throwing an	1080	below, for details.
794	exception, encoding the reference as if it weren't blessed, or provide
795	your own serialiser method.
796		1081
797	=item simple scalars	1082	=item simple scalars
798		1083
799	Simple Perl scalars (any scalar that is not a reference) are the most	1084	Simple Perl scalars (any scalar that is not a reference) are the most
800	difficult objects to encode: JSON::XS will encode undefined scalars as	1085	difficult objects to encode: JSON::XS will encode undefined scalars as
…		…
828		1113
829	You can not currently force the type in other, less obscure, ways. Tell me	1114	You can not currently force the type in other, less obscure, ways. Tell me
830	if you need this capability (but don't forget to explain why it's needed	1115	if you need this capability (but don't forget to explain why it's needed
831	:).	1116	:).
832		1117
		1118	Note that numerical precision has the same meaning as under Perl (so
		1119	binary to decimal conversion follows the same rules as in Perl, which
		1120	can differ to other languages). Also, your perl interpreter might expose
		1121	extensions to the floating point numbers of your platform, such as
		1122	infinities or NaN's - these cannot be represented in JSON, and it is an
		1123	error to pass those in.
		1124
833	=back	1125	=back
		1126
		1127	=head2 OBJECT SERIALISATION
		1128
		1129	As JSON cannot directly represent Perl objects, you have to choose between
		1130	a pure JSON representation (without the ability to deserialise the object
		1131	automatically again), and a nonstandard extension to the JSON syntax,
		1132	tagged values.
		1133
		1134	=head3 SERIALISATION
		1135
		1136	What happens when C<JSON::XS> encounters a Perl object depends on the
		1137	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
		1138	used in this order:
		1139
		1140	=over
		1141
		1142	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
		1143
		1144	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1145	serialisation protocol to create a tagged JSON value, using a nonstandard
		1146	extension to the JSON syntax.
		1147
		1148	This works by invoking the C<FREEZE> method on the object, with the first
		1149	argument being the object to serialise, and the second argument being the
		1150	constant string C<JSON> to distinguish it from other serialisers.
		1151
		1152	The C<FREEZE> method can return any number of values (i.e. zero or
		1153	more). These values and the paclkage/classname of the object will then be
		1154	encoded as a tagged JSON value in the following format:
		1155
		1156	("classname")[FREEZE return values...]
		1157
		1158	e.g.:
		1159
		1160	("URI")["http://www.google.com/"]
		1161	("MyDate")[2013,10,29]
		1162	("ImageData::JPEG")["Z3...VlCg=="]
		1163
		1164	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1165	objects C<type> and C<id> members to encode the object:
		1166
		1167	sub My::Object::FREEZE {
		1168	my ($self, $serialiser) = @_;
		1169
		1170	($self->{type}, $self->{id})
		1171	}
		1172
		1173	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
		1174
		1175	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1176	context. It must return a single scalar that can be directly encoded into
		1177	JSON. This scalar replaces the object in the JSON text.
		1178
		1179	For example, the following C<TO_JSON> method will convert all L<URI>
		1180	objects to JSON strings when serialised. The fatc that these values
		1181	originally were L<URI> objects is lost.
		1182
		1183	sub URI::TO_JSON {
		1184	my ($uri) = @_;
		1185	$uri->as_string
		1186	}
		1187
		1188	=item 3. C<allow_blessed> is enabled.
		1189
		1190	The object will be serialised as a JSON null value.
		1191
		1192	=item 4. none of the above
		1193
		1194	If none of the settings are enabled or the respective methods are missing,
		1195	C<JSON::XS> throws an exception.
		1196
		1197	=back
		1198
		1199	=head3 DESERIALISATION
		1200
		1201	For deserialisation there are only two cases to consider: either
		1202	nonstandard tagging was used, in which case C<allow_tags> decides,
		1203	or objects cannot be automatically be deserialised, in which
		1204	case you can use postprocessing or the C<filter_json_object> or
		1205	C<filter_json_single_key_object> callbacks to get some real objects our of
		1206	your JSON.
		1207
		1208	This section only considers the tagged value case: I a tagged JSON object
		1209	is encountered during decoding and C<allow_tags> is disabled, a parse
		1210	error will result (as if tagged values were not part of the grammar).
		1211
		1212	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1213	of the package/classname used during serialisation (it will not attempt
		1214	to load the package as a Perl module). If there is no such method, the
		1215	decoding will fail with an error.
		1216
		1217	Otherwise, the C<THAW> method is invoked with the classname as first
		1218	argument, the constant string C<JSON> as second argument, and all the
		1219	values from the JSON array (the values originally returned by the
		1220	C<FREEZE> method) as remaining arguments.
		1221
		1222	The method must then return the object. While technically you can return
		1223	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1224	make that work in all cases, so better return an actual blessed reference.
		1225
		1226	As an example, let's implement a C<THAW> function that regenerates the
		1227	C<My::Object> from the C<FREEZE> example earlier:
		1228
		1229	sub My::Object::THAW {
		1230	my ($class, $serialiser, $type, $id) = @_;
		1231
		1232	$class->new (type => $type, id => $id)
		1233	}
834		1234
835		1235
836	=head1 ENCODING/CODESET FLAG NOTES	1236	=head1 ENCODING/CODESET FLAG NOTES
837		1237
838	The interested reader might have seen a number of flags that signify	1238	The interested reader might have seen a number of flags that signify
…		…
856	takes those codepoint numbers and I<encodes> them, in our case into	1256	takes those codepoint numbers and I<encodes> them, in our case into
857	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,	1257	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
858	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at	1258	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
859	the same time, which can be confusing.	1259	the same time, which can be confusing.
860		1260
861	=over 4	1261	=over
862		1262
863	=item C<utf8> flag disabled	1263	=item C<utf8> flag disabled
864		1264
865	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate	1265	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
866	and expect Unicode strings, that is, characters with high ordinal Unicode	1266	and expect Unicode strings, that is, characters with high ordinal Unicode
867	values (> 255) will be encoded as such characters, and likewise such	1267	values (> 255) will be encoded as such characters, and likewise such
868	characters are decoded as-is, no canges to them will be done, except	1268	characters are decoded as-is, no changes to them will be done, except
869	"(re-)interpreting" them as Unicode codepoints or Unicode characters,	1269	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
870	respectively (to Perl, these are the same thing in strings unless you do	1270	respectively (to Perl, these are the same thing in strings unless you do
871	funny/weird/dumb stuff).	1271	funny/weird/dumb stuff).
872		1272
873	This is useful when you want to do the encoding yourself (e.g. when you	1273	This is useful when you want to do the encoding yourself (e.g. when you
…		…
883	expect your input strings to be encoded as UTF-8, that is, no "character"	1283	expect your input strings to be encoded as UTF-8, that is, no "character"
884	of the input string must have any value > 255, as UTF-8 does not allow	1284	of the input string must have any value > 255, as UTF-8 does not allow
885	that.	1285	that.
886		1286
887	The C<utf8> flag therefore switches between two modes: disabled means you	1287	The C<utf8> flag therefore switches between two modes: disabled means you
888	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded	1288	will get a Unicode string in Perl, enabled means you get a UTF-8 encoded
889	octet/binary string in Perl.	1289	octet/binary string in Perl.
890		1290
891	=item C<latin1> or C<ascii> flags enabled	1291	=item C<latin1> or C<ascii> flags enabled
892		1292
893	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters	1293	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
…		…
929	proper subset of most 8-bit and multibyte encodings in use in the world.	1329	proper subset of most 8-bit and multibyte encodings in use in the world.
930		1330
931	=back	1331	=back
932		1332
933		1333
934	=head1 COMPARISON	1334	=head2 JSON and ECMAscript
935		1335
936	As already mentioned, this module was created because none of the existing	1336	JSON syntax is based on how literals are represented in javascript (the
937	JSON modules could be made to work correctly. First I will describe the	1337	not-standardised predecessor of ECMAscript) which is presumably why it is
938	problems (or pleasures) I encountered with various existing JSON modules,	1338	called "JavaScript Object Notation".
939	followed by some benchmark values. JSON::XS was designed not to suffer
940	from any of these problems or limitations.
941		1339
942	=over 4	1340	However, JSON is not a subset (and also not a superset of course) of
		1341	ECMAscript (the standard) or javascript (whatever browsers actually
		1342	implement).
943		1343
944	=item JSON 2.xx	1344	If you want to use javascript's C<eval> function to "parse" JSON, you
		1345	might run into parse errors for valid JSON texts, or the resulting data
		1346	structure might not be queryable:
945		1347
946	A marvellous piece of engineering, this module either uses JSON::XS	1348	One of the problems is that U+2028 and U+2029 are valid characters inside
947	directly when available (so will be 100% compatible with it, including	1349	JSON strings, but are not allowed in ECMAscript string literals, so the
948	speed), or it uses JSON::PP, which is basically JSON::XS translated to	1350	following Perl fragment will not output something that can be guaranteed
949	Pure Perl, which should be 100% compatible with JSON::XS, just a bit	1351	to be parsable by javascript's C<eval>:
950	slower.
951		1352
952	You cannot really lose by using this module, especially as it tries very	1353	use JSON::XS;
953	hard to work even with ancient Perl versions, while JSON::XS does not.
954		1354
955	=item JSON 1.07	1355	print encode_json [chr 0x2028];
956		1356
957	Slow (but very portable, as it is written in pure Perl).	1357	The right fix for this is to use a proper JSON parser in your javascript
		1358	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1359	F<json2.js> parser).
958		1360
959	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1361	If this is not an option, you can, as a stop-gap measure, simply encode to
960	undocumented. One can get far by feeding it Unicode strings and doing	1362	ASCII-only JSON:
961	en-/decoding oneself, but Unicode escapes are not working properly).
962		1363
963	No round-tripping (strings get clobbered if they look like numbers, e.g.	1364	use JSON::XS;
964	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
965	decode into the number 2.
966		1365
967	=item JSON::PC 0.01	1366	print JSON::XS->new->ascii->encode ([chr 0x2028]);
968		1367
969	Very fast.	1368	Note that this will enlarge the resulting JSON text quite a bit if you
		1369	have many non-ASCII characters. You might be tempted to run some regexes
		1370	to only escape U+2028 and U+2029, e.g.:
970		1371
971	Undocumented/buggy Unicode handling.	1372	# DO NOT USE THIS!
		1373	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1374	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1375	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1376	print $json;
972		1377
973	No round-tripping.	1378	Note that I<this is a bad idea>: the above only works for U+2028 and
		1379	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1380	javascript implementations, however, have issues with other characters as
		1381	well - using C<eval> naively simply I<will> cause problems.
974		1382
975	Has problems handling many Perl values (e.g. regex results and other magic	1383	Another problem is that some javascript implementations reserve
976	values will make it croak).	1384	some property names for their own purposes (which probably makes
		1385	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1386	C<__proto__> property name for its own purposes.
977		1387
978	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1388	If that is a problem, you could parse try to filter the resulting JSON
979	which is not a valid JSON text.	1389	output for these property strings, e.g.:
980		1390
981	Unmaintained (maintainer unresponsive for many months, bugs are not	1391	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
982	getting fixed).
983		1392
984	=item JSON::Syck 0.21	1393	This works because C<__proto__> is not valid outside of strings, so every
		1394	occurrence of C<"__proto__"\s*:> must be a string used as property name.
985		1395
986	Very buggy (often crashes).	1396	If you know of other incompatibilities, please let me know.
987
988	Very inflexible (no human-readable format supported, format pretty much
989	undocumented. I need at least a format for easy reading by humans and a
990	single-line compact format for use in a protocol, and preferably a way to
991	generate ASCII-only JSON texts).
992
993	Completely broken (and confusingly documented) Unicode handling (Unicode
994	escapes are not working properly, you need to set ImplicitUnicode to
995	I<different> values on en- and decoding to get symmetric behaviour).
996
997	No round-tripping (simple cases work, but this depends on whether the scalar
998	value was used in a numeric context or not).
999
1000	Dumping hashes may skip hash values depending on iterator state.
1001
1002	Unmaintained (maintainer unresponsive for many months, bugs are not
1003	getting fixed).
1004
1005	Does not check input for validity (i.e. will accept non-JSON input and
1006	return "something" instead of raising an exception. This is a security
1007	issue: imagine two banks transferring money between each other using
1008	JSON. One bank might parse a given non-JSON request and deduct money,
1009	while the other might reject the transaction with a syntax error. While a
1010	good protocol will at least recover, that is extra unnecessary work and
1011	the transaction will still not succeed).
1012
1013	=item JSON::DWIW 0.04
1014
1015	Very fast. Very natural. Very nice.
1016
1017	Undocumented Unicode handling (but the best of the pack. Unicode escapes
1018	still don't get parsed properly).
1019
1020	Very inflexible.
1021
1022	No round-tripping.
1023
1024	Does not generate valid JSON texts (key strings are often unquoted, empty keys
1025	result in nothing being output)
1026
1027	Does not check input for validity.
1028
1029	=back
1030		1397
1031		1398
1032	=head2 JSON and YAML	1399	=head2 JSON and YAML
1033		1400
1034	You often hear that JSON is a subset of YAML. This is, however, a mass	1401	You often hear that JSON is a subset of YAML. This is, however, a mass
…		…
1044	my $yaml = $to_yaml->encode ($ref) . "\n";	1411	my $yaml = $to_yaml->encode ($ref) . "\n";
1045		1412
1046	This will I<usually> generate JSON texts that also parse as valid	1413	This will I<usually> generate JSON texts that also parse as valid
1047	YAML. Please note that YAML has hardcoded limits on (simple) object key	1414	YAML. Please note that YAML has hardcoded limits on (simple) object key
1048	lengths that JSON doesn't have and also has different and incompatible	1415	lengths that JSON doesn't have and also has different and incompatible
1049	unicode handling, so you should make sure that your hash keys are	1416	unicode character escape syntax, so you should make sure that your hash
1050	noticeably shorter than the 1024 "stream characters" YAML allows and that	1417	keys are noticeably shorter than the 1024 "stream characters" YAML allows
1051	you do not have characters with codepoint values outside the Unicode BMP	1418	and that you do not have characters with codepoint values outside the
1052	(basic multilingual page). YAML also does not allow C<\/> sequences in	1419	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
1053	strings (which JSON::XS does not I<currently> generate, but other JSON	1420	sequences in strings (which JSON::XS does not I<currently> generate, but
1054	generators might).	1421	other JSON generators might).
1055		1422
1056	There might be other incompatibilities that I am not aware of (or the YAML	1423	There might be other incompatibilities that I am not aware of (or the YAML
1057	specification has been changed yet again - it does so quite often). In	1424	specification has been changed yet again - it does so quite often). In
1058	general you should not try to generate YAML with a JSON generator or vice	1425	general you should not try to generate YAML with a JSON generator or vice
1059	versa, or try to parse JSON with a YAML parser or vice versa: chances are	1426	versa, or try to parse JSON with a YAML parser or vice versa: chances are
1060	high that you will run into severe interoperability problems when you	1427	high that you will run into severe interoperability problems when you
1061	least expect it.	1428	least expect it.
1062		1429
1063	=over 4	1430	=over
1064		1431
1065	=item (*)	1432	=item (*)
1066		1433
1067	I have been pressured multiple times by Brian Ingerson (one of the	1434	I have been pressured multiple times by Brian Ingerson (one of the
1068	authors of the YAML specification) to remove this paragraph, despite him	1435	authors of the YAML specification) to remove this paragraph, despite him
…		…
1078	that difficult or long) and finally make YAML compatible to it, and	1445	that difficult or long) and finally make YAML compatible to it, and
1079	educating users about the changes, instead of spreading lies about the	1446	educating users about the changes, instead of spreading lies about the
1080	real compatibility for many I<years> and trying to silence people who	1447	real compatibility for many I<years> and trying to silence people who
1081	point out that it isn't true.	1448	point out that it isn't true.
1082		1449
		1450	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1451	though the incompatibilities have been documented (and are known to Brian)
		1452	for many years and the spec makes explicit claims that YAML is a superset
		1453	of JSON. It would be so easy to fix, but apparently, bullying people and
		1454	corrupting userdata is so much easier.
		1455
1083	=back	1456	=back
1084		1457
1085		1458
1086	=head2 SPEED	1459	=head2 SPEED
1087		1460
…		…
1092		1465
1093	First comes a comparison between various modules using	1466	First comes a comparison between various modules using
1094	a very short single-line JSON string (also available at	1467	a very short single-line JSON string (also available at
1095	L<http://dist.schmorp.de/misc/json/short.json>).	1468	L<http://dist.schmorp.de/misc/json/short.json>).
1096		1469
1097	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1470	{"method": "handleMessage", "params": ["user1",
1098	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1471	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1472	1, 0]}
1099		1473
1100	It shows the number of encodes/decodes per second (JSON::XS uses	1474	It shows the number of encodes/decodes per second (JSON::XS uses
1101	the functional interface, while JSON::XS/2 uses the OO interface	1475	the functional interface, while JSON::XS/2 uses the OO interface
1102	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1476	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
1103	shrink). Higher is better:	1477	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1478	uses the from_json method). Higher is better:
1104		1479
1105	module | encode | decode |	1480	module | encode | decode |
1106	-----------|------------|------------|	1481	--------------|------------|------------|
1107	JSON 1.x | 4990.842 | 4088.813 |	1482	JSON::DWIW/DS | 86302.551 | 102300.098 |
1108	JSON::DWIW | 51653.990 | 71575.154 |	1483	JSON::DWIW/FJ | 86302.551 | 75983.768 |
1109	JSON::PC | 65948.176 | 74631.744 |	1484	JSON::PP | 15827.562 | 6638.658 |
1110	JSON::PP | 8931.652 | 3817.168 |	1485	JSON::Syck | 63358.066 | 47662.545 |
1111	JSON::Syck | 24877.248 | 27776.848 |	1486	JSON::XS | 511500.488 | 511500.488 |
1112	JSON::XS | 388361.481 | 227951.304 |	1487	JSON::XS/2 | 291271.111 | 388361.481 |
1113	JSON::XS/2 | 227951.304 | 218453.333 |	1488	JSON::XS/3 | 361577.931 | 361577.931 |
1114	JSON::XS/3 | 338250.323 | 218453.333 |	1489	Storable | 66788.280 | 265462.278 |
1115	Storable | 16500.016 | 135300.129 |
1116	-----------+------------+------------+	1490	--------------+------------+------------+
1117		1491
1118	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1492	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
1119	about three times faster on decoding, and over forty times faster	1493	about five times faster on decoding, and over thirty to seventy times
1120	than JSON, even with pretty-printing and key sorting. It also compares	1494	faster than JSON's pure perl implementation. It also compares favourably
1121	favourably to Storable for small amounts of data.	1495	to Storable for small amounts of data.
1122		1496
1123	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1497	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1124	search API (L<http://dist.schmorp.de/misc/json/long.json>).	1498	search API (L<http://dist.schmorp.de/misc/json/long.json>).
1125		1499
1126	module | encode | decode |	1500	module | encode | decode |
1127	-----------|------------|------------|	1501	--------------|------------|------------|
1128	JSON 1.x | 55.260 | 34.971 |	1502	JSON::DWIW/DS | 1647.927 | 2673.916 |
1129	JSON::DWIW | 825.228 | 1082.513 |	1503	JSON::DWIW/FJ | 1630.249 | 2596.128 |
1130	JSON::PC | 3571.444 | 2394.829 |
1131	JSON::PP | 210.987 | 32.574 |	1504	JSON::PP | 400.640 | 62.311 |
1132	JSON::Syck | 552.551 | 787.544 |	1505	JSON::Syck | 1481.040 | 1524.869 |
1133	JSON::XS | 5780.463 | 4854.519 |	1506	JSON::XS | 20661.596 | 9541.183 |
1134	JSON::XS/2 | 3869.998 | 4798.975 |	1507	JSON::XS/2 | 10683.403 | 9416.938 |
1135	JSON::XS/3 | 5862.880 | 4798.975 |	1508	JSON::XS/3 | 20661.596 | 9400.054 |
1136	Storable | 4445.002 | 5235.027 |	1509	Storable | 19765.806 | 10000.725 |
1137	-----------+------------+------------+	1510	--------------+------------+------------+
1138		1511
1139	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1512	Again, JSON::XS leads by far (except for Storable which non-surprisingly
1140	decodes faster).	1513	decodes a bit faster).
1141		1514
1142	On large strings containing lots of high Unicode characters, some modules	1515	On large strings containing lots of high Unicode characters, some modules
1143	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1516	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
1144	will be broken due to missing (or wrong) Unicode handling. Others refuse	1517	will be broken due to missing (or wrong) Unicode handling. Others refuse
1145	to decode or encode properly, so it was impossible to prepare a fair	1518	to decode or encode properly, so it was impossible to prepare a fair
…		…
1181	information you might want to make sure that exceptions thrown by JSON::XS	1554	information you might want to make sure that exceptions thrown by JSON::XS
1182	will not end up in front of untrusted eyes.	1555	will not end up in front of untrusted eyes.
1183		1556
1184	If you are using JSON::XS to return packets to consumption	1557	If you are using JSON::XS to return packets to consumption
1185	by JavaScript scripts in a browser you should have a look at	1558	by JavaScript scripts in a browser you should have a look at
1186	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1559	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
1187	you are vulnerable to some common attack vectors (which really are browser	1560	see whether you are vulnerable to some common attack vectors (which really
1188	design bugs, but it is still you who will have to deal with it, as major	1561	are browser design bugs, but it is still you who will have to deal with
1189	browser developers care only for features, not about getting security	1562	it, as major browser developers care only for features, not about getting
1190	right).	1563	security right).
1191		1564
1192		1565
		1566	=head2 "OLD" VS. "NEW" JSON (RFC4627 VS. RFC7159)
		1567
		1568	JSON originally required JSON texts to represent an array or object -
		1569	scalar values were explicitly not allowed. This has changed, and versions
		1570	of JSON::XS beginning with C<4.0> reflect this by allowing scalar values
		1571	by default.
		1572
		1573	One reason why one might not want this is that this removes a fundamental
		1574	property of JSON texts, namely that they are self-delimited and
		1575	self-contained, or in other words, you could take any number of "old"
		1576	JSON texts and paste them together, and the result would be unambiguously
		1577	parseable:
		1578
		1579	[1,3]{"k":5}[][null] # four JSON texts, without doubt
		1580
		1581	By allowing scalars, this property is lost: in the following example, is
		1582	this one JSON text (the number 12) or two JSON texts (the numbers 1 and
		1583	2):
		1584
		1585	12 # could be 12, or 1 and 2
		1586
		1587	Another lost property of "old" JSON is that no lookahead is required to
		1588	know the end of a JSON text, i.e. the JSON text definitely ended at the
		1589	last C<]> or C<}> character, there was no need to read extra characters.
		1590
		1591	For example, a viable network protocol with "old" JSON was to simply
		1592	exchange JSON texts without delimiter. For "new" JSON, you have to use a
		1593	suitable delimiter (such as a newline) after every JSON text or ensure you
		1594	never encode/decode scalar values.
		1595
		1596	Most protocols do work by only transferring arrays or objects, and the
		1597	easiest way to avoid problems with the "new" JSON definition is to
		1598	explicitly disallow scalar values in your encoder and decoder:
		1599
		1600	$json_coder = JSON::XS->new->allow_nonref (0)
		1601
		1602	This is a somewhat unhappy situation, and the blame can fully be put on
		1603	JSON's inmventor, Douglas Crockford, who unilaterally changed the format
		1604	in 2006 without consulting the IETF, forcing the IETF to either fork the
		1605	format or go with it (as I was told, the IETF wasn't amused).
		1606
		1607
		1608	=head1 RELATIONSHIP WITH I-JSON
		1609
		1610	JSON is a somewhat sloppily-defined format - it carries around obvious
		1611	Javascript baggage, such as not really defining number range, probably
		1612	because Javascript only has one type of numbers: IEEE 64 bit floats
		1613	("binary64").
		1614
		1615	For this reaosn, RFC7493 defines "Internet JSON", which is a restricted
		1616	subset of JSON that is supposedly more interoperable on the internet.
		1617
		1618	While C<JSON::XS> does not offer specific support for I-JSON, it of course
		1619	accepts valid I-JSON and by default implements some of the limitations
		1620	of I-JSON, such as parsing numbers as perl numbers, which are usually a
		1621	superset of binary64 numbers.
		1622
		1623	To generate I-JSON, follow these rules:
		1624
		1625	=over
		1626
		1627	=item * always generate UTF-8
		1628
		1629	I-JSON must be encoded in UTF-8, the default for C<encode_json>.
		1630
		1631	=item * numbers should be within IEEE 754 binary64 range
		1632
		1633	Basically all existing perl installations use binary64 to represent
		1634	floating point numbers, so all you need to do is to avoid large integers.
		1635
		1636	=item * objects must not have duplicate keys
		1637
		1638	This is trivially done, as C<JSON::XS> does not allow duplicate keys.
		1639
		1640	=item * do not generate scalar JSON texts, use C<< ->allow_nonref (0) >>
		1641
		1642	I-JSON strongly requests you to only encode arrays and objects into JSON.
		1643
		1644	=item * times should be strings in ISO 8601 format
		1645
		1646	There are a myriad of modules on CPAN dealing with ISO 8601 - search for
		1647	C<ISO8601> on CPAN and use one.
		1648
		1649	=item * encode binary data as base64
		1650
		1651	While it's tempting to just dump binary data as a string (and let
		1652	C<JSON::XS> do the escaping), for I-JSON, it's I<recommended> to encode
		1653	binary data as base64.
		1654
		1655	=back
		1656
		1657	There are some other considerations - read RFC7493 for the details if
		1658	interested.
		1659
		1660
		1661	=head1 INTEROPERABILITY WITH OTHER MODULES
		1662
		1663	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1664	constants. That means that the JSON true and false values will be
		1665	comaptible to true and false values of other modules that do the same,
		1666	such as L<JSON::PP> and L<CBOR::XS>.
		1667
		1668
		1669	=head1 INTEROPERABILITY WITH OTHER JSON DECODERS
		1670
		1671	As long as you only serialise data that can be directly expressed in JSON,
		1672	C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs,
		1673	but C<JSON::XS> has found more bugs in the official JSON testsuite (1)
		1674	than the official JSON testsuite has found in C<JSON::XS> (0)).
		1675
		1676	When you have trouble decoding JSON generated by this module using other
		1677	decoders, then it is very likely that you have an encoding mismatch or the
		1678	other decoder is broken.
		1679
		1680	When decoding, C<JSON::XS> is strict by default and will likely catch all
		1681	errors. There are currently two settings that change this: C<relaxed>
		1682	makes C<JSON::XS> accept (but not generate) some non-standard extensions,
		1683	and C<allow_tags> will allow you to encode and decode Perl objects, at the
		1684	cost of not outputting valid JSON anymore.
		1685
		1686	=head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
		1687
		1688	When you use C<allow_tags> to use the extended (and also nonstandard and
		1689	invalid) JSON syntax for serialised objects, and you still want to decode
		1690	the generated When you want to serialise objects, you can run a regex
		1691	to replace the tagged syntax by standard JSON arrays (it only works for
		1692	"normal" package names without comma, newlines or single colons). First,
		1693	the readable Perl version:
		1694
		1695	# if your FREEZE methods return no values, you need this replace first:
		1696	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
		1697
		1698	# this works for non-empty constructor arg lists:
		1699	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
		1700
		1701	And here is a less readable version that is easy to adapt to other
		1702	languages:
		1703
		1704	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
		1705
		1706	Here is an ECMAScript version (same regex):
		1707
		1708	json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
		1709
		1710	Since this syntax converts to standard JSON arrays, it might be hard to
		1711	distinguish serialised objects from normal arrays. You can prepend a
		1712	"magic number" as first array element to reduce chances of a collision:
		1713
		1714	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
		1715
		1716	And after decoding the JSON text, you could walk the data
		1717	structure looking for arrays with a first element of
		1718	C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>.
		1719
		1720	The same approach can be used to create the tagged format with another
		1721	encoder. First, you create an array with the magic string as first member,
		1722	the classname as second, and constructor arguments last, encode it as part
		1723	of your JSON structure, and then:
		1724
		1725	$json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
		1726
		1727	Again, this has some limitations - the magic string must not be encoded
		1728	with character escapes, and the constructor arguments must be non-empty.
		1729
		1730
1193	=head1 THREADS	1731	=head1 (I-)THREADS
1194		1732
1195	This module is I<not> guaranteed to be thread safe and there are no	1733	This module is I<not> guaranteed to be ithread (or MULTIPLICITY-) safe
1196	plans to change this until Perl gets thread support (as opposed to the	1734	and there are no plans to change this. Note that perl's builtin so-called
1197	horribly slow so-called "threads" which are simply slow and bloated	1735	threads/ithreads are officially deprecated and should not be used.
1198	process simulations - use fork, it's I<much> faster, cheaper, better).
1199		1736
1200	(It might actually work, but you have been warned).	1737
		1738	=head1 THE PERILS OF SETLOCALE
		1739
		1740	Sometimes people avoid the Perl locale support and directly call the
		1741	system's setlocale function with C<LC_ALL>.
		1742
		1743	This breaks both perl and modules such as JSON::XS, as stringification of
		1744	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1745	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1746	perl to stringify numbers).
		1747
		1748	The solution is simple: don't call C<setlocale>, or use it for only those
		1749	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1750
		1751	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1752	actually needs it (avoiding stringification of numbers), and restore it
		1753	afterwards.
		1754
		1755
		1756	=head1 SOME HISTORY
		1757
		1758	At the time this module was created there already were a number of JSON
		1759	modules available on CPAN, so what was the reason to write yet another
		1760	JSON module? While it seems there are many JSON modules, none of them
		1761	correctly handled all corner cases, and in most cases their maintainers
		1762	are unresponsive, gone missing, or not listening to bug reports for other
		1763	reasons.
		1764
		1765	Beginning with version 2.0 of the JSON module, when both JSON and
		1766	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		1767	overridden) with no overhead due to emulation (by inheriting constructor
		1768	and methods). If JSON::XS is not available, it will fall back to the
		1769	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		1770	gives you a portable JSON API that can be fast when you need it and
		1771	doesn't require a C compiler when that is a problem.
		1772
		1773	Somewhere around version 3, this module was forked into
		1774	C<Cpanel::JSON::XS>, because its maintainer had serious trouble
		1775	understanding JSON and insisted on a fork with many bugs "fixed" that
		1776	weren't actually bugs, while spreading FUD about this module without
		1777	actually giving any details on his accusations. You be the judge, but
		1778	in my personal opinion, if you want quality, you will stay away from
		1779	dangerous forks like that.
1201		1780
1202		1781
1203	=head1 BUGS	1782	=head1 BUGS
1204		1783
1205	While the goal of this module is to be correct, that unfortunately does	1784	While the goal of this module is to be correct, that unfortunately does
1206	not mean it's bug-free, only that I think its design is bug-free. It is	1785	not mean it's bug-free, only that I think its design is bug-free. If you
1207	still relatively early in its development. If you keep reporting bugs they	1786	keep reporting bugs they will be fixed swiftly, though.
1208	will be fixed swiftly, though.
1209		1787
1210	Please refrain from using rt.cpan.org or any other bug reporting	1788	Please refrain from using rt.cpan.org or any other bug reporting
1211	service. I put the contact address into my modules for a reason.	1789	service. I put the contact address into my modules for a reason.
1212		1790
1213	=cut	1791	=cut
1214		1792
1215	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1793	BEGIN {
1216	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };	1794	*true = \$Types::Serialiser::true;
		1795	*true = \&Types::Serialiser::true;
		1796	*false = \$Types::Serialiser::false;
		1797	*false = \&Types::Serialiser::false;
		1798	*is_bool = \&Types::Serialiser::is_bool;
1217		1799
1218	sub true() { $true }	1800	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
1219	sub false() { $false }
1220
1221	sub is_bool($) {
1222	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1223	# or UNIVERSAL::isa $_[0], "JSON::Literal"
1224	}	1801	}
1225		1802
1226	XSLoader::load "JSON::XS", $VERSION;	1803	XSLoader::load "JSON::XS", $VERSION;
1227
1228	package JSON::XS::Boolean;
1229
1230	use overload
1231	"0+" => sub { ${$_[0]} },
1232	"++" => sub { $_[0] = ${$_[0]} + 1 },
1233	"--" => sub { $_[0] = ${$_[0]} - 1 },
1234	fallback => 1;
1235
1236	1;
1237		1804
1238	=head1 SEE ALSO	1805	=head1 SEE ALSO
1239		1806
1240	The F<json_xs> command line utility for quick experiments.	1807	The F<json_xs> command line utility for quick experiments.
1241		1808
…		…
1244	Marc Lehmann <schmorp@schmorp.de>	1811	Marc Lehmann <schmorp@schmorp.de>
1245	http://home.schmorp.de/	1812	http://home.schmorp.de/
1246		1813
1247	=cut	1814	=cut
1248		1815
		1816	1
		1817

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