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Revision 1.86 by root, Wed Mar 19 03:17:38 2008 UTC vs.
Revision 1.169 by root, Thu Nov 15 20:49:12 2018 UTC

		1	=head1 NAME
		2
		3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
1	=encoding utf-8	5	=encoding utf-8
2
3	=head1 NAME
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
…		…
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	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	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	42	overridden) with no overhead due to emulation (by inheriting constructor
43	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
44	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
45	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 it and
46	require a C compiler when that is a problem.	46	doesn't require a C compiler when that is a problem.
47		47
48	As this is the n-th-something JSON module on CPAN, what was the reason	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	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	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	51	their maintainers are unresponsive, gone missing, or not listening to bug
52	reports for other reasons.	52	reports for other reasons.
53		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	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
57	vice versa.	55	vice versa.
58		56
59	=head2 FEATURES	57	=head2 FEATURES
60		58
…		…
65	This module knows how to handle Unicode, documents how and when it does	63	This module knows how to handle Unicode, documents how and when it does
66	so, and even documents what "correct" means.	64	so, and even documents what "correct" means.
67		65
68	=item * round-trip integrity	66	=item * round-trip integrity
69		67
70	When you serialise a perl data structure using only datatypes supported	68	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.	69	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	70	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	71	it looks like a number). There I<are> minor exceptions to this, read the
74	section below to learn about those.	72	MAPPING section below to learn about those.
75		73
76	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
77		75
78	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,
79	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
…		…
84	Compared to other JSON modules and other serialisers such as Storable,	82	Compared to other JSON modules and other serialisers such as Storable,
85	this module usually compares favourably in terms of speed, too.	83	this module usually compares favourably in terms of speed, too.
86		84
87	=item * simple to use	85	=item * simple to use
88		86
89	This module has both a simple functional interface as well as an objetc	87	This module has both a simple functional interface as well as an object
90	oriented interface interface.	88	oriented interface.
91		89
92	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
93		91
94	You can choose between the most compact guaranteed-single-line format	92	You can choose between the most compact guaranteed-single-line format
95	possible (nice for simple line-based protocols), a pure-ascii format	93	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	94	(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	95	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.	96	stuff). Or you can combine those features in whatever way you like.
99		97
100	=back	98	=back
101		99
102	=cut	100	=cut
103		101
104	package JSON::XS;	102	package JSON::XS;
105		103
106	use strict;	104	use common::sense;
107		105
108	our $VERSION = '2.01';	106	our $VERSION = 3.04;
109	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
110		108
111	our @EXPORT = qw(encode_json decode_json to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
112
113	sub to_json($) {
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		110
123	use Exporter;	111	use Exporter;
124	use XSLoader;	112	use XSLoader;
125		113
		114	use Types::Serialiser ();
		115
126	=head1 FUNCTIONAL INTERFACE	116	=head1 FUNCTIONAL INTERFACE
127		117
128	The following convenience methods are provided by this module. They are	118	The following convenience methods are provided by this module. They are
129	exported by default:	119	exported by default:
130		120
…		…
137		127
138	This function call is functionally identical to:	128	This function call is functionally identical to:
139		129
140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	130	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
141		131
142	except being faster.	132	Except being faster.
143		133
144	=item $perl_scalar = decode_json $json_text	134	=item $perl_scalar = decode_json $json_text
145		135
146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries	136	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	137	to parse that as a UTF-8 encoded JSON text, returning the resulting
148	reference. Croaks on error.	138	reference. Croaks on error.
149		139
150	This function call is functionally identical to:	140	This function call is functionally identical to:
151		141
152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	142	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
153		143
154	except being faster.	144	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		145
165	=back	146	=back
166		147
167		148
168	=head1 A FEW NOTES ON UNICODE AND PERL	149	=head1 A FEW NOTES ON UNICODE AND PERL
…		…
197		178
198	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
199	exist.	180	exist.
200		181
201	=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
202	validly interpreted as a Unicode codepoint.	183	validly interpreted as a Unicode code point.
203		184
204	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
205	Unicode string encoded in UTF-8, giving you a binary string.	186	Unicode string encoded in UTF-8, giving you a binary string.
206		187
207	=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.
…		…
221	=over 4	202	=over 4
222		203
223	=item $json = new JSON::XS	204	=item $json = new JSON::XS
224		205
225	Creates a new JSON::XS object that can be used to de/encode JSON	206	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>.	207	strings. All boolean flags described below are by default I<disabled>
		208	(with the exception of C<allow_nonref>, which defaults to I<enabled> since
		209	version C<4.0>).
227		210
228	The mutators for flags all return the JSON object again and thus calls can	211	The mutators for flags all return the JSON object again and thus calls can
229	be chained:	212	be chained:
230		213
231	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	214	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
…		…
245		228
246	If C<$enable> is false, then the C<encode> method will not escape Unicode	229	If C<$enable> is false, then the C<encode> method will not escape Unicode
247	characters unless required by the JSON syntax or other flags. This results	230	characters unless required by the JSON syntax or other flags. This results
248	in a faster and more compact format.	231	in a faster and more compact format.
249		232
		233	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		234	document.
		235
250	The main use for this flag is to produce JSON texts that can be	236	The main use for this flag is to produce JSON texts that can be
251	transmitted over a 7-bit channel, as the encoded JSON texts will not	237	transmitted over a 7-bit channel, as the encoded JSON texts will not
252	contain any 8 bit characters.	238	contain any 8 bit characters.
253		239
254	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	240	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
265	will not be affected in any way by this flag, as C<decode> by default	251	will not be affected in any way by this flag, as C<decode> by default
266	expects Unicode, which is a strict superset of latin1.	252	expects Unicode, which is a strict superset of latin1.
267		253
268	If C<$enable> is false, then the C<encode> method will not escape Unicode	254	If C<$enable> is false, then the C<encode> method will not escape Unicode
269	characters unless required by the JSON syntax or other flags.	255	characters unless required by the JSON syntax or other flags.
		256
		257	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		258	document.
270		259
271	The main use for this flag is efficiently encoding binary data as JSON	260	The main use for this flag is efficiently encoding binary data as JSON
272	text, as most octets will not be escaped, resulting in a smaller encoded	261	text, as most octets will not be escaped, resulting in a smaller encoded
273	size. The disadvantage is that the resulting JSON text is encoded	262	size. The disadvantage is that the resulting JSON text is encoded
274	in latin1 (and must correctly be treated as such when storing and	263	in latin1 (and must correctly be treated as such when storing and
…		…
283		272
284	=item $enabled = $json->get_utf8	273	=item $enabled = $json->get_utf8
285		274
286	If C<$enable> is true (or missing), then the C<encode> method will encode	275	If C<$enable> is true (or missing), then the C<encode> method will encode
287	the JSON result into UTF-8, as required by many protocols, while the	276	the JSON result into UTF-8, as required by many protocols, while the
288	C<decode> method expects to be handled an UTF-8-encoded string. Please	277	C<decode> method expects to be handed a UTF-8-encoded string. Please
289	note that UTF-8-encoded strings do not contain any characters outside the	278	note that UTF-8-encoded strings do not contain any characters outside the
290	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	279	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
291	versions, enabling this option might enable autodetection of the UTF-16	280	versions, enabling this option might enable autodetection of the UTF-16
292	and UTF-32 encoding families, as described in RFC4627.	281	and UTF-32 encoding families, as described in RFC4627.
293		282
294	If C<$enable> is false, then the C<encode> method will return the JSON	283	If C<$enable> is false, then the C<encode> method will return the JSON
295	string as a (non-encoded) Unicode string, while C<decode> expects thus a	284	string as a (non-encoded) Unicode string, while C<decode> expects thus a
296	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	285	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
297	to be done yourself, e.g. using the Encode module.	286	to be done yourself, e.g. using the Encode module.
		287
		288	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		289	document.
298		290
299	Example, output UTF-16BE-encoded JSON:	291	Example, output UTF-16BE-encoded JSON:
300		292
301	use Encode;	293	use Encode;
302	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	294	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
375		367
376	=item $enabled = $json->get_relaxed	368	=item $enabled = $json->get_relaxed
377		369
378	If C<$enable> is true (or missing), then C<decode> will accept some	370	If C<$enable> is true (or missing), then C<decode> will accept some
379	extensions to normal JSON syntax (see below). C<encode> will not be	371	extensions to normal JSON syntax (see below). C<encode> will not be
380	affected in anyway. I<Be aware that this option makes you accept invalid	372	affected in any way. I<Be aware that this option makes you accept invalid
381	JSON texts as if they were valid!>. I suggest only to use this option to	373	JSON texts as if they were valid!>. I suggest only to use this option to
382	parse application-specific files written by humans (configuration files,	374	parse application-specific files written by humans (configuration files,
383	resource files etc.)	375	resource files etc.)
384		376
385	If C<$enable> is false (the default), then C<decode> will only accept	377	If C<$enable> is false (the default), then C<decode> will only accept
…		…
414	[	406	[
415	1, # this comment not allowed in JSON	407	1, # this comment not allowed in JSON
416	# neither this one...	408	# neither this one...
417	]	409	]
418		410
		411	=item * literal ASCII TAB characters in strings
		412
		413	Literal ASCII TAB characters are now allowed in strings (and treated as
		414	C<\t>).
		415
		416	[
		417	"Hello\tWorld",
		418	"Hello<TAB>World", # literal <TAB> would not normally be allowed
		419	]
		420
419	=back	421	=back
420		422
421	=item $json = $json->canonical ([$enable])	423	=item $json = $json->canonical ([$enable])
422		424
423	=item $enabled = $json->get_canonical	425	=item $enabled = $json->get_canonical
…		…
425	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	427	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
426	by sorting their keys. This is adding a comparatively high overhead.	428	by sorting their keys. This is adding a comparatively high overhead.
427		429
428	If C<$enable> is false, then the C<encode> method will output key-value	430	If C<$enable> is false, then the C<encode> method will output key-value
429	pairs in the order Perl stores them (which will likely change between runs	431	pairs in the order Perl stores them (which will likely change between runs
430	of the same script).	432	of the same script, and can change even within the same run from 5.18
		433	onwards).
431		434
432	This option is useful if you want the same data structure to be encoded as	435	This option is useful if you want the same data structure to be encoded as
433	the same JSON text (given the same overall settings). If it is disabled,	436	the same JSON text (given the same overall settings). If it is disabled,
434	the same hash might be encoded differently even if contains the same data,	437	the same hash might be encoded differently even if contains the same data,
435	as key-value pairs have no inherent ordering in Perl.	438	as key-value pairs have no inherent ordering in Perl.
436		439
437	This setting has no effect when decoding JSON texts.	440	This setting has no effect when decoding JSON texts.
438		441
		442	This setting has currently no effect on tied hashes.
		443
439	=item $json = $json->allow_nonref ([$enable])	444	=item $json = $json->allow_nonref ([$enable])
440		445
441	=item $enabled = $json->get_allow_nonref	446	=item $enabled = $json->get_allow_nonref
		447
		448	Unlike other boolean options, this opotion is enabled by default beginning
		449	with version C<4.0>. See L<SECURITY CONSIDERATIONS> for the gory details.
442		450
443	If C<$enable> is true (or missing), then the C<encode> method can convert a	451	If C<$enable> is true (or missing), then the C<encode> method can convert a
444	non-reference into its corresponding string, number or null JSON value,	452	non-reference into its corresponding string, number or null JSON value,
445	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	453	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
446	values instead of croaking.	454	values instead of croaking.
…		…
448	If C<$enable> is false, then the C<encode> method will croak if it isn't	456	If C<$enable> is false, then the C<encode> method will croak if it isn't
449	passed an arrayref or hashref, as JSON texts must either be an object	457	passed an arrayref or hashref, as JSON texts must either be an object
450	or array. Likewise, C<decode> will croak if given something that is not a	458	or array. Likewise, C<decode> will croak if given something that is not a
451	JSON object or array.	459	JSON object or array.
452		460
453	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,	461	Example, encode a Perl scalar as JSON value without enabled C<allow_nonref>,
454	resulting in an invalid JSON text:	462	resulting in an error:
455		463
456	JSON::XS->new->allow_nonref->encode ("Hello, World!")	464	JSON::XS->new->allow_nonref (0)->encode ("Hello, World!")
457	=> "Hello, World!"	465	=> hash- or arrayref expected...
		466
		467	=item $json = $json->allow_unknown ([$enable])
		468
		469	=item $enabled = $json->get_allow_unknown
		470
		471	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		472	exception when it encounters values it cannot represent in JSON (for
		473	example, filehandles) but instead will encode a JSON C<null> value. Note
		474	that blessed objects are not included here and are handled separately by
		475	c<allow_nonref>.
		476
		477	If C<$enable> is false (the default), then C<encode> will throw an
		478	exception when it encounters anything it cannot encode as JSON.
		479
		480	This option does not affect C<decode> in any way, and it is recommended to
		481	leave it off unless you know your communications partner.
458		482
459	=item $json = $json->allow_blessed ([$enable])	483	=item $json = $json->allow_blessed ([$enable])
460		484
461	=item $enabled = $json->get_allow_blessed	485	=item $enabled = $json->get_allow_blessed
462		486
		487	See L<OBJECT SERIALISATION> for details.
		488
463	If C<$enable> is true (or missing), then the C<encode> method will not	489	If C<$enable> is true (or missing), then the C<encode> method will not
464	barf when it encounters a blessed reference. Instead, the value of the	490	barf when it encounters a blessed reference that it cannot convert
465	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>	491	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
466	disabled or no C<TO_JSON> method found) or a representation of the
467	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
468	encoded. Has no effect on C<decode>.
469		492
470	If C<$enable> is false (the default), then C<encode> will throw an	493	If C<$enable> is false (the default), then C<encode> will throw an
471	exception when it encounters a blessed object.	494	exception when it encounters a blessed object that it cannot convert
		495	otherwise.
		496
		497	This setting has no effect on C<decode>.
472		498
473	=item $json = $json->convert_blessed ([$enable])	499	=item $json = $json->convert_blessed ([$enable])
474		500
475	=item $enabled = $json->get_convert_blessed	501	=item $enabled = $json->get_convert_blessed
		502
		503	See L<OBJECT SERIALISATION> for details.
476		504
477	If C<$enable> is true (or missing), then C<encode>, upon encountering a	505	If C<$enable> is true (or missing), then C<encode>, upon encountering a
478	blessed object, will check for the availability of the C<TO_JSON> method	506	blessed object, will check for the availability of the C<TO_JSON> method
479	on the object's class. If found, it will be called in scalar context	507	on the object's class. If found, it will be called in scalar context and
480	and the resulting scalar will be encoded instead of the object. If no	508	the resulting scalar will be encoded instead of the object.
481	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
482	to do.
483		509
484	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	510	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
485	returns other blessed objects, those will be handled in the same	511	returns other blessed objects, those will be handled in the same
486	way. C<TO_JSON> must take care of not causing an endless recursion cycle	512	way. C<TO_JSON> must take care of not causing an endless recursion cycle
487	(== crash) in this case. The name of C<TO_JSON> was chosen because other	513	(== crash) in this case. The name of C<TO_JSON> was chosen because other
488	methods called by the Perl core (== not by the user of the object) are	514	methods called by the Perl core (== not by the user of the object) are
489	usually in upper case letters and to avoid collisions with any C<to_json>	515	usually in upper case letters and to avoid collisions with any C<to_json>
490	function or method.	516	function or method.
491		517
492	This setting does not yet influence C<decode> in any way, but in the	518	If C<$enable> is false (the default), then C<encode> will not consider
493	future, global hooks might get installed that influence C<decode> and are	519	this type of conversion.
494	enabled by this setting.
495		520
496	If C<$enable> is false, then the C<allow_blessed> setting will decide what	521	This setting has no effect on C<decode>.
497	to do when a blessed object is found.	522
		523	=item $json = $json->allow_tags ([$enable])
		524
		525	=item $enabled = $json->get_allow_tags
		526
		527	See L<OBJECT SERIALISATION> for details.
		528
		529	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		530	blessed object, will check for the availability of the C<FREEZE> method on
		531	the object's class. If found, it will be used to serialise the object into
		532	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		533
		534	It also causes C<decode> to parse such tagged JSON values and deserialise
		535	them via a call to the C<THAW> method.
		536
		537	If C<$enable> is false (the default), then C<encode> will not consider
		538	this type of conversion, and tagged JSON values will cause a parse error
		539	in C<decode>, as if tags were not part of the grammar.
498		540
499	=item $json = $json->filter_json_object ([$coderef->($hashref)])	541	=item $json = $json->filter_json_object ([$coderef->($hashref)])
500		542
501	When C<$coderef> is specified, it will be called from C<decode> each	543	When C<$coderef> is specified, it will be called from C<decode> each
502	time it decodes a JSON object. The only argument is a reference to the	544	time it decodes a JSON object. The only argument is a reference to
503	newly-created hash. If the code references returns a single scalar (which	545	the newly-created hash. If the code reference returns a single scalar
504	need not be a reference), this value (i.e. a copy of that scalar to avoid	546	(which need not be a reference), this value (or rather a copy of it) is
505	aliasing) is inserted into the deserialised data structure. If it returns	547	inserted into the deserialised data structure. If it returns an empty
506	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the	548	list (NOTE: I<not> C<undef>, which is a valid scalar), the original
507	original deserialised hash will be inserted. This setting can slow down	549	deserialised hash will be inserted. This setting can slow down decoding
508	decoding considerably.	550	considerably.
509		551
510	When C<$coderef> is omitted or undefined, any existing callback will	552	When C<$coderef> is omitted or undefined, any existing callback will
511	be removed and C<decode> will not change the deserialised hash in any	553	be removed and C<decode> will not change the deserialised hash in any
512	way.	554	way.
513		555
…		…
603	=item $json = $json->max_depth ([$maximum_nesting_depth])	645	=item $json = $json->max_depth ([$maximum_nesting_depth])
604		646
605	=item $max_depth = $json->get_max_depth	647	=item $max_depth = $json->get_max_depth
606		648
607	Sets the maximum nesting level (default C<512>) accepted while encoding	649	Sets the maximum nesting level (default C<512>) accepted while encoding
608	or decoding. If the JSON text or Perl data structure has an equal or	650	or decoding. If a higher nesting level is detected in JSON text or a Perl
609	higher nesting level then this limit, then the encoder and decoder will	651	data structure, then the encoder and decoder will stop and croak at that
610	stop and croak at that point.	652	point.
611		653
612	Nesting level is defined by number of hash- or arrayrefs that the encoder	654	Nesting level is defined by number of hash- or arrayrefs that the encoder
613	needs to traverse to reach a given point or the number of C<{> or C<[>	655	needs to traverse to reach a given point or the number of C<{> or C<[>
614	characters without their matching closing parenthesis crossed to reach a	656	characters without their matching closing parenthesis crossed to reach a
615	given character in a string.	657	given character in a string.
616		658
617	Setting the maximum depth to one disallows any nesting, so that ensures	659	Setting the maximum depth to one disallows any nesting, so that ensures
618	that the object is only a single hash/object or array.	660	that the object is only a single hash/object or array.
619		661
620	The argument to C<max_depth> will be rounded up to the next highest power
621	of two. If no argument is given, the highest possible setting will be	662	If no argument is given, the highest possible setting will be used, which
622	used, which is rarely useful.	663	is rarely useful.
		664
		665	Note that nesting is implemented by recursion in C. The default value has
		666	been chosen to be as large as typical operating systems allow without
		667	crashing.
623		668
624	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.
625		670
626	=item $json = $json->max_size ([$maximum_string_size])	671	=item $json = $json->max_size ([$maximum_string_size])
627		672
628	=item $max_size = $json->get_max_size	673	=item $max_size = $json->get_max_size
629		674
630	Set the maximum length a JSON text may have (in bytes) where decoding is	675	Set the maximum length a JSON text may have (in bytes) where decoding is
631	being attempted. The default is C<0>, meaning no limit. When C<decode>	676	being attempted. The default is C<0>, meaning no limit. When C<decode>
632	is called on a string longer then this number of characters it will not	677	is called on a string that is longer then this many bytes, it will not
633	attempt to decode the string but throw an exception. This setting has no	678	attempt to decode the string but throw an exception. This setting has no
634	effect on C<encode> (yet).	679	effect on C<encode> (yet).
635		680
636	The argument to C<max_size> will be rounded up to the next B<highest>	681	If no argument is given, the limit check will be deactivated (same as when
637	power of two (so may be more than requested). If no argument is given, the	682	C<0> is specified).
638	limit check will be deactivated (same as when C<0> is specified).
639		683
640	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	684	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
641		685
642	=item $json_text = $json->encode ($perl_scalar)	686	=item $json_text = $json->encode ($perl_scalar)
643		687
644	Converts the given Perl data structure (a simple scalar or a reference	688	Converts the given Perl value or data structure to its JSON
645	to a hash or array) to its JSON representation. Simple scalars will be	689	representation. Croaks on error.
646	converted into JSON string or number sequences, while references to arrays
647	become JSON arrays and references to hashes become JSON objects. Undefined
648	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
649	nor C<false> values will be generated.
650		690
651	=item $perl_scalar = $json->decode ($json_text)	691	=item $perl_scalar = $json->decode ($json_text)
652		692
653	The opposite of C<encode>: expects a JSON text and tries to parse it,	693	The opposite of C<encode>: expects a JSON text and tries to parse it,
654	returning the resulting simple scalar or reference. Croaks on error.	694	returning the resulting simple scalar or reference. Croaks on error.
655
656	JSON numbers and strings become simple Perl scalars. JSON arrays become
657	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
658	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
659		695
660	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	696	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
661		697
662	This works like the C<decode> method, but instead of raising an exception	698	This works like the C<decode> method, but instead of raising an exception
663	when there is trailing garbage after the first JSON object, it will	699	when there is trailing garbage after the first JSON object, it will
664	silently stop parsing there and return the number of characters consumed	700	silently stop parsing there and return the number of characters consumed
665	so far.	701	so far.
666		702
667	This is useful if your JSON texts are not delimited by an outer protocol	703	This is useful if your JSON texts are not delimited by an outer protocol
668	(which is not the brightest thing to do in the first place) and you need
669	to know where the JSON text ends.	704	and you need to know where the JSON text ends.
670		705
671	JSON::XS->new->decode_prefix ("[1] the tail")	706	JSON::XS->new->decode_prefix ("[1] the tail")
672	=> ([], 3)	707	=> ([1], 3)
673		708
674	=back	709	=back
		710
		711
		712	=head1 INCREMENTAL PARSING
		713
		714	In some cases, there is the need for incremental parsing of JSON
		715	texts. While this module always has to keep both JSON text and resulting
		716	Perl data structure in memory at one time, it does allow you to parse a
		717	JSON stream incrementally. It does so by accumulating text until it has
		718	a full JSON object, which it then can decode. This process is similar to
		719	using C<decode_prefix> to see if a full JSON object is available, but
		720	is much more efficient (and can be implemented with a minimum of method
		721	calls).
		722
		723	JSON::XS will only attempt to parse the JSON text once it is sure it
		724	has enough text to get a decisive result, using a very simple but
		725	truly incremental parser. This means that it sometimes won't stop as
		726	early as the full parser, for example, it doesn't detect mismatched
		727	parentheses. The only thing it guarantees is that it starts decoding as
		728	soon as a syntactically valid JSON text has been seen. This means you need
		729	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		730	parsing in the presence if syntax errors.
		731
		732	The following methods implement this incremental parser.
		733
		734	=over 4
		735
		736	=item [void, scalar or list context] = $json->incr_parse ([$string])
		737
		738	This is the central parsing function. It can both append new text and
		739	extract objects from the stream accumulated so far (both of these
		740	functions are optional).
		741
		742	If C<$string> is given, then this string is appended to the already
		743	existing JSON fragment stored in the C<$json> object.
		744
		745	After that, if the function is called in void context, it will simply
		746	return without doing anything further. This can be used to add more text
		747	in as many chunks as you want.
		748
		749	If the method is called in scalar context, then it will try to extract
		750	exactly I<one> JSON object. If that is successful, it will return this
		751	object, otherwise it will return C<undef>. If there is a parse error,
		752	this method will croak just as C<decode> would do (one can then use
		753	C<incr_skip> to skip the erroneous part). This is the most common way of
		754	using the method.
		755
		756	And finally, in list context, it will try to extract as many objects
		757	from the stream as it can find and return them, or the empty list
		758	otherwise. For this to work, there must be no separators (other than
		759	whitespace) between the JSON objects or arrays, instead they must be
		760	concatenated back-to-back. If an error occurs, an exception will be
		761	raised as in the scalar context case. Note that in this case, any
		762	previously-parsed JSON texts will be lost.
		763
		764	Example: Parse some JSON arrays/objects in a given string and return
		765	them.
		766
		767	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		768
		769	=item $lvalue_string = $json->incr_text
		770
		771	This method returns the currently stored JSON fragment as an lvalue, that
		772	is, you can manipulate it. This I<only> works when a preceding call to
		773	C<incr_parse> in I<scalar context> successfully returned an object. Under
		774	all other circumstances you must not call this function (I mean it.
		775	although in simple tests it might actually work, it I<will> fail under
		776	real world conditions). As a special exception, you can also call this
		777	method before having parsed anything.
		778
		779	That means you can only use this function to look at or manipulate text
		780	before or after complete JSON objects, not while the parser is in the
		781	middle of parsing a JSON object.
		782
		783	This function is useful in two cases: a) finding the trailing text after a
		784	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		785	(such as commas).
		786
		787	=item $json->incr_skip
		788
		789	This will reset the state of the incremental parser and will remove
		790	the parsed text from the input buffer so far. This is useful after
		791	C<incr_parse> died, in which case the input buffer and incremental parser
		792	state is left unchanged, to skip the text parsed so far and to reset the
		793	parse state.
		794
		795	The difference to C<incr_reset> is that only text until the parse error
		796	occurred is removed.
		797
		798	=item $json->incr_reset
		799
		800	This completely resets the incremental parser, that is, after this call,
		801	it will be as if the parser had never parsed anything.
		802
		803	This is useful if you want to repeatedly parse JSON objects and want to
		804	ignore any trailing data, which means you have to reset the parser after
		805	each successful decode.
		806
		807	=back
		808
		809	=head2 LIMITATIONS
		810
		811	All options that affect decoding are supported, except
		812	C<allow_nonref>. The reason for this is that it cannot be made to work
		813	sensibly: JSON objects and arrays are self-delimited, i.e. you can
		814	concatenate them back to back and still decode them perfectly. This does
		815	not hold true for JSON numbers, however.
		816
		817	For example, is the string C<1> a single JSON number, or is it simply the
		818	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		819	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		820	takes the conservative route and disallows this case.
		821
		822	=head2 EXAMPLES
		823
		824	Some examples will make all this clearer. First, a simple example that
		825	works similarly to C<decode_prefix>: We want to decode the JSON object at
		826	the start of a string and identify the portion after the JSON object:
		827
		828	my $text = "[1,2,3] hello";
		829
		830	my $json = new JSON::XS;
		831
		832	my $obj = $json->incr_parse ($text)
		833	or die "expected JSON object or array at beginning of string";
		834
		835	my $tail = $json->incr_text;
		836	# $tail now contains " hello"
		837
		838	Easy, isn't it?
		839
		840	Now for a more complicated example: Imagine a hypothetical protocol where
		841	you read some requests from a TCP stream, and each request is a JSON
		842	array, without any separation between them (in fact, it is often useful to
		843	use newlines as "separators", as these get interpreted as whitespace at
		844	the start of the JSON text, which makes it possible to test said protocol
		845	with C<telnet>...).
		846
		847	Here is how you'd do it (it is trivial to write this in an event-based
		848	manner):
		849
		850	my $json = new JSON::XS;
		851
		852	# read some data from the socket
		853	while (sysread $socket, my $buf, 4096) {
		854
		855	# split and decode as many requests as possible
		856	for my $request ($json->incr_parse ($buf)) {
		857	# act on the $request
		858	}
		859	}
		860
		861	Another complicated example: Assume you have a string with JSON objects
		862	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		863	[3]>). To parse them, we have to skip the commas between the JSON texts,
		864	and here is where the lvalue-ness of C<incr_text> comes in useful:
		865
		866	my $text = "[1],[2], [3]";
		867	my $json = new JSON::XS;
		868
		869	# void context, so no parsing done
		870	$json->incr_parse ($text);
		871
		872	# now extract as many objects as possible. note the
		873	# use of scalar context so incr_text can be called.
		874	while (my $obj = $json->incr_parse) {
		875	# do something with $obj
		876
		877	# now skip the optional comma
		878	$json->incr_text =~ s/^ \s* , //x;
		879	}
		880
		881	Now lets go for a very complex example: Assume that you have a gigantic
		882	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		883	but you cannot load it into memory fully (this has actually happened in
		884	the real world :).
		885
		886	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		887	can still help you: You implement a (very simple) array parser and let
		888	JSON decode the array elements, which are all full JSON objects on their
		889	own (this wouldn't work if the array elements could be JSON numbers, for
		890	example):
		891
		892	my $json = new JSON::XS;
		893
		894	# open the monster
		895	open my $fh, "<bigfile.json"
		896	or die "bigfile: $!";
		897
		898	# first parse the initial "["
		899	for (;;) {
		900	sysread $fh, my $buf, 65536
		901	or die "read error: $!";
		902	$json->incr_parse ($buf); # void context, so no parsing
		903
		904	# Exit the loop once we found and removed(!) the initial "[".
		905	# In essence, we are (ab-)using the $json object as a simple scalar
		906	# we append data to.
		907	last if $json->incr_text =~ s/^ \s* \[ //x;
		908	}
		909
		910	# now we have the skipped the initial "[", so continue
		911	# parsing all the elements.
		912	for (;;) {
		913	# in this loop we read data until we got a single JSON object
		914	for (;;) {
		915	if (my $obj = $json->incr_parse) {
		916	# do something with $obj
		917	last;
		918	}
		919
		920	# add more data
		921	sysread $fh, my $buf, 65536
		922	or die "read error: $!";
		923	$json->incr_parse ($buf); # void context, so no parsing
		924	}
		925
		926	# in this loop we read data until we either found and parsed the
		927	# separating "," between elements, or the final "]"
		928	for (;;) {
		929	# first skip whitespace
		930	$json->incr_text =~ s/^\s*//;
		931
		932	# if we find "]", we are done
		933	if ($json->incr_text =~ s/^\]//) {
		934	print "finished.\n";
		935	exit;
		936	}
		937
		938	# if we find ",", we can continue with the next element
		939	if ($json->incr_text =~ s/^,//) {
		940	last;
		941	}
		942
		943	# if we find anything else, we have a parse error!
		944	if (length $json->incr_text) {
		945	die "parse error near ", $json->incr_text;
		946	}
		947
		948	# else add more data
		949	sysread $fh, my $buf, 65536
		950	or die "read error: $!";
		951	$json->incr_parse ($buf); # void context, so no parsing
		952	}
		953
		954	This is a complex example, but most of the complexity comes from the fact
		955	that we are trying to be correct (bear with me if I am wrong, I never ran
		956	the above example :).
		957
675		958
676		959
677	=head1 MAPPING	960	=head1 MAPPING
678		961
679	This section describes how JSON::XS maps Perl values to JSON values and	962	This section describes how JSON::XS maps Perl values to JSON values and
…		…
716	If the number consists of digits only, JSON::XS will try to represent	999	If the number consists of digits only, JSON::XS will try to represent
717	it as an integer value. If that fails, it will try to represent it as	1000	it as an integer value. If that fails, it will try to represent it as
718	a numeric (floating point) value if that is possible without loss of	1001	a numeric (floating point) value if that is possible without loss of
719	precision. Otherwise it will preserve the number as a string value (in	1002	precision. Otherwise it will preserve the number as a string value (in
720	which case you lose roundtripping ability, as the JSON number will be	1003	which case you lose roundtripping ability, as the JSON number will be
721	re-encoded toa JSON string).	1004	re-encoded to a JSON string).
722		1005
723	Numbers containing a fractional or exponential part will always be	1006	Numbers containing a fractional or exponential part will always be
724	represented as numeric (floating point) values, possibly at a loss of	1007	represented as numeric (floating point) values, possibly at a loss of
725	precision (in which case you might lose perfect roundtripping ability, but	1008	precision (in which case you might lose perfect roundtripping ability, but
726	the JSON number will still be re-encoded as a JSON number).	1009	the JSON number will still be re-encoded as a JSON number).
727		1010
		1011	Note that precision is not accuracy - binary floating point values cannot
		1012	represent most decimal fractions exactly, and when converting from and to
		1013	floating point, JSON::XS only guarantees precision up to but not including
		1014	the least significant bit.
		1015
728	=item true, false	1016	=item true, false
729		1017
730	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	1018	These JSON atoms become C<Types::Serialiser::true> and
731	respectively. They are overloaded to act almost exactly like the numbers	1019	C<Types::Serialiser::false>, respectively. They are overloaded to act
732	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using	1020	almost exactly like the numbers C<1> and C<0>. You can check whether
733	the C<JSON::XS::is_bool> function.	1021	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1022	function (after C<use Types::Serialier>, of course).
734		1023
735	=item null	1024	=item null
736		1025
737	A JSON null atom becomes C<undef> in Perl.	1026	A JSON null atom becomes C<undef> in Perl.
		1027
		1028	=item shell-style comments (C<< # I<text> >>)
		1029
		1030	As a nonstandard extension to the JSON syntax that is enabled by the
		1031	C<relaxed> setting, shell-style comments are allowed. They can start
		1032	anywhere outside strings and go till the end of the line.
		1033
		1034	=item tagged values (C<< (I<tag>)I<value> >>).
		1035
		1036	Another nonstandard extension to the JSON syntax, enabled with the
		1037	C<allow_tags> setting, are tagged values. In this implementation, the
		1038	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1039	I<value> must be a JSON array encoding optional constructor arguments.
		1040
		1041	See L<OBJECT SERIALISATION>, below, for details.
738		1042
739	=back	1043	=back
740		1044
741		1045
742	=head2 PERL -> JSON	1046	=head2 PERL -> JSON
…		…
747		1051
748	=over 4	1052	=over 4
749		1053
750	=item hash references	1054	=item hash references
751		1055
752	Perl hash references become JSON objects. As there is no inherent ordering	1056	Perl hash references become JSON objects. As there is no inherent
753	in hash keys (or JSON objects), they will usually be encoded in a	1057	ordering in hash keys (or JSON objects), they will usually be encoded
754	pseudo-random order that can change between runs of the same program but	1058	in a pseudo-random order. JSON::XS can optionally sort the hash keys
755	stays generally the same within a single run of a program. JSON::XS can	1059	(determined by the I<canonical> flag), so the same datastructure will
756	optionally sort the hash keys (determined by the I<canonical> flag), so	1060	serialise to the same JSON text (given same settings and version of
757	the same datastructure will serialise to the same JSON text (given same	1061	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
758	settings and version of JSON::XS), but this incurs a runtime overhead	1062	e.g. when you want to compare some JSON text against another for equality.
759	and is only rarely useful, e.g. when you want to compare some JSON text
760	against another for equality.
761		1063
762	=item array references	1064	=item array references
763		1065
764	Perl array references become JSON arrays.	1066	Perl array references become JSON arrays.
765		1067
766	=item other references	1068	=item other references
767		1069
768	Other unblessed references are generally not allowed and will cause an	1070	Other unblessed references are generally not allowed and will cause an
769	exception to be thrown, except for references to the integers C<0> and	1071	exception to be thrown, except for references to the integers C<0> and
770	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1072	C<1>, which get turned into C<false> and C<true> atoms in JSON.
771	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
772		1073
		1074	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1075	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1076	and C<Types::Serialiser::true> to improve readability.
		1077
		1078	use Types::Serialiser;
773	encode_json [\0,JSON::XS::true] # yields [false,true]	1079	encode_json [\0, Types::Serialiser::true] # yields [false,true]
774		1080
775	=item JSON::XS::true, JSON::XS::false	1081	=item Types::Serialiser::true, Types::Serialiser::false
776		1082
777	These special values become JSON true and JSON false values,	1083	These special values from the L<Types::Serialiser> module become JSON true
778	respectively. You can also use C<\1> and C<\0> directly if you want.	1084	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1085	directly if you want.
779		1086
780	=item blessed objects	1087	=item blessed objects
781		1088
782	Blessed objects are not directly representable in JSON. See the	1089	Blessed objects are not directly representable in JSON, but C<JSON::XS>
783	C<allow_blessed> and C<convert_blessed> methods on various options on	1090	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
784	how to deal with this: basically, you can choose between throwing an	1091	below, for details.
785	exception, encoding the reference as if it weren't blessed, or provide
786	your own serialiser method.
787		1092
788	=item simple scalars	1093	=item simple scalars
789		1094
790	Simple Perl scalars (any scalar that is not a reference) are the most	1095	Simple Perl scalars (any scalar that is not a reference) are the most
791	difficult objects to encode: JSON::XS will encode undefined scalars as	1096	difficult objects to encode: JSON::XS will encode undefined scalars as
…		…
816	my $x = "3"; # some variable containing a string	1121	my $x = "3"; # some variable containing a string
817	$x += 0; # numify it, ensuring it will be dumped as a number	1122	$x += 0; # numify it, ensuring it will be dumped as a number
818	$x *= 1; # same thing, the choice is yours.	1123	$x *= 1; # same thing, the choice is yours.
819		1124
820	You can not currently force the type in other, less obscure, ways. Tell me	1125	You can not currently force the type in other, less obscure, ways. Tell me
821	if you need this capability (but don't forget to explain why its needed	1126	if you need this capability (but don't forget to explain why it's needed
822	:).	1127	:).
823		1128
		1129	Note that numerical precision has the same meaning as under Perl (so
		1130	binary to decimal conversion follows the same rules as in Perl, which
		1131	can differ to other languages). Also, your perl interpreter might expose
		1132	extensions to the floating point numbers of your platform, such as
		1133	infinities or NaN's - these cannot be represented in JSON, and it is an
		1134	error to pass those in.
		1135
824	=back	1136	=back
		1137
		1138	=head2 OBJECT SERIALISATION
		1139
		1140	As JSON cannot directly represent Perl objects, you have to choose between
		1141	a pure JSON representation (without the ability to deserialise the object
		1142	automatically again), and a nonstandard extension to the JSON syntax,
		1143	tagged values.
		1144
		1145	=head3 SERIALISATION
		1146
		1147	What happens when C<JSON::XS> encounters a Perl object depends on the
		1148	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
		1149	used in this order:
		1150
		1151	=over 4
		1152
		1153	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
		1154
		1155	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1156	serialisation protocol to create a tagged JSON value, using a nonstandard
		1157	extension to the JSON syntax.
		1158
		1159	This works by invoking the C<FREEZE> method on the object, with the first
		1160	argument being the object to serialise, and the second argument being the
		1161	constant string C<JSON> to distinguish it from other serialisers.
		1162
		1163	The C<FREEZE> method can return any number of values (i.e. zero or
		1164	more). These values and the paclkage/classname of the object will then be
		1165	encoded as a tagged JSON value in the following format:
		1166
		1167	("classname")[FREEZE return values...]
		1168
		1169	e.g.:
		1170
		1171	("URI")["http://www.google.com/"]
		1172	("MyDate")[2013,10,29]
		1173	("ImageData::JPEG")["Z3...VlCg=="]
		1174
		1175	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1176	objects C<type> and C<id> members to encode the object:
		1177
		1178	sub My::Object::FREEZE {
		1179	my ($self, $serialiser) = @_;
		1180
		1181	($self->{type}, $self->{id})
		1182	}
		1183
		1184	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
		1185
		1186	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1187	context. It must return a single scalar that can be directly encoded into
		1188	JSON. This scalar replaces the object in the JSON text.
		1189
		1190	For example, the following C<TO_JSON> method will convert all L<URI>
		1191	objects to JSON strings when serialised. The fatc that these values
		1192	originally were L<URI> objects is lost.
		1193
		1194	sub URI::TO_JSON {
		1195	my ($uri) = @_;
		1196	$uri->as_string
		1197	}
		1198
		1199	=item 3. C<allow_blessed> is enabled.
		1200
		1201	The object will be serialised as a JSON null value.
		1202
		1203	=item 4. none of the above
		1204
		1205	If none of the settings are enabled or the respective methods are missing,
		1206	C<JSON::XS> throws an exception.
		1207
		1208	=back
		1209
		1210	=head3 DESERIALISATION
		1211
		1212	For deserialisation there are only two cases to consider: either
		1213	nonstandard tagging was used, in which case C<allow_tags> decides,
		1214	or objects cannot be automatically be deserialised, in which
		1215	case you can use postprocessing or the C<filter_json_object> or
		1216	C<filter_json_single_key_object> callbacks to get some real objects our of
		1217	your JSON.
		1218
		1219	This section only considers the tagged value case: I a tagged JSON object
		1220	is encountered during decoding and C<allow_tags> is disabled, a parse
		1221	error will result (as if tagged values were not part of the grammar).
		1222
		1223	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1224	of the package/classname used during serialisation (it will not attempt
		1225	to load the package as a Perl module). If there is no such method, the
		1226	decoding will fail with an error.
		1227
		1228	Otherwise, the C<THAW> method is invoked with the classname as first
		1229	argument, the constant string C<JSON> as second argument, and all the
		1230	values from the JSON array (the values originally returned by the
		1231	C<FREEZE> method) as remaining arguments.
		1232
		1233	The method must then return the object. While technically you can return
		1234	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1235	make that work in all cases, so better return an actual blessed reference.
		1236
		1237	As an example, let's implement a C<THAW> function that regenerates the
		1238	C<My::Object> from the C<FREEZE> example earlier:
		1239
		1240	sub My::Object::THAW {
		1241	my ($class, $serialiser, $type, $id) = @_;
		1242
		1243	$class->new (type => $type, id => $id)
		1244	}
825		1245
826		1246
827	=head1 ENCODING/CODESET FLAG NOTES	1247	=head1 ENCODING/CODESET FLAG NOTES
828		1248
829	The interested reader might have seen a number of flags that signify	1249	The interested reader might have seen a number of flags that signify
830	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be	1250	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
831	some confusion on what these do, so here is a short comparison:	1251	some confusion on what these do, so here is a short comparison:
832		1252
833	C<utf8> controls wether the JSON text created by C<encode> (and expected	1253	C<utf8> controls whether the JSON text created by C<encode> (and expected
834	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only	1254	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
835	control wether C<encode> escapes character values outside their respective	1255	control whether C<encode> escapes character values outside their respective
836	codeset range. Neither of these flags conflict with each other, although	1256	codeset range. Neither of these flags conflict with each other, although
837	some combinations make less sense than others.	1257	some combinations make less sense than others.
838		1258
839	Care has been taken to make all flags symmetrical with respect to	1259	Care has been taken to make all flags symmetrical with respect to
840	C<encode> and C<decode>, that is, texts encoded with any combination of	1260	C<encode> and C<decode>, that is, texts encoded with any combination of
…		…
854	=item C<utf8> flag disabled	1274	=item C<utf8> flag disabled
855		1275
856	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate	1276	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
857	and expect Unicode strings, that is, characters with high ordinal Unicode	1277	and expect Unicode strings, that is, characters with high ordinal Unicode
858	values (> 255) will be encoded as such characters, and likewise such	1278	values (> 255) will be encoded as such characters, and likewise such
859	characters are decoded as-is, no canges to them will be done, except	1279	characters are decoded as-is, no changes to them will be done, except
860	"(re-)interpreting" them as Unicode codepoints or Unicode characters,	1280	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
861	respectively (to Perl, these are the same thing in strings unless you do	1281	respectively (to Perl, these are the same thing in strings unless you do
862	funny/weird/dumb stuff).	1282	funny/weird/dumb stuff).
863		1283
864	This is useful when you want to do the encoding yourself (e.g. when you	1284	This is useful when you want to do the encoding yourself (e.g. when you
…		…
874	expect your input strings to be encoded as UTF-8, that is, no "character"	1294	expect your input strings to be encoded as UTF-8, that is, no "character"
875	of the input string must have any value > 255, as UTF-8 does not allow	1295	of the input string must have any value > 255, as UTF-8 does not allow
876	that.	1296	that.
877		1297
878	The C<utf8> flag therefore switches between two modes: disabled means you	1298	The C<utf8> flag therefore switches between two modes: disabled means you
879	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded	1299	will get a Unicode string in Perl, enabled means you get a UTF-8 encoded
880	octet/binary string in Perl.	1300	octet/binary string in Perl.
881		1301
882	=item C<latin1> or C<ascii> flags enabled	1302	=item C<latin1> or C<ascii> flags enabled
883		1303
884	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters	1304	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
…		…
920	proper subset of most 8-bit and multibyte encodings in use in the world.	1340	proper subset of most 8-bit and multibyte encodings in use in the world.
921		1341
922	=back	1342	=back
923		1343
924		1344
925	=head1 COMPARISON	1345	=head2 JSON and ECMAscript
926		1346
927	As already mentioned, this module was created because none of the existing	1347	JSON syntax is based on how literals are represented in javascript (the
928	JSON modules could be made to work correctly. First I will describe the	1348	not-standardised predecessor of ECMAscript) which is presumably why it is
929	problems (or pleasures) I encountered with various existing JSON modules,	1349	called "JavaScript Object Notation".
930	followed by some benchmark values. JSON::XS was designed not to suffer
931	from any of these problems or limitations.
932		1350
933	=over 4	1351	However, JSON is not a subset (and also not a superset of course) of
		1352	ECMAscript (the standard) or javascript (whatever browsers actually
		1353	implement).
934		1354
935	=item JSON 2.xx	1355	If you want to use javascript's C<eval> function to "parse" JSON, you
		1356	might run into parse errors for valid JSON texts, or the resulting data
		1357	structure might not be queryable:
936		1358
937	A marvellous piece of engineering, this module either uses JSON::XS	1359	One of the problems is that U+2028 and U+2029 are valid characters inside
938	directly when available (so will be 100% compatible with it, including	1360	JSON strings, but are not allowed in ECMAscript string literals, so the
939	speed), or it uses JSON::PP, which is basically JSON::XS translated to	1361	following Perl fragment will not output something that can be guaranteed
940	Pure Perl, which should be 100% compatible with JSON::XS, just a bit	1362	to be parsable by javascript's C<eval>:
941	slower.
942		1363
943	You cannot really lose by using this module, especially as it tries very	1364	use JSON::XS;
944	hard to work even with ancient Perl versions, while JSON::XS does not.
945		1365
946	=item JSON 1.07	1366	print encode_json [chr 0x2028];
947		1367
948	Slow (but very portable, as it is written in pure Perl).	1368	The right fix for this is to use a proper JSON parser in your javascript
		1369	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1370	F<json2.js> parser).
949		1371
950	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1372	If this is not an option, you can, as a stop-gap measure, simply encode to
951	undocumented. One can get far by feeding it Unicode strings and doing	1373	ASCII-only JSON:
952	en-/decoding oneself, but Unicode escapes are not working properly).
953		1374
954	No round-tripping (strings get clobbered if they look like numbers, e.g.	1375	use JSON::XS;
955	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
956	decode into the number 2.
957		1376
958	=item JSON::PC 0.01	1377	print JSON::XS->new->ascii->encode ([chr 0x2028]);
959		1378
960	Very fast.	1379	Note that this will enlarge the resulting JSON text quite a bit if you
		1380	have many non-ASCII characters. You might be tempted to run some regexes
		1381	to only escape U+2028 and U+2029, e.g.:
961		1382
962	Undocumented/buggy Unicode handling.	1383	# DO NOT USE THIS!
		1384	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1385	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1386	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1387	print $json;
963		1388
964	No round-tripping.	1389	Note that I<this is a bad idea>: the above only works for U+2028 and
		1390	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1391	javascript implementations, however, have issues with other characters as
		1392	well - using C<eval> naively simply I<will> cause problems.
965		1393
966	Has problems handling many Perl values (e.g. regex results and other magic	1394	Another problem is that some javascript implementations reserve
967	values will make it croak).	1395	some property names for their own purposes (which probably makes
		1396	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1397	C<__proto__> property name for its own purposes.
968		1398
969	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1399	If that is a problem, you could parse try to filter the resulting JSON
970	which is not a valid JSON text.	1400	output for these property strings, e.g.:
971		1401
972	Unmaintained (maintainer unresponsive for many months, bugs are not	1402	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
973	getting fixed).
974		1403
975	=item JSON::Syck 0.21	1404	This works because C<__proto__> is not valid outside of strings, so every
		1405	occurrence of C<"__proto__"\s*:> must be a string used as property name.
976		1406
977	Very buggy (often crashes).	1407	If you know of other incompatibilities, please let me know.
978
979	Very inflexible (no human-readable format supported, format pretty much
980	undocumented. I need at least a format for easy reading by humans and a
981	single-line compact format for use in a protocol, and preferably a way to
982	generate ASCII-only JSON texts).
983
984	Completely broken (and confusingly documented) Unicode handling (Unicode
985	escapes are not working properly, you need to set ImplicitUnicode to
986	I<different> values on en- and decoding to get symmetric behaviour).
987
988	No round-tripping (simple cases work, but this depends on whether the scalar
989	value was used in a numeric context or not).
990
991	Dumping hashes may skip hash values depending on iterator state.
992
993	Unmaintained (maintainer unresponsive for many months, bugs are not
994	getting fixed).
995
996	Does not check input for validity (i.e. will accept non-JSON input and
997	return "something" instead of raising an exception. This is a security
998	issue: imagine two banks transferring money between each other using
999	JSON. One bank might parse a given non-JSON request and deduct money,
1000	while the other might reject the transaction with a syntax error. While a
1001	good protocol will at least recover, that is extra unnecessary work and
1002	the transaction will still not succeed).
1003
1004	=item JSON::DWIW 0.04
1005
1006	Very fast. Very natural. Very nice.
1007
1008	Undocumented Unicode handling (but the best of the pack. Unicode escapes
1009	still don't get parsed properly).
1010
1011	Very inflexible.
1012
1013	No round-tripping.
1014
1015	Does not generate valid JSON texts (key strings are often unquoted, empty keys
1016	result in nothing being output)
1017
1018	Does not check input for validity.
1019
1020	=back
1021		1408
1022		1409
1023	=head2 JSON and YAML	1410	=head2 JSON and YAML
1024		1411
1025	You often hear that JSON is a subset of YAML. This is, however, a mass	1412	You often hear that JSON is a subset of YAML. This is, however, a mass
1026	hysteria(*) and very far from the truth. In general, there is no way to	1413	hysteria(*) and very far from the truth (as of the time of this writing),
		1414	so let me state it clearly: I<in general, there is no way to configure
1027	configure JSON::XS to output a data structure as valid YAML that works for	1415	JSON::XS to output a data structure as valid YAML> that works in all
1028	all cases.	1416	cases.
1029		1417
1030	If you really must use JSON::XS to generate YAML, you should use this	1418	If you really must use JSON::XS to generate YAML, you should use this
1031	algorithm (subject to change in future versions):	1419	algorithm (subject to change in future versions):
1032		1420
1033	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1421	my $to_yaml = JSON::XS->new->utf8->space_after (1);
1034	my $yaml = $to_yaml->encode ($ref) . "\n";	1422	my $yaml = $to_yaml->encode ($ref) . "\n";
1035		1423
1036	This will I<usually> generate JSON texts that also parse as valid	1424	This will I<usually> generate JSON texts that also parse as valid
1037	YAML. Please note that YAML has hardcoded limits on (simple) object key	1425	YAML. Please note that YAML has hardcoded limits on (simple) object key
1038	lengths that JSON doesn't have and also has different and incompatible	1426	lengths that JSON doesn't have and also has different and incompatible
1039	unicode handling, so you should make sure that your hash keys are	1427	unicode character escape syntax, so you should make sure that your hash
1040	noticeably shorter than the 1024 "stream characters" YAML allows and that	1428	keys are noticeably shorter than the 1024 "stream characters" YAML allows
1041	you do not have codepoints with values outside the Unicode BMP (basic	1429	and that you do not have characters with codepoint values outside the
1042	multilingual page). YAML also does not allow C<\/> sequences in strings	1430	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
1043	(which JSON::XS does not I<currently> generate).	1431	sequences in strings (which JSON::XS does not I<currently> generate, but
		1432	other JSON generators might).
1044		1433
1045	There might be other incompatibilities that I am not aware of (or the YAML	1434	There might be other incompatibilities that I am not aware of (or the YAML
1046	specification has been changed yet again - it does so quite often). In	1435	specification has been changed yet again - it does so quite often). In
1047	general you should not try to generate YAML with a JSON generator or vice	1436	general you should not try to generate YAML with a JSON generator or vice
1048	versa, or try to parse JSON with a YAML parser or vice versa: chances are	1437	versa, or try to parse JSON with a YAML parser or vice versa: chances are
…		…
1051		1440
1052	=over 4	1441	=over 4
1053		1442
1054	=item (*)	1443	=item (*)
1055		1444
1056	This is spread actively by the YAML team, however. For many years now they	1445	I have been pressured multiple times by Brian Ingerson (one of the
1057	claim YAML were a superset of JSON, even when proven otherwise.	1446	authors of the YAML specification) to remove this paragraph, despite him
		1447	acknowledging that the actual incompatibilities exist. As I was personally
		1448	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1449	educate people about these issues, so others do not run into the same
		1450	problem again and again. After this, Brian called me a (quote)I<complete
		1451	and worthless idiot>(unquote).
1058		1452
1059	Even the author of this manpage was at some point accused of providing	1453	In my opinion, instead of pressuring and insulting people who actually
1060	"incorrect" information, despite the evidence presented (claims ranged	1454	clarify issues with YAML and the wrong statements of some of its
1061	from "your documentation contains inaccurate and negative statements about	1455	proponents, I would kindly suggest reading the JSON spec (which is not
1062	YAML" (the only negative comment is this footnote, and it didn't exist	1456	that difficult or long) and finally make YAML compatible to it, and
1063	back then; the question on which claims were inaccurate was never answered	1457	educating users about the changes, instead of spreading lies about the
1064	etc.) to "the YAML spec is not up-to-date" (the *real* and supposedly	1458	real compatibility for many I<years> and trying to silence people who
1065	JSON-compatible spec is apparently not currently publicly available)	1459	point out that it isn't true.
1066	to actual requests to replace this section by *incorrect* information,
1067	suppressing information about the real problem).
1068		1460
1069	So whenever you are told that YAML was a superset of JSON, first check	1461	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
1070	wether it is really true (it might be when you check it, but it certainly	1462	though the incompatibilities have been documented (and are known to Brian)
1071	was not true when this was written). I would much prefer if the YAML team	1463	for many years and the spec makes explicit claims that YAML is a superset
1072	would spent their time on actually making JSON compatibility a truth	1464	of JSON. It would be so easy to fix, but apparently, bullying people and
1073	(JSON, after all, has a very small and simple specification) instead of	1465	corrupting userdata is so much easier.
1074	trying to lobby/force people into reporting untruths.
1075		1466
1076	=back	1467	=back
1077		1468
1078		1469
1079	=head2 SPEED	1470	=head2 SPEED
…		…
1081	It seems that JSON::XS is surprisingly fast, as shown in the following	1472	It seems that JSON::XS is surprisingly fast, as shown in the following
1082	tables. They have been generated with the help of the C<eg/bench> program	1473	tables. They have been generated with the help of the C<eg/bench> program
1083	in the JSON::XS distribution, to make it easy to compare on your own	1474	in the JSON::XS distribution, to make it easy to compare on your own
1084	system.	1475	system.
1085		1476
1086	First comes a comparison between various modules using a very short	1477	First comes a comparison between various modules using
1087	single-line JSON string:	1478	a very short single-line JSON string (also available at
		1479	L<http://dist.schmorp.de/misc/json/short.json>).
1088		1480
1089	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1481	{"method": "handleMessage", "params": ["user1",
1090	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1482	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1483	1, 0]}
1091		1484
1092	It shows the number of encodes/decodes per second (JSON::XS uses	1485	It shows the number of encodes/decodes per second (JSON::XS uses
1093	the functional interface, while JSON::XS/2 uses the OO interface	1486	the functional interface, while JSON::XS/2 uses the OO interface
1094	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1487	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
1095	shrink). Higher is better:	1488	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1489	uses the from_json method). Higher is better:
1096		1490
1097	module | encode | decode |	1491	module | encode | decode |
1098	-----------|------------|------------|	1492	--------------|------------|------------|
1099	JSON 1.x | 4990.842 | 4088.813 |	1493	JSON::DWIW/DS | 86302.551 | 102300.098 |
1100	JSON::DWIW | 51653.990 | 71575.154 |	1494	JSON::DWIW/FJ | 86302.551 | 75983.768 |
1101	JSON::PC | 65948.176 | 74631.744 |	1495	JSON::PP | 15827.562 | 6638.658 |
1102	JSON::PP | 8931.652 | 3817.168 |	1496	JSON::Syck | 63358.066 | 47662.545 |
1103	JSON::Syck | 24877.248 | 27776.848 |	1497	JSON::XS | 511500.488 | 511500.488 |
1104	JSON::XS | 388361.481 | 227951.304 |	1498	JSON::XS/2 | 291271.111 | 388361.481 |
1105	JSON::XS/2 | 227951.304 | 218453.333 |	1499	JSON::XS/3 | 361577.931 | 361577.931 |
1106	JSON::XS/3 | 338250.323 | 218453.333 |	1500	Storable | 66788.280 | 265462.278 |
1107	Storable | 16500.016 | 135300.129 |
1108	-----------+------------+------------+	1501	--------------+------------+------------+
1109		1502
1110	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1503	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
1111	about three times faster on decoding, and over forty times faster	1504	about five times faster on decoding, and over thirty to seventy times
1112	than JSON, even with pretty-printing and key sorting. It also compares	1505	faster than JSON's pure perl implementation. It also compares favourably
1113	favourably to Storable for small amounts of data.	1506	to Storable for small amounts of data.
1114		1507
1115	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1508	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1116	search API (http://nanoref.com/yahooapis/mgPdGg):	1509	search API (L<http://dist.schmorp.de/misc/json/long.json>).
1117		1510
1118	module | encode | decode |	1511	module | encode | decode |
1119	-----------|------------|------------|	1512	--------------|------------|------------|
1120	JSON 1.x | 55.260 | 34.971 |	1513	JSON::DWIW/DS | 1647.927 | 2673.916 |
1121	JSON::DWIW | 825.228 | 1082.513 |	1514	JSON::DWIW/FJ | 1630.249 | 2596.128 |
1122	JSON::PC | 3571.444 | 2394.829 |
1123	JSON::PP | 210.987 | 32.574 |	1515	JSON::PP | 400.640 | 62.311 |
1124	JSON::Syck | 552.551 | 787.544 |	1516	JSON::Syck | 1481.040 | 1524.869 |
1125	JSON::XS | 5780.463 | 4854.519 |	1517	JSON::XS | 20661.596 | 9541.183 |
1126	JSON::XS/2 | 3869.998 | 4798.975 |	1518	JSON::XS/2 | 10683.403 | 9416.938 |
1127	JSON::XS/3 | 5862.880 | 4798.975 |	1519	JSON::XS/3 | 20661.596 | 9400.054 |
1128	Storable | 4445.002 | 5235.027 |	1520	Storable | 19765.806 | 10000.725 |
1129	-----------+------------+------------+	1521	--------------+------------+------------+
1130		1522
1131	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1523	Again, JSON::XS leads by far (except for Storable which non-surprisingly
1132	decodes faster).	1524	decodes a bit faster).
1133		1525
1134	On large strings containing lots of high Unicode characters, some modules	1526	On large strings containing lots of high Unicode characters, some modules
1135	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1527	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
1136	will be broken due to missing (or wrong) Unicode handling. Others refuse	1528	will be broken due to missing (or wrong) Unicode handling. Others refuse
1137	to decode or encode properly, so it was impossible to prepare a fair	1529	to decode or encode properly, so it was impossible to prepare a fair
…		…
1173	information you might want to make sure that exceptions thrown by JSON::XS	1565	information you might want to make sure that exceptions thrown by JSON::XS
1174	will not end up in front of untrusted eyes.	1566	will not end up in front of untrusted eyes.
1175		1567
1176	If you are using JSON::XS to return packets to consumption	1568	If you are using JSON::XS to return packets to consumption
1177	by JavaScript scripts in a browser you should have a look at	1569	by JavaScript scripts in a browser you should have a look at
1178	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1570	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
1179	you are vulnerable to some common attack vectors (which really are browser	1571	see whether you are vulnerable to some common attack vectors (which really
1180	design bugs, but it is still you who will have to deal with it, as major	1572	are browser design bugs, but it is still you who will have to deal with
1181	browser developers care only for features, not about getting security	1573	it, as major browser developers care only for features, not about getting
1182	right).	1574	security right).
1183		1575
1184		1576
		1577	=head2 "OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)
		1578
		1579	JSON originally required JSON texts to represent an array or object -
		1580	scalar values were explicitly not allowed. This has changed, and versions
		1581	of JSON::XS beginning with C<4.0> reflect this by allowing scalar values
		1582	by default.
		1583
		1584	One reason why one might not want this is that this removes a fundamental
		1585	property of JSON texts, namely that they are self-delimited and
		1586	self-contained, or in other words, you could take any number of "old"
		1587	JSON texts and paste them together, and the result would be unambiguously
		1588	parseable:
		1589
		1590	[1,3]{"k":5}[][null] # four JSON texts, without doubt
		1591
		1592	By allowing scalars, this property is lost: in the following example, is
		1593	this one JSON text (the number 12) or two JSON texts (the numbers 1 and
		1594	2):
		1595
		1596	12 # could be 12, or 1 and 2
		1597
		1598	Another lost property of "old" JSON is that no lookahead is required to
		1599	know the end of a JSON text, i.e. the JSON text definitely ended at the
		1600	last C<]> or C<}> character, there was no need to read extra characters.
		1601
		1602	For example, a viable network protocol with "old" JSON was to simply
		1603	exchange JSON texts without delimiter. For "new" JSON, you have to use a
		1604	suitable delimiter (such as a newline) after every JSON text or ensure you
		1605	never encode/decode scalar values.
		1606
		1607	Most protocols do work by only transferring arrays or objects, and the
		1608	easiest way to avoid problems with the "new" JSON definition is to
		1609	explicitly disallow scalar values in your encoder and decoder:
		1610
		1611	$json_coder = JSON::XS->new->allow_nonref (0)
		1612
		1613	This is a somewhat unhappy situation, and the blame can fully be put on
		1614	JSON's inmventor, Douglas Crockford, who unilaterally changed the format
		1615	in 2006 without consulting the IETF, forcing the IETF to either fork the
		1616	format or go with it (as I was told, the IETF wasn't amused).
		1617
		1618
		1619	=head1 INTEROPERABILITY WITH OTHER MODULES
		1620
		1621	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1622	constants. That means that the JSON true and false values will be
		1623	comaptible to true and false values of other modules that do the same,
		1624	such as L<JSON::PP> and L<CBOR::XS>.
		1625
		1626
		1627	=head1 INTEROPERABILITY WITH OTHER JSON DECODERS
		1628
		1629	As long as you only serialise data that can be directly expressed in JSON,
		1630	C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs,
		1631	but C<JSON::XS> has found more bugs in the official JSON testsuite (1)
		1632	than the official JSON testsuite has found in C<JSON::XS> (0)).
		1633
		1634	When you have trouble decoding JSON generated by this module using other
		1635	decoders, then it is very likely that you have an encoding mismatch or the
		1636	other decoder is broken.
		1637
		1638	When decoding, C<JSON::XS> is strict by default and will likely catch all
		1639	errors. There are currently two settings that change this: C<relaxed>
		1640	makes C<JSON::XS> accept (but not generate) some non-standard extensions,
		1641	and C<allow_tags> will allow you to encode and decode Perl objects, at the
		1642	cost of not outputting valid JSON anymore.
		1643
		1644	=head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
		1645
		1646	When you use C<allow_tags> to use the extended (and also nonstandard and
		1647	invalid) JSON syntax for serialised objects, and you still want to decode
		1648	the generated When you want to serialise objects, you can run a regex
		1649	to replace the tagged syntax by standard JSON arrays (it only works for
		1650	"normal" package names without comma, newlines or single colons). First,
		1651	the readable Perl version:
		1652
		1653	# if your FREEZE methods return no values, you need this replace first:
		1654	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
		1655
		1656	# this works for non-empty constructor arg lists:
		1657	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
		1658
		1659	And here is a less readable version that is easy to adapt to other
		1660	languages:
		1661
		1662	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
		1663
		1664	Here is an ECMAScript version (same regex):
		1665
		1666	json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
		1667
		1668	Since this syntax converts to standard JSON arrays, it might be hard to
		1669	distinguish serialised objects from normal arrays. You can prepend a
		1670	"magic number" as first array element to reduce chances of a collision:
		1671
		1672	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
		1673
		1674	And after decoding the JSON text, you could walk the data
		1675	structure looking for arrays with a first element of
		1676	C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>.
		1677
		1678	The same approach can be used to create the tagged format with another
		1679	encoder. First, you create an array with the magic string as first member,
		1680	the classname as second, and constructor arguments last, encode it as part
		1681	of your JSON structure, and then:
		1682
		1683	$json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
		1684
		1685	Again, this has some limitations - the magic string must not be encoded
		1686	with character escapes, and the constructor arguments must be non-empty.
		1687
		1688
		1689	=head1 RFC7159
		1690
		1691	Since this module was written, Google has written a new JSON RFC, RFC 7159
		1692	(and RFC7158). Unfortunately, this RFC breaks compatibility with both the
		1693	original JSON specification on www.json.org and RFC4627.
		1694
		1695	As far as I can see, you can get partial compatibility when parsing by
		1696	using C<< ->allow_nonref >>. However, consider the security implications
		1697	of doing so.
		1698
		1699	I haven't decided yet when to break compatibility with RFC4627 by default
		1700	(and potentially leave applications insecure) and change the default to
		1701	follow RFC7159, but application authors are well advised to call C<<
		1702	->allow_nonref(0) >> even if this is the current default, if they cannot
		1703	handle non-reference values, in preparation for the day when the default
		1704	will change.
		1705
		1706
1185	=head1 THREADS	1707	=head1 (I-)THREADS
1186		1708
1187	This module is I<not> guaranteed to be thread safe and there are no	1709	This module is I<not> guaranteed to be ithread (or MULTIPLICITY-) safe
1188	plans to change this until Perl gets thread support (as opposed to the	1710	and there are no plans to change this. Note that perl's builtin so-called
1189	horribly slow so-called "threads" which are simply slow and bloated	1711	threads/ithreads are officially deprecated and should not be used.
1190	process simulations - use fork, its I<much> faster, cheaper, better).
1191		1712
1192	(It might actually work, but you have been warned).	1713
		1714	=head1 THE PERILS OF SETLOCALE
		1715
		1716	Sometimes people avoid the Perl locale support and directly call the
		1717	system's setlocale function with C<LC_ALL>.
		1718
		1719	This breaks both perl and modules such as JSON::XS, as stringification of
		1720	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1721	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1722	perl to stringify numbers).
		1723
		1724	The solution is simple: don't call C<setlocale>, or use it for only those
		1725	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1726
		1727	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1728	actually needs it (avoiding stringification of numbers), and restore it
		1729	afterwards.
1193		1730
1194		1731
1195	=head1 BUGS	1732	=head1 BUGS
1196		1733
1197	While the goal of this module is to be correct, that unfortunately does	1734	While the goal of this module is to be correct, that unfortunately does
1198	not mean its bug-free, only that I think its design is bug-free. It is	1735	not mean it's bug-free, only that I think its design is bug-free. If you
1199	still relatively early in its development. If you keep reporting bugs they	1736	keep reporting bugs they will be fixed swiftly, though.
1200	will be fixed swiftly, though.
1201		1737
1202	Please refrain from using rt.cpan.org or any other bug reporting	1738	Please refrain from using rt.cpan.org or any other bug reporting
1203	service. I put the contact address into my modules for a reason.	1739	service. I put the contact address into my modules for a reason.
1204		1740
1205	=cut	1741	=cut
1206		1742
1207	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1743	BEGIN {
1208	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };	1744	*true = \$Types::Serialiser::true;
		1745	*true = \&Types::Serialiser::true;
		1746	*false = \$Types::Serialiser::false;
		1747	*false = \&Types::Serialiser::false;
		1748	*is_bool = \&Types::Serialiser::is_bool;
1209		1749
1210	sub true() { $true }	1750	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
1211	sub false() { $false }
1212
1213	sub is_bool($) {
1214	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1215	# or UNIVERSAL::isa $_[0], "JSON::Literal"
1216	}	1751	}
1217		1752
1218	XSLoader::load "JSON::XS", $VERSION;	1753	XSLoader::load "JSON::XS", $VERSION;
1219		1754
1220	package JSON::XS::Boolean;	1755	=head1 SEE ALSO
1221		1756
1222	use overload	1757	The F<json_xs> command line utility for quick experiments.
1223	"0+" => sub { ${$_[0]} },
1224	"++" => sub { $_[0] = ${$_[0]} + 1 },
1225	"--" => sub { $_[0] = ${$_[0]} - 1 },
1226	fallback => 1;
1227
1228	1;
1229		1758
1230	=head1 AUTHOR	1759	=head1 AUTHOR
1231		1760
1232	Marc Lehmann <schmorp@schmorp.de>	1761	Marc Lehmann <schmorp@schmorp.de>
1233	http://home.schmorp.de/	1762	http://home.schmorp.de/
1234		1763
1235	=cut	1764	=cut
1236		1765
		1766	1
		1767

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