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Revision 1.78 by root, Wed Dec 5 10:59:28 2007 UTC vs.
Revision 1.169 by root, Thu Nov 15 20:49:12 2018 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
		5	=encoding utf-8
4		6
5	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ	7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
6	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)	8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7		9
8	=head1 SYNOPSIS	10	=head1 SYNOPSIS
…		…
35	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
36	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
37		39
38	Beginning with version 2.0 of the JSON module, when both JSON and	40	Beginning with version 2.0 of the JSON module, when both JSON and
39	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be	41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
40	overriden) with no overhead due to emulation (by inheritign constructor	42	overridden) with no overhead due to emulation (by inheriting constructor
41	and methods). If JSON::XS is not available, it will fall back to the	43	and methods). If JSON::XS is not available, it will fall back to the
42	compatible JSON::PP module as backend, so using JSON instead of JSON::XS	44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
43	gives you a portable JSON API that can be fast when you need and doesn't	45	gives you a portable JSON API that can be fast when you need it and
44	require a C compiler when that is a problem.	46	doesn't require a C compiler when that is a problem.
45		47
46	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
47	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
48	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
49	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
50	reports for other reasons.	52	reports for other reasons.
51		53
52	See COMPARISON, below, for a comparison to some other JSON modules.
53
54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
55	vice versa.	55	vice versa.
56		56
57	=head2 FEATURES	57	=head2 FEATURES
58		58
59	=over 4	59	=over 4
60		60
61	=item * correct Unicode handling	61	=item * correct Unicode handling
62		62
63	This module knows how to handle Unicode, and even documents how and when	63	This module knows how to handle Unicode, documents how and when it does
64	it does so.	64	so, and even documents what "correct" means.
65		65
66	=item * round-trip integrity	66	=item * round-trip integrity
67		67
68	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
69	by JSON, the deserialised data structure is identical on the Perl level.	69	by JSON and Perl, the deserialised data structure is identical on the Perl
70	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
71	like a number).	71	it looks like a number). There I<are> minor exceptions to this, read the
		72	MAPPING section below to learn about those.
72		73
73	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
74		75
75	There is no guessing, no generating of illegal JSON texts by default,	76	There is no guessing, no generating of illegal JSON texts by default,
76	and only JSON is accepted as input by default (the latter is a security	77	and only JSON is accepted as input by default (the latter is a security
77	feature).	78	feature).
78		79
79	=item * fast	80	=item * fast
80		81
81	Compared to other JSON modules, this module compares favourably in terms	82	Compared to other JSON modules and other serialisers such as Storable,
82	of speed, too.	83	this module usually compares favourably in terms of speed, too.
83		84
84	=item * simple to use	85	=item * simple to use
85		86
86	This module has both a simple functional interface as well as an OO	87	This module has both a simple functional interface as well as an object
87	interface.	88	oriented interface.
88		89
89	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
90		91
91	You can choose between the most compact guaranteed single-line format	92	You can choose between the most compact guaranteed-single-line format
92	possible (nice for simple line-based protocols), a pure-ascii format	93	possible (nice for simple line-based protocols), a pure-ASCII format
93	(for when your transport is not 8-bit clean, still supports the whole	94	(for when your transport is not 8-bit clean, still supports the whole
94	Unicode range), or a pretty-printed format (for when you want to read that	95	Unicode range), or a pretty-printed format (for when you want to read that
95	stuff). Or you can combine those features in whatever way you like.	96	stuff). Or you can combine those features in whatever way you like.
96		97
97	=back	98	=back
98		99
99	=cut	100	=cut
100		101
101	package JSON::XS;	102	package JSON::XS;
102		103
103	use strict;	104	use common::sense;
104		105
105	our $VERSION = '2.01';	106	our $VERSION = 3.04;
106	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
107		108
108	our @EXPORT = qw(encode_json decode_json to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
109
110	sub to_json($) {
111	require Carp;
112	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
113	}
114
115	sub from_json($) {
116	require Carp;
117	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
118	}
119		110
120	use Exporter;	111	use Exporter;
121	use XSLoader;	112	use XSLoader;
122		113
		114	use Types::Serialiser ();
		115
123	=head1 FUNCTIONAL INTERFACE	116	=head1 FUNCTIONAL INTERFACE
124		117
125	The following convenience methods are provided by this module. They are	118	The following convenience methods are provided by this module. They are
126	exported by default:	119	exported by default:
127		120
…		…
134		127
135	This function call is functionally identical to:	128	This function call is functionally identical to:
136		129
137	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	130	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
138		131
139	except being faster.	132	Except being faster.
140		133
141	=item $perl_scalar = decode_json $json_text	134	=item $perl_scalar = decode_json $json_text
142		135
143	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries	136	The opposite of C<encode_json>: expects a UTF-8 (binary) string and tries
144	to parse that as an UTF-8 encoded JSON text, returning the resulting	137	to parse that as a UTF-8 encoded JSON text, returning the resulting
145	reference. Croaks on error.	138	reference. Croaks on error.
146		139
147	This function call is functionally identical to:	140	This function call is functionally identical to:
148		141
149	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	142	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
150		143
151	except being faster.	144	Except being faster.
152
153	=item $is_boolean = JSON::XS::is_bool $scalar
154
155	Returns true if the passed scalar represents either JSON::XS::true or
156	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
157	and are used to represent JSON C<true> and C<false> values in Perl.
158
159	See MAPPING, below, for more information on how JSON values are mapped to
160	Perl.
161		145
162	=back	146	=back
163		147
164		148
165	=head1 A FEW NOTES ON UNICODE AND PERL	149	=head1 A FEW NOTES ON UNICODE AND PERL
…		…
174	This enables you to store Unicode characters as single characters in a	158	This enables you to store Unicode characters as single characters in a
175	Perl string - very natural.	159	Perl string - very natural.
176		160
177	=item 2. Perl does I<not> associate an encoding with your strings.	161	=item 2. Perl does I<not> associate an encoding with your strings.
178		162
179	Unless you force it to, e.g. when matching it against a regex, or printing	163	... until you force it to, e.g. when matching it against a regex, or
180	the scalar to a file, in which case Perl either interprets your string as	164	printing the scalar to a file, in which case Perl either interprets your
181	locale-encoded text, octets/binary, or as Unicode, depending on various	165	string as locale-encoded text, octets/binary, or as Unicode, depending
182	settings. In no case is an encoding stored together with your data, it is	166	on various settings. In no case is an encoding stored together with your
183	I<use> that decides encoding, not any magical metadata.	167	data, it is I<use> that decides encoding, not any magical meta data.
184		168
185	=item 3. The internal utf-8 flag has no meaning with regards to the	169	=item 3. The internal utf-8 flag has no meaning with regards to the
186	encoding of your string.	170	encoding of your string.
187		171
188	Just ignore that flag unless you debug a Perl bug, a module written in	172	Just ignore that flag unless you debug a Perl bug, a module written in
…		…
194		178
195	If you didn't know about that flag, just the better, pretend it doesn't	179	If you didn't know about that flag, just the better, pretend it doesn't
196	exist.	180	exist.
197		181
198	=item 4. A "Unicode String" is simply a string where each character can be	182	=item 4. A "Unicode String" is simply a string where each character can be
199	validly interpreted as a Unicode codepoint.	183	validly interpreted as a Unicode code point.
200		184
201	If you have UTF-8 encoded data, it is no longer a Unicode string, but a	185	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
202	Unicode string encoded in UTF-8, giving you a binary string.	186	Unicode string encoded in UTF-8, giving you a binary string.
203		187
204	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.	188	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
…		…
218	=over 4	202	=over 4
219		203
220	=item $json = new JSON::XS	204	=item $json = new JSON::XS
221		205
222	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
223	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>).
224		210
225	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
226	be chained:	212	be chained:
227		213
228	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	214	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
…		…
242		228
243	If C<$enable> is false, then the C<encode> method will not escape Unicode	229	If C<$enable> is false, then the C<encode> method will not escape Unicode
244	characters unless required by the JSON syntax or other flags. This results	230	characters unless required by the JSON syntax or other flags. This results
245	in a faster and more compact format.	231	in a faster and more compact format.
246		232
		233	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		234	document.
		235
247	The main use for this flag is to produce JSON texts that can be	236	The main use for this flag is to produce JSON texts that can be
248	transmitted over a 7-bit channel, as the encoded JSON texts will not	237	transmitted over a 7-bit channel, as the encoded JSON texts will not
249	contain any 8 bit characters.	238	contain any 8 bit characters.
250		239
251	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	240	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
262	will not be affected in any way by this flag, as C<decode> by default	251	will not be affected in any way by this flag, as C<decode> by default
263	expects Unicode, which is a strict superset of latin1.	252	expects Unicode, which is a strict superset of latin1.
264		253
265	If C<$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
266	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.
267		259
268	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
269	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
270	size. The disadvantage is that the resulting JSON text is encoded	262	size. The disadvantage is that the resulting JSON text is encoded
271	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
…		…
280		272
281	=item $enabled = $json->get_utf8	273	=item $enabled = $json->get_utf8
282		274
283	If C<$enable> is true (or missing), then the C<encode> method will encode	275	If C<$enable> is true (or missing), then the C<encode> method will encode
284	the JSON result into UTF-8, as required by many protocols, while the	276	the JSON result into UTF-8, as required by many protocols, while the
285	C<decode> method expects to be handled an UTF-8-encoded string. Please	277	C<decode> method expects to be handed a UTF-8-encoded string. Please
286	note that UTF-8-encoded strings do not contain any characters outside the	278	note that UTF-8-encoded strings do not contain any characters outside the
287	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	279	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
288	versions, enabling this option might enable autodetection of the UTF-16	280	versions, enabling this option might enable autodetection of the UTF-16
289	and UTF-32 encoding families, as described in RFC4627.	281	and UTF-32 encoding families, as described in RFC4627.
290		282
291	If C<$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
292	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
293	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
294	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.
295		290
296	Example, output UTF-16BE-encoded JSON:	291	Example, output UTF-16BE-encoded JSON:
297		292
298	use Encode;	293	use Encode;
299	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	294	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
372		367
373	=item $enabled = $json->get_relaxed	368	=item $enabled = $json->get_relaxed
374		369
375	If C<$enable> is true (or missing), then C<decode> will accept some	370	If C<$enable> is true (or missing), then C<decode> will accept some
376	extensions to normal JSON syntax (see below). C<encode> will not be	371	extensions to normal JSON syntax (see below). C<encode> will not be
377	affected in anyway. I<Be aware that this option makes you accept invalid	372	affected in any way. I<Be aware that this option makes you accept invalid
378	JSON texts as if they were valid!>. I suggest only to use this option to	373	JSON texts as if they were valid!>. I suggest only to use this option to
379	parse application-specific files written by humans (configuration files,	374	parse application-specific files written by humans (configuration files,
380	resource files etc.)	375	resource files etc.)
381		376
382	If C<$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
…		…
411	[	406	[
412	1, # this comment not allowed in JSON	407	1, # this comment not allowed in JSON
413	# neither this one...	408	# neither this one...
414	]	409	]
415		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
416	=back	421	=back
417		422
418	=item $json = $json->canonical ([$enable])	423	=item $json = $json->canonical ([$enable])
419		424
420	=item $enabled = $json->get_canonical	425	=item $enabled = $json->get_canonical
…		…
422	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	427	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
423	by sorting their keys. This is adding a comparatively high overhead.	428	by sorting their keys. This is adding a comparatively high overhead.
424		429
425	If C<$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
426	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
427	of the same script).	432	of the same script, and can change even within the same run from 5.18
		433	onwards).
428		434
429	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
430	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,
431	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,
432	as key-value pairs have no inherent ordering in Perl.	438	as key-value pairs have no inherent ordering in Perl.
433		439
434	This setting has no effect when decoding JSON texts.	440	This setting has no effect when decoding JSON texts.
435		441
		442	This setting has currently no effect on tied hashes.
		443
436	=item $json = $json->allow_nonref ([$enable])	444	=item $json = $json->allow_nonref ([$enable])
437		445
438	=item $enabled = $json->get_allow_nonref	446	=item $enabled = $json->get_allow_nonref
		447
		448	Unlike other boolean options, this opotion is enabled by default beginning
		449	with version C<4.0>. See L<SECURITY CONSIDERATIONS> for the gory details.
439		450
440	If C<$enable> is true (or missing), then the C<encode> method can convert a	451	If C<$enable> is true (or missing), then the C<encode> method can convert a
441	non-reference into its corresponding string, number or null JSON value,	452	non-reference into its corresponding string, number or null JSON value,
442	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	453	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
443	values instead of croaking.	454	values instead of croaking.
…		…
445	If C<$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
446	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
447	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
448	JSON object or array.	459	JSON object or array.
449		460
450	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>,
451	resulting in an invalid JSON text:	462	resulting in an error:
452		463
453	JSON::XS->new->allow_nonref->encode ("Hello, World!")	464	JSON::XS->new->allow_nonref (0)->encode ("Hello, World!")
454	=> "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.
455		482
456	=item $json = $json->allow_blessed ([$enable])	483	=item $json = $json->allow_blessed ([$enable])
457		484
458	=item $enabled = $json->get_allow_blessed	485	=item $enabled = $json->get_allow_blessed
459		486
		487	See L<OBJECT SERIALISATION> for details.
		488
460	If C<$enable> is true (or missing), then the C<encode> method will not	489	If C<$enable> is true (or missing), then the C<encode> method will not
461	barf when it encounters a blessed reference. Instead, the value of the	490	barf when it encounters a blessed reference that it cannot convert
462	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>	491	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
463	disabled or no C<TO_JSON> method found) or a representation of the
464	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
465	encoded. Has no effect on C<decode>.
466		492
467	If C<$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
468	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>.
469		498
470	=item $json = $json->convert_blessed ([$enable])	499	=item $json = $json->convert_blessed ([$enable])
471		500
472	=item $enabled = $json->get_convert_blessed	501	=item $enabled = $json->get_convert_blessed
		502
		503	See L<OBJECT SERIALISATION> for details.
473		504
474	If C<$enable> is true (or missing), then C<encode>, upon encountering a	505	If C<$enable> is true (or missing), then C<encode>, upon encountering a
475	blessed object, will check for the availability of the C<TO_JSON> method	506	blessed object, will check for the availability of the C<TO_JSON> method
476	on the object's class. If found, it will be called in scalar context	507	on the object's class. If found, it will be called in scalar context and
477	and the resulting scalar will be encoded instead of the object. If no	508	the resulting scalar will be encoded instead of the object.
478	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
479	to do.
480		509
481	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	510	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
482	returns other blessed objects, those will be handled in the same	511	returns other blessed objects, those will be handled in the same
483	way. C<TO_JSON> must take care of not causing an endless recursion cycle	512	way. C<TO_JSON> must take care of not causing an endless recursion cycle
484	(== crash) in this case. The name of C<TO_JSON> was chosen because other	513	(== crash) in this case. The name of C<TO_JSON> was chosen because other
485	methods called by the Perl core (== not by the user of the object) are	514	methods called by the Perl core (== not by the user of the object) are
486	usually in upper case letters and to avoid collisions with any C<to_json>	515	usually in upper case letters and to avoid collisions with any C<to_json>
487	function or method.	516	function or method.
488		517
489	This setting does not yet influence C<decode> in any way, but in the	518	If C<$enable> is false (the default), then C<encode> will not consider
490	future, global hooks might get installed that influence C<decode> and are	519	this type of conversion.
491	enabled by this setting.
492		520
493	If C<$enable> is false, then the C<allow_blessed> setting will decide what	521	This setting has no effect on C<decode>.
494	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.
495		540
496	=item $json = $json->filter_json_object ([$coderef->($hashref)])	541	=item $json = $json->filter_json_object ([$coderef->($hashref)])
497		542
498	When C<$coderef> is specified, it will be called from C<decode> each	543	When C<$coderef> is specified, it will be called from C<decode> each
499	time it decodes a JSON object. The only argument is a reference to the	544	time it decodes a JSON object. The only argument is a reference to
500	newly-created hash. If the code references returns a single scalar (which	545	the newly-created hash. If the code reference returns a single scalar
501	need not be a reference), this value (i.e. a copy of that scalar to avoid	546	(which need not be a reference), this value (or rather a copy of it) is
502	aliasing) is inserted into the deserialised data structure. If it returns	547	inserted into the deserialised data structure. If it returns an empty
503	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the	548	list (NOTE: I<not> C<undef>, which is a valid scalar), the original
504	original deserialised hash will be inserted. This setting can slow down	549	deserialised hash will be inserted. This setting can slow down decoding
505	decoding considerably.	550	considerably.
506		551
507	When C<$coderef> is omitted or undefined, any existing callback will	552	When C<$coderef> is omitted or undefined, any existing callback will
508	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
509	way.	554	way.
510		555
…		…
600	=item $json = $json->max_depth ([$maximum_nesting_depth])	645	=item $json = $json->max_depth ([$maximum_nesting_depth])
601		646
602	=item $max_depth = $json->get_max_depth	647	=item $max_depth = $json->get_max_depth
603		648
604	Sets the maximum nesting level (default C<512>) accepted while encoding	649	Sets the maximum nesting level (default C<512>) accepted while encoding
605	or decoding. If the JSON text or Perl data structure has an equal or	650	or decoding. If a higher nesting level is detected in JSON text or a Perl
606	higher nesting level then this limit, then the encoder and decoder will	651	data structure, then the encoder and decoder will stop and croak at that
607	stop and croak at that point.	652	point.
608		653
609	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
610	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<[>
611	characters without their matching closing parenthesis crossed to reach a	656	characters without their matching closing parenthesis crossed to reach a
612	given character in a string.	657	given character in a string.
613		658
614	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
615	that the object is only a single hash/object or array.	660	that the object is only a single hash/object or array.
616		661
617	The argument to C<max_depth> will be rounded up to the next highest power
618	of two. If no argument is given, the highest possible setting will be	662	If no argument is given, the highest possible setting will be used, which
619	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.
620		668
621	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.
622		670
623	=item $json = $json->max_size ([$maximum_string_size])	671	=item $json = $json->max_size ([$maximum_string_size])
624		672
625	=item $max_size = $json->get_max_size	673	=item $max_size = $json->get_max_size
626		674
627	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
628	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>
629	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
630	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
631	effect on C<encode> (yet).	679	effect on C<encode> (yet).
632		680
633	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
634	power of two (so may be more than requested). If no argument is given, the	682	C<0> is specified).
635	limit check will be deactivated (same as when C<0> is specified).
636		683
637	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.
638		685
639	=item $json_text = $json->encode ($perl_scalar)	686	=item $json_text = $json->encode ($perl_scalar)
640		687
641	Converts the given Perl data structure (a simple scalar or a reference	688	Converts the given Perl value or data structure to its JSON
642	to a hash or array) to its JSON representation. Simple scalars will be	689	representation. Croaks on error.
643	converted into JSON string or number sequences, while references to arrays
644	become JSON arrays and references to hashes become JSON objects. Undefined
645	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
646	nor C<false> values will be generated.
647		690
648	=item $perl_scalar = $json->decode ($json_text)	691	=item $perl_scalar = $json->decode ($json_text)
649		692
650	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,
651	returning the resulting simple scalar or reference. Croaks on error.	694	returning the resulting simple scalar or reference. Croaks on error.
652
653	JSON numbers and strings become simple Perl scalars. JSON arrays become
654	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
655	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
656		695
657	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	696	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
658		697
659	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
660	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
661	silently stop parsing there and return the number of characters consumed	700	silently stop parsing there and return the number of characters consumed
662	so far.	701	so far.
663		702
664	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
665	(which is not the brightest thing to do in the first place) and you need
666	to know where the JSON text ends.	704	and you need to know where the JSON text ends.
667		705
668	JSON::XS->new->decode_prefix ("[1] the tail")	706	JSON::XS->new->decode_prefix ("[1] the tail")
669	=> ([], 3)	707	=> ([1], 3)
670		708
671	=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
672		958
673		959
674	=head1 MAPPING	960	=head1 MAPPING
675		961
676	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
…		…
706		992
707	A JSON number becomes either an integer, numeric (floating point) or	993	A JSON number becomes either an integer, numeric (floating point) or
708	string scalar in perl, depending on its range and any fractional parts. On	994	string scalar in perl, depending on its range and any fractional parts. On
709	the Perl level, there is no difference between those as Perl handles all	995	the Perl level, there is no difference between those as Perl handles all
710	the conversion details, but an integer may take slightly less memory and	996	the conversion details, but an integer may take slightly less memory and
711	might represent more values exactly than (floating point) numbers.	997	might represent more values exactly than floating point numbers.
712		998
713	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
714	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
715	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
716	precision. Otherwise it will preserve the number as a string value.	1002	precision. Otherwise it will preserve the number as a string value (in
		1003	which case you lose roundtripping ability, as the JSON number will be
		1004	re-encoded to a JSON string).
717		1005
718	Numbers containing a fractional or exponential part will always be	1006	Numbers containing a fractional or exponential part will always be
719	represented as numeric (floating point) values, possibly at a loss of	1007	represented as numeric (floating point) values, possibly at a loss of
720	precision.	1008	precision (in which case you might lose perfect roundtripping ability, but
		1009	the JSON number will still be re-encoded as a JSON number).
721		1010
722	This might create round-tripping problems as numbers might become strings,	1011	Note that precision is not accuracy - binary floating point values cannot
723	but as Perl is typeless there is no other way to do it.	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.
724		1015
725	=item true, false	1016	=item true, false
726		1017
727	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	1018	These JSON atoms become C<Types::Serialiser::true> and
728	respectively. They are overloaded to act almost exactly like the numbers	1019	C<Types::Serialiser::false>, respectively. They are overloaded to act
729	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using	1020	almost exactly like the numbers C<1> and C<0>. You can check whether
730	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).
731		1023
732	=item null	1024	=item null
733		1025
734	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.
735		1042
736	=back	1043	=back
737		1044
738		1045
739	=head2 PERL -> JSON	1046	=head2 PERL -> JSON
…		…
744		1051
745	=over 4	1052	=over 4
746		1053
747	=item hash references	1054	=item hash references
748		1055
749	Perl hash references become JSON objects. As there is no inherent ordering	1056	Perl hash references become JSON objects. As there is no inherent
750	in hash keys (or JSON objects), they will usually be encoded in a	1057	ordering in hash keys (or JSON objects), they will usually be encoded
751	pseudo-random order that can change between runs of the same program but	1058	in a pseudo-random order. JSON::XS can optionally sort the hash keys
752	stays generally the same within a single run of a program. JSON::XS can	1059	(determined by the I<canonical> flag), so the same datastructure will
753	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
754	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,
755	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.
756	and is only rarely useful, e.g. when you want to compare some JSON text
757	against another for equality.
758		1063
759	=item array references	1064	=item array references
760		1065
761	Perl array references become JSON arrays.	1066	Perl array references become JSON arrays.
762		1067
763	=item other references	1068	=item other references
764		1069
765	Other unblessed references are generally not allowed and will cause an	1070	Other unblessed references are generally not allowed and will cause an
766	exception to be thrown, except for references to the integers C<0> and	1071	exception to be thrown, except for references to the integers C<0> and
767	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1072	C<1>, which get turned into C<false> and C<true> atoms in JSON.
768	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
769		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;
770	encode_json [\0,JSON::XS::true] # yields [false,true]	1079	encode_json [\0, Types::Serialiser::true] # yields [false,true]
771		1080
772	=item JSON::XS::true, JSON::XS::false	1081	=item Types::Serialiser::true, Types::Serialiser::false
773		1082
774	These special values become JSON true and JSON false values,	1083	These special values from the L<Types::Serialiser> module become JSON true
775	respectively. You can also use C<\1> and C<\0> directly if you want.	1084	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1085	directly if you want.
776		1086
777	=item blessed objects	1087	=item blessed objects
778		1088
779	Blessed objects are not allowed. JSON::XS currently tries to encode their	1089	Blessed objects are not directly representable in JSON, but C<JSON::XS>
780	underlying representation (hash- or arrayref), but this behaviour might	1090	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
781	change in future versions.	1091	below, for details.
782		1092
783	=item simple scalars	1093	=item simple scalars
784		1094
785	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
786	difficult objects to encode: JSON::XS will encode undefined scalars as	1096	difficult objects to encode: JSON::XS will encode undefined scalars as
787	JSON null value, scalars that have last been used in a string context	1097	JSON C<null> values, scalars that have last been used in a string context
788	before encoding as JSON strings and anything else as number value:	1098	before encoding as JSON strings, and anything else as number value:
789		1099
790	# dump as number	1100	# dump as number
791	encode_json [2] # yields [2]	1101	encode_json [2] # yields [2]
792	encode_json [-3.0e17] # yields [-3e+17]	1102	encode_json [-3.0e17] # yields [-3e+17]
793	my $value = 5; encode_json [$value] # yields [5]	1103	my $value = 5; encode_json [$value] # yields [5]
…		…
811	my $x = "3"; # some variable containing a string	1121	my $x = "3"; # some variable containing a string
812	$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
813	$x *= 1; # same thing, the choice is yours.	1123	$x *= 1; # same thing, the choice is yours.
814		1124
815	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
816	if you need this capability.	1126	if you need this capability (but don't forget to explain why it's needed
		1127	:).
		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.
817		1135
818	=back	1136	=back
819		1137
		1138	=head2 OBJECT SERIALISATION
820		1139
821	=head1 COMPARISON	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.
822		1144
823	As already mentioned, this module was created because none of the existing	1145	=head3 SERIALISATION
824	JSON modules could be made to work correctly. First I will describe the	1146
825	problems (or pleasures) I encountered with various existing JSON modules,	1147	What happens when C<JSON::XS> encounters a Perl object depends on the
826	followed by some benchmark values. JSON::XS was designed not to suffer	1148	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
827	from any of these problems or limitations.	1149	used in this order:
828		1150
829	=over 4	1151	=over 4
830		1152
831	=item JSON 1.07	1153	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
832		1154
833	Slow (but very portable, as it is written in pure Perl).	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.
834		1158
835	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1159	This works by invoking the C<FREEZE> method on the object, with the first
836	undocumented. One can get far by feeding it Unicode strings and doing	1160	argument being the object to serialise, and the second argument being the
837	en-/decoding oneself, but Unicode escapes are not working properly).	1161	constant string C<JSON> to distinguish it from other serialisers.
838		1162
839	No round-tripping (strings get clobbered if they look like numbers, e.g.	1163	The C<FREEZE> method can return any number of values (i.e. zero or
840	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	1164	more). These values and the paclkage/classname of the object will then be
841	decode into the number 2.	1165	encoded as a tagged JSON value in the following format:
842		1166
843	=item JSON::PC 0.01	1167	("classname")[FREEZE return values...]
844		1168
845	Very fast.	1169	e.g.:
846		1170
847	Undocumented/buggy Unicode handling.	1171	("URI")["http://www.google.com/"]
		1172	("MyDate")[2013,10,29]
		1173	("ImageData::JPEG")["Z3...VlCg=="]
848		1174
849	No round-tripping.	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:
850		1177
851	Has problems handling many Perl values (e.g. regex results and other magic	1178	sub My::Object::FREEZE {
852	values will make it croak).	1179	my ($self, $serialiser) = @_;
853		1180
854	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1181	($self->{type}, $self->{id})
855	which is not a valid JSON text.	1182	}
856		1183
857	Unmaintained (maintainer unresponsive for many months, bugs are not	1184	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
858	getting fixed).
859		1185
860	=item JSON::Syck 0.21	1186	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1187	context. It must return a single scalar that can be directly encoded into
		1188	JSON. This scalar replaces the object in the JSON text.
861		1189
862	Very buggy (often crashes).	1190	For example, the following C<TO_JSON> method will convert all L<URI>
		1191	objects to JSON strings when serialised. The fatc that these values
		1192	originally were L<URI> objects is lost.
863		1193
864	Very inflexible (no human-readable format supported, format pretty much	1194	sub URI::TO_JSON {
865	undocumented. I need at least a format for easy reading by humans and a	1195	my ($uri) = @_;
866	single-line compact format for use in a protocol, and preferably a way to	1196	$uri->as_string
867	generate ASCII-only JSON texts).	1197	}
868		1198
869	Completely broken (and confusingly documented) Unicode handling (Unicode	1199	=item 3. C<allow_blessed> is enabled.
870	escapes are not working properly, you need to set ImplicitUnicode to
871	I<different> values on en- and decoding to get symmetric behaviour).
872		1200
873	No round-tripping (simple cases work, but this depends on whether the scalar	1201	The object will be serialised as a JSON null value.
874	value was used in a numeric context or not).
875		1202
876	Dumping hashes may skip hash values depending on iterator state.	1203	=item 4. none of the above
877		1204
878	Unmaintained (maintainer unresponsive for many months, bugs are not	1205	If none of the settings are enabled or the respective methods are missing,
879	getting fixed).	1206	C<JSON::XS> throws an exception.
880
881	Does not check input for validity (i.e. will accept non-JSON input and
882	return "something" instead of raising an exception. This is a security
883	issue: imagine two banks transferring money between each other using
884	JSON. One bank might parse a given non-JSON request and deduct money,
885	while the other might reject the transaction with a syntax error. While a
886	good protocol will at least recover, that is extra unnecessary work and
887	the transaction will still not succeed).
888
889	=item JSON::DWIW 0.04
890
891	Very fast. Very natural. Very nice.
892
893	Undocumented Unicode handling (but the best of the pack. Unicode escapes
894	still don't get parsed properly).
895
896	Very inflexible.
897
898	No round-tripping.
899
900	Does not generate valid JSON texts (key strings are often unquoted, empty keys
901	result in nothing being output)
902
903	Does not check input for validity.
904		1207
905	=back	1208	=back
906		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	}
		1245
		1246
		1247	=head1 ENCODING/CODESET FLAG NOTES
		1248
		1249	The interested reader might have seen a number of flags that signify
		1250	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1251	some confusion on what these do, so here is a short comparison:
		1252
		1253	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1254	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1255	control whether C<encode> escapes character values outside their respective
		1256	codeset range. Neither of these flags conflict with each other, although
		1257	some combinations make less sense than others.
		1258
		1259	Care has been taken to make all flags symmetrical with respect to
		1260	C<encode> and C<decode>, that is, texts encoded with any combination of
		1261	these flag values will be correctly decoded when the same flags are used
		1262	- in general, if you use different flag settings while encoding vs. when
		1263	decoding you likely have a bug somewhere.
		1264
		1265	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1266	simply an abstract set of character-codepoint pairs, while an encoding
		1267	takes those codepoint numbers and I<encodes> them, in our case into
		1268	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1269	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1270	the same time, which can be confusing.
		1271
		1272	=over 4
		1273
		1274	=item C<utf8> flag disabled
		1275
		1276	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1277	and expect Unicode strings, that is, characters with high ordinal Unicode
		1278	values (> 255) will be encoded as such characters, and likewise such
		1279	characters are decoded as-is, no changes to them will be done, except
		1280	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1281	respectively (to Perl, these are the same thing in strings unless you do
		1282	funny/weird/dumb stuff).
		1283
		1284	This is useful when you want to do the encoding yourself (e.g. when you
		1285	want to have UTF-16 encoded JSON texts) or when some other layer does
		1286	the encoding for you (for example, when printing to a terminal using a
		1287	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1288	to UTF-8 encode your data first and have Perl encode it another time).
		1289
		1290	=item C<utf8> flag enabled
		1291
		1292	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1293	characters using the corresponding UTF-8 multi-byte sequence, and will
		1294	expect your input strings to be encoded as UTF-8, that is, no "character"
		1295	of the input string must have any value > 255, as UTF-8 does not allow
		1296	that.
		1297
		1298	The C<utf8> flag therefore switches between two modes: disabled means you
		1299	will get a Unicode string in Perl, enabled means you get a UTF-8 encoded
		1300	octet/binary string in Perl.
		1301
		1302	=item C<latin1> or C<ascii> flags enabled
		1303
		1304	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1305	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1306	characters as specified by the C<utf8> flag.
		1307
		1308	If C<utf8> is disabled, then the result is also correctly encoded in those
		1309	character sets (as both are proper subsets of Unicode, meaning that a
		1310	Unicode string with all character values < 256 is the same thing as a
		1311	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1312	the same thing as an ASCII string in Perl).
		1313
		1314	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1315	regardless of these flags, just some more characters will be escaped using
		1316	C<\uXXXX> then before.
		1317
		1318	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1319	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1320	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1321	a subset of Unicode), while ASCII is.
		1322
		1323	Surprisingly, C<decode> will ignore these flags and so treat all input
		1324	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1325	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1326	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1327
		1328	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1329	they only govern when the JSON output engine escapes a character or not.
		1330
		1331	The main use for C<latin1> is to relatively efficiently store binary data
		1332	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1333
		1334	The main use for C<ascii> is to force the output to not contain characters
		1335	with values > 127, which means you can interpret the resulting string
		1336	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1337	8-bit-encoding, and still get the same data structure back. This is useful
		1338	when your channel for JSON transfer is not 8-bit clean or the encoding
		1339	might be mangled in between (e.g. in mail), and works because ASCII is a
		1340	proper subset of most 8-bit and multibyte encodings in use in the world.
		1341
		1342	=back
		1343
		1344
		1345	=head2 JSON and ECMAscript
		1346
		1347	JSON syntax is based on how literals are represented in javascript (the
		1348	not-standardised predecessor of ECMAscript) which is presumably why it is
		1349	called "JavaScript Object Notation".
		1350
		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).
		1354
		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:
		1358
		1359	One of the problems is that U+2028 and U+2029 are valid characters inside
		1360	JSON strings, but are not allowed in ECMAscript string literals, so the
		1361	following Perl fragment will not output something that can be guaranteed
		1362	to be parsable by javascript's C<eval>:
		1363
		1364	use JSON::XS;
		1365
		1366	print encode_json [chr 0x2028];
		1367
		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).
		1371
		1372	If this is not an option, you can, as a stop-gap measure, simply encode to
		1373	ASCII-only JSON:
		1374
		1375	use JSON::XS;
		1376
		1377	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1378
		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.:
		1382
		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;
		1388
		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.
		1393
		1394	Another problem is that some javascript implementations reserve
		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.
		1398
		1399	If that is a problem, you could parse try to filter the resulting JSON
		1400	output for these property strings, e.g.:
		1401
		1402	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1403
		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.
		1406
		1407	If you know of other incompatibilities, please let me know.
		1408
907		1409
908	=head2 JSON and YAML	1410	=head2 JSON and YAML
909		1411
910	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1412	You often hear that JSON is a subset of YAML. This is, however, a mass
911	however, a mass hysteria and very far from the truth. In general, there is	1413	hysteria(*) and very far from the truth (as of the time of this writing),
912	no way to configure JSON::XS to output a data structure as valid YAML.	1414	so let me state it clearly: I<in general, there is no way to configure
		1415	JSON::XS to output a data structure as valid YAML> that works in all
		1416	cases.
913		1417
914	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
915	algorithm (subject to change in future versions):	1419	algorithm (subject to change in future versions):
916		1420
917	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1421	my $to_yaml = JSON::XS->new->utf8->space_after (1);
918	my $yaml = $to_yaml->encode ($ref) . "\n";	1422	my $yaml = $to_yaml->encode ($ref) . "\n";
919		1423
920	This will usually generate JSON texts that also parse as valid	1424	This will I<usually> generate JSON texts that also parse as valid
921	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
922	lengths that JSON doesn't have, so you should make sure that your hash	1426	lengths that JSON doesn't have and also has different and incompatible
		1427	unicode character escape syntax, so you should make sure that your hash
923	keys are noticeably shorter than the 1024 characters YAML allows.	1428	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1429	and that you do not have characters with codepoint values outside the
		1430	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1431	sequences in strings (which JSON::XS does not I<currently> generate, but
		1432	other JSON generators might).
924		1433
925	There might be other incompatibilities that I am not aware of. In general	1434	There might be other incompatibilities that I am not aware of (or the YAML
		1435	specification has been changed yet again - it does so quite often). In
926	you should not try to generate YAML with a JSON generator or vice versa,	1436	general you should not try to generate YAML with a JSON generator or vice
927	or try to parse JSON with a YAML parser or vice versa: chances are high	1437	versa, or try to parse JSON with a YAML parser or vice versa: chances are
928	that you will run into severe interoperability problems.	1438	high that you will run into severe interoperability problems when you
		1439	least expect it.
		1440
		1441	=over 4
		1442
		1443	=item (*)
		1444
		1445	I have been pressured multiple times by Brian Ingerson (one of the
		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).
		1452
		1453	In my opinion, instead of pressuring and insulting people who actually
		1454	clarify issues with YAML and the wrong statements of some of its
		1455	proponents, I would kindly suggest reading the JSON spec (which is not
		1456	that difficult or long) and finally make YAML compatible to it, and
		1457	educating users about the changes, instead of spreading lies about the
		1458	real compatibility for many I<years> and trying to silence people who
		1459	point out that it isn't true.
		1460
		1461	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1462	though the incompatibilities have been documented (and are known to Brian)
		1463	for many years and the spec makes explicit claims that YAML is a superset
		1464	of JSON. It would be so easy to fix, but apparently, bullying people and
		1465	corrupting userdata is so much easier.
		1466
		1467	=back
929		1468
930		1469
931	=head2 SPEED	1470	=head2 SPEED
932		1471
933	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
934	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
935	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
936	system.	1475	system.
937		1476
938	First comes a comparison between various modules using a very short	1477	First comes a comparison between various modules using
939	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>).
940		1480
941	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1481	{"method": "handleMessage", "params": ["user1",
942	"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]}
943		1484
944	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
945	the functional interface, while JSON::XS/2 uses the OO interface	1486	the functional interface, while JSON::XS/2 uses the OO interface
946	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1487	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
947	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:
948		1490
949	module | encode | decode |	1491	module | encode | decode |
950	-----------|------------|------------|	1492	--------------|------------|------------|
951	JSON 1.x | 4990.842 | 4088.813 |	1493	JSON::DWIW/DS | 86302.551 | 102300.098 |
952	JSON::DWIW | 51653.990 | 71575.154 |	1494	JSON::DWIW/FJ | 86302.551 | 75983.768 |
953	JSON::PC | 65948.176 | 74631.744 |	1495	JSON::PP | 15827.562 | 6638.658 |
954	JSON::PP | 8931.652 | 3817.168 |	1496	JSON::Syck | 63358.066 | 47662.545 |
955	JSON::Syck | 24877.248 | 27776.848 |	1497	JSON::XS | 511500.488 | 511500.488 |
956	JSON::XS | 388361.481 | 227951.304 |	1498	JSON::XS/2 | 291271.111 | 388361.481 |
957	JSON::XS/2 | 227951.304 | 218453.333 |	1499	JSON::XS/3 | 361577.931 | 361577.931 |
958	JSON::XS/3 | 338250.323 | 218453.333 |	1500	Storable | 66788.280 | 265462.278 |
959	Storable | 16500.016 | 135300.129 |
960	-----------+------------+------------+	1501	--------------+------------+------------+
961		1502
962	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,
963	about three times faster on decoding, and over forty times faster	1504	about five times faster on decoding, and over thirty to seventy times
964	than JSON, even with pretty-printing and key sorting. It also compares	1505	faster than JSON's pure perl implementation. It also compares favourably
965	favourably to Storable for small amounts of data.	1506	to Storable for small amounts of data.
966		1507
967	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1508	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
968	search API (http://nanoref.com/yahooapis/mgPdGg):	1509	search API (L<http://dist.schmorp.de/misc/json/long.json>).
969		1510
970	module | encode | decode |	1511	module | encode | decode |
971	-----------|------------|------------|	1512	--------------|------------|------------|
972	JSON 1.x | 55.260 | 34.971 |	1513	JSON::DWIW/DS | 1647.927 | 2673.916 |
973	JSON::DWIW | 825.228 | 1082.513 |	1514	JSON::DWIW/FJ | 1630.249 | 2596.128 |
974	JSON::PC | 3571.444 | 2394.829 |
975	JSON::PP | 210.987 | 32.574 |	1515	JSON::PP | 400.640 | 62.311 |
976	JSON::Syck | 552.551 | 787.544 |	1516	JSON::Syck | 1481.040 | 1524.869 |
977	JSON::XS | 5780.463 | 4854.519 |	1517	JSON::XS | 20661.596 | 9541.183 |
978	JSON::XS/2 | 3869.998 | 4798.975 |	1518	JSON::XS/2 | 10683.403 | 9416.938 |
979	JSON::XS/3 | 5862.880 | 4798.975 |	1519	JSON::XS/3 | 20661.596 | 9400.054 |
980	Storable | 4445.002 | 5235.027 |	1520	Storable | 19765.806 | 10000.725 |
981	-----------+------------+------------+	1521	--------------+------------+------------+
982		1522
983	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
984	decodes faster).	1524	decodes a bit faster).
985		1525
986	On large strings containing lots of high Unicode characters, some modules	1526	On large strings containing lots of high Unicode characters, some modules
987	(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
988	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
989	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
…		…
1010		1550
1011	Third, JSON::XS recurses using the C stack when decoding objects and	1551	Third, JSON::XS recurses using the C stack when decoding objects and
1012	arrays. The C stack is a limited resource: for instance, on my amd64	1552	arrays. The C stack is a limited resource: for instance, on my amd64
1013	machine with 8MB of stack size I can decode around 180k nested arrays but	1553	machine with 8MB of stack size I can decode around 180k nested arrays but
1014	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1554	only 14k nested JSON objects (due to perl itself recursing deeply on croak
1015	to free the temporary). If that is exceeded, the program crashes. to be	1555	to free the temporary). If that is exceeded, the program crashes. To be
1016	conservative, the default nesting limit is set to 512. If your process	1556	conservative, the default nesting limit is set to 512. If your process
1017	has a smaller stack, you should adjust this setting accordingly with the	1557	has a smaller stack, you should adjust this setting accordingly with the
1018	C<max_depth> method.	1558	C<max_depth> method.
1019		1559
1020	And last but least, something else could bomb you that I forgot to think	1560	Something else could bomb you, too, that I forgot to think of. In that
1021	of. In that case, you get to keep the pieces. I am always open for hints,	1561	case, you get to keep the pieces. I am always open for hints, though...
1022	though...	1562
		1563	Also keep in mind that JSON::XS might leak contents of your Perl data
		1564	structures in its error messages, so when you serialise sensitive
		1565	information you might want to make sure that exceptions thrown by JSON::XS
		1566	will not end up in front of untrusted eyes.
1023		1567
1024	If you are using JSON::XS to return packets to consumption	1568	If you are using JSON::XS to return packets to consumption
1025	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
1026	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
1027	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
1028	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
1029	browser developers care only for features, not about doing security	1573	it, as major browser developers care only for features, not about getting
1030	right).	1574	security right).
1031		1575
1032		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
1033	=head1 THREADS	1707	=head1 (I-)THREADS
1034		1708
1035	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
1036	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
1037	horribly slow so-called "threads" which are simply slow and bloated	1711	threads/ithreads are officially deprecated and should not be used.
1038	process simulations - use fork, its I<much> faster, cheaper, better).
1039		1712
1040	(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.
1041		1730
1042		1731
1043	=head1 BUGS	1732	=head1 BUGS
1044		1733
1045	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
1046	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
1047	still relatively early in its development. If you keep reporting bugs they	1736	keep reporting bugs they will be fixed swiftly, though.
1048	will be fixed swiftly, though.
1049		1737
1050	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
1051	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.
1052		1740
1053	=cut	1741	=cut
1054		1742
1055	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1743	BEGIN {
1056	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;
1057		1749
1058	sub true() { $true }	1750	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
1059	sub false() { $false }
1060
1061	sub is_bool($) {
1062	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1063	# or UNIVERSAL::isa $_[0], "JSON::Literal"
1064	}	1751	}
1065		1752
1066	XSLoader::load "JSON::XS", $VERSION;	1753	XSLoader::load "JSON::XS", $VERSION;
1067		1754
1068	package JSON::XS::Boolean;	1755	=head1 SEE ALSO
1069		1756
1070	use overload	1757	The F<json_xs> command line utility for quick experiments.
1071	"0+" => sub { ${$_[0]} },
1072	"++" => sub { $_[0] = ${$_[0]} + 1 },
1073	"--" => sub { $_[0] = ${$_[0]} - 1 },
1074	fallback => 1;
1075
1076	1;
1077		1758
1078	=head1 AUTHOR	1759	=head1 AUTHOR
1079		1760
1080	Marc Lehmann <schmorp@schmorp.de>	1761	Marc Lehmann <schmorp@schmorp.de>
1081	http://home.schmorp.de/	1762	http://home.schmorp.de/
1082		1763
1083	=cut	1764	=cut
1084		1765
		1766	1
		1767

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