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Revision 1.78 by root, Wed Dec 5 10:59:28 2007 UTC vs.
Revision 1.173 by root, Mon Nov 19 10:27:29 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
…		…
33		35
34	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
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
39	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
41	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
43	gives you a portable JSON API that can be fast when you need and doesn't
44	require a C compiler when that is a problem.
45
46	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
48	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
50	reports for other reasons.
51
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	40	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
55	vice versa.	41	vice versa.
56		42
57	=head2 FEATURES	43	=head2 FEATURES
58		44
59	=over 4	45	=over
60		46
61	=item * correct Unicode handling	47	=item * correct Unicode handling
62		48
63	This module knows how to handle Unicode, and even documents how and when	49	This module knows how to handle Unicode, documents how and when it does
64	it does so.	50	so, and even documents what "correct" means.
65		51
66	=item * round-trip integrity	52	=item * round-trip integrity
67		53
68	When you serialise a perl data structure using only datatypes supported	54	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.	55	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	56	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
71	like a number).	57	it looks like a number). There I<are> minor exceptions to this, read the
		58	MAPPING section below to learn about those.
72		59
73	=item * strict checking of JSON correctness	60	=item * strict checking of JSON correctness
74		61
75	There is no guessing, no generating of illegal JSON texts by default,	62	There is no guessing, no generating of illegal JSON texts by default,
76	and only JSON is accepted as input by default (the latter is a security	63	and only JSON is accepted as input by default (the latter is a security
77	feature).	64	feature).
78		65
79	=item * fast	66	=item * fast
80		67
81	Compared to other JSON modules, this module compares favourably in terms	68	Compared to other JSON modules and other serialisers such as Storable,
82	of speed, too.	69	this module usually compares favourably in terms of speed, too.
83		70
84	=item * simple to use	71	=item * simple to use
85		72
86	This module has both a simple functional interface as well as an OO	73	This module has both a simple functional interface as well as an object
87	interface.	74	oriented interface.
88		75
89	=item * reasonably versatile output formats	76	=item * reasonably versatile output formats
90		77
91	You can choose between the most compact guaranteed single-line format	78	You can choose between the most compact guaranteed-single-line format
92	possible (nice for simple line-based protocols), a pure-ascii format	79	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	80	(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	81	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.	82	stuff). Or you can combine those features in whatever way you like.
96		83
97	=back	84	=back
98		85
99	=cut	86	=cut
100		87
101	package JSON::XS;	88	package JSON::XS;
102		89
103	use strict;	90	use common::sense;
104		91
105	our $VERSION = '2.01';	92	our $VERSION = '4.0';
106	our @ISA = qw(Exporter);	93	our @ISA = qw(Exporter);
107		94
108	our @EXPORT = qw(encode_json decode_json to_json from_json);	95	our @EXPORT = qw(encode_json decode_json);
109
110	sub to_json($) {
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		96
120	use Exporter;	97	use Exporter;
121	use XSLoader;	98	use XSLoader;
122		99
		100	use Types::Serialiser ();
		101
123	=head1 FUNCTIONAL INTERFACE	102	=head1 FUNCTIONAL INTERFACE
124		103
125	The following convenience methods are provided by this module. They are	104	The following convenience methods are provided by this module. They are
126	exported by default:	105	exported by default:
127		106
128	=over 4	107	=over
129		108
130	=item $json_text = encode_json $perl_scalar	109	=item $json_text = encode_json $perl_scalar
131		110
132	Converts the given Perl data structure to a UTF-8 encoded, binary string	111	Converts the given Perl data structure to a UTF-8 encoded, binary string
133	(that is, the string contains octets only). Croaks on error.	112	(that is, the string contains octets only). Croaks on error.
134		113
135	This function call is functionally identical to:	114	This function call is functionally identical to:
136		115
137	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	116	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
138		117
139	except being faster.	118	Except being faster.
140		119
141	=item $perl_scalar = decode_json $json_text	120	=item $perl_scalar = decode_json $json_text
142		121
143	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries	122	The opposite of C<encode_json>: expects a UTF-8 (binary) string and tries
144	to parse that as an UTF-8 encoded JSON text, returning the resulting	123	to parse that as a UTF-8 encoded JSON text, returning the resulting
145	reference. Croaks on error.	124	reference. Croaks on error.
146		125
147	This function call is functionally identical to:	126	This function call is functionally identical to:
148		127
149	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	128	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
150		129
151	except being faster.	130	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		131
162	=back	132	=back
163		133
164		134
165	=head1 A FEW NOTES ON UNICODE AND PERL	135	=head1 A FEW NOTES ON UNICODE AND PERL
166		136
167	Since this often leads to confusion, here are a few very clear words on	137	Since this often leads to confusion, here are a few very clear words on
168	how Unicode works in Perl, modulo bugs.	138	how Unicode works in Perl, modulo bugs.
169		139
170	=over 4	140	=over
171		141
172	=item 1. Perl strings can store characters with ordinal values > 255.	142	=item 1. Perl strings can store characters with ordinal values > 255.
173		143
174	This enables you to store Unicode characters as single characters in a	144	This enables you to store Unicode characters as single characters in a
175	Perl string - very natural.	145	Perl string - very natural.
176		146
177	=item 2. Perl does I<not> associate an encoding with your strings.	147	=item 2. Perl does I<not> associate an encoding with your strings.
178		148
179	Unless you force it to, e.g. when matching it against a regex, or printing	149	... 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	150	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	151	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	152	on various settings. In no case is an encoding stored together with your
183	I<use> that decides encoding, not any magical metadata.	153	data, it is I<use> that decides encoding, not any magical meta data.
184		154
185	=item 3. The internal utf-8 flag has no meaning with regards to the	155	=item 3. The internal utf-8 flag has no meaning with regards to the
186	encoding of your string.	156	encoding of your string.
187		157
188	Just ignore that flag unless you debug a Perl bug, a module written in	158	Just ignore that flag unless you debug a Perl bug, a module written in
…		…
194		164
195	If you didn't know about that flag, just the better, pretend it doesn't	165	If you didn't know about that flag, just the better, pretend it doesn't
196	exist.	166	exist.
197		167
198	=item 4. A "Unicode String" is simply a string where each character can be	168	=item 4. A "Unicode String" is simply a string where each character can be
199	validly interpreted as a Unicode codepoint.	169	validly interpreted as a Unicode code point.
200		170
201	If you have UTF-8 encoded data, it is no longer a Unicode string, but a	171	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
202	Unicode string encoded in UTF-8, giving you a binary string.	172	Unicode string encoded in UTF-8, giving you a binary string.
203		173
204	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.	174	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
…		…
213	=head1 OBJECT-ORIENTED INTERFACE	183	=head1 OBJECT-ORIENTED INTERFACE
214		184
215	The object oriented interface lets you configure your own encoding or	185	The object oriented interface lets you configure your own encoding or
216	decoding style, within the limits of supported formats.	186	decoding style, within the limits of supported formats.
217		187
218	=over 4	188	=over
219		189
220	=item $json = new JSON::XS	190	=item $json = new JSON::XS
221		191
222	Creates a new JSON::XS object that can be used to de/encode JSON	192	Creates a new JSON::XS object that can be used to de/encode JSON
223	strings. All boolean flags described below are by default I<disabled>.	193	strings. All boolean flags described below are by default I<disabled>
		194	(with the exception of C<allow_nonref>, which defaults to I<enabled> since
		195	version C<4.0>).
224		196
225	The mutators for flags all return the JSON object again and thus calls can	197	The mutators for flags all return the JSON object again and thus calls can
226	be chained:	198	be chained:
227		199
228	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	200	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
…		…
242		214
243	If C<$enable> is false, then the C<encode> method will not escape Unicode	215	If C<$enable> is false, then the C<encode> method will not escape Unicode
244	characters unless required by the JSON syntax or other flags. This results	216	characters unless required by the JSON syntax or other flags. This results
245	in a faster and more compact format.	217	in a faster and more compact format.
246		218
		219	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		220	document.
		221
247	The main use for this flag is to produce JSON texts that can be	222	The main use for this flag is to produce JSON texts that can be
248	transmitted over a 7-bit channel, as the encoded JSON texts will not	223	transmitted over a 7-bit channel, as the encoded JSON texts will not
249	contain any 8 bit characters.	224	contain any 8 bit characters.
250		225
251	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	226	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
262	will not be affected in any way by this flag, as C<decode> by default	237	will not be affected in any way by this flag, as C<decode> by default
263	expects Unicode, which is a strict superset of latin1.	238	expects Unicode, which is a strict superset of latin1.
264		239
265	If C<$enable> is false, then the C<encode> method will not escape Unicode	240	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.	241	characters unless required by the JSON syntax or other flags.
		242
		243	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		244	document.
267		245
268	The main use for this flag is efficiently encoding binary data as JSON	246	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	247	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	248	size. The disadvantage is that the resulting JSON text is encoded
271	in latin1 (and must correctly be treated as such when storing and	249	in latin1 (and must correctly be treated as such when storing and
…		…
280		258
281	=item $enabled = $json->get_utf8	259	=item $enabled = $json->get_utf8
282		260
283	If C<$enable> is true (or missing), then the C<encode> method will encode	261	If C<$enable> is true (or missing), then the C<encode> method will encode
284	the JSON result into UTF-8, as required by many protocols, while the	262	the JSON result into UTF-8, as required by many protocols, while the
285	C<decode> method expects to be handled an UTF-8-encoded string. Please	263	C<decode> method expects to be handed a UTF-8-encoded string. Please
286	note that UTF-8-encoded strings do not contain any characters outside the	264	note that UTF-8-encoded strings do not contain any characters outside the
287	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	265	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
288	versions, enabling this option might enable autodetection of the UTF-16	266	versions, enabling this option might enable autodetection of the UTF-16
289	and UTF-32 encoding families, as described in RFC4627.	267	and UTF-32 encoding families, as described in RFC4627.
290		268
291	If C<$enable> is false, then the C<encode> method will return the JSON	269	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	270	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	271	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.	272	to be done yourself, e.g. using the Encode module.
		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
295		276
296	Example, output UTF-16BE-encoded JSON:	277	Example, output UTF-16BE-encoded JSON:
297		278
298	use Encode;	279	use Encode;
299	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	280	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
372		353
373	=item $enabled = $json->get_relaxed	354	=item $enabled = $json->get_relaxed
374		355
375	If C<$enable> is true (or missing), then C<decode> will accept some	356	If C<$enable> is true (or missing), then C<decode> will accept some
376	extensions to normal JSON syntax (see below). C<encode> will not be	357	extensions to normal JSON syntax (see below). C<encode> will not be
377	affected in anyway. I<Be aware that this option makes you accept invalid	358	affected in any way. I<Be aware that this option makes you accept invalid
378	JSON texts as if they were valid!>. I suggest only to use this option to	359	JSON texts as if they were valid!>. I suggest only to use this option to
379	parse application-specific files written by humans (configuration files,	360	parse application-specific files written by humans (configuration files,
380	resource files etc.)	361	resource files etc.)
381		362
382	If C<$enable> is false (the default), then C<decode> will only accept	363	If C<$enable> is false (the default), then C<decode> will only accept
383	valid JSON texts.	364	valid JSON texts.
384		365
385	Currently accepted extensions are:	366	Currently accepted extensions are:
386		367
387	=over 4	368	=over
388		369
389	=item * list items can have an end-comma	370	=item * list items can have an end-comma
390		371
391	JSON I<separates> array elements and key-value pairs with commas. This	372	JSON I<separates> array elements and key-value pairs with commas. This
392	can be annoying if you write JSON texts manually and want to be able to	373	can be annoying if you write JSON texts manually and want to be able to
…		…
411	[	392	[
412	1, # this comment not allowed in JSON	393	1, # this comment not allowed in JSON
413	# neither this one...	394	# neither this one...
414	]	395	]
415		396
		397	=item * literal ASCII TAB characters in strings
		398
		399	Literal ASCII TAB characters are now allowed in strings (and treated as
		400	C<\t>).
		401
		402	[
		403	"Hello\tWorld",
		404	"Hello<TAB>World", # literal <TAB> would not normally be allowed
		405	]
		406
416	=back	407	=back
417		408
418	=item $json = $json->canonical ([$enable])	409	=item $json = $json->canonical ([$enable])
419		410
420	=item $enabled = $json->get_canonical	411	=item $enabled = $json->get_canonical
…		…
422	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	413	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
423	by sorting their keys. This is adding a comparatively high overhead.	414	by sorting their keys. This is adding a comparatively high overhead.
424		415
425	If C<$enable> is false, then the C<encode> method will output key-value	416	If C<$enable> is false, then the C<encode> method will output key-value
426	pairs in the order Perl stores them (which will likely change between runs	417	pairs in the order Perl stores them (which will likely change between runs
427	of the same script).	418	of the same script, and can change even within the same run from 5.18
		419	onwards).
428		420
429	This option is useful if you want the same data structure to be encoded as	421	This option is useful if you want the same data structure to be encoded as
430	the same JSON text (given the same overall settings). If it is disabled,	422	the same JSON text (given the same overall settings). If it is disabled,
431	the same hash might be encoded differently even if contains the same data,	423	the same hash might be encoded differently even if contains the same data,
432	as key-value pairs have no inherent ordering in Perl.	424	as key-value pairs have no inherent ordering in Perl.
433		425
434	This setting has no effect when decoding JSON texts.	426	This setting has no effect when decoding JSON texts.
435		427
		428	This setting has currently no effect on tied hashes.
		429
436	=item $json = $json->allow_nonref ([$enable])	430	=item $json = $json->allow_nonref ([$enable])
437		431
438	=item $enabled = $json->get_allow_nonref	432	=item $enabled = $json->get_allow_nonref
		433
		434	Unlike other boolean options, this opotion is enabled by default beginning
		435	with version C<4.0>. See L<SECURITY CONSIDERATIONS> for the gory details.
439		436
440	If C<$enable> is true (or missing), then the C<encode> method can convert a	437	If C<$enable> is true (or missing), then the C<encode> method can convert a
441	non-reference into its corresponding string, number or null JSON value,	438	non-reference into its corresponding string, number or null JSON value,
442	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	439	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
443	values instead of croaking.	440	values instead of croaking.
…		…
445	If C<$enable> is false, then the C<encode> method will croak if it isn't	442	If C<$enable> is false, then the C<encode> method will croak if it isn't
446	passed an arrayref or hashref, as JSON texts must either be an object	443	passed an arrayref or hashref, as JSON texts must either be an object
447	or array. Likewise, C<decode> will croak if given something that is not a	444	or array. Likewise, C<decode> will croak if given something that is not a
448	JSON object or array.	445	JSON object or array.
449		446
450	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,	447	Example, encode a Perl scalar as JSON value without enabled C<allow_nonref>,
451	resulting in an invalid JSON text:	448	resulting in an error:
452		449
453	JSON::XS->new->allow_nonref->encode ("Hello, World!")	450	JSON::XS->new->allow_nonref (0)->encode ("Hello, World!")
454	=> "Hello, World!"	451	=> hash- or arrayref expected...
		452
		453	=item $json = $json->allow_unknown ([$enable])
		454
		455	=item $enabled = $json->get_allow_unknown
		456
		457	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		458	exception when it encounters values it cannot represent in JSON (for
		459	example, filehandles) but instead will encode a JSON C<null> value. Note
		460	that blessed objects are not included here and are handled separately by
		461	c<allow_nonref>.
		462
		463	If C<$enable> is false (the default), then C<encode> will throw an
		464	exception when it encounters anything it cannot encode as JSON.
		465
		466	This option does not affect C<decode> in any way, and it is recommended to
		467	leave it off unless you know your communications partner.
455		468
456	=item $json = $json->allow_blessed ([$enable])	469	=item $json = $json->allow_blessed ([$enable])
457		470
458	=item $enabled = $json->get_allow_blessed	471	=item $enabled = $json->get_allow_blessed
459		472
		473	See L<OBJECT SERIALISATION> for details.
		474
460	If C<$enable> is true (or missing), then the C<encode> method will not	475	If C<$enable> is true (or missing), then the C<encode> method will not
461	barf when it encounters a blessed reference. Instead, the value of the	476	barf when it encounters a blessed reference that it cannot convert
462	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>	477	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
463	disabled or no C<TO_JSON> method found) or a representation of the
464	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
465	encoded. Has no effect on C<decode>.
466		478
467	If C<$enable> is false (the default), then C<encode> will throw an	479	If C<$enable> is false (the default), then C<encode> will throw an
468	exception when it encounters a blessed object.	480	exception when it encounters a blessed object that it cannot convert
		481	otherwise.
		482
		483	This setting has no effect on C<decode>.
469		484
470	=item $json = $json->convert_blessed ([$enable])	485	=item $json = $json->convert_blessed ([$enable])
471		486
472	=item $enabled = $json->get_convert_blessed	487	=item $enabled = $json->get_convert_blessed
		488
		489	See L<OBJECT SERIALISATION> for details.
473		490
474	If C<$enable> is true (or missing), then C<encode>, upon encountering a	491	If C<$enable> is true (or missing), then C<encode>, upon encountering a
475	blessed object, will check for the availability of the C<TO_JSON> method	492	blessed object, will check for the availability of the C<TO_JSON> method
476	on the object's class. If found, it will be called in scalar context	493	on the object's class. If found, it will be called in scalar context and
477	and the resulting scalar will be encoded instead of the object. If no	494	the resulting scalar will be encoded instead of the object.
478	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
479	to do.
480		495
481	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	496	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
482	returns other blessed objects, those will be handled in the same	497	returns other blessed objects, those will be handled in the same
483	way. C<TO_JSON> must take care of not causing an endless recursion cycle	498	way. C<TO_JSON> must take care of not causing an endless recursion cycle
484	(== crash) in this case. The name of C<TO_JSON> was chosen because other	499	(== crash) in this case. The name of C<TO_JSON> was chosen because other
485	methods called by the Perl core (== not by the user of the object) are	500	methods called by the Perl core (== not by the user of the object) are
486	usually in upper case letters and to avoid collisions with any C<to_json>	501	usually in upper case letters and to avoid collisions with any C<to_json>
487	function or method.	502	function or method.
488		503
489	This setting does not yet influence C<decode> in any way, but in the	504	If C<$enable> is false (the default), then C<encode> will not consider
490	future, global hooks might get installed that influence C<decode> and are	505	this type of conversion.
491	enabled by this setting.
492		506
493	If C<$enable> is false, then the C<allow_blessed> setting will decide what	507	This setting has no effect on C<decode>.
494	to do when a blessed object is found.	508
		509	=item $json = $json->allow_tags ([$enable])
		510
		511	=item $enabled = $json->get_allow_tags
		512
		513	See L<OBJECT SERIALISATION> for details.
		514
		515	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		516	blessed object, will check for the availability of the C<FREEZE> method on
		517	the object's class. If found, it will be used to serialise the object into
		518	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		519
		520	It also causes C<decode> to parse such tagged JSON values and deserialise
		521	them via a call to the C<THAW> method.
		522
		523	If C<$enable> is false (the default), then C<encode> will not consider
		524	this type of conversion, and tagged JSON values will cause a parse error
		525	in C<decode>, as if tags were not part of the grammar.
		526
		527	=item $json->boolean_values ([$false, $true])
		528
		529	=item ($false, $true) = $json->get_boolean_values
		530
		531	By default, JSON booleans will be decoded as overloaded
		532	C<$Types::Serialiser::false> and C<$Types::Serialiser::true> objects.
		533
		534	With this method you can specify your own boolean values for decoding -
		535	on decode, JSON C<false> will be decoded as a copy of C<$false>, and JSON
		536	C<true> will be decoded as C<$true> ("copy" here is the same thing as
		537	assigning a value to another variable, i.e. C<$copy = $false>).
		538
		539	Calling this method without any arguments will reset the booleans
		540	to their default values.
		541
		542	C<get_boolean_values> will return both C<$false> and C<$true> values, or
		543	the empty list when they are set to the default.
495		544
496	=item $json = $json->filter_json_object ([$coderef->($hashref)])	545	=item $json = $json->filter_json_object ([$coderef->($hashref)])
497		546
498	When C<$coderef> is specified, it will be called from C<decode> each	547	When C<$coderef> is specified, it will be called from C<decode> each
499	time it decodes a JSON object. The only argument is a reference to the	548	time it decodes a JSON object. The only argument is a reference to
500	newly-created hash. If the code references returns a single scalar (which	549	the newly-created hash. If the code reference returns a single scalar
501	need not be a reference), this value (i.e. a copy of that scalar to avoid	550	(which need not be a reference), this value (or rather a copy of it) is
502	aliasing) is inserted into the deserialised data structure. If it returns	551	inserted into the deserialised data structure. If it returns an empty
503	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the	552	list (NOTE: I<not> C<undef>, which is a valid scalar), the original
504	original deserialised hash will be inserted. This setting can slow down	553	deserialised hash will be inserted. This setting can slow down decoding
505	decoding considerably.	554	considerably.
506		555
507	When C<$coderef> is omitted or undefined, any existing callback will	556	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	557	be removed and C<decode> will not change the deserialised hash in any
509	way.	558	way.
510		559
…		…
600	=item $json = $json->max_depth ([$maximum_nesting_depth])	649	=item $json = $json->max_depth ([$maximum_nesting_depth])
601		650
602	=item $max_depth = $json->get_max_depth	651	=item $max_depth = $json->get_max_depth
603		652
604	Sets the maximum nesting level (default C<512>) accepted while encoding	653	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	654	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	655	data structure, then the encoder and decoder will stop and croak at that
607	stop and croak at that point.	656	point.
608		657
609	Nesting level is defined by number of hash- or arrayrefs that the encoder	658	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<[>	659	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	660	characters without their matching closing parenthesis crossed to reach a
612	given character in a string.	661	given character in a string.
613		662
614	Setting the maximum depth to one disallows any nesting, so that ensures	663	Setting the maximum depth to one disallows any nesting, so that ensures
615	that the object is only a single hash/object or array.	664	that the object is only a single hash/object or array.
616		665
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	666	If no argument is given, the highest possible setting will be used, which
619	used, which is rarely useful.	667	is rarely useful.
		668
		669	Note that nesting is implemented by recursion in C. The default value has
		670	been chosen to be as large as typical operating systems allow without
		671	crashing.
620		672
621	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	673	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
622		674
623	=item $json = $json->max_size ([$maximum_string_size])	675	=item $json = $json->max_size ([$maximum_string_size])
624		676
625	=item $max_size = $json->get_max_size	677	=item $max_size = $json->get_max_size
626		678
627	Set the maximum length a JSON text may have (in bytes) where decoding is	679	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>	680	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	681	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	682	attempt to decode the string but throw an exception. This setting has no
631	effect on C<encode> (yet).	683	effect on C<encode> (yet).
632		684
633	The argument to C<max_size> will be rounded up to the next B<highest>	685	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	686	C<0> is specified).
635	limit check will be deactivated (same as when C<0> is specified).
636		687
637	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	688	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
638		689
639	=item $json_text = $json->encode ($perl_scalar)	690	=item $json_text = $json->encode ($perl_scalar)
640		691
641	Converts the given Perl data structure (a simple scalar or a reference	692	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	693	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		694
648	=item $perl_scalar = $json->decode ($json_text)	695	=item $perl_scalar = $json->decode ($json_text)
649		696
650	The opposite of C<encode>: expects a JSON text and tries to parse it,	697	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.	698	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		699
657	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	700	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
658		701
659	This works like the C<decode> method, but instead of raising an exception	702	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	703	when there is trailing garbage after the first JSON object, it will
661	silently stop parsing there and return the number of characters consumed	704	silently stop parsing there and return the number of characters consumed
662	so far.	705	so far.
663		706
664	This is useful if your JSON texts are not delimited by an outer protocol	707	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.	708	and you need to know where the JSON text ends.
667		709
668	JSON::XS->new->decode_prefix ("[1] the tail")	710	JSON::XS->new->decode_prefix ("[1] the tail")
669	=> ([], 3)	711	=> ([1], 3)
670		712
671	=back	713	=back
		714
		715
		716	=head1 INCREMENTAL PARSING
		717
		718	In some cases, there is the need for incremental parsing of JSON
		719	texts. While this module always has to keep both JSON text and resulting
		720	Perl data structure in memory at one time, it does allow you to parse a
		721	JSON stream incrementally. It does so by accumulating text until it has
		722	a full JSON object, which it then can decode. This process is similar to
		723	using C<decode_prefix> to see if a full JSON object is available, but
		724	is much more efficient (and can be implemented with a minimum of method
		725	calls).
		726
		727	JSON::XS will only attempt to parse the JSON text once it is sure it
		728	has enough text to get a decisive result, using a very simple but
		729	truly incremental parser. This means that it sometimes won't stop as
		730	early as the full parser, for example, it doesn't detect mismatched
		731	parentheses. The only thing it guarantees is that it starts decoding as
		732	soon as a syntactically valid JSON text has been seen. This means you need
		733	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		734	parsing in the presence if syntax errors.
		735
		736	The following methods implement this incremental parser.
		737
		738	=over
		739
		740	=item [void, scalar or list context] = $json->incr_parse ([$string])
		741
		742	This is the central parsing function. It can both append new text and
		743	extract objects from the stream accumulated so far (both of these
		744	functions are optional).
		745
		746	If C<$string> is given, then this string is appended to the already
		747	existing JSON fragment stored in the C<$json> object.
		748
		749	After that, if the function is called in void context, it will simply
		750	return without doing anything further. This can be used to add more text
		751	in as many chunks as you want.
		752
		753	If the method is called in scalar context, then it will try to extract
		754	exactly I<one> JSON object. If that is successful, it will return this
		755	object, otherwise it will return C<undef>. If there is a parse error,
		756	this method will croak just as C<decode> would do (one can then use
		757	C<incr_skip> to skip the erroneous part). This is the most common way of
		758	using the method.
		759
		760	And finally, in list context, it will try to extract as many objects
		761	from the stream as it can find and return them, or the empty list
		762	otherwise. For this to work, there must be no separators (other than
		763	whitespace) between the JSON objects or arrays, instead they must be
		764	concatenated back-to-back. If an error occurs, an exception will be
		765	raised as in the scalar context case. Note that in this case, any
		766	previously-parsed JSON texts will be lost.
		767
		768	Example: Parse some JSON arrays/objects in a given string and return
		769	them.
		770
		771	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		772
		773	=item $lvalue_string = $json->incr_text
		774
		775	This method returns the currently stored JSON fragment as an lvalue, that
		776	is, you can manipulate it. This I<only> works when a preceding call to
		777	C<incr_parse> in I<scalar context> successfully returned an object. Under
		778	all other circumstances you must not call this function (I mean it.
		779	although in simple tests it might actually work, it I<will> fail under
		780	real world conditions). As a special exception, you can also call this
		781	method before having parsed anything.
		782
		783	That means you can only use this function to look at or manipulate text
		784	before or after complete JSON objects, not while the parser is in the
		785	middle of parsing a JSON object.
		786
		787	This function is useful in two cases: a) finding the trailing text after a
		788	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		789	(such as commas).
		790
		791	=item $json->incr_skip
		792
		793	This will reset the state of the incremental parser and will remove
		794	the parsed text from the input buffer so far. This is useful after
		795	C<incr_parse> died, in which case the input buffer and incremental parser
		796	state is left unchanged, to skip the text parsed so far and to reset the
		797	parse state.
		798
		799	The difference to C<incr_reset> is that only text until the parse error
		800	occurred is removed.
		801
		802	=item $json->incr_reset
		803
		804	This completely resets the incremental parser, that is, after this call,
		805	it will be as if the parser had never parsed anything.
		806
		807	This is useful if you want to repeatedly parse JSON objects and want to
		808	ignore any trailing data, which means you have to reset the parser after
		809	each successful decode.
		810
		811	=back
		812
		813	=head2 LIMITATIONS
		814
		815	The incremental parser is a non-exact parser: it works by gathering as
		816	much text as possible that I<could> be a valid JSON text, followed by
		817	trying to decode it.
		818
		819	That means it sometimes needs to read more data than strictly necessary to
		820	diagnose an invalid JSON text. For example, after parsing the following
		821	fragment, the parser I<could> stop with an error, as this fragment
		822	I<cannot> be the beginning of a valid JSON text:
		823
		824	[,
		825
		826	In reality, hopwever, the parser might continue to read data until a
		827	length limit is exceeded or it finds a closing bracket.
		828
		829	=head2 EXAMPLES
		830
		831	Some examples will make all this clearer. First, a simple example that
		832	works similarly to C<decode_prefix>: We want to decode the JSON object at
		833	the start of a string and identify the portion after the JSON object:
		834
		835	my $text = "[1,2,3] hello";
		836
		837	my $json = new JSON::XS;
		838
		839	my $obj = $json->incr_parse ($text)
		840	or die "expected JSON object or array at beginning of string";
		841
		842	my $tail = $json->incr_text;
		843	# $tail now contains " hello"
		844
		845	Easy, isn't it?
		846
		847	Now for a more complicated example: Imagine a hypothetical protocol where
		848	you read some requests from a TCP stream, and each request is a JSON
		849	array, without any separation between them (in fact, it is often useful to
		850	use newlines as "separators", as these get interpreted as whitespace at
		851	the start of the JSON text, which makes it possible to test said protocol
		852	with C<telnet>...).
		853
		854	Here is how you'd do it (it is trivial to write this in an event-based
		855	manner):
		856
		857	my $json = new JSON::XS;
		858
		859	# read some data from the socket
		860	while (sysread $socket, my $buf, 4096) {
		861
		862	# split and decode as many requests as possible
		863	for my $request ($json->incr_parse ($buf)) {
		864	# act on the $request
		865	}
		866	}
		867
		868	Another complicated example: Assume you have a string with JSON objects
		869	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		870	[3]>). To parse them, we have to skip the commas between the JSON texts,
		871	and here is where the lvalue-ness of C<incr_text> comes in useful:
		872
		873	my $text = "[1],[2], [3]";
		874	my $json = new JSON::XS;
		875
		876	# void context, so no parsing done
		877	$json->incr_parse ($text);
		878
		879	# now extract as many objects as possible. note the
		880	# use of scalar context so incr_text can be called.
		881	while (my $obj = $json->incr_parse) {
		882	# do something with $obj
		883
		884	# now skip the optional comma
		885	$json->incr_text =~ s/^ \s* , //x;
		886	}
		887
		888	Now lets go for a very complex example: Assume that you have a gigantic
		889	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		890	but you cannot load it into memory fully (this has actually happened in
		891	the real world :).
		892
		893	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		894	can still help you: You implement a (very simple) array parser and let
		895	JSON decode the array elements, which are all full JSON objects on their
		896	own (this wouldn't work if the array elements could be JSON numbers, for
		897	example):
		898
		899	my $json = new JSON::XS;
		900
		901	# open the monster
		902	open my $fh, "<bigfile.json"
		903	or die "bigfile: $!";
		904
		905	# first parse the initial "["
		906	for (;;) {
		907	sysread $fh, my $buf, 65536
		908	or die "read error: $!";
		909	$json->incr_parse ($buf); # void context, so no parsing
		910
		911	# Exit the loop once we found and removed(!) the initial "[".
		912	# In essence, we are (ab-)using the $json object as a simple scalar
		913	# we append data to.
		914	last if $json->incr_text =~ s/^ \s* \[ //x;
		915	}
		916
		917	# now we have the skipped the initial "[", so continue
		918	# parsing all the elements.
		919	for (;;) {
		920	# in this loop we read data until we got a single JSON object
		921	for (;;) {
		922	if (my $obj = $json->incr_parse) {
		923	# do something with $obj
		924	last;
		925	}
		926
		927	# add more data
		928	sysread $fh, my $buf, 65536
		929	or die "read error: $!";
		930	$json->incr_parse ($buf); # void context, so no parsing
		931	}
		932
		933	# in this loop we read data until we either found and parsed the
		934	# separating "," between elements, or the final "]"
		935	for (;;) {
		936	# first skip whitespace
		937	$json->incr_text =~ s/^\s*//;
		938
		939	# if we find "]", we are done
		940	if ($json->incr_text =~ s/^\]//) {
		941	print "finished.\n";
		942	exit;
		943	}
		944
		945	# if we find ",", we can continue with the next element
		946	if ($json->incr_text =~ s/^,//) {
		947	last;
		948	}
		949
		950	# if we find anything else, we have a parse error!
		951	if (length $json->incr_text) {
		952	die "parse error near ", $json->incr_text;
		953	}
		954
		955	# else add more data
		956	sysread $fh, my $buf, 65536
		957	or die "read error: $!";
		958	$json->incr_parse ($buf); # void context, so no parsing
		959	}
		960
		961	This is a complex example, but most of the complexity comes from the fact
		962	that we are trying to be correct (bear with me if I am wrong, I never ran
		963	the above example :).
		964
672		965
673		966
674	=head1 MAPPING	967	=head1 MAPPING
675		968
676	This section describes how JSON::XS maps Perl values to JSON values and	969	This section describes how JSON::XS maps Perl values to JSON values and
…		…
683	refers to the abstract Perl language itself.	976	refers to the abstract Perl language itself.
684		977
685		978
686	=head2 JSON -> PERL	979	=head2 JSON -> PERL
687		980
688	=over 4	981	=over
689		982
690	=item object	983	=item object
691		984
692	A JSON object becomes a reference to a hash in Perl. No ordering of object	985	A JSON object becomes a reference to a hash in Perl. No ordering of object
693	keys is preserved (JSON does not preserve object key ordering itself).	986	keys is preserved (JSON does not preserve object key ordering itself).
…		…
706		999
707	A JSON number becomes either an integer, numeric (floating point) or	1000	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	1001	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	1002	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	1003	the conversion details, but an integer may take slightly less memory and
711	might represent more values exactly than (floating point) numbers.	1004	might represent more values exactly than floating point numbers.
712		1005
713	If the number consists of digits only, JSON::XS will try to represent	1006	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	1007	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	1008	a numeric (floating point) value if that is possible without loss of
716	precision. Otherwise it will preserve the number as a string value.	1009	precision. Otherwise it will preserve the number as a string value (in
		1010	which case you lose roundtripping ability, as the JSON number will be
		1011	re-encoded to a JSON string).
717		1012
718	Numbers containing a fractional or exponential part will always be	1013	Numbers containing a fractional or exponential part will always be
719	represented as numeric (floating point) values, possibly at a loss of	1014	represented as numeric (floating point) values, possibly at a loss of
720	precision.	1015	precision (in which case you might lose perfect roundtripping ability, but
		1016	the JSON number will still be re-encoded as a JSON number).
721		1017
722	This might create round-tripping problems as numbers might become strings,	1018	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.	1019	represent most decimal fractions exactly, and when converting from and to
		1020	floating point, JSON::XS only guarantees precision up to but not including
		1021	the least significant bit.
724		1022
725	=item true, false	1023	=item true, false
726		1024
727	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	1025	These JSON atoms become C<Types::Serialiser::true> and
728	respectively. They are overloaded to act almost exactly like the numbers	1026	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	1027	almost exactly like the numbers C<1> and C<0>. You can check whether
730	the C<JSON::XS::is_bool> function.	1028	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1029	function (after C<use Types::Serialier>, of course).
731		1030
732	=item null	1031	=item null
733		1032
734	A JSON null atom becomes C<undef> in Perl.	1033	A JSON null atom becomes C<undef> in Perl.
		1034
		1035	=item shell-style comments (C<< # I<text> >>)
		1036
		1037	As a nonstandard extension to the JSON syntax that is enabled by the
		1038	C<relaxed> setting, shell-style comments are allowed. They can start
		1039	anywhere outside strings and go till the end of the line.
		1040
		1041	=item tagged values (C<< (I<tag>)I<value> >>).
		1042
		1043	Another nonstandard extension to the JSON syntax, enabled with the
		1044	C<allow_tags> setting, are tagged values. In this implementation, the
		1045	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1046	I<value> must be a JSON array encoding optional constructor arguments.
		1047
		1048	See L<OBJECT SERIALISATION>, below, for details.
735		1049
736	=back	1050	=back
737		1051
738		1052
739	=head2 PERL -> JSON	1053	=head2 PERL -> JSON
740		1054
741	The mapping from Perl to JSON is slightly more difficult, as Perl is a	1055	The mapping from Perl to JSON is slightly more difficult, as Perl is a
742	truly typeless language, so we can only guess which JSON type is meant by	1056	truly typeless language, so we can only guess which JSON type is meant by
743	a Perl value.	1057	a Perl value.
744		1058
745	=over 4	1059	=over
746		1060
747	=item hash references	1061	=item hash references
748		1062
749	Perl hash references become JSON objects. As there is no inherent ordering	1063	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	1064	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	1065	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	1066	(determined by the I<canonical> flag), so the same datastructure will
753	optionally sort the hash keys (determined by the I<canonical> flag), so	1067	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	1068	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	1069	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		1070
759	=item array references	1071	=item array references
760		1072
761	Perl array references become JSON arrays.	1073	Perl array references become JSON arrays.
762		1074
763	=item other references	1075	=item other references
764		1076
765	Other unblessed references are generally not allowed and will cause an	1077	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	1078	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	1079	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		1080
		1081	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1082	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1083	and C<Types::Serialiser::true> to improve readability.
		1084
		1085	use Types::Serialiser;
770	encode_json [\0,JSON::XS::true] # yields [false,true]	1086	encode_json [\0, Types::Serialiser::true] # yields [false,true]
771		1087
772	=item JSON::XS::true, JSON::XS::false	1088	=item Types::Serialiser::true, Types::Serialiser::false
773		1089
774	These special values become JSON true and JSON false values,	1090	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.	1091	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1092	directly if you want.
776		1093
777	=item blessed objects	1094	=item blessed objects
778		1095
779	Blessed objects are not allowed. JSON::XS currently tries to encode their	1096	Blessed objects are not directly representable in JSON, but C<JSON::XS>
780	underlying representation (hash- or arrayref), but this behaviour might	1097	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
781	change in future versions.	1098	below, for details.
782		1099
783	=item simple scalars	1100	=item simple scalars
784		1101
785	Simple Perl scalars (any scalar that is not a reference) are the most	1102	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	1103	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	1104	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:	1105	before encoding as JSON strings, and anything else as number value:
789		1106
790	# dump as number	1107	# dump as number
791	encode_json [2] # yields [2]	1108	encode_json [2] # yields [2]
792	encode_json [-3.0e17] # yields [-3e+17]	1109	encode_json [-3.0e17] # yields [-3e+17]
793	my $value = 5; encode_json [$value] # yields [5]	1110	my $value = 5; encode_json [$value] # yields [5]
…		…
811	my $x = "3"; # some variable containing a string	1128	my $x = "3"; # some variable containing a string
812	$x += 0; # numify it, ensuring it will be dumped as a number	1129	$x += 0; # numify it, ensuring it will be dumped as a number
813	$x *= 1; # same thing, the choice is yours.	1130	$x *= 1; # same thing, the choice is yours.
814		1131
815	You can not currently force the type in other, less obscure, ways. Tell me	1132	You can not currently force the type in other, less obscure, ways. Tell me
816	if you need this capability.	1133	if you need this capability (but don't forget to explain why it's needed
		1134	:).
		1135
		1136	Note that numerical precision has the same meaning as under Perl (so
		1137	binary to decimal conversion follows the same rules as in Perl, which
		1138	can differ to other languages). Also, your perl interpreter might expose
		1139	extensions to the floating point numbers of your platform, such as
		1140	infinities or NaN's - these cannot be represented in JSON, and it is an
		1141	error to pass those in.
817		1142
818	=back	1143	=back
819		1144
		1145	=head2 OBJECT SERIALISATION
820		1146
821	=head1 COMPARISON	1147	As JSON cannot directly represent Perl objects, you have to choose between
		1148	a pure JSON representation (without the ability to deserialise the object
		1149	automatically again), and a nonstandard extension to the JSON syntax,
		1150	tagged values.
822		1151
823	As already mentioned, this module was created because none of the existing	1152	=head3 SERIALISATION
824	JSON modules could be made to work correctly. First I will describe the
825	problems (or pleasures) I encountered with various existing JSON modules,
826	followed by some benchmark values. JSON::XS was designed not to suffer
827	from any of these problems or limitations.
828		1153
		1154	What happens when C<JSON::XS> encounters a Perl object depends on the
		1155	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
		1156	used in this order:
		1157
829	=over 4	1158	=over
830		1159
831	=item JSON 1.07	1160	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
832		1161
833	Slow (but very portable, as it is written in pure Perl).	1162	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1163	serialisation protocol to create a tagged JSON value, using a nonstandard
		1164	extension to the JSON syntax.
834		1165
835	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1166	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	1167	argument being the object to serialise, and the second argument being the
837	en-/decoding oneself, but Unicode escapes are not working properly).	1168	constant string C<JSON> to distinguish it from other serialisers.
838		1169
839	No round-tripping (strings get clobbered if they look like numbers, e.g.	1170	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	1171	more). These values and the paclkage/classname of the object will then be
841	decode into the number 2.	1172	encoded as a tagged JSON value in the following format:
842		1173
843	=item JSON::PC 0.01	1174	("classname")[FREEZE return values...]
844		1175
845	Very fast.	1176	e.g.:
846		1177
847	Undocumented/buggy Unicode handling.	1178	("URI")["http://www.google.com/"]
		1179	("MyDate")[2013,10,29]
		1180	("ImageData::JPEG")["Z3...VlCg=="]
848		1181
849	No round-tripping.	1182	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1183	objects C<type> and C<id> members to encode the object:
850		1184
851	Has problems handling many Perl values (e.g. regex results and other magic	1185	sub My::Object::FREEZE {
852	values will make it croak).	1186	my ($self, $serialiser) = @_;
853		1187
854	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1188	($self->{type}, $self->{id})
855	which is not a valid JSON text.	1189	}
856		1190
857	Unmaintained (maintainer unresponsive for many months, bugs are not	1191	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
858	getting fixed).
859		1192
860	=item JSON::Syck 0.21	1193	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1194	context. It must return a single scalar that can be directly encoded into
		1195	JSON. This scalar replaces the object in the JSON text.
861		1196
862	Very buggy (often crashes).	1197	For example, the following C<TO_JSON> method will convert all L<URI>
		1198	objects to JSON strings when serialised. The fatc that these values
		1199	originally were L<URI> objects is lost.
863		1200
864	Very inflexible (no human-readable format supported, format pretty much	1201	sub URI::TO_JSON {
865	undocumented. I need at least a format for easy reading by humans and a	1202	my ($uri) = @_;
866	single-line compact format for use in a protocol, and preferably a way to	1203	$uri->as_string
867	generate ASCII-only JSON texts).	1204	}
868		1205
869	Completely broken (and confusingly documented) Unicode handling (Unicode	1206	=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		1207
873	No round-tripping (simple cases work, but this depends on whether the scalar	1208	The object will be serialised as a JSON null value.
874	value was used in a numeric context or not).
875		1209
876	Dumping hashes may skip hash values depending on iterator state.	1210	=item 4. none of the above
877		1211
878	Unmaintained (maintainer unresponsive for many months, bugs are not	1212	If none of the settings are enabled or the respective methods are missing,
879	getting fixed).	1213	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		1214
905	=back	1215	=back
906		1216
		1217	=head3 DESERIALISATION
		1218
		1219	For deserialisation there are only two cases to consider: either
		1220	nonstandard tagging was used, in which case C<allow_tags> decides,
		1221	or objects cannot be automatically be deserialised, in which
		1222	case you can use postprocessing or the C<filter_json_object> or
		1223	C<filter_json_single_key_object> callbacks to get some real objects our of
		1224	your JSON.
		1225
		1226	This section only considers the tagged value case: I a tagged JSON object
		1227	is encountered during decoding and C<allow_tags> is disabled, a parse
		1228	error will result (as if tagged values were not part of the grammar).
		1229
		1230	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1231	of the package/classname used during serialisation (it will not attempt
		1232	to load the package as a Perl module). If there is no such method, the
		1233	decoding will fail with an error.
		1234
		1235	Otherwise, the C<THAW> method is invoked with the classname as first
		1236	argument, the constant string C<JSON> as second argument, and all the
		1237	values from the JSON array (the values originally returned by the
		1238	C<FREEZE> method) as remaining arguments.
		1239
		1240	The method must then return the object. While technically you can return
		1241	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1242	make that work in all cases, so better return an actual blessed reference.
		1243
		1244	As an example, let's implement a C<THAW> function that regenerates the
		1245	C<My::Object> from the C<FREEZE> example earlier:
		1246
		1247	sub My::Object::THAW {
		1248	my ($class, $serialiser, $type, $id) = @_;
		1249
		1250	$class->new (type => $type, id => $id)
		1251	}
		1252
		1253
		1254	=head1 ENCODING/CODESET FLAG NOTES
		1255
		1256	The interested reader might have seen a number of flags that signify
		1257	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1258	some confusion on what these do, so here is a short comparison:
		1259
		1260	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1261	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1262	control whether C<encode> escapes character values outside their respective
		1263	codeset range. Neither of these flags conflict with each other, although
		1264	some combinations make less sense than others.
		1265
		1266	Care has been taken to make all flags symmetrical with respect to
		1267	C<encode> and C<decode>, that is, texts encoded with any combination of
		1268	these flag values will be correctly decoded when the same flags are used
		1269	- in general, if you use different flag settings while encoding vs. when
		1270	decoding you likely have a bug somewhere.
		1271
		1272	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1273	simply an abstract set of character-codepoint pairs, while an encoding
		1274	takes those codepoint numbers and I<encodes> them, in our case into
		1275	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1276	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1277	the same time, which can be confusing.
		1278
		1279	=over
		1280
		1281	=item C<utf8> flag disabled
		1282
		1283	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1284	and expect Unicode strings, that is, characters with high ordinal Unicode
		1285	values (> 255) will be encoded as such characters, and likewise such
		1286	characters are decoded as-is, no changes to them will be done, except
		1287	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1288	respectively (to Perl, these are the same thing in strings unless you do
		1289	funny/weird/dumb stuff).
		1290
		1291	This is useful when you want to do the encoding yourself (e.g. when you
		1292	want to have UTF-16 encoded JSON texts) or when some other layer does
		1293	the encoding for you (for example, when printing to a terminal using a
		1294	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1295	to UTF-8 encode your data first and have Perl encode it another time).
		1296
		1297	=item C<utf8> flag enabled
		1298
		1299	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1300	characters using the corresponding UTF-8 multi-byte sequence, and will
		1301	expect your input strings to be encoded as UTF-8, that is, no "character"
		1302	of the input string must have any value > 255, as UTF-8 does not allow
		1303	that.
		1304
		1305	The C<utf8> flag therefore switches between two modes: disabled means you
		1306	will get a Unicode string in Perl, enabled means you get a UTF-8 encoded
		1307	octet/binary string in Perl.
		1308
		1309	=item C<latin1> or C<ascii> flags enabled
		1310
		1311	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1312	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1313	characters as specified by the C<utf8> flag.
		1314
		1315	If C<utf8> is disabled, then the result is also correctly encoded in those
		1316	character sets (as both are proper subsets of Unicode, meaning that a
		1317	Unicode string with all character values < 256 is the same thing as a
		1318	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1319	the same thing as an ASCII string in Perl).
		1320
		1321	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1322	regardless of these flags, just some more characters will be escaped using
		1323	C<\uXXXX> then before.
		1324
		1325	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1326	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1327	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1328	a subset of Unicode), while ASCII is.
		1329
		1330	Surprisingly, C<decode> will ignore these flags and so treat all input
		1331	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1332	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1333	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1334
		1335	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1336	they only govern when the JSON output engine escapes a character or not.
		1337
		1338	The main use for C<latin1> is to relatively efficiently store binary data
		1339	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1340
		1341	The main use for C<ascii> is to force the output to not contain characters
		1342	with values > 127, which means you can interpret the resulting string
		1343	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1344	8-bit-encoding, and still get the same data structure back. This is useful
		1345	when your channel for JSON transfer is not 8-bit clean or the encoding
		1346	might be mangled in between (e.g. in mail), and works because ASCII is a
		1347	proper subset of most 8-bit and multibyte encodings in use in the world.
		1348
		1349	=back
		1350
		1351
		1352	=head2 JSON and ECMAscript
		1353
		1354	JSON syntax is based on how literals are represented in javascript (the
		1355	not-standardised predecessor of ECMAscript) which is presumably why it is
		1356	called "JavaScript Object Notation".
		1357
		1358	However, JSON is not a subset (and also not a superset of course) of
		1359	ECMAscript (the standard) or javascript (whatever browsers actually
		1360	implement).
		1361
		1362	If you want to use javascript's C<eval> function to "parse" JSON, you
		1363	might run into parse errors for valid JSON texts, or the resulting data
		1364	structure might not be queryable:
		1365
		1366	One of the problems is that U+2028 and U+2029 are valid characters inside
		1367	JSON strings, but are not allowed in ECMAscript string literals, so the
		1368	following Perl fragment will not output something that can be guaranteed
		1369	to be parsable by javascript's C<eval>:
		1370
		1371	use JSON::XS;
		1372
		1373	print encode_json [chr 0x2028];
		1374
		1375	The right fix for this is to use a proper JSON parser in your javascript
		1376	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1377	F<json2.js> parser).
		1378
		1379	If this is not an option, you can, as a stop-gap measure, simply encode to
		1380	ASCII-only JSON:
		1381
		1382	use JSON::XS;
		1383
		1384	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1385
		1386	Note that this will enlarge the resulting JSON text quite a bit if you
		1387	have many non-ASCII characters. You might be tempted to run some regexes
		1388	to only escape U+2028 and U+2029, e.g.:
		1389
		1390	# DO NOT USE THIS!
		1391	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1392	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1393	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1394	print $json;
		1395
		1396	Note that I<this is a bad idea>: the above only works for U+2028 and
		1397	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1398	javascript implementations, however, have issues with other characters as
		1399	well - using C<eval> naively simply I<will> cause problems.
		1400
		1401	Another problem is that some javascript implementations reserve
		1402	some property names for their own purposes (which probably makes
		1403	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1404	C<__proto__> property name for its own purposes.
		1405
		1406	If that is a problem, you could parse try to filter the resulting JSON
		1407	output for these property strings, e.g.:
		1408
		1409	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1410
		1411	This works because C<__proto__> is not valid outside of strings, so every
		1412	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1413
		1414	If you know of other incompatibilities, please let me know.
		1415
907		1416
908	=head2 JSON and YAML	1417	=head2 JSON and YAML
909		1418
910	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1419	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	1420	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.	1421	so let me state it clearly: I<in general, there is no way to configure
		1422	JSON::XS to output a data structure as valid YAML> that works in all
		1423	cases.
913		1424
914	If you really must use JSON::XS to generate YAML, you should use this	1425	If you really must use JSON::XS to generate YAML, you should use this
915	algorithm (subject to change in future versions):	1426	algorithm (subject to change in future versions):
916		1427
917	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1428	my $to_yaml = JSON::XS->new->utf8->space_after (1);
918	my $yaml = $to_yaml->encode ($ref) . "\n";	1429	my $yaml = $to_yaml->encode ($ref) . "\n";
919		1430
920	This will usually generate JSON texts that also parse as valid	1431	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	1432	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	1433	lengths that JSON doesn't have and also has different and incompatible
		1434	unicode character escape syntax, so you should make sure that your hash
923	keys are noticeably shorter than the 1024 characters YAML allows.	1435	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1436	and that you do not have characters with codepoint values outside the
		1437	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1438	sequences in strings (which JSON::XS does not I<currently> generate, but
		1439	other JSON generators might).
924		1440
925	There might be other incompatibilities that I am not aware of. In general	1441	There might be other incompatibilities that I am not aware of (or the YAML
		1442	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,	1443	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	1444	versa, or try to parse JSON with a YAML parser or vice versa: chances are
928	that you will run into severe interoperability problems.	1445	high that you will run into severe interoperability problems when you
		1446	least expect it.
		1447
		1448	=over
		1449
		1450	=item (*)
		1451
		1452	I have been pressured multiple times by Brian Ingerson (one of the
		1453	authors of the YAML specification) to remove this paragraph, despite him
		1454	acknowledging that the actual incompatibilities exist. As I was personally
		1455	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1456	educate people about these issues, so others do not run into the same
		1457	problem again and again. After this, Brian called me a (quote)I<complete
		1458	and worthless idiot>(unquote).
		1459
		1460	In my opinion, instead of pressuring and insulting people who actually
		1461	clarify issues with YAML and the wrong statements of some of its
		1462	proponents, I would kindly suggest reading the JSON spec (which is not
		1463	that difficult or long) and finally make YAML compatible to it, and
		1464	educating users about the changes, instead of spreading lies about the
		1465	real compatibility for many I<years> and trying to silence people who
		1466	point out that it isn't true.
		1467
		1468	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1469	though the incompatibilities have been documented (and are known to Brian)
		1470	for many years and the spec makes explicit claims that YAML is a superset
		1471	of JSON. It would be so easy to fix, but apparently, bullying people and
		1472	corrupting userdata is so much easier.
		1473
		1474	=back
929		1475
930		1476
931	=head2 SPEED	1477	=head2 SPEED
932		1478
933	It seems that JSON::XS is surprisingly fast, as shown in the following	1479	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	1480	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	1481	in the JSON::XS distribution, to make it easy to compare on your own
936	system.	1482	system.
937		1483
938	First comes a comparison between various modules using a very short	1484	First comes a comparison between various modules using
939	single-line JSON string:	1485	a very short single-line JSON string (also available at
		1486	L<http://dist.schmorp.de/misc/json/short.json>).
940		1487
941	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1488	{"method": "handleMessage", "params": ["user1",
942	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1489	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1490	1, 0]}
943		1491
944	It shows the number of encodes/decodes per second (JSON::XS uses	1492	It shows the number of encodes/decodes per second (JSON::XS uses
945	the functional interface, while JSON::XS/2 uses the OO interface	1493	the functional interface, while JSON::XS/2 uses the OO interface
946	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1494	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
947	shrink). Higher is better:	1495	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1496	uses the from_json method). Higher is better:
948		1497
949	module | encode | decode |	1498	module | encode | decode |
950	-----------|------------|------------|	1499	--------------|------------|------------|
951	JSON 1.x | 4990.842 | 4088.813 |	1500	JSON::DWIW/DS | 86302.551 | 102300.098 |
952	JSON::DWIW | 51653.990 | 71575.154 |	1501	JSON::DWIW/FJ | 86302.551 | 75983.768 |
953	JSON::PC | 65948.176 | 74631.744 |	1502	JSON::PP | 15827.562 | 6638.658 |
954	JSON::PP | 8931.652 | 3817.168 |	1503	JSON::Syck | 63358.066 | 47662.545 |
955	JSON::Syck | 24877.248 | 27776.848 |	1504	JSON::XS | 511500.488 | 511500.488 |
956	JSON::XS | 388361.481 | 227951.304 |	1505	JSON::XS/2 | 291271.111 | 388361.481 |
957	JSON::XS/2 | 227951.304 | 218453.333 |	1506	JSON::XS/3 | 361577.931 | 361577.931 |
958	JSON::XS/3 | 338250.323 | 218453.333 |	1507	Storable | 66788.280 | 265462.278 |
959	Storable | 16500.016 | 135300.129 |
960	-----------+------------+------------+	1508	--------------+------------+------------+
961		1509
962	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1510	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	1511	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	1512	faster than JSON's pure perl implementation. It also compares favourably
965	favourably to Storable for small amounts of data.	1513	to Storable for small amounts of data.
966		1514
967	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1515	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
968	search API (http://nanoref.com/yahooapis/mgPdGg):	1516	search API (L<http://dist.schmorp.de/misc/json/long.json>).
969		1517
970	module | encode | decode |	1518	module | encode | decode |
971	-----------|------------|------------|	1519	--------------|------------|------------|
972	JSON 1.x | 55.260 | 34.971 |	1520	JSON::DWIW/DS | 1647.927 | 2673.916 |
973	JSON::DWIW | 825.228 | 1082.513 |	1521	JSON::DWIW/FJ | 1630.249 | 2596.128 |
974	JSON::PC | 3571.444 | 2394.829 |
975	JSON::PP | 210.987 | 32.574 |	1522	JSON::PP | 400.640 | 62.311 |
976	JSON::Syck | 552.551 | 787.544 |	1523	JSON::Syck | 1481.040 | 1524.869 |
977	JSON::XS | 5780.463 | 4854.519 |	1524	JSON::XS | 20661.596 | 9541.183 |
978	JSON::XS/2 | 3869.998 | 4798.975 |	1525	JSON::XS/2 | 10683.403 | 9416.938 |
979	JSON::XS/3 | 5862.880 | 4798.975 |	1526	JSON::XS/3 | 20661.596 | 9400.054 |
980	Storable | 4445.002 | 5235.027 |	1527	Storable | 19765.806 | 10000.725 |
981	-----------+------------+------------+	1528	--------------+------------+------------+
982		1529
983	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1530	Again, JSON::XS leads by far (except for Storable which non-surprisingly
984	decodes faster).	1531	decodes a bit faster).
985		1532
986	On large strings containing lots of high Unicode characters, some modules	1533	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	1534	(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	1535	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	1536	to decode or encode properly, so it was impossible to prepare a fair
…		…
1010		1557
1011	Third, JSON::XS recurses using the C stack when decoding objects and	1558	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	1559	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	1560	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	1561	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	1562	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	1563	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	1564	has a smaller stack, you should adjust this setting accordingly with the
1018	C<max_depth> method.	1565	C<max_depth> method.
1019		1566
1020	And last but least, something else could bomb you that I forgot to think	1567	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,	1568	case, you get to keep the pieces. I am always open for hints, though...
1022	though...	1569
		1570	Also keep in mind that JSON::XS might leak contents of your Perl data
		1571	structures in its error messages, so when you serialise sensitive
		1572	information you might want to make sure that exceptions thrown by JSON::XS
		1573	will not end up in front of untrusted eyes.
1023		1574
1024	If you are using JSON::XS to return packets to consumption	1575	If you are using JSON::XS to return packets to consumption
1025	by JavaScript scripts in a browser you should have a look at	1576	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	1577	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	1578	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	1579	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	1580	it, as major browser developers care only for features, not about getting
1030	right).	1581	security right).
1031		1582
1032		1583
		1584	=head2 "OLD" VS. "NEW" JSON (RFC4627 VS. RFC7159)
		1585
		1586	JSON originally required JSON texts to represent an array or object -
		1587	scalar values were explicitly not allowed. This has changed, and versions
		1588	of JSON::XS beginning with C<4.0> reflect this by allowing scalar values
		1589	by default.
		1590
		1591	One reason why one might not want this is that this removes a fundamental
		1592	property of JSON texts, namely that they are self-delimited and
		1593	self-contained, or in other words, you could take any number of "old"
		1594	JSON texts and paste them together, and the result would be unambiguously
		1595	parseable:
		1596
		1597	[1,3]{"k":5}[][null] # four JSON texts, without doubt
		1598
		1599	By allowing scalars, this property is lost: in the following example, is
		1600	this one JSON text (the number 12) or two JSON texts (the numbers 1 and
		1601	2):
		1602
		1603	12 # could be 12, or 1 and 2
		1604
		1605	Another lost property of "old" JSON is that no lookahead is required to
		1606	know the end of a JSON text, i.e. the JSON text definitely ended at the
		1607	last C<]> or C<}> character, there was no need to read extra characters.
		1608
		1609	For example, a viable network protocol with "old" JSON was to simply
		1610	exchange JSON texts without delimiter. For "new" JSON, you have to use a
		1611	suitable delimiter (such as a newline) after every JSON text or ensure you
		1612	never encode/decode scalar values.
		1613
		1614	Most protocols do work by only transferring arrays or objects, and the
		1615	easiest way to avoid problems with the "new" JSON definition is to
		1616	explicitly disallow scalar values in your encoder and decoder:
		1617
		1618	$json_coder = JSON::XS->new->allow_nonref (0)
		1619
		1620	This is a somewhat unhappy situation, and the blame can fully be put on
		1621	JSON's inmventor, Douglas Crockford, who unilaterally changed the format
		1622	in 2006 without consulting the IETF, forcing the IETF to either fork the
		1623	format or go with it (as I was told, the IETF wasn't amused).
		1624
		1625
		1626	=head1 RELATIONSHIP WITH I-JSON
		1627
		1628	JSON is a somewhat sloppily-defined format - it carries around obvious
		1629	Javascript baggage, such as not really defining number range, probably
		1630	because Javascript only has one type of numbers: IEEE 64 bit floats
		1631	("binary64").
		1632
		1633	For this reaosn, RFC7493 defines "Internet JSON", which is a restricted
		1634	subset of JSON that is supposedly more interoperable on the internet.
		1635
		1636	While C<JSON::XS> does not offer specific support for I-JSON, it of course
		1637	accepts valid I-JSON and by default implements some of the limitations
		1638	of I-JSON, such as parsing numbers as perl numbers, which are usually a
		1639	superset of binary64 numbers.
		1640
		1641	To generate I-JSON, follow these rules:
		1642
		1643	=over
		1644
		1645	=item * always generate UTF-8
		1646
		1647	I-JSON must be encoded in UTF-8, the default for C<encode_json>.
		1648
		1649	=item * numbers should be within IEEE 754 binary64 range
		1650
		1651	Basically all existing perl installations use binary64 to represent
		1652	floating point numbers, so all you need to do is to avoid large integers.
		1653
		1654	=item * objects must not have duplicate keys
		1655
		1656	This is trivially done, as C<JSON::XS> does not allow duplicate keys.
		1657
		1658	=item * do not generate scalar JSON texts, use C<< ->allow_nonref (0) >>
		1659
		1660	I-JSON strongly requests you to only encode arrays and objects into JSON.
		1661
		1662	=item * times should be strings in ISO 8601 format
		1663
		1664	There are a myriad of modules on CPAN dealing with ISO 8601 - search for
		1665	C<ISO8601> on CPAN and use one.
		1666
		1667	=item * encode binary data as base64
		1668
		1669	While it's tempting to just dump binary data as a string (and let
		1670	C<JSON::XS> do the escaping), for I-JSON, it's I<recommended> to encode
		1671	binary data as base64.
		1672
		1673	=back
		1674
		1675	There are some other considerations - read RFC7493 for the details if
		1676	interested.
		1677
		1678
		1679	=head1 INTEROPERABILITY WITH OTHER MODULES
		1680
		1681	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1682	constants. That means that the JSON true and false values will be
		1683	comaptible to true and false values of other modules that do the same,
		1684	such as L<JSON::PP> and L<CBOR::XS>.
		1685
		1686
		1687	=head1 INTEROPERABILITY WITH OTHER JSON DECODERS
		1688
		1689	As long as you only serialise data that can be directly expressed in JSON,
		1690	C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs,
		1691	but C<JSON::XS> has found more bugs in the official JSON testsuite (1)
		1692	than the official JSON testsuite has found in C<JSON::XS> (0)).
		1693
		1694	When you have trouble decoding JSON generated by this module using other
		1695	decoders, then it is very likely that you have an encoding mismatch or the
		1696	other decoder is broken.
		1697
		1698	When decoding, C<JSON::XS> is strict by default and will likely catch all
		1699	errors. There are currently two settings that change this: C<relaxed>
		1700	makes C<JSON::XS> accept (but not generate) some non-standard extensions,
		1701	and C<allow_tags> will allow you to encode and decode Perl objects, at the
		1702	cost of not outputting valid JSON anymore.
		1703
		1704	=head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
		1705
		1706	When you use C<allow_tags> to use the extended (and also nonstandard and
		1707	invalid) JSON syntax for serialised objects, and you still want to decode
		1708	the generated When you want to serialise objects, you can run a regex
		1709	to replace the tagged syntax by standard JSON arrays (it only works for
		1710	"normal" package names without comma, newlines or single colons). First,
		1711	the readable Perl version:
		1712
		1713	# if your FREEZE methods return no values, you need this replace first:
		1714	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
		1715
		1716	# this works for non-empty constructor arg lists:
		1717	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
		1718
		1719	And here is a less readable version that is easy to adapt to other
		1720	languages:
		1721
		1722	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
		1723
		1724	Here is an ECMAScript version (same regex):
		1725
		1726	json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
		1727
		1728	Since this syntax converts to standard JSON arrays, it might be hard to
		1729	distinguish serialised objects from normal arrays. You can prepend a
		1730	"magic number" as first array element to reduce chances of a collision:
		1731
		1732	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
		1733
		1734	And after decoding the JSON text, you could walk the data
		1735	structure looking for arrays with a first element of
		1736	C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>.
		1737
		1738	The same approach can be used to create the tagged format with another
		1739	encoder. First, you create an array with the magic string as first member,
		1740	the classname as second, and constructor arguments last, encode it as part
		1741	of your JSON structure, and then:
		1742
		1743	$json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
		1744
		1745	Again, this has some limitations - the magic string must not be encoded
		1746	with character escapes, and the constructor arguments must be non-empty.
		1747
		1748
1033	=head1 THREADS	1749	=head1 (I-)THREADS
1034		1750
1035	This module is I<not> guaranteed to be thread safe and there are no	1751	This module is I<not> guaranteed to be ithread (or MULTIPLICITY-) safe
1036	plans to change this until Perl gets thread support (as opposed to the	1752	and there are no plans to change this. Note that perl's builtin so-called
1037	horribly slow so-called "threads" which are simply slow and bloated	1753	threads/ithreads are officially deprecated and should not be used.
1038	process simulations - use fork, its I<much> faster, cheaper, better).
1039		1754
1040	(It might actually work, but you have been warned).	1755
		1756	=head1 THE PERILS OF SETLOCALE
		1757
		1758	Sometimes people avoid the Perl locale support and directly call the
		1759	system's setlocale function with C<LC_ALL>.
		1760
		1761	This breaks both perl and modules such as JSON::XS, as stringification of
		1762	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1763	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1764	perl to stringify numbers).
		1765
		1766	The solution is simple: don't call C<setlocale>, or use it for only those
		1767	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1768
		1769	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1770	actually needs it (avoiding stringification of numbers), and restore it
		1771	afterwards.
		1772
		1773
		1774	=head1 SOME HISTORY
		1775
		1776	At the time this module was created there already were a number of JSON
		1777	modules available on CPAN, so what was the reason to write yet another
		1778	JSON module? While it seems there are many JSON modules, none of them
		1779	correctly handled all corner cases, and in most cases their maintainers
		1780	are unresponsive, gone missing, or not listening to bug reports for other
		1781	reasons.
		1782
		1783	Beginning with version 2.0 of the JSON module, when both JSON and
		1784	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		1785	overridden) with no overhead due to emulation (by inheriting constructor
		1786	and methods). If JSON::XS is not available, it will fall back to the
		1787	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		1788	gives you a portable JSON API that can be fast when you need it and
		1789	doesn't require a C compiler when that is a problem.
		1790
		1791	Somewhere around version 3, this module was forked into
		1792	C<Cpanel::JSON::XS>, because its maintainer had serious trouble
		1793	understanding JSON and insisted on a fork with many bugs "fixed" that
		1794	weren't actually bugs, while spreading FUD about this module without
		1795	actually giving any details on his accusations. You be the judge, but
		1796	in my personal opinion, if you want quality, you will stay away from
		1797	dangerous forks like that.
1041		1798
1042		1799
1043	=head1 BUGS	1800	=head1 BUGS
1044		1801
1045	While the goal of this module is to be correct, that unfortunately does	1802	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	1803	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	1804	keep reporting bugs they will be fixed swiftly, though.
1048	will be fixed swiftly, though.
1049		1805
1050	Please refrain from using rt.cpan.org or any other bug reporting	1806	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.	1807	service. I put the contact address into my modules for a reason.
1052		1808
1053	=cut	1809	=cut
1054		1810
1055	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1811	BEGIN {
1056	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };	1812	*true = \$Types::Serialiser::true;
		1813	*true = \&Types::Serialiser::true;
		1814	*false = \$Types::Serialiser::false;
		1815	*false = \&Types::Serialiser::false;
		1816	*is_bool = \&Types::Serialiser::is_bool;
1057		1817
1058	sub true() { $true }	1818	*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	}	1819	}
1065		1820
1066	XSLoader::load "JSON::XS", $VERSION;	1821	XSLoader::load "JSON::XS", $VERSION;
1067		1822
1068	package JSON::XS::Boolean;	1823	=head1 SEE ALSO
1069		1824
1070	use overload	1825	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		1826
1078	=head1 AUTHOR	1827	=head1 AUTHOR
1079		1828
1080	Marc Lehmann <schmorp@schmorp.de>	1829	Marc Lehmann <schmorp@schmorp.de>
1081	http://home.schmorp.de/	1830	http://home.schmorp.de/
1082		1831
1083	=cut	1832	=cut
1084		1833
		1834	1
		1835

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