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Revision 1.84 by root, Wed Mar 19 02:52:15 2008 UTC vs.
Revision 1.176 by root, Tue Oct 27 18:05:58 2020 UTC

		1	=head1 NAME
		2
		3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
1	=encoding utf-8	5	=encoding utf-8
2
3	=head1 NAME
4
5	JSON::XS - JSON serialising/deserialising, done correctly and fast
6		6
7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ	7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)	8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
9		9
10	=head1 SYNOPSIS	10	=head1 SYNOPSIS
…		…
35		35
36	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
37	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
38	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
39		39
40	Beginning with version 2.0 of the JSON module, when both JSON and
41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
42	overriden) with no overhead due to emulation (by inheritign constructor
43	and methods). If JSON::XS is not available, it will fall back to the
44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
45	gives you a portable JSON API that can be fast when you need and doesn't
46	require a C compiler when that is a problem.
47
48	As this is the n-th-something JSON module on CPAN, what was the reason
49	to write yet another JSON module? While it seems there are many JSON
50	modules, none of them correctly handle all corner cases, and in most cases
51	their maintainers are unresponsive, gone missing, or not listening to bug
52	reports for other reasons.
53
54	See COMPARISON, below, for a comparison to some other JSON modules.
55
56	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	40	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
57	vice versa.	41	vice versa.
58		42
59	=head2 FEATURES	43	=head2 FEATURES
60		44
61	=over 4	45	=over
62		46
63	=item * correct Unicode handling	47	=item * correct Unicode handling
64		48
65	This module knows how to handle Unicode, documents how and when it does	49	This module knows how to handle Unicode, documents how and when it does
66	so, and even documents what "correct" means.	50	so, and even documents what "correct" means.
67		51
68	=item * round-trip integrity	52	=item * round-trip integrity
69		53
70	When you serialise a perl data structure using only datatypes supported	54	When you serialise a perl data structure using only data types supported
71	by JSON, the deserialised data structure is identical on the Perl level.	55	by JSON and Perl, the deserialised data structure is identical on the Perl
72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	56	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
73	like a number). There minor I<are> exceptions to this, read the MAPPING	57	it looks like a number). There I<are> minor exceptions to this, read the
74	section below to learn about those.	58	MAPPING section below to learn about those.
75		59
76	=item * strict checking of JSON correctness	60	=item * strict checking of JSON correctness
77		61
78	There is no guessing, no generating of illegal JSON texts by default,	62	There is no guessing, no generating of illegal JSON texts by default,
79	and only JSON is accepted as input by default (the latter is a security	63	and only JSON is accepted as input by default (the latter is a security
…		…
84	Compared to other JSON modules and other serialisers such as Storable,	68	Compared to other JSON modules and other serialisers such as Storable,
85	this module usually compares favourably in terms of speed, too.	69	this module usually compares favourably in terms of speed, too.
86		70
87	=item * simple to use	71	=item * simple to use
88		72
89	This module has both a simple functional interface as well as an objetc	73	This module has both a simple functional interface as well as an object
90	oriented interface interface.	74	oriented interface.
91		75
92	=item * reasonably versatile output formats	76	=item * reasonably versatile output formats
93		77
94	You can choose between the most compact guaranteed-single-line format	78	You can choose between the most compact guaranteed-single-line format
95	possible (nice for simple line-based protocols), a pure-ascii format	79	possible (nice for simple line-based protocols), a pure-ASCII format
96	(for when your transport is not 8-bit clean, still supports the whole	80	(for when your transport is not 8-bit clean, still supports the whole
97	Unicode range), or a pretty-printed format (for when you want to read that	81	Unicode range), or a pretty-printed format (for when you want to read that
98	stuff). Or you can combine those features in whatever way you like.	82	stuff). Or you can combine those features in whatever way you like.
99		83
100	=back	84	=back
101		85
102	=cut	86	=cut
103		87
104	package JSON::XS;	88	package JSON::XS;
105		89
106	use strict;	90	use common::sense;
107		91
108	our $VERSION = '2.01';	92	our $VERSION = '4.03';
109	our @ISA = qw(Exporter);	93	our @ISA = qw(Exporter);
110		94
111	our @EXPORT = qw(encode_json decode_json to_json from_json);	95	our @EXPORT = qw(encode_json decode_json);
112
113	sub to_json($) {
114	require Carp;
115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
116	}
117
118	sub from_json($) {
119	require Carp;
120	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
121	}
122		96
123	use Exporter;	97	use Exporter;
124	use XSLoader;	98	use XSLoader;
125		99
		100	use Types::Serialiser ();
		101
126	=head1 FUNCTIONAL INTERFACE	102	=head1 FUNCTIONAL INTERFACE
127		103
128	The following convenience methods are provided by this module. They are	104	The following convenience methods are provided by this module. They are
129	exported by default:	105	exported by default:
130		106
131	=over 4	107	=over
132		108
133	=item $json_text = encode_json $perl_scalar	109	=item $json_text = encode_json $perl_scalar
134		110
135	Converts the given Perl data structure to a UTF-8 encoded, binary string	111	Converts the given Perl data structure to a UTF-8 encoded, binary string
136	(that is, the string contains octets only). Croaks on error.	112	(that is, the string contains octets only). Croaks on error.
137		113
138	This function call is functionally identical to:	114	This function call is functionally identical to:
139		115
140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	116	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
141		117
142	except being faster.	118	Except being faster.
143		119
144	=item $perl_scalar = decode_json $json_text	120	=item $perl_scalar = decode_json $json_text
145		121
146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries	122	The opposite of C<encode_json>: expects a UTF-8 (binary) string and tries
147	to parse that as an UTF-8 encoded JSON text, returning the resulting	123	to parse that as a UTF-8 encoded JSON text, returning the resulting
148	reference. Croaks on error.	124	reference. Croaks on error.
149		125
150	This function call is functionally identical to:	126	This function call is functionally identical to:
151		127
152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	128	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
153		129
154	except being faster.	130	Except being faster.
155
156	=item $is_boolean = JSON::XS::is_bool $scalar
157
158	Returns true if the passed scalar represents either JSON::XS::true or
159	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
160	and are used to represent JSON C<true> and C<false> values in Perl.
161
162	See MAPPING, below, for more information on how JSON values are mapped to
163	Perl.
164		131
165	=back	132	=back
166		133
167		134
168	=head1 A FEW NOTES ON UNICODE AND PERL	135	=head1 A FEW NOTES ON UNICODE AND PERL
169		136
170	Since this often leads to confusion, here are a few very clear words on	137	Since this often leads to confusion, here are a few very clear words on
171	how Unicode works in Perl, modulo bugs.	138	how Unicode works in Perl, modulo bugs.
172		139
173	=over 4	140	=over
174		141
175	=item 1. Perl strings can store characters with ordinal values > 255.	142	=item 1. Perl strings can store characters with ordinal values > 255.
176		143
177	This enables you to store Unicode characters as single characters in a	144	This enables you to store Unicode characters as single characters in a
178	Perl string - very natural.	145	Perl string - very natural.
…		…
197		164
198	If you didn't know about that flag, just the better, pretend it doesn't	165	If you didn't know about that flag, just the better, pretend it doesn't
199	exist.	166	exist.
200		167
201	=item 4. A "Unicode String" is simply a string where each character can be	168	=item 4. A "Unicode String" is simply a string where each character can be
202	validly interpreted as a Unicode codepoint.	169	validly interpreted as a Unicode code point.
203		170
204	If you have UTF-8 encoded data, it is no longer a Unicode string, but a	171	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
205	Unicode string encoded in UTF-8, giving you a binary string.	172	Unicode string encoded in UTF-8, giving you a binary string.
206		173
207	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.	174	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
…		…
216	=head1 OBJECT-ORIENTED INTERFACE	183	=head1 OBJECT-ORIENTED INTERFACE
217		184
218	The object oriented interface lets you configure your own encoding or	185	The object oriented interface lets you configure your own encoding or
219	decoding style, within the limits of supported formats.	186	decoding style, within the limits of supported formats.
220		187
221	=over 4	188	=over
222		189
223	=item $json = new JSON::XS	190	=item $json = new JSON::XS
224		191
225	Creates a new JSON::XS object that can be used to de/encode JSON	192	Creates a new JSON::XS object that can be used to de/encode JSON
226	strings. All boolean flags described below are by default I<disabled>.	193	strings. All boolean flags described below are by default I<disabled>
		194	(with the exception of C<allow_nonref>, which defaults to I<enabled> since
		195	version C<4.0>).
227		196
228	The mutators for flags all return the JSON object again and thus calls can	197	The mutators for flags all return the JSON object again and thus calls can
229	be chained:	198	be chained:
230		199
231	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	200	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
…		…
245		214
246	If C<$enable> is false, then the C<encode> method will not escape Unicode	215	If C<$enable> is false, then the C<encode> method will not escape Unicode
247	characters unless required by the JSON syntax or other flags. This results	216	characters unless required by the JSON syntax or other flags. This results
248	in a faster and more compact format.	217	in a faster and more compact format.
249		218
		219	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		220	document.
		221
250	The main use for this flag is to produce JSON texts that can be	222	The main use for this flag is to produce JSON texts that can be
251	transmitted over a 7-bit channel, as the encoded JSON texts will not	223	transmitted over a 7-bit channel, as the encoded JSON texts will not
252	contain any 8 bit characters.	224	contain any 8 bit characters.
253		225
254	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	226	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
265	will not be affected in any way by this flag, as C<decode> by default	237	will not be affected in any way by this flag, as C<decode> by default
266	expects Unicode, which is a strict superset of latin1.	238	expects Unicode, which is a strict superset of latin1.
267		239
268	If C<$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
269	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.
270		245
271	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
272	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
273	size. The disadvantage is that the resulting JSON text is encoded	248	size. The disadvantage is that the resulting JSON text is encoded
274	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
…		…
283		258
284	=item $enabled = $json->get_utf8	259	=item $enabled = $json->get_utf8
285		260
286	If C<$enable> is true (or missing), then the C<encode> method will encode	261	If C<$enable> is true (or missing), then the C<encode> method will encode
287	the JSON result into UTF-8, as required by many protocols, while the	262	the JSON result into UTF-8, as required by many protocols, while the
288	C<decode> method expects to be handled an UTF-8-encoded string. Please	263	C<decode> method expects to be handed a UTF-8-encoded string. Please
289	note that UTF-8-encoded strings do not contain any characters outside the	264	note that UTF-8-encoded strings do not contain any characters outside the
290	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	265	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
291	versions, enabling this option might enable autodetection of the UTF-16	266	versions, enabling this option might enable autodetection of the UTF-16
292	and UTF-32 encoding families, as described in RFC4627.	267	and UTF-32 encoding families, as described in RFC4627.
293		268
294	If C<$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
295	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
296	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
297	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.
298		276
299	Example, output UTF-16BE-encoded JSON:	277	Example, output UTF-16BE-encoded JSON:
300		278
301	use Encode;	279	use Encode;
302	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	280	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
375		353
376	=item $enabled = $json->get_relaxed	354	=item $enabled = $json->get_relaxed
377		355
378	If C<$enable> is true (or missing), then C<decode> will accept some	356	If C<$enable> is true (or missing), then C<decode> will accept some
379	extensions to normal JSON syntax (see below). C<encode> will not be	357	extensions to normal JSON syntax (see below). C<encode> will not be
380	affected in anyway. I<Be aware that this option makes you accept invalid	358	affected in any way. I<Be aware that this option makes you accept invalid
381	JSON texts as if they were valid!>. I suggest only to use this option to	359	JSON texts as if they were valid!>. I suggest only to use this option to
382	parse application-specific files written by humans (configuration files,	360	parse application-specific files written by humans (configuration files,
383	resource files etc.)	361	resource files etc.)
384		362
385	If C<$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
386	valid JSON texts.	364	valid JSON texts.
387		365
388	Currently accepted extensions are:	366	Currently accepted extensions are:
389		367
390	=over 4	368	=over
391		369
392	=item * list items can have an end-comma	370	=item * list items can have an end-comma
393		371
394	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
395	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
…		…
414	[	392	[
415	1, # this comment not allowed in JSON	393	1, # this comment not allowed in JSON
416	# neither this one...	394	# neither this one...
417	]	395	]
418		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
419	=back	407	=back
420		408
421	=item $json = $json->canonical ([$enable])	409	=item $json = $json->canonical ([$enable])
422		410
423	=item $enabled = $json->get_canonical	411	=item $enabled = $json->get_canonical
…		…
425	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	413	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
426	by sorting their keys. This is adding a comparatively high overhead.	414	by sorting their keys. This is adding a comparatively high overhead.
427		415
428	If C<$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
429	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
430	of the same script).	418	of the same script, and can change even within the same run from 5.18
		419	onwards).
431		420
432	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
433	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,
434	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,
435	as key-value pairs have no inherent ordering in Perl.	424	as key-value pairs have no inherent ordering in Perl.
436		425
437	This setting has no effect when decoding JSON texts.	426	This setting has no effect when decoding JSON texts.
438		427
		428	This setting has currently no effect on tied hashes.
		429
439	=item $json = $json->allow_nonref ([$enable])	430	=item $json = $json->allow_nonref ([$enable])
440		431
441	=item $enabled = $json->get_allow_nonref	432	=item $enabled = $json->get_allow_nonref
		433
		434	Unlike other boolean options, this opotion is enabled by default beginning
		435	with version C<4.0>. See L<SECURITY CONSIDERATIONS> for the gory details.
442		436
443	If C<$enable> is true (or missing), then the C<encode> method can convert a	437	If C<$enable> is true (or missing), then the C<encode> method can convert a
444	non-reference into its corresponding string, number or null JSON value,	438	non-reference into its corresponding string, number or null JSON value,
445	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	439	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
446	values instead of croaking.	440	values instead of croaking.
…		…
448	If C<$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
449	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
450	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
451	JSON object or array.	445	JSON object or array.
452		446
453	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>,
454	resulting in an invalid JSON text:	448	resulting in an error:
455		449
456	JSON::XS->new->allow_nonref->encode ("Hello, World!")	450	JSON::XS->new->allow_nonref (0)->encode ("Hello, World!")
457	=> "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.
458		468
459	=item $json = $json->allow_blessed ([$enable])	469	=item $json = $json->allow_blessed ([$enable])
460		470
461	=item $enabled = $json->get_allow_blessed	471	=item $enabled = $json->get_allow_blessed
462		472
		473	See L<OBJECT SERIALISATION> for details.
		474
463	If C<$enable> is true (or missing), then the C<encode> method will not	475	If C<$enable> is true (or missing), then the C<encode> method will not
464	barf when it encounters a blessed reference. Instead, the value of the	476	barf when it encounters a blessed reference that it cannot convert
465	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>	477	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
466	disabled or no C<TO_JSON> method found) or a representation of the
467	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
468	encoded. Has no effect on C<decode>.
469		478
470	If C<$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
471	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>.
472		484
473	=item $json = $json->convert_blessed ([$enable])	485	=item $json = $json->convert_blessed ([$enable])
474		486
475	=item $enabled = $json->get_convert_blessed	487	=item $enabled = $json->get_convert_blessed
		488
		489	See L<OBJECT SERIALISATION> for details.
476		490
477	If C<$enable> is true (or missing), then C<encode>, upon encountering a	491	If C<$enable> is true (or missing), then C<encode>, upon encountering a
478	blessed object, will check for the availability of the C<TO_JSON> method	492	blessed object, will check for the availability of the C<TO_JSON> method
479	on the object's class. If found, it will be called in scalar context	493	on the object's class. If found, it will be called in scalar context and
480	and the resulting scalar will be encoded instead of the object. If no	494	the resulting scalar will be encoded instead of the object.
481	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
482	to do.
483		495
484	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	496	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
485	returns other blessed objects, those will be handled in the same	497	returns other blessed objects, those will be handled in the same
486	way. C<TO_JSON> must take care of not causing an endless recursion cycle	498	way. C<TO_JSON> must take care of not causing an endless recursion cycle
487	(== crash) in this case. The name of C<TO_JSON> was chosen because other	499	(== crash) in this case. The name of C<TO_JSON> was chosen because other
488	methods called by the Perl core (== not by the user of the object) are	500	methods called by the Perl core (== not by the user of the object) are
489	usually in upper case letters and to avoid collisions with any C<to_json>	501	usually in upper case letters and to avoid collisions with any C<to_json>
490	function or method.	502	function or method.
491		503
492	This setting does not yet influence C<decode> in any way, but in the	504	If C<$enable> is false (the default), then C<encode> will not consider
493	future, global hooks might get installed that influence C<decode> and are	505	this type of conversion.
494	enabled by this setting.
495		506
496	If C<$enable> is false, then the C<allow_blessed> setting will decide what	507	This setting has no effect on C<decode>.
497	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.
498		544
499	=item $json = $json->filter_json_object ([$coderef->($hashref)])	545	=item $json = $json->filter_json_object ([$coderef->($hashref)])
500		546
501	When C<$coderef> is specified, it will be called from C<decode> each	547	When C<$coderef> is specified, it will be called from C<decode> each
502	time it decodes a JSON object. The only argument is a reference to the	548	time it decodes a JSON object. The only argument is a reference to
503	newly-created hash. If the code references returns a single scalar (which	549	the newly-created hash. If the code reference returns a single scalar
504	need not be a reference), this value (i.e. a copy of that scalar to avoid	550	(which need not be a reference), this value (or rather a copy of it) is
505	aliasing) is inserted into the deserialised data structure. If it returns	551	inserted into the deserialised data structure. If it returns an empty
506	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the	552	list (NOTE: I<not> C<undef>, which is a valid scalar), the original
507	original deserialised hash will be inserted. This setting can slow down	553	deserialised hash will be inserted. This setting can slow down decoding
508	decoding considerably.	554	considerably.
509		555
510	When C<$coderef> is omitted or undefined, any existing callback will	556	When C<$coderef> is omitted or undefined, any existing callback will
511	be removed and C<decode> will not change the deserialised hash in any	557	be removed and C<decode> will not change the deserialised hash in any
512	way.	558	way.
513		559
…		…
603	=item $json = $json->max_depth ([$maximum_nesting_depth])	649	=item $json = $json->max_depth ([$maximum_nesting_depth])
604		650
605	=item $max_depth = $json->get_max_depth	651	=item $max_depth = $json->get_max_depth
606		652
607	Sets the maximum nesting level (default C<512>) accepted while encoding	653	Sets the maximum nesting level (default C<512>) accepted while encoding
608	or decoding. If the JSON text or Perl data structure has an equal or	654	or decoding. If a higher nesting level is detected in JSON text or a Perl
609	higher nesting level then this limit, then the encoder and decoder will	655	data structure, then the encoder and decoder will stop and croak at that
610	stop and croak at that point.	656	point.
611		657
612	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
613	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<[>
614	characters without their matching closing parenthesis crossed to reach a	660	characters without their matching closing parenthesis crossed to reach a
615	given character in a string.	661	given character in a string.
616		662
617	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
618	that the object is only a single hash/object or array.	664	that the object is only a single hash/object or array.
619		665
620	The argument to C<max_depth> will be rounded up to the next highest power
621	of two. If no argument is given, the highest possible setting will be	666	If no argument is given, the highest possible setting will be used, which
622	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.
623		672
624	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.
625		674
626	=item $json = $json->max_size ([$maximum_string_size])	675	=item $json = $json->max_size ([$maximum_string_size])
627		676
628	=item $max_size = $json->get_max_size	677	=item $max_size = $json->get_max_size
629		678
630	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
631	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>
632	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
633	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
634	effect on C<encode> (yet).	683	effect on C<encode> (yet).
635		684
636	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
637	power of two (so may be more than requested). If no argument is given, the	686	C<0> is specified).
638	limit check will be deactivated (same as when C<0> is specified).
639		687
640	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.
641		689
642	=item $json_text = $json->encode ($perl_scalar)	690	=item $json_text = $json->encode ($perl_scalar)
643		691
644	Converts the given Perl data structure (a simple scalar or a reference	692	Converts the given Perl value or data structure to its JSON
645	to a hash or array) to its JSON representation. Simple scalars will be	693	representation. Croaks on error.
646	converted into JSON string or number sequences, while references to arrays
647	become JSON arrays and references to hashes become JSON objects. Undefined
648	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
649	nor C<false> values will be generated.
650		694
651	=item $perl_scalar = $json->decode ($json_text)	695	=item $perl_scalar = $json->decode ($json_text)
652		696
653	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,
654	returning the resulting simple scalar or reference. Croaks on error.	698	returning the resulting simple scalar or reference. Croaks on error.
655
656	JSON numbers and strings become simple Perl scalars. JSON arrays become
657	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
658	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
659		699
660	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	700	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
661		701
662	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
663	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
664	silently stop parsing there and return the number of characters consumed	704	silently stop parsing there and return the number of characters consumed
665	so far.	705	so far.
666		706
667	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
668	(which is not the brightest thing to do in the first place) and you need
669	to know where the JSON text ends.	708	and you need to know where the JSON text ends.
670		709
671	JSON::XS->new->decode_prefix ("[1] the tail")	710	JSON::XS->new->decode_prefix ("[1] the tail")
672	=> ([], 3)	711	=> ([1], 3)
673		712
674	=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
675		965
676		966
677	=head1 MAPPING	967	=head1 MAPPING
678		968
679	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
…		…
686	refers to the abstract Perl language itself.	976	refers to the abstract Perl language itself.
687		977
688		978
689	=head2 JSON -> PERL	979	=head2 JSON -> PERL
690		980
691	=over 4	981	=over
692		982
693	=item object	983	=item object
694		984
695	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
696	keys is preserved (JSON does not preserve object key ordering itself).	986	keys is preserved (JSON does not preserve object key ordering itself).
…		…
716	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
717	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
718	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
719	precision. Otherwise it will preserve the number as a string value (in	1009	precision. Otherwise it will preserve the number as a string value (in
720	which case you lose roundtripping ability, as the JSON number will be	1010	which case you lose roundtripping ability, as the JSON number will be
721	re-encoded toa JSON string).	1011	re-encoded to a JSON string).
722		1012
723	Numbers containing a fractional or exponential part will always be	1013	Numbers containing a fractional or exponential part will always be
724	represented as numeric (floating point) values, possibly at a loss of	1014	represented as numeric (floating point) values, possibly at a loss of
725	precision (in which case you might lose perfect roundtripping ability, but	1015	precision (in which case you might lose perfect roundtripping ability, but
726	the JSON number will still be re-encoded as a JSON number).	1016	the JSON number will still be re-encoded as a JSON number).
727		1017
		1018	Note that precision is not accuracy - binary floating point values cannot
		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.
		1022
728	=item true, false	1023	=item true, false
729		1024
730	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	1025	These JSON atoms become C<Types::Serialiser::true> and
731	respectively. They are overloaded to act almost exactly like the numbers	1026	C<Types::Serialiser::false>, respectively. They are overloaded to act
732	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using	1027	almost exactly like the numbers C<1> and C<0>. You can check whether
733	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).
734		1030
735	=item null	1031	=item null
736		1032
737	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.
738		1049
739	=back	1050	=back
740		1051
741		1052
742	=head2 PERL -> JSON	1053	=head2 PERL -> JSON
743		1054
744	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
745	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
746	a Perl value.	1057	a Perl value.
747		1058
748	=over 4	1059	=over
749		1060
750	=item hash references	1061	=item hash references
751		1062
752	Perl hash references become JSON objects. As there is no inherent ordering	1063	Perl hash references become JSON objects. As there is no inherent
753	in hash keys (or JSON objects), they will usually be encoded in a	1064	ordering in hash keys (or JSON objects), they will usually be encoded
754	pseudo-random order that can change between runs of the same program but	1065	in a pseudo-random order. JSON::XS can optionally sort the hash keys
755	stays generally the same within a single run of a program. JSON::XS can	1066	(determined by the I<canonical> flag), so the same datastructure will
756	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
757	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,
758	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.
759	and is only rarely useful, e.g. when you want to compare some JSON text
760	against another for equality.
761		1070
762	=item array references	1071	=item array references
763		1072
764	Perl array references become JSON arrays.	1073	Perl array references become JSON arrays.
765		1074
766	=item other references	1075	=item other references
767		1076
768	Other unblessed references are generally not allowed and will cause an	1077	Other unblessed references are generally not allowed and will cause an
769	exception to be thrown, except for references to the integers C<0> and	1078	exception to be thrown, except for references to the integers C<0> and
770	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1079	C<1>, which get turned into C<false> and C<true> atoms in JSON.
771	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
772		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;
773	encode_json [\0,JSON::XS::true] # yields [false,true]	1086	encode_json [\0, Types::Serialiser::true] # yields [false,true]
774		1087
775	=item JSON::XS::true, JSON::XS::false	1088	=item Types::Serialiser::true, Types::Serialiser::false
776		1089
777	These special values become JSON true and JSON false values,	1090	These special values from the L<Types::Serialiser> module become JSON true
778	respectively. You can also use C<\1> and C<\0> directly if you want.	1091	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1092	directly if you want.
779		1093
780	=item blessed objects	1094	=item blessed objects
781		1095
782	Blessed objects are not directly representable in JSON. See the	1096	Blessed objects are not directly representable in JSON, but C<JSON::XS>
783	C<allow_blessed> and C<convert_blessed> methods on various options on	1097	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
784	how to deal with this: basically, you can choose between throwing an	1098	below, for details.
785	exception, encoding the reference as if it weren't blessed, or provide
786	your own serialiser method.
787		1099
788	=item simple scalars	1100	=item simple scalars
789		1101
790	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
791	difficult objects to encode: JSON::XS will encode undefined scalars as	1103	difficult objects to encode: JSON::XS will encode undefined scalars as
…		…
816	my $x = "3"; # some variable containing a string	1128	my $x = "3"; # some variable containing a string
817	$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
818	$x *= 1; # same thing, the choice is yours.	1130	$x *= 1; # same thing, the choice is yours.
819		1131
820	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
821	if you need this capability (but don't forget to explain why its needed	1133	if you need this capability (but don't forget to explain why it's needed
822	:).	1134	:).
823		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.
		1142
824	=back	1143	=back
		1144
		1145	=head2 OBJECT SERIALISATION
		1146
		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.
		1151
		1152	=head3 SERIALISATION
		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
		1158	=over
		1159
		1160	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
		1161
		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.
		1165
		1166	This works by invoking the C<FREEZE> method on the object, with the first
		1167	argument being the object to serialise, and the second argument being the
		1168	constant string C<JSON> to distinguish it from other serialisers.
		1169
		1170	The C<FREEZE> method can return any number of values (i.e. zero or
		1171	more). These values and the paclkage/classname of the object will then be
		1172	encoded as a tagged JSON value in the following format:
		1173
		1174	("classname")[FREEZE return values...]
		1175
		1176	e.g.:
		1177
		1178	("URI")["http://www.google.com/"]
		1179	("MyDate")[2013,10,29]
		1180	("ImageData::JPEG")["Z3...VlCg=="]
		1181
		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:
		1184
		1185	sub My::Object::FREEZE {
		1186	my ($self, $serialiser) = @_;
		1187
		1188	($self->{type}, $self->{id})
		1189	}
		1190
		1191	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
		1192
		1193	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1194	context. It must return a single scalar that can be directly encoded into
		1195	JSON. This scalar replaces the object in the JSON text.
		1196
		1197	For example, the following C<TO_JSON> method will convert all L<URI>
		1198	objects to JSON strings when serialised. The fatc that these values
		1199	originally were L<URI> objects is lost.
		1200
		1201	sub URI::TO_JSON {
		1202	my ($uri) = @_;
		1203	$uri->as_string
		1204	}
		1205
		1206	=item 3. C<allow_blessed> is enabled.
		1207
		1208	The object will be serialised as a JSON null value.
		1209
		1210	=item 4. none of the above
		1211
		1212	If none of the settings are enabled or the respective methods are missing,
		1213	C<JSON::XS> throws an exception.
		1214
		1215	=back
		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	}
825		1252
826		1253
827	=head1 ENCODING/CODESET FLAG NOTES	1254	=head1 ENCODING/CODESET FLAG NOTES
828		1255
829	The interested reader might have seen a number of flags that signify	1256	The interested reader might have seen a number of flags that signify
830	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be	1257	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
831	some confusion on what these do, so here is a short comparison:	1258	some confusion on what these do, so here is a short comparison:
832		1259
833	C<utf8> controls wether the JSON text created by C<encode> (and expected	1260	C<utf8> controls whether the JSON text created by C<encode> (and expected
834	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only	1261	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
835	control wether C<encode> escapes character values outside their respective	1262	control whether C<encode> escapes character values outside their respective
836	codeset range. Neither of these flags conflict with each other, although	1263	codeset range. Neither of these flags conflict with each other, although
837	some combinations make less sense than others.	1264	some combinations make less sense than others.
838		1265
839	Care has been taken to make all flags symmetrical with respect to	1266	Care has been taken to make all flags symmetrical with respect to
840	C<encode> and C<decode>, that is, texts encoded with any combination of	1267	C<encode> and C<decode>, that is, texts encoded with any combination of
…		…
847	takes those codepoint numbers and I<encodes> them, in our case into	1274	takes those codepoint numbers and I<encodes> them, in our case into
848	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,	1275	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
849	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at	1276	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
850	the same time, which can be confusing.	1277	the same time, which can be confusing.
851		1278
852	=over 4	1279	=over
853		1280
854	=item C<utf8> flag disabled	1281	=item C<utf8> flag disabled
855		1282
856	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate	1283	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
857	and expect Unicode strings, that is, characters with high ordinal Unicode	1284	and expect Unicode strings, that is, characters with high ordinal Unicode
858	values (> 255) will be encoded as such characters, and likewise such	1285	values (> 255) will be encoded as such characters, and likewise such
859	characters are decoded as-is, no canges to them will be done, except	1286	characters are decoded as-is, no changes to them will be done, except
860	"(re-)interpreting" them as Unicode codepoints or Unicode characters,	1287	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
861	respectively (to Perl, these are the same thing in strings unless you do	1288	respectively (to Perl, these are the same thing in strings unless you do
862	funny/weird/dumb stuff).	1289	funny/weird/dumb stuff).
863		1290
864	This is useful when you want to do the encoding yourself (e.g. when you	1291	This is useful when you want to do the encoding yourself (e.g. when you
…		…
874	expect your input strings to be encoded as UTF-8, that is, no "character"	1301	expect your input strings to be encoded as UTF-8, that is, no "character"
875	of the input string must have any value > 255, as UTF-8 does not allow	1302	of the input string must have any value > 255, as UTF-8 does not allow
876	that.	1303	that.
877		1304
878	The C<utf8> flag therefore switches between two modes: disabled means you	1305	The C<utf8> flag therefore switches between two modes: disabled means you
879	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded	1306	will get a Unicode string in Perl, enabled means you get a UTF-8 encoded
880	octet/binary string in Perl.	1307	octet/binary string in Perl.
881		1308
882	=item C<latin1> or C<ascii> flags enabled	1309	=item C<latin1> or C<ascii> flags enabled
883		1310
884	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters	1311	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
…		…
920	proper subset of most 8-bit and multibyte encodings in use in the world.	1347	proper subset of most 8-bit and multibyte encodings in use in the world.
921		1348
922	=back	1349	=back
923		1350
924		1351
925	=head1 COMPARISON	1352	=head2 JSON and ECMAscript
926		1353
927	As already mentioned, this module was created because none of the existing	1354	JSON syntax is based on how literals are represented in javascript (the
928	JSON modules could be made to work correctly. First I will describe the	1355	not-standardised predecessor of ECMAscript) which is presumably why it is
929	problems (or pleasures) I encountered with various existing JSON modules,	1356	called "JavaScript Object Notation".
930	followed by some benchmark values. JSON::XS was designed not to suffer
931	from any of these problems or limitations.
932		1357
933	=over 4	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).
934		1361
935	=item JSON 2.xx	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:
936		1365
937	A marvellous piece of engineering, this module either uses JSON::XS	1366	One of the problems is that U+2028 and U+2029 are valid characters inside
938	directly when available (so will be 100% compatible with it, including	1367	JSON strings, but are not allowed in ECMAscript string literals, so the
939	speed), or it uses JSON::PP, which is basically JSON::XS translated to	1368	following Perl fragment will not output something that can be guaranteed
940	Pure Perl, which should be 100% compatible with JSON::XS, just a bit	1369	to be parsable by javascript's C<eval>:
941	slower.
942		1370
943	You cannot really lose by using this module.	1371	use JSON::XS;
944		1372
945	=item JSON 1.07	1373	print encode_json [chr 0x2028];
946		1374
947	Slow (but very portable, as it is written in pure Perl).	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).
948		1378
949	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1379	If this is not an option, you can, as a stop-gap measure, simply encode to
950	undocumented. One can get far by feeding it Unicode strings and doing	1380	ASCII-only JSON:
951	en-/decoding oneself, but Unicode escapes are not working properly).
952		1381
953	No round-tripping (strings get clobbered if they look like numbers, e.g.	1382	use JSON::XS;
954	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
955	decode into the number 2.
956		1383
957	=item JSON::PC 0.01	1384	print JSON::XS->new->ascii->encode ([chr 0x2028]);
958		1385
959	Very fast.	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.:
960		1389
961	Undocumented/buggy Unicode handling.	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;
962		1395
963	No round-tripping.	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.
964		1400
965	Has problems handling many Perl values (e.g. regex results and other magic	1401	Another problem is that some javascript implementations reserve
966	values will make it croak).	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.
967		1405
968	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1406	If that is a problem, you could parse try to filter the resulting JSON
969	which is not a valid JSON text.	1407	output for these property strings, e.g.:
970		1408
971	Unmaintained (maintainer unresponsive for many months, bugs are not	1409	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
972	getting fixed).
973		1410
974	=item JSON::Syck 0.21	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.
975		1413
976	Very buggy (often crashes).	1414	If you know of other incompatibilities, please let me know.
977
978	Very inflexible (no human-readable format supported, format pretty much
979	undocumented. I need at least a format for easy reading by humans and a
980	single-line compact format for use in a protocol, and preferably a way to
981	generate ASCII-only JSON texts).
982
983	Completely broken (and confusingly documented) Unicode handling (Unicode
984	escapes are not working properly, you need to set ImplicitUnicode to
985	I<different> values on en- and decoding to get symmetric behaviour).
986
987	No round-tripping (simple cases work, but this depends on whether the scalar
988	value was used in a numeric context or not).
989
990	Dumping hashes may skip hash values depending on iterator state.
991
992	Unmaintained (maintainer unresponsive for many months, bugs are not
993	getting fixed).
994
995	Does not check input for validity (i.e. will accept non-JSON input and
996	return "something" instead of raising an exception. This is a security
997	issue: imagine two banks transferring money between each other using
998	JSON. One bank might parse a given non-JSON request and deduct money,
999	while the other might reject the transaction with a syntax error. While a
1000	good protocol will at least recover, that is extra unnecessary work and
1001	the transaction will still not succeed).
1002
1003	=item JSON::DWIW 0.04
1004
1005	Very fast. Very natural. Very nice.
1006
1007	Undocumented Unicode handling (but the best of the pack. Unicode escapes
1008	still don't get parsed properly).
1009
1010	Very inflexible.
1011
1012	No round-tripping.
1013
1014	Does not generate valid JSON texts (key strings are often unquoted, empty keys
1015	result in nothing being output)
1016
1017	Does not check input for validity.
1018
1019	=back
1020		1415
1021		1416
1022	=head2 JSON and YAML	1417	=head2 JSON and YAML
1023		1418
1024	You often hear that JSON is a subset of YAML. This is, however, a mass	1419	You often hear that JSON is a subset of YAML. This is, however, a mass
1025	hysteria(*) and very far from the truth. In general, there is no way to	1420	hysteria(*) and very far from the truth (as of the time of this writing),
		1421	so let me state it clearly: I<in general, there is no way to configure
1026	configure JSON::XS to output a data structure as valid YAML that works for	1422	JSON::XS to output a data structure as valid YAML> that works in all
1027	all cases.	1423	cases.
1028		1424
1029	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
1030	algorithm (subject to change in future versions):	1426	algorithm (subject to change in future versions):
1031		1427
1032	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1428	my $to_yaml = JSON::XS->new->utf8->space_after (1);
1033	my $yaml = $to_yaml->encode ($ref) . "\n";	1429	my $yaml = $to_yaml->encode ($ref) . "\n";
1034		1430
1035	This will I<usually> generate JSON texts that also parse as valid	1431	This will I<usually> generate JSON texts that also parse as valid
1036	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
1037	lengths that JSON doesn't have and also has different and incompatible	1433	lengths that JSON doesn't have and also has different and incompatible
1038	unicode handling, so you should make sure that your hash keys are	1434	unicode character escape syntax, so you should make sure that your hash
1039	noticeably shorter than the 1024 "stream characters" YAML allows and that	1435	keys are noticeably shorter than the 1024 "stream characters" YAML allows
1040	you do not have codepoints with values outside the Unicode BMP (basic	1436	and that you do not have characters with codepoint values outside the
1041	multilingual page). YAML also does not allow C<\/> sequences in strings	1437	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
1042	(which JSON::XS does not I<currently> generate).	1438	sequences in strings (which JSON::XS does not I<currently> generate, but
		1439	other JSON generators might).
1043		1440
1044	There might be other incompatibilities that I am not aware of (or the YAML	1441	There might be other incompatibilities that I am not aware of (or the YAML
1045	specification has been changed yet again - it does so quite often). In	1442	specification has been changed yet again - it does so quite often). In
1046	general you should not try to generate YAML with a JSON generator or vice	1443	general you should not try to generate YAML with a JSON generator or vice
1047	versa, or try to parse JSON with a YAML parser or vice versa: chances are	1444	versa, or try to parse JSON with a YAML parser or vice versa: chances are
1048	high that you will run into severe interoperability problems when you	1445	high that you will run into severe interoperability problems when you
1049	least expect it.	1446	least expect it.
1050		1447
1051	=over 4	1448	=over
1052		1449
1053	=item (*)	1450	=item (*)
1054		1451
1055	This is spread actively by the YAML team, however. For many years now they	1452	I have been pressured multiple times by Brian Ingerson (one of the
1056	claim YAML were a superset of JSON, even when proven otherwise.	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).
1057		1459
1058	Even the author of this manpage was at some point accused of providing	1460	In my opinion, instead of pressuring and insulting people who actually
1059	"incorrect" information, despite the evidence presented (claims ranged	1461	clarify issues with YAML and the wrong statements of some of its
1060	from "your documentation contains inaccurate and negative statements about	1462	proponents, I would kindly suggest reading the JSON spec (which is not
1061	YAML" (the only negative comment is this footnote, and it didn't exist	1463	that difficult or long) and finally make YAML compatible to it, and
1062	back then; the question on which claims were inaccurate was never answered	1464	educating users about the changes, instead of spreading lies about the
1063	etc.) to "the YAML spec is not up-to-date" (the *real* and supposedly	1465	real compatibility for many I<years> and trying to silence people who
1064	JSON-compatible spec is apparently not currently publicly available)	1466	point out that it isn't true.
1065	to actual requests to replace this section by *incorrect* information,
1066	suppressing information about the real problem).
1067		1467
1068	So whenever you are told that YAML was a superset of JSON, first check	1468	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
1069	wether it is really true (it might be when you check it, but it certainly	1469	though the incompatibilities have been documented (and are known to Brian)
1070	was not true when this was written). I would much prefer if the YAML team	1470	for many years and the spec makes explicit claims that YAML is a superset
1071	would spent their time on actually making JSON compatibility a truth	1471	of JSON. It would be so easy to fix, but apparently, bullying people and
1072	(JSON, after all, has a very small and simple specification) instead of	1472	corrupting userdata is so much easier.
1073	trying to lobby/force people into reporting untruths.
1074		1473
1075	=back	1474	=back
1076		1475
1077		1476
1078	=head2 SPEED	1477	=head2 SPEED
…		…
1080	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
1081	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
1082	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
1083	system.	1482	system.
1084		1483
1085	First comes a comparison between various modules using a very short	1484	First comes a comparison between various modules using
1086	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>).
1087		1487
1088	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1488	{"method": "handleMessage", "params": ["user1",
1089	"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]}
1090		1491
1091	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
1092	the functional interface, while JSON::XS/2 uses the OO interface	1493	the functional interface, while JSON::XS/2 uses the OO interface
1093	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1494	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
1094	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:
1095		1497
1096	module | encode | decode |	1498	module | encode | decode |
1097	-----------|------------|------------|	1499	--------------|------------|------------|
1098	JSON 1.x | 4990.842 | 4088.813 |	1500	JSON::DWIW/DS | 86302.551 | 102300.098 |
1099	JSON::DWIW | 51653.990 | 71575.154 |	1501	JSON::DWIW/FJ | 86302.551 | 75983.768 |
1100	JSON::PC | 65948.176 | 74631.744 |	1502	JSON::PP | 15827.562 | 6638.658 |
1101	JSON::PP | 8931.652 | 3817.168 |	1503	JSON::Syck | 63358.066 | 47662.545 |
1102	JSON::Syck | 24877.248 | 27776.848 |	1504	JSON::XS | 511500.488 | 511500.488 |
1103	JSON::XS | 388361.481 | 227951.304 |	1505	JSON::XS/2 | 291271.111 | 388361.481 |
1104	JSON::XS/2 | 227951.304 | 218453.333 |	1506	JSON::XS/3 | 361577.931 | 361577.931 |
1105	JSON::XS/3 | 338250.323 | 218453.333 |	1507	Storable | 66788.280 | 265462.278 |
1106	Storable | 16500.016 | 135300.129 |
1107	-----------+------------+------------+	1508	--------------+------------+------------+
1108		1509
1109	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,
1110	about three times faster on decoding, and over forty times faster	1511	about five times faster on decoding, and over thirty to seventy times
1111	than JSON, even with pretty-printing and key sorting. It also compares	1512	faster than JSON's pure perl implementation. It also compares favourably
1112	favourably to Storable for small amounts of data.	1513	to Storable for small amounts of data.
1113		1514
1114	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1515	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1115	search API (http://nanoref.com/yahooapis/mgPdGg):	1516	search API (L<http://dist.schmorp.de/misc/json/long.json>).
1116		1517
1117	module | encode | decode |	1518	module | encode | decode |
1118	-----------|------------|------------|	1519	--------------|------------|------------|
1119	JSON 1.x | 55.260 | 34.971 |	1520	JSON::DWIW/DS | 1647.927 | 2673.916 |
1120	JSON::DWIW | 825.228 | 1082.513 |	1521	JSON::DWIW/FJ | 1630.249 | 2596.128 |
1121	JSON::PC | 3571.444 | 2394.829 |
1122	JSON::PP | 210.987 | 32.574 |	1522	JSON::PP | 400.640 | 62.311 |
1123	JSON::Syck | 552.551 | 787.544 |	1523	JSON::Syck | 1481.040 | 1524.869 |
1124	JSON::XS | 5780.463 | 4854.519 |	1524	JSON::XS | 20661.596 | 9541.183 |
1125	JSON::XS/2 | 3869.998 | 4798.975 |	1525	JSON::XS/2 | 10683.403 | 9416.938 |
1126	JSON::XS/3 | 5862.880 | 4798.975 |	1526	JSON::XS/3 | 20661.596 | 9400.054 |
1127	Storable | 4445.002 | 5235.027 |	1527	Storable | 19765.806 | 10000.725 |
1128	-----------+------------+------------+	1528	--------------+------------+------------+
1129		1529
1130	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
1131	decodes faster).	1531	decodes a bit faster).
1132		1532
1133	On large strings containing lots of high Unicode characters, some modules	1533	On large strings containing lots of high Unicode characters, some modules
1134	(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
1135	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
1136	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
…		…
1162	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
1163	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
1164	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
1165	C<max_depth> method.	1565	C<max_depth> method.
1166		1566
1167	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
1168	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...
1169	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.
1170		1574
1171	If you are using JSON::XS to return packets to consumption	1575	If you are using JSON::XS to return packets to consumption
1172	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
1173	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
1174	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
1175	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
1176	browser developers care only for features, not about getting security	1580	it, as major browser developers care only for features, not about getting
1177	right).	1581	security right).
1178		1582
1179		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*,/($1)[/g;
		1744
		1745	Again, this has some limitations - the magic string must not be encoded
		1746	with character escapes, and the constructor arguments must be non-empty.
		1747
		1748
1180	=head1 THREADS	1749	=head1 (I-)THREADS
1181		1750
1182	This module is I<not> guaranteed to be thread safe and there are no	1751	This module is I<not> guaranteed to be ithread (or MULTIPLICITY-) safe
1183	plans to change this until Perl gets thread support (as opposed to the	1752	and there are no plans to change this. Note that perl's builtin so-called
1184	horribly slow so-called "threads" which are simply slow and bloated	1753	threads/ithreads are officially deprecated and should not be used.
1185	process simulations - use fork, its I<much> faster, cheaper, better).
1186		1754
1187	(It might actually work, but you have been warned).	1755
		1756	=head1 THE PERILS OF SETLOCALE
		1757
		1758	Sometimes people avoid the Perl locale support and directly call the
		1759	system's setlocale function with C<LC_ALL>.
		1760
		1761	This breaks both perl and modules such as JSON::XS, as stringification of
		1762	numbers no longer works correctly (e.g. C<$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.
1188		1798
1189		1799
1190	=head1 BUGS	1800	=head1 BUGS
1191		1801
1192	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
1193	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
1194	still relatively early in its development. If you keep reporting bugs they	1804	keep reporting bugs they will be fixed swiftly, though.
1195	will be fixed swiftly, though.
1196		1805
1197	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
1198	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.
1199		1808
1200	=cut	1809	=cut
1201		1810
1202	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1811	BEGIN {
1203	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;
1204		1817
1205	sub true() { $true }	1818	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
1206	sub false() { $false }
1207
1208	sub is_bool($) {
1209	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1210	# or UNIVERSAL::isa $_[0], "JSON::Literal"
1211	}	1819	}
1212		1820
1213	XSLoader::load "JSON::XS", $VERSION;	1821	XSLoader::load "JSON::XS", $VERSION;
1214		1822
1215	package JSON::XS::Boolean;	1823	=head1 SEE ALSO
1216		1824
1217	use overload	1825	The F<json_xs> command line utility for quick experiments.
1218	"0+" => sub { ${$_[0]} },
1219	"++" => sub { $_[0] = ${$_[0]} + 1 },
1220	"--" => sub { $_[0] = ${$_[0]} - 1 },
1221	fallback => 1;
1222
1223	1;
1224		1826
1225	=head1 AUTHOR	1827	=head1 AUTHOR
1226		1828
1227	Marc Lehmann <schmorp@schmorp.de>	1829	Marc Lehmann <schmorp@schmorp.de>
1228	http://home.schmorp.de/	1830	http://home.schmorp.de/
1229		1831
1230	=cut	1832	=cut
1231		1833
		1834	1
		1835

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