[ViewVC] Diff of: cvs/JSON-XS/XS.pm

Comparing JSON-XS/XS.pm (file contents):
Revision 1.84 by root, Wed Mar 19 02:52:15 2008 UTC vs.
Revision 1.150 by root, Tue Oct 29 00:48:07 2013 UTC

…		…
		1	=head1 NAME
		2
		3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
1	=encoding utf-8	5	=encoding utf-8
2
3	=head1 NAME
4
5	JSON::XS - JSON serialising/deserialising, done correctly and fast
6		6
7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ	7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)	8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
9		9
10	=head1 SYNOPSIS	10	=head1 SYNOPSIS
37	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
38	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
39		39
40	Beginning with version 2.0 of the JSON module, when both JSON and	40	Beginning with version 2.0 of the JSON module, when both JSON and
41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be	41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
42	overriden) with no overhead due to emulation (by inheritign constructor	42	overridden) with no overhead due to emulation (by inheriting constructor
43	and methods). If JSON::XS is not available, it will fall back to the	43	and methods). If JSON::XS is not available, it will fall back to the
44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS	44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
45	gives you a portable JSON API that can be fast when you need and doesn't	45	gives you a portable JSON API that can be fast when you need and doesn't
46	require a C compiler when that is a problem.	46	require a C compiler when that is a problem.
47		47
…		…
49	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
50	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
51	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
52	reports for other reasons.	52	reports for other reasons.
53		53
54	See COMPARISON, below, for a comparison to some other JSON modules.
55
56	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
57	vice versa.	55	vice versa.
58		56
59	=head2 FEATURES	57	=head2 FEATURES
60		58
…		…
65	This module knows how to handle Unicode, documents how and when it does	63	This module knows how to handle Unicode, documents how and when it does
66	so, and even documents what "correct" means.	64	so, and even documents what "correct" means.
67		65
68	=item * round-trip integrity	66	=item * round-trip integrity
69		67
70	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
71	by JSON, the deserialised data structure is identical on the Perl level.	69	by JSON and Perl, the deserialised data structure is identical on the Perl
72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
73	like a number). There minor I<are> exceptions to this, read the MAPPING	71	it looks like a number). There I<are> minor exceptions to this, read the
74	section below to learn about those.	72	MAPPING section below to learn about those.
75		73
76	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
77		75
78	There is no guessing, no generating of illegal JSON texts by default,	76	There is no guessing, no generating of illegal JSON texts by default,
79	and only JSON is accepted as input by default (the latter is a security	77	and only JSON is accepted as input by default (the latter is a security
…		…
84	Compared to other JSON modules and other serialisers such as Storable,	82	Compared to other JSON modules and other serialisers such as Storable,
85	this module usually compares favourably in terms of speed, too.	83	this module usually compares favourably in terms of speed, too.
86		84
87	=item * simple to use	85	=item * simple to use
88		86
89	This module has both a simple functional interface as well as an objetc	87	This module has both a simple functional interface as well as an object
90	oriented interface interface.	88	oriented interface.
91		89
92	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
93		91
94	You can choose between the most compact guaranteed-single-line format	92	You can choose between the most compact guaranteed-single-line format
95	possible (nice for simple line-based protocols), a pure-ascii format	93	possible (nice for simple line-based protocols), a pure-ASCII format
96	(for when your transport is not 8-bit clean, still supports the whole	94	(for when your transport is not 8-bit clean, still supports the whole
97	Unicode range), or a pretty-printed format (for when you want to read that	95	Unicode range), or a pretty-printed format (for when you want to read that
98	stuff). Or you can combine those features in whatever way you like.	96	stuff). Or you can combine those features in whatever way you like.
99		97
100	=back	98	=back
101		99
102	=cut	100	=cut
103		101
104	package JSON::XS;	102	package JSON::XS;
105		103
106	use strict;	104	use common::sense;
107		105
108	our $VERSION = '2.01';	106	our $VERSION = '3.0';
109	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
110		108
111	our @EXPORT = qw(encode_json decode_json to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
112
113	sub to_json($) {
114	require Carp;
115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
116	}
117
118	sub from_json($) {
119	require Carp;
120	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
121	}
122		110
123	use Exporter;	111	use Exporter;
124	use XSLoader;	112	use XSLoader;
125		113
		114	use Types::Serialiser ();
		115
126	=head1 FUNCTIONAL INTERFACE	116	=head1 FUNCTIONAL INTERFACE
127		117
128	The following convenience methods are provided by this module. They are	118	The following convenience methods are provided by this module. They are
129	exported by default:	119	exported by default:
130		120
…		…
137		127
138	This function call is functionally identical to:	128	This function call is functionally identical to:
139		129
140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	130	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
141		131
142	except being faster.	132	Except being faster.
143		133
144	=item $perl_scalar = decode_json $json_text	134	=item $perl_scalar = decode_json $json_text
145		135
146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries	136	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
147	to parse that as an UTF-8 encoded JSON text, returning the resulting	137	to parse that as an UTF-8 encoded JSON text, returning the resulting
…		…
149		139
150	This function call is functionally identical to:	140	This function call is functionally identical to:
151		141
152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	142	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
153		143
154	except being faster.	144	Except being faster.
155
156	=item $is_boolean = JSON::XS::is_bool $scalar
157
158	Returns true if the passed scalar represents either JSON::XS::true or
159	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
160	and are used to represent JSON C<true> and C<false> values in Perl.
161
162	See MAPPING, below, for more information on how JSON values are mapped to
163	Perl.
164		145
165	=back	146	=back
166		147
167		148
168	=head1 A FEW NOTES ON UNICODE AND PERL	149	=head1 A FEW NOTES ON UNICODE AND PERL
…		…
197		178
198	If you didn't know about that flag, just the better, pretend it doesn't	179	If you didn't know about that flag, just the better, pretend it doesn't
199	exist.	180	exist.
200		181
201	=item 4. A "Unicode String" is simply a string where each character can be	182	=item 4. A "Unicode String" is simply a string where each character can be
202	validly interpreted as a Unicode codepoint.	183	validly interpreted as a Unicode code point.
203		184
204	If you have UTF-8 encoded data, it is no longer a Unicode string, but a	185	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
205	Unicode string encoded in UTF-8, giving you a binary string.	186	Unicode string encoded in UTF-8, giving you a binary string.
206		187
207	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.	188	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
…		…
245		226
246	If C<$enable> is false, then the C<encode> method will not escape Unicode	227	If C<$enable> is false, then the C<encode> method will not escape Unicode
247	characters unless required by the JSON syntax or other flags. This results	228	characters unless required by the JSON syntax or other flags. This results
248	in a faster and more compact format.	229	in a faster and more compact format.
249		230
		231	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		232	document.
		233
250	The main use for this flag is to produce JSON texts that can be	234	The main use for this flag is to produce JSON texts that can be
251	transmitted over a 7-bit channel, as the encoded JSON texts will not	235	transmitted over a 7-bit channel, as the encoded JSON texts will not
252	contain any 8 bit characters.	236	contain any 8 bit characters.
253		237
254	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	238	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
265	will not be affected in any way by this flag, as C<decode> by default	249	will not be affected in any way by this flag, as C<decode> by default
266	expects Unicode, which is a strict superset of latin1.	250	expects Unicode, which is a strict superset of latin1.
267		251
268	If C<$enable> is false, then the C<encode> method will not escape Unicode	252	If C<$enable> is false, then the C<encode> method will not escape Unicode
269	characters unless required by the JSON syntax or other flags.	253	characters unless required by the JSON syntax or other flags.
		254
		255	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		256	document.
270		257
271	The main use for this flag is efficiently encoding binary data as JSON	258	The main use for this flag is efficiently encoding binary data as JSON
272	text, as most octets will not be escaped, resulting in a smaller encoded	259	text, as most octets will not be escaped, resulting in a smaller encoded
273	size. The disadvantage is that the resulting JSON text is encoded	260	size. The disadvantage is that the resulting JSON text is encoded
274	in latin1 (and must correctly be treated as such when storing and	261	in latin1 (and must correctly be treated as such when storing and
…		…
293		280
294	If C<$enable> is false, then the C<encode> method will return the JSON	281	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	282	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	283	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.	284	to be done yourself, e.g. using the Encode module.
		285
		286	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		287	document.
298		288
299	Example, output UTF-16BE-encoded JSON:	289	Example, output UTF-16BE-encoded JSON:
300		290
301	use Encode;	291	use Encode;
302	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	292	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
425	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	415	If C<$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.	416	by sorting their keys. This is adding a comparatively high overhead.
427		417
428	If C<$enable> is false, then the C<encode> method will output key-value	418	If C<$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	419	pairs in the order Perl stores them (which will likely change between runs
430	of the same script).	420	of the same script, and can change even within the same run from 5.18
		421	onwards).
431		422
432	This option is useful if you want the same data structure to be encoded as	423	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,	424	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,	425	the same hash might be encoded differently even if contains the same data,
435	as key-value pairs have no inherent ordering in Perl.	426	as key-value pairs have no inherent ordering in Perl.
436		427
437	This setting has no effect when decoding JSON texts.	428	This setting has no effect when decoding JSON texts.
438		429
		430	This setting has currently no effect on tied hashes.
		431
439	=item $json = $json->allow_nonref ([$enable])	432	=item $json = $json->allow_nonref ([$enable])
440		433
441	=item $enabled = $json->get_allow_nonref	434	=item $enabled = $json->get_allow_nonref
442		435
443	If C<$enable> is true (or missing), then the C<encode> method can convert a	436	If C<$enable> is true (or missing), then the C<encode> method can convert a
…		…
454	resulting in an invalid JSON text:	447	resulting in an invalid JSON text:
455		448
456	JSON::XS->new->allow_nonref->encode ("Hello, World!")	449	JSON::XS->new->allow_nonref->encode ("Hello, World!")
457	=> "Hello, World!"	450	=> "Hello, World!"
458		451
		452	=item $json = $json->allow_unknown ([$enable])
		453
		454	=item $enabled = $json->get_allow_unknown
		455
		456	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		457	exception when it encounters values it cannot represent in JSON (for
		458	example, filehandles) but instead will encode a JSON C<null> value. Note
		459	that blessed objects are not included here and are handled separately by
		460	c<allow_nonref>.
		461
		462	If C<$enable> is false (the default), then C<encode> will throw an
		463	exception when it encounters anything it cannot encode as JSON.
		464
		465	This option does not affect C<decode> in any way, and it is recommended to
		466	leave it off unless you know your communications partner.
		467
459	=item $json = $json->allow_blessed ([$enable])	468	=item $json = $json->allow_blessed ([$enable])
460		469
461	=item $enabled = $json->get_allow_blessed	470	=item $enabled = $json->get_allow_blessed
462		471
		472	See L<OBJECT SERIALISATION> for details.
		473
463	If C<$enable> is true (or missing), then the C<encode> method will not	474	If C<$enable> is true (or missing), then the C<encode> method will not
464	barf when it encounters a blessed reference. Instead, the value of the	475	barf when it encounters a blessed reference that it cannot convert
465	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>	476	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
466	disabled or no C<TO_JSON> method found) or a representation of the
467	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
468	encoded. Has no effect on C<decode>.
469		477
470	If C<$enable> is false (the default), then C<encode> will throw an	478	If C<$enable> is false (the default), then C<encode> will throw an
471	exception when it encounters a blessed object.	479	exception when it encounters a blessed object that it cannot convert
		480	otherwise.
		481
		482	This setting has no effect on C<decode>.
472		483
473	=item $json = $json->convert_blessed ([$enable])	484	=item $json = $json->convert_blessed ([$enable])
474		485
475	=item $enabled = $json->get_convert_blessed	486	=item $enabled = $json->get_convert_blessed
		487
		488	See L<OBJECT SERIALISATION> for details.
476		489
477	If C<$enable> is true (or missing), then C<encode>, upon encountering a	490	If C<$enable> is true (or missing), then C<encode>, upon encountering a
478	blessed object, will check for the availability of the C<TO_JSON> method	491	blessed object, will check for the availability of the C<TO_JSON> method
479	on the object's class. If found, it will be called in scalar context	492	on the object's class. If found, it will be called in scalar context and
480	and the resulting scalar will be encoded instead of the object. If no	493	the resulting scalar will be encoded instead of the object.
481	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
482	to do.
483		494
484	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	495	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
485	returns other blessed objects, those will be handled in the same	496	returns other blessed objects, those will be handled in the same
486	way. C<TO_JSON> must take care of not causing an endless recursion cycle	497	way. C<TO_JSON> must take care of not causing an endless recursion cycle
487	(== crash) in this case. The name of C<TO_JSON> was chosen because other	498	(== crash) in this case. The name of C<TO_JSON> was chosen because other
488	methods called by the Perl core (== not by the user of the object) are	499	methods called by the Perl core (== not by the user of the object) are
489	usually in upper case letters and to avoid collisions with any C<to_json>	500	usually in upper case letters and to avoid collisions with any C<to_json>
490	function or method.	501	function or method.
491		502
492	This setting does not yet influence C<decode> in any way, but in the	503	If C<$enable> is false (the default), then C<encode> will not consider
493	future, global hooks might get installed that influence C<decode> and are	504	this type of conversion.
494	enabled by this setting.
495		505
496	If C<$enable> is false, then the C<allow_blessed> setting will decide what	506	This setting has no effect on C<decode>.
497	to do when a blessed object is found.	507
		508	=item $json = $json->allow_tags ([$enable])
		509
		510	=item $enabled = $json->allow_tags
		511
		512	See L<OBJECT SERIALISATION> for details.
		513
		514	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		515	blessed object, will check for the availability of the C<FREEZE> method on
		516	the object's class. If found, it will be used to serialise the object into
		517	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		518
		519	It also causes C<decode> to parse such tagged JSON values and deserialise
		520	them via a call to the C<THAW> method.
		521
		522	If C<$enable> is false (the default), then C<encode> will not consider
		523	this type of conversion, and tagged JSON values will cause a parse error
		524	in C<decode>, as if tags were not part of the grammar.
498		525
499	=item $json = $json->filter_json_object ([$coderef->($hashref)])	526	=item $json = $json->filter_json_object ([$coderef->($hashref)])
500		527
501	When C<$coderef> is specified, it will be called from C<decode> each	528	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	529	time it decodes a JSON object. The only argument is a reference to the
…		…
603	=item $json = $json->max_depth ([$maximum_nesting_depth])	630	=item $json = $json->max_depth ([$maximum_nesting_depth])
604		631
605	=item $max_depth = $json->get_max_depth	632	=item $max_depth = $json->get_max_depth
606		633
607	Sets the maximum nesting level (default C<512>) accepted while encoding	634	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	635	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	636	data structure, then the encoder and decoder will stop and croak at that
610	stop and croak at that point.	637	point.
611		638
612	Nesting level is defined by number of hash- or arrayrefs that the encoder	639	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<[>	640	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	641	characters without their matching closing parenthesis crossed to reach a
615	given character in a string.	642	given character in a string.
616		643
617	Setting the maximum depth to one disallows any nesting, so that ensures	644	Setting the maximum depth to one disallows any nesting, so that ensures
618	that the object is only a single hash/object or array.	645	that the object is only a single hash/object or array.
619		646
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	647	If no argument is given, the highest possible setting will be used, which
622	used, which is rarely useful.	648	is rarely useful.
		649
		650	Note that nesting is implemented by recursion in C. The default value has
		651	been chosen to be as large as typical operating systems allow without
		652	crashing.
623		653
624	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	654	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
625		655
626	=item $json = $json->max_size ([$maximum_string_size])	656	=item $json = $json->max_size ([$maximum_string_size])
627		657
628	=item $max_size = $json->get_max_size	658	=item $max_size = $json->get_max_size
629		659
630	Set the maximum length a JSON text may have (in bytes) where decoding is	660	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>	661	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	662	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	663	attempt to decode the string but throw an exception. This setting has no
634	effect on C<encode> (yet).	664	effect on C<encode> (yet).
635		665
636	The argument to C<max_size> will be rounded up to the next B<highest>	666	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	667	C<0> is specified).
638	limit check will be deactivated (same as when C<0> is specified).
639		668
640	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	669	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
641		670
642	=item $json_text = $json->encode ($perl_scalar)	671	=item $json_text = $json->encode ($perl_scalar)
643		672
644	Converts the given Perl data structure (a simple scalar or a reference	673	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	674	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		675
651	=item $perl_scalar = $json->decode ($json_text)	676	=item $perl_scalar = $json->decode ($json_text)
652		677
653	The opposite of C<encode>: expects a JSON text and tries to parse it,	678	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.	679	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		680
660	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	681	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
661		682
662	This works like the C<decode> method, but instead of raising an exception	683	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	684	when there is trailing garbage after the first JSON object, it will
664	silently stop parsing there and return the number of characters consumed	685	silently stop parsing there and return the number of characters consumed
665	so far.	686	so far.
666		687
667	This is useful if your JSON texts are not delimited by an outer protocol	688	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.	689	and you need to know where the JSON text ends.
670		690
671	JSON::XS->new->decode_prefix ("[1] the tail")	691	JSON::XS->new->decode_prefix ("[1] the tail")
672	=> ([], 3)	692	=> ([], 3)
673		693
674	=back	694	=back
		695
		696
		697	=head1 INCREMENTAL PARSING
		698
		699	In some cases, there is the need for incremental parsing of JSON
		700	texts. While this module always has to keep both JSON text and resulting
		701	Perl data structure in memory at one time, it does allow you to parse a
		702	JSON stream incrementally. It does so by accumulating text until it has
		703	a full JSON object, which it then can decode. This process is similar to
		704	using C<decode_prefix> to see if a full JSON object is available, but
		705	is much more efficient (and can be implemented with a minimum of method
		706	calls).
		707
		708	JSON::XS will only attempt to parse the JSON text once it is sure it
		709	has enough text to get a decisive result, using a very simple but
		710	truly incremental parser. This means that it sometimes won't stop as
		711	early as the full parser, for example, it doesn't detect mismatched
		712	parentheses. The only thing it guarantees is that it starts decoding as
		713	soon as a syntactically valid JSON text has been seen. This means you need
		714	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		715	parsing in the presence if syntax errors.
		716
		717	The following methods implement this incremental parser.
		718
		719	=over 4
		720
		721	=item [void, scalar or list context] = $json->incr_parse ([$string])
		722
		723	This is the central parsing function. It can both append new text and
		724	extract objects from the stream accumulated so far (both of these
		725	functions are optional).
		726
		727	If C<$string> is given, then this string is appended to the already
		728	existing JSON fragment stored in the C<$json> object.
		729
		730	After that, if the function is called in void context, it will simply
		731	return without doing anything further. This can be used to add more text
		732	in as many chunks as you want.
		733
		734	If the method is called in scalar context, then it will try to extract
		735	exactly I<one> JSON object. If that is successful, it will return this
		736	object, otherwise it will return C<undef>. If there is a parse error,
		737	this method will croak just as C<decode> would do (one can then use
		738	C<incr_skip> to skip the erroneous part). This is the most common way of
		739	using the method.
		740
		741	And finally, in list context, it will try to extract as many objects
		742	from the stream as it can find and return them, or the empty list
		743	otherwise. For this to work, there must be no separators between the JSON
		744	objects or arrays, instead they must be concatenated back-to-back. If
		745	an error occurs, an exception will be raised as in the scalar context
		746	case. Note that in this case, any previously-parsed JSON texts will be
		747	lost.
		748
		749	Example: Parse some JSON arrays/objects in a given string and return
		750	them.
		751
		752	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		753
		754	=item $lvalue_string = $json->incr_text
		755
		756	This method returns the currently stored JSON fragment as an lvalue, that
		757	is, you can manipulate it. This I<only> works when a preceding call to
		758	C<incr_parse> in I<scalar context> successfully returned an object. Under
		759	all other circumstances you must not call this function (I mean it.
		760	although in simple tests it might actually work, it I<will> fail under
		761	real world conditions). As a special exception, you can also call this
		762	method before having parsed anything.
		763
		764	This function is useful in two cases: a) finding the trailing text after a
		765	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		766	(such as commas).
		767
		768	=item $json->incr_skip
		769
		770	This will reset the state of the incremental parser and will remove
		771	the parsed text from the input buffer so far. This is useful after
		772	C<incr_parse> died, in which case the input buffer and incremental parser
		773	state is left unchanged, to skip the text parsed so far and to reset the
		774	parse state.
		775
		776	The difference to C<incr_reset> is that only text until the parse error
		777	occurred is removed.
		778
		779	=item $json->incr_reset
		780
		781	This completely resets the incremental parser, that is, after this call,
		782	it will be as if the parser had never parsed anything.
		783
		784	This is useful if you want to repeatedly parse JSON objects and want to
		785	ignore any trailing data, which means you have to reset the parser after
		786	each successful decode.
		787
		788	=back
		789
		790	=head2 LIMITATIONS
		791
		792	All options that affect decoding are supported, except
		793	C<allow_nonref>. The reason for this is that it cannot be made to work
		794	sensibly: JSON objects and arrays are self-delimited, i.e. you can
		795	concatenate them back to back and still decode them perfectly. This does
		796	not hold true for JSON numbers, however.
		797
		798	For example, is the string C<1> a single JSON number, or is it simply the
		799	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		800	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		801	takes the conservative route and disallows this case.
		802
		803	=head2 EXAMPLES
		804
		805	Some examples will make all this clearer. First, a simple example that
		806	works similarly to C<decode_prefix>: We want to decode the JSON object at
		807	the start of a string and identify the portion after the JSON object:
		808
		809	my $text = "[1,2,3] hello";
		810
		811	my $json = new JSON::XS;
		812
		813	my $obj = $json->incr_parse ($text)
		814	or die "expected JSON object or array at beginning of string";
		815
		816	my $tail = $json->incr_text;
		817	# $tail now contains " hello"
		818
		819	Easy, isn't it?
		820
		821	Now for a more complicated example: Imagine a hypothetical protocol where
		822	you read some requests from a TCP stream, and each request is a JSON
		823	array, without any separation between them (in fact, it is often useful to
		824	use newlines as "separators", as these get interpreted as whitespace at
		825	the start of the JSON text, which makes it possible to test said protocol
		826	with C<telnet>...).
		827
		828	Here is how you'd do it (it is trivial to write this in an event-based
		829	manner):
		830
		831	my $json = new JSON::XS;
		832
		833	# read some data from the socket
		834	while (sysread $socket, my $buf, 4096) {
		835
		836	# split and decode as many requests as possible
		837	for my $request ($json->incr_parse ($buf)) {
		838	# act on the $request
		839	}
		840	}
		841
		842	Another complicated example: Assume you have a string with JSON objects
		843	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		844	[3]>). To parse them, we have to skip the commas between the JSON texts,
		845	and here is where the lvalue-ness of C<incr_text> comes in useful:
		846
		847	my $text = "[1],[2], [3]";
		848	my $json = new JSON::XS;
		849
		850	# void context, so no parsing done
		851	$json->incr_parse ($text);
		852
		853	# now extract as many objects as possible. note the
		854	# use of scalar context so incr_text can be called.
		855	while (my $obj = $json->incr_parse) {
		856	# do something with $obj
		857
		858	# now skip the optional comma
		859	$json->incr_text =~ s/^ \s* , //x;
		860	}
		861
		862	Now lets go for a very complex example: Assume that you have a gigantic
		863	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		864	but you cannot load it into memory fully (this has actually happened in
		865	the real world :).
		866
		867	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		868	can still help you: You implement a (very simple) array parser and let
		869	JSON decode the array elements, which are all full JSON objects on their
		870	own (this wouldn't work if the array elements could be JSON numbers, for
		871	example):
		872
		873	my $json = new JSON::XS;
		874
		875	# open the monster
		876	open my $fh, "<bigfile.json"
		877	or die "bigfile: $!";
		878
		879	# first parse the initial "["
		880	for (;;) {
		881	sysread $fh, my $buf, 65536
		882	or die "read error: $!";
		883	$json->incr_parse ($buf); # void context, so no parsing
		884
		885	# Exit the loop once we found and removed(!) the initial "[".
		886	# In essence, we are (ab-)using the $json object as a simple scalar
		887	# we append data to.
		888	last if $json->incr_text =~ s/^ \s* \[ //x;
		889	}
		890
		891	# now we have the skipped the initial "[", so continue
		892	# parsing all the elements.
		893	for (;;) {
		894	# in this loop we read data until we got a single JSON object
		895	for (;;) {
		896	if (my $obj = $json->incr_parse) {
		897	# do something with $obj
		898	last;
		899	}
		900
		901	# add more data
		902	sysread $fh, my $buf, 65536
		903	or die "read error: $!";
		904	$json->incr_parse ($buf); # void context, so no parsing
		905	}
		906
		907	# in this loop we read data until we either found and parsed the
		908	# separating "," between elements, or the final "]"
		909	for (;;) {
		910	# first skip whitespace
		911	$json->incr_text =~ s/^\s*//;
		912
		913	# if we find "]", we are done
		914	if ($json->incr_text =~ s/^\]//) {
		915	print "finished.\n";
		916	exit;
		917	}
		918
		919	# if we find ",", we can continue with the next element
		920	if ($json->incr_text =~ s/^,//) {
		921	last;
		922	}
		923
		924	# if we find anything else, we have a parse error!
		925	if (length $json->incr_text) {
		926	die "parse error near ", $json->incr_text;
		927	}
		928
		929	# else add more data
		930	sysread $fh, my $buf, 65536
		931	or die "read error: $!";
		932	$json->incr_parse ($buf); # void context, so no parsing
		933	}
		934
		935	This is a complex example, but most of the complexity comes from the fact
		936	that we are trying to be correct (bear with me if I am wrong, I never ran
		937	the above example :).
		938
675		939
676		940
677	=head1 MAPPING	941	=head1 MAPPING
678		942
679	This section describes how JSON::XS maps Perl values to JSON values and	943	This section describes how JSON::XS maps Perl values to JSON values and
…		…
716	If the number consists of digits only, JSON::XS will try to represent	980	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	981	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	982	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	983	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	984	which case you lose roundtripping ability, as the JSON number will be
721	re-encoded toa JSON string).	985	re-encoded to a JSON string).
722		986
723	Numbers containing a fractional or exponential part will always be	987	Numbers containing a fractional or exponential part will always be
724	represented as numeric (floating point) values, possibly at a loss of	988	represented as numeric (floating point) values, possibly at a loss of
725	precision (in which case you might lose perfect roundtripping ability, but	989	precision (in which case you might lose perfect roundtripping ability, but
726	the JSON number will still be re-encoded as a JSON number).	990	the JSON number will still be re-encoded as a JSON number).
727		991
		992	Note that precision is not accuracy - binary floating point values cannot
		993	represent most decimal fractions exactly, and when converting from and to
		994	floating point, JSON::XS only guarantees precision up to but not including
		995	the least significant bit.
		996
728	=item true, false	997	=item true, false
729		998
730	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	999	These JSON atoms become C<Types::Serialiser::true> and
731	respectively. They are overloaded to act almost exactly like the numbers	1000	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	1001	almost exactly like the numbers C<1> and C<0>. You can check whether
733	the C<JSON::XS::is_bool> function.	1002	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1003	function (after C<use Types::Serialier>, of course).
734		1004
735	=item null	1005	=item null
736		1006
737	A JSON null atom becomes C<undef> in Perl.	1007	A JSON null atom becomes C<undef> in Perl.
		1008
		1009	=item shell-style comments (C<< # I<text> >>)
		1010
		1011	As a nonstandard extension to the JSON syntax that is enabled by the
		1012	C<relaxed> setting, shell-style comments are allowed. They can start
		1013	anywhere outside strings and go till the end of the line.
		1014
		1015	=item tagged values (C<< (I<tag>)I<value> >>).
		1016
		1017	Another nonstandard extension to the JSON syntax, enabled with the
		1018	C<allow_tags> setting, are tagged values. In this implementation, the
		1019	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1020	I<value> must be a JSON array encoding optional constructor arguments.
		1021
		1022	See L<OBJECT SERIALISATION>, below, for details.
738		1023
739	=back	1024	=back
740		1025
741		1026
742	=head2 PERL -> JSON	1027	=head2 PERL -> JSON
…		…
747		1032
748	=over 4	1033	=over 4
749		1034
750	=item hash references	1035	=item hash references
751		1036
752	Perl hash references become JSON objects. As there is no inherent ordering	1037	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	1038	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	1039	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	1040	(determined by the I<canonical> flag), so the same datastructure will
756	optionally sort the hash keys (determined by the I<canonical> flag), so	1041	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	1042	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	1043	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		1044
762	=item array references	1045	=item array references
763		1046
764	Perl array references become JSON arrays.	1047	Perl array references become JSON arrays.
765		1048
766	=item other references	1049	=item other references
767		1050
768	Other unblessed references are generally not allowed and will cause an	1051	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	1052	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	1053	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		1054
		1055	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1056	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1057	and C<Types::Serialiser::true> to improve readability.
		1058
		1059	use Types::Serialiser;
773	encode_json [\0,JSON::XS::true] # yields [false,true]	1060	encode_json [\0, Types::Serialiser::true] # yields [false,true]
774		1061
775	=item JSON::XS::true, JSON::XS::false	1062	=item Types::Serialiser::true, Types::Serialiser::false
776		1063
777	These special values become JSON true and JSON false values,	1064	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.	1065	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1066	directly if you want.
779		1067
780	=item blessed objects	1068	=item blessed objects
781		1069
782	Blessed objects are not directly representable in JSON. See the	1070	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	1071	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
784	how to deal with this: basically, you can choose between throwing an	1072	below, for details.
785	exception, encoding the reference as if it weren't blessed, or provide
786	your own serialiser method.
787		1073
788	=item simple scalars	1074	=item simple scalars
789		1075
790	Simple Perl scalars (any scalar that is not a reference) are the most	1076	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	1077	difficult objects to encode: JSON::XS will encode undefined scalars as
…		…
816	my $x = "3"; # some variable containing a string	1102	my $x = "3"; # some variable containing a string
817	$x += 0; # numify it, ensuring it will be dumped as a number	1103	$x += 0; # numify it, ensuring it will be dumped as a number
818	$x *= 1; # same thing, the choice is yours.	1104	$x *= 1; # same thing, the choice is yours.
819		1105
820	You can not currently force the type in other, less obscure, ways. Tell me	1106	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	1107	if you need this capability (but don't forget to explain why it's needed
822	:).	1108	:).
823		1109
		1110	Note that numerical precision has the same meaning as under Perl (so
		1111	binary to decimal conversion follows the same rules as in Perl, which
		1112	can differ to other languages). Also, your perl interpreter might expose
		1113	extensions to the floating point numbers of your platform, such as
		1114	infinities or NaN's - these cannot be represented in JSON, and it is an
		1115	error to pass those in.
		1116
824	=back	1117	=back
		1118
		1119	=head2 OBJECT SERIALISATION
		1120
		1121	As JSON cannot directly represent Perl objects, you have to choose between
		1122	a pure JSON representation (without the ability to deserialise the object
		1123	automatically again), and a nonstandard extension to the JSON syntax,
		1124	tagged values.
		1125
		1126	=head3 SERIALISATION
		1127
		1128	What happens when C<JSON::XS> encounters a Perl object depends on the
		1129	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
		1130	used in this order:
		1131
		1132	=over 4
		1133
		1134	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
		1135
		1136	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1137	serialisation protocol to create a tagged JSON value, using a nonstandard
		1138	extension to the JSON syntax.
		1139
		1140	This works by invoking the C<FREEZE> method on the object, with the first
		1141	argument being the object to serialise, and the second argument being the
		1142	constant string C<JSON> to distinguish it from other serialisers.
		1143
		1144	The C<FREEZE> method can return any number of values (i.e. zero or
		1145	more). These values and the paclkage/classname of the object will then be
		1146	encoded as a tagged JSON value in the following format:
		1147
		1148	("classname")[FREEZE return values...]
		1149
		1150	e.g.:
		1151
		1152	("URI")["http://www.google.com/"]
		1153	("MyDate")[2013,10,29]
		1154	("ImageData::JPEG")["Z3...VlCg=="]
		1155
		1156	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1157	objects C<type> and C<id> members to encode the object:
		1158
		1159	sub My::Object::FREEZE {
		1160	my ($self, $serialiser) = @_;
		1161
		1162	($self->{type}, $self->{id})
		1163	}
		1164
		1165	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
		1166
		1167	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1168	context. It must return a single scalar that can be directly encoded into
		1169	JSON. This scalar replaces the object in the JSON text.
		1170
		1171	For example, the following C<TO_JSON> method will convert all L<URI>
		1172	objects to JSON strings when serialised. The fatc that these values
		1173	originally were L<URI> objects is lost.
		1174
		1175	sub URI::TO_JSON {
		1176	my ($uri) = @_;
		1177	$uri->as_string
		1178	}
		1179
		1180	=item 3. C<allow_blessed> is enabled.
		1181
		1182	The object will be serialised as a JSON null value.
		1183
		1184	=item 4. none of the above
		1185
		1186	If none of the settings are enabled or the respective methods are missing,
		1187	C<JSON::XS> throws an exception.
		1188
		1189	=back
		1190
		1191	=head3 DESERIALISATION
		1192
		1193	For deserialisation there are only two cases to consider: either
		1194	nonstandard tagging was used, in which case C<allow_tags> decides,
		1195	or objects cannot be automatically be deserialised, in which
		1196	case you can use postprocessing or the C<filter_json_object> or
		1197	C<filter_json_single_key_object> callbacks to get some real objects our of
		1198	your JSON.
		1199
		1200	This section only considers the tagged value case: I a tagged JSON object
		1201	is encountered during decoding and C<allow_tags> is disabled, a parse
		1202	error will result (as if tagged values were not part of the grammar).
		1203
		1204	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1205	of the package/classname used during serialisation (it will not attempt
		1206	to load the package as a Perl module). If there is no such method, the
		1207	decoding will fail with an error.
		1208
		1209	Otherwise, the C<THAW> method is invoked with the classname as first
		1210	argument, the constant string C<JSON> as second argument, and all the
		1211	values from the JSON array (the values originally returned by the
		1212	C<FREEZE> method) as remaining arguments.
		1213
		1214	The method must then return the object. While technically you can return
		1215	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1216	make that work in all cases, so better return an actual blessed reference.
		1217
		1218	As an example, let's implement a C<THAW> function that regenerates the
		1219	C<My::Object> from the C<FREEZE> example earlier:
		1220
		1221	sub My::Object::THAW {
		1222	my ($class, $serialiser, $type, $id) = @_;
		1223
		1224	$class->new (type => $type, id => $id)
		1225	}
825		1226
826		1227
827	=head1 ENCODING/CODESET FLAG NOTES	1228	=head1 ENCODING/CODESET FLAG NOTES
828		1229
829	The interested reader might have seen a number of flags that signify	1230	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	1231	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:	1232	some confusion on what these do, so here is a short comparison:
832		1233
833	C<utf8> controls wether the JSON text created by C<encode> (and expected	1234	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	1235	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	1236	control whether C<encode> escapes character values outside their respective
836	codeset range. Neither of these flags conflict with each other, although	1237	codeset range. Neither of these flags conflict with each other, although
837	some combinations make less sense than others.	1238	some combinations make less sense than others.
838		1239
839	Care has been taken to make all flags symmetrical with respect to	1240	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	1241	C<encode> and C<decode>, that is, texts encoded with any combination of
…		…
854	=item C<utf8> flag disabled	1255	=item C<utf8> flag disabled
855		1256
856	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate	1257	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	1258	and expect Unicode strings, that is, characters with high ordinal Unicode
858	values (> 255) will be encoded as such characters, and likewise such	1259	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	1260	characters are decoded as-is, no changes to them will be done, except
860	"(re-)interpreting" them as Unicode codepoints or Unicode characters,	1261	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
861	respectively (to Perl, these are the same thing in strings unless you do	1262	respectively (to Perl, these are the same thing in strings unless you do
862	funny/weird/dumb stuff).	1263	funny/weird/dumb stuff).
863		1264
864	This is useful when you want to do the encoding yourself (e.g. when you	1265	This is useful when you want to do the encoding yourself (e.g. when you
…		…
920	proper subset of most 8-bit and multibyte encodings in use in the world.	1321	proper subset of most 8-bit and multibyte encodings in use in the world.
921		1322
922	=back	1323	=back
923		1324
924		1325
925	=head1 COMPARISON	1326	=head2 JSON and ECMAscript
926		1327
927	As already mentioned, this module was created because none of the existing	1328	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	1329	not-standardised predecessor of ECMAscript) which is presumably why it is
929	problems (or pleasures) I encountered with various existing JSON modules,	1330	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		1331
933	=over 4	1332	However, JSON is not a subset (and also not a superset of course) of
		1333	ECMAscript (the standard) or javascript (whatever browsers actually
		1334	implement).
934		1335
935	=item JSON 2.xx	1336	If you want to use javascript's C<eval> function to "parse" JSON, you
		1337	might run into parse errors for valid JSON texts, or the resulting data
		1338	structure might not be queryable:
936		1339
937	A marvellous piece of engineering, this module either uses JSON::XS	1340	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	1341	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	1342	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	1343	to be parsable by javascript's C<eval>:
941	slower.
942		1344
943	You cannot really lose by using this module.	1345	use JSON::XS;
944		1346
945	=item JSON 1.07	1347	print encode_json [chr 0x2028];
946		1348
947	Slow (but very portable, as it is written in pure Perl).	1349	The right fix for this is to use a proper JSON parser in your javascript
		1350	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1351	F<json2.js> parser).
948		1352
949	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1353	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	1354	ASCII-only JSON:
951	en-/decoding oneself, but Unicode escapes are not working properly).
952		1355
953	No round-tripping (strings get clobbered if they look like numbers, e.g.	1356	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		1357
957	=item JSON::PC 0.01	1358	print JSON::XS->new->ascii->encode ([chr 0x2028]);
958		1359
959	Very fast.	1360	Note that this will enlarge the resulting JSON text quite a bit if you
		1361	have many non-ASCII characters. You might be tempted to run some regexes
		1362	to only escape U+2028 and U+2029, e.g.:
960		1363
961	Undocumented/buggy Unicode handling.	1364	# DO NOT USE THIS!
		1365	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1366	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1367	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1368	print $json;
962		1369
963	No round-tripping.	1370	Note that I<this is a bad idea>: the above only works for U+2028 and
		1371	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1372	javascript implementations, however, have issues with other characters as
		1373	well - using C<eval> naively simply I<will> cause problems.
964		1374
965	Has problems handling many Perl values (e.g. regex results and other magic	1375	Another problem is that some javascript implementations reserve
966	values will make it croak).	1376	some property names for their own purposes (which probably makes
		1377	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1378	C<__proto__> property name for its own purposes.
967		1379
968	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1380	If that is a problem, you could parse try to filter the resulting JSON
969	which is not a valid JSON text.	1381	output for these property strings, e.g.:
970		1382
971	Unmaintained (maintainer unresponsive for many months, bugs are not	1383	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
972	getting fixed).
973		1384
974	=item JSON::Syck 0.21	1385	This works because C<__proto__> is not valid outside of strings, so every
		1386	occurrence of C<"__proto__"\s*:> must be a string used as property name.
975		1387
976	Very buggy (often crashes).	1388	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		1389
1021		1390
1022	=head2 JSON and YAML	1391	=head2 JSON and YAML
1023		1392
1024	You often hear that JSON is a subset of YAML. This is, however, a mass	1393	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	1394	hysteria(*) and very far from the truth (as of the time of this writing),
		1395	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	1396	JSON::XS to output a data structure as valid YAML> that works in all
1027	all cases.	1397	cases.
1028		1398
1029	If you really must use JSON::XS to generate YAML, you should use this	1399	If you really must use JSON::XS to generate YAML, you should use this
1030	algorithm (subject to change in future versions):	1400	algorithm (subject to change in future versions):
1031		1401
1032	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1402	my $to_yaml = JSON::XS->new->utf8->space_after (1);
1033	my $yaml = $to_yaml->encode ($ref) . "\n";	1403	my $yaml = $to_yaml->encode ($ref) . "\n";
1034		1404
1035	This will I<usually> generate JSON texts that also parse as valid	1405	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	1406	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	1407	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	1408	unicode character escape syntax, so you should make sure that your hash
1039	noticeably shorter than the 1024 "stream characters" YAML allows and that	1409	keys are noticeably shorter than the 1024 "stream characters" YAML allows
1040	you do not have codepoints with values outside the Unicode BMP (basic	1410	and that you do not have characters with codepoint values outside the
1041	multilingual page). YAML also does not allow C<\/> sequences in strings	1411	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
1042	(which JSON::XS does not I<currently> generate).	1412	sequences in strings (which JSON::XS does not I<currently> generate, but
		1413	other JSON generators might).
1043		1414
1044	There might be other incompatibilities that I am not aware of (or the YAML	1415	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	1416	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	1417	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	1418	versa, or try to parse JSON with a YAML parser or vice versa: chances are
…		…
1050		1421
1051	=over 4	1422	=over 4
1052		1423
1053	=item (*)	1424	=item (*)
1054		1425
1055	This is spread actively by the YAML team, however. For many years now they	1426	I have been pressured multiple times by Brian Ingerson (one of the
1056	claim YAML were a superset of JSON, even when proven otherwise.	1427	authors of the YAML specification) to remove this paragraph, despite him
		1428	acknowledging that the actual incompatibilities exist. As I was personally
		1429	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1430	educate people about these issues, so others do not run into the same
		1431	problem again and again. After this, Brian called me a (quote)I<complete
		1432	and worthless idiot>(unquote).
1057		1433
1058	Even the author of this manpage was at some point accused of providing	1434	In my opinion, instead of pressuring and insulting people who actually
1059	"incorrect" information, despite the evidence presented (claims ranged	1435	clarify issues with YAML and the wrong statements of some of its
1060	from "your documentation contains inaccurate and negative statements about	1436	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	1437	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	1438	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	1439	real compatibility for many I<years> and trying to silence people who
1064	JSON-compatible spec is apparently not currently publicly available)	1440	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		1441
1068	So whenever you are told that YAML was a superset of JSON, first check	1442	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	1443	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	1444	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	1445	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	1446	corrupting userdata is so much easier.
1073	trying to lobby/force people into reporting untruths.
1074		1447
1075	=back	1448	=back
1076		1449
1077		1450
1078	=head2 SPEED	1451	=head2 SPEED
…		…
1080	It seems that JSON::XS is surprisingly fast, as shown in the following	1453	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	1454	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	1455	in the JSON::XS distribution, to make it easy to compare on your own
1083	system.	1456	system.
1084		1457
1085	First comes a comparison between various modules using a very short	1458	First comes a comparison between various modules using
1086	single-line JSON string:	1459	a very short single-line JSON string (also available at
		1460	L<http://dist.schmorp.de/misc/json/short.json>).
1087		1461
1088	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1462	{"method": "handleMessage", "params": ["user1",
1089	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1463	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1464	1, 0]}
1090		1465
1091	It shows the number of encodes/decodes per second (JSON::XS uses	1466	It shows the number of encodes/decodes per second (JSON::XS uses
1092	the functional interface, while JSON::XS/2 uses the OO interface	1467	the functional interface, while JSON::XS/2 uses the OO interface
1093	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1468	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
1094	shrink). Higher is better:	1469	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1470	uses the from_json method). Higher is better:
1095		1471
1096	module \| encode \| decode \|	1472	module \| encode \| decode \|
1097	-----------\|------------\|------------\|	1473	--------------\|------------\|------------\|
1098	JSON 1.x \| 4990.842 \| 4088.813 \|	1474	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
1099	JSON::DWIW \| 51653.990 \| 71575.154 \|	1475	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
1100	JSON::PC \| 65948.176 \| 74631.744 \|	1476	JSON::PP \| 15827.562 \| 6638.658 \|
1101	JSON::PP \| 8931.652 \| 3817.168 \|	1477	JSON::Syck \| 63358.066 \| 47662.545 \|
1102	JSON::Syck \| 24877.248 \| 27776.848 \|	1478	JSON::XS \| 511500.488 \| 511500.488 \|
1103	JSON::XS \| 388361.481 \| 227951.304 \|	1479	JSON::XS/2 \| 291271.111 \| 388361.481 \|
1104	JSON::XS/2 \| 227951.304 \| 218453.333 \|	1480	JSON::XS/3 \| 361577.931 \| 361577.931 \|
1105	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1481	Storable \| 66788.280 \| 265462.278 \|
1106	Storable \| 16500.016 \| 135300.129 \|
1107	-----------+------------+------------+	1482	--------------+------------+------------+
1108		1483
1109	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1484	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	1485	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	1486	faster than JSON's pure perl implementation. It also compares favourably
1112	favourably to Storable for small amounts of data.	1487	to Storable for small amounts of data.
1113		1488
1114	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1489	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1115	search API (http://nanoref.com/yahooapis/mgPdGg):	1490	search API (L<http://dist.schmorp.de/misc/json/long.json>).
1116		1491
1117	module \| encode \| decode \|	1492	module \| encode \| decode \|
1118	-----------\|------------\|------------\|	1493	--------------\|------------\|------------\|
1119	JSON 1.x \| 55.260 \| 34.971 \|	1494	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
1120	JSON::DWIW \| 825.228 \| 1082.513 \|	1495	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
1121	JSON::PC \| 3571.444 \| 2394.829 \|
1122	JSON::PP \| 210.987 \| 32.574 \|	1496	JSON::PP \| 400.640 \| 62.311 \|
1123	JSON::Syck \| 552.551 \| 787.544 \|	1497	JSON::Syck \| 1481.040 \| 1524.869 \|
1124	JSON::XS \| 5780.463 \| 4854.519 \|	1498	JSON::XS \| 20661.596 \| 9541.183 \|
1125	JSON::XS/2 \| 3869.998 \| 4798.975 \|	1499	JSON::XS/2 \| 10683.403 \| 9416.938 \|
1126	JSON::XS/3 \| 5862.880 \| 4798.975 \|	1500	JSON::XS/3 \| 20661.596 \| 9400.054 \|
1127	Storable \| 4445.002 \| 5235.027 \|	1501	Storable \| 19765.806 \| 10000.725 \|
1128	-----------+------------+------------+	1502	--------------+------------+------------+
1129		1503
1130	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1504	Again, JSON::XS leads by far (except for Storable which non-surprisingly
1131	decodes faster).	1505	decodes a bit faster).
1132		1506
1133	On large strings containing lots of high Unicode characters, some modules	1507	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	1508	(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	1509	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	1510	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	1536	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	1537	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	1538	has a smaller stack, you should adjust this setting accordingly with the
1165	C<max_depth> method.	1539	C<max_depth> method.
1166		1540
1167	And last but least, something else could bomb you that I forgot to think	1541	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,	1542	case, you get to keep the pieces. I am always open for hints, though...
1169	though...	1543
		1544	Also keep in mind that JSON::XS might leak contents of your Perl data
		1545	structures in its error messages, so when you serialise sensitive
		1546	information you might want to make sure that exceptions thrown by JSON::XS
		1547	will not end up in front of untrusted eyes.
1170		1548
1171	If you are using JSON::XS to return packets to consumption	1549	If you are using JSON::XS to return packets to consumption
1172	by JavaScript scripts in a browser you should have a look at	1550	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	1551	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	1552	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	1553	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	1554	it, as major browser developers care only for features, not about getting
1177	right).	1555	security right).
		1556
		1557
		1558	=head1 INTEROPERABILITY WITH OTHER MODULES
		1559
		1560	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1561	constants. That means that the JSON true and false values will be
		1562	comaptible to true and false values of iother modules that do the same,
		1563	such as L<JSON::PP> and L<CBOR::XS>.
1178		1564
1179		1565
1180	=head1 THREADS	1566	=head1 THREADS
1181		1567
1182	This module is I<not> guaranteed to be thread safe and there are no	1568	This module is I<not> guaranteed to be thread safe and there are no
1183	plans to change this until Perl gets thread support (as opposed to the	1569	plans to change this until Perl gets thread support (as opposed to the
1184	horribly slow so-called "threads" which are simply slow and bloated	1570	horribly slow so-called "threads" which are simply slow and bloated
1185	process simulations - use fork, its I<much> faster, cheaper, better).	1571	process simulations - use fork, it's I<much> faster, cheaper, better).
1186		1572
1187	(It might actually work, but you have been warned).	1573	(It might actually work, but you have been warned).
1188		1574
1189		1575
		1576	=head1 THE PERILS OF SETLOCALE
		1577
		1578	Sometimes people avoid the Perl locale support and directly call the
		1579	system's setlocale function with C<LC_ALL>.
		1580
		1581	This breaks both perl and modules such as JSON::XS, as stringification of
		1582	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1583	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1584	perl to stringify numbers).
		1585
		1586	The solution is simple: don't call C<setlocale>, or use it for only those
		1587	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1588
		1589	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1590	actually needs it (avoiding stringification of numbers), and restore it
		1591	afterwards.
		1592
		1593
1190	=head1 BUGS	1594	=head1 BUGS
1191		1595
1192	While the goal of this module is to be correct, that unfortunately does	1596	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	1597	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	1598	keep reporting bugs they will be fixed swiftly, though.
1195	will be fixed swiftly, though.
1196		1599
1197	Please refrain from using rt.cpan.org or any other bug reporting	1600	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.	1601	service. I put the contact address into my modules for a reason.
1199		1602
1200	=cut	1603	=cut
1201		1604
1202	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1605	BEGIN {
1203	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };	1606	*true = \$Types::Serialiser::true;
		1607	*true = \&Types::Serialiser::true;
		1608	*false = \$Types::Serialiser::false;
		1609	*false = \&Types::Serialiser::false;
		1610	*is_bool = \&Types::Serialiser::is_bool;
1204		1611
1205	sub true() { $true }	1612	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	}	1613	}
1212		1614
1213	XSLoader::load "JSON::XS", $VERSION;	1615	XSLoader::load "JSON::XS", $VERSION;
1214		1616
1215	package JSON::XS::Boolean;	1617	=head1 SEE ALSO
1216		1618
1217	use overload	1619	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		1620
1225	=head1 AUTHOR	1621	=head1 AUTHOR
1226		1622
1227	Marc Lehmann <schmorp@schmorp.de>	1623	Marc Lehmann <schmorp@schmorp.de>
1228	http://home.schmorp.de/	1624	http://home.schmorp.de/
1229		1625
1230	=cut	1626	=cut
1231		1627
		1628	1
		1629

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Comparing JSON-XS/XS.pm (file contents): Revision 1.84 by root, Wed Mar 19 02:52:15 2008 UTC vs. Revision 1.150 by root, Tue Oct 29 00:48:07 2013 UTC

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Comparing JSON-XS/XS.pm (file contents):
Revision 1.84 by root, Wed Mar 19 02:52:15 2008 UTC vs.
Revision 1.150 by root, Tue Oct 29 00:48:07 2013 UTC