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Revision 1.75 by root, Thu Nov 29 13:35:35 2007 UTC vs.
Revision 1.156 by root, Sun Feb 21 15:37:53 2016 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
		5	=encoding utf-8
4		6
5	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ	7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
6	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)	8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7		9
8	=head1 SYNOPSIS	10	=head1 SYNOPSIS
…		…
10	use JSON::XS;	12	use JSON::XS;
11		13
12	# exported functions, they croak on error	14	# exported functions, they croak on error
13	# and expect/generate UTF-8	15	# and expect/generate UTF-8
14		16
15	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
16	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
17		19
18	# OO-interface	20	# OO-interface
19		21
20	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
21	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
22	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
23		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
		33
24	=head1 DESCRIPTION	34	=head1 DESCRIPTION
25		35
26	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
27	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
28	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
		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	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
		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.
29		47
30	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
31	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
32	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
33	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
34	reports for other reasons.	52	reports for other reasons.
35		53
36	See COMPARISON, below, for a comparison to some other JSON modules.
37
38	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
39	vice versa.	55	vice versa.
40		56
41	=head2 FEATURES	57	=head2 FEATURES
42		58
43	=over 4	59	=over 4
44		60
45	=item * correct Unicode handling	61	=item * correct Unicode handling
46		62
47	This module knows how to handle Unicode, and even documents how and when	63	This module knows how to handle Unicode, documents how and when it does
48	it does so.	64	so, and even documents what "correct" means.
49		65
50	=item * round-trip integrity	66	=item * round-trip integrity
51		67
52	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
53	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
54	(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
55	like a number).	71	it looks like a number). There I<are> minor exceptions to this, read the
		72	MAPPING section below to learn about those.
56		73
57	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
58		75
59	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,
60	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
61	feature).	78	feature).
62		79
63	=item * fast	80	=item * fast
64		81
65	Compared to other JSON modules, this module compares favourably in terms	82	Compared to other JSON modules and other serialisers such as Storable,
66	of speed, too.	83	this module usually compares favourably in terms of speed, too.
67		84
68	=item * simple to use	85	=item * simple to use
69		86
70	This module has both a simple functional interface as well as an OO	87	This module has both a simple functional interface as well as an object
71	interface.	88	oriented interface.
72		89
73	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
74		91
75	You can choose between the most compact guaranteed single-line format	92	You can choose between the most compact guaranteed-single-line format
76	possible (nice for simple line-based protocols), a pure-ascii format	93	possible (nice for simple line-based protocols), a pure-ASCII format
77	(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
78	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
79	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.
80		97
81	=back	98	=back
82		99
83	=cut	100	=cut
84		101
85	package JSON::XS;	102	package JSON::XS;
86		103
87	use strict;	104	use common::sense;
88		105
89	our $VERSION = '2.0';	106	our $VERSION = 3.01;
90	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
91		108
92	our @EXPORT = qw(to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
93		110
94	use Exporter;	111	use Exporter;
95	use XSLoader;	112	use XSLoader;
96		113
		114	use Types::Serialiser ();
		115
97	=head1 FUNCTIONAL INTERFACE	116	=head1 FUNCTIONAL INTERFACE
98		117
99	The following convenience methods are provided by this module. They are	118	The following convenience methods are provided by this module. They are
100	exported by default:	119	exported by default:
101		120
102	=over 4	121	=over 4
103		122
104	=item $json_text = to_json $perl_scalar	123	=item $json_text = encode_json $perl_scalar
105		124
106	Converts the given Perl data structure to a UTF-8 encoded, binary string	125	Converts the given Perl data structure to a UTF-8 encoded, binary string
107	(that is, the string contains octets only). Croaks on error.	126	(that is, the string contains octets only). Croaks on error.
108		127
109	This function call is functionally identical to:	128	This function call is functionally identical to:
110		129
111	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	130	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
112		131
113	except being faster.	132	Except being faster.
114		133
115	=item $perl_scalar = from_json $json_text	134	=item $perl_scalar = decode_json $json_text
116		135
117	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries	136	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
118	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
119	reference. Croaks on error.	138	reference. Croaks on error.
120		139
121	This function call is functionally identical to:	140	This function call is functionally identical to:
122		141
123	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	142	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
124		143
125	except being faster.	144	Except being faster.
126
127	=item $is_boolean = JSON::XS::is_bool $scalar
128
129	Returns true if the passed scalar represents either JSON::XS::true or
130	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
131	and are used to represent JSON C<true> and C<false> values in Perl.
132
133	See MAPPING, below, for more information on how JSON values are mapped to
134	Perl.
135		145
136	=back	146	=back
137		147
138		148
139	=head1 A FEW NOTES ON UNICODE AND PERL	149	=head1 A FEW NOTES ON UNICODE AND PERL
…		…
148	This enables you to store Unicode characters as single characters in a	158	This enables you to store Unicode characters as single characters in a
149	Perl string - very natural.	159	Perl string - very natural.
150		160
151	=item 2. Perl does I<not> associate an encoding with your strings.	161	=item 2. Perl does I<not> associate an encoding with your strings.
152		162
153	Unless you force it to, e.g. when matching it against a regex, or printing	163	... until you force it to, e.g. when matching it against a regex, or
154	the scalar to a file, in which case Perl either interprets your string as	164	printing the scalar to a file, in which case Perl either interprets your
155	locale-encoded text, octets/binary, or as Unicode, depending on various	165	string as locale-encoded text, octets/binary, or as Unicode, depending
156	settings. In no case is an encoding stored together with your data, it is	166	on various settings. In no case is an encoding stored together with your
157	I<use> that decides encoding, not any magical metadata.	167	data, it is I<use> that decides encoding, not any magical meta data.
158		168
159	=item 3. The internal utf-8 flag has no meaning with regards to the	169	=item 3. The internal utf-8 flag has no meaning with regards to the
160	encoding of your string.	170	encoding of your string.
161		171
162	Just ignore that flag unless you debug a Perl bug, a module written in	172	Just ignore that flag unless you debug a Perl bug, a module written in
…		…
168		178
169	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
170	exist.	180	exist.
171		181
172	=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
173	validly interpreted as a Unicode codepoint.	183	validly interpreted as a Unicode code point.
174		184
175	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
176	Unicode string encoded in UTF-8, giving you a binary string.	186	Unicode string encoded in UTF-8, giving you a binary string.
177		187
178	=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.
…		…
216		226
217	If C<$enable> is false, then the C<encode> method will not escape Unicode	227	If C<$enable> is false, then the C<encode> method will not escape Unicode
218	characters unless required by the JSON syntax or other flags. This results	228	characters unless required by the JSON syntax or other flags. This results
219	in a faster and more compact format.	229	in a faster and more compact format.
220		230
		231	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		232	document.
		233
221	The main use for this flag is to produce JSON texts that can be	234	The main use for this flag is to produce JSON texts that can be
222	transmitted over a 7-bit channel, as the encoded JSON texts will not	235	transmitted over a 7-bit channel, as the encoded JSON texts will not
223	contain any 8 bit characters.	236	contain any 8 bit characters.
224		237
225	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	238	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
236	will not be affected in any way by this flag, as C<decode> by default	249	will not be affected in any way by this flag, as C<decode> by default
237	expects Unicode, which is a strict superset of latin1.	250	expects Unicode, which is a strict superset of latin1.
238		251
239	If C<$enable> is false, then the C<encode> method will not escape Unicode	252	If C<$enable> is false, then the C<encode> method will not escape Unicode
240	characters unless required by the JSON syntax or other flags.	253	characters unless required by the JSON syntax or other flags.
		254
		255	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		256	document.
241		257
242	The main use for this flag is efficiently encoding binary data as JSON	258	The main use for this flag is efficiently encoding binary data as JSON
243	text, as most octets will not be escaped, resulting in a smaller encoded	259	text, as most octets will not be escaped, resulting in a smaller encoded
244	size. The disadvantage is that the resulting JSON text is encoded	260	size. The disadvantage is that the resulting JSON text is encoded
245	in latin1 (and must correctly be treated as such when storing and	261	in latin1 (and must correctly be treated as such when storing and
…		…
264		280
265	If C<$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
266	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
267	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
268	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.
269		288
270	Example, output UTF-16BE-encoded JSON:	289	Example, output UTF-16BE-encoded JSON:
271		290
272	use Encode;	291	use Encode;
273	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	292	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
385	[	404	[
386	1, # this comment not allowed in JSON	405	1, # this comment not allowed in JSON
387	# neither this one...	406	# neither this one...
388	]	407	]
389		408
		409	=item * literal ASCII TAB characters in strings
		410
		411	Literal ASCII TAB characters are now allowed in strings (and treated as
		412	C<\t>).
		413
		414	[
		415	"Hello\tWorld",
		416	"Hello<TAB>World", # literal <TAB> would not normally be allowed
		417	]
		418
390	=back	419	=back
391		420
392	=item $json = $json->canonical ([$enable])	421	=item $json = $json->canonical ([$enable])
393		422
394	=item $enabled = $json->get_canonical	423	=item $enabled = $json->get_canonical
…		…
396	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	425	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
397	by sorting their keys. This is adding a comparatively high overhead.	426	by sorting their keys. This is adding a comparatively high overhead.
398		427
399	If C<$enable> is false, then the C<encode> method will output key-value	428	If C<$enable> is false, then the C<encode> method will output key-value
400	pairs in the order Perl stores them (which will likely change between runs	429	pairs in the order Perl stores them (which will likely change between runs
401	of the same script).	430	of the same script, and can change even within the same run from 5.18
		431	onwards).
402		432
403	This option is useful if you want the same data structure to be encoded as	433	This option is useful if you want the same data structure to be encoded as
404	the same JSON text (given the same overall settings). If it is disabled,	434	the same JSON text (given the same overall settings). If it is disabled,
405	the same hash might be encoded differently even if contains the same data,	435	the same hash might be encoded differently even if contains the same data,
406	as key-value pairs have no inherent ordering in Perl.	436	as key-value pairs have no inherent ordering in Perl.
407		437
408	This setting has no effect when decoding JSON texts.	438	This setting has no effect when decoding JSON texts.
409		439
		440	This setting has currently no effect on tied hashes.
		441
410	=item $json = $json->allow_nonref ([$enable])	442	=item $json = $json->allow_nonref ([$enable])
411		443
412	=item $enabled = $json->get_allow_nonref	444	=item $enabled = $json->get_allow_nonref
413		445
414	If C<$enable> is true (or missing), then the C<encode> method can convert a	446	If C<$enable> is true (or missing), then the C<encode> method can convert a
…		…
425	resulting in an invalid JSON text:	457	resulting in an invalid JSON text:
426		458
427	JSON::XS->new->allow_nonref->encode ("Hello, World!")	459	JSON::XS->new->allow_nonref->encode ("Hello, World!")
428	=> "Hello, World!"	460	=> "Hello, World!"
429		461
		462	=item $json = $json->allow_unknown ([$enable])
		463
		464	=item $enabled = $json->get_allow_unknown
		465
		466	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		467	exception when it encounters values it cannot represent in JSON (for
		468	example, filehandles) but instead will encode a JSON C<null> value. Note
		469	that blessed objects are not included here and are handled separately by
		470	c<allow_nonref>.
		471
		472	If C<$enable> is false (the default), then C<encode> will throw an
		473	exception when it encounters anything it cannot encode as JSON.
		474
		475	This option does not affect C<decode> in any way, and it is recommended to
		476	leave it off unless you know your communications partner.
		477
430	=item $json = $json->allow_blessed ([$enable])	478	=item $json = $json->allow_blessed ([$enable])
431		479
432	=item $enabled = $json->get_allow_blessed	480	=item $enabled = $json->get_allow_blessed
433		481
		482	See L<OBJECT SERIALISATION> for details.
		483
434	If C<$enable> is true (or missing), then the C<encode> method will not	484	If C<$enable> is true (or missing), then the C<encode> method will not
435	barf when it encounters a blessed reference. Instead, the value of the	485	barf when it encounters a blessed reference that it cannot convert
436	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>	486	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
437	disabled or no C<to_json> method found) or a representation of the
438	object (C<convert_blessed> enabled and C<to_json> method found) is being
439	encoded. Has no effect on C<decode>.
440		487
441	If C<$enable> is false (the default), then C<encode> will throw an	488	If C<$enable> is false (the default), then C<encode> will throw an
442	exception when it encounters a blessed object.	489	exception when it encounters a blessed object that it cannot convert
		490	otherwise.
		491
		492	This setting has no effect on C<decode>.
443		493
444	=item $json = $json->convert_blessed ([$enable])	494	=item $json = $json->convert_blessed ([$enable])
445		495
446	=item $enabled = $json->get_convert_blessed	496	=item $enabled = $json->get_convert_blessed
		497
		498	See L<OBJECT SERIALISATION> for details.
447		499
448	If C<$enable> is true (or missing), then C<encode>, upon encountering a	500	If C<$enable> is true (or missing), then C<encode>, upon encountering a
449	blessed object, will check for the availability of the C<TO_JSON> method	501	blessed object, will check for the availability of the C<TO_JSON> method
450	on the object's class. If found, it will be called in scalar context	502	on the object's class. If found, it will be called in scalar context and
451	and the resulting scalar will be encoded instead of the object. If no	503	the resulting scalar will be encoded instead of the object.
452	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
453	to do.
454		504
455	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	505	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
456	returns other blessed objects, those will be handled in the same	506	returns other blessed objects, those will be handled in the same
457	way. C<TO_JSON> must take care of not causing an endless recursion cycle	507	way. C<TO_JSON> must take care of not causing an endless recursion cycle
458	(== crash) in this case. The name of C<TO_JSON> was chosen because other	508	(== crash) in this case. The name of C<TO_JSON> was chosen because other
459	methods called by the Perl core (== not by the user of the object) are	509	methods called by the Perl core (== not by the user of the object) are
460	usually in upper case letters and to avoid collisions with the C<to_json>	510	usually in upper case letters and to avoid collisions with any C<to_json>
461	function.	511	function or method.
462		512
463	This setting does not yet influence C<decode> in any way, but in the	513	If C<$enable> is false (the default), then C<encode> will not consider
464	future, global hooks might get installed that influence C<decode> and are	514	this type of conversion.
465	enabled by this setting.
466		515
467	If C<$enable> is false, then the C<allow_blessed> setting will decide what	516	This setting has no effect on C<decode>.
468	to do when a blessed object is found.	517
		518	=item $json = $json->allow_tags ([$enable])
		519
		520	=item $enabled = $json->allow_tags
		521
		522	See L<OBJECT SERIALISATION> for details.
		523
		524	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		525	blessed object, will check for the availability of the C<FREEZE> method on
		526	the object's class. If found, it will be used to serialise the object into
		527	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		528
		529	It also causes C<decode> to parse such tagged JSON values and deserialise
		530	them via a call to the C<THAW> method.
		531
		532	If C<$enable> is false (the default), then C<encode> will not consider
		533	this type of conversion, and tagged JSON values will cause a parse error
		534	in C<decode>, as if tags were not part of the grammar.
469		535
470	=item $json = $json->filter_json_object ([$coderef->($hashref)])	536	=item $json = $json->filter_json_object ([$coderef->($hashref)])
471		537
472	When C<$coderef> is specified, it will be called from C<decode> each	538	When C<$coderef> is specified, it will be called from C<decode> each
473	time it decodes a JSON object. The only argument is a reference to the	539	time it decodes a JSON object. The only argument is a reference to the
…		…
574	=item $json = $json->max_depth ([$maximum_nesting_depth])	640	=item $json = $json->max_depth ([$maximum_nesting_depth])
575		641
576	=item $max_depth = $json->get_max_depth	642	=item $max_depth = $json->get_max_depth
577		643
578	Sets the maximum nesting level (default C<512>) accepted while encoding	644	Sets the maximum nesting level (default C<512>) accepted while encoding
579	or decoding. If the JSON text or Perl data structure has an equal or	645	or decoding. If a higher nesting level is detected in JSON text or a Perl
580	higher nesting level then this limit, then the encoder and decoder will	646	data structure, then the encoder and decoder will stop and croak at that
581	stop and croak at that point.	647	point.
582		648
583	Nesting level is defined by number of hash- or arrayrefs that the encoder	649	Nesting level is defined by number of hash- or arrayrefs that the encoder
584	needs to traverse to reach a given point or the number of C<{> or C<[>	650	needs to traverse to reach a given point or the number of C<{> or C<[>
585	characters without their matching closing parenthesis crossed to reach a	651	characters without their matching closing parenthesis crossed to reach a
586	given character in a string.	652	given character in a string.
587		653
588	Setting the maximum depth to one disallows any nesting, so that ensures	654	Setting the maximum depth to one disallows any nesting, so that ensures
589	that the object is only a single hash/object or array.	655	that the object is only a single hash/object or array.
590		656
591	The argument to C<max_depth> will be rounded up to the next highest power
592	of two. If no argument is given, the highest possible setting will be	657	If no argument is given, the highest possible setting will be used, which
593	used, which is rarely useful.	658	is rarely useful.
		659
		660	Note that nesting is implemented by recursion in C. The default value has
		661	been chosen to be as large as typical operating systems allow without
		662	crashing.
594		663
595	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	664	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
596		665
597	=item $json = $json->max_size ([$maximum_string_size])	666	=item $json = $json->max_size ([$maximum_string_size])
598		667
599	=item $max_size = $json->get_max_size	668	=item $max_size = $json->get_max_size
600		669
601	Set the maximum length a JSON text may have (in bytes) where decoding is	670	Set the maximum length a JSON text may have (in bytes) where decoding is
602	being attempted. The default is C<0>, meaning no limit. When C<decode>	671	being attempted. The default is C<0>, meaning no limit. When C<decode>
603	is called on a string longer then this number of characters it will not	672	is called on a string that is longer then this many bytes, it will not
604	attempt to decode the string but throw an exception. This setting has no	673	attempt to decode the string but throw an exception. This setting has no
605	effect on C<encode> (yet).	674	effect on C<encode> (yet).
606		675
607	The argument to C<max_size> will be rounded up to the next B<highest>	676	If no argument is given, the limit check will be deactivated (same as when
608	power of two (so may be more than requested). If no argument is given, the	677	C<0> is specified).
609	limit check will be deactivated (same as when C<0> is specified).
610		678
611	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	679	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
612		680
613	=item $json_text = $json->encode ($perl_scalar)	681	=item $json_text = $json->encode ($perl_scalar)
614		682
615	Converts the given Perl data structure (a simple scalar or a reference	683	Converts the given Perl value or data structure to its JSON
616	to a hash or array) to its JSON representation. Simple scalars will be	684	representation. Croaks on error.
617	converted into JSON string or number sequences, while references to arrays
618	become JSON arrays and references to hashes become JSON objects. Undefined
619	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
620	nor C<false> values will be generated.
621		685
622	=item $perl_scalar = $json->decode ($json_text)	686	=item $perl_scalar = $json->decode ($json_text)
623		687
624	The opposite of C<encode>: expects a JSON text and tries to parse it,	688	The opposite of C<encode>: expects a JSON text and tries to parse it,
625	returning the resulting simple scalar or reference. Croaks on error.	689	returning the resulting simple scalar or reference. Croaks on error.
626
627	JSON numbers and strings become simple Perl scalars. JSON arrays become
628	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
629	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
630		690
631	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	691	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
632		692
633	This works like the C<decode> method, but instead of raising an exception	693	This works like the C<decode> method, but instead of raising an exception
634	when there is trailing garbage after the first JSON object, it will	694	when there is trailing garbage after the first JSON object, it will
635	silently stop parsing there and return the number of characters consumed	695	silently stop parsing there and return the number of characters consumed
636	so far.	696	so far.
637		697
638	This is useful if your JSON texts are not delimited by an outer protocol	698	This is useful if your JSON texts are not delimited by an outer protocol
639	(which is not the brightest thing to do in the first place) and you need
640	to know where the JSON text ends.	699	and you need to know where the JSON text ends.
641		700
642	JSON::XS->new->decode_prefix ("[1] the tail")	701	JSON::XS->new->decode_prefix ("[1] the tail")
643	=> ([], 3)	702	=> ([1], 3)
644		703
645	=back	704	=back
		705
		706
		707	=head1 INCREMENTAL PARSING
		708
		709	In some cases, there is the need for incremental parsing of JSON
		710	texts. While this module always has to keep both JSON text and resulting
		711	Perl data structure in memory at one time, it does allow you to parse a
		712	JSON stream incrementally. It does so by accumulating text until it has
		713	a full JSON object, which it then can decode. This process is similar to
		714	using C<decode_prefix> to see if a full JSON object is available, but
		715	is much more efficient (and can be implemented with a minimum of method
		716	calls).
		717
		718	JSON::XS will only attempt to parse the JSON text once it is sure it
		719	has enough text to get a decisive result, using a very simple but
		720	truly incremental parser. This means that it sometimes won't stop as
		721	early as the full parser, for example, it doesn't detect mismatched
		722	parentheses. The only thing it guarantees is that it starts decoding as
		723	soon as a syntactically valid JSON text has been seen. This means you need
		724	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		725	parsing in the presence if syntax errors.
		726
		727	The following methods implement this incremental parser.
		728
		729	=over 4
		730
		731	=item [void, scalar or list context] = $json->incr_parse ([$string])
		732
		733	This is the central parsing function. It can both append new text and
		734	extract objects from the stream accumulated so far (both of these
		735	functions are optional).
		736
		737	If C<$string> is given, then this string is appended to the already
		738	existing JSON fragment stored in the C<$json> object.
		739
		740	After that, if the function is called in void context, it will simply
		741	return without doing anything further. This can be used to add more text
		742	in as many chunks as you want.
		743
		744	If the method is called in scalar context, then it will try to extract
		745	exactly I<one> JSON object. If that is successful, it will return this
		746	object, otherwise it will return C<undef>. If there is a parse error,
		747	this method will croak just as C<decode> would do (one can then use
		748	C<incr_skip> to skip the erroneous part). This is the most common way of
		749	using the method.
		750
		751	And finally, in list context, it will try to extract as many objects
		752	from the stream as it can find and return them, or the empty list
		753	otherwise. For this to work, there must be no separators between the JSON
		754	objects or arrays, instead they must be concatenated back-to-back. If
		755	an error occurs, an exception will be raised as in the scalar context
		756	case. Note that in this case, any previously-parsed JSON texts will be
		757	lost.
		758
		759	Example: Parse some JSON arrays/objects in a given string and return
		760	them.
		761
		762	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		763
		764	=item $lvalue_string = $json->incr_text
		765
		766	This method returns the currently stored JSON fragment as an lvalue, that
		767	is, you can manipulate it. This I<only> works when a preceding call to
		768	C<incr_parse> in I<scalar context> successfully returned an object. Under
		769	all other circumstances you must not call this function (I mean it.
		770	although in simple tests it might actually work, it I<will> fail under
		771	real world conditions). As a special exception, you can also call this
		772	method before having parsed anything.
		773
		774	This function is useful in two cases: a) finding the trailing text after a
		775	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		776	(such as commas).
		777
		778	=item $json->incr_skip
		779
		780	This will reset the state of the incremental parser and will remove
		781	the parsed text from the input buffer so far. This is useful after
		782	C<incr_parse> died, in which case the input buffer and incremental parser
		783	state is left unchanged, to skip the text parsed so far and to reset the
		784	parse state.
		785
		786	The difference to C<incr_reset> is that only text until the parse error
		787	occurred is removed.
		788
		789	=item $json->incr_reset
		790
		791	This completely resets the incremental parser, that is, after this call,
		792	it will be as if the parser had never parsed anything.
		793
		794	This is useful if you want to repeatedly parse JSON objects and want to
		795	ignore any trailing data, which means you have to reset the parser after
		796	each successful decode.
		797
		798	=back
		799
		800	=head2 LIMITATIONS
		801
		802	All options that affect decoding are supported, except
		803	C<allow_nonref>. The reason for this is that it cannot be made to work
		804	sensibly: JSON objects and arrays are self-delimited, i.e. you can
		805	concatenate them back to back and still decode them perfectly. This does
		806	not hold true for JSON numbers, however.
		807
		808	For example, is the string C<1> a single JSON number, or is it simply the
		809	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		810	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		811	takes the conservative route and disallows this case.
		812
		813	=head2 EXAMPLES
		814
		815	Some examples will make all this clearer. First, a simple example that
		816	works similarly to C<decode_prefix>: We want to decode the JSON object at
		817	the start of a string and identify the portion after the JSON object:
		818
		819	my $text = "[1,2,3] hello";
		820
		821	my $json = new JSON::XS;
		822
		823	my $obj = $json->incr_parse ($text)
		824	or die "expected JSON object or array at beginning of string";
		825
		826	my $tail = $json->incr_text;
		827	# $tail now contains " hello"
		828
		829	Easy, isn't it?
		830
		831	Now for a more complicated example: Imagine a hypothetical protocol where
		832	you read some requests from a TCP stream, and each request is a JSON
		833	array, without any separation between them (in fact, it is often useful to
		834	use newlines as "separators", as these get interpreted as whitespace at
		835	the start of the JSON text, which makes it possible to test said protocol
		836	with C<telnet>...).
		837
		838	Here is how you'd do it (it is trivial to write this in an event-based
		839	manner):
		840
		841	my $json = new JSON::XS;
		842
		843	# read some data from the socket
		844	while (sysread $socket, my $buf, 4096) {
		845
		846	# split and decode as many requests as possible
		847	for my $request ($json->incr_parse ($buf)) {
		848	# act on the $request
		849	}
		850	}
		851
		852	Another complicated example: Assume you have a string with JSON objects
		853	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		854	[3]>). To parse them, we have to skip the commas between the JSON texts,
		855	and here is where the lvalue-ness of C<incr_text> comes in useful:
		856
		857	my $text = "[1],[2], [3]";
		858	my $json = new JSON::XS;
		859
		860	# void context, so no parsing done
		861	$json->incr_parse ($text);
		862
		863	# now extract as many objects as possible. note the
		864	# use of scalar context so incr_text can be called.
		865	while (my $obj = $json->incr_parse) {
		866	# do something with $obj
		867
		868	# now skip the optional comma
		869	$json->incr_text =~ s/^ \s* , //x;
		870	}
		871
		872	Now lets go for a very complex example: Assume that you have a gigantic
		873	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		874	but you cannot load it into memory fully (this has actually happened in
		875	the real world :).
		876
		877	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		878	can still help you: You implement a (very simple) array parser and let
		879	JSON decode the array elements, which are all full JSON objects on their
		880	own (this wouldn't work if the array elements could be JSON numbers, for
		881	example):
		882
		883	my $json = new JSON::XS;
		884
		885	# open the monster
		886	open my $fh, "<bigfile.json"
		887	or die "bigfile: $!";
		888
		889	# first parse the initial "["
		890	for (;;) {
		891	sysread $fh, my $buf, 65536
		892	or die "read error: $!";
		893	$json->incr_parse ($buf); # void context, so no parsing
		894
		895	# Exit the loop once we found and removed(!) the initial "[".
		896	# In essence, we are (ab-)using the $json object as a simple scalar
		897	# we append data to.
		898	last if $json->incr_text =~ s/^ \s* \[ //x;
		899	}
		900
		901	# now we have the skipped the initial "[", so continue
		902	# parsing all the elements.
		903	for (;;) {
		904	# in this loop we read data until we got a single JSON object
		905	for (;;) {
		906	if (my $obj = $json->incr_parse) {
		907	# do something with $obj
		908	last;
		909	}
		910
		911	# add more data
		912	sysread $fh, my $buf, 65536
		913	or die "read error: $!";
		914	$json->incr_parse ($buf); # void context, so no parsing
		915	}
		916
		917	# in this loop we read data until we either found and parsed the
		918	# separating "," between elements, or the final "]"
		919	for (;;) {
		920	# first skip whitespace
		921	$json->incr_text =~ s/^\s*//;
		922
		923	# if we find "]", we are done
		924	if ($json->incr_text =~ s/^\]//) {
		925	print "finished.\n";
		926	exit;
		927	}
		928
		929	# if we find ",", we can continue with the next element
		930	if ($json->incr_text =~ s/^,//) {
		931	last;
		932	}
		933
		934	# if we find anything else, we have a parse error!
		935	if (length $json->incr_text) {
		936	die "parse error near ", $json->incr_text;
		937	}
		938
		939	# else add more data
		940	sysread $fh, my $buf, 65536
		941	or die "read error: $!";
		942	$json->incr_parse ($buf); # void context, so no parsing
		943	}
		944
		945	This is a complex example, but most of the complexity comes from the fact
		946	that we are trying to be correct (bear with me if I am wrong, I never ran
		947	the above example :).
		948
646		949
647		950
648	=head1 MAPPING	951	=head1 MAPPING
649		952
650	This section describes how JSON::XS maps Perl values to JSON values and	953	This section describes how JSON::XS maps Perl values to JSON values and
…		…
680		983
681	A JSON number becomes either an integer, numeric (floating point) or	984	A JSON number becomes either an integer, numeric (floating point) or
682	string scalar in perl, depending on its range and any fractional parts. On	985	string scalar in perl, depending on its range and any fractional parts. On
683	the Perl level, there is no difference between those as Perl handles all	986	the Perl level, there is no difference between those as Perl handles all
684	the conversion details, but an integer may take slightly less memory and	987	the conversion details, but an integer may take slightly less memory and
685	might represent more values exactly than (floating point) numbers.	988	might represent more values exactly than floating point numbers.
686		989
687	If the number consists of digits only, JSON::XS will try to represent	990	If the number consists of digits only, JSON::XS will try to represent
688	it as an integer value. If that fails, it will try to represent it as	991	it as an integer value. If that fails, it will try to represent it as
689	a numeric (floating point) value if that is possible without loss of	992	a numeric (floating point) value if that is possible without loss of
690	precision. Otherwise it will preserve the number as a string value.	993	precision. Otherwise it will preserve the number as a string value (in
		994	which case you lose roundtripping ability, as the JSON number will be
		995	re-encoded to a JSON string).
691		996
692	Numbers containing a fractional or exponential part will always be	997	Numbers containing a fractional or exponential part will always be
693	represented as numeric (floating point) values, possibly at a loss of	998	represented as numeric (floating point) values, possibly at a loss of
694	precision.	999	precision (in which case you might lose perfect roundtripping ability, but
		1000	the JSON number will still be re-encoded as a JSON number).
695		1001
696	This might create round-tripping problems as numbers might become strings,	1002	Note that precision is not accuracy - binary floating point values cannot
697	but as Perl is typeless there is no other way to do it.	1003	represent most decimal fractions exactly, and when converting from and to
		1004	floating point, JSON::XS only guarantees precision up to but not including
		1005	the least significant bit.
698		1006
699	=item true, false	1007	=item true, false
700		1008
701	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	1009	These JSON atoms become C<Types::Serialiser::true> and
702	respectively. They are overloaded to act almost exactly like the numbers	1010	C<Types::Serialiser::false>, respectively. They are overloaded to act
703	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using	1011	almost exactly like the numbers C<1> and C<0>. You can check whether
704	the C<JSON::XS::is_bool> function.	1012	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1013	function (after C<use Types::Serialier>, of course).
705		1014
706	=item null	1015	=item null
707		1016
708	A JSON null atom becomes C<undef> in Perl.	1017	A JSON null atom becomes C<undef> in Perl.
		1018
		1019	=item shell-style comments (C<< # I<text> >>)
		1020
		1021	As a nonstandard extension to the JSON syntax that is enabled by the
		1022	C<relaxed> setting, shell-style comments are allowed. They can start
		1023	anywhere outside strings and go till the end of the line.
		1024
		1025	=item tagged values (C<< (I<tag>)I<value> >>).
		1026
		1027	Another nonstandard extension to the JSON syntax, enabled with the
		1028	C<allow_tags> setting, are tagged values. In this implementation, the
		1029	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1030	I<value> must be a JSON array encoding optional constructor arguments.
		1031
		1032	See L<OBJECT SERIALISATION>, below, for details.
709		1033
710	=back	1034	=back
711		1035
712		1036
713	=head2 PERL -> JSON	1037	=head2 PERL -> JSON
…		…
718		1042
719	=over 4	1043	=over 4
720		1044
721	=item hash references	1045	=item hash references
722		1046
723	Perl hash references become JSON objects. As there is no inherent ordering	1047	Perl hash references become JSON objects. As there is no inherent
724	in hash keys (or JSON objects), they will usually be encoded in a	1048	ordering in hash keys (or JSON objects), they will usually be encoded
725	pseudo-random order that can change between runs of the same program but	1049	in a pseudo-random order. JSON::XS can optionally sort the hash keys
726	stays generally the same within a single run of a program. JSON::XS can	1050	(determined by the I<canonical> flag), so the same datastructure will
727	optionally sort the hash keys (determined by the I<canonical> flag), so	1051	serialise to the same JSON text (given same settings and version of
728	the same datastructure will serialise to the same JSON text (given same	1052	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
729	settings and version of JSON::XS), but this incurs a runtime overhead	1053	e.g. when you want to compare some JSON text against another for equality.
730	and is only rarely useful, e.g. when you want to compare some JSON text
731	against another for equality.
732		1054
733	=item array references	1055	=item array references
734		1056
735	Perl array references become JSON arrays.	1057	Perl array references become JSON arrays.
736		1058
737	=item other references	1059	=item other references
738		1060
739	Other unblessed references are generally not allowed and will cause an	1061	Other unblessed references are generally not allowed and will cause an
740	exception to be thrown, except for references to the integers C<0> and	1062	exception to be thrown, except for references to the integers C<0> and
741	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1063	C<1>, which get turned into C<false> and C<true> atoms in JSON.
742	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
743		1064
		1065	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1066	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1067	and C<Types::Serialiser::true> to improve readability.
		1068
		1069	use Types::Serialiser;
744	to_json [\0,JSON::XS::true] # yields [false,true]	1070	encode_json [\0, Types::Serialiser::true] # yields [false,true]
745		1071
746	=item JSON::XS::true, JSON::XS::false	1072	=item Types::Serialiser::true, Types::Serialiser::false
747		1073
748	These special values become JSON true and JSON false values,	1074	These special values from the L<Types::Serialiser> module become JSON true
749	respectively. You can also use C<\1> and C<\0> directly if you want.	1075	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1076	directly if you want.
750		1077
751	=item blessed objects	1078	=item blessed objects
752		1079
753	Blessed objects are not allowed. JSON::XS currently tries to encode their	1080	Blessed objects are not directly representable in JSON, but C<JSON::XS>
754	underlying representation (hash- or arrayref), but this behaviour might	1081	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
755	change in future versions.	1082	below, for details.
756		1083
757	=item simple scalars	1084	=item simple scalars
758		1085
759	Simple Perl scalars (any scalar that is not a reference) are the most	1086	Simple Perl scalars (any scalar that is not a reference) are the most
760	difficult objects to encode: JSON::XS will encode undefined scalars as	1087	difficult objects to encode: JSON::XS will encode undefined scalars as
761	JSON null value, scalars that have last been used in a string context	1088	JSON C<null> values, scalars that have last been used in a string context
762	before encoding as JSON strings and anything else as number value:	1089	before encoding as JSON strings, and anything else as number value:
763		1090
764	# dump as number	1091	# dump as number
765	to_json [2] # yields [2]	1092	encode_json [2] # yields [2]
766	to_json [-3.0e17] # yields [-3e+17]	1093	encode_json [-3.0e17] # yields [-3e+17]
767	my $value = 5; to_json [$value] # yields [5]	1094	my $value = 5; encode_json [$value] # yields [5]
768		1095
769	# used as string, so dump as string	1096	# used as string, so dump as string
770	print $value;	1097	print $value;
771	to_json [$value] # yields ["5"]	1098	encode_json [$value] # yields ["5"]
772		1099
773	# undef becomes null	1100	# undef becomes null
774	to_json [undef] # yields [null]	1101	encode_json [undef] # yields [null]
775		1102
776	You can force the type to be a JSON string by stringifying it:	1103	You can force the type to be a JSON string by stringifying it:
777		1104
778	my $x = 3.1; # some variable containing a number	1105	my $x = 3.1; # some variable containing a number
779	"$x"; # stringified	1106	"$x"; # stringified
…		…
785	my $x = "3"; # some variable containing a string	1112	my $x = "3"; # some variable containing a string
786	$x += 0; # numify it, ensuring it will be dumped as a number	1113	$x += 0; # numify it, ensuring it will be dumped as a number
787	$x *= 1; # same thing, the choice is yours.	1114	$x *= 1; # same thing, the choice is yours.
788		1115
789	You can not currently force the type in other, less obscure, ways. Tell me	1116	You can not currently force the type in other, less obscure, ways. Tell me
790	if you need this capability.	1117	if you need this capability (but don't forget to explain why it's needed
		1118	:).
		1119
		1120	Note that numerical precision has the same meaning as under Perl (so
		1121	binary to decimal conversion follows the same rules as in Perl, which
		1122	can differ to other languages). Also, your perl interpreter might expose
		1123	extensions to the floating point numbers of your platform, such as
		1124	infinities or NaN's - these cannot be represented in JSON, and it is an
		1125	error to pass those in.
791		1126
792	=back	1127	=back
793		1128
		1129	=head2 OBJECT SERIALISATION
794		1130
795	=head1 COMPARISON	1131	As JSON cannot directly represent Perl objects, you have to choose between
		1132	a pure JSON representation (without the ability to deserialise the object
		1133	automatically again), and a nonstandard extension to the JSON syntax,
		1134	tagged values.
796		1135
797	As already mentioned, this module was created because none of the existing	1136	=head3 SERIALISATION
798	JSON modules could be made to work correctly. First I will describe the	1137
799	problems (or pleasures) I encountered with various existing JSON modules,	1138	What happens when C<JSON::XS> encounters a Perl object depends on the
800	followed by some benchmark values. JSON::XS was designed not to suffer	1139	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
801	from any of these problems or limitations.	1140	used in this order:
802		1141
803	=over 4	1142	=over 4
804		1143
805	=item JSON 1.07	1144	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
806		1145
807	Slow (but very portable, as it is written in pure Perl).	1146	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1147	serialisation protocol to create a tagged JSON value, using a nonstandard
		1148	extension to the JSON syntax.
808		1149
809	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1150	This works by invoking the C<FREEZE> method on the object, with the first
810	undocumented. One can get far by feeding it Unicode strings and doing	1151	argument being the object to serialise, and the second argument being the
811	en-/decoding oneself, but Unicode escapes are not working properly).	1152	constant string C<JSON> to distinguish it from other serialisers.
812		1153
813	No round-tripping (strings get clobbered if they look like numbers, e.g.	1154	The C<FREEZE> method can return any number of values (i.e. zero or
814	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	1155	more). These values and the paclkage/classname of the object will then be
815	decode into the number 2.	1156	encoded as a tagged JSON value in the following format:
816		1157
817	=item JSON::PC 0.01	1158	("classname")[FREEZE return values...]
818		1159
819	Very fast.	1160	e.g.:
820		1161
821	Undocumented/buggy Unicode handling.	1162	("URI")["http://www.google.com/"]
		1163	("MyDate")[2013,10,29]
		1164	("ImageData::JPEG")["Z3...VlCg=="]
822		1165
823	No round-tripping.	1166	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1167	objects C<type> and C<id> members to encode the object:
824		1168
825	Has problems handling many Perl values (e.g. regex results and other magic	1169	sub My::Object::FREEZE {
826	values will make it croak).	1170	my ($self, $serialiser) = @_;
827		1171
828	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1172	($self->{type}, $self->{id})
829	which is not a valid JSON text.	1173	}
830		1174
831	Unmaintained (maintainer unresponsive for many months, bugs are not	1175	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
832	getting fixed).
833		1176
834	=item JSON::Syck 0.21	1177	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1178	context. It must return a single scalar that can be directly encoded into
		1179	JSON. This scalar replaces the object in the JSON text.
835		1180
836	Very buggy (often crashes).	1181	For example, the following C<TO_JSON> method will convert all L<URI>
		1182	objects to JSON strings when serialised. The fatc that these values
		1183	originally were L<URI> objects is lost.
837		1184
838	Very inflexible (no human-readable format supported, format pretty much	1185	sub URI::TO_JSON {
839	undocumented. I need at least a format for easy reading by humans and a	1186	my ($uri) = @_;
840	single-line compact format for use in a protocol, and preferably a way to	1187	$uri->as_string
841	generate ASCII-only JSON texts).	1188	}
842		1189
843	Completely broken (and confusingly documented) Unicode handling (Unicode	1190	=item 3. C<allow_blessed> is enabled.
844	escapes are not working properly, you need to set ImplicitUnicode to
845	I<different> values on en- and decoding to get symmetric behaviour).
846		1191
847	No round-tripping (simple cases work, but this depends on whether the scalar	1192	The object will be serialised as a JSON null value.
848	value was used in a numeric context or not).
849		1193
850	Dumping hashes may skip hash values depending on iterator state.	1194	=item 4. none of the above
851		1195
852	Unmaintained (maintainer unresponsive for many months, bugs are not	1196	If none of the settings are enabled or the respective methods are missing,
853	getting fixed).	1197	C<JSON::XS> throws an exception.
854
855	Does not check input for validity (i.e. will accept non-JSON input and
856	return "something" instead of raising an exception. This is a security
857	issue: imagine two banks transferring money between each other using
858	JSON. One bank might parse a given non-JSON request and deduct money,
859	while the other might reject the transaction with a syntax error. While a
860	good protocol will at least recover, that is extra unnecessary work and
861	the transaction will still not succeed).
862
863	=item JSON::DWIW 0.04
864
865	Very fast. Very natural. Very nice.
866
867	Undocumented Unicode handling (but the best of the pack. Unicode escapes
868	still don't get parsed properly).
869
870	Very inflexible.
871
872	No round-tripping.
873
874	Does not generate valid JSON texts (key strings are often unquoted, empty keys
875	result in nothing being output)
876
877	Does not check input for validity.
878		1198
879	=back	1199	=back
880		1200
		1201	=head3 DESERIALISATION
		1202
		1203	For deserialisation there are only two cases to consider: either
		1204	nonstandard tagging was used, in which case C<allow_tags> decides,
		1205	or objects cannot be automatically be deserialised, in which
		1206	case you can use postprocessing or the C<filter_json_object> or
		1207	C<filter_json_single_key_object> callbacks to get some real objects our of
		1208	your JSON.
		1209
		1210	This section only considers the tagged value case: I a tagged JSON object
		1211	is encountered during decoding and C<allow_tags> is disabled, a parse
		1212	error will result (as if tagged values were not part of the grammar).
		1213
		1214	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1215	of the package/classname used during serialisation (it will not attempt
		1216	to load the package as a Perl module). If there is no such method, the
		1217	decoding will fail with an error.
		1218
		1219	Otherwise, the C<THAW> method is invoked with the classname as first
		1220	argument, the constant string C<JSON> as second argument, and all the
		1221	values from the JSON array (the values originally returned by the
		1222	C<FREEZE> method) as remaining arguments.
		1223
		1224	The method must then return the object. While technically you can return
		1225	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1226	make that work in all cases, so better return an actual blessed reference.
		1227
		1228	As an example, let's implement a C<THAW> function that regenerates the
		1229	C<My::Object> from the C<FREEZE> example earlier:
		1230
		1231	sub My::Object::THAW {
		1232	my ($class, $serialiser, $type, $id) = @_;
		1233
		1234	$class->new (type => $type, id => $id)
		1235	}
		1236
		1237
		1238	=head1 ENCODING/CODESET FLAG NOTES
		1239
		1240	The interested reader might have seen a number of flags that signify
		1241	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1242	some confusion on what these do, so here is a short comparison:
		1243
		1244	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1245	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1246	control whether C<encode> escapes character values outside their respective
		1247	codeset range. Neither of these flags conflict with each other, although
		1248	some combinations make less sense than others.
		1249
		1250	Care has been taken to make all flags symmetrical with respect to
		1251	C<encode> and C<decode>, that is, texts encoded with any combination of
		1252	these flag values will be correctly decoded when the same flags are used
		1253	- in general, if you use different flag settings while encoding vs. when
		1254	decoding you likely have a bug somewhere.
		1255
		1256	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1257	simply an abstract set of character-codepoint pairs, while an encoding
		1258	takes those codepoint numbers and I<encodes> them, in our case into
		1259	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1260	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1261	the same time, which can be confusing.
		1262
		1263	=over 4
		1264
		1265	=item C<utf8> flag disabled
		1266
		1267	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1268	and expect Unicode strings, that is, characters with high ordinal Unicode
		1269	values (> 255) will be encoded as such characters, and likewise such
		1270	characters are decoded as-is, no changes to them will be done, except
		1271	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1272	respectively (to Perl, these are the same thing in strings unless you do
		1273	funny/weird/dumb stuff).
		1274
		1275	This is useful when you want to do the encoding yourself (e.g. when you
		1276	want to have UTF-16 encoded JSON texts) or when some other layer does
		1277	the encoding for you (for example, when printing to a terminal using a
		1278	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1279	to UTF-8 encode your data first and have Perl encode it another time).
		1280
		1281	=item C<utf8> flag enabled
		1282
		1283	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1284	characters using the corresponding UTF-8 multi-byte sequence, and will
		1285	expect your input strings to be encoded as UTF-8, that is, no "character"
		1286	of the input string must have any value > 255, as UTF-8 does not allow
		1287	that.
		1288
		1289	The C<utf8> flag therefore switches between two modes: disabled means you
		1290	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1291	octet/binary string in Perl.
		1292
		1293	=item C<latin1> or C<ascii> flags enabled
		1294
		1295	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1296	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1297	characters as specified by the C<utf8> flag.
		1298
		1299	If C<utf8> is disabled, then the result is also correctly encoded in those
		1300	character sets (as both are proper subsets of Unicode, meaning that a
		1301	Unicode string with all character values < 256 is the same thing as a
		1302	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1303	the same thing as an ASCII string in Perl).
		1304
		1305	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1306	regardless of these flags, just some more characters will be escaped using
		1307	C<\uXXXX> then before.
		1308
		1309	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1310	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1311	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1312	a subset of Unicode), while ASCII is.
		1313
		1314	Surprisingly, C<decode> will ignore these flags and so treat all input
		1315	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1316	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1317	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1318
		1319	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1320	they only govern when the JSON output engine escapes a character or not.
		1321
		1322	The main use for C<latin1> is to relatively efficiently store binary data
		1323	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1324
		1325	The main use for C<ascii> is to force the output to not contain characters
		1326	with values > 127, which means you can interpret the resulting string
		1327	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1328	8-bit-encoding, and still get the same data structure back. This is useful
		1329	when your channel for JSON transfer is not 8-bit clean or the encoding
		1330	might be mangled in between (e.g. in mail), and works because ASCII is a
		1331	proper subset of most 8-bit and multibyte encodings in use in the world.
		1332
		1333	=back
		1334
		1335
		1336	=head2 JSON and ECMAscript
		1337
		1338	JSON syntax is based on how literals are represented in javascript (the
		1339	not-standardised predecessor of ECMAscript) which is presumably why it is
		1340	called "JavaScript Object Notation".
		1341
		1342	However, JSON is not a subset (and also not a superset of course) of
		1343	ECMAscript (the standard) or javascript (whatever browsers actually
		1344	implement).
		1345
		1346	If you want to use javascript's C<eval> function to "parse" JSON, you
		1347	might run into parse errors for valid JSON texts, or the resulting data
		1348	structure might not be queryable:
		1349
		1350	One of the problems is that U+2028 and U+2029 are valid characters inside
		1351	JSON strings, but are not allowed in ECMAscript string literals, so the
		1352	following Perl fragment will not output something that can be guaranteed
		1353	to be parsable by javascript's C<eval>:
		1354
		1355	use JSON::XS;
		1356
		1357	print encode_json [chr 0x2028];
		1358
		1359	The right fix for this is to use a proper JSON parser in your javascript
		1360	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1361	F<json2.js> parser).
		1362
		1363	If this is not an option, you can, as a stop-gap measure, simply encode to
		1364	ASCII-only JSON:
		1365
		1366	use JSON::XS;
		1367
		1368	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1369
		1370	Note that this will enlarge the resulting JSON text quite a bit if you
		1371	have many non-ASCII characters. You might be tempted to run some regexes
		1372	to only escape U+2028 and U+2029, e.g.:
		1373
		1374	# DO NOT USE THIS!
		1375	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1376	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1377	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1378	print $json;
		1379
		1380	Note that I<this is a bad idea>: the above only works for U+2028 and
		1381	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1382	javascript implementations, however, have issues with other characters as
		1383	well - using C<eval> naively simply I<will> cause problems.
		1384
		1385	Another problem is that some javascript implementations reserve
		1386	some property names for their own purposes (which probably makes
		1387	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1388	C<__proto__> property name for its own purposes.
		1389
		1390	If that is a problem, you could parse try to filter the resulting JSON
		1391	output for these property strings, e.g.:
		1392
		1393	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1394
		1395	This works because C<__proto__> is not valid outside of strings, so every
		1396	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1397
		1398	If you know of other incompatibilities, please let me know.
		1399
881		1400
882	=head2 JSON and YAML	1401	=head2 JSON and YAML
883		1402
884	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1403	You often hear that JSON is a subset of YAML. This is, however, a mass
885	however, a mass hysteria and very far from the truth. In general, there is	1404	hysteria(*) and very far from the truth (as of the time of this writing),
886	no way to configure JSON::XS to output a data structure as valid YAML.	1405	so let me state it clearly: I<in general, there is no way to configure
		1406	JSON::XS to output a data structure as valid YAML> that works in all
		1407	cases.
887		1408
888	If you really must use JSON::XS to generate YAML, you should use this	1409	If you really must use JSON::XS to generate YAML, you should use this
889	algorithm (subject to change in future versions):	1410	algorithm (subject to change in future versions):
890		1411
891	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1412	my $to_yaml = JSON::XS->new->utf8->space_after (1);
892	my $yaml = $to_yaml->encode ($ref) . "\n";	1413	my $yaml = $to_yaml->encode ($ref) . "\n";
893		1414
894	This will usually generate JSON texts that also parse as valid	1415	This will I<usually> generate JSON texts that also parse as valid
895	YAML. Please note that YAML has hardcoded limits on (simple) object key	1416	YAML. Please note that YAML has hardcoded limits on (simple) object key
896	lengths that JSON doesn't have, so you should make sure that your hash	1417	lengths that JSON doesn't have and also has different and incompatible
		1418	unicode character escape syntax, so you should make sure that your hash
897	keys are noticeably shorter than the 1024 characters YAML allows.	1419	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1420	and that you do not have characters with codepoint values outside the
		1421	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1422	sequences in strings (which JSON::XS does not I<currently> generate, but
		1423	other JSON generators might).
898		1424
899	There might be other incompatibilities that I am not aware of. In general	1425	There might be other incompatibilities that I am not aware of (or the YAML
		1426	specification has been changed yet again - it does so quite often). In
900	you should not try to generate YAML with a JSON generator or vice versa,	1427	general you should not try to generate YAML with a JSON generator or vice
901	or try to parse JSON with a YAML parser or vice versa: chances are high	1428	versa, or try to parse JSON with a YAML parser or vice versa: chances are
902	that you will run into severe interoperability problems.	1429	high that you will run into severe interoperability problems when you
		1430	least expect it.
		1431
		1432	=over 4
		1433
		1434	=item (*)
		1435
		1436	I have been pressured multiple times by Brian Ingerson (one of the
		1437	authors of the YAML specification) to remove this paragraph, despite him
		1438	acknowledging that the actual incompatibilities exist. As I was personally
		1439	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1440	educate people about these issues, so others do not run into the same
		1441	problem again and again. After this, Brian called me a (quote)I<complete
		1442	and worthless idiot>(unquote).
		1443
		1444	In my opinion, instead of pressuring and insulting people who actually
		1445	clarify issues with YAML and the wrong statements of some of its
		1446	proponents, I would kindly suggest reading the JSON spec (which is not
		1447	that difficult or long) and finally make YAML compatible to it, and
		1448	educating users about the changes, instead of spreading lies about the
		1449	real compatibility for many I<years> and trying to silence people who
		1450	point out that it isn't true.
		1451
		1452	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1453	though the incompatibilities have been documented (and are known to Brian)
		1454	for many years and the spec makes explicit claims that YAML is a superset
		1455	of JSON. It would be so easy to fix, but apparently, bullying people and
		1456	corrupting userdata is so much easier.
		1457
		1458	=back
903		1459
904		1460
905	=head2 SPEED	1461	=head2 SPEED
906		1462
907	It seems that JSON::XS is surprisingly fast, as shown in the following	1463	It seems that JSON::XS is surprisingly fast, as shown in the following
908	tables. They have been generated with the help of the C<eg/bench> program	1464	tables. They have been generated with the help of the C<eg/bench> program
909	in the JSON::XS distribution, to make it easy to compare on your own	1465	in the JSON::XS distribution, to make it easy to compare on your own
910	system.	1466	system.
911		1467
912	First comes a comparison between various modules using a very short	1468	First comes a comparison between various modules using
913	single-line JSON string:	1469	a very short single-line JSON string (also available at
		1470	L<http://dist.schmorp.de/misc/json/short.json>).
914		1471
915	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1472	{"method": "handleMessage", "params": ["user1",
916	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1473	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1474	1, 0]}
917		1475
918	It shows the number of encodes/decodes per second (JSON::XS uses	1476	It shows the number of encodes/decodes per second (JSON::XS uses
919	the functional interface, while JSON::XS/2 uses the OO interface	1477	the functional interface, while JSON::XS/2 uses the OO interface
920	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1478	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
921	shrink). Higher is better:	1479	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1480	uses the from_json method). Higher is better:
922		1481
923	module | encode | decode |	1482	module | encode | decode |
924	-----------|------------|------------|	1483	--------------|------------|------------|
925	JSON 1.x | 4990.842 | 4088.813 |	1484	JSON::DWIW/DS | 86302.551 | 102300.098 |
926	JSON::DWIW | 51653.990 | 71575.154 |	1485	JSON::DWIW/FJ | 86302.551 | 75983.768 |
927	JSON::PC | 65948.176 | 74631.744 |	1486	JSON::PP | 15827.562 | 6638.658 |
928	JSON::PP | 8931.652 | 3817.168 |	1487	JSON::Syck | 63358.066 | 47662.545 |
929	JSON::Syck | 24877.248 | 27776.848 |	1488	JSON::XS | 511500.488 | 511500.488 |
930	JSON::XS | 388361.481 | 227951.304 |	1489	JSON::XS/2 | 291271.111 | 388361.481 |
931	JSON::XS/2 | 227951.304 | 218453.333 |	1490	JSON::XS/3 | 361577.931 | 361577.931 |
932	JSON::XS/3 | 338250.323 | 218453.333 |	1491	Storable | 66788.280 | 265462.278 |
933	Storable | 16500.016 | 135300.129 |
934	-----------+------------+------------+	1492	--------------+------------+------------+
935		1493
936	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1494	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
937	about three times faster on decoding, and over forty times faster	1495	about five times faster on decoding, and over thirty to seventy times
938	than JSON, even with pretty-printing and key sorting. It also compares	1496	faster than JSON's pure perl implementation. It also compares favourably
939	favourably to Storable for small amounts of data.	1497	to Storable for small amounts of data.
940		1498
941	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1499	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
942	search API (http://nanoref.com/yahooapis/mgPdGg):	1500	search API (L<http://dist.schmorp.de/misc/json/long.json>).
943		1501
944	module | encode | decode |	1502	module | encode | decode |
945	-----------|------------|------------|	1503	--------------|------------|------------|
946	JSON 1.x | 55.260 | 34.971 |	1504	JSON::DWIW/DS | 1647.927 | 2673.916 |
947	JSON::DWIW | 825.228 | 1082.513 |	1505	JSON::DWIW/FJ | 1630.249 | 2596.128 |
948	JSON::PC | 3571.444 | 2394.829 |
949	JSON::PP | 210.987 | 32.574 |	1506	JSON::PP | 400.640 | 62.311 |
950	JSON::Syck | 552.551 | 787.544 |	1507	JSON::Syck | 1481.040 | 1524.869 |
951	JSON::XS | 5780.463 | 4854.519 |	1508	JSON::XS | 20661.596 | 9541.183 |
952	JSON::XS/2 | 3869.998 | 4798.975 |	1509	JSON::XS/2 | 10683.403 | 9416.938 |
953	JSON::XS/3 | 5862.880 | 4798.975 |	1510	JSON::XS/3 | 20661.596 | 9400.054 |
954	Storable | 4445.002 | 5235.027 |	1511	Storable | 19765.806 | 10000.725 |
955	-----------+------------+------------+	1512	--------------+------------+------------+
956		1513
957	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1514	Again, JSON::XS leads by far (except for Storable which non-surprisingly
958	decodes faster).	1515	decodes a bit faster).
959		1516
960	On large strings containing lots of high Unicode characters, some modules	1517	On large strings containing lots of high Unicode characters, some modules
961	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1518	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
962	will be broken due to missing (or wrong) Unicode handling. Others refuse	1519	will be broken due to missing (or wrong) Unicode handling. Others refuse
963	to decode or encode properly, so it was impossible to prepare a fair	1520	to decode or encode properly, so it was impossible to prepare a fair
…		…
984		1541
985	Third, JSON::XS recurses using the C stack when decoding objects and	1542	Third, JSON::XS recurses using the C stack when decoding objects and
986	arrays. The C stack is a limited resource: for instance, on my amd64	1543	arrays. The C stack is a limited resource: for instance, on my amd64
987	machine with 8MB of stack size I can decode around 180k nested arrays but	1544	machine with 8MB of stack size I can decode around 180k nested arrays but
988	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1545	only 14k nested JSON objects (due to perl itself recursing deeply on croak
989	to free the temporary). If that is exceeded, the program crashes. to be	1546	to free the temporary). If that is exceeded, the program crashes. To be
990	conservative, the default nesting limit is set to 512. If your process	1547	conservative, the default nesting limit is set to 512. If your process
991	has a smaller stack, you should adjust this setting accordingly with the	1548	has a smaller stack, you should adjust this setting accordingly with the
992	C<max_depth> method.	1549	C<max_depth> method.
993		1550
994	And last but least, something else could bomb you that I forgot to think	1551	Something else could bomb you, too, that I forgot to think of. In that
995	of. In that case, you get to keep the pieces. I am always open for hints,	1552	case, you get to keep the pieces. I am always open for hints, though...
996	though...	1553
		1554	Also keep in mind that JSON::XS might leak contents of your Perl data
		1555	structures in its error messages, so when you serialise sensitive
		1556	information you might want to make sure that exceptions thrown by JSON::XS
		1557	will not end up in front of untrusted eyes.
997		1558
998	If you are using JSON::XS to return packets to consumption	1559	If you are using JSON::XS to return packets to consumption
999	by JavaScript scripts in a browser you should have a look at	1560	by JavaScript scripts in a browser you should have a look at
1000	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1561	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
1001	you are vulnerable to some common attack vectors (which really are browser	1562	see whether you are vulnerable to some common attack vectors (which really
1002	design bugs, but it is still you who will have to deal with it, as major	1563	are browser design bugs, but it is still you who will have to deal with
1003	browser developers care only for features, not about doing security	1564	it, as major browser developers care only for features, not about getting
1004	right).	1565	security right).
		1566
		1567
		1568	=head1 INTEROPERABILITY WITH OTHER MODULES
		1569
		1570	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1571	constants. That means that the JSON true and false values will be
		1572	comaptible to true and false values of iother modules that do the same,
		1573	such as L<JSON::PP> and L<CBOR::XS>.
		1574
		1575
		1576	=head1 INTEROPERABILITY WITH OTHER JSON DECODERS
		1577
		1578	As long as you only serialise data that can be directly expressed in JSON,
		1579	C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs,
		1580	but C<JSON::XS> has found more bugs in the official JSON testsuite (1)
		1581	than the official JSON testsuite has found in C<JSON::XS> (0)).
		1582
		1583	When you have trouble decoding JSON generated by this module using other
		1584	decoders, then it is very likely that you have an encoding mismatch or the
		1585	other decoder is broken.
		1586
		1587	When decoding, C<JSON::XS> is strict by default and will likely catch all
		1588	errors. There are currently two settings that change this: C<relaxed>
		1589	makes C<JSON::XS> accept (but not generate) some non-standard extensions,
		1590	and C<allow_tags> will allow you to encode and decode Perl objects, at the
		1591	cost of not outputting valid JSON anymore.
		1592
		1593	=head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
		1594
		1595	When you use C<allow_tags> to use the extended (and also nonstandard and
		1596	invalid) JSON syntax for serialised objects, and you still want to decode
		1597	the generated When you want to serialise objects, you can run a regex
		1598	to replace the tagged syntax by standard JSON arrays (it only works for
		1599	"normal" packagesnames without comma, newlines or single colons). First,
		1600	the readable Perl version:
		1601
		1602	# if your FREEZE methods return no values, you need this replace first:
		1603	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
		1604
		1605	# this works for non-empty constructor arg lists:
		1606	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
		1607
		1608	And here is a less readable version that is easy to adapt to other
		1609	languages:
		1610
		1611	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
		1612
		1613	Here is an ECMAScript version (same regex):
		1614
		1615	json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
		1616
		1617	Since this syntax converts to standard JSON arrays, it might be hard to
		1618	distinguish serialised objects from normal arrays. You can prepend a
		1619	"magic number" as first array element to reduce chances of a collision:
		1620
		1621	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
		1622
		1623	And after decoding the JSON text, you could walk the data
		1624	structure looking for arrays with a first element of
		1625	C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>.
		1626
		1627	The same approach can be used to create the tagged format with another
		1628	encoder. First, you create an array with the magic string as first member,
		1629	the classname as second, and constructor arguments last, encode it as part
		1630	of your JSON structure, and then:
		1631
		1632	$json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
		1633
		1634	Again, this has some limitations - the magic string must not be encoded
		1635	with character escapes, and the constructor arguments must be non-empty.
		1636
		1637
		1638	=head1 RFC7159
		1639
		1640	Since this module was written, Google has written a new JSON RFC, RFC 7159
		1641	(and RFC7158). Unfortunately, this RFC breaks compatibility with both the
		1642	original JSON specification on www.json.org and RFC4627.
		1643
		1644	As far as I can see, you can get partial compatibility when parsing by
		1645	using C<< ->allow_nonref >>. However, consider thew security implications
		1646	of doing so.
		1647
		1648	I haven't decided yet when to break compatibility with RFC4627 by default
		1649	(and potentially leave applications insecure) and change the default to
		1650	follow RFC7159, but application authors are well advised to call C<<
		1651	->allow_nonref(0) >> even if this is the current default, if they cannot
		1652	handle non-reference values, in preparation for the day when the4 default
		1653	will change.
1005		1654
1006		1655
1007	=head1 THREADS	1656	=head1 THREADS
1008		1657
1009	This module is I<not> guaranteed to be thread safe and there are no	1658	This module is I<not> guaranteed to be thread safe and there are no
1010	plans to change this until Perl gets thread support (as opposed to the	1659	plans to change this until Perl gets thread support (as opposed to the
1011	horribly slow so-called "threads" which are simply slow and bloated	1660	horribly slow so-called "threads" which are simply slow and bloated
1012	process simulations - use fork, its I<much> faster, cheaper, better).	1661	process simulations - use fork, it's I<much> faster, cheaper, better).
1013		1662
1014	(It might actually work, but you have been warned).	1663	(It might actually work, but you have been warned).
1015		1664
1016		1665
		1666	=head1 THE PERILS OF SETLOCALE
		1667
		1668	Sometimes people avoid the Perl locale support and directly call the
		1669	system's setlocale function with C<LC_ALL>.
		1670
		1671	This breaks both perl and modules such as JSON::XS, as stringification of
		1672	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1673	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1674	perl to stringify numbers).
		1675
		1676	The solution is simple: don't call C<setlocale>, or use it for only those
		1677	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1678
		1679	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1680	actually needs it (avoiding stringification of numbers), and restore it
		1681	afterwards.
		1682
		1683
1017	=head1 BUGS	1684	=head1 BUGS
1018		1685
1019	While the goal of this module is to be correct, that unfortunately does	1686	While the goal of this module is to be correct, that unfortunately does
1020	not mean its bug-free, only that I think its design is bug-free. It is	1687	not mean it's bug-free, only that I think its design is bug-free. If you
1021	still relatively early in its development. If you keep reporting bugs they	1688	keep reporting bugs they will be fixed swiftly, though.
1022	will be fixed swiftly, though.
1023		1689
1024	Please refrain from using rt.cpan.org or any other bug reporting	1690	Please refrain from using rt.cpan.org or any other bug reporting
1025	service. I put the contact address into my modules for a reason.	1691	service. I put the contact address into my modules for a reason.
1026		1692
1027	=cut	1693	=cut
1028		1694
1029	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1695	BEGIN {
1030	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };	1696	*true = \$Types::Serialiser::true;
		1697	*true = \&Types::Serialiser::true;
		1698	*false = \$Types::Serialiser::false;
		1699	*false = \&Types::Serialiser::false;
		1700	*is_bool = \&Types::Serialiser::is_bool;
1031		1701
1032	sub true() { $true }	1702	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
1033	sub false() { $false }
1034
1035	sub is_bool($) {
1036	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1037	# or UNIVERSAL::isa $_[0], "JSON::Literal"
1038	}	1703	}
1039		1704
1040	XSLoader::load "JSON::XS", $VERSION;	1705	XSLoader::load "JSON::XS", $VERSION;
1041		1706
1042	package JSON::XS::Boolean;	1707	=head1 SEE ALSO
1043		1708
1044	use overload	1709	The F<json_xs> command line utility for quick experiments.
1045	"0+" => sub { ${$_[0]} },
1046	"++" => sub { $_[0] = ${$_[0]} + 1 },
1047	"--" => sub { $_[0] = ${$_[0]} - 1 },
1048	fallback => 1;
1049
1050	1;
1051		1710
1052	=head1 AUTHOR	1711	=head1 AUTHOR
1053		1712
1054	Marc Lehmann <schmorp@schmorp.de>	1713	Marc Lehmann <schmorp@schmorp.de>
1055	http://home.schmorp.de/	1714	http://home.schmorp.de/
1056		1715
1057	=cut	1716	=cut
1058		1717
		1718	1
		1719

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