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Revision 1.8 by root, Fri Mar 23 15:57:18 2007 UTC vs.
Revision 1.145 by root, Tue Oct 29 00:06:40 2013 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		4
		5	=encoding utf-8
		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
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
		13
		14	# exported functions, they croak on error
		15	# and expect/generate UTF-8
		16
		17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
		18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
		19
		20	# OO-interface
		21
		22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
		23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
		24	$perl_scalar = $coder->decode ($unicode_json_text);
		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.
8		33
9	=head1 DESCRIPTION	34	=head1 DESCRIPTION
10		35
11	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
12	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
13	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.
14		47
15	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
16	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
17	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
18	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
19	reports for other reasons.	52	reports for other reasons.
20		53
21	See COMPARISON, below, for a comparison to some other JSON modules.	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
		55	vice versa.
22		56
23	=head2 FEATURES	57	=head2 FEATURES
24		58
25	=over 4	59	=over 4
26		60
27	=item * correct handling of unicode issues	61	=item * correct Unicode handling
28		62
29	This module knows how to handle Unicode, and even documents how it does so.	63	This module knows how to handle Unicode, documents how and when it does
		64	so, and even documents what "correct" means.
30		65
31	=item * round-trip integrity	66	=item * round-trip integrity
32		67
33	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
34	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
35	(e.g. the string "2.0" doesn't suddenly become "2").	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
		71	it looks like a number). There I<are> minor exceptions to this, read the
		72	MAPPING section below to learn about those.
36		73
37	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
38		75
39	There is no guessing, no generating of illegal JSON strings by default,	76	There is no guessing, no generating of illegal JSON texts by default,
40	and only JSON is accepted as input (the latter is a security feature).	77	and only JSON is accepted as input by default (the latter is a security
		78	feature).
41		79
42	=item * fast	80	=item * fast
43		81
44	compared to other JSON modules, this module compares favourably.	82	Compared to other JSON modules and other serialisers such as Storable,
		83	this module usually compares favourably in terms of speed, too.
45		84
46	=item * simple to use	85	=item * simple to use
47		86
48	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
49	interface.	88	oriented interface.
50		89
51	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
52		91
53	You can choose between the most compact format possible, a pure-ascii	92	You can choose between the most compact guaranteed-single-line format
54	format, or a pretty-printed format. Or you can combine those features in	93	possible (nice for simple line-based protocols), a pure-ASCII format
55	whatever way you like.	94	(for when your transport is not 8-bit clean, still supports the whole
		95	Unicode range), or a pretty-printed format (for when you want to read that
		96	stuff). Or you can combine those features in whatever way you like.
56		97
57	=back	98	=back
58		99
59	=cut	100	=cut
60		101
61	package JSON::XS;	102	package JSON::XS;
62		103
63	BEGIN {	104	use common::sense;
		105
64	$VERSION = '0.2';	106	our $VERSION = '3.0';
65	@ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
66		108
67	@EXPORT = qw(to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
68	require Exporter;
69		110
70	require XSLoader;	111	use Exporter;
71	XSLoader::load JSON::XS::, $VERSION;	112	use XSLoader;
72	}	113
		114	use Types::Serialiser ();
73		115
74	=head1 FUNCTIONAL INTERFACE	116	=head1 FUNCTIONAL INTERFACE
75		117
76	The following convinience methods are provided by this module. They are	118	The following convenience methods are provided by this module. They are
77	exported by default:	119	exported by default:
78		120
79	=over 4	121	=over 4
80		122
81	=item $json_string = to_json $perl_scalar	123	=item $json_text = encode_json $perl_scalar
82		124
83	Converts the given Perl data structure (a simple scalar or a reference to	125	Converts the given Perl data structure to a UTF-8 encoded, binary string
84	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	126	(that is, the string contains octets only). Croaks on error.
85	octets only). Croaks on error.
86		127
87	This function call is functionally identical to C<< JSON::XS->new->utf8	128	This function call is functionally identical to:
88	(1)->encode ($perl_scalar) >>.
89		129
		130	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		131
		132	Except being faster.
		133
90	=item $perl_scalar = from_json $json_string	134	=item $perl_scalar = decode_json $json_text
91		135
92	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	136	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
93	parse that as an UTF-8 encoded JSON string, returning the resulting simple	137	to parse that as an UTF-8 encoded JSON text, returning the resulting
94	scalar or reference. Croaks on error.	138	reference. Croaks on error.
95		139
96	This function call is functionally identical to C<< JSON::XS->new->utf8	140	This function call is functionally identical to:
97	(1)->decode ($json_string) >>.	141
		142	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		143
		144	Except being faster.
98		145
99	=back	146	=back
		147
		148
		149	=head1 A FEW NOTES ON UNICODE AND PERL
		150
		151	Since this often leads to confusion, here are a few very clear words on
		152	how Unicode works in Perl, modulo bugs.
		153
		154	=over 4
		155
		156	=item 1. Perl strings can store characters with ordinal values > 255.
		157
		158	This enables you to store Unicode characters as single characters in a
		159	Perl string - very natural.
		160
		161	=item 2. Perl does I<not> associate an encoding with your strings.
		162
		163	... until you force it to, e.g. when matching it against a regex, or
		164	printing the scalar to a file, in which case Perl either interprets your
		165	string as locale-encoded text, octets/binary, or as Unicode, depending
		166	on various settings. In no case is an encoding stored together with your
		167	data, it is I<use> that decides encoding, not any magical meta data.
		168
		169	=item 3. The internal utf-8 flag has no meaning with regards to the
		170	encoding of your string.
		171
		172	Just ignore that flag unless you debug a Perl bug, a module written in
		173	XS or want to dive into the internals of perl. Otherwise it will only
		174	confuse you, as, despite the name, it says nothing about how your string
		175	is encoded. You can have Unicode strings with that flag set, with that
		176	flag clear, and you can have binary data with that flag set and that flag
		177	clear. Other possibilities exist, too.
		178
		179	If you didn't know about that flag, just the better, pretend it doesn't
		180	exist.
		181
		182	=item 4. A "Unicode String" is simply a string where each character can be
		183	validly interpreted as a Unicode code point.
		184
		185	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		186	Unicode string encoded in UTF-8, giving you a binary string.
		187
		188	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		189
		190	It's a fact. Learn to live with it.
		191
		192	=back
		193
		194	I hope this helps :)
		195
100		196
101	=head1 OBJECT-ORIENTED INTERFACE	197	=head1 OBJECT-ORIENTED INTERFACE
102		198
103	The object oriented interface lets you configure your own encoding or	199	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	200	decoding style, within the limits of supported formats.
…		…
111	strings. All boolean flags described below are by default I<disabled>.	207	strings. All boolean flags described below are by default I<disabled>.
112		208
113	The mutators for flags all return the JSON object again and thus calls can	209	The mutators for flags all return the JSON object again and thus calls can
114	be chained:	210	be chained:
115		211
116	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	212	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
117	=> {"a": [1, 2]}	213	=> {"a": [1, 2]}
118		214
119	=item $json = $json->ascii ([$enable])	215	=item $json = $json->ascii ([$enable])
120		216
		217	=item $enabled = $json->get_ascii
		218
121	If C<$enable> is true (or missing), then the C<encode> method will	219	If C<$enable> is true (or missing), then the C<encode> method will not
122	not generate characters outside the code range C<0..127>. Any unicode	220	generate characters outside the code range C<0..127> (which is ASCII). Any
123	characters outside that range will be escaped using either a single	221	Unicode characters outside that range will be escaped using either a
124	\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per	222	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
125	RFC4627.	223	as per RFC4627. The resulting encoded JSON text can be treated as a native
		224	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		225	or any other superset of ASCII.
126		226
127	If C<$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
128	characters unless necessary.	228	characters unless required by the JSON syntax or other flags. This results
		229	in a faster and more compact format.
129		230
		231	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		232	document.
		233
		234	The main use for this flag is to produce JSON texts that can be
		235	transmitted over a 7-bit channel, as the encoded JSON texts will not
		236	contain any 8 bit characters.
		237
130	JSON::XS->new->ascii (1)->encode (chr 0x10401)	238	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
131	=> \ud801\udc01	239	=> ["\ud801\udc01"]
		240
		241	=item $json = $json->latin1 ([$enable])
		242
		243	=item $enabled = $json->get_latin1
		244
		245	If C<$enable> is true (or missing), then the C<encode> method will encode
		246	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		247	outside the code range C<0..255>. The resulting string can be treated as a
		248	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		249	will not be affected in any way by this flag, as C<decode> by default
		250	expects Unicode, which is a strict superset of latin1.
		251
		252	If C<$enable> is false, then the C<encode> method will not escape Unicode
		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.
		257
		258	The main use for this flag is efficiently encoding binary data as JSON
		259	text, as most octets will not be escaped, resulting in a smaller encoded
		260	size. The disadvantage is that the resulting JSON text is encoded
		261	in latin1 (and must correctly be treated as such when storing and
		262	transferring), a rare encoding for JSON. It is therefore most useful when
		263	you want to store data structures known to contain binary data efficiently
		264	in files or databases, not when talking to other JSON encoders/decoders.
		265
		266	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		267	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
132		268
133	=item $json = $json->utf8 ([$enable])	269	=item $json = $json->utf8 ([$enable])
134		270
		271	=item $enabled = $json->get_utf8
		272
135	If C<$enable> is true (or missing), then the C<encode> method will encode	273	If C<$enable> is true (or missing), then the C<encode> method will encode
136	the JSON string into UTF-8, as required by many protocols, while the	274	the JSON result into UTF-8, as required by many protocols, while the
137	C<decode> method expects to be handled an UTF-8-encoded string. Please	275	C<decode> method expects to be handled an UTF-8-encoded string. Please
138	note that UTF-8-encoded strings do not contain any characters outside the	276	note that UTF-8-encoded strings do not contain any characters outside the
139	range C<0..255>, they are thus useful for bytewise/binary I/O.	277	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		278	versions, enabling this option might enable autodetection of the UTF-16
		279	and UTF-32 encoding families, as described in RFC4627.
140		280
141	If C<$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
142	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
143	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
144	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.
		288
		289	Example, output UTF-16BE-encoded JSON:
		290
		291	use Encode;
		292	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		293
		294	Example, decode UTF-32LE-encoded JSON:
		295
		296	use Encode;
		297	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
145		298
146	=item $json = $json->pretty ([$enable])	299	=item $json = $json->pretty ([$enable])
147		300
148	This enables (or disables) all of the C<indent>, C<space_before> and	301	This enables (or disables) all of the C<indent>, C<space_before> and
149	C<space_after> (and in the future possibly more) flags in one call to	302	C<space_after> (and in the future possibly more) flags in one call to
150	generate the most readable (or most compact) form possible.	303	generate the most readable (or most compact) form possible.
		304
		305	Example, pretty-print some simple structure:
151		306
152	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})	307	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
153	=>	308	=>
154	{	309	{
155	"a" : [	310	"a" : [
…		…
158	]	313	]
159	}	314	}
160		315
161	=item $json = $json->indent ([$enable])	316	=item $json = $json->indent ([$enable])
162		317
		318	=item $enabled = $json->get_indent
		319
163	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	320	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
164	format as output, putting every array member or object/hash key-value pair	321	format as output, putting every array member or object/hash key-value pair
165	into its own line, identing them properly.	322	into its own line, indenting them properly.
166		323
167	If C<$enable> is false, no newlines or indenting will be produced, and the	324	If C<$enable> is false, no newlines or indenting will be produced, and the
168	resulting JSON strings is guarenteed not to contain any C<newlines>.	325	resulting JSON text is guaranteed not to contain any C<newlines>.
169		326
170	This setting has no effect when decoding JSON strings.	327	This setting has no effect when decoding JSON texts.
171		328
172	=item $json = $json->space_before ([$enable])	329	=item $json = $json->space_before ([$enable])
		330
		331	=item $enabled = $json->get_space_before
173		332
174	If C<$enable> is true (or missing), then the C<encode> method will add an extra	333	If C<$enable> is true (or missing), then the C<encode> method will add an extra
175	optional space before the C<:> separating keys from values in JSON objects.	334	optional space before the C<:> separating keys from values in JSON objects.
176		335
177	If C<$enable> is false, then the C<encode> method will not add any extra	336	If C<$enable> is false, then the C<encode> method will not add any extra
178	space at those places.	337	space at those places.
179		338
180	This setting has no effect when decoding JSON strings. You will also most	339	This setting has no effect when decoding JSON texts. You will also
181	likely combine this setting with C<space_after>.	340	most likely combine this setting with C<space_after>.
		341
		342	Example, space_before enabled, space_after and indent disabled:
		343
		344	{"key" :"value"}
182		345
183	=item $json = $json->space_after ([$enable])	346	=item $json = $json->space_after ([$enable])
		347
		348	=item $enabled = $json->get_space_after
184		349
185	If C<$enable> is true (or missing), then the C<encode> method will add an extra	350	If C<$enable> is true (or missing), then the C<encode> method will add an extra
186	optional space after the C<:> separating keys from values in JSON objects	351	optional space after the C<:> separating keys from values in JSON objects
187	and extra whitespace after the C<,> separating key-value pairs and array	352	and extra whitespace after the C<,> separating key-value pairs and array
188	members.	353	members.
189		354
190	If C<$enable> is false, then the C<encode> method will not add any extra	355	If C<$enable> is false, then the C<encode> method will not add any extra
191	space at those places.	356	space at those places.
192		357
193	This setting has no effect when decoding JSON strings.	358	This setting has no effect when decoding JSON texts.
		359
		360	Example, space_before and indent disabled, space_after enabled:
		361
		362	{"key": "value"}
		363
		364	=item $json = $json->relaxed ([$enable])
		365
		366	=item $enabled = $json->get_relaxed
		367
		368	If C<$enable> is true (or missing), then C<decode> will accept some
		369	extensions to normal JSON syntax (see below). C<encode> will not be
		370	affected in anyway. I<Be aware that this option makes you accept invalid
		371	JSON texts as if they were valid!>. I suggest only to use this option to
		372	parse application-specific files written by humans (configuration files,
		373	resource files etc.)
		374
		375	If C<$enable> is false (the default), then C<decode> will only accept
		376	valid JSON texts.
		377
		378	Currently accepted extensions are:
		379
		380	=over 4
		381
		382	=item * list items can have an end-comma
		383
		384	JSON I<separates> array elements and key-value pairs with commas. This
		385	can be annoying if you write JSON texts manually and want to be able to
		386	quickly append elements, so this extension accepts comma at the end of
		387	such items not just between them:
		388
		389	[
		390	1,
		391	2, <- this comma not normally allowed
		392	]
		393	{
		394	"k1": "v1",
		395	"k2": "v2", <- this comma not normally allowed
		396	}
		397
		398	=item * shell-style '#'-comments
		399
		400	Whenever JSON allows whitespace, shell-style comments are additionally
		401	allowed. They are terminated by the first carriage-return or line-feed
		402	character, after which more white-space and comments are allowed.
		403
		404	[
		405	1, # this comment not allowed in JSON
		406	# neither this one...
		407	]
		408
		409	=back
194		410
195	=item $json = $json->canonical ([$enable])	411	=item $json = $json->canonical ([$enable])
		412
		413	=item $enabled = $json->get_canonical
196		414
197	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	415	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
198	by sorting their keys. This is adding a comparatively high overhead.	416	by sorting their keys. This is adding a comparatively high overhead.
199		417
200	If C<$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
201	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
202	of the same script).	420	of the same script, and can change even within the same run from 5.18
		421	onwards).
203		422
204	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
205	the same JSON string (given the same overall settings). If it is disabled,	424	the same JSON text (given the same overall settings). If it is disabled,
206	the same hash migh be encoded differently even if contains the same data,	425	the same hash might be encoded differently even if contains the same data,
207	as key-value pairs have no inherent ordering in Perl.	426	as key-value pairs have no inherent ordering in Perl.
208		427
209	This setting has no effect when decoding JSON strings.	428	This setting has no effect when decoding JSON texts.
		429
		430	This setting has currently no effect on tied hashes.
210		431
211	=item $json = $json->allow_nonref ([$enable])	432	=item $json = $json->allow_nonref ([$enable])
		433
		434	=item $enabled = $json->get_allow_nonref
212		435
213	If C<$enable> is true (or missing), then the C<encode> method can convert a	436	If C<$enable> is true (or missing), then the C<encode> method can convert a
214	non-reference into its corresponding string, number or null JSON value,	437	non-reference into its corresponding string, number or null JSON value,
215	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	438	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
216	values instead of croaking.	439	values instead of croaking.
217		440
218	If C<$enable> is false, then the C<encode> method will croak if it isn't	441	If C<$enable> is false, then the C<encode> method will croak if it isn't
219	passed an arrayref or hashref, as JSON strings must either be an object	442	passed an arrayref or hashref, as JSON texts must either be an object
220	or array. Likewise, C<decode> will croak if given something that is not a	443	or array. Likewise, C<decode> will croak if given something that is not a
221	JSON object or array.	444	JSON object or array.
222		445
		446	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
		447	resulting in an invalid JSON text:
		448
		449	JSON::XS->new->allow_nonref->encode ("Hello, World!")
		450	=> "Hello, World!"
		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
		468	=item $json = $json->allow_blessed ([$enable])
		469
		470	=item $enabled = $json->get_allow_blessed
		471
		472	If C<$enable> is true (or missing), then the C<encode> method will not
		473	barf when it encounters a blessed reference. Instead, the value of the
		474	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		475	disabled or no C<TO_JSON> method found) or a representation of the
		476	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		477	encoded. Has no effect on C<decode>.
		478
		479	If C<$enable> is false (the default), then C<encode> will throw an
		480	exception when it encounters a blessed object.
		481
		482	=item $json = $json->convert_blessed ([$enable])
		483
		484	=item $enabled = $json->get_convert_blessed
		485
		486	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		487	blessed object, will check for the availability of the C<TO_JSON> method
		488	on the object's class. If found, it will be called in scalar context
		489	and the resulting scalar will be encoded instead of the object. If no
		490	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		491	to do.
		492
		493	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		494	returns other blessed objects, those will be handled in the same
		495	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		496	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		497	methods called by the Perl core (== not by the user of the object) are
		498	usually in upper case letters and to avoid collisions with any C<to_json>
		499	function or method.
		500
		501	This setting does not yet influence C<decode> in any way, but in the
		502	future, global hooks might get installed that influence C<decode> and are
		503	enabled by this setting.
		504
		505	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		506	to do when a blessed object is found.
		507
		508	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		509
		510	When C<$coderef> is specified, it will be called from C<decode> each
		511	time it decodes a JSON object. The only argument is a reference to the
		512	newly-created hash. If the code references returns a single scalar (which
		513	need not be a reference), this value (i.e. a copy of that scalar to avoid
		514	aliasing) is inserted into the deserialised data structure. If it returns
		515	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		516	original deserialised hash will be inserted. This setting can slow down
		517	decoding considerably.
		518
		519	When C<$coderef> is omitted or undefined, any existing callback will
		520	be removed and C<decode> will not change the deserialised hash in any
		521	way.
		522
		523	Example, convert all JSON objects into the integer 5:
		524
		525	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		526	# returns [5]
		527	$js->decode ('[{}]')
		528	# throw an exception because allow_nonref is not enabled
		529	# so a lone 5 is not allowed.
		530	$js->decode ('{"a":1, "b":2}');
		531
		532	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		533
		534	Works remotely similar to C<filter_json_object>, but is only called for
		535	JSON objects having a single key named C<$key>.
		536
		537	This C<$coderef> is called before the one specified via
		538	C<filter_json_object>, if any. It gets passed the single value in the JSON
		539	object. If it returns a single value, it will be inserted into the data
		540	structure. If it returns nothing (not even C<undef> but the empty list),
		541	the callback from C<filter_json_object> will be called next, as if no
		542	single-key callback were specified.
		543
		544	If C<$coderef> is omitted or undefined, the corresponding callback will be
		545	disabled. There can only ever be one callback for a given key.
		546
		547	As this callback gets called less often then the C<filter_json_object>
		548	one, decoding speed will not usually suffer as much. Therefore, single-key
		549	objects make excellent targets to serialise Perl objects into, especially
		550	as single-key JSON objects are as close to the type-tagged value concept
		551	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		552	support this in any way, so you need to make sure your data never looks
		553	like a serialised Perl hash.
		554
		555	Typical names for the single object key are C<__class_whatever__>, or
		556	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		557	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		558	with real hashes.
		559
		560	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		561	into the corresponding C<< $WIDGET{<id>} >> object:
		562
		563	# return whatever is in $WIDGET{5}:
		564	JSON::XS
		565	->new
		566	->filter_json_single_key_object (__widget__ => sub {
		567	$WIDGET{ $_[0] }
		568	})
		569	->decode ('{"__widget__": 5')
		570
		571	# this can be used with a TO_JSON method in some "widget" class
		572	# for serialisation to json:
		573	sub WidgetBase::TO_JSON {
		574	my ($self) = @_;
		575
		576	unless ($self->{id}) {
		577	$self->{id} = ..get..some..id..;
		578	$WIDGET{$self->{id}} = $self;
		579	}
		580
		581	{ __widget__ => $self->{id} }
		582	}
		583
223	=item $json = $json->shrink ([$enable])	584	=item $json = $json->shrink ([$enable])
224		585
		586	=item $enabled = $json->get_shrink
		587
225	Perl usually over-allocates memory a bit when allocating space for	588	Perl usually over-allocates memory a bit when allocating space for
226	strings. This flag optionally resizes strings generated by either	589	strings. This flag optionally resizes strings generated by either
227	C<encode> or C<decode> to their minimum size possible. This can save	590	C<encode> or C<decode> to their minimum size possible. This can save
228	memory when your JSON strings are either very very long or you have many	591	memory when your JSON texts are either very very long or you have many
229	short strings. It will also try to downgrade any strings to octet-form	592	short strings. It will also try to downgrade any strings to octet-form
230	if possible: perl stores strings internally either in an encoding called	593	if possible: perl stores strings internally either in an encoding called
231	UTF-X or in octet-form. The latter cannot store everything but uses less	594	UTF-X or in octet-form. The latter cannot store everything but uses less
232	space in general.	595	space in general (and some buggy Perl or C code might even rely on that
		596	internal representation being used).
233		597
		598	The actual definition of what shrink does might change in future versions,
		599	but it will always try to save space at the expense of time.
		600
234	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	601	If C<$enable> is true (or missing), the string returned by C<encode> will
235	while all strings generated by C<decode> will also be shrunk-to-fit.	602	be shrunk-to-fit, while all strings generated by C<decode> will also be
		603	shrunk-to-fit.
236		604
237	If C<$enable> is false, then the normal perl allocation algorithms are used.	605	If C<$enable> is false, then the normal perl allocation algorithms are used.
238	If you work with your data, then this is likely to be faster.	606	If you work with your data, then this is likely to be faster.
239		607
240	In the future, this setting might control other things, such as converting	608	In the future, this setting might control other things, such as converting
241	strings that look like integers or floats into integers or floats	609	strings that look like integers or floats into integers or floats
242	internally (there is no difference on the Perl level), saving space.	610	internally (there is no difference on the Perl level), saving space.
243		611
		612	=item $json = $json->max_depth ([$maximum_nesting_depth])
		613
		614	=item $max_depth = $json->get_max_depth
		615
		616	Sets the maximum nesting level (default C<512>) accepted while encoding
		617	or decoding. If a higher nesting level is detected in JSON text or a Perl
		618	data structure, then the encoder and decoder will stop and croak at that
		619	point.
		620
		621	Nesting level is defined by number of hash- or arrayrefs that the encoder
		622	needs to traverse to reach a given point or the number of C<{> or C<[>
		623	characters without their matching closing parenthesis crossed to reach a
		624	given character in a string.
		625
		626	Setting the maximum depth to one disallows any nesting, so that ensures
		627	that the object is only a single hash/object or array.
		628
		629	If no argument is given, the highest possible setting will be used, which
		630	is rarely useful.
		631
		632	Note that nesting is implemented by recursion in C. The default value has
		633	been chosen to be as large as typical operating systems allow without
		634	crashing.
		635
		636	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		637
		638	=item $json = $json->max_size ([$maximum_string_size])
		639
		640	=item $max_size = $json->get_max_size
		641
		642	Set the maximum length a JSON text may have (in bytes) where decoding is
		643	being attempted. The default is C<0>, meaning no limit. When C<decode>
		644	is called on a string that is longer then this many bytes, it will not
		645	attempt to decode the string but throw an exception. This setting has no
		646	effect on C<encode> (yet).
		647
		648	If no argument is given, the limit check will be deactivated (same as when
		649	C<0> is specified).
		650
		651	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		652
244	=item $json_string = $json->encode ($perl_scalar)	653	=item $json_text = $json->encode ($perl_scalar)
245		654
246	Converts the given Perl data structure (a simple scalar or a reference	655	Converts the given Perl value or data structure to its JSON
247	to a hash or array) to its JSON representation. Simple scalars will be	656	representation. Croaks on error.
248	converted into JSON string or number sequences, while references to arrays
249	become JSON arrays and references to hashes become JSON objects. Undefined
250	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
251	nor C<false> values will be generated.
252		657
253	=item $perl_scalar = $json->decode ($json_string)	658	=item $perl_scalar = $json->decode ($json_text)
254		659
255	The opposite of C<encode>: expects a JSON string and tries to parse it,	660	The opposite of C<encode>: expects a JSON text and tries to parse it,
256	returning the resulting simple scalar or reference. Croaks on error.	661	returning the resulting simple scalar or reference. Croaks on error.
257		662
258	JSON numbers and strings become simple Perl scalars. JSON arrays become	663	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
259	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	664
260	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	665	This works like the C<decode> method, but instead of raising an exception
		666	when there is trailing garbage after the first JSON object, it will
		667	silently stop parsing there and return the number of characters consumed
		668	so far.
		669
		670	This is useful if your JSON texts are not delimited by an outer protocol
		671	and you need to know where the JSON text ends.
		672
		673	JSON::XS->new->decode_prefix ("[1] the tail")
		674	=> ([], 3)
261		675
262	=back	676	=back
263		677
264	=head1 COMPARISON
265		678
266	As already mentioned, this module was created because none of the existing	679	=head1 INCREMENTAL PARSING
267	JSON modules could be made to work correctly. First I will describe the	680
268	problems (or pleasures) I encountered with various existing JSON modules,	681	In some cases, there is the need for incremental parsing of JSON
269	followed by some benchmark values. JSON::XS was designed not to suffer	682	texts. While this module always has to keep both JSON text and resulting
270	from any of these problems or limitations.	683	Perl data structure in memory at one time, it does allow you to parse a
		684	JSON stream incrementally. It does so by accumulating text until it has
		685	a full JSON object, which it then can decode. This process is similar to
		686	using C<decode_prefix> to see if a full JSON object is available, but
		687	is much more efficient (and can be implemented with a minimum of method
		688	calls).
		689
		690	JSON::XS will only attempt to parse the JSON text once it is sure it
		691	has enough text to get a decisive result, using a very simple but
		692	truly incremental parser. This means that it sometimes won't stop as
		693	early as the full parser, for example, it doesn't detect mismatched
		694	parentheses. The only thing it guarantees is that it starts decoding as
		695	soon as a syntactically valid JSON text has been seen. This means you need
		696	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		697	parsing in the presence if syntax errors.
		698
		699	The following methods implement this incremental parser.
271		700
272	=over 4	701	=over 4
273		702
274	=item JSON 1.07	703	=item [void, scalar or list context] = $json->incr_parse ([$string])
275		704
276	Slow (but very portable, as it is written in pure Perl).	705	This is the central parsing function. It can both append new text and
		706	extract objects from the stream accumulated so far (both of these
		707	functions are optional).
277		708
278	Undocumented/buggy Unicode handling (how JSON handles unicode values is	709	If C<$string> is given, then this string is appended to the already
279	undocumented. One can get far by feeding it unicode strings and doing	710	existing JSON fragment stored in the C<$json> object.
280	en-/decoding oneself, but unicode escapes are not working properly).
281		711
282	No roundtripping (strings get clobbered if they look like numbers, e.g.	712	After that, if the function is called in void context, it will simply
283	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	713	return without doing anything further. This can be used to add more text
284	decode into the number 2.	714	in as many chunks as you want.
285		715
286	=item JSON::PC 0.01	716	If the method is called in scalar context, then it will try to extract
		717	exactly I<one> JSON object. If that is successful, it will return this
		718	object, otherwise it will return C<undef>. If there is a parse error,
		719	this method will croak just as C<decode> would do (one can then use
		720	C<incr_skip> to skip the erroneous part). This is the most common way of
		721	using the method.
287		722
288	Very fast.	723	And finally, in list context, it will try to extract as many objects
		724	from the stream as it can find and return them, or the empty list
		725	otherwise. For this to work, there must be no separators between the JSON
		726	objects or arrays, instead they must be concatenated back-to-back. If
		727	an error occurs, an exception will be raised as in the scalar context
		728	case. Note that in this case, any previously-parsed JSON texts will be
		729	lost.
289		730
290	Undocumented/buggy Unicode handling.	731	Example: Parse some JSON arrays/objects in a given string and return
		732	them.
291		733
292	No roundtripping.	734	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
293		735
294	Has problems handling many Perl values (e.g. regex results and other magic	736	=item $lvalue_string = $json->incr_text
295	values will make it croak).
296		737
297	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	738	This method returns the currently stored JSON fragment as an lvalue, that
298	which is not a valid JSON string.	739	is, you can manipulate it. This I<only> works when a preceding call to
		740	C<incr_parse> in I<scalar context> successfully returned an object. Under
		741	all other circumstances you must not call this function (I mean it.
		742	although in simple tests it might actually work, it I<will> fail under
		743	real world conditions). As a special exception, you can also call this
		744	method before having parsed anything.
299		745
300	Unmaintained (maintainer unresponsive for many months, bugs are not	746	This function is useful in two cases: a) finding the trailing text after a
301	getting fixed).	747	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		748	(such as commas).
302		749
303	=item JSON::Syck 0.21	750	=item $json->incr_skip
304		751
305	Very buggy (often crashes).	752	This will reset the state of the incremental parser and will remove
		753	the parsed text from the input buffer so far. This is useful after
		754	C<incr_parse> died, in which case the input buffer and incremental parser
		755	state is left unchanged, to skip the text parsed so far and to reset the
		756	parse state.
306		757
307	Very inflexible (no human-readable format supported, format pretty much	758	The difference to C<incr_reset> is that only text until the parse error
308	undocumented. I need at least a format for easy reading by humans and a	759	occurred is removed.
309	single-line compact format for use in a protocol, and preferably a way to
310	generate ASCII-only JSON strings).
311		760
312	Completely broken (and confusingly documented) Unicode handling (unicode	761	=item $json->incr_reset
313	escapes are not working properly, you need to set ImplicitUnicode to
314	I<different> values on en- and decoding to get symmetric behaviour).
315		762
316	No roundtripping (simple cases work, but this depends on wether the scalar	763	This completely resets the incremental parser, that is, after this call,
317	value was used in a numeric context or not).	764	it will be as if the parser had never parsed anything.
318		765
319	Dumping hashes may skip hash values depending on iterator state.	766	This is useful if you want to repeatedly parse JSON objects and want to
320		767	ignore any trailing data, which means you have to reset the parser after
321	Unmaintained (maintainer unresponsive for many months, bugs are not	768	each successful decode.
322	getting fixed).
323
324	Does not check input for validity (i.e. will accept non-JSON input and
325	return "something" instead of raising an exception. This is a security
326	issue: imagine two banks transfering money between each other using
327	JSON. One bank might parse a given non-JSON request and deduct money,
328	while the other might reject the transaction with a syntax error. While a
329	good protocol will at least recover, that is extra unnecessary work and
330	the transaction will still not succeed).
331
332	=item JSON::DWIW 0.04
333
334	Very fast. Very natural. Very nice.
335
336	Undocumented unicode handling (but the best of the pack. Unicode escapes
337	still don't get parsed properly).
338
339	Very inflexible.
340
341	No roundtripping.
342
343	Does not generate valid JSON (key strings are often unquoted, empty keys
344	result in nothing being output)
345
346	Does not check input for validity.
347		769
348	=back	770	=back
		771
		772	=head2 LIMITATIONS
		773
		774	All options that affect decoding are supported, except
		775	C<allow_nonref>. The reason for this is that it cannot be made to work
		776	sensibly: JSON objects and arrays are self-delimited, i.e. you can
		777	concatenate them back to back and still decode them perfectly. This does
		778	not hold true for JSON numbers, however.
		779
		780	For example, is the string C<1> a single JSON number, or is it simply the
		781	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		782	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		783	takes the conservative route and disallows this case.
		784
		785	=head2 EXAMPLES
		786
		787	Some examples will make all this clearer. First, a simple example that
		788	works similarly to C<decode_prefix>: We want to decode the JSON object at
		789	the start of a string and identify the portion after the JSON object:
		790
		791	my $text = "[1,2,3] hello";
		792
		793	my $json = new JSON::XS;
		794
		795	my $obj = $json->incr_parse ($text)
		796	or die "expected JSON object or array at beginning of string";
		797
		798	my $tail = $json->incr_text;
		799	# $tail now contains " hello"
		800
		801	Easy, isn't it?
		802
		803	Now for a more complicated example: Imagine a hypothetical protocol where
		804	you read some requests from a TCP stream, and each request is a JSON
		805	array, without any separation between them (in fact, it is often useful to
		806	use newlines as "separators", as these get interpreted as whitespace at
		807	the start of the JSON text, which makes it possible to test said protocol
		808	with C<telnet>...).
		809
		810	Here is how you'd do it (it is trivial to write this in an event-based
		811	manner):
		812
		813	my $json = new JSON::XS;
		814
		815	# read some data from the socket
		816	while (sysread $socket, my $buf, 4096) {
		817
		818	# split and decode as many requests as possible
		819	for my $request ($json->incr_parse ($buf)) {
		820	# act on the $request
		821	}
		822	}
		823
		824	Another complicated example: Assume you have a string with JSON objects
		825	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		826	[3]>). To parse them, we have to skip the commas between the JSON texts,
		827	and here is where the lvalue-ness of C<incr_text> comes in useful:
		828
		829	my $text = "[1],[2], [3]";
		830	my $json = new JSON::XS;
		831
		832	# void context, so no parsing done
		833	$json->incr_parse ($text);
		834
		835	# now extract as many objects as possible. note the
		836	# use of scalar context so incr_text can be called.
		837	while (my $obj = $json->incr_parse) {
		838	# do something with $obj
		839
		840	# now skip the optional comma
		841	$json->incr_text =~ s/^ \s* , //x;
		842	}
		843
		844	Now lets go for a very complex example: Assume that you have a gigantic
		845	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		846	but you cannot load it into memory fully (this has actually happened in
		847	the real world :).
		848
		849	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		850	can still help you: You implement a (very simple) array parser and let
		851	JSON decode the array elements, which are all full JSON objects on their
		852	own (this wouldn't work if the array elements could be JSON numbers, for
		853	example):
		854
		855	my $json = new JSON::XS;
		856
		857	# open the monster
		858	open my $fh, "<bigfile.json"
		859	or die "bigfile: $!";
		860
		861	# first parse the initial "["
		862	for (;;) {
		863	sysread $fh, my $buf, 65536
		864	or die "read error: $!";
		865	$json->incr_parse ($buf); # void context, so no parsing
		866
		867	# Exit the loop once we found and removed(!) the initial "[".
		868	# In essence, we are (ab-)using the $json object as a simple scalar
		869	# we append data to.
		870	last if $json->incr_text =~ s/^ \s* \[ //x;
		871	}
		872
		873	# now we have the skipped the initial "[", so continue
		874	# parsing all the elements.
		875	for (;;) {
		876	# in this loop we read data until we got a single JSON object
		877	for (;;) {
		878	if (my $obj = $json->incr_parse) {
		879	# do something with $obj
		880	last;
		881	}
		882
		883	# add more data
		884	sysread $fh, my $buf, 65536
		885	or die "read error: $!";
		886	$json->incr_parse ($buf); # void context, so no parsing
		887	}
		888
		889	# in this loop we read data until we either found and parsed the
		890	# separating "," between elements, or the final "]"
		891	for (;;) {
		892	# first skip whitespace
		893	$json->incr_text =~ s/^\s*//;
		894
		895	# if we find "]", we are done
		896	if ($json->incr_text =~ s/^\]//) {
		897	print "finished.\n";
		898	exit;
		899	}
		900
		901	# if we find ",", we can continue with the next element
		902	if ($json->incr_text =~ s/^,//) {
		903	last;
		904	}
		905
		906	# if we find anything else, we have a parse error!
		907	if (length $json->incr_text) {
		908	die "parse error near ", $json->incr_text;
		909	}
		910
		911	# else 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	This is a complex example, but most of the complexity comes from the fact
		918	that we are trying to be correct (bear with me if I am wrong, I never ran
		919	the above example :).
		920
		921
		922
		923	=head1 MAPPING
		924
		925	This section describes how JSON::XS maps Perl values to JSON values and
		926	vice versa. These mappings are designed to "do the right thing" in most
		927	circumstances automatically, preserving round-tripping characteristics
		928	(what you put in comes out as something equivalent).
		929
		930	For the more enlightened: note that in the following descriptions,
		931	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		932	refers to the abstract Perl language itself.
		933
		934
		935	=head2 JSON -> PERL
		936
		937	=over 4
		938
		939	=item object
		940
		941	A JSON object becomes a reference to a hash in Perl. No ordering of object
		942	keys is preserved (JSON does not preserve object key ordering itself).
		943
		944	=item array
		945
		946	A JSON array becomes a reference to an array in Perl.
		947
		948	=item string
		949
		950	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		951	are represented by the same codepoints in the Perl string, so no manual
		952	decoding is necessary.
		953
		954	=item number
		955
		956	A JSON number becomes either an integer, numeric (floating point) or
		957	string scalar in perl, depending on its range and any fractional parts. On
		958	the Perl level, there is no difference between those as Perl handles all
		959	the conversion details, but an integer may take slightly less memory and
		960	might represent more values exactly than floating point numbers.
		961
		962	If the number consists of digits only, JSON::XS will try to represent
		963	it as an integer value. If that fails, it will try to represent it as
		964	a numeric (floating point) value if that is possible without loss of
		965	precision. Otherwise it will preserve the number as a string value (in
		966	which case you lose roundtripping ability, as the JSON number will be
		967	re-encoded to a JSON string).
		968
		969	Numbers containing a fractional or exponential part will always be
		970	represented as numeric (floating point) values, possibly at a loss of
		971	precision (in which case you might lose perfect roundtripping ability, but
		972	the JSON number will still be re-encoded as a JSON number).
		973
		974	Note that precision is not accuracy - binary floating point values cannot
		975	represent most decimal fractions exactly, and when converting from and to
		976	floating point, JSON::XS only guarantees precision up to but not including
		977	the least significant bit.
		978
		979	=item true, false
		980
		981	These JSON atoms become C<Types::Serialiser::true> and
		982	C<Types::Serialiser::false>, respectively. They are overloaded to act
		983	almost exactly like the numbers C<1> and C<0>. You can check whether
		984	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		985	function (after C<use Types::Serialier>, of course).
		986
		987	=item null
		988
		989	A JSON null atom becomes C<undef> in Perl.
		990
		991	=item shell-style comments (C<< # I<text> >>)
		992
		993	As a nonstandard extension to the JSON syntax that is enabled by the
		994	C<relaxed> setting, shell-style comments are allowed. They can start
		995	anywhere outside strings and go till the end of the line.
		996
		997	=item tagged values (C<< (I<tag>)I<value> >>).
		998
		999	Another nonstandard extension to the JSON syntax, enabled with the
		1000	C<allow_tags> setting, are tagged values. In this implementation, the
		1001	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1002	I<value> must be a JSON array encoding optional constructor arguments.
		1003
		1004	See "OBJECT SERIALISATION", below, for details.
		1005
		1006	=back
		1007
		1008
		1009	=head2 PERL -> JSON
		1010
		1011	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		1012	truly typeless language, so we can only guess which JSON type is meant by
		1013	a Perl value.
		1014
		1015	=over 4
		1016
		1017	=item hash references
		1018
		1019	Perl hash references become JSON objects. As there is no inherent
		1020	ordering in hash keys (or JSON objects), they will usually be encoded
		1021	in a pseudo-random order. JSON::XS can optionally sort the hash keys
		1022	(determined by the I<canonical> flag), so the same datastructure will
		1023	serialise to the same JSON text (given same settings and version of
		1024	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
		1025	e.g. when you want to compare some JSON text against another for equality.
		1026
		1027	=item array references
		1028
		1029	Perl array references become JSON arrays.
		1030
		1031	=item other references
		1032
		1033	Other unblessed references are generally not allowed and will cause an
		1034	exception to be thrown, except for references to the integers C<0> and
		1035	C<1>, which get turned into C<false> and C<true> atoms in JSON.
		1036
		1037	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1038	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1039	and C<Types::Serialiser::true> to improve readability.
		1040
		1041	use Types::Serialiser;
		1042	encode_json [\0, Types::Serialiser::true] # yields [false,true]
		1043
		1044	=item Types::Serialiser::true, Types::Serialiser::false
		1045
		1046	These special values from the L<Types::Serialiser> module become JSON true
		1047	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1048	directly if you want.
		1049
		1050	=item blessed objects
		1051
		1052	Blessed objects are not directly representable in JSON, but C<JSON::XS>
		1053	allows various ways of handling objects. See "OBJECT SERIALISATION",
		1054	below, for details.
		1055
		1056	=item simple scalars
		1057
		1058	Simple Perl scalars (any scalar that is not a reference) are the most
		1059	difficult objects to encode: JSON::XS will encode undefined scalars as
		1060	JSON C<null> values, scalars that have last been used in a string context
		1061	before encoding as JSON strings, and anything else as number value:
		1062
		1063	# dump as number
		1064	encode_json [2] # yields [2]
		1065	encode_json [-3.0e17] # yields [-3e+17]
		1066	my $value = 5; encode_json [$value] # yields [5]
		1067
		1068	# used as string, so dump as string
		1069	print $value;
		1070	encode_json [$value] # yields ["5"]
		1071
		1072	# undef becomes null
		1073	encode_json [undef] # yields [null]
		1074
		1075	You can force the type to be a JSON string by stringifying it:
		1076
		1077	my $x = 3.1; # some variable containing a number
		1078	"$x"; # stringified
		1079	$x .= ""; # another, more awkward way to stringify
		1080	print $x; # perl does it for you, too, quite often
		1081
		1082	You can force the type to be a JSON number by numifying it:
		1083
		1084	my $x = "3"; # some variable containing a string
		1085	$x += 0; # numify it, ensuring it will be dumped as a number
		1086	$x *= 1; # same thing, the choice is yours.
		1087
		1088	You can not currently force the type in other, less obscure, ways. Tell me
		1089	if you need this capability (but don't forget to explain why it's needed
		1090	:).
		1091
		1092	Note that numerical precision has the same meaning as under Perl (so
		1093	binary to decimal conversion follows the same rules as in Perl, which
		1094	can differ to other languages). Also, your perl interpreter might expose
		1095	extensions to the floating point numbers of your platform, such as
		1096	infinities or NaN's - these cannot be represented in JSON, and it is an
		1097	error to pass those in.
		1098
		1099	=back
		1100
		1101	=head2 OBJECT SERIALISATION
		1102
		1103	As JSON cannot directly represent Perl objects, you have to choose between
		1104	a pure JSON representation (without the ability to deserialise the object
		1105	automatically again), and a nonstandard extension to the JSON syntax,
		1106	tagged values.
		1107
		1108	=head3 SERIALISATION
		1109
		1110	What happens when C<JSON::XS> encounters a Perl object depends on the
		1111	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
		1112	used in this order:
		1113
		1114	=over 4
		1115
		1116	=item 1. C<allow_tags> is enabled and object has a C<FREEZE> method.
		1117
		1118	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1119	serialisation protocol to create a tagged JSON value, using a nonstandard
		1120	extension to the JSON syntax.
		1121
		1122	This works by invoking the C<FREEZE> method on the object, with the first
		1123	argument being the object to serialise, and the second argument being the
		1124	constant string C<JSON> to distinguish it from other serialisers.
		1125
		1126	The C<FREEZE> method can return any number of values (i.e. zero or
		1127	more). These values and the paclkage/classname of the object will then be
		1128	encoded as a tagged JSON value in the following format:
		1129
		1130	("classname")[FREEZE return values...]
		1131
		1132	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1133	objects C<type> and C<id> members to encode the object:
		1134
		1135	sub My::Object::FREEZE {
		1136	my ($self, $serialiser) = @_;
		1137
		1138	($self->{type}, $self->{id})
		1139	}
		1140
		1141	=item 2. C<convert_blessed> is enabled and object has a C<TO_JSON> method.
		1142
		1143	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1144	context. It must return a single scalar that can be directly encoded into
		1145	JSON. This scalar replaces the object in the JSON text.
		1146
		1147	For example, the following C<TO_JSON> method will convert all L<URI>
		1148	objects to JSON strings when serialised. The fatc that these values
		1149	originally were L<URI> objects is lost.
		1150
		1151	sub URI::TO_JSON {
		1152	my ($uri) = @_;
		1153	$uri->as_string
		1154	}
		1155
		1156	=item 3. C<allow_blessed> is enabled.
		1157
		1158	The object will be serialised as a JSON null value.
		1159
		1160	=item 4. none of the above
		1161
		1162	If none of the settings are enabled or the respective methods are missing,
		1163	C<JSON::XS> throws an exception.
		1164
		1165	=back
		1166
		1167	=head3 DESERIALISATION
		1168
		1169	For deserialisation there are only two cases to consider: either
		1170	nonstandard tagging was used, in which case C<allow_tags> decides,
		1171	or objects cannot be automatically be deserialised, in which
		1172	case you can use postprocessing or the C<filter_json_object> or
		1173	C<filter_json_single_key_object> callbacks to get some real objects our of
		1174	your JSON.
		1175
		1176	This section only considers the tagged value case: I a tagged JSON object
		1177	is encountered during decoding and C<allow_tags> is disabled, a parse
		1178	error will result (as if tagged values were not part of the grammar).
		1179
		1180	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1181	of the package/classname used during serialisation. If there is no such
		1182	method, the decoding will fail with an error.
		1183
		1184	Otherwise, the C<THAW> method is invoked with the classname as first
		1185	argument, the constant string C<JSON> as second argument, and all the
		1186	values from the JSON array (the values originally returned by the
		1187	C<FREEZE> method) as remaining arguments.
		1188
		1189	The method must then return the object. While technically you can return
		1190	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1191	make that work in all cases, so better return an actual blessed reference.
		1192
		1193	As an example, let's implement a C<THAW> function that regenerates the
		1194	C<My::Object> from the C<FREEZE> example earlier:
		1195
		1196	sub My::Object::THAW {
		1197	my ($class, $serialiser, $type, $id) = @_;
		1198
		1199	$class->new (type => $type, id => $id)
		1200	}
		1201
		1202
		1203	=head1 ENCODING/CODESET FLAG NOTES
		1204
		1205	The interested reader might have seen a number of flags that signify
		1206	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1207	some confusion on what these do, so here is a short comparison:
		1208
		1209	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1210	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1211	control whether C<encode> escapes character values outside their respective
		1212	codeset range. Neither of these flags conflict with each other, although
		1213	some combinations make less sense than others.
		1214
		1215	Care has been taken to make all flags symmetrical with respect to
		1216	C<encode> and C<decode>, that is, texts encoded with any combination of
		1217	these flag values will be correctly decoded when the same flags are used
		1218	- in general, if you use different flag settings while encoding vs. when
		1219	decoding you likely have a bug somewhere.
		1220
		1221	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1222	simply an abstract set of character-codepoint pairs, while an encoding
		1223	takes those codepoint numbers and I<encodes> them, in our case into
		1224	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1225	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1226	the same time, which can be confusing.
		1227
		1228	=over 4
		1229
		1230	=item C<utf8> flag disabled
		1231
		1232	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1233	and expect Unicode strings, that is, characters with high ordinal Unicode
		1234	values (> 255) will be encoded as such characters, and likewise such
		1235	characters are decoded as-is, no changes to them will be done, except
		1236	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1237	respectively (to Perl, these are the same thing in strings unless you do
		1238	funny/weird/dumb stuff).
		1239
		1240	This is useful when you want to do the encoding yourself (e.g. when you
		1241	want to have UTF-16 encoded JSON texts) or when some other layer does
		1242	the encoding for you (for example, when printing to a terminal using a
		1243	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1244	to UTF-8 encode your data first and have Perl encode it another time).
		1245
		1246	=item C<utf8> flag enabled
		1247
		1248	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1249	characters using the corresponding UTF-8 multi-byte sequence, and will
		1250	expect your input strings to be encoded as UTF-8, that is, no "character"
		1251	of the input string must have any value > 255, as UTF-8 does not allow
		1252	that.
		1253
		1254	The C<utf8> flag therefore switches between two modes: disabled means you
		1255	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1256	octet/binary string in Perl.
		1257
		1258	=item C<latin1> or C<ascii> flags enabled
		1259
		1260	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1261	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1262	characters as specified by the C<utf8> flag.
		1263
		1264	If C<utf8> is disabled, then the result is also correctly encoded in those
		1265	character sets (as both are proper subsets of Unicode, meaning that a
		1266	Unicode string with all character values < 256 is the same thing as a
		1267	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1268	the same thing as an ASCII string in Perl).
		1269
		1270	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1271	regardless of these flags, just some more characters will be escaped using
		1272	C<\uXXXX> then before.
		1273
		1274	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1275	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1276	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1277	a subset of Unicode), while ASCII is.
		1278
		1279	Surprisingly, C<decode> will ignore these flags and so treat all input
		1280	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1281	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1282	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1283
		1284	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1285	they only govern when the JSON output engine escapes a character or not.
		1286
		1287	The main use for C<latin1> is to relatively efficiently store binary data
		1288	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1289
		1290	The main use for C<ascii> is to force the output to not contain characters
		1291	with values > 127, which means you can interpret the resulting string
		1292	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1293	8-bit-encoding, and still get the same data structure back. This is useful
		1294	when your channel for JSON transfer is not 8-bit clean or the encoding
		1295	might be mangled in between (e.g. in mail), and works because ASCII is a
		1296	proper subset of most 8-bit and multibyte encodings in use in the world.
		1297
		1298	=back
		1299
		1300
		1301	=head2 JSON and ECMAscript
		1302
		1303	JSON syntax is based on how literals are represented in javascript (the
		1304	not-standardised predecessor of ECMAscript) which is presumably why it is
		1305	called "JavaScript Object Notation".
		1306
		1307	However, JSON is not a subset (and also not a superset of course) of
		1308	ECMAscript (the standard) or javascript (whatever browsers actually
		1309	implement).
		1310
		1311	If you want to use javascript's C<eval> function to "parse" JSON, you
		1312	might run into parse errors for valid JSON texts, or the resulting data
		1313	structure might not be queryable:
		1314
		1315	One of the problems is that U+2028 and U+2029 are valid characters inside
		1316	JSON strings, but are not allowed in ECMAscript string literals, so the
		1317	following Perl fragment will not output something that can be guaranteed
		1318	to be parsable by javascript's C<eval>:
		1319
		1320	use JSON::XS;
		1321
		1322	print encode_json [chr 0x2028];
		1323
		1324	The right fix for this is to use a proper JSON parser in your javascript
		1325	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1326	F<json2.js> parser).
		1327
		1328	If this is not an option, you can, as a stop-gap measure, simply encode to
		1329	ASCII-only JSON:
		1330
		1331	use JSON::XS;
		1332
		1333	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1334
		1335	Note that this will enlarge the resulting JSON text quite a bit if you
		1336	have many non-ASCII characters. You might be tempted to run some regexes
		1337	to only escape U+2028 and U+2029, e.g.:
		1338
		1339	# DO NOT USE THIS!
		1340	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1341	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1342	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1343	print $json;
		1344
		1345	Note that I<this is a bad idea>: the above only works for U+2028 and
		1346	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1347	javascript implementations, however, have issues with other characters as
		1348	well - using C<eval> naively simply I<will> cause problems.
		1349
		1350	Another problem is that some javascript implementations reserve
		1351	some property names for their own purposes (which probably makes
		1352	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1353	C<__proto__> property name for its own purposes.
		1354
		1355	If that is a problem, you could parse try to filter the resulting JSON
		1356	output for these property strings, e.g.:
		1357
		1358	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1359
		1360	This works because C<__proto__> is not valid outside of strings, so every
		1361	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1362
		1363	If you know of other incompatibilities, please let me know.
		1364
		1365
		1366	=head2 JSON and YAML
		1367
		1368	You often hear that JSON is a subset of YAML. This is, however, a mass
		1369	hysteria(*) and very far from the truth (as of the time of this writing),
		1370	so let me state it clearly: I<in general, there is no way to configure
		1371	JSON::XS to output a data structure as valid YAML> that works in all
		1372	cases.
		1373
		1374	If you really must use JSON::XS to generate YAML, you should use this
		1375	algorithm (subject to change in future versions):
		1376
		1377	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1378	my $yaml = $to_yaml->encode ($ref) . "\n";
		1379
		1380	This will I<usually> generate JSON texts that also parse as valid
		1381	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1382	lengths that JSON doesn't have and also has different and incompatible
		1383	unicode character escape syntax, so you should make sure that your hash
		1384	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1385	and that you do not have characters with codepoint values outside the
		1386	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1387	sequences in strings (which JSON::XS does not I<currently> generate, but
		1388	other JSON generators might).
		1389
		1390	There might be other incompatibilities that I am not aware of (or the YAML
		1391	specification has been changed yet again - it does so quite often). In
		1392	general you should not try to generate YAML with a JSON generator or vice
		1393	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1394	high that you will run into severe interoperability problems when you
		1395	least expect it.
		1396
		1397	=over 4
		1398
		1399	=item (*)
		1400
		1401	I have been pressured multiple times by Brian Ingerson (one of the
		1402	authors of the YAML specification) to remove this paragraph, despite him
		1403	acknowledging that the actual incompatibilities exist. As I was personally
		1404	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1405	educate people about these issues, so others do not run into the same
		1406	problem again and again. After this, Brian called me a (quote)I<complete
		1407	and worthless idiot>(unquote).
		1408
		1409	In my opinion, instead of pressuring and insulting people who actually
		1410	clarify issues with YAML and the wrong statements of some of its
		1411	proponents, I would kindly suggest reading the JSON spec (which is not
		1412	that difficult or long) and finally make YAML compatible to it, and
		1413	educating users about the changes, instead of spreading lies about the
		1414	real compatibility for many I<years> and trying to silence people who
		1415	point out that it isn't true.
		1416
		1417	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1418	though the incompatibilities have been documented (and are known to Brian)
		1419	for many years and the spec makes explicit claims that YAML is a superset
		1420	of JSON. It would be so easy to fix, but apparently, bullying people and
		1421	corrupting userdata is so much easier.
		1422
		1423	=back
		1424
349		1425
350	=head2 SPEED	1426	=head2 SPEED
351		1427
352	It seems that JSON::XS is surprisingly fast, as shown in the following	1428	It seems that JSON::XS is surprisingly fast, as shown in the following
353	tables. They have been generated with the help of the C<eg/bench> program	1429	tables. They have been generated with the help of the C<eg/bench> program
354	in the JSON::XS distribution, to make it easy to compare on your own	1430	in the JSON::XS distribution, to make it easy to compare on your own
355	system.	1431	system.
356		1432
357	First is a comparison between various modules using a very simple JSON	1433	First comes a comparison between various modules using
		1434	a very short single-line JSON string (also available at
		1435	L<http://dist.schmorp.de/misc/json/short.json>).
		1436
		1437	{"method": "handleMessage", "params": ["user1",
		1438	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1439	1, 0]}
		1440
358	string, showing the number of encodes/decodes per second (JSON::XS is	1441	It shows the number of encodes/decodes per second (JSON::XS uses
359	the functional interface, while JSON::XS/2 is the OO interface with	1442	the functional interface, while JSON::XS/2 uses the OO interface
360	pretty-printing and hashkey sorting enabled).	1443	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1444	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1445	uses the from_json method). Higher is better:
361		1446
362	module | encode | decode |	1447	module | encode | decode |
363	-----------|------------|------------|	1448	--------------|------------|------------|
364	JSON | 14006 | 6820 |	1449	JSON::DWIW/DS | 86302.551 | 102300.098 |
365	JSON::DWIW | 200937 | 120386 |	1450	JSON::DWIW/FJ | 86302.551 | 75983.768 |
366	JSON::PC | 85065 | 129366 |	1451	JSON::PP | 15827.562 | 6638.658 |
367	JSON::Syck | 59898 | 44232 |	1452	JSON::Syck | 63358.066 | 47662.545 |
368	JSON::XS | 1171478 | 342435 |	1453	JSON::XS | 511500.488 | 511500.488 |
369	JSON::XS/2 | 730760 | 328714 |	1454	JSON::XS/2 | 291271.111 | 388361.481 |
		1455	JSON::XS/3 | 361577.931 | 361577.931 |
		1456	Storable | 66788.280 | 265462.278 |
370	-----------+------------+------------+	1457	--------------+------------+------------+
371		1458
372	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1459	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
373	times faster than JSON, even with pretty-printing and key sorting.	1460	about five times faster on decoding, and over thirty to seventy times
		1461	faster than JSON's pure perl implementation. It also compares favourably
		1462	to Storable for small amounts of data.
374		1463
375	Using a longer test string (roughly 8KB, generated from Yahoo! Locals	1464	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
376	search API (http://nanoref.com/yahooapis/mgPdGg):	1465	search API (L<http://dist.schmorp.de/misc/json/long.json>).
377		1466
378	module | encode | decode |	1467	module | encode | decode |
379	-----------|------------|------------|	1468	--------------|------------|------------|
380	JSON | 673 | 38 |	1469	JSON::DWIW/DS | 1647.927 | 2673.916 |
381	JSON::DWIW | 5271 | 770 |	1470	JSON::DWIW/FJ | 1630.249 | 2596.128 |
382	JSON::PC | 9901 | 2491 |	1471	JSON::PP | 400.640 | 62.311 |
383	JSON::Syck | 2360 | 786 |	1472	JSON::Syck | 1481.040 | 1524.869 |
384	JSON::XS | 37398 | 3202 |	1473	JSON::XS | 20661.596 | 9541.183 |
385	JSON::XS/2 | 13765 | 3153 |	1474	JSON::XS/2 | 10683.403 | 9416.938 |
		1475	JSON::XS/3 | 20661.596 | 9400.054 |
		1476	Storable | 19765.806 | 10000.725 |
386	-----------+------------+------------+	1477	--------------+------------+------------+
387		1478
388	Again, JSON::XS leads by far in the encoding case, while still beating	1479	Again, JSON::XS leads by far (except for Storable which non-surprisingly
389	every other module in the decoding case.	1480	decodes a bit faster).
390		1481
391	Last example is an almost 8MB large hash with many large binary values	1482	On large strings containing lots of high Unicode characters, some modules
392	(PNG files), resulting in a lot of escaping:	1483	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1484	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1485	to decode or encode properly, so it was impossible to prepare a fair
		1486	comparison table for that case.
		1487
		1488
		1489	=head1 SECURITY CONSIDERATIONS
		1490
		1491	When you are using JSON in a protocol, talking to untrusted potentially
		1492	hostile creatures requires relatively few measures.
		1493
		1494	First of all, your JSON decoder should be secure, that is, should not have
		1495	any buffer overflows. Obviously, this module should ensure that and I am
		1496	trying hard on making that true, but you never know.
		1497
		1498	Second, you need to avoid resource-starving attacks. That means you should
		1499	limit the size of JSON texts you accept, or make sure then when your
		1500	resources run out, that's just fine (e.g. by using a separate process that
		1501	can crash safely). The size of a JSON text in octets or characters is
		1502	usually a good indication of the size of the resources required to decode
		1503	it into a Perl structure. While JSON::XS can check the size of the JSON
		1504	text, it might be too late when you already have it in memory, so you
		1505	might want to check the size before you accept the string.
		1506
		1507	Third, JSON::XS recurses using the C stack when decoding objects and
		1508	arrays. The C stack is a limited resource: for instance, on my amd64
		1509	machine with 8MB of stack size I can decode around 180k nested arrays but
		1510	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1511	to free the temporary). If that is exceeded, the program crashes. To be
		1512	conservative, the default nesting limit is set to 512. If your process
		1513	has a smaller stack, you should adjust this setting accordingly with the
		1514	C<max_depth> method.
		1515
		1516	Something else could bomb you, too, that I forgot to think of. In that
		1517	case, you get to keep the pieces. I am always open for hints, though...
		1518
		1519	Also keep in mind that JSON::XS might leak contents of your Perl data
		1520	structures in its error messages, so when you serialise sensitive
		1521	information you might want to make sure that exceptions thrown by JSON::XS
		1522	will not end up in front of untrusted eyes.
		1523
		1524	If you are using JSON::XS to return packets to consumption
		1525	by JavaScript scripts in a browser you should have a look at
		1526	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
		1527	see whether you are vulnerable to some common attack vectors (which really
		1528	are browser design bugs, but it is still you who will have to deal with
		1529	it, as major browser developers care only for features, not about getting
		1530	security right).
		1531
		1532
		1533	=head1 INTEROPERABILITY WITH OTHER MODULES
		1534
		1535	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1536	constants. That means that the JSON true and false values will be
		1537	comaptible to true and false values of iother modules that do the same,
		1538	such as L<JSON::PP> and L<CBOR::XS>.
		1539
		1540
		1541	=head1 THREADS
		1542
		1543	This module is I<not> guaranteed to be thread safe and there are no
		1544	plans to change this until Perl gets thread support (as opposed to the
		1545	horribly slow so-called "threads" which are simply slow and bloated
		1546	process simulations - use fork, it's I<much> faster, cheaper, better).
		1547
		1548	(It might actually work, but you have been warned).
		1549
		1550
		1551	=head1 THE PERILS OF SETLOCALE
		1552
		1553	Sometimes people avoid the Perl locale support and directly call the
		1554	system's setlocale function with C<LC_ALL>.
		1555
		1556	This breaks both perl and modules such as JSON::XS, as stringification of
		1557	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1558	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1559	perl to stringify numbers).
		1560
		1561	The solution is simple: don't call C<setlocale>, or use it for only those
		1562	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1563
		1564	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1565	actually needs it (avoiding stringification of numbers), and restore it
		1566	afterwards.
		1567
393		1568
394	=head1 BUGS	1569	=head1 BUGS
395		1570
396	While the goal of this module is to be correct, that unfortunately does	1571	While the goal of this module is to be correct, that unfortunately does
397	not mean its bug-free, only that I think its design is bug-free. It is	1572	not mean it's bug-free, only that I think its design is bug-free. If you
398	still very young and not well-tested. If you keep reporting bugs they will	1573	keep reporting bugs they will be fixed swiftly, though.
399	be fixed swiftly, though.	1574
		1575	Please refrain from using rt.cpan.org or any other bug reporting
		1576	service. I put the contact address into my modules for a reason.
400		1577
401	=cut	1578	=cut
402		1579
403	1;	1580	BEGIN {
		1581	*true = \$Types::Serialiser::true;
		1582	*true = \&Types::Serialiser::true;
		1583	*false = \$Types::Serialiser::false;
		1584	*false = \&Types::Serialiser::false;
		1585	*is_bool = \&Types::Serialiser::is_bool;
		1586
		1587	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
		1588	}
		1589
		1590	XSLoader::load "JSON::XS", $VERSION;
		1591
		1592	=head1 SEE ALSO
		1593
		1594	The F<json_xs> command line utility for quick experiments.
404		1595
405	=head1 AUTHOR	1596	=head1 AUTHOR
406		1597
407	Marc Lehmann <schmorp@schmorp.de>	1598	Marc Lehmann <schmorp@schmorp.de>
408	http://home.schmorp.de/	1599	http://home.schmorp.de/
409		1600
410	=cut	1601	=cut
411		1602
		1603	1
		1604

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