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Revision 1.6 by root, Thu Mar 22 23:24:18 2007 UTC vs.
Revision 1.147 by root, Tue Oct 29 00:19:08 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, then the C<encode> method will not generate	219	If C<$enable> is true (or missing), then the C<encode> method will not
122	characters outside the code range C<0..127>. Any unicode characters	220	generate characters outside the code range C<0..127> (which is ASCII). Any
123	outside that range will be escaped using either a single \uXXXX (BMP	221	Unicode characters outside that range will be escaped using either a
124	characters) or a double \uHHHH\uLLLLL escape sequence, as per RFC4627.	222	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
		223	as per RFC4627. The resulting encoded JSON text can be treated as a native
		224	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		225	or any other superset of ASCII.
125		226
126	If C<$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
127	characters unless necessary.	228	characters unless required by the JSON syntax or other flags. This results
		229	in a faster and more compact format.
128		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
129	JSON::XS->new->ascii (1)->encode (chr 0x10401)	238	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
130	=> \ud801\udc01	239	=> ["\ud801\udc01"]
131		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)
		268
132	=item $json = $json->utf8 ($enable)	269	=item $json = $json->utf8 ([$enable])
133		270
		271	=item $enabled = $json->get_utf8
		272
134	If C<$enable> is true, then the C<encode> method will encode the JSON	273	If C<$enable> is true (or missing), then the C<encode> method will encode
135	string into UTF-8, as required by many protocols, while the C<decode>	274	the JSON result into UTF-8, as required by many protocols, while the
136	method expects to be handled an UTF-8-encoded string. Please note that	275	C<decode> method expects to be handled an UTF-8-encoded string. Please
137	UTF-8-encoded strings do not contain any characters outside the range	276	note that UTF-8-encoded strings do not contain any characters outside the
138	C<0..255>, they are thus useful for bytewise/binary I/O.	277	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		278	versions, enabling this option might enable autodetection of the UTF-16
		279	and UTF-32 encoding families, as described in RFC4627.
139		280
140	If C<$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
141	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
142	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
143	to be done yourself, e.g. using the Encode module.	284	to be done yourself, e.g. using the Encode module.
144		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);
		298
145	=item $json = $json->pretty ($enable)	299	=item $json = $json->pretty ([$enable])
146		300
147	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
148	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
149	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:
150		306
151	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})	307	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
152	=>	308	=>
153	{	309	{
154	"a" : [	310	"a" : [
155	1,	311	1,
156	2	312	2
157	]	313	]
158	}	314	}
159		315
160	=item $json = $json->indent ($enable)	316	=item $json = $json->indent ([$enable])
161		317
		318	=item $enabled = $json->get_indent
		319
162	If C<$enable> is true, then the C<encode> method will use a multiline	320	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
163	format as output, putting every array member or object/hash key-value pair	321	format as output, putting every array member or object/hash key-value pair
164	into its own line, identing them properly.	322	into its own line, indenting them properly.
165		323
166	If C<$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
167	resulting JSON strings is guarenteed not to contain any C<newlines>.	325	resulting JSON text is guaranteed not to contain any C<newlines>.
168		326
169	This setting has no effect when decoding JSON strings.	327	This setting has no effect when decoding JSON texts.
170		328
171	=item $json = $json->space_before ($enable)	329	=item $json = $json->space_before ([$enable])
172		330
		331	=item $enabled = $json->get_space_before
		332
173	If C<$enable> is true, then the C<encode> method will add an extra	333	If C<$enable> is true (or missing), then the C<encode> method will add an extra
174	optional space before the C<:> separating keys from values in JSON objects.	334	optional space before the C<:> separating keys from values in JSON objects.
175		335
176	If C<$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
177	space at those places.	337	space at those places.
178		338
179	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
180	likely combine this setting with C<space_after>.	340	most likely combine this setting with C<space_after>.
181		341
		342	Example, space_before enabled, space_after and indent disabled:
		343
		344	{"key" :"value"}
		345
182	=item $json = $json->space_after ($enable)	346	=item $json = $json->space_after ([$enable])
183		347
		348	=item $enabled = $json->get_space_after
		349
184	If C<$enable> is true, then the C<encode> method will add an extra	350	If C<$enable> is true (or missing), then the C<encode> method will add an extra
185	optional space after the C<:> separating keys from values in JSON objects	351	optional space after the C<:> separating keys from values in JSON objects
186	and extra whitespace after the C<,> separating key-value pairs and array	352	and extra whitespace after the C<,> separating key-value pairs and array
187	members.	353	members.
188		354
189	If C<$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
190	space at those places.	356	space at those places.
191		357
192	This setting has no effect when decoding JSON strings.	358	This setting has no effect when decoding JSON texts.
193		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
		410
194	=item $json = $json->canonical ($enable)	411	=item $json = $json->canonical ([$enable])
195		412
		413	=item $enabled = $json->get_canonical
		414
196	If C<$enable> is true, then the C<encode> method will output JSON objects	415	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
197	by sorting their keys. This is adding a comparatively high overhead.	416	by sorting their keys. This is adding a comparatively high overhead.
198		417
199	If C<$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
200	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
201	of the same script).	420	of the same script, and can change even within the same run from 5.18
		421	onwards).
202		422
203	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
204	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,
205	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,
206	as key-value pairs have no inherent ordering in Perl.	426	as key-value pairs have no inherent ordering in Perl.
207		427
208	This setting has no effect when decoding JSON strings.	428	This setting has no effect when decoding JSON texts.
209		429
		430	This setting has currently no effect on tied hashes.
		431
210	=item $json = $json->allow_nonref ($enable)	432	=item $json = $json->allow_nonref ([$enable])
211		433
		434	=item $enabled = $json->get_allow_nonref
		435
212	If C<$enable> is true, then the C<encode> method can convert a	436	If C<$enable> is true (or missing), then the C<encode> method can convert a
213	non-reference into its corresponding string, number or null JSON value,	437	non-reference into its corresponding string, number or null JSON value,
214	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	438	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
215	values instead of croaking.	439	values instead of croaking.
216		440
217	If C<$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
218	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
219	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
220	JSON object or array.	444	JSON object or array.
221		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 = $json->get_allow_blessed
		471
		472	See L<OBJECT SERIALISATION> for details.
		473
		474	If C<$enable> is true (or missing), then the C<encode> method will not
		475	barf when it encounters a blessed reference that it cannot convert
		476	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
		477
		478	If C<$enable> is false (the default), then C<encode> will throw an
		479	exception when it encounters a blessed object that it cannot convert
		480	otherwise.
		481
		482	This setting has no effect on C<decode>.
		483
		484	=item $json = $json->convert_blessed ([$enable])
		485
		486	=item $enabled = $json->get_convert_blessed
		487
		488	See "OBJECT SERIALISATION" for details.
		489
		490	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		491	blessed object, will check for the availability of the C<TO_JSON> method
		492	on the object's class. If found, it will be called in scalar context and
		493	the resulting scalar will be encoded instead of the object.
		494
		495	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		496	returns other blessed objects, those will be handled in the same
		497	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		498	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		499	methods called by the Perl core (== not by the user of the object) are
		500	usually in upper case letters and to avoid collisions with any C<to_json>
		501	function or method.
		502
		503	If C<$enable> is false (the default), then C<encode> will not consider
		504	this type of conversion.
		505
		506	This setting has no effect on C<decode>.
		507
		508	=item $json = $json->allow_tags ([$enable])
		509
		510	=item $enabled = $json->allow_tags
		511
		512	See "OBJECT SERIALISATION" for details.
		513
		514	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		515	blessed object, will check for the availability of the C<FREEZE> method on
		516	the object's class. If found, it will be used to serialise the object into
		517	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		518
		519	It also causes C<decode> to parse such tagged JSON values and deserialise
		520	them via a call to the C<THAW> method.
		521
		522	If C<$enable> is false (the default), then C<encode> will not consider
		523	this type of conversion, and tagged JSON values will cause a parse error
		524	in C<decode>, as if tags were not part of the grammar.
		525
		526	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		527
		528	When C<$coderef> is specified, it will be called from C<decode> each
		529	time it decodes a JSON object. The only argument is a reference to the
		530	newly-created hash. If the code references returns a single scalar (which
		531	need not be a reference), this value (i.e. a copy of that scalar to avoid
		532	aliasing) is inserted into the deserialised data structure. If it returns
		533	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		534	original deserialised hash will be inserted. This setting can slow down
		535	decoding considerably.
		536
		537	When C<$coderef> is omitted or undefined, any existing callback will
		538	be removed and C<decode> will not change the deserialised hash in any
		539	way.
		540
		541	Example, convert all JSON objects into the integer 5:
		542
		543	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		544	# returns [5]
		545	$js->decode ('[{}]')
		546	# throw an exception because allow_nonref is not enabled
		547	# so a lone 5 is not allowed.
		548	$js->decode ('{"a":1, "b":2}');
		549
		550	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		551
		552	Works remotely similar to C<filter_json_object>, but is only called for
		553	JSON objects having a single key named C<$key>.
		554
		555	This C<$coderef> is called before the one specified via
		556	C<filter_json_object>, if any. It gets passed the single value in the JSON
		557	object. If it returns a single value, it will be inserted into the data
		558	structure. If it returns nothing (not even C<undef> but the empty list),
		559	the callback from C<filter_json_object> will be called next, as if no
		560	single-key callback were specified.
		561
		562	If C<$coderef> is omitted or undefined, the corresponding callback will be
		563	disabled. There can only ever be one callback for a given key.
		564
		565	As this callback gets called less often then the C<filter_json_object>
		566	one, decoding speed will not usually suffer as much. Therefore, single-key
		567	objects make excellent targets to serialise Perl objects into, especially
		568	as single-key JSON objects are as close to the type-tagged value concept
		569	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		570	support this in any way, so you need to make sure your data never looks
		571	like a serialised Perl hash.
		572
		573	Typical names for the single object key are C<__class_whatever__>, or
		574	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		575	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		576	with real hashes.
		577
		578	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		579	into the corresponding C<< $WIDGET{<id>} >> object:
		580
		581	# return whatever is in $WIDGET{5}:
		582	JSON::XS
		583	->new
		584	->filter_json_single_key_object (__widget__ => sub {
		585	$WIDGET{ $_[0] }
		586	})
		587	->decode ('{"__widget__": 5')
		588
		589	# this can be used with a TO_JSON method in some "widget" class
		590	# for serialisation to json:
		591	sub WidgetBase::TO_JSON {
		592	my ($self) = @_;
		593
		594	unless ($self->{id}) {
		595	$self->{id} = ..get..some..id..;
		596	$WIDGET{$self->{id}} = $self;
		597	}
		598
		599	{ __widget__ => $self->{id} }
		600	}
		601
		602	=item $json = $json->shrink ([$enable])
		603
		604	=item $enabled = $json->get_shrink
		605
		606	Perl usually over-allocates memory a bit when allocating space for
		607	strings. This flag optionally resizes strings generated by either
		608	C<encode> or C<decode> to their minimum size possible. This can save
		609	memory when your JSON texts are either very very long or you have many
		610	short strings. It will also try to downgrade any strings to octet-form
		611	if possible: perl stores strings internally either in an encoding called
		612	UTF-X or in octet-form. The latter cannot store everything but uses less
		613	space in general (and some buggy Perl or C code might even rely on that
		614	internal representation being used).
		615
		616	The actual definition of what shrink does might change in future versions,
		617	but it will always try to save space at the expense of time.
		618
		619	If C<$enable> is true (or missing), the string returned by C<encode> will
		620	be shrunk-to-fit, while all strings generated by C<decode> will also be
		621	shrunk-to-fit.
		622
		623	If C<$enable> is false, then the normal perl allocation algorithms are used.
		624	If you work with your data, then this is likely to be faster.
		625
		626	In the future, this setting might control other things, such as converting
		627	strings that look like integers or floats into integers or floats
		628	internally (there is no difference on the Perl level), saving space.
		629
		630	=item $json = $json->max_depth ([$maximum_nesting_depth])
		631
		632	=item $max_depth = $json->get_max_depth
		633
		634	Sets the maximum nesting level (default C<512>) accepted while encoding
		635	or decoding. If a higher nesting level is detected in JSON text or a Perl
		636	data structure, then the encoder and decoder will stop and croak at that
		637	point.
		638
		639	Nesting level is defined by number of hash- or arrayrefs that the encoder
		640	needs to traverse to reach a given point or the number of C<{> or C<[>
		641	characters without their matching closing parenthesis crossed to reach a
		642	given character in a string.
		643
		644	Setting the maximum depth to one disallows any nesting, so that ensures
		645	that the object is only a single hash/object or array.
		646
		647	If no argument is given, the highest possible setting will be used, which
		648	is rarely useful.
		649
		650	Note that nesting is implemented by recursion in C. The default value has
		651	been chosen to be as large as typical operating systems allow without
		652	crashing.
		653
		654	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		655
		656	=item $json = $json->max_size ([$maximum_string_size])
		657
		658	=item $max_size = $json->get_max_size
		659
		660	Set the maximum length a JSON text may have (in bytes) where decoding is
		661	being attempted. The default is C<0>, meaning no limit. When C<decode>
		662	is called on a string that is longer then this many bytes, it will not
		663	attempt to decode the string but throw an exception. This setting has no
		664	effect on C<encode> (yet).
		665
		666	If no argument is given, the limit check will be deactivated (same as when
		667	C<0> is specified).
		668
		669	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		670
222	=item $json_string = $json->encode ($perl_scalar)	671	=item $json_text = $json->encode ($perl_scalar)
223		672
224	Converts the given Perl data structure (a simple scalar or a reference	673	Converts the given Perl value or data structure to its JSON
225	to a hash or array) to its JSON representation. Simple scalars will be	674	representation. Croaks on error.
226	converted into JSON string or number sequences, while references to arrays
227	become JSON arrays and references to hashes become JSON objects. Undefined
228	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
229	nor C<false> values will be generated.
230		675
231	=item $perl_scalar = $json->decode ($json_string)	676	=item $perl_scalar = $json->decode ($json_text)
232		677
233	The opposite of C<encode>: expects a JSON string and tries to parse it,	678	The opposite of C<encode>: expects a JSON text and tries to parse it,
234	returning the resulting simple scalar or reference. Croaks on error.	679	returning the resulting simple scalar or reference. Croaks on error.
235		680
236	JSON numbers and strings become simple Perl scalars. JSON arrays become	681	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
237	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	682
238	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	683	This works like the C<decode> method, but instead of raising an exception
		684	when there is trailing garbage after the first JSON object, it will
		685	silently stop parsing there and return the number of characters consumed
		686	so far.
		687
		688	This is useful if your JSON texts are not delimited by an outer protocol
		689	and you need to know where the JSON text ends.
		690
		691	JSON::XS->new->decode_prefix ("[1] the tail")
		692	=> ([], 3)
239		693
240	=back	694	=back
241		695
242	=head1 COMPARISON
243		696
244	As already mentioned, this module was created because none of the existing	697	=head1 INCREMENTAL PARSING
245	JSON modules could be made to work correctly. First I will describe the	698
246	problems (or pleasures) I encountered with various existing JSON modules,	699	In some cases, there is the need for incremental parsing of JSON
247	followed by some benchmark values. JSON::XS was designed not to suffer	700	texts. While this module always has to keep both JSON text and resulting
248	from any of these problems or limitations.	701	Perl data structure in memory at one time, it does allow you to parse a
		702	JSON stream incrementally. It does so by accumulating text until it has
		703	a full JSON object, which it then can decode. This process is similar to
		704	using C<decode_prefix> to see if a full JSON object is available, but
		705	is much more efficient (and can be implemented with a minimum of method
		706	calls).
		707
		708	JSON::XS will only attempt to parse the JSON text once it is sure it
		709	has enough text to get a decisive result, using a very simple but
		710	truly incremental parser. This means that it sometimes won't stop as
		711	early as the full parser, for example, it doesn't detect mismatched
		712	parentheses. The only thing it guarantees is that it starts decoding as
		713	soon as a syntactically valid JSON text has been seen. This means you need
		714	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		715	parsing in the presence if syntax errors.
		716
		717	The following methods implement this incremental parser.
249		718
250	=over 4	719	=over 4
251		720
252	=item JSON 1.07	721	=item [void, scalar or list context] = $json->incr_parse ([$string])
253		722
254	Slow (but very portable, as it is written in pure Perl).	723	This is the central parsing function. It can both append new text and
		724	extract objects from the stream accumulated so far (both of these
		725	functions are optional).
255		726
256	Undocumented/buggy Unicode handling (how JSON handles unicode values is	727	If C<$string> is given, then this string is appended to the already
257	undocumented. One can get far by feeding it unicode strings and doing	728	existing JSON fragment stored in the C<$json> object.
258	en-/decoding oneself, but unicode escapes are not working properly).
259		729
260	No roundtripping (strings get clobbered if they look like numbers, e.g.	730	After that, if the function is called in void context, it will simply
261	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	731	return without doing anything further. This can be used to add more text
262	decode into the number 2.	732	in as many chunks as you want.
263		733
264	=item JSON::PC 0.01	734	If the method is called in scalar context, then it will try to extract
		735	exactly I<one> JSON object. If that is successful, it will return this
		736	object, otherwise it will return C<undef>. If there is a parse error,
		737	this method will croak just as C<decode> would do (one can then use
		738	C<incr_skip> to skip the erroneous part). This is the most common way of
		739	using the method.
265		740
266	Very fast.	741	And finally, in list context, it will try to extract as many objects
		742	from the stream as it can find and return them, or the empty list
		743	otherwise. For this to work, there must be no separators between the JSON
		744	objects or arrays, instead they must be concatenated back-to-back. If
		745	an error occurs, an exception will be raised as in the scalar context
		746	case. Note that in this case, any previously-parsed JSON texts will be
		747	lost.
267		748
268	Undocumented/buggy Unicode handling.	749	Example: Parse some JSON arrays/objects in a given string and return
		750	them.
269		751
270	No roundtripping.	752	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
271		753
272	Has problems handling many Perl values (e.g. regex results and other magic	754	=item $lvalue_string = $json->incr_text
273	values will make it croak).
274		755
275	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	756	This method returns the currently stored JSON fragment as an lvalue, that
276	which is not a valid JSON string.	757	is, you can manipulate it. This I<only> works when a preceding call to
		758	C<incr_parse> in I<scalar context> successfully returned an object. Under
		759	all other circumstances you must not call this function (I mean it.
		760	although in simple tests it might actually work, it I<will> fail under
		761	real world conditions). As a special exception, you can also call this
		762	method before having parsed anything.
277		763
278	Unmaintained (maintainer unresponsive for many months, bugs are not	764	This function is useful in two cases: a) finding the trailing text after a
279	getting fixed).	765	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		766	(such as commas).
280		767
281	=item JSON::Syck 0.21	768	=item $json->incr_skip
282		769
283	Very buggy (often crashes).	770	This will reset the state of the incremental parser and will remove
		771	the parsed text from the input buffer so far. This is useful after
		772	C<incr_parse> died, in which case the input buffer and incremental parser
		773	state is left unchanged, to skip the text parsed so far and to reset the
		774	parse state.
284		775
285	Very inflexible (no human-readable format supported, format pretty much	776	The difference to C<incr_reset> is that only text until the parse error
286	undocumented. I need at least a format for easy reading by humans and a	777	occurred is removed.
287	single-line compact format for use in a protocol, and preferably a way to
288	generate ASCII-only JSON strings).
289		778
290	Completely broken (and confusingly documented) Unicode handling (unicode	779	=item $json->incr_reset
291	escapes are not working properly, you need to set ImplicitUnicode to
292	I<different> values on en- and decoding to get symmetric behaviour).
293		780
294	No roundtripping (simple cases work, but this depends on wether the scalar	781	This completely resets the incremental parser, that is, after this call,
295	value was used in a numeric context or not).	782	it will be as if the parser had never parsed anything.
296		783
297	Dumping hashes may skip hash values depending on iterator state.	784	This is useful if you want to repeatedly parse JSON objects and want to
298		785	ignore any trailing data, which means you have to reset the parser after
299	Unmaintained (maintainer unresponsive for many months, bugs are not	786	each successful decode.
300	getting fixed).
301
302	Does not check input for validity (i.e. will accept non-JSON input and
303	return "something" instead of raising an exception. This is a security
304	issue: imagine two banks transfering money between each other using
305	JSON. One bank might parse a given non-JSON request and deduct money,
306	while the other might reject the transaction with a syntax error. While a
307	good protocol will at least recover, that is extra unnecessary work and
308	the transaction will still not succeed).
309
310	=item JSON::DWIW 0.04
311
312	Very fast. Very natural. Very nice.
313
314	Undocumented unicode handling (but the best of the pack. Unicode escapes
315	still don't get parsed properly).
316
317	Very inflexible.
318
319	No roundtripping.
320
321	Does not generate valid JSON (key strings are often unquoted, empty keys
322	result in nothing being output)
323
324	Does not check input for validity.
325		787
326	=back	788	=back
		789
		790	=head2 LIMITATIONS
		791
		792	All options that affect decoding are supported, except
		793	C<allow_nonref>. The reason for this is that it cannot be made to work
		794	sensibly: JSON objects and arrays are self-delimited, i.e. you can
		795	concatenate them back to back and still decode them perfectly. This does
		796	not hold true for JSON numbers, however.
		797
		798	For example, is the string C<1> a single JSON number, or is it simply the
		799	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		800	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		801	takes the conservative route and disallows this case.
		802
		803	=head2 EXAMPLES
		804
		805	Some examples will make all this clearer. First, a simple example that
		806	works similarly to C<decode_prefix>: We want to decode the JSON object at
		807	the start of a string and identify the portion after the JSON object:
		808
		809	my $text = "[1,2,3] hello";
		810
		811	my $json = new JSON::XS;
		812
		813	my $obj = $json->incr_parse ($text)
		814	or die "expected JSON object or array at beginning of string";
		815
		816	my $tail = $json->incr_text;
		817	# $tail now contains " hello"
		818
		819	Easy, isn't it?
		820
		821	Now for a more complicated example: Imagine a hypothetical protocol where
		822	you read some requests from a TCP stream, and each request is a JSON
		823	array, without any separation between them (in fact, it is often useful to
		824	use newlines as "separators", as these get interpreted as whitespace at
		825	the start of the JSON text, which makes it possible to test said protocol
		826	with C<telnet>...).
		827
		828	Here is how you'd do it (it is trivial to write this in an event-based
		829	manner):
		830
		831	my $json = new JSON::XS;
		832
		833	# read some data from the socket
		834	while (sysread $socket, my $buf, 4096) {
		835
		836	# split and decode as many requests as possible
		837	for my $request ($json->incr_parse ($buf)) {
		838	# act on the $request
		839	}
		840	}
		841
		842	Another complicated example: Assume you have a string with JSON objects
		843	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		844	[3]>). To parse them, we have to skip the commas between the JSON texts,
		845	and here is where the lvalue-ness of C<incr_text> comes in useful:
		846
		847	my $text = "[1],[2], [3]";
		848	my $json = new JSON::XS;
		849
		850	# void context, so no parsing done
		851	$json->incr_parse ($text);
		852
		853	# now extract as many objects as possible. note the
		854	# use of scalar context so incr_text can be called.
		855	while (my $obj = $json->incr_parse) {
		856	# do something with $obj
		857
		858	# now skip the optional comma
		859	$json->incr_text =~ s/^ \s* , //x;
		860	}
		861
		862	Now lets go for a very complex example: Assume that you have a gigantic
		863	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		864	but you cannot load it into memory fully (this has actually happened in
		865	the real world :).
		866
		867	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		868	can still help you: You implement a (very simple) array parser and let
		869	JSON decode the array elements, which are all full JSON objects on their
		870	own (this wouldn't work if the array elements could be JSON numbers, for
		871	example):
		872
		873	my $json = new JSON::XS;
		874
		875	# open the monster
		876	open my $fh, "<bigfile.json"
		877	or die "bigfile: $!";
		878
		879	# first parse the initial "["
		880	for (;;) {
		881	sysread $fh, my $buf, 65536
		882	or die "read error: $!";
		883	$json->incr_parse ($buf); # void context, so no parsing
		884
		885	# Exit the loop once we found and removed(!) the initial "[".
		886	# In essence, we are (ab-)using the $json object as a simple scalar
		887	# we append data to.
		888	last if $json->incr_text =~ s/^ \s* \[ //x;
		889	}
		890
		891	# now we have the skipped the initial "[", so continue
		892	# parsing all the elements.
		893	for (;;) {
		894	# in this loop we read data until we got a single JSON object
		895	for (;;) {
		896	if (my $obj = $json->incr_parse) {
		897	# do something with $obj
		898	last;
		899	}
		900
		901	# add more data
		902	sysread $fh, my $buf, 65536
		903	or die "read error: $!";
		904	$json->incr_parse ($buf); # void context, so no parsing
		905	}
		906
		907	# in this loop we read data until we either found and parsed the
		908	# separating "," between elements, or the final "]"
		909	for (;;) {
		910	# first skip whitespace
		911	$json->incr_text =~ s/^\s*//;
		912
		913	# if we find "]", we are done
		914	if ($json->incr_text =~ s/^\]//) {
		915	print "finished.\n";
		916	exit;
		917	}
		918
		919	# if we find ",", we can continue with the next element
		920	if ($json->incr_text =~ s/^,//) {
		921	last;
		922	}
		923
		924	# if we find anything else, we have a parse error!
		925	if (length $json->incr_text) {
		926	die "parse error near ", $json->incr_text;
		927	}
		928
		929	# else add more data
		930	sysread $fh, my $buf, 65536
		931	or die "read error: $!";
		932	$json->incr_parse ($buf); # void context, so no parsing
		933	}
		934
		935	This is a complex example, but most of the complexity comes from the fact
		936	that we are trying to be correct (bear with me if I am wrong, I never ran
		937	the above example :).
		938
		939
		940
		941	=head1 MAPPING
		942
		943	This section describes how JSON::XS maps Perl values to JSON values and
		944	vice versa. These mappings are designed to "do the right thing" in most
		945	circumstances automatically, preserving round-tripping characteristics
		946	(what you put in comes out as something equivalent).
		947
		948	For the more enlightened: note that in the following descriptions,
		949	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		950	refers to the abstract Perl language itself.
		951
		952
		953	=head2 JSON -> PERL
		954
		955	=over 4
		956
		957	=item object
		958
		959	A JSON object becomes a reference to a hash in Perl. No ordering of object
		960	keys is preserved (JSON does not preserve object key ordering itself).
		961
		962	=item array
		963
		964	A JSON array becomes a reference to an array in Perl.
		965
		966	=item string
		967
		968	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		969	are represented by the same codepoints in the Perl string, so no manual
		970	decoding is necessary.
		971
		972	=item number
		973
		974	A JSON number becomes either an integer, numeric (floating point) or
		975	string scalar in perl, depending on its range and any fractional parts. On
		976	the Perl level, there is no difference between those as Perl handles all
		977	the conversion details, but an integer may take slightly less memory and
		978	might represent more values exactly than floating point numbers.
		979
		980	If the number consists of digits only, JSON::XS will try to represent
		981	it as an integer value. If that fails, it will try to represent it as
		982	a numeric (floating point) value if that is possible without loss of
		983	precision. Otherwise it will preserve the number as a string value (in
		984	which case you lose roundtripping ability, as the JSON number will be
		985	re-encoded to a JSON string).
		986
		987	Numbers containing a fractional or exponential part will always be
		988	represented as numeric (floating point) values, possibly at a loss of
		989	precision (in which case you might lose perfect roundtripping ability, but
		990	the JSON number will still be re-encoded as a JSON number).
		991
		992	Note that precision is not accuracy - binary floating point values cannot
		993	represent most decimal fractions exactly, and when converting from and to
		994	floating point, JSON::XS only guarantees precision up to but not including
		995	the least significant bit.
		996
		997	=item true, false
		998
		999	These JSON atoms become C<Types::Serialiser::true> and
		1000	C<Types::Serialiser::false>, respectively. They are overloaded to act
		1001	almost exactly like the numbers C<1> and C<0>. You can check whether
		1002	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1003	function (after C<use Types::Serialier>, of course).
		1004
		1005	=item null
		1006
		1007	A JSON null atom becomes C<undef> in Perl.
		1008
		1009	=item shell-style comments (C<< # I<text> >>)
		1010
		1011	As a nonstandard extension to the JSON syntax that is enabled by the
		1012	C<relaxed> setting, shell-style comments are allowed. They can start
		1013	anywhere outside strings and go till the end of the line.
		1014
		1015	=item tagged values (C<< (I<tag>)I<value> >>).
		1016
		1017	Another nonstandard extension to the JSON syntax, enabled with the
		1018	C<allow_tags> setting, are tagged values. In this implementation, the
		1019	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1020	I<value> must be a JSON array encoding optional constructor arguments.
		1021
		1022	See "OBJECT SERIALISATION", below, for details.
		1023
		1024	=back
		1025
		1026
		1027	=head2 PERL -> JSON
		1028
		1029	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		1030	truly typeless language, so we can only guess which JSON type is meant by
		1031	a Perl value.
		1032
		1033	=over 4
		1034
		1035	=item hash references
		1036
		1037	Perl hash references become JSON objects. As there is no inherent
		1038	ordering in hash keys (or JSON objects), they will usually be encoded
		1039	in a pseudo-random order. JSON::XS can optionally sort the hash keys
		1040	(determined by the I<canonical> flag), so the same datastructure will
		1041	serialise to the same JSON text (given same settings and version of
		1042	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
		1043	e.g. when you want to compare some JSON text against another for equality.
		1044
		1045	=item array references
		1046
		1047	Perl array references become JSON arrays.
		1048
		1049	=item other references
		1050
		1051	Other unblessed references are generally not allowed and will cause an
		1052	exception to be thrown, except for references to the integers C<0> and
		1053	C<1>, which get turned into C<false> and C<true> atoms in JSON.
		1054
		1055	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1056	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1057	and C<Types::Serialiser::true> to improve readability.
		1058
		1059	use Types::Serialiser;
		1060	encode_json [\0, Types::Serialiser::true] # yields [false,true]
		1061
		1062	=item Types::Serialiser::true, Types::Serialiser::false
		1063
		1064	These special values from the L<Types::Serialiser> module become JSON true
		1065	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1066	directly if you want.
		1067
		1068	=item blessed objects
		1069
		1070	Blessed objects are not directly representable in JSON, but C<JSON::XS>
		1071	allows various ways of handling objects. See "OBJECT SERIALISATION",
		1072	below, for details.
		1073
		1074	=item simple scalars
		1075
		1076	Simple Perl scalars (any scalar that is not a reference) are the most
		1077	difficult objects to encode: JSON::XS will encode undefined scalars as
		1078	JSON C<null> values, scalars that have last been used in a string context
		1079	before encoding as JSON strings, and anything else as number value:
		1080
		1081	# dump as number
		1082	encode_json [2] # yields [2]
		1083	encode_json [-3.0e17] # yields [-3e+17]
		1084	my $value = 5; encode_json [$value] # yields [5]
		1085
		1086	# used as string, so dump as string
		1087	print $value;
		1088	encode_json [$value] # yields ["5"]
		1089
		1090	# undef becomes null
		1091	encode_json [undef] # yields [null]
		1092
		1093	You can force the type to be a JSON string by stringifying it:
		1094
		1095	my $x = 3.1; # some variable containing a number
		1096	"$x"; # stringified
		1097	$x .= ""; # another, more awkward way to stringify
		1098	print $x; # perl does it for you, too, quite often
		1099
		1100	You can force the type to be a JSON number by numifying it:
		1101
		1102	my $x = "3"; # some variable containing a string
		1103	$x += 0; # numify it, ensuring it will be dumped as a number
		1104	$x *= 1; # same thing, the choice is yours.
		1105
		1106	You can not currently force the type in other, less obscure, ways. Tell me
		1107	if you need this capability (but don't forget to explain why it's needed
		1108	:).
		1109
		1110	Note that numerical precision has the same meaning as under Perl (so
		1111	binary to decimal conversion follows the same rules as in Perl, which
		1112	can differ to other languages). Also, your perl interpreter might expose
		1113	extensions to the floating point numbers of your platform, such as
		1114	infinities or NaN's - these cannot be represented in JSON, and it is an
		1115	error to pass those in.
		1116
		1117	=back
		1118
		1119	=head2 OBJECT SERIALISATION
		1120
		1121	As JSON cannot directly represent Perl objects, you have to choose between
		1122	a pure JSON representation (without the ability to deserialise the object
		1123	automatically again), and a nonstandard extension to the JSON syntax,
		1124	tagged values.
		1125
		1126	=head3 SERIALISATION
		1127
		1128	What happens when C<JSON::XS> encounters a Perl object depends on the
		1129	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
		1130	used in this order:
		1131
		1132	=over 4
		1133
		1134	=item 1. C<allow_tags> is enabled and object has a C<FREEZE> method.
		1135
		1136	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1137	serialisation protocol to create a tagged JSON value, using a nonstandard
		1138	extension to the JSON syntax.
		1139
		1140	This works by invoking the C<FREEZE> method on the object, with the first
		1141	argument being the object to serialise, and the second argument being the
		1142	constant string C<JSON> to distinguish it from other serialisers.
		1143
		1144	The C<FREEZE> method can return any number of values (i.e. zero or
		1145	more). These values and the paclkage/classname of the object will then be
		1146	encoded as a tagged JSON value in the following format:
		1147
		1148	("classname")[FREEZE return values...]
		1149
		1150	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1151	objects C<type> and C<id> members to encode the object:
		1152
		1153	sub My::Object::FREEZE {
		1154	my ($self, $serialiser) = @_;
		1155
		1156	($self->{type}, $self->{id})
		1157	}
		1158
		1159	=item 2. C<convert_blessed> is enabled and object has a C<TO_JSON> method.
		1160
		1161	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1162	context. It must return a single scalar that can be directly encoded into
		1163	JSON. This scalar replaces the object in the JSON text.
		1164
		1165	For example, the following C<TO_JSON> method will convert all L<URI>
		1166	objects to JSON strings when serialised. The fatc that these values
		1167	originally were L<URI> objects is lost.
		1168
		1169	sub URI::TO_JSON {
		1170	my ($uri) = @_;
		1171	$uri->as_string
		1172	}
		1173
		1174	=item 3. C<allow_blessed> is enabled.
		1175
		1176	The object will be serialised as a JSON null value.
		1177
		1178	=item 4. none of the above
		1179
		1180	If none of the settings are enabled or the respective methods are missing,
		1181	C<JSON::XS> throws an exception.
		1182
		1183	=back
		1184
		1185	=head3 DESERIALISATION
		1186
		1187	For deserialisation there are only two cases to consider: either
		1188	nonstandard tagging was used, in which case C<allow_tags> decides,
		1189	or objects cannot be automatically be deserialised, in which
		1190	case you can use postprocessing or the C<filter_json_object> or
		1191	C<filter_json_single_key_object> callbacks to get some real objects our of
		1192	your JSON.
		1193
		1194	This section only considers the tagged value case: I a tagged JSON object
		1195	is encountered during decoding and C<allow_tags> is disabled, a parse
		1196	error will result (as if tagged values were not part of the grammar).
		1197
		1198	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1199	of the package/classname used during serialisation (it will not attempt
		1200	to load the package as a Perl module). If there is no such method, the
		1201	decoding will fail with an error.
		1202
		1203	Otherwise, the C<THAW> method is invoked with the classname as first
		1204	argument, the constant string C<JSON> as second argument, and all the
		1205	values from the JSON array (the values originally returned by the
		1206	C<FREEZE> method) as remaining arguments.
		1207
		1208	The method must then return the object. While technically you can return
		1209	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1210	make that work in all cases, so better return an actual blessed reference.
		1211
		1212	As an example, let's implement a C<THAW> function that regenerates the
		1213	C<My::Object> from the C<FREEZE> example earlier:
		1214
		1215	sub My::Object::THAW {
		1216	my ($class, $serialiser, $type, $id) = @_;
		1217
		1218	$class->new (type => $type, id => $id)
		1219	}
		1220
		1221
		1222	=head1 ENCODING/CODESET FLAG NOTES
		1223
		1224	The interested reader might have seen a number of flags that signify
		1225	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1226	some confusion on what these do, so here is a short comparison:
		1227
		1228	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1229	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1230	control whether C<encode> escapes character values outside their respective
		1231	codeset range. Neither of these flags conflict with each other, although
		1232	some combinations make less sense than others.
		1233
		1234	Care has been taken to make all flags symmetrical with respect to
		1235	C<encode> and C<decode>, that is, texts encoded with any combination of
		1236	these flag values will be correctly decoded when the same flags are used
		1237	- in general, if you use different flag settings while encoding vs. when
		1238	decoding you likely have a bug somewhere.
		1239
		1240	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1241	simply an abstract set of character-codepoint pairs, while an encoding
		1242	takes those codepoint numbers and I<encodes> them, in our case into
		1243	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1244	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1245	the same time, which can be confusing.
		1246
		1247	=over 4
		1248
		1249	=item C<utf8> flag disabled
		1250
		1251	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1252	and expect Unicode strings, that is, characters with high ordinal Unicode
		1253	values (> 255) will be encoded as such characters, and likewise such
		1254	characters are decoded as-is, no changes to them will be done, except
		1255	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1256	respectively (to Perl, these are the same thing in strings unless you do
		1257	funny/weird/dumb stuff).
		1258
		1259	This is useful when you want to do the encoding yourself (e.g. when you
		1260	want to have UTF-16 encoded JSON texts) or when some other layer does
		1261	the encoding for you (for example, when printing to a terminal using a
		1262	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1263	to UTF-8 encode your data first and have Perl encode it another time).
		1264
		1265	=item C<utf8> flag enabled
		1266
		1267	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1268	characters using the corresponding UTF-8 multi-byte sequence, and will
		1269	expect your input strings to be encoded as UTF-8, that is, no "character"
		1270	of the input string must have any value > 255, as UTF-8 does not allow
		1271	that.
		1272
		1273	The C<utf8> flag therefore switches between two modes: disabled means you
		1274	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1275	octet/binary string in Perl.
		1276
		1277	=item C<latin1> or C<ascii> flags enabled
		1278
		1279	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1280	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1281	characters as specified by the C<utf8> flag.
		1282
		1283	If C<utf8> is disabled, then the result is also correctly encoded in those
		1284	character sets (as both are proper subsets of Unicode, meaning that a
		1285	Unicode string with all character values < 256 is the same thing as a
		1286	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1287	the same thing as an ASCII string in Perl).
		1288
		1289	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1290	regardless of these flags, just some more characters will be escaped using
		1291	C<\uXXXX> then before.
		1292
		1293	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1294	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1295	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1296	a subset of Unicode), while ASCII is.
		1297
		1298	Surprisingly, C<decode> will ignore these flags and so treat all input
		1299	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1300	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1301	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1302
		1303	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1304	they only govern when the JSON output engine escapes a character or not.
		1305
		1306	The main use for C<latin1> is to relatively efficiently store binary data
		1307	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1308
		1309	The main use for C<ascii> is to force the output to not contain characters
		1310	with values > 127, which means you can interpret the resulting string
		1311	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1312	8-bit-encoding, and still get the same data structure back. This is useful
		1313	when your channel for JSON transfer is not 8-bit clean or the encoding
		1314	might be mangled in between (e.g. in mail), and works because ASCII is a
		1315	proper subset of most 8-bit and multibyte encodings in use in the world.
		1316
		1317	=back
		1318
		1319
		1320	=head2 JSON and ECMAscript
		1321
		1322	JSON syntax is based on how literals are represented in javascript (the
		1323	not-standardised predecessor of ECMAscript) which is presumably why it is
		1324	called "JavaScript Object Notation".
		1325
		1326	However, JSON is not a subset (and also not a superset of course) of
		1327	ECMAscript (the standard) or javascript (whatever browsers actually
		1328	implement).
		1329
		1330	If you want to use javascript's C<eval> function to "parse" JSON, you
		1331	might run into parse errors for valid JSON texts, or the resulting data
		1332	structure might not be queryable:
		1333
		1334	One of the problems is that U+2028 and U+2029 are valid characters inside
		1335	JSON strings, but are not allowed in ECMAscript string literals, so the
		1336	following Perl fragment will not output something that can be guaranteed
		1337	to be parsable by javascript's C<eval>:
		1338
		1339	use JSON::XS;
		1340
		1341	print encode_json [chr 0x2028];
		1342
		1343	The right fix for this is to use a proper JSON parser in your javascript
		1344	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1345	F<json2.js> parser).
		1346
		1347	If this is not an option, you can, as a stop-gap measure, simply encode to
		1348	ASCII-only JSON:
		1349
		1350	use JSON::XS;
		1351
		1352	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1353
		1354	Note that this will enlarge the resulting JSON text quite a bit if you
		1355	have many non-ASCII characters. You might be tempted to run some regexes
		1356	to only escape U+2028 and U+2029, e.g.:
		1357
		1358	# DO NOT USE THIS!
		1359	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1360	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1361	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1362	print $json;
		1363
		1364	Note that I<this is a bad idea>: the above only works for U+2028 and
		1365	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1366	javascript implementations, however, have issues with other characters as
		1367	well - using C<eval> naively simply I<will> cause problems.
		1368
		1369	Another problem is that some javascript implementations reserve
		1370	some property names for their own purposes (which probably makes
		1371	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1372	C<__proto__> property name for its own purposes.
		1373
		1374	If that is a problem, you could parse try to filter the resulting JSON
		1375	output for these property strings, e.g.:
		1376
		1377	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1378
		1379	This works because C<__proto__> is not valid outside of strings, so every
		1380	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1381
		1382	If you know of other incompatibilities, please let me know.
		1383
		1384
		1385	=head2 JSON and YAML
		1386
		1387	You often hear that JSON is a subset of YAML. This is, however, a mass
		1388	hysteria(*) and very far from the truth (as of the time of this writing),
		1389	so let me state it clearly: I<in general, there is no way to configure
		1390	JSON::XS to output a data structure as valid YAML> that works in all
		1391	cases.
		1392
		1393	If you really must use JSON::XS to generate YAML, you should use this
		1394	algorithm (subject to change in future versions):
		1395
		1396	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1397	my $yaml = $to_yaml->encode ($ref) . "\n";
		1398
		1399	This will I<usually> generate JSON texts that also parse as valid
		1400	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1401	lengths that JSON doesn't have and also has different and incompatible
		1402	unicode character escape syntax, so you should make sure that your hash
		1403	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1404	and that you do not have characters with codepoint values outside the
		1405	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1406	sequences in strings (which JSON::XS does not I<currently> generate, but
		1407	other JSON generators might).
		1408
		1409	There might be other incompatibilities that I am not aware of (or the YAML
		1410	specification has been changed yet again - it does so quite often). In
		1411	general you should not try to generate YAML with a JSON generator or vice
		1412	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1413	high that you will run into severe interoperability problems when you
		1414	least expect it.
		1415
		1416	=over 4
		1417
		1418	=item (*)
		1419
		1420	I have been pressured multiple times by Brian Ingerson (one of the
		1421	authors of the YAML specification) to remove this paragraph, despite him
		1422	acknowledging that the actual incompatibilities exist. As I was personally
		1423	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1424	educate people about these issues, so others do not run into the same
		1425	problem again and again. After this, Brian called me a (quote)I<complete
		1426	and worthless idiot>(unquote).
		1427
		1428	In my opinion, instead of pressuring and insulting people who actually
		1429	clarify issues with YAML and the wrong statements of some of its
		1430	proponents, I would kindly suggest reading the JSON spec (which is not
		1431	that difficult or long) and finally make YAML compatible to it, and
		1432	educating users about the changes, instead of spreading lies about the
		1433	real compatibility for many I<years> and trying to silence people who
		1434	point out that it isn't true.
		1435
		1436	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1437	though the incompatibilities have been documented (and are known to Brian)
		1438	for many years and the spec makes explicit claims that YAML is a superset
		1439	of JSON. It would be so easy to fix, but apparently, bullying people and
		1440	corrupting userdata is so much easier.
		1441
		1442	=back
		1443
327		1444
328	=head2 SPEED	1445	=head2 SPEED
329		1446
330	It seems that JSON::XS is surprisingly fast, as shown in the following	1447	It seems that JSON::XS is surprisingly fast, as shown in the following
331	tables. They have been generated with the help of the C<eg/bench> program	1448	tables. They have been generated with the help of the C<eg/bench> program
332	in the JSON::XS distribution, to make it easy to compare on your own	1449	in the JSON::XS distribution, to make it easy to compare on your own
333	system.	1450	system.
334		1451
335	First is a comparison between various modules using a very simple JSON	1452	First comes a comparison between various modules using
		1453	a very short single-line JSON string (also available at
		1454	L<http://dist.schmorp.de/misc/json/short.json>).
		1455
		1456	{"method": "handleMessage", "params": ["user1",
		1457	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1458	1, 0]}
		1459
336	string, showing the number of encodes/decodes per second (JSON::XS is	1460	It shows the number of encodes/decodes per second (JSON::XS uses
337	the functional interface, while JSON::XS/2 is the OO interface with	1461	the functional interface, while JSON::XS/2 uses the OO interface
338	pretty-printing and hashkey sorting enabled).	1462	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1463	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1464	uses the from_json method). Higher is better:
339		1465
340	module | encode | decode |	1466	module | encode | decode |
341	-----------|------------|------------|	1467	--------------|------------|------------|
342	JSON | 14006 | 6820 |	1468	JSON::DWIW/DS | 86302.551 | 102300.098 |
343	JSON::DWIW | 200937 | 120386 |	1469	JSON::DWIW/FJ | 86302.551 | 75983.768 |
344	JSON::PC | 85065 | 129366 |	1470	JSON::PP | 15827.562 | 6638.658 |
345	JSON::Syck | 59898 | 44232 |	1471	JSON::Syck | 63358.066 | 47662.545 |
346	JSON::XS | 1171478 | 342435 |	1472	JSON::XS | 511500.488 | 511500.488 |
347	JSON::XS/2 | 730760 | 328714 |	1473	JSON::XS/2 | 291271.111 | 388361.481 |
		1474	JSON::XS/3 | 361577.931 | 361577.931 |
		1475	Storable | 66788.280 | 265462.278 |
348	-----------+------------+------------+	1476	--------------+------------+------------+
349		1477
350	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1478	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
351	times faster than JSON, even with pretty-printing and key sorting.	1479	about five times faster on decoding, and over thirty to seventy times
		1480	faster than JSON's pure perl implementation. It also compares favourably
		1481	to Storable for small amounts of data.
352		1482
353	Using a longer test string (roughly 8KB, generated from Yahoo! Locals	1483	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
354	search API (http://nanoref.com/yahooapis/mgPdGg):	1484	search API (L<http://dist.schmorp.de/misc/json/long.json>).
355		1485
356	module | encode | decode |	1486	module | encode | decode |
357	-----------|------------|------------|	1487	--------------|------------|------------|
358	JSON | 673 | 38 |	1488	JSON::DWIW/DS | 1647.927 | 2673.916 |
359	JSON::DWIW | 5271 | 770 |	1489	JSON::DWIW/FJ | 1630.249 | 2596.128 |
360	JSON::PC | 9901 | 2491 |	1490	JSON::PP | 400.640 | 62.311 |
361	JSON::Syck | 2360 | 786 |	1491	JSON::Syck | 1481.040 | 1524.869 |
362	JSON::XS | 37398 | 3202 |	1492	JSON::XS | 20661.596 | 9541.183 |
363	JSON::XS/2 | 13765 | 3153 |	1493	JSON::XS/2 | 10683.403 | 9416.938 |
		1494	JSON::XS/3 | 20661.596 | 9400.054 |
		1495	Storable | 19765.806 | 10000.725 |
364	-----------+------------+------------+	1496	--------------+------------+------------+
365		1497
366	Again, JSON::XS leads by far in the encoding case, while still beating	1498	Again, JSON::XS leads by far (except for Storable which non-surprisingly
367	every other module in the decoding case.	1499	decodes a bit faster).
368		1500
369	Last example is an almost 8MB large hash with many large binary values	1501	On large strings containing lots of high Unicode characters, some modules
370	(PNG files), resulting in a lot of escaping:	1502	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1503	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1504	to decode or encode properly, so it was impossible to prepare a fair
		1505	comparison table for that case.
		1506
		1507
		1508	=head1 SECURITY CONSIDERATIONS
		1509
		1510	When you are using JSON in a protocol, talking to untrusted potentially
		1511	hostile creatures requires relatively few measures.
		1512
		1513	First of all, your JSON decoder should be secure, that is, should not have
		1514	any buffer overflows. Obviously, this module should ensure that and I am
		1515	trying hard on making that true, but you never know.
		1516
		1517	Second, you need to avoid resource-starving attacks. That means you should
		1518	limit the size of JSON texts you accept, or make sure then when your
		1519	resources run out, that's just fine (e.g. by using a separate process that
		1520	can crash safely). The size of a JSON text in octets or characters is
		1521	usually a good indication of the size of the resources required to decode
		1522	it into a Perl structure. While JSON::XS can check the size of the JSON
		1523	text, it might be too late when you already have it in memory, so you
		1524	might want to check the size before you accept the string.
		1525
		1526	Third, JSON::XS recurses using the C stack when decoding objects and
		1527	arrays. The C stack is a limited resource: for instance, on my amd64
		1528	machine with 8MB of stack size I can decode around 180k nested arrays but
		1529	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1530	to free the temporary). If that is exceeded, the program crashes. To be
		1531	conservative, the default nesting limit is set to 512. If your process
		1532	has a smaller stack, you should adjust this setting accordingly with the
		1533	C<max_depth> method.
		1534
		1535	Something else could bomb you, too, that I forgot to think of. In that
		1536	case, you get to keep the pieces. I am always open for hints, though...
		1537
		1538	Also keep in mind that JSON::XS might leak contents of your Perl data
		1539	structures in its error messages, so when you serialise sensitive
		1540	information you might want to make sure that exceptions thrown by JSON::XS
		1541	will not end up in front of untrusted eyes.
		1542
		1543	If you are using JSON::XS to return packets to consumption
		1544	by JavaScript scripts in a browser you should have a look at
		1545	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
		1546	see whether you are vulnerable to some common attack vectors (which really
		1547	are browser design bugs, but it is still you who will have to deal with
		1548	it, as major browser developers care only for features, not about getting
		1549	security right).
		1550
		1551
		1552	=head1 INTEROPERABILITY WITH OTHER MODULES
		1553
		1554	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1555	constants. That means that the JSON true and false values will be
		1556	comaptible to true and false values of iother modules that do the same,
		1557	such as L<JSON::PP> and L<CBOR::XS>.
		1558
		1559
		1560	=head1 THREADS
		1561
		1562	This module is I<not> guaranteed to be thread safe and there are no
		1563	plans to change this until Perl gets thread support (as opposed to the
		1564	horribly slow so-called "threads" which are simply slow and bloated
		1565	process simulations - use fork, it's I<much> faster, cheaper, better).
		1566
		1567	(It might actually work, but you have been warned).
		1568
		1569
		1570	=head1 THE PERILS OF SETLOCALE
		1571
		1572	Sometimes people avoid the Perl locale support and directly call the
		1573	system's setlocale function with C<LC_ALL>.
		1574
		1575	This breaks both perl and modules such as JSON::XS, as stringification of
		1576	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1577	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1578	perl to stringify numbers).
		1579
		1580	The solution is simple: don't call C<setlocale>, or use it for only those
		1581	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1582
		1583	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1584	actually needs it (avoiding stringification of numbers), and restore it
		1585	afterwards.
		1586
371		1587
372	=head1 BUGS	1588	=head1 BUGS
373		1589
374	While the goal of this module is to be correct, that unfortunately does	1590	While the goal of this module is to be correct, that unfortunately does
375	not mean its bug-free, only that I think its design is bug-free. It is	1591	not mean it's bug-free, only that I think its design is bug-free. If you
376	still very young and not well-tested. If you keep reporting bugs they will	1592	keep reporting bugs they will be fixed swiftly, though.
377	be fixed swiftly, though.	1593
		1594	Please refrain from using rt.cpan.org or any other bug reporting
		1595	service. I put the contact address into my modules for a reason.
378		1596
379	=cut	1597	=cut
380		1598
381	1;	1599	BEGIN {
		1600	*true = \$Types::Serialiser::true;
		1601	*true = \&Types::Serialiser::true;
		1602	*false = \$Types::Serialiser::false;
		1603	*false = \&Types::Serialiser::false;
		1604	*is_bool = \&Types::Serialiser::is_bool;
		1605
		1606	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
		1607	}
		1608
		1609	XSLoader::load "JSON::XS", $VERSION;
		1610
		1611	=head1 SEE ALSO
		1612
		1613	The F<json_xs> command line utility for quick experiments.
382		1614
383	=head1 AUTHOR	1615	=head1 AUTHOR
384		1616
385	Marc Lehmann <schmorp@schmorp.de>	1617	Marc Lehmann <schmorp@schmorp.de>
386	http://home.schmorp.de/	1618	http://home.schmorp.de/
387		1619
388	=cut	1620	=cut
389		1621
		1622	1
		1623

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