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Revision 1.41 by root, Mon Jun 11 03:45:26 2007 UTC vs.
Revision 1.152 by root, Wed Oct 30 22:11:01 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
		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)
4		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
8		13
9	# exported functions, they croak on error	14	# exported functions, they croak on error
10	# and expect/generate UTF-8	15	# and expect/generate UTF-8
11		16
12	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
13	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
14
15	# objToJson and jsonToObj aliases to to_json and from_json
16	# are exported for compatibility to the JSON module,
17	# but should not be used in new code.
18		19
19	# OO-interface	20	# OO-interface
20		21
21	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
22	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
23	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
24		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
		33
25	=head1 DESCRIPTION	34	=head1 DESCRIPTION
26		35
27	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
28	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
29	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.
30		47
31	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
32	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
33	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
34	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
35	reports for other reasons.	52	reports for other reasons.
36		53
37	See COMPARISON, below, for a comparison to some other JSON modules.
38
39	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
40	vice versa.	55	vice versa.
41		56
42	=head2 FEATURES	57	=head2 FEATURES
43		58
44	=over 4	59	=over 4
45		60
46	=item * correct unicode handling	61	=item * correct Unicode handling
47		62
48	This module knows how to handle Unicode, and even documents how and when	63	This module knows how to handle Unicode, documents how and when it does
49	it does so.	64	so, and even documents what "correct" means.
50		65
51	=item * round-trip integrity	66	=item * round-trip integrity
52		67
53	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
54	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
55	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
56	like a number).	71	it looks like a number). There I<are> minor exceptions to this, read the
		72	MAPPING section below to learn about those.
57		73
58	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
59		75
60	There is no guessing, no generating of illegal JSON texts by default,	76	There is no guessing, no generating of illegal JSON texts by default,
61	and only JSON is accepted as input by default (the latter is a security	77	and only JSON is accepted as input by default (the latter is a security
62	feature).	78	feature).
63		79
64	=item * fast	80	=item * fast
65		81
66	Compared to other JSON modules, this module compares favourably in terms	82	Compared to other JSON modules and other serialisers such as Storable,
67	of speed, too.	83	this module usually compares favourably in terms of speed, too.
68		84
69	=item * simple to use	85	=item * simple to use
70		86
71	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
72	interface.	88	oriented interface.
73		89
74	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
75		91
76	You can choose between the most compact guarenteed single-line format	92	You can choose between the most compact guaranteed-single-line format
77	possible (nice for simple line-based protocols), a pure-ascii format	93	possible (nice for simple line-based protocols), a pure-ASCII format
78	(for when your transport is not 8-bit clean, still supports the whole	94	(for when your transport is not 8-bit clean, still supports the whole
79	unicode range), or a pretty-printed format (for when you want to read that	95	Unicode range), or a pretty-printed format (for when you want to read that
80	stuff). Or you can combine those features in whatever way you like.	96	stuff). Or you can combine those features in whatever way you like.
81		97
82	=back	98	=back
83		99
84	=cut	100	=cut
85		101
86	package JSON::XS;	102	package JSON::XS;
87		103
88	use strict;	104	use common::sense;
89		105
90	BEGIN {
91	our $VERSION = '1.24';	106	our $VERSION = 3.01;
92	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
93		108
94	our @EXPORT = qw(to_json from_json objToJson jsonToObj);	109	our @EXPORT = qw(encode_json decode_json);
95	require Exporter;
96		110
97	require XSLoader;	111	use Exporter;
98	XSLoader::load JSON::XS::, $VERSION;	112	use XSLoader;
99	}	113
		114	use Types::Serialiser ();
100		115
101	=head1 FUNCTIONAL INTERFACE	116	=head1 FUNCTIONAL INTERFACE
102		117
103	The following convinience methods are provided by this module. They are	118	The following convenience methods are provided by this module. They are
104	exported by default:	119	exported by default:
105		120
106	=over 4	121	=over 4
107		122
108	=item $json_text = to_json $perl_scalar	123	=item $json_text = encode_json $perl_scalar
109		124
110	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
111	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.
112	octets only). Croaks on error.
113		127
114	This function call is functionally identical to:	128	This function call is functionally identical to:
115		129
116	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	130	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
117		131
118	except being faster.	132	Except being faster.
119		133
120	=item $perl_scalar = from_json $json_text	134	=item $perl_scalar = decode_json $json_text
121		135
122	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
123	parse that as an UTF-8 encoded JSON text, returning the resulting simple	137	to parse that as an UTF-8 encoded JSON text, returning the resulting
124	scalar or reference. Croaks on error.	138	reference. Croaks on error.
125		139
126	This function call is functionally identical to:	140	This function call is functionally identical to:
127		141
128	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	142	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
129		143
130	except being faster.	144	Except being faster.
131		145
132	=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 :)
133		195
134		196
135	=head1 OBJECT-ORIENTED INTERFACE	197	=head1 OBJECT-ORIENTED INTERFACE
136		198
137	The object oriented interface lets you configure your own encoding or	199	The object oriented interface lets you configure your own encoding or
…		…
150	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	212	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
151	=> {"a": [1, 2]}	213	=> {"a": [1, 2]}
152		214
153	=item $json = $json->ascii ([$enable])	215	=item $json = $json->ascii ([$enable])
154		216
		217	=item $enabled = $json->get_ascii
		218
155	If C<$enable> is true (or missing), then the C<encode> method will not	219	If C<$enable> is true (or missing), then the C<encode> method will not
156	generate characters outside the code range C<0..127> (which is ASCII). Any	220	generate characters outside the code range C<0..127> (which is ASCII). Any
157	unicode characters outside that range will be escaped using either a	221	Unicode characters outside that range will be escaped using either a
158	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,	222	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
159	as per RFC4627. The resulting encoded JSON text can be treated as a native	223	as per RFC4627. The resulting encoded JSON text can be treated as a native
160	unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,	224	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
161	or any other superset of ASCII.	225	or any other superset of ASCII.
162		226
163	If C<$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
164	characters unless required by the JSON syntax or other flags. This results	228	characters unless required by the JSON syntax or other flags. This results
165	in a faster and more compact format.	229	in a faster and more compact format.
166		230
		231	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		232	document.
		233
167	The main use for this flag is to produce JSON texts that can be	234	The main use for this flag is to produce JSON texts that can be
168	transmitted over a 7-bit channel, as the encoded JSON texts will not	235	transmitted over a 7-bit channel, as the encoded JSON texts will not
169	contain any 8 bit characters.	236	contain any 8 bit characters.
170		237
171	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	238	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
172	=> ["\ud801\udc01"]	239	=> ["\ud801\udc01"]
173		240
174	=item $json = $json->latin1 ([$enable])	241	=item $json = $json->latin1 ([$enable])
175		242
		243	=item $enabled = $json->get_latin1
		244
176	If C<$enable> is true (or missing), then the C<encode> method will encode	245	If C<$enable> is true (or missing), then the C<encode> method will encode
177	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters	246	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
178	outside the code range C<0..255>. The resulting string can be treated as a	247	outside the code range C<0..255>. The resulting string can be treated as a
179	latin1-encoded JSON text or a native unicode string. The C<decode> method	248	latin1-encoded JSON text or a native Unicode string. The C<decode> method
180	will not be affected in any way by this flag, as C<decode> by default	249	will not be affected in any way by this flag, as C<decode> by default
181	expects unicode, which is a strict superset of latin1.	250	expects Unicode, which is a strict superset of latin1.
182		251
183	If C<$enable> is false, then the C<encode> method will not escape Unicode	252	If C<$enable> is false, then the C<encode> method will not escape Unicode
184	characters unless required by the JSON syntax or other flags.	253	characters unless required by the JSON syntax or other flags.
		254
		255	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		256	document.
185		257
186	The main use for this flag is efficiently encoding binary data as JSON	258	The main use for this flag is efficiently encoding binary data as JSON
187	text, as most octets will not be escaped, resulting in a smaller encoded	259	text, as most octets will not be escaped, resulting in a smaller encoded
188	size. The disadvantage is that the resulting JSON text is encoded	260	size. The disadvantage is that the resulting JSON text is encoded
189	in latin1 (and must correctly be treated as such when storing and	261	in latin1 (and must correctly be treated as such when storing and
190	transfering), a rare encoding for JSON. It is therefore most useful when	262	transferring), a rare encoding for JSON. It is therefore most useful when
191	you want to store data structures known to contain binary data efficiently	263	you want to store data structures known to contain binary data efficiently
192	in files or databases, not when talking to other JSON encoders/decoders.	264	in files or databases, not when talking to other JSON encoders/decoders.
193		265
194	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	266	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
195	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	267	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
196		268
197	=item $json = $json->utf8 ([$enable])	269	=item $json = $json->utf8 ([$enable])
		270
		271	=item $enabled = $json->get_utf8
198		272
199	If C<$enable> is true (or missing), then the C<encode> method will encode	273	If C<$enable> is true (or missing), then the C<encode> method will encode
200	the JSON result into UTF-8, as required by many protocols, while the	274	the JSON result into UTF-8, as required by many protocols, while the
201	C<decode> method expects to be handled an UTF-8-encoded string. Please	275	C<decode> method expects to be handled an UTF-8-encoded string. Please
202	note that UTF-8-encoded strings do not contain any characters outside the	276	note that UTF-8-encoded strings do not contain any characters outside the
203	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	277	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
204	versions, enabling this option might enable autodetection of the UTF-16	278	versions, enabling this option might enable autodetection of the UTF-16
205	and UTF-32 encoding families, as described in RFC4627.	279	and UTF-32 encoding families, as described in RFC4627.
206		280
207	If C<$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
208	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
209	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
210	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.
211		288
212	Example, output UTF-16BE-encoded JSON:	289	Example, output UTF-16BE-encoded JSON:
213		290
214	use Encode;	291	use Encode;
215	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	292	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
236	]	313	]
237	}	314	}
238		315
239	=item $json = $json->indent ([$enable])	316	=item $json = $json->indent ([$enable])
240		317
		318	=item $enabled = $json->get_indent
		319
241	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	320	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
242	format as output, putting every array member or object/hash key-value pair	321	format as output, putting every array member or object/hash key-value pair
243	into its own line, identing them properly.	322	into its own line, indenting them properly.
244		323
245	If C<$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
246	resulting JSON text is guarenteed not to contain any C<newlines>.	325	resulting JSON text is guaranteed not to contain any C<newlines>.
247		326
248	This setting has no effect when decoding JSON texts.	327	This setting has no effect when decoding JSON texts.
249		328
250	=item $json = $json->space_before ([$enable])	329	=item $json = $json->space_before ([$enable])
		330
		331	=item $enabled = $json->get_space_before
251		332
252	If C<$enable> is true (or missing), then the C<encode> method will add an extra	333	If C<$enable> is true (or missing), then the C<encode> method will add an extra
253	optional space before the C<:> separating keys from values in JSON objects.	334	optional space before the C<:> separating keys from values in JSON objects.
254		335
255	If C<$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
…		…
261	Example, space_before enabled, space_after and indent disabled:	342	Example, space_before enabled, space_after and indent disabled:
262		343
263	{"key" :"value"}	344	{"key" :"value"}
264		345
265	=item $json = $json->space_after ([$enable])	346	=item $json = $json->space_after ([$enable])
		347
		348	=item $enabled = $json->get_space_after
266		349
267	If C<$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
268	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
269	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
270	members.	353	members.
…		…
276		359
277	Example, space_before and indent disabled, space_after enabled:	360	Example, space_before and indent disabled, space_after enabled:
278		361
279	{"key": "value"}	362	{"key": "value"}
280		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
281	=item $json = $json->canonical ([$enable])	411	=item $json = $json->canonical ([$enable])
		412
		413	=item $enabled = $json->get_canonical
282		414
283	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	415	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
284	by sorting their keys. This is adding a comparatively high overhead.	416	by sorting their keys. This is adding a comparatively high overhead.
285		417
286	If C<$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
287	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
288	of the same script).	420	of the same script, and can change even within the same run from 5.18
		421	onwards).
289		422
290	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
291	the same JSON text (given the same overall settings). If it is disabled,	424	the same JSON text (given the same overall settings). If it is disabled,
292	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,
293	as key-value pairs have no inherent ordering in Perl.	426	as key-value pairs have no inherent ordering in Perl.
294		427
295	This setting has no effect when decoding JSON texts.	428	This setting has no effect when decoding JSON texts.
296		429
		430	This setting has currently no effect on tied hashes.
		431
297	=item $json = $json->allow_nonref ([$enable])	432	=item $json = $json->allow_nonref ([$enable])
		433
		434	=item $enabled = $json->get_allow_nonref
298		435
299	If C<$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
300	non-reference into its corresponding string, number or null JSON value,	437	non-reference into its corresponding string, number or null JSON value,
301	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
302	values instead of croaking.	439	values instead of croaking.
…		…
310	resulting in an invalid JSON text:	447	resulting in an invalid JSON text:
311		448
312	JSON::XS->new->allow_nonref->encode ("Hello, World!")	449	JSON::XS->new->allow_nonref->encode ("Hello, World!")
313	=> "Hello, World!"	450	=> "Hello, World!"
314		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 = $json->get_convert_blessed
		487
		488	See L<OBJECT SERIALISATION> for details.
		489
		490	If C<$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 = $json->allow_tags
		511
		512	See L<OBJECT SERIALISATION> for details.
		513
		514	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		515	blessed object, will check for the availability of the C<FREEZE> method on
		516	the object's class. If found, it will be used to serialise the object into
		517	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		518
		519	It also causes C<decode> to parse such tagged JSON values and deserialise
		520	them via a call to the C<THAW> method.
		521
		522	If C<$enable> is false (the default), then C<encode> will not consider
		523	this type of conversion, and tagged JSON values will cause a parse error
		524	in C<decode>, as if tags were not part of the grammar.
		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
315	=item $json = $json->shrink ([$enable])	602	=item $json = $json->shrink ([$enable])
		603
		604	=item $enabled = $json->get_shrink
316		605
317	Perl usually over-allocates memory a bit when allocating space for	606	Perl usually over-allocates memory a bit when allocating space for
318	strings. This flag optionally resizes strings generated by either	607	strings. This flag optionally resizes strings generated by either
319	C<encode> or C<decode> to their minimum size possible. This can save	608	C<encode> or C<decode> to their minimum size possible. This can save
320	memory when your JSON texts are either very very long or you have many	609	memory when your JSON texts are either very very long or you have many
…		…
338	strings that look like integers or floats into integers or floats	627	strings that look like integers or floats into integers or floats
339	internally (there is no difference on the Perl level), saving space.	628	internally (there is no difference on the Perl level), saving space.
340		629
341	=item $json = $json->max_depth ([$maximum_nesting_depth])	630	=item $json = $json->max_depth ([$maximum_nesting_depth])
342		631
		632	=item $max_depth = $json->get_max_depth
		633
343	Sets the maximum nesting level (default C<512>) accepted while encoding	634	Sets the maximum nesting level (default C<512>) accepted while encoding
344	or decoding. If the JSON text or Perl data structure has an equal or	635	or decoding. If a higher nesting level is detected in JSON text or a Perl
345	higher nesting level then this limit, then the encoder and decoder will	636	data structure, then the encoder and decoder will stop and croak at that
346	stop and croak at that point.	637	point.
347		638
348	Nesting level is defined by number of hash- or arrayrefs that the encoder	639	Nesting level is defined by number of hash- or arrayrefs that the encoder
349	needs to traverse to reach a given point or the number of C<{> or C<[>	640	needs to traverse to reach a given point or the number of C<{> or C<[>
350	characters without their matching closing parenthesis crossed to reach a	641	characters without their matching closing parenthesis crossed to reach a
351	given character in a string.	642	given character in a string.
352		643
353	Setting the maximum depth to one disallows any nesting, so that ensures	644	Setting the maximum depth to one disallows any nesting, so that ensures
354	that the object is only a single hash/object or array.	645	that the object is only a single hash/object or array.
355		646
356	The argument to C<max_depth> will be rounded up to the next nearest power	647	If no argument is given, the highest possible setting will be used, which
357	of two.	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.
358		653
359	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	654	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
360		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
361	=item $json_text = $json->encode ($perl_scalar)	671	=item $json_text = $json->encode ($perl_scalar)
362		672
363	Converts the given Perl data structure (a simple scalar or a reference	673	Converts the given Perl value or data structure to its JSON
364	to a hash or array) to its JSON representation. Simple scalars will be	674	representation. Croaks on error.
365	converted into JSON string or number sequences, while references to arrays
366	become JSON arrays and references to hashes become JSON objects. Undefined
367	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
368	nor C<false> values will be generated.
369		675
370	=item $perl_scalar = $json->decode ($json_text)	676	=item $perl_scalar = $json->decode ($json_text)
371		677
372	The opposite of C<encode>: expects a JSON text and tries to parse it,	678	The opposite of C<encode>: expects a JSON text and tries to parse it,
373	returning the resulting simple scalar or reference. Croaks on error.	679	returning the resulting simple scalar or reference. Croaks on error.
374
375	JSON numbers and strings become simple Perl scalars. JSON arrays become
376	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
377	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
378		680
379	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	681	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
380		682
381	This works like the C<decode> method, but instead of raising an exception	683	This works like the C<decode> method, but instead of raising an exception
382	when there is trailing garbage after the first JSON object, it will	684	when there is trailing garbage after the first JSON object, it will
383	silently stop parsing there and return the number of characters consumed	685	silently stop parsing there and return the number of characters consumed
384	so far.	686	so far.
385		687
386	This is useful if your JSON texts are not delimited by an outer protocol	688	This is useful if your JSON texts are not delimited by an outer protocol
387	(which is not the brightest thing to do in the first place) and you need
388	to know where the JSON text ends.	689	and you need to know where the JSON text ends.
389		690
390	JSON::XS->new->decode_prefix ("[1] the tail")	691	JSON::XS->new->decode_prefix ("[1] the tail")
391	=> ([], 3)	692	=> ([], 3)
392		693
393	=back	694	=back
		695
		696
		697	=head1 INCREMENTAL PARSING
		698
		699	In some cases, there is the need for incremental parsing of JSON
		700	texts. While this module always has to keep both JSON text and resulting
		701	Perl data structure in memory at one time, it does allow you to parse a
		702	JSON stream incrementally. It does so by accumulating text until it has
		703	a full JSON object, which it then can decode. This process is similar to
		704	using C<decode_prefix> to see if a full JSON object is available, but
		705	is much more efficient (and can be implemented with a minimum of method
		706	calls).
		707
		708	JSON::XS will only attempt to parse the JSON text once it is sure it
		709	has enough text to get a decisive result, using a very simple but
		710	truly incremental parser. This means that it sometimes won't stop as
		711	early as the full parser, for example, it doesn't detect mismatched
		712	parentheses. The only thing it guarantees is that it starts decoding as
		713	soon as a syntactically valid JSON text has been seen. This means you need
		714	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		715	parsing in the presence if syntax errors.
		716
		717	The following methods implement this incremental parser.
		718
		719	=over 4
		720
		721	=item [void, scalar or list context] = $json->incr_parse ([$string])
		722
		723	This is the central parsing function. It can both append new text and
		724	extract objects from the stream accumulated so far (both of these
		725	functions are optional).
		726
		727	If C<$string> is given, then this string is appended to the already
		728	existing JSON fragment stored in the C<$json> object.
		729
		730	After that, if the function is called in void context, it will simply
		731	return without doing anything further. This can be used to add more text
		732	in as many chunks as you want.
		733
		734	If the method is called in scalar context, then it will try to extract
		735	exactly I<one> JSON object. If that is successful, it will return this
		736	object, otherwise it will return C<undef>. If there is a parse error,
		737	this method will croak just as C<decode> would do (one can then use
		738	C<incr_skip> to skip the erroneous part). This is the most common way of
		739	using the method.
		740
		741	And finally, in list context, it will try to extract as many objects
		742	from the stream as it can find and return them, or the empty list
		743	otherwise. For this to work, there must be no separators between the JSON
		744	objects or arrays, instead they must be concatenated back-to-back. If
		745	an error occurs, an exception will be raised as in the scalar context
		746	case. Note that in this case, any previously-parsed JSON texts will be
		747	lost.
		748
		749	Example: Parse some JSON arrays/objects in a given string and return
		750	them.
		751
		752	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		753
		754	=item $lvalue_string = $json->incr_text
		755
		756	This method returns the currently stored JSON fragment as an lvalue, that
		757	is, you can manipulate it. This I<only> works when a preceding call to
		758	C<incr_parse> in I<scalar context> successfully returned an object. Under
		759	all other circumstances you must not call this function (I mean it.
		760	although in simple tests it might actually work, it I<will> fail under
		761	real world conditions). As a special exception, you can also call this
		762	method before having parsed anything.
		763
		764	This function is useful in two cases: a) finding the trailing text after a
		765	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		766	(such as commas).
		767
		768	=item $json->incr_skip
		769
		770	This will reset the state of the incremental parser and will remove
		771	the parsed text from the input buffer so far. This is useful after
		772	C<incr_parse> died, in which case the input buffer and incremental parser
		773	state is left unchanged, to skip the text parsed so far and to reset the
		774	parse state.
		775
		776	The difference to C<incr_reset> is that only text until the parse error
		777	occurred is removed.
		778
		779	=item $json->incr_reset
		780
		781	This completely resets the incremental parser, that is, after this call,
		782	it will be as if the parser had never parsed anything.
		783
		784	This is useful if you want to repeatedly parse JSON objects and want to
		785	ignore any trailing data, which means you have to reset the parser after
		786	each successful decode.
		787
		788	=back
		789
		790	=head2 LIMITATIONS
		791
		792	All options that affect decoding are supported, except
		793	C<allow_nonref>. The reason for this is that it cannot be made to work
		794	sensibly: JSON objects and arrays are self-delimited, i.e. you can
		795	concatenate them back to back and still decode them perfectly. This does
		796	not hold true for JSON numbers, however.
		797
		798	For example, is the string C<1> a single JSON number, or is it simply the
		799	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		800	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		801	takes the conservative route and disallows this case.
		802
		803	=head2 EXAMPLES
		804
		805	Some examples will make all this clearer. First, a simple example that
		806	works similarly to C<decode_prefix>: We want to decode the JSON object at
		807	the start of a string and identify the portion after the JSON object:
		808
		809	my $text = "[1,2,3] hello";
		810
		811	my $json = new JSON::XS;
		812
		813	my $obj = $json->incr_parse ($text)
		814	or die "expected JSON object or array at beginning of string";
		815
		816	my $tail = $json->incr_text;
		817	# $tail now contains " hello"
		818
		819	Easy, isn't it?
		820
		821	Now for a more complicated example: Imagine a hypothetical protocol where
		822	you read some requests from a TCP stream, and each request is a JSON
		823	array, without any separation between them (in fact, it is often useful to
		824	use newlines as "separators", as these get interpreted as whitespace at
		825	the start of the JSON text, which makes it possible to test said protocol
		826	with C<telnet>...).
		827
		828	Here is how you'd do it (it is trivial to write this in an event-based
		829	manner):
		830
		831	my $json = new JSON::XS;
		832
		833	# read some data from the socket
		834	while (sysread $socket, my $buf, 4096) {
		835
		836	# split and decode as many requests as possible
		837	for my $request ($json->incr_parse ($buf)) {
		838	# act on the $request
		839	}
		840	}
		841
		842	Another complicated example: Assume you have a string with JSON objects
		843	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		844	[3]>). To parse them, we have to skip the commas between the JSON texts,
		845	and here is where the lvalue-ness of C<incr_text> comes in useful:
		846
		847	my $text = "[1],[2], [3]";
		848	my $json = new JSON::XS;
		849
		850	# void context, so no parsing done
		851	$json->incr_parse ($text);
		852
		853	# now extract as many objects as possible. note the
		854	# use of scalar context so incr_text can be called.
		855	while (my $obj = $json->incr_parse) {
		856	# do something with $obj
		857
		858	# now skip the optional comma
		859	$json->incr_text =~ s/^ \s* , //x;
		860	}
		861
		862	Now lets go for a very complex example: Assume that you have a gigantic
		863	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		864	but you cannot load it into memory fully (this has actually happened in
		865	the real world :).
		866
		867	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		868	can still help you: You implement a (very simple) array parser and let
		869	JSON decode the array elements, which are all full JSON objects on their
		870	own (this wouldn't work if the array elements could be JSON numbers, for
		871	example):
		872
		873	my $json = new JSON::XS;
		874
		875	# open the monster
		876	open my $fh, "<bigfile.json"
		877	or die "bigfile: $!";
		878
		879	# first parse the initial "["
		880	for (;;) {
		881	sysread $fh, my $buf, 65536
		882	or die "read error: $!";
		883	$json->incr_parse ($buf); # void context, so no parsing
		884
		885	# Exit the loop once we found and removed(!) the initial "[".
		886	# In essence, we are (ab-)using the $json object as a simple scalar
		887	# we append data to.
		888	last if $json->incr_text =~ s/^ \s* \[ //x;
		889	}
		890
		891	# now we have the skipped the initial "[", so continue
		892	# parsing all the elements.
		893	for (;;) {
		894	# in this loop we read data until we got a single JSON object
		895	for (;;) {
		896	if (my $obj = $json->incr_parse) {
		897	# do something with $obj
		898	last;
		899	}
		900
		901	# add more data
		902	sysread $fh, my $buf, 65536
		903	or die "read error: $!";
		904	$json->incr_parse ($buf); # void context, so no parsing
		905	}
		906
		907	# in this loop we read data until we either found and parsed the
		908	# separating "," between elements, or the final "]"
		909	for (;;) {
		910	# first skip whitespace
		911	$json->incr_text =~ s/^\s*//;
		912
		913	# if we find "]", we are done
		914	if ($json->incr_text =~ s/^\]//) {
		915	print "finished.\n";
		916	exit;
		917	}
		918
		919	# if we find ",", we can continue with the next element
		920	if ($json->incr_text =~ s/^,//) {
		921	last;
		922	}
		923
		924	# if we find anything else, we have a parse error!
		925	if (length $json->incr_text) {
		926	die "parse error near ", $json->incr_text;
		927	}
		928
		929	# else add more data
		930	sysread $fh, my $buf, 65536
		931	or die "read error: $!";
		932	$json->incr_parse ($buf); # void context, so no parsing
		933	}
		934
		935	This is a complex example, but most of the complexity comes from the fact
		936	that we are trying to be correct (bear with me if I am wrong, I never ran
		937	the above example :).
		938
394		939
395		940
396	=head1 MAPPING	941	=head1 MAPPING
397		942
398	This section describes how JSON::XS maps Perl values to JSON values and	943	This section describes how JSON::XS maps Perl values to JSON values and
399	vice versa. These mappings are designed to "do the right thing" in most	944	vice versa. These mappings are designed to "do the right thing" in most
400	circumstances automatically, preserving round-tripping characteristics	945	circumstances automatically, preserving round-tripping characteristics
401	(what you put in comes out as something equivalent).	946	(what you put in comes out as something equivalent).
402		947
403	For the more enlightened: note that in the following descriptions,	948	For the more enlightened: note that in the following descriptions,
404	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	949	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
405	refers to the abstract Perl language itself.	950	refers to the abstract Perl language itself.
406		951
407		952
408	=head2 JSON -> PERL	953	=head2 JSON -> PERL
409		954
410	=over 4	955	=over 4
411		956
412	=item object	957	=item object
413		958
414	A JSON object becomes a reference to a hash in Perl. No ordering of object	959	A JSON object becomes a reference to a hash in Perl. No ordering of object
415	keys is preserved (JSON does not preserver object key ordering itself).	960	keys is preserved (JSON does not preserve object key ordering itself).
416		961
417	=item array	962	=item array
418		963
419	A JSON array becomes a reference to an array in Perl.	964	A JSON array becomes a reference to an array in Perl.
420		965
…		…
424	are represented by the same codepoints in the Perl string, so no manual	969	are represented by the same codepoints in the Perl string, so no manual
425	decoding is necessary.	970	decoding is necessary.
426		971
427	=item number	972	=item number
428		973
429	A JSON number becomes either an integer or numeric (floating point)	974	A JSON number becomes either an integer, numeric (floating point) or
430	scalar in perl, depending on its range and any fractional parts. On the	975	string scalar in perl, depending on its range and any fractional parts. On
431	Perl level, there is no difference between those as Perl handles all the	976	the Perl level, there is no difference between those as Perl handles all
432	conversion details, but an integer may take slightly less memory and might	977	the conversion details, but an integer may take slightly less memory and
433	represent more values exactly than (floating point) numbers.	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.
434		996
435	=item true, false	997	=item true, false
436		998
437	These JSON atoms become C<0>, C<1>, respectively. Information is lost in	999	These JSON atoms become C<Types::Serialiser::true> and
438	this process. Future versions might represent those values differently,	1000	C<Types::Serialiser::false>, respectively. They are overloaded to act
439	but they will be guarenteed to act like these integers would normally in	1001	almost exactly like the numbers C<1> and C<0>. You can check whether
440	Perl.	1002	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1003	function (after C<use Types::Serialier>, of course).
441		1004
442	=item null	1005	=item null
443		1006
444	A JSON null atom becomes C<undef> in Perl.	1007	A JSON null atom becomes C<undef> in Perl.
		1008
		1009	=item shell-style comments (C<< # I<text> >>)
		1010
		1011	As a nonstandard extension to the JSON syntax that is enabled by the
		1012	C<relaxed> setting, shell-style comments are allowed. They can start
		1013	anywhere outside strings and go till the end of the line.
		1014
		1015	=item tagged values (C<< (I<tag>)I<value> >>).
		1016
		1017	Another nonstandard extension to the JSON syntax, enabled with the
		1018	C<allow_tags> setting, are tagged values. In this implementation, the
		1019	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1020	I<value> must be a JSON array encoding optional constructor arguments.
		1021
		1022	See L<OBJECT SERIALISATION>, below, for details.
445		1023
446	=back	1024	=back
447		1025
448		1026
449	=head2 PERL -> JSON	1027	=head2 PERL -> JSON
…		…
454		1032
455	=over 4	1033	=over 4
456		1034
457	=item hash references	1035	=item hash references
458		1036
459	Perl hash references become JSON objects. As there is no inherent ordering	1037	Perl hash references become JSON objects. As there is no inherent
460	in hash keys (or JSON objects), they will usually be encoded in a	1038	ordering in hash keys (or JSON objects), they will usually be encoded
461	pseudo-random order that can change between runs of the same program but	1039	in a pseudo-random order. JSON::XS can optionally sort the hash keys
462	stays generally the same within a single run of a program. JSON::XS can	1040	(determined by the I<canonical> flag), so the same datastructure will
463	optionally sort the hash keys (determined by the I<canonical> flag), so	1041	serialise to the same JSON text (given same settings and version of
464	the same datastructure will serialise to the same JSON text (given same	1042	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
465	settings and version of JSON::XS), but this incurs a runtime overhead	1043	e.g. when you want to compare some JSON text against another for equality.
466	and is only rarely useful, e.g. when you want to compare some JSON text
467	against another for equality.
468		1044
469	=item array references	1045	=item array references
470		1046
471	Perl array references become JSON arrays.	1047	Perl array references become JSON arrays.
472		1048
473	=item other references	1049	=item other references
474		1050
475	Other unblessed references are generally not allowed and will cause an	1051	Other unblessed references are generally not allowed and will cause an
476	exception to be thrown, except for references to the integers C<0> and	1052	exception to be thrown, except for references to the integers C<0> and
477	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1053	C<1>, which get turned into C<false> and C<true> atoms in JSON.
478	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
479		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;
480	to_json [\0,JSON::XS::true] # yields [false,true]	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.
481		1067
482	=item blessed objects	1068	=item blessed objects
483		1069
484	Blessed objects are not allowed. JSON::XS currently tries to encode their	1070	Blessed objects are not directly representable in JSON, but C<JSON::XS>
485	underlying representation (hash- or arrayref), but this behaviour might	1071	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
486	change in future versions.	1072	below, for details.
487		1073
488	=item simple scalars	1074	=item simple scalars
489		1075
490	Simple Perl scalars (any scalar that is not a reference) are the most	1076	Simple Perl scalars (any scalar that is not a reference) are the most
491	difficult objects to encode: JSON::XS will encode undefined scalars as	1077	difficult objects to encode: JSON::XS will encode undefined scalars as
492	JSON null value, scalars that have last been used in a string context	1078	JSON C<null> values, scalars that have last been used in a string context
493	before encoding as JSON strings and anything else as number value:	1079	before encoding as JSON strings, and anything else as number value:
494		1080
495	# dump as number	1081	# dump as number
496	to_json [2] # yields [2]	1082	encode_json [2] # yields [2]
497	to_json [-3.0e17] # yields [-3e+17]	1083	encode_json [-3.0e17] # yields [-3e+17]
498	my $value = 5; to_json [$value] # yields [5]	1084	my $value = 5; encode_json [$value] # yields [5]
499		1085
500	# used as string, so dump as string	1086	# used as string, so dump as string
501	print $value;	1087	print $value;
502	to_json [$value] # yields ["5"]	1088	encode_json [$value] # yields ["5"]
503		1089
504	# undef becomes null	1090	# undef becomes null
505	to_json [undef] # yields [null]	1091	encode_json [undef] # yields [null]
506		1092
507	You can force the type to be a string by stringifying it:	1093	You can force the type to be a JSON string by stringifying it:
508		1094
509	my $x = 3.1; # some variable containing a number	1095	my $x = 3.1; # some variable containing a number
510	"$x"; # stringified	1096	"$x"; # stringified
511	$x .= ""; # another, more awkward way to stringify	1097	$x .= ""; # another, more awkward way to stringify
512	print $x; # perl does it for you, too, quite often	1098	print $x; # perl does it for you, too, quite often
513		1099
514	You can force the type to be a number by numifying it:	1100	You can force the type to be a JSON number by numifying it:
515		1101
516	my $x = "3"; # some variable containing a string	1102	my $x = "3"; # some variable containing a string
517	$x += 0; # numify it, ensuring it will be dumped as a number	1103	$x += 0; # numify it, ensuring it will be dumped as a number
518	$x *= 1; # same thing, the choise is yours.	1104	$x *= 1; # same thing, the choice is yours.
519		1105
520	You can not currently output JSON booleans or force the type in other,	1106	You can not currently force the type in other, less obscure, ways. Tell me
521	less obscure, ways. Tell me if you need this capability.	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.
522		1116
523	=back	1117	=back
524		1118
		1119	=head2 OBJECT SERIALISATION
525		1120
526	=head1 COMPARISON	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.
527		1125
528	As already mentioned, this module was created because none of the existing	1126	=head3 SERIALISATION
529	JSON modules could be made to work correctly. First I will describe the	1127
530	problems (or pleasures) I encountered with various existing JSON modules,	1128	What happens when C<JSON::XS> encounters a Perl object depends on the
531	followed by some benchmark values. JSON::XS was designed not to suffer	1129	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
532	from any of these problems or limitations.	1130	used in this order:
533		1131
534	=over 4	1132	=over 4
535		1133
536	=item JSON 1.07	1134	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
537		1135
538	Slow (but very portable, as it is written in pure Perl).	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.
539		1139
540	Undocumented/buggy Unicode handling (how JSON handles unicode values is	1140	This works by invoking the C<FREEZE> method on the object, with the first
541	undocumented. One can get far by feeding it unicode strings and doing	1141	argument being the object to serialise, and the second argument being the
542	en-/decoding oneself, but unicode escapes are not working properly).	1142	constant string C<JSON> to distinguish it from other serialisers.
543		1143
544	No roundtripping (strings get clobbered if they look like numbers, e.g.	1144	The C<FREEZE> method can return any number of values (i.e. zero or
545	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	1145	more). These values and the paclkage/classname of the object will then be
546	decode into the number 2.	1146	encoded as a tagged JSON value in the following format:
547		1147
548	=item JSON::PC 0.01	1148	("classname")[FREEZE return values...]
549		1149
550	Very fast.	1150	e.g.:
551		1151
552	Undocumented/buggy Unicode handling.	1152	("URI")["http://www.google.com/"]
		1153	("MyDate")[2013,10,29]
		1154	("ImageData::JPEG")["Z3...VlCg=="]
553		1155
554	No roundtripping.	1156	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1157	objects C<type> and C<id> members to encode the object:
555		1158
556	Has problems handling many Perl values (e.g. regex results and other magic	1159	sub My::Object::FREEZE {
557	values will make it croak).	1160	my ($self, $serialiser) = @_;
558		1161
559	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1162	($self->{type}, $self->{id})
560	which is not a valid JSON text.	1163	}
561		1164
562	Unmaintained (maintainer unresponsive for many months, bugs are not	1165	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
563	getting fixed).
564		1166
565	=item JSON::Syck 0.21	1167	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1168	context. It must return a single scalar that can be directly encoded into
		1169	JSON. This scalar replaces the object in the JSON text.
566		1170
567	Very buggy (often crashes).	1171	For example, the following C<TO_JSON> method will convert all L<URI>
		1172	objects to JSON strings when serialised. The fatc that these values
		1173	originally were L<URI> objects is lost.
568		1174
569	Very inflexible (no human-readable format supported, format pretty much	1175	sub URI::TO_JSON {
570	undocumented. I need at least a format for easy reading by humans and a	1176	my ($uri) = @_;
571	single-line compact format for use in a protocol, and preferably a way to	1177	$uri->as_string
572	generate ASCII-only JSON texts).	1178	}
573		1179
574	Completely broken (and confusingly documented) Unicode handling (unicode	1180	=item 3. C<allow_blessed> is enabled.
575	escapes are not working properly, you need to set ImplicitUnicode to
576	I<different> values on en- and decoding to get symmetric behaviour).
577		1181
578	No roundtripping (simple cases work, but this depends on wether the scalar	1182	The object will be serialised as a JSON null value.
579	value was used in a numeric context or not).
580		1183
581	Dumping hashes may skip hash values depending on iterator state.	1184	=item 4. none of the above
582		1185
583	Unmaintained (maintainer unresponsive for many months, bugs are not	1186	If none of the settings are enabled or the respective methods are missing,
584	getting fixed).	1187	C<JSON::XS> throws an exception.
585
586	Does not check input for validity (i.e. will accept non-JSON input and
587	return "something" instead of raising an exception. This is a security
588	issue: imagine two banks transfering money between each other using
589	JSON. One bank might parse a given non-JSON request and deduct money,
590	while the other might reject the transaction with a syntax error. While a
591	good protocol will at least recover, that is extra unnecessary work and
592	the transaction will still not succeed).
593
594	=item JSON::DWIW 0.04
595
596	Very fast. Very natural. Very nice.
597
598	Undocumented unicode handling (but the best of the pack. Unicode escapes
599	still don't get parsed properly).
600
601	Very inflexible.
602
603	No roundtripping.
604
605	Does not generate valid JSON texts (key strings are often unquoted, empty keys
606	result in nothing being output)
607
608	Does not check input for validity.
609		1188
610	=back	1189	=back
611		1190
		1191	=head3 DESERIALISATION
		1192
		1193	For deserialisation there are only two cases to consider: either
		1194	nonstandard tagging was used, in which case C<allow_tags> decides,
		1195	or objects cannot be automatically be deserialised, in which
		1196	case you can use postprocessing or the C<filter_json_object> or
		1197	C<filter_json_single_key_object> callbacks to get some real objects our of
		1198	your JSON.
		1199
		1200	This section only considers the tagged value case: I a tagged JSON object
		1201	is encountered during decoding and C<allow_tags> is disabled, a parse
		1202	error will result (as if tagged values were not part of the grammar).
		1203
		1204	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1205	of the package/classname used during serialisation (it will not attempt
		1206	to load the package as a Perl module). If there is no such method, the
		1207	decoding will fail with an error.
		1208
		1209	Otherwise, the C<THAW> method is invoked with the classname as first
		1210	argument, the constant string C<JSON> as second argument, and all the
		1211	values from the JSON array (the values originally returned by the
		1212	C<FREEZE> method) as remaining arguments.
		1213
		1214	The method must then return the object. While technically you can return
		1215	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1216	make that work in all cases, so better return an actual blessed reference.
		1217
		1218	As an example, let's implement a C<THAW> function that regenerates the
		1219	C<My::Object> from the C<FREEZE> example earlier:
		1220
		1221	sub My::Object::THAW {
		1222	my ($class, $serialiser, $type, $id) = @_;
		1223
		1224	$class->new (type => $type, id => $id)
		1225	}
		1226
		1227
		1228	=head1 ENCODING/CODESET FLAG NOTES
		1229
		1230	The interested reader might have seen a number of flags that signify
		1231	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1232	some confusion on what these do, so here is a short comparison:
		1233
		1234	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1235	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1236	control whether C<encode> escapes character values outside their respective
		1237	codeset range. Neither of these flags conflict with each other, although
		1238	some combinations make less sense than others.
		1239
		1240	Care has been taken to make all flags symmetrical with respect to
		1241	C<encode> and C<decode>, that is, texts encoded with any combination of
		1242	these flag values will be correctly decoded when the same flags are used
		1243	- in general, if you use different flag settings while encoding vs. when
		1244	decoding you likely have a bug somewhere.
		1245
		1246	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1247	simply an abstract set of character-codepoint pairs, while an encoding
		1248	takes those codepoint numbers and I<encodes> them, in our case into
		1249	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1250	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1251	the same time, which can be confusing.
		1252
		1253	=over 4
		1254
		1255	=item C<utf8> flag disabled
		1256
		1257	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1258	and expect Unicode strings, that is, characters with high ordinal Unicode
		1259	values (> 255) will be encoded as such characters, and likewise such
		1260	characters are decoded as-is, no changes to them will be done, except
		1261	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1262	respectively (to Perl, these are the same thing in strings unless you do
		1263	funny/weird/dumb stuff).
		1264
		1265	This is useful when you want to do the encoding yourself (e.g. when you
		1266	want to have UTF-16 encoded JSON texts) or when some other layer does
		1267	the encoding for you (for example, when printing to a terminal using a
		1268	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1269	to UTF-8 encode your data first and have Perl encode it another time).
		1270
		1271	=item C<utf8> flag enabled
		1272
		1273	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1274	characters using the corresponding UTF-8 multi-byte sequence, and will
		1275	expect your input strings to be encoded as UTF-8, that is, no "character"
		1276	of the input string must have any value > 255, as UTF-8 does not allow
		1277	that.
		1278
		1279	The C<utf8> flag therefore switches between two modes: disabled means you
		1280	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1281	octet/binary string in Perl.
		1282
		1283	=item C<latin1> or C<ascii> flags enabled
		1284
		1285	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1286	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1287	characters as specified by the C<utf8> flag.
		1288
		1289	If C<utf8> is disabled, then the result is also correctly encoded in those
		1290	character sets (as both are proper subsets of Unicode, meaning that a
		1291	Unicode string with all character values < 256 is the same thing as a
		1292	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1293	the same thing as an ASCII string in Perl).
		1294
		1295	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1296	regardless of these flags, just some more characters will be escaped using
		1297	C<\uXXXX> then before.
		1298
		1299	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1300	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1301	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1302	a subset of Unicode), while ASCII is.
		1303
		1304	Surprisingly, C<decode> will ignore these flags and so treat all input
		1305	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1306	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1307	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1308
		1309	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1310	they only govern when the JSON output engine escapes a character or not.
		1311
		1312	The main use for C<latin1> is to relatively efficiently store binary data
		1313	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1314
		1315	The main use for C<ascii> is to force the output to not contain characters
		1316	with values > 127, which means you can interpret the resulting string
		1317	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1318	8-bit-encoding, and still get the same data structure back. This is useful
		1319	when your channel for JSON transfer is not 8-bit clean or the encoding
		1320	might be mangled in between (e.g. in mail), and works because ASCII is a
		1321	proper subset of most 8-bit and multibyte encodings in use in the world.
		1322
		1323	=back
		1324
		1325
		1326	=head2 JSON and ECMAscript
		1327
		1328	JSON syntax is based on how literals are represented in javascript (the
		1329	not-standardised predecessor of ECMAscript) which is presumably why it is
		1330	called "JavaScript Object Notation".
		1331
		1332	However, JSON is not a subset (and also not a superset of course) of
		1333	ECMAscript (the standard) or javascript (whatever browsers actually
		1334	implement).
		1335
		1336	If you want to use javascript's C<eval> function to "parse" JSON, you
		1337	might run into parse errors for valid JSON texts, or the resulting data
		1338	structure might not be queryable:
		1339
		1340	One of the problems is that U+2028 and U+2029 are valid characters inside
		1341	JSON strings, but are not allowed in ECMAscript string literals, so the
		1342	following Perl fragment will not output something that can be guaranteed
		1343	to be parsable by javascript's C<eval>:
		1344
		1345	use JSON::XS;
		1346
		1347	print encode_json [chr 0x2028];
		1348
		1349	The right fix for this is to use a proper JSON parser in your javascript
		1350	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1351	F<json2.js> parser).
		1352
		1353	If this is not an option, you can, as a stop-gap measure, simply encode to
		1354	ASCII-only JSON:
		1355
		1356	use JSON::XS;
		1357
		1358	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1359
		1360	Note that this will enlarge the resulting JSON text quite a bit if you
		1361	have many non-ASCII characters. You might be tempted to run some regexes
		1362	to only escape U+2028 and U+2029, e.g.:
		1363
		1364	# DO NOT USE THIS!
		1365	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1366	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1367	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1368	print $json;
		1369
		1370	Note that I<this is a bad idea>: the above only works for U+2028 and
		1371	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1372	javascript implementations, however, have issues with other characters as
		1373	well - using C<eval> naively simply I<will> cause problems.
		1374
		1375	Another problem is that some javascript implementations reserve
		1376	some property names for their own purposes (which probably makes
		1377	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1378	C<__proto__> property name for its own purposes.
		1379
		1380	If that is a problem, you could parse try to filter the resulting JSON
		1381	output for these property strings, e.g.:
		1382
		1383	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1384
		1385	This works because C<__proto__> is not valid outside of strings, so every
		1386	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1387
		1388	If you know of other incompatibilities, please let me know.
		1389
612		1390
613	=head2 JSON and YAML	1391	=head2 JSON and YAML
614		1392
615	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1393	You often hear that JSON is a subset of YAML. This is, however, a mass
616	however, a mass hysteria and very far from the truth. In general, there is	1394	hysteria(*) and very far from the truth (as of the time of this writing),
617	no way to configure JSON::XS to output a data structure as valid YAML.	1395	so let me state it clearly: I<in general, there is no way to configure
		1396	JSON::XS to output a data structure as valid YAML> that works in all
		1397	cases.
618		1398
619	If you really must use JSON::XS to generate YAML, you should use this	1399	If you really must use JSON::XS to generate YAML, you should use this
620	algorithm (subject to change in future versions):	1400	algorithm (subject to change in future versions):
621		1401
622	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1402	my $to_yaml = JSON::XS->new->utf8->space_after (1);
623	my $yaml = $to_yaml->encode ($ref) . "\n";	1403	my $yaml = $to_yaml->encode ($ref) . "\n";
624		1404
625	This will usually generate JSON texts that also parse as valid	1405	This will I<usually> generate JSON texts that also parse as valid
626	YAML. Please note that YAML has hardcoded limits on (simple) object key	1406	YAML. Please note that YAML has hardcoded limits on (simple) object key
627	lengths that JSON doesn't have, so you should make sure that your hash	1407	lengths that JSON doesn't have and also has different and incompatible
		1408	unicode character escape syntax, so you should make sure that your hash
628	keys are noticably shorter than the 1024 characters YAML allows.	1409	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1410	and that you do not have characters with codepoint values outside the
		1411	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1412	sequences in strings (which JSON::XS does not I<currently> generate, but
		1413	other JSON generators might).
629		1414
630	There might be other incompatibilities that I am not aware of. In general	1415	There might be other incompatibilities that I am not aware of (or the YAML
		1416	specification has been changed yet again - it does so quite often). In
631	you should not try to generate YAML with a JSON generator or vice versa,	1417	general you should not try to generate YAML with a JSON generator or vice
632	or try to parse JSON with a YAML parser or vice versa: chances are high	1418	versa, or try to parse JSON with a YAML parser or vice versa: chances are
633	that you will run into severe interoperability problems.	1419	high that you will run into severe interoperability problems when you
		1420	least expect it.
		1421
		1422	=over 4
		1423
		1424	=item (*)
		1425
		1426	I have been pressured multiple times by Brian Ingerson (one of the
		1427	authors of the YAML specification) to remove this paragraph, despite him
		1428	acknowledging that the actual incompatibilities exist. As I was personally
		1429	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1430	educate people about these issues, so others do not run into the same
		1431	problem again and again. After this, Brian called me a (quote)I<complete
		1432	and worthless idiot>(unquote).
		1433
		1434	In my opinion, instead of pressuring and insulting people who actually
		1435	clarify issues with YAML and the wrong statements of some of its
		1436	proponents, I would kindly suggest reading the JSON spec (which is not
		1437	that difficult or long) and finally make YAML compatible to it, and
		1438	educating users about the changes, instead of spreading lies about the
		1439	real compatibility for many I<years> and trying to silence people who
		1440	point out that it isn't true.
		1441
		1442	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1443	though the incompatibilities have been documented (and are known to Brian)
		1444	for many years and the spec makes explicit claims that YAML is a superset
		1445	of JSON. It would be so easy to fix, but apparently, bullying people and
		1446	corrupting userdata is so much easier.
		1447
		1448	=back
634		1449
635		1450
636	=head2 SPEED	1451	=head2 SPEED
637		1452
638	It seems that JSON::XS is surprisingly fast, as shown in the following	1453	It seems that JSON::XS is surprisingly fast, as shown in the following
639	tables. They have been generated with the help of the C<eg/bench> program	1454	tables. They have been generated with the help of the C<eg/bench> program
640	in the JSON::XS distribution, to make it easy to compare on your own	1455	in the JSON::XS distribution, to make it easy to compare on your own
641	system.	1456	system.
642		1457
643	First comes a comparison between various modules using a very short	1458	First comes a comparison between various modules using
644	single-line JSON string:	1459	a very short single-line JSON string (also available at
		1460	L<http://dist.schmorp.de/misc/json/short.json>).
645		1461
646	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1462	{"method": "handleMessage", "params": ["user1",
647	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1463	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1464	1, 0]}
648		1465
649	It shows the number of encodes/decodes per second (JSON::XS uses	1466	It shows the number of encodes/decodes per second (JSON::XS uses
650	the functional interface, while JSON::XS/2 uses the OO interface	1467	the functional interface, while JSON::XS/2 uses the OO interface
651	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1468	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
652	shrink). Higher is better:	1469	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1470	uses the from_json method). Higher is better:
653		1471
654	module | encode | decode |	1472	module | encode | decode |
655	-----------|------------|------------|	1473	--------------|------------|------------|
656	JSON | 7645.468 | 4208.613 |	1474	JSON::DWIW/DS | 86302.551 | 102300.098 |
657	JSON::DWIW | 40721.398 | 77101.176 |	1475	JSON::DWIW/FJ | 86302.551 | 75983.768 |
658	JSON::PC | 65948.176 | 78251.940 |	1476	JSON::PP | 15827.562 | 6638.658 |
659	JSON::Syck | 22844.793 | 26479.192 |	1477	JSON::Syck | 63358.066 | 47662.545 |
660	JSON::XS | 388361.481 | 199728.762 |	1478	JSON::XS | 511500.488 | 511500.488 |
661	JSON::XS/2 | 218453.333 | 192399.266 |	1479	JSON::XS/2 | 291271.111 | 388361.481 |
662	JSON::XS/3 | 338250.323 | 192399.266 |	1480	JSON::XS/3 | 361577.931 | 361577.931 |
663	Storable | 15779.925 | 14169.946 |	1481	Storable | 66788.280 | 265462.278 |
664	-----------+------------+------------+	1482	--------------+------------+------------+
665		1483
666	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1484	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
667	about three times faster on decoding, and over fourty times faster	1485	about five times faster on decoding, and over thirty to seventy times
668	than JSON, even with pretty-printing and key sorting. It also compares	1486	faster than JSON's pure perl implementation. It also compares favourably
669	favourably to Storable for small amounts of data.	1487	to Storable for small amounts of data.
670		1488
671	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1489	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
672	search API (http://nanoref.com/yahooapis/mgPdGg):	1490	search API (L<http://dist.schmorp.de/misc/json/long.json>).
673		1491
674	module | encode | decode |	1492	module | encode | decode |
675	-----------|------------|------------|	1493	--------------|------------|------------|
676	JSON | 254.685 | 37.665 |	1494	JSON::DWIW/DS | 1647.927 | 2673.916 |
677	JSON::DWIW | 843.343 | 1049.731 |	1495	JSON::DWIW/FJ | 1630.249 | 2596.128 |
678	JSON::PC | 3602.116 | 2307.352 |	1496	JSON::PP | 400.640 | 62.311 |
679	JSON::Syck | 505.107 | 787.899 |	1497	JSON::Syck | 1481.040 | 1524.869 |
680	JSON::XS | 5747.196 | 3690.220 |	1498	JSON::XS | 20661.596 | 9541.183 |
681	JSON::XS/2 | 3968.121 | 3676.634 |	1499	JSON::XS/2 | 10683.403 | 9416.938 |
682	JSON::XS/3 | 6105.246 | 3662.508 |	1500	JSON::XS/3 | 20661.596 | 9400.054 |
683	Storable | 4417.337 | 5285.161 |	1501	Storable | 19765.806 | 10000.725 |
684	-----------+------------+------------+	1502	--------------+------------+------------+
685		1503
686	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1504	Again, JSON::XS leads by far (except for Storable which non-surprisingly
687	decodes faster).	1505	decodes a bit faster).
688		1506
689	On large strings containing lots of high unicode characters, some modules	1507	On large strings containing lots of high Unicode characters, some modules
690	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1508	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
691	will be broken due to missing (or wrong) unicode handling. Others refuse	1509	will be broken due to missing (or wrong) Unicode handling. Others refuse
692	to decode or encode properly, so it was impossible to prepare a fair	1510	to decode or encode properly, so it was impossible to prepare a fair
693	comparison table for that case.	1511	comparison table for that case.
694		1512
695		1513
696	=head1 SECURITY CONSIDERATIONS	1514	=head1 SECURITY CONSIDERATIONS
…		…
702	any buffer overflows. Obviously, this module should ensure that and I am	1520	any buffer overflows. Obviously, this module should ensure that and I am
703	trying hard on making that true, but you never know.	1521	trying hard on making that true, but you never know.
704		1522
705	Second, you need to avoid resource-starving attacks. That means you should	1523	Second, you need to avoid resource-starving attacks. That means you should
706	limit the size of JSON texts you accept, or make sure then when your	1524	limit the size of JSON texts you accept, or make sure then when your
707	resources run out, thats just fine (e.g. by using a separate process that	1525	resources run out, that's just fine (e.g. by using a separate process that
708	can crash safely). The size of a JSON text in octets or characters is	1526	can crash safely). The size of a JSON text in octets or characters is
709	usually a good indication of the size of the resources required to decode	1527	usually a good indication of the size of the resources required to decode
710	it into a Perl structure.	1528	it into a Perl structure. While JSON::XS can check the size of the JSON
		1529	text, it might be too late when you already have it in memory, so you
		1530	might want to check the size before you accept the string.
711		1531
712	Third, JSON::XS recurses using the C stack when decoding objects and	1532	Third, JSON::XS recurses using the C stack when decoding objects and
713	arrays. The C stack is a limited resource: for instance, on my amd64	1533	arrays. The C stack is a limited resource: for instance, on my amd64
714	machine with 8MB of stack size I can decode around 180k nested arrays but	1534	machine with 8MB of stack size I can decode around 180k nested arrays but
715	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1535	only 14k nested JSON objects (due to perl itself recursing deeply on croak
716	to free the temporary). If that is exceeded, the program crashes. to be	1536	to free the temporary). If that is exceeded, the program crashes. To be
717	conservative, the default nesting limit is set to 512. If your process	1537	conservative, the default nesting limit is set to 512. If your process
718	has a smaller stack, you should adjust this setting accordingly with the	1538	has a smaller stack, you should adjust this setting accordingly with the
719	C<max_depth> method.	1539	C<max_depth> method.
720		1540
721	And last but least, something else could bomb you that I forgot to think	1541	Something else could bomb you, too, that I forgot to think of. In that
722	of. In that case, you get to keep the pieces. I am always open for hints,	1542	case, you get to keep the pieces. I am always open for hints, though...
723	though...	1543
		1544	Also keep in mind that JSON::XS might leak contents of your Perl data
		1545	structures in its error messages, so when you serialise sensitive
		1546	information you might want to make sure that exceptions thrown by JSON::XS
		1547	will not end up in front of untrusted eyes.
		1548
		1549	If you are using JSON::XS to return packets to consumption
		1550	by JavaScript scripts in a browser you should have a look at
		1551	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
		1552	see whether you are vulnerable to some common attack vectors (which really
		1553	are browser design bugs, but it is still you who will have to deal with
		1554	it, as major browser developers care only for features, not about getting
		1555	security right).
		1556
		1557
		1558	=head1 INTEROPERABILITY WITH OTHER MODULES
		1559
		1560	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1561	constants. That means that the JSON true and false values will be
		1562	comaptible to true and false values of iother modules that do the same,
		1563	such as L<JSON::PP> and L<CBOR::XS>.
		1564
		1565
		1566	=head1 INTEROPERABILITY WITH OTHER JSON DECODERS
		1567
		1568	As long as you only serialise data that can be directly expressed in JSON,
		1569	C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs,
		1570	but C<JSON::XS> has found more bugs in the official JSON testsuite (1)
		1571	than the official JSON testsuite has found in C<JSON::XS> (0)).
		1572
		1573	When you have trouble decoding JSON generated by this module using other
		1574	decoders, then it is very likely that you have an encoding mismatch or the
		1575	other decoder is broken.
		1576
		1577	When decoding, C<JSON::XS> is strict by default and will likely catch all
		1578	errors. There are currently two settings that change this: C<relaxed>
		1579	makes C<JSON::XS> accept (but not generate) some non-standard extensions,
		1580	and C<allow_tags> will allow you to encode and decode Perl objects, at the
		1581	cost of not outputting valid JSON anymore.
		1582
		1583	=head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
		1584
		1585	When you use C<allow_tags> to use the extended (and also nonstandard and
		1586	invalid) JSON syntax for serialised objects, and you still want to decode
		1587	the generated When you want to serialise objects, you can run a regex
		1588	to replace the tagged syntax by standard JSON arrays (it only works for
		1589	"normal" packagesnames without comma, newlines or single colons). First,
		1590	the readable Perl version:
		1591
		1592	# if your FREEZE methods return no values, you need this replace first:
		1593	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
		1594
		1595	# this works for non-empty constructor arg lists:
		1596	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
		1597
		1598	And here is a less readable version that is easy to adapt to other
		1599	languages:
		1600
		1601	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
		1602
		1603	Here is an ECMAScript version (same regex):
		1604
		1605	json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
		1606
		1607	Since this syntax converts to standard JSON arrays, it might be hard to
		1608	distinguish serialised objects from normal arrays. You can prepend a
		1609	"magic number" as first array element to reduce chances of a collision:
		1610
		1611	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
		1612
		1613	And after decoding the JSON text, you could walk the data
		1614	structure looking for arrays with a first element of
		1615	C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>.
		1616
		1617	The same approach cna be used to create the tagged format with another
		1618	encoder. First, you create an array with the magic string as first member,
		1619	the classname as second, and constructor arguments last, encode it as part
		1620	of your JSON structure, and then:
		1621
		1622	$json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
		1623
		1624	Again, this has some limitations - the magic string must not be encoded
		1625	with character escapes, and the constructor arguments must be non-empty.
		1626
		1627	=head1 THREADS
		1628
		1629	This module is I<not> guaranteed to be thread safe and there are no
		1630	plans to change this until Perl gets thread support (as opposed to the
		1631	horribly slow so-called "threads" which are simply slow and bloated
		1632	process simulations - use fork, it's I<much> faster, cheaper, better).
		1633
		1634	(It might actually work, but you have been warned).
		1635
		1636
		1637	=head1 THE PERILS OF SETLOCALE
		1638
		1639	Sometimes people avoid the Perl locale support and directly call the
		1640	system's setlocale function with C<LC_ALL>.
		1641
		1642	This breaks both perl and modules such as JSON::XS, as stringification of
		1643	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1644	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1645	perl to stringify numbers).
		1646
		1647	The solution is simple: don't call C<setlocale>, or use it for only those
		1648	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1649
		1650	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1651	actually needs it (avoiding stringification of numbers), and restore it
		1652	afterwards.
724		1653
725		1654
726	=head1 BUGS	1655	=head1 BUGS
727		1656
728	While the goal of this module is to be correct, that unfortunately does	1657	While the goal of this module is to be correct, that unfortunately does
729	not mean its bug-free, only that I think its design is bug-free. It is	1658	not mean it's bug-free, only that I think its design is bug-free. If you
730	still relatively early in its development. If you keep reporting bugs they	1659	keep reporting bugs they will be fixed swiftly, though.
731	will be fixed swiftly, though.	1660
		1661	Please refrain from using rt.cpan.org or any other bug reporting
		1662	service. I put the contact address into my modules for a reason.
732		1663
733	=cut	1664	=cut
734		1665
735	sub true() { \1 }	1666	BEGIN {
736	sub false() { \0 }	1667	*true = \$Types::Serialiser::true;
		1668	*true = \&Types::Serialiser::true;
		1669	*false = \$Types::Serialiser::false;
		1670	*false = \&Types::Serialiser::false;
		1671	*is_bool = \&Types::Serialiser::is_bool;
737		1672
738	1;	1673	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
		1674	}
		1675
		1676	XSLoader::load "JSON::XS", $VERSION;
		1677
		1678	=head1 SEE ALSO
		1679
		1680	The F<json_xs> command line utility for quick experiments.
739		1681
740	=head1 AUTHOR	1682	=head1 AUTHOR
741		1683
742	Marc Lehmann <schmorp@schmorp.de>	1684	Marc Lehmann <schmorp@schmorp.de>
743	http://home.schmorp.de/	1685	http://home.schmorp.de/
744		1686
745	=cut	1687	=cut
746		1688
		1689	1
		1690

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