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Revision 1.31 by root, Wed Apr 11 12:23:02 2007 UTC vs.
Revision 1.170 by root, Thu Nov 15 22:35:35 2018 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.
30		39
31	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
33	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
35	reports for other reasons.
36
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	40	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
40	vice versa.	41	vice versa.
41		42
42	=head2 FEATURES	43	=head2 FEATURES
43		44
44	=over 4	45	=over
45		46
46	=item * correct unicode handling	47	=item * correct Unicode handling
47		48
48	This module knows how to handle Unicode, and even documents how and when	49	This module knows how to handle Unicode, documents how and when it does
49	it does so.	50	so, and even documents what "correct" means.
50		51
51	=item * round-trip integrity	52	=item * round-trip integrity
52		53
53	When you serialise a perl data structure using only datatypes supported	54	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.	55	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	56	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
56	like a number).	57	it looks like a number). There I<are> minor exceptions to this, read the
		58	MAPPING section below to learn about those.
57		59
58	=item * strict checking of JSON correctness	60	=item * strict checking of JSON correctness
59		61
60	There is no guessing, no generating of illegal JSON texts by default,	62	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	63	and only JSON is accepted as input by default (the latter is a security
62	feature).	64	feature).
63		65
64	=item * fast	66	=item * fast
65		67
66	Compared to other JSON modules, this module compares favourably in terms	68	Compared to other JSON modules and other serialisers such as Storable,
67	of speed, too.	69	this module usually compares favourably in terms of speed, too.
68		70
69	=item * simple to use	71	=item * simple to use
70		72
71	This module has both a simple functional interface as well as an OO	73	This module has both a simple functional interface as well as an object
72	interface.	74	oriented interface.
73		75
74	=item * reasonably versatile output formats	76	=item * reasonably versatile output formats
75		77
76	You can choose between the most compact guarenteed single-line format	78	You can choose between the most compact guaranteed-single-line format
77	possible (nice for simple line-based protocols), a pure-ascii format	79	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	80	(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	81	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.	82	stuff). Or you can combine those features in whatever way you like.
81		83
82	=back	84	=back
83		85
84	=cut	86	=cut
85		87
86	package JSON::XS;	88	package JSON::XS;
87		89
88	use strict;	90	use common::sense;
89		91
90	BEGIN {
91	our $VERSION = '1.12';	92	our $VERSION = '4.0';
92	our @ISA = qw(Exporter);	93	our @ISA = qw(Exporter);
93		94
94	our @EXPORT = qw(to_json from_json objToJson jsonToObj);	95	our @EXPORT = qw(encode_json decode_json);
95	require Exporter;
96		96
97	require XSLoader;	97	use Exporter;
98	XSLoader::load JSON::XS::, $VERSION;	98	use XSLoader;
99	}	99
		100	use Types::Serialiser ();
100		101
101	=head1 FUNCTIONAL INTERFACE	102	=head1 FUNCTIONAL INTERFACE
102		103
103	The following convinience methods are provided by this module. They are	104	The following convenience methods are provided by this module. They are
104	exported by default:	105	exported by default:
105		106
106	=over 4	107	=over
107		108
108	=item $json_text = to_json $perl_scalar	109	=item $json_text = encode_json $perl_scalar
109		110
110	Converts the given Perl data structure (a simple scalar or a reference to	111	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	112	(that is, the string contains octets only). Croaks on error.
112	octets only). Croaks on error.
113		113
114	This function call is functionally identical to:	114	This function call is functionally identical to:
115		115
116	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	116	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
117		117
118	except being faster.	118	Except being faster.
119		119
120	=item $perl_scalar = from_json $json_text	120	=item $perl_scalar = decode_json $json_text
121		121
122	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	122	The opposite of C<encode_json>: expects a UTF-8 (binary) string and tries
123	parse that as an UTF-8 encoded JSON text, returning the resulting simple	123	to parse that as a UTF-8 encoded JSON text, returning the resulting
124	scalar or reference. Croaks on error.	124	reference. Croaks on error.
125		125
126	This function call is functionally identical to:	126	This function call is functionally identical to:
127		127
128	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	128	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
129		129
130	except being faster.	130	Except being faster.
131		131
132	=back	132	=back
		133
		134
		135	=head1 A FEW NOTES ON UNICODE AND PERL
		136
		137	Since this often leads to confusion, here are a few very clear words on
		138	how Unicode works in Perl, modulo bugs.
		139
		140	=over
		141
		142	=item 1. Perl strings can store characters with ordinal values > 255.
		143
		144	This enables you to store Unicode characters as single characters in a
		145	Perl string - very natural.
		146
		147	=item 2. Perl does I<not> associate an encoding with your strings.
		148
		149	... until you force it to, e.g. when matching it against a regex, or
		150	printing the scalar to a file, in which case Perl either interprets your
		151	string as locale-encoded text, octets/binary, or as Unicode, depending
		152	on various settings. In no case is an encoding stored together with your
		153	data, it is I<use> that decides encoding, not any magical meta data.
		154
		155	=item 3. The internal utf-8 flag has no meaning with regards to the
		156	encoding of your string.
		157
		158	Just ignore that flag unless you debug a Perl bug, a module written in
		159	XS or want to dive into the internals of perl. Otherwise it will only
		160	confuse you, as, despite the name, it says nothing about how your string
		161	is encoded. You can have Unicode strings with that flag set, with that
		162	flag clear, and you can have binary data with that flag set and that flag
		163	clear. Other possibilities exist, too.
		164
		165	If you didn't know about that flag, just the better, pretend it doesn't
		166	exist.
		167
		168	=item 4. A "Unicode String" is simply a string where each character can be
		169	validly interpreted as a Unicode code point.
		170
		171	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		172	Unicode string encoded in UTF-8, giving you a binary string.
		173
		174	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		175
		176	It's a fact. Learn to live with it.
		177
		178	=back
		179
		180	I hope this helps :)
133		181
134		182
135	=head1 OBJECT-ORIENTED INTERFACE	183	=head1 OBJECT-ORIENTED INTERFACE
136		184
137	The object oriented interface lets you configure your own encoding or	185	The object oriented interface lets you configure your own encoding or
138	decoding style, within the limits of supported formats.	186	decoding style, within the limits of supported formats.
139		187
140	=over 4	188	=over
141		189
142	=item $json = new JSON::XS	190	=item $json = new JSON::XS
143		191
144	Creates a new JSON::XS object that can be used to de/encode JSON	192	Creates a new JSON::XS object that can be used to de/encode JSON
145	strings. All boolean flags described below are by default I<disabled>.	193	strings. All boolean flags described below are by default I<disabled>
		194	(with the exception of C<allow_nonref>, which defaults to I<enabled> since
		195	version C<4.0>).
146		196
147	The mutators for flags all return the JSON object again and thus calls can	197	The mutators for flags all return the JSON object again and thus calls can
148	be chained:	198	be chained:
149		199
150	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	200	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
151	=> {"a": [1, 2]}	201	=> {"a": [1, 2]}
152		202
153	=item $json = $json->ascii ([$enable])	203	=item $json = $json->ascii ([$enable])
154		204
		205	=item $enabled = $json->get_ascii
		206
155	If C<$enable> is true (or missing), then the C<encode> method will not	207	If C<$enable> is true (or missing), then the C<encode> method will not
156	generate characters outside the code range C<0..127> (which is ASCII). Any	208	generate characters outside the code range C<0..127> (which is ASCII). Any
157	unicode characters outside that range will be escaped using either a	209	Unicode characters outside that range will be escaped using either a
158	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,	210	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
159	as per RFC4627.	211	as per RFC4627. The resulting encoded JSON text can be treated as a native
		212	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		213	or any other superset of ASCII.
160		214
161	If C<$enable> is false, then the C<encode> method will not escape Unicode	215	If C<$enable> is false, then the C<encode> method will not escape Unicode
162	characters unless required by the JSON syntax. This results in a faster	216	characters unless required by the JSON syntax or other flags. This results
163	and more compact format.	217	in a faster and more compact format.
		218
		219	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		220	document.
		221
		222	The main use for this flag is to produce JSON texts that can be
		223	transmitted over a 7-bit channel, as the encoded JSON texts will not
		224	contain any 8 bit characters.
164		225
165	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	226	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
166	=> ["\ud801\udc01"]	227	=> ["\ud801\udc01"]
167		228
		229	=item $json = $json->latin1 ([$enable])
		230
		231	=item $enabled = $json->get_latin1
		232
		233	If C<$enable> is true (or missing), then the C<encode> method will encode
		234	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		235	outside the code range C<0..255>. The resulting string can be treated as a
		236	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		237	will not be affected in any way by this flag, as C<decode> by default
		238	expects Unicode, which is a strict superset of latin1.
		239
		240	If C<$enable> is false, then the C<encode> method will not escape Unicode
		241	characters unless required by the JSON syntax or other flags.
		242
		243	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		244	document.
		245
		246	The main use for this flag is efficiently encoding binary data as JSON
		247	text, as most octets will not be escaped, resulting in a smaller encoded
		248	size. The disadvantage is that the resulting JSON text is encoded
		249	in latin1 (and must correctly be treated as such when storing and
		250	transferring), a rare encoding for JSON. It is therefore most useful when
		251	you want to store data structures known to contain binary data efficiently
		252	in files or databases, not when talking to other JSON encoders/decoders.
		253
		254	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		255	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
		256
168	=item $json = $json->utf8 ([$enable])	257	=item $json = $json->utf8 ([$enable])
		258
		259	=item $enabled = $json->get_utf8
169		260
170	If C<$enable> is true (or missing), then the C<encode> method will encode	261	If C<$enable> is true (or missing), then the C<encode> method will encode
171	the JSON result into UTF-8, as required by many protocols, while the	262	the JSON result into UTF-8, as required by many protocols, while the
172	C<decode> method expects to be handled an UTF-8-encoded string. Please	263	C<decode> method expects to be handed a UTF-8-encoded string. Please
173	note that UTF-8-encoded strings do not contain any characters outside the	264	note that UTF-8-encoded strings do not contain any characters outside the
174	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	265	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
175	versions, enabling this option might enable autodetection of the UTF-16	266	versions, enabling this option might enable autodetection of the UTF-16
176	and UTF-32 encoding families, as described in RFC4627.	267	and UTF-32 encoding families, as described in RFC4627.
177		268
178	If C<$enable> is false, then the C<encode> method will return the JSON	269	If C<$enable> is false, then the C<encode> method will return the JSON
179	string as a (non-encoded) unicode string, while C<decode> expects thus a	270	string as a (non-encoded) Unicode string, while C<decode> expects thus a
180	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	271	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
181	to be done yourself, e.g. using the Encode module.	272	to be done yourself, e.g. using the Encode module.
		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
182		276
183	Example, output UTF-16BE-encoded JSON:	277	Example, output UTF-16BE-encoded JSON:
184		278
185	use Encode;	279	use Encode;
186	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	280	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
207	]	301	]
208	}	302	}
209		303
210	=item $json = $json->indent ([$enable])	304	=item $json = $json->indent ([$enable])
211		305
		306	=item $enabled = $json->get_indent
		307
212	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	308	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
213	format as output, putting every array member or object/hash key-value pair	309	format as output, putting every array member or object/hash key-value pair
214	into its own line, identing them properly.	310	into its own line, indenting them properly.
215		311
216	If C<$enable> is false, no newlines or indenting will be produced, and the	312	If C<$enable> is false, no newlines or indenting will be produced, and the
217	resulting JSON text is guarenteed not to contain any C<newlines>.	313	resulting JSON text is guaranteed not to contain any C<newlines>.
218		314
219	This setting has no effect when decoding JSON texts.	315	This setting has no effect when decoding JSON texts.
220		316
221	=item $json = $json->space_before ([$enable])	317	=item $json = $json->space_before ([$enable])
		318
		319	=item $enabled = $json->get_space_before
222		320
223	If C<$enable> is true (or missing), then the C<encode> method will add an extra	321	If C<$enable> is true (or missing), then the C<encode> method will add an extra
224	optional space before the C<:> separating keys from values in JSON objects.	322	optional space before the C<:> separating keys from values in JSON objects.
225		323
226	If C<$enable> is false, then the C<encode> method will not add any extra	324	If C<$enable> is false, then the C<encode> method will not add any extra
…		…
232	Example, space_before enabled, space_after and indent disabled:	330	Example, space_before enabled, space_after and indent disabled:
233		331
234	{"key" :"value"}	332	{"key" :"value"}
235		333
236	=item $json = $json->space_after ([$enable])	334	=item $json = $json->space_after ([$enable])
		335
		336	=item $enabled = $json->get_space_after
237		337
238	If C<$enable> is true (or missing), then the C<encode> method will add an extra	338	If C<$enable> is true (or missing), then the C<encode> method will add an extra
239	optional space after the C<:> separating keys from values in JSON objects	339	optional space after the C<:> separating keys from values in JSON objects
240	and extra whitespace after the C<,> separating key-value pairs and array	340	and extra whitespace after the C<,> separating key-value pairs and array
241	members.	341	members.
…		…
247		347
248	Example, space_before and indent disabled, space_after enabled:	348	Example, space_before and indent disabled, space_after enabled:
249		349
250	{"key": "value"}	350	{"key": "value"}
251		351
		352	=item $json = $json->relaxed ([$enable])
		353
		354	=item $enabled = $json->get_relaxed
		355
		356	If C<$enable> is true (or missing), then C<decode> will accept some
		357	extensions to normal JSON syntax (see below). C<encode> will not be
		358	affected in any way. I<Be aware that this option makes you accept invalid
		359	JSON texts as if they were valid!>. I suggest only to use this option to
		360	parse application-specific files written by humans (configuration files,
		361	resource files etc.)
		362
		363	If C<$enable> is false (the default), then C<decode> will only accept
		364	valid JSON texts.
		365
		366	Currently accepted extensions are:
		367
		368	=over
		369
		370	=item * list items can have an end-comma
		371
		372	JSON I<separates> array elements and key-value pairs with commas. This
		373	can be annoying if you write JSON texts manually and want to be able to
		374	quickly append elements, so this extension accepts comma at the end of
		375	such items not just between them:
		376
		377	[
		378	1,
		379	2, <- this comma not normally allowed
		380	]
		381	{
		382	"k1": "v1",
		383	"k2": "v2", <- this comma not normally allowed
		384	}
		385
		386	=item * shell-style '#'-comments
		387
		388	Whenever JSON allows whitespace, shell-style comments are additionally
		389	allowed. They are terminated by the first carriage-return or line-feed
		390	character, after which more white-space and comments are allowed.
		391
		392	[
		393	1, # this comment not allowed in JSON
		394	# neither this one...
		395	]
		396
		397	=item * literal ASCII TAB characters in strings
		398
		399	Literal ASCII TAB characters are now allowed in strings (and treated as
		400	C<\t>).
		401
		402	[
		403	"Hello\tWorld",
		404	"Hello<TAB>World", # literal <TAB> would not normally be allowed
		405	]
		406
		407	=back
		408
252	=item $json = $json->canonical ([$enable])	409	=item $json = $json->canonical ([$enable])
		410
		411	=item $enabled = $json->get_canonical
253		412
254	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	413	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
255	by sorting their keys. This is adding a comparatively high overhead.	414	by sorting their keys. This is adding a comparatively high overhead.
256		415
257	If C<$enable> is false, then the C<encode> method will output key-value	416	If C<$enable> is false, then the C<encode> method will output key-value
258	pairs in the order Perl stores them (which will likely change between runs	417	pairs in the order Perl stores them (which will likely change between runs
259	of the same script).	418	of the same script, and can change even within the same run from 5.18
		419	onwards).
260		420
261	This option is useful if you want the same data structure to be encoded as	421	This option is useful if you want the same data structure to be encoded as
262	the same JSON text (given the same overall settings). If it is disabled,	422	the same JSON text (given the same overall settings). If it is disabled,
263	the same hash migh be encoded differently even if contains the same data,	423	the same hash might be encoded differently even if contains the same data,
264	as key-value pairs have no inherent ordering in Perl.	424	as key-value pairs have no inherent ordering in Perl.
265		425
266	This setting has no effect when decoding JSON texts.	426	This setting has no effect when decoding JSON texts.
267		427
		428	This setting has currently no effect on tied hashes.
		429
268	=item $json = $json->allow_nonref ([$enable])	430	=item $json = $json->allow_nonref ([$enable])
		431
		432	=item $enabled = $json->get_allow_nonref
		433
		434	Unlike other boolean options, this opotion is enabled by default beginning
		435	with version C<4.0>. See L<SECURITY CONSIDERATIONS> for the gory details.
269		436
270	If C<$enable> is true (or missing), then the C<encode> method can convert a	437	If C<$enable> is true (or missing), then the C<encode> method can convert a
271	non-reference into its corresponding string, number or null JSON value,	438	non-reference into its corresponding string, number or null JSON value,
272	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	439	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
273	values instead of croaking.	440	values instead of croaking.
…		…
275	If C<$enable> is false, then the C<encode> method will croak if it isn't	442	If C<$enable> is false, then the C<encode> method will croak if it isn't
276	passed an arrayref or hashref, as JSON texts must either be an object	443	passed an arrayref or hashref, as JSON texts must either be an object
277	or array. Likewise, C<decode> will croak if given something that is not a	444	or array. Likewise, C<decode> will croak if given something that is not a
278	JSON object or array.	445	JSON object or array.
279		446
280	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,	447	Example, encode a Perl scalar as JSON value without enabled C<allow_nonref>,
281	resulting in an invalid JSON text:	448	resulting in an error:
282		449
283	JSON::XS->new->allow_nonref->encode ("Hello, World!")	450	JSON::XS->new->allow_nonref (0)->encode ("Hello, World!")
284	=> "Hello, World!"	451	=> hash- or arrayref expected...
		452
		453	=item $json = $json->allow_unknown ([$enable])
		454
		455	=item $enabled = $json->get_allow_unknown
		456
		457	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		458	exception when it encounters values it cannot represent in JSON (for
		459	example, filehandles) but instead will encode a JSON C<null> value. Note
		460	that blessed objects are not included here and are handled separately by
		461	c<allow_nonref>.
		462
		463	If C<$enable> is false (the default), then C<encode> will throw an
		464	exception when it encounters anything it cannot encode as JSON.
		465
		466	This option does not affect C<decode> in any way, and it is recommended to
		467	leave it off unless you know your communications partner.
		468
		469	=item $json = $json->allow_blessed ([$enable])
		470
		471	=item $enabled = $json->get_allow_blessed
		472
		473	See L<OBJECT SERIALISATION> for details.
		474
		475	If C<$enable> is true (or missing), then the C<encode> method will not
		476	barf when it encounters a blessed reference that it cannot convert
		477	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
		478
		479	If C<$enable> is false (the default), then C<encode> will throw an
		480	exception when it encounters a blessed object that it cannot convert
		481	otherwise.
		482
		483	This setting has no effect on C<decode>.
		484
		485	=item $json = $json->convert_blessed ([$enable])
		486
		487	=item $enabled = $json->get_convert_blessed
		488
		489	See L<OBJECT SERIALISATION> for details.
		490
		491	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		492	blessed object, will check for the availability of the C<TO_JSON> method
		493	on the object's class. If found, it will be called in scalar context and
		494	the resulting scalar will be encoded instead of the object.
		495
		496	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		497	returns other blessed objects, those will be handled in the same
		498	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		499	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		500	methods called by the Perl core (== not by the user of the object) are
		501	usually in upper case letters and to avoid collisions with any C<to_json>
		502	function or method.
		503
		504	If C<$enable> is false (the default), then C<encode> will not consider
		505	this type of conversion.
		506
		507	This setting has no effect on C<decode>.
		508
		509	=item $json = $json->allow_tags ([$enable])
		510
		511	=item $enabled = $json->get_allow_tags
		512
		513	See L<OBJECT SERIALISATION> for details.
		514
		515	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		516	blessed object, will check for the availability of the C<FREEZE> method on
		517	the object's class. If found, it will be used to serialise the object into
		518	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		519
		520	It also causes C<decode> to parse such tagged JSON values and deserialise
		521	them via a call to the C<THAW> method.
		522
		523	If C<$enable> is false (the default), then C<encode> will not consider
		524	this type of conversion, and tagged JSON values will cause a parse error
		525	in C<decode>, as if tags were not part of the grammar.
		526
		527	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		528
		529	When C<$coderef> is specified, it will be called from C<decode> each
		530	time it decodes a JSON object. The only argument is a reference to
		531	the newly-created hash. If the code reference returns a single scalar
		532	(which need not be a reference), this value (or rather a copy of it) is
		533	inserted into the deserialised data structure. If it returns an empty
		534	list (NOTE: I<not> C<undef>, which is a valid scalar), the original
		535	deserialised hash will be inserted. This setting can slow down decoding
		536	considerably.
		537
		538	When C<$coderef> is omitted or undefined, any existing callback will
		539	be removed and C<decode> will not change the deserialised hash in any
		540	way.
		541
		542	Example, convert all JSON objects into the integer 5:
		543
		544	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		545	# returns [5]
		546	$js->decode ('[{}]')
		547	# throw an exception because allow_nonref is not enabled
		548	# so a lone 5 is not allowed.
		549	$js->decode ('{"a":1, "b":2}');
		550
		551	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		552
		553	Works remotely similar to C<filter_json_object>, but is only called for
		554	JSON objects having a single key named C<$key>.
		555
		556	This C<$coderef> is called before the one specified via
		557	C<filter_json_object>, if any. It gets passed the single value in the JSON
		558	object. If it returns a single value, it will be inserted into the data
		559	structure. If it returns nothing (not even C<undef> but the empty list),
		560	the callback from C<filter_json_object> will be called next, as if no
		561	single-key callback were specified.
		562
		563	If C<$coderef> is omitted or undefined, the corresponding callback will be
		564	disabled. There can only ever be one callback for a given key.
		565
		566	As this callback gets called less often then the C<filter_json_object>
		567	one, decoding speed will not usually suffer as much. Therefore, single-key
		568	objects make excellent targets to serialise Perl objects into, especially
		569	as single-key JSON objects are as close to the type-tagged value concept
		570	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		571	support this in any way, so you need to make sure your data never looks
		572	like a serialised Perl hash.
		573
		574	Typical names for the single object key are C<__class_whatever__>, or
		575	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		576	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		577	with real hashes.
		578
		579	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		580	into the corresponding C<< $WIDGET{<id>} >> object:
		581
		582	# return whatever is in $WIDGET{5}:
		583	JSON::XS
		584	->new
		585	->filter_json_single_key_object (__widget__ => sub {
		586	$WIDGET{ $_[0] }
		587	})
		588	->decode ('{"__widget__": 5')
		589
		590	# this can be used with a TO_JSON method in some "widget" class
		591	# for serialisation to json:
		592	sub WidgetBase::TO_JSON {
		593	my ($self) = @_;
		594
		595	unless ($self->{id}) {
		596	$self->{id} = ..get..some..id..;
		597	$WIDGET{$self->{id}} = $self;
		598	}
		599
		600	{ __widget__ => $self->{id} }
		601	}
285		602
286	=item $json = $json->shrink ([$enable])	603	=item $json = $json->shrink ([$enable])
		604
		605	=item $enabled = $json->get_shrink
287		606
288	Perl usually over-allocates memory a bit when allocating space for	607	Perl usually over-allocates memory a bit when allocating space for
289	strings. This flag optionally resizes strings generated by either	608	strings. This flag optionally resizes strings generated by either
290	C<encode> or C<decode> to their minimum size possible. This can save	609	C<encode> or C<decode> to their minimum size possible. This can save
291	memory when your JSON texts are either very very long or you have many	610	memory when your JSON texts are either very very long or you have many
…		…
309	strings that look like integers or floats into integers or floats	628	strings that look like integers or floats into integers or floats
310	internally (there is no difference on the Perl level), saving space.	629	internally (there is no difference on the Perl level), saving space.
311		630
312	=item $json = $json->max_depth ([$maximum_nesting_depth])	631	=item $json = $json->max_depth ([$maximum_nesting_depth])
313		632
		633	=item $max_depth = $json->get_max_depth
		634
314	Sets the maximum nesting level (default C<512>) accepted while encoding	635	Sets the maximum nesting level (default C<512>) accepted while encoding
315	or decoding. If the JSON text or Perl data structure has an equal or	636	or decoding. If a higher nesting level is detected in JSON text or a Perl
316	higher nesting level then this limit, then the encoder and decoder will	637	data structure, then the encoder and decoder will stop and croak at that
317	stop and croak at that point.	638	point.
318		639
319	Nesting level is defined by number of hash- or arrayrefs that the encoder	640	Nesting level is defined by number of hash- or arrayrefs that the encoder
320	needs to traverse to reach a given point or the number of C<{> or C<[>	641	needs to traverse to reach a given point or the number of C<{> or C<[>
321	characters without their matching closing parenthesis crossed to reach a	642	characters without their matching closing parenthesis crossed to reach a
322	given character in a string.	643	given character in a string.
323		644
324	Setting the maximum depth to one disallows any nesting, so that ensures	645	Setting the maximum depth to one disallows any nesting, so that ensures
325	that the object is only a single hash/object or array.	646	that the object is only a single hash/object or array.
326		647
327	The argument to C<max_depth> will be rounded up to the next nearest power	648	If no argument is given, the highest possible setting will be used, which
328	of two.	649	is rarely useful.
		650
		651	Note that nesting is implemented by recursion in C. The default value has
		652	been chosen to be as large as typical operating systems allow without
		653	crashing.
329		654
330	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	655	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
331		656
		657	=item $json = $json->max_size ([$maximum_string_size])
		658
		659	=item $max_size = $json->get_max_size
		660
		661	Set the maximum length a JSON text may have (in bytes) where decoding is
		662	being attempted. The default is C<0>, meaning no limit. When C<decode>
		663	is called on a string that is longer then this many bytes, it will not
		664	attempt to decode the string but throw an exception. This setting has no
		665	effect on C<encode> (yet).
		666
		667	If no argument is given, the limit check will be deactivated (same as when
		668	C<0> is specified).
		669
		670	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		671
332	=item $json_text = $json->encode ($perl_scalar)	672	=item $json_text = $json->encode ($perl_scalar)
333		673
334	Converts the given Perl data structure (a simple scalar or a reference	674	Converts the given Perl value or data structure to its JSON
335	to a hash or array) to its JSON representation. Simple scalars will be	675	representation. Croaks on error.
336	converted into JSON string or number sequences, while references to arrays
337	become JSON arrays and references to hashes become JSON objects. Undefined
338	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
339	nor C<false> values will be generated.
340		676
341	=item $perl_scalar = $json->decode ($json_text)	677	=item $perl_scalar = $json->decode ($json_text)
342		678
343	The opposite of C<encode>: expects a JSON text and tries to parse it,	679	The opposite of C<encode>: expects a JSON text and tries to parse it,
344	returning the resulting simple scalar or reference. Croaks on error.	680	returning the resulting simple scalar or reference. Croaks on error.
345		681
346	JSON numbers and strings become simple Perl scalars. JSON arrays become	682	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
347	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	683
348	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	684	This works like the C<decode> method, but instead of raising an exception
		685	when there is trailing garbage after the first JSON object, it will
		686	silently stop parsing there and return the number of characters consumed
		687	so far.
		688
		689	This is useful if your JSON texts are not delimited by an outer protocol
		690	and you need to know where the JSON text ends.
		691
		692	JSON::XS->new->decode_prefix ("[1] the tail")
		693	=> ([1], 3)
349		694
350	=back	695	=back
		696
		697
		698	=head1 INCREMENTAL PARSING
		699
		700	In some cases, there is the need for incremental parsing of JSON
		701	texts. While this module always has to keep both JSON text and resulting
		702	Perl data structure in memory at one time, it does allow you to parse a
		703	JSON stream incrementally. It does so by accumulating text until it has
		704	a full JSON object, which it then can decode. This process is similar to
		705	using C<decode_prefix> to see if a full JSON object is available, but
		706	is much more efficient (and can be implemented with a minimum of method
		707	calls).
		708
		709	JSON::XS will only attempt to parse the JSON text once it is sure it
		710	has enough text to get a decisive result, using a very simple but
		711	truly incremental parser. This means that it sometimes won't stop as
		712	early as the full parser, for example, it doesn't detect mismatched
		713	parentheses. The only thing it guarantees is that it starts decoding as
		714	soon as a syntactically valid JSON text has been seen. This means you need
		715	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		716	parsing in the presence if syntax errors.
		717
		718	The following methods implement this incremental parser.
		719
		720	=over
		721
		722	=item [void, scalar or list context] = $json->incr_parse ([$string])
		723
		724	This is the central parsing function. It can both append new text and
		725	extract objects from the stream accumulated so far (both of these
		726	functions are optional).
		727
		728	If C<$string> is given, then this string is appended to the already
		729	existing JSON fragment stored in the C<$json> object.
		730
		731	After that, if the function is called in void context, it will simply
		732	return without doing anything further. This can be used to add more text
		733	in as many chunks as you want.
		734
		735	If the method is called in scalar context, then it will try to extract
		736	exactly I<one> JSON object. If that is successful, it will return this
		737	object, otherwise it will return C<undef>. If there is a parse error,
		738	this method will croak just as C<decode> would do (one can then use
		739	C<incr_skip> to skip the erroneous part). This is the most common way of
		740	using the method.
		741
		742	And finally, in list context, it will try to extract as many objects
		743	from the stream as it can find and return them, or the empty list
		744	otherwise. For this to work, there must be no separators (other than
		745	whitespace) between the JSON objects or arrays, instead they must be
		746	concatenated back-to-back. If an error occurs, an exception will be
		747	raised as in the scalar context case. Note that in this case, any
		748	previously-parsed JSON texts will be lost.
		749
		750	Example: Parse some JSON arrays/objects in a given string and return
		751	them.
		752
		753	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		754
		755	=item $lvalue_string = $json->incr_text
		756
		757	This method returns the currently stored JSON fragment as an lvalue, that
		758	is, you can manipulate it. This I<only> works when a preceding call to
		759	C<incr_parse> in I<scalar context> successfully returned an object. Under
		760	all other circumstances you must not call this function (I mean it.
		761	although in simple tests it might actually work, it I<will> fail under
		762	real world conditions). As a special exception, you can also call this
		763	method before having parsed anything.
		764
		765	That means you can only use this function to look at or manipulate text
		766	before or after complete JSON objects, not while the parser is in the
		767	middle of parsing a JSON object.
		768
		769	This function is useful in two cases: a) finding the trailing text after a
		770	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		771	(such as commas).
		772
		773	=item $json->incr_skip
		774
		775	This will reset the state of the incremental parser and will remove
		776	the parsed text from the input buffer so far. This is useful after
		777	C<incr_parse> died, in which case the input buffer and incremental parser
		778	state is left unchanged, to skip the text parsed so far and to reset the
		779	parse state.
		780
		781	The difference to C<incr_reset> is that only text until the parse error
		782	occurred is removed.
		783
		784	=item $json->incr_reset
		785
		786	This completely resets the incremental parser, that is, after this call,
		787	it will be as if the parser had never parsed anything.
		788
		789	This is useful if you want to repeatedly parse JSON objects and want to
		790	ignore any trailing data, which means you have to reset the parser after
		791	each successful decode.
		792
		793	=back
		794
		795	=head2 LIMITATIONS
		796
		797	The incremental parser is a non-exact parser: it works by gathering as
		798	much text as possible that I<could> be a valid JSON text, followed by
		799	trying to decode it.
		800
		801	That means it sometimes needs to read more data than strictly necessary to
		802	diagnose an invalid JSON text. For example, after parsing the following
		803	fragment, the parser I<could> stop with an error, as this fragment
		804	I<cannot> be the beginning of a valid JSON text:
		805
		806	[,
		807
		808	In reality, hopwever, the parser might continue to read data until a
		809	length limit is exceeded or it finds a closing bracket.
		810
		811	=head2 EXAMPLES
		812
		813	Some examples will make all this clearer. First, a simple example that
		814	works similarly to C<decode_prefix>: We want to decode the JSON object at
		815	the start of a string and identify the portion after the JSON object:
		816
		817	my $text = "[1,2,3] hello";
		818
		819	my $json = new JSON::XS;
		820
		821	my $obj = $json->incr_parse ($text)
		822	or die "expected JSON object or array at beginning of string";
		823
		824	my $tail = $json->incr_text;
		825	# $tail now contains " hello"
		826
		827	Easy, isn't it?
		828
		829	Now for a more complicated example: Imagine a hypothetical protocol where
		830	you read some requests from a TCP stream, and each request is a JSON
		831	array, without any separation between them (in fact, it is often useful to
		832	use newlines as "separators", as these get interpreted as whitespace at
		833	the start of the JSON text, which makes it possible to test said protocol
		834	with C<telnet>...).
		835
		836	Here is how you'd do it (it is trivial to write this in an event-based
		837	manner):
		838
		839	my $json = new JSON::XS;
		840
		841	# read some data from the socket
		842	while (sysread $socket, my $buf, 4096) {
		843
		844	# split and decode as many requests as possible
		845	for my $request ($json->incr_parse ($buf)) {
		846	# act on the $request
		847	}
		848	}
		849
		850	Another complicated example: Assume you have a string with JSON objects
		851	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		852	[3]>). To parse them, we have to skip the commas between the JSON texts,
		853	and here is where the lvalue-ness of C<incr_text> comes in useful:
		854
		855	my $text = "[1],[2], [3]";
		856	my $json = new JSON::XS;
		857
		858	# void context, so no parsing done
		859	$json->incr_parse ($text);
		860
		861	# now extract as many objects as possible. note the
		862	# use of scalar context so incr_text can be called.
		863	while (my $obj = $json->incr_parse) {
		864	# do something with $obj
		865
		866	# now skip the optional comma
		867	$json->incr_text =~ s/^ \s* , //x;
		868	}
		869
		870	Now lets go for a very complex example: Assume that you have a gigantic
		871	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		872	but you cannot load it into memory fully (this has actually happened in
		873	the real world :).
		874
		875	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		876	can still help you: You implement a (very simple) array parser and let
		877	JSON decode the array elements, which are all full JSON objects on their
		878	own (this wouldn't work if the array elements could be JSON numbers, for
		879	example):
		880
		881	my $json = new JSON::XS;
		882
		883	# open the monster
		884	open my $fh, "<bigfile.json"
		885	or die "bigfile: $!";
		886
		887	# first parse the initial "["
		888	for (;;) {
		889	sysread $fh, my $buf, 65536
		890	or die "read error: $!";
		891	$json->incr_parse ($buf); # void context, so no parsing
		892
		893	# Exit the loop once we found and removed(!) the initial "[".
		894	# In essence, we are (ab-)using the $json object as a simple scalar
		895	# we append data to.
		896	last if $json->incr_text =~ s/^ \s* \[ //x;
		897	}
		898
		899	# now we have the skipped the initial "[", so continue
		900	# parsing all the elements.
		901	for (;;) {
		902	# in this loop we read data until we got a single JSON object
		903	for (;;) {
		904	if (my $obj = $json->incr_parse) {
		905	# do something with $obj
		906	last;
		907	}
		908
		909	# add more data
		910	sysread $fh, my $buf, 65536
		911	or die "read error: $!";
		912	$json->incr_parse ($buf); # void context, so no parsing
		913	}
		914
		915	# in this loop we read data until we either found and parsed the
		916	# separating "," between elements, or the final "]"
		917	for (;;) {
		918	# first skip whitespace
		919	$json->incr_text =~ s/^\s*//;
		920
		921	# if we find "]", we are done
		922	if ($json->incr_text =~ s/^\]//) {
		923	print "finished.\n";
		924	exit;
		925	}
		926
		927	# if we find ",", we can continue with the next element
		928	if ($json->incr_text =~ s/^,//) {
		929	last;
		930	}
		931
		932	# if we find anything else, we have a parse error!
		933	if (length $json->incr_text) {
		934	die "parse error near ", $json->incr_text;
		935	}
		936
		937	# else add more data
		938	sysread $fh, my $buf, 65536
		939	or die "read error: $!";
		940	$json->incr_parse ($buf); # void context, so no parsing
		941	}
		942
		943	This is a complex example, but most of the complexity comes from the fact
		944	that we are trying to be correct (bear with me if I am wrong, I never ran
		945	the above example :).
		946
351		947
352		948
353	=head1 MAPPING	949	=head1 MAPPING
354		950
355	This section describes how JSON::XS maps Perl values to JSON values and	951	This section describes how JSON::XS maps Perl values to JSON values and
356	vice versa. These mappings are designed to "do the right thing" in most	952	vice versa. These mappings are designed to "do the right thing" in most
357	circumstances automatically, preserving round-tripping characteristics	953	circumstances automatically, preserving round-tripping characteristics
358	(what you put in comes out as something equivalent).	954	(what you put in comes out as something equivalent).
359		955
360	For the more enlightened: note that in the following descriptions,	956	For the more enlightened: note that in the following descriptions,
361	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	957	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
362	refers to the abstract Perl language itself.	958	refers to the abstract Perl language itself.
363		959
		960
364	=head2 JSON -> PERL	961	=head2 JSON -> PERL
365		962
366	=over 4	963	=over
367		964
368	=item object	965	=item object
369		966
370	A JSON object becomes a reference to a hash in Perl. No ordering of object	967	A JSON object becomes a reference to a hash in Perl. No ordering of object
371	keys is preserved (JSON does not preserver object key ordering itself).	968	keys is preserved (JSON does not preserve object key ordering itself).
372		969
373	=item array	970	=item array
374		971
375	A JSON array becomes a reference to an array in Perl.	972	A JSON array becomes a reference to an array in Perl.
376		973
…		…
380	are represented by the same codepoints in the Perl string, so no manual	977	are represented by the same codepoints in the Perl string, so no manual
381	decoding is necessary.	978	decoding is necessary.
382		979
383	=item number	980	=item number
384		981
385	A JSON number becomes either an integer or numeric (floating point)	982	A JSON number becomes either an integer, numeric (floating point) or
386	scalar in perl, depending on its range and any fractional parts. On the	983	string scalar in perl, depending on its range and any fractional parts. On
387	Perl level, there is no difference between those as Perl handles all the	984	the Perl level, there is no difference between those as Perl handles all
388	conversion details, but an integer may take slightly less memory and might	985	the conversion details, but an integer may take slightly less memory and
389	represent more values exactly than (floating point) numbers.	986	might represent more values exactly than floating point numbers.
		987
		988	If the number consists of digits only, JSON::XS will try to represent
		989	it as an integer value. If that fails, it will try to represent it as
		990	a numeric (floating point) value if that is possible without loss of
		991	precision. Otherwise it will preserve the number as a string value (in
		992	which case you lose roundtripping ability, as the JSON number will be
		993	re-encoded to a JSON string).
		994
		995	Numbers containing a fractional or exponential part will always be
		996	represented as numeric (floating point) values, possibly at a loss of
		997	precision (in which case you might lose perfect roundtripping ability, but
		998	the JSON number will still be re-encoded as a JSON number).
		999
		1000	Note that precision is not accuracy - binary floating point values cannot
		1001	represent most decimal fractions exactly, and when converting from and to
		1002	floating point, JSON::XS only guarantees precision up to but not including
		1003	the least significant bit.
390		1004
391	=item true, false	1005	=item true, false
392		1006
393	These JSON atoms become C<0>, C<1>, respectively. Information is lost in	1007	These JSON atoms become C<Types::Serialiser::true> and
394	this process. Future versions might represent those values differently,	1008	C<Types::Serialiser::false>, respectively. They are overloaded to act
395	but they will be guarenteed to act like these integers would normally in	1009	almost exactly like the numbers C<1> and C<0>. You can check whether
396	Perl.	1010	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1011	function (after C<use Types::Serialier>, of course).
397		1012
398	=item null	1013	=item null
399		1014
400	A JSON null atom becomes C<undef> in Perl.	1015	A JSON null atom becomes C<undef> in Perl.
401		1016
		1017	=item shell-style comments (C<< # I<text> >>)
		1018
		1019	As a nonstandard extension to the JSON syntax that is enabled by the
		1020	C<relaxed> setting, shell-style comments are allowed. They can start
		1021	anywhere outside strings and go till the end of the line.
		1022
		1023	=item tagged values (C<< (I<tag>)I<value> >>).
		1024
		1025	Another nonstandard extension to the JSON syntax, enabled with the
		1026	C<allow_tags> setting, are tagged values. In this implementation, the
		1027	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1028	I<value> must be a JSON array encoding optional constructor arguments.
		1029
		1030	See L<OBJECT SERIALISATION>, below, for details.
		1031
402	=back	1032	=back
		1033
403		1034
404	=head2 PERL -> JSON	1035	=head2 PERL -> JSON
405		1036
406	The mapping from Perl to JSON is slightly more difficult, as Perl is a	1037	The mapping from Perl to JSON is slightly more difficult, as Perl is a
407	truly typeless language, so we can only guess which JSON type is meant by	1038	truly typeless language, so we can only guess which JSON type is meant by
408	a Perl value.	1039	a Perl value.
409		1040
410	=over 4	1041	=over
411		1042
412	=item hash references	1043	=item hash references
413		1044
414	Perl hash references become JSON objects. As there is no inherent ordering	1045	Perl hash references become JSON objects. As there is no inherent
415	in hash keys (or JSON objects), they will usually be encoded in a	1046	ordering in hash keys (or JSON objects), they will usually be encoded
416	pseudo-random order that can change between runs of the same program but	1047	in a pseudo-random order. JSON::XS can optionally sort the hash keys
417	stays generally the same within a single run of a program. JSON::XS can	1048	(determined by the I<canonical> flag), so the same datastructure will
418	optionally sort the hash keys (determined by the I<canonical> flag), so	1049	serialise to the same JSON text (given same settings and version of
419	the same datastructure will serialise to the same JSON text (given same	1050	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
420	settings and version of JSON::XS), but this incurs a runtime overhead	1051	e.g. when you want to compare some JSON text against another for equality.
421	and is only rarely useful, e.g. when you want to compare some JSON text
422	against another for equality.
423		1052
424	=item array references	1053	=item array references
425		1054
426	Perl array references become JSON arrays.	1055	Perl array references become JSON arrays.
427		1056
428	=item other references	1057	=item other references
429		1058
430	Other unblessed references are generally not allowed and will cause an	1059	Other unblessed references are generally not allowed and will cause an
431	exception to be thrown, except for references to the integers C<0> and	1060	exception to be thrown, except for references to the integers C<0> and
432	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1061	C<1>, which get turned into C<false> and C<true> atoms in JSON.
433	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
434		1062
		1063	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1064	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1065	and C<Types::Serialiser::true> to improve readability.
		1066
		1067	use Types::Serialiser;
435	to_json [\0,JSON::XS::true] # yields [false,true]	1068	encode_json [\0, Types::Serialiser::true] # yields [false,true]
		1069
		1070	=item Types::Serialiser::true, Types::Serialiser::false
		1071
		1072	These special values from the L<Types::Serialiser> module become JSON true
		1073	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1074	directly if you want.
436		1075
437	=item blessed objects	1076	=item blessed objects
438		1077
439	Blessed objects are not allowed. JSON::XS currently tries to encode their	1078	Blessed objects are not directly representable in JSON, but C<JSON::XS>
440	underlying representation (hash- or arrayref), but this behaviour might	1079	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
441	change in future versions.	1080	below, for details.
442		1081
443	=item simple scalars	1082	=item simple scalars
444		1083
445	Simple Perl scalars (any scalar that is not a reference) are the most	1084	Simple Perl scalars (any scalar that is not a reference) are the most
446	difficult objects to encode: JSON::XS will encode undefined scalars as	1085	difficult objects to encode: JSON::XS will encode undefined scalars as
447	JSON null value, scalars that have last been used in a string context	1086	JSON C<null> values, scalars that have last been used in a string context
448	before encoding as JSON strings and anything else as number value:	1087	before encoding as JSON strings, and anything else as number value:
449		1088
450	# dump as number	1089	# dump as number
451	to_json [2] # yields [2]	1090	encode_json [2] # yields [2]
452	to_json [-3.0e17] # yields [-3e+17]	1091	encode_json [-3.0e17] # yields [-3e+17]
453	my $value = 5; to_json [$value] # yields [5]	1092	my $value = 5; encode_json [$value] # yields [5]
454		1093
455	# used as string, so dump as string	1094	# used as string, so dump as string
456	print $value;	1095	print $value;
457	to_json [$value] # yields ["5"]	1096	encode_json [$value] # yields ["5"]
458		1097
459	# undef becomes null	1098	# undef becomes null
460	to_json [undef] # yields [null]	1099	encode_json [undef] # yields [null]
461		1100
462	You can force the type to be a string by stringifying it:	1101	You can force the type to be a JSON string by stringifying it:
463		1102
464	my $x = 3.1; # some variable containing a number	1103	my $x = 3.1; # some variable containing a number
465	"$x"; # stringified	1104	"$x"; # stringified
466	$x .= ""; # another, more awkward way to stringify	1105	$x .= ""; # another, more awkward way to stringify
467	print $x; # perl does it for you, too, quite often	1106	print $x; # perl does it for you, too, quite often
468		1107
469	You can force the type to be a number by numifying it:	1108	You can force the type to be a JSON number by numifying it:
470		1109
471	my $x = "3"; # some variable containing a string	1110	my $x = "3"; # some variable containing a string
472	$x += 0; # numify it, ensuring it will be dumped as a number	1111	$x += 0; # numify it, ensuring it will be dumped as a number
473	$x *= 1; # same thing, the choise is yours.	1112	$x *= 1; # same thing, the choice is yours.
474		1113
475	You can not currently output JSON booleans or force the type in other,	1114	You can not currently force the type in other, less obscure, ways. Tell me
476	less obscure, ways. Tell me if you need this capability.	1115	if you need this capability (but don't forget to explain why it's needed
		1116	:).
		1117
		1118	Note that numerical precision has the same meaning as under Perl (so
		1119	binary to decimal conversion follows the same rules as in Perl, which
		1120	can differ to other languages). Also, your perl interpreter might expose
		1121	extensions to the floating point numbers of your platform, such as
		1122	infinities or NaN's - these cannot be represented in JSON, and it is an
		1123	error to pass those in.
477		1124
478	=back	1125	=back
479		1126
		1127	=head2 OBJECT SERIALISATION
480		1128
481	=head1 COMPARISON	1129	As JSON cannot directly represent Perl objects, you have to choose between
		1130	a pure JSON representation (without the ability to deserialise the object
		1131	automatically again), and a nonstandard extension to the JSON syntax,
		1132	tagged values.
482		1133
483	As already mentioned, this module was created because none of the existing	1134	=head3 SERIALISATION
484	JSON modules could be made to work correctly. First I will describe the
485	problems (or pleasures) I encountered with various existing JSON modules,
486	followed by some benchmark values. JSON::XS was designed not to suffer
487	from any of these problems or limitations.
488		1135
		1136	What happens when C<JSON::XS> encounters a Perl object depends on the
		1137	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
		1138	used in this order:
		1139
489	=over 4	1140	=over
490		1141
491	=item JSON 1.07	1142	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
492		1143
493	Slow (but very portable, as it is written in pure Perl).	1144	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1145	serialisation protocol to create a tagged JSON value, using a nonstandard
		1146	extension to the JSON syntax.
494		1147
495	Undocumented/buggy Unicode handling (how JSON handles unicode values is	1148	This works by invoking the C<FREEZE> method on the object, with the first
496	undocumented. One can get far by feeding it unicode strings and doing	1149	argument being the object to serialise, and the second argument being the
497	en-/decoding oneself, but unicode escapes are not working properly).	1150	constant string C<JSON> to distinguish it from other serialisers.
498		1151
499	No roundtripping (strings get clobbered if they look like numbers, e.g.	1152	The C<FREEZE> method can return any number of values (i.e. zero or
500	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	1153	more). These values and the paclkage/classname of the object will then be
501	decode into the number 2.	1154	encoded as a tagged JSON value in the following format:
502		1155
503	=item JSON::PC 0.01	1156	("classname")[FREEZE return values...]
504		1157
505	Very fast.	1158	e.g.:
506		1159
507	Undocumented/buggy Unicode handling.	1160	("URI")["http://www.google.com/"]
		1161	("MyDate")[2013,10,29]
		1162	("ImageData::JPEG")["Z3...VlCg=="]
508		1163
509	No roundtripping.	1164	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1165	objects C<type> and C<id> members to encode the object:
510		1166
511	Has problems handling many Perl values (e.g. regex results and other magic	1167	sub My::Object::FREEZE {
512	values will make it croak).	1168	my ($self, $serialiser) = @_;
513		1169
514	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1170	($self->{type}, $self->{id})
515	which is not a valid JSON text.	1171	}
516		1172
517	Unmaintained (maintainer unresponsive for many months, bugs are not	1173	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
518	getting fixed).
519		1174
520	=item JSON::Syck 0.21	1175	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1176	context. It must return a single scalar that can be directly encoded into
		1177	JSON. This scalar replaces the object in the JSON text.
521		1178
522	Very buggy (often crashes).	1179	For example, the following C<TO_JSON> method will convert all L<URI>
		1180	objects to JSON strings when serialised. The fatc that these values
		1181	originally were L<URI> objects is lost.
523		1182
524	Very inflexible (no human-readable format supported, format pretty much	1183	sub URI::TO_JSON {
525	undocumented. I need at least a format for easy reading by humans and a	1184	my ($uri) = @_;
526	single-line compact format for use in a protocol, and preferably a way to	1185	$uri->as_string
527	generate ASCII-only JSON texts).	1186	}
528		1187
529	Completely broken (and confusingly documented) Unicode handling (unicode	1188	=item 3. C<allow_blessed> is enabled.
530	escapes are not working properly, you need to set ImplicitUnicode to
531	I<different> values on en- and decoding to get symmetric behaviour).
532		1189
533	No roundtripping (simple cases work, but this depends on wether the scalar	1190	The object will be serialised as a JSON null value.
534	value was used in a numeric context or not).
535		1191
536	Dumping hashes may skip hash values depending on iterator state.	1192	=item 4. none of the above
537		1193
538	Unmaintained (maintainer unresponsive for many months, bugs are not	1194	If none of the settings are enabled or the respective methods are missing,
539	getting fixed).	1195	C<JSON::XS> throws an exception.
540
541	Does not check input for validity (i.e. will accept non-JSON input and
542	return "something" instead of raising an exception. This is a security
543	issue: imagine two banks transfering money between each other using
544	JSON. One bank might parse a given non-JSON request and deduct money,
545	while the other might reject the transaction with a syntax error. While a
546	good protocol will at least recover, that is extra unnecessary work and
547	the transaction will still not succeed).
548
549	=item JSON::DWIW 0.04
550
551	Very fast. Very natural. Very nice.
552
553	Undocumented unicode handling (but the best of the pack. Unicode escapes
554	still don't get parsed properly).
555
556	Very inflexible.
557
558	No roundtripping.
559
560	Does not generate valid JSON texts (key strings are often unquoted, empty keys
561	result in nothing being output)
562
563	Does not check input for validity.
564		1196
565	=back	1197	=back
		1198
		1199	=head3 DESERIALISATION
		1200
		1201	For deserialisation there are only two cases to consider: either
		1202	nonstandard tagging was used, in which case C<allow_tags> decides,
		1203	or objects cannot be automatically be deserialised, in which
		1204	case you can use postprocessing or the C<filter_json_object> or
		1205	C<filter_json_single_key_object> callbacks to get some real objects our of
		1206	your JSON.
		1207
		1208	This section only considers the tagged value case: I a tagged JSON object
		1209	is encountered during decoding and C<allow_tags> is disabled, a parse
		1210	error will result (as if tagged values were not part of the grammar).
		1211
		1212	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1213	of the package/classname used during serialisation (it will not attempt
		1214	to load the package as a Perl module). If there is no such method, the
		1215	decoding will fail with an error.
		1216
		1217	Otherwise, the C<THAW> method is invoked with the classname as first
		1218	argument, the constant string C<JSON> as second argument, and all the
		1219	values from the JSON array (the values originally returned by the
		1220	C<FREEZE> method) as remaining arguments.
		1221
		1222	The method must then return the object. While technically you can return
		1223	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1224	make that work in all cases, so better return an actual blessed reference.
		1225
		1226	As an example, let's implement a C<THAW> function that regenerates the
		1227	C<My::Object> from the C<FREEZE> example earlier:
		1228
		1229	sub My::Object::THAW {
		1230	my ($class, $serialiser, $type, $id) = @_;
		1231
		1232	$class->new (type => $type, id => $id)
		1233	}
		1234
		1235
		1236	=head1 ENCODING/CODESET FLAG NOTES
		1237
		1238	The interested reader might have seen a number of flags that signify
		1239	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1240	some confusion on what these do, so here is a short comparison:
		1241
		1242	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1243	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1244	control whether C<encode> escapes character values outside their respective
		1245	codeset range. Neither of these flags conflict with each other, although
		1246	some combinations make less sense than others.
		1247
		1248	Care has been taken to make all flags symmetrical with respect to
		1249	C<encode> and C<decode>, that is, texts encoded with any combination of
		1250	these flag values will be correctly decoded when the same flags are used
		1251	- in general, if you use different flag settings while encoding vs. when
		1252	decoding you likely have a bug somewhere.
		1253
		1254	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1255	simply an abstract set of character-codepoint pairs, while an encoding
		1256	takes those codepoint numbers and I<encodes> them, in our case into
		1257	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1258	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1259	the same time, which can be confusing.
		1260
		1261	=over
		1262
		1263	=item C<utf8> flag disabled
		1264
		1265	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1266	and expect Unicode strings, that is, characters with high ordinal Unicode
		1267	values (> 255) will be encoded as such characters, and likewise such
		1268	characters are decoded as-is, no changes to them will be done, except
		1269	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1270	respectively (to Perl, these are the same thing in strings unless you do
		1271	funny/weird/dumb stuff).
		1272
		1273	This is useful when you want to do the encoding yourself (e.g. when you
		1274	want to have UTF-16 encoded JSON texts) or when some other layer does
		1275	the encoding for you (for example, when printing to a terminal using a
		1276	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1277	to UTF-8 encode your data first and have Perl encode it another time).
		1278
		1279	=item C<utf8> flag enabled
		1280
		1281	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1282	characters using the corresponding UTF-8 multi-byte sequence, and will
		1283	expect your input strings to be encoded as UTF-8, that is, no "character"
		1284	of the input string must have any value > 255, as UTF-8 does not allow
		1285	that.
		1286
		1287	The C<utf8> flag therefore switches between two modes: disabled means you
		1288	will get a Unicode string in Perl, enabled means you get a UTF-8 encoded
		1289	octet/binary string in Perl.
		1290
		1291	=item C<latin1> or C<ascii> flags enabled
		1292
		1293	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1294	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1295	characters as specified by the C<utf8> flag.
		1296
		1297	If C<utf8> is disabled, then the result is also correctly encoded in those
		1298	character sets (as both are proper subsets of Unicode, meaning that a
		1299	Unicode string with all character values < 256 is the same thing as a
		1300	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1301	the same thing as an ASCII string in Perl).
		1302
		1303	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1304	regardless of these flags, just some more characters will be escaped using
		1305	C<\uXXXX> then before.
		1306
		1307	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1308	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1309	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1310	a subset of Unicode), while ASCII is.
		1311
		1312	Surprisingly, C<decode> will ignore these flags and so treat all input
		1313	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1314	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1315	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1316
		1317	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1318	they only govern when the JSON output engine escapes a character or not.
		1319
		1320	The main use for C<latin1> is to relatively efficiently store binary data
		1321	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1322
		1323	The main use for C<ascii> is to force the output to not contain characters
		1324	with values > 127, which means you can interpret the resulting string
		1325	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1326	8-bit-encoding, and still get the same data structure back. This is useful
		1327	when your channel for JSON transfer is not 8-bit clean or the encoding
		1328	might be mangled in between (e.g. in mail), and works because ASCII is a
		1329	proper subset of most 8-bit and multibyte encodings in use in the world.
		1330
		1331	=back
		1332
		1333
		1334	=head2 JSON and ECMAscript
		1335
		1336	JSON syntax is based on how literals are represented in javascript (the
		1337	not-standardised predecessor of ECMAscript) which is presumably why it is
		1338	called "JavaScript Object Notation".
		1339
		1340	However, JSON is not a subset (and also not a superset of course) of
		1341	ECMAscript (the standard) or javascript (whatever browsers actually
		1342	implement).
		1343
		1344	If you want to use javascript's C<eval> function to "parse" JSON, you
		1345	might run into parse errors for valid JSON texts, or the resulting data
		1346	structure might not be queryable:
		1347
		1348	One of the problems is that U+2028 and U+2029 are valid characters inside
		1349	JSON strings, but are not allowed in ECMAscript string literals, so the
		1350	following Perl fragment will not output something that can be guaranteed
		1351	to be parsable by javascript's C<eval>:
		1352
		1353	use JSON::XS;
		1354
		1355	print encode_json [chr 0x2028];
		1356
		1357	The right fix for this is to use a proper JSON parser in your javascript
		1358	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1359	F<json2.js> parser).
		1360
		1361	If this is not an option, you can, as a stop-gap measure, simply encode to
		1362	ASCII-only JSON:
		1363
		1364	use JSON::XS;
		1365
		1366	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1367
		1368	Note that this will enlarge the resulting JSON text quite a bit if you
		1369	have many non-ASCII characters. You might be tempted to run some regexes
		1370	to only escape U+2028 and U+2029, e.g.:
		1371
		1372	# DO NOT USE THIS!
		1373	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1374	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1375	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1376	print $json;
		1377
		1378	Note that I<this is a bad idea>: the above only works for U+2028 and
		1379	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1380	javascript implementations, however, have issues with other characters as
		1381	well - using C<eval> naively simply I<will> cause problems.
		1382
		1383	Another problem is that some javascript implementations reserve
		1384	some property names for their own purposes (which probably makes
		1385	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1386	C<__proto__> property name for its own purposes.
		1387
		1388	If that is a problem, you could parse try to filter the resulting JSON
		1389	output for these property strings, e.g.:
		1390
		1391	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1392
		1393	This works because C<__proto__> is not valid outside of strings, so every
		1394	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1395
		1396	If you know of other incompatibilities, please let me know.
		1397
		1398
		1399	=head2 JSON and YAML
		1400
		1401	You often hear that JSON is a subset of YAML. This is, however, a mass
		1402	hysteria(*) and very far from the truth (as of the time of this writing),
		1403	so let me state it clearly: I<in general, there is no way to configure
		1404	JSON::XS to output a data structure as valid YAML> that works in all
		1405	cases.
		1406
		1407	If you really must use JSON::XS to generate YAML, you should use this
		1408	algorithm (subject to change in future versions):
		1409
		1410	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1411	my $yaml = $to_yaml->encode ($ref) . "\n";
		1412
		1413	This will I<usually> generate JSON texts that also parse as valid
		1414	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1415	lengths that JSON doesn't have and also has different and incompatible
		1416	unicode character escape syntax, so you should make sure that your hash
		1417	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1418	and that you do not have characters with codepoint values outside the
		1419	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1420	sequences in strings (which JSON::XS does not I<currently> generate, but
		1421	other JSON generators might).
		1422
		1423	There might be other incompatibilities that I am not aware of (or the YAML
		1424	specification has been changed yet again - it does so quite often). In
		1425	general you should not try to generate YAML with a JSON generator or vice
		1426	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1427	high that you will run into severe interoperability problems when you
		1428	least expect it.
		1429
		1430	=over
		1431
		1432	=item (*)
		1433
		1434	I have been pressured multiple times by Brian Ingerson (one of the
		1435	authors of the YAML specification) to remove this paragraph, despite him
		1436	acknowledging that the actual incompatibilities exist. As I was personally
		1437	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1438	educate people about these issues, so others do not run into the same
		1439	problem again and again. After this, Brian called me a (quote)I<complete
		1440	and worthless idiot>(unquote).
		1441
		1442	In my opinion, instead of pressuring and insulting people who actually
		1443	clarify issues with YAML and the wrong statements of some of its
		1444	proponents, I would kindly suggest reading the JSON spec (which is not
		1445	that difficult or long) and finally make YAML compatible to it, and
		1446	educating users about the changes, instead of spreading lies about the
		1447	real compatibility for many I<years> and trying to silence people who
		1448	point out that it isn't true.
		1449
		1450	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1451	though the incompatibilities have been documented (and are known to Brian)
		1452	for many years and the spec makes explicit claims that YAML is a superset
		1453	of JSON. It would be so easy to fix, but apparently, bullying people and
		1454	corrupting userdata is so much easier.
		1455
		1456	=back
		1457
566		1458
567	=head2 SPEED	1459	=head2 SPEED
568		1460
569	It seems that JSON::XS is surprisingly fast, as shown in the following	1461	It seems that JSON::XS is surprisingly fast, as shown in the following
570	tables. They have been generated with the help of the C<eg/bench> program	1462	tables. They have been generated with the help of the C<eg/bench> program
571	in the JSON::XS distribution, to make it easy to compare on your own	1463	in the JSON::XS distribution, to make it easy to compare on your own
572	system.	1464	system.
573		1465
574	First comes a comparison between various modules using a very short JSON	1466	First comes a comparison between various modules using
575	string:	1467	a very short single-line JSON string (also available at
		1468	L<http://dist.schmorp.de/misc/json/short.json>).
576		1469
577	{"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null}	1470	{"method": "handleMessage", "params": ["user1",
		1471	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1472	1, 0]}
578		1473
579	It shows the number of encodes/decodes per second (JSON::XS uses the	1474	It shows the number of encodes/decodes per second (JSON::XS uses
580	functional interface, while JSON::XS/2 uses the OO interface with	1475	the functional interface, while JSON::XS/2 uses the OO interface
581	pretty-printing and hashkey sorting enabled). Higher is better:	1476	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1477	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1478	uses the from_json method). Higher is better:
582		1479
583	module | encode | decode |	1480	module | encode | decode |
584	-----------|------------|------------|	1481	--------------|------------|------------|
585	JSON | 11488.516 | 7823.035 |	1482	JSON::DWIW/DS | 86302.551 | 102300.098 |
586	JSON::DWIW | 94708.054 | 129094.260 |	1483	JSON::DWIW/FJ | 86302.551 | 75983.768 |
587	JSON::PC | 63884.157 | 128528.212 |	1484	JSON::PP | 15827.562 | 6638.658 |
588	JSON::Syck | 34898.677 | 42096.911 |	1485	JSON::Syck | 63358.066 | 47662.545 |
589	JSON::XS | 654027.064 | 396423.669 |	1486	JSON::XS | 511500.488 | 511500.488 |
590	JSON::XS/2 | 371564.190 | 371725.613 |	1487	JSON::XS/2 | 291271.111 | 388361.481 |
		1488	JSON::XS/3 | 361577.931 | 361577.931 |
		1489	Storable | 66788.280 | 265462.278 |
591	-----------+------------+------------+	1490	--------------+------------+------------+
592		1491
593	That is, JSON::XS is more than six times faster than JSON::DWIW on	1492	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
594	encoding, more than three times faster on decoding, and about thirty times	1493	about five times faster on decoding, and over thirty to seventy times
595	faster than JSON, even with pretty-printing and key sorting.	1494	faster than JSON's pure perl implementation. It also compares favourably
		1495	to Storable for small amounts of data.
596		1496
597	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1497	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
598	search API (http://nanoref.com/yahooapis/mgPdGg):	1498	search API (L<http://dist.schmorp.de/misc/json/long.json>).
599		1499
600	module | encode | decode |	1500	module | encode | decode |
601	-----------|------------|------------|	1501	--------------|------------|------------|
602	JSON | 273.023 | 44.674 |	1502	JSON::DWIW/DS | 1647.927 | 2673.916 |
603	JSON::DWIW | 1089.383 | 1145.704 |	1503	JSON::DWIW/FJ | 1630.249 | 2596.128 |
604	JSON::PC | 3097.419 | 2393.921 |	1504	JSON::PP | 400.640 | 62.311 |
605	JSON::Syck | 514.060 | 843.053 |	1505	JSON::Syck | 1481.040 | 1524.869 |
606	JSON::XS | 6479.668 | 3636.364 |	1506	JSON::XS | 20661.596 | 9541.183 |
607	JSON::XS/2 | 3774.221 | 3599.124 |	1507	JSON::XS/2 | 10683.403 | 9416.938 |
		1508	JSON::XS/3 | 20661.596 | 9400.054 |
		1509	Storable | 19765.806 | 10000.725 |
608	-----------+------------+------------+	1510	--------------+------------+------------+
609		1511
610	Again, JSON::XS leads by far.	1512	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1513	decodes a bit faster).
611		1514
612	On large strings containing lots of high unicode characters, some modules	1515	On large strings containing lots of high Unicode characters, some modules
613	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1516	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
614	will be broken due to missing (or wrong) unicode handling. Others refuse	1517	will be broken due to missing (or wrong) Unicode handling. Others refuse
615	to decode or encode properly, so it was impossible to prepare a fair	1518	to decode or encode properly, so it was impossible to prepare a fair
616	comparison table for that case.	1519	comparison table for that case.
617		1520
618		1521
619	=head1 SECURITY CONSIDERATIONS	1522	=head1 SECURITY CONSIDERATIONS
…		…
625	any buffer overflows. Obviously, this module should ensure that and I am	1528	any buffer overflows. Obviously, this module should ensure that and I am
626	trying hard on making that true, but you never know.	1529	trying hard on making that true, but you never know.
627		1530
628	Second, you need to avoid resource-starving attacks. That means you should	1531	Second, you need to avoid resource-starving attacks. That means you should
629	limit the size of JSON texts you accept, or make sure then when your	1532	limit the size of JSON texts you accept, or make sure then when your
630	resources run out, thats just fine (e.g. by using a separate process that	1533	resources run out, that's just fine (e.g. by using a separate process that
631	can crash safely). The size of a JSON text in octets or characters is	1534	can crash safely). The size of a JSON text in octets or characters is
632	usually a good indication of the size of the resources required to decode	1535	usually a good indication of the size of the resources required to decode
633	it into a Perl structure.	1536	it into a Perl structure. While JSON::XS can check the size of the JSON
		1537	text, it might be too late when you already have it in memory, so you
		1538	might want to check the size before you accept the string.
634		1539
635	Third, JSON::XS recurses using the C stack when decoding objects and	1540	Third, JSON::XS recurses using the C stack when decoding objects and
636	arrays. The C stack is a limited resource: for instance, on my amd64	1541	arrays. The C stack is a limited resource: for instance, on my amd64
637	machine with 8MB of stack size I can decode around 180k nested arrays but	1542	machine with 8MB of stack size I can decode around 180k nested arrays but
638	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1543	only 14k nested JSON objects (due to perl itself recursing deeply on croak
639	to free the temporary). If that is exceeded, the program crashes. to be	1544	to free the temporary). If that is exceeded, the program crashes. To be
640	conservative, the default nesting limit is set to 512. If your process	1545	conservative, the default nesting limit is set to 512. If your process
641	has a smaller stack, you should adjust this setting accordingly with the	1546	has a smaller stack, you should adjust this setting accordingly with the
642	C<max_depth> method.	1547	C<max_depth> method.
643		1548
644	And last but least, something else could bomb you that I forgot to think	1549	Something else could bomb you, too, that I forgot to think of. In that
645	of. In that case, you get to keep the pieces. I am always open for hints,	1550	case, you get to keep the pieces. I am always open for hints, though...
646	though...	1551
		1552	Also keep in mind that JSON::XS might leak contents of your Perl data
		1553	structures in its error messages, so when you serialise sensitive
		1554	information you might want to make sure that exceptions thrown by JSON::XS
		1555	will not end up in front of untrusted eyes.
		1556
		1557	If you are using JSON::XS to return packets to consumption
		1558	by JavaScript scripts in a browser you should have a look at
		1559	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
		1560	see whether you are vulnerable to some common attack vectors (which really
		1561	are browser design bugs, but it is still you who will have to deal with
		1562	it, as major browser developers care only for features, not about getting
		1563	security right).
		1564
		1565
		1566	=head2 "OLD" VS. "NEW" JSON (RFC4627 VS. RFC7159)
		1567
		1568	JSON originally required JSON texts to represent an array or object -
		1569	scalar values were explicitly not allowed. This has changed, and versions
		1570	of JSON::XS beginning with C<4.0> reflect this by allowing scalar values
		1571	by default.
		1572
		1573	One reason why one might not want this is that this removes a fundamental
		1574	property of JSON texts, namely that they are self-delimited and
		1575	self-contained, or in other words, you could take any number of "old"
		1576	JSON texts and paste them together, and the result would be unambiguously
		1577	parseable:
		1578
		1579	[1,3]{"k":5}[][null] # four JSON texts, without doubt
		1580
		1581	By allowing scalars, this property is lost: in the following example, is
		1582	this one JSON text (the number 12) or two JSON texts (the numbers 1 and
		1583	2):
		1584
		1585	12 # could be 12, or 1 and 2
		1586
		1587	Another lost property of "old" JSON is that no lookahead is required to
		1588	know the end of a JSON text, i.e. the JSON text definitely ended at the
		1589	last C<]> or C<}> character, there was no need to read extra characters.
		1590
		1591	For example, a viable network protocol with "old" JSON was to simply
		1592	exchange JSON texts without delimiter. For "new" JSON, you have to use a
		1593	suitable delimiter (such as a newline) after every JSON text or ensure you
		1594	never encode/decode scalar values.
		1595
		1596	Most protocols do work by only transferring arrays or objects, and the
		1597	easiest way to avoid problems with the "new" JSON definition is to
		1598	explicitly disallow scalar values in your encoder and decoder:
		1599
		1600	$json_coder = JSON::XS->new->allow_nonref (0)
		1601
		1602	This is a somewhat unhappy situation, and the blame can fully be put on
		1603	JSON's inmventor, Douglas Crockford, who unilaterally changed the format
		1604	in 2006 without consulting the IETF, forcing the IETF to either fork the
		1605	format or go with it (as I was told, the IETF wasn't amused).
		1606
		1607
		1608	=head1 RELATIONSHIP WITH I-JSON
		1609
		1610	JSON is a somewhat sloppily-defined format - it carries around obvious
		1611	Javascript baggage, such as not really defining number range, probably
		1612	because Javascript only has one type of numbers: IEEE 64 bit floats
		1613	("binary64").
		1614
		1615	For this reaosn, RFC7493 defines "Internet JSON", which is a restricted
		1616	subset of JSON that is supposedly more interoperable on the internet.
		1617
		1618	While C<JSON::XS> does not offer specific support for I-JSON, it of course
		1619	accepts valid I-JSON and by default implements some of the limitations
		1620	of I-JSON, such as parsing numbers as perl numbers, which are usually a
		1621	superset of binary64 numbers.
		1622
		1623	To generate I-JSON, follow these rules:
		1624
		1625	=over
		1626
		1627	=item * always generate UTF-8
		1628
		1629	I-JSON must be encoded in UTF-8, the default for C<encode_json>.
		1630
		1631	=item * numbers should be within IEEE 754 binary64 range
		1632
		1633	Basically all existing perl installations use binary64 to represent
		1634	floating point numbers, so all you need to do is to avoid large integers.
		1635
		1636	=item * objects must not have duplicate keys
		1637
		1638	This is trivially done, as C<JSON::XS> does not allow duplicate keys.
		1639
		1640	=item * do not generate scalar JSON texts, use C<< ->allow_nonref (0) >>
		1641
		1642	I-JSON strongly requests you to only encode arrays and objects into JSON.
		1643
		1644	=item * times should be strings in ISO 8601 format
		1645
		1646	There are a myriad of modules on CPAN dealing with ISO 8601 - search for
		1647	C<ISO8601> on CPAN and use one.
		1648
		1649	=item * encode binary data as base64
		1650
		1651	While it's tempting to just dump binary data as a string (and let
		1652	C<JSON::XS> do the escaping), for I-JSON, it's I<recommended> to encode
		1653	binary data as base64.
		1654
		1655	=back
		1656
		1657	There are some other considerations - read RFC7493 for the details if
		1658	interested.
		1659
		1660
		1661	=head1 INTEROPERABILITY WITH OTHER MODULES
		1662
		1663	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1664	constants. That means that the JSON true and false values will be
		1665	comaptible to true and false values of other modules that do the same,
		1666	such as L<JSON::PP> and L<CBOR::XS>.
		1667
		1668
		1669	=head1 INTEROPERABILITY WITH OTHER JSON DECODERS
		1670
		1671	As long as you only serialise data that can be directly expressed in JSON,
		1672	C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs,
		1673	but C<JSON::XS> has found more bugs in the official JSON testsuite (1)
		1674	than the official JSON testsuite has found in C<JSON::XS> (0)).
		1675
		1676	When you have trouble decoding JSON generated by this module using other
		1677	decoders, then it is very likely that you have an encoding mismatch or the
		1678	other decoder is broken.
		1679
		1680	When decoding, C<JSON::XS> is strict by default and will likely catch all
		1681	errors. There are currently two settings that change this: C<relaxed>
		1682	makes C<JSON::XS> accept (but not generate) some non-standard extensions,
		1683	and C<allow_tags> will allow you to encode and decode Perl objects, at the
		1684	cost of not outputting valid JSON anymore.
		1685
		1686	=head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
		1687
		1688	When you use C<allow_tags> to use the extended (and also nonstandard and
		1689	invalid) JSON syntax for serialised objects, and you still want to decode
		1690	the generated When you want to serialise objects, you can run a regex
		1691	to replace the tagged syntax by standard JSON arrays (it only works for
		1692	"normal" package names without comma, newlines or single colons). First,
		1693	the readable Perl version:
		1694
		1695	# if your FREEZE methods return no values, you need this replace first:
		1696	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
		1697
		1698	# this works for non-empty constructor arg lists:
		1699	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
		1700
		1701	And here is a less readable version that is easy to adapt to other
		1702	languages:
		1703
		1704	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
		1705
		1706	Here is an ECMAScript version (same regex):
		1707
		1708	json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
		1709
		1710	Since this syntax converts to standard JSON arrays, it might be hard to
		1711	distinguish serialised objects from normal arrays. You can prepend a
		1712	"magic number" as first array element to reduce chances of a collision:
		1713
		1714	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
		1715
		1716	And after decoding the JSON text, you could walk the data
		1717	structure looking for arrays with a first element of
		1718	C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>.
		1719
		1720	The same approach can be used to create the tagged format with another
		1721	encoder. First, you create an array with the magic string as first member,
		1722	the classname as second, and constructor arguments last, encode it as part
		1723	of your JSON structure, and then:
		1724
		1725	$json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
		1726
		1727	Again, this has some limitations - the magic string must not be encoded
		1728	with character escapes, and the constructor arguments must be non-empty.
		1729
		1730
		1731	=head1 (I-)THREADS
		1732
		1733	This module is I<not> guaranteed to be ithread (or MULTIPLICITY-) safe
		1734	and there are no plans to change this. Note that perl's builtin so-called
		1735	threads/ithreads are officially deprecated and should not be used.
		1736
		1737
		1738	=head1 THE PERILS OF SETLOCALE
		1739
		1740	Sometimes people avoid the Perl locale support and directly call the
		1741	system's setlocale function with C<LC_ALL>.
		1742
		1743	This breaks both perl and modules such as JSON::XS, as stringification of
		1744	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1745	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1746	perl to stringify numbers).
		1747
		1748	The solution is simple: don't call C<setlocale>, or use it for only those
		1749	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1750
		1751	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1752	actually needs it (avoiding stringification of numbers), and restore it
		1753	afterwards.
		1754
		1755
		1756	=head1 SOME HISTORY
		1757
		1758	At the time this module was created there already were a number of JSON
		1759	modules available on CPAN, so what was the reason to write yet another
		1760	JSON module? While it seems there are many JSON modules, none of them
		1761	correctly handled all corner cases, and in most cases their maintainers
		1762	are unresponsive, gone missing, or not listening to bug reports for other
		1763	reasons.
		1764
		1765	Beginning with version 2.0 of the JSON module, when both JSON and
		1766	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		1767	overridden) with no overhead due to emulation (by inheriting constructor
		1768	and methods). If JSON::XS is not available, it will fall back to the
		1769	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		1770	gives you a portable JSON API that can be fast when you need it and
		1771	doesn't require a C compiler when that is a problem.
		1772
		1773	Somewhere around version 3, this module was forked into
		1774	C<Cpanel::JSON::XS>, because its maintainer had serious trouble
		1775	understanding JSON and insisted on a fork with many bugs "fixed" that
		1776	weren't actually bugs, while spreading FUD about this module without
		1777	actually giving any details on his accusations. You be the judge, but
		1778	in my personal opinion, if you want quality, you will stay away from
		1779	dangerous forks like that.
647		1780
648		1781
649	=head1 BUGS	1782	=head1 BUGS
650		1783
651	While the goal of this module is to be correct, that unfortunately does	1784	While the goal of this module is to be correct, that unfortunately does
652	not mean its bug-free, only that I think its design is bug-free. It is	1785	not mean it's bug-free, only that I think its design is bug-free. If you
653	still relatively early in its development. If you keep reporting bugs they	1786	keep reporting bugs they will be fixed swiftly, though.
654	will be fixed swiftly, though.	1787
		1788	Please refrain from using rt.cpan.org or any other bug reporting
		1789	service. I put the contact address into my modules for a reason.
655		1790
656	=cut	1791	=cut
657		1792
658	sub true() { \1 }	1793	BEGIN {
659	sub false() { \0 }	1794	*true = \$Types::Serialiser::true;
		1795	*true = \&Types::Serialiser::true;
		1796	*false = \$Types::Serialiser::false;
		1797	*false = \&Types::Serialiser::false;
		1798	*is_bool = \&Types::Serialiser::is_bool;
660		1799
661	1;	1800	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
		1801	}
		1802
		1803	XSLoader::load "JSON::XS", $VERSION;
		1804
		1805	=head1 SEE ALSO
		1806
		1807	The F<json_xs> command line utility for quick experiments.
662		1808
663	=head1 AUTHOR	1809	=head1 AUTHOR
664		1810
665	Marc Lehmann <schmorp@schmorp.de>	1811	Marc Lehmann <schmorp@schmorp.de>
666	http://home.schmorp.de/	1812	http://home.schmorp.de/
667		1813
668	=cut	1814	=cut
669		1815
		1816	1
		1817

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