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Revision 1.51 by root, Mon Jul 2 01:12:27 2007 UTC vs.
Revision 1.150 by root, Tue Oct 29 00:48:07 2013 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
		5	=encoding utf-8
		6
		7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
4		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
8		13
9	# exported functions, they croak on error	14	# exported functions, they croak on error
10	# and expect/generate UTF-8	15	# and expect/generate UTF-8
11		16
12	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
13	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
14		19
15	# OO-interface	20	# OO-interface
16		21
17	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
18	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
19	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
20		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
21	=head1 DESCRIPTION	34	=head1 DESCRIPTION
22		35
23	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
24	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
25	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overridden) with no overhead due to emulation (by inheriting constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
26		47
27	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
28	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
29	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
30	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
31	reports for other reasons.	52	reports for other reasons.
32		53
33	See COMPARISON, below, for a comparison to some other JSON modules.
34
35	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
36	vice versa.	55	vice versa.
37		56
38	=head2 FEATURES	57	=head2 FEATURES
39		58
40	=over 4	59	=over 4
41		60
42	=item * correct unicode handling	61	=item * correct Unicode handling
43		62
44	This module knows how to handle Unicode, and even documents how and when	63	This module knows how to handle Unicode, documents how and when it does
45	it does so.	64	so, and even documents what "correct" means.
46		65
47	=item * round-trip integrity	66	=item * round-trip integrity
48		67
49	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
50	by JSON, the deserialised data structure is identical on the Perl level.	69	by JSON and Perl, the deserialised data structure is identical on the Perl
51	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
52	like a number).	71	it looks like a number). There I<are> minor exceptions to this, read the
		72	MAPPING section below to learn about those.
53		73
54	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
55		75
56	There is no guessing, no generating of illegal JSON texts by default,	76	There is no guessing, no generating of illegal JSON texts by default,
57	and only JSON is accepted as input by default (the latter is a security	77	and only JSON is accepted as input by default (the latter is a security
58	feature).	78	feature).
59		79
60	=item * fast	80	=item * fast
61		81
62	Compared to other JSON modules, this module compares favourably in terms	82	Compared to other JSON modules and other serialisers such as Storable,
63	of speed, too.	83	this module usually compares favourably in terms of speed, too.
64		84
65	=item * simple to use	85	=item * simple to use
66		86
67	This module has both a simple functional interface as well as an OO	87	This module has both a simple functional interface as well as an object
68	interface.	88	oriented interface.
69		89
70	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
71		91
72	You can choose between the most compact guarenteed single-line format	92	You can choose between the most compact guaranteed-single-line format
73	possible (nice for simple line-based protocols), a pure-ascii format	93	possible (nice for simple line-based protocols), a pure-ASCII format
74	(for when your transport is not 8-bit clean, still supports the whole	94	(for when your transport is not 8-bit clean, still supports the whole
75	unicode range), or a pretty-printed format (for when you want to read that	95	Unicode range), or a pretty-printed format (for when you want to read that
76	stuff). Or you can combine those features in whatever way you like.	96	stuff). Or you can combine those features in whatever way you like.
77		97
78	=back	98	=back
79		99
80	=cut	100	=cut
81		101
82	package JSON::XS;	102	package JSON::XS;
83		103
84	use strict;	104	use common::sense;
85		105
86	our $VERSION = '1.4';	106	our $VERSION = '3.0';
87	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
88		108
89	our @EXPORT = qw(to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
90		110
91	use Exporter;	111	use Exporter;
92	use XSLoader;	112	use XSLoader;
93		113
		114	use Types::Serialiser ();
		115
94	=head1 FUNCTIONAL INTERFACE	116	=head1 FUNCTIONAL INTERFACE
95		117
96	The following convinience methods are provided by this module. They are	118	The following convenience methods are provided by this module. They are
97	exported by default:	119	exported by default:
98		120
99	=over 4	121	=over 4
100		122
101	=item $json_text = to_json $perl_scalar	123	=item $json_text = encode_json $perl_scalar
102		124
103	Converts the given Perl data structure (a simple scalar or a reference to	125	Converts the given Perl data structure to a UTF-8 encoded, binary string
104	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	126	(that is, the string contains octets only). Croaks on error.
105	octets only). Croaks on error.
106		127
107	This function call is functionally identical to:	128	This function call is functionally identical to:
108		129
109	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	130	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
110		131
111	except being faster.	132	Except being faster.
112		133
113	=item $perl_scalar = from_json $json_text	134	=item $perl_scalar = decode_json $json_text
114		135
115	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	136	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
116	parse that as an UTF-8 encoded JSON text, returning the resulting simple	137	to parse that as an UTF-8 encoded JSON text, returning the resulting
117	scalar or reference. Croaks on error.	138	reference. Croaks on error.
118		139
119	This function call is functionally identical to:	140	This function call is functionally identical to:
120		141
121	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	142	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
122		143
123	except being faster.	144	Except being faster.
124
125	=item $is_boolean = JSON::XS::is_bool $scalar
126
127	Returns true if the passed scalar represents either JSON::XS::true or
128	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
129	and are used to represent JSON C<true> and C<false> values in Perl.
130
131	See MAPPING, below, for more information on how JSON values are mapped to
132	Perl.
133		145
134	=back	146	=back
		147
		148
		149	=head1 A FEW NOTES ON UNICODE AND PERL
		150
		151	Since this often leads to confusion, here are a few very clear words on
		152	how Unicode works in Perl, modulo bugs.
		153
		154	=over 4
		155
		156	=item 1. Perl strings can store characters with ordinal values > 255.
		157
		158	This enables you to store Unicode characters as single characters in a
		159	Perl string - very natural.
		160
		161	=item 2. Perl does I<not> associate an encoding with your strings.
		162
		163	... until you force it to, e.g. when matching it against a regex, or
		164	printing the scalar to a file, in which case Perl either interprets your
		165	string as locale-encoded text, octets/binary, or as Unicode, depending
		166	on various settings. In no case is an encoding stored together with your
		167	data, it is I<use> that decides encoding, not any magical meta data.
		168
		169	=item 3. The internal utf-8 flag has no meaning with regards to the
		170	encoding of your string.
		171
		172	Just ignore that flag unless you debug a Perl bug, a module written in
		173	XS or want to dive into the internals of perl. Otherwise it will only
		174	confuse you, as, despite the name, it says nothing about how your string
		175	is encoded. You can have Unicode strings with that flag set, with that
		176	flag clear, and you can have binary data with that flag set and that flag
		177	clear. Other possibilities exist, too.
		178
		179	If you didn't know about that flag, just the better, pretend it doesn't
		180	exist.
		181
		182	=item 4. A "Unicode String" is simply a string where each character can be
		183	validly interpreted as a Unicode code point.
		184
		185	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		186	Unicode string encoded in UTF-8, giving you a binary string.
		187
		188	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		189
		190	It's a fact. Learn to live with it.
		191
		192	=back
		193
		194	I hope this helps :)
135		195
136		196
137	=head1 OBJECT-ORIENTED INTERFACE	197	=head1 OBJECT-ORIENTED INTERFACE
138		198
139	The object oriented interface lets you configure your own encoding or	199	The object oriented interface lets you configure your own encoding or
…		…
152	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	212	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
153	=> {"a": [1, 2]}	213	=> {"a": [1, 2]}
154		214
155	=item $json = $json->ascii ([$enable])	215	=item $json = $json->ascii ([$enable])
156		216
		217	=item $enabled = $json->get_ascii
		218
157	If C<$enable> is true (or missing), then the C<encode> method will not	219	If C<$enable> is true (or missing), then the C<encode> method will not
158	generate characters outside the code range C<0..127> (which is ASCII). Any	220	generate characters outside the code range C<0..127> (which is ASCII). Any
159	unicode characters outside that range will be escaped using either a	221	Unicode characters outside that range will be escaped using either a
160	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,	222	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
161	as per RFC4627. The resulting encoded JSON text can be treated as a native	223	as per RFC4627. The resulting encoded JSON text can be treated as a native
162	unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,	224	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
163	or any other superset of ASCII.	225	or any other superset of ASCII.
164		226
165	If C<$enable> is false, then the C<encode> method will not escape Unicode	227	If C<$enable> is false, then the C<encode> method will not escape Unicode
166	characters unless required by the JSON syntax or other flags. This results	228	characters unless required by the JSON syntax or other flags. This results
167	in a faster and more compact format.	229	in a faster and more compact format.
168		230
		231	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		232	document.
		233
169	The main use for this flag is to produce JSON texts that can be	234	The main use for this flag is to produce JSON texts that can be
170	transmitted over a 7-bit channel, as the encoded JSON texts will not	235	transmitted over a 7-bit channel, as the encoded JSON texts will not
171	contain any 8 bit characters.	236	contain any 8 bit characters.
172		237
173	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	238	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
174	=> ["\ud801\udc01"]	239	=> ["\ud801\udc01"]
175		240
176	=item $json = $json->latin1 ([$enable])	241	=item $json = $json->latin1 ([$enable])
177		242
		243	=item $enabled = $json->get_latin1
		244
178	If C<$enable> is true (or missing), then the C<encode> method will encode	245	If C<$enable> is true (or missing), then the C<encode> method will encode
179	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters	246	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
180	outside the code range C<0..255>. The resulting string can be treated as a	247	outside the code range C<0..255>. The resulting string can be treated as a
181	latin1-encoded JSON text or a native unicode string. The C<decode> method	248	latin1-encoded JSON text or a native Unicode string. The C<decode> method
182	will not be affected in any way by this flag, as C<decode> by default	249	will not be affected in any way by this flag, as C<decode> by default
183	expects unicode, which is a strict superset of latin1.	250	expects Unicode, which is a strict superset of latin1.
184		251
185	If C<$enable> is false, then the C<encode> method will not escape Unicode	252	If C<$enable> is false, then the C<encode> method will not escape Unicode
186	characters unless required by the JSON syntax or other flags.	253	characters unless required by the JSON syntax or other flags.
		254
		255	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		256	document.
187		257
188	The main use for this flag is efficiently encoding binary data as JSON	258	The main use for this flag is efficiently encoding binary data as JSON
189	text, as most octets will not be escaped, resulting in a smaller encoded	259	text, as most octets will not be escaped, resulting in a smaller encoded
190	size. The disadvantage is that the resulting JSON text is encoded	260	size. The disadvantage is that the resulting JSON text is encoded
191	in latin1 (and must correctly be treated as such when storing and	261	in latin1 (and must correctly be treated as such when storing and
192	transfering), a rare encoding for JSON. It is therefore most useful when	262	transferring), a rare encoding for JSON. It is therefore most useful when
193	you want to store data structures known to contain binary data efficiently	263	you want to store data structures known to contain binary data efficiently
194	in files or databases, not when talking to other JSON encoders/decoders.	264	in files or databases, not when talking to other JSON encoders/decoders.
195		265
196	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	266	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
197	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	267	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
198		268
199	=item $json = $json->utf8 ([$enable])	269	=item $json = $json->utf8 ([$enable])
		270
		271	=item $enabled = $json->get_utf8
200		272
201	If C<$enable> is true (or missing), then the C<encode> method will encode	273	If C<$enable> is true (or missing), then the C<encode> method will encode
202	the JSON result into UTF-8, as required by many protocols, while the	274	the JSON result into UTF-8, as required by many protocols, while the
203	C<decode> method expects to be handled an UTF-8-encoded string. Please	275	C<decode> method expects to be handled an UTF-8-encoded string. Please
204	note that UTF-8-encoded strings do not contain any characters outside the	276	note that UTF-8-encoded strings do not contain any characters outside the
205	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	277	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
206	versions, enabling this option might enable autodetection of the UTF-16	278	versions, enabling this option might enable autodetection of the UTF-16
207	and UTF-32 encoding families, as described in RFC4627.	279	and UTF-32 encoding families, as described in RFC4627.
208		280
209	If C<$enable> is false, then the C<encode> method will return the JSON	281	If C<$enable> is false, then the C<encode> method will return the JSON
210	string as a (non-encoded) unicode string, while C<decode> expects thus a	282	string as a (non-encoded) Unicode string, while C<decode> expects thus a
211	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	283	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
212	to be done yourself, e.g. using the Encode module.	284	to be done yourself, e.g. using the Encode module.
		285
		286	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		287	document.
213		288
214	Example, output UTF-16BE-encoded JSON:	289	Example, output UTF-16BE-encoded JSON:
215		290
216	use Encode;	291	use Encode;
217	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	292	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
238	]	313	]
239	}	314	}
240		315
241	=item $json = $json->indent ([$enable])	316	=item $json = $json->indent ([$enable])
242		317
		318	=item $enabled = $json->get_indent
		319
243	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	320	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
244	format as output, putting every array member or object/hash key-value pair	321	format as output, putting every array member or object/hash key-value pair
245	into its own line, identing them properly.	322	into its own line, indenting them properly.
246		323
247	If C<$enable> is false, no newlines or indenting will be produced, and the	324	If C<$enable> is false, no newlines or indenting will be produced, and the
248	resulting JSON text is guarenteed not to contain any C<newlines>.	325	resulting JSON text is guaranteed not to contain any C<newlines>.
249		326
250	This setting has no effect when decoding JSON texts.	327	This setting has no effect when decoding JSON texts.
251		328
252	=item $json = $json->space_before ([$enable])	329	=item $json = $json->space_before ([$enable])
		330
		331	=item $enabled = $json->get_space_before
253		332
254	If C<$enable> is true (or missing), then the C<encode> method will add an extra	333	If C<$enable> is true (or missing), then the C<encode> method will add an extra
255	optional space before the C<:> separating keys from values in JSON objects.	334	optional space before the C<:> separating keys from values in JSON objects.
256		335
257	If C<$enable> is false, then the C<encode> method will not add any extra	336	If C<$enable> is false, then the C<encode> method will not add any extra
…		…
263	Example, space_before enabled, space_after and indent disabled:	342	Example, space_before enabled, space_after and indent disabled:
264		343
265	{"key" :"value"}	344	{"key" :"value"}
266		345
267	=item $json = $json->space_after ([$enable])	346	=item $json = $json->space_after ([$enable])
		347
		348	=item $enabled = $json->get_space_after
268		349
269	If C<$enable> is true (or missing), then the C<encode> method will add an extra	350	If C<$enable> is true (or missing), then the C<encode> method will add an extra
270	optional space after the C<:> separating keys from values in JSON objects	351	optional space after the C<:> separating keys from values in JSON objects
271	and extra whitespace after the C<,> separating key-value pairs and array	352	and extra whitespace after the C<,> separating key-value pairs and array
272	members.	353	members.
…		…
278		359
279	Example, space_before and indent disabled, space_after enabled:	360	Example, space_before and indent disabled, space_after enabled:
280		361
281	{"key": "value"}	362	{"key": "value"}
282		363
		364	=item $json = $json->relaxed ([$enable])
		365
		366	=item $enabled = $json->get_relaxed
		367
		368	If C<$enable> is true (or missing), then C<decode> will accept some
		369	extensions to normal JSON syntax (see below). C<encode> will not be
		370	affected in anyway. I<Be aware that this option makes you accept invalid
		371	JSON texts as if they were valid!>. I suggest only to use this option to
		372	parse application-specific files written by humans (configuration files,
		373	resource files etc.)
		374
		375	If C<$enable> is false (the default), then C<decode> will only accept
		376	valid JSON texts.
		377
		378	Currently accepted extensions are:
		379
		380	=over 4
		381
		382	=item * list items can have an end-comma
		383
		384	JSON I<separates> array elements and key-value pairs with commas. This
		385	can be annoying if you write JSON texts manually and want to be able to
		386	quickly append elements, so this extension accepts comma at the end of
		387	such items not just between them:
		388
		389	[
		390	1,
		391	2, <- this comma not normally allowed
		392	]
		393	{
		394	"k1": "v1",
		395	"k2": "v2", <- this comma not normally allowed
		396	}
		397
		398	=item * shell-style '#'-comments
		399
		400	Whenever JSON allows whitespace, shell-style comments are additionally
		401	allowed. They are terminated by the first carriage-return or line-feed
		402	character, after which more white-space and comments are allowed.
		403
		404	[
		405	1, # this comment not allowed in JSON
		406	# neither this one...
		407	]
		408
		409	=back
		410
283	=item $json = $json->canonical ([$enable])	411	=item $json = $json->canonical ([$enable])
		412
		413	=item $enabled = $json->get_canonical
284		414
285	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	415	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
286	by sorting their keys. This is adding a comparatively high overhead.	416	by sorting their keys. This is adding a comparatively high overhead.
287		417
288	If C<$enable> is false, then the C<encode> method will output key-value	418	If C<$enable> is false, then the C<encode> method will output key-value
289	pairs in the order Perl stores them (which will likely change between runs	419	pairs in the order Perl stores them (which will likely change between runs
290	of the same script).	420	of the same script, and can change even within the same run from 5.18
		421	onwards).
291		422
292	This option is useful if you want the same data structure to be encoded as	423	This option is useful if you want the same data structure to be encoded as
293	the same JSON text (given the same overall settings). If it is disabled,	424	the same JSON text (given the same overall settings). If it is disabled,
294	the same hash migh be encoded differently even if contains the same data,	425	the same hash might be encoded differently even if contains the same data,
295	as key-value pairs have no inherent ordering in Perl.	426	as key-value pairs have no inherent ordering in Perl.
296		427
297	This setting has no effect when decoding JSON texts.	428	This setting has no effect when decoding JSON texts.
298		429
		430	This setting has currently no effect on tied hashes.
		431
299	=item $json = $json->allow_nonref ([$enable])	432	=item $json = $json->allow_nonref ([$enable])
		433
		434	=item $enabled = $json->get_allow_nonref
300		435
301	If C<$enable> is true (or missing), then the C<encode> method can convert a	436	If C<$enable> is true (or missing), then the C<encode> method can convert a
302	non-reference into its corresponding string, number or null JSON value,	437	non-reference into its corresponding string, number or null JSON value,
303	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	438	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
304	values instead of croaking.	439	values instead of croaking.
…		…
312	resulting in an invalid JSON text:	447	resulting in an invalid JSON text:
313		448
314	JSON::XS->new->allow_nonref->encode ("Hello, World!")	449	JSON::XS->new->allow_nonref->encode ("Hello, World!")
315	=> "Hello, World!"	450	=> "Hello, World!"
316		451
		452	=item $json = $json->allow_unknown ([$enable])
		453
		454	=item $enabled = $json->get_allow_unknown
		455
		456	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		457	exception when it encounters values it cannot represent in JSON (for
		458	example, filehandles) but instead will encode a JSON C<null> value. Note
		459	that blessed objects are not included here and are handled separately by
		460	c<allow_nonref>.
		461
		462	If C<$enable> is false (the default), then C<encode> will throw an
		463	exception when it encounters anything it cannot encode as JSON.
		464
		465	This option does not affect C<decode> in any way, and it is recommended to
		466	leave it off unless you know your communications partner.
		467
317	=item $json = $json->allow_blessed ([$enable])	468	=item $json = $json->allow_blessed ([$enable])
318		469
		470	=item $enabled = $json->get_allow_blessed
		471
		472	See L<OBJECT SERIALISATION> for details.
		473
319	If C<$enable> is true (or missing), then the C<encode> method will not	474	If C<$enable> is true (or missing), then the C<encode> method will not
320	barf when it encounters a blessed reference. Instead, the value of the	475	barf when it encounters a blessed reference that it cannot convert
321	B<convert_blessed> option will decide wether C<null> (C<convert_blessed>	476	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
322	disabled or no C<to_json> method found) or a representation of the
323	object (C<convert_blessed> enabled and C<to_json> method found) is being
324	encoded. Has no effect on C<decode>.
325		477
326	If C<$enable> is false (the default), then C<encode> will throw an	478	If C<$enable> is false (the default), then C<encode> will throw an
327	exception when it encounters a blessed object.	479	exception when it encounters a blessed object that it cannot convert
		480	otherwise.
		481
		482	This setting has no effect on C<decode>.
328		483
329	=item $json = $json->convert_blessed ([$enable])	484	=item $json = $json->convert_blessed ([$enable])
		485
		486	=item $enabled = $json->get_convert_blessed
		487
		488	See L<OBJECT SERIALISATION> for details.
330		489
331	If C<$enable> is true (or missing), then C<encode>, upon encountering a	490	If C<$enable> is true (or missing), then C<encode>, upon encountering a
332	blessed object, will check for the availability of the C<TO_JSON> method	491	blessed object, will check for the availability of the C<TO_JSON> method
333	on the object's class. If found, it will be called in scalar context	492	on the object's class. If found, it will be called in scalar context and
334	and the resulting scalar will be encoded instead of the object. If no	493	the resulting scalar will be encoded instead of the object.
335	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
336	to do.
337		494
338	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	495	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
339	returns other blessed objects, those will be handled in the same	496	returns other blessed objects, those will be handled in the same
340	way. C<TO_JSON> must take care of not causing an endless recursion cycle	497	way. C<TO_JSON> must take care of not causing an endless recursion cycle
341	(== crash) in this case. The name of C<TO_JSON> was chosen because other	498	(== crash) in this case. The name of C<TO_JSON> was chosen because other
342	methods called by the Perl core (== not by the user of the object) are	499	methods called by the Perl core (== not by the user of the object) are
343	usually in upper case letters and to avoid collisions with the C<to_json>	500	usually in upper case letters and to avoid collisions with any C<to_json>
344	function.	501	function or method.
345		502
346	This setting does not yet influence C<decode> in any way, but in the	503	If C<$enable> is false (the default), then C<encode> will not consider
347	future, global hooks might get installed that influence C<decode> and are	504	this type of conversion.
348	enabled by this setting.
349		505
350	If C<$enable> is false, then the C<allow_blessed> setting will decide what	506	This setting has no effect on C<decode>.
351	to do when a blessed object is found.
352		507
		508	=item $json = $json->allow_tags ([$enable])
		509
		510	=item $enabled = $json->allow_tags
		511
		512	See L<OBJECT SERIALISATION> for details.
		513
		514	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		515	blessed object, will check for the availability of the C<FREEZE> method on
		516	the object's class. If found, it will be used to serialise the object into
		517	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		518
		519	It also causes C<decode> to parse such tagged JSON values and deserialise
		520	them via a call to the C<THAW> method.
		521
		522	If C<$enable> is false (the default), then C<encode> will not consider
		523	this type of conversion, and tagged JSON values will cause a parse error
		524	in C<decode>, as if tags were not part of the grammar.
		525
353	=item $json = $json->filter_json_object ([$coderef])	526	=item $json = $json->filter_json_object ([$coderef->($hashref)])
354		527
355	When C<$coderef> is specified, it will be called from C<decode> each	528	When C<$coderef> is specified, it will be called from C<decode> each
356	time it decodes a JSON object. The only argument is a reference to the	529	time it decodes a JSON object. The only argument is a reference to the
357	newly-created hash. If the code references returns a single scalar (which	530	newly-created hash. If the code references returns a single scalar (which
358	need not be a reference), this value (i.e. a copy of that scalar to avoid	531	need not be a reference), this value (i.e. a copy of that scalar to avoid
359	aliasing) is inserted into the deserialised data structure. If it returns	532	aliasing) is inserted into the deserialised data structure. If it returns
360	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the	533	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
361	original deserialised hash will be inserted. This setting can slow down	534	original deserialised hash will be inserted. This setting can slow down
362	decoding considerably.	535	decoding considerably.
363		536
364	When C<$coderef> is omitted or undefined, C<decode> will not change the	537	When C<$coderef> is omitted or undefined, any existing callback will
365	deserialised hash in any way. This is maximally fast.	538	be removed and C<decode> will not change the deserialised hash in any
		539	way.
366		540
367	Example, convert all JSON objects into the integer 5:	541	Example, convert all JSON objects into the integer 5:
368		542
369	my $js = JSON::XS->new->filter_json_object (sub { 5 });	543	my $js = JSON::XS->new->filter_json_object (sub { 5 });
370	# returns [5]	544	# returns [5]
371	$js->decode ('[{}]')	545	$js->decode ('[{}]')
372	# throw an exception because allow_nonref is not enabled:	546	# throw an exception because allow_nonref is not enabled
		547	# so a lone 5 is not allowed.
373	$js->decode ('{"a":1, "b":2}');	548	$js->decode ('{"a":1, "b":2}');
374		549
375	=item $json = $json->filter_json_single_key_object ([$coderef])	550	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
376		551
377	Works like C<filter_json_object>, but is only called for JSON objects	552	Works remotely similar to C<filter_json_object>, but is only called for
378	having only a single key.	553	JSON objects having a single key named C<$key>.
379		554
380	This C<$coderef> is called before the one specified via	555	This C<$coderef> is called before the one specified via
381	C<filter_json_object>, if any. If it returns something, that will be	556	C<filter_json_object>, if any. It gets passed the single value in the JSON
382	inserted into the data structure. If it returns nothing, the callback	557	object. If it returns a single value, it will be inserted into the data
383	from C<filter_json_object> will be called next. If you want to force	558	structure. If it returns nothing (not even C<undef> but the empty list),
384	insertion of single-key objects even in the presence of a mutating	559	the callback from C<filter_json_object> will be called next, as if no
385	C<filter_json_object> callback, simply return the passed hash.	560	single-key callback were specified.
		561
		562	If C<$coderef> is omitted or undefined, the corresponding callback will be
		563	disabled. There can only ever be one callback for a given key.
386		564
387	As this callback gets called less often then the C<filter_json_object>	565	As this callback gets called less often then the C<filter_json_object>
388	one, decoding speed will not usually suffer as much. Therefore, single-key	566	one, decoding speed will not usually suffer as much. Therefore, single-key
389	objects make excellent targets to serialise Perl objects into, especially	567	objects make excellent targets to serialise Perl objects into, especially
390	as single-key JSON objects are as close to the type-tagged value concept	568	as single-key JSON objects are as close to the type-tagged value concept
391	as JSON gets (its basically an ID/VALUE tuple). Of course, JSON does not	569	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
392	support this in any way, so you need to make sure your data never looks	570	support this in any way, so you need to make sure your data never looks
393	like a serialised Perl hash.	571	like a serialised Perl hash.
394		572
395	Typical names for the single object key are C<__class_whatever__>, or	573	Typical names for the single object key are C<__class_whatever__>, or
396	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even	574	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
…		…
401	into the corresponding C<< $WIDGET{<id>} >> object:	579	into the corresponding C<< $WIDGET{<id>} >> object:
402		580
403	# return whatever is in $WIDGET{5}:	581	# return whatever is in $WIDGET{5}:
404	JSON::XS	582	JSON::XS
405	->new	583	->new
406	->filter_json_single_key_object (sub {	584	->filter_json_single_key_object (__widget__ => sub {
407	exists $_[0]{__widget__}
408	? $WIDGET{ $_[0]{__widget__} }	585	$WIDGET{ $_[0] }
409	: ()
410	})	586	})
411	->decode ('{"__widget__": 5')	587	->decode ('{"__widget__": 5')
412		588
413	# this can be used with a TO_JSON method in some "widget" class	589	# this can be used with a TO_JSON method in some "widget" class
414	# for serialisation to json:	590	# for serialisation to json:
…		…
422		598
423	{ __widget__ => $self->{id} }	599	{ __widget__ => $self->{id} }
424	}	600	}
425		601
426	=item $json = $json->shrink ([$enable])	602	=item $json = $json->shrink ([$enable])
		603
		604	=item $enabled = $json->get_shrink
427		605
428	Perl usually over-allocates memory a bit when allocating space for	606	Perl usually over-allocates memory a bit when allocating space for
429	strings. This flag optionally resizes strings generated by either	607	strings. This flag optionally resizes strings generated by either
430	C<encode> or C<decode> to their minimum size possible. This can save	608	C<encode> or C<decode> to their minimum size possible. This can save
431	memory when your JSON texts are either very very long or you have many	609	memory when your JSON texts are either very very long or you have many
…		…
449	strings that look like integers or floats into integers or floats	627	strings that look like integers or floats into integers or floats
450	internally (there is no difference on the Perl level), saving space.	628	internally (there is no difference on the Perl level), saving space.
451		629
452	=item $json = $json->max_depth ([$maximum_nesting_depth])	630	=item $json = $json->max_depth ([$maximum_nesting_depth])
453		631
		632	=item $max_depth = $json->get_max_depth
		633
454	Sets the maximum nesting level (default C<512>) accepted while encoding	634	Sets the maximum nesting level (default C<512>) accepted while encoding
455	or decoding. If the JSON text or Perl data structure has an equal or	635	or decoding. If a higher nesting level is detected in JSON text or a Perl
456	higher nesting level then this limit, then the encoder and decoder will	636	data structure, then the encoder and decoder will stop and croak at that
457	stop and croak at that point.	637	point.
458		638
459	Nesting level is defined by number of hash- or arrayrefs that the encoder	639	Nesting level is defined by number of hash- or arrayrefs that the encoder
460	needs to traverse to reach a given point or the number of C<{> or C<[>	640	needs to traverse to reach a given point or the number of C<{> or C<[>
461	characters without their matching closing parenthesis crossed to reach a	641	characters without their matching closing parenthesis crossed to reach a
462	given character in a string.	642	given character in a string.
463		643
464	Setting the maximum depth to one disallows any nesting, so that ensures	644	Setting the maximum depth to one disallows any nesting, so that ensures
465	that the object is only a single hash/object or array.	645	that the object is only a single hash/object or array.
466		646
467	The argument to C<max_depth> will be rounded up to the next highest power
468	of two. If no argument is given, the highest possible setting will be	647	If no argument is given, the highest possible setting will be used, which
469	used, which is rarely useful.	648	is rarely useful.
		649
		650	Note that nesting is implemented by recursion in C. The default value has
		651	been chosen to be as large as typical operating systems allow without
		652	crashing.
470		653
471	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	654	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
472		655
473	=item $json = $json->max_size ([$maximum_string_size])	656	=item $json = $json->max_size ([$maximum_string_size])
		657
		658	=item $max_size = $json->get_max_size
474		659
475	Set the maximum length a JSON text may have (in bytes) where decoding is	660	Set the maximum length a JSON text may have (in bytes) where decoding is
476	being attempted. The default is C<0>, meaning no limit. When C<decode>	661	being attempted. The default is C<0>, meaning no limit. When C<decode>
477	is called on a string longer then this number of characters it will not	662	is called on a string that is longer then this many bytes, it will not
478	attempt to decode the string but throw an exception. This setting has no	663	attempt to decode the string but throw an exception. This setting has no
479	effect on C<encode> (yet).	664	effect on C<encode> (yet).
480		665
481	The argument to C<max_size> will be rounded up to the next B<highest>	666	If no argument is given, the limit check will be deactivated (same as when
482	power of two (so may be more than requested). If no argument is given, the	667	C<0> is specified).
483	limit check will be deactivated (same as when C<0> is specified).
484		668
485	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	669	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
486		670
487	=item $json_text = $json->encode ($perl_scalar)	671	=item $json_text = $json->encode ($perl_scalar)
488		672
489	Converts the given Perl data structure (a simple scalar or a reference	673	Converts the given Perl value or data structure to its JSON
490	to a hash or array) to its JSON representation. Simple scalars will be	674	representation. Croaks on error.
491	converted into JSON string or number sequences, while references to arrays
492	become JSON arrays and references to hashes become JSON objects. Undefined
493	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
494	nor C<false> values will be generated.
495		675
496	=item $perl_scalar = $json->decode ($json_text)	676	=item $perl_scalar = $json->decode ($json_text)
497		677
498	The opposite of C<encode>: expects a JSON text and tries to parse it,	678	The opposite of C<encode>: expects a JSON text and tries to parse it,
499	returning the resulting simple scalar or reference. Croaks on error.	679	returning the resulting simple scalar or reference. Croaks on error.
500
501	JSON numbers and strings become simple Perl scalars. JSON arrays become
502	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
503	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
504		680
505	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	681	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
506		682
507	This works like the C<decode> method, but instead of raising an exception	683	This works like the C<decode> method, but instead of raising an exception
508	when there is trailing garbage after the first JSON object, it will	684	when there is trailing garbage after the first JSON object, it will
509	silently stop parsing there and return the number of characters consumed	685	silently stop parsing there and return the number of characters consumed
510	so far.	686	so far.
511		687
512	This is useful if your JSON texts are not delimited by an outer protocol	688	This is useful if your JSON texts are not delimited by an outer protocol
513	(which is not the brightest thing to do in the first place) and you need
514	to know where the JSON text ends.	689	and you need to know where the JSON text ends.
515		690
516	JSON::XS->new->decode_prefix ("[1] the tail")	691	JSON::XS->new->decode_prefix ("[1] the tail")
517	=> ([], 3)	692	=> ([], 3)
518		693
519	=back	694	=back
		695
		696
		697	=head1 INCREMENTAL PARSING
		698
		699	In some cases, there is the need for incremental parsing of JSON
		700	texts. While this module always has to keep both JSON text and resulting
		701	Perl data structure in memory at one time, it does allow you to parse a
		702	JSON stream incrementally. It does so by accumulating text until it has
		703	a full JSON object, which it then can decode. This process is similar to
		704	using C<decode_prefix> to see if a full JSON object is available, but
		705	is much more efficient (and can be implemented with a minimum of method
		706	calls).
		707
		708	JSON::XS will only attempt to parse the JSON text once it is sure it
		709	has enough text to get a decisive result, using a very simple but
		710	truly incremental parser. This means that it sometimes won't stop as
		711	early as the full parser, for example, it doesn't detect mismatched
		712	parentheses. The only thing it guarantees is that it starts decoding as
		713	soon as a syntactically valid JSON text has been seen. This means you need
		714	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		715	parsing in the presence if syntax errors.
		716
		717	The following methods implement this incremental parser.
		718
		719	=over 4
		720
		721	=item [void, scalar or list context] = $json->incr_parse ([$string])
		722
		723	This is the central parsing function. It can both append new text and
		724	extract objects from the stream accumulated so far (both of these
		725	functions are optional).
		726
		727	If C<$string> is given, then this string is appended to the already
		728	existing JSON fragment stored in the C<$json> object.
		729
		730	After that, if the function is called in void context, it will simply
		731	return without doing anything further. This can be used to add more text
		732	in as many chunks as you want.
		733
		734	If the method is called in scalar context, then it will try to extract
		735	exactly I<one> JSON object. If that is successful, it will return this
		736	object, otherwise it will return C<undef>. If there is a parse error,
		737	this method will croak just as C<decode> would do (one can then use
		738	C<incr_skip> to skip the erroneous part). This is the most common way of
		739	using the method.
		740
		741	And finally, in list context, it will try to extract as many objects
		742	from the stream as it can find and return them, or the empty list
		743	otherwise. For this to work, there must be no separators between the JSON
		744	objects or arrays, instead they must be concatenated back-to-back. If
		745	an error occurs, an exception will be raised as in the scalar context
		746	case. Note that in this case, any previously-parsed JSON texts will be
		747	lost.
		748
		749	Example: Parse some JSON arrays/objects in a given string and return
		750	them.
		751
		752	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		753
		754	=item $lvalue_string = $json->incr_text
		755
		756	This method returns the currently stored JSON fragment as an lvalue, that
		757	is, you can manipulate it. This I<only> works when a preceding call to
		758	C<incr_parse> in I<scalar context> successfully returned an object. Under
		759	all other circumstances you must not call this function (I mean it.
		760	although in simple tests it might actually work, it I<will> fail under
		761	real world conditions). As a special exception, you can also call this
		762	method before having parsed anything.
		763
		764	This function is useful in two cases: a) finding the trailing text after a
		765	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		766	(such as commas).
		767
		768	=item $json->incr_skip
		769
		770	This will reset the state of the incremental parser and will remove
		771	the parsed text from the input buffer so far. This is useful after
		772	C<incr_parse> died, in which case the input buffer and incremental parser
		773	state is left unchanged, to skip the text parsed so far and to reset the
		774	parse state.
		775
		776	The difference to C<incr_reset> is that only text until the parse error
		777	occurred is removed.
		778
		779	=item $json->incr_reset
		780
		781	This completely resets the incremental parser, that is, after this call,
		782	it will be as if the parser had never parsed anything.
		783
		784	This is useful if you want to repeatedly parse JSON objects and want to
		785	ignore any trailing data, which means you have to reset the parser after
		786	each successful decode.
		787
		788	=back
		789
		790	=head2 LIMITATIONS
		791
		792	All options that affect decoding are supported, except
		793	C<allow_nonref>. The reason for this is that it cannot be made to work
		794	sensibly: JSON objects and arrays are self-delimited, i.e. you can
		795	concatenate them back to back and still decode them perfectly. This does
		796	not hold true for JSON numbers, however.
		797
		798	For example, is the string C<1> a single JSON number, or is it simply the
		799	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		800	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		801	takes the conservative route and disallows this case.
		802
		803	=head2 EXAMPLES
		804
		805	Some examples will make all this clearer. First, a simple example that
		806	works similarly to C<decode_prefix>: We want to decode the JSON object at
		807	the start of a string and identify the portion after the JSON object:
		808
		809	my $text = "[1,2,3] hello";
		810
		811	my $json = new JSON::XS;
		812
		813	my $obj = $json->incr_parse ($text)
		814	or die "expected JSON object or array at beginning of string";
		815
		816	my $tail = $json->incr_text;
		817	# $tail now contains " hello"
		818
		819	Easy, isn't it?
		820
		821	Now for a more complicated example: Imagine a hypothetical protocol where
		822	you read some requests from a TCP stream, and each request is a JSON
		823	array, without any separation between them (in fact, it is often useful to
		824	use newlines as "separators", as these get interpreted as whitespace at
		825	the start of the JSON text, which makes it possible to test said protocol
		826	with C<telnet>...).
		827
		828	Here is how you'd do it (it is trivial to write this in an event-based
		829	manner):
		830
		831	my $json = new JSON::XS;
		832
		833	# read some data from the socket
		834	while (sysread $socket, my $buf, 4096) {
		835
		836	# split and decode as many requests as possible
		837	for my $request ($json->incr_parse ($buf)) {
		838	# act on the $request
		839	}
		840	}
		841
		842	Another complicated example: Assume you have a string with JSON objects
		843	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		844	[3]>). To parse them, we have to skip the commas between the JSON texts,
		845	and here is where the lvalue-ness of C<incr_text> comes in useful:
		846
		847	my $text = "[1],[2], [3]";
		848	my $json = new JSON::XS;
		849
		850	# void context, so no parsing done
		851	$json->incr_parse ($text);
		852
		853	# now extract as many objects as possible. note the
		854	# use of scalar context so incr_text can be called.
		855	while (my $obj = $json->incr_parse) {
		856	# do something with $obj
		857
		858	# now skip the optional comma
		859	$json->incr_text =~ s/^ \s* , //x;
		860	}
		861
		862	Now lets go for a very complex example: Assume that you have a gigantic
		863	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		864	but you cannot load it into memory fully (this has actually happened in
		865	the real world :).
		866
		867	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		868	can still help you: You implement a (very simple) array parser and let
		869	JSON decode the array elements, which are all full JSON objects on their
		870	own (this wouldn't work if the array elements could be JSON numbers, for
		871	example):
		872
		873	my $json = new JSON::XS;
		874
		875	# open the monster
		876	open my $fh, "<bigfile.json"
		877	or die "bigfile: $!";
		878
		879	# first parse the initial "["
		880	for (;;) {
		881	sysread $fh, my $buf, 65536
		882	or die "read error: $!";
		883	$json->incr_parse ($buf); # void context, so no parsing
		884
		885	# Exit the loop once we found and removed(!) the initial "[".
		886	# In essence, we are (ab-)using the $json object as a simple scalar
		887	# we append data to.
		888	last if $json->incr_text =~ s/^ \s* \[ //x;
		889	}
		890
		891	# now we have the skipped the initial "[", so continue
		892	# parsing all the elements.
		893	for (;;) {
		894	# in this loop we read data until we got a single JSON object
		895	for (;;) {
		896	if (my $obj = $json->incr_parse) {
		897	# do something with $obj
		898	last;
		899	}
		900
		901	# add more data
		902	sysread $fh, my $buf, 65536
		903	or die "read error: $!";
		904	$json->incr_parse ($buf); # void context, so no parsing
		905	}
		906
		907	# in this loop we read data until we either found and parsed the
		908	# separating "," between elements, or the final "]"
		909	for (;;) {
		910	# first skip whitespace
		911	$json->incr_text =~ s/^\s*//;
		912
		913	# if we find "]", we are done
		914	if ($json->incr_text =~ s/^\]//) {
		915	print "finished.\n";
		916	exit;
		917	}
		918
		919	# if we find ",", we can continue with the next element
		920	if ($json->incr_text =~ s/^,//) {
		921	last;
		922	}
		923
		924	# if we find anything else, we have a parse error!
		925	if (length $json->incr_text) {
		926	die "parse error near ", $json->incr_text;
		927	}
		928
		929	# else add more data
		930	sysread $fh, my $buf, 65536
		931	or die "read error: $!";
		932	$json->incr_parse ($buf); # void context, so no parsing
		933	}
		934
		935	This is a complex example, but most of the complexity comes from the fact
		936	that we are trying to be correct (bear with me if I am wrong, I never ran
		937	the above example :).
		938
520		939
521		940
522	=head1 MAPPING	941	=head1 MAPPING
523		942
524	This section describes how JSON::XS maps Perl values to JSON values and	943	This section describes how JSON::XS maps Perl values to JSON values and
525	vice versa. These mappings are designed to "do the right thing" in most	944	vice versa. These mappings are designed to "do the right thing" in most
526	circumstances automatically, preserving round-tripping characteristics	945	circumstances automatically, preserving round-tripping characteristics
527	(what you put in comes out as something equivalent).	946	(what you put in comes out as something equivalent).
528		947
529	For the more enlightened: note that in the following descriptions,	948	For the more enlightened: note that in the following descriptions,
530	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	949	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
531	refers to the abstract Perl language itself.	950	refers to the abstract Perl language itself.
532		951
533		952
534	=head2 JSON -> PERL	953	=head2 JSON -> PERL
535		954
536	=over 4	955	=over 4
537		956
538	=item object	957	=item object
539		958
540	A JSON object becomes a reference to a hash in Perl. No ordering of object	959	A JSON object becomes a reference to a hash in Perl. No ordering of object
541	keys is preserved (JSON does not preserver object key ordering itself).	960	keys is preserved (JSON does not preserve object key ordering itself).
542		961
543	=item array	962	=item array
544		963
545	A JSON array becomes a reference to an array in Perl.	964	A JSON array becomes a reference to an array in Perl.
546		965
…		…
550	are represented by the same codepoints in the Perl string, so no manual	969	are represented by the same codepoints in the Perl string, so no manual
551	decoding is necessary.	970	decoding is necessary.
552		971
553	=item number	972	=item number
554		973
555	A JSON number becomes either an integer or numeric (floating point)	974	A JSON number becomes either an integer, numeric (floating point) or
556	scalar in perl, depending on its range and any fractional parts. On the	975	string scalar in perl, depending on its range and any fractional parts. On
557	Perl level, there is no difference between those as Perl handles all the	976	the Perl level, there is no difference between those as Perl handles all
558	conversion details, but an integer may take slightly less memory and might	977	the conversion details, but an integer may take slightly less memory and
559	represent more values exactly than (floating point) numbers.	978	might represent more values exactly than floating point numbers.
		979
		980	If the number consists of digits only, JSON::XS will try to represent
		981	it as an integer value. If that fails, it will try to represent it as
		982	a numeric (floating point) value if that is possible without loss of
		983	precision. Otherwise it will preserve the number as a string value (in
		984	which case you lose roundtripping ability, as the JSON number will be
		985	re-encoded to a JSON string).
		986
		987	Numbers containing a fractional or exponential part will always be
		988	represented as numeric (floating point) values, possibly at a loss of
		989	precision (in which case you might lose perfect roundtripping ability, but
		990	the JSON number will still be re-encoded as a JSON number).
		991
		992	Note that precision is not accuracy - binary floating point values cannot
		993	represent most decimal fractions exactly, and when converting from and to
		994	floating point, JSON::XS only guarantees precision up to but not including
		995	the least significant bit.
560		996
561	=item true, false	997	=item true, false
562		998
563	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	999	These JSON atoms become C<Types::Serialiser::true> and
564	respectively. They are overloaded to act almost exactly like the numbers	1000	C<Types::Serialiser::false>, respectively. They are overloaded to act
565	C<1> and C<0>. You can check wether a scalar is a JSON boolean by using	1001	almost exactly like the numbers C<1> and C<0>. You can check whether
566	the C<JSON::XS::is_bool> function.	1002	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1003	function (after C<use Types::Serialier>, of course).
567		1004
568	=item null	1005	=item null
569		1006
570	A JSON null atom becomes C<undef> in Perl.	1007	A JSON null atom becomes C<undef> in Perl.
		1008
		1009	=item shell-style comments (C<< # I<text> >>)
		1010
		1011	As a nonstandard extension to the JSON syntax that is enabled by the
		1012	C<relaxed> setting, shell-style comments are allowed. They can start
		1013	anywhere outside strings and go till the end of the line.
		1014
		1015	=item tagged values (C<< (I<tag>)I<value> >>).
		1016
		1017	Another nonstandard extension to the JSON syntax, enabled with the
		1018	C<allow_tags> setting, are tagged values. In this implementation, the
		1019	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1020	I<value> must be a JSON array encoding optional constructor arguments.
		1021
		1022	See L<OBJECT SERIALISATION>, below, for details.
571		1023
572	=back	1024	=back
573		1025
574		1026
575	=head2 PERL -> JSON	1027	=head2 PERL -> JSON
…		…
580		1032
581	=over 4	1033	=over 4
582		1034
583	=item hash references	1035	=item hash references
584		1036
585	Perl hash references become JSON objects. As there is no inherent ordering	1037	Perl hash references become JSON objects. As there is no inherent
586	in hash keys (or JSON objects), they will usually be encoded in a	1038	ordering in hash keys (or JSON objects), they will usually be encoded
587	pseudo-random order that can change between runs of the same program but	1039	in a pseudo-random order. JSON::XS can optionally sort the hash keys
588	stays generally the same within a single run of a program. JSON::XS can	1040	(determined by the I<canonical> flag), so the same datastructure will
589	optionally sort the hash keys (determined by the I<canonical> flag), so	1041	serialise to the same JSON text (given same settings and version of
590	the same datastructure will serialise to the same JSON text (given same	1042	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
591	settings and version of JSON::XS), but this incurs a runtime overhead	1043	e.g. when you want to compare some JSON text against another for equality.
592	and is only rarely useful, e.g. when you want to compare some JSON text
593	against another for equality.
594		1044
595	=item array references	1045	=item array references
596		1046
597	Perl array references become JSON arrays.	1047	Perl array references become JSON arrays.
598		1048
599	=item other references	1049	=item other references
600		1050
601	Other unblessed references are generally not allowed and will cause an	1051	Other unblessed references are generally not allowed and will cause an
602	exception to be thrown, except for references to the integers C<0> and	1052	exception to be thrown, except for references to the integers C<0> and
603	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1053	C<1>, which get turned into C<false> and C<true> atoms in JSON.
604	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
605		1054
		1055	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1056	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1057	and C<Types::Serialiser::true> to improve readability.
		1058
		1059	use Types::Serialiser;
606	to_json [\0,JSON::XS::true] # yields [false,true]	1060	encode_json [\0, Types::Serialiser::true] # yields [false,true]
607		1061
608	=item JSON::XS::true, JSON::XS::false	1062	=item Types::Serialiser::true, Types::Serialiser::false
609		1063
610	These special values become JSON true and JSON false values,	1064	These special values from the L<Types::Serialiser> module become JSON true
611	respectively. You cna alos use C<\1> and C<\0> directly if you want.	1065	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1066	directly if you want.
612		1067
613	=item blessed objects	1068	=item blessed objects
614		1069
615	Blessed objects are not allowed. JSON::XS currently tries to encode their	1070	Blessed objects are not directly representable in JSON, but C<JSON::XS>
616	underlying representation (hash- or arrayref), but this behaviour might	1071	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
617	change in future versions.	1072	below, for details.
618		1073
619	=item simple scalars	1074	=item simple scalars
620		1075
621	Simple Perl scalars (any scalar that is not a reference) are the most	1076	Simple Perl scalars (any scalar that is not a reference) are the most
622	difficult objects to encode: JSON::XS will encode undefined scalars as	1077	difficult objects to encode: JSON::XS will encode undefined scalars as
623	JSON null value, scalars that have last been used in a string context	1078	JSON C<null> values, scalars that have last been used in a string context
624	before encoding as JSON strings and anything else as number value:	1079	before encoding as JSON strings, and anything else as number value:
625		1080
626	# dump as number	1081	# dump as number
627	to_json [2] # yields [2]	1082	encode_json [2] # yields [2]
628	to_json [-3.0e17] # yields [-3e+17]	1083	encode_json [-3.0e17] # yields [-3e+17]
629	my $value = 5; to_json [$value] # yields [5]	1084	my $value = 5; encode_json [$value] # yields [5]
630		1085
631	# used as string, so dump as string	1086	# used as string, so dump as string
632	print $value;	1087	print $value;
633	to_json [$value] # yields ["5"]	1088	encode_json [$value] # yields ["5"]
634		1089
635	# undef becomes null	1090	# undef becomes null
636	to_json [undef] # yields [null]	1091	encode_json [undef] # yields [null]
637		1092
638	You can force the type to be a string by stringifying it:	1093	You can force the type to be a JSON string by stringifying it:
639		1094
640	my $x = 3.1; # some variable containing a number	1095	my $x = 3.1; # some variable containing a number
641	"$x"; # stringified	1096	"$x"; # stringified
642	$x .= ""; # another, more awkward way to stringify	1097	$x .= ""; # another, more awkward way to stringify
643	print $x; # perl does it for you, too, quite often	1098	print $x; # perl does it for you, too, quite often
644		1099
645	You can force the type to be a number by numifying it:	1100	You can force the type to be a JSON number by numifying it:
646		1101
647	my $x = "3"; # some variable containing a string	1102	my $x = "3"; # some variable containing a string
648	$x += 0; # numify it, ensuring it will be dumped as a number	1103	$x += 0; # numify it, ensuring it will be dumped as a number
649	$x *= 1; # same thing, the choise is yours.	1104	$x *= 1; # same thing, the choice is yours.
650		1105
651	You can not currently output JSON booleans or force the type in other,	1106	You can not currently force the type in other, less obscure, ways. Tell me
652	less obscure, ways. Tell me if you need this capability.	1107	if you need this capability (but don't forget to explain why it's needed
		1108	:).
		1109
		1110	Note that numerical precision has the same meaning as under Perl (so
		1111	binary to decimal conversion follows the same rules as in Perl, which
		1112	can differ to other languages). Also, your perl interpreter might expose
		1113	extensions to the floating point numbers of your platform, such as
		1114	infinities or NaN's - these cannot be represented in JSON, and it is an
		1115	error to pass those in.
653		1116
654	=back	1117	=back
655		1118
		1119	=head2 OBJECT SERIALISATION
656		1120
657	=head1 COMPARISON	1121	As JSON cannot directly represent Perl objects, you have to choose between
		1122	a pure JSON representation (without the ability to deserialise the object
		1123	automatically again), and a nonstandard extension to the JSON syntax,
		1124	tagged values.
658		1125
659	As already mentioned, this module was created because none of the existing	1126	=head3 SERIALISATION
660	JSON modules could be made to work correctly. First I will describe the	1127
661	problems (or pleasures) I encountered with various existing JSON modules,	1128	What happens when C<JSON::XS> encounters a Perl object depends on the
662	followed by some benchmark values. JSON::XS was designed not to suffer	1129	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
663	from any of these problems or limitations.	1130	used in this order:
664		1131
665	=over 4	1132	=over 4
666		1133
667	=item JSON 1.07	1134	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
668		1135
669	Slow (but very portable, as it is written in pure Perl).	1136	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1137	serialisation protocol to create a tagged JSON value, using a nonstandard
		1138	extension to the JSON syntax.
670		1139
671	Undocumented/buggy Unicode handling (how JSON handles unicode values is	1140	This works by invoking the C<FREEZE> method on the object, with the first
672	undocumented. One can get far by feeding it unicode strings and doing	1141	argument being the object to serialise, and the second argument being the
673	en-/decoding oneself, but unicode escapes are not working properly).	1142	constant string C<JSON> to distinguish it from other serialisers.
674		1143
675	No roundtripping (strings get clobbered if they look like numbers, e.g.	1144	The C<FREEZE> method can return any number of values (i.e. zero or
676	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	1145	more). These values and the paclkage/classname of the object will then be
677	decode into the number 2.	1146	encoded as a tagged JSON value in the following format:
678		1147
679	=item JSON::PC 0.01	1148	("classname")[FREEZE return values...]
680		1149
681	Very fast.	1150	e.g.:
682		1151
683	Undocumented/buggy Unicode handling.	1152	("URI")["http://www.google.com/"]
		1153	("MyDate")[2013,10,29]
		1154	("ImageData::JPEG")["Z3...VlCg=="]
684		1155
685	No roundtripping.	1156	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1157	objects C<type> and C<id> members to encode the object:
686		1158
687	Has problems handling many Perl values (e.g. regex results and other magic	1159	sub My::Object::FREEZE {
688	values will make it croak).	1160	my ($self, $serialiser) = @_;
689		1161
690	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1162	($self->{type}, $self->{id})
691	which is not a valid JSON text.	1163	}
692		1164
693	Unmaintained (maintainer unresponsive for many months, bugs are not	1165	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
694	getting fixed).
695		1166
696	=item JSON::Syck 0.21	1167	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1168	context. It must return a single scalar that can be directly encoded into
		1169	JSON. This scalar replaces the object in the JSON text.
697		1170
698	Very buggy (often crashes).	1171	For example, the following C<TO_JSON> method will convert all L<URI>
		1172	objects to JSON strings when serialised. The fatc that these values
		1173	originally were L<URI> objects is lost.
699		1174
700	Very inflexible (no human-readable format supported, format pretty much	1175	sub URI::TO_JSON {
701	undocumented. I need at least a format for easy reading by humans and a	1176	my ($uri) = @_;
702	single-line compact format for use in a protocol, and preferably a way to	1177	$uri->as_string
703	generate ASCII-only JSON texts).	1178	}
704		1179
705	Completely broken (and confusingly documented) Unicode handling (unicode	1180	=item 3. C<allow_blessed> is enabled.
706	escapes are not working properly, you need to set ImplicitUnicode to
707	I<different> values on en- and decoding to get symmetric behaviour).
708		1181
709	No roundtripping (simple cases work, but this depends on wether the scalar	1182	The object will be serialised as a JSON null value.
710	value was used in a numeric context or not).
711		1183
712	Dumping hashes may skip hash values depending on iterator state.	1184	=item 4. none of the above
713		1185
714	Unmaintained (maintainer unresponsive for many months, bugs are not	1186	If none of the settings are enabled or the respective methods are missing,
715	getting fixed).	1187	C<JSON::XS> throws an exception.
716
717	Does not check input for validity (i.e. will accept non-JSON input and
718	return "something" instead of raising an exception. This is a security
719	issue: imagine two banks transfering money between each other using
720	JSON. One bank might parse a given non-JSON request and deduct money,
721	while the other might reject the transaction with a syntax error. While a
722	good protocol will at least recover, that is extra unnecessary work and
723	the transaction will still not succeed).
724
725	=item JSON::DWIW 0.04
726
727	Very fast. Very natural. Very nice.
728
729	Undocumented unicode handling (but the best of the pack. Unicode escapes
730	still don't get parsed properly).
731
732	Very inflexible.
733
734	No roundtripping.
735
736	Does not generate valid JSON texts (key strings are often unquoted, empty keys
737	result in nothing being output)
738
739	Does not check input for validity.
740		1188
741	=back	1189	=back
742		1190
		1191	=head3 DESERIALISATION
		1192
		1193	For deserialisation there are only two cases to consider: either
		1194	nonstandard tagging was used, in which case C<allow_tags> decides,
		1195	or objects cannot be automatically be deserialised, in which
		1196	case you can use postprocessing or the C<filter_json_object> or
		1197	C<filter_json_single_key_object> callbacks to get some real objects our of
		1198	your JSON.
		1199
		1200	This section only considers the tagged value case: I a tagged JSON object
		1201	is encountered during decoding and C<allow_tags> is disabled, a parse
		1202	error will result (as if tagged values were not part of the grammar).
		1203
		1204	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1205	of the package/classname used during serialisation (it will not attempt
		1206	to load the package as a Perl module). If there is no such method, the
		1207	decoding will fail with an error.
		1208
		1209	Otherwise, the C<THAW> method is invoked with the classname as first
		1210	argument, the constant string C<JSON> as second argument, and all the
		1211	values from the JSON array (the values originally returned by the
		1212	C<FREEZE> method) as remaining arguments.
		1213
		1214	The method must then return the object. While technically you can return
		1215	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1216	make that work in all cases, so better return an actual blessed reference.
		1217
		1218	As an example, let's implement a C<THAW> function that regenerates the
		1219	C<My::Object> from the C<FREEZE> example earlier:
		1220
		1221	sub My::Object::THAW {
		1222	my ($class, $serialiser, $type, $id) = @_;
		1223
		1224	$class->new (type => $type, id => $id)
		1225	}
		1226
		1227
		1228	=head1 ENCODING/CODESET FLAG NOTES
		1229
		1230	The interested reader might have seen a number of flags that signify
		1231	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1232	some confusion on what these do, so here is a short comparison:
		1233
		1234	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1235	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1236	control whether C<encode> escapes character values outside their respective
		1237	codeset range. Neither of these flags conflict with each other, although
		1238	some combinations make less sense than others.
		1239
		1240	Care has been taken to make all flags symmetrical with respect to
		1241	C<encode> and C<decode>, that is, texts encoded with any combination of
		1242	these flag values will be correctly decoded when the same flags are used
		1243	- in general, if you use different flag settings while encoding vs. when
		1244	decoding you likely have a bug somewhere.
		1245
		1246	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1247	simply an abstract set of character-codepoint pairs, while an encoding
		1248	takes those codepoint numbers and I<encodes> them, in our case into
		1249	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1250	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1251	the same time, which can be confusing.
		1252
		1253	=over 4
		1254
		1255	=item C<utf8> flag disabled
		1256
		1257	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1258	and expect Unicode strings, that is, characters with high ordinal Unicode
		1259	values (> 255) will be encoded as such characters, and likewise such
		1260	characters are decoded as-is, no changes to them will be done, except
		1261	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1262	respectively (to Perl, these are the same thing in strings unless you do
		1263	funny/weird/dumb stuff).
		1264
		1265	This is useful when you want to do the encoding yourself (e.g. when you
		1266	want to have UTF-16 encoded JSON texts) or when some other layer does
		1267	the encoding for you (for example, when printing to a terminal using a
		1268	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1269	to UTF-8 encode your data first and have Perl encode it another time).
		1270
		1271	=item C<utf8> flag enabled
		1272
		1273	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1274	characters using the corresponding UTF-8 multi-byte sequence, and will
		1275	expect your input strings to be encoded as UTF-8, that is, no "character"
		1276	of the input string must have any value > 255, as UTF-8 does not allow
		1277	that.
		1278
		1279	The C<utf8> flag therefore switches between two modes: disabled means you
		1280	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1281	octet/binary string in Perl.
		1282
		1283	=item C<latin1> or C<ascii> flags enabled
		1284
		1285	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1286	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1287	characters as specified by the C<utf8> flag.
		1288
		1289	If C<utf8> is disabled, then the result is also correctly encoded in those
		1290	character sets (as both are proper subsets of Unicode, meaning that a
		1291	Unicode string with all character values < 256 is the same thing as a
		1292	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1293	the same thing as an ASCII string in Perl).
		1294
		1295	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1296	regardless of these flags, just some more characters will be escaped using
		1297	C<\uXXXX> then before.
		1298
		1299	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1300	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1301	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1302	a subset of Unicode), while ASCII is.
		1303
		1304	Surprisingly, C<decode> will ignore these flags and so treat all input
		1305	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1306	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1307	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1308
		1309	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1310	they only govern when the JSON output engine escapes a character or not.
		1311
		1312	The main use for C<latin1> is to relatively efficiently store binary data
		1313	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1314
		1315	The main use for C<ascii> is to force the output to not contain characters
		1316	with values > 127, which means you can interpret the resulting string
		1317	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1318	8-bit-encoding, and still get the same data structure back. This is useful
		1319	when your channel for JSON transfer is not 8-bit clean or the encoding
		1320	might be mangled in between (e.g. in mail), and works because ASCII is a
		1321	proper subset of most 8-bit and multibyte encodings in use in the world.
		1322
		1323	=back
		1324
		1325
		1326	=head2 JSON and ECMAscript
		1327
		1328	JSON syntax is based on how literals are represented in javascript (the
		1329	not-standardised predecessor of ECMAscript) which is presumably why it is
		1330	called "JavaScript Object Notation".
		1331
		1332	However, JSON is not a subset (and also not a superset of course) of
		1333	ECMAscript (the standard) or javascript (whatever browsers actually
		1334	implement).
		1335
		1336	If you want to use javascript's C<eval> function to "parse" JSON, you
		1337	might run into parse errors for valid JSON texts, or the resulting data
		1338	structure might not be queryable:
		1339
		1340	One of the problems is that U+2028 and U+2029 are valid characters inside
		1341	JSON strings, but are not allowed in ECMAscript string literals, so the
		1342	following Perl fragment will not output something that can be guaranteed
		1343	to be parsable by javascript's C<eval>:
		1344
		1345	use JSON::XS;
		1346
		1347	print encode_json [chr 0x2028];
		1348
		1349	The right fix for this is to use a proper JSON parser in your javascript
		1350	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1351	F<json2.js> parser).
		1352
		1353	If this is not an option, you can, as a stop-gap measure, simply encode to
		1354	ASCII-only JSON:
		1355
		1356	use JSON::XS;
		1357
		1358	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1359
		1360	Note that this will enlarge the resulting JSON text quite a bit if you
		1361	have many non-ASCII characters. You might be tempted to run some regexes
		1362	to only escape U+2028 and U+2029, e.g.:
		1363
		1364	# DO NOT USE THIS!
		1365	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1366	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1367	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1368	print $json;
		1369
		1370	Note that I<this is a bad idea>: the above only works for U+2028 and
		1371	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1372	javascript implementations, however, have issues with other characters as
		1373	well - using C<eval> naively simply I<will> cause problems.
		1374
		1375	Another problem is that some javascript implementations reserve
		1376	some property names for their own purposes (which probably makes
		1377	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1378	C<__proto__> property name for its own purposes.
		1379
		1380	If that is a problem, you could parse try to filter the resulting JSON
		1381	output for these property strings, e.g.:
		1382
		1383	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1384
		1385	This works because C<__proto__> is not valid outside of strings, so every
		1386	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1387
		1388	If you know of other incompatibilities, please let me know.
		1389
743		1390
744	=head2 JSON and YAML	1391	=head2 JSON and YAML
745		1392
746	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1393	You often hear that JSON is a subset of YAML. This is, however, a mass
747	however, a mass hysteria and very far from the truth. In general, there is	1394	hysteria(*) and very far from the truth (as of the time of this writing),
748	no way to configure JSON::XS to output a data structure as valid YAML.	1395	so let me state it clearly: I<in general, there is no way to configure
		1396	JSON::XS to output a data structure as valid YAML> that works in all
		1397	cases.
749		1398
750	If you really must use JSON::XS to generate YAML, you should use this	1399	If you really must use JSON::XS to generate YAML, you should use this
751	algorithm (subject to change in future versions):	1400	algorithm (subject to change in future versions):
752		1401
753	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1402	my $to_yaml = JSON::XS->new->utf8->space_after (1);
754	my $yaml = $to_yaml->encode ($ref) . "\n";	1403	my $yaml = $to_yaml->encode ($ref) . "\n";
755		1404
756	This will usually generate JSON texts that also parse as valid	1405	This will I<usually> generate JSON texts that also parse as valid
757	YAML. Please note that YAML has hardcoded limits on (simple) object key	1406	YAML. Please note that YAML has hardcoded limits on (simple) object key
758	lengths that JSON doesn't have, so you should make sure that your hash	1407	lengths that JSON doesn't have and also has different and incompatible
		1408	unicode character escape syntax, so you should make sure that your hash
759	keys are noticably shorter than the 1024 characters YAML allows.	1409	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1410	and that you do not have characters with codepoint values outside the
		1411	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1412	sequences in strings (which JSON::XS does not I<currently> generate, but
		1413	other JSON generators might).
760		1414
761	There might be other incompatibilities that I am not aware of. In general	1415	There might be other incompatibilities that I am not aware of (or the YAML
		1416	specification has been changed yet again - it does so quite often). In
762	you should not try to generate YAML with a JSON generator or vice versa,	1417	general you should not try to generate YAML with a JSON generator or vice
763	or try to parse JSON with a YAML parser or vice versa: chances are high	1418	versa, or try to parse JSON with a YAML parser or vice versa: chances are
764	that you will run into severe interoperability problems.	1419	high that you will run into severe interoperability problems when you
		1420	least expect it.
		1421
		1422	=over 4
		1423
		1424	=item (*)
		1425
		1426	I have been pressured multiple times by Brian Ingerson (one of the
		1427	authors of the YAML specification) to remove this paragraph, despite him
		1428	acknowledging that the actual incompatibilities exist. As I was personally
		1429	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1430	educate people about these issues, so others do not run into the same
		1431	problem again and again. After this, Brian called me a (quote)I<complete
		1432	and worthless idiot>(unquote).
		1433
		1434	In my opinion, instead of pressuring and insulting people who actually
		1435	clarify issues with YAML and the wrong statements of some of its
		1436	proponents, I would kindly suggest reading the JSON spec (which is not
		1437	that difficult or long) and finally make YAML compatible to it, and
		1438	educating users about the changes, instead of spreading lies about the
		1439	real compatibility for many I<years> and trying to silence people who
		1440	point out that it isn't true.
		1441
		1442	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1443	though the incompatibilities have been documented (and are known to Brian)
		1444	for many years and the spec makes explicit claims that YAML is a superset
		1445	of JSON. It would be so easy to fix, but apparently, bullying people and
		1446	corrupting userdata is so much easier.
		1447
		1448	=back
765		1449
766		1450
767	=head2 SPEED	1451	=head2 SPEED
768		1452
769	It seems that JSON::XS is surprisingly fast, as shown in the following	1453	It seems that JSON::XS is surprisingly fast, as shown in the following
770	tables. They have been generated with the help of the C<eg/bench> program	1454	tables. They have been generated with the help of the C<eg/bench> program
771	in the JSON::XS distribution, to make it easy to compare on your own	1455	in the JSON::XS distribution, to make it easy to compare on your own
772	system.	1456	system.
773		1457
774	First comes a comparison between various modules using a very short	1458	First comes a comparison between various modules using
775	single-line JSON string:	1459	a very short single-line JSON string (also available at
		1460	L<http://dist.schmorp.de/misc/json/short.json>).
776		1461
777	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1462	{"method": "handleMessage", "params": ["user1",
778	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1463	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1464	1, 0]}
779		1465
780	It shows the number of encodes/decodes per second (JSON::XS uses	1466	It shows the number of encodes/decodes per second (JSON::XS uses
781	the functional interface, while JSON::XS/2 uses the OO interface	1467	the functional interface, while JSON::XS/2 uses the OO interface
782	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1468	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
783	shrink). Higher is better:	1469	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1470	uses the from_json method). Higher is better:
784		1471
785	Storable | 15779.925 | 14169.946 |
786	-----------+------------+------------+
787	module | encode | decode |	1472	module | encode | decode |
788	-----------|------------|------------|	1473	--------------|------------|------------|
789	JSON | 4990.842 | 4088.813 |	1474	JSON::DWIW/DS | 86302.551 | 102300.098 |
790	JSON::DWIW | 51653.990 | 71575.154 |	1475	JSON::DWIW/FJ | 86302.551 | 75983.768 |
791	JSON::PC | 65948.176 | 74631.744 |	1476	JSON::PP | 15827.562 | 6638.658 |
792	JSON::PP | 8931.652 | 3817.168 |	1477	JSON::Syck | 63358.066 | 47662.545 |
793	JSON::Syck | 24877.248 | 27776.848 |	1478	JSON::XS | 511500.488 | 511500.488 |
794	JSON::XS | 388361.481 | 227951.304 |	1479	JSON::XS/2 | 291271.111 | 388361.481 |
795	JSON::XS/2 | 227951.304 | 218453.333 |	1480	JSON::XS/3 | 361577.931 | 361577.931 |
796	JSON::XS/3 | 338250.323 | 218453.333 |	1481	Storable | 66788.280 | 265462.278 |
797	Storable | 16500.016 | 135300.129 |
798	-----------+------------+------------+	1482	--------------+------------+------------+
799		1483
800	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1484	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
801	about three times faster on decoding, and over fourty times faster	1485	about five times faster on decoding, and over thirty to seventy times
802	than JSON, even with pretty-printing and key sorting. It also compares	1486	faster than JSON's pure perl implementation. It also compares favourably
803	favourably to Storable for small amounts of data.	1487	to Storable for small amounts of data.
804		1488
805	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1489	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
806	search API (http://nanoref.com/yahooapis/mgPdGg):	1490	search API (L<http://dist.schmorp.de/misc/json/long.json>).
807		1491
808	module | encode | decode |	1492	module | encode | decode |
809	-----------|------------|------------|	1493	--------------|------------|------------|
810	JSON | 55.260 | 34.971 |	1494	JSON::DWIW/DS | 1647.927 | 2673.916 |
811	JSON::DWIW | 825.228 | 1082.513 |	1495	JSON::DWIW/FJ | 1630.249 | 2596.128 |
812	JSON::PC | 3571.444 | 2394.829 |
813	JSON::PP | 210.987 | 32.574 |	1496	JSON::PP | 400.640 | 62.311 |
814	JSON::Syck | 552.551 | 787.544 |	1497	JSON::Syck | 1481.040 | 1524.869 |
815	JSON::XS | 5780.463 | 4854.519 |	1498	JSON::XS | 20661.596 | 9541.183 |
816	JSON::XS/2 | 3869.998 | 4798.975 |	1499	JSON::XS/2 | 10683.403 | 9416.938 |
817	JSON::XS/3 | 5862.880 | 4798.975 |	1500	JSON::XS/3 | 20661.596 | 9400.054 |
818	Storable | 4445.002 | 5235.027 |	1501	Storable | 19765.806 | 10000.725 |
819	-----------+------------+------------+	1502	--------------+------------+------------+
820		1503
821	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1504	Again, JSON::XS leads by far (except for Storable which non-surprisingly
822	decodes faster).	1505	decodes a bit faster).
823		1506
824	On large strings containing lots of high unicode characters, some modules	1507	On large strings containing lots of high Unicode characters, some modules
825	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1508	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
826	will be broken due to missing (or wrong) unicode handling. Others refuse	1509	will be broken due to missing (or wrong) Unicode handling. Others refuse
827	to decode or encode properly, so it was impossible to prepare a fair	1510	to decode or encode properly, so it was impossible to prepare a fair
828	comparison table for that case.	1511	comparison table for that case.
829		1512
830		1513
831	=head1 SECURITY CONSIDERATIONS	1514	=head1 SECURITY CONSIDERATIONS
…		…
837	any buffer overflows. Obviously, this module should ensure that and I am	1520	any buffer overflows. Obviously, this module should ensure that and I am
838	trying hard on making that true, but you never know.	1521	trying hard on making that true, but you never know.
839		1522
840	Second, you need to avoid resource-starving attacks. That means you should	1523	Second, you need to avoid resource-starving attacks. That means you should
841	limit the size of JSON texts you accept, or make sure then when your	1524	limit the size of JSON texts you accept, or make sure then when your
842	resources run out, thats just fine (e.g. by using a separate process that	1525	resources run out, that's just fine (e.g. by using a separate process that
843	can crash safely). The size of a JSON text in octets or characters is	1526	can crash safely). The size of a JSON text in octets or characters is
844	usually a good indication of the size of the resources required to decode	1527	usually a good indication of the size of the resources required to decode
845	it into a Perl structure. While JSON::XS can check the size of the JSON	1528	it into a Perl structure. While JSON::XS can check the size of the JSON
846	text, it might be too late when you already have it in memory, so you	1529	text, it might be too late when you already have it in memory, so you
847	might want to check the size before you accept the string.	1530	might want to check the size before you accept the string.
848		1531
849	Third, JSON::XS recurses using the C stack when decoding objects and	1532	Third, JSON::XS recurses using the C stack when decoding objects and
850	arrays. The C stack is a limited resource: for instance, on my amd64	1533	arrays. The C stack is a limited resource: for instance, on my amd64
851	machine with 8MB of stack size I can decode around 180k nested arrays but	1534	machine with 8MB of stack size I can decode around 180k nested arrays but
852	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1535	only 14k nested JSON objects (due to perl itself recursing deeply on croak
853	to free the temporary). If that is exceeded, the program crashes. to be	1536	to free the temporary). If that is exceeded, the program crashes. To be
854	conservative, the default nesting limit is set to 512. If your process	1537	conservative, the default nesting limit is set to 512. If your process
855	has a smaller stack, you should adjust this setting accordingly with the	1538	has a smaller stack, you should adjust this setting accordingly with the
856	C<max_depth> method.	1539	C<max_depth> method.
857		1540
858	And last but least, something else could bomb you that I forgot to think	1541	Something else could bomb you, too, that I forgot to think of. In that
859	of. In that case, you get to keep the pieces. I am always open for hints,	1542	case, you get to keep the pieces. I am always open for hints, though...
860	though...	1543
		1544	Also keep in mind that JSON::XS might leak contents of your Perl data
		1545	structures in its error messages, so when you serialise sensitive
		1546	information you might want to make sure that exceptions thrown by JSON::XS
		1547	will not end up in front of untrusted eyes.
861		1548
862	If you are using JSON::XS to return packets to consumption	1549	If you are using JSON::XS to return packets to consumption
863	by javascript scripts in a browser you should have a look at	1550	by JavaScript scripts in a browser you should have a look at
864	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether	1551	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
865	you are vulnerable to some common attack vectors (which really are browser	1552	see whether you are vulnerable to some common attack vectors (which really
866	design bugs, but it is still you who will have to deal with it, as major	1553	are browser design bugs, but it is still you who will have to deal with
867	browser developers care only for features, not about doing security	1554	it, as major browser developers care only for features, not about getting
868	right).	1555	security right).
		1556
		1557
		1558	=head1 INTEROPERABILITY WITH OTHER MODULES
		1559
		1560	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1561	constants. That means that the JSON true and false values will be
		1562	comaptible to true and false values of iother modules that do the same,
		1563	such as L<JSON::PP> and L<CBOR::XS>.
		1564
		1565
		1566	=head1 THREADS
		1567
		1568	This module is I<not> guaranteed to be thread safe and there are no
		1569	plans to change this until Perl gets thread support (as opposed to the
		1570	horribly slow so-called "threads" which are simply slow and bloated
		1571	process simulations - use fork, it's I<much> faster, cheaper, better).
		1572
		1573	(It might actually work, but you have been warned).
		1574
		1575
		1576	=head1 THE PERILS OF SETLOCALE
		1577
		1578	Sometimes people avoid the Perl locale support and directly call the
		1579	system's setlocale function with C<LC_ALL>.
		1580
		1581	This breaks both perl and modules such as JSON::XS, as stringification of
		1582	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1583	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1584	perl to stringify numbers).
		1585
		1586	The solution is simple: don't call C<setlocale>, or use it for only those
		1587	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1588
		1589	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1590	actually needs it (avoiding stringification of numbers), and restore it
		1591	afterwards.
869		1592
870		1593
871	=head1 BUGS	1594	=head1 BUGS
872		1595
873	While the goal of this module is to be correct, that unfortunately does	1596	While the goal of this module is to be correct, that unfortunately does
874	not mean its bug-free, only that I think its design is bug-free. It is	1597	not mean it's bug-free, only that I think its design is bug-free. If you
875	still relatively early in its development. If you keep reporting bugs they	1598	keep reporting bugs they will be fixed swiftly, though.
876	will be fixed swiftly, though.	1599
		1600	Please refrain from using rt.cpan.org or any other bug reporting
		1601	service. I put the contact address into my modules for a reason.
877		1602
878	=cut	1603	=cut
879		1604
880	our $true = do { bless \(my $dummy = "1"), "JSON::XS::Boolean" };	1605	BEGIN {
881	our $false = do { bless \(my $dummy = "0"), "JSON::XS::Boolean" };	1606	*true = \$Types::Serialiser::true;
		1607	*true = \&Types::Serialiser::true;
		1608	*false = \$Types::Serialiser::false;
		1609	*false = \&Types::Serialiser::false;
		1610	*is_bool = \&Types::Serialiser::is_bool;
882		1611
883	sub true() { $true }	1612	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
884	sub false() { $false }
885
886	sub is_bool($) {
887	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
888	# or UNIVERSAL::isa $_[0], "JSON::Literal"
889	}	1613	}
890		1614
891	XSLoader::load "JSON::XS", $VERSION;	1615	XSLoader::load "JSON::XS", $VERSION;
892		1616
893	package JSON::XS::Boolean;	1617	=head1 SEE ALSO
894		1618
895	use overload	1619	The F<json_xs> command line utility for quick experiments.
896	"0+" => sub { ${$_[0]} },
897	"++" => sub { $_[0] = ${$_[0]} + 1 },
898	"--" => sub { $_[0] = ${$_[0]} - 1 },
899	fallback => 1;
900
901	1;
902		1620
903	=head1 AUTHOR	1621	=head1 AUTHOR
904		1622
905	Marc Lehmann <schmorp@schmorp.de>	1623	Marc Lehmann <schmorp@schmorp.de>
906	http://home.schmorp.de/	1624	http://home.schmorp.de/
907		1625
908	=cut	1626	=cut
909		1627
		1628	1
		1629

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