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Revision 1.51 by root, Mon Jul 2 01:12:27 2007 UTC vs.
Revision 1.139 by root, Thu May 23 09:31:32 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 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 $VERSION = 2.34;
87	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
88		108
89	our @EXPORT = qw(to_json from_json);	109	our @EXPORT = qw(encode_json decode_json to_json from_json);
		110
		111	sub to_json($) {
		112	require Carp;
		113	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
		114	}
		115
		116	sub from_json($) {
		117	require Carp;
		118	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
		119	}
90		120
91	use Exporter;	121	use Exporter;
92	use XSLoader;	122	use XSLoader;
93		123
94	=head1 FUNCTIONAL INTERFACE	124	=head1 FUNCTIONAL INTERFACE
95		125
96	The following convinience methods are provided by this module. They are	126	The following convenience methods are provided by this module. They are
97	exported by default:	127	exported by default:
98		128
99	=over 4	129	=over 4
100		130
101	=item $json_text = to_json $perl_scalar	131	=item $json_text = encode_json $perl_scalar
102		132
103	Converts the given Perl data structure (a simple scalar or a reference to	133	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	134	(that is, the string contains octets only). Croaks on error.
105	octets only). Croaks on error.
106		135
107	This function call is functionally identical to:	136	This function call is functionally identical to:
108		137
109	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	138	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
110		139
111	except being faster.	140	Except being faster.
112		141
113	=item $perl_scalar = from_json $json_text	142	=item $perl_scalar = decode_json $json_text
114		143
115	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	144	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	145	to parse that as an UTF-8 encoded JSON text, returning the resulting
117	scalar or reference. Croaks on error.	146	reference. Croaks on error.
118		147
119	This function call is functionally identical to:	148	This function call is functionally identical to:
120		149
121	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	150	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
122		151
123	except being faster.	152	Except being faster.
124		153
125	=item $is_boolean = JSON::XS::is_bool $scalar	154	=item $is_boolean = JSON::XS::is_bool $scalar
126		155
127	Returns true if the passed scalar represents either JSON::XS::true or	156	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	157	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
…		…
132	Perl.	161	Perl.
133		162
134	=back	163	=back
135		164
136		165
		166	=head1 A FEW NOTES ON UNICODE AND PERL
		167
		168	Since this often leads to confusion, here are a few very clear words on
		169	how Unicode works in Perl, modulo bugs.
		170
		171	=over 4
		172
		173	=item 1. Perl strings can store characters with ordinal values > 255.
		174
		175	This enables you to store Unicode characters as single characters in a
		176	Perl string - very natural.
		177
		178	=item 2. Perl does I<not> associate an encoding with your strings.
		179
		180	... until you force it to, e.g. when matching it against a regex, or
		181	printing the scalar to a file, in which case Perl either interprets your
		182	string as locale-encoded text, octets/binary, or as Unicode, depending
		183	on various settings. In no case is an encoding stored together with your
		184	data, it is I<use> that decides encoding, not any magical meta data.
		185
		186	=item 3. The internal utf-8 flag has no meaning with regards to the
		187	encoding of your string.
		188
		189	Just ignore that flag unless you debug a Perl bug, a module written in
		190	XS or want to dive into the internals of perl. Otherwise it will only
		191	confuse you, as, despite the name, it says nothing about how your string
		192	is encoded. You can have Unicode strings with that flag set, with that
		193	flag clear, and you can have binary data with that flag set and that flag
		194	clear. Other possibilities exist, too.
		195
		196	If you didn't know about that flag, just the better, pretend it doesn't
		197	exist.
		198
		199	=item 4. A "Unicode String" is simply a string where each character can be
		200	validly interpreted as a Unicode code point.
		201
		202	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		203	Unicode string encoded in UTF-8, giving you a binary string.
		204
		205	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		206
		207	It's a fact. Learn to live with it.
		208
		209	=back
		210
		211	I hope this helps :)
		212
		213
137	=head1 OBJECT-ORIENTED INTERFACE	214	=head1 OBJECT-ORIENTED INTERFACE
138		215
139	The object oriented interface lets you configure your own encoding or	216	The object oriented interface lets you configure your own encoding or
140	decoding style, within the limits of supported formats.	217	decoding style, within the limits of supported formats.
141		218
…		…
152	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	229	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
153	=> {"a": [1, 2]}	230	=> {"a": [1, 2]}
154		231
155	=item $json = $json->ascii ([$enable])	232	=item $json = $json->ascii ([$enable])
156		233
		234	=item $enabled = $json->get_ascii
		235
157	If C<$enable> is true (or missing), then the C<encode> method will not	236	If C<$enable> is true (or missing), then the C<encode> method will not
158	generate characters outside the code range C<0..127> (which is ASCII). Any	237	generate characters outside the code range C<0..127> (which is ASCII). Any
159	unicode characters outside that range will be escaped using either a	238	Unicode characters outside that range will be escaped using either a
160	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,	239	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
161	as per RFC4627. The resulting encoded JSON text can be treated as a native	240	as per RFC4627. The resulting encoded JSON text can be treated as a native
162	unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,	241	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
163	or any other superset of ASCII.	242	or any other superset of ASCII.
164		243
165	If C<$enable> is false, then the C<encode> method will not escape Unicode	244	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	245	characters unless required by the JSON syntax or other flags. This results
167	in a faster and more compact format.	246	in a faster and more compact format.
168		247
		248	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		249	document.
		250
169	The main use for this flag is to produce JSON texts that can be	251	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	252	transmitted over a 7-bit channel, as the encoded JSON texts will not
171	contain any 8 bit characters.	253	contain any 8 bit characters.
172		254
173	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	255	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
174	=> ["\ud801\udc01"]	256	=> ["\ud801\udc01"]
175		257
176	=item $json = $json->latin1 ([$enable])	258	=item $json = $json->latin1 ([$enable])
177		259
		260	=item $enabled = $json->get_latin1
		261
178	If C<$enable> is true (or missing), then the C<encode> method will encode	262	If C<$enable> is true (or missing), then the C<encode> method will encode
179	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters	263	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
180	outside the code range C<0..255>. The resulting string can be treated as a	264	outside the code range C<0..255>. The resulting string can be treated as a
181	latin1-encoded JSON text or a native unicode string. The C<decode> method	265	latin1-encoded JSON text or a native Unicode string. The C<decode> method
182	will not be affected in any way by this flag, as C<decode> by default	266	will not be affected in any way by this flag, as C<decode> by default
183	expects unicode, which is a strict superset of latin1.	267	expects Unicode, which is a strict superset of latin1.
184		268
185	If C<$enable> is false, then the C<encode> method will not escape Unicode	269	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.	270	characters unless required by the JSON syntax or other flags.
		271
		272	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		273	document.
187		274
188	The main use for this flag is efficiently encoding binary data as JSON	275	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	276	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	277	size. The disadvantage is that the resulting JSON text is encoded
191	in latin1 (and must correctly be treated as such when storing and	278	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	279	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	280	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.	281	in files or databases, not when talking to other JSON encoders/decoders.
195		282
196	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	283	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
197	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	284	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
198		285
199	=item $json = $json->utf8 ([$enable])	286	=item $json = $json->utf8 ([$enable])
		287
		288	=item $enabled = $json->get_utf8
200		289
201	If C<$enable> is true (or missing), then the C<encode> method will encode	290	If C<$enable> is true (or missing), then the C<encode> method will encode
202	the JSON result into UTF-8, as required by many protocols, while the	291	the JSON result into UTF-8, as required by many protocols, while the
203	C<decode> method expects to be handled an UTF-8-encoded string. Please	292	C<decode> method expects to be handled an UTF-8-encoded string. Please
204	note that UTF-8-encoded strings do not contain any characters outside the	293	note that UTF-8-encoded strings do not contain any characters outside the
205	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	294	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
206	versions, enabling this option might enable autodetection of the UTF-16	295	versions, enabling this option might enable autodetection of the UTF-16
207	and UTF-32 encoding families, as described in RFC4627.	296	and UTF-32 encoding families, as described in RFC4627.
208		297
209	If C<$enable> is false, then the C<encode> method will return the JSON	298	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	299	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	300	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.	301	to be done yourself, e.g. using the Encode module.
		302
		303	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		304	document.
213		305
214	Example, output UTF-16BE-encoded JSON:	306	Example, output UTF-16BE-encoded JSON:
215		307
216	use Encode;	308	use Encode;
217	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	309	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
238	]	330	]
239	}	331	}
240		332
241	=item $json = $json->indent ([$enable])	333	=item $json = $json->indent ([$enable])
242		334
		335	=item $enabled = $json->get_indent
		336
243	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	337	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
244	format as output, putting every array member or object/hash key-value pair	338	format as output, putting every array member or object/hash key-value pair
245	into its own line, identing them properly.	339	into its own line, indenting them properly.
246		340
247	If C<$enable> is false, no newlines or indenting will be produced, and the	341	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>.	342	resulting JSON text is guaranteed not to contain any C<newlines>.
249		343
250	This setting has no effect when decoding JSON texts.	344	This setting has no effect when decoding JSON texts.
251		345
252	=item $json = $json->space_before ([$enable])	346	=item $json = $json->space_before ([$enable])
		347
		348	=item $enabled = $json->get_space_before
253		349
254	If C<$enable> is true (or missing), then the C<encode> method will add an extra	350	If C<$enable> is true (or missing), then the C<encode> method will add an extra
255	optional space before the C<:> separating keys from values in JSON objects.	351	optional space before the C<:> separating keys from values in JSON objects.
256		352
257	If C<$enable> is false, then the C<encode> method will not add any extra	353	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:	359	Example, space_before enabled, space_after and indent disabled:
264		360
265	{"key" :"value"}	361	{"key" :"value"}
266		362
267	=item $json = $json->space_after ([$enable])	363	=item $json = $json->space_after ([$enable])
		364
		365	=item $enabled = $json->get_space_after
268		366
269	If C<$enable> is true (or missing), then the C<encode> method will add an extra	367	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	368	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	369	and extra whitespace after the C<,> separating key-value pairs and array
272	members.	370	members.
…		…
278		376
279	Example, space_before and indent disabled, space_after enabled:	377	Example, space_before and indent disabled, space_after enabled:
280		378
281	{"key": "value"}	379	{"key": "value"}
282		380
		381	=item $json = $json->relaxed ([$enable])
		382
		383	=item $enabled = $json->get_relaxed
		384
		385	If C<$enable> is true (or missing), then C<decode> will accept some
		386	extensions to normal JSON syntax (see below). C<encode> will not be
		387	affected in anyway. I<Be aware that this option makes you accept invalid
		388	JSON texts as if they were valid!>. I suggest only to use this option to
		389	parse application-specific files written by humans (configuration files,
		390	resource files etc.)
		391
		392	If C<$enable> is false (the default), then C<decode> will only accept
		393	valid JSON texts.
		394
		395	Currently accepted extensions are:
		396
		397	=over 4
		398
		399	=item * list items can have an end-comma
		400
		401	JSON I<separates> array elements and key-value pairs with commas. This
		402	can be annoying if you write JSON texts manually and want to be able to
		403	quickly append elements, so this extension accepts comma at the end of
		404	such items not just between them:
		405
		406	[
		407	1,
		408	2, <- this comma not normally allowed
		409	]
		410	{
		411	"k1": "v1",
		412	"k2": "v2", <- this comma not normally allowed
		413	}
		414
		415	=item * shell-style '#'-comments
		416
		417	Whenever JSON allows whitespace, shell-style comments are additionally
		418	allowed. They are terminated by the first carriage-return or line-feed
		419	character, after which more white-space and comments are allowed.
		420
		421	[
		422	1, # this comment not allowed in JSON
		423	# neither this one...
		424	]
		425
		426	=back
		427
283	=item $json = $json->canonical ([$enable])	428	=item $json = $json->canonical ([$enable])
		429
		430	=item $enabled = $json->get_canonical
284		431
285	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	432	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
286	by sorting their keys. This is adding a comparatively high overhead.	433	by sorting their keys. This is adding a comparatively high overhead.
287		434
288	If C<$enable> is false, then the C<encode> method will output key-value	435	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	436	pairs in the order Perl stores them (which will likely change between runs
290	of the same script).	437	of the same script, and can change even within the same run from 5.18
		438	onwards).
291		439
292	This option is useful if you want the same data structure to be encoded as	440	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,	441	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,	442	the same hash might be encoded differently even if contains the same data,
295	as key-value pairs have no inherent ordering in Perl.	443	as key-value pairs have no inherent ordering in Perl.
296		444
297	This setting has no effect when decoding JSON texts.	445	This setting has no effect when decoding JSON texts.
298		446
		447	This setting has currently no effect on tied hashes.
		448
299	=item $json = $json->allow_nonref ([$enable])	449	=item $json = $json->allow_nonref ([$enable])
		450
		451	=item $enabled = $json->get_allow_nonref
300		452
301	If C<$enable> is true (or missing), then the C<encode> method can convert a	453	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,	454	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	455	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
304	values instead of croaking.	456	values instead of croaking.
…		…
312	resulting in an invalid JSON text:	464	resulting in an invalid JSON text:
313		465
314	JSON::XS->new->allow_nonref->encode ("Hello, World!")	466	JSON::XS->new->allow_nonref->encode ("Hello, World!")
315	=> "Hello, World!"	467	=> "Hello, World!"
316		468
		469	=item $json = $json->allow_unknown ([$enable])
		470
		471	=item $enabled = $json->get_allow_unknown
		472
		473	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		474	exception when it encounters values it cannot represent in JSON (for
		475	example, filehandles) but instead will encode a JSON C<null> value. Note
		476	that blessed objects are not included here and are handled separately by
		477	c<allow_nonref>.
		478
		479	If C<$enable> is false (the default), then C<encode> will throw an
		480	exception when it encounters anything it cannot encode as JSON.
		481
		482	This option does not affect C<decode> in any way, and it is recommended to
		483	leave it off unless you know your communications partner.
		484
317	=item $json = $json->allow_blessed ([$enable])	485	=item $json = $json->allow_blessed ([$enable])
		486
		487	=item $enabled = $json->get_allow_blessed
318		488
319	If C<$enable> is true (or missing), then the C<encode> method will not	489	If C<$enable> is true (or missing), then the C<encode> method will not
320	barf when it encounters a blessed reference. Instead, the value of the	490	barf when it encounters a blessed reference. Instead, the value of the
321	B<convert_blessed> option will decide wether C<null> (C<convert_blessed>	491	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
322	disabled or no C<to_json> method found) or a representation of the	492	disabled or no C<TO_JSON> method found) or a representation of the
323	object (C<convert_blessed> enabled and C<to_json> method found) is being	493	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
324	encoded. Has no effect on C<decode>.	494	encoded. Has no effect on C<decode>.
325		495
326	If C<$enable> is false (the default), then C<encode> will throw an	496	If C<$enable> is false (the default), then C<encode> will throw an
327	exception when it encounters a blessed object.	497	exception when it encounters a blessed object.
328		498
329	=item $json = $json->convert_blessed ([$enable])	499	=item $json = $json->convert_blessed ([$enable])
		500
		501	=item $enabled = $json->get_convert_blessed
330		502
331	If C<$enable> is true (or missing), then C<encode>, upon encountering a	503	If C<$enable> is true (or missing), then C<encode>, upon encountering a
332	blessed object, will check for the availability of the C<TO_JSON> method	504	blessed object, will check for the availability of the C<TO_JSON> method
333	on the object's class. If found, it will be called in scalar context	505	on the object's class. If found, it will be called in scalar context
334	and the resulting scalar will be encoded instead of the object. If no	506	and the resulting scalar will be encoded instead of the object. If no
…		…
338	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	510	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
339	returns other blessed objects, those will be handled in the same	511	returns other blessed objects, those will be handled in the same
340	way. C<TO_JSON> must take care of not causing an endless recursion cycle	512	way. C<TO_JSON> must take care of not causing an endless recursion cycle
341	(== crash) in this case. The name of C<TO_JSON> was chosen because other	513	(== crash) in this case. The name of C<TO_JSON> was chosen because other
342	methods called by the Perl core (== not by the user of the object) are	514	methods called by the Perl core (== not by the user of the object) are
343	usually in upper case letters and to avoid collisions with the C<to_json>	515	usually in upper case letters and to avoid collisions with any C<to_json>
344	function.	516	function or method.
345		517
346	This setting does not yet influence C<decode> in any way, but in the	518	This setting does not yet influence C<decode> in any way, but in the
347	future, global hooks might get installed that influence C<decode> and are	519	future, global hooks might get installed that influence C<decode> and are
348	enabled by this setting.	520	enabled by this setting.
349		521
350	If C<$enable> is false, then the C<allow_blessed> setting will decide what	522	If C<$enable> is false, then the C<allow_blessed> setting will decide what
351	to do when a blessed object is found.	523	to do when a blessed object is found.
352		524
353	=item $json = $json->filter_json_object ([$coderef])	525	=item $json = $json->filter_json_object ([$coderef->($hashref)])
354		526
355	When C<$coderef> is specified, it will be called from C<decode> each	527	When C<$coderef> is specified, it will be called from C<decode> each
356	time it decodes a JSON object. The only argument is a reference to the	528	time it decodes a JSON object. The only argument is a reference to the
357	newly-created hash. If the code references returns a single scalar (which	529	newly-created hash. If the code references returns a single scalar (which
358	need not be a reference), this value (i.e. a copy of that scalar to avoid	530	need not be a reference), this value (i.e. a copy of that scalar to avoid
359	aliasing) is inserted into the deserialised data structure. If it returns	531	aliasing) is inserted into the deserialised data structure. If it returns
360	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the	532	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
361	original deserialised hash will be inserted. This setting can slow down	533	original deserialised hash will be inserted. This setting can slow down
362	decoding considerably.	534	decoding considerably.
363		535
364	When C<$coderef> is omitted or undefined, C<decode> will not change the	536	When C<$coderef> is omitted or undefined, any existing callback will
365	deserialised hash in any way. This is maximally fast.	537	be removed and C<decode> will not change the deserialised hash in any
		538	way.
366		539
367	Example, convert all JSON objects into the integer 5:	540	Example, convert all JSON objects into the integer 5:
368		541
369	my $js = JSON::XS->new->filter_json_object (sub { 5 });	542	my $js = JSON::XS->new->filter_json_object (sub { 5 });
370	# returns [5]	543	# returns [5]
371	$js->decode ('[{}]')	544	$js->decode ('[{}]')
372	# throw an exception because allow_nonref is not enabled:	545	# throw an exception because allow_nonref is not enabled
		546	# so a lone 5 is not allowed.
373	$js->decode ('{"a":1, "b":2}');	547	$js->decode ('{"a":1, "b":2}');
374		548
375	=item $json = $json->filter_json_single_key_object ([$coderef])	549	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
376		550
377	Works like C<filter_json_object>, but is only called for JSON objects	551	Works remotely similar to C<filter_json_object>, but is only called for
378	having only a single key.	552	JSON objects having a single key named C<$key>.
379		553
380	This C<$coderef> is called before the one specified via	554	This C<$coderef> is called before the one specified via
381	C<filter_json_object>, if any. If it returns something, that will be	555	C<filter_json_object>, if any. It gets passed the single value in the JSON
382	inserted into the data structure. If it returns nothing, the callback	556	object. If it returns a single value, it will be inserted into the data
383	from C<filter_json_object> will be called next. If you want to force	557	structure. If it returns nothing (not even C<undef> but the empty list),
384	insertion of single-key objects even in the presence of a mutating	558	the callback from C<filter_json_object> will be called next, as if no
385	C<filter_json_object> callback, simply return the passed hash.	559	single-key callback were specified.
		560
		561	If C<$coderef> is omitted or undefined, the corresponding callback will be
		562	disabled. There can only ever be one callback for a given key.
386		563
387	As this callback gets called less often then the C<filter_json_object>	564	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	565	one, decoding speed will not usually suffer as much. Therefore, single-key
389	objects make excellent targets to serialise Perl objects into, especially	566	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	567	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	568	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	569	support this in any way, so you need to make sure your data never looks
393	like a serialised Perl hash.	570	like a serialised Perl hash.
394		571
395	Typical names for the single object key are C<__class_whatever__>, or	572	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	573	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
…		…
401	into the corresponding C<< $WIDGET{<id>} >> object:	578	into the corresponding C<< $WIDGET{<id>} >> object:
402		579
403	# return whatever is in $WIDGET{5}:	580	# return whatever is in $WIDGET{5}:
404	JSON::XS	581	JSON::XS
405	->new	582	->new
406	->filter_json_single_key_object (sub {	583	->filter_json_single_key_object (__widget__ => sub {
407	exists $_[0]{__widget__}
408	? $WIDGET{ $_[0]{__widget__} }	584	$WIDGET{ $_[0] }
409	: ()
410	})	585	})
411	->decode ('{"__widget__": 5')	586	->decode ('{"__widget__": 5')
412		587
413	# this can be used with a TO_JSON method in some "widget" class	588	# this can be used with a TO_JSON method in some "widget" class
414	# for serialisation to json:	589	# for serialisation to json:
…		…
422		597
423	{ __widget__ => $self->{id} }	598	{ __widget__ => $self->{id} }
424	}	599	}
425		600
426	=item $json = $json->shrink ([$enable])	601	=item $json = $json->shrink ([$enable])
		602
		603	=item $enabled = $json->get_shrink
427		604
428	Perl usually over-allocates memory a bit when allocating space for	605	Perl usually over-allocates memory a bit when allocating space for
429	strings. This flag optionally resizes strings generated by either	606	strings. This flag optionally resizes strings generated by either
430	C<encode> or C<decode> to their minimum size possible. This can save	607	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	608	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	626	strings that look like integers or floats into integers or floats
450	internally (there is no difference on the Perl level), saving space.	627	internally (there is no difference on the Perl level), saving space.
451		628
452	=item $json = $json->max_depth ([$maximum_nesting_depth])	629	=item $json = $json->max_depth ([$maximum_nesting_depth])
453		630
		631	=item $max_depth = $json->get_max_depth
		632
454	Sets the maximum nesting level (default C<512>) accepted while encoding	633	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	634	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	635	data structure, then the encoder and decoder will stop and croak at that
457	stop and croak at that point.	636	point.
458		637
459	Nesting level is defined by number of hash- or arrayrefs that the encoder	638	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<[>	639	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	640	characters without their matching closing parenthesis crossed to reach a
462	given character in a string.	641	given character in a string.
463		642
464	Setting the maximum depth to one disallows any nesting, so that ensures	643	Setting the maximum depth to one disallows any nesting, so that ensures
465	that the object is only a single hash/object or array.	644	that the object is only a single hash/object or array.
466		645
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	646	If no argument is given, the highest possible setting will be used, which
469	used, which is rarely useful.	647	is rarely useful.
		648
		649	Note that nesting is implemented by recursion in C. The default value has
		650	been chosen to be as large as typical operating systems allow without
		651	crashing.
470		652
471	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	653	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
472		654
473	=item $json = $json->max_size ([$maximum_string_size])	655	=item $json = $json->max_size ([$maximum_string_size])
		656
		657	=item $max_size = $json->get_max_size
474		658
475	Set the maximum length a JSON text may have (in bytes) where decoding is	659	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>	660	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	661	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	662	attempt to decode the string but throw an exception. This setting has no
479	effect on C<encode> (yet).	663	effect on C<encode> (yet).
480		664
481	The argument to C<max_size> will be rounded up to the next B<highest>	665	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	666	C<0> is specified).
483	limit check will be deactivated (same as when C<0> is specified).
484		667
485	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	668	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
486		669
487	=item $json_text = $json->encode ($perl_scalar)	670	=item $json_text = $json->encode ($perl_scalar)
488		671
…		…
517	=> ([], 3)	700	=> ([], 3)
518		701
519	=back	702	=back
520		703
521		704
		705	=head1 INCREMENTAL PARSING
		706
		707	In some cases, there is the need for incremental parsing of JSON
		708	texts. While this module always has to keep both JSON text and resulting
		709	Perl data structure in memory at one time, it does allow you to parse a
		710	JSON stream incrementally. It does so by accumulating text until it has
		711	a full JSON object, which it then can decode. This process is similar to
		712	using C<decode_prefix> to see if a full JSON object is available, but
		713	is much more efficient (and can be implemented with a minimum of method
		714	calls).
		715
		716	JSON::XS will only attempt to parse the JSON text once it is sure it
		717	has enough text to get a decisive result, using a very simple but
		718	truly incremental parser. This means that it sometimes won't stop as
		719	early as the full parser, for example, it doesn't detect mismatched
		720	parentheses. The only thing it guarantees is that it starts decoding as
		721	soon as a syntactically valid JSON text has been seen. This means you need
		722	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		723	parsing in the presence if syntax errors.
		724
		725	The following methods implement this incremental parser.
		726
		727	=over 4
		728
		729	=item [void, scalar or list context] = $json->incr_parse ([$string])
		730
		731	This is the central parsing function. It can both append new text and
		732	extract objects from the stream accumulated so far (both of these
		733	functions are optional).
		734
		735	If C<$string> is given, then this string is appended to the already
		736	existing JSON fragment stored in the C<$json> object.
		737
		738	After that, if the function is called in void context, it will simply
		739	return without doing anything further. This can be used to add more text
		740	in as many chunks as you want.
		741
		742	If the method is called in scalar context, then it will try to extract
		743	exactly I<one> JSON object. If that is successful, it will return this
		744	object, otherwise it will return C<undef>. If there is a parse error,
		745	this method will croak just as C<decode> would do (one can then use
		746	C<incr_skip> to skip the errornous part). This is the most common way of
		747	using the method.
		748
		749	And finally, in list context, it will try to extract as many objects
		750	from the stream as it can find and return them, or the empty list
		751	otherwise. For this to work, there must be no separators between the JSON
		752	objects or arrays, instead they must be concatenated back-to-back. If
		753	an error occurs, an exception will be raised as in the scalar context
		754	case. Note that in this case, any previously-parsed JSON texts will be
		755	lost.
		756
		757	Example: Parse some JSON arrays/objects in a given string and return
		758	them.
		759
		760	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		761
		762	=item $lvalue_string = $json->incr_text
		763
		764	This method returns the currently stored JSON fragment as an lvalue, that
		765	is, you can manipulate it. This I<only> works when a preceding call to
		766	C<incr_parse> in I<scalar context> successfully returned an object. Under
		767	all other circumstances you must not call this function (I mean it.
		768	although in simple tests it might actually work, it I<will> fail under
		769	real world conditions). As a special exception, you can also call this
		770	method before having parsed anything.
		771
		772	This function is useful in two cases: a) finding the trailing text after a
		773	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		774	(such as commas).
		775
		776	=item $json->incr_skip
		777
		778	This will reset the state of the incremental parser and will remove
		779	the parsed text from the input buffer so far. This is useful after
		780	C<incr_parse> died, in which case the input buffer and incremental parser
		781	state is left unchanged, to skip the text parsed so far and to reset the
		782	parse state.
		783
		784	The difference to C<incr_reset> is that only text until the parse error
		785	occured is removed.
		786
		787	=item $json->incr_reset
		788
		789	This completely resets the incremental parser, that is, after this call,
		790	it will be as if the parser had never parsed anything.
		791
		792	This is useful if you want to repeatedly parse JSON objects and want to
		793	ignore any trailing data, which means you have to reset the parser after
		794	each successful decode.
		795
		796	=back
		797
		798	=head2 LIMITATIONS
		799
		800	All options that affect decoding are supported, except
		801	C<allow_nonref>. The reason for this is that it cannot be made to
		802	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		803	them back to back and still decode them perfectly. This does not hold true
		804	for JSON numbers, however.
		805
		806	For example, is the string C<1> a single JSON number, or is it simply the
		807	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		808	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		809	takes the conservative route and disallows this case.
		810
		811	=head2 EXAMPLES
		812
		813	Some examples will make all this clearer. First, a simple example that
		814	works similarly to C<decode_prefix>: We want to decode the JSON object at
		815	the start of a string and identify the portion after the JSON object:
		816
		817	my $text = "[1,2,3] hello";
		818
		819	my $json = new JSON::XS;
		820
		821	my $obj = $json->incr_parse ($text)
		822	or die "expected JSON object or array at beginning of string";
		823
		824	my $tail = $json->incr_text;
		825	# $tail now contains " hello"
		826
		827	Easy, isn't it?
		828
		829	Now for a more complicated example: Imagine a hypothetical protocol where
		830	you read some requests from a TCP stream, and each request is a JSON
		831	array, without any separation between them (in fact, it is often useful to
		832	use newlines as "separators", as these get interpreted as whitespace at
		833	the start of the JSON text, which makes it possible to test said protocol
		834	with C<telnet>...).
		835
		836	Here is how you'd do it (it is trivial to write this in an event-based
		837	manner):
		838
		839	my $json = new JSON::XS;
		840
		841	# read some data from the socket
		842	while (sysread $socket, my $buf, 4096) {
		843
		844	# split and decode as many requests as possible
		845	for my $request ($json->incr_parse ($buf)) {
		846	# act on the $request
		847	}
		848	}
		849
		850	Another complicated example: Assume you have a string with JSON objects
		851	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		852	[3]>). To parse them, we have to skip the commas between the JSON texts,
		853	and here is where the lvalue-ness of C<incr_text> comes in useful:
		854
		855	my $text = "[1],[2], [3]";
		856	my $json = new JSON::XS;
		857
		858	# void context, so no parsing done
		859	$json->incr_parse ($text);
		860
		861	# now extract as many objects as possible. note the
		862	# use of scalar context so incr_text can be called.
		863	while (my $obj = $json->incr_parse) {
		864	# do something with $obj
		865
		866	# now skip the optional comma
		867	$json->incr_text =~ s/^ \s* , //x;
		868	}
		869
		870	Now lets go for a very complex example: Assume that you have a gigantic
		871	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		872	but you cannot load it into memory fully (this has actually happened in
		873	the real world :).
		874
		875	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		876	can still help you: You implement a (very simple) array parser and let
		877	JSON decode the array elements, which are all full JSON objects on their
		878	own (this wouldn't work if the array elements could be JSON numbers, for
		879	example):
		880
		881	my $json = new JSON::XS;
		882
		883	# open the monster
		884	open my $fh, "<bigfile.json"
		885	or die "bigfile: $!";
		886
		887	# first parse the initial "["
		888	for (;;) {
		889	sysread $fh, my $buf, 65536
		890	or die "read error: $!";
		891	$json->incr_parse ($buf); # void context, so no parsing
		892
		893	# Exit the loop once we found and removed(!) the initial "[".
		894	# In essence, we are (ab-)using the $json object as a simple scalar
		895	# we append data to.
		896	last if $json->incr_text =~ s/^ \s* \[ //x;
		897	}
		898
		899	# now we have the skipped the initial "[", so continue
		900	# parsing all the elements.
		901	for (;;) {
		902	# in this loop we read data until we got a single JSON object
		903	for (;;) {
		904	if (my $obj = $json->incr_parse) {
		905	# do something with $obj
		906	last;
		907	}
		908
		909	# add more data
		910	sysread $fh, my $buf, 65536
		911	or die "read error: $!";
		912	$json->incr_parse ($buf); # void context, so no parsing
		913	}
		914
		915	# in this loop we read data until we either found and parsed the
		916	# separating "," between elements, or the final "]"
		917	for (;;) {
		918	# first skip whitespace
		919	$json->incr_text =~ s/^\s*//;
		920
		921	# if we find "]", we are done
		922	if ($json->incr_text =~ s/^\]//) {
		923	print "finished.\n";
		924	exit;
		925	}
		926
		927	# if we find ",", we can continue with the next element
		928	if ($json->incr_text =~ s/^,//) {
		929	last;
		930	}
		931
		932	# if we find anything else, we have a parse error!
		933	if (length $json->incr_text) {
		934	die "parse error near ", $json->incr_text;
		935	}
		936
		937	# else add more data
		938	sysread $fh, my $buf, 65536
		939	or die "read error: $!";
		940	$json->incr_parse ($buf); # void context, so no parsing
		941	}
		942
		943	This is a complex example, but most of the complexity comes from the fact
		944	that we are trying to be correct (bear with me if I am wrong, I never ran
		945	the above example :).
		946
		947
		948
522	=head1 MAPPING	949	=head1 MAPPING
523		950
524	This section describes how JSON::XS maps Perl values to JSON values and	951	This section describes how JSON::XS maps Perl values to JSON values and
525	vice versa. These mappings are designed to "do the right thing" in most	952	vice versa. These mappings are designed to "do the right thing" in most
526	circumstances automatically, preserving round-tripping characteristics	953	circumstances automatically, preserving round-tripping characteristics
527	(what you put in comes out as something equivalent).	954	(what you put in comes out as something equivalent).
528		955
529	For the more enlightened: note that in the following descriptions,	956	For the more enlightened: note that in the following descriptions,
530	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	957	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
531	refers to the abstract Perl language itself.	958	refers to the abstract Perl language itself.
532		959
533		960
534	=head2 JSON -> PERL	961	=head2 JSON -> PERL
535		962
536	=over 4	963	=over 4
537		964
538	=item object	965	=item object
539		966
540	A JSON object becomes a reference to a hash in Perl. No ordering of object	967	A JSON object becomes a reference to a hash in Perl. No ordering of object
541	keys is preserved (JSON does not preserver object key ordering itself).	968	keys is preserved (JSON does not preserve object key ordering itself).
542		969
543	=item array	970	=item array
544		971
545	A JSON array becomes a reference to an array in Perl.	972	A JSON array becomes a reference to an array in Perl.
546		973
…		…
550	are represented by the same codepoints in the Perl string, so no manual	977	are represented by the same codepoints in the Perl string, so no manual
551	decoding is necessary.	978	decoding is necessary.
552		979
553	=item number	980	=item number
554		981
555	A JSON number becomes either an integer or numeric (floating point)	982	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	983	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	984	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	985	the conversion details, but an integer may take slightly less memory and
559	represent more values exactly than (floating point) numbers.	986	might represent more values exactly than floating point numbers.
		987
		988	If the number consists of digits only, JSON::XS will try to represent
		989	it as an integer value. If that fails, it will try to represent it as
		990	a numeric (floating point) value if that is possible without loss of
		991	precision. Otherwise it will preserve the number as a string value (in
		992	which case you lose roundtripping ability, as the JSON number will be
		993	re-encoded toa JSON string).
		994
		995	Numbers containing a fractional or exponential part will always be
		996	represented as numeric (floating point) values, possibly at a loss of
		997	precision (in which case you might lose perfect roundtripping ability, but
		998	the JSON number will still be re-encoded as a JSON number).
		999
		1000	Note that precision is not accuracy - binary floating point values cannot
		1001	represent most decimal fractions exactly, and when converting from and to
		1002	floating point, JSON::XS only guarantees precision up to but not including
		1003	the leats significant bit.
560		1004
561	=item true, false	1005	=item true, false
562		1006
563	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	1007	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
564	respectively. They are overloaded to act almost exactly like the numbers	1008	respectively. They are overloaded to act almost exactly like the numbers
565	C<1> and C<0>. You can check wether a scalar is a JSON boolean by using	1009	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
566	the C<JSON::XS::is_bool> function.	1010	the C<JSON::XS::is_bool> function.
567		1011
568	=item null	1012	=item null
569		1013
570	A JSON null atom becomes C<undef> in Perl.	1014	A JSON null atom becomes C<undef> in Perl.
…		…
601	Other unblessed references are generally not allowed and will cause an	1045	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	1046	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	1047	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
604	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.	1048	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
605		1049
606	to_json [\0,JSON::XS::true] # yields [false,true]	1050	encode_json [\0, JSON::XS::true] # yields [false,true]
607		1051
608	=item JSON::XS::true, JSON::XS::false	1052	=item JSON::XS::true, JSON::XS::false
609		1053
610	These special values become JSON true and JSON false values,	1054	These special values become JSON true and JSON false values,
611	respectively. You cna alos use C<\1> and C<\0> directly if you want.	1055	respectively. You can also use C<\1> and C<\0> directly if you want.
612		1056
613	=item blessed objects	1057	=item blessed objects
614		1058
615	Blessed objects are not allowed. JSON::XS currently tries to encode their	1059	Blessed objects are not directly representable in JSON. See the
616	underlying representation (hash- or arrayref), but this behaviour might	1060	C<allow_blessed> and C<convert_blessed> methods on various options on
617	change in future versions.	1061	how to deal with this: basically, you can choose between throwing an
		1062	exception, encoding the reference as if it weren't blessed, or provide
		1063	your own serialiser method.
618		1064
619	=item simple scalars	1065	=item simple scalars
620		1066
621	Simple Perl scalars (any scalar that is not a reference) are the most	1067	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	1068	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	1069	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:	1070	before encoding as JSON strings, and anything else as number value:
625		1071
626	# dump as number	1072	# dump as number
627	to_json [2] # yields [2]	1073	encode_json [2] # yields [2]
628	to_json [-3.0e17] # yields [-3e+17]	1074	encode_json [-3.0e17] # yields [-3e+17]
629	my $value = 5; to_json [$value] # yields [5]	1075	my $value = 5; encode_json [$value] # yields [5]
630		1076
631	# used as string, so dump as string	1077	# used as string, so dump as string
632	print $value;	1078	print $value;
633	to_json [$value] # yields ["5"]	1079	encode_json [$value] # yields ["5"]
634		1080
635	# undef becomes null	1081	# undef becomes null
636	to_json [undef] # yields [null]	1082	encode_json [undef] # yields [null]
637		1083
638	You can force the type to be a string by stringifying it:	1084	You can force the type to be a JSON string by stringifying it:
639		1085
640	my $x = 3.1; # some variable containing a number	1086	my $x = 3.1; # some variable containing a number
641	"$x"; # stringified	1087	"$x"; # stringified
642	$x .= ""; # another, more awkward way to stringify	1088	$x .= ""; # another, more awkward way to stringify
643	print $x; # perl does it for you, too, quite often	1089	print $x; # perl does it for you, too, quite often
644		1090
645	You can force the type to be a number by numifying it:	1091	You can force the type to be a JSON number by numifying it:
646		1092
647	my $x = "3"; # some variable containing a string	1093	my $x = "3"; # some variable containing a string
648	$x += 0; # numify it, ensuring it will be dumped as a number	1094	$x += 0; # numify it, ensuring it will be dumped as a number
649	$x *= 1; # same thing, the choise is yours.	1095	$x *= 1; # same thing, the choice is yours.
650		1096
651	You can not currently output JSON booleans or force the type in other,	1097	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.	1098	if you need this capability (but don't forget to explain why it's needed
		1099	:).
		1100
		1101	Note that numerical precision has the same meaning as under Perl (so
		1102	binary to decimal conversion follows the same rules as in Perl, which
		1103	can differ to other languages). Also, your perl interpreter might expose
		1104	extensions to the floating point numbers of your platform, such as
		1105	infinities or NaN's - these cannot be represented in JSON, and it is an
		1106	error to pass those in.
653		1107
654	=back	1108	=back
655		1109
656		1110
657	=head1 COMPARISON	1111	=head1 ENCODING/CODESET FLAG NOTES
658		1112
659	As already mentioned, this module was created because none of the existing	1113	The interested reader might have seen a number of flags that signify
660	JSON modules could be made to work correctly. First I will describe the	1114	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
661	problems (or pleasures) I encountered with various existing JSON modules,	1115	some confusion on what these do, so here is a short comparison:
662	followed by some benchmark values. JSON::XS was designed not to suffer	1116
663	from any of these problems or limitations.	1117	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1118	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1119	control whether C<encode> escapes character values outside their respective
		1120	codeset range. Neither of these flags conflict with each other, although
		1121	some combinations make less sense than others.
		1122
		1123	Care has been taken to make all flags symmetrical with respect to
		1124	C<encode> and C<decode>, that is, texts encoded with any combination of
		1125	these flag values will be correctly decoded when the same flags are used
		1126	- in general, if you use different flag settings while encoding vs. when
		1127	decoding you likely have a bug somewhere.
		1128
		1129	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1130	simply an abstract set of character-codepoint pairs, while an encoding
		1131	takes those codepoint numbers and I<encodes> them, in our case into
		1132	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1133	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1134	the same time, which can be confusing.
664		1135
665	=over 4	1136	=over 4
666		1137
667	=item JSON 1.07	1138	=item C<utf8> flag disabled
668		1139
669	Slow (but very portable, as it is written in pure Perl).	1140	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1141	and expect Unicode strings, that is, characters with high ordinal Unicode
		1142	values (> 255) will be encoded as such characters, and likewise such
		1143	characters are decoded as-is, no canges to them will be done, except
		1144	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1145	respectively (to Perl, these are the same thing in strings unless you do
		1146	funny/weird/dumb stuff).
670		1147
671	Undocumented/buggy Unicode handling (how JSON handles unicode values is	1148	This is useful when you want to do the encoding yourself (e.g. when you
672	undocumented. One can get far by feeding it unicode strings and doing	1149	want to have UTF-16 encoded JSON texts) or when some other layer does
673	en-/decoding oneself, but unicode escapes are not working properly).	1150	the encoding for you (for example, when printing to a terminal using a
		1151	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1152	to UTF-8 encode your data first and have Perl encode it another time).
674		1153
675	No roundtripping (strings get clobbered if they look like numbers, e.g.	1154	=item C<utf8> flag enabled
676	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
677	decode into the number 2.
678		1155
679	=item JSON::PC 0.01	1156	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1157	characters using the corresponding UTF-8 multi-byte sequence, and will
		1158	expect your input strings to be encoded as UTF-8, that is, no "character"
		1159	of the input string must have any value > 255, as UTF-8 does not allow
		1160	that.
680		1161
681	Very fast.	1162	The C<utf8> flag therefore switches between two modes: disabled means you
		1163	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1164	octet/binary string in Perl.
682		1165
683	Undocumented/buggy Unicode handling.	1166	=item C<latin1> or C<ascii> flags enabled
684		1167
685	No roundtripping.	1168	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1169	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1170	characters as specified by the C<utf8> flag.
686		1171
687	Has problems handling many Perl values (e.g. regex results and other magic	1172	If C<utf8> is disabled, then the result is also correctly encoded in those
688	values will make it croak).	1173	character sets (as both are proper subsets of Unicode, meaning that a
		1174	Unicode string with all character values < 256 is the same thing as a
		1175	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1176	the same thing as an ASCII string in Perl).
689		1177
690	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1178	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
691	which is not a valid JSON text.	1179	regardless of these flags, just some more characters will be escaped using
		1180	C<\uXXXX> then before.
692		1181
693	Unmaintained (maintainer unresponsive for many months, bugs are not	1182	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
694	getting fixed).	1183	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1184	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1185	a subset of Unicode), while ASCII is.
695		1186
696	=item JSON::Syck 0.21	1187	Surprisingly, C<decode> will ignore these flags and so treat all input
		1188	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1189	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1190	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
697		1191
698	Very buggy (often crashes).	1192	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1193	they only govern when the JSON output engine escapes a character or not.
699		1194
700	Very inflexible (no human-readable format supported, format pretty much	1195	The main use for C<latin1> is to relatively efficiently store binary data
701	undocumented. I need at least a format for easy reading by humans and a	1196	as JSON, at the expense of breaking compatibility with most JSON decoders.
702	single-line compact format for use in a protocol, and preferably a way to
703	generate ASCII-only JSON texts).
704		1197
705	Completely broken (and confusingly documented) Unicode handling (unicode	1198	The main use for C<ascii> is to force the output to not contain characters
706	escapes are not working properly, you need to set ImplicitUnicode to	1199	with values > 127, which means you can interpret the resulting string
707	I<different> values on en- and decoding to get symmetric behaviour).	1200	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
708		1201	8-bit-encoding, and still get the same data structure back. This is useful
709	No roundtripping (simple cases work, but this depends on wether the scalar	1202	when your channel for JSON transfer is not 8-bit clean or the encoding
710	value was used in a numeric context or not).	1203	might be mangled in between (e.g. in mail), and works because ASCII is a
711		1204	proper subset of most 8-bit and multibyte encodings in use in the world.
712	Dumping hashes may skip hash values depending on iterator state.
713
714	Unmaintained (maintainer unresponsive for many months, bugs are not
715	getting fixed).
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		1205
741	=back	1206	=back
742		1207
743		1208
		1209	=head2 JSON and ECMAscript
		1210
		1211	JSON syntax is based on how literals are represented in javascript (the
		1212	not-standardised predecessor of ECMAscript) which is presumably why it is
		1213	called "JavaScript Object Notation".
		1214
		1215	However, JSON is not a subset (and also not a superset of course) of
		1216	ECMAscript (the standard) or javascript (whatever browsers actually
		1217	implement).
		1218
		1219	If you want to use javascript's C<eval> function to "parse" JSON, you
		1220	might run into parse errors for valid JSON texts, or the resulting data
		1221	structure might not be queryable:
		1222
		1223	One of the problems is that U+2028 and U+2029 are valid characters inside
		1224	JSON strings, but are not allowed in ECMAscript string literals, so the
		1225	following Perl fragment will not output something that can be guaranteed
		1226	to be parsable by javascript's C<eval>:
		1227
		1228	use JSON::XS;
		1229
		1230	print encode_json [chr 0x2028];
		1231
		1232	The right fix for this is to use a proper JSON parser in your javascript
		1233	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1234	F<json2.js> parser).
		1235
		1236	If this is not an option, you can, as a stop-gap measure, simply encode to
		1237	ASCII-only JSON:
		1238
		1239	use JSON::XS;
		1240
		1241	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1242
		1243	Note that this will enlarge the resulting JSON text quite a bit if you
		1244	have many non-ASCII characters. You might be tempted to run some regexes
		1245	to only escape U+2028 and U+2029, e.g.:
		1246
		1247	# DO NOT USE THIS!
		1248	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1249	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1250	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1251	print $json;
		1252
		1253	Note that I<this is a bad idea>: the above only works for U+2028 and
		1254	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1255	javascript implementations, however, have issues with other characters as
		1256	well - using C<eval> naively simply I<will> cause problems.
		1257
		1258	Another problem is that some javascript implementations reserve
		1259	some property names for their own purposes (which probably makes
		1260	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1261	C<__proto__> property name for its own purposes.
		1262
		1263	If that is a problem, you could parse try to filter the resulting JSON
		1264	output for these property strings, e.g.:
		1265
		1266	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1267
		1268	This works because C<__proto__> is not valid outside of strings, so every
		1269	occurence of C<"__proto__"\s*:> must be a string used as property name.
		1270
		1271	If you know of other incompatibilities, please let me know.
		1272
		1273
744	=head2 JSON and YAML	1274	=head2 JSON and YAML
745		1275
746	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1276	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	1277	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.	1278	so let me state it clearly: I<in general, there is no way to configure
		1279	JSON::XS to output a data structure as valid YAML> that works in all
		1280	cases.
749		1281
750	If you really must use JSON::XS to generate YAML, you should use this	1282	If you really must use JSON::XS to generate YAML, you should use this
751	algorithm (subject to change in future versions):	1283	algorithm (subject to change in future versions):
752		1284
753	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1285	my $to_yaml = JSON::XS->new->utf8->space_after (1);
754	my $yaml = $to_yaml->encode ($ref) . "\n";	1286	my $yaml = $to_yaml->encode ($ref) . "\n";
755		1287
756	This will usually generate JSON texts that also parse as valid	1288	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	1289	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	1290	lengths that JSON doesn't have and also has different and incompatible
		1291	unicode character escape syntax, so you should make sure that your hash
759	keys are noticably shorter than the 1024 characters YAML allows.	1292	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1293	and that you do not have characters with codepoint values outside the
		1294	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1295	sequences in strings (which JSON::XS does not I<currently> generate, but
		1296	other JSON generators might).
760		1297
761	There might be other incompatibilities that I am not aware of. In general	1298	There might be other incompatibilities that I am not aware of (or the YAML
		1299	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,	1300	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	1301	versa, or try to parse JSON with a YAML parser or vice versa: chances are
764	that you will run into severe interoperability problems.	1302	high that you will run into severe interoperability problems when you
		1303	least expect it.
		1304
		1305	=over 4
		1306
		1307	=item (*)
		1308
		1309	I have been pressured multiple times by Brian Ingerson (one of the
		1310	authors of the YAML specification) to remove this paragraph, despite him
		1311	acknowledging that the actual incompatibilities exist. As I was personally
		1312	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1313	educate people about these issues, so others do not run into the same
		1314	problem again and again. After this, Brian called me a (quote)I<complete
		1315	and worthless idiot>(unquote).
		1316
		1317	In my opinion, instead of pressuring and insulting people who actually
		1318	clarify issues with YAML and the wrong statements of some of its
		1319	proponents, I would kindly suggest reading the JSON spec (which is not
		1320	that difficult or long) and finally make YAML compatible to it, and
		1321	educating users about the changes, instead of spreading lies about the
		1322	real compatibility for many I<years> and trying to silence people who
		1323	point out that it isn't true.
		1324
		1325	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1326	though the incompatibilities have been documented (and are known to Brian)
		1327	for many years and the spec makes explicit claims that YAML is a superset
		1328	of JSON. It would be so easy to fix, but apparently, bullying people and
		1329	corrupting userdata is so much easier.
		1330
		1331	=back
765		1332
766		1333
767	=head2 SPEED	1334	=head2 SPEED
768		1335
769	It seems that JSON::XS is surprisingly fast, as shown in the following	1336	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	1337	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	1338	in the JSON::XS distribution, to make it easy to compare on your own
772	system.	1339	system.
773		1340
774	First comes a comparison between various modules using a very short	1341	First comes a comparison between various modules using
775	single-line JSON string:	1342	a very short single-line JSON string (also available at
		1343	L<http://dist.schmorp.de/misc/json/short.json>).
776		1344
777	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1345	{"method": "handleMessage", "params": ["user1",
778	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1346	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1347	1, 0]}
779		1348
780	It shows the number of encodes/decodes per second (JSON::XS uses	1349	It shows the number of encodes/decodes per second (JSON::XS uses
781	the functional interface, while JSON::XS/2 uses the OO interface	1350	the functional interface, while JSON::XS/2 uses the OO interface
782	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1351	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
783	shrink). Higher is better:	1352	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1353	uses the from_json method). Higher is better:
784		1354
785	Storable | 15779.925 | 14169.946 |
786	-----------+------------+------------+
787	module | encode | decode |	1355	module | encode | decode |
788	-----------|------------|------------|	1356	--------------|------------|------------|
789	JSON | 4990.842 | 4088.813 |	1357	JSON::DWIW/DS | 86302.551 | 102300.098 |
790	JSON::DWIW | 51653.990 | 71575.154 |	1358	JSON::DWIW/FJ | 86302.551 | 75983.768 |
791	JSON::PC | 65948.176 | 74631.744 |	1359	JSON::PP | 15827.562 | 6638.658 |
792	JSON::PP | 8931.652 | 3817.168 |	1360	JSON::Syck | 63358.066 | 47662.545 |
793	JSON::Syck | 24877.248 | 27776.848 |	1361	JSON::XS | 511500.488 | 511500.488 |
794	JSON::XS | 388361.481 | 227951.304 |	1362	JSON::XS/2 | 291271.111 | 388361.481 |
795	JSON::XS/2 | 227951.304 | 218453.333 |	1363	JSON::XS/3 | 361577.931 | 361577.931 |
796	JSON::XS/3 | 338250.323 | 218453.333 |	1364	Storable | 66788.280 | 265462.278 |
797	Storable | 16500.016 | 135300.129 |
798	-----------+------------+------------+	1365	--------------+------------+------------+
799		1366
800	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1367	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	1368	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	1369	faster than JSON's pure perl implementation. It also compares favourably
803	favourably to Storable for small amounts of data.	1370	to Storable for small amounts of data.
804		1371
805	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1372	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
806	search API (http://nanoref.com/yahooapis/mgPdGg):	1373	search API (L<http://dist.schmorp.de/misc/json/long.json>).
807		1374
808	module | encode | decode |	1375	module | encode | decode |
809	-----------|------------|------------|	1376	--------------|------------|------------|
810	JSON | 55.260 | 34.971 |	1377	JSON::DWIW/DS | 1647.927 | 2673.916 |
811	JSON::DWIW | 825.228 | 1082.513 |	1378	JSON::DWIW/FJ | 1630.249 | 2596.128 |
812	JSON::PC | 3571.444 | 2394.829 |
813	JSON::PP | 210.987 | 32.574 |	1379	JSON::PP | 400.640 | 62.311 |
814	JSON::Syck | 552.551 | 787.544 |	1380	JSON::Syck | 1481.040 | 1524.869 |
815	JSON::XS | 5780.463 | 4854.519 |	1381	JSON::XS | 20661.596 | 9541.183 |
816	JSON::XS/2 | 3869.998 | 4798.975 |	1382	JSON::XS/2 | 10683.403 | 9416.938 |
817	JSON::XS/3 | 5862.880 | 4798.975 |	1383	JSON::XS/3 | 20661.596 | 9400.054 |
818	Storable | 4445.002 | 5235.027 |	1384	Storable | 19765.806 | 10000.725 |
819	-----------+------------+------------+	1385	--------------+------------+------------+
820		1386
821	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1387	Again, JSON::XS leads by far (except for Storable which non-surprisingly
822	decodes faster).	1388	decodes a bit faster).
823		1389
824	On large strings containing lots of high unicode characters, some modules	1390	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	1391	(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	1392	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	1393	to decode or encode properly, so it was impossible to prepare a fair
828	comparison table for that case.	1394	comparison table for that case.
829		1395
830		1396
831	=head1 SECURITY CONSIDERATIONS	1397	=head1 SECURITY CONSIDERATIONS
…		…
837	any buffer overflows. Obviously, this module should ensure that and I am	1403	any buffer overflows. Obviously, this module should ensure that and I am
838	trying hard on making that true, but you never know.	1404	trying hard on making that true, but you never know.
839		1405
840	Second, you need to avoid resource-starving attacks. That means you should	1406	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	1407	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	1408	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	1409	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	1410	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	1411	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	1412	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.	1413	might want to check the size before you accept the string.
848		1414
849	Third, JSON::XS recurses using the C stack when decoding objects and	1415	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	1416	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	1417	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	1418	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	1419	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	1420	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	1421	has a smaller stack, you should adjust this setting accordingly with the
856	C<max_depth> method.	1422	C<max_depth> method.
857		1423
858	And last but least, something else could bomb you that I forgot to think	1424	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,	1425	case, you get to keep the pieces. I am always open for hints, though...
860	though...	1426
		1427	Also keep in mind that JSON::XS might leak contents of your Perl data
		1428	structures in its error messages, so when you serialise sensitive
		1429	information you might want to make sure that exceptions thrown by JSON::XS
		1430	will not end up in front of untrusted eyes.
861		1431
862	If you are using JSON::XS to return packets to consumption	1432	If you are using JSON::XS to return packets to consumption
863	by javascript scripts in a browser you should have a look at	1433	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	1434	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	1435	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	1436	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	1437	it, as major browser developers care only for features, not about getting
868	right).	1438	security right).
		1439
		1440
		1441	=head1 THREADS
		1442
		1443	This module is I<not> guaranteed to be thread safe and there are no
		1444	plans to change this until Perl gets thread support (as opposed to the
		1445	horribly slow so-called "threads" which are simply slow and bloated
		1446	process simulations - use fork, it's I<much> faster, cheaper, better).
		1447
		1448	(It might actually work, but you have been warned).
		1449
		1450
		1451	=head1 THE PERILS OF SETLOCALE
		1452
		1453	Sometimes people avoid the Perl locale support and directly call the
		1454	system's setlocale function with C<LC_ALL>.
		1455
		1456	This breaks both perl and modules such as JSON::XS, as stringification of
		1457	numbers no longer works correcly (e.g. C<$x = 0.1; print "$x"+1> might
		1458	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1459	perl to stringify numbers).
		1460
		1461	The solution is simple: don't call C<setlocale>, or use it for only those
		1462	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1463
		1464	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1465	actually needs it (avoiding stringification of numbers), and restore it
		1466	afterwards.
869		1467
870		1468
871	=head1 BUGS	1469	=head1 BUGS
872		1470
873	While the goal of this module is to be correct, that unfortunately does	1471	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	1472	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	1473	keep reporting bugs they will be fixed swiftly, though.
876	will be fixed swiftly, though.	1474
		1475	Please refrain from using rt.cpan.org or any other bug reporting
		1476	service. I put the contact address into my modules for a reason.
877		1477
878	=cut	1478	=cut
879		1479
880	our $true = do { bless \(my $dummy = "1"), "JSON::XS::Boolean" };	1480	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
881	our $false = do { bless \(my $dummy = "0"), "JSON::XS::Boolean" };	1481	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
882		1482
883	sub true() { $true }	1483	sub true() { $true }
884	sub false() { $false }	1484	sub false() { $false }
885		1485
886	sub is_bool($) {	1486	sub is_bool($) {
…		…
898	"--" => sub { $_[0] = ${$_[0]} - 1 },	1498	"--" => sub { $_[0] = ${$_[0]} - 1 },
899	fallback => 1;	1499	fallback => 1;
900		1500
901	1;	1501	1;
902		1502
		1503	=head1 SEE ALSO
		1504
		1505	The F<json_xs> command line utility for quick experiments.
		1506
903	=head1 AUTHOR	1507	=head1 AUTHOR
904		1508
905	Marc Lehmann <schmorp@schmorp.de>	1509	Marc Lehmann <schmorp@schmorp.de>
906	http://home.schmorp.de/	1510	http://home.schmorp.de/
907		1511

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