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Revision 1.44 by root, Mon Jun 25 04:08:17 2007 UTC vs.
Revision 1.143 by root, Fri Oct 25 20:02:54 2013 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
		5	=encoding utf-8
		6
		7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
4		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
8		13
9	# exported functions, they croak on error	14	# exported functions, they croak on error
10	# and expect/generate UTF-8	15	# and expect/generate UTF-8
11		16
12	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
13	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
14
15	# objToJson and jsonToObj aliases to to_json and from_json
16	# are exported for compatibility to the JSON module,
17	# but should not be used in new code.
18		19
19	# OO-interface	20	# OO-interface
20		21
21	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
22	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
23	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
24		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
		33
25	=head1 DESCRIPTION	34	=head1 DESCRIPTION
26		35
27	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
28	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
29	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overridden) with no overhead due to emulation (by inheriting constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
30		47
31	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
32	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
33	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
34	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
35	reports for other reasons.	52	reports for other reasons.
36		53
37	See COMPARISON, below, for a comparison to some other JSON modules.
38
39	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
40	vice versa.	55	vice versa.
41		56
42	=head2 FEATURES	57	=head2 FEATURES
43		58
44	=over 4	59	=over 4
45		60
46	=item * correct unicode handling	61	=item * correct Unicode handling
47		62
48	This module knows how to handle Unicode, and even documents how and when	63	This module knows how to handle Unicode, documents how and when it does
49	it does so.	64	so, and even documents what "correct" means.
50		65
51	=item * round-trip integrity	66	=item * round-trip integrity
52		67
53	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
54	by JSON, the deserialised data structure is identical on the Perl level.	69	by JSON and Perl, the deserialised data structure is identical on the Perl
55	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
56	like a number).	71	it looks like a number). There I<are> minor exceptions to this, read the
		72	MAPPING section below to learn about those.
57		73
58	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
59		75
60	There is no guessing, no generating of illegal JSON texts by default,	76	There is no guessing, no generating of illegal JSON texts by default,
61	and only JSON is accepted as input by default (the latter is a security	77	and only JSON is accepted as input by default (the latter is a security
62	feature).	78	feature).
63		79
64	=item * fast	80	=item * fast
65		81
66	Compared to other JSON modules, this module compares favourably in terms	82	Compared to other JSON modules and other serialisers such as Storable,
67	of speed, too.	83	this module usually compares favourably in terms of speed, too.
68		84
69	=item * simple to use	85	=item * simple to use
70		86
71	This module has both a simple functional interface as well as an OO	87	This module has both a simple functional interface as well as an object
72	interface.	88	oriented interface.
73		89
74	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
75		91
76	You can choose between the most compact guarenteed single-line format	92	You can choose between the most compact guaranteed-single-line format
77	possible (nice for simple line-based protocols), a pure-ascii format	93	possible (nice for simple line-based protocols), a pure-ASCII format
78	(for when your transport is not 8-bit clean, still supports the whole	94	(for when your transport is not 8-bit clean, still supports the whole
79	unicode range), or a pretty-printed format (for when you want to read that	95	Unicode range), or a pretty-printed format (for when you want to read that
80	stuff). Or you can combine those features in whatever way you like.	96	stuff). Or you can combine those features in whatever way you like.
81		97
82	=back	98	=back
83		99
84	=cut	100	=cut
85		101
86	package JSON::XS;	102	package JSON::XS;
87		103
88	use strict;	104	use common::sense;
89		105
90	our $VERSION = '1.4';	106	our $VERSION = 2.34;
91	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
92		108
93	our @EXPORT = qw(to_json from_json objToJson jsonToObj);	109	our @EXPORT = qw(encode_json decode_json);
94		110
95	use Exporter;	111	use Exporter;
96	use XSLoader;	112	use XSLoader;
97		113
98	=head1 FUNCTIONAL INTERFACE	114	=head1 FUNCTIONAL INTERFACE
99		115
100	The following convinience methods are provided by this module. They are	116	The following convenience methods are provided by this module. They are
101	exported by default:	117	exported by default:
102		118
103	=over 4	119	=over 4
104		120
105	=item $json_text = to_json $perl_scalar	121	=item $json_text = encode_json $perl_scalar
106		122
107	Converts the given Perl data structure (a simple scalar or a reference to	123	Converts the given Perl data structure to a UTF-8 encoded, binary string
108	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	124	(that is, the string contains octets only). Croaks on error.
109	octets only). Croaks on error.
110		125
111	This function call is functionally identical to:	126	This function call is functionally identical to:
112		127
113	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	128	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
114		129
115	except being faster.	130	Except being faster.
116		131
117	=item $perl_scalar = from_json $json_text	132	=item $perl_scalar = decode_json $json_text
118		133
119	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	134	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
120	parse that as an UTF-8 encoded JSON text, returning the resulting simple	135	to parse that as an UTF-8 encoded JSON text, returning the resulting
121	scalar or reference. Croaks on error.	136	reference. Croaks on error.
122		137
123	This function call is functionally identical to:	138	This function call is functionally identical to:
124		139
125	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	140	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
126		141
127	except being faster.	142	Except being faster.
128		143
129	=item $is_boolean = JSON::XS::is_bool $scalar	144	=item $is_boolean = JSON::XS::is_bool $scalar
130		145
131	Returns true if the passed scalar represents either JSON::XS::true or	146	Returns true if the passed scalar represents either JSON::XS::true or
132	JSON::XS::false, two constants that act like C<1> and C<0>, respectively	147	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
…		…
136	Perl.	151	Perl.
137		152
138	=back	153	=back
139		154
140		155
		156	=head1 A FEW NOTES ON UNICODE AND PERL
		157
		158	Since this often leads to confusion, here are a few very clear words on
		159	how Unicode works in Perl, modulo bugs.
		160
		161	=over 4
		162
		163	=item 1. Perl strings can store characters with ordinal values > 255.
		164
		165	This enables you to store Unicode characters as single characters in a
		166	Perl string - very natural.
		167
		168	=item 2. Perl does I<not> associate an encoding with your strings.
		169
		170	... until you force it to, e.g. when matching it against a regex, or
		171	printing the scalar to a file, in which case Perl either interprets your
		172	string as locale-encoded text, octets/binary, or as Unicode, depending
		173	on various settings. In no case is an encoding stored together with your
		174	data, it is I<use> that decides encoding, not any magical meta data.
		175
		176	=item 3. The internal utf-8 flag has no meaning with regards to the
		177	encoding of your string.
		178
		179	Just ignore that flag unless you debug a Perl bug, a module written in
		180	XS or want to dive into the internals of perl. Otherwise it will only
		181	confuse you, as, despite the name, it says nothing about how your string
		182	is encoded. You can have Unicode strings with that flag set, with that
		183	flag clear, and you can have binary data with that flag set and that flag
		184	clear. Other possibilities exist, too.
		185
		186	If you didn't know about that flag, just the better, pretend it doesn't
		187	exist.
		188
		189	=item 4. A "Unicode String" is simply a string where each character can be
		190	validly interpreted as a Unicode code point.
		191
		192	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		193	Unicode string encoded in UTF-8, giving you a binary string.
		194
		195	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		196
		197	It's a fact. Learn to live with it.
		198
		199	=back
		200
		201	I hope this helps :)
		202
		203
141	=head1 OBJECT-ORIENTED INTERFACE	204	=head1 OBJECT-ORIENTED INTERFACE
142		205
143	The object oriented interface lets you configure your own encoding or	206	The object oriented interface lets you configure your own encoding or
144	decoding style, within the limits of supported formats.	207	decoding style, within the limits of supported formats.
145		208
…		…
156	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	219	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
157	=> {"a": [1, 2]}	220	=> {"a": [1, 2]}
158		221
159	=item $json = $json->ascii ([$enable])	222	=item $json = $json->ascii ([$enable])
160		223
		224	=item $enabled = $json->get_ascii
		225
161	If C<$enable> is true (or missing), then the C<encode> method will not	226	If C<$enable> is true (or missing), then the C<encode> method will not
162	generate characters outside the code range C<0..127> (which is ASCII). Any	227	generate characters outside the code range C<0..127> (which is ASCII). Any
163	unicode characters outside that range will be escaped using either a	228	Unicode characters outside that range will be escaped using either a
164	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,	229	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
165	as per RFC4627. The resulting encoded JSON text can be treated as a native	230	as per RFC4627. The resulting encoded JSON text can be treated as a native
166	unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,	231	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
167	or any other superset of ASCII.	232	or any other superset of ASCII.
168		233
169	If C<$enable> is false, then the C<encode> method will not escape Unicode	234	If C<$enable> is false, then the C<encode> method will not escape Unicode
170	characters unless required by the JSON syntax or other flags. This results	235	characters unless required by the JSON syntax or other flags. This results
171	in a faster and more compact format.	236	in a faster and more compact format.
172		237
		238	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		239	document.
		240
173	The main use for this flag is to produce JSON texts that can be	241	The main use for this flag is to produce JSON texts that can be
174	transmitted over a 7-bit channel, as the encoded JSON texts will not	242	transmitted over a 7-bit channel, as the encoded JSON texts will not
175	contain any 8 bit characters.	243	contain any 8 bit characters.
176		244
177	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	245	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
178	=> ["\ud801\udc01"]	246	=> ["\ud801\udc01"]
179		247
180	=item $json = $json->latin1 ([$enable])	248	=item $json = $json->latin1 ([$enable])
181		249
		250	=item $enabled = $json->get_latin1
		251
182	If C<$enable> is true (or missing), then the C<encode> method will encode	252	If C<$enable> is true (or missing), then the C<encode> method will encode
183	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters	253	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
184	outside the code range C<0..255>. The resulting string can be treated as a	254	outside the code range C<0..255>. The resulting string can be treated as a
185	latin1-encoded JSON text or a native unicode string. The C<decode> method	255	latin1-encoded JSON text or a native Unicode string. The C<decode> method
186	will not be affected in any way by this flag, as C<decode> by default	256	will not be affected in any way by this flag, as C<decode> by default
187	expects unicode, which is a strict superset of latin1.	257	expects Unicode, which is a strict superset of latin1.
188		258
189	If C<$enable> is false, then the C<encode> method will not escape Unicode	259	If C<$enable> is false, then the C<encode> method will not escape Unicode
190	characters unless required by the JSON syntax or other flags.	260	characters unless required by the JSON syntax or other flags.
		261
		262	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		263	document.
191		264
192	The main use for this flag is efficiently encoding binary data as JSON	265	The main use for this flag is efficiently encoding binary data as JSON
193	text, as most octets will not be escaped, resulting in a smaller encoded	266	text, as most octets will not be escaped, resulting in a smaller encoded
194	size. The disadvantage is that the resulting JSON text is encoded	267	size. The disadvantage is that the resulting JSON text is encoded
195	in latin1 (and must correctly be treated as such when storing and	268	in latin1 (and must correctly be treated as such when storing and
196	transfering), a rare encoding for JSON. It is therefore most useful when	269	transferring), a rare encoding for JSON. It is therefore most useful when
197	you want to store data structures known to contain binary data efficiently	270	you want to store data structures known to contain binary data efficiently
198	in files or databases, not when talking to other JSON encoders/decoders.	271	in files or databases, not when talking to other JSON encoders/decoders.
199		272
200	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	273	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
201	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	274	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
202		275
203	=item $json = $json->utf8 ([$enable])	276	=item $json = $json->utf8 ([$enable])
		277
		278	=item $enabled = $json->get_utf8
204		279
205	If C<$enable> is true (or missing), then the C<encode> method will encode	280	If C<$enable> is true (or missing), then the C<encode> method will encode
206	the JSON result into UTF-8, as required by many protocols, while the	281	the JSON result into UTF-8, as required by many protocols, while the
207	C<decode> method expects to be handled an UTF-8-encoded string. Please	282	C<decode> method expects to be handled an UTF-8-encoded string. Please
208	note that UTF-8-encoded strings do not contain any characters outside the	283	note that UTF-8-encoded strings do not contain any characters outside the
209	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	284	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
210	versions, enabling this option might enable autodetection of the UTF-16	285	versions, enabling this option might enable autodetection of the UTF-16
211	and UTF-32 encoding families, as described in RFC4627.	286	and UTF-32 encoding families, as described in RFC4627.
212		287
213	If C<$enable> is false, then the C<encode> method will return the JSON	288	If C<$enable> is false, then the C<encode> method will return the JSON
214	string as a (non-encoded) unicode string, while C<decode> expects thus a	289	string as a (non-encoded) Unicode string, while C<decode> expects thus a
215	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	290	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
216	to be done yourself, e.g. using the Encode module.	291	to be done yourself, e.g. using the Encode module.
		292
		293	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		294	document.
217		295
218	Example, output UTF-16BE-encoded JSON:	296	Example, output UTF-16BE-encoded JSON:
219		297
220	use Encode;	298	use Encode;
221	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	299	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
242	]	320	]
243	}	321	}
244		322
245	=item $json = $json->indent ([$enable])	323	=item $json = $json->indent ([$enable])
246		324
		325	=item $enabled = $json->get_indent
		326
247	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	327	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
248	format as output, putting every array member or object/hash key-value pair	328	format as output, putting every array member or object/hash key-value pair
249	into its own line, identing them properly.	329	into its own line, indenting them properly.
250		330
251	If C<$enable> is false, no newlines or indenting will be produced, and the	331	If C<$enable> is false, no newlines or indenting will be produced, and the
252	resulting JSON text is guarenteed not to contain any C<newlines>.	332	resulting JSON text is guaranteed not to contain any C<newlines>.
253		333
254	This setting has no effect when decoding JSON texts.	334	This setting has no effect when decoding JSON texts.
255		335
256	=item $json = $json->space_before ([$enable])	336	=item $json = $json->space_before ([$enable])
		337
		338	=item $enabled = $json->get_space_before
257		339
258	If C<$enable> is true (or missing), then the C<encode> method will add an extra	340	If C<$enable> is true (or missing), then the C<encode> method will add an extra
259	optional space before the C<:> separating keys from values in JSON objects.	341	optional space before the C<:> separating keys from values in JSON objects.
260		342
261	If C<$enable> is false, then the C<encode> method will not add any extra	343	If C<$enable> is false, then the C<encode> method will not add any extra
…		…
267	Example, space_before enabled, space_after and indent disabled:	349	Example, space_before enabled, space_after and indent disabled:
268		350
269	{"key" :"value"}	351	{"key" :"value"}
270		352
271	=item $json = $json->space_after ([$enable])	353	=item $json = $json->space_after ([$enable])
		354
		355	=item $enabled = $json->get_space_after
272		356
273	If C<$enable> is true (or missing), then the C<encode> method will add an extra	357	If C<$enable> is true (or missing), then the C<encode> method will add an extra
274	optional space after the C<:> separating keys from values in JSON objects	358	optional space after the C<:> separating keys from values in JSON objects
275	and extra whitespace after the C<,> separating key-value pairs and array	359	and extra whitespace after the C<,> separating key-value pairs and array
276	members.	360	members.
…		…
282		366
283	Example, space_before and indent disabled, space_after enabled:	367	Example, space_before and indent disabled, space_after enabled:
284		368
285	{"key": "value"}	369	{"key": "value"}
286		370
		371	=item $json = $json->relaxed ([$enable])
		372
		373	=item $enabled = $json->get_relaxed
		374
		375	If C<$enable> is true (or missing), then C<decode> will accept some
		376	extensions to normal JSON syntax (see below). C<encode> will not be
		377	affected in anyway. I<Be aware that this option makes you accept invalid
		378	JSON texts as if they were valid!>. I suggest only to use this option to
		379	parse application-specific files written by humans (configuration files,
		380	resource files etc.)
		381
		382	If C<$enable> is false (the default), then C<decode> will only accept
		383	valid JSON texts.
		384
		385	Currently accepted extensions are:
		386
		387	=over 4
		388
		389	=item * list items can have an end-comma
		390
		391	JSON I<separates> array elements and key-value pairs with commas. This
		392	can be annoying if you write JSON texts manually and want to be able to
		393	quickly append elements, so this extension accepts comma at the end of
		394	such items not just between them:
		395
		396	[
		397	1,
		398	2, <- this comma not normally allowed
		399	]
		400	{
		401	"k1": "v1",
		402	"k2": "v2", <- this comma not normally allowed
		403	}
		404
		405	=item * shell-style '#'-comments
		406
		407	Whenever JSON allows whitespace, shell-style comments are additionally
		408	allowed. They are terminated by the first carriage-return or line-feed
		409	character, after which more white-space and comments are allowed.
		410
		411	[
		412	1, # this comment not allowed in JSON
		413	# neither this one...
		414	]
		415
		416	=back
		417
287	=item $json = $json->canonical ([$enable])	418	=item $json = $json->canonical ([$enable])
		419
		420	=item $enabled = $json->get_canonical
288		421
289	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	422	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
290	by sorting their keys. This is adding a comparatively high overhead.	423	by sorting their keys. This is adding a comparatively high overhead.
291		424
292	If C<$enable> is false, then the C<encode> method will output key-value	425	If C<$enable> is false, then the C<encode> method will output key-value
293	pairs in the order Perl stores them (which will likely change between runs	426	pairs in the order Perl stores them (which will likely change between runs
294	of the same script).	427	of the same script, and can change even within the same run from 5.18
		428	onwards).
295		429
296	This option is useful if you want the same data structure to be encoded as	430	This option is useful if you want the same data structure to be encoded as
297	the same JSON text (given the same overall settings). If it is disabled,	431	the same JSON text (given the same overall settings). If it is disabled,
298	the same hash migh be encoded differently even if contains the same data,	432	the same hash might be encoded differently even if contains the same data,
299	as key-value pairs have no inherent ordering in Perl.	433	as key-value pairs have no inherent ordering in Perl.
300		434
301	This setting has no effect when decoding JSON texts.	435	This setting has no effect when decoding JSON texts.
302		436
		437	This setting has currently no effect on tied hashes.
		438
303	=item $json = $json->allow_nonref ([$enable])	439	=item $json = $json->allow_nonref ([$enable])
		440
		441	=item $enabled = $json->get_allow_nonref
304		442
305	If C<$enable> is true (or missing), then the C<encode> method can convert a	443	If C<$enable> is true (or missing), then the C<encode> method can convert a
306	non-reference into its corresponding string, number or null JSON value,	444	non-reference into its corresponding string, number or null JSON value,
307	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	445	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
308	values instead of croaking.	446	values instead of croaking.
…		…
316	resulting in an invalid JSON text:	454	resulting in an invalid JSON text:
317		455
318	JSON::XS->new->allow_nonref->encode ("Hello, World!")	456	JSON::XS->new->allow_nonref->encode ("Hello, World!")
319	=> "Hello, World!"	457	=> "Hello, World!"
320		458
		459	=item $json = $json->allow_unknown ([$enable])
		460
		461	=item $enabled = $json->get_allow_unknown
		462
		463	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		464	exception when it encounters values it cannot represent in JSON (for
		465	example, filehandles) but instead will encode a JSON C<null> value. Note
		466	that blessed objects are not included here and are handled separately by
		467	c<allow_nonref>.
		468
		469	If C<$enable> is false (the default), then C<encode> will throw an
		470	exception when it encounters anything it cannot encode as JSON.
		471
		472	This option does not affect C<decode> in any way, and it is recommended to
		473	leave it off unless you know your communications partner.
		474
321	=item $json = $json->allow_blessed ([$enable])	475	=item $json = $json->allow_blessed ([$enable])
		476
		477	=item $enabled = $json->get_allow_blessed
322		478
323	If C<$enable> is true (or missing), then the C<encode> method will not	479	If C<$enable> is true (or missing), then the C<encode> method will not
324	barf when it encounters a blessed reference. Instead, the value of the	480	barf when it encounters a blessed reference. Instead, the value of the
325	B<convert_blessed> option will decide wether C<null> (C<convert_blessed>	481	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
326	disabled or no C<to_json> method found) or a representation of the	482	disabled or no C<TO_JSON> method found) or a representation of the
327	object (C<convert_blessed> enabled and C<to_json> method found) is being	483	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
328	encoded. Has no effect on C<decode>.	484	encoded. Has no effect on C<decode>.
329		485
330	If C<$enable> is false (the default), then C<encode> will throw an	486	If C<$enable> is false (the default), then C<encode> will throw an
331	exception when it encounters a blessed object.	487	exception when it encounters a blessed object.
332		488
333	=item $json = $json->convert_blessed ([$enable])	489	=item $json = $json->convert_blessed ([$enable])
		490
		491	=item $enabled = $json->get_convert_blessed
334		492
335	If C<$enable> is true (or missing), then C<encode>, upon encountering a	493	If C<$enable> is true (or missing), then C<encode>, upon encountering a
336	blessed object, will check for the availability of the C<TO_JSON> method	494	blessed object, will check for the availability of the C<TO_JSON> method
337	on the object's class. If found, it will be called in scalar context	495	on the object's class. If found, it will be called in scalar context
338	and the resulting scalar will be encoded instead of the object. If no	496	and the resulting scalar will be encoded instead of the object. If no
…		…
341		499
342	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	500	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
343	returns other blessed objects, those will be handled in the same	501	returns other blessed objects, those will be handled in the same
344	way. C<TO_JSON> must take care of not causing an endless recursion cycle	502	way. C<TO_JSON> must take care of not causing an endless recursion cycle
345	(== crash) in this case. The name of C<TO_JSON> was chosen because other	503	(== crash) in this case. The name of C<TO_JSON> was chosen because other
346	methods called by the Perl core (== not the user of the object) are	504	methods called by the Perl core (== not by the user of the object) are
347	usually in upper case letters and to avoid collisions with the C<to_json>	505	usually in upper case letters and to avoid collisions with any C<to_json>
348	function.	506	function or method.
		507
		508	This setting does not yet influence C<decode> in any way, but in the
		509	future, global hooks might get installed that influence C<decode> and are
		510	enabled by this setting.
349		511
350	If C<$enable> is false, then the C<allow_blessed> setting will decide what	512	If C<$enable> is false, then the C<allow_blessed> setting will decide what
351	to do when a blessed object is found.	513	to do when a blessed object is found.
352		514
		515	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		516
		517	When C<$coderef> is specified, it will be called from C<decode> each
		518	time it decodes a JSON object. The only argument is a reference to the
		519	newly-created hash. If the code references returns a single scalar (which
		520	need not be a reference), this value (i.e. a copy of that scalar to avoid
		521	aliasing) is inserted into the deserialised data structure. If it returns
		522	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		523	original deserialised hash will be inserted. This setting can slow down
		524	decoding considerably.
		525
		526	When C<$coderef> is omitted or undefined, any existing callback will
		527	be removed and C<decode> will not change the deserialised hash in any
		528	way.
		529
		530	Example, convert all JSON objects into the integer 5:
		531
		532	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		533	# returns [5]
		534	$js->decode ('[{}]')
		535	# throw an exception because allow_nonref is not enabled
		536	# so a lone 5 is not allowed.
		537	$js->decode ('{"a":1, "b":2}');
		538
		539	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		540
		541	Works remotely similar to C<filter_json_object>, but is only called for
		542	JSON objects having a single key named C<$key>.
		543
		544	This C<$coderef> is called before the one specified via
		545	C<filter_json_object>, if any. It gets passed the single value in the JSON
		546	object. If it returns a single value, it will be inserted into the data
		547	structure. If it returns nothing (not even C<undef> but the empty list),
		548	the callback from C<filter_json_object> will be called next, as if no
		549	single-key callback were specified.
		550
		551	If C<$coderef> is omitted or undefined, the corresponding callback will be
		552	disabled. There can only ever be one callback for a given key.
		553
		554	As this callback gets called less often then the C<filter_json_object>
		555	one, decoding speed will not usually suffer as much. Therefore, single-key
		556	objects make excellent targets to serialise Perl objects into, especially
		557	as single-key JSON objects are as close to the type-tagged value concept
		558	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		559	support this in any way, so you need to make sure your data never looks
		560	like a serialised Perl hash.
		561
		562	Typical names for the single object key are C<__class_whatever__>, or
		563	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		564	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		565	with real hashes.
		566
		567	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		568	into the corresponding C<< $WIDGET{<id>} >> object:
		569
		570	# return whatever is in $WIDGET{5}:
		571	JSON::XS
		572	->new
		573	->filter_json_single_key_object (__widget__ => sub {
		574	$WIDGET{ $_[0] }
		575	})
		576	->decode ('{"__widget__": 5')
		577
		578	# this can be used with a TO_JSON method in some "widget" class
		579	# for serialisation to json:
		580	sub WidgetBase::TO_JSON {
		581	my ($self) = @_;
		582
		583	unless ($self->{id}) {
		584	$self->{id} = ..get..some..id..;
		585	$WIDGET{$self->{id}} = $self;
		586	}
		587
		588	{ __widget__ => $self->{id} }
		589	}
		590
353	=item $json = $json->shrink ([$enable])	591	=item $json = $json->shrink ([$enable])
		592
		593	=item $enabled = $json->get_shrink
354		594
355	Perl usually over-allocates memory a bit when allocating space for	595	Perl usually over-allocates memory a bit when allocating space for
356	strings. This flag optionally resizes strings generated by either	596	strings. This flag optionally resizes strings generated by either
357	C<encode> or C<decode> to their minimum size possible. This can save	597	C<encode> or C<decode> to their minimum size possible. This can save
358	memory when your JSON texts are either very very long or you have many	598	memory when your JSON texts are either very very long or you have many
…		…
376	strings that look like integers or floats into integers or floats	616	strings that look like integers or floats into integers or floats
377	internally (there is no difference on the Perl level), saving space.	617	internally (there is no difference on the Perl level), saving space.
378		618
379	=item $json = $json->max_depth ([$maximum_nesting_depth])	619	=item $json = $json->max_depth ([$maximum_nesting_depth])
380		620
		621	=item $max_depth = $json->get_max_depth
		622
381	Sets the maximum nesting level (default C<512>) accepted while encoding	623	Sets the maximum nesting level (default C<512>) accepted while encoding
382	or decoding. If the JSON text or Perl data structure has an equal or	624	or decoding. If a higher nesting level is detected in JSON text or a Perl
383	higher nesting level then this limit, then the encoder and decoder will	625	data structure, then the encoder and decoder will stop and croak at that
384	stop and croak at that point.	626	point.
385		627
386	Nesting level is defined by number of hash- or arrayrefs that the encoder	628	Nesting level is defined by number of hash- or arrayrefs that the encoder
387	needs to traverse to reach a given point or the number of C<{> or C<[>	629	needs to traverse to reach a given point or the number of C<{> or C<[>
388	characters without their matching closing parenthesis crossed to reach a	630	characters without their matching closing parenthesis crossed to reach a
389	given character in a string.	631	given character in a string.
390		632
391	Setting the maximum depth to one disallows any nesting, so that ensures	633	Setting the maximum depth to one disallows any nesting, so that ensures
392	that the object is only a single hash/object or array.	634	that the object is only a single hash/object or array.
393		635
394	The argument to C<max_depth> will be rounded up to the next nearest power	636	If no argument is given, the highest possible setting will be used, which
395	of two.	637	is rarely useful.
		638
		639	Note that nesting is implemented by recursion in C. The default value has
		640	been chosen to be as large as typical operating systems allow without
		641	crashing.
396		642
397	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	643	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
398		644
		645	=item $json = $json->max_size ([$maximum_string_size])
		646
		647	=item $max_size = $json->get_max_size
		648
		649	Set the maximum length a JSON text may have (in bytes) where decoding is
		650	being attempted. The default is C<0>, meaning no limit. When C<decode>
		651	is called on a string that is longer then this many bytes, it will not
		652	attempt to decode the string but throw an exception. This setting has no
		653	effect on C<encode> (yet).
		654
		655	If no argument is given, the limit check will be deactivated (same as when
		656	C<0> is specified).
		657
		658	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		659
399	=item $json_text = $json->encode ($perl_scalar)	660	=item $json_text = $json->encode ($perl_scalar)
400		661
401	Converts the given Perl data structure (a simple scalar or a reference	662	Converts the given Perl value or data structure to its JSON
402	to a hash or array) to its JSON representation. Simple scalars will be	663	representation. Croaks on error.
403	converted into JSON string or number sequences, while references to arrays
404	become JSON arrays and references to hashes become JSON objects. Undefined
405	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
406	nor C<false> values will be generated.
407		664
408	=item $perl_scalar = $json->decode ($json_text)	665	=item $perl_scalar = $json->decode ($json_text)
409		666
410	The opposite of C<encode>: expects a JSON text and tries to parse it,	667	The opposite of C<encode>: expects a JSON text and tries to parse it,
411	returning the resulting simple scalar or reference. Croaks on error.	668	returning the resulting simple scalar or reference. Croaks on error.
412
413	JSON numbers and strings become simple Perl scalars. JSON arrays become
414	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
415	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
416		669
417	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	670	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
418		671
419	This works like the C<decode> method, but instead of raising an exception	672	This works like the C<decode> method, but instead of raising an exception
420	when there is trailing garbage after the first JSON object, it will	673	when there is trailing garbage after the first JSON object, it will
421	silently stop parsing there and return the number of characters consumed	674	silently stop parsing there and return the number of characters consumed
422	so far.	675	so far.
423		676
424	This is useful if your JSON texts are not delimited by an outer protocol	677	This is useful if your JSON texts are not delimited by an outer protocol
425	(which is not the brightest thing to do in the first place) and you need
426	to know where the JSON text ends.	678	and you need to know where the JSON text ends.
427		679
428	JSON::XS->new->decode_prefix ("[1] the tail")	680	JSON::XS->new->decode_prefix ("[1] the tail")
429	=> ([], 3)	681	=> ([], 3)
430		682
431	=back	683	=back
		684
		685
		686	=head1 INCREMENTAL PARSING
		687
		688	In some cases, there is the need for incremental parsing of JSON
		689	texts. While this module always has to keep both JSON text and resulting
		690	Perl data structure in memory at one time, it does allow you to parse a
		691	JSON stream incrementally. It does so by accumulating text until it has
		692	a full JSON object, which it then can decode. This process is similar to
		693	using C<decode_prefix> to see if a full JSON object is available, but
		694	is much more efficient (and can be implemented with a minimum of method
		695	calls).
		696
		697	JSON::XS will only attempt to parse the JSON text once it is sure it
		698	has enough text to get a decisive result, using a very simple but
		699	truly incremental parser. This means that it sometimes won't stop as
		700	early as the full parser, for example, it doesn't detect mismatched
		701	parentheses. The only thing it guarantees is that it starts decoding as
		702	soon as a syntactically valid JSON text has been seen. This means you need
		703	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		704	parsing in the presence if syntax errors.
		705
		706	The following methods implement this incremental parser.
		707
		708	=over 4
		709
		710	=item [void, scalar or list context] = $json->incr_parse ([$string])
		711
		712	This is the central parsing function. It can both append new text and
		713	extract objects from the stream accumulated so far (both of these
		714	functions are optional).
		715
		716	If C<$string> is given, then this string is appended to the already
		717	existing JSON fragment stored in the C<$json> object.
		718
		719	After that, if the function is called in void context, it will simply
		720	return without doing anything further. This can be used to add more text
		721	in as many chunks as you want.
		722
		723	If the method is called in scalar context, then it will try to extract
		724	exactly I<one> JSON object. If that is successful, it will return this
		725	object, otherwise it will return C<undef>. If there is a parse error,
		726	this method will croak just as C<decode> would do (one can then use
		727	C<incr_skip> to skip the erroneous part). This is the most common way of
		728	using the method.
		729
		730	And finally, in list context, it will try to extract as many objects
		731	from the stream as it can find and return them, or the empty list
		732	otherwise. For this to work, there must be no separators between the JSON
		733	objects or arrays, instead they must be concatenated back-to-back. If
		734	an error occurs, an exception will be raised as in the scalar context
		735	case. Note that in this case, any previously-parsed JSON texts will be
		736	lost.
		737
		738	Example: Parse some JSON arrays/objects in a given string and return
		739	them.
		740
		741	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		742
		743	=item $lvalue_string = $json->incr_text
		744
		745	This method returns the currently stored JSON fragment as an lvalue, that
		746	is, you can manipulate it. This I<only> works when a preceding call to
		747	C<incr_parse> in I<scalar context> successfully returned an object. Under
		748	all other circumstances you must not call this function (I mean it.
		749	although in simple tests it might actually work, it I<will> fail under
		750	real world conditions). As a special exception, you can also call this
		751	method before having parsed anything.
		752
		753	This function is useful in two cases: a) finding the trailing text after a
		754	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		755	(such as commas).
		756
		757	=item $json->incr_skip
		758
		759	This will reset the state of the incremental parser and will remove
		760	the parsed text from the input buffer so far. This is useful after
		761	C<incr_parse> died, in which case the input buffer and incremental parser
		762	state is left unchanged, to skip the text parsed so far and to reset the
		763	parse state.
		764
		765	The difference to C<incr_reset> is that only text until the parse error
		766	occurred is removed.
		767
		768	=item $json->incr_reset
		769
		770	This completely resets the incremental parser, that is, after this call,
		771	it will be as if the parser had never parsed anything.
		772
		773	This is useful if you want to repeatedly parse JSON objects and want to
		774	ignore any trailing data, which means you have to reset the parser after
		775	each successful decode.
		776
		777	=back
		778
		779	=head2 LIMITATIONS
		780
		781	All options that affect decoding are supported, except
		782	C<allow_nonref>. The reason for this is that it cannot be made to work
		783	sensibly: JSON objects and arrays are self-delimited, i.e. you can
		784	concatenate them back to back and still decode them perfectly. This does
		785	not hold true for JSON numbers, however.
		786
		787	For example, is the string C<1> a single JSON number, or is it simply the
		788	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		789	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		790	takes the conservative route and disallows this case.
		791
		792	=head2 EXAMPLES
		793
		794	Some examples will make all this clearer. First, a simple example that
		795	works similarly to C<decode_prefix>: We want to decode the JSON object at
		796	the start of a string and identify the portion after the JSON object:
		797
		798	my $text = "[1,2,3] hello";
		799
		800	my $json = new JSON::XS;
		801
		802	my $obj = $json->incr_parse ($text)
		803	or die "expected JSON object or array at beginning of string";
		804
		805	my $tail = $json->incr_text;
		806	# $tail now contains " hello"
		807
		808	Easy, isn't it?
		809
		810	Now for a more complicated example: Imagine a hypothetical protocol where
		811	you read some requests from a TCP stream, and each request is a JSON
		812	array, without any separation between them (in fact, it is often useful to
		813	use newlines as "separators", as these get interpreted as whitespace at
		814	the start of the JSON text, which makes it possible to test said protocol
		815	with C<telnet>...).
		816
		817	Here is how you'd do it (it is trivial to write this in an event-based
		818	manner):
		819
		820	my $json = new JSON::XS;
		821
		822	# read some data from the socket
		823	while (sysread $socket, my $buf, 4096) {
		824
		825	# split and decode as many requests as possible
		826	for my $request ($json->incr_parse ($buf)) {
		827	# act on the $request
		828	}
		829	}
		830
		831	Another complicated example: Assume you have a string with JSON objects
		832	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		833	[3]>). To parse them, we have to skip the commas between the JSON texts,
		834	and here is where the lvalue-ness of C<incr_text> comes in useful:
		835
		836	my $text = "[1],[2], [3]";
		837	my $json = new JSON::XS;
		838
		839	# void context, so no parsing done
		840	$json->incr_parse ($text);
		841
		842	# now extract as many objects as possible. note the
		843	# use of scalar context so incr_text can be called.
		844	while (my $obj = $json->incr_parse) {
		845	# do something with $obj
		846
		847	# now skip the optional comma
		848	$json->incr_text =~ s/^ \s* , //x;
		849	}
		850
		851	Now lets go for a very complex example: Assume that you have a gigantic
		852	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		853	but you cannot load it into memory fully (this has actually happened in
		854	the real world :).
		855
		856	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		857	can still help you: You implement a (very simple) array parser and let
		858	JSON decode the array elements, which are all full JSON objects on their
		859	own (this wouldn't work if the array elements could be JSON numbers, for
		860	example):
		861
		862	my $json = new JSON::XS;
		863
		864	# open the monster
		865	open my $fh, "<bigfile.json"
		866	or die "bigfile: $!";
		867
		868	# first parse the initial "["
		869	for (;;) {
		870	sysread $fh, my $buf, 65536
		871	or die "read error: $!";
		872	$json->incr_parse ($buf); # void context, so no parsing
		873
		874	# Exit the loop once we found and removed(!) the initial "[".
		875	# In essence, we are (ab-)using the $json object as a simple scalar
		876	# we append data to.
		877	last if $json->incr_text =~ s/^ \s* \[ //x;
		878	}
		879
		880	# now we have the skipped the initial "[", so continue
		881	# parsing all the elements.
		882	for (;;) {
		883	# in this loop we read data until we got a single JSON object
		884	for (;;) {
		885	if (my $obj = $json->incr_parse) {
		886	# do something with $obj
		887	last;
		888	}
		889
		890	# add more data
		891	sysread $fh, my $buf, 65536
		892	or die "read error: $!";
		893	$json->incr_parse ($buf); # void context, so no parsing
		894	}
		895
		896	# in this loop we read data until we either found and parsed the
		897	# separating "," between elements, or the final "]"
		898	for (;;) {
		899	# first skip whitespace
		900	$json->incr_text =~ s/^\s*//;
		901
		902	# if we find "]", we are done
		903	if ($json->incr_text =~ s/^\]//) {
		904	print "finished.\n";
		905	exit;
		906	}
		907
		908	# if we find ",", we can continue with the next element
		909	if ($json->incr_text =~ s/^,//) {
		910	last;
		911	}
		912
		913	# if we find anything else, we have a parse error!
		914	if (length $json->incr_text) {
		915	die "parse error near ", $json->incr_text;
		916	}
		917
		918	# else add more data
		919	sysread $fh, my $buf, 65536
		920	or die "read error: $!";
		921	$json->incr_parse ($buf); # void context, so no parsing
		922	}
		923
		924	This is a complex example, but most of the complexity comes from the fact
		925	that we are trying to be correct (bear with me if I am wrong, I never ran
		926	the above example :).
		927
432		928
433		929
434	=head1 MAPPING	930	=head1 MAPPING
435		931
436	This section describes how JSON::XS maps Perl values to JSON values and	932	This section describes how JSON::XS maps Perl values to JSON values and
437	vice versa. These mappings are designed to "do the right thing" in most	933	vice versa. These mappings are designed to "do the right thing" in most
438	circumstances automatically, preserving round-tripping characteristics	934	circumstances automatically, preserving round-tripping characteristics
439	(what you put in comes out as something equivalent).	935	(what you put in comes out as something equivalent).
440		936
441	For the more enlightened: note that in the following descriptions,	937	For the more enlightened: note that in the following descriptions,
442	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	938	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
443	refers to the abstract Perl language itself.	939	refers to the abstract Perl language itself.
444		940
445		941
446	=head2 JSON -> PERL	942	=head2 JSON -> PERL
447		943
448	=over 4	944	=over 4
449		945
450	=item object	946	=item object
451		947
452	A JSON object becomes a reference to a hash in Perl. No ordering of object	948	A JSON object becomes a reference to a hash in Perl. No ordering of object
453	keys is preserved (JSON does not preserver object key ordering itself).	949	keys is preserved (JSON does not preserve object key ordering itself).
454		950
455	=item array	951	=item array
456		952
457	A JSON array becomes a reference to an array in Perl.	953	A JSON array becomes a reference to an array in Perl.
458		954
…		…
462	are represented by the same codepoints in the Perl string, so no manual	958	are represented by the same codepoints in the Perl string, so no manual
463	decoding is necessary.	959	decoding is necessary.
464		960
465	=item number	961	=item number
466		962
467	A JSON number becomes either an integer or numeric (floating point)	963	A JSON number becomes either an integer, numeric (floating point) or
468	scalar in perl, depending on its range and any fractional parts. On the	964	string scalar in perl, depending on its range and any fractional parts. On
469	Perl level, there is no difference between those as Perl handles all the	965	the Perl level, there is no difference between those as Perl handles all
470	conversion details, but an integer may take slightly less memory and might	966	the conversion details, but an integer may take slightly less memory and
471	represent more values exactly than (floating point) numbers.	967	might represent more values exactly than floating point numbers.
		968
		969	If the number consists of digits only, JSON::XS will try to represent
		970	it as an integer value. If that fails, it will try to represent it as
		971	a numeric (floating point) value if that is possible without loss of
		972	precision. Otherwise it will preserve the number as a string value (in
		973	which case you lose roundtripping ability, as the JSON number will be
		974	re-encoded to a JSON string).
		975
		976	Numbers containing a fractional or exponential part will always be
		977	represented as numeric (floating point) values, possibly at a loss of
		978	precision (in which case you might lose perfect roundtripping ability, but
		979	the JSON number will still be re-encoded as a JSON number).
		980
		981	Note that precision is not accuracy - binary floating point values cannot
		982	represent most decimal fractions exactly, and when converting from and to
		983	floating point, JSON::XS only guarantees precision up to but not including
		984	the least significant bit.
472		985
473	=item true, false	986	=item true, false
474		987
475	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	988	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
476	respectively. They are overloaded to act almost exactly like the numbers	989	respectively. They are overloaded to act almost exactly like the numbers
477	C<1> and C<0>. You can check wether a scalar is a JSON boolean by using	990	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
478	the C<JSON::XS::is_bool> function.	991	the C<JSON::XS::is_bool> function.
479		992
480	=item null	993	=item null
481		994
482	A JSON null atom becomes C<undef> in Perl.	995	A JSON null atom becomes C<undef> in Perl.
…		…
492		1005
493	=over 4	1006	=over 4
494		1007
495	=item hash references	1008	=item hash references
496		1009
497	Perl hash references become JSON objects. As there is no inherent ordering	1010	Perl hash references become JSON objects. As there is no inherent
498	in hash keys (or JSON objects), they will usually be encoded in a	1011	ordering in hash keys (or JSON objects), they will usually be encoded
499	pseudo-random order that can change between runs of the same program but	1012	in a pseudo-random order. JSON::XS can optionally sort the hash keys
500	stays generally the same within a single run of a program. JSON::XS can	1013	(determined by the I<canonical> flag), so the same datastructure will
501	optionally sort the hash keys (determined by the I<canonical> flag), so	1014	serialise to the same JSON text (given same settings and version of
502	the same datastructure will serialise to the same JSON text (given same	1015	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
503	settings and version of JSON::XS), but this incurs a runtime overhead	1016	e.g. when you want to compare some JSON text against another for equality.
504	and is only rarely useful, e.g. when you want to compare some JSON text
505	against another for equality.
506		1017
507	=item array references	1018	=item array references
508		1019
509	Perl array references become JSON arrays.	1020	Perl array references become JSON arrays.
510		1021
…		…
513	Other unblessed references are generally not allowed and will cause an	1024	Other unblessed references are generally not allowed and will cause an
514	exception to be thrown, except for references to the integers C<0> and	1025	exception to be thrown, except for references to the integers C<0> and
515	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1026	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
516	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.	1027	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
517		1028
518	to_json [\0,JSON::XS::true] # yields [false,true]	1029	encode_json [\0, JSON::XS::true] # yields [false,true]
519		1030
520	=item JSON::XS::true, JSON::XS::false	1031	=item JSON::XS::true, JSON::XS::false
521		1032
522	These special values become JSON true and JSON false values,	1033	These special values become JSON true and JSON false values,
523	respectively. You cna alos use C<\1> and C<\0> directly if you want.	1034	respectively. You can also use C<\1> and C<\0> directly if you want.
524		1035
525	=item blessed objects	1036	=item blessed objects
526		1037
527	Blessed objects are not allowed. JSON::XS currently tries to encode their	1038	Blessed objects are not directly representable in JSON. See the
528	underlying representation (hash- or arrayref), but this behaviour might	1039	C<allow_blessed> and C<convert_blessed> methods on various options on
529	change in future versions.	1040	how to deal with this: basically, you can choose between throwing an
		1041	exception, encoding the reference as if it weren't blessed, or provide
		1042	your own serialiser method.
530		1043
531	=item simple scalars	1044	=item simple scalars
532		1045
533	Simple Perl scalars (any scalar that is not a reference) are the most	1046	Simple Perl scalars (any scalar that is not a reference) are the most
534	difficult objects to encode: JSON::XS will encode undefined scalars as	1047	difficult objects to encode: JSON::XS will encode undefined scalars as
535	JSON null value, scalars that have last been used in a string context	1048	JSON C<null> values, scalars that have last been used in a string context
536	before encoding as JSON strings and anything else as number value:	1049	before encoding as JSON strings, and anything else as number value:
537		1050
538	# dump as number	1051	# dump as number
539	to_json [2] # yields [2]	1052	encode_json [2] # yields [2]
540	to_json [-3.0e17] # yields [-3e+17]	1053	encode_json [-3.0e17] # yields [-3e+17]
541	my $value = 5; to_json [$value] # yields [5]	1054	my $value = 5; encode_json [$value] # yields [5]
542		1055
543	# used as string, so dump as string	1056	# used as string, so dump as string
544	print $value;	1057	print $value;
545	to_json [$value] # yields ["5"]	1058	encode_json [$value] # yields ["5"]
546		1059
547	# undef becomes null	1060	# undef becomes null
548	to_json [undef] # yields [null]	1061	encode_json [undef] # yields [null]
549		1062
550	You can force the type to be a string by stringifying it:	1063	You can force the type to be a JSON string by stringifying it:
551		1064
552	my $x = 3.1; # some variable containing a number	1065	my $x = 3.1; # some variable containing a number
553	"$x"; # stringified	1066	"$x"; # stringified
554	$x .= ""; # another, more awkward way to stringify	1067	$x .= ""; # another, more awkward way to stringify
555	print $x; # perl does it for you, too, quite often	1068	print $x; # perl does it for you, too, quite often
556		1069
557	You can force the type to be a number by numifying it:	1070	You can force the type to be a JSON number by numifying it:
558		1071
559	my $x = "3"; # some variable containing a string	1072	my $x = "3"; # some variable containing a string
560	$x += 0; # numify it, ensuring it will be dumped as a number	1073	$x += 0; # numify it, ensuring it will be dumped as a number
561	$x *= 1; # same thing, the choise is yours.	1074	$x *= 1; # same thing, the choice is yours.
562		1075
563	You can not currently output JSON booleans or force the type in other,	1076	You can not currently force the type in other, less obscure, ways. Tell me
564	less obscure, ways. Tell me if you need this capability.	1077	if you need this capability (but don't forget to explain why it's needed
		1078	:).
		1079
		1080	Note that numerical precision has the same meaning as under Perl (so
		1081	binary to decimal conversion follows the same rules as in Perl, which
		1082	can differ to other languages). Also, your perl interpreter might expose
		1083	extensions to the floating point numbers of your platform, such as
		1084	infinities or NaN's - these cannot be represented in JSON, and it is an
		1085	error to pass those in.
565		1086
566	=back	1087	=back
567		1088
568		1089
569	=head1 COMPARISON	1090	=head1 ENCODING/CODESET FLAG NOTES
570		1091
571	As already mentioned, this module was created because none of the existing	1092	The interested reader might have seen a number of flags that signify
572	JSON modules could be made to work correctly. First I will describe the	1093	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
573	problems (or pleasures) I encountered with various existing JSON modules,	1094	some confusion on what these do, so here is a short comparison:
574	followed by some benchmark values. JSON::XS was designed not to suffer	1095
575	from any of these problems or limitations.	1096	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1097	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1098	control whether C<encode> escapes character values outside their respective
		1099	codeset range. Neither of these flags conflict with each other, although
		1100	some combinations make less sense than others.
		1101
		1102	Care has been taken to make all flags symmetrical with respect to
		1103	C<encode> and C<decode>, that is, texts encoded with any combination of
		1104	these flag values will be correctly decoded when the same flags are used
		1105	- in general, if you use different flag settings while encoding vs. when
		1106	decoding you likely have a bug somewhere.
		1107
		1108	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1109	simply an abstract set of character-codepoint pairs, while an encoding
		1110	takes those codepoint numbers and I<encodes> them, in our case into
		1111	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1112	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1113	the same time, which can be confusing.
576		1114
577	=over 4	1115	=over 4
578		1116
579	=item JSON 1.07	1117	=item C<utf8> flag disabled
580		1118
581	Slow (but very portable, as it is written in pure Perl).	1119	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1120	and expect Unicode strings, that is, characters with high ordinal Unicode
		1121	values (> 255) will be encoded as such characters, and likewise such
		1122	characters are decoded as-is, no changes to them will be done, except
		1123	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1124	respectively (to Perl, these are the same thing in strings unless you do
		1125	funny/weird/dumb stuff).
582		1126
583	Undocumented/buggy Unicode handling (how JSON handles unicode values is	1127	This is useful when you want to do the encoding yourself (e.g. when you
584	undocumented. One can get far by feeding it unicode strings and doing	1128	want to have UTF-16 encoded JSON texts) or when some other layer does
585	en-/decoding oneself, but unicode escapes are not working properly).	1129	the encoding for you (for example, when printing to a terminal using a
		1130	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1131	to UTF-8 encode your data first and have Perl encode it another time).
586		1132
587	No roundtripping (strings get clobbered if they look like numbers, e.g.	1133	=item C<utf8> flag enabled
588	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
589	decode into the number 2.
590		1134
591	=item JSON::PC 0.01	1135	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1136	characters using the corresponding UTF-8 multi-byte sequence, and will
		1137	expect your input strings to be encoded as UTF-8, that is, no "character"
		1138	of the input string must have any value > 255, as UTF-8 does not allow
		1139	that.
592		1140
593	Very fast.	1141	The C<utf8> flag therefore switches between two modes: disabled means you
		1142	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1143	octet/binary string in Perl.
594		1144
595	Undocumented/buggy Unicode handling.	1145	=item C<latin1> or C<ascii> flags enabled
596		1146
597	No roundtripping.	1147	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1148	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1149	characters as specified by the C<utf8> flag.
598		1150
599	Has problems handling many Perl values (e.g. regex results and other magic	1151	If C<utf8> is disabled, then the result is also correctly encoded in those
600	values will make it croak).	1152	character sets (as both are proper subsets of Unicode, meaning that a
		1153	Unicode string with all character values < 256 is the same thing as a
		1154	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1155	the same thing as an ASCII string in Perl).
601		1156
602	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1157	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
603	which is not a valid JSON text.	1158	regardless of these flags, just some more characters will be escaped using
		1159	C<\uXXXX> then before.
604		1160
605	Unmaintained (maintainer unresponsive for many months, bugs are not	1161	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
606	getting fixed).	1162	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1163	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1164	a subset of Unicode), while ASCII is.
607		1165
608	=item JSON::Syck 0.21	1166	Surprisingly, C<decode> will ignore these flags and so treat all input
		1167	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1168	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1169	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
609		1170
610	Very buggy (often crashes).	1171	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1172	they only govern when the JSON output engine escapes a character or not.
611		1173
612	Very inflexible (no human-readable format supported, format pretty much	1174	The main use for C<latin1> is to relatively efficiently store binary data
613	undocumented. I need at least a format for easy reading by humans and a	1175	as JSON, at the expense of breaking compatibility with most JSON decoders.
614	single-line compact format for use in a protocol, and preferably a way to
615	generate ASCII-only JSON texts).
616		1176
617	Completely broken (and confusingly documented) Unicode handling (unicode	1177	The main use for C<ascii> is to force the output to not contain characters
618	escapes are not working properly, you need to set ImplicitUnicode to	1178	with values > 127, which means you can interpret the resulting string
619	I<different> values on en- and decoding to get symmetric behaviour).	1179	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
620		1180	8-bit-encoding, and still get the same data structure back. This is useful
621	No roundtripping (simple cases work, but this depends on wether the scalar	1181	when your channel for JSON transfer is not 8-bit clean or the encoding
622	value was used in a numeric context or not).	1182	might be mangled in between (e.g. in mail), and works because ASCII is a
623		1183	proper subset of most 8-bit and multibyte encodings in use in the world.
624	Dumping hashes may skip hash values depending on iterator state.
625
626	Unmaintained (maintainer unresponsive for many months, bugs are not
627	getting fixed).
628
629	Does not check input for validity (i.e. will accept non-JSON input and
630	return "something" instead of raising an exception. This is a security
631	issue: imagine two banks transfering money between each other using
632	JSON. One bank might parse a given non-JSON request and deduct money,
633	while the other might reject the transaction with a syntax error. While a
634	good protocol will at least recover, that is extra unnecessary work and
635	the transaction will still not succeed).
636
637	=item JSON::DWIW 0.04
638
639	Very fast. Very natural. Very nice.
640
641	Undocumented unicode handling (but the best of the pack. Unicode escapes
642	still don't get parsed properly).
643
644	Very inflexible.
645
646	No roundtripping.
647
648	Does not generate valid JSON texts (key strings are often unquoted, empty keys
649	result in nothing being output)
650
651	Does not check input for validity.
652		1184
653	=back	1185	=back
654		1186
655		1187
		1188	=head2 JSON and ECMAscript
		1189
		1190	JSON syntax is based on how literals are represented in javascript (the
		1191	not-standardised predecessor of ECMAscript) which is presumably why it is
		1192	called "JavaScript Object Notation".
		1193
		1194	However, JSON is not a subset (and also not a superset of course) of
		1195	ECMAscript (the standard) or javascript (whatever browsers actually
		1196	implement).
		1197
		1198	If you want to use javascript's C<eval> function to "parse" JSON, you
		1199	might run into parse errors for valid JSON texts, or the resulting data
		1200	structure might not be queryable:
		1201
		1202	One of the problems is that U+2028 and U+2029 are valid characters inside
		1203	JSON strings, but are not allowed in ECMAscript string literals, so the
		1204	following Perl fragment will not output something that can be guaranteed
		1205	to be parsable by javascript's C<eval>:
		1206
		1207	use JSON::XS;
		1208
		1209	print encode_json [chr 0x2028];
		1210
		1211	The right fix for this is to use a proper JSON parser in your javascript
		1212	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1213	F<json2.js> parser).
		1214
		1215	If this is not an option, you can, as a stop-gap measure, simply encode to
		1216	ASCII-only JSON:
		1217
		1218	use JSON::XS;
		1219
		1220	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1221
		1222	Note that this will enlarge the resulting JSON text quite a bit if you
		1223	have many non-ASCII characters. You might be tempted to run some regexes
		1224	to only escape U+2028 and U+2029, e.g.:
		1225
		1226	# DO NOT USE THIS!
		1227	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1228	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1229	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1230	print $json;
		1231
		1232	Note that I<this is a bad idea>: the above only works for U+2028 and
		1233	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1234	javascript implementations, however, have issues with other characters as
		1235	well - using C<eval> naively simply I<will> cause problems.
		1236
		1237	Another problem is that some javascript implementations reserve
		1238	some property names for their own purposes (which probably makes
		1239	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1240	C<__proto__> property name for its own purposes.
		1241
		1242	If that is a problem, you could parse try to filter the resulting JSON
		1243	output for these property strings, e.g.:
		1244
		1245	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1246
		1247	This works because C<__proto__> is not valid outside of strings, so every
		1248	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1249
		1250	If you know of other incompatibilities, please let me know.
		1251
		1252
656	=head2 JSON and YAML	1253	=head2 JSON and YAML
657		1254
658	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1255	You often hear that JSON is a subset of YAML. This is, however, a mass
659	however, a mass hysteria and very far from the truth. In general, there is	1256	hysteria(*) and very far from the truth (as of the time of this writing),
660	no way to configure JSON::XS to output a data structure as valid YAML.	1257	so let me state it clearly: I<in general, there is no way to configure
		1258	JSON::XS to output a data structure as valid YAML> that works in all
		1259	cases.
661		1260
662	If you really must use JSON::XS to generate YAML, you should use this	1261	If you really must use JSON::XS to generate YAML, you should use this
663	algorithm (subject to change in future versions):	1262	algorithm (subject to change in future versions):
664		1263
665	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1264	my $to_yaml = JSON::XS->new->utf8->space_after (1);
666	my $yaml = $to_yaml->encode ($ref) . "\n";	1265	my $yaml = $to_yaml->encode ($ref) . "\n";
667		1266
668	This will usually generate JSON texts that also parse as valid	1267	This will I<usually> generate JSON texts that also parse as valid
669	YAML. Please note that YAML has hardcoded limits on (simple) object key	1268	YAML. Please note that YAML has hardcoded limits on (simple) object key
670	lengths that JSON doesn't have, so you should make sure that your hash	1269	lengths that JSON doesn't have and also has different and incompatible
		1270	unicode character escape syntax, so you should make sure that your hash
671	keys are noticably shorter than the 1024 characters YAML allows.	1271	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1272	and that you do not have characters with codepoint values outside the
		1273	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1274	sequences in strings (which JSON::XS does not I<currently> generate, but
		1275	other JSON generators might).
672		1276
673	There might be other incompatibilities that I am not aware of. In general	1277	There might be other incompatibilities that I am not aware of (or the YAML
		1278	specification has been changed yet again - it does so quite often). In
674	you should not try to generate YAML with a JSON generator or vice versa,	1279	general you should not try to generate YAML with a JSON generator or vice
675	or try to parse JSON with a YAML parser or vice versa: chances are high	1280	versa, or try to parse JSON with a YAML parser or vice versa: chances are
676	that you will run into severe interoperability problems.	1281	high that you will run into severe interoperability problems when you
		1282	least expect it.
		1283
		1284	=over 4
		1285
		1286	=item (*)
		1287
		1288	I have been pressured multiple times by Brian Ingerson (one of the
		1289	authors of the YAML specification) to remove this paragraph, despite him
		1290	acknowledging that the actual incompatibilities exist. As I was personally
		1291	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1292	educate people about these issues, so others do not run into the same
		1293	problem again and again. After this, Brian called me a (quote)I<complete
		1294	and worthless idiot>(unquote).
		1295
		1296	In my opinion, instead of pressuring and insulting people who actually
		1297	clarify issues with YAML and the wrong statements of some of its
		1298	proponents, I would kindly suggest reading the JSON spec (which is not
		1299	that difficult or long) and finally make YAML compatible to it, and
		1300	educating users about the changes, instead of spreading lies about the
		1301	real compatibility for many I<years> and trying to silence people who
		1302	point out that it isn't true.
		1303
		1304	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1305	though the incompatibilities have been documented (and are known to Brian)
		1306	for many years and the spec makes explicit claims that YAML is a superset
		1307	of JSON. It would be so easy to fix, but apparently, bullying people and
		1308	corrupting userdata is so much easier.
		1309
		1310	=back
677		1311
678		1312
679	=head2 SPEED	1313	=head2 SPEED
680		1314
681	It seems that JSON::XS is surprisingly fast, as shown in the following	1315	It seems that JSON::XS is surprisingly fast, as shown in the following
682	tables. They have been generated with the help of the C<eg/bench> program	1316	tables. They have been generated with the help of the C<eg/bench> program
683	in the JSON::XS distribution, to make it easy to compare on your own	1317	in the JSON::XS distribution, to make it easy to compare on your own
684	system.	1318	system.
685		1319
686	First comes a comparison between various modules using a very short	1320	First comes a comparison between various modules using
687	single-line JSON string:	1321	a very short single-line JSON string (also available at
		1322	L<http://dist.schmorp.de/misc/json/short.json>).
688		1323
689	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1324	{"method": "handleMessage", "params": ["user1",
690	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1325	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1326	1, 0]}
691		1327
692	It shows the number of encodes/decodes per second (JSON::XS uses	1328	It shows the number of encodes/decodes per second (JSON::XS uses
693	the functional interface, while JSON::XS/2 uses the OO interface	1329	the functional interface, while JSON::XS/2 uses the OO interface
694	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1330	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
695	shrink). Higher is better:	1331	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1332	uses the from_json method). Higher is better:
696		1333
697	module | encode | decode |	1334	module | encode | decode |
698	-----------|------------|------------|	1335	--------------|------------|------------|
699	JSON | 7645.468 | 4208.613 |	1336	JSON::DWIW/DS | 86302.551 | 102300.098 |
700	JSON::DWIW | 40721.398 | 77101.176 |	1337	JSON::DWIW/FJ | 86302.551 | 75983.768 |
701	JSON::PC | 65948.176 | 78251.940 |	1338	JSON::PP | 15827.562 | 6638.658 |
702	JSON::Syck | 22844.793 | 26479.192 |	1339	JSON::Syck | 63358.066 | 47662.545 |
703	JSON::XS | 388361.481 | 199728.762 |	1340	JSON::XS | 511500.488 | 511500.488 |
704	JSON::XS/2 | 218453.333 | 192399.266 |	1341	JSON::XS/2 | 291271.111 | 388361.481 |
705	JSON::XS/3 | 338250.323 | 192399.266 |	1342	JSON::XS/3 | 361577.931 | 361577.931 |
706	Storable | 15779.925 | 14169.946 |	1343	Storable | 66788.280 | 265462.278 |
707	-----------+------------+------------+	1344	--------------+------------+------------+
708		1345
709	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1346	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
710	about three times faster on decoding, and over fourty times faster	1347	about five times faster on decoding, and over thirty to seventy times
711	than JSON, even with pretty-printing and key sorting. It also compares	1348	faster than JSON's pure perl implementation. It also compares favourably
712	favourably to Storable for small amounts of data.	1349	to Storable for small amounts of data.
713		1350
714	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1351	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
715	search API (http://nanoref.com/yahooapis/mgPdGg):	1352	search API (L<http://dist.schmorp.de/misc/json/long.json>).
716		1353
717	module | encode | decode |	1354	module | encode | decode |
718	-----------|------------|------------|	1355	--------------|------------|------------|
719	JSON | 254.685 | 37.665 |	1356	JSON::DWIW/DS | 1647.927 | 2673.916 |
720	JSON::DWIW | 843.343 | 1049.731 |	1357	JSON::DWIW/FJ | 1630.249 | 2596.128 |
721	JSON::PC | 3602.116 | 2307.352 |	1358	JSON::PP | 400.640 | 62.311 |
722	JSON::Syck | 505.107 | 787.899 |	1359	JSON::Syck | 1481.040 | 1524.869 |
723	JSON::XS | 5747.196 | 3690.220 |	1360	JSON::XS | 20661.596 | 9541.183 |
724	JSON::XS/2 | 3968.121 | 3676.634 |	1361	JSON::XS/2 | 10683.403 | 9416.938 |
725	JSON::XS/3 | 6105.246 | 3662.508 |	1362	JSON::XS/3 | 20661.596 | 9400.054 |
726	Storable | 4417.337 | 5285.161 |	1363	Storable | 19765.806 | 10000.725 |
727	-----------+------------+------------+	1364	--------------+------------+------------+
728		1365
729	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1366	Again, JSON::XS leads by far (except for Storable which non-surprisingly
730	decodes faster).	1367	decodes a bit faster).
731		1368
732	On large strings containing lots of high unicode characters, some modules	1369	On large strings containing lots of high Unicode characters, some modules
733	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1370	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
734	will be broken due to missing (or wrong) unicode handling. Others refuse	1371	will be broken due to missing (or wrong) Unicode handling. Others refuse
735	to decode or encode properly, so it was impossible to prepare a fair	1372	to decode or encode properly, so it was impossible to prepare a fair
736	comparison table for that case.	1373	comparison table for that case.
737		1374
738		1375
739	=head1 SECURITY CONSIDERATIONS	1376	=head1 SECURITY CONSIDERATIONS
…		…
745	any buffer overflows. Obviously, this module should ensure that and I am	1382	any buffer overflows. Obviously, this module should ensure that and I am
746	trying hard on making that true, but you never know.	1383	trying hard on making that true, but you never know.
747		1384
748	Second, you need to avoid resource-starving attacks. That means you should	1385	Second, you need to avoid resource-starving attacks. That means you should
749	limit the size of JSON texts you accept, or make sure then when your	1386	limit the size of JSON texts you accept, or make sure then when your
750	resources run out, thats just fine (e.g. by using a separate process that	1387	resources run out, that's just fine (e.g. by using a separate process that
751	can crash safely). The size of a JSON text in octets or characters is	1388	can crash safely). The size of a JSON text in octets or characters is
752	usually a good indication of the size of the resources required to decode	1389	usually a good indication of the size of the resources required to decode
753	it into a Perl structure.	1390	it into a Perl structure. While JSON::XS can check the size of the JSON
		1391	text, it might be too late when you already have it in memory, so you
		1392	might want to check the size before you accept the string.
754		1393
755	Third, JSON::XS recurses using the C stack when decoding objects and	1394	Third, JSON::XS recurses using the C stack when decoding objects and
756	arrays. The C stack is a limited resource: for instance, on my amd64	1395	arrays. The C stack is a limited resource: for instance, on my amd64
757	machine with 8MB of stack size I can decode around 180k nested arrays but	1396	machine with 8MB of stack size I can decode around 180k nested arrays but
758	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1397	only 14k nested JSON objects (due to perl itself recursing deeply on croak
759	to free the temporary). If that is exceeded, the program crashes. to be	1398	to free the temporary). If that is exceeded, the program crashes. To be
760	conservative, the default nesting limit is set to 512. If your process	1399	conservative, the default nesting limit is set to 512. If your process
761	has a smaller stack, you should adjust this setting accordingly with the	1400	has a smaller stack, you should adjust this setting accordingly with the
762	C<max_depth> method.	1401	C<max_depth> method.
763		1402
764	And last but least, something else could bomb you that I forgot to think	1403	Something else could bomb you, too, that I forgot to think of. In that
765	of. In that case, you get to keep the pieces. I am always open for hints,	1404	case, you get to keep the pieces. I am always open for hints, though...
766	though...	1405
		1406	Also keep in mind that JSON::XS might leak contents of your Perl data
		1407	structures in its error messages, so when you serialise sensitive
		1408	information you might want to make sure that exceptions thrown by JSON::XS
		1409	will not end up in front of untrusted eyes.
767		1410
768	If you are using JSON::XS to return packets to consumption	1411	If you are using JSON::XS to return packets to consumption
769	by javascript scripts in a browser you should have a look at	1412	by JavaScript scripts in a browser you should have a look at
770	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether	1413	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
771	you are vulnerable to some common attack vectors (which really are browser	1414	see whether you are vulnerable to some common attack vectors (which really
772	design bugs, but it is still you who will have to deal with it, as major	1415	are browser design bugs, but it is still you who will have to deal with
773	browser developers care only for features, not about doing security	1416	it, as major browser developers care only for features, not about getting
774	right).	1417	security right).
		1418
		1419
		1420	=head1 THREADS
		1421
		1422	This module is I<not> guaranteed to be thread safe and there are no
		1423	plans to change this until Perl gets thread support (as opposed to the
		1424	horribly slow so-called "threads" which are simply slow and bloated
		1425	process simulations - use fork, it's I<much> faster, cheaper, better).
		1426
		1427	(It might actually work, but you have been warned).
		1428
		1429
		1430	=head1 THE PERILS OF SETLOCALE
		1431
		1432	Sometimes people avoid the Perl locale support and directly call the
		1433	system's setlocale function with C<LC_ALL>.
		1434
		1435	This breaks both perl and modules such as JSON::XS, as stringification of
		1436	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1437	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1438	perl to stringify numbers).
		1439
		1440	The solution is simple: don't call C<setlocale>, or use it for only those
		1441	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1442
		1443	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1444	actually needs it (avoiding stringification of numbers), and restore it
		1445	afterwards.
775		1446
776		1447
777	=head1 BUGS	1448	=head1 BUGS
778		1449
779	While the goal of this module is to be correct, that unfortunately does	1450	While the goal of this module is to be correct, that unfortunately does
780	not mean its bug-free, only that I think its design is bug-free. It is	1451	not mean it's bug-free, only that I think its design is bug-free. If you
781	still relatively early in its development. If you keep reporting bugs they	1452	keep reporting bugs they will be fixed swiftly, though.
782	will be fixed swiftly, though.	1453
		1454	Please refrain from using rt.cpan.org or any other bug reporting
		1455	service. I put the contact address into my modules for a reason.
783		1456
784	=cut	1457	=cut
785		1458
786	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1459	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
787	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };	1460	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
…		…
804	"--" => sub { $_[0] = ${$_[0]} - 1 },	1477	"--" => sub { $_[0] = ${$_[0]} - 1 },
805	fallback => 1;	1478	fallback => 1;
806		1479
807	1;	1480	1;
808		1481
		1482	=head1 SEE ALSO
		1483
		1484	The F<json_xs> command line utility for quick experiments.
		1485
809	=head1 AUTHOR	1486	=head1 AUTHOR
810		1487
811	Marc Lehmann <schmorp@schmorp.de>	1488	Marc Lehmann <schmorp@schmorp.de>
812	http://home.schmorp.de/	1489	http://home.schmorp.de/
813		1490

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