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Revision 1.45 by root, Mon Jun 25 04:16:46 2007 UTC vs.
Revision 1.134 by root, Mon Feb 21 15:38:06 2011 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 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 $VERSION = '2.3';
91	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
92		108
93	our @EXPORT = qw(to_json from_json objToJson jsonToObj);	109	our @EXPORT = qw(encode_json decode_json to_json from_json);
		110
		111	sub to_json($) {
		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	}
94		120
95	use Exporter;	121	use Exporter;
96	use XSLoader;	122	use XSLoader;
97		123
98	=head1 FUNCTIONAL INTERFACE	124	=head1 FUNCTIONAL INTERFACE
99		125
100	The following convinience methods are provided by this module. They are	126	The following convenience methods are provided by this module. They are
101	exported by default:	127	exported by default:
102		128
103	=over 4	129	=over 4
104		130
105	=item $json_text = to_json $perl_scalar	131	=item $json_text = encode_json $perl_scalar
106		132
107	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
108	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.
109	octets only). Croaks on error.
110		135
111	This function call is functionally identical to:	136	This function call is functionally identical to:
112		137
113	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	138	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
114		139
115	except being faster.	140	Except being faster.
116		141
117	=item $perl_scalar = from_json $json_text	142	=item $perl_scalar = decode_json $json_text
118		143
119	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
120	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
121	scalar or reference. Croaks on error.	146	reference. Croaks on error.
122		147
123	This function call is functionally identical to:	148	This function call is functionally identical to:
124		149
125	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	150	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
126		151
127	except being faster.	152	Except being faster.
128		153
129	=item $is_boolean = JSON::XS::is_bool $scalar	154	=item $is_boolean = JSON::XS::is_bool $scalar
130		155
131	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
132	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
…		…
136	Perl.	161	Perl.
137		162
138	=back	163	=back
139		164
140		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
141	=head1 OBJECT-ORIENTED INTERFACE	214	=head1 OBJECT-ORIENTED INTERFACE
142		215
143	The object oriented interface lets you configure your own encoding or	216	The object oriented interface lets you configure your own encoding or
144	decoding style, within the limits of supported formats.	217	decoding style, within the limits of supported formats.
145		218
…		…
156	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]})
157	=> {"a": [1, 2]}	230	=> {"a": [1, 2]}
158		231
159	=item $json = $json->ascii ([$enable])	232	=item $json = $json->ascii ([$enable])
160		233
		234	=item $enabled = $json->get_ascii
		235
161	If C<$enable> is true (or missing), then the C<encode> method will not	236	If C<$enable> is true (or missing), then the C<encode> method will not
162	generate characters outside the code range C<0..127> (which is ASCII). Any	237	generate characters outside the code range C<0..127> (which is ASCII). Any
163	unicode characters outside that range will be escaped using either a	238	Unicode characters outside that range will be escaped using either a
164	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,	239	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
165	as per RFC4627. The resulting encoded JSON text can be treated as a native	240	as per RFC4627. The resulting encoded JSON text can be treated as a native
166	unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,	241	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
167	or any other superset of ASCII.	242	or any other superset of ASCII.
168		243
169	If C<$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
170	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
171	in a faster and more compact format.	246	in a faster and more compact format.
172		247
		248	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		249	document.
		250
173	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
174	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
175	contain any 8 bit characters.	253	contain any 8 bit characters.
176		254
177	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	255	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
178	=> ["\ud801\udc01"]	256	=> ["\ud801\udc01"]
179		257
180	=item $json = $json->latin1 ([$enable])	258	=item $json = $json->latin1 ([$enable])
181		259
		260	=item $enabled = $json->get_latin1
		261
182	If C<$enable> is true (or missing), then the C<encode> method will encode	262	If C<$enable> is true (or missing), then the C<encode> method will encode
183	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters	263	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
184	outside the code range C<0..255>. The resulting string can be treated as a	264	outside the code range C<0..255>. The resulting string can be treated as a
185	latin1-encoded JSON text or a native unicode string. The C<decode> method	265	latin1-encoded JSON text or a native Unicode string. The C<decode> method
186	will not be affected in any way by this flag, as C<decode> by default	266	will not be affected in any way by this flag, as C<decode> by default
187	expects unicode, which is a strict superset of latin1.	267	expects Unicode, which is a strict superset of latin1.
188		268
189	If C<$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
190	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.
191		274
192	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
193	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
194	size. The disadvantage is that the resulting JSON text is encoded	277	size. The disadvantage is that the resulting JSON text is encoded
195	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
196	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
197	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
198	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.
199		282
200	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	283	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
201	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	284	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
202		285
203	=item $json = $json->utf8 ([$enable])	286	=item $json = $json->utf8 ([$enable])
		287
		288	=item $enabled = $json->get_utf8
204		289
205	If C<$enable> is true (or missing), then the C<encode> method will encode	290	If C<$enable> is true (or missing), then the C<encode> method will encode
206	the JSON result into UTF-8, as required by many protocols, while the	291	the JSON result into UTF-8, as required by many protocols, while the
207	C<decode> method expects to be handled an UTF-8-encoded string. Please	292	C<decode> method expects to be handled an UTF-8-encoded string. Please
208	note that UTF-8-encoded strings do not contain any characters outside the	293	note that UTF-8-encoded strings do not contain any characters outside the
209	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	294	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
210	versions, enabling this option might enable autodetection of the UTF-16	295	versions, enabling this option might enable autodetection of the UTF-16
211	and UTF-32 encoding families, as described in RFC4627.	296	and UTF-32 encoding families, as described in RFC4627.
212		297
213	If C<$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
214	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
215	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
216	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.
217		305
218	Example, output UTF-16BE-encoded JSON:	306	Example, output UTF-16BE-encoded JSON:
219		307
220	use Encode;	308	use Encode;
221	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	309	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
242	]	330	]
243	}	331	}
244		332
245	=item $json = $json->indent ([$enable])	333	=item $json = $json->indent ([$enable])
246		334
		335	=item $enabled = $json->get_indent
		336
247	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	337	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
248	format as output, putting every array member or object/hash key-value pair	338	format as output, putting every array member or object/hash key-value pair
249	into its own line, identing them properly.	339	into its own line, indenting them properly.
250		340
251	If C<$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
252	resulting JSON text is guarenteed not to contain any C<newlines>.	342	resulting JSON text is guaranteed not to contain any C<newlines>.
253		343
254	This setting has no effect when decoding JSON texts.	344	This setting has no effect when decoding JSON texts.
255		345
256	=item $json = $json->space_before ([$enable])	346	=item $json = $json->space_before ([$enable])
		347
		348	=item $enabled = $json->get_space_before
257		349
258	If C<$enable> is true (or missing), then the C<encode> method will add an extra	350	If C<$enable> is true (or missing), then the C<encode> method will add an extra
259	optional space before the C<:> separating keys from values in JSON objects.	351	optional space before the C<:> separating keys from values in JSON objects.
260		352
261	If C<$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
…		…
267	Example, space_before enabled, space_after and indent disabled:	359	Example, space_before enabled, space_after and indent disabled:
268		360
269	{"key" :"value"}	361	{"key" :"value"}
270		362
271	=item $json = $json->space_after ([$enable])	363	=item $json = $json->space_after ([$enable])
		364
		365	=item $enabled = $json->get_space_after
272		366
273	If C<$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
274	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
275	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
276	members.	370	members.
…		…
282		376
283	Example, space_before and indent disabled, space_after enabled:	377	Example, space_before and indent disabled, space_after enabled:
284		378
285	{"key": "value"}	379	{"key": "value"}
286		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
287	=item $json = $json->canonical ([$enable])	428	=item $json = $json->canonical ([$enable])
		429
		430	=item $enabled = $json->get_canonical
288		431
289	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	432	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
290	by sorting their keys. This is adding a comparatively high overhead.	433	by sorting their keys. This is adding a comparatively high overhead.
291		434
292	If C<$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
293	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
294	of the same script).	437	of the same script).
295		438
296	This option is useful if you want the same data structure to be encoded as	439	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,	440	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,	441	the same hash might be encoded differently even if contains the same data,
299	as key-value pairs have no inherent ordering in Perl.	442	as key-value pairs have no inherent ordering in Perl.
300		443
301	This setting has no effect when decoding JSON texts.	444	This setting has no effect when decoding JSON texts.
302		445
		446	This setting has currently no effect on tied hashes.
		447
303	=item $json = $json->allow_nonref ([$enable])	448	=item $json = $json->allow_nonref ([$enable])
		449
		450	=item $enabled = $json->get_allow_nonref
304		451
305	If C<$enable> is true (or missing), then the C<encode> method can convert a	452	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,	453	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	454	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
308	values instead of croaking.	455	values instead of croaking.
…		…
316	resulting in an invalid JSON text:	463	resulting in an invalid JSON text:
317		464
318	JSON::XS->new->allow_nonref->encode ("Hello, World!")	465	JSON::XS->new->allow_nonref->encode ("Hello, World!")
319	=> "Hello, World!"	466	=> "Hello, World!"
320		467
		468	=item $json = $json->allow_unknown ([$enable])
		469
		470	=item $enabled = $json->get_allow_unknown
		471
		472	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		473	exception when it encounters values it cannot represent in JSON (for
		474	example, filehandles) but instead will encode a JSON C<null> value. Note
		475	that blessed objects are not included here and are handled separately by
		476	c<allow_nonref>.
		477
		478	If C<$enable> is false (the default), then C<encode> will throw an
		479	exception when it encounters anything it cannot encode as JSON.
		480
		481	This option does not affect C<decode> in any way, and it is recommended to
		482	leave it off unless you know your communications partner.
		483
321	=item $json = $json->allow_blessed ([$enable])	484	=item $json = $json->allow_blessed ([$enable])
		485
		486	=item $enabled = $json->get_allow_blessed
322		487
323	If C<$enable> is true (or missing), then the C<encode> method will not	488	If C<$enable> is true (or missing), then the C<encode> method will not
324	barf when it encounters a blessed reference. Instead, the value of the	489	barf when it encounters a blessed reference. Instead, the value of the
325	B<convert_blessed> option will decide wether C<null> (C<convert_blessed>	490	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
326	disabled or no C<to_json> method found) or a representation of the	491	disabled or no C<TO_JSON> method found) or a representation of the
327	object (C<convert_blessed> enabled and C<to_json> method found) is being	492	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
328	encoded. Has no effect on C<decode>.	493	encoded. Has no effect on C<decode>.
329		494
330	If C<$enable> is false (the default), then C<encode> will throw an	495	If C<$enable> is false (the default), then C<encode> will throw an
331	exception when it encounters a blessed object.	496	exception when it encounters a blessed object.
332		497
333	=item $json = $json->convert_blessed ([$enable])	498	=item $json = $json->convert_blessed ([$enable])
		499
		500	=item $enabled = $json->get_convert_blessed
334		501
335	If C<$enable> is true (or missing), then C<encode>, upon encountering a	502	If C<$enable> is true (or missing), then C<encode>, upon encountering a
336	blessed object, will check for the availability of the C<TO_JSON> method	503	blessed object, will check for the availability of the C<TO_JSON> method
337	on the object's class. If found, it will be called in scalar context	504	on the object's class. If found, it will be called in scalar context
338	and the resulting scalar will be encoded instead of the object. If no	505	and the resulting scalar will be encoded instead of the object. If no
…		…
341		508
342	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	509	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
343	returns other blessed objects, those will be handled in the same	510	returns other blessed objects, those will be handled in the same
344	way. C<TO_JSON> must take care of not causing an endless recursion cycle	511	way. C<TO_JSON> must take care of not causing an endless recursion cycle
345	(== crash) in this case. The name of C<TO_JSON> was chosen because other	512	(== crash) in this case. The name of C<TO_JSON> was chosen because other
346	methods called by the Perl core (== not the user of the object) are	513	methods called by the Perl core (== not by the user of the object) are
347	usually in upper case letters and to avoid collisions with the C<to_json>	514	usually in upper case letters and to avoid collisions with any C<to_json>
348	function.	515	function or method.
349		516
350	This setting does not yet influence C<decode> in any way, but in the	517	This setting does not yet influence C<decode> in any way, but in the
351	future, global hooks might get installed that influence C<decode> and are	518	future, global hooks might get installed that influence C<decode> and are
352	enabled by this setting.	519	enabled by this setting.
353		520
354	If C<$enable> is false, then the C<allow_blessed> setting will decide what	521	If C<$enable> is false, then the C<allow_blessed> setting will decide what
355	to do when a blessed object is found.	522	to do when a blessed object is found.
356		523
		524	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		525
		526	When C<$coderef> is specified, it will be called from C<decode> each
		527	time it decodes a JSON object. The only argument is a reference to the
		528	newly-created hash. If the code references returns a single scalar (which
		529	need not be a reference), this value (i.e. a copy of that scalar to avoid
		530	aliasing) is inserted into the deserialised data structure. If it returns
		531	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		532	original deserialised hash will be inserted. This setting can slow down
		533	decoding considerably.
		534
		535	When C<$coderef> is omitted or undefined, any existing callback will
		536	be removed and C<decode> will not change the deserialised hash in any
		537	way.
		538
		539	Example, convert all JSON objects into the integer 5:
		540
		541	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		542	# returns [5]
		543	$js->decode ('[{}]')
		544	# throw an exception because allow_nonref is not enabled
		545	# so a lone 5 is not allowed.
		546	$js->decode ('{"a":1, "b":2}');
		547
		548	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		549
		550	Works remotely similar to C<filter_json_object>, but is only called for
		551	JSON objects having a single key named C<$key>.
		552
		553	This C<$coderef> is called before the one specified via
		554	C<filter_json_object>, if any. It gets passed the single value in the JSON
		555	object. If it returns a single value, it will be inserted into the data
		556	structure. If it returns nothing (not even C<undef> but the empty list),
		557	the callback from C<filter_json_object> will be called next, as if no
		558	single-key callback were specified.
		559
		560	If C<$coderef> is omitted or undefined, the corresponding callback will be
		561	disabled. There can only ever be one callback for a given key.
		562
		563	As this callback gets called less often then the C<filter_json_object>
		564	one, decoding speed will not usually suffer as much. Therefore, single-key
		565	objects make excellent targets to serialise Perl objects into, especially
		566	as single-key JSON objects are as close to the type-tagged value concept
		567	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		568	support this in any way, so you need to make sure your data never looks
		569	like a serialised Perl hash.
		570
		571	Typical names for the single object key are C<__class_whatever__>, or
		572	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		573	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		574	with real hashes.
		575
		576	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		577	into the corresponding C<< $WIDGET{<id>} >> object:
		578
		579	# return whatever is in $WIDGET{5}:
		580	JSON::XS
		581	->new
		582	->filter_json_single_key_object (__widget__ => sub {
		583	$WIDGET{ $_[0] }
		584	})
		585	->decode ('{"__widget__": 5')
		586
		587	# this can be used with a TO_JSON method in some "widget" class
		588	# for serialisation to json:
		589	sub WidgetBase::TO_JSON {
		590	my ($self) = @_;
		591
		592	unless ($self->{id}) {
		593	$self->{id} = ..get..some..id..;
		594	$WIDGET{$self->{id}} = $self;
		595	}
		596
		597	{ __widget__ => $self->{id} }
		598	}
		599
357	=item $json = $json->shrink ([$enable])	600	=item $json = $json->shrink ([$enable])
		601
		602	=item $enabled = $json->get_shrink
358		603
359	Perl usually over-allocates memory a bit when allocating space for	604	Perl usually over-allocates memory a bit when allocating space for
360	strings. This flag optionally resizes strings generated by either	605	strings. This flag optionally resizes strings generated by either
361	C<encode> or C<decode> to their minimum size possible. This can save	606	C<encode> or C<decode> to their minimum size possible. This can save
362	memory when your JSON texts are either very very long or you have many	607	memory when your JSON texts are either very very long or you have many
…		…
380	strings that look like integers or floats into integers or floats	625	strings that look like integers or floats into integers or floats
381	internally (there is no difference on the Perl level), saving space.	626	internally (there is no difference on the Perl level), saving space.
382		627
383	=item $json = $json->max_depth ([$maximum_nesting_depth])	628	=item $json = $json->max_depth ([$maximum_nesting_depth])
384		629
		630	=item $max_depth = $json->get_max_depth
		631
385	Sets the maximum nesting level (default C<512>) accepted while encoding	632	Sets the maximum nesting level (default C<512>) accepted while encoding
386	or decoding. If the JSON text or Perl data structure has an equal or	633	or decoding. If a higher nesting level is detected in JSON text or a Perl
387	higher nesting level then this limit, then the encoder and decoder will	634	data structure, then the encoder and decoder will stop and croak at that
388	stop and croak at that point.	635	point.
389		636
390	Nesting level is defined by number of hash- or arrayrefs that the encoder	637	Nesting level is defined by number of hash- or arrayrefs that the encoder
391	needs to traverse to reach a given point or the number of C<{> or C<[>	638	needs to traverse to reach a given point or the number of C<{> or C<[>
392	characters without their matching closing parenthesis crossed to reach a	639	characters without their matching closing parenthesis crossed to reach a
393	given character in a string.	640	given character in a string.
394		641
395	Setting the maximum depth to one disallows any nesting, so that ensures	642	Setting the maximum depth to one disallows any nesting, so that ensures
396	that the object is only a single hash/object or array.	643	that the object is only a single hash/object or array.
397		644
398	The argument to C<max_depth> will be rounded up to the next nearest power	645	If no argument is given, the highest possible setting will be used, which
399	of two.	646	is rarely useful.
		647
		648	Note that nesting is implemented by recursion in C. The default value has
		649	been chosen to be as large as typical operating systems allow without
		650	crashing.
		651
		652	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		653
		654	=item $json = $json->max_size ([$maximum_string_size])
		655
		656	=item $max_size = $json->get_max_size
		657
		658	Set the maximum length a JSON text may have (in bytes) where decoding is
		659	being attempted. The default is C<0>, meaning no limit. When C<decode>
		660	is called on a string that is longer then this many bytes, it will not
		661	attempt to decode the string but throw an exception. This setting has no
		662	effect on C<encode> (yet).
		663
		664	If no argument is given, the limit check will be deactivated (same as when
		665	C<0> is specified).
400		666
401	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	667	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
402		668
403	=item $json_text = $json->encode ($perl_scalar)	669	=item $json_text = $json->encode ($perl_scalar)
404		670
…		…
433	=> ([], 3)	699	=> ([], 3)
434		700
435	=back	701	=back
436		702
437		703
		704	=head1 INCREMENTAL PARSING
		705
		706	In some cases, there is the need for incremental parsing of JSON
		707	texts. While this module always has to keep both JSON text and resulting
		708	Perl data structure in memory at one time, it does allow you to parse a
		709	JSON stream incrementally. It does so by accumulating text until it has
		710	a full JSON object, which it then can decode. This process is similar to
		711	using C<decode_prefix> to see if a full JSON object is available, but
		712	is much more efficient (and can be implemented with a minimum of method
		713	calls).
		714
		715	JSON::XS will only attempt to parse the JSON text once it is sure it
		716	has enough text to get a decisive result, using a very simple but
		717	truly incremental parser. This means that it sometimes won't stop as
		718	early as the full parser, for example, it doesn't detect mismatched
		719	parentheses. The only thing it guarantees is that it starts decoding as
		720	soon as a syntactically valid JSON text has been seen. This means you need
		721	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		722	parsing in the presence if syntax errors.
		723
		724	The following methods implement this incremental parser.
		725
		726	=over 4
		727
		728	=item [void, scalar or list context] = $json->incr_parse ([$string])
		729
		730	This is the central parsing function. It can both append new text and
		731	extract objects from the stream accumulated so far (both of these
		732	functions are optional).
		733
		734	If C<$string> is given, then this string is appended to the already
		735	existing JSON fragment stored in the C<$json> object.
		736
		737	After that, if the function is called in void context, it will simply
		738	return without doing anything further. This can be used to add more text
		739	in as many chunks as you want.
		740
		741	If the method is called in scalar context, then it will try to extract
		742	exactly I<one> JSON object. If that is successful, it will return this
		743	object, otherwise it will return C<undef>. If there is a parse error,
		744	this method will croak just as C<decode> would do (one can then use
		745	C<incr_skip> to skip the errornous part). This is the most common way of
		746	using the method.
		747
		748	And finally, in list context, it will try to extract as many objects
		749	from the stream as it can find and return them, or the empty list
		750	otherwise. For this to work, there must be no separators between the JSON
		751	objects or arrays, instead they must be concatenated back-to-back. If
		752	an error occurs, an exception will be raised as in the scalar context
		753	case. Note that in this case, any previously-parsed JSON texts will be
		754	lost.
		755
		756	Example: Parse some JSON arrays/objects in a given string and return
		757	them.
		758
		759	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		760
		761	=item $lvalue_string = $json->incr_text
		762
		763	This method returns the currently stored JSON fragment as an lvalue, that
		764	is, you can manipulate it. This I<only> works when a preceding call to
		765	C<incr_parse> in I<scalar context> successfully returned an object. Under
		766	all other circumstances you must not call this function (I mean it.
		767	although in simple tests it might actually work, it I<will> fail under
		768	real world conditions). As a special exception, you can also call this
		769	method before having parsed anything.
		770
		771	This function is useful in two cases: a) finding the trailing text after a
		772	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		773	(such as commas).
		774
		775	=item $json->incr_skip
		776
		777	This will reset the state of the incremental parser and will remove
		778	the parsed text from the input buffer so far. This is useful after
		779	C<incr_parse> died, in which case the input buffer and incremental parser
		780	state is left unchanged, to skip the text parsed so far and to reset the
		781	parse state.
		782
		783	The difference to C<incr_reset> is that only text until the parse error
		784	occured is removed.
		785
		786	=item $json->incr_reset
		787
		788	This completely resets the incremental parser, that is, after this call,
		789	it will be as if the parser had never parsed anything.
		790
		791	This is useful if you want to repeatedly parse JSON objects and want to
		792	ignore any trailing data, which means you have to reset the parser after
		793	each successful decode.
		794
		795	=back
		796
		797	=head2 LIMITATIONS
		798
		799	All options that affect decoding are supported, except
		800	C<allow_nonref>. The reason for this is that it cannot be made to
		801	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		802	them back to back and still decode them perfectly. This does not hold true
		803	for JSON numbers, however.
		804
		805	For example, is the string C<1> a single JSON number, or is it simply the
		806	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		807	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		808	takes the conservative route and disallows this case.
		809
		810	=head2 EXAMPLES
		811
		812	Some examples will make all this clearer. First, a simple example that
		813	works similarly to C<decode_prefix>: We want to decode the JSON object at
		814	the start of a string and identify the portion after the JSON object:
		815
		816	my $text = "[1,2,3] hello";
		817
		818	my $json = new JSON::XS;
		819
		820	my $obj = $json->incr_parse ($text)
		821	or die "expected JSON object or array at beginning of string";
		822
		823	my $tail = $json->incr_text;
		824	# $tail now contains " hello"
		825
		826	Easy, isn't it?
		827
		828	Now for a more complicated example: Imagine a hypothetical protocol where
		829	you read some requests from a TCP stream, and each request is a JSON
		830	array, without any separation between them (in fact, it is often useful to
		831	use newlines as "separators", as these get interpreted as whitespace at
		832	the start of the JSON text, which makes it possible to test said protocol
		833	with C<telnet>...).
		834
		835	Here is how you'd do it (it is trivial to write this in an event-based
		836	manner):
		837
		838	my $json = new JSON::XS;
		839
		840	# read some data from the socket
		841	while (sysread $socket, my $buf, 4096) {
		842
		843	# split and decode as many requests as possible
		844	for my $request ($json->incr_parse ($buf)) {
		845	# act on the $request
		846	}
		847	}
		848
		849	Another complicated example: Assume you have a string with JSON objects
		850	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		851	[3]>). To parse them, we have to skip the commas between the JSON texts,
		852	and here is where the lvalue-ness of C<incr_text> comes in useful:
		853
		854	my $text = "[1],[2], [3]";
		855	my $json = new JSON::XS;
		856
		857	# void context, so no parsing done
		858	$json->incr_parse ($text);
		859
		860	# now extract as many objects as possible. note the
		861	# use of scalar context so incr_text can be called.
		862	while (my $obj = $json->incr_parse) {
		863	# do something with $obj
		864
		865	# now skip the optional comma
		866	$json->incr_text =~ s/^ \s* , //x;
		867	}
		868
		869	Now lets go for a very complex example: Assume that you have a gigantic
		870	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		871	but you cannot load it into memory fully (this has actually happened in
		872	the real world :).
		873
		874	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		875	can still help you: You implement a (very simple) array parser and let
		876	JSON decode the array elements, which are all full JSON objects on their
		877	own (this wouldn't work if the array elements could be JSON numbers, for
		878	example):
		879
		880	my $json = new JSON::XS;
		881
		882	# open the monster
		883	open my $fh, "<bigfile.json"
		884	or die "bigfile: $!";
		885
		886	# first parse the initial "["
		887	for (;;) {
		888	sysread $fh, my $buf, 65536
		889	or die "read error: $!";
		890	$json->incr_parse ($buf); # void context, so no parsing
		891
		892	# Exit the loop once we found and removed(!) the initial "[".
		893	# In essence, we are (ab-)using the $json object as a simple scalar
		894	# we append data to.
		895	last if $json->incr_text =~ s/^ \s* \[ //x;
		896	}
		897
		898	# now we have the skipped the initial "[", so continue
		899	# parsing all the elements.
		900	for (;;) {
		901	# in this loop we read data until we got a single JSON object
		902	for (;;) {
		903	if (my $obj = $json->incr_parse) {
		904	# do something with $obj
		905	last;
		906	}
		907
		908	# add more data
		909	sysread $fh, my $buf, 65536
		910	or die "read error: $!";
		911	$json->incr_parse ($buf); # void context, so no parsing
		912	}
		913
		914	# in this loop we read data until we either found and parsed the
		915	# separating "," between elements, or the final "]"
		916	for (;;) {
		917	# first skip whitespace
		918	$json->incr_text =~ s/^\s*//;
		919
		920	# if we find "]", we are done
		921	if ($json->incr_text =~ s/^\]//) {
		922	print "finished.\n";
		923	exit;
		924	}
		925
		926	# if we find ",", we can continue with the next element
		927	if ($json->incr_text =~ s/^,//) {
		928	last;
		929	}
		930
		931	# if we find anything else, we have a parse error!
		932	if (length $json->incr_text) {
		933	die "parse error near ", $json->incr_text;
		934	}
		935
		936	# else add more data
		937	sysread $fh, my $buf, 65536
		938	or die "read error: $!";
		939	$json->incr_parse ($buf); # void context, so no parsing
		940	}
		941
		942	This is a complex example, but most of the complexity comes from the fact
		943	that we are trying to be correct (bear with me if I am wrong, I never ran
		944	the above example :).
		945
		946
		947
438	=head1 MAPPING	948	=head1 MAPPING
439		949
440	This section describes how JSON::XS maps Perl values to JSON values and	950	This section describes how JSON::XS maps Perl values to JSON values and
441	vice versa. These mappings are designed to "do the right thing" in most	951	vice versa. These mappings are designed to "do the right thing" in most
442	circumstances automatically, preserving round-tripping characteristics	952	circumstances automatically, preserving round-tripping characteristics
443	(what you put in comes out as something equivalent).	953	(what you put in comes out as something equivalent).
444		954
445	For the more enlightened: note that in the following descriptions,	955	For the more enlightened: note that in the following descriptions,
446	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	956	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
447	refers to the abstract Perl language itself.	957	refers to the abstract Perl language itself.
448		958
449		959
450	=head2 JSON -> PERL	960	=head2 JSON -> PERL
451		961
452	=over 4	962	=over 4
453		963
454	=item object	964	=item object
455		965
456	A JSON object becomes a reference to a hash in Perl. No ordering of object	966	A JSON object becomes a reference to a hash in Perl. No ordering of object
457	keys is preserved (JSON does not preserver object key ordering itself).	967	keys is preserved (JSON does not preserve object key ordering itself).
458		968
459	=item array	969	=item array
460		970
461	A JSON array becomes a reference to an array in Perl.	971	A JSON array becomes a reference to an array in Perl.
462		972
…		…
466	are represented by the same codepoints in the Perl string, so no manual	976	are represented by the same codepoints in the Perl string, so no manual
467	decoding is necessary.	977	decoding is necessary.
468		978
469	=item number	979	=item number
470		980
471	A JSON number becomes either an integer or numeric (floating point)	981	A JSON number becomes either an integer, numeric (floating point) or
472	scalar in perl, depending on its range and any fractional parts. On the	982	string scalar in perl, depending on its range and any fractional parts. On
473	Perl level, there is no difference between those as Perl handles all the	983	the Perl level, there is no difference between those as Perl handles all
474	conversion details, but an integer may take slightly less memory and might	984	the conversion details, but an integer may take slightly less memory and
475	represent more values exactly than (floating point) numbers.	985	might represent more values exactly than floating point numbers.
		986
		987	If the number consists of digits only, JSON::XS will try to represent
		988	it as an integer value. If that fails, it will try to represent it as
		989	a numeric (floating point) value if that is possible without loss of
		990	precision. Otherwise it will preserve the number as a string value (in
		991	which case you lose roundtripping ability, as the JSON number will be
		992	re-encoded toa JSON string).
		993
		994	Numbers containing a fractional or exponential part will always be
		995	represented as numeric (floating point) values, possibly at a loss of
		996	precision (in which case you might lose perfect roundtripping ability, but
		997	the JSON number will still be re-encoded as a JSON number).
		998
		999	Note that precision is not accuracy - binary floating point values cannot
		1000	represent most decimal fractions exactly, and when converting from and to
		1001	floating point, JSON::XS only guarantees precision up to but not including
		1002	the leats significant bit.
476		1003
477	=item true, false	1004	=item true, false
478		1005
479	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	1006	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
480	respectively. They are overloaded to act almost exactly like the numbers	1007	respectively. They are overloaded to act almost exactly like the numbers
481	C<1> and C<0>. You can check wether a scalar is a JSON boolean by using	1008	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
482	the C<JSON::XS::is_bool> function.	1009	the C<JSON::XS::is_bool> function.
483		1010
484	=item null	1011	=item null
485		1012
486	A JSON null atom becomes C<undef> in Perl.	1013	A JSON null atom becomes C<undef> in Perl.
…		…
517	Other unblessed references are generally not allowed and will cause an	1044	Other unblessed references are generally not allowed and will cause an
518	exception to be thrown, except for references to the integers C<0> and	1045	exception to be thrown, except for references to the integers C<0> and
519	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1046	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
520	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.	1047	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
521		1048
522	to_json [\0,JSON::XS::true] # yields [false,true]	1049	encode_json [\0, JSON::XS::true] # yields [false,true]
523		1050
524	=item JSON::XS::true, JSON::XS::false	1051	=item JSON::XS::true, JSON::XS::false
525		1052
526	These special values become JSON true and JSON false values,	1053	These special values become JSON true and JSON false values,
527	respectively. You cna alos use C<\1> and C<\0> directly if you want.	1054	respectively. You can also use C<\1> and C<\0> directly if you want.
528		1055
529	=item blessed objects	1056	=item blessed objects
530		1057
531	Blessed objects are not allowed. JSON::XS currently tries to encode their	1058	Blessed objects are not directly representable in JSON. See the
532	underlying representation (hash- or arrayref), but this behaviour might	1059	C<allow_blessed> and C<convert_blessed> methods on various options on
533	change in future versions.	1060	how to deal with this: basically, you can choose between throwing an
		1061	exception, encoding the reference as if it weren't blessed, or provide
		1062	your own serialiser method.
534		1063
535	=item simple scalars	1064	=item simple scalars
536		1065
537	Simple Perl scalars (any scalar that is not a reference) are the most	1066	Simple Perl scalars (any scalar that is not a reference) are the most
538	difficult objects to encode: JSON::XS will encode undefined scalars as	1067	difficult objects to encode: JSON::XS will encode undefined scalars as
539	JSON null value, scalars that have last been used in a string context	1068	JSON C<null> values, scalars that have last been used in a string context
540	before encoding as JSON strings and anything else as number value:	1069	before encoding as JSON strings, and anything else as number value:
541		1070
542	# dump as number	1071	# dump as number
543	to_json [2] # yields [2]	1072	encode_json [2] # yields [2]
544	to_json [-3.0e17] # yields [-3e+17]	1073	encode_json [-3.0e17] # yields [-3e+17]
545	my $value = 5; to_json [$value] # yields [5]	1074	my $value = 5; encode_json [$value] # yields [5]
546		1075
547	# used as string, so dump as string	1076	# used as string, so dump as string
548	print $value;	1077	print $value;
549	to_json [$value] # yields ["5"]	1078	encode_json [$value] # yields ["5"]
550		1079
551	# undef becomes null	1080	# undef becomes null
552	to_json [undef] # yields [null]	1081	encode_json [undef] # yields [null]
553		1082
554	You can force the type to be a string by stringifying it:	1083	You can force the type to be a JSON string by stringifying it:
555		1084
556	my $x = 3.1; # some variable containing a number	1085	my $x = 3.1; # some variable containing a number
557	"$x"; # stringified	1086	"$x"; # stringified
558	$x .= ""; # another, more awkward way to stringify	1087	$x .= ""; # another, more awkward way to stringify
559	print $x; # perl does it for you, too, quite often	1088	print $x; # perl does it for you, too, quite often
560		1089
561	You can force the type to be a number by numifying it:	1090	You can force the type to be a JSON number by numifying it:
562		1091
563	my $x = "3"; # some variable containing a string	1092	my $x = "3"; # some variable containing a string
564	$x += 0; # numify it, ensuring it will be dumped as a number	1093	$x += 0; # numify it, ensuring it will be dumped as a number
565	$x *= 1; # same thing, the choise is yours.	1094	$x *= 1; # same thing, the choice is yours.
566		1095
567	You can not currently output JSON booleans or force the type in other,	1096	You can not currently force the type in other, less obscure, ways. Tell me
568	less obscure, ways. Tell me if you need this capability.	1097	if you need this capability (but don't forget to explain why it's needed
		1098	:).
		1099
		1100	Note that numerical precision has the same meaning as under Perl (so
		1101	binary to decimal conversion follows the same rules as in Perl, which
		1102	can differ to other languages). Also, your perl interpreter might expose
		1103	extensions to the floating point numbers of your platform, such as
		1104	infinities or NaN's - these cannot be represented in JSON, and it is an
		1105	error to pass those in.
569		1106
570	=back	1107	=back
571		1108
572		1109
573	=head1 COMPARISON	1110	=head1 ENCODING/CODESET FLAG NOTES
574		1111
575	As already mentioned, this module was created because none of the existing	1112	The interested reader might have seen a number of flags that signify
576	JSON modules could be made to work correctly. First I will describe the	1113	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
577	problems (or pleasures) I encountered with various existing JSON modules,	1114	some confusion on what these do, so here is a short comparison:
578	followed by some benchmark values. JSON::XS was designed not to suffer	1115
579	from any of these problems or limitations.	1116	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1117	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1118	control whether C<encode> escapes character values outside their respective
		1119	codeset range. Neither of these flags conflict with each other, although
		1120	some combinations make less sense than others.
		1121
		1122	Care has been taken to make all flags symmetrical with respect to
		1123	C<encode> and C<decode>, that is, texts encoded with any combination of
		1124	these flag values will be correctly decoded when the same flags are used
		1125	- in general, if you use different flag settings while encoding vs. when
		1126	decoding you likely have a bug somewhere.
		1127
		1128	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1129	simply an abstract set of character-codepoint pairs, while an encoding
		1130	takes those codepoint numbers and I<encodes> them, in our case into
		1131	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1132	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1133	the same time, which can be confusing.
580		1134
581	=over 4	1135	=over 4
582		1136
583	=item JSON 1.07	1137	=item C<utf8> flag disabled
584		1138
585	Slow (but very portable, as it is written in pure Perl).	1139	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1140	and expect Unicode strings, that is, characters with high ordinal Unicode
		1141	values (> 255) will be encoded as such characters, and likewise such
		1142	characters are decoded as-is, no canges to them will be done, except
		1143	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1144	respectively (to Perl, these are the same thing in strings unless you do
		1145	funny/weird/dumb stuff).
586		1146
587	Undocumented/buggy Unicode handling (how JSON handles unicode values is	1147	This is useful when you want to do the encoding yourself (e.g. when you
588	undocumented. One can get far by feeding it unicode strings and doing	1148	want to have UTF-16 encoded JSON texts) or when some other layer does
589	en-/decoding oneself, but unicode escapes are not working properly).	1149	the encoding for you (for example, when printing to a terminal using a
		1150	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1151	to UTF-8 encode your data first and have Perl encode it another time).
590		1152
591	No roundtripping (strings get clobbered if they look like numbers, e.g.	1153	=item C<utf8> flag enabled
592	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
593	decode into the number 2.
594		1154
595	=item JSON::PC 0.01	1155	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1156	characters using the corresponding UTF-8 multi-byte sequence, and will
		1157	expect your input strings to be encoded as UTF-8, that is, no "character"
		1158	of the input string must have any value > 255, as UTF-8 does not allow
		1159	that.
596		1160
597	Very fast.	1161	The C<utf8> flag therefore switches between two modes: disabled means you
		1162	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1163	octet/binary string in Perl.
598		1164
599	Undocumented/buggy Unicode handling.	1165	=item C<latin1> or C<ascii> flags enabled
600		1166
601	No roundtripping.	1167	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1168	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1169	characters as specified by the C<utf8> flag.
602		1170
603	Has problems handling many Perl values (e.g. regex results and other magic	1171	If C<utf8> is disabled, then the result is also correctly encoded in those
604	values will make it croak).	1172	character sets (as both are proper subsets of Unicode, meaning that a
		1173	Unicode string with all character values < 256 is the same thing as a
		1174	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1175	the same thing as an ASCII string in Perl).
605		1176
606	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1177	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
607	which is not a valid JSON text.	1178	regardless of these flags, just some more characters will be escaped using
		1179	C<\uXXXX> then before.
608		1180
609	Unmaintained (maintainer unresponsive for many months, bugs are not	1181	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
610	getting fixed).	1182	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1183	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1184	a subset of Unicode), while ASCII is.
611		1185
612	=item JSON::Syck 0.21	1186	Surprisingly, C<decode> will ignore these flags and so treat all input
		1187	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1188	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1189	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
613		1190
614	Very buggy (often crashes).	1191	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1192	they only govern when the JSON output engine escapes a character or not.
615		1193
616	Very inflexible (no human-readable format supported, format pretty much	1194	The main use for C<latin1> is to relatively efficiently store binary data
617	undocumented. I need at least a format for easy reading by humans and a	1195	as JSON, at the expense of breaking compatibility with most JSON decoders.
618	single-line compact format for use in a protocol, and preferably a way to
619	generate ASCII-only JSON texts).
620		1196
621	Completely broken (and confusingly documented) Unicode handling (unicode	1197	The main use for C<ascii> is to force the output to not contain characters
622	escapes are not working properly, you need to set ImplicitUnicode to	1198	with values > 127, which means you can interpret the resulting string
623	I<different> values on en- and decoding to get symmetric behaviour).	1199	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
624		1200	8-bit-encoding, and still get the same data structure back. This is useful
625	No roundtripping (simple cases work, but this depends on wether the scalar	1201	when your channel for JSON transfer is not 8-bit clean or the encoding
626	value was used in a numeric context or not).	1202	might be mangled in between (e.g. in mail), and works because ASCII is a
627		1203	proper subset of most 8-bit and multibyte encodings in use in the world.
628	Dumping hashes may skip hash values depending on iterator state.
629
630	Unmaintained (maintainer unresponsive for many months, bugs are not
631	getting fixed).
632
633	Does not check input for validity (i.e. will accept non-JSON input and
634	return "something" instead of raising an exception. This is a security
635	issue: imagine two banks transfering money between each other using
636	JSON. One bank might parse a given non-JSON request and deduct money,
637	while the other might reject the transaction with a syntax error. While a
638	good protocol will at least recover, that is extra unnecessary work and
639	the transaction will still not succeed).
640
641	=item JSON::DWIW 0.04
642
643	Very fast. Very natural. Very nice.
644
645	Undocumented unicode handling (but the best of the pack. Unicode escapes
646	still don't get parsed properly).
647
648	Very inflexible.
649
650	No roundtripping.
651
652	Does not generate valid JSON texts (key strings are often unquoted, empty keys
653	result in nothing being output)
654
655	Does not check input for validity.
656		1204
657	=back	1205	=back
658		1206
659		1207
		1208	=head2 JSON and ECMAscript
		1209
		1210	JSON syntax is based on how literals are represented in javascript (the
		1211	not-standardised predecessor of ECMAscript) which is presumably why it is
		1212	called "JavaScript Object Notation".
		1213
		1214	However, JSON is not a subset (and also not a superset of course) of
		1215	ECMAscript (the standard) or javascript (whatever browsers actually
		1216	implement).
		1217
		1218	If you want to use javascript's C<eval> function to "parse" JSON, you
		1219	might run into parse errors for valid JSON texts, or the resulting data
		1220	structure might not be queryable:
		1221
		1222	One of the problems is that U+2028 and U+2029 are valid characters inside
		1223	JSON strings, but are not allowed in ECMAscript string literals, so the
		1224	following Perl fragment will not output something that can be guaranteed
		1225	to be parsable by javascript's C<eval>:
		1226
		1227	use JSON::XS;
		1228
		1229	print encode_json [chr 0x2028];
		1230
		1231	The right fix for this is to use a proper JSON parser in your javascript
		1232	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1233	F<json2.js> parser).
		1234
		1235	If this is not an option, you can, as a stop-gap measure, simply encode to
		1236	ASCII-only JSON:
		1237
		1238	use JSON::XS;
		1239
		1240	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1241
		1242	Note that this will enlarge the resulting JSON text quite a bit if you
		1243	have many non-ASCII characters. You might be tempted to run some regexes
		1244	to only escape U+2028 and U+2029, e.g.:
		1245
		1246	# DO NOT USE THIS!
		1247	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1248	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1249	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1250	print $json;
		1251
		1252	Note that I<this is a bad idea>: the above only works for U+2028 and
		1253	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1254	javascript implementations, however, have issues with other characters as
		1255	well - using C<eval> naively simply I<will> cause problems.
		1256
		1257	Another problem is that some javascript implementations reserve
		1258	some property names for their own purposes (which probably makes
		1259	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1260	C<__proto__> property name for its own purposes.
		1261
		1262	If that is a problem, you could parse try to filter the resulting JSON
		1263	output for these property strings, e.g.:
		1264
		1265	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1266
		1267	This works because C<__proto__> is not valid outside of strings, so every
		1268	occurence of C<"__proto__"\s*:> must be a string used as property name.
		1269
		1270	If you know of other incompatibilities, please let me know.
		1271
		1272
660	=head2 JSON and YAML	1273	=head2 JSON and YAML
661		1274
662	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1275	You often hear that JSON is a subset of YAML. This is, however, a mass
663	however, a mass hysteria and very far from the truth. In general, there is	1276	hysteria(*) and very far from the truth (as of the time of this writing),
664	no way to configure JSON::XS to output a data structure as valid YAML.	1277	so let me state it clearly: I<in general, there is no way to configure
		1278	JSON::XS to output a data structure as valid YAML> that works in all
		1279	cases.
665		1280
666	If you really must use JSON::XS to generate YAML, you should use this	1281	If you really must use JSON::XS to generate YAML, you should use this
667	algorithm (subject to change in future versions):	1282	algorithm (subject to change in future versions):
668		1283
669	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1284	my $to_yaml = JSON::XS->new->utf8->space_after (1);
670	my $yaml = $to_yaml->encode ($ref) . "\n";	1285	my $yaml = $to_yaml->encode ($ref) . "\n";
671		1286
672	This will usually generate JSON texts that also parse as valid	1287	This will I<usually> generate JSON texts that also parse as valid
673	YAML. Please note that YAML has hardcoded limits on (simple) object key	1288	YAML. Please note that YAML has hardcoded limits on (simple) object key
674	lengths that JSON doesn't have, so you should make sure that your hash	1289	lengths that JSON doesn't have and also has different and incompatible
		1290	unicode character escape syntax, so you should make sure that your hash
675	keys are noticably shorter than the 1024 characters YAML allows.	1291	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1292	and that you do not have characters with codepoint values outside the
		1293	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1294	sequences in strings (which JSON::XS does not I<currently> generate, but
		1295	other JSON generators might).
676		1296
677	There might be other incompatibilities that I am not aware of. In general	1297	There might be other incompatibilities that I am not aware of (or the YAML
		1298	specification has been changed yet again - it does so quite often). In
678	you should not try to generate YAML with a JSON generator or vice versa,	1299	general you should not try to generate YAML with a JSON generator or vice
679	or try to parse JSON with a YAML parser or vice versa: chances are high	1300	versa, or try to parse JSON with a YAML parser or vice versa: chances are
680	that you will run into severe interoperability problems.	1301	high that you will run into severe interoperability problems when you
		1302	least expect it.
		1303
		1304	=over 4
		1305
		1306	=item (*)
		1307
		1308	I have been pressured multiple times by Brian Ingerson (one of the
		1309	authors of the YAML specification) to remove this paragraph, despite him
		1310	acknowledging that the actual incompatibilities exist. As I was personally
		1311	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1312	educate people about these issues, so others do not run into the same
		1313	problem again and again. After this, Brian called me a (quote)I<complete
		1314	and worthless idiot>(unquote).
		1315
		1316	In my opinion, instead of pressuring and insulting people who actually
		1317	clarify issues with YAML and the wrong statements of some of its
		1318	proponents, I would kindly suggest reading the JSON spec (which is not
		1319	that difficult or long) and finally make YAML compatible to it, and
		1320	educating users about the changes, instead of spreading lies about the
		1321	real compatibility for many I<years> and trying to silence people who
		1322	point out that it isn't true.
		1323
		1324	Addendum/2009: the YAML 1.2 spec is still incomaptible with JSON, even
		1325	though the incompatibilities have been documented (and are known to
		1326	Brian) for many years and the spec makes explicit claims that YAML is a
		1327	superset of JSON. It would be so easy to fix, but apparently, bullying and
		1328	corrupting userdata is so much easier.
		1329
		1330	=back
681		1331
682		1332
683	=head2 SPEED	1333	=head2 SPEED
684		1334
685	It seems that JSON::XS is surprisingly fast, as shown in the following	1335	It seems that JSON::XS is surprisingly fast, as shown in the following
686	tables. They have been generated with the help of the C<eg/bench> program	1336	tables. They have been generated with the help of the C<eg/bench> program
687	in the JSON::XS distribution, to make it easy to compare on your own	1337	in the JSON::XS distribution, to make it easy to compare on your own
688	system.	1338	system.
689		1339
690	First comes a comparison between various modules using a very short	1340	First comes a comparison between various modules using
691	single-line JSON string:	1341	a very short single-line JSON string (also available at
		1342	L<http://dist.schmorp.de/misc/json/short.json>).
692		1343
693	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1344	{"method": "handleMessage", "params": ["user1",
694	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1345	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1346	1, 0]}
695		1347
696	It shows the number of encodes/decodes per second (JSON::XS uses	1348	It shows the number of encodes/decodes per second (JSON::XS uses
697	the functional interface, while JSON::XS/2 uses the OO interface	1349	the functional interface, while JSON::XS/2 uses the OO interface
698	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1350	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
699	shrink). Higher is better:	1351	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1352	uses the from_json method). Higher is better:
700		1353
701	module | encode | decode |	1354	module | encode | decode |
702	-----------|------------|------------|	1355	--------------|------------|------------|
703	JSON | 7645.468 | 4208.613 |	1356	JSON::DWIW/DS | 86302.551 | 102300.098 |
704	JSON::DWIW | 40721.398 | 77101.176 |	1357	JSON::DWIW/FJ | 86302.551 | 75983.768 |
705	JSON::PC | 65948.176 | 78251.940 |	1358	JSON::PP | 15827.562 | 6638.658 |
706	JSON::Syck | 22844.793 | 26479.192 |	1359	JSON::Syck | 63358.066 | 47662.545 |
707	JSON::XS | 388361.481 | 199728.762 |	1360	JSON::XS | 511500.488 | 511500.488 |
708	JSON::XS/2 | 218453.333 | 192399.266 |	1361	JSON::XS/2 | 291271.111 | 388361.481 |
709	JSON::XS/3 | 338250.323 | 192399.266 |	1362	JSON::XS/3 | 361577.931 | 361577.931 |
710	Storable | 15779.925 | 14169.946 |	1363	Storable | 66788.280 | 265462.278 |
711	-----------+------------+------------+	1364	--------------+------------+------------+
712		1365
713	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1366	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
714	about three times faster on decoding, and over fourty times faster	1367	about five times faster on decoding, and over thirty to seventy times
715	than JSON, even with pretty-printing and key sorting. It also compares	1368	faster than JSON's pure perl implementation. It also compares favourably
716	favourably to Storable for small amounts of data.	1369	to Storable for small amounts of data.
717		1370
718	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1371	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
719	search API (http://nanoref.com/yahooapis/mgPdGg):	1372	search API (L<http://dist.schmorp.de/misc/json/long.json>).
720		1373
721	module | encode | decode |	1374	module | encode | decode |
722	-----------|------------|------------|	1375	--------------|------------|------------|
723	JSON | 254.685 | 37.665 |	1376	JSON::DWIW/DS | 1647.927 | 2673.916 |
724	JSON::DWIW | 843.343 | 1049.731 |	1377	JSON::DWIW/FJ | 1630.249 | 2596.128 |
725	JSON::PC | 3602.116 | 2307.352 |	1378	JSON::PP | 400.640 | 62.311 |
726	JSON::Syck | 505.107 | 787.899 |	1379	JSON::Syck | 1481.040 | 1524.869 |
727	JSON::XS | 5747.196 | 3690.220 |	1380	JSON::XS | 20661.596 | 9541.183 |
728	JSON::XS/2 | 3968.121 | 3676.634 |	1381	JSON::XS/2 | 10683.403 | 9416.938 |
729	JSON::XS/3 | 6105.246 | 3662.508 |	1382	JSON::XS/3 | 20661.596 | 9400.054 |
730	Storable | 4417.337 | 5285.161 |	1383	Storable | 19765.806 | 10000.725 |
731	-----------+------------+------------+	1384	--------------+------------+------------+
732		1385
733	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1386	Again, JSON::XS leads by far (except for Storable which non-surprisingly
734	decodes faster).	1387	decodes a bit faster).
735		1388
736	On large strings containing lots of high unicode characters, some modules	1389	On large strings containing lots of high Unicode characters, some modules
737	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1390	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
738	will be broken due to missing (or wrong) unicode handling. Others refuse	1391	will be broken due to missing (or wrong) Unicode handling. Others refuse
739	to decode or encode properly, so it was impossible to prepare a fair	1392	to decode or encode properly, so it was impossible to prepare a fair
740	comparison table for that case.	1393	comparison table for that case.
741		1394
742		1395
743	=head1 SECURITY CONSIDERATIONS	1396	=head1 SECURITY CONSIDERATIONS
…		…
749	any buffer overflows. Obviously, this module should ensure that and I am	1402	any buffer overflows. Obviously, this module should ensure that and I am
750	trying hard on making that true, but you never know.	1403	trying hard on making that true, but you never know.
751		1404
752	Second, you need to avoid resource-starving attacks. That means you should	1405	Second, you need to avoid resource-starving attacks. That means you should
753	limit the size of JSON texts you accept, or make sure then when your	1406	limit the size of JSON texts you accept, or make sure then when your
754	resources run out, thats just fine (e.g. by using a separate process that	1407	resources run out, that's just fine (e.g. by using a separate process that
755	can crash safely). The size of a JSON text in octets or characters is	1408	can crash safely). The size of a JSON text in octets or characters is
756	usually a good indication of the size of the resources required to decode	1409	usually a good indication of the size of the resources required to decode
757	it into a Perl structure.	1410	it into a Perl structure. While JSON::XS can check the size of the JSON
		1411	text, it might be too late when you already have it in memory, so you
		1412	might want to check the size before you accept the string.
758		1413
759	Third, JSON::XS recurses using the C stack when decoding objects and	1414	Third, JSON::XS recurses using the C stack when decoding objects and
760	arrays. The C stack is a limited resource: for instance, on my amd64	1415	arrays. The C stack is a limited resource: for instance, on my amd64
761	machine with 8MB of stack size I can decode around 180k nested arrays but	1416	machine with 8MB of stack size I can decode around 180k nested arrays but
762	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1417	only 14k nested JSON objects (due to perl itself recursing deeply on croak
763	to free the temporary). If that is exceeded, the program crashes. to be	1418	to free the temporary). If that is exceeded, the program crashes. To be
764	conservative, the default nesting limit is set to 512. If your process	1419	conservative, the default nesting limit is set to 512. If your process
765	has a smaller stack, you should adjust this setting accordingly with the	1420	has a smaller stack, you should adjust this setting accordingly with the
766	C<max_depth> method.	1421	C<max_depth> method.
767		1422
768	And last but least, something else could bomb you that I forgot to think	1423	Something else could bomb you, too, that I forgot to think of. In that
769	of. In that case, you get to keep the pieces. I am always open for hints,	1424	case, you get to keep the pieces. I am always open for hints, though...
770	though...	1425
		1426	Also keep in mind that JSON::XS might leak contents of your Perl data
		1427	structures in its error messages, so when you serialise sensitive
		1428	information you might want to make sure that exceptions thrown by JSON::XS
		1429	will not end up in front of untrusted eyes.
771		1430
772	If you are using JSON::XS to return packets to consumption	1431	If you are using JSON::XS to return packets to consumption
773	by javascript scripts in a browser you should have a look at	1432	by JavaScript scripts in a browser you should have a look at
774	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether	1433	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
775	you are vulnerable to some common attack vectors (which really are browser	1434	see whether you are vulnerable to some common attack vectors (which really
776	design bugs, but it is still you who will have to deal with it, as major	1435	are browser design bugs, but it is still you who will have to deal with
777	browser developers care only for features, not about doing security	1436	it, as major browser developers care only for features, not about getting
778	right).	1437	security right).
		1438
		1439
		1440	=head1 THREADS
		1441
		1442	This module is I<not> guaranteed to be thread safe and there are no
		1443	plans to change this until Perl gets thread support (as opposed to the
		1444	horribly slow so-called "threads" which are simply slow and bloated
		1445	process simulations - use fork, it's I<much> faster, cheaper, better).
		1446
		1447	(It might actually work, but you have been warned).
779		1448
780		1449
781	=head1 BUGS	1450	=head1 BUGS
782		1451
783	While the goal of this module is to be correct, that unfortunately does	1452	While the goal of this module is to be correct, that unfortunately does
784	not mean its bug-free, only that I think its design is bug-free. It is	1453	not mean it's bug-free, only that I think its design is bug-free. If you
785	still relatively early in its development. If you keep reporting bugs they	1454	keep reporting bugs they will be fixed swiftly, though.
786	will be fixed swiftly, though.	1455
		1456	Please refrain from using rt.cpan.org or any other bug reporting
		1457	service. I put the contact address into my modules for a reason.
787		1458
788	=cut	1459	=cut
789		1460
790	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1461	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
791	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };	1462	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
…		…
808	"--" => sub { $_[0] = ${$_[0]} - 1 },	1479	"--" => sub { $_[0] = ${$_[0]} - 1 },
809	fallback => 1;	1480	fallback => 1;
810		1481
811	1;	1482	1;
812		1483
		1484	=head1 SEE ALSO
		1485
		1486	The F<json_xs> command line utility for quick experiments.
		1487
813	=head1 AUTHOR	1488	=head1 AUTHOR
814		1489
815	Marc Lehmann <schmorp@schmorp.de>	1490	Marc Lehmann <schmorp@schmorp.de>
816	http://home.schmorp.de/	1491	http://home.schmorp.de/
817		1492

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