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Revision 1.54 by root, Tue Jul 10 16:22:31 2007 UTC vs.
Revision 1.142 by root, Fri Oct 25 19:57:42 2013 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
		5	=encoding utf-8
		6
		7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
4		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
8		13
9	# exported functions, they croak on error	14	# exported functions, they croak on error
10	# and expect/generate UTF-8	15	# and expect/generate UTF-8
11		16
12	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
13	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
14		19
15	# OO-interface	20	# OO-interface
16		21
17	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
18	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
19	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
20		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
		33
21	=head1 DESCRIPTION	34	=head1 DESCRIPTION
22		35
23	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
24	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
25	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overridden) with no overhead due to emulation (by inheriting constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
26		47
27	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
28	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
29	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
30	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
31	reports for other reasons.	52	reports for other reasons.
32		53
33	See COMPARISON, below, for a comparison to some other JSON modules.
34
35	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
36	vice versa.	55	vice versa.
37		56
38	=head2 FEATURES	57	=head2 FEATURES
39		58
40	=over 4	59	=over 4
41		60
42	=item * correct unicode handling	61	=item * correct Unicode handling
43		62
44	This module knows how to handle Unicode, and even documents how and when	63	This module knows how to handle Unicode, documents how and when it does
45	it does so.	64	so, and even documents what "correct" means.
46		65
47	=item * round-trip integrity	66	=item * round-trip integrity
48		67
49	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
50	by JSON, the deserialised data structure is identical on the Perl level.	69	by JSON and Perl, the deserialised data structure is identical on the Perl
51	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
52	like a number).	71	it looks like a number). There I<are> minor exceptions to this, read the
		72	MAPPING section below to learn about those.
53		73
54	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
55		75
56	There is no guessing, no generating of illegal JSON texts by default,	76	There is no guessing, no generating of illegal JSON texts by default,
57	and only JSON is accepted as input by default (the latter is a security	77	and only JSON is accepted as input by default (the latter is a security
58	feature).	78	feature).
59		79
60	=item * fast	80	=item * fast
61		81
62	Compared to other JSON modules, this module compares favourably in terms	82	Compared to other JSON modules and other serialisers such as Storable,
63	of speed, too.	83	this module usually compares favourably in terms of speed, too.
64		84
65	=item * simple to use	85	=item * simple to use
66		86
67	This module has both a simple functional interface as well as an OO	87	This module has both a simple functional interface as well as an object
68	interface.	88	oriented interface.
69		89
70	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
71		91
72	You can choose between the most compact guarenteed single-line format	92	You can choose between the most compact guaranteed-single-line format
73	possible (nice for simple line-based protocols), a pure-ascii format	93	possible (nice for simple line-based protocols), a pure-ASCII format
74	(for when your transport is not 8-bit clean, still supports the whole	94	(for when your transport is not 8-bit clean, still supports the whole
75	unicode range), or a pretty-printed format (for when you want to read that	95	Unicode range), or a pretty-printed format (for when you want to read that
76	stuff). Or you can combine those features in whatever way you like.	96	stuff). Or you can combine those features in whatever way you like.
77		97
78	=back	98	=back
79		99
80	=cut	100	=cut
81		101
82	package JSON::XS;	102	package JSON::XS;
83		103
84	use strict;	104	use common::sense;
85		105
86	our $VERSION = '1.41';	106	our $VERSION = 2.34;
87	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
88		108
89	our @EXPORT = qw(to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
90		110
91	use Exporter;	111	use Exporter;
92	use XSLoader;	112	use XSLoader;
93		113
94	=head1 FUNCTIONAL INTERFACE	114	=head1 FUNCTIONAL INTERFACE
95		115
96	The following convinience methods are provided by this module. They are	116	The following convenience methods are provided by this module. They are
97	exported by default:	117	exported by default:
98		118
99	=over 4	119	=over 4
100		120
101	=item $json_text = to_json $perl_scalar	121	=item $json_text = encode_json $perl_scalar
102		122
103	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
104	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.
105	octets only). Croaks on error.
106		125
107	This function call is functionally identical to:	126	This function call is functionally identical to:
108		127
109	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	128	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
110		129
111	except being faster.	130	Except being faster.
112		131
113	=item $perl_scalar = from_json $json_text	132	=item $perl_scalar = decode_json $json_text
114		133
115	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
116	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
117	scalar or reference. Croaks on error.	136	reference. Croaks on error.
118		137
119	This function call is functionally identical to:	138	This function call is functionally identical to:
120		139
121	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	140	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
122		141
123	except being faster.	142	Except being faster.
124		143
125	=item $is_boolean = JSON::XS::is_bool $scalar	144	=item $is_boolean = JSON::XS::is_bool $scalar
126		145
127	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
128	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
…		…
132	Perl.	151	Perl.
133		152
134	=back	153	=back
135		154
136		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
137	=head1 OBJECT-ORIENTED INTERFACE	204	=head1 OBJECT-ORIENTED INTERFACE
138		205
139	The object oriented interface lets you configure your own encoding or	206	The object oriented interface lets you configure your own encoding or
140	decoding style, within the limits of supported formats.	207	decoding style, within the limits of supported formats.
141		208
…		…
152	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]})
153	=> {"a": [1, 2]}	220	=> {"a": [1, 2]}
154		221
155	=item $json = $json->ascii ([$enable])	222	=item $json = $json->ascii ([$enable])
156		223
		224	=item $enabled = $json->get_ascii
		225
157	If C<$enable> is true (or missing), then the C<encode> method will not	226	If C<$enable> is true (or missing), then the C<encode> method will not
158	generate characters outside the code range C<0..127> (which is ASCII). Any	227	generate characters outside the code range C<0..127> (which is ASCII). Any
159	unicode characters outside that range will be escaped using either a	228	Unicode characters outside that range will be escaped using either a
160	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,	229	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
161	as per RFC4627. The resulting encoded JSON text can be treated as a native	230	as per RFC4627. The resulting encoded JSON text can be treated as a native
162	unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,	231	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
163	or any other superset of ASCII.	232	or any other superset of ASCII.
164		233
165	If C<$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
166	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
167	in a faster and more compact format.	236	in a faster and more compact format.
168		237
		238	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		239	document.
		240
169	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
170	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
171	contain any 8 bit characters.	243	contain any 8 bit characters.
172		244
173	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	245	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
174	=> ["\ud801\udc01"]	246	=> ["\ud801\udc01"]
175		247
176	=item $json = $json->latin1 ([$enable])	248	=item $json = $json->latin1 ([$enable])
177		249
		250	=item $enabled = $json->get_latin1
		251
178	If C<$enable> is true (or missing), then the C<encode> method will encode	252	If C<$enable> is true (or missing), then the C<encode> method will encode
179	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters	253	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
180	outside the code range C<0..255>. The resulting string can be treated as a	254	outside the code range C<0..255>. The resulting string can be treated as a
181	latin1-encoded JSON text or a native unicode string. The C<decode> method	255	latin1-encoded JSON text or a native Unicode string. The C<decode> method
182	will not be affected in any way by this flag, as C<decode> by default	256	will not be affected in any way by this flag, as C<decode> by default
183	expects unicode, which is a strict superset of latin1.	257	expects Unicode, which is a strict superset of latin1.
184		258
185	If C<$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
186	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.
187		264
188	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
189	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
190	size. The disadvantage is that the resulting JSON text is encoded	267	size. The disadvantage is that the resulting JSON text is encoded
191	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
192	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
193	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
194	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.
195		272
196	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	273	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
197	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	274	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
198		275
199	=item $json = $json->utf8 ([$enable])	276	=item $json = $json->utf8 ([$enable])
		277
		278	=item $enabled = $json->get_utf8
200		279
201	If C<$enable> is true (or missing), then the C<encode> method will encode	280	If C<$enable> is true (or missing), then the C<encode> method will encode
202	the JSON result into UTF-8, as required by many protocols, while the	281	the JSON result into UTF-8, as required by many protocols, while the
203	C<decode> method expects to be handled an UTF-8-encoded string. Please	282	C<decode> method expects to be handled an UTF-8-encoded string. Please
204	note that UTF-8-encoded strings do not contain any characters outside the	283	note that UTF-8-encoded strings do not contain any characters outside the
205	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	284	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
206	versions, enabling this option might enable autodetection of the UTF-16	285	versions, enabling this option might enable autodetection of the UTF-16
207	and UTF-32 encoding families, as described in RFC4627.	286	and UTF-32 encoding families, as described in RFC4627.
208		287
209	If C<$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
210	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
211	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
212	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.
213		295
214	Example, output UTF-16BE-encoded JSON:	296	Example, output UTF-16BE-encoded JSON:
215		297
216	use Encode;	298	use Encode;
217	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	299	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
238	]	320	]
239	}	321	}
240		322
241	=item $json = $json->indent ([$enable])	323	=item $json = $json->indent ([$enable])
242		324
		325	=item $enabled = $json->get_indent
		326
243	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	327	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
244	format as output, putting every array member or object/hash key-value pair	328	format as output, putting every array member or object/hash key-value pair
245	into its own line, identing them properly.	329	into its own line, indenting them properly.
246		330
247	If C<$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
248	resulting JSON text is guarenteed not to contain any C<newlines>.	332	resulting JSON text is guaranteed not to contain any C<newlines>.
249		333
250	This setting has no effect when decoding JSON texts.	334	This setting has no effect when decoding JSON texts.
251		335
252	=item $json = $json->space_before ([$enable])	336	=item $json = $json->space_before ([$enable])
		337
		338	=item $enabled = $json->get_space_before
253		339
254	If C<$enable> is true (or missing), then the C<encode> method will add an extra	340	If C<$enable> is true (or missing), then the C<encode> method will add an extra
255	optional space before the C<:> separating keys from values in JSON objects.	341	optional space before the C<:> separating keys from values in JSON objects.
256		342
257	If C<$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
…		…
263	Example, space_before enabled, space_after and indent disabled:	349	Example, space_before enabled, space_after and indent disabled:
264		350
265	{"key" :"value"}	351	{"key" :"value"}
266		352
267	=item $json = $json->space_after ([$enable])	353	=item $json = $json->space_after ([$enable])
		354
		355	=item $enabled = $json->get_space_after
268		356
269	If C<$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
270	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
271	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
272	members.	360	members.
…		…
278		366
279	Example, space_before and indent disabled, space_after enabled:	367	Example, space_before and indent disabled, space_after enabled:
280		368
281	{"key": "value"}	369	{"key": "value"}
282		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
283	=item $json = $json->canonical ([$enable])	418	=item $json = $json->canonical ([$enable])
		419
		420	=item $enabled = $json->get_canonical
284		421
285	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	422	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
286	by sorting their keys. This is adding a comparatively high overhead.	423	by sorting their keys. This is adding a comparatively high overhead.
287		424
288	If C<$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
289	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
290	of the same script).	427	of the same script, and can change even within the same run from 5.18
		428	onwards).
291		429
292	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
293	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,
294	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,
295	as key-value pairs have no inherent ordering in Perl.	433	as key-value pairs have no inherent ordering in Perl.
296		434
297	This setting has no effect when decoding JSON texts.	435	This setting has no effect when decoding JSON texts.
298		436
		437	This setting has currently no effect on tied hashes.
		438
299	=item $json = $json->allow_nonref ([$enable])	439	=item $json = $json->allow_nonref ([$enable])
		440
		441	=item $enabled = $json->get_allow_nonref
300		442
301	If C<$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
302	non-reference into its corresponding string, number or null JSON value,	444	non-reference into its corresponding string, number or null JSON value,
303	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	445	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
304	values instead of croaking.	446	values instead of croaking.
…		…
312	resulting in an invalid JSON text:	454	resulting in an invalid JSON text:
313		455
314	JSON::XS->new->allow_nonref->encode ("Hello, World!")	456	JSON::XS->new->allow_nonref->encode ("Hello, World!")
315	=> "Hello, World!"	457	=> "Hello, World!"
316		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
317	=item $json = $json->allow_blessed ([$enable])	475	=item $json = $json->allow_blessed ([$enable])
		476
		477	=item $enabled = $json->get_allow_blessed
318		478
319	If C<$enable> is true (or missing), then the C<encode> method will not	479	If C<$enable> is true (or missing), then the C<encode> method will not
320	barf when it encounters a blessed reference. Instead, the value of the	480	barf when it encounters a blessed reference. Instead, the value of the
321	B<convert_blessed> option will decide wether C<null> (C<convert_blessed>	481	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
322	disabled or no C<to_json> method found) or a representation of the	482	disabled or no C<TO_JSON> method found) or a representation of the
323	object (C<convert_blessed> enabled and C<to_json> method found) is being	483	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
324	encoded. Has no effect on C<decode>.	484	encoded. Has no effect on C<decode>.
325		485
326	If C<$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
327	exception when it encounters a blessed object.	487	exception when it encounters a blessed object.
328		488
329	=item $json = $json->convert_blessed ([$enable])	489	=item $json = $json->convert_blessed ([$enable])
		490
		491	=item $enabled = $json->get_convert_blessed
330		492
331	If C<$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
332	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
333	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
334	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
…		…
338	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>
339	returns other blessed objects, those will be handled in the same	501	returns other blessed objects, those will be handled in the same
340	way. C<TO_JSON> must take care of not causing an endless recursion cycle	502	way. C<TO_JSON> must take care of not causing an endless recursion cycle
341	(== crash) in this case. The name of C<TO_JSON> was chosen because other	503	(== crash) in this case. The name of C<TO_JSON> was chosen because other
342	methods called by the Perl core (== not by the user of the object) are	504	methods called by the Perl core (== not by the user of the object) are
343	usually in upper case letters and to avoid collisions with the C<to_json>	505	usually in upper case letters and to avoid collisions with any C<to_json>
344	function.	506	function or method.
345		507
346	This setting does not yet influence C<decode> in any way, but in the	508	This setting does not yet influence C<decode> in any way, but in the
347	future, global hooks might get installed that influence C<decode> and are	509	future, global hooks might get installed that influence C<decode> and are
348	enabled by this setting.	510	enabled by this setting.
349		511
…		…
391		553
392	As this callback gets called less often then the C<filter_json_object>	554	As this callback gets called less often then the C<filter_json_object>
393	one, decoding speed will not usually suffer as much. Therefore, single-key	555	one, decoding speed will not usually suffer as much. Therefore, single-key
394	objects make excellent targets to serialise Perl objects into, especially	556	objects make excellent targets to serialise Perl objects into, especially
395	as single-key JSON objects are as close to the type-tagged value concept	557	as single-key JSON objects are as close to the type-tagged value concept
396	as JSON gets (its basically an ID/VALUE tuple). Of course, JSON does not	558	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
397	support this in any way, so you need to make sure your data never looks	559	support this in any way, so you need to make sure your data never looks
398	like a serialised Perl hash.	560	like a serialised Perl hash.
399		561
400	Typical names for the single object key are C<__class_whatever__>, or	562	Typical names for the single object key are C<__class_whatever__>, or
401	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even	563	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
…		…
425		587
426	{ __widget__ => $self->{id} }	588	{ __widget__ => $self->{id} }
427	}	589	}
428		590
429	=item $json = $json->shrink ([$enable])	591	=item $json = $json->shrink ([$enable])
		592
		593	=item $enabled = $json->get_shrink
430		594
431	Perl usually over-allocates memory a bit when allocating space for	595	Perl usually over-allocates memory a bit when allocating space for
432	strings. This flag optionally resizes strings generated by either	596	strings. This flag optionally resizes strings generated by either
433	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
434	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
…		…
452	strings that look like integers or floats into integers or floats	616	strings that look like integers or floats into integers or floats
453	internally (there is no difference on the Perl level), saving space.	617	internally (there is no difference on the Perl level), saving space.
454		618
455	=item $json = $json->max_depth ([$maximum_nesting_depth])	619	=item $json = $json->max_depth ([$maximum_nesting_depth])
456		620
		621	=item $max_depth = $json->get_max_depth
		622
457	Sets the maximum nesting level (default C<512>) accepted while encoding	623	Sets the maximum nesting level (default C<512>) accepted while encoding
458	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
459	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
460	stop and croak at that point.	626	point.
461		627
462	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
463	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<[>
464	characters without their matching closing parenthesis crossed to reach a	630	characters without their matching closing parenthesis crossed to reach a
465	given character in a string.	631	given character in a string.
466		632
467	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
468	that the object is only a single hash/object or array.	634	that the object is only a single hash/object or array.
469		635
470	The argument to C<max_depth> will be rounded up to the next highest power
471	of two. If no argument is given, the highest possible setting will be	636	If no argument is given, the highest possible setting will be used, which
472	used, which is rarely useful.	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.
473		642
474	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.
475		644
476	=item $json = $json->max_size ([$maximum_string_size])	645	=item $json = $json->max_size ([$maximum_string_size])
		646
		647	=item $max_size = $json->get_max_size
477		648
478	Set the maximum length a JSON text may have (in bytes) where decoding is	649	Set the maximum length a JSON text may have (in bytes) where decoding is
479	being attempted. The default is C<0>, meaning no limit. When C<decode>	650	being attempted. The default is C<0>, meaning no limit. When C<decode>
480	is called on a string longer then this number of characters it will not	651	is called on a string that is longer then this many bytes, it will not
481	attempt to decode the string but throw an exception. This setting has no	652	attempt to decode the string but throw an exception. This setting has no
482	effect on C<encode> (yet).	653	effect on C<encode> (yet).
483		654
484	The argument to C<max_size> will be rounded up to the next B<highest>	655	If no argument is given, the limit check will be deactivated (same as when
485	power of two (so may be more than requested). If no argument is given, the	656	C<0> is specified).
486	limit check will be deactivated (same as when C<0> is specified).
487		657
488	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	658	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
489		659
490	=item $json_text = $json->encode ($perl_scalar)	660	=item $json_text = $json->encode ($perl_scalar)
491		661
492	Converts the given Perl data structure (a simple scalar or a reference	662	Converts the given Perl value or data structure to its JSON
493	to a hash or array) to its JSON representation. Simple scalars will be	663	representation. Croaks on error.
494	converted into JSON string or number sequences, while references to arrays
495	become JSON arrays and references to hashes become JSON objects. Undefined
496	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
497	nor C<false> values will be generated.
498		664
499	=item $perl_scalar = $json->decode ($json_text)	665	=item $perl_scalar = $json->decode ($json_text)
500		666
501	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,
502	returning the resulting simple scalar or reference. Croaks on error.	668	returning the resulting simple scalar or reference. Croaks on error.
503
504	JSON numbers and strings become simple Perl scalars. JSON arrays become
505	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
506	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
507		669
508	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	670	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
509		671
510	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
511	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
…		…
520	=> ([], 3)	682	=> ([], 3)
521		683
522	=back	684	=back
523		685
524		686
		687	=head1 INCREMENTAL PARSING
		688
		689	In some cases, there is the need for incremental parsing of JSON
		690	texts. While this module always has to keep both JSON text and resulting
		691	Perl data structure in memory at one time, it does allow you to parse a
		692	JSON stream incrementally. It does so by accumulating text until it has
		693	a full JSON object, which it then can decode. This process is similar to
		694	using C<decode_prefix> to see if a full JSON object is available, but
		695	is much more efficient (and can be implemented with a minimum of method
		696	calls).
		697
		698	JSON::XS will only attempt to parse the JSON text once it is sure it
		699	has enough text to get a decisive result, using a very simple but
		700	truly incremental parser. This means that it sometimes won't stop as
		701	early as the full parser, for example, it doesn't detect mismatched
		702	parentheses. The only thing it guarantees is that it starts decoding as
		703	soon as a syntactically valid JSON text has been seen. This means you need
		704	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		705	parsing in the presence if syntax errors.
		706
		707	The following methods implement this incremental parser.
		708
		709	=over 4
		710
		711	=item [void, scalar or list context] = $json->incr_parse ([$string])
		712
		713	This is the central parsing function. It can both append new text and
		714	extract objects from the stream accumulated so far (both of these
		715	functions are optional).
		716
		717	If C<$string> is given, then this string is appended to the already
		718	existing JSON fragment stored in the C<$json> object.
		719
		720	After that, if the function is called in void context, it will simply
		721	return without doing anything further. This can be used to add more text
		722	in as many chunks as you want.
		723
		724	If the method is called in scalar context, then it will try to extract
		725	exactly I<one> JSON object. If that is successful, it will return this
		726	object, otherwise it will return C<undef>. If there is a parse error,
		727	this method will croak just as C<decode> would do (one can then use
		728	C<incr_skip> to skip the erroneous part). This is the most common way of
		729	using the method.
		730
		731	And finally, in list context, it will try to extract as many objects
		732	from the stream as it can find and return them, or the empty list
		733	otherwise. For this to work, there must be no separators between the JSON
		734	objects or arrays, instead they must be concatenated back-to-back. If
		735	an error occurs, an exception will be raised as in the scalar context
		736	case. Note that in this case, any previously-parsed JSON texts will be
		737	lost.
		738
		739	Example: Parse some JSON arrays/objects in a given string and return
		740	them.
		741
		742	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		743
		744	=item $lvalue_string = $json->incr_text
		745
		746	This method returns the currently stored JSON fragment as an lvalue, that
		747	is, you can manipulate it. This I<only> works when a preceding call to
		748	C<incr_parse> in I<scalar context> successfully returned an object. Under
		749	all other circumstances you must not call this function (I mean it.
		750	although in simple tests it might actually work, it I<will> fail under
		751	real world conditions). As a special exception, you can also call this
		752	method before having parsed anything.
		753
		754	This function is useful in two cases: a) finding the trailing text after a
		755	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		756	(such as commas).
		757
		758	=item $json->incr_skip
		759
		760	This will reset the state of the incremental parser and will remove
		761	the parsed text from the input buffer so far. This is useful after
		762	C<incr_parse> died, in which case the input buffer and incremental parser
		763	state is left unchanged, to skip the text parsed so far and to reset the
		764	parse state.
		765
		766	The difference to C<incr_reset> is that only text until the parse error
		767	occurred is removed.
		768
		769	=item $json->incr_reset
		770
		771	This completely resets the incremental parser, that is, after this call,
		772	it will be as if the parser had never parsed anything.
		773
		774	This is useful if you want to repeatedly parse JSON objects and want to
		775	ignore any trailing data, which means you have to reset the parser after
		776	each successful decode.
		777
		778	=back
		779
		780	=head2 LIMITATIONS
		781
		782	All options that affect decoding are supported, except
		783	C<allow_nonref>. The reason for this is that it cannot be made to
		784	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		785	them back to back and still decode them perfectly. This does not hold true
		786	for JSON numbers, however.
		787
		788	For example, is the string C<1> a single JSON number, or is it simply the
		789	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		790	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		791	takes the conservative route and disallows this case.
		792
		793	=head2 EXAMPLES
		794
		795	Some examples will make all this clearer. First, a simple example that
		796	works similarly to C<decode_prefix>: We want to decode the JSON object at
		797	the start of a string and identify the portion after the JSON object:
		798
		799	my $text = "[1,2,3] hello";
		800
		801	my $json = new JSON::XS;
		802
		803	my $obj = $json->incr_parse ($text)
		804	or die "expected JSON object or array at beginning of string";
		805
		806	my $tail = $json->incr_text;
		807	# $tail now contains " hello"
		808
		809	Easy, isn't it?
		810
		811	Now for a more complicated example: Imagine a hypothetical protocol where
		812	you read some requests from a TCP stream, and each request is a JSON
		813	array, without any separation between them (in fact, it is often useful to
		814	use newlines as "separators", as these get interpreted as whitespace at
		815	the start of the JSON text, which makes it possible to test said protocol
		816	with C<telnet>...).
		817
		818	Here is how you'd do it (it is trivial to write this in an event-based
		819	manner):
		820
		821	my $json = new JSON::XS;
		822
		823	# read some data from the socket
		824	while (sysread $socket, my $buf, 4096) {
		825
		826	# split and decode as many requests as possible
		827	for my $request ($json->incr_parse ($buf)) {
		828	# act on the $request
		829	}
		830	}
		831
		832	Another complicated example: Assume you have a string with JSON objects
		833	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		834	[3]>). To parse them, we have to skip the commas between the JSON texts,
		835	and here is where the lvalue-ness of C<incr_text> comes in useful:
		836
		837	my $text = "[1],[2], [3]";
		838	my $json = new JSON::XS;
		839
		840	# void context, so no parsing done
		841	$json->incr_parse ($text);
		842
		843	# now extract as many objects as possible. note the
		844	# use of scalar context so incr_text can be called.
		845	while (my $obj = $json->incr_parse) {
		846	# do something with $obj
		847
		848	# now skip the optional comma
		849	$json->incr_text =~ s/^ \s* , //x;
		850	}
		851
		852	Now lets go for a very complex example: Assume that you have a gigantic
		853	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		854	but you cannot load it into memory fully (this has actually happened in
		855	the real world :).
		856
		857	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		858	can still help you: You implement a (very simple) array parser and let
		859	JSON decode the array elements, which are all full JSON objects on their
		860	own (this wouldn't work if the array elements could be JSON numbers, for
		861	example):
		862
		863	my $json = new JSON::XS;
		864
		865	# open the monster
		866	open my $fh, "<bigfile.json"
		867	or die "bigfile: $!";
		868
		869	# first parse the initial "["
		870	for (;;) {
		871	sysread $fh, my $buf, 65536
		872	or die "read error: $!";
		873	$json->incr_parse ($buf); # void context, so no parsing
		874
		875	# Exit the loop once we found and removed(!) the initial "[".
		876	# In essence, we are (ab-)using the $json object as a simple scalar
		877	# we append data to.
		878	last if $json->incr_text =~ s/^ \s* \[ //x;
		879	}
		880
		881	# now we have the skipped the initial "[", so continue
		882	# parsing all the elements.
		883	for (;;) {
		884	# in this loop we read data until we got a single JSON object
		885	for (;;) {
		886	if (my $obj = $json->incr_parse) {
		887	# do something with $obj
		888	last;
		889	}
		890
		891	# add more data
		892	sysread $fh, my $buf, 65536
		893	or die "read error: $!";
		894	$json->incr_parse ($buf); # void context, so no parsing
		895	}
		896
		897	# in this loop we read data until we either found and parsed the
		898	# separating "," between elements, or the final "]"
		899	for (;;) {
		900	# first skip whitespace
		901	$json->incr_text =~ s/^\s*//;
		902
		903	# if we find "]", we are done
		904	if ($json->incr_text =~ s/^\]//) {
		905	print "finished.\n";
		906	exit;
		907	}
		908
		909	# if we find ",", we can continue with the next element
		910	if ($json->incr_text =~ s/^,//) {
		911	last;
		912	}
		913
		914	# if we find anything else, we have a parse error!
		915	if (length $json->incr_text) {
		916	die "parse error near ", $json->incr_text;
		917	}
		918
		919	# else add more data
		920	sysread $fh, my $buf, 65536
		921	or die "read error: $!";
		922	$json->incr_parse ($buf); # void context, so no parsing
		923	}
		924
		925	This is a complex example, but most of the complexity comes from the fact
		926	that we are trying to be correct (bear with me if I am wrong, I never ran
		927	the above example :).
		928
		929
		930
525	=head1 MAPPING	931	=head1 MAPPING
526		932
527	This section describes how JSON::XS maps Perl values to JSON values and	933	This section describes how JSON::XS maps Perl values to JSON values and
528	vice versa. These mappings are designed to "do the right thing" in most	934	vice versa. These mappings are designed to "do the right thing" in most
529	circumstances automatically, preserving round-tripping characteristics	935	circumstances automatically, preserving round-tripping characteristics
530	(what you put in comes out as something equivalent).	936	(what you put in comes out as something equivalent).
531		937
532	For the more enlightened: note that in the following descriptions,	938	For the more enlightened: note that in the following descriptions,
533	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	939	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
534	refers to the abstract Perl language itself.	940	refers to the abstract Perl language itself.
535		941
536		942
537	=head2 JSON -> PERL	943	=head2 JSON -> PERL
538		944
539	=over 4	945	=over 4
540		946
541	=item object	947	=item object
542		948
543	A JSON object becomes a reference to a hash in Perl. No ordering of object	949	A JSON object becomes a reference to a hash in Perl. No ordering of object
544	keys is preserved (JSON does not preserver object key ordering itself).	950	keys is preserved (JSON does not preserve object key ordering itself).
545		951
546	=item array	952	=item array
547		953
548	A JSON array becomes a reference to an array in Perl.	954	A JSON array becomes a reference to an array in Perl.
549		955
…		…
553	are represented by the same codepoints in the Perl string, so no manual	959	are represented by the same codepoints in the Perl string, so no manual
554	decoding is necessary.	960	decoding is necessary.
555		961
556	=item number	962	=item number
557		963
558	A JSON number becomes either an integer or numeric (floating point)	964	A JSON number becomes either an integer, numeric (floating point) or
559	scalar in perl, depending on its range and any fractional parts. On the	965	string scalar in perl, depending on its range and any fractional parts. On
560	Perl level, there is no difference between those as Perl handles all the	966	the Perl level, there is no difference between those as Perl handles all
561	conversion details, but an integer may take slightly less memory and might	967	the conversion details, but an integer may take slightly less memory and
562	represent more values exactly than (floating point) numbers.	968	might represent more values exactly than floating point numbers.
		969
		970	If the number consists of digits only, JSON::XS will try to represent
		971	it as an integer value. If that fails, it will try to represent it as
		972	a numeric (floating point) value if that is possible without loss of
		973	precision. Otherwise it will preserve the number as a string value (in
		974	which case you lose roundtripping ability, as the JSON number will be
		975	re-encoded to a JSON string).
		976
		977	Numbers containing a fractional or exponential part will always be
		978	represented as numeric (floating point) values, possibly at a loss of
		979	precision (in which case you might lose perfect roundtripping ability, but
		980	the JSON number will still be re-encoded as a JSON number).
		981
		982	Note that precision is not accuracy - binary floating point values cannot
		983	represent most decimal fractions exactly, and when converting from and to
		984	floating point, JSON::XS only guarantees precision up to but not including
		985	the least significant bit.
563		986
564	=item true, false	987	=item true, false
565		988
566	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	989	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
567	respectively. They are overloaded to act almost exactly like the numbers	990	respectively. They are overloaded to act almost exactly like the numbers
568	C<1> and C<0>. You can check wether a scalar is a JSON boolean by using	991	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
569	the C<JSON::XS::is_bool> function.	992	the C<JSON::XS::is_bool> function.
570		993
571	=item null	994	=item null
572		995
573	A JSON null atom becomes C<undef> in Perl.	996	A JSON null atom becomes C<undef> in Perl.
…		…
583		1006
584	=over 4	1007	=over 4
585		1008
586	=item hash references	1009	=item hash references
587		1010
588	Perl hash references become JSON objects. As there is no inherent ordering	1011	Perl hash references become JSON objects. As there is no inherent
589	in hash keys (or JSON objects), they will usually be encoded in a	1012	ordering in hash keys (or JSON objects), they will usually be encoded
590	pseudo-random order that can change between runs of the same program but	1013	in a pseudo-random order. JSON::XS can optionally sort the hash keys
591	stays generally the same within a single run of a program. JSON::XS can	1014	(determined by the I<canonical> flag), so the same datastructure will
592	optionally sort the hash keys (determined by the I<canonical> flag), so	1015	serialise to the same JSON text (given same settings and version of
593	the same datastructure will serialise to the same JSON text (given same	1016	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
594	settings and version of JSON::XS), but this incurs a runtime overhead	1017	e.g. when you want to compare some JSON text against another for equality.
595	and is only rarely useful, e.g. when you want to compare some JSON text
596	against another for equality.
597		1018
598	=item array references	1019	=item array references
599		1020
600	Perl array references become JSON arrays.	1021	Perl array references become JSON arrays.
601		1022
…		…
604	Other unblessed references are generally not allowed and will cause an	1025	Other unblessed references are generally not allowed and will cause an
605	exception to be thrown, except for references to the integers C<0> and	1026	exception to be thrown, except for references to the integers C<0> and
606	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1027	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
607	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.	1028	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
608		1029
609	to_json [\0,JSON::XS::true] # yields [false,true]	1030	encode_json [\0, JSON::XS::true] # yields [false,true]
610		1031
611	=item JSON::XS::true, JSON::XS::false	1032	=item JSON::XS::true, JSON::XS::false
612		1033
613	These special values become JSON true and JSON false values,	1034	These special values become JSON true and JSON false values,
614	respectively. You cna alos use C<\1> and C<\0> directly if you want.	1035	respectively. You can also use C<\1> and C<\0> directly if you want.
615		1036
616	=item blessed objects	1037	=item blessed objects
617		1038
618	Blessed objects are not allowed. JSON::XS currently tries to encode their	1039	Blessed objects are not directly representable in JSON. See the
619	underlying representation (hash- or arrayref), but this behaviour might	1040	C<allow_blessed> and C<convert_blessed> methods on various options on
620	change in future versions.	1041	how to deal with this: basically, you can choose between throwing an
		1042	exception, encoding the reference as if it weren't blessed, or provide
		1043	your own serialiser method.
621		1044
622	=item simple scalars	1045	=item simple scalars
623		1046
624	Simple Perl scalars (any scalar that is not a reference) are the most	1047	Simple Perl scalars (any scalar that is not a reference) are the most
625	difficult objects to encode: JSON::XS will encode undefined scalars as	1048	difficult objects to encode: JSON::XS will encode undefined scalars as
626	JSON null value, scalars that have last been used in a string context	1049	JSON C<null> values, scalars that have last been used in a string context
627	before encoding as JSON strings and anything else as number value:	1050	before encoding as JSON strings, and anything else as number value:
628		1051
629	# dump as number	1052	# dump as number
630	to_json [2] # yields [2]	1053	encode_json [2] # yields [2]
631	to_json [-3.0e17] # yields [-3e+17]	1054	encode_json [-3.0e17] # yields [-3e+17]
632	my $value = 5; to_json [$value] # yields [5]	1055	my $value = 5; encode_json [$value] # yields [5]
633		1056
634	# used as string, so dump as string	1057	# used as string, so dump as string
635	print $value;	1058	print $value;
636	to_json [$value] # yields ["5"]	1059	encode_json [$value] # yields ["5"]
637		1060
638	# undef becomes null	1061	# undef becomes null
639	to_json [undef] # yields [null]	1062	encode_json [undef] # yields [null]
640		1063
641	You can force the type to be a string by stringifying it:	1064	You can force the type to be a JSON string by stringifying it:
642		1065
643	my $x = 3.1; # some variable containing a number	1066	my $x = 3.1; # some variable containing a number
644	"$x"; # stringified	1067	"$x"; # stringified
645	$x .= ""; # another, more awkward way to stringify	1068	$x .= ""; # another, more awkward way to stringify
646	print $x; # perl does it for you, too, quite often	1069	print $x; # perl does it for you, too, quite often
647		1070
648	You can force the type to be a number by numifying it:	1071	You can force the type to be a JSON number by numifying it:
649		1072
650	my $x = "3"; # some variable containing a string	1073	my $x = "3"; # some variable containing a string
651	$x += 0; # numify it, ensuring it will be dumped as a number	1074	$x += 0; # numify it, ensuring it will be dumped as a number
652	$x *= 1; # same thing, the choise is yours.	1075	$x *= 1; # same thing, the choice is yours.
653		1076
654	You can not currently output JSON booleans or force the type in other,	1077	You can not currently force the type in other, less obscure, ways. Tell me
655	less obscure, ways. Tell me if you need this capability.	1078	if you need this capability (but don't forget to explain why it's needed
		1079	:).
		1080
		1081	Note that numerical precision has the same meaning as under Perl (so
		1082	binary to decimal conversion follows the same rules as in Perl, which
		1083	can differ to other languages). Also, your perl interpreter might expose
		1084	extensions to the floating point numbers of your platform, such as
		1085	infinities or NaN's - these cannot be represented in JSON, and it is an
		1086	error to pass those in.
656		1087
657	=back	1088	=back
658		1089
659		1090
660	=head1 COMPARISON	1091	=head1 ENCODING/CODESET FLAG NOTES
661		1092
662	As already mentioned, this module was created because none of the existing	1093	The interested reader might have seen a number of flags that signify
663	JSON modules could be made to work correctly. First I will describe the	1094	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
664	problems (or pleasures) I encountered with various existing JSON modules,	1095	some confusion on what these do, so here is a short comparison:
665	followed by some benchmark values. JSON::XS was designed not to suffer	1096
666	from any of these problems or limitations.	1097	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1098	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1099	control whether C<encode> escapes character values outside their respective
		1100	codeset range. Neither of these flags conflict with each other, although
		1101	some combinations make less sense than others.
		1102
		1103	Care has been taken to make all flags symmetrical with respect to
		1104	C<encode> and C<decode>, that is, texts encoded with any combination of
		1105	these flag values will be correctly decoded when the same flags are used
		1106	- in general, if you use different flag settings while encoding vs. when
		1107	decoding you likely have a bug somewhere.
		1108
		1109	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1110	simply an abstract set of character-codepoint pairs, while an encoding
		1111	takes those codepoint numbers and I<encodes> them, in our case into
		1112	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1113	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1114	the same time, which can be confusing.
667		1115
668	=over 4	1116	=over 4
669		1117
670	=item JSON 1.07	1118	=item C<utf8> flag disabled
671		1119
672	Slow (but very portable, as it is written in pure Perl).	1120	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1121	and expect Unicode strings, that is, characters with high ordinal Unicode
		1122	values (> 255) will be encoded as such characters, and likewise such
		1123	characters are decoded as-is, no changes to them will be done, except
		1124	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1125	respectively (to Perl, these are the same thing in strings unless you do
		1126	funny/weird/dumb stuff).
673		1127
674	Undocumented/buggy Unicode handling (how JSON handles unicode values is	1128	This is useful when you want to do the encoding yourself (e.g. when you
675	undocumented. One can get far by feeding it unicode strings and doing	1129	want to have UTF-16 encoded JSON texts) or when some other layer does
676	en-/decoding oneself, but unicode escapes are not working properly).	1130	the encoding for you (for example, when printing to a terminal using a
		1131	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1132	to UTF-8 encode your data first and have Perl encode it another time).
677		1133
678	No roundtripping (strings get clobbered if they look like numbers, e.g.	1134	=item C<utf8> flag enabled
679	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
680	decode into the number 2.
681		1135
682	=item JSON::PC 0.01	1136	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1137	characters using the corresponding UTF-8 multi-byte sequence, and will
		1138	expect your input strings to be encoded as UTF-8, that is, no "character"
		1139	of the input string must have any value > 255, as UTF-8 does not allow
		1140	that.
683		1141
684	Very fast.	1142	The C<utf8> flag therefore switches between two modes: disabled means you
		1143	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1144	octet/binary string in Perl.
685		1145
686	Undocumented/buggy Unicode handling.	1146	=item C<latin1> or C<ascii> flags enabled
687		1147
688	No roundtripping.	1148	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1149	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1150	characters as specified by the C<utf8> flag.
689		1151
690	Has problems handling many Perl values (e.g. regex results and other magic	1152	If C<utf8> is disabled, then the result is also correctly encoded in those
691	values will make it croak).	1153	character sets (as both are proper subsets of Unicode, meaning that a
		1154	Unicode string with all character values < 256 is the same thing as a
		1155	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1156	the same thing as an ASCII string in Perl).
692		1157
693	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1158	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
694	which is not a valid JSON text.	1159	regardless of these flags, just some more characters will be escaped using
		1160	C<\uXXXX> then before.
695		1161
696	Unmaintained (maintainer unresponsive for many months, bugs are not	1162	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
697	getting fixed).	1163	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1164	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1165	a subset of Unicode), while ASCII is.
698		1166
699	=item JSON::Syck 0.21	1167	Surprisingly, C<decode> will ignore these flags and so treat all input
		1168	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1169	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1170	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
700		1171
701	Very buggy (often crashes).	1172	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1173	they only govern when the JSON output engine escapes a character or not.
702		1174
703	Very inflexible (no human-readable format supported, format pretty much	1175	The main use for C<latin1> is to relatively efficiently store binary data
704	undocumented. I need at least a format for easy reading by humans and a	1176	as JSON, at the expense of breaking compatibility with most JSON decoders.
705	single-line compact format for use in a protocol, and preferably a way to
706	generate ASCII-only JSON texts).
707		1177
708	Completely broken (and confusingly documented) Unicode handling (unicode	1178	The main use for C<ascii> is to force the output to not contain characters
709	escapes are not working properly, you need to set ImplicitUnicode to	1179	with values > 127, which means you can interpret the resulting string
710	I<different> values on en- and decoding to get symmetric behaviour).	1180	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
711		1181	8-bit-encoding, and still get the same data structure back. This is useful
712	No roundtripping (simple cases work, but this depends on wether the scalar	1182	when your channel for JSON transfer is not 8-bit clean or the encoding
713	value was used in a numeric context or not).	1183	might be mangled in between (e.g. in mail), and works because ASCII is a
714		1184	proper subset of most 8-bit and multibyte encodings in use in the world.
715	Dumping hashes may skip hash values depending on iterator state.
716
717	Unmaintained (maintainer unresponsive for many months, bugs are not
718	getting fixed).
719
720	Does not check input for validity (i.e. will accept non-JSON input and
721	return "something" instead of raising an exception. This is a security
722	issue: imagine two banks transfering money between each other using
723	JSON. One bank might parse a given non-JSON request and deduct money,
724	while the other might reject the transaction with a syntax error. While a
725	good protocol will at least recover, that is extra unnecessary work and
726	the transaction will still not succeed).
727
728	=item JSON::DWIW 0.04
729
730	Very fast. Very natural. Very nice.
731
732	Undocumented unicode handling (but the best of the pack. Unicode escapes
733	still don't get parsed properly).
734
735	Very inflexible.
736
737	No roundtripping.
738
739	Does not generate valid JSON texts (key strings are often unquoted, empty keys
740	result in nothing being output)
741
742	Does not check input for validity.
743		1185
744	=back	1186	=back
745		1187
746		1188
		1189	=head2 JSON and ECMAscript
		1190
		1191	JSON syntax is based on how literals are represented in javascript (the
		1192	not-standardised predecessor of ECMAscript) which is presumably why it is
		1193	called "JavaScript Object Notation".
		1194
		1195	However, JSON is not a subset (and also not a superset of course) of
		1196	ECMAscript (the standard) or javascript (whatever browsers actually
		1197	implement).
		1198
		1199	If you want to use javascript's C<eval> function to "parse" JSON, you
		1200	might run into parse errors for valid JSON texts, or the resulting data
		1201	structure might not be queryable:
		1202
		1203	One of the problems is that U+2028 and U+2029 are valid characters inside
		1204	JSON strings, but are not allowed in ECMAscript string literals, so the
		1205	following Perl fragment will not output something that can be guaranteed
		1206	to be parsable by javascript's C<eval>:
		1207
		1208	use JSON::XS;
		1209
		1210	print encode_json [chr 0x2028];
		1211
		1212	The right fix for this is to use a proper JSON parser in your javascript
		1213	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1214	F<json2.js> parser).
		1215
		1216	If this is not an option, you can, as a stop-gap measure, simply encode to
		1217	ASCII-only JSON:
		1218
		1219	use JSON::XS;
		1220
		1221	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1222
		1223	Note that this will enlarge the resulting JSON text quite a bit if you
		1224	have many non-ASCII characters. You might be tempted to run some regexes
		1225	to only escape U+2028 and U+2029, e.g.:
		1226
		1227	# DO NOT USE THIS!
		1228	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1229	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1230	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1231	print $json;
		1232
		1233	Note that I<this is a bad idea>: the above only works for U+2028 and
		1234	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1235	javascript implementations, however, have issues with other characters as
		1236	well - using C<eval> naively simply I<will> cause problems.
		1237
		1238	Another problem is that some javascript implementations reserve
		1239	some property names for their own purposes (which probably makes
		1240	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1241	C<__proto__> property name for its own purposes.
		1242
		1243	If that is a problem, you could parse try to filter the resulting JSON
		1244	output for these property strings, e.g.:
		1245
		1246	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1247
		1248	This works because C<__proto__> is not valid outside of strings, so every
		1249	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1250
		1251	If you know of other incompatibilities, please let me know.
		1252
		1253
747	=head2 JSON and YAML	1254	=head2 JSON and YAML
748		1255
749	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1256	You often hear that JSON is a subset of YAML. This is, however, a mass
750	however, a mass hysteria and very far from the truth. In general, there is	1257	hysteria(*) and very far from the truth (as of the time of this writing),
751	no way to configure JSON::XS to output a data structure as valid YAML.	1258	so let me state it clearly: I<in general, there is no way to configure
		1259	JSON::XS to output a data structure as valid YAML> that works in all
		1260	cases.
752		1261
753	If you really must use JSON::XS to generate YAML, you should use this	1262	If you really must use JSON::XS to generate YAML, you should use this
754	algorithm (subject to change in future versions):	1263	algorithm (subject to change in future versions):
755		1264
756	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1265	my $to_yaml = JSON::XS->new->utf8->space_after (1);
757	my $yaml = $to_yaml->encode ($ref) . "\n";	1266	my $yaml = $to_yaml->encode ($ref) . "\n";
758		1267
759	This will usually generate JSON texts that also parse as valid	1268	This will I<usually> generate JSON texts that also parse as valid
760	YAML. Please note that YAML has hardcoded limits on (simple) object key	1269	YAML. Please note that YAML has hardcoded limits on (simple) object key
761	lengths that JSON doesn't have, so you should make sure that your hash	1270	lengths that JSON doesn't have and also has different and incompatible
		1271	unicode character escape syntax, so you should make sure that your hash
762	keys are noticably shorter than the 1024 characters YAML allows.	1272	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1273	and that you do not have characters with codepoint values outside the
		1274	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1275	sequences in strings (which JSON::XS does not I<currently> generate, but
		1276	other JSON generators might).
763		1277
764	There might be other incompatibilities that I am not aware of. In general	1278	There might be other incompatibilities that I am not aware of (or the YAML
		1279	specification has been changed yet again - it does so quite often). In
765	you should not try to generate YAML with a JSON generator or vice versa,	1280	general you should not try to generate YAML with a JSON generator or vice
766	or try to parse JSON with a YAML parser or vice versa: chances are high	1281	versa, or try to parse JSON with a YAML parser or vice versa: chances are
767	that you will run into severe interoperability problems.	1282	high that you will run into severe interoperability problems when you
		1283	least expect it.
		1284
		1285	=over 4
		1286
		1287	=item (*)
		1288
		1289	I have been pressured multiple times by Brian Ingerson (one of the
		1290	authors of the YAML specification) to remove this paragraph, despite him
		1291	acknowledging that the actual incompatibilities exist. As I was personally
		1292	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1293	educate people about these issues, so others do not run into the same
		1294	problem again and again. After this, Brian called me a (quote)I<complete
		1295	and worthless idiot>(unquote).
		1296
		1297	In my opinion, instead of pressuring and insulting people who actually
		1298	clarify issues with YAML and the wrong statements of some of its
		1299	proponents, I would kindly suggest reading the JSON spec (which is not
		1300	that difficult or long) and finally make YAML compatible to it, and
		1301	educating users about the changes, instead of spreading lies about the
		1302	real compatibility for many I<years> and trying to silence people who
		1303	point out that it isn't true.
		1304
		1305	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1306	though the incompatibilities have been documented (and are known to Brian)
		1307	for many years and the spec makes explicit claims that YAML is a superset
		1308	of JSON. It would be so easy to fix, but apparently, bullying people and
		1309	corrupting userdata is so much easier.
		1310
		1311	=back
768		1312
769		1313
770	=head2 SPEED	1314	=head2 SPEED
771		1315
772	It seems that JSON::XS is surprisingly fast, as shown in the following	1316	It seems that JSON::XS is surprisingly fast, as shown in the following
773	tables. They have been generated with the help of the C<eg/bench> program	1317	tables. They have been generated with the help of the C<eg/bench> program
774	in the JSON::XS distribution, to make it easy to compare on your own	1318	in the JSON::XS distribution, to make it easy to compare on your own
775	system.	1319	system.
776		1320
777	First comes a comparison between various modules using a very short	1321	First comes a comparison between various modules using
778	single-line JSON string:	1322	a very short single-line JSON string (also available at
		1323	L<http://dist.schmorp.de/misc/json/short.json>).
779		1324
780	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1325	{"method": "handleMessage", "params": ["user1",
781	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1326	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1327	1, 0]}
782		1328
783	It shows the number of encodes/decodes per second (JSON::XS uses	1329	It shows the number of encodes/decodes per second (JSON::XS uses
784	the functional interface, while JSON::XS/2 uses the OO interface	1330	the functional interface, while JSON::XS/2 uses the OO interface
785	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1331	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
786	shrink). Higher is better:	1332	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1333	uses the from_json method). Higher is better:
787		1334
788	Storable | 15779.925 | 14169.946 |
789	-----------+------------+------------+
790	module | encode | decode |	1335	module | encode | decode |
791	-----------|------------|------------|	1336	--------------|------------|------------|
792	JSON | 4990.842 | 4088.813 |	1337	JSON::DWIW/DS | 86302.551 | 102300.098 |
793	JSON::DWIW | 51653.990 | 71575.154 |	1338	JSON::DWIW/FJ | 86302.551 | 75983.768 |
794	JSON::PC | 65948.176 | 74631.744 |	1339	JSON::PP | 15827.562 | 6638.658 |
795	JSON::PP | 8931.652 | 3817.168 |	1340	JSON::Syck | 63358.066 | 47662.545 |
796	JSON::Syck | 24877.248 | 27776.848 |	1341	JSON::XS | 511500.488 | 511500.488 |
797	JSON::XS | 388361.481 | 227951.304 |	1342	JSON::XS/2 | 291271.111 | 388361.481 |
798	JSON::XS/2 | 227951.304 | 218453.333 |	1343	JSON::XS/3 | 361577.931 | 361577.931 |
799	JSON::XS/3 | 338250.323 | 218453.333 |	1344	Storable | 66788.280 | 265462.278 |
800	Storable | 16500.016 | 135300.129 |
801	-----------+------------+------------+	1345	--------------+------------+------------+
802		1346
803	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1347	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
804	about three times faster on decoding, and over fourty times faster	1348	about five times faster on decoding, and over thirty to seventy times
805	than JSON, even with pretty-printing and key sorting. It also compares	1349	faster than JSON's pure perl implementation. It also compares favourably
806	favourably to Storable for small amounts of data.	1350	to Storable for small amounts of data.
807		1351
808	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1352	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
809	search API (http://nanoref.com/yahooapis/mgPdGg):	1353	search API (L<http://dist.schmorp.de/misc/json/long.json>).
810		1354
811	module | encode | decode |	1355	module | encode | decode |
812	-----------|------------|------------|	1356	--------------|------------|------------|
813	JSON | 55.260 | 34.971 |	1357	JSON::DWIW/DS | 1647.927 | 2673.916 |
814	JSON::DWIW | 825.228 | 1082.513 |	1358	JSON::DWIW/FJ | 1630.249 | 2596.128 |
815	JSON::PC | 3571.444 | 2394.829 |
816	JSON::PP | 210.987 | 32.574 |	1359	JSON::PP | 400.640 | 62.311 |
817	JSON::Syck | 552.551 | 787.544 |	1360	JSON::Syck | 1481.040 | 1524.869 |
818	JSON::XS | 5780.463 | 4854.519 |	1361	JSON::XS | 20661.596 | 9541.183 |
819	JSON::XS/2 | 3869.998 | 4798.975 |	1362	JSON::XS/2 | 10683.403 | 9416.938 |
820	JSON::XS/3 | 5862.880 | 4798.975 |	1363	JSON::XS/3 | 20661.596 | 9400.054 |
821	Storable | 4445.002 | 5235.027 |	1364	Storable | 19765.806 | 10000.725 |
822	-----------+------------+------------+	1365	--------------+------------+------------+
823		1366
824	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1367	Again, JSON::XS leads by far (except for Storable which non-surprisingly
825	decodes faster).	1368	decodes a bit faster).
826		1369
827	On large strings containing lots of high unicode characters, some modules	1370	On large strings containing lots of high Unicode characters, some modules
828	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1371	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
829	will be broken due to missing (or wrong) unicode handling. Others refuse	1372	will be broken due to missing (or wrong) Unicode handling. Others refuse
830	to decode or encode properly, so it was impossible to prepare a fair	1373	to decode or encode properly, so it was impossible to prepare a fair
831	comparison table for that case.	1374	comparison table for that case.
832		1375
833		1376
834	=head1 SECURITY CONSIDERATIONS	1377	=head1 SECURITY CONSIDERATIONS
…		…
840	any buffer overflows. Obviously, this module should ensure that and I am	1383	any buffer overflows. Obviously, this module should ensure that and I am
841	trying hard on making that true, but you never know.	1384	trying hard on making that true, but you never know.
842		1385
843	Second, you need to avoid resource-starving attacks. That means you should	1386	Second, you need to avoid resource-starving attacks. That means you should
844	limit the size of JSON texts you accept, or make sure then when your	1387	limit the size of JSON texts you accept, or make sure then when your
845	resources run out, thats just fine (e.g. by using a separate process that	1388	resources run out, that's just fine (e.g. by using a separate process that
846	can crash safely). The size of a JSON text in octets or characters is	1389	can crash safely). The size of a JSON text in octets or characters is
847	usually a good indication of the size of the resources required to decode	1390	usually a good indication of the size of the resources required to decode
848	it into a Perl structure. While JSON::XS can check the size of the JSON	1391	it into a Perl structure. While JSON::XS can check the size of the JSON
849	text, it might be too late when you already have it in memory, so you	1392	text, it might be too late when you already have it in memory, so you
850	might want to check the size before you accept the string.	1393	might want to check the size before you accept the string.
851		1394
852	Third, JSON::XS recurses using the C stack when decoding objects and	1395	Third, JSON::XS recurses using the C stack when decoding objects and
853	arrays. The C stack is a limited resource: for instance, on my amd64	1396	arrays. The C stack is a limited resource: for instance, on my amd64
854	machine with 8MB of stack size I can decode around 180k nested arrays but	1397	machine with 8MB of stack size I can decode around 180k nested arrays but
855	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1398	only 14k nested JSON objects (due to perl itself recursing deeply on croak
856	to free the temporary). If that is exceeded, the program crashes. to be	1399	to free the temporary). If that is exceeded, the program crashes. To be
857	conservative, the default nesting limit is set to 512. If your process	1400	conservative, the default nesting limit is set to 512. If your process
858	has a smaller stack, you should adjust this setting accordingly with the	1401	has a smaller stack, you should adjust this setting accordingly with the
859	C<max_depth> method.	1402	C<max_depth> method.
860		1403
861	And last but least, something else could bomb you that I forgot to think	1404	Something else could bomb you, too, that I forgot to think of. In that
862	of. In that case, you get to keep the pieces. I am always open for hints,	1405	case, you get to keep the pieces. I am always open for hints, though...
863	though...	1406
		1407	Also keep in mind that JSON::XS might leak contents of your Perl data
		1408	structures in its error messages, so when you serialise sensitive
		1409	information you might want to make sure that exceptions thrown by JSON::XS
		1410	will not end up in front of untrusted eyes.
864		1411
865	If you are using JSON::XS to return packets to consumption	1412	If you are using JSON::XS to return packets to consumption
866	by javascript scripts in a browser you should have a look at	1413	by JavaScript scripts in a browser you should have a look at
867	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether	1414	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
868	you are vulnerable to some common attack vectors (which really are browser	1415	see whether you are vulnerable to some common attack vectors (which really
869	design bugs, but it is still you who will have to deal with it, as major	1416	are browser design bugs, but it is still you who will have to deal with
870	browser developers care only for features, not about doing security	1417	it, as major browser developers care only for features, not about getting
871	right).	1418	security right).
		1419
		1420
		1421	=head1 THREADS
		1422
		1423	This module is I<not> guaranteed to be thread safe and there are no
		1424	plans to change this until Perl gets thread support (as opposed to the
		1425	horribly slow so-called "threads" which are simply slow and bloated
		1426	process simulations - use fork, it's I<much> faster, cheaper, better).
		1427
		1428	(It might actually work, but you have been warned).
		1429
		1430
		1431	=head1 THE PERILS OF SETLOCALE
		1432
		1433	Sometimes people avoid the Perl locale support and directly call the
		1434	system's setlocale function with C<LC_ALL>.
		1435
		1436	This breaks both perl and modules such as JSON::XS, as stringification of
		1437	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1438	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1439	perl to stringify numbers).
		1440
		1441	The solution is simple: don't call C<setlocale>, or use it for only those
		1442	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1443
		1444	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1445	actually needs it (avoiding stringification of numbers), and restore it
		1446	afterwards.
872		1447
873		1448
874	=head1 BUGS	1449	=head1 BUGS
875		1450
876	While the goal of this module is to be correct, that unfortunately does	1451	While the goal of this module is to be correct, that unfortunately does
877	not mean its bug-free, only that I think its design is bug-free. It is	1452	not mean it's bug-free, only that I think its design is bug-free. If you
878	still relatively early in its development. If you keep reporting bugs they	1453	keep reporting bugs they will be fixed swiftly, though.
879	will be fixed swiftly, though.	1454
		1455	Please refrain from using rt.cpan.org or any other bug reporting
		1456	service. I put the contact address into my modules for a reason.
880		1457
881	=cut	1458	=cut
882		1459
883	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1460	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
884	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };	1461	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
…		…
901	"--" => sub { $_[0] = ${$_[0]} - 1 },	1478	"--" => sub { $_[0] = ${$_[0]} - 1 },
902	fallback => 1;	1479	fallback => 1;
903		1480
904	1;	1481	1;
905		1482
		1483	=head1 SEE ALSO
		1484
		1485	The F<json_xs> command line utility for quick experiments.
		1486
906	=head1 AUTHOR	1487	=head1 AUTHOR
907		1488
908	Marc Lehmann <schmorp@schmorp.de>	1489	Marc Lehmann <schmorp@schmorp.de>
909	http://home.schmorp.de/	1490	http://home.schmorp.de/
910		1491

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