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Revision 1.8 by root, Fri Mar 23 15:57:18 2007 UTC vs.
Revision 1.116 by root, Tue Feb 17 23:41:20 2009 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		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)
		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
		13
		14	# exported functions, they croak on error
		15	# and expect/generate UTF-8
		16
		17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
		18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
		19
		20	# OO-interface
		21
		22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
		23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
		24	$perl_scalar = $coder->decode ($unicode_json_text);
		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.
8		33
9	=head1 DESCRIPTION	34	=head1 DESCRIPTION
10		35
11	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
12	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
13	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.
14		47
15	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
16	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
17	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
18	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
19	reports for other reasons.	52	reports for other reasons.
20		53
21	See COMPARISON, below, for a comparison to some other JSON modules.	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
		55	vice versa.
22		56
23	=head2 FEATURES	57	=head2 FEATURES
24		58
25	=over 4	59	=over 4
26		60
27	=item * correct handling of unicode issues	61	=item * correct Unicode handling
28		62
29	This module knows how to handle Unicode, and even documents how it does so.	63	This module knows how to handle Unicode, documents how and when it does
		64	so, and even documents what "correct" means.
30		65
31	=item * round-trip integrity	66	=item * round-trip integrity
32		67
33	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
34	by JSON, the deserialised data structure is identical on the Perl level.	69	by JSON, the deserialised data structure is identical on the Perl level.
35	(e.g. the string "2.0" doesn't suddenly become "2").	70	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
		71	like a number). There minor I<are> exceptions to this, read the MAPPING
		72	section below to learn about those.
36		73
37	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
38		75
39	There is no guessing, no generating of illegal JSON strings by default,	76	There is no guessing, no generating of illegal JSON texts by default,
40	and only JSON is accepted as input (the latter is a security feature).	77	and only JSON is accepted as input by default (the latter is a security
		78	feature).
41		79
42	=item * fast	80	=item * fast
43		81
44	compared to other JSON modules, this module compares favourably.	82	Compared to other JSON modules and other serialisers such as Storable,
		83	this module usually compares favourably in terms of speed, too.
45		84
46	=item * simple to use	85	=item * simple to use
47		86
48	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
49	interface.	88	oriented interface interface.
50		89
51	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
52		91
53	You can choose between the most compact format possible, a pure-ascii	92	You can choose between the most compact guaranteed-single-line format
54	format, or a pretty-printed format. Or you can combine those features in	93	possible (nice for simple line-based protocols), a pure-ASCII format
55	whatever way you like.	94	(for when your transport is not 8-bit clean, still supports the whole
		95	Unicode range), or a pretty-printed format (for when you want to read that
		96	stuff). Or you can combine those features in whatever way you like.
56		97
57	=back	98	=back
58		99
59	=cut	100	=cut
60		101
61	package JSON::XS;	102	package JSON::XS;
62		103
63	BEGIN {	104	no warnings;
		105	use strict;
		106
64	$VERSION = '0.2';	107	our $VERSION = '2.232';
65	@ISA = qw(Exporter);	108	our @ISA = qw(Exporter);
66		109
67	@EXPORT = qw(to_json from_json);	110	our @EXPORT = qw(encode_json decode_json to_json from_json);
68	require Exporter;
69		111
		112	sub to_json($) {
70	require XSLoader;	113	require Carp;
71	XSLoader::load JSON::XS::, $VERSION;	114	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
72	}	115	}
73		116
		117	sub from_json($) {
		118	require Carp;
		119	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");
		120	}
		121
		122	use Exporter;
		123	use XSLoader;
		124
74	=head1 FUNCTIONAL INTERFACE	125	=head1 FUNCTIONAL INTERFACE
75		126
76	The following convinience methods are provided by this module. They are	127	The following convenience methods are provided by this module. They are
77	exported by default:	128	exported by default:
78		129
79	=over 4	130	=over 4
80		131
81	=item $json_string = to_json $perl_scalar	132	=item $json_text = encode_json $perl_scalar
82		133
83	Converts the given Perl data structure (a simple scalar or a reference to	134	Converts the given Perl data structure to a UTF-8 encoded, binary string
84	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	135	(that is, the string contains octets only). Croaks on error.
85	octets only). Croaks on error.
86		136
87	This function call is functionally identical to C<< JSON::XS->new->utf8	137	This function call is functionally identical to:
88	(1)->encode ($perl_scalar) >>.
89		138
		139	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		140
		141	Except being faster.
		142
90	=item $perl_scalar = from_json $json_string	143	=item $perl_scalar = decode_json $json_text
91		144
92	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	145	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
93	parse that as an UTF-8 encoded JSON string, returning the resulting simple	146	to parse that as an UTF-8 encoded JSON text, returning the resulting
94	scalar or reference. Croaks on error.	147	reference. Croaks on error.
95		148
96	This function call is functionally identical to C<< JSON::XS->new->utf8	149	This function call is functionally identical to:
97	(1)->decode ($json_string) >>.	150
		151	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		152
		153	Except being faster.
		154
		155	=item $is_boolean = JSON::XS::is_bool $scalar
		156
		157	Returns true if the passed scalar represents either JSON::XS::true or
		158	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		159	and are used to represent JSON C<true> and C<false> values in Perl.
		160
		161	See MAPPING, below, for more information on how JSON values are mapped to
		162	Perl.
98		163
99	=back	164	=back
		165
		166
		167	=head1 A FEW NOTES ON UNICODE AND PERL
		168
		169	Since this often leads to confusion, here are a few very clear words on
		170	how Unicode works in Perl, modulo bugs.
		171
		172	=over 4
		173
		174	=item 1. Perl strings can store characters with ordinal values > 255.
		175
		176	This enables you to store Unicode characters as single characters in a
		177	Perl string - very natural.
		178
		179	=item 2. Perl does I<not> associate an encoding with your strings.
		180
		181	... until you force it to, e.g. when matching it against a regex, or
		182	printing the scalar to a file, in which case Perl either interprets your
		183	string as locale-encoded text, octets/binary, or as Unicode, depending
		184	on various settings. In no case is an encoding stored together with your
		185	data, it is I<use> that decides encoding, not any magical meta data.
		186
		187	=item 3. The internal utf-8 flag has no meaning with regards to the
		188	encoding of your string.
		189
		190	Just ignore that flag unless you debug a Perl bug, a module written in
		191	XS or want to dive into the internals of perl. Otherwise it will only
		192	confuse you, as, despite the name, it says nothing about how your string
		193	is encoded. You can have Unicode strings with that flag set, with that
		194	flag clear, and you can have binary data with that flag set and that flag
		195	clear. Other possibilities exist, too.
		196
		197	If you didn't know about that flag, just the better, pretend it doesn't
		198	exist.
		199
		200	=item 4. A "Unicode String" is simply a string where each character can be
		201	validly interpreted as a Unicode code point.
		202
		203	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		204	Unicode string encoded in UTF-8, giving you a binary string.
		205
		206	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		207
		208	It's a fact. Learn to live with it.
		209
		210	=back
		211
		212	I hope this helps :)
		213
100		214
101	=head1 OBJECT-ORIENTED INTERFACE	215	=head1 OBJECT-ORIENTED INTERFACE
102		216
103	The object oriented interface lets you configure your own encoding or	217	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	218	decoding style, within the limits of supported formats.
…		…
111	strings. All boolean flags described below are by default I<disabled>.	225	strings. All boolean flags described below are by default I<disabled>.
112		226
113	The mutators for flags all return the JSON object again and thus calls can	227	The mutators for flags all return the JSON object again and thus calls can
114	be chained:	228	be chained:
115		229
116	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	230	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
117	=> {"a": [1, 2]}	231	=> {"a": [1, 2]}
118		232
119	=item $json = $json->ascii ([$enable])	233	=item $json = $json->ascii ([$enable])
120		234
		235	=item $enabled = $json->get_ascii
		236
121	If C<$enable> is true (or missing), then the C<encode> method will	237	If C<$enable> is true (or missing), then the C<encode> method will not
122	not generate characters outside the code range C<0..127>. Any unicode	238	generate characters outside the code range C<0..127> (which is ASCII). Any
123	characters outside that range will be escaped using either a single	239	Unicode characters outside that range will be escaped using either a
124	\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per	240	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
125	RFC4627.	241	as per RFC4627. The resulting encoded JSON text can be treated as a native
		242	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		243	or any other superset of ASCII.
126		244
127	If C<$enable> is false, then the C<encode> method will not escape Unicode	245	If C<$enable> is false, then the C<encode> method will not escape Unicode
128	characters unless necessary.	246	characters unless required by the JSON syntax or other flags. This results
		247	in a faster and more compact format.
129		248
		249	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		250	document.
		251
		252	The main use for this flag is to produce JSON texts that can be
		253	transmitted over a 7-bit channel, as the encoded JSON texts will not
		254	contain any 8 bit characters.
		255
130	JSON::XS->new->ascii (1)->encode (chr 0x10401)	256	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
131	=> \ud801\udc01	257	=> ["\ud801\udc01"]
		258
		259	=item $json = $json->latin1 ([$enable])
		260
		261	=item $enabled = $json->get_latin1
		262
		263	If C<$enable> is true (or missing), then the C<encode> method will encode
		264	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		265	outside the code range C<0..255>. The resulting string can be treated as a
		266	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		267	will not be affected in any way by this flag, as C<decode> by default
		268	expects Unicode, which is a strict superset of latin1.
		269
		270	If C<$enable> is false, then the C<encode> method will not escape Unicode
		271	characters unless required by the JSON syntax or other flags.
		272
		273	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		274	document.
		275
		276	The main use for this flag is efficiently encoding binary data as JSON
		277	text, as most octets will not be escaped, resulting in a smaller encoded
		278	size. The disadvantage is that the resulting JSON text is encoded
		279	in latin1 (and must correctly be treated as such when storing and
		280	transferring), a rare encoding for JSON. It is therefore most useful when
		281	you want to store data structures known to contain binary data efficiently
		282	in files or databases, not when talking to other JSON encoders/decoders.
		283
		284	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		285	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
132		286
133	=item $json = $json->utf8 ([$enable])	287	=item $json = $json->utf8 ([$enable])
134		288
		289	=item $enabled = $json->get_utf8
		290
135	If C<$enable> is true (or missing), then the C<encode> method will encode	291	If C<$enable> is true (or missing), then the C<encode> method will encode
136	the JSON string into UTF-8, as required by many protocols, while the	292	the JSON result into UTF-8, as required by many protocols, while the
137	C<decode> method expects to be handled an UTF-8-encoded string. Please	293	C<decode> method expects to be handled an UTF-8-encoded string. Please
138	note that UTF-8-encoded strings do not contain any characters outside the	294	note that UTF-8-encoded strings do not contain any characters outside the
139	range C<0..255>, they are thus useful for bytewise/binary I/O.	295	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		296	versions, enabling this option might enable autodetection of the UTF-16
		297	and UTF-32 encoding families, as described in RFC4627.
140		298
141	If C<$enable> is false, then the C<encode> method will return the JSON	299	If C<$enable> is false, then the C<encode> method will return the JSON
142	string as a (non-encoded) unicode string, while C<decode> expects thus a	300	string as a (non-encoded) Unicode string, while C<decode> expects thus a
143	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	301	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
144	to be done yourself, e.g. using the Encode module.	302	to be done yourself, e.g. using the Encode module.
		303
		304	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		305	document.
		306
		307	Example, output UTF-16BE-encoded JSON:
		308
		309	use Encode;
		310	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		311
		312	Example, decode UTF-32LE-encoded JSON:
		313
		314	use Encode;
		315	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
145		316
146	=item $json = $json->pretty ([$enable])	317	=item $json = $json->pretty ([$enable])
147		318
148	This enables (or disables) all of the C<indent>, C<space_before> and	319	This enables (or disables) all of the C<indent>, C<space_before> and
149	C<space_after> (and in the future possibly more) flags in one call to	320	C<space_after> (and in the future possibly more) flags in one call to
150	generate the most readable (or most compact) form possible.	321	generate the most readable (or most compact) form possible.
		322
		323	Example, pretty-print some simple structure:
151		324
152	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})	325	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
153	=>	326	=>
154	{	327	{
155	"a" : [	328	"a" : [
…		…
158	]	331	]
159	}	332	}
160		333
161	=item $json = $json->indent ([$enable])	334	=item $json = $json->indent ([$enable])
162		335
		336	=item $enabled = $json->get_indent
		337
163	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	338	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
164	format as output, putting every array member or object/hash key-value pair	339	format as output, putting every array member or object/hash key-value pair
165	into its own line, identing them properly.	340	into its own line, indenting them properly.
166		341
167	If C<$enable> is false, no newlines or indenting will be produced, and the	342	If C<$enable> is false, no newlines or indenting will be produced, and the
168	resulting JSON strings is guarenteed not to contain any C<newlines>.	343	resulting JSON text is guaranteed not to contain any C<newlines>.
169		344
170	This setting has no effect when decoding JSON strings.	345	This setting has no effect when decoding JSON texts.
171		346
172	=item $json = $json->space_before ([$enable])	347	=item $json = $json->space_before ([$enable])
		348
		349	=item $enabled = $json->get_space_before
173		350
174	If C<$enable> is true (or missing), then the C<encode> method will add an extra	351	If C<$enable> is true (or missing), then the C<encode> method will add an extra
175	optional space before the C<:> separating keys from values in JSON objects.	352	optional space before the C<:> separating keys from values in JSON objects.
176		353
177	If C<$enable> is false, then the C<encode> method will not add any extra	354	If C<$enable> is false, then the C<encode> method will not add any extra
178	space at those places.	355	space at those places.
179		356
180	This setting has no effect when decoding JSON strings. You will also most	357	This setting has no effect when decoding JSON texts. You will also
181	likely combine this setting with C<space_after>.	358	most likely combine this setting with C<space_after>.
		359
		360	Example, space_before enabled, space_after and indent disabled:
		361
		362	{"key" :"value"}
182		363
183	=item $json = $json->space_after ([$enable])	364	=item $json = $json->space_after ([$enable])
		365
		366	=item $enabled = $json->get_space_after
184		367
185	If C<$enable> is true (or missing), then the C<encode> method will add an extra	368	If C<$enable> is true (or missing), then the C<encode> method will add an extra
186	optional space after the C<:> separating keys from values in JSON objects	369	optional space after the C<:> separating keys from values in JSON objects
187	and extra whitespace after the C<,> separating key-value pairs and array	370	and extra whitespace after the C<,> separating key-value pairs and array
188	members.	371	members.
189		372
190	If C<$enable> is false, then the C<encode> method will not add any extra	373	If C<$enable> is false, then the C<encode> method will not add any extra
191	space at those places.	374	space at those places.
192		375
193	This setting has no effect when decoding JSON strings.	376	This setting has no effect when decoding JSON texts.
		377
		378	Example, space_before and indent disabled, space_after enabled:
		379
		380	{"key": "value"}
		381
		382	=item $json = $json->relaxed ([$enable])
		383
		384	=item $enabled = $json->get_relaxed
		385
		386	If C<$enable> is true (or missing), then C<decode> will accept some
		387	extensions to normal JSON syntax (see below). C<encode> will not be
		388	affected in anyway. I<Be aware that this option makes you accept invalid
		389	JSON texts as if they were valid!>. I suggest only to use this option to
		390	parse application-specific files written by humans (configuration files,
		391	resource files etc.)
		392
		393	If C<$enable> is false (the default), then C<decode> will only accept
		394	valid JSON texts.
		395
		396	Currently accepted extensions are:
		397
		398	=over 4
		399
		400	=item * list items can have an end-comma
		401
		402	JSON I<separates> array elements and key-value pairs with commas. This
		403	can be annoying if you write JSON texts manually and want to be able to
		404	quickly append elements, so this extension accepts comma at the end of
		405	such items not just between them:
		406
		407	[
		408	1,
		409	2, <- this comma not normally allowed
		410	]
		411	{
		412	"k1": "v1",
		413	"k2": "v2", <- this comma not normally allowed
		414	}
		415
		416	=item * shell-style '#'-comments
		417
		418	Whenever JSON allows whitespace, shell-style comments are additionally
		419	allowed. They are terminated by the first carriage-return or line-feed
		420	character, after which more white-space and comments are allowed.
		421
		422	[
		423	1, # this comment not allowed in JSON
		424	# neither this one...
		425	]
		426
		427	=back
194		428
195	=item $json = $json->canonical ([$enable])	429	=item $json = $json->canonical ([$enable])
		430
		431	=item $enabled = $json->get_canonical
196		432
197	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	433	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
198	by sorting their keys. This is adding a comparatively high overhead.	434	by sorting their keys. This is adding a comparatively high overhead.
199		435
200	If C<$enable> is false, then the C<encode> method will output key-value	436	If C<$enable> is false, then the C<encode> method will output key-value
201	pairs in the order Perl stores them (which will likely change between runs	437	pairs in the order Perl stores them (which will likely change between runs
202	of the same script).	438	of the same script).
203		439
204	This option is useful if you want the same data structure to be encoded as	440	This option is useful if you want the same data structure to be encoded as
205	the same JSON string (given the same overall settings). If it is disabled,	441	the same JSON text (given the same overall settings). If it is disabled,
206	the same hash migh be encoded differently even if contains the same data,	442	the same hash might be encoded differently even if contains the same data,
207	as key-value pairs have no inherent ordering in Perl.	443	as key-value pairs have no inherent ordering in Perl.
208		444
209	This setting has no effect when decoding JSON strings.	445	This setting has no effect when decoding JSON texts.
210		446
211	=item $json = $json->allow_nonref ([$enable])	447	=item $json = $json->allow_nonref ([$enable])
		448
		449	=item $enabled = $json->get_allow_nonref
212		450
213	If C<$enable> is true (or missing), then the C<encode> method can convert a	451	If C<$enable> is true (or missing), then the C<encode> method can convert a
214	non-reference into its corresponding string, number or null JSON value,	452	non-reference into its corresponding string, number or null JSON value,
215	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	453	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
216	values instead of croaking.	454	values instead of croaking.
217		455
218	If C<$enable> is false, then the C<encode> method will croak if it isn't	456	If C<$enable> is false, then the C<encode> method will croak if it isn't
219	passed an arrayref or hashref, as JSON strings must either be an object	457	passed an arrayref or hashref, as JSON texts must either be an object
220	or array. Likewise, C<decode> will croak if given something that is not a	458	or array. Likewise, C<decode> will croak if given something that is not a
221	JSON object or array.	459	JSON object or array.
222		460
		461	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
		462	resulting in an invalid JSON text:
		463
		464	JSON::XS->new->allow_nonref->encode ("Hello, World!")
		465	=> "Hello, World!"
		466
		467	=item $json = $json->allow_unknown ([$enable])
		468
		469	=item $enabled = $json->get_allow_unknown
		470
		471	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		472	exception when it encounters values it cannot represent in JSON (for
		473	example, filehandles) but instead will encode a JSON C<null> value. Note
		474	that blessed objects are not included here and are handled separately by
		475	c<allow_nonref>.
		476
		477	If C<$enable> is false (the default), then C<encode> will throw an
		478	exception when it encounters anything it cannot encode as JSON.
		479
		480	This option does not affect C<decode> in any way, and it is recommended to
		481	leave it off unless you know your communications partner.
		482
		483	=item $json = $json->allow_blessed ([$enable])
		484
		485	=item $enabled = $json->get_allow_blessed
		486
		487	If C<$enable> is true (or missing), then the C<encode> method will not
		488	barf when it encounters a blessed reference. Instead, the value of the
		489	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		490	disabled or no C<TO_JSON> method found) or a representation of the
		491	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		492	encoded. Has no effect on C<decode>.
		493
		494	If C<$enable> is false (the default), then C<encode> will throw an
		495	exception when it encounters a blessed object.
		496
		497	=item $json = $json->convert_blessed ([$enable])
		498
		499	=item $enabled = $json->get_convert_blessed
		500
		501	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		502	blessed object, will check for the availability of the C<TO_JSON> method
		503	on the object's class. If found, it will be called in scalar context
		504	and the resulting scalar will be encoded instead of the object. If no
		505	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		506	to do.
		507
		508	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		509	returns other blessed objects, those will be handled in the same
		510	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		511	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		512	methods called by the Perl core (== not by the user of the object) are
		513	usually in upper case letters and to avoid collisions with any C<to_json>
		514	function or method.
		515
		516	This setting does not yet influence C<decode> in any way, but in the
		517	future, global hooks might get installed that influence C<decode> and are
		518	enabled by this setting.
		519
		520	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		521	to do when a blessed object is found.
		522
		523	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		524
		525	When C<$coderef> is specified, it will be called from C<decode> each
		526	time it decodes a JSON object. The only argument is a reference to the
		527	newly-created hash. If the code references returns a single scalar (which
		528	need not be a reference), this value (i.e. a copy of that scalar to avoid
		529	aliasing) is inserted into the deserialised data structure. If it returns
		530	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		531	original deserialised hash will be inserted. This setting can slow down
		532	decoding considerably.
		533
		534	When C<$coderef> is omitted or undefined, any existing callback will
		535	be removed and C<decode> will not change the deserialised hash in any
		536	way.
		537
		538	Example, convert all JSON objects into the integer 5:
		539
		540	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		541	# returns [5]
		542	$js->decode ('[{}]')
		543	# throw an exception because allow_nonref is not enabled
		544	# so a lone 5 is not allowed.
		545	$js->decode ('{"a":1, "b":2}');
		546
		547	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		548
		549	Works remotely similar to C<filter_json_object>, but is only called for
		550	JSON objects having a single key named C<$key>.
		551
		552	This C<$coderef> is called before the one specified via
		553	C<filter_json_object>, if any. It gets passed the single value in the JSON
		554	object. If it returns a single value, it will be inserted into the data
		555	structure. If it returns nothing (not even C<undef> but the empty list),
		556	the callback from C<filter_json_object> will be called next, as if no
		557	single-key callback were specified.
		558
		559	If C<$coderef> is omitted or undefined, the corresponding callback will be
		560	disabled. There can only ever be one callback for a given key.
		561
		562	As this callback gets called less often then the C<filter_json_object>
		563	one, decoding speed will not usually suffer as much. Therefore, single-key
		564	objects make excellent targets to serialise Perl objects into, especially
		565	as single-key JSON objects are as close to the type-tagged value concept
		566	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		567	support this in any way, so you need to make sure your data never looks
		568	like a serialised Perl hash.
		569
		570	Typical names for the single object key are C<__class_whatever__>, or
		571	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		572	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		573	with real hashes.
		574
		575	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		576	into the corresponding C<< $WIDGET{<id>} >> object:
		577
		578	# return whatever is in $WIDGET{5}:
		579	JSON::XS
		580	->new
		581	->filter_json_single_key_object (__widget__ => sub {
		582	$WIDGET{ $_[0] }
		583	})
		584	->decode ('{"__widget__": 5')
		585
		586	# this can be used with a TO_JSON method in some "widget" class
		587	# for serialisation to json:
		588	sub WidgetBase::TO_JSON {
		589	my ($self) = @_;
		590
		591	unless ($self->{id}) {
		592	$self->{id} = ..get..some..id..;
		593	$WIDGET{$self->{id}} = $self;
		594	}
		595
		596	{ __widget__ => $self->{id} }
		597	}
		598
223	=item $json = $json->shrink ([$enable])	599	=item $json = $json->shrink ([$enable])
224		600
		601	=item $enabled = $json->get_shrink
		602
225	Perl usually over-allocates memory a bit when allocating space for	603	Perl usually over-allocates memory a bit when allocating space for
226	strings. This flag optionally resizes strings generated by either	604	strings. This flag optionally resizes strings generated by either
227	C<encode> or C<decode> to their minimum size possible. This can save	605	C<encode> or C<decode> to their minimum size possible. This can save
228	memory when your JSON strings are either very very long or you have many	606	memory when your JSON texts are either very very long or you have many
229	short strings. It will also try to downgrade any strings to octet-form	607	short strings. It will also try to downgrade any strings to octet-form
230	if possible: perl stores strings internally either in an encoding called	608	if possible: perl stores strings internally either in an encoding called
231	UTF-X or in octet-form. The latter cannot store everything but uses less	609	UTF-X or in octet-form. The latter cannot store everything but uses less
232	space in general.	610	space in general (and some buggy Perl or C code might even rely on that
		611	internal representation being used).
233		612
		613	The actual definition of what shrink does might change in future versions,
		614	but it will always try to save space at the expense of time.
		615
234	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	616	If C<$enable> is true (or missing), the string returned by C<encode> will
235	while all strings generated by C<decode> will also be shrunk-to-fit.	617	be shrunk-to-fit, while all strings generated by C<decode> will also be
		618	shrunk-to-fit.
236		619
237	If C<$enable> is false, then the normal perl allocation algorithms are used.	620	If C<$enable> is false, then the normal perl allocation algorithms are used.
238	If you work with your data, then this is likely to be faster.	621	If you work with your data, then this is likely to be faster.
239		622
240	In the future, this setting might control other things, such as converting	623	In the future, this setting might control other things, such as converting
241	strings that look like integers or floats into integers or floats	624	strings that look like integers or floats into integers or floats
242	internally (there is no difference on the Perl level), saving space.	625	internally (there is no difference on the Perl level), saving space.
243		626
		627	=item $json = $json->max_depth ([$maximum_nesting_depth])
		628
		629	=item $max_depth = $json->get_max_depth
		630
		631	Sets the maximum nesting level (default C<512>) accepted while encoding
		632	or decoding. If a higher nesting level is detected in JSON text or a Perl
		633	data structure, then the encoder and decoder will stop and croak at that
		634	point.
		635
		636	Nesting level is defined by number of hash- or arrayrefs that the encoder
		637	needs to traverse to reach a given point or the number of C<{> or C<[>
		638	characters without their matching closing parenthesis crossed to reach a
		639	given character in a string.
		640
		641	Setting the maximum depth to one disallows any nesting, so that ensures
		642	that the object is only a single hash/object or array.
		643
		644	If no argument is given, the highest possible setting will be used, which
		645	is rarely useful.
		646
		647	Note that nesting is implemented by recursion in C. The default value has
		648	been chosen to be as large as typical operating systems allow without
		649	crashing.
		650
		651	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		652
		653	=item $json = $json->max_size ([$maximum_string_size])
		654
		655	=item $max_size = $json->get_max_size
		656
		657	Set the maximum length a JSON text may have (in bytes) where decoding is
		658	being attempted. The default is C<0>, meaning no limit. When C<decode>
		659	is called on a string that is longer then this many bytes, it will not
		660	attempt to decode the string but throw an exception. This setting has no
		661	effect on C<encode> (yet).
		662
		663	If no argument is given, the limit check will be deactivated (same as when
		664	C<0> is specified).
		665
		666	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		667
244	=item $json_string = $json->encode ($perl_scalar)	668	=item $json_text = $json->encode ($perl_scalar)
245		669
246	Converts the given Perl data structure (a simple scalar or a reference	670	Converts the given Perl data structure (a simple scalar or a reference
247	to a hash or array) to its JSON representation. Simple scalars will be	671	to a hash or array) to its JSON representation. Simple scalars will be
248	converted into JSON string or number sequences, while references to arrays	672	converted into JSON string or number sequences, while references to arrays
249	become JSON arrays and references to hashes become JSON objects. Undefined	673	become JSON arrays and references to hashes become JSON objects. Undefined
250	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>	674	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
251	nor C<false> values will be generated.	675	nor C<false> values will be generated.
252		676
253	=item $perl_scalar = $json->decode ($json_string)	677	=item $perl_scalar = $json->decode ($json_text)
254		678
255	The opposite of C<encode>: expects a JSON string and tries to parse it,	679	The opposite of C<encode>: expects a JSON text and tries to parse it,
256	returning the resulting simple scalar or reference. Croaks on error.	680	returning the resulting simple scalar or reference. Croaks on error.
257		681
258	JSON numbers and strings become simple Perl scalars. JSON arrays become	682	JSON numbers and strings become simple Perl scalars. JSON arrays become
259	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	683	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
260	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	684	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
261		685
		686	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		687
		688	This works like the C<decode> method, but instead of raising an exception
		689	when there is trailing garbage after the first JSON object, it will
		690	silently stop parsing there and return the number of characters consumed
		691	so far.
		692
		693	This is useful if your JSON texts are not delimited by an outer protocol
		694	(which is not the brightest thing to do in the first place) and you need
		695	to know where the JSON text ends.
		696
		697	JSON::XS->new->decode_prefix ("[1] the tail")
		698	=> ([], 3)
		699
262	=back	700	=back
263		701
264	=head1 COMPARISON
265		702
266	As already mentioned, this module was created because none of the existing	703	=head1 INCREMENTAL PARSING
267	JSON modules could be made to work correctly. First I will describe the	704
268	problems (or pleasures) I encountered with various existing JSON modules,	705	In some cases, there is the need for incremental parsing of JSON
269	followed by some benchmark values. JSON::XS was designed not to suffer	706	texts. While this module always has to keep both JSON text and resulting
270	from any of these problems or limitations.	707	Perl data structure in memory at one time, it does allow you to parse a
		708	JSON stream incrementally. It does so by accumulating text until it has
		709	a full JSON object, which it then can decode. This process is similar to
		710	using C<decode_prefix> to see if a full JSON object is available, but
		711	is much more efficient (and can be implemented with a minimum of method
		712	calls).
		713
		714	JSON::XS will only attempt to parse the JSON text once it is sure it
		715	has enough text to get a decisive result, using a very simple but
		716	truly incremental parser. This means that it sometimes won't stop as
		717	early as the full parser, for example, it doesn't detect parenthese
		718	mismatches. The only thing it guarantees is that it starts decoding as
		719	soon as a syntactically valid JSON text has been seen. This means you need
		720	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		721	parsing in the presence if syntax errors.
		722
		723	The following methods implement this incremental parser.
271		724
272	=over 4	725	=over 4
273		726
274	=item JSON 1.07	727	=item [void, scalar or list context] = $json->incr_parse ([$string])
275		728
276	Slow (but very portable, as it is written in pure Perl).	729	This is the central parsing function. It can both append new text and
		730	extract objects from the stream accumulated so far (both of these
		731	functions are optional).
277		732
278	Undocumented/buggy Unicode handling (how JSON handles unicode values is	733	If C<$string> is given, then this string is appended to the already
279	undocumented. One can get far by feeding it unicode strings and doing	734	existing JSON fragment stored in the C<$json> object.
280	en-/decoding oneself, but unicode escapes are not working properly).
281		735
282	No roundtripping (strings get clobbered if they look like numbers, e.g.	736	After that, if the function is called in void context, it will simply
283	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	737	return without doing anything further. This can be used to add more text
284	decode into the number 2.	738	in as many chunks as you want.
285		739
286	=item JSON::PC 0.01	740	If the method is called in scalar context, then it will try to extract
		741	exactly I<one> JSON object. If that is successful, it will return this
		742	object, otherwise it will return C<undef>. If there is a parse error,
		743	this method will croak just as C<decode> would do (one can then use
		744	C<incr_skip> to skip the errornous part). This is the most common way of
		745	using the method.
287		746
288	Very fast.	747	And finally, in list context, it will try to extract as many objects
		748	from the stream as it can find and return them, or the empty list
		749	otherwise. For this to work, there must be no separators between the JSON
		750	objects or arrays, instead they must be concatenated back-to-back. If
		751	an error occurs, an exception will be raised as in the scalar context
		752	case. Note that in this case, any previously-parsed JSON texts will be
		753	lost.
289		754
290	Undocumented/buggy Unicode handling.	755	=item $lvalue_string = $json->incr_text
291		756
292	No roundtripping.	757	This method returns the currently stored JSON fragment as an lvalue, that
		758	is, you can manipulate it. This I<only> works when a preceding call to
		759	C<incr_parse> in I<scalar context> successfully returned an object. Under
		760	all other circumstances you must not call this function (I mean it.
		761	although in simple tests it might actually work, it I<will> fail under
		762	real world conditions). As a special exception, you can also call this
		763	method before having parsed anything.
293		764
294	Has problems handling many Perl values (e.g. regex results and other magic	765	This function is useful in two cases: a) finding the trailing text after a
295	values will make it croak).	766	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		767	(such as commas).
296		768
297	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	769	=item $json->incr_skip
298	which is not a valid JSON string.
299		770
300	Unmaintained (maintainer unresponsive for many months, bugs are not	771	This will reset the state of the incremental parser and will remove
301	getting fixed).	772	the parsed text from the input buffer so far. This is useful after
		773	C<incr_parse> died, in which case the input buffer and incremental parser
		774	state is left unchanged, to skip the text parsed so far and to reset the
		775	parse state.
302		776
303	=item JSON::Syck 0.21	777	The difference to C<incr_reset> is that only text until the parse error
		778	occured is removed.
304		779
305	Very buggy (often crashes).	780	=item $json->incr_reset
306		781
307	Very inflexible (no human-readable format supported, format pretty much	782	This completely resets the incremental parser, that is, after this call,
308	undocumented. I need at least a format for easy reading by humans and a	783	it will be as if the parser had never parsed anything.
309	single-line compact format for use in a protocol, and preferably a way to
310	generate ASCII-only JSON strings).
311		784
312	Completely broken (and confusingly documented) Unicode handling (unicode	785	This is useful if you want to repeatedly parse JSON objects and want to
313	escapes are not working properly, you need to set ImplicitUnicode to	786	ignore any trailing data, which means you have to reset the parser after
314	I<different> values on en- and decoding to get symmetric behaviour).	787	each successful decode.
315
316	No roundtripping (simple cases work, but this depends on wether the scalar
317	value was used in a numeric context or not).
318
319	Dumping hashes may skip hash values depending on iterator state.
320
321	Unmaintained (maintainer unresponsive for many months, bugs are not
322	getting fixed).
323
324	Does not check input for validity (i.e. will accept non-JSON input and
325	return "something" instead of raising an exception. This is a security
326	issue: imagine two banks transfering money between each other using
327	JSON. One bank might parse a given non-JSON request and deduct money,
328	while the other might reject the transaction with a syntax error. While a
329	good protocol will at least recover, that is extra unnecessary work and
330	the transaction will still not succeed).
331
332	=item JSON::DWIW 0.04
333
334	Very fast. Very natural. Very nice.
335
336	Undocumented unicode handling (but the best of the pack. Unicode escapes
337	still don't get parsed properly).
338
339	Very inflexible.
340
341	No roundtripping.
342
343	Does not generate valid JSON (key strings are often unquoted, empty keys
344	result in nothing being output)
345
346	Does not check input for validity.
347		788
348	=back	789	=back
		790
		791	=head2 LIMITATIONS
		792
		793	All options that affect decoding are supported, except
		794	C<allow_nonref>. The reason for this is that it cannot be made to
		795	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		796	them back to back and still decode them perfectly. This does not hold true
		797	for JSON numbers, however.
		798
		799	For example, is the string C<1> a single JSON number, or is it simply the
		800	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		801	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		802	takes the conservative route and disallows this case.
		803
		804	=head2 EXAMPLES
		805
		806	Some examples will make all this clearer. First, a simple example that
		807	works similarly to C<decode_prefix>: We want to decode the JSON object at
		808	the start of a string and identify the portion after the JSON object:
		809
		810	my $text = "[1,2,3] hello";
		811
		812	my $json = new JSON::XS;
		813
		814	my $obj = $json->incr_parse ($text)
		815	or die "expected JSON object or array at beginning of string";
		816
		817	my $tail = $json->incr_text;
		818	# $tail now contains " hello"
		819
		820	Easy, isn't it?
		821
		822	Now for a more complicated example: Imagine a hypothetical protocol where
		823	you read some requests from a TCP stream, and each request is a JSON
		824	array, without any separation between them (in fact, it is often useful to
		825	use newlines as "separators", as these get interpreted as whitespace at
		826	the start of the JSON text, which makes it possible to test said protocol
		827	with C<telnet>...).
		828
		829	Here is how you'd do it (it is trivial to write this in an event-based
		830	manner):
		831
		832	my $json = new JSON::XS;
		833
		834	# read some data from the socket
		835	while (sysread $socket, my $buf, 4096) {
		836
		837	# split and decode as many requests as possible
		838	for my $request ($json->incr_parse ($buf)) {
		839	# act on the $request
		840	}
		841	}
		842
		843	Another complicated example: Assume you have a string with JSON objects
		844	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		845	[3]>). To parse them, we have to skip the commas between the JSON texts,
		846	and here is where the lvalue-ness of C<incr_text> comes in useful:
		847
		848	my $text = "[1],[2], [3]";
		849	my $json = new JSON::XS;
		850
		851	# void context, so no parsing done
		852	$json->incr_parse ($text);
		853
		854	# now extract as many objects as possible. note the
		855	# use of scalar context so incr_text can be called.
		856	while (my $obj = $json->incr_parse) {
		857	# do something with $obj
		858
		859	# now skip the optional comma
		860	$json->incr_text =~ s/^ \s* , //x;
		861	}
		862
		863	Now lets go for a very complex example: Assume that you have a gigantic
		864	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		865	but you cannot load it into memory fully (this has actually happened in
		866	the real world :).
		867
		868	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		869	can still help you: You implement a (very simple) array parser and let
		870	JSON decode the array elements, which are all full JSON objects on their
		871	own (this wouldn't work if the array elements could be JSON numbers, for
		872	example):
		873
		874	my $json = new JSON::XS;
		875
		876	# open the monster
		877	open my $fh, "<bigfile.json"
		878	or die "bigfile: $!";
		879
		880	# first parse the initial "["
		881	for (;;) {
		882	sysread $fh, my $buf, 65536
		883	or die "read error: $!";
		884	$json->incr_parse ($buf); # void context, so no parsing
		885
		886	# Exit the loop once we found and removed(!) the initial "[".
		887	# In essence, we are (ab-)using the $json object as a simple scalar
		888	# we append data to.
		889	last if $json->incr_text =~ s/^ \s* \[ //x;
		890	}
		891
		892	# now we have the skipped the initial "[", so continue
		893	# parsing all the elements.
		894	for (;;) {
		895	# in this loop we read data until we got a single JSON object
		896	for (;;) {
		897	if (my $obj = $json->incr_parse) {
		898	# do something with $obj
		899	last;
		900	}
		901
		902	# add more data
		903	sysread $fh, my $buf, 65536
		904	or die "read error: $!";
		905	$json->incr_parse ($buf); # void context, so no parsing
		906	}
		907
		908	# in this loop we read data until we either found and parsed the
		909	# separating "," between elements, or the final "]"
		910	for (;;) {
		911	# first skip whitespace
		912	$json->incr_text =~ s/^\s*//;
		913
		914	# if we find "]", we are done
		915	if ($json->incr_text =~ s/^\]//) {
		916	print "finished.\n";
		917	exit;
		918	}
		919
		920	# if we find ",", we can continue with the next element
		921	if ($json->incr_text =~ s/^,//) {
		922	last;
		923	}
		924
		925	# if we find anything else, we have a parse error!
		926	if (length $json->incr_text) {
		927	die "parse error near ", $json->incr_text;
		928	}
		929
		930	# else add more data
		931	sysread $fh, my $buf, 65536
		932	or die "read error: $!";
		933	$json->incr_parse ($buf); # void context, so no parsing
		934	}
		935
		936	This is a complex example, but most of the complexity comes from the fact
		937	that we are trying to be correct (bear with me if I am wrong, I never ran
		938	the above example :).
		939
		940
		941
		942	=head1 MAPPING
		943
		944	This section describes how JSON::XS maps Perl values to JSON values and
		945	vice versa. These mappings are designed to "do the right thing" in most
		946	circumstances automatically, preserving round-tripping characteristics
		947	(what you put in comes out as something equivalent).
		948
		949	For the more enlightened: note that in the following descriptions,
		950	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		951	refers to the abstract Perl language itself.
		952
		953
		954	=head2 JSON -> PERL
		955
		956	=over 4
		957
		958	=item object
		959
		960	A JSON object becomes a reference to a hash in Perl. No ordering of object
		961	keys is preserved (JSON does not preserve object key ordering itself).
		962
		963	=item array
		964
		965	A JSON array becomes a reference to an array in Perl.
		966
		967	=item string
		968
		969	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		970	are represented by the same codepoints in the Perl string, so no manual
		971	decoding is necessary.
		972
		973	=item number
		974
		975	A JSON number becomes either an integer, numeric (floating point) or
		976	string scalar in perl, depending on its range and any fractional parts. On
		977	the Perl level, there is no difference between those as Perl handles all
		978	the conversion details, but an integer may take slightly less memory and
		979	might represent more values exactly than floating point numbers.
		980
		981	If the number consists of digits only, JSON::XS will try to represent
		982	it as an integer value. If that fails, it will try to represent it as
		983	a numeric (floating point) value if that is possible without loss of
		984	precision. Otherwise it will preserve the number as a string value (in
		985	which case you lose roundtripping ability, as the JSON number will be
		986	re-encoded toa JSON string).
		987
		988	Numbers containing a fractional or exponential part will always be
		989	represented as numeric (floating point) values, possibly at a loss of
		990	precision (in which case you might lose perfect roundtripping ability, but
		991	the JSON number will still be re-encoded as a JSON number).
		992
		993	=item true, false
		994
		995	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
		996	respectively. They are overloaded to act almost exactly like the numbers
		997	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
		998	the C<JSON::XS::is_bool> function.
		999
		1000	=item null
		1001
		1002	A JSON null atom becomes C<undef> in Perl.
		1003
		1004	=back
		1005
		1006
		1007	=head2 PERL -> JSON
		1008
		1009	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		1010	truly typeless language, so we can only guess which JSON type is meant by
		1011	a Perl value.
		1012
		1013	=over 4
		1014
		1015	=item hash references
		1016
		1017	Perl hash references become JSON objects. As there is no inherent ordering
		1018	in hash keys (or JSON objects), they will usually be encoded in a
		1019	pseudo-random order that can change between runs of the same program but
		1020	stays generally the same within a single run of a program. JSON::XS can
		1021	optionally sort the hash keys (determined by the I<canonical> flag), so
		1022	the same datastructure will serialise to the same JSON text (given same
		1023	settings and version of JSON::XS), but this incurs a runtime overhead
		1024	and is only rarely useful, e.g. when you want to compare some JSON text
		1025	against another for equality.
		1026
		1027	=item array references
		1028
		1029	Perl array references become JSON arrays.
		1030
		1031	=item other references
		1032
		1033	Other unblessed references are generally not allowed and will cause an
		1034	exception to be thrown, except for references to the integers C<0> and
		1035	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		1036	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		1037
		1038	encode_json [\0, JSON::XS::true] # yields [false,true]
		1039
		1040	=item JSON::XS::true, JSON::XS::false
		1041
		1042	These special values become JSON true and JSON false values,
		1043	respectively. You can also use C<\1> and C<\0> directly if you want.
		1044
		1045	=item blessed objects
		1046
		1047	Blessed objects are not directly representable in JSON. See the
		1048	C<allow_blessed> and C<convert_blessed> methods on various options on
		1049	how to deal with this: basically, you can choose between throwing an
		1050	exception, encoding the reference as if it weren't blessed, or provide
		1051	your own serialiser method.
		1052
		1053	=item simple scalars
		1054
		1055	Simple Perl scalars (any scalar that is not a reference) are the most
		1056	difficult objects to encode: JSON::XS will encode undefined scalars as
		1057	JSON C<null> values, scalars that have last been used in a string context
		1058	before encoding as JSON strings, and anything else as number value:
		1059
		1060	# dump as number
		1061	encode_json [2] # yields [2]
		1062	encode_json [-3.0e17] # yields [-3e+17]
		1063	my $value = 5; encode_json [$value] # yields [5]
		1064
		1065	# used as string, so dump as string
		1066	print $value;
		1067	encode_json [$value] # yields ["5"]
		1068
		1069	# undef becomes null
		1070	encode_json [undef] # yields [null]
		1071
		1072	You can force the type to be a JSON string by stringifying it:
		1073
		1074	my $x = 3.1; # some variable containing a number
		1075	"$x"; # stringified
		1076	$x .= ""; # another, more awkward way to stringify
		1077	print $x; # perl does it for you, too, quite often
		1078
		1079	You can force the type to be a JSON number by numifying it:
		1080
		1081	my $x = "3"; # some variable containing a string
		1082	$x += 0; # numify it, ensuring it will be dumped as a number
		1083	$x *= 1; # same thing, the choice is yours.
		1084
		1085	You can not currently force the type in other, less obscure, ways. Tell me
		1086	if you need this capability (but don't forget to explain why it's needed
		1087	:).
		1088
		1089	=back
		1090
		1091
		1092	=head1 ENCODING/CODESET FLAG NOTES
		1093
		1094	The interested reader might have seen a number of flags that signify
		1095	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1096	some confusion on what these do, so here is a short comparison:
		1097
		1098	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1099	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1100	control whether C<encode> escapes character values outside their respective
		1101	codeset range. Neither of these flags conflict with each other, although
		1102	some combinations make less sense than others.
		1103
		1104	Care has been taken to make all flags symmetrical with respect to
		1105	C<encode> and C<decode>, that is, texts encoded with any combination of
		1106	these flag values will be correctly decoded when the same flags are used
		1107	- in general, if you use different flag settings while encoding vs. when
		1108	decoding you likely have a bug somewhere.
		1109
		1110	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1111	simply an abstract set of character-codepoint pairs, while an encoding
		1112	takes those codepoint numbers and I<encodes> them, in our case into
		1113	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1114	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1115	the same time, which can be confusing.
		1116
		1117	=over 4
		1118
		1119	=item C<utf8> flag disabled
		1120
		1121	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1122	and expect Unicode strings, that is, characters with high ordinal Unicode
		1123	values (> 255) will be encoded as such characters, and likewise such
		1124	characters are decoded as-is, no canges to them will be done, except
		1125	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1126	respectively (to Perl, these are the same thing in strings unless you do
		1127	funny/weird/dumb stuff).
		1128
		1129	This is useful when you want to do the encoding yourself (e.g. when you
		1130	want to have UTF-16 encoded JSON texts) or when some other layer does
		1131	the encoding for you (for example, when printing to a terminal using a
		1132	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1133	to UTF-8 encode your data first and have Perl encode it another time).
		1134
		1135	=item C<utf8> flag enabled
		1136
		1137	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1138	characters using the corresponding UTF-8 multi-byte sequence, and will
		1139	expect your input strings to be encoded as UTF-8, that is, no "character"
		1140	of the input string must have any value > 255, as UTF-8 does not allow
		1141	that.
		1142
		1143	The C<utf8> flag therefore switches between two modes: disabled means you
		1144	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1145	octet/binary string in Perl.
		1146
		1147	=item C<latin1> or C<ascii> flags enabled
		1148
		1149	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1150	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1151	characters as specified by the C<utf8> flag.
		1152
		1153	If C<utf8> is disabled, then the result is also correctly encoded in those
		1154	character sets (as both are proper subsets of Unicode, meaning that a
		1155	Unicode string with all character values < 256 is the same thing as a
		1156	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1157	the same thing as an ASCII string in Perl).
		1158
		1159	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1160	regardless of these flags, just some more characters will be escaped using
		1161	C<\uXXXX> then before.
		1162
		1163	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1164	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1165	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1166	a subset of Unicode), while ASCII is.
		1167
		1168	Surprisingly, C<decode> will ignore these flags and so treat all input
		1169	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1170	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1171	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1172
		1173	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1174	they only govern when the JSON output engine escapes a character or not.
		1175
		1176	The main use for C<latin1> is to relatively efficiently store binary data
		1177	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1178
		1179	The main use for C<ascii> is to force the output to not contain characters
		1180	with values > 127, which means you can interpret the resulting string
		1181	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1182	8-bit-encoding, and still get the same data structure back. This is useful
		1183	when your channel for JSON transfer is not 8-bit clean or the encoding
		1184	might be mangled in between (e.g. in mail), and works because ASCII is a
		1185	proper subset of most 8-bit and multibyte encodings in use in the world.
		1186
		1187	=back
		1188
		1189
		1190	=head2 JSON and ECMAscript
		1191
		1192	JSON syntax is based on how literals are represented in javascript (the
		1193	not-standardised predecessor of ECMAscript) which is presumably why it is
		1194	called "JavaScript Object Notation".
		1195
		1196	However, JSON is not a subset (and also not a superset of course) of
		1197	ECMAscript (the standard) or javascript (whatever browsers actually
		1198	implement).
		1199
		1200	If you want to use javascript's C<eval> function to "parse" JSON, you
		1201	might run into parse errors for valid JSON texts, or the resulting data
		1202	structure might not be queryable:
		1203
		1204	One of the problems is that U+2028 and U+2029 are valid characters inside
		1205	JSON strings, but are not allowed in ECMAscript string literals, so the
		1206	following Perl fragment will not output something that can be guaranteed
		1207	to be parsable by javascript's C<eval>:
		1208
		1209	use JSON::XS;
		1210
		1211	print encode_json [chr 0x2028];
		1212
		1213	The right fix for this is to use a proper JSON parser in your javascript
		1214	programs, and not rely on C<eval>.
		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	And if you are concerned about the size of the resulting JSON text, you
		1224	can run some regexes to only escape U+2028 and U+2029:
		1225
		1226	use JSON::XS;
		1227
		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	This works because U+2028/U+2029 are not allowed outside of strings and
		1234	are not used for syntax, so replacing them unconditionally just works.
		1235
		1236	Note, however, that fixing the broken JSON parser is better than working
		1237	around it in every other generator. The above regexes should work well in
		1238	other languages, as long as they operate on UTF-8. It is equally valid to
		1239	replace all occurences of U+2028/2029 directly by their \\u-escaped forms
		1240	in unicode texts, so they can simply be used to fix any parsers relying on
		1241	C<eval> by first applying the regexes on the encoded texts.
		1242
		1243	Note also that the above only works for U+2028 and U+2029 and thus
		1244	only for fully ECMAscript-compliant parsers. Many existing javascript
		1245	implementations misparse other characters as well. Best rely on a good
		1246	JSON parser, such as Douglas Crockfords F<json2.js>, which escapes the
		1247	above and many more problematic characters properly before passing them
		1248	into C<eval>.
		1249
		1250	Another problem is that some javascript implementations reserve
		1251	some property names for their own purposes (which probably makes
		1252	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1253	C<__proto__> property name for it's own purposes.
		1254
		1255	If that is a problem, you could parse try to filter the resulting JSON
		1256	output for these property strings, e.g.:
		1257
		1258	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1259
		1260	This works because C<__proto__> is not valid outside of strings, so every
		1261	occurence of C<"__proto__"\s*:> must be a string used as property name.
		1262
		1263	If you know of other incompatibilities, please let me know.
		1264
		1265
		1266	=head2 JSON and YAML
		1267
		1268	You often hear that JSON is a subset of YAML. This is, however, a mass
		1269	hysteria(*) and very far from the truth (as of the time of this writing),
		1270	so let me state it clearly: I<in general, there is no way to configure
		1271	JSON::XS to output a data structure as valid YAML> that works in all
		1272	cases.
		1273
		1274	If you really must use JSON::XS to generate YAML, you should use this
		1275	algorithm (subject to change in future versions):
		1276
		1277	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1278	my $yaml = $to_yaml->encode ($ref) . "\n";
		1279
		1280	This will I<usually> generate JSON texts that also parse as valid
		1281	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1282	lengths that JSON doesn't have and also has different and incompatible
		1283	unicode handling, so you should make sure that your hash keys are
		1284	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1285	you do not have characters with codepoint values outside the Unicode BMP
		1286	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1287	strings (which JSON::XS does not I<currently> generate, but other JSON
		1288	generators might).
		1289
		1290	There might be other incompatibilities that I am not aware of (or the YAML
		1291	specification has been changed yet again - it does so quite often). In
		1292	general you should not try to generate YAML with a JSON generator or vice
		1293	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1294	high that you will run into severe interoperability problems when you
		1295	least expect it.
		1296
		1297	=over 4
		1298
		1299	=item (*)
		1300
		1301	I have been pressured multiple times by Brian Ingerson (one of the
		1302	authors of the YAML specification) to remove this paragraph, despite him
		1303	acknowledging that the actual incompatibilities exist. As I was personally
		1304	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1305	educate people about these issues, so others do not run into the same
		1306	problem again and again. After this, Brian called me a (quote)I<complete
		1307	and worthless idiot>(unquote).
		1308
		1309	In my opinion, instead of pressuring and insulting people who actually
		1310	clarify issues with YAML and the wrong statements of some of its
		1311	proponents, I would kindly suggest reading the JSON spec (which is not
		1312	that difficult or long) and finally make YAML compatible to it, and
		1313	educating users about the changes, instead of spreading lies about the
		1314	real compatibility for many I<years> and trying to silence people who
		1315	point out that it isn't true.
		1316
		1317	=back
		1318
349		1319
350	=head2 SPEED	1320	=head2 SPEED
351		1321
352	It seems that JSON::XS is surprisingly fast, as shown in the following	1322	It seems that JSON::XS is surprisingly fast, as shown in the following
353	tables. They have been generated with the help of the C<eg/bench> program	1323	tables. They have been generated with the help of the C<eg/bench> program
354	in the JSON::XS distribution, to make it easy to compare on your own	1324	in the JSON::XS distribution, to make it easy to compare on your own
355	system.	1325	system.
356		1326
357	First is a comparison between various modules using a very simple JSON	1327	First comes a comparison between various modules using
		1328	a very short single-line JSON string (also available at
		1329	L<http://dist.schmorp.de/misc/json/short.json>).
		1330
		1331	{"method": "handleMessage", "params": ["user1",
		1332	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1333	true, false]}
		1334
358	string, showing the number of encodes/decodes per second (JSON::XS is	1335	It shows the number of encodes/decodes per second (JSON::XS uses
359	the functional interface, while JSON::XS/2 is the OO interface with	1336	the functional interface, while JSON::XS/2 uses the OO interface
360	pretty-printing and hashkey sorting enabled).	1337	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1338	shrink). Higher is better:
361		1339
362	module | encode | decode |	1340	module | encode | decode |
363	-----------|------------|------------|	1341	-----------|------------|------------|
364	JSON | 14006 | 6820 |	1342	JSON 1.x | 4990.842 | 4088.813 |
365	JSON::DWIW | 200937 | 120386 |	1343	JSON::DWIW | 51653.990 | 71575.154 |
366	JSON::PC | 85065 | 129366 |	1344	JSON::PC | 65948.176 | 74631.744 |
367	JSON::Syck | 59898 | 44232 |	1345	JSON::PP | 8931.652 | 3817.168 |
368	JSON::XS | 1171478 | 342435 |	1346	JSON::Syck | 24877.248 | 27776.848 |
369	JSON::XS/2 | 730760 | 328714 |	1347	JSON::XS | 388361.481 | 227951.304 |
		1348	JSON::XS/2 | 227951.304 | 218453.333 |
		1349	JSON::XS/3 | 338250.323 | 218453.333 |
		1350	Storable | 16500.016 | 135300.129 |
370	-----------+------------+------------+	1351	-----------+------------+------------+
371		1352
372	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1353	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
		1354	about three times faster on decoding, and over forty times faster
373	times faster than JSON, even with pretty-printing and key sorting.	1355	than JSON, even with pretty-printing and key sorting. It also compares
		1356	favourably to Storable for small amounts of data.
374		1357
375	Using a longer test string (roughly 8KB, generated from Yahoo! Locals	1358	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
376	search API (http://nanoref.com/yahooapis/mgPdGg):	1359	search API (L<http://dist.schmorp.de/misc/json/long.json>).
377		1360
378	module | encode | decode |	1361	module | encode | decode |
379	-----------|------------|------------|	1362	-----------|------------|------------|
380	JSON | 673 | 38 |	1363	JSON 1.x | 55.260 | 34.971 |
381	JSON::DWIW | 5271 | 770 |	1364	JSON::DWIW | 825.228 | 1082.513 |
382	JSON::PC | 9901 | 2491 |	1365	JSON::PC | 3571.444 | 2394.829 |
383	JSON::Syck | 2360 | 786 |	1366	JSON::PP | 210.987 | 32.574 |
384	JSON::XS | 37398 | 3202 |	1367	JSON::Syck | 552.551 | 787.544 |
385	JSON::XS/2 | 13765 | 3153 |	1368	JSON::XS | 5780.463 | 4854.519 |
		1369	JSON::XS/2 | 3869.998 | 4798.975 |
		1370	JSON::XS/3 | 5862.880 | 4798.975 |
		1371	Storable | 4445.002 | 5235.027 |
386	-----------+------------+------------+	1372	-----------+------------+------------+
387		1373
388	Again, JSON::XS leads by far in the encoding case, while still beating	1374	Again, JSON::XS leads by far (except for Storable which non-surprisingly
389	every other module in the decoding case.	1375	decodes faster).
390		1376
391	Last example is an almost 8MB large hash with many large binary values	1377	On large strings containing lots of high Unicode characters, some modules
392	(PNG files), resulting in a lot of escaping:	1378	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1379	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1380	to decode or encode properly, so it was impossible to prepare a fair
		1381	comparison table for that case.
		1382
		1383
		1384	=head1 SECURITY CONSIDERATIONS
		1385
		1386	When you are using JSON in a protocol, talking to untrusted potentially
		1387	hostile creatures requires relatively few measures.
		1388
		1389	First of all, your JSON decoder should be secure, that is, should not have
		1390	any buffer overflows. Obviously, this module should ensure that and I am
		1391	trying hard on making that true, but you never know.
		1392
		1393	Second, you need to avoid resource-starving attacks. That means you should
		1394	limit the size of JSON texts you accept, or make sure then when your
		1395	resources run out, that's just fine (e.g. by using a separate process that
		1396	can crash safely). The size of a JSON text in octets or characters is
		1397	usually a good indication of the size of the resources required to decode
		1398	it into a Perl structure. While JSON::XS can check the size of the JSON
		1399	text, it might be too late when you already have it in memory, so you
		1400	might want to check the size before you accept the string.
		1401
		1402	Third, JSON::XS recurses using the C stack when decoding objects and
		1403	arrays. The C stack is a limited resource: for instance, on my amd64
		1404	machine with 8MB of stack size I can decode around 180k nested arrays but
		1405	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1406	to free the temporary). If that is exceeded, the program crashes. To be
		1407	conservative, the default nesting limit is set to 512. If your process
		1408	has a smaller stack, you should adjust this setting accordingly with the
		1409	C<max_depth> method.
		1410
		1411	Something else could bomb you, too, that I forgot to think of. In that
		1412	case, you get to keep the pieces. I am always open for hints, though...
		1413
		1414	Also keep in mind that JSON::XS might leak contents of your Perl data
		1415	structures in its error messages, so when you serialise sensitive
		1416	information you might want to make sure that exceptions thrown by JSON::XS
		1417	will not end up in front of untrusted eyes.
		1418
		1419	If you are using JSON::XS to return packets to consumption
		1420	by JavaScript scripts in a browser you should have a look at
		1421	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1422	you are vulnerable to some common attack vectors (which really are browser
		1423	design bugs, but it is still you who will have to deal with it, as major
		1424	browser developers care only for features, not about getting security
		1425	right).
		1426
		1427
		1428	=head1 THREADS
		1429
		1430	This module is I<not> guaranteed to be thread safe and there are no
		1431	plans to change this until Perl gets thread support (as opposed to the
		1432	horribly slow so-called "threads" which are simply slow and bloated
		1433	process simulations - use fork, it's I<much> faster, cheaper, better).
		1434
		1435	(It might actually work, but you have been warned).
		1436
393		1437
394	=head1 BUGS	1438	=head1 BUGS
395		1439
396	While the goal of this module is to be correct, that unfortunately does	1440	While the goal of this module is to be correct, that unfortunately does
397	not mean its bug-free, only that I think its design is bug-free. It is	1441	not mean it's bug-free, only that I think its design is bug-free. If you
398	still very young and not well-tested. If you keep reporting bugs they will	1442	keep reporting bugs they will be fixed swiftly, though.
399	be fixed swiftly, though.	1443
		1444	Please refrain from using rt.cpan.org or any other bug reporting
		1445	service. I put the contact address into my modules for a reason.
400		1446
401	=cut	1447	=cut
402		1448
		1449	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1450	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1451
		1452	sub true() { $true }
		1453	sub false() { $false }
		1454
		1455	sub is_bool($) {
		1456	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1457	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1458	}
		1459
		1460	XSLoader::load "JSON::XS", $VERSION;
		1461
		1462	package JSON::XS::Boolean;
		1463
		1464	use overload
		1465	"0+" => sub { ${$_[0]} },
		1466	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1467	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1468	fallback => 1;
		1469
403	1;	1470	1;
		1471
		1472	=head1 SEE ALSO
		1473
		1474	The F<json_xs> command line utility for quick experiments.
404		1475
405	=head1 AUTHOR	1476	=head1 AUTHOR
406		1477
407	Marc Lehmann <schmorp@schmorp.de>	1478	Marc Lehmann <schmorp@schmorp.de>
408	http://home.schmorp.de/	1479	http://home.schmorp.de/

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