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Revision 1.9 by root, Fri Mar 23 16:00:19 2007 UTC vs.
Revision 1.105 by root, Sat May 24 21:55:43 2008 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 COMPARISON, below, for a comparison to some other JSON modules.
22		55
		56	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
		57	vice versa.
		58
23	=head2 FEATURES	59	=head2 FEATURES
24		60
25	=over 4	61	=over 4
26		62
27	=item * correct handling of unicode issues	63	=item * correct Unicode handling
28		64
29	This module knows how to handle Unicode, and even documents how it does so.	65	This module knows how to handle Unicode, documents how and when it does
		66	so, and even documents what "correct" means.
30		67
31	=item * round-trip integrity	68	=item * round-trip integrity
32		69
33	When you serialise a perl data structure using only datatypes supported	70	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.	71	by JSON, the deserialised data structure is identical on the Perl level.
35	(e.g. the string "2.0" doesn't suddenly become "2").	72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
		73	like a number). There minor I<are> exceptions to this, read the MAPPING
		74	section below to learn about those.
36		75
37	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
38		77
39	There is no guessing, no generating of illegal JSON strings by default,	78	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).	79	and only JSON is accepted as input by default (the latter is a security
		80	feature).
41		81
42	=item * fast	82	=item * fast
43		83
44	compared to other JSON modules, this module compares favourably.	84	Compared to other JSON modules and other serialisers such as Storable,
		85	this module usually compares favourably in terms of speed, too.
45		86
46	=item * simple to use	87	=item * simple to use
47		88
48	This module has both a simple functional interface as well as an OO	89	This module has both a simple functional interface as well as an object
49	interface.	90	oriented interface interface.
50		91
51	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
52		93
53	You can choose between the most compact format possible, a pure-ascii	94	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	95	possible (nice for simple line-based protocols), a pure-ASCII format
55	whatever way you like.	96	(for when your transport is not 8-bit clean, still supports the whole
		97	Unicode range), or a pretty-printed format (for when you want to read that
		98	stuff). Or you can combine those features in whatever way you like.
56		99
57	=back	100	=back
58		101
59	=cut	102	=cut
60		103
61	package JSON::XS;	104	package JSON::XS;
62		105
63	BEGIN {	106	use strict;
		107
64	$VERSION = '0.3';	108	our $VERSION = '2.2';
65	@ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
66		110
67	@EXPORT = qw(to_json from_json);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
68	require Exporter;
69		112
		113	sub to_json($) {
70	require XSLoader;	114	require Carp;
71	XSLoader::load JSON::XS::, $VERSION;	115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
72	}	116	}
73		117
		118	sub from_json($) {
		119	require Carp;
		120	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");
		121	}
		122
		123	use Exporter;
		124	use XSLoader;
		125
74	=head1 FUNCTIONAL INTERFACE	126	=head1 FUNCTIONAL INTERFACE
75		127
76	The following convinience methods are provided by this module. They are	128	The following convenience methods are provided by this module. They are
77	exported by default:	129	exported by default:
78		130
79	=over 4	131	=over 4
80		132
81	=item $json_string = to_json $perl_scalar	133	=item $json_text = encode_json $perl_scalar
82		134
83	Converts the given Perl data structure (a simple scalar or a reference to	135	Converts the given Perl data structure to a UTF-8 encoded, binary string
84	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	136	(that is, the string contains octets only). Croaks on error.
85	octets only). Croaks on error.
86		137
87	This function call is functionally identical to C<< JSON::XS->new->utf8	138	This function call is functionally identical to:
88	(1)->encode ($perl_scalar) >>.
89		139
		140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		141
		142	Except being faster.
		143
90	=item $perl_scalar = from_json $json_string	144	=item $perl_scalar = decode_json $json_text
91		145
92	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
93	parse that as an UTF-8 encoded JSON string, returning the resulting simple	147	to parse that as an UTF-8 encoded JSON text, returning the resulting
94	scalar or reference. Croaks on error.	148	reference. Croaks on error.
95		149
96	This function call is functionally identical to C<< JSON::XS->new->utf8	150	This function call is functionally identical to:
97	(1)->decode ($json_string) >>.	151
		152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		153
		154	Except being faster.
		155
		156	=item $is_boolean = JSON::XS::is_bool $scalar
		157
		158	Returns true if the passed scalar represents either JSON::XS::true or
		159	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		160	and are used to represent JSON C<true> and C<false> values in Perl.
		161
		162	See MAPPING, below, for more information on how JSON values are mapped to
		163	Perl.
98		164
99	=back	165	=back
		166
		167
		168	=head1 A FEW NOTES ON UNICODE AND PERL
		169
		170	Since this often leads to confusion, here are a few very clear words on
		171	how Unicode works in Perl, modulo bugs.
		172
		173	=over 4
		174
		175	=item 1. Perl strings can store characters with ordinal values > 255.
		176
		177	This enables you to store Unicode characters as single characters in a
		178	Perl string - very natural.
		179
		180	=item 2. Perl does I<not> associate an encoding with your strings.
		181
		182	... until you force it to, e.g. when matching it against a regex, or
		183	printing the scalar to a file, in which case Perl either interprets your
		184	string as locale-encoded text, octets/binary, or as Unicode, depending
		185	on various settings. In no case is an encoding stored together with your
		186	data, it is I<use> that decides encoding, not any magical meta data.
		187
		188	=item 3. The internal utf-8 flag has no meaning with regards to the
		189	encoding of your string.
		190
		191	Just ignore that flag unless you debug a Perl bug, a module written in
		192	XS or want to dive into the internals of perl. Otherwise it will only
		193	confuse you, as, despite the name, it says nothing about how your string
		194	is encoded. You can have Unicode strings with that flag set, with that
		195	flag clear, and you can have binary data with that flag set and that flag
		196	clear. Other possibilities exist, too.
		197
		198	If you didn't know about that flag, just the better, pretend it doesn't
		199	exist.
		200
		201	=item 4. A "Unicode String" is simply a string where each character can be
		202	validly interpreted as a Unicode code point.
		203
		204	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		205	Unicode string encoded in UTF-8, giving you a binary string.
		206
		207	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		208
		209	It's a fact. Learn to live with it.
		210
		211	=back
		212
		213	I hope this helps :)
		214
100		215
101	=head1 OBJECT-ORIENTED INTERFACE	216	=head1 OBJECT-ORIENTED INTERFACE
102		217
103	The object oriented interface lets you configure your own encoding or	218	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	219	decoding style, within the limits of supported formats.
…		…
111	strings. All boolean flags described below are by default I<disabled>.	226	strings. All boolean flags described below are by default I<disabled>.
112		227
113	The mutators for flags all return the JSON object again and thus calls can	228	The mutators for flags all return the JSON object again and thus calls can
114	be chained:	229	be chained:
115		230
116	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	231	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
117	=> {"a": [1, 2]}	232	=> {"a": [1, 2]}
118		233
119	=item $json = $json->ascii ([$enable])	234	=item $json = $json->ascii ([$enable])
120		235
		236	=item $enabled = $json->get_ascii
		237
121	If C<$enable> is true (or missing), then the C<encode> method will	238	If C<$enable> is true (or missing), then the C<encode> method will not
122	not generate characters outside the code range C<0..127>. Any unicode	239	generate characters outside the code range C<0..127> (which is ASCII). Any
123	characters outside that range will be escaped using either a single	240	Unicode characters outside that range will be escaped using either a
124	\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per	241	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
125	RFC4627.	242	as per RFC4627. The resulting encoded JSON text can be treated as a native
		243	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		244	or any other superset of ASCII.
126		245
127	If C<$enable> is false, then the C<encode> method will not escape Unicode	246	If C<$enable> is false, then the C<encode> method will not escape Unicode
128	characters unless necessary.	247	characters unless required by the JSON syntax or other flags. This results
		248	in a faster and more compact format.
129		249
		250	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		251	document.
		252
		253	The main use for this flag is to produce JSON texts that can be
		254	transmitted over a 7-bit channel, as the encoded JSON texts will not
		255	contain any 8 bit characters.
		256
130	JSON::XS->new->ascii (1)->encode (chr 0x10401)	257	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
131	=> \ud801\udc01	258	=> ["\ud801\udc01"]
		259
		260	=item $json = $json->latin1 ([$enable])
		261
		262	=item $enabled = $json->get_latin1
		263
		264	If C<$enable> is true (or missing), then the C<encode> method will encode
		265	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		266	outside the code range C<0..255>. The resulting string can be treated as a
		267	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		268	will not be affected in any way by this flag, as C<decode> by default
		269	expects Unicode, which is a strict superset of latin1.
		270
		271	If C<$enable> is false, then the C<encode> method will not escape Unicode
		272	characters unless required by the JSON syntax or other flags.
		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
		276
		277	The main use for this flag is efficiently encoding binary data as JSON
		278	text, as most octets will not be escaped, resulting in a smaller encoded
		279	size. The disadvantage is that the resulting JSON text is encoded
		280	in latin1 (and must correctly be treated as such when storing and
		281	transferring), a rare encoding for JSON. It is therefore most useful when
		282	you want to store data structures known to contain binary data efficiently
		283	in files or databases, not when talking to other JSON encoders/decoders.
		284
		285	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		286	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
132		287
133	=item $json = $json->utf8 ([$enable])	288	=item $json = $json->utf8 ([$enable])
134		289
		290	=item $enabled = $json->get_utf8
		291
135	If C<$enable> is true (or missing), then the C<encode> method will encode	292	If C<$enable> is true (or missing), then the C<encode> method will encode
136	the JSON string into UTF-8, as required by many protocols, while the	293	the JSON result into UTF-8, as required by many protocols, while the
137	C<decode> method expects to be handled an UTF-8-encoded string. Please	294	C<decode> method expects to be handled an UTF-8-encoded string. Please
138	note that UTF-8-encoded strings do not contain any characters outside the	295	note that UTF-8-encoded strings do not contain any characters outside the
139	range C<0..255>, they are thus useful for bytewise/binary I/O.	296	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		297	versions, enabling this option might enable autodetection of the UTF-16
		298	and UTF-32 encoding families, as described in RFC4627.
140		299
141	If C<$enable> is false, then the C<encode> method will return the JSON	300	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	301	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	302	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.	303	to be done yourself, e.g. using the Encode module.
		304
		305	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		306	document.
		307
		308	Example, output UTF-16BE-encoded JSON:
		309
		310	use Encode;
		311	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		312
		313	Example, decode UTF-32LE-encoded JSON:
		314
		315	use Encode;
		316	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
145		317
146	=item $json = $json->pretty ([$enable])	318	=item $json = $json->pretty ([$enable])
147		319
148	This enables (or disables) all of the C<indent>, C<space_before> and	320	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	321	C<space_after> (and in the future possibly more) flags in one call to
150	generate the most readable (or most compact) form possible.	322	generate the most readable (or most compact) form possible.
		323
		324	Example, pretty-print some simple structure:
151		325
152	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})	326	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
153	=>	327	=>
154	{	328	{
155	"a" : [	329	"a" : [
…		…
158	]	332	]
159	}	333	}
160		334
161	=item $json = $json->indent ([$enable])	335	=item $json = $json->indent ([$enable])
162		336
		337	=item $enabled = $json->get_indent
		338
163	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	339	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
164	format as output, putting every array member or object/hash key-value pair	340	format as output, putting every array member or object/hash key-value pair
165	into its own line, identing them properly.	341	into its own line, indenting them properly.
166		342
167	If C<$enable> is false, no newlines or indenting will be produced, and the	343	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>.	344	resulting JSON text is guaranteed not to contain any C<newlines>.
169		345
170	This setting has no effect when decoding JSON strings.	346	This setting has no effect when decoding JSON texts.
171		347
172	=item $json = $json->space_before ([$enable])	348	=item $json = $json->space_before ([$enable])
		349
		350	=item $enabled = $json->get_space_before
173		351
174	If C<$enable> is true (or missing), then the C<encode> method will add an extra	352	If C<$enable> is true (or missing), then the C<encode> method will add an extra
175	optional space before the C<:> separating keys from values in JSON objects.	353	optional space before the C<:> separating keys from values in JSON objects.
176		354
177	If C<$enable> is false, then the C<encode> method will not add any extra	355	If C<$enable> is false, then the C<encode> method will not add any extra
178	space at those places.	356	space at those places.
179		357
180	This setting has no effect when decoding JSON strings. You will also most	358	This setting has no effect when decoding JSON texts. You will also
181	likely combine this setting with C<space_after>.	359	most likely combine this setting with C<space_after>.
		360
		361	Example, space_before enabled, space_after and indent disabled:
		362
		363	{"key" :"value"}
182		364
183	=item $json = $json->space_after ([$enable])	365	=item $json = $json->space_after ([$enable])
		366
		367	=item $enabled = $json->get_space_after
184		368
185	If C<$enable> is true (or missing), then the C<encode> method will add an extra	369	If C<$enable> is true (or missing), then the C<encode> method will add an extra
186	optional space after the C<:> separating keys from values in JSON objects	370	optional space after the C<:> separating keys from values in JSON objects
187	and extra whitespace after the C<,> separating key-value pairs and array	371	and extra whitespace after the C<,> separating key-value pairs and array
188	members.	372	members.
189		373
190	If C<$enable> is false, then the C<encode> method will not add any extra	374	If C<$enable> is false, then the C<encode> method will not add any extra
191	space at those places.	375	space at those places.
192		376
193	This setting has no effect when decoding JSON strings.	377	This setting has no effect when decoding JSON texts.
		378
		379	Example, space_before and indent disabled, space_after enabled:
		380
		381	{"key": "value"}
		382
		383	=item $json = $json->relaxed ([$enable])
		384
		385	=item $enabled = $json->get_relaxed
		386
		387	If C<$enable> is true (or missing), then C<decode> will accept some
		388	extensions to normal JSON syntax (see below). C<encode> will not be
		389	affected in anyway. I<Be aware that this option makes you accept invalid
		390	JSON texts as if they were valid!>. I suggest only to use this option to
		391	parse application-specific files written by humans (configuration files,
		392	resource files etc.)
		393
		394	If C<$enable> is false (the default), then C<decode> will only accept
		395	valid JSON texts.
		396
		397	Currently accepted extensions are:
		398
		399	=over 4
		400
		401	=item * list items can have an end-comma
		402
		403	JSON I<separates> array elements and key-value pairs with commas. This
		404	can be annoying if you write JSON texts manually and want to be able to
		405	quickly append elements, so this extension accepts comma at the end of
		406	such items not just between them:
		407
		408	[
		409	1,
		410	2, <- this comma not normally allowed
		411	]
		412	{
		413	"k1": "v1",
		414	"k2": "v2", <- this comma not normally allowed
		415	}
		416
		417	=item * shell-style '#'-comments
		418
		419	Whenever JSON allows whitespace, shell-style comments are additionally
		420	allowed. They are terminated by the first carriage-return or line-feed
		421	character, after which more white-space and comments are allowed.
		422
		423	[
		424	1, # this comment not allowed in JSON
		425	# neither this one...
		426	]
		427
		428	=back
194		429
195	=item $json = $json->canonical ([$enable])	430	=item $json = $json->canonical ([$enable])
		431
		432	=item $enabled = $json->get_canonical
196		433
197	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	434	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
198	by sorting their keys. This is adding a comparatively high overhead.	435	by sorting their keys. This is adding a comparatively high overhead.
199		436
200	If C<$enable> is false, then the C<encode> method will output key-value	437	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	438	pairs in the order Perl stores them (which will likely change between runs
202	of the same script).	439	of the same script).
203		440
204	This option is useful if you want the same data structure to be encoded as	441	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,	442	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,	443	the same hash might be encoded differently even if contains the same data,
207	as key-value pairs have no inherent ordering in Perl.	444	as key-value pairs have no inherent ordering in Perl.
208		445
209	This setting has no effect when decoding JSON strings.	446	This setting has no effect when decoding JSON texts.
210		447
211	=item $json = $json->allow_nonref ([$enable])	448	=item $json = $json->allow_nonref ([$enable])
		449
		450	=item $enabled = $json->get_allow_nonref
212		451
213	If C<$enable> is true (or missing), then the C<encode> method can convert a	452	If C<$enable> is true (or missing), then the C<encode> method can convert a
214	non-reference into its corresponding string, number or null JSON value,	453	non-reference into its corresponding string, number or null JSON value,
215	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	454	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
216	values instead of croaking.	455	values instead of croaking.
217		456
218	If C<$enable> is false, then the C<encode> method will croak if it isn't	457	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	458	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	459	or array. Likewise, C<decode> will croak if given something that is not a
221	JSON object or array.	460	JSON object or array.
222		461
		462	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
		463	resulting in an invalid JSON text:
		464
		465	JSON::XS->new->allow_nonref->encode ("Hello, World!")
		466	=> "Hello, World!"
		467
		468	=item $json = $json->allow_unknown ([$enable])
		469
		470	=item $enabled = $json->get_allow_unknown
		471
		472	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		473	exception when it encounters values it cannot represent in JSON (for
		474	example, filehandles) but instead will encode a JSON C<null> value. Note
		475	that blessed objects are not included here and are handled separately by
		476	c<allow_nonref>.
		477
		478	If C<$enable> is false (the default), then C<encode> will throw an
		479	exception when it encounters anything it cannot encode as JSON.
		480
		481	This option does not affect C<decode> in any way, and it is recommended to
		482	leave it off unless you know your communications partner.
		483
		484	=item $json = $json->allow_blessed ([$enable])
		485
		486	=item $enabled = $json->get_allow_blessed
		487
		488	If C<$enable> is true (or missing), then the C<encode> method will not
		489	barf when it encounters a blessed reference. Instead, the value of the
		490	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		491	disabled or no C<TO_JSON> method found) or a representation of the
		492	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		493	encoded. Has no effect on C<decode>.
		494
		495	If C<$enable> is false (the default), then C<encode> will throw an
		496	exception when it encounters a blessed object.
		497
		498	=item $json = $json->convert_blessed ([$enable])
		499
		500	=item $enabled = $json->get_convert_blessed
		501
		502	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		503	blessed object, will check for the availability of the C<TO_JSON> method
		504	on the object's class. If found, it will be called in scalar context
		505	and the resulting scalar will be encoded instead of the object. If no
		506	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		507	to do.
		508
		509	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		510	returns other blessed objects, those will be handled in the same
		511	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		512	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		513	methods called by the Perl core (== not by the user of the object) are
		514	usually in upper case letters and to avoid collisions with any C<to_json>
		515	function or method.
		516
		517	This setting does not yet influence C<decode> in any way, but in the
		518	future, global hooks might get installed that influence C<decode> and are
		519	enabled by this setting.
		520
		521	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		522	to do when a blessed object is found.
		523
		524	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		525
		526	When C<$coderef> is specified, it will be called from C<decode> each
		527	time it decodes a JSON object. The only argument is a reference to the
		528	newly-created hash. If the code references returns a single scalar (which
		529	need not be a reference), this value (i.e. a copy of that scalar to avoid
		530	aliasing) is inserted into the deserialised data structure. If it returns
		531	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		532	original deserialised hash will be inserted. This setting can slow down
		533	decoding considerably.
		534
		535	When C<$coderef> is omitted or undefined, any existing callback will
		536	be removed and C<decode> will not change the deserialised hash in any
		537	way.
		538
		539	Example, convert all JSON objects into the integer 5:
		540
		541	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		542	# returns [5]
		543	$js->decode ('[{}]')
		544	# throw an exception because allow_nonref is not enabled
		545	# so a lone 5 is not allowed.
		546	$js->decode ('{"a":1, "b":2}');
		547
		548	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		549
		550	Works remotely similar to C<filter_json_object>, but is only called for
		551	JSON objects having a single key named C<$key>.
		552
		553	This C<$coderef> is called before the one specified via
		554	C<filter_json_object>, if any. It gets passed the single value in the JSON
		555	object. If it returns a single value, it will be inserted into the data
		556	structure. If it returns nothing (not even C<undef> but the empty list),
		557	the callback from C<filter_json_object> will be called next, as if no
		558	single-key callback were specified.
		559
		560	If C<$coderef> is omitted or undefined, the corresponding callback will be
		561	disabled. There can only ever be one callback for a given key.
		562
		563	As this callback gets called less often then the C<filter_json_object>
		564	one, decoding speed will not usually suffer as much. Therefore, single-key
		565	objects make excellent targets to serialise Perl objects into, especially
		566	as single-key JSON objects are as close to the type-tagged value concept
		567	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		568	support this in any way, so you need to make sure your data never looks
		569	like a serialised Perl hash.
		570
		571	Typical names for the single object key are C<__class_whatever__>, or
		572	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		573	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		574	with real hashes.
		575
		576	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		577	into the corresponding C<< $WIDGET{<id>} >> object:
		578
		579	# return whatever is in $WIDGET{5}:
		580	JSON::XS
		581	->new
		582	->filter_json_single_key_object (__widget__ => sub {
		583	$WIDGET{ $_[0] }
		584	})
		585	->decode ('{"__widget__": 5')
		586
		587	# this can be used with a TO_JSON method in some "widget" class
		588	# for serialisation to json:
		589	sub WidgetBase::TO_JSON {
		590	my ($self) = @_;
		591
		592	unless ($self->{id}) {
		593	$self->{id} = ..get..some..id..;
		594	$WIDGET{$self->{id}} = $self;
		595	}
		596
		597	{ __widget__ => $self->{id} }
		598	}
		599
223	=item $json = $json->shrink ([$enable])	600	=item $json = $json->shrink ([$enable])
224		601
		602	=item $enabled = $json->get_shrink
		603
225	Perl usually over-allocates memory a bit when allocating space for	604	Perl usually over-allocates memory a bit when allocating space for
226	strings. This flag optionally resizes strings generated by either	605	strings. This flag optionally resizes strings generated by either
227	C<encode> or C<decode> to their minimum size possible. This can save	606	C<encode> or C<decode> to their minimum size possible. This can save
228	memory when your JSON strings are either very very long or you have many	607	memory when your JSON texts are either very very long or you have many
229	short strings. It will also try to downgrade any strings to octet-form	608	short strings. It will also try to downgrade any strings to octet-form
230	if possible: perl stores strings internally either in an encoding called	609	if possible: perl stores strings internally either in an encoding called
231	UTF-X or in octet-form. The latter cannot store everything but uses less	610	UTF-X or in octet-form. The latter cannot store everything but uses less
232	space in general.	611	space in general (and some buggy Perl or C code might even rely on that
		612	internal representation being used).
233		613
		614	The actual definition of what shrink does might change in future versions,
		615	but it will always try to save space at the expense of time.
		616
234	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	617	If C<$enable> is true (or missing), the string returned by C<encode> will
235	while all strings generated by C<decode> will also be shrunk-to-fit.	618	be shrunk-to-fit, while all strings generated by C<decode> will also be
		619	shrunk-to-fit.
236		620
237	If C<$enable> is false, then the normal perl allocation algorithms are used.	621	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.	622	If you work with your data, then this is likely to be faster.
239		623
240	In the future, this setting might control other things, such as converting	624	In the future, this setting might control other things, such as converting
241	strings that look like integers or floats into integers or floats	625	strings that look like integers or floats into integers or floats
242	internally (there is no difference on the Perl level), saving space.	626	internally (there is no difference on the Perl level), saving space.
243		627
		628	=item $json = $json->max_depth ([$maximum_nesting_depth])
		629
		630	=item $max_depth = $json->get_max_depth
		631
		632	Sets the maximum nesting level (default C<512>) accepted while encoding
		633	or decoding. If a higher nesting level is detected in JSON text or a Perl
		634	data structure, then the encoder and decoder will stop and croak at that
		635	point.
		636
		637	Nesting level is defined by number of hash- or arrayrefs that the encoder
		638	needs to traverse to reach a given point or the number of C<{> or C<[>
		639	characters without their matching closing parenthesis crossed to reach a
		640	given character in a string.
		641
		642	Setting the maximum depth to one disallows any nesting, so that ensures
		643	that the object is only a single hash/object or array.
		644
		645	If no argument is given, the highest possible setting will be used, which
		646	is rarely useful.
		647
		648	Note that nesting is implemented by recursion in C. The default value has
		649	been chosen to be as large as typical operating systems allow without
		650	crashing.
		651
		652	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		653
		654	=item $json = $json->max_size ([$maximum_string_size])
		655
		656	=item $max_size = $json->get_max_size
		657
		658	Set the maximum length a JSON text may have (in bytes) where decoding is
		659	being attempted. The default is C<0>, meaning no limit. When C<decode>
		660	is called on a string that is longer then this many bytes, it will not
		661	attempt to decode the string but throw an exception. This setting has no
		662	effect on C<encode> (yet).
		663
		664	If no argument is given, the limit check will be deactivated (same as when
		665	C<0> is specified).
		666
		667	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		668
244	=item $json_string = $json->encode ($perl_scalar)	669	=item $json_text = $json->encode ($perl_scalar)
245		670
246	Converts the given Perl data structure (a simple scalar or a reference	671	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	672	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	673	converted into JSON string or number sequences, while references to arrays
249	become JSON arrays and references to hashes become JSON objects. Undefined	674	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>	675	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
251	nor C<false> values will be generated.	676	nor C<false> values will be generated.
252		677
253	=item $perl_scalar = $json->decode ($json_string)	678	=item $perl_scalar = $json->decode ($json_text)
254		679
255	The opposite of C<encode>: expects a JSON string and tries to parse it,	680	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.	681	returning the resulting simple scalar or reference. Croaks on error.
257		682
258	JSON numbers and strings become simple Perl scalars. JSON arrays become	683	JSON numbers and strings become simple Perl scalars. JSON arrays become
259	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	684	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>.	685	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
261		686
		687	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		688
		689	This works like the C<decode> method, but instead of raising an exception
		690	when there is trailing garbage after the first JSON object, it will
		691	silently stop parsing there and return the number of characters consumed
		692	so far.
		693
		694	This is useful if your JSON texts are not delimited by an outer protocol
		695	(which is not the brightest thing to do in the first place) and you need
		696	to know where the JSON text ends.
		697
		698	JSON::XS->new->decode_prefix ("[1] the tail")
		699	=> ([], 3)
		700
262	=back	701	=back
263		702
264	=head1 COMPARISON
265		703
266	As already mentioned, this module was created because none of the existing	704	=head1 INCREMENTAL PARSING
267	JSON modules could be made to work correctly. First I will describe the	705
268	problems (or pleasures) I encountered with various existing JSON modules,	706	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	707	texts. While this module always has to keep both JSON text and resulting
270	from any of these problems or limitations.	708	Perl data structure in memory at one time, it does allow you to parse a
		709	JSON stream incrementally. It does so by accumulating text until it has
		710	a full JSON object, which it then can decode. This process is similar to
		711	using C<decode_prefix> to see if a full JSON object is available, but is
		712	much more efficient (JSON::XS will only attempt to parse the JSON text
		713	once it is sure it has enough text to get a decisive result, using a very
		714	simple but truly incremental parser).
		715
		716	The following two methods deal with this.
271		717
272	=over 4	718	=over 4
273		719
274	=item JSON 1.07	720	=item [void, scalar or list context] = $json->incr_parse ([$string])
275		721
276	Slow (but very portable, as it is written in pure Perl).	722	This is the central parsing function. It can both append new text and
		723	extract objects from the stream accumulated so far (both of these
		724	functions are optional).
277		725
278	Undocumented/buggy Unicode handling (how JSON handles unicode values is	726	If C<$string> is given, then this string is appended to the already
279	undocumented. One can get far by feeding it unicode strings and doing	727	existing JSON fragment stored in the C<$json> object.
280	en-/decoding oneself, but unicode escapes are not working properly).
281		728
282	No roundtripping (strings get clobbered if they look like numbers, e.g.	729	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	730	return without doing anything further. This can be used to add more text
284	decode into the number 2.	731	in as many chunks as you want.
285		732
286	=item JSON::PC 0.01	733	If the method is called in scalar context, then it will try to extract
		734	exactly I<one> JSON object. If that is successful, it will return this
		735	object, otherwise it will return C<undef>. If there is a parse error,
		736	this method will croak just as C<decode> would do (one can then use
		737	C<incr_skip> to skip the errornous part). This is the most common way of
		738	using the method.
287		739
288	Very fast.	740	And finally, in list context, it will try to extract as many objects
		741	from the stream as it can find and return them, or the empty list
		742	otherwise. For this to work, there must be no separators between the JSON
		743	objects or arrays, instead they must be concatenated back-to-back. If
		744	an error occurs, an exception will be raised as in the scalar context
		745	case. Note that in this case, any previously-parsed JSON texts will be
		746	lost.
289		747
290	Undocumented/buggy Unicode handling.	748	=item $lvalue_string = $json->incr_text
291		749
292	No roundtripping.	750	This method returns the currently stored JSON fragment as an lvalue, that
		751	is, you can manipulate it. This I<only> works when a preceding call to
		752	C<incr_parse> in I<scalar context> successfully returned an object. Under
		753	all other circumstances you must not call this function (I mean it.
		754	although in simple tests it might actually work, it I<will> fail under
		755	real world conditions). As a special exception, you can also call this
		756	method before having parsed anything.
293		757
294	Has problems handling many Perl values (e.g. regex results and other magic	758	This function is useful in two cases: a) finding the trailing text after a
295	values will make it croak).	759	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		760	(such as commas).
296		761
297	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	762	=item $json->incr_skip
298	which is not a valid JSON string.
299		763
300	Unmaintained (maintainer unresponsive for many months, bugs are not	764	This will reset the state of the incremental parser and will remove the
301	getting fixed).	765	parsed text from the input buffer. This is useful after C<incr_parse>
302		766	died, in which case the input buffer and incremental parser state is left
303	=item JSON::Syck 0.21	767	unchanged, to skip the text parsed so far and to reset the parse state.
304
305	Very buggy (often crashes).
306
307	Very inflexible (no human-readable format supported, format pretty much
308	undocumented. I need at least a format for easy reading by humans and a
309	single-line compact format for use in a protocol, and preferably a way to
310	generate ASCII-only JSON strings).
311
312	Completely broken (and confusingly documented) Unicode handling (unicode
313	escapes are not working properly, you need to set ImplicitUnicode to
314	I<different> values on en- and decoding to get symmetric behaviour).
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		768
348	=back	769	=back
		770
		771	=head2 LIMITATIONS
		772
		773	All options that affect decoding are supported, except
		774	C<allow_nonref>. The reason for this is that it cannot be made to
		775	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		776	them back to back and still decode them perfectly. This does not hold true
		777	for JSON numbers, however.
		778
		779	For example, is the string C<1> a single JSON number, or is it simply the
		780	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		781	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		782	takes the conservative route and disallows this case.
		783
		784	=head2 EXAMPLES
		785
		786	Some examples will make all this clearer. First, a simple example that
		787	works similarly to C<decode_prefix>: We want to decode the JSON object at
		788	the start of a string and identify the portion after the JSON object:
		789
		790	my $text = "[1,2,3] hello";
		791
		792	my $json = new JSON::XS;
		793
		794	my $obj = $json->incr_parse ($text)
		795	or die "expected JSON object or array at beginning of string";
		796
		797	my $tail = $json->incr_text;
		798	# $tail now contains " hello"
		799
		800	Easy, isn't it?
		801
		802	Now for a more complicated example: Imagine a hypothetical protocol where
		803	you read some requests from a TCP stream, and each request is a JSON
		804	array, without any separation between them (in fact, it is often useful to
		805	use newlines as "separators", as these get interpreted as whitespace at
		806	the start of the JSON text, which makes it possible to test said protocol
		807	with C<telnet>...).
		808
		809	Here is how you'd do it (it is trivial to write this in an event-based
		810	manner):
		811
		812	my $json = new JSON::XS;
		813
		814	# read some data from the socket
		815	while (sysread $socket, my $buf, 4096) {
		816
		817	# split and decode as many requests as possible
		818	for my $request ($json->incr_parse ($buf)) {
		819	# act on the $request
		820	}
		821	}
		822
		823	Another complicated example: Assume you have a string with JSON objects
		824	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		825	[3]>). To parse them, we have to skip the commas between the JSON texts,
		826	and here is where the lvalue-ness of C<incr_text> comes in useful:
		827
		828	my $text = "[1],[2], [3]";
		829	my $json = new JSON::XS;
		830
		831	# void context, so no parsing done
		832	$json->incr_parse ($text);
		833
		834	# now extract as many objects as possible. note the
		835	# use of scalar context so incr_text can be called.
		836	while (my $obj = $json->incr_parse) {
		837	# do something with $obj
		838
		839	# now skip the optional comma
		840	$json->incr_text =~ s/^ \s* , //x;
		841	}
		842
		843	Now lets go for a very complex example: Assume that you have a gigantic
		844	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		845	but you cannot load it into memory fully (this has actually happened in
		846	the real world :).
		847
		848	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		849	can still help you: You implement a (very simple) array parser and let
		850	JSON decode the array elements, which are all full JSON objects on their
		851	own (this wouldn't work if the array elements could be JSON numbers, for
		852	example):
		853
		854	my $json = new JSON::XS;
		855
		856	# open the monster
		857	open my $fh, "<bigfile.json"
		858	or die "bigfile: $!";
		859
		860	# first parse the initial "["
		861	for (;;) {
		862	sysread $fh, my $buf, 65536
		863	or die "read error: $!";
		864	$json->incr_parse ($buf); # void context, so no parsing
		865
		866	# Exit the loop once we found and removed(!) the initial "[".
		867	# In essence, we are (ab-)using the $json object as a simple scalar
		868	# we append data to.
		869	last if $json->incr_text =~ s/^ \s* \[ //x;
		870	}
		871
		872	# now we have the skipped the initial "[", so continue
		873	# parsing all the elements.
		874	for (;;) {
		875	# in this loop we read data until we got a single JSON object
		876	for (;;) {
		877	if (my $obj = $json->incr_parse) {
		878	# do something with $obj
		879	last;
		880	}
		881
		882	# add more data
		883	sysread $fh, my $buf, 65536
		884	or die "read error: $!";
		885	$json->incr_parse ($buf); # void context, so no parsing
		886	}
		887
		888	# in this loop we read data until we either found and parsed the
		889	# separating "," between elements, or the final "]"
		890	for (;;) {
		891	# first skip whitespace
		892	$json->incr_text =~ s/^\s*//;
		893
		894	# if we find "]", we are done
		895	if ($json->incr_text =~ s/^\]//) {
		896	print "finished.\n";
		897	exit;
		898	}
		899
		900	# if we find ",", we can continue with the next element
		901	if ($json->incr_text =~ s/^,//) {
		902	last;
		903	}
		904
		905	# if we find anything else, we have a parse error!
		906	if (length $json->incr_text) {
		907	die "parse error near ", $json->incr_text;
		908	}
		909
		910	# else add more data
		911	sysread $fh, my $buf, 65536
		912	or die "read error: $!";
		913	$json->incr_parse ($buf); # void context, so no parsing
		914	}
		915
		916	This is a complex example, but most of the complexity comes from the fact
		917	that we are trying to be correct (bear with me if I am wrong, I never ran
		918	the above example :).
		919
		920
		921
		922	=head1 MAPPING
		923
		924	This section describes how JSON::XS maps Perl values to JSON values and
		925	vice versa. These mappings are designed to "do the right thing" in most
		926	circumstances automatically, preserving round-tripping characteristics
		927	(what you put in comes out as something equivalent).
		928
		929	For the more enlightened: note that in the following descriptions,
		930	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		931	refers to the abstract Perl language itself.
		932
		933
		934	=head2 JSON -> PERL
		935
		936	=over 4
		937
		938	=item object
		939
		940	A JSON object becomes a reference to a hash in Perl. No ordering of object
		941	keys is preserved (JSON does not preserve object key ordering itself).
		942
		943	=item array
		944
		945	A JSON array becomes a reference to an array in Perl.
		946
		947	=item string
		948
		949	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		950	are represented by the same codepoints in the Perl string, so no manual
		951	decoding is necessary.
		952
		953	=item number
		954
		955	A JSON number becomes either an integer, numeric (floating point) or
		956	string scalar in perl, depending on its range and any fractional parts. On
		957	the Perl level, there is no difference between those as Perl handles all
		958	the conversion details, but an integer may take slightly less memory and
		959	might represent more values exactly than floating point numbers.
		960
		961	If the number consists of digits only, JSON::XS will try to represent
		962	it as an integer value. If that fails, it will try to represent it as
		963	a numeric (floating point) value if that is possible without loss of
		964	precision. Otherwise it will preserve the number as a string value (in
		965	which case you lose roundtripping ability, as the JSON number will be
		966	re-encoded toa JSON string).
		967
		968	Numbers containing a fractional or exponential part will always be
		969	represented as numeric (floating point) values, possibly at a loss of
		970	precision (in which case you might lose perfect roundtripping ability, but
		971	the JSON number will still be re-encoded as a JSON number).
		972
		973	=item true, false
		974
		975	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
		976	respectively. They are overloaded to act almost exactly like the numbers
		977	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
		978	the C<JSON::XS::is_bool> function.
		979
		980	=item null
		981
		982	A JSON null atom becomes C<undef> in Perl.
		983
		984	=back
		985
		986
		987	=head2 PERL -> JSON
		988
		989	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		990	truly typeless language, so we can only guess which JSON type is meant by
		991	a Perl value.
		992
		993	=over 4
		994
		995	=item hash references
		996
		997	Perl hash references become JSON objects. As there is no inherent ordering
		998	in hash keys (or JSON objects), they will usually be encoded in a
		999	pseudo-random order that can change between runs of the same program but
		1000	stays generally the same within a single run of a program. JSON::XS can
		1001	optionally sort the hash keys (determined by the I<canonical> flag), so
		1002	the same datastructure will serialise to the same JSON text (given same
		1003	settings and version of JSON::XS), but this incurs a runtime overhead
		1004	and is only rarely useful, e.g. when you want to compare some JSON text
		1005	against another for equality.
		1006
		1007	=item array references
		1008
		1009	Perl array references become JSON arrays.
		1010
		1011	=item other references
		1012
		1013	Other unblessed references are generally not allowed and will cause an
		1014	exception to be thrown, except for references to the integers C<0> and
		1015	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		1016	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		1017
		1018	encode_json [\0, JSON::XS::true] # yields [false,true]
		1019
		1020	=item JSON::XS::true, JSON::XS::false
		1021
		1022	These special values become JSON true and JSON false values,
		1023	respectively. You can also use C<\1> and C<\0> directly if you want.
		1024
		1025	=item blessed objects
		1026
		1027	Blessed objects are not directly representable in JSON. See the
		1028	C<allow_blessed> and C<convert_blessed> methods on various options on
		1029	how to deal with this: basically, you can choose between throwing an
		1030	exception, encoding the reference as if it weren't blessed, or provide
		1031	your own serialiser method.
		1032
		1033	=item simple scalars
		1034
		1035	Simple Perl scalars (any scalar that is not a reference) are the most
		1036	difficult objects to encode: JSON::XS will encode undefined scalars as
		1037	JSON C<null> values, scalars that have last been used in a string context
		1038	before encoding as JSON strings, and anything else as number value:
		1039
		1040	# dump as number
		1041	encode_json [2] # yields [2]
		1042	encode_json [-3.0e17] # yields [-3e+17]
		1043	my $value = 5; encode_json [$value] # yields [5]
		1044
		1045	# used as string, so dump as string
		1046	print $value;
		1047	encode_json [$value] # yields ["5"]
		1048
		1049	# undef becomes null
		1050	encode_json [undef] # yields [null]
		1051
		1052	You can force the type to be a JSON string by stringifying it:
		1053
		1054	my $x = 3.1; # some variable containing a number
		1055	"$x"; # stringified
		1056	$x .= ""; # another, more awkward way to stringify
		1057	print $x; # perl does it for you, too, quite often
		1058
		1059	You can force the type to be a JSON number by numifying it:
		1060
		1061	my $x = "3"; # some variable containing a string
		1062	$x += 0; # numify it, ensuring it will be dumped as a number
		1063	$x *= 1; # same thing, the choice is yours.
		1064
		1065	You can not currently force the type in other, less obscure, ways. Tell me
		1066	if you need this capability (but don't forget to explain why it's needed
		1067	:).
		1068
		1069	=back
		1070
		1071
		1072	=head1 ENCODING/CODESET FLAG NOTES
		1073
		1074	The interested reader might have seen a number of flags that signify
		1075	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1076	some confusion on what these do, so here is a short comparison:
		1077
		1078	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1079	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1080	control whether C<encode> escapes character values outside their respective
		1081	codeset range. Neither of these flags conflict with each other, although
		1082	some combinations make less sense than others.
		1083
		1084	Care has been taken to make all flags symmetrical with respect to
		1085	C<encode> and C<decode>, that is, texts encoded with any combination of
		1086	these flag values will be correctly decoded when the same flags are used
		1087	- in general, if you use different flag settings while encoding vs. when
		1088	decoding you likely have a bug somewhere.
		1089
		1090	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1091	simply an abstract set of character-codepoint pairs, while an encoding
		1092	takes those codepoint numbers and I<encodes> them, in our case into
		1093	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1094	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1095	the same time, which can be confusing.
		1096
		1097	=over 4
		1098
		1099	=item C<utf8> flag disabled
		1100
		1101	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1102	and expect Unicode strings, that is, characters with high ordinal Unicode
		1103	values (> 255) will be encoded as such characters, and likewise such
		1104	characters are decoded as-is, no canges to them will be done, except
		1105	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1106	respectively (to Perl, these are the same thing in strings unless you do
		1107	funny/weird/dumb stuff).
		1108
		1109	This is useful when you want to do the encoding yourself (e.g. when you
		1110	want to have UTF-16 encoded JSON texts) or when some other layer does
		1111	the encoding for you (for example, when printing to a terminal using a
		1112	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1113	to UTF-8 encode your data first and have Perl encode it another time).
		1114
		1115	=item C<utf8> flag enabled
		1116
		1117	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1118	characters using the corresponding UTF-8 multi-byte sequence, and will
		1119	expect your input strings to be encoded as UTF-8, that is, no "character"
		1120	of the input string must have any value > 255, as UTF-8 does not allow
		1121	that.
		1122
		1123	The C<utf8> flag therefore switches between two modes: disabled means you
		1124	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1125	octet/binary string in Perl.
		1126
		1127	=item C<latin1> or C<ascii> flags enabled
		1128
		1129	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1130	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1131	characters as specified by the C<utf8> flag.
		1132
		1133	If C<utf8> is disabled, then the result is also correctly encoded in those
		1134	character sets (as both are proper subsets of Unicode, meaning that a
		1135	Unicode string with all character values < 256 is the same thing as a
		1136	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1137	the same thing as an ASCII string in Perl).
		1138
		1139	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1140	regardless of these flags, just some more characters will be escaped using
		1141	C<\uXXXX> then before.
		1142
		1143	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1144	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1145	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1146	a subset of Unicode), while ASCII is.
		1147
		1148	Surprisingly, C<decode> will ignore these flags and so treat all input
		1149	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1150	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1151	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1152
		1153	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1154	they only govern when the JSON output engine escapes a character or not.
		1155
		1156	The main use for C<latin1> is to relatively efficiently store binary data
		1157	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1158
		1159	The main use for C<ascii> is to force the output to not contain characters
		1160	with values > 127, which means you can interpret the resulting string
		1161	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1162	8-bit-encoding, and still get the same data structure back. This is useful
		1163	when your channel for JSON transfer is not 8-bit clean or the encoding
		1164	might be mangled in between (e.g. in mail), and works because ASCII is a
		1165	proper subset of most 8-bit and multibyte encodings in use in the world.
		1166
		1167	=back
		1168
		1169
		1170	=head2 JSON and YAML
		1171
		1172	You often hear that JSON is a subset of YAML. This is, however, a mass
		1173	hysteria(*) and very far from the truth (as of the time of this writing),
		1174	so let me state it clearly: I<in general, there is no way to configure
		1175	JSON::XS to output a data structure as valid YAML> that works in all
		1176	cases.
		1177
		1178	If you really must use JSON::XS to generate YAML, you should use this
		1179	algorithm (subject to change in future versions):
		1180
		1181	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1182	my $yaml = $to_yaml->encode ($ref) . "\n";
		1183
		1184	This will I<usually> generate JSON texts that also parse as valid
		1185	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1186	lengths that JSON doesn't have and also has different and incompatible
		1187	unicode handling, so you should make sure that your hash keys are
		1188	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1189	you do not have characters with codepoint values outside the Unicode BMP
		1190	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1191	strings (which JSON::XS does not I<currently> generate, but other JSON
		1192	generators might).
		1193
		1194	There might be other incompatibilities that I am not aware of (or the YAML
		1195	specification has been changed yet again - it does so quite often). In
		1196	general you should not try to generate YAML with a JSON generator or vice
		1197	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1198	high that you will run into severe interoperability problems when you
		1199	least expect it.
		1200
		1201	=over 4
		1202
		1203	=item (*)
		1204
		1205	I have been pressured multiple times by Brian Ingerson (one of the
		1206	authors of the YAML specification) to remove this paragraph, despite him
		1207	acknowledging that the actual incompatibilities exist. As I was personally
		1208	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1209	educate people about these issues, so others do not run into the same
		1210	problem again and again. After this, Brian called me a (quote)I<complete
		1211	and worthless idiot>(unquote).
		1212
		1213	In my opinion, instead of pressuring and insulting people who actually
		1214	clarify issues with YAML and the wrong statements of some of its
		1215	proponents, I would kindly suggest reading the JSON spec (which is not
		1216	that difficult or long) and finally make YAML compatible to it, and
		1217	educating users about the changes, instead of spreading lies about the
		1218	real compatibility for many I<years> and trying to silence people who
		1219	point out that it isn't true.
		1220
		1221	=back
		1222
349		1223
350	=head2 SPEED	1224	=head2 SPEED
351		1225
352	It seems that JSON::XS is surprisingly fast, as shown in the following	1226	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	1227	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	1228	in the JSON::XS distribution, to make it easy to compare on your own
355	system.	1229	system.
356		1230
357	First is a comparison between various modules using a very simple JSON	1231	First comes a comparison between various modules using
		1232	a very short single-line JSON string (also available at
		1233	L<http://dist.schmorp.de/misc/json/short.json>).
		1234
		1235	{"method": "handleMessage", "params": ["user1",
		1236	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1237	true, false]}
		1238
358	string, showing the number of encodes/decodes per second (JSON::XS is	1239	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	1240	the functional interface, while JSON::XS/2 uses the OO interface
360	pretty-printing and hashkey sorting enabled).	1241	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1242	shrink). Higher is better:
361		1243
362	module | encode | decode |	1244	module | encode | decode |
363	-----------|------------|------------|	1245	-----------|------------|------------|
364	JSON | 14006 | 6820 |	1246	JSON 1.x | 4990.842 | 4088.813 |
365	JSON::DWIW | 200937 | 120386 |	1247	JSON::DWIW | 51653.990 | 71575.154 |
366	JSON::PC | 85065 | 129366 |	1248	JSON::PC | 65948.176 | 74631.744 |
367	JSON::Syck | 59898 | 44232 |	1249	JSON::PP | 8931.652 | 3817.168 |
368	JSON::XS | 1171478 | 342435 |	1250	JSON::Syck | 24877.248 | 27776.848 |
369	JSON::XS/2 | 730760 | 328714 |	1251	JSON::XS | 388361.481 | 227951.304 |
		1252	JSON::XS/2 | 227951.304 | 218453.333 |
		1253	JSON::XS/3 | 338250.323 | 218453.333 |
		1254	Storable | 16500.016 | 135300.129 |
370	-----------+------------+------------+	1255	-----------+------------+------------+
371		1256
372	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1257	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
		1258	about three times faster on decoding, and over forty times faster
373	times faster than JSON, even with pretty-printing and key sorting.	1259	than JSON, even with pretty-printing and key sorting. It also compares
		1260	favourably to Storable for small amounts of data.
374		1261
375	Using a longer test string (roughly 8KB, generated from Yahoo! Locals	1262	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
376	search API (http://nanoref.com/yahooapis/mgPdGg):	1263	search API (L<http://dist.schmorp.de/misc/json/long.json>).
377		1264
378	module | encode | decode |	1265	module | encode | decode |
379	-----------|------------|------------|	1266	-----------|------------|------------|
380	JSON | 673 | 38 |	1267	JSON 1.x | 55.260 | 34.971 |
381	JSON::DWIW | 5271 | 770 |	1268	JSON::DWIW | 825.228 | 1082.513 |
382	JSON::PC | 9901 | 2491 |	1269	JSON::PC | 3571.444 | 2394.829 |
383	JSON::Syck | 2360 | 786 |	1270	JSON::PP | 210.987 | 32.574 |
384	JSON::XS | 37398 | 3202 |	1271	JSON::Syck | 552.551 | 787.544 |
385	JSON::XS/2 | 13765 | 3153 |	1272	JSON::XS | 5780.463 | 4854.519 |
		1273	JSON::XS/2 | 3869.998 | 4798.975 |
		1274	JSON::XS/3 | 5862.880 | 4798.975 |
		1275	Storable | 4445.002 | 5235.027 |
386	-----------+------------+------------+	1276	-----------+------------+------------+
387		1277
388	Again, JSON::XS leads by far in the encoding case, while still beating	1278	Again, JSON::XS leads by far (except for Storable which non-surprisingly
389	every other module in the decoding case.	1279	decodes faster).
390		1280
391	Last example is an almost 8MB large hash with many large binary values	1281	On large strings containing lots of high Unicode characters, some modules
392	(PNG files), resulting in a lot of escaping:	1282	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1283	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1284	to decode or encode properly, so it was impossible to prepare a fair
		1285	comparison table for that case.
		1286
		1287
		1288	=head1 SECURITY CONSIDERATIONS
		1289
		1290	When you are using JSON in a protocol, talking to untrusted potentially
		1291	hostile creatures requires relatively few measures.
		1292
		1293	First of all, your JSON decoder should be secure, that is, should not have
		1294	any buffer overflows. Obviously, this module should ensure that and I am
		1295	trying hard on making that true, but you never know.
		1296
		1297	Second, you need to avoid resource-starving attacks. That means you should
		1298	limit the size of JSON texts you accept, or make sure then when your
		1299	resources run out, that's just fine (e.g. by using a separate process that
		1300	can crash safely). The size of a JSON text in octets or characters is
		1301	usually a good indication of the size of the resources required to decode
		1302	it into a Perl structure. While JSON::XS can check the size of the JSON
		1303	text, it might be too late when you already have it in memory, so you
		1304	might want to check the size before you accept the string.
		1305
		1306	Third, JSON::XS recurses using the C stack when decoding objects and
		1307	arrays. The C stack is a limited resource: for instance, on my amd64
		1308	machine with 8MB of stack size I can decode around 180k nested arrays but
		1309	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1310	to free the temporary). If that is exceeded, the program crashes. To be
		1311	conservative, the default nesting limit is set to 512. If your process
		1312	has a smaller stack, you should adjust this setting accordingly with the
		1313	C<max_depth> method.
		1314
		1315	Something else could bomb you, too, that I forgot to think of. In that
		1316	case, you get to keep the pieces. I am always open for hints, though...
		1317
		1318	Also keep in mind that JSON::XS might leak contents of your Perl data
		1319	structures in its error messages, so when you serialise sensitive
		1320	information you might want to make sure that exceptions thrown by JSON::XS
		1321	will not end up in front of untrusted eyes.
		1322
		1323	If you are using JSON::XS to return packets to consumption
		1324	by JavaScript scripts in a browser you should have a look at
		1325	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1326	you are vulnerable to some common attack vectors (which really are browser
		1327	design bugs, but it is still you who will have to deal with it, as major
		1328	browser developers care only for features, not about getting security
		1329	right).
		1330
		1331
		1332	=head1 THREADS
		1333
		1334	This module is I<not> guaranteed to be thread safe and there are no
		1335	plans to change this until Perl gets thread support (as opposed to the
		1336	horribly slow so-called "threads" which are simply slow and bloated
		1337	process simulations - use fork, it's I<much> faster, cheaper, better).
		1338
		1339	(It might actually work, but you have been warned).
		1340
393		1341
394	=head1 BUGS	1342	=head1 BUGS
395		1343
396	While the goal of this module is to be correct, that unfortunately does	1344	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	1345	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	1346	keep reporting bugs they will be fixed swiftly, though.
399	be fixed swiftly, though.	1347
		1348	Please refrain from using rt.cpan.org or any other bug reporting
		1349	service. I put the contact address into my modules for a reason.
400		1350
401	=cut	1351	=cut
402		1352
		1353	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1354	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1355
		1356	sub true() { $true }
		1357	sub false() { $false }
		1358
		1359	sub is_bool($) {
		1360	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1361	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1362	}
		1363
		1364	XSLoader::load "JSON::XS", $VERSION;
		1365
		1366	package JSON::XS::Boolean;
		1367
		1368	use overload
		1369	"0+" => sub { ${$_[0]} },
		1370	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1371	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1372	fallback => 1;
		1373
403	1;	1374	1;
		1375
		1376	=head1 SEE ALSO
		1377
		1378	The F<json_xs> command line utility for quick experiments.
404		1379
405	=head1 AUTHOR	1380	=head1 AUTHOR
406		1381
407	Marc Lehmann <schmorp@schmorp.de>	1382	Marc Lehmann <schmorp@schmorp.de>
408	http://home.schmorp.de/	1383	http://home.schmorp.de/

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