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Revision 1.7 by root, Fri Mar 23 15:10:55 2007 UTC vs.
Revision 1.136 by root, Wed Jul 27 15:53:40 2011 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
4		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 and Perl, the deserialised data structure is identical on the Perl
35	(e.g. the string "2.0" doesn't suddenly become "2").	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
		71	it looks like a number). There I<are> minor exceptions to this, read the
		72	MAPPING 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	use common::sense;
		105
64	$VERSION = '0.2';	106	our $VERSION = '2.31';
65	@ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
66		108
67	@EXPORT = qw(to_json from_json);	109	our @EXPORT = qw(encode_json decode_json to_json from_json);
68	require Exporter;
69		110
		111	sub to_json($) {
70	require XSLoader;	112	require Carp;
71	XSLoader::load JSON::XS::, $VERSION;	113	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
72	}	114	}
73		115
		116	sub from_json($) {
		117	require Carp;
		118	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
		119	}
		120
		121	use Exporter;
		122	use XSLoader;
		123
74	=head1 FUNCTIONAL INTERFACE	124	=head1 FUNCTIONAL INTERFACE
75		125
76	The following convinience methods are provided by this module. They are	126	The following convenience methods are provided by this module. They are
77	exported by default:	127	exported by default:
78		128
79	=over 4	129	=over 4
80		130
81	=item $json_string = to_json $perl_scalar	131	=item $json_text = encode_json $perl_scalar
82		132
83	Converts the given Perl data structure (a simple scalar or a reference to	133	Converts the given Perl data structure to a UTF-8 encoded, binary string
84	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	134	(that is, the string contains octets only). Croaks on error.
85	octets only). Croaks on error.
86		135
87	This function call is functionally identical to C<< JSON::XS->new->utf8	136	This function call is functionally identical to:
88	(1)->encode ($perl_scalar) >>.
89		137
		138	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		139
		140	Except being faster.
		141
90	=item $perl_scalar = from_json $json_string	142	=item $perl_scalar = decode_json $json_text
91		143
92	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	144	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
93	parse that as an UTF-8 encoded JSON string, returning the resulting simple	145	to parse that as an UTF-8 encoded JSON text, returning the resulting
94	scalar or reference. Croaks on error.	146	reference. Croaks on error.
95		147
96	This function call is functionally identical to C<< JSON::XS->new->utf8	148	This function call is functionally identical to:
97	(1)->decode ($json_string) >>.	149
		150	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		151
		152	Except being faster.
		153
		154	=item $is_boolean = JSON::XS::is_bool $scalar
		155
		156	Returns true if the passed scalar represents either JSON::XS::true or
		157	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		158	and are used to represent JSON C<true> and C<false> values in Perl.
		159
		160	See MAPPING, below, for more information on how JSON values are mapped to
		161	Perl.
98		162
99	=back	163	=back
		164
		165
		166	=head1 A FEW NOTES ON UNICODE AND PERL
		167
		168	Since this often leads to confusion, here are a few very clear words on
		169	how Unicode works in Perl, modulo bugs.
		170
		171	=over 4
		172
		173	=item 1. Perl strings can store characters with ordinal values > 255.
		174
		175	This enables you to store Unicode characters as single characters in a
		176	Perl string - very natural.
		177
		178	=item 2. Perl does I<not> associate an encoding with your strings.
		179
		180	... until you force it to, e.g. when matching it against a regex, or
		181	printing the scalar to a file, in which case Perl either interprets your
		182	string as locale-encoded text, octets/binary, or as Unicode, depending
		183	on various settings. In no case is an encoding stored together with your
		184	data, it is I<use> that decides encoding, not any magical meta data.
		185
		186	=item 3. The internal utf-8 flag has no meaning with regards to the
		187	encoding of your string.
		188
		189	Just ignore that flag unless you debug a Perl bug, a module written in
		190	XS or want to dive into the internals of perl. Otherwise it will only
		191	confuse you, as, despite the name, it says nothing about how your string
		192	is encoded. You can have Unicode strings with that flag set, with that
		193	flag clear, and you can have binary data with that flag set and that flag
		194	clear. Other possibilities exist, too.
		195
		196	If you didn't know about that flag, just the better, pretend it doesn't
		197	exist.
		198
		199	=item 4. A "Unicode String" is simply a string where each character can be
		200	validly interpreted as a Unicode code point.
		201
		202	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		203	Unicode string encoded in UTF-8, giving you a binary string.
		204
		205	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		206
		207	It's a fact. Learn to live with it.
		208
		209	=back
		210
		211	I hope this helps :)
		212
100		213
101	=head1 OBJECT-ORIENTED INTERFACE	214	=head1 OBJECT-ORIENTED INTERFACE
102		215
103	The object oriented interface lets you configure your own encoding or	216	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	217	decoding style, within the limits of supported formats.
…		…
111	strings. All boolean flags described below are by default I<disabled>.	224	strings. All boolean flags described below are by default I<disabled>.
112		225
113	The mutators for flags all return the JSON object again and thus calls can	226	The mutators for flags all return the JSON object again and thus calls can
114	be chained:	227	be chained:
115		228
116	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	229	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
117	=> {"a": [1, 2]}	230	=> {"a": [1, 2]}
118		231
119	=item $json = $json->ascii ([$enable])	232	=item $json = $json->ascii ([$enable])
120		233
		234	=item $enabled = $json->get_ascii
		235
121	If C<$enable> is true (or missing), then the C<encode> method will	236	If C<$enable> is true (or missing), then the C<encode> method will not
122	not generate characters outside the code range C<0..127>. Any unicode	237	generate characters outside the code range C<0..127> (which is ASCII). Any
123	characters outside that range will be escaped using either a single	238	Unicode characters outside that range will be escaped using either a
124	\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per	239	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
125	RFC4627.	240	as per RFC4627. The resulting encoded JSON text can be treated as a native
		241	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		242	or any other superset of ASCII.
126		243
127	If C<$enable> is false, then the C<encode> method will not escape Unicode	244	If C<$enable> is false, then the C<encode> method will not escape Unicode
128	characters unless necessary.	245	characters unless required by the JSON syntax or other flags. This results
		246	in a faster and more compact format.
129		247
		248	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		249	document.
		250
		251	The main use for this flag is to produce JSON texts that can be
		252	transmitted over a 7-bit channel, as the encoded JSON texts will not
		253	contain any 8 bit characters.
		254
130	JSON::XS->new->ascii (1)->encode (chr 0x10401)	255	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
131	=> \ud801\udc01	256	=> ["\ud801\udc01"]
		257
		258	=item $json = $json->latin1 ([$enable])
		259
		260	=item $enabled = $json->get_latin1
		261
		262	If C<$enable> is true (or missing), then the C<encode> method will encode
		263	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		264	outside the code range C<0..255>. The resulting string can be treated as a
		265	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		266	will not be affected in any way by this flag, as C<decode> by default
		267	expects Unicode, which is a strict superset of latin1.
		268
		269	If C<$enable> is false, then the C<encode> method will not escape Unicode
		270	characters unless required by the JSON syntax or other flags.
		271
		272	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		273	document.
		274
		275	The main use for this flag is efficiently encoding binary data as JSON
		276	text, as most octets will not be escaped, resulting in a smaller encoded
		277	size. The disadvantage is that the resulting JSON text is encoded
		278	in latin1 (and must correctly be treated as such when storing and
		279	transferring), a rare encoding for JSON. It is therefore most useful when
		280	you want to store data structures known to contain binary data efficiently
		281	in files or databases, not when talking to other JSON encoders/decoders.
		282
		283	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		284	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
132		285
133	=item $json = $json->utf8 ([$enable])	286	=item $json = $json->utf8 ([$enable])
134		287
		288	=item $enabled = $json->get_utf8
		289
135	If C<$enable> is true (or missing), then the C<encode> method will encode	290	If C<$enable> is true (or missing), then the C<encode> method will encode
136	the JSON string into UTF-8, as required by many protocols, while the	291	the JSON result into UTF-8, as required by many protocols, while the
137	C<decode> method expects to be handled an UTF-8-encoded string. Please	292	C<decode> method expects to be handled an UTF-8-encoded string. Please
138	note that UTF-8-encoded strings do not contain any characters outside the	293	note that UTF-8-encoded strings do not contain any characters outside the
139	range C<0..255>, they are thus useful for bytewise/binary I/O.	294	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		295	versions, enabling this option might enable autodetection of the UTF-16
		296	and UTF-32 encoding families, as described in RFC4627.
140		297
141	If C<$enable> is false, then the C<encode> method will return the JSON	298	If C<$enable> is false, then the C<encode> method will return the JSON
142	string as a (non-encoded) unicode string, while C<decode> expects thus a	299	string as a (non-encoded) Unicode string, while C<decode> expects thus a
143	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	300	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
144	to be done yourself, e.g. using the Encode module.	301	to be done yourself, e.g. using the Encode module.
		302
		303	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		304	document.
		305
		306	Example, output UTF-16BE-encoded JSON:
		307
		308	use Encode;
		309	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		310
		311	Example, decode UTF-32LE-encoded JSON:
		312
		313	use Encode;
		314	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
145		315
146	=item $json = $json->pretty ([$enable])	316	=item $json = $json->pretty ([$enable])
147		317
148	This enables (or disables) all of the C<indent>, C<space_before> and	318	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	319	C<space_after> (and in the future possibly more) flags in one call to
150	generate the most readable (or most compact) form possible.	320	generate the most readable (or most compact) form possible.
		321
		322	Example, pretty-print some simple structure:
151		323
152	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})	324	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
153	=>	325	=>
154	{	326	{
155	"a" : [	327	"a" : [
…		…
158	]	330	]
159	}	331	}
160		332
161	=item $json = $json->indent ([$enable])	333	=item $json = $json->indent ([$enable])
162		334
		335	=item $enabled = $json->get_indent
		336
163	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	337	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
164	format as output, putting every array member or object/hash key-value pair	338	format as output, putting every array member or object/hash key-value pair
165	into its own line, identing them properly.	339	into its own line, indenting them properly.
166		340
167	If C<$enable> is false, no newlines or indenting will be produced, and the	341	If C<$enable> is false, no newlines or indenting will be produced, and the
168	resulting JSON strings is guarenteed not to contain any C<newlines>.	342	resulting JSON text is guaranteed not to contain any C<newlines>.
169		343
170	This setting has no effect when decoding JSON strings.	344	This setting has no effect when decoding JSON texts.
171		345
172	=item $json = $json->space_before ([$enable])	346	=item $json = $json->space_before ([$enable])
		347
		348	=item $enabled = $json->get_space_before
173		349
174	If C<$enable> is true (or missing), then the C<encode> method will add an extra	350	If C<$enable> is true (or missing), then the C<encode> method will add an extra
175	optional space before the C<:> separating keys from values in JSON objects.	351	optional space before the C<:> separating keys from values in JSON objects.
176		352
177	If C<$enable> is false, then the C<encode> method will not add any extra	353	If C<$enable> is false, then the C<encode> method will not add any extra
178	space at those places.	354	space at those places.
179		355
180	This setting has no effect when decoding JSON strings. You will also most	356	This setting has no effect when decoding JSON texts. You will also
181	likely combine this setting with C<space_after>.	357	most likely combine this setting with C<space_after>.
		358
		359	Example, space_before enabled, space_after and indent disabled:
		360
		361	{"key" :"value"}
182		362
183	=item $json = $json->space_after ([$enable])	363	=item $json = $json->space_after ([$enable])
		364
		365	=item $enabled = $json->get_space_after
184		366
185	If C<$enable> is true (or missing), then the C<encode> method will add an extra	367	If C<$enable> is true (or missing), then the C<encode> method will add an extra
186	optional space after the C<:> separating keys from values in JSON objects	368	optional space after the C<:> separating keys from values in JSON objects
187	and extra whitespace after the C<,> separating key-value pairs and array	369	and extra whitespace after the C<,> separating key-value pairs and array
188	members.	370	members.
189		371
190	If C<$enable> is false, then the C<encode> method will not add any extra	372	If C<$enable> is false, then the C<encode> method will not add any extra
191	space at those places.	373	space at those places.
192		374
193	This setting has no effect when decoding JSON strings.	375	This setting has no effect when decoding JSON texts.
		376
		377	Example, space_before and indent disabled, space_after enabled:
		378
		379	{"key": "value"}
		380
		381	=item $json = $json->relaxed ([$enable])
		382
		383	=item $enabled = $json->get_relaxed
		384
		385	If C<$enable> is true (or missing), then C<decode> will accept some
		386	extensions to normal JSON syntax (see below). C<encode> will not be
		387	affected in anyway. I<Be aware that this option makes you accept invalid
		388	JSON texts as if they were valid!>. I suggest only to use this option to
		389	parse application-specific files written by humans (configuration files,
		390	resource files etc.)
		391
		392	If C<$enable> is false (the default), then C<decode> will only accept
		393	valid JSON texts.
		394
		395	Currently accepted extensions are:
		396
		397	=over 4
		398
		399	=item * list items can have an end-comma
		400
		401	JSON I<separates> array elements and key-value pairs with commas. This
		402	can be annoying if you write JSON texts manually and want to be able to
		403	quickly append elements, so this extension accepts comma at the end of
		404	such items not just between them:
		405
		406	[
		407	1,
		408	2, <- this comma not normally allowed
		409	]
		410	{
		411	"k1": "v1",
		412	"k2": "v2", <- this comma not normally allowed
		413	}
		414
		415	=item * shell-style '#'-comments
		416
		417	Whenever JSON allows whitespace, shell-style comments are additionally
		418	allowed. They are terminated by the first carriage-return or line-feed
		419	character, after which more white-space and comments are allowed.
		420
		421	[
		422	1, # this comment not allowed in JSON
		423	# neither this one...
		424	]
		425
		426	=back
194		427
195	=item $json = $json->canonical ([$enable])	428	=item $json = $json->canonical ([$enable])
		429
		430	=item $enabled = $json->get_canonical
196		431
197	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	432	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
198	by sorting their keys. This is adding a comparatively high overhead.	433	by sorting their keys. This is adding a comparatively high overhead.
199		434
200	If C<$enable> is false, then the C<encode> method will output key-value	435	If C<$enable> is false, then the C<encode> method will output key-value
201	pairs in the order Perl stores them (which will likely change between runs	436	pairs in the order Perl stores them (which will likely change between runs
202	of the same script).	437	of the same script).
203		438
204	This option is useful if you want the same data structure to be encoded as	439	This option is useful if you want the same data structure to be encoded as
205	the same JSON string (given the same overall settings). If it is disabled,	440	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,	441	the same hash might be encoded differently even if contains the same data,
207	as key-value pairs have no inherent ordering in Perl.	442	as key-value pairs have no inherent ordering in Perl.
208		443
209	This setting has no effect when decoding JSON strings.	444	This setting has no effect when decoding JSON texts.
		445
		446	This setting has currently no effect on tied hashes.
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 = $json->get_shrink
		603
225	Perl usually over-allocates memory a bit when allocating space for	604	Perl usually over-allocates memory a bit when allocating space for
226	strings. This flag optionally resizes strings generated by either	605	strings. This flag optionally resizes strings generated by either
227	C<encode> or C<decode> to their minimum size possible. This can save	606	C<encode> or C<decode> to their minimum size possible. This can save
228	memory when your JSON strings are either very very long or you have many	607	memory when your JSON texts are either very very long or you have many
229	short strings.	608	short strings. It will also try to downgrade any strings to octet-form
		609	if possible: perl stores strings internally either in an encoding called
		610	UTF-X or in octet-form. The latter cannot store everything but uses less
		611	space in general (and some buggy Perl or C code might even rely on that
		612	internal representation being used).
230		613
		614	The actual definition of what shrink does might change in future versions,
		615	but it will always try to save space at the expense of time.
		616
231	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	617	If C<$enable> is true (or missing), the string returned by C<encode> will
232	while all strings generated by C<decode> will also be shrunk-to-fit.	618	be shrunk-to-fit, while all strings generated by C<decode> will also be
		619	shrunk-to-fit.
233		620
234	If C<$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.
235	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.
236		623
237	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
238	strings that look like integers or floats into integers or floats	625	strings that look like integers or floats into integers or floats
239	internally (there is no difference on the Perl level), saving space.	626	internally (there is no difference on the Perl level), saving space.
240		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
241	=item $json_string = $json->encode ($perl_scalar)	669	=item $json_text = $json->encode ($perl_scalar)
242		670
243	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
244	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
245	converted into JSON string or number sequences, while references to arrays	673	converted into JSON string or number sequences, while references to arrays
246	become JSON arrays and references to hashes become JSON objects. Undefined	674	become JSON arrays and references to hashes become JSON objects. Undefined
247	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>
248	nor C<false> values will be generated.	676	nor C<false> values will be generated.
249		677
250	=item $perl_scalar = $json->decode ($json_string)	678	=item $perl_scalar = $json->decode ($json_text)
251		679
252	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,
253	returning the resulting simple scalar or reference. Croaks on error.	681	returning the resulting simple scalar or reference. Croaks on error.
254		682
255	JSON numbers and strings become simple Perl scalars. JSON arrays become	683	JSON numbers and strings become simple Perl scalars. JSON arrays become
256	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	684	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
257	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>.
258		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
259	=back	701	=back
260		702
261	=head1 COMPARISON
262		703
263	As already mentioned, this module was created because none of the existing	704	=head1 INCREMENTAL PARSING
264	JSON modules could be made to work correctly. First I will describe the	705
265	problems (or pleasures) I encountered with various existing JSON modules,	706	In some cases, there is the need for incremental parsing of JSON
266	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
267	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
		712	is much more efficient (and can be implemented with a minimum of method
		713	calls).
		714
		715	JSON::XS will only attempt to parse the JSON text once it is sure it
		716	has enough text to get a decisive result, using a very simple but
		717	truly incremental parser. This means that it sometimes won't stop as
		718	early as the full parser, for example, it doesn't detect mismatched
		719	parentheses. The only thing it guarantees is that it starts decoding as
		720	soon as a syntactically valid JSON text has been seen. This means you need
		721	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		722	parsing in the presence if syntax errors.
		723
		724	The following methods implement this incremental parser.
268		725
269	=over 4	726	=over 4
270		727
271	=item JSON 1.07	728	=item [void, scalar or list context] = $json->incr_parse ([$string])
272		729
273	Slow (but very portable, as it is written in pure Perl).	730	This is the central parsing function. It can both append new text and
		731	extract objects from the stream accumulated so far (both of these
		732	functions are optional).
274		733
275	Undocumented/buggy Unicode handling (how JSON handles unicode values is	734	If C<$string> is given, then this string is appended to the already
276	undocumented. One can get far by feeding it unicode strings and doing	735	existing JSON fragment stored in the C<$json> object.
277	en-/decoding oneself, but unicode escapes are not working properly).
278		736
279	No roundtripping (strings get clobbered if they look like numbers, e.g.	737	After that, if the function is called in void context, it will simply
280	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	738	return without doing anything further. This can be used to add more text
281	decode into the number 2.	739	in as many chunks as you want.
282		740
283	=item JSON::PC 0.01	741	If the method is called in scalar context, then it will try to extract
		742	exactly I<one> JSON object. If that is successful, it will return this
		743	object, otherwise it will return C<undef>. If there is a parse error,
		744	this method will croak just as C<decode> would do (one can then use
		745	C<incr_skip> to skip the errornous part). This is the most common way of
		746	using the method.
284		747
285	Very fast.	748	And finally, in list context, it will try to extract as many objects
		749	from the stream as it can find and return them, or the empty list
		750	otherwise. For this to work, there must be no separators between the JSON
		751	objects or arrays, instead they must be concatenated back-to-back. If
		752	an error occurs, an exception will be raised as in the scalar context
		753	case. Note that in this case, any previously-parsed JSON texts will be
		754	lost.
286		755
287	Undocumented/buggy Unicode handling.	756	Example: Parse some JSON arrays/objects in a given string and return
		757	them.
288		758
289	No roundtripping.	759	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
290		760
291	Has problems handling many Perl values (e.g. regex results and other magic	761	=item $lvalue_string = $json->incr_text
292	values will make it croak).
293		762
294	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	763	This method returns the currently stored JSON fragment as an lvalue, that
295	which is not a valid JSON string.	764	is, you can manipulate it. This I<only> works when a preceding call to
		765	C<incr_parse> in I<scalar context> successfully returned an object. Under
		766	all other circumstances you must not call this function (I mean it.
		767	although in simple tests it might actually work, it I<will> fail under
		768	real world conditions). As a special exception, you can also call this
		769	method before having parsed anything.
296		770
297	Unmaintained (maintainer unresponsive for many months, bugs are not	771	This function is useful in two cases: a) finding the trailing text after a
298	getting fixed).	772	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		773	(such as commas).
299		774
300	=item JSON::Syck 0.21	775	=item $json->incr_skip
301		776
302	Very buggy (often crashes).	777	This will reset the state of the incremental parser and will remove
		778	the parsed text from the input buffer so far. This is useful after
		779	C<incr_parse> died, in which case the input buffer and incremental parser
		780	state is left unchanged, to skip the text parsed so far and to reset the
		781	parse state.
303		782
304	Very inflexible (no human-readable format supported, format pretty much	783	The difference to C<incr_reset> is that only text until the parse error
305	undocumented. I need at least a format for easy reading by humans and a	784	occured is removed.
306	single-line compact format for use in a protocol, and preferably a way to
307	generate ASCII-only JSON strings).
308		785
309	Completely broken (and confusingly documented) Unicode handling (unicode	786	=item $json->incr_reset
310	escapes are not working properly, you need to set ImplicitUnicode to
311	I<different> values on en- and decoding to get symmetric behaviour).
312		787
313	No roundtripping (simple cases work, but this depends on wether the scalar	788	This completely resets the incremental parser, that is, after this call,
314	value was used in a numeric context or not).	789	it will be as if the parser had never parsed anything.
315		790
316	Dumping hashes may skip hash values depending on iterator state.	791	This is useful if you want to repeatedly parse JSON objects and want to
317		792	ignore any trailing data, which means you have to reset the parser after
318	Unmaintained (maintainer unresponsive for many months, bugs are not	793	each successful decode.
319	getting fixed).
320
321	Does not check input for validity (i.e. will accept non-JSON input and
322	return "something" instead of raising an exception. This is a security
323	issue: imagine two banks transfering money between each other using
324	JSON. One bank might parse a given non-JSON request and deduct money,
325	while the other might reject the transaction with a syntax error. While a
326	good protocol will at least recover, that is extra unnecessary work and
327	the transaction will still not succeed).
328
329	=item JSON::DWIW 0.04
330
331	Very fast. Very natural. Very nice.
332
333	Undocumented unicode handling (but the best of the pack. Unicode escapes
334	still don't get parsed properly).
335
336	Very inflexible.
337
338	No roundtripping.
339
340	Does not generate valid JSON (key strings are often unquoted, empty keys
341	result in nothing being output)
342
343	Does not check input for validity.
344		794
345	=back	795	=back
		796
		797	=head2 LIMITATIONS
		798
		799	All options that affect decoding are supported, except
		800	C<allow_nonref>. The reason for this is that it cannot be made to
		801	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		802	them back to back and still decode them perfectly. This does not hold true
		803	for JSON numbers, however.
		804
		805	For example, is the string C<1> a single JSON number, or is it simply the
		806	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		807	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		808	takes the conservative route and disallows this case.
		809
		810	=head2 EXAMPLES
		811
		812	Some examples will make all this clearer. First, a simple example that
		813	works similarly to C<decode_prefix>: We want to decode the JSON object at
		814	the start of a string and identify the portion after the JSON object:
		815
		816	my $text = "[1,2,3] hello";
		817
		818	my $json = new JSON::XS;
		819
		820	my $obj = $json->incr_parse ($text)
		821	or die "expected JSON object or array at beginning of string";
		822
		823	my $tail = $json->incr_text;
		824	# $tail now contains " hello"
		825
		826	Easy, isn't it?
		827
		828	Now for a more complicated example: Imagine a hypothetical protocol where
		829	you read some requests from a TCP stream, and each request is a JSON
		830	array, without any separation between them (in fact, it is often useful to
		831	use newlines as "separators", as these get interpreted as whitespace at
		832	the start of the JSON text, which makes it possible to test said protocol
		833	with C<telnet>...).
		834
		835	Here is how you'd do it (it is trivial to write this in an event-based
		836	manner):
		837
		838	my $json = new JSON::XS;
		839
		840	# read some data from the socket
		841	while (sysread $socket, my $buf, 4096) {
		842
		843	# split and decode as many requests as possible
		844	for my $request ($json->incr_parse ($buf)) {
		845	# act on the $request
		846	}
		847	}
		848
		849	Another complicated example: Assume you have a string with JSON objects
		850	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		851	[3]>). To parse them, we have to skip the commas between the JSON texts,
		852	and here is where the lvalue-ness of C<incr_text> comes in useful:
		853
		854	my $text = "[1],[2], [3]";
		855	my $json = new JSON::XS;
		856
		857	# void context, so no parsing done
		858	$json->incr_parse ($text);
		859
		860	# now extract as many objects as possible. note the
		861	# use of scalar context so incr_text can be called.
		862	while (my $obj = $json->incr_parse) {
		863	# do something with $obj
		864
		865	# now skip the optional comma
		866	$json->incr_text =~ s/^ \s* , //x;
		867	}
		868
		869	Now lets go for a very complex example: Assume that you have a gigantic
		870	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		871	but you cannot load it into memory fully (this has actually happened in
		872	the real world :).
		873
		874	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		875	can still help you: You implement a (very simple) array parser and let
		876	JSON decode the array elements, which are all full JSON objects on their
		877	own (this wouldn't work if the array elements could be JSON numbers, for
		878	example):
		879
		880	my $json = new JSON::XS;
		881
		882	# open the monster
		883	open my $fh, "<bigfile.json"
		884	or die "bigfile: $!";
		885
		886	# first parse the initial "["
		887	for (;;) {
		888	sysread $fh, my $buf, 65536
		889	or die "read error: $!";
		890	$json->incr_parse ($buf); # void context, so no parsing
		891
		892	# Exit the loop once we found and removed(!) the initial "[".
		893	# In essence, we are (ab-)using the $json object as a simple scalar
		894	# we append data to.
		895	last if $json->incr_text =~ s/^ \s* \[ //x;
		896	}
		897
		898	# now we have the skipped the initial "[", so continue
		899	# parsing all the elements.
		900	for (;;) {
		901	# in this loop we read data until we got a single JSON object
		902	for (;;) {
		903	if (my $obj = $json->incr_parse) {
		904	# do something with $obj
		905	last;
		906	}
		907
		908	# add more data
		909	sysread $fh, my $buf, 65536
		910	or die "read error: $!";
		911	$json->incr_parse ($buf); # void context, so no parsing
		912	}
		913
		914	# in this loop we read data until we either found and parsed the
		915	# separating "," between elements, or the final "]"
		916	for (;;) {
		917	# first skip whitespace
		918	$json->incr_text =~ s/^\s*//;
		919
		920	# if we find "]", we are done
		921	if ($json->incr_text =~ s/^\]//) {
		922	print "finished.\n";
		923	exit;
		924	}
		925
		926	# if we find ",", we can continue with the next element
		927	if ($json->incr_text =~ s/^,//) {
		928	last;
		929	}
		930
		931	# if we find anything else, we have a parse error!
		932	if (length $json->incr_text) {
		933	die "parse error near ", $json->incr_text;
		934	}
		935
		936	# else add more data
		937	sysread $fh, my $buf, 65536
		938	or die "read error: $!";
		939	$json->incr_parse ($buf); # void context, so no parsing
		940	}
		941
		942	This is a complex example, but most of the complexity comes from the fact
		943	that we are trying to be correct (bear with me if I am wrong, I never ran
		944	the above example :).
		945
		946
		947
		948	=head1 MAPPING
		949
		950	This section describes how JSON::XS maps Perl values to JSON values and
		951	vice versa. These mappings are designed to "do the right thing" in most
		952	circumstances automatically, preserving round-tripping characteristics
		953	(what you put in comes out as something equivalent).
		954
		955	For the more enlightened: note that in the following descriptions,
		956	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		957	refers to the abstract Perl language itself.
		958
		959
		960	=head2 JSON -> PERL
		961
		962	=over 4
		963
		964	=item object
		965
		966	A JSON object becomes a reference to a hash in Perl. No ordering of object
		967	keys is preserved (JSON does not preserve object key ordering itself).
		968
		969	=item array
		970
		971	A JSON array becomes a reference to an array in Perl.
		972
		973	=item string
		974
		975	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		976	are represented by the same codepoints in the Perl string, so no manual
		977	decoding is necessary.
		978
		979	=item number
		980
		981	A JSON number becomes either an integer, numeric (floating point) or
		982	string scalar in perl, depending on its range and any fractional parts. On
		983	the Perl level, there is no difference between those as Perl handles all
		984	the conversion details, but an integer may take slightly less memory and
		985	might represent more values exactly than floating point numbers.
		986
		987	If the number consists of digits only, JSON::XS will try to represent
		988	it as an integer value. If that fails, it will try to represent it as
		989	a numeric (floating point) value if that is possible without loss of
		990	precision. Otherwise it will preserve the number as a string value (in
		991	which case you lose roundtripping ability, as the JSON number will be
		992	re-encoded toa JSON string).
		993
		994	Numbers containing a fractional or exponential part will always be
		995	represented as numeric (floating point) values, possibly at a loss of
		996	precision (in which case you might lose perfect roundtripping ability, but
		997	the JSON number will still be re-encoded as a JSON number).
		998
		999	Note that precision is not accuracy - binary floating point values cannot
		1000	represent most decimal fractions exactly, and when converting from and to
		1001	floating point, JSON::XS only guarantees precision up to but not including
		1002	the leats significant bit.
		1003
		1004	=item true, false
		1005
		1006	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
		1007	respectively. They are overloaded to act almost exactly like the numbers
		1008	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
		1009	the C<JSON::XS::is_bool> function.
		1010
		1011	=item null
		1012
		1013	A JSON null atom becomes C<undef> in Perl.
		1014
		1015	=back
		1016
		1017
		1018	=head2 PERL -> JSON
		1019
		1020	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		1021	truly typeless language, so we can only guess which JSON type is meant by
		1022	a Perl value.
		1023
		1024	=over 4
		1025
		1026	=item hash references
		1027
		1028	Perl hash references become JSON objects. As there is no inherent ordering
		1029	in hash keys (or JSON objects), they will usually be encoded in a
		1030	pseudo-random order that can change between runs of the same program but
		1031	stays generally the same within a single run of a program. JSON::XS can
		1032	optionally sort the hash keys (determined by the I<canonical> flag), so
		1033	the same datastructure will serialise to the same JSON text (given same
		1034	settings and version of JSON::XS), but this incurs a runtime overhead
		1035	and is only rarely useful, e.g. when you want to compare some JSON text
		1036	against another for equality.
		1037
		1038	=item array references
		1039
		1040	Perl array references become JSON arrays.
		1041
		1042	=item other references
		1043
		1044	Other unblessed references are generally not allowed and will cause an
		1045	exception to be thrown, except for references to the integers C<0> and
		1046	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		1047	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		1048
		1049	encode_json [\0, JSON::XS::true] # yields [false,true]
		1050
		1051	=item JSON::XS::true, JSON::XS::false
		1052
		1053	These special values become JSON true and JSON false values,
		1054	respectively. You can also use C<\1> and C<\0> directly if you want.
		1055
		1056	=item blessed objects
		1057
		1058	Blessed objects are not directly representable in JSON. See the
		1059	C<allow_blessed> and C<convert_blessed> methods on various options on
		1060	how to deal with this: basically, you can choose between throwing an
		1061	exception, encoding the reference as if it weren't blessed, or provide
		1062	your own serialiser method.
		1063
		1064	=item simple scalars
		1065
		1066	Simple Perl scalars (any scalar that is not a reference) are the most
		1067	difficult objects to encode: JSON::XS will encode undefined scalars as
		1068	JSON C<null> values, scalars that have last been used in a string context
		1069	before encoding as JSON strings, and anything else as number value:
		1070
		1071	# dump as number
		1072	encode_json [2] # yields [2]
		1073	encode_json [-3.0e17] # yields [-3e+17]
		1074	my $value = 5; encode_json [$value] # yields [5]
		1075
		1076	# used as string, so dump as string
		1077	print $value;
		1078	encode_json [$value] # yields ["5"]
		1079
		1080	# undef becomes null
		1081	encode_json [undef] # yields [null]
		1082
		1083	You can force the type to be a JSON string by stringifying it:
		1084
		1085	my $x = 3.1; # some variable containing a number
		1086	"$x"; # stringified
		1087	$x .= ""; # another, more awkward way to stringify
		1088	print $x; # perl does it for you, too, quite often
		1089
		1090	You can force the type to be a JSON number by numifying it:
		1091
		1092	my $x = "3"; # some variable containing a string
		1093	$x += 0; # numify it, ensuring it will be dumped as a number
		1094	$x *= 1; # same thing, the choice is yours.
		1095
		1096	You can not currently force the type in other, less obscure, ways. Tell me
		1097	if you need this capability (but don't forget to explain why it's needed
		1098	:).
		1099
		1100	Note that numerical precision has the same meaning as under Perl (so
		1101	binary to decimal conversion follows the same rules as in Perl, which
		1102	can differ to other languages). Also, your perl interpreter might expose
		1103	extensions to the floating point numbers of your platform, such as
		1104	infinities or NaN's - these cannot be represented in JSON, and it is an
		1105	error to pass those in.
		1106
		1107	=back
		1108
		1109
		1110	=head1 ENCODING/CODESET FLAG NOTES
		1111
		1112	The interested reader might have seen a number of flags that signify
		1113	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1114	some confusion on what these do, so here is a short comparison:
		1115
		1116	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1117	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1118	control whether C<encode> escapes character values outside their respective
		1119	codeset range. Neither of these flags conflict with each other, although
		1120	some combinations make less sense than others.
		1121
		1122	Care has been taken to make all flags symmetrical with respect to
		1123	C<encode> and C<decode>, that is, texts encoded with any combination of
		1124	these flag values will be correctly decoded when the same flags are used
		1125	- in general, if you use different flag settings while encoding vs. when
		1126	decoding you likely have a bug somewhere.
		1127
		1128	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1129	simply an abstract set of character-codepoint pairs, while an encoding
		1130	takes those codepoint numbers and I<encodes> them, in our case into
		1131	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1132	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1133	the same time, which can be confusing.
		1134
		1135	=over 4
		1136
		1137	=item C<utf8> flag disabled
		1138
		1139	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1140	and expect Unicode strings, that is, characters with high ordinal Unicode
		1141	values (> 255) will be encoded as such characters, and likewise such
		1142	characters are decoded as-is, no canges to them will be done, except
		1143	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1144	respectively (to Perl, these are the same thing in strings unless you do
		1145	funny/weird/dumb stuff).
		1146
		1147	This is useful when you want to do the encoding yourself (e.g. when you
		1148	want to have UTF-16 encoded JSON texts) or when some other layer does
		1149	the encoding for you (for example, when printing to a terminal using a
		1150	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1151	to UTF-8 encode your data first and have Perl encode it another time).
		1152
		1153	=item C<utf8> flag enabled
		1154
		1155	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1156	characters using the corresponding UTF-8 multi-byte sequence, and will
		1157	expect your input strings to be encoded as UTF-8, that is, no "character"
		1158	of the input string must have any value > 255, as UTF-8 does not allow
		1159	that.
		1160
		1161	The C<utf8> flag therefore switches between two modes: disabled means you
		1162	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1163	octet/binary string in Perl.
		1164
		1165	=item C<latin1> or C<ascii> flags enabled
		1166
		1167	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1168	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1169	characters as specified by the C<utf8> flag.
		1170
		1171	If C<utf8> is disabled, then the result is also correctly encoded in those
		1172	character sets (as both are proper subsets of Unicode, meaning that a
		1173	Unicode string with all character values < 256 is the same thing as a
		1174	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1175	the same thing as an ASCII string in Perl).
		1176
		1177	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1178	regardless of these flags, just some more characters will be escaped using
		1179	C<\uXXXX> then before.
		1180
		1181	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1182	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1183	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1184	a subset of Unicode), while ASCII is.
		1185
		1186	Surprisingly, C<decode> will ignore these flags and so treat all input
		1187	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1188	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1189	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1190
		1191	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1192	they only govern when the JSON output engine escapes a character or not.
		1193
		1194	The main use for C<latin1> is to relatively efficiently store binary data
		1195	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1196
		1197	The main use for C<ascii> is to force the output to not contain characters
		1198	with values > 127, which means you can interpret the resulting string
		1199	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1200	8-bit-encoding, and still get the same data structure back. This is useful
		1201	when your channel for JSON transfer is not 8-bit clean or the encoding
		1202	might be mangled in between (e.g. in mail), and works because ASCII is a
		1203	proper subset of most 8-bit and multibyte encodings in use in the world.
		1204
		1205	=back
		1206
		1207
		1208	=head2 JSON and ECMAscript
		1209
		1210	JSON syntax is based on how literals are represented in javascript (the
		1211	not-standardised predecessor of ECMAscript) which is presumably why it is
		1212	called "JavaScript Object Notation".
		1213
		1214	However, JSON is not a subset (and also not a superset of course) of
		1215	ECMAscript (the standard) or javascript (whatever browsers actually
		1216	implement).
		1217
		1218	If you want to use javascript's C<eval> function to "parse" JSON, you
		1219	might run into parse errors for valid JSON texts, or the resulting data
		1220	structure might not be queryable:
		1221
		1222	One of the problems is that U+2028 and U+2029 are valid characters inside
		1223	JSON strings, but are not allowed in ECMAscript string literals, so the
		1224	following Perl fragment will not output something that can be guaranteed
		1225	to be parsable by javascript's C<eval>:
		1226
		1227	use JSON::XS;
		1228
		1229	print encode_json [chr 0x2028];
		1230
		1231	The right fix for this is to use a proper JSON parser in your javascript
		1232	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1233	F<json2.js> parser).
		1234
		1235	If this is not an option, you can, as a stop-gap measure, simply encode to
		1236	ASCII-only JSON:
		1237
		1238	use JSON::XS;
		1239
		1240	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1241
		1242	Note that this will enlarge the resulting JSON text quite a bit if you
		1243	have many non-ASCII characters. You might be tempted to run some regexes
		1244	to only escape U+2028 and U+2029, e.g.:
		1245
		1246	# DO NOT USE THIS!
		1247	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1248	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1249	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1250	print $json;
		1251
		1252	Note that I<this is a bad idea>: the above only works for U+2028 and
		1253	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1254	javascript implementations, however, have issues with other characters as
		1255	well - using C<eval> naively simply I<will> cause problems.
		1256
		1257	Another problem is that some javascript implementations reserve
		1258	some property names for their own purposes (which probably makes
		1259	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1260	C<__proto__> property name for its own purposes.
		1261
		1262	If that is a problem, you could parse try to filter the resulting JSON
		1263	output for these property strings, e.g.:
		1264
		1265	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1266
		1267	This works because C<__proto__> is not valid outside of strings, so every
		1268	occurence of C<"__proto__"\s*:> must be a string used as property name.
		1269
		1270	If you know of other incompatibilities, please let me know.
		1271
		1272
		1273	=head2 JSON and YAML
		1274
		1275	You often hear that JSON is a subset of YAML. This is, however, a mass
		1276	hysteria(*) and very far from the truth (as of the time of this writing),
		1277	so let me state it clearly: I<in general, there is no way to configure
		1278	JSON::XS to output a data structure as valid YAML> that works in all
		1279	cases.
		1280
		1281	If you really must use JSON::XS to generate YAML, you should use this
		1282	algorithm (subject to change in future versions):
		1283
		1284	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1285	my $yaml = $to_yaml->encode ($ref) . "\n";
		1286
		1287	This will I<usually> generate JSON texts that also parse as valid
		1288	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1289	lengths that JSON doesn't have and also has different and incompatible
		1290	unicode character escape syntax, so you should make sure that your hash
		1291	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1292	and that you do not have characters with codepoint values outside the
		1293	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1294	sequences in strings (which JSON::XS does not I<currently> generate, but
		1295	other JSON generators might).
		1296
		1297	There might be other incompatibilities that I am not aware of (or the YAML
		1298	specification has been changed yet again - it does so quite often). In
		1299	general you should not try to generate YAML with a JSON generator or vice
		1300	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1301	high that you will run into severe interoperability problems when you
		1302	least expect it.
		1303
		1304	=over 4
		1305
		1306	=item (*)
		1307
		1308	I have been pressured multiple times by Brian Ingerson (one of the
		1309	authors of the YAML specification) to remove this paragraph, despite him
		1310	acknowledging that the actual incompatibilities exist. As I was personally
		1311	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1312	educate people about these issues, so others do not run into the same
		1313	problem again and again. After this, Brian called me a (quote)I<complete
		1314	and worthless idiot>(unquote).
		1315
		1316	In my opinion, instead of pressuring and insulting people who actually
		1317	clarify issues with YAML and the wrong statements of some of its
		1318	proponents, I would kindly suggest reading the JSON spec (which is not
		1319	that difficult or long) and finally make YAML compatible to it, and
		1320	educating users about the changes, instead of spreading lies about the
		1321	real compatibility for many I<years> and trying to silence people who
		1322	point out that it isn't true.
		1323
		1324	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1325	though the incompatibilities have been documented (and are known to Brian)
		1326	for many years and the spec makes explicit claims that YAML is a superset
		1327	of JSON. It would be so easy to fix, but apparently, bullying people and
		1328	corrupting userdata is so much easier.
		1329
		1330	=back
		1331
346		1332
347	=head2 SPEED	1333	=head2 SPEED
348		1334
349	It seems that JSON::XS is surprisingly fast, as shown in the following	1335	It seems that JSON::XS is surprisingly fast, as shown in the following
350	tables. They have been generated with the help of the C<eg/bench> program	1336	tables. They have been generated with the help of the C<eg/bench> program
351	in the JSON::XS distribution, to make it easy to compare on your own	1337	in the JSON::XS distribution, to make it easy to compare on your own
352	system.	1338	system.
353		1339
354	First is a comparison between various modules using a very simple JSON	1340	First comes a comparison between various modules using
		1341	a very short single-line JSON string (also available at
		1342	L<http://dist.schmorp.de/misc/json/short.json>).
		1343
		1344	{"method": "handleMessage", "params": ["user1",
		1345	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1346	1, 0]}
		1347
355	string, showing the number of encodes/decodes per second (JSON::XS is	1348	It shows the number of encodes/decodes per second (JSON::XS uses
356	the functional interface, while JSON::XS/2 is the OO interface with	1349	the functional interface, while JSON::XS/2 uses the OO interface
357	pretty-printing and hashkey sorting enabled).	1350	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1351	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1352	uses the from_json method). Higher is better:
358		1353
359	module | encode | decode |	1354	module | encode | decode |
360	-----------|------------|------------|	1355	--------------|------------|------------|
361	JSON | 14006 | 6820 |	1356	JSON::DWIW/DS | 86302.551 | 102300.098 |
362	JSON::DWIW | 200937 | 120386 |	1357	JSON::DWIW/FJ | 86302.551 | 75983.768 |
363	JSON::PC | 85065 | 129366 |	1358	JSON::PP | 15827.562 | 6638.658 |
364	JSON::Syck | 59898 | 44232 |	1359	JSON::Syck | 63358.066 | 47662.545 |
365	JSON::XS | 1171478 | 342435 |	1360	JSON::XS | 511500.488 | 511500.488 |
366	JSON::XS/2 | 730760 | 328714 |	1361	JSON::XS/2 | 291271.111 | 388361.481 |
		1362	JSON::XS/3 | 361577.931 | 361577.931 |
		1363	Storable | 66788.280 | 265462.278 |
367	-----------+------------+------------+	1364	--------------+------------+------------+
368		1365
369	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1366	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
370	times faster than JSON, even with pretty-printing and key sorting.	1367	about five times faster on decoding, and over thirty to seventy times
		1368	faster than JSON's pure perl implementation. It also compares favourably
		1369	to Storable for small amounts of data.
371		1370
372	Using a longer test string (roughly 8KB, generated from Yahoo! Locals	1371	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
373	search API (http://nanoref.com/yahooapis/mgPdGg):	1372	search API (L<http://dist.schmorp.de/misc/json/long.json>).
374		1373
375	module | encode | decode |	1374	module | encode | decode |
376	-----------|------------|------------|	1375	--------------|------------|------------|
377	JSON | 673 | 38 |	1376	JSON::DWIW/DS | 1647.927 | 2673.916 |
378	JSON::DWIW | 5271 | 770 |	1377	JSON::DWIW/FJ | 1630.249 | 2596.128 |
379	JSON::PC | 9901 | 2491 |	1378	JSON::PP | 400.640 | 62.311 |
380	JSON::Syck | 2360 | 786 |	1379	JSON::Syck | 1481.040 | 1524.869 |
381	JSON::XS | 37398 | 3202 |	1380	JSON::XS | 20661.596 | 9541.183 |
382	JSON::XS/2 | 13765 | 3153 |	1381	JSON::XS/2 | 10683.403 | 9416.938 |
		1382	JSON::XS/3 | 20661.596 | 9400.054 |
		1383	Storable | 19765.806 | 10000.725 |
383	-----------+------------+------------+	1384	--------------+------------+------------+
384		1385
385	Again, JSON::XS leads by far in the encoding case, while still beating	1386	Again, JSON::XS leads by far (except for Storable which non-surprisingly
386	every other module in the decoding case.	1387	decodes a bit faster).
387		1388
388	Last example is an almost 8MB large hash with many large binary values	1389	On large strings containing lots of high Unicode characters, some modules
389	(PNG files), resulting in a lot of escaping:	1390	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1391	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1392	to decode or encode properly, so it was impossible to prepare a fair
		1393	comparison table for that case.
		1394
		1395
		1396	=head1 SECURITY CONSIDERATIONS
		1397
		1398	When you are using JSON in a protocol, talking to untrusted potentially
		1399	hostile creatures requires relatively few measures.
		1400
		1401	First of all, your JSON decoder should be secure, that is, should not have
		1402	any buffer overflows. Obviously, this module should ensure that and I am
		1403	trying hard on making that true, but you never know.
		1404
		1405	Second, you need to avoid resource-starving attacks. That means you should
		1406	limit the size of JSON texts you accept, or make sure then when your
		1407	resources run out, that's just fine (e.g. by using a separate process that
		1408	can crash safely). The size of a JSON text in octets or characters is
		1409	usually a good indication of the size of the resources required to decode
		1410	it into a Perl structure. While JSON::XS can check the size of the JSON
		1411	text, it might be too late when you already have it in memory, so you
		1412	might want to check the size before you accept the string.
		1413
		1414	Third, JSON::XS recurses using the C stack when decoding objects and
		1415	arrays. The C stack is a limited resource: for instance, on my amd64
		1416	machine with 8MB of stack size I can decode around 180k nested arrays but
		1417	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1418	to free the temporary). If that is exceeded, the program crashes. To be
		1419	conservative, the default nesting limit is set to 512. If your process
		1420	has a smaller stack, you should adjust this setting accordingly with the
		1421	C<max_depth> method.
		1422
		1423	Something else could bomb you, too, that I forgot to think of. In that
		1424	case, you get to keep the pieces. I am always open for hints, though...
		1425
		1426	Also keep in mind that JSON::XS might leak contents of your Perl data
		1427	structures in its error messages, so when you serialise sensitive
		1428	information you might want to make sure that exceptions thrown by JSON::XS
		1429	will not end up in front of untrusted eyes.
		1430
		1431	If you are using JSON::XS to return packets to consumption
		1432	by JavaScript scripts in a browser you should have a look at
		1433	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
		1434	see whether you are vulnerable to some common attack vectors (which really
		1435	are browser design bugs, but it is still you who will have to deal with
		1436	it, as major browser developers care only for features, not about getting
		1437	security right).
		1438
		1439
		1440	=head1 THREADS
		1441
		1442	This module is I<not> guaranteed to be thread safe and there are no
		1443	plans to change this until Perl gets thread support (as opposed to the
		1444	horribly slow so-called "threads" which are simply slow and bloated
		1445	process simulations - use fork, it's I<much> faster, cheaper, better).
		1446
		1447	(It might actually work, but you have been warned).
		1448
390		1449
391	=head1 BUGS	1450	=head1 BUGS
392		1451
393	While the goal of this module is to be correct, that unfortunately does	1452	While the goal of this module is to be correct, that unfortunately does
394	not mean its bug-free, only that I think its design is bug-free. It is	1453	not mean it's bug-free, only that I think its design is bug-free. If you
395	still very young and not well-tested. If you keep reporting bugs they will	1454	keep reporting bugs they will be fixed swiftly, though.
396	be fixed swiftly, though.	1455
		1456	Please refrain from using rt.cpan.org or any other bug reporting
		1457	service. I put the contact address into my modules for a reason.
397		1458
398	=cut	1459	=cut
399		1460
		1461	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1462	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1463
		1464	sub true() { $true }
		1465	sub false() { $false }
		1466
		1467	sub is_bool($) {
		1468	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1469	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1470	}
		1471
		1472	XSLoader::load "JSON::XS", $VERSION;
		1473
		1474	package JSON::XS::Boolean;
		1475
		1476	use overload
		1477	"0+" => sub { ${$_[0]} },
		1478	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1479	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1480	fallback => 1;
		1481
400	1;	1482	1;
		1483
		1484	=head1 SEE ALSO
		1485
		1486	The F<json_xs> command line utility for quick experiments.
401		1487
402	=head1 AUTHOR	1488	=head1 AUTHOR
403		1489
404	Marc Lehmann <schmorp@schmorp.de>	1490	Marc Lehmann <schmorp@schmorp.de>
405	http://home.schmorp.de/	1491	http://home.schmorp.de/

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