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Revision 1.4 by root, Thu Mar 22 21:13:58 2007 UTC vs.
Revision 1.170 by root, Thu Nov 15 22:35:35 2018 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.
14		39
15	As this is the n-th-something JSON module on CPAN, what was the reason	40	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
16	to write yet another JSON module? While it seems there are many JSON	41	vice versa.
17	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
19	reports for other reasons.
20
21	See COMPARISON, below, for a comparison to some other JSON modules.
22		42
23	=head2 FEATURES	43	=head2 FEATURES
24		44
25	=over 4	45	=over
26		46
27	=item * correct handling of unicode issues	47	=item * correct Unicode handling
28		48
29	This module knows how to handle Unicode, and even documents how it does so.	49	This module knows how to handle Unicode, documents how and when it does
		50	so, and even documents what "correct" means.
30		51
31	=item * round-trip integrity	52	=item * round-trip integrity
32		53
33	When you serialise a perl data structure using only datatypes supported	54	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.	55	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").	56	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
		57	it looks like a number). There I<are> minor exceptions to this, read the
		58	MAPPING section below to learn about those.
36		59
37	=item * strict checking of JSON correctness	60	=item * strict checking of JSON correctness
38		61
39	There is no guessing, no generating of illegal JSON strings by default,	62	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).	63	and only JSON is accepted as input by default (the latter is a security
		64	feature).
41		65
42	=item * fast	66	=item * fast
43		67
44	compared to other JSON modules, this module compares favourably.	68	Compared to other JSON modules and other serialisers such as Storable,
		69	this module usually compares favourably in terms of speed, too.
45		70
46	=item * simple to use	71	=item * simple to use
47		72
48	This module has both a simple functional interface as well as an OO	73	This module has both a simple functional interface as well as an object
49	interface.	74	oriented interface.
50		75
51	=item * reasonably versatile output formats	76	=item * reasonably versatile output formats
52		77
53	You can choose between the most compact format possible, a pure-ascii	78	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	79	possible (nice for simple line-based protocols), a pure-ASCII format
55	whatever way you like.	80	(for when your transport is not 8-bit clean, still supports the whole
		81	Unicode range), or a pretty-printed format (for when you want to read that
		82	stuff). Or you can combine those features in whatever way you like.
56		83
57	=back	84	=back
58		85
59	=cut	86	=cut
60		87
61	package JSON::XS;	88	package JSON::XS;
62		89
63	BEGIN {	90	use common::sense;
		91
64	$VERSION = '0.1';	92	our $VERSION = '4.0';
65	@ISA = qw(Exporter);	93	our @ISA = qw(Exporter);
66		94
67	@EXPORT = qw(to_json from_json);	95	our @EXPORT = qw(encode_json decode_json);
68	require Exporter;
69		96
70	require XSLoader;	97	use Exporter;
71	XSLoader::load JSON::XS::, $VERSION;	98	use XSLoader;
72	}	99
		100	use Types::Serialiser ();
73		101
74	=head1 FUNCTIONAL INTERFACE	102	=head1 FUNCTIONAL INTERFACE
75		103
76	The following convinience methods are provided by this module. They are	104	The following convenience methods are provided by this module. They are
77	exported by default:	105	exported by default:
78		106
79	=over 4	107	=over
80		108
81	=item $json_string = to_json $perl_scalar	109	=item $json_text = encode_json $perl_scalar
82		110
83	Converts the given Perl data structure (a simple scalar or a reference to	111	Converts the given Perl data structure to a UTF-8 encoded, binary string
84	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	112	(that is, the string contains octets only). Croaks on error.
85	octets only). Croaks on error.
86		113
87	This function call is functionally identical to C<< JSON::XS->new->utf8	114	This function call is functionally identical to:
88	(1)->encode ($perl_scalar) >>.
89		115
		116	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		117
		118	Except being faster.
		119
90	=item $perl_scalar = from_json $json_string	120	=item $perl_scalar = decode_json $json_text
91		121
92	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	122	The opposite of C<encode_json>: expects a UTF-8 (binary) string and tries
93	parse that as an UTF-8 encoded JSON string, returning the resulting simple	123	to parse that as a UTF-8 encoded JSON text, returning the resulting
94	scalar or reference. Croaks on error.	124	reference. Croaks on error.
95		125
96	This function call is functionally identical to C<< JSON::XS->new->utf8	126	This function call is functionally identical to:
97	(1)->decode ($json_string) >>.	127
		128	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		129
		130	Except being faster.
98		131
99	=back	132	=back
		133
		134
		135	=head1 A FEW NOTES ON UNICODE AND PERL
		136
		137	Since this often leads to confusion, here are a few very clear words on
		138	how Unicode works in Perl, modulo bugs.
		139
		140	=over
		141
		142	=item 1. Perl strings can store characters with ordinal values > 255.
		143
		144	This enables you to store Unicode characters as single characters in a
		145	Perl string - very natural.
		146
		147	=item 2. Perl does I<not> associate an encoding with your strings.
		148
		149	... until you force it to, e.g. when matching it against a regex, or
		150	printing the scalar to a file, in which case Perl either interprets your
		151	string as locale-encoded text, octets/binary, or as Unicode, depending
		152	on various settings. In no case is an encoding stored together with your
		153	data, it is I<use> that decides encoding, not any magical meta data.
		154
		155	=item 3. The internal utf-8 flag has no meaning with regards to the
		156	encoding of your string.
		157
		158	Just ignore that flag unless you debug a Perl bug, a module written in
		159	XS or want to dive into the internals of perl. Otherwise it will only
		160	confuse you, as, despite the name, it says nothing about how your string
		161	is encoded. You can have Unicode strings with that flag set, with that
		162	flag clear, and you can have binary data with that flag set and that flag
		163	clear. Other possibilities exist, too.
		164
		165	If you didn't know about that flag, just the better, pretend it doesn't
		166	exist.
		167
		168	=item 4. A "Unicode String" is simply a string where each character can be
		169	validly interpreted as a Unicode code point.
		170
		171	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		172	Unicode string encoded in UTF-8, giving you a binary string.
		173
		174	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		175
		176	It's a fact. Learn to live with it.
		177
		178	=back
		179
		180	I hope this helps :)
		181
100		182
101	=head1 OBJECT-ORIENTED INTERFACE	183	=head1 OBJECT-ORIENTED INTERFACE
102		184
103	The object oriented interface lets you configure your own encoding or	185	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	186	decoding style, within the limits of supported formats.
105		187
106	=over 4	188	=over
107		189
108	=item $json = new JSON::XS	190	=item $json = new JSON::XS
109		191
110	Creates a new JSON::XS object that can be used to de/encode JSON	192	Creates a new JSON::XS object that can be used to de/encode JSON
111	strings. All boolean flags described below are by default I<disabled>.	193	strings. All boolean flags described below are by default I<disabled>
		194	(with the exception of C<allow_nonref>, which defaults to I<enabled> since
		195	version C<4.0>).
112		196
113	The mutators for flags all return the JSON object again and thus calls can	197	The mutators for flags all return the JSON object again and thus calls can
114	be chained:	198	be chained:
115		199
116	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	200	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
117	=> {"a": [1, 2]}	201	=> {"a": [1, 2]}
118		202
119	=item $json = $json->ascii ($enable)	203	=item $json = $json->ascii ([$enable])
120		204
		205	=item $enabled = $json->get_ascii
		206
121	If C<$enable> is true, then the C<encode> method will not generate	207	If C<$enable> is true (or missing), then the C<encode> method will not
122	characters outside the code range C<0..127>. Any unicode characters	208	generate characters outside the code range C<0..127> (which is ASCII). Any
123	outside that range will be escaped using either a single \uXXXX (BMP	209	Unicode characters outside that range will be escaped using either a
124	characters) or a double \uHHHH\uLLLLL escape sequence, as per RFC4627.	210	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
		211	as per RFC4627. The resulting encoded JSON text can be treated as a native
		212	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		213	or any other superset of ASCII.
125		214
126	If C<$enable> is false, then the C<encode> method will not escape Unicode	215	If C<$enable> is false, then the C<encode> method will not escape Unicode
127	characters unless necessary.	216	characters unless required by the JSON syntax or other flags. This results
		217	in a faster and more compact format.
128		218
		219	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		220	document.
		221
		222	The main use for this flag is to produce JSON texts that can be
		223	transmitted over a 7-bit channel, as the encoded JSON texts will not
		224	contain any 8 bit characters.
		225
129	JSON::XS->new->ascii (1)->encode (chr 0x10401)	226	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
130	=> \ud801\udc01	227	=> ["\ud801\udc01"]
131		228
		229	=item $json = $json->latin1 ([$enable])
		230
		231	=item $enabled = $json->get_latin1
		232
		233	If C<$enable> is true (or missing), then the C<encode> method will encode
		234	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		235	outside the code range C<0..255>. The resulting string can be treated as a
		236	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		237	will not be affected in any way by this flag, as C<decode> by default
		238	expects Unicode, which is a strict superset of latin1.
		239
		240	If C<$enable> is false, then the C<encode> method will not escape Unicode
		241	characters unless required by the JSON syntax or other flags.
		242
		243	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		244	document.
		245
		246	The main use for this flag is efficiently encoding binary data as JSON
		247	text, as most octets will not be escaped, resulting in a smaller encoded
		248	size. The disadvantage is that the resulting JSON text is encoded
		249	in latin1 (and must correctly be treated as such when storing and
		250	transferring), a rare encoding for JSON. It is therefore most useful when
		251	you want to store data structures known to contain binary data efficiently
		252	in files or databases, not when talking to other JSON encoders/decoders.
		253
		254	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		255	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
		256
132	=item $json = $json->utf8 ($enable)	257	=item $json = $json->utf8 ([$enable])
133		258
		259	=item $enabled = $json->get_utf8
		260
134	If C<$enable> is true, then the C<encode> method will encode the JSON	261	If C<$enable> is true (or missing), then the C<encode> method will encode
135	string into UTF-8, as required by many protocols, while the C<decode>	262	the JSON result into UTF-8, as required by many protocols, while the
136	method expects to be handled an UTF-8-encoded string. Please note that	263	C<decode> method expects to be handed a UTF-8-encoded string. Please
137	UTF-8-encoded strings do not contain any characters outside the range	264	note that UTF-8-encoded strings do not contain any characters outside the
138	C<0..255>, they are thus useful for bytewise/binary I/O.	265	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		266	versions, enabling this option might enable autodetection of the UTF-16
		267	and UTF-32 encoding families, as described in RFC4627.
139		268
140	If C<$enable> is false, then the C<encode> method will return the JSON	269	If C<$enable> is false, then the C<encode> method will return the JSON
141	string as a (non-encoded) unicode string, while C<decode> expects thus a	270	string as a (non-encoded) Unicode string, while C<decode> expects thus a
142	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	271	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
143	to be done yourself, e.g. using the Encode module.	272	to be done yourself, e.g. using the Encode module.
144		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
		276
		277	Example, output UTF-16BE-encoded JSON:
		278
		279	use Encode;
		280	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		281
		282	Example, decode UTF-32LE-encoded JSON:
		283
		284	use Encode;
		285	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
		286
145	=item $json = $json->pretty ($enable)	287	=item $json = $json->pretty ([$enable])
146		288
147	This enables (or disables) all of the C<indent>, C<space_before> and	289	This enables (or disables) all of the C<indent>, C<space_before> and
148	C<space_after> (and in the future possibly more) flags in one call to	290	C<space_after> (and in the future possibly more) flags in one call to
149	generate the most readable (or most compact) form possible.	291	generate the most readable (or most compact) form possible.
		292
		293	Example, pretty-print some simple structure:
150		294
151	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})	295	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
152	=>	296	=>
153	{	297	{
154	"a" : [	298	"a" : [
155	1,	299	1,
156	2	300	2
157	]	301	]
158	}	302	}
159		303
160	=item $json = $json->indent ($enable)	304	=item $json = $json->indent ([$enable])
161		305
		306	=item $enabled = $json->get_indent
		307
162	If C<$enable> is true, then the C<encode> method will use a multiline	308	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
163	format as output, putting every array member or object/hash key-value pair	309	format as output, putting every array member or object/hash key-value pair
164	into its own line, identing them properly.	310	into its own line, indenting them properly.
165		311
166	If C<$enable> is false, no newlines or indenting will be produced, and the	312	If C<$enable> is false, no newlines or indenting will be produced, and the
167	resulting JSON strings is guarenteed not to contain any C<newlines>.	313	resulting JSON text is guaranteed not to contain any C<newlines>.
168		314
169	This setting has no effect when decoding JSON strings.	315	This setting has no effect when decoding JSON texts.
170		316
171	=item $json = $json->space_before ($enable)	317	=item $json = $json->space_before ([$enable])
172		318
		319	=item $enabled = $json->get_space_before
		320
173	If C<$enable> is true, then the C<encode> method will add an extra	321	If C<$enable> is true (or missing), then the C<encode> method will add an extra
174	optional space before the C<:> separating keys from values in JSON objects.	322	optional space before the C<:> separating keys from values in JSON objects.
175		323
176	If C<$enable> is false, then the C<encode> method will not add any extra	324	If C<$enable> is false, then the C<encode> method will not add any extra
177	space at those places.	325	space at those places.
178		326
179	This setting has no effect when decoding JSON strings. You will also most	327	This setting has no effect when decoding JSON texts. You will also
180	likely combine this setting with C<space_after>.	328	most likely combine this setting with C<space_after>.
181		329
		330	Example, space_before enabled, space_after and indent disabled:
		331
		332	{"key" :"value"}
		333
182	=item $json = $json->space_after ($enable)	334	=item $json = $json->space_after ([$enable])
183		335
		336	=item $enabled = $json->get_space_after
		337
184	If C<$enable> is true, then the C<encode> method will add an extra	338	If C<$enable> is true (or missing), then the C<encode> method will add an extra
185	optional space after the C<:> separating keys from values in JSON objects	339	optional space after the C<:> separating keys from values in JSON objects
186	and extra whitespace after the C<,> separating key-value pairs and array	340	and extra whitespace after the C<,> separating key-value pairs and array
187	members.	341	members.
188		342
189	If C<$enable> is false, then the C<encode> method will not add any extra	343	If C<$enable> is false, then the C<encode> method will not add any extra
190	space at those places.	344	space at those places.
191		345
192	This setting has no effect when decoding JSON strings.	346	This setting has no effect when decoding JSON texts.
193		347
		348	Example, space_before and indent disabled, space_after enabled:
		349
		350	{"key": "value"}
		351
		352	=item $json = $json->relaxed ([$enable])
		353
		354	=item $enabled = $json->get_relaxed
		355
		356	If C<$enable> is true (or missing), then C<decode> will accept some
		357	extensions to normal JSON syntax (see below). C<encode> will not be
		358	affected in any way. I<Be aware that this option makes you accept invalid
		359	JSON texts as if they were valid!>. I suggest only to use this option to
		360	parse application-specific files written by humans (configuration files,
		361	resource files etc.)
		362
		363	If C<$enable> is false (the default), then C<decode> will only accept
		364	valid JSON texts.
		365
		366	Currently accepted extensions are:
		367
		368	=over
		369
		370	=item * list items can have an end-comma
		371
		372	JSON I<separates> array elements and key-value pairs with commas. This
		373	can be annoying if you write JSON texts manually and want to be able to
		374	quickly append elements, so this extension accepts comma at the end of
		375	such items not just between them:
		376
		377	[
		378	1,
		379	2, <- this comma not normally allowed
		380	]
		381	{
		382	"k1": "v1",
		383	"k2": "v2", <- this comma not normally allowed
		384	}
		385
		386	=item * shell-style '#'-comments
		387
		388	Whenever JSON allows whitespace, shell-style comments are additionally
		389	allowed. They are terminated by the first carriage-return or line-feed
		390	character, after which more white-space and comments are allowed.
		391
		392	[
		393	1, # this comment not allowed in JSON
		394	# neither this one...
		395	]
		396
		397	=item * literal ASCII TAB characters in strings
		398
		399	Literal ASCII TAB characters are now allowed in strings (and treated as
		400	C<\t>).
		401
		402	[
		403	"Hello\tWorld",
		404	"Hello<TAB>World", # literal <TAB> would not normally be allowed
		405	]
		406
		407	=back
		408
194	=item $json = $json->canonical ($enable)	409	=item $json = $json->canonical ([$enable])
195		410
		411	=item $enabled = $json->get_canonical
		412
196	If C<$enable> is true, then the C<encode> method will output JSON objects	413	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
197	by sorting their keys. This is adding a comparatively high overhead.	414	by sorting their keys. This is adding a comparatively high overhead.
198		415
199	If C<$enable> is false, then the C<encode> method will output key-value	416	If C<$enable> is false, then the C<encode> method will output key-value
200	pairs in the order Perl stores them (which will likely change between runs	417	pairs in the order Perl stores them (which will likely change between runs
201	of the same script).	418	of the same script, and can change even within the same run from 5.18
		419	onwards).
202		420
203	This option is useful if you want the same data structure to be encoded as	421	This option is useful if you want the same data structure to be encoded as
204	the same JSON string (given the same overall settings). If it is disabled,	422	the same JSON text (given the same overall settings). If it is disabled,
205	the same hash migh be encoded differently even if contains the same data,	423	the same hash might be encoded differently even if contains the same data,
206	as key-value pairs have no inherent ordering in Perl.	424	as key-value pairs have no inherent ordering in Perl.
207		425
208	This setting has no effect when decoding JSON strings.	426	This setting has no effect when decoding JSON texts.
209		427
		428	This setting has currently no effect on tied hashes.
		429
210	=item $json = $json->allow_nonref ($enable)	430	=item $json = $json->allow_nonref ([$enable])
211		431
		432	=item $enabled = $json->get_allow_nonref
		433
		434	Unlike other boolean options, this opotion is enabled by default beginning
		435	with version C<4.0>. See L<SECURITY CONSIDERATIONS> for the gory details.
		436
212	If C<$enable> is true, then the C<encode> method can convert a	437	If C<$enable> is true (or missing), then the C<encode> method can convert a
213	non-reference into its corresponding string, number or null JSON value,	438	non-reference into its corresponding string, number or null JSON value,
214	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	439	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
215	values instead of croaking.	440	values instead of croaking.
216		441
217	If C<$enable> is false, then the C<encode> method will croak if it isn't	442	If C<$enable> is false, then the C<encode> method will croak if it isn't
218	passed an arrayref or hashref, as JSON strings must either be an object	443	passed an arrayref or hashref, as JSON texts must either be an object
219	or array. Likewise, C<decode> will croak if given something that is not a	444	or array. Likewise, C<decode> will croak if given something that is not a
220	JSON object or array.	445	JSON object or array.
221		446
		447	Example, encode a Perl scalar as JSON value without enabled C<allow_nonref>,
		448	resulting in an error:
		449
		450	JSON::XS->new->allow_nonref (0)->encode ("Hello, World!")
		451	=> hash- or arrayref expected...
		452
		453	=item $json = $json->allow_unknown ([$enable])
		454
		455	=item $enabled = $json->get_allow_unknown
		456
		457	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		458	exception when it encounters values it cannot represent in JSON (for
		459	example, filehandles) but instead will encode a JSON C<null> value. Note
		460	that blessed objects are not included here and are handled separately by
		461	c<allow_nonref>.
		462
		463	If C<$enable> is false (the default), then C<encode> will throw an
		464	exception when it encounters anything it cannot encode as JSON.
		465
		466	This option does not affect C<decode> in any way, and it is recommended to
		467	leave it off unless you know your communications partner.
		468
		469	=item $json = $json->allow_blessed ([$enable])
		470
		471	=item $enabled = $json->get_allow_blessed
		472
		473	See L<OBJECT SERIALISATION> for details.
		474
		475	If C<$enable> is true (or missing), then the C<encode> method will not
		476	barf when it encounters a blessed reference that it cannot convert
		477	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
		478
		479	If C<$enable> is false (the default), then C<encode> will throw an
		480	exception when it encounters a blessed object that it cannot convert
		481	otherwise.
		482
		483	This setting has no effect on C<decode>.
		484
		485	=item $json = $json->convert_blessed ([$enable])
		486
		487	=item $enabled = $json->get_convert_blessed
		488
		489	See L<OBJECT SERIALISATION> for details.
		490
		491	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		492	blessed object, will check for the availability of the C<TO_JSON> method
		493	on the object's class. If found, it will be called in scalar context and
		494	the resulting scalar will be encoded instead of the object.
		495
		496	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		497	returns other blessed objects, those will be handled in the same
		498	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		499	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		500	methods called by the Perl core (== not by the user of the object) are
		501	usually in upper case letters and to avoid collisions with any C<to_json>
		502	function or method.
		503
		504	If C<$enable> is false (the default), then C<encode> will not consider
		505	this type of conversion.
		506
		507	This setting has no effect on C<decode>.
		508
		509	=item $json = $json->allow_tags ([$enable])
		510
		511	=item $enabled = $json->get_allow_tags
		512
		513	See L<OBJECT SERIALISATION> for details.
		514
		515	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		516	blessed object, will check for the availability of the C<FREEZE> method on
		517	the object's class. If found, it will be used to serialise the object into
		518	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		519
		520	It also causes C<decode> to parse such tagged JSON values and deserialise
		521	them via a call to the C<THAW> method.
		522
		523	If C<$enable> is false (the default), then C<encode> will not consider
		524	this type of conversion, and tagged JSON values will cause a parse error
		525	in C<decode>, as if tags were not part of the grammar.
		526
		527	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		528
		529	When C<$coderef> is specified, it will be called from C<decode> each
		530	time it decodes a JSON object. The only argument is a reference to
		531	the newly-created hash. If the code reference returns a single scalar
		532	(which need not be a reference), this value (or rather a copy of it) is
		533	inserted into the deserialised data structure. If it returns an empty
		534	list (NOTE: I<not> C<undef>, which is a valid scalar), the original
		535	deserialised hash will be inserted. This setting can slow down decoding
		536	considerably.
		537
		538	When C<$coderef> is omitted or undefined, any existing callback will
		539	be removed and C<decode> will not change the deserialised hash in any
		540	way.
		541
		542	Example, convert all JSON objects into the integer 5:
		543
		544	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		545	# returns [5]
		546	$js->decode ('[{}]')
		547	# throw an exception because allow_nonref is not enabled
		548	# so a lone 5 is not allowed.
		549	$js->decode ('{"a":1, "b":2}');
		550
		551	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		552
		553	Works remotely similar to C<filter_json_object>, but is only called for
		554	JSON objects having a single key named C<$key>.
		555
		556	This C<$coderef> is called before the one specified via
		557	C<filter_json_object>, if any. It gets passed the single value in the JSON
		558	object. If it returns a single value, it will be inserted into the data
		559	structure. If it returns nothing (not even C<undef> but the empty list),
		560	the callback from C<filter_json_object> will be called next, as if no
		561	single-key callback were specified.
		562
		563	If C<$coderef> is omitted or undefined, the corresponding callback will be
		564	disabled. There can only ever be one callback for a given key.
		565
		566	As this callback gets called less often then the C<filter_json_object>
		567	one, decoding speed will not usually suffer as much. Therefore, single-key
		568	objects make excellent targets to serialise Perl objects into, especially
		569	as single-key JSON objects are as close to the type-tagged value concept
		570	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		571	support this in any way, so you need to make sure your data never looks
		572	like a serialised Perl hash.
		573
		574	Typical names for the single object key are C<__class_whatever__>, or
		575	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		576	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		577	with real hashes.
		578
		579	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		580	into the corresponding C<< $WIDGET{<id>} >> object:
		581
		582	# return whatever is in $WIDGET{5}:
		583	JSON::XS
		584	->new
		585	->filter_json_single_key_object (__widget__ => sub {
		586	$WIDGET{ $_[0] }
		587	})
		588	->decode ('{"__widget__": 5')
		589
		590	# this can be used with a TO_JSON method in some "widget" class
		591	# for serialisation to json:
		592	sub WidgetBase::TO_JSON {
		593	my ($self) = @_;
		594
		595	unless ($self->{id}) {
		596	$self->{id} = ..get..some..id..;
		597	$WIDGET{$self->{id}} = $self;
		598	}
		599
		600	{ __widget__ => $self->{id} }
		601	}
		602
		603	=item $json = $json->shrink ([$enable])
		604
		605	=item $enabled = $json->get_shrink
		606
		607	Perl usually over-allocates memory a bit when allocating space for
		608	strings. This flag optionally resizes strings generated by either
		609	C<encode> or C<decode> to their minimum size possible. This can save
		610	memory when your JSON texts are either very very long or you have many
		611	short strings. It will also try to downgrade any strings to octet-form
		612	if possible: perl stores strings internally either in an encoding called
		613	UTF-X or in octet-form. The latter cannot store everything but uses less
		614	space in general (and some buggy Perl or C code might even rely on that
		615	internal representation being used).
		616
		617	The actual definition of what shrink does might change in future versions,
		618	but it will always try to save space at the expense of time.
		619
		620	If C<$enable> is true (or missing), the string returned by C<encode> will
		621	be shrunk-to-fit, while all strings generated by C<decode> will also be
		622	shrunk-to-fit.
		623
		624	If C<$enable> is false, then the normal perl allocation algorithms are used.
		625	If you work with your data, then this is likely to be faster.
		626
		627	In the future, this setting might control other things, such as converting
		628	strings that look like integers or floats into integers or floats
		629	internally (there is no difference on the Perl level), saving space.
		630
		631	=item $json = $json->max_depth ([$maximum_nesting_depth])
		632
		633	=item $max_depth = $json->get_max_depth
		634
		635	Sets the maximum nesting level (default C<512>) accepted while encoding
		636	or decoding. If a higher nesting level is detected in JSON text or a Perl
		637	data structure, then the encoder and decoder will stop and croak at that
		638	point.
		639
		640	Nesting level is defined by number of hash- or arrayrefs that the encoder
		641	needs to traverse to reach a given point or the number of C<{> or C<[>
		642	characters without their matching closing parenthesis crossed to reach a
		643	given character in a string.
		644
		645	Setting the maximum depth to one disallows any nesting, so that ensures
		646	that the object is only a single hash/object or array.
		647
		648	If no argument is given, the highest possible setting will be used, which
		649	is rarely useful.
		650
		651	Note that nesting is implemented by recursion in C. The default value has
		652	been chosen to be as large as typical operating systems allow without
		653	crashing.
		654
		655	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		656
		657	=item $json = $json->max_size ([$maximum_string_size])
		658
		659	=item $max_size = $json->get_max_size
		660
		661	Set the maximum length a JSON text may have (in bytes) where decoding is
		662	being attempted. The default is C<0>, meaning no limit. When C<decode>
		663	is called on a string that is longer then this many bytes, it will not
		664	attempt to decode the string but throw an exception. This setting has no
		665	effect on C<encode> (yet).
		666
		667	If no argument is given, the limit check will be deactivated (same as when
		668	C<0> is specified).
		669
		670	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		671
222	=item $json_string = $json->encode ($perl_scalar)	672	=item $json_text = $json->encode ($perl_scalar)
223		673
224	Converts the given Perl data structure (a simple scalar or a reference	674	Converts the given Perl value or data structure to its JSON
225	to a hash or array) to its JSON representation. Simple scalars will be	675	representation. Croaks on error.
226	converted into JSON string or number sequences, while references to arrays
227	become JSON arrays and references to hashes become JSON objects. Undefined
228	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
229	nor C<false> values will be generated.
230		676
231	=item $perl_scalar = $json->decode ($json_string)	677	=item $perl_scalar = $json->decode ($json_text)
232		678
233	The opposite of C<encode>: expects a JSON string and tries to parse it,	679	The opposite of C<encode>: expects a JSON text and tries to parse it,
234	returning the resulting simple scalar or reference. Croaks on error.	680	returning the resulting simple scalar or reference. Croaks on error.
235		681
236	JSON numbers and strings become simple Perl scalars. JSON arrays become	682	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
237	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	683
238	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	684	This works like the C<decode> method, but instead of raising an exception
		685	when there is trailing garbage after the first JSON object, it will
		686	silently stop parsing there and return the number of characters consumed
		687	so far.
		688
		689	This is useful if your JSON texts are not delimited by an outer protocol
		690	and you need to know where the JSON text ends.
		691
		692	JSON::XS->new->decode_prefix ("[1] the tail")
		693	=> ([1], 3)
239		694
240	=back	695	=back
241		696
242	=head1 COMPARISON
243		697
244	As already mentioned, this module was created because none of the existing	698	=head1 INCREMENTAL PARSING
245	JSON modules could be made to work correctly. First I will describe the
246	problems (or pleasures) I encountered with various existing JSON modules,
247	followed by some benchmark values. JSON::XS was designed not to suffer
248	from any of these problems or limitations.
249		699
		700	In some cases, there is the need for incremental parsing of JSON
		701	texts. While this module always has to keep both JSON text and resulting
		702	Perl data structure in memory at one time, it does allow you to parse a
		703	JSON stream incrementally. It does so by accumulating text until it has
		704	a full JSON object, which it then can decode. This process is similar to
		705	using C<decode_prefix> to see if a full JSON object is available, but
		706	is much more efficient (and can be implemented with a minimum of method
		707	calls).
		708
		709	JSON::XS will only attempt to parse the JSON text once it is sure it
		710	has enough text to get a decisive result, using a very simple but
		711	truly incremental parser. This means that it sometimes won't stop as
		712	early as the full parser, for example, it doesn't detect mismatched
		713	parentheses. The only thing it guarantees is that it starts decoding as
		714	soon as a syntactically valid JSON text has been seen. This means you need
		715	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		716	parsing in the presence if syntax errors.
		717
		718	The following methods implement this incremental parser.
		719
250	=over 4	720	=over
251		721
252	=item JSON	722	=item [void, scalar or list context] = $json->incr_parse ([$string])
253		723
254	Slow (but very portable, as it is written in pure Perl).	724	This is the central parsing function. It can both append new text and
		725	extract objects from the stream accumulated so far (both of these
		726	functions are optional).
255		727
256	Undocumented/buggy Unicode handling (how JSON handles unicode values is	728	If C<$string> is given, then this string is appended to the already
257	undocumented. One can get far by feeding it unicode strings and doing	729	existing JSON fragment stored in the C<$json> object.
258	en-/decoding oneself, but unicode escapes are not working properly).
259		730
260	No roundtripping (strings get clobbered if they look like numbers, e.g.	731	After that, if the function is called in void context, it will simply
261	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	732	return without doing anything further. This can be used to add more text
262	decode into the number 2.	733	in as many chunks as you want.
263		734
264	=item JSON::PC	735	If the method is called in scalar context, then it will try to extract
		736	exactly I<one> JSON object. If that is successful, it will return this
		737	object, otherwise it will return C<undef>. If there is a parse error,
		738	this method will croak just as C<decode> would do (one can then use
		739	C<incr_skip> to skip the erroneous part). This is the most common way of
		740	using the method.
265		741
266	Very fast.	742	And finally, in list context, it will try to extract as many objects
		743	from the stream as it can find and return them, or the empty list
		744	otherwise. For this to work, there must be no separators (other than
		745	whitespace) between the JSON objects or arrays, instead they must be
		746	concatenated back-to-back. If an error occurs, an exception will be
		747	raised as in the scalar context case. Note that in this case, any
		748	previously-parsed JSON texts will be lost.
267		749
268	Undocumented/buggy Unicode handling.	750	Example: Parse some JSON arrays/objects in a given string and return
		751	them.
269		752
270	No roundtripping.	753	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
271		754
272	Has problems handling many Perl values (e.g. regex results and other magic	755	=item $lvalue_string = $json->incr_text
273	values will make it croak).
274		756
275	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	757	This method returns the currently stored JSON fragment as an lvalue, that
276	which is not a valid JSON string.	758	is, you can manipulate it. This I<only> works when a preceding call to
		759	C<incr_parse> in I<scalar context> successfully returned an object. Under
		760	all other circumstances you must not call this function (I mean it.
		761	although in simple tests it might actually work, it I<will> fail under
		762	real world conditions). As a special exception, you can also call this
		763	method before having parsed anything.
277		764
278	Unmaintained (maintainer unresponsive for many months, bugs are not	765	That means you can only use this function to look at or manipulate text
279	getting fixed).	766	before or after complete JSON objects, not while the parser is in the
		767	middle of parsing a JSON object.
280		768
281	=item JSON::Syck	769	This function is useful in two cases: a) finding the trailing text after a
		770	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		771	(such as commas).
282		772
283	Very buggy (often crashes).	773	=item $json->incr_skip
284		774
285	Very inflexible (no human-readable format supported, format pretty much	775	This will reset the state of the incremental parser and will remove
286	undocumented. I need at least a format for easy reading by humans and a	776	the parsed text from the input buffer so far. This is useful after
287	single-line compact format for use in a protocol, and preferably a way to	777	C<incr_parse> died, in which case the input buffer and incremental parser
288	generate ASCII-only JSON strings).	778	state is left unchanged, to skip the text parsed so far and to reset the
		779	parse state.
289		780
290	Completely broken (and confusingly documented) Unicode handling (unicode	781	The difference to C<incr_reset> is that only text until the parse error
291	escapes are not working properly, you need to set ImplicitUnicode to	782	occurred is removed.
292	I<different> values on en- and decoding to get symmetric behaviour).
293		783
294	No roundtripping (simple cases work, but this depends on wether the scalar	784	=item $json->incr_reset
295	value was used in a numeric context or not).
296		785
297	Dumping hashes may skip hash values depending on iterator state.	786	This completely resets the incremental parser, that is, after this call,
		787	it will be as if the parser had never parsed anything.
298		788
299	Unmaintained (maintainer unresponsive for many months, bugs are not	789	This is useful if you want to repeatedly parse JSON objects and want to
300	getting fixed).	790	ignore any trailing data, which means you have to reset the parser after
301		791	each successful decode.
302	Does not check input for validity (i.e. will accept non-JSON input and
303	return "something" instead of raising an exception. This is a security
304	issue: imagine two banks transfering money between each other using
305	JSON. One bank might parse a given non-JSON request and deduct money,
306	while the other might reject the transaction with a syntax error. While a
307	good protocol will at least recover, that is extra unnecessary work and
308	the transaction will still not succeed).
309
310	=item JSON::DWIW
311
312	Very fast. Very natural. Very nice.
313
314	Undocumented unicode handling (but the best of the pack. Unicode escapes
315	still don't get parsed properly).
316
317	Very inflexible.
318
319	No roundtripping.
320
321	Does not generate valid JSON (key strings are often unquoted, empty keys
322	result in nothing being output)
323
324	Does not check input for validity.
325		792
326	=back	793	=back
		794
		795	=head2 LIMITATIONS
		796
		797	The incremental parser is a non-exact parser: it works by gathering as
		798	much text as possible that I<could> be a valid JSON text, followed by
		799	trying to decode it.
		800
		801	That means it sometimes needs to read more data than strictly necessary to
		802	diagnose an invalid JSON text. For example, after parsing the following
		803	fragment, the parser I<could> stop with an error, as this fragment
		804	I<cannot> be the beginning of a valid JSON text:
		805
		806	[,
		807
		808	In reality, hopwever, the parser might continue to read data until a
		809	length limit is exceeded or it finds a closing bracket.
		810
		811	=head2 EXAMPLES
		812
		813	Some examples will make all this clearer. First, a simple example that
		814	works similarly to C<decode_prefix>: We want to decode the JSON object at
		815	the start of a string and identify the portion after the JSON object:
		816
		817	my $text = "[1,2,3] hello";
		818
		819	my $json = new JSON::XS;
		820
		821	my $obj = $json->incr_parse ($text)
		822	or die "expected JSON object or array at beginning of string";
		823
		824	my $tail = $json->incr_text;
		825	# $tail now contains " hello"
		826
		827	Easy, isn't it?
		828
		829	Now for a more complicated example: Imagine a hypothetical protocol where
		830	you read some requests from a TCP stream, and each request is a JSON
		831	array, without any separation between them (in fact, it is often useful to
		832	use newlines as "separators", as these get interpreted as whitespace at
		833	the start of the JSON text, which makes it possible to test said protocol
		834	with C<telnet>...).
		835
		836	Here is how you'd do it (it is trivial to write this in an event-based
		837	manner):
		838
		839	my $json = new JSON::XS;
		840
		841	# read some data from the socket
		842	while (sysread $socket, my $buf, 4096) {
		843
		844	# split and decode as many requests as possible
		845	for my $request ($json->incr_parse ($buf)) {
		846	# act on the $request
		847	}
		848	}
		849
		850	Another complicated example: Assume you have a string with JSON objects
		851	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		852	[3]>). To parse them, we have to skip the commas between the JSON texts,
		853	and here is where the lvalue-ness of C<incr_text> comes in useful:
		854
		855	my $text = "[1],[2], [3]";
		856	my $json = new JSON::XS;
		857
		858	# void context, so no parsing done
		859	$json->incr_parse ($text);
		860
		861	# now extract as many objects as possible. note the
		862	# use of scalar context so incr_text can be called.
		863	while (my $obj = $json->incr_parse) {
		864	# do something with $obj
		865
		866	# now skip the optional comma
		867	$json->incr_text =~ s/^ \s* , //x;
		868	}
		869
		870	Now lets go for a very complex example: Assume that you have a gigantic
		871	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		872	but you cannot load it into memory fully (this has actually happened in
		873	the real world :).
		874
		875	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		876	can still help you: You implement a (very simple) array parser and let
		877	JSON decode the array elements, which are all full JSON objects on their
		878	own (this wouldn't work if the array elements could be JSON numbers, for
		879	example):
		880
		881	my $json = new JSON::XS;
		882
		883	# open the monster
		884	open my $fh, "<bigfile.json"
		885	or die "bigfile: $!";
		886
		887	# first parse the initial "["
		888	for (;;) {
		889	sysread $fh, my $buf, 65536
		890	or die "read error: $!";
		891	$json->incr_parse ($buf); # void context, so no parsing
		892
		893	# Exit the loop once we found and removed(!) the initial "[".
		894	# In essence, we are (ab-)using the $json object as a simple scalar
		895	# we append data to.
		896	last if $json->incr_text =~ s/^ \s* \[ //x;
		897	}
		898
		899	# now we have the skipped the initial "[", so continue
		900	# parsing all the elements.
		901	for (;;) {
		902	# in this loop we read data until we got a single JSON object
		903	for (;;) {
		904	if (my $obj = $json->incr_parse) {
		905	# do something with $obj
		906	last;
		907	}
		908
		909	# add more data
		910	sysread $fh, my $buf, 65536
		911	or die "read error: $!";
		912	$json->incr_parse ($buf); # void context, so no parsing
		913	}
		914
		915	# in this loop we read data until we either found and parsed the
		916	# separating "," between elements, or the final "]"
		917	for (;;) {
		918	# first skip whitespace
		919	$json->incr_text =~ s/^\s*//;
		920
		921	# if we find "]", we are done
		922	if ($json->incr_text =~ s/^\]//) {
		923	print "finished.\n";
		924	exit;
		925	}
		926
		927	# if we find ",", we can continue with the next element
		928	if ($json->incr_text =~ s/^,//) {
		929	last;
		930	}
		931
		932	# if we find anything else, we have a parse error!
		933	if (length $json->incr_text) {
		934	die "parse error near ", $json->incr_text;
		935	}
		936
		937	# else add more data
		938	sysread $fh, my $buf, 65536
		939	or die "read error: $!";
		940	$json->incr_parse ($buf); # void context, so no parsing
		941	}
		942
		943	This is a complex example, but most of the complexity comes from the fact
		944	that we are trying to be correct (bear with me if I am wrong, I never ran
		945	the above example :).
		946
		947
		948
		949	=head1 MAPPING
		950
		951	This section describes how JSON::XS maps Perl values to JSON values and
		952	vice versa. These mappings are designed to "do the right thing" in most
		953	circumstances automatically, preserving round-tripping characteristics
		954	(what you put in comes out as something equivalent).
		955
		956	For the more enlightened: note that in the following descriptions,
		957	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		958	refers to the abstract Perl language itself.
		959
		960
		961	=head2 JSON -> PERL
		962
		963	=over
		964
		965	=item object
		966
		967	A JSON object becomes a reference to a hash in Perl. No ordering of object
		968	keys is preserved (JSON does not preserve object key ordering itself).
		969
		970	=item array
		971
		972	A JSON array becomes a reference to an array in Perl.
		973
		974	=item string
		975
		976	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		977	are represented by the same codepoints in the Perl string, so no manual
		978	decoding is necessary.
		979
		980	=item number
		981
		982	A JSON number becomes either an integer, numeric (floating point) or
		983	string scalar in perl, depending on its range and any fractional parts. On
		984	the Perl level, there is no difference between those as Perl handles all
		985	the conversion details, but an integer may take slightly less memory and
		986	might represent more values exactly than floating point numbers.
		987
		988	If the number consists of digits only, JSON::XS will try to represent
		989	it as an integer value. If that fails, it will try to represent it as
		990	a numeric (floating point) value if that is possible without loss of
		991	precision. Otherwise it will preserve the number as a string value (in
		992	which case you lose roundtripping ability, as the JSON number will be
		993	re-encoded to a JSON string).
		994
		995	Numbers containing a fractional or exponential part will always be
		996	represented as numeric (floating point) values, possibly at a loss of
		997	precision (in which case you might lose perfect roundtripping ability, but
		998	the JSON number will still be re-encoded as a JSON number).
		999
		1000	Note that precision is not accuracy - binary floating point values cannot
		1001	represent most decimal fractions exactly, and when converting from and to
		1002	floating point, JSON::XS only guarantees precision up to but not including
		1003	the least significant bit.
		1004
		1005	=item true, false
		1006
		1007	These JSON atoms become C<Types::Serialiser::true> and
		1008	C<Types::Serialiser::false>, respectively. They are overloaded to act
		1009	almost exactly like the numbers C<1> and C<0>. You can check whether
		1010	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1011	function (after C<use Types::Serialier>, of course).
		1012
		1013	=item null
		1014
		1015	A JSON null atom becomes C<undef> in Perl.
		1016
		1017	=item shell-style comments (C<< # I<text> >>)
		1018
		1019	As a nonstandard extension to the JSON syntax that is enabled by the
		1020	C<relaxed> setting, shell-style comments are allowed. They can start
		1021	anywhere outside strings and go till the end of the line.
		1022
		1023	=item tagged values (C<< (I<tag>)I<value> >>).
		1024
		1025	Another nonstandard extension to the JSON syntax, enabled with the
		1026	C<allow_tags> setting, are tagged values. In this implementation, the
		1027	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1028	I<value> must be a JSON array encoding optional constructor arguments.
		1029
		1030	See L<OBJECT SERIALISATION>, below, for details.
		1031
		1032	=back
		1033
		1034
		1035	=head2 PERL -> JSON
		1036
		1037	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		1038	truly typeless language, so we can only guess which JSON type is meant by
		1039	a Perl value.
		1040
		1041	=over
		1042
		1043	=item hash references
		1044
		1045	Perl hash references become JSON objects. As there is no inherent
		1046	ordering in hash keys (or JSON objects), they will usually be encoded
		1047	in a pseudo-random order. JSON::XS can optionally sort the hash keys
		1048	(determined by the I<canonical> flag), so the same datastructure will
		1049	serialise to the same JSON text (given same settings and version of
		1050	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
		1051	e.g. when you want to compare some JSON text against another for equality.
		1052
		1053	=item array references
		1054
		1055	Perl array references become JSON arrays.
		1056
		1057	=item other references
		1058
		1059	Other unblessed references are generally not allowed and will cause an
		1060	exception to be thrown, except for references to the integers C<0> and
		1061	C<1>, which get turned into C<false> and C<true> atoms in JSON.
		1062
		1063	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1064	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1065	and C<Types::Serialiser::true> to improve readability.
		1066
		1067	use Types::Serialiser;
		1068	encode_json [\0, Types::Serialiser::true] # yields [false,true]
		1069
		1070	=item Types::Serialiser::true, Types::Serialiser::false
		1071
		1072	These special values from the L<Types::Serialiser> module become JSON true
		1073	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1074	directly if you want.
		1075
		1076	=item blessed objects
		1077
		1078	Blessed objects are not directly representable in JSON, but C<JSON::XS>
		1079	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
		1080	below, for details.
		1081
		1082	=item simple scalars
		1083
		1084	Simple Perl scalars (any scalar that is not a reference) are the most
		1085	difficult objects to encode: JSON::XS will encode undefined scalars as
		1086	JSON C<null> values, scalars that have last been used in a string context
		1087	before encoding as JSON strings, and anything else as number value:
		1088
		1089	# dump as number
		1090	encode_json [2] # yields [2]
		1091	encode_json [-3.0e17] # yields [-3e+17]
		1092	my $value = 5; encode_json [$value] # yields [5]
		1093
		1094	# used as string, so dump as string
		1095	print $value;
		1096	encode_json [$value] # yields ["5"]
		1097
		1098	# undef becomes null
		1099	encode_json [undef] # yields [null]
		1100
		1101	You can force the type to be a JSON string by stringifying it:
		1102
		1103	my $x = 3.1; # some variable containing a number
		1104	"$x"; # stringified
		1105	$x .= ""; # another, more awkward way to stringify
		1106	print $x; # perl does it for you, too, quite often
		1107
		1108	You can force the type to be a JSON number by numifying it:
		1109
		1110	my $x = "3"; # some variable containing a string
		1111	$x += 0; # numify it, ensuring it will be dumped as a number
		1112	$x *= 1; # same thing, the choice is yours.
		1113
		1114	You can not currently force the type in other, less obscure, ways. Tell me
		1115	if you need this capability (but don't forget to explain why it's needed
		1116	:).
		1117
		1118	Note that numerical precision has the same meaning as under Perl (so
		1119	binary to decimal conversion follows the same rules as in Perl, which
		1120	can differ to other languages). Also, your perl interpreter might expose
		1121	extensions to the floating point numbers of your platform, such as
		1122	infinities or NaN's - these cannot be represented in JSON, and it is an
		1123	error to pass those in.
		1124
		1125	=back
		1126
		1127	=head2 OBJECT SERIALISATION
		1128
		1129	As JSON cannot directly represent Perl objects, you have to choose between
		1130	a pure JSON representation (without the ability to deserialise the object
		1131	automatically again), and a nonstandard extension to the JSON syntax,
		1132	tagged values.
		1133
		1134	=head3 SERIALISATION
		1135
		1136	What happens when C<JSON::XS> encounters a Perl object depends on the
		1137	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
		1138	used in this order:
		1139
		1140	=over
		1141
		1142	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
		1143
		1144	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1145	serialisation protocol to create a tagged JSON value, using a nonstandard
		1146	extension to the JSON syntax.
		1147
		1148	This works by invoking the C<FREEZE> method on the object, with the first
		1149	argument being the object to serialise, and the second argument being the
		1150	constant string C<JSON> to distinguish it from other serialisers.
		1151
		1152	The C<FREEZE> method can return any number of values (i.e. zero or
		1153	more). These values and the paclkage/classname of the object will then be
		1154	encoded as a tagged JSON value in the following format:
		1155
		1156	("classname")[FREEZE return values...]
		1157
		1158	e.g.:
		1159
		1160	("URI")["http://www.google.com/"]
		1161	("MyDate")[2013,10,29]
		1162	("ImageData::JPEG")["Z3...VlCg=="]
		1163
		1164	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1165	objects C<type> and C<id> members to encode the object:
		1166
		1167	sub My::Object::FREEZE {
		1168	my ($self, $serialiser) = @_;
		1169
		1170	($self->{type}, $self->{id})
		1171	}
		1172
		1173	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
		1174
		1175	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1176	context. It must return a single scalar that can be directly encoded into
		1177	JSON. This scalar replaces the object in the JSON text.
		1178
		1179	For example, the following C<TO_JSON> method will convert all L<URI>
		1180	objects to JSON strings when serialised. The fatc that these values
		1181	originally were L<URI> objects is lost.
		1182
		1183	sub URI::TO_JSON {
		1184	my ($uri) = @_;
		1185	$uri->as_string
		1186	}
		1187
		1188	=item 3. C<allow_blessed> is enabled.
		1189
		1190	The object will be serialised as a JSON null value.
		1191
		1192	=item 4. none of the above
		1193
		1194	If none of the settings are enabled or the respective methods are missing,
		1195	C<JSON::XS> throws an exception.
		1196
		1197	=back
		1198
		1199	=head3 DESERIALISATION
		1200
		1201	For deserialisation there are only two cases to consider: either
		1202	nonstandard tagging was used, in which case C<allow_tags> decides,
		1203	or objects cannot be automatically be deserialised, in which
		1204	case you can use postprocessing or the C<filter_json_object> or
		1205	C<filter_json_single_key_object> callbacks to get some real objects our of
		1206	your JSON.
		1207
		1208	This section only considers the tagged value case: I a tagged JSON object
		1209	is encountered during decoding and C<allow_tags> is disabled, a parse
		1210	error will result (as if tagged values were not part of the grammar).
		1211
		1212	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1213	of the package/classname used during serialisation (it will not attempt
		1214	to load the package as a Perl module). If there is no such method, the
		1215	decoding will fail with an error.
		1216
		1217	Otherwise, the C<THAW> method is invoked with the classname as first
		1218	argument, the constant string C<JSON> as second argument, and all the
		1219	values from the JSON array (the values originally returned by the
		1220	C<FREEZE> method) as remaining arguments.
		1221
		1222	The method must then return the object. While technically you can return
		1223	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1224	make that work in all cases, so better return an actual blessed reference.
		1225
		1226	As an example, let's implement a C<THAW> function that regenerates the
		1227	C<My::Object> from the C<FREEZE> example earlier:
		1228
		1229	sub My::Object::THAW {
		1230	my ($class, $serialiser, $type, $id) = @_;
		1231
		1232	$class->new (type => $type, id => $id)
		1233	}
		1234
		1235
		1236	=head1 ENCODING/CODESET FLAG NOTES
		1237
		1238	The interested reader might have seen a number of flags that signify
		1239	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1240	some confusion on what these do, so here is a short comparison:
		1241
		1242	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1243	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1244	control whether C<encode> escapes character values outside their respective
		1245	codeset range. Neither of these flags conflict with each other, although
		1246	some combinations make less sense than others.
		1247
		1248	Care has been taken to make all flags symmetrical with respect to
		1249	C<encode> and C<decode>, that is, texts encoded with any combination of
		1250	these flag values will be correctly decoded when the same flags are used
		1251	- in general, if you use different flag settings while encoding vs. when
		1252	decoding you likely have a bug somewhere.
		1253
		1254	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1255	simply an abstract set of character-codepoint pairs, while an encoding
		1256	takes those codepoint numbers and I<encodes> them, in our case into
		1257	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1258	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1259	the same time, which can be confusing.
		1260
		1261	=over
		1262
		1263	=item C<utf8> flag disabled
		1264
		1265	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1266	and expect Unicode strings, that is, characters with high ordinal Unicode
		1267	values (> 255) will be encoded as such characters, and likewise such
		1268	characters are decoded as-is, no changes to them will be done, except
		1269	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1270	respectively (to Perl, these are the same thing in strings unless you do
		1271	funny/weird/dumb stuff).
		1272
		1273	This is useful when you want to do the encoding yourself (e.g. when you
		1274	want to have UTF-16 encoded JSON texts) or when some other layer does
		1275	the encoding for you (for example, when printing to a terminal using a
		1276	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1277	to UTF-8 encode your data first and have Perl encode it another time).
		1278
		1279	=item C<utf8> flag enabled
		1280
		1281	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1282	characters using the corresponding UTF-8 multi-byte sequence, and will
		1283	expect your input strings to be encoded as UTF-8, that is, no "character"
		1284	of the input string must have any value > 255, as UTF-8 does not allow
		1285	that.
		1286
		1287	The C<utf8> flag therefore switches between two modes: disabled means you
		1288	will get a Unicode string in Perl, enabled means you get a UTF-8 encoded
		1289	octet/binary string in Perl.
		1290
		1291	=item C<latin1> or C<ascii> flags enabled
		1292
		1293	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1294	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1295	characters as specified by the C<utf8> flag.
		1296
		1297	If C<utf8> is disabled, then the result is also correctly encoded in those
		1298	character sets (as both are proper subsets of Unicode, meaning that a
		1299	Unicode string with all character values < 256 is the same thing as a
		1300	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1301	the same thing as an ASCII string in Perl).
		1302
		1303	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1304	regardless of these flags, just some more characters will be escaped using
		1305	C<\uXXXX> then before.
		1306
		1307	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1308	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1309	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1310	a subset of Unicode), while ASCII is.
		1311
		1312	Surprisingly, C<decode> will ignore these flags and so treat all input
		1313	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1314	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1315	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1316
		1317	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1318	they only govern when the JSON output engine escapes a character or not.
		1319
		1320	The main use for C<latin1> is to relatively efficiently store binary data
		1321	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1322
		1323	The main use for C<ascii> is to force the output to not contain characters
		1324	with values > 127, which means you can interpret the resulting string
		1325	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1326	8-bit-encoding, and still get the same data structure back. This is useful
		1327	when your channel for JSON transfer is not 8-bit clean or the encoding
		1328	might be mangled in between (e.g. in mail), and works because ASCII is a
		1329	proper subset of most 8-bit and multibyte encodings in use in the world.
		1330
		1331	=back
		1332
		1333
		1334	=head2 JSON and ECMAscript
		1335
		1336	JSON syntax is based on how literals are represented in javascript (the
		1337	not-standardised predecessor of ECMAscript) which is presumably why it is
		1338	called "JavaScript Object Notation".
		1339
		1340	However, JSON is not a subset (and also not a superset of course) of
		1341	ECMAscript (the standard) or javascript (whatever browsers actually
		1342	implement).
		1343
		1344	If you want to use javascript's C<eval> function to "parse" JSON, you
		1345	might run into parse errors for valid JSON texts, or the resulting data
		1346	structure might not be queryable:
		1347
		1348	One of the problems is that U+2028 and U+2029 are valid characters inside
		1349	JSON strings, but are not allowed in ECMAscript string literals, so the
		1350	following Perl fragment will not output something that can be guaranteed
		1351	to be parsable by javascript's C<eval>:
		1352
		1353	use JSON::XS;
		1354
		1355	print encode_json [chr 0x2028];
		1356
		1357	The right fix for this is to use a proper JSON parser in your javascript
		1358	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1359	F<json2.js> parser).
		1360
		1361	If this is not an option, you can, as a stop-gap measure, simply encode to
		1362	ASCII-only JSON:
		1363
		1364	use JSON::XS;
		1365
		1366	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1367
		1368	Note that this will enlarge the resulting JSON text quite a bit if you
		1369	have many non-ASCII characters. You might be tempted to run some regexes
		1370	to only escape U+2028 and U+2029, e.g.:
		1371
		1372	# DO NOT USE THIS!
		1373	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1374	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1375	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1376	print $json;
		1377
		1378	Note that I<this is a bad idea>: the above only works for U+2028 and
		1379	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1380	javascript implementations, however, have issues with other characters as
		1381	well - using C<eval> naively simply I<will> cause problems.
		1382
		1383	Another problem is that some javascript implementations reserve
		1384	some property names for their own purposes (which probably makes
		1385	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1386	C<__proto__> property name for its own purposes.
		1387
		1388	If that is a problem, you could parse try to filter the resulting JSON
		1389	output for these property strings, e.g.:
		1390
		1391	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1392
		1393	This works because C<__proto__> is not valid outside of strings, so every
		1394	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1395
		1396	If you know of other incompatibilities, please let me know.
		1397
		1398
		1399	=head2 JSON and YAML
		1400
		1401	You often hear that JSON is a subset of YAML. This is, however, a mass
		1402	hysteria(*) and very far from the truth (as of the time of this writing),
		1403	so let me state it clearly: I<in general, there is no way to configure
		1404	JSON::XS to output a data structure as valid YAML> that works in all
		1405	cases.
		1406
		1407	If you really must use JSON::XS to generate YAML, you should use this
		1408	algorithm (subject to change in future versions):
		1409
		1410	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1411	my $yaml = $to_yaml->encode ($ref) . "\n";
		1412
		1413	This will I<usually> generate JSON texts that also parse as valid
		1414	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1415	lengths that JSON doesn't have and also has different and incompatible
		1416	unicode character escape syntax, so you should make sure that your hash
		1417	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1418	and that you do not have characters with codepoint values outside the
		1419	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1420	sequences in strings (which JSON::XS does not I<currently> generate, but
		1421	other JSON generators might).
		1422
		1423	There might be other incompatibilities that I am not aware of (or the YAML
		1424	specification has been changed yet again - it does so quite often). In
		1425	general you should not try to generate YAML with a JSON generator or vice
		1426	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1427	high that you will run into severe interoperability problems when you
		1428	least expect it.
		1429
		1430	=over
		1431
		1432	=item (*)
		1433
		1434	I have been pressured multiple times by Brian Ingerson (one of the
		1435	authors of the YAML specification) to remove this paragraph, despite him
		1436	acknowledging that the actual incompatibilities exist. As I was personally
		1437	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1438	educate people about these issues, so others do not run into the same
		1439	problem again and again. After this, Brian called me a (quote)I<complete
		1440	and worthless idiot>(unquote).
		1441
		1442	In my opinion, instead of pressuring and insulting people who actually
		1443	clarify issues with YAML and the wrong statements of some of its
		1444	proponents, I would kindly suggest reading the JSON spec (which is not
		1445	that difficult or long) and finally make YAML compatible to it, and
		1446	educating users about the changes, instead of spreading lies about the
		1447	real compatibility for many I<years> and trying to silence people who
		1448	point out that it isn't true.
		1449
		1450	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1451	though the incompatibilities have been documented (and are known to Brian)
		1452	for many years and the spec makes explicit claims that YAML is a superset
		1453	of JSON. It would be so easy to fix, but apparently, bullying people and
		1454	corrupting userdata is so much easier.
		1455
		1456	=back
		1457
327		1458
328	=head2 SPEED	1459	=head2 SPEED
329		1460
330	It seems that JSON::XS is surprisingly fast, as shown in the following	1461	It seems that JSON::XS is surprisingly fast, as shown in the following
331	tables. They have been generated with the help of the C<eg/bench> program	1462	tables. They have been generated with the help of the C<eg/bench> program
332	in the JSON::XS distribution, to make it easy to compare on your own	1463	in the JSON::XS distribution, to make it easy to compare on your own
333	system.	1464	system.
334		1465
335	First is a comparison between various modules using a very simple JSON	1466	First comes a comparison between various modules using
		1467	a very short single-line JSON string (also available at
		1468	L<http://dist.schmorp.de/misc/json/short.json>).
		1469
		1470	{"method": "handleMessage", "params": ["user1",
		1471	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1472	1, 0]}
		1473
336	string, showing the number of encodes/decodes per second (JSON::XS is	1474	It shows the number of encodes/decodes per second (JSON::XS uses
337	the functional interface, while JSON::XS/2 is the OO interface with	1475	the functional interface, while JSON::XS/2 uses the OO interface
338	pretty-printing and hashkey sorting enabled).	1476	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1477	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1478	uses the from_json method). Higher is better:
339		1479
340	module | encode | decode |	1480	module | encode | decode |
341	-----------|------------|------------|	1481	--------------|------------|------------|
342	JSON | 14006 | 6820 |	1482	JSON::DWIW/DS | 86302.551 | 102300.098 |
343	JSON::DWIW | 200937 | 120386 |	1483	JSON::DWIW/FJ | 86302.551 | 75983.768 |
344	JSON::PC | 85065 | 129366 |	1484	JSON::PP | 15827.562 | 6638.658 |
345	JSON::Syck | 59898 | 44232 |	1485	JSON::Syck | 63358.066 | 47662.545 |
346	JSON::XS | 1171478 | 342435 |	1486	JSON::XS | 511500.488 | 511500.488 |
347	JSON::XS/2 | 730760 | 328714 |	1487	JSON::XS/2 | 291271.111 | 388361.481 |
		1488	JSON::XS/3 | 361577.931 | 361577.931 |
		1489	Storable | 66788.280 | 265462.278 |
348	-----------+------------+------------+	1490	--------------+------------+------------+
349		1491
350	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1492	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
351	times faster than JSON, even with pretty-printing and key sorting.	1493	about five times faster on decoding, and over thirty to seventy times
		1494	faster than JSON's pure perl implementation. It also compares favourably
		1495	to Storable for small amounts of data.
352		1496
353	Using a longer test string (roughly 8KB, generated from Yahoo! Locals	1497	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
354	search API (http://nanoref.com/yahooapis/mgPdGg):	1498	search API (L<http://dist.schmorp.de/misc/json/long.json>).
355		1499
356	module | encode | decode |	1500	module | encode | decode |
357	-----------|------------|------------|	1501	--------------|------------|------------|
358	JSON | 673 | 38 |	1502	JSON::DWIW/DS | 1647.927 | 2673.916 |
359	JSON::DWIW | 5271 | 770 |	1503	JSON::DWIW/FJ | 1630.249 | 2596.128 |
360	JSON::PC | 9901 | 2491 |	1504	JSON::PP | 400.640 | 62.311 |
361	JSON::Syck | 2360 | 786 |	1505	JSON::Syck | 1481.040 | 1524.869 |
362	JSON::XS | 37398 | 3202 |	1506	JSON::XS | 20661.596 | 9541.183 |
363	JSON::XS/2 | 13765 | 3153 |	1507	JSON::XS/2 | 10683.403 | 9416.938 |
		1508	JSON::XS/3 | 20661.596 | 9400.054 |
		1509	Storable | 19765.806 | 10000.725 |
364	-----------+------------+------------+	1510	--------------+------------+------------+
365		1511
366	Again, JSON::XS leads by far in the encoding case, while still beating	1512	Again, JSON::XS leads by far (except for Storable which non-surprisingly
367	every other module in the decoding case.	1513	decodes a bit faster).
368		1514
369	Last example is an almost 8MB large hash with many large binary values	1515	On large strings containing lots of high Unicode characters, some modules
370	(PNG files), resulting in a lot of escaping:	1516	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1517	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1518	to decode or encode properly, so it was impossible to prepare a fair
		1519	comparison table for that case.
		1520
		1521
		1522	=head1 SECURITY CONSIDERATIONS
		1523
		1524	When you are using JSON in a protocol, talking to untrusted potentially
		1525	hostile creatures requires relatively few measures.
		1526
		1527	First of all, your JSON decoder should be secure, that is, should not have
		1528	any buffer overflows. Obviously, this module should ensure that and I am
		1529	trying hard on making that true, but you never know.
		1530
		1531	Second, you need to avoid resource-starving attacks. That means you should
		1532	limit the size of JSON texts you accept, or make sure then when your
		1533	resources run out, that's just fine (e.g. by using a separate process that
		1534	can crash safely). The size of a JSON text in octets or characters is
		1535	usually a good indication of the size of the resources required to decode
		1536	it into a Perl structure. While JSON::XS can check the size of the JSON
		1537	text, it might be too late when you already have it in memory, so you
		1538	might want to check the size before you accept the string.
		1539
		1540	Third, JSON::XS recurses using the C stack when decoding objects and
		1541	arrays. The C stack is a limited resource: for instance, on my amd64
		1542	machine with 8MB of stack size I can decode around 180k nested arrays but
		1543	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1544	to free the temporary). If that is exceeded, the program crashes. To be
		1545	conservative, the default nesting limit is set to 512. If your process
		1546	has a smaller stack, you should adjust this setting accordingly with the
		1547	C<max_depth> method.
		1548
		1549	Something else could bomb you, too, that I forgot to think of. In that
		1550	case, you get to keep the pieces. I am always open for hints, though...
		1551
		1552	Also keep in mind that JSON::XS might leak contents of your Perl data
		1553	structures in its error messages, so when you serialise sensitive
		1554	information you might want to make sure that exceptions thrown by JSON::XS
		1555	will not end up in front of untrusted eyes.
		1556
		1557	If you are using JSON::XS to return packets to consumption
		1558	by JavaScript scripts in a browser you should have a look at
		1559	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
		1560	see whether you are vulnerable to some common attack vectors (which really
		1561	are browser design bugs, but it is still you who will have to deal with
		1562	it, as major browser developers care only for features, not about getting
		1563	security right).
		1564
		1565
		1566	=head2 "OLD" VS. "NEW" JSON (RFC4627 VS. RFC7159)
		1567
		1568	JSON originally required JSON texts to represent an array or object -
		1569	scalar values were explicitly not allowed. This has changed, and versions
		1570	of JSON::XS beginning with C<4.0> reflect this by allowing scalar values
		1571	by default.
		1572
		1573	One reason why one might not want this is that this removes a fundamental
		1574	property of JSON texts, namely that they are self-delimited and
		1575	self-contained, or in other words, you could take any number of "old"
		1576	JSON texts and paste them together, and the result would be unambiguously
		1577	parseable:
		1578
		1579	[1,3]{"k":5}[][null] # four JSON texts, without doubt
		1580
		1581	By allowing scalars, this property is lost: in the following example, is
		1582	this one JSON text (the number 12) or two JSON texts (the numbers 1 and
		1583	2):
		1584
		1585	12 # could be 12, or 1 and 2
		1586
		1587	Another lost property of "old" JSON is that no lookahead is required to
		1588	know the end of a JSON text, i.e. the JSON text definitely ended at the
		1589	last C<]> or C<}> character, there was no need to read extra characters.
		1590
		1591	For example, a viable network protocol with "old" JSON was to simply
		1592	exchange JSON texts without delimiter. For "new" JSON, you have to use a
		1593	suitable delimiter (such as a newline) after every JSON text or ensure you
		1594	never encode/decode scalar values.
		1595
		1596	Most protocols do work by only transferring arrays or objects, and the
		1597	easiest way to avoid problems with the "new" JSON definition is to
		1598	explicitly disallow scalar values in your encoder and decoder:
		1599
		1600	$json_coder = JSON::XS->new->allow_nonref (0)
		1601
		1602	This is a somewhat unhappy situation, and the blame can fully be put on
		1603	JSON's inmventor, Douglas Crockford, who unilaterally changed the format
		1604	in 2006 without consulting the IETF, forcing the IETF to either fork the
		1605	format or go with it (as I was told, the IETF wasn't amused).
		1606
		1607
		1608	=head1 RELATIONSHIP WITH I-JSON
		1609
		1610	JSON is a somewhat sloppily-defined format - it carries around obvious
		1611	Javascript baggage, such as not really defining number range, probably
		1612	because Javascript only has one type of numbers: IEEE 64 bit floats
		1613	("binary64").
		1614
		1615	For this reaosn, RFC7493 defines "Internet JSON", which is a restricted
		1616	subset of JSON that is supposedly more interoperable on the internet.
		1617
		1618	While C<JSON::XS> does not offer specific support for I-JSON, it of course
		1619	accepts valid I-JSON and by default implements some of the limitations
		1620	of I-JSON, such as parsing numbers as perl numbers, which are usually a
		1621	superset of binary64 numbers.
		1622
		1623	To generate I-JSON, follow these rules:
		1624
		1625	=over
		1626
		1627	=item * always generate UTF-8
		1628
		1629	I-JSON must be encoded in UTF-8, the default for C<encode_json>.
		1630
		1631	=item * numbers should be within IEEE 754 binary64 range
		1632
		1633	Basically all existing perl installations use binary64 to represent
		1634	floating point numbers, so all you need to do is to avoid large integers.
		1635
		1636	=item * objects must not have duplicate keys
		1637
		1638	This is trivially done, as C<JSON::XS> does not allow duplicate keys.
		1639
		1640	=item * do not generate scalar JSON texts, use C<< ->allow_nonref (0) >>
		1641
		1642	I-JSON strongly requests you to only encode arrays and objects into JSON.
		1643
		1644	=item * times should be strings in ISO 8601 format
		1645
		1646	There are a myriad of modules on CPAN dealing with ISO 8601 - search for
		1647	C<ISO8601> on CPAN and use one.
		1648
		1649	=item * encode binary data as base64
		1650
		1651	While it's tempting to just dump binary data as a string (and let
		1652	C<JSON::XS> do the escaping), for I-JSON, it's I<recommended> to encode
		1653	binary data as base64.
		1654
		1655	=back
		1656
		1657	There are some other considerations - read RFC7493 for the details if
		1658	interested.
		1659
		1660
		1661	=head1 INTEROPERABILITY WITH OTHER MODULES
		1662
		1663	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1664	constants. That means that the JSON true and false values will be
		1665	comaptible to true and false values of other modules that do the same,
		1666	such as L<JSON::PP> and L<CBOR::XS>.
		1667
		1668
		1669	=head1 INTEROPERABILITY WITH OTHER JSON DECODERS
		1670
		1671	As long as you only serialise data that can be directly expressed in JSON,
		1672	C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs,
		1673	but C<JSON::XS> has found more bugs in the official JSON testsuite (1)
		1674	than the official JSON testsuite has found in C<JSON::XS> (0)).
		1675
		1676	When you have trouble decoding JSON generated by this module using other
		1677	decoders, then it is very likely that you have an encoding mismatch or the
		1678	other decoder is broken.
		1679
		1680	When decoding, C<JSON::XS> is strict by default and will likely catch all
		1681	errors. There are currently two settings that change this: C<relaxed>
		1682	makes C<JSON::XS> accept (but not generate) some non-standard extensions,
		1683	and C<allow_tags> will allow you to encode and decode Perl objects, at the
		1684	cost of not outputting valid JSON anymore.
		1685
		1686	=head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
		1687
		1688	When you use C<allow_tags> to use the extended (and also nonstandard and
		1689	invalid) JSON syntax for serialised objects, and you still want to decode
		1690	the generated When you want to serialise objects, you can run a regex
		1691	to replace the tagged syntax by standard JSON arrays (it only works for
		1692	"normal" package names without comma, newlines or single colons). First,
		1693	the readable Perl version:
		1694
		1695	# if your FREEZE methods return no values, you need this replace first:
		1696	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
		1697
		1698	# this works for non-empty constructor arg lists:
		1699	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
		1700
		1701	And here is a less readable version that is easy to adapt to other
		1702	languages:
		1703
		1704	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
		1705
		1706	Here is an ECMAScript version (same regex):
		1707
		1708	json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
		1709
		1710	Since this syntax converts to standard JSON arrays, it might be hard to
		1711	distinguish serialised objects from normal arrays. You can prepend a
		1712	"magic number" as first array element to reduce chances of a collision:
		1713
		1714	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
		1715
		1716	And after decoding the JSON text, you could walk the data
		1717	structure looking for arrays with a first element of
		1718	C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>.
		1719
		1720	The same approach can be used to create the tagged format with another
		1721	encoder. First, you create an array with the magic string as first member,
		1722	the classname as second, and constructor arguments last, encode it as part
		1723	of your JSON structure, and then:
		1724
		1725	$json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
		1726
		1727	Again, this has some limitations - the magic string must not be encoded
		1728	with character escapes, and the constructor arguments must be non-empty.
		1729
		1730
		1731	=head1 (I-)THREADS
		1732
		1733	This module is I<not> guaranteed to be ithread (or MULTIPLICITY-) safe
		1734	and there are no plans to change this. Note that perl's builtin so-called
		1735	threads/ithreads are officially deprecated and should not be used.
		1736
		1737
		1738	=head1 THE PERILS OF SETLOCALE
		1739
		1740	Sometimes people avoid the Perl locale support and directly call the
		1741	system's setlocale function with C<LC_ALL>.
		1742
		1743	This breaks both perl and modules such as JSON::XS, as stringification of
		1744	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1745	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1746	perl to stringify numbers).
		1747
		1748	The solution is simple: don't call C<setlocale>, or use it for only those
		1749	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1750
		1751	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1752	actually needs it (avoiding stringification of numbers), and restore it
		1753	afterwards.
		1754
		1755
		1756	=head1 SOME HISTORY
		1757
		1758	At the time this module was created there already were a number of JSON
		1759	modules available on CPAN, so what was the reason to write yet another
		1760	JSON module? While it seems there are many JSON modules, none of them
		1761	correctly handled all corner cases, and in most cases their maintainers
		1762	are unresponsive, gone missing, or not listening to bug reports for other
		1763	reasons.
		1764
		1765	Beginning with version 2.0 of the JSON module, when both JSON and
		1766	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		1767	overridden) with no overhead due to emulation (by inheriting constructor
		1768	and methods). If JSON::XS is not available, it will fall back to the
		1769	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		1770	gives you a portable JSON API that can be fast when you need it and
		1771	doesn't require a C compiler when that is a problem.
		1772
		1773	Somewhere around version 3, this module was forked into
		1774	C<Cpanel::JSON::XS>, because its maintainer had serious trouble
		1775	understanding JSON and insisted on a fork with many bugs "fixed" that
		1776	weren't actually bugs, while spreading FUD about this module without
		1777	actually giving any details on his accusations. You be the judge, but
		1778	in my personal opinion, if you want quality, you will stay away from
		1779	dangerous forks like that.
		1780
371		1781
372	=head1 BUGS	1782	=head1 BUGS
373		1783
374	While the goal of this module is to be correct, that unfortunately does	1784	While the goal of this module is to be correct, that unfortunately does
375	not mean its bug-free, only that I think its design is bug-free. It is	1785	not mean it's bug-free, only that I think its design is bug-free. If you
376	still very young and not well-tested. If you keep reporting bugs they will	1786	keep reporting bugs they will be fixed swiftly, though.
377	be fixed swiftly, though.	1787
		1788	Please refrain from using rt.cpan.org or any other bug reporting
		1789	service. I put the contact address into my modules for a reason.
378		1790
379	=cut	1791	=cut
380		1792
381	1;	1793	BEGIN {
		1794	*true = \$Types::Serialiser::true;
		1795	*true = \&Types::Serialiser::true;
		1796	*false = \$Types::Serialiser::false;
		1797	*false = \&Types::Serialiser::false;
		1798	*is_bool = \&Types::Serialiser::is_bool;
		1799
		1800	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
		1801	}
		1802
		1803	XSLoader::load "JSON::XS", $VERSION;
		1804
		1805	=head1 SEE ALSO
		1806
		1807	The F<json_xs> command line utility for quick experiments.
382		1808
383	=head1 AUTHOR	1809	=head1 AUTHOR
384		1810
385	Marc Lehmann <schmorp@schmorp.de>	1811	Marc Lehmann <schmorp@schmorp.de>
386	http://home.schmorp.de/	1812	http://home.schmorp.de/
387		1813
388	=cut	1814	=cut
389		1815
		1816	1
		1817

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