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Revision 1.23 by root, Sun Mar 25 21:19:13 2007 UTC vs.
Revision 1.164 by root, Thu Aug 17 03:47:54 2017 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
		5	=encoding utf-8
		6
		7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
4		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
8		13
9	# exported functions, they croak on error	14	# exported functions, they croak on error
10	# and expect/generate UTF-8	15	# and expect/generate UTF-8
11		16
12	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
13	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
14
15	# objToJson and jsonToObj aliases to to_json and from_json
16	# are exported for compatibility to the JSON module,
17	# but should not be used in new code.
18		19
19	# OO-interface	20	# OO-interface
20		21
21	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
22	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
23	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
24		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
		33
25	=head1 DESCRIPTION	34	=head1 DESCRIPTION
26		35
27	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
28	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
29	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overridden) with no overhead due to emulation (by inheriting constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need it and
		46	doesn't require a C compiler when that is a problem.
30		47
31	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
32	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
33	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
34	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
35	reports for other reasons.	52	reports for other reasons.
36		53
37	See COMPARISON, below, for a comparison to some other JSON modules.
38
39	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
40	vice versa.	55	vice versa.
41		56
42	=head2 FEATURES	57	=head2 FEATURES
43		58
44	=over 4	59	=over 4
45		60
46	=item * correct unicode handling	61	=item * correct Unicode handling
47		62
48	This module knows how to handle Unicode, and even documents how and when	63	This module knows how to handle Unicode, documents how and when it does
49	it does so.	64	so, and even documents what "correct" means.
50		65
51	=item * round-trip integrity	66	=item * round-trip integrity
52		67
53	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
54	by JSON, the deserialised data structure is identical on the Perl level.	69	by JSON and Perl, the deserialised data structure is identical on the Perl
55	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
56	like a number).	71	it looks like a number). There I<are> minor exceptions to this, read the
		72	MAPPING section below to learn about those.
57		73
58	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
59		75
60	There is no guessing, no generating of illegal JSON texts by default,	76	There is no guessing, no generating of illegal JSON texts by default,
61	and only JSON is accepted as input by default (the latter is a security	77	and only JSON is accepted as input by default (the latter is a security
62	feature).	78	feature).
63		79
64	=item * fast	80	=item * fast
65		81
66	Compared to other JSON modules, this module compares favourably in terms	82	Compared to other JSON modules and other serialisers such as Storable,
67	of speed, too.	83	this module usually compares favourably in terms of speed, too.
68		84
69	=item * simple to use	85	=item * simple to use
70		86
71	This module has both a simple functional interface as well as an OO	87	This module has both a simple functional interface as well as an object
72	interface.	88	oriented interface.
73		89
74	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
75		91
76	You can choose between the most compact guarenteed single-line format	92	You can choose between the most compact guaranteed-single-line format
77	possible (nice for simple line-based protocols), a pure-ascii format	93	possible (nice for simple line-based protocols), a pure-ASCII format
78	(for when your transport is not 8-bit clean, still supports the whole	94	(for when your transport is not 8-bit clean, still supports the whole
79	unicode range), or a pretty-printed format (for when you want to read that	95	Unicode range), or a pretty-printed format (for when you want to read that
80	stuff). Or you can combine those features in whatever way you like.	96	stuff). Or you can combine those features in whatever way you like.
81		97
82	=back	98	=back
83		99
84	=cut	100	=cut
85		101
86	package JSON::XS;	102	package JSON::XS;
87		103
88	use strict;	104	use common::sense;
89		105
90	BEGIN {
91	our $VERSION = '0.8';	106	our $VERSION = 3.04;
92	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
93		108
94	our @EXPORT = qw(to_json from_json objToJson jsonToObj);	109	our @EXPORT = qw(encode_json decode_json);
95	require Exporter;
96		110
97	require XSLoader;	111	use Exporter;
98	XSLoader::load JSON::XS::, $VERSION;	112	use XSLoader;
99	}	113
		114	use Types::Serialiser ();
100		115
101	=head1 FUNCTIONAL INTERFACE	116	=head1 FUNCTIONAL INTERFACE
102		117
103	The following convinience methods are provided by this module. They are	118	The following convenience methods are provided by this module. They are
104	exported by default:	119	exported by default:
105		120
106	=over 4	121	=over 4
107		122
108	=item $json_text = to_json $perl_scalar	123	=item $json_text = encode_json $perl_scalar
109		124
110	Converts the given Perl data structure (a simple scalar or a reference to	125	Converts the given Perl data structure to a UTF-8 encoded, binary string
111	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	126	(that is, the string contains octets only). Croaks on error.
112	octets only). Croaks on error.
113		127
114	This function call is functionally identical to:	128	This function call is functionally identical to:
115		129
116	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	130	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
117		131
118	except being faster.	132	Except being faster.
119		133
120	=item $perl_scalar = from_json $json_text	134	=item $perl_scalar = decode_json $json_text
121		135
122	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	136	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
123	parse that as an UTF-8 encoded JSON text, returning the resulting simple	137	to parse that as an UTF-8 encoded JSON text, returning the resulting
124	scalar or reference. Croaks on error.	138	reference. Croaks on error.
125		139
126	This function call is functionally identical to:	140	This function call is functionally identical to:
127		141
128	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	142	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
129		143
130	except being faster.	144	Except being faster.
131		145
132	=back	146	=back
		147
		148
		149	=head1 A FEW NOTES ON UNICODE AND PERL
		150
		151	Since this often leads to confusion, here are a few very clear words on
		152	how Unicode works in Perl, modulo bugs.
		153
		154	=over 4
		155
		156	=item 1. Perl strings can store characters with ordinal values > 255.
		157
		158	This enables you to store Unicode characters as single characters in a
		159	Perl string - very natural.
		160
		161	=item 2. Perl does I<not> associate an encoding with your strings.
		162
		163	... until you force it to, e.g. when matching it against a regex, or
		164	printing the scalar to a file, in which case Perl either interprets your
		165	string as locale-encoded text, octets/binary, or as Unicode, depending
		166	on various settings. In no case is an encoding stored together with your
		167	data, it is I<use> that decides encoding, not any magical meta data.
		168
		169	=item 3. The internal utf-8 flag has no meaning with regards to the
		170	encoding of your string.
		171
		172	Just ignore that flag unless you debug a Perl bug, a module written in
		173	XS or want to dive into the internals of perl. Otherwise it will only
		174	confuse you, as, despite the name, it says nothing about how your string
		175	is encoded. You can have Unicode strings with that flag set, with that
		176	flag clear, and you can have binary data with that flag set and that flag
		177	clear. Other possibilities exist, too.
		178
		179	If you didn't know about that flag, just the better, pretend it doesn't
		180	exist.
		181
		182	=item 4. A "Unicode String" is simply a string where each character can be
		183	validly interpreted as a Unicode code point.
		184
		185	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		186	Unicode string encoded in UTF-8, giving you a binary string.
		187
		188	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		189
		190	It's a fact. Learn to live with it.
		191
		192	=back
		193
		194	I hope this helps :)
133		195
134		196
135	=head1 OBJECT-ORIENTED INTERFACE	197	=head1 OBJECT-ORIENTED INTERFACE
136		198
137	The object oriented interface lets you configure your own encoding or	199	The object oriented interface lets you configure your own encoding or
…		…
150	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	212	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
151	=> {"a": [1, 2]}	213	=> {"a": [1, 2]}
152		214
153	=item $json = $json->ascii ([$enable])	215	=item $json = $json->ascii ([$enable])
154		216
		217	=item $enabled = $json->get_ascii
		218
155	If C<$enable> is true (or missing), then the C<encode> method will not	219	If C<$enable> is true (or missing), then the C<encode> method will not
156	generate characters outside the code range C<0..127> (which is ASCII). Any	220	generate characters outside the code range C<0..127> (which is ASCII). Any
157	unicode characters outside that range will be escaped using either a	221	Unicode characters outside that range will be escaped using either a
158	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,	222	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
159	as per RFC4627.	223	as per RFC4627. The resulting encoded JSON text can be treated as a native
		224	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		225	or any other superset of ASCII.
160		226
161	If C<$enable> is false, then the C<encode> method will not escape Unicode	227	If C<$enable> is false, then the C<encode> method will not escape Unicode
162	characters unless required by the JSON syntax. This results in a faster	228	characters unless required by the JSON syntax or other flags. This results
163	and more compact format.	229	in a faster and more compact format.
		230
		231	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		232	document.
		233
		234	The main use for this flag is to produce JSON texts that can be
		235	transmitted over a 7-bit channel, as the encoded JSON texts will not
		236	contain any 8 bit characters.
164		237
165	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	238	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
166	=> ["\ud801\udc01"]	239	=> ["\ud801\udc01"]
167		240
		241	=item $json = $json->latin1 ([$enable])
		242
		243	=item $enabled = $json->get_latin1
		244
		245	If C<$enable> is true (or missing), then the C<encode> method will encode
		246	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		247	outside the code range C<0..255>. The resulting string can be treated as a
		248	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		249	will not be affected in any way by this flag, as C<decode> by default
		250	expects Unicode, which is a strict superset of latin1.
		251
		252	If C<$enable> is false, then the C<encode> method will not escape Unicode
		253	characters unless required by the JSON syntax or other flags.
		254
		255	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		256	document.
		257
		258	The main use for this flag is efficiently encoding binary data as JSON
		259	text, as most octets will not be escaped, resulting in a smaller encoded
		260	size. The disadvantage is that the resulting JSON text is encoded
		261	in latin1 (and must correctly be treated as such when storing and
		262	transferring), a rare encoding for JSON. It is therefore most useful when
		263	you want to store data structures known to contain binary data efficiently
		264	in files or databases, not when talking to other JSON encoders/decoders.
		265
		266	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		267	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
		268
168	=item $json = $json->utf8 ([$enable])	269	=item $json = $json->utf8 ([$enable])
		270
		271	=item $enabled = $json->get_utf8
169		272
170	If C<$enable> is true (or missing), then the C<encode> method will encode	273	If C<$enable> is true (or missing), then the C<encode> method will encode
171	the JSON result into UTF-8, as required by many protocols, while the	274	the JSON result into UTF-8, as required by many protocols, while the
172	C<decode> method expects to be handled an UTF-8-encoded string. Please	275	C<decode> method expects to be handled an UTF-8-encoded string. Please
173	note that UTF-8-encoded strings do not contain any characters outside the	276	note that UTF-8-encoded strings do not contain any characters outside the
174	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	277	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
175	versions, enabling this option might enable autodetection of the UTF-16	278	versions, enabling this option might enable autodetection of the UTF-16
176	and UTF-32 encoding families, as described in RFC4627.	279	and UTF-32 encoding families, as described in RFC4627.
177		280
178	If C<$enable> is false, then the C<encode> method will return the JSON	281	If C<$enable> is false, then the C<encode> method will return the JSON
179	string as a (non-encoded) unicode string, while C<decode> expects thus a	282	string as a (non-encoded) Unicode string, while C<decode> expects thus a
180	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	283	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
181	to be done yourself, e.g. using the Encode module.	284	to be done yourself, e.g. using the Encode module.
		285
		286	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		287	document.
182		288
183	Example, output UTF-16BE-encoded JSON:	289	Example, output UTF-16BE-encoded JSON:
184		290
185	use Encode;	291	use Encode;
186	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	292	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
207	]	313	]
208	}	314	}
209		315
210	=item $json = $json->indent ([$enable])	316	=item $json = $json->indent ([$enable])
211		317
		318	=item $enabled = $json->get_indent
		319
212	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	320	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
213	format as output, putting every array member or object/hash key-value pair	321	format as output, putting every array member or object/hash key-value pair
214	into its own line, identing them properly.	322	into its own line, indenting them properly.
215		323
216	If C<$enable> is false, no newlines or indenting will be produced, and the	324	If C<$enable> is false, no newlines or indenting will be produced, and the
217	resulting JSON text is guarenteed not to contain any C<newlines>.	325	resulting JSON text is guaranteed not to contain any C<newlines>.
218		326
219	This setting has no effect when decoding JSON texts.	327	This setting has no effect when decoding JSON texts.
220		328
221	=item $json = $json->space_before ([$enable])	329	=item $json = $json->space_before ([$enable])
		330
		331	=item $enabled = $json->get_space_before
222		332
223	If C<$enable> is true (or missing), then the C<encode> method will add an extra	333	If C<$enable> is true (or missing), then the C<encode> method will add an extra
224	optional space before the C<:> separating keys from values in JSON objects.	334	optional space before the C<:> separating keys from values in JSON objects.
225		335
226	If C<$enable> is false, then the C<encode> method will not add any extra	336	If C<$enable> is false, then the C<encode> method will not add any extra
…		…
232	Example, space_before enabled, space_after and indent disabled:	342	Example, space_before enabled, space_after and indent disabled:
233		343
234	{"key" :"value"}	344	{"key" :"value"}
235		345
236	=item $json = $json->space_after ([$enable])	346	=item $json = $json->space_after ([$enable])
		347
		348	=item $enabled = $json->get_space_after
237		349
238	If C<$enable> is true (or missing), then the C<encode> method will add an extra	350	If C<$enable> is true (or missing), then the C<encode> method will add an extra
239	optional space after the C<:> separating keys from values in JSON objects	351	optional space after the C<:> separating keys from values in JSON objects
240	and extra whitespace after the C<,> separating key-value pairs and array	352	and extra whitespace after the C<,> separating key-value pairs and array
241	members.	353	members.
…		…
247		359
248	Example, space_before and indent disabled, space_after enabled:	360	Example, space_before and indent disabled, space_after enabled:
249		361
250	{"key": "value"}	362	{"key": "value"}
251		363
		364	=item $json = $json->relaxed ([$enable])
		365
		366	=item $enabled = $json->get_relaxed
		367
		368	If C<$enable> is true (or missing), then C<decode> will accept some
		369	extensions to normal JSON syntax (see below). C<encode> will not be
		370	affected in anyway. I<Be aware that this option makes you accept invalid
		371	JSON texts as if they were valid!>. I suggest only to use this option to
		372	parse application-specific files written by humans (configuration files,
		373	resource files etc.)
		374
		375	If C<$enable> is false (the default), then C<decode> will only accept
		376	valid JSON texts.
		377
		378	Currently accepted extensions are:
		379
		380	=over 4
		381
		382	=item * list items can have an end-comma
		383
		384	JSON I<separates> array elements and key-value pairs with commas. This
		385	can be annoying if you write JSON texts manually and want to be able to
		386	quickly append elements, so this extension accepts comma at the end of
		387	such items not just between them:
		388
		389	[
		390	1,
		391	2, <- this comma not normally allowed
		392	]
		393	{
		394	"k1": "v1",
		395	"k2": "v2", <- this comma not normally allowed
		396	}
		397
		398	=item * shell-style '#'-comments
		399
		400	Whenever JSON allows whitespace, shell-style comments are additionally
		401	allowed. They are terminated by the first carriage-return or line-feed
		402	character, after which more white-space and comments are allowed.
		403
		404	[
		405	1, # this comment not allowed in JSON
		406	# neither this one...
		407	]
		408
		409	=item * literal ASCII TAB characters in strings
		410
		411	Literal ASCII TAB characters are now allowed in strings (and treated as
		412	C<\t>).
		413
		414	[
		415	"Hello\tWorld",
		416	"Hello<TAB>World", # literal <TAB> would not normally be allowed
		417	]
		418
		419	=back
		420
252	=item $json = $json->canonical ([$enable])	421	=item $json = $json->canonical ([$enable])
		422
		423	=item $enabled = $json->get_canonical
253		424
254	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	425	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
255	by sorting their keys. This is adding a comparatively high overhead.	426	by sorting their keys. This is adding a comparatively high overhead.
256		427
257	If C<$enable> is false, then the C<encode> method will output key-value	428	If C<$enable> is false, then the C<encode> method will output key-value
258	pairs in the order Perl stores them (which will likely change between runs	429	pairs in the order Perl stores them (which will likely change between runs
259	of the same script).	430	of the same script, and can change even within the same run from 5.18
		431	onwards).
260		432
261	This option is useful if you want the same data structure to be encoded as	433	This option is useful if you want the same data structure to be encoded as
262	the same JSON text (given the same overall settings). If it is disabled,	434	the same JSON text (given the same overall settings). If it is disabled,
263	the same hash migh be encoded differently even if contains the same data,	435	the same hash might be encoded differently even if contains the same data,
264	as key-value pairs have no inherent ordering in Perl.	436	as key-value pairs have no inherent ordering in Perl.
265		437
266	This setting has no effect when decoding JSON texts.	438	This setting has no effect when decoding JSON texts.
267		439
		440	This setting has currently no effect on tied hashes.
		441
268	=item $json = $json->allow_nonref ([$enable])	442	=item $json = $json->allow_nonref ([$enable])
		443
		444	=item $enabled = $json->get_allow_nonref
269		445
270	If C<$enable> is true (or missing), then the C<encode> method can convert a	446	If C<$enable> is true (or missing), then the C<encode> method can convert a
271	non-reference into its corresponding string, number or null JSON value,	447	non-reference into its corresponding string, number or null JSON value,
272	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	448	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
273	values instead of croaking.	449	values instead of croaking.
…		…
281	resulting in an invalid JSON text:	457	resulting in an invalid JSON text:
282		458
283	JSON::XS->new->allow_nonref->encode ("Hello, World!")	459	JSON::XS->new->allow_nonref->encode ("Hello, World!")
284	=> "Hello, World!"	460	=> "Hello, World!"
285		461
		462	=item $json = $json->allow_unknown ([$enable])
		463
		464	=item $enabled = $json->get_allow_unknown
		465
		466	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		467	exception when it encounters values it cannot represent in JSON (for
		468	example, filehandles) but instead will encode a JSON C<null> value. Note
		469	that blessed objects are not included here and are handled separately by
		470	c<allow_nonref>.
		471
		472	If C<$enable> is false (the default), then C<encode> will throw an
		473	exception when it encounters anything it cannot encode as JSON.
		474
		475	This option does not affect C<decode> in any way, and it is recommended to
		476	leave it off unless you know your communications partner.
		477
		478	=item $json = $json->allow_blessed ([$enable])
		479
		480	=item $enabled = $json->get_allow_blessed
		481
		482	See L<OBJECT SERIALISATION> for details.
		483
		484	If C<$enable> is true (or missing), then the C<encode> method will not
		485	barf when it encounters a blessed reference that it cannot convert
		486	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
		487
		488	If C<$enable> is false (the default), then C<encode> will throw an
		489	exception when it encounters a blessed object that it cannot convert
		490	otherwise.
		491
		492	This setting has no effect on C<decode>.
		493
		494	=item $json = $json->convert_blessed ([$enable])
		495
		496	=item $enabled = $json->get_convert_blessed
		497
		498	See L<OBJECT SERIALISATION> for details.
		499
		500	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		501	blessed object, will check for the availability of the C<TO_JSON> method
		502	on the object's class. If found, it will be called in scalar context and
		503	the resulting scalar will be encoded instead of the object.
		504
		505	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		506	returns other blessed objects, those will be handled in the same
		507	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		508	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		509	methods called by the Perl core (== not by the user of the object) are
		510	usually in upper case letters and to avoid collisions with any C<to_json>
		511	function or method.
		512
		513	If C<$enable> is false (the default), then C<encode> will not consider
		514	this type of conversion.
		515
		516	This setting has no effect on C<decode>.
		517
		518	=item $json = $json->allow_tags ([$enable])
		519
		520	=item $enabled = $json->allow_tags
		521
		522	See L<OBJECT SERIALISATION> for details.
		523
		524	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		525	blessed object, will check for the availability of the C<FREEZE> method on
		526	the object's class. If found, it will be used to serialise the object into
		527	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		528
		529	It also causes C<decode> to parse such tagged JSON values and deserialise
		530	them via a call to the C<THAW> method.
		531
		532	If C<$enable> is false (the default), then C<encode> will not consider
		533	this type of conversion, and tagged JSON values will cause a parse error
		534	in C<decode>, as if tags were not part of the grammar.
		535
		536	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		537
		538	When C<$coderef> is specified, it will be called from C<decode> each
		539	time it decodes a JSON object. The only argument is a reference to the
		540	newly-created hash. If the code references returns a single scalar (which
		541	need not be a reference), this value (i.e. a copy of that scalar to avoid
		542	aliasing) is inserted into the deserialised data structure. If it returns
		543	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		544	original deserialised hash will be inserted. This setting can slow down
		545	decoding considerably.
		546
		547	When C<$coderef> is omitted or undefined, any existing callback will
		548	be removed and C<decode> will not change the deserialised hash in any
		549	way.
		550
		551	Example, convert all JSON objects into the integer 5:
		552
		553	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		554	# returns [5]
		555	$js->decode ('[{}]')
		556	# throw an exception because allow_nonref is not enabled
		557	# so a lone 5 is not allowed.
		558	$js->decode ('{"a":1, "b":2}');
		559
		560	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		561
		562	Works remotely similar to C<filter_json_object>, but is only called for
		563	JSON objects having a single key named C<$key>.
		564
		565	This C<$coderef> is called before the one specified via
		566	C<filter_json_object>, if any. It gets passed the single value in the JSON
		567	object. If it returns a single value, it will be inserted into the data
		568	structure. If it returns nothing (not even C<undef> but the empty list),
		569	the callback from C<filter_json_object> will be called next, as if no
		570	single-key callback were specified.
		571
		572	If C<$coderef> is omitted or undefined, the corresponding callback will be
		573	disabled. There can only ever be one callback for a given key.
		574
		575	As this callback gets called less often then the C<filter_json_object>
		576	one, decoding speed will not usually suffer as much. Therefore, single-key
		577	objects make excellent targets to serialise Perl objects into, especially
		578	as single-key JSON objects are as close to the type-tagged value concept
		579	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		580	support this in any way, so you need to make sure your data never looks
		581	like a serialised Perl hash.
		582
		583	Typical names for the single object key are C<__class_whatever__>, or
		584	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		585	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		586	with real hashes.
		587
		588	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		589	into the corresponding C<< $WIDGET{<id>} >> object:
		590
		591	# return whatever is in $WIDGET{5}:
		592	JSON::XS
		593	->new
		594	->filter_json_single_key_object (__widget__ => sub {
		595	$WIDGET{ $_[0] }
		596	})
		597	->decode ('{"__widget__": 5')
		598
		599	# this can be used with a TO_JSON method in some "widget" class
		600	# for serialisation to json:
		601	sub WidgetBase::TO_JSON {
		602	my ($self) = @_;
		603
		604	unless ($self->{id}) {
		605	$self->{id} = ..get..some..id..;
		606	$WIDGET{$self->{id}} = $self;
		607	}
		608
		609	{ __widget__ => $self->{id} }
		610	}
		611
286	=item $json = $json->shrink ([$enable])	612	=item $json = $json->shrink ([$enable])
287		613
		614	=item $enabled = $json->get_shrink
		615
288	Perl usually over-allocates memory a bit when allocating space for	616	Perl usually over-allocates memory a bit when allocating space for
289	strings. This flag optionally resizes strings generated by either	617	strings. This flag optionally resizes strings generated by either
290	C<encode> or C<decode> to their minimum size possible. This can save	618	C<encode> or C<decode> to their minimum size possible. This can save
291	memory when your JSON texts are either very very long or you have many	619	memory when your JSON texts are either very very long or you have many
292	short strings. It will also try to downgrade any strings to octet-form	620	short strings. It will also try to downgrade any strings to octet-form
293	if possible: perl stores strings internally either in an encoding called	621	if possible: perl stores strings internally either in an encoding called
294	UTF-X or in octet-form. The latter cannot store everything but uses less	622	UTF-X or in octet-form. The latter cannot store everything but uses less
295	space in general.	623	space in general (and some buggy Perl or C code might even rely on that
		624	internal representation being used).
296		625
		626	The actual definition of what shrink does might change in future versions,
		627	but it will always try to save space at the expense of time.
		628
297	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	629	If C<$enable> is true (or missing), the string returned by C<encode> will
298	while all strings generated by C<decode> will also be shrunk-to-fit.	630	be shrunk-to-fit, while all strings generated by C<decode> will also be
		631	shrunk-to-fit.
299		632
300	If C<$enable> is false, then the normal perl allocation algorithms are used.	633	If C<$enable> is false, then the normal perl allocation algorithms are used.
301	If you work with your data, then this is likely to be faster.	634	If you work with your data, then this is likely to be faster.
302		635
303	In the future, this setting might control other things, such as converting	636	In the future, this setting might control other things, such as converting
304	strings that look like integers or floats into integers or floats	637	strings that look like integers or floats into integers or floats
305	internally (there is no difference on the Perl level), saving space.	638	internally (there is no difference on the Perl level), saving space.
306		639
307	=item $json = $json->max_depth ([$maximum_nesting_depth])	640	=item $json = $json->max_depth ([$maximum_nesting_depth])
308		641
		642	=item $max_depth = $json->get_max_depth
		643
309	Sets the maximum nesting level (default C<8192>) accepted while encoding	644	Sets the maximum nesting level (default C<512>) accepted while encoding
310	or decoding. If the JSON text or Perl data structure has an equal or	645	or decoding. If a higher nesting level is detected in JSON text or a Perl
311	higher nesting level then this limit, then the encoder and decoder will	646	data structure, then the encoder and decoder will stop and croak at that
312	stop and croak at that point.	647	point.
313		648
314	Nesting level is defined by number of hash- or arrayrefs that the encoder	649	Nesting level is defined by number of hash- or arrayrefs that the encoder
315	needs to traverse to reach a given point or the number of C<{> or C<[>	650	needs to traverse to reach a given point or the number of C<{> or C<[>
316	characters without their matching closing parenthesis crossed to reach a	651	characters without their matching closing parenthesis crossed to reach a
317	given character in a string.	652	given character in a string.
318		653
319	Setting the maximum depth to one disallows any nesting, so that ensures	654	Setting the maximum depth to one disallows any nesting, so that ensures
320	that the object is only a single hash/object or array.	655	that the object is only a single hash/object or array.
321		656
322	The argument to C<max_depth> will be rounded up to the next nearest power	657	If no argument is given, the highest possible setting will be used, which
323	of two.	658	is rarely useful.
		659
		660	Note that nesting is implemented by recursion in C. The default value has
		661	been chosen to be as large as typical operating systems allow without
		662	crashing.
324		663
325	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	664	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
326		665
		666	=item $json = $json->max_size ([$maximum_string_size])
		667
		668	=item $max_size = $json->get_max_size
		669
		670	Set the maximum length a JSON text may have (in bytes) where decoding is
		671	being attempted. The default is C<0>, meaning no limit. When C<decode>
		672	is called on a string that is longer then this many bytes, it will not
		673	attempt to decode the string but throw an exception. This setting has no
		674	effect on C<encode> (yet).
		675
		676	If no argument is given, the limit check will be deactivated (same as when
		677	C<0> is specified).
		678
		679	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		680
327	=item $json_text = $json->encode ($perl_scalar)	681	=item $json_text = $json->encode ($perl_scalar)
328		682
329	Converts the given Perl data structure (a simple scalar or a reference	683	Converts the given Perl value or data structure to its JSON
330	to a hash or array) to its JSON representation. Simple scalars will be	684	representation. Croaks on error.
331	converted into JSON string or number sequences, while references to arrays
332	become JSON arrays and references to hashes become JSON objects. Undefined
333	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
334	nor C<false> values will be generated.
335		685
336	=item $perl_scalar = $json->decode ($json_text)	686	=item $perl_scalar = $json->decode ($json_text)
337		687
338	The opposite of C<encode>: expects a JSON text and tries to parse it,	688	The opposite of C<encode>: expects a JSON text and tries to parse it,
339	returning the resulting simple scalar or reference. Croaks on error.	689	returning the resulting simple scalar or reference. Croaks on error.
340		690
341	JSON numbers and strings become simple Perl scalars. JSON arrays become	691	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
342	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	692
343	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	693	This works like the C<decode> method, but instead of raising an exception
		694	when there is trailing garbage after the first JSON object, it will
		695	silently stop parsing there and return the number of characters consumed
		696	so far.
		697
		698	This is useful if your JSON texts are not delimited by an outer protocol
		699	and you need to know where the JSON text ends.
		700
		701	JSON::XS->new->decode_prefix ("[1] the tail")
		702	=> ([1], 3)
344		703
345	=back	704	=back
		705
		706
		707	=head1 INCREMENTAL PARSING
		708
		709	In some cases, there is the need for incremental parsing of JSON
		710	texts. While this module always has to keep both JSON text and resulting
		711	Perl data structure in memory at one time, it does allow you to parse a
		712	JSON stream incrementally. It does so by accumulating text until it has
		713	a full JSON object, which it then can decode. This process is similar to
		714	using C<decode_prefix> to see if a full JSON object is available, but
		715	is much more efficient (and can be implemented with a minimum of method
		716	calls).
		717
		718	JSON::XS will only attempt to parse the JSON text once it is sure it
		719	has enough text to get a decisive result, using a very simple but
		720	truly incremental parser. This means that it sometimes won't stop as
		721	early as the full parser, for example, it doesn't detect mismatched
		722	parentheses. The only thing it guarantees is that it starts decoding as
		723	soon as a syntactically valid JSON text has been seen. This means you need
		724	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		725	parsing in the presence if syntax errors.
		726
		727	The following methods implement this incremental parser.
		728
		729	=over 4
		730
		731	=item [void, scalar or list context] = $json->incr_parse ([$string])
		732
		733	This is the central parsing function. It can both append new text and
		734	extract objects from the stream accumulated so far (both of these
		735	functions are optional).
		736
		737	If C<$string> is given, then this string is appended to the already
		738	existing JSON fragment stored in the C<$json> object.
		739
		740	After that, if the function is called in void context, it will simply
		741	return without doing anything further. This can be used to add more text
		742	in as many chunks as you want.
		743
		744	If the method is called in scalar context, then it will try to extract
		745	exactly I<one> JSON object. If that is successful, it will return this
		746	object, otherwise it will return C<undef>. If there is a parse error,
		747	this method will croak just as C<decode> would do (one can then use
		748	C<incr_skip> to skip the erroneous part). This is the most common way of
		749	using the method.
		750
		751	And finally, in list context, it will try to extract as many objects
		752	from the stream as it can find and return them, or the empty list
		753	otherwise. For this to work, there must be no separators (other than
		754	whitespace) between the JSON objects or arrays, instead they must be
		755	concatenated back-to-back. If an error occurs, an exception will be
		756	raised as in the scalar context case. Note that in this case, any
		757	previously-parsed JSON texts will be lost.
		758
		759	Example: Parse some JSON arrays/objects in a given string and return
		760	them.
		761
		762	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		763
		764	=item $lvalue_string = $json->incr_text
		765
		766	This method returns the currently stored JSON fragment as an lvalue, that
		767	is, you can manipulate it. This I<only> works when a preceding call to
		768	C<incr_parse> in I<scalar context> successfully returned an object. Under
		769	all other circumstances you must not call this function (I mean it.
		770	although in simple tests it might actually work, it I<will> fail under
		771	real world conditions). As a special exception, you can also call this
		772	method before having parsed anything.
		773
		774	That means you can only use this function to look at or manipulate text
		775	before or after complete JSON objects, not while the parser is in the
		776	middle of parsing a JSON object.
		777
		778	This function is useful in two cases: a) finding the trailing text after a
		779	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		780	(such as commas).
		781
		782	=item $json->incr_skip
		783
		784	This will reset the state of the incremental parser and will remove
		785	the parsed text from the input buffer so far. This is useful after
		786	C<incr_parse> died, in which case the input buffer and incremental parser
		787	state is left unchanged, to skip the text parsed so far and to reset the
		788	parse state.
		789
		790	The difference to C<incr_reset> is that only text until the parse error
		791	occurred is removed.
		792
		793	=item $json->incr_reset
		794
		795	This completely resets the incremental parser, that is, after this call,
		796	it will be as if the parser had never parsed anything.
		797
		798	This is useful if you want to repeatedly parse JSON objects and want to
		799	ignore any trailing data, which means you have to reset the parser after
		800	each successful decode.
		801
		802	=back
		803
		804	=head2 LIMITATIONS
		805
		806	All options that affect decoding are supported, except
		807	C<allow_nonref>. The reason for this is that it cannot be made to work
		808	sensibly: JSON objects and arrays are self-delimited, i.e. you can
		809	concatenate them back to back and still decode them perfectly. This does
		810	not hold true for JSON numbers, however.
		811
		812	For example, is the string C<1> a single JSON number, or is it simply the
		813	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		814	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		815	takes the conservative route and disallows this case.
		816
		817	=head2 EXAMPLES
		818
		819	Some examples will make all this clearer. First, a simple example that
		820	works similarly to C<decode_prefix>: We want to decode the JSON object at
		821	the start of a string and identify the portion after the JSON object:
		822
		823	my $text = "[1,2,3] hello";
		824
		825	my $json = new JSON::XS;
		826
		827	my $obj = $json->incr_parse ($text)
		828	or die "expected JSON object or array at beginning of string";
		829
		830	my $tail = $json->incr_text;
		831	# $tail now contains " hello"
		832
		833	Easy, isn't it?
		834
		835	Now for a more complicated example: Imagine a hypothetical protocol where
		836	you read some requests from a TCP stream, and each request is a JSON
		837	array, without any separation between them (in fact, it is often useful to
		838	use newlines as "separators", as these get interpreted as whitespace at
		839	the start of the JSON text, which makes it possible to test said protocol
		840	with C<telnet>...).
		841
		842	Here is how you'd do it (it is trivial to write this in an event-based
		843	manner):
		844
		845	my $json = new JSON::XS;
		846
		847	# read some data from the socket
		848	while (sysread $socket, my $buf, 4096) {
		849
		850	# split and decode as many requests as possible
		851	for my $request ($json->incr_parse ($buf)) {
		852	# act on the $request
		853	}
		854	}
		855
		856	Another complicated example: Assume you have a string with JSON objects
		857	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		858	[3]>). To parse them, we have to skip the commas between the JSON texts,
		859	and here is where the lvalue-ness of C<incr_text> comes in useful:
		860
		861	my $text = "[1],[2], [3]";
		862	my $json = new JSON::XS;
		863
		864	# void context, so no parsing done
		865	$json->incr_parse ($text);
		866
		867	# now extract as many objects as possible. note the
		868	# use of scalar context so incr_text can be called.
		869	while (my $obj = $json->incr_parse) {
		870	# do something with $obj
		871
		872	# now skip the optional comma
		873	$json->incr_text =~ s/^ \s* , //x;
		874	}
		875
		876	Now lets go for a very complex example: Assume that you have a gigantic
		877	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		878	but you cannot load it into memory fully (this has actually happened in
		879	the real world :).
		880
		881	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		882	can still help you: You implement a (very simple) array parser and let
		883	JSON decode the array elements, which are all full JSON objects on their
		884	own (this wouldn't work if the array elements could be JSON numbers, for
		885	example):
		886
		887	my $json = new JSON::XS;
		888
		889	# open the monster
		890	open my $fh, "<bigfile.json"
		891	or die "bigfile: $!";
		892
		893	# first parse the initial "["
		894	for (;;) {
		895	sysread $fh, my $buf, 65536
		896	or die "read error: $!";
		897	$json->incr_parse ($buf); # void context, so no parsing
		898
		899	# Exit the loop once we found and removed(!) the initial "[".
		900	# In essence, we are (ab-)using the $json object as a simple scalar
		901	# we append data to.
		902	last if $json->incr_text =~ s/^ \s* \[ //x;
		903	}
		904
		905	# now we have the skipped the initial "[", so continue
		906	# parsing all the elements.
		907	for (;;) {
		908	# in this loop we read data until we got a single JSON object
		909	for (;;) {
		910	if (my $obj = $json->incr_parse) {
		911	# do something with $obj
		912	last;
		913	}
		914
		915	# add more data
		916	sysread $fh, my $buf, 65536
		917	or die "read error: $!";
		918	$json->incr_parse ($buf); # void context, so no parsing
		919	}
		920
		921	# in this loop we read data until we either found and parsed the
		922	# separating "," between elements, or the final "]"
		923	for (;;) {
		924	# first skip whitespace
		925	$json->incr_text =~ s/^\s*//;
		926
		927	# if we find "]", we are done
		928	if ($json->incr_text =~ s/^\]//) {
		929	print "finished.\n";
		930	exit;
		931	}
		932
		933	# if we find ",", we can continue with the next element
		934	if ($json->incr_text =~ s/^,//) {
		935	last;
		936	}
		937
		938	# if we find anything else, we have a parse error!
		939	if (length $json->incr_text) {
		940	die "parse error near ", $json->incr_text;
		941	}
		942
		943	# else add more data
		944	sysread $fh, my $buf, 65536
		945	or die "read error: $!";
		946	$json->incr_parse ($buf); # void context, so no parsing
		947	}
		948
		949	This is a complex example, but most of the complexity comes from the fact
		950	that we are trying to be correct (bear with me if I am wrong, I never ran
		951	the above example :).
		952
346		953
347		954
348	=head1 MAPPING	955	=head1 MAPPING
349		956
350	This section describes how JSON::XS maps Perl values to JSON values and	957	This section describes how JSON::XS maps Perl values to JSON values and
351	vice versa. These mappings are designed to "do the right thing" in most	958	vice versa. These mappings are designed to "do the right thing" in most
352	circumstances automatically, preserving round-tripping characteristics	959	circumstances automatically, preserving round-tripping characteristics
353	(what you put in comes out as something equivalent).	960	(what you put in comes out as something equivalent).
354		961
355	For the more enlightened: note that in the following descriptions,	962	For the more enlightened: note that in the following descriptions,
356	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	963	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
357	refers to the abstract Perl language itself.	964	refers to the abstract Perl language itself.
358		965
		966
359	=head2 JSON -> PERL	967	=head2 JSON -> PERL
360		968
361	=over 4	969	=over 4
362		970
363	=item object	971	=item object
364		972
365	A JSON object becomes a reference to a hash in Perl. No ordering of object	973	A JSON object becomes a reference to a hash in Perl. No ordering of object
366	keys is preserved (JSON does not preserver object key ordering itself).	974	keys is preserved (JSON does not preserve object key ordering itself).
367		975
368	=item array	976	=item array
369		977
370	A JSON array becomes a reference to an array in Perl.	978	A JSON array becomes a reference to an array in Perl.
371		979
…		…
375	are represented by the same codepoints in the Perl string, so no manual	983	are represented by the same codepoints in the Perl string, so no manual
376	decoding is necessary.	984	decoding is necessary.
377		985
378	=item number	986	=item number
379		987
380	A JSON number becomes either an integer or numeric (floating point)	988	A JSON number becomes either an integer, numeric (floating point) or
381	scalar in perl, depending on its range and any fractional parts. On the	989	string scalar in perl, depending on its range and any fractional parts. On
382	Perl level, there is no difference between those as Perl handles all the	990	the Perl level, there is no difference between those as Perl handles all
383	conversion details, but an integer may take slightly less memory and might	991	the conversion details, but an integer may take slightly less memory and
384	represent more values exactly than (floating point) numbers.	992	might represent more values exactly than floating point numbers.
		993
		994	If the number consists of digits only, JSON::XS will try to represent
		995	it as an integer value. If that fails, it will try to represent it as
		996	a numeric (floating point) value if that is possible without loss of
		997	precision. Otherwise it will preserve the number as a string value (in
		998	which case you lose roundtripping ability, as the JSON number will be
		999	re-encoded to a JSON string).
		1000
		1001	Numbers containing a fractional or exponential part will always be
		1002	represented as numeric (floating point) values, possibly at a loss of
		1003	precision (in which case you might lose perfect roundtripping ability, but
		1004	the JSON number will still be re-encoded as a JSON number).
		1005
		1006	Note that precision is not accuracy - binary floating point values cannot
		1007	represent most decimal fractions exactly, and when converting from and to
		1008	floating point, JSON::XS only guarantees precision up to but not including
		1009	the least significant bit.
385		1010
386	=item true, false	1011	=item true, false
387		1012
388	These JSON atoms become C<0>, C<1>, respectively. Information is lost in	1013	These JSON atoms become C<Types::Serialiser::true> and
389	this process. Future versions might represent those values differently,	1014	C<Types::Serialiser::false>, respectively. They are overloaded to act
390	but they will be guarenteed to act like these integers would normally in	1015	almost exactly like the numbers C<1> and C<0>. You can check whether
391	Perl.	1016	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1017	function (after C<use Types::Serialier>, of course).
392		1018
393	=item null	1019	=item null
394		1020
395	A JSON null atom becomes C<undef> in Perl.	1021	A JSON null atom becomes C<undef> in Perl.
396		1022
		1023	=item shell-style comments (C<< # I<text> >>)
		1024
		1025	As a nonstandard extension to the JSON syntax that is enabled by the
		1026	C<relaxed> setting, shell-style comments are allowed. They can start
		1027	anywhere outside strings and go till the end of the line.
		1028
		1029	=item tagged values (C<< (I<tag>)I<value> >>).
		1030
		1031	Another nonstandard extension to the JSON syntax, enabled with the
		1032	C<allow_tags> setting, are tagged values. In this implementation, the
		1033	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1034	I<value> must be a JSON array encoding optional constructor arguments.
		1035
		1036	See L<OBJECT SERIALISATION>, below, for details.
		1037
397	=back	1038	=back
		1039
398		1040
399	=head2 PERL -> JSON	1041	=head2 PERL -> JSON
400		1042
401	The mapping from Perl to JSON is slightly more difficult, as Perl is a	1043	The mapping from Perl to JSON is slightly more difficult, as Perl is a
402	truly typeless language, so we can only guess which JSON type is meant by	1044	truly typeless language, so we can only guess which JSON type is meant by
…		…
404		1046
405	=over 4	1047	=over 4
406		1048
407	=item hash references	1049	=item hash references
408		1050
409	Perl hash references become JSON objects. As there is no inherent ordering	1051	Perl hash references become JSON objects. As there is no inherent
410	in hash keys, they will usually be encoded in a pseudo-random order that	1052	ordering in hash keys (or JSON objects), they will usually be encoded
411	can change between runs of the same program but stays generally the same	1053	in a pseudo-random order. JSON::XS can optionally sort the hash keys
412	within a single run of a program. JSON::XS can optionally sort the hash
413	keys (determined by the I<canonical> flag), so the same datastructure	1054	(determined by the I<canonical> flag), so the same datastructure will
414	will serialise to the same JSON text (given same settings and version of	1055	serialise to the same JSON text (given same settings and version of
415	JSON::XS), but this incurs a runtime overhead.	1056	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
		1057	e.g. when you want to compare some JSON text against another for equality.
416		1058
417	=item array references	1059	=item array references
418		1060
419	Perl array references become JSON arrays.	1061	Perl array references become JSON arrays.
420		1062
		1063	=item other references
		1064
		1065	Other unblessed references are generally not allowed and will cause an
		1066	exception to be thrown, except for references to the integers C<0> and
		1067	C<1>, which get turned into C<false> and C<true> atoms in JSON.
		1068
		1069	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1070	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1071	and C<Types::Serialiser::true> to improve readability.
		1072
		1073	use Types::Serialiser;
		1074	encode_json [\0, Types::Serialiser::true] # yields [false,true]
		1075
		1076	=item Types::Serialiser::true, Types::Serialiser::false
		1077
		1078	These special values from the L<Types::Serialiser> module become JSON true
		1079	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1080	directly if you want.
		1081
421	=item blessed objects	1082	=item blessed objects
422		1083
423	Blessed objects are not allowed. JSON::XS currently tries to encode their	1084	Blessed objects are not directly representable in JSON, but C<JSON::XS>
424	underlying representation (hash- or arrayref), but this behaviour might	1085	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
425	change in future versions.	1086	below, for details.
426		1087
427	=item simple scalars	1088	=item simple scalars
428		1089
429	Simple Perl scalars (any scalar that is not a reference) are the most	1090	Simple Perl scalars (any scalar that is not a reference) are the most
430	difficult objects to encode: JSON::XS will encode undefined scalars as	1091	difficult objects to encode: JSON::XS will encode undefined scalars as
431	JSON null value, scalars that have last been used in a string context	1092	JSON C<null> values, scalars that have last been used in a string context
432	before encoding as JSON strings and anything else as number value:	1093	before encoding as JSON strings, and anything else as number value:
433		1094
434	# dump as number	1095	# dump as number
435	to_json [2] # yields [2]	1096	encode_json [2] # yields [2]
436	to_json [-3.0e17] # yields [-3e+17]	1097	encode_json [-3.0e17] # yields [-3e+17]
437	my $value = 5; to_json [$value] # yields [5]	1098	my $value = 5; encode_json [$value] # yields [5]
438		1099
439	# used as string, so dump as string	1100	# used as string, so dump as string
440	print $value;	1101	print $value;
441	to_json [$value] # yields ["5"]	1102	encode_json [$value] # yields ["5"]
442		1103
443	# undef becomes null	1104	# undef becomes null
444	to_json [undef] # yields [null]	1105	encode_json [undef] # yields [null]
445		1106
446	You can force the type to be a string by stringifying it:	1107	You can force the type to be a JSON string by stringifying it:
447		1108
448	my $x = 3.1; # some variable containing a number	1109	my $x = 3.1; # some variable containing a number
449	"$x"; # stringified	1110	"$x"; # stringified
450	$x .= ""; # another, more awkward way to stringify	1111	$x .= ""; # another, more awkward way to stringify
451	print $x; # perl does it for you, too, quite often	1112	print $x; # perl does it for you, too, quite often
452		1113
453	You can force the type to be a number by numifying it:	1114	You can force the type to be a JSON number by numifying it:
454		1115
455	my $x = "3"; # some variable containing a string	1116	my $x = "3"; # some variable containing a string
456	$x += 0; # numify it, ensuring it will be dumped as a number	1117	$x += 0; # numify it, ensuring it will be dumped as a number
457	$x *= 1; # same thing, the choise is yours.	1118	$x *= 1; # same thing, the choice is yours.
458		1119
459	You can not currently output JSON booleans or force the type in other,	1120	You can not currently force the type in other, less obscure, ways. Tell me
460	less obscure, ways. Tell me if you need this capability.	1121	if you need this capability (but don't forget to explain why it's needed
		1122	:).
461		1123
462	=item circular data structures	1124	Note that numerical precision has the same meaning as under Perl (so
463		1125	binary to decimal conversion follows the same rules as in Perl, which
464	Those will be encoded until memory or stackspace runs out.	1126	can differ to other languages). Also, your perl interpreter might expose
		1127	extensions to the floating point numbers of your platform, such as
		1128	infinities or NaN's - these cannot be represented in JSON, and it is an
		1129	error to pass those in.
465		1130
466	=back	1131	=back
467		1132
		1133	=head2 OBJECT SERIALISATION
468		1134
469	=head1 COMPARISON	1135	As JSON cannot directly represent Perl objects, you have to choose between
		1136	a pure JSON representation (without the ability to deserialise the object
		1137	automatically again), and a nonstandard extension to the JSON syntax,
		1138	tagged values.
470		1139
471	As already mentioned, this module was created because none of the existing	1140	=head3 SERIALISATION
472	JSON modules could be made to work correctly. First I will describe the	1141
473	problems (or pleasures) I encountered with various existing JSON modules,	1142	What happens when C<JSON::XS> encounters a Perl object depends on the
474	followed by some benchmark values. JSON::XS was designed not to suffer	1143	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
475	from any of these problems or limitations.	1144	used in this order:
476		1145
477	=over 4	1146	=over 4
478		1147
479	=item JSON 1.07	1148	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
480		1149
481	Slow (but very portable, as it is written in pure Perl).	1150	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1151	serialisation protocol to create a tagged JSON value, using a nonstandard
		1152	extension to the JSON syntax.
482		1153
483	Undocumented/buggy Unicode handling (how JSON handles unicode values is	1154	This works by invoking the C<FREEZE> method on the object, with the first
484	undocumented. One can get far by feeding it unicode strings and doing	1155	argument being the object to serialise, and the second argument being the
485	en-/decoding oneself, but unicode escapes are not working properly).	1156	constant string C<JSON> to distinguish it from other serialisers.
486		1157
487	No roundtripping (strings get clobbered if they look like numbers, e.g.	1158	The C<FREEZE> method can return any number of values (i.e. zero or
488	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	1159	more). These values and the paclkage/classname of the object will then be
489	decode into the number 2.	1160	encoded as a tagged JSON value in the following format:
490		1161
491	=item JSON::PC 0.01	1162	("classname")[FREEZE return values...]
492		1163
493	Very fast.	1164	e.g.:
494		1165
495	Undocumented/buggy Unicode handling.	1166	("URI")["http://www.google.com/"]
		1167	("MyDate")[2013,10,29]
		1168	("ImageData::JPEG")["Z3...VlCg=="]
496		1169
497	No roundtripping.	1170	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1171	objects C<type> and C<id> members to encode the object:
498		1172
499	Has problems handling many Perl values (e.g. regex results and other magic	1173	sub My::Object::FREEZE {
500	values will make it croak).	1174	my ($self, $serialiser) = @_;
501		1175
502	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1176	($self->{type}, $self->{id})
503	which is not a valid JSON text.	1177	}
504		1178
505	Unmaintained (maintainer unresponsive for many months, bugs are not	1179	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
506	getting fixed).
507		1180
508	=item JSON::Syck 0.21	1181	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1182	context. It must return a single scalar that can be directly encoded into
		1183	JSON. This scalar replaces the object in the JSON text.
509		1184
510	Very buggy (often crashes).	1185	For example, the following C<TO_JSON> method will convert all L<URI>
		1186	objects to JSON strings when serialised. The fatc that these values
		1187	originally were L<URI> objects is lost.
511		1188
512	Very inflexible (no human-readable format supported, format pretty much	1189	sub URI::TO_JSON {
513	undocumented. I need at least a format for easy reading by humans and a	1190	my ($uri) = @_;
514	single-line compact format for use in a protocol, and preferably a way to	1191	$uri->as_string
515	generate ASCII-only JSON texts).	1192	}
516		1193
517	Completely broken (and confusingly documented) Unicode handling (unicode	1194	=item 3. C<allow_blessed> is enabled.
518	escapes are not working properly, you need to set ImplicitUnicode to
519	I<different> values on en- and decoding to get symmetric behaviour).
520		1195
521	No roundtripping (simple cases work, but this depends on wether the scalar	1196	The object will be serialised as a JSON null value.
522	value was used in a numeric context or not).
523		1197
524	Dumping hashes may skip hash values depending on iterator state.	1198	=item 4. none of the above
525		1199
526	Unmaintained (maintainer unresponsive for many months, bugs are not	1200	If none of the settings are enabled or the respective methods are missing,
527	getting fixed).	1201	C<JSON::XS> throws an exception.
528
529	Does not check input for validity (i.e. will accept non-JSON input and
530	return "something" instead of raising an exception. This is a security
531	issue: imagine two banks transfering money between each other using
532	JSON. One bank might parse a given non-JSON request and deduct money,
533	while the other might reject the transaction with a syntax error. While a
534	good protocol will at least recover, that is extra unnecessary work and
535	the transaction will still not succeed).
536
537	=item JSON::DWIW 0.04
538
539	Very fast. Very natural. Very nice.
540
541	Undocumented unicode handling (but the best of the pack. Unicode escapes
542	still don't get parsed properly).
543
544	Very inflexible.
545
546	No roundtripping.
547
548	Does not generate valid JSON texts (key strings are often unquoted, empty keys
549	result in nothing being output)
550
551	Does not check input for validity.
552		1202
553	=back	1203	=back
		1204
		1205	=head3 DESERIALISATION
		1206
		1207	For deserialisation there are only two cases to consider: either
		1208	nonstandard tagging was used, in which case C<allow_tags> decides,
		1209	or objects cannot be automatically be deserialised, in which
		1210	case you can use postprocessing or the C<filter_json_object> or
		1211	C<filter_json_single_key_object> callbacks to get some real objects our of
		1212	your JSON.
		1213
		1214	This section only considers the tagged value case: I a tagged JSON object
		1215	is encountered during decoding and C<allow_tags> is disabled, a parse
		1216	error will result (as if tagged values were not part of the grammar).
		1217
		1218	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1219	of the package/classname used during serialisation (it will not attempt
		1220	to load the package as a Perl module). If there is no such method, the
		1221	decoding will fail with an error.
		1222
		1223	Otherwise, the C<THAW> method is invoked with the classname as first
		1224	argument, the constant string C<JSON> as second argument, and all the
		1225	values from the JSON array (the values originally returned by the
		1226	C<FREEZE> method) as remaining arguments.
		1227
		1228	The method must then return the object. While technically you can return
		1229	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1230	make that work in all cases, so better return an actual blessed reference.
		1231
		1232	As an example, let's implement a C<THAW> function that regenerates the
		1233	C<My::Object> from the C<FREEZE> example earlier:
		1234
		1235	sub My::Object::THAW {
		1236	my ($class, $serialiser, $type, $id) = @_;
		1237
		1238	$class->new (type => $type, id => $id)
		1239	}
		1240
		1241
		1242	=head1 ENCODING/CODESET FLAG NOTES
		1243
		1244	The interested reader might have seen a number of flags that signify
		1245	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1246	some confusion on what these do, so here is a short comparison:
		1247
		1248	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1249	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1250	control whether C<encode> escapes character values outside their respective
		1251	codeset range. Neither of these flags conflict with each other, although
		1252	some combinations make less sense than others.
		1253
		1254	Care has been taken to make all flags symmetrical with respect to
		1255	C<encode> and C<decode>, that is, texts encoded with any combination of
		1256	these flag values will be correctly decoded when the same flags are used
		1257	- in general, if you use different flag settings while encoding vs. when
		1258	decoding you likely have a bug somewhere.
		1259
		1260	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1261	simply an abstract set of character-codepoint pairs, while an encoding
		1262	takes those codepoint numbers and I<encodes> them, in our case into
		1263	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1264	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1265	the same time, which can be confusing.
		1266
		1267	=over 4
		1268
		1269	=item C<utf8> flag disabled
		1270
		1271	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1272	and expect Unicode strings, that is, characters with high ordinal Unicode
		1273	values (> 255) will be encoded as such characters, and likewise such
		1274	characters are decoded as-is, no changes to them will be done, except
		1275	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1276	respectively (to Perl, these are the same thing in strings unless you do
		1277	funny/weird/dumb stuff).
		1278
		1279	This is useful when you want to do the encoding yourself (e.g. when you
		1280	want to have UTF-16 encoded JSON texts) or when some other layer does
		1281	the encoding for you (for example, when printing to a terminal using a
		1282	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1283	to UTF-8 encode your data first and have Perl encode it another time).
		1284
		1285	=item C<utf8> flag enabled
		1286
		1287	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1288	characters using the corresponding UTF-8 multi-byte sequence, and will
		1289	expect your input strings to be encoded as UTF-8, that is, no "character"
		1290	of the input string must have any value > 255, as UTF-8 does not allow
		1291	that.
		1292
		1293	The C<utf8> flag therefore switches between two modes: disabled means you
		1294	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1295	octet/binary string in Perl.
		1296
		1297	=item C<latin1> or C<ascii> flags enabled
		1298
		1299	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1300	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1301	characters as specified by the C<utf8> flag.
		1302
		1303	If C<utf8> is disabled, then the result is also correctly encoded in those
		1304	character sets (as both are proper subsets of Unicode, meaning that a
		1305	Unicode string with all character values < 256 is the same thing as a
		1306	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1307	the same thing as an ASCII string in Perl).
		1308
		1309	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1310	regardless of these flags, just some more characters will be escaped using
		1311	C<\uXXXX> then before.
		1312
		1313	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1314	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1315	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1316	a subset of Unicode), while ASCII is.
		1317
		1318	Surprisingly, C<decode> will ignore these flags and so treat all input
		1319	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1320	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1321	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1322
		1323	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1324	they only govern when the JSON output engine escapes a character or not.
		1325
		1326	The main use for C<latin1> is to relatively efficiently store binary data
		1327	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1328
		1329	The main use for C<ascii> is to force the output to not contain characters
		1330	with values > 127, which means you can interpret the resulting string
		1331	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1332	8-bit-encoding, and still get the same data structure back. This is useful
		1333	when your channel for JSON transfer is not 8-bit clean or the encoding
		1334	might be mangled in between (e.g. in mail), and works because ASCII is a
		1335	proper subset of most 8-bit and multibyte encodings in use in the world.
		1336
		1337	=back
		1338
		1339
		1340	=head2 JSON and ECMAscript
		1341
		1342	JSON syntax is based on how literals are represented in javascript (the
		1343	not-standardised predecessor of ECMAscript) which is presumably why it is
		1344	called "JavaScript Object Notation".
		1345
		1346	However, JSON is not a subset (and also not a superset of course) of
		1347	ECMAscript (the standard) or javascript (whatever browsers actually
		1348	implement).
		1349
		1350	If you want to use javascript's C<eval> function to "parse" JSON, you
		1351	might run into parse errors for valid JSON texts, or the resulting data
		1352	structure might not be queryable:
		1353
		1354	One of the problems is that U+2028 and U+2029 are valid characters inside
		1355	JSON strings, but are not allowed in ECMAscript string literals, so the
		1356	following Perl fragment will not output something that can be guaranteed
		1357	to be parsable by javascript's C<eval>:
		1358
		1359	use JSON::XS;
		1360
		1361	print encode_json [chr 0x2028];
		1362
		1363	The right fix for this is to use a proper JSON parser in your javascript
		1364	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1365	F<json2.js> parser).
		1366
		1367	If this is not an option, you can, as a stop-gap measure, simply encode to
		1368	ASCII-only JSON:
		1369
		1370	use JSON::XS;
		1371
		1372	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1373
		1374	Note that this will enlarge the resulting JSON text quite a bit if you
		1375	have many non-ASCII characters. You might be tempted to run some regexes
		1376	to only escape U+2028 and U+2029, e.g.:
		1377
		1378	# DO NOT USE THIS!
		1379	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1380	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1381	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1382	print $json;
		1383
		1384	Note that I<this is a bad idea>: the above only works for U+2028 and
		1385	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1386	javascript implementations, however, have issues with other characters as
		1387	well - using C<eval> naively simply I<will> cause problems.
		1388
		1389	Another problem is that some javascript implementations reserve
		1390	some property names for their own purposes (which probably makes
		1391	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1392	C<__proto__> property name for its own purposes.
		1393
		1394	If that is a problem, you could parse try to filter the resulting JSON
		1395	output for these property strings, e.g.:
		1396
		1397	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1398
		1399	This works because C<__proto__> is not valid outside of strings, so every
		1400	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1401
		1402	If you know of other incompatibilities, please let me know.
		1403
		1404
		1405	=head2 JSON and YAML
		1406
		1407	You often hear that JSON is a subset of YAML. This is, however, a mass
		1408	hysteria(*) and very far from the truth (as of the time of this writing),
		1409	so let me state it clearly: I<in general, there is no way to configure
		1410	JSON::XS to output a data structure as valid YAML> that works in all
		1411	cases.
		1412
		1413	If you really must use JSON::XS to generate YAML, you should use this
		1414	algorithm (subject to change in future versions):
		1415
		1416	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1417	my $yaml = $to_yaml->encode ($ref) . "\n";
		1418
		1419	This will I<usually> generate JSON texts that also parse as valid
		1420	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1421	lengths that JSON doesn't have and also has different and incompatible
		1422	unicode character escape syntax, so you should make sure that your hash
		1423	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1424	and that you do not have characters with codepoint values outside the
		1425	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1426	sequences in strings (which JSON::XS does not I<currently> generate, but
		1427	other JSON generators might).
		1428
		1429	There might be other incompatibilities that I am not aware of (or the YAML
		1430	specification has been changed yet again - it does so quite often). In
		1431	general you should not try to generate YAML with a JSON generator or vice
		1432	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1433	high that you will run into severe interoperability problems when you
		1434	least expect it.
		1435
		1436	=over 4
		1437
		1438	=item (*)
		1439
		1440	I have been pressured multiple times by Brian Ingerson (one of the
		1441	authors of the YAML specification) to remove this paragraph, despite him
		1442	acknowledging that the actual incompatibilities exist. As I was personally
		1443	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1444	educate people about these issues, so others do not run into the same
		1445	problem again and again. After this, Brian called me a (quote)I<complete
		1446	and worthless idiot>(unquote).
		1447
		1448	In my opinion, instead of pressuring and insulting people who actually
		1449	clarify issues with YAML and the wrong statements of some of its
		1450	proponents, I would kindly suggest reading the JSON spec (which is not
		1451	that difficult or long) and finally make YAML compatible to it, and
		1452	educating users about the changes, instead of spreading lies about the
		1453	real compatibility for many I<years> and trying to silence people who
		1454	point out that it isn't true.
		1455
		1456	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1457	though the incompatibilities have been documented (and are known to Brian)
		1458	for many years and the spec makes explicit claims that YAML is a superset
		1459	of JSON. It would be so easy to fix, but apparently, bullying people and
		1460	corrupting userdata is so much easier.
		1461
		1462	=back
		1463
554		1464
555	=head2 SPEED	1465	=head2 SPEED
556		1466
557	It seems that JSON::XS is surprisingly fast, as shown in the following	1467	It seems that JSON::XS is surprisingly fast, as shown in the following
558	tables. They have been generated with the help of the C<eg/bench> program	1468	tables. They have been generated with the help of the C<eg/bench> program
559	in the JSON::XS distribution, to make it easy to compare on your own	1469	in the JSON::XS distribution, to make it easy to compare on your own
560	system.	1470	system.
561		1471
562	First comes a comparison between various modules using a very short JSON	1472	First comes a comparison between various modules using
563	string:	1473	a very short single-line JSON string (also available at
		1474	L<http://dist.schmorp.de/misc/json/short.json>).
564		1475
565	{"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null}	1476	{"method": "handleMessage", "params": ["user1",
		1477	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1478	1, 0]}
566		1479
567	It shows the number of encodes/decodes per second (JSON::XS uses the	1480	It shows the number of encodes/decodes per second (JSON::XS uses
568	functional interface, while JSON::XS/2 uses the OO interface with	1481	the functional interface, while JSON::XS/2 uses the OO interface
569	pretty-printing and hashkey sorting enabled). Higher is better:	1482	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1483	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1484	uses the from_json method). Higher is better:
570		1485
571	module | encode | decode |	1486	module | encode | decode |
572	-----------|------------|------------|	1487	--------------|------------|------------|
573	JSON | 11488.516 | 7823.035 |	1488	JSON::DWIW/DS | 86302.551 | 102300.098 |
574	JSON::DWIW | 94708.054 | 129094.260 |	1489	JSON::DWIW/FJ | 86302.551 | 75983.768 |
575	JSON::PC | 63884.157 | 128528.212 |	1490	JSON::PP | 15827.562 | 6638.658 |
576	JSON::Syck | 34898.677 | 42096.911 |	1491	JSON::Syck | 63358.066 | 47662.545 |
577	JSON::XS | 654027.064 | 396423.669 |	1492	JSON::XS | 511500.488 | 511500.488 |
578	JSON::XS/2 | 371564.190 | 371725.613 |	1493	JSON::XS/2 | 291271.111 | 388361.481 |
		1494	JSON::XS/3 | 361577.931 | 361577.931 |
		1495	Storable | 66788.280 | 265462.278 |
579	-----------+------------+------------+	1496	--------------+------------+------------+
580		1497
581	That is, JSON::XS is more than six times faster than JSON::DWIW on	1498	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
582	encoding, more than three times faster on decoding, and about thirty times	1499	about five times faster on decoding, and over thirty to seventy times
583	faster than JSON, even with pretty-printing and key sorting.	1500	faster than JSON's pure perl implementation. It also compares favourably
		1501	to Storable for small amounts of data.
584		1502
585	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1503	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
586	search API (http://nanoref.com/yahooapis/mgPdGg):	1504	search API (L<http://dist.schmorp.de/misc/json/long.json>).
587		1505
588	module | encode | decode |	1506	module | encode | decode |
589	-----------|------------|------------|	1507	--------------|------------|------------|
590	JSON | 273.023 | 44.674 |	1508	JSON::DWIW/DS | 1647.927 | 2673.916 |
591	JSON::DWIW | 1089.383 | 1145.704 |	1509	JSON::DWIW/FJ | 1630.249 | 2596.128 |
592	JSON::PC | 3097.419 | 2393.921 |	1510	JSON::PP | 400.640 | 62.311 |
593	JSON::Syck | 514.060 | 843.053 |	1511	JSON::Syck | 1481.040 | 1524.869 |
594	JSON::XS | 6479.668 | 3636.364 |	1512	JSON::XS | 20661.596 | 9541.183 |
595	JSON::XS/2 | 3774.221 | 3599.124 |	1513	JSON::XS/2 | 10683.403 | 9416.938 |
		1514	JSON::XS/3 | 20661.596 | 9400.054 |
		1515	Storable | 19765.806 | 10000.725 |
596	-----------+------------+------------+	1516	--------------+------------+------------+
597		1517
598	Again, JSON::XS leads by far.	1518	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1519	decodes a bit faster).
599		1520
600	On large strings containing lots of high unicode characters, some modules	1521	On large strings containing lots of high Unicode characters, some modules
601	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1522	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
602	will be broken due to missing (or wrong) unicode handling. Others refuse	1523	will be broken due to missing (or wrong) Unicode handling. Others refuse
603	to decode or encode properly, so it was impossible to prepare a fair	1524	to decode or encode properly, so it was impossible to prepare a fair
604	comparison table for that case.	1525	comparison table for that case.
605		1526
606		1527
607	=head1 SECURITY CONSIDERATIONS	1528	=head1 SECURITY CONSIDERATIONS
…		…
613	any buffer overflows. Obviously, this module should ensure that and I am	1534	any buffer overflows. Obviously, this module should ensure that and I am
614	trying hard on making that true, but you never know.	1535	trying hard on making that true, but you never know.
615		1536
616	Second, you need to avoid resource-starving attacks. That means you should	1537	Second, you need to avoid resource-starving attacks. That means you should
617	limit the size of JSON texts you accept, or make sure then when your	1538	limit the size of JSON texts you accept, or make sure then when your
618	resources run out, thats just fine (e.g. by using a separate process that	1539	resources run out, that's just fine (e.g. by using a separate process that
619	can crash safely). The size of a JSON text in octets or characters is	1540	can crash safely). The size of a JSON text in octets or characters is
620	usually a good indication of the size of the resources required to decode	1541	usually a good indication of the size of the resources required to decode
621	it into a Perl structure.	1542	it into a Perl structure. While JSON::XS can check the size of the JSON
		1543	text, it might be too late when you already have it in memory, so you
		1544	might want to check the size before you accept the string.
622		1545
623	Third, JSON::XS recurses using the C stack when decoding objects and	1546	Third, JSON::XS recurses using the C stack when decoding objects and
624	arrays. The C stack is a limited resource: for instance, on my amd64	1547	arrays. The C stack is a limited resource: for instance, on my amd64
625	machine with 8MB of stack size I can decode around 180k nested arrays	1548	machine with 8MB of stack size I can decode around 180k nested arrays but
626	but only 14k nested JSON objects. If that is exceeded, the program	1549	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1550	to free the temporary). If that is exceeded, the program crashes. To be
627	crashes. Thats why the default nesting limit is set to 8192. If your	1551	conservative, the default nesting limit is set to 512. If your process
628	process has a smaller stack, you should adjust this setting accordingly	1552	has a smaller stack, you should adjust this setting accordingly with the
629	with the C<max_depth> method.	1553	C<max_depth> method.
630		1554
631	And last but least, something else could bomb you that I forgot to think	1555	Something else could bomb you, too, that I forgot to think of. In that
632	of. In that case, you get to keep the pieces. I am alway sopen for hints,	1556	case, you get to keep the pieces. I am always open for hints, though...
633	though...	1557
		1558	Also keep in mind that JSON::XS might leak contents of your Perl data
		1559	structures in its error messages, so when you serialise sensitive
		1560	information you might want to make sure that exceptions thrown by JSON::XS
		1561	will not end up in front of untrusted eyes.
		1562
		1563	If you are using JSON::XS to return packets to consumption
		1564	by JavaScript scripts in a browser you should have a look at
		1565	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
		1566	see whether you are vulnerable to some common attack vectors (which really
		1567	are browser design bugs, but it is still you who will have to deal with
		1568	it, as major browser developers care only for features, not about getting
		1569	security right).
		1570
		1571
		1572	=head1 "OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)
		1573
		1574	TL;DR: Due to security concerns, JSON::XS will not allow scalar data in
		1575	JSON texts by default - you need to create your own JSON::XS object and
		1576	enable C<allow_nonref>:
		1577
		1578
		1579	my $json = JSON::XS->new->allow_nonref;
		1580
		1581	$text = $json->encode ($data);
		1582	$data = $json->decode ($text);
		1583
		1584	The long version: JSON being an important and supposedly stable format,
		1585	the IETF standardised it as RFC 4627 in 2006. Unfortunately, the inventor
		1586	of JSON, Dougles Crockford, unilaterally changed the definition of JSON in
		1587	javascript. Rather than create a fork, the IETF decided to standardise the
		1588	new syntax (apparently, so Iw as told, without finding it very amusing).
		1589
		1590	The biggest difference between thed original JSON and the new JSON is that
		1591	the new JSON supports scalars (anything other than arrays and objects) at
		1592	the toplevel of a JSON text. While this is strictly backwards compatible
		1593	to older versions, it breaks a number of protocols that relied on sending
		1594	JSON back-to-back, and is a minor security concern.
		1595
		1596	For example, imagine you have two banks communicating, and on one side,
		1597	trhe JSON coder gets upgraded. Two messages, such as C<10> and C<1000>
		1598	might then be confused to mean C<101000>, something that couldn't happen
		1599	in the original JSON, because niether of these messages would be valid
		1600	JSON.
		1601
		1602	If one side accepts these messages, then an upgrade in the coder on either
		1603	side could result in this becoming exploitable.
		1604
		1605	This module has always allowed these messages as an optional extension, by
		1606	default disabled. The security concerns are the reason why the default is
		1607	still disabled, but future versions might/will likely upgrade to the newer
		1608	RFC as default format, so you are advised to check your implementation
		1609	and/or override the default with C<< ->allow_nonref (0) >> to ensure that
		1610	future versions are safe.
		1611
		1612
		1613	=head1 INTEROPERABILITY WITH OTHER MODULES
		1614
		1615	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1616	constants. That means that the JSON true and false values will be
		1617	comaptible to true and false values of other modules that do the same,
		1618	such as L<JSON::PP> and L<CBOR::XS>.
		1619
		1620
		1621	=head1 INTEROPERABILITY WITH OTHER JSON DECODERS
		1622
		1623	As long as you only serialise data that can be directly expressed in JSON,
		1624	C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs,
		1625	but C<JSON::XS> has found more bugs in the official JSON testsuite (1)
		1626	than the official JSON testsuite has found in C<JSON::XS> (0)).
		1627
		1628	When you have trouble decoding JSON generated by this module using other
		1629	decoders, then it is very likely that you have an encoding mismatch or the
		1630	other decoder is broken.
		1631
		1632	When decoding, C<JSON::XS> is strict by default and will likely catch all
		1633	errors. There are currently two settings that change this: C<relaxed>
		1634	makes C<JSON::XS> accept (but not generate) some non-standard extensions,
		1635	and C<allow_tags> will allow you to encode and decode Perl objects, at the
		1636	cost of not outputting valid JSON anymore.
		1637
		1638	=head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
		1639
		1640	When you use C<allow_tags> to use the extended (and also nonstandard and
		1641	invalid) JSON syntax for serialised objects, and you still want to decode
		1642	the generated When you want to serialise objects, you can run a regex
		1643	to replace the tagged syntax by standard JSON arrays (it only works for
		1644	"normal" package names without comma, newlines or single colons). First,
		1645	the readable Perl version:
		1646
		1647	# if your FREEZE methods return no values, you need this replace first:
		1648	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
		1649
		1650	# this works for non-empty constructor arg lists:
		1651	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
		1652
		1653	And here is a less readable version that is easy to adapt to other
		1654	languages:
		1655
		1656	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
		1657
		1658	Here is an ECMAScript version (same regex):
		1659
		1660	json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
		1661
		1662	Since this syntax converts to standard JSON arrays, it might be hard to
		1663	distinguish serialised objects from normal arrays. You can prepend a
		1664	"magic number" as first array element to reduce chances of a collision:
		1665
		1666	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
		1667
		1668	And after decoding the JSON text, you could walk the data
		1669	structure looking for arrays with a first element of
		1670	C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>.
		1671
		1672	The same approach can be used to create the tagged format with another
		1673	encoder. First, you create an array with the magic string as first member,
		1674	the classname as second, and constructor arguments last, encode it as part
		1675	of your JSON structure, and then:
		1676
		1677	$json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
		1678
		1679	Again, this has some limitations - the magic string must not be encoded
		1680	with character escapes, and the constructor arguments must be non-empty.
		1681
		1682
		1683	=head1 RFC7159
		1684
		1685	Since this module was written, Google has written a new JSON RFC, RFC 7159
		1686	(and RFC7158). Unfortunately, this RFC breaks compatibility with both the
		1687	original JSON specification on www.json.org and RFC4627.
		1688
		1689	As far as I can see, you can get partial compatibility when parsing by
		1690	using C<< ->allow_nonref >>. However, consider the security implications
		1691	of doing so.
		1692
		1693	I haven't decided yet when to break compatibility with RFC4627 by default
		1694	(and potentially leave applications insecure) and change the default to
		1695	follow RFC7159, but application authors are well advised to call C<<
		1696	->allow_nonref(0) >> even if this is the current default, if they cannot
		1697	handle non-reference values, in preparation for the day when the default
		1698	will change.
		1699
		1700
		1701	=head1 (I-)THREADS
		1702
		1703	This module is I<not> guaranteed to be ithread (or MULTIPLICITY-) safe
		1704	and there are no plans to change this. Note that perl's builtin so-called
		1705	theeads/ithreads are officially deprecated and should not be used.
		1706
		1707
		1708	=head1 THE PERILS OF SETLOCALE
		1709
		1710	Sometimes people avoid the Perl locale support and directly call the
		1711	system's setlocale function with C<LC_ALL>.
		1712
		1713	This breaks both perl and modules such as JSON::XS, as stringification of
		1714	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1715	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1716	perl to stringify numbers).
		1717
		1718	The solution is simple: don't call C<setlocale>, or use it for only those
		1719	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1720
		1721	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1722	actually needs it (avoiding stringification of numbers), and restore it
		1723	afterwards.
634		1724
635		1725
636	=head1 BUGS	1726	=head1 BUGS
637		1727
638	While the goal of this module is to be correct, that unfortunately does	1728	While the goal of this module is to be correct, that unfortunately does
639	not mean its bug-free, only that I think its design is bug-free. It is	1729	not mean it's bug-free, only that I think its design is bug-free. If you
640	still relatively early in its development. If you keep reporting bugs they	1730	keep reporting bugs they will be fixed swiftly, though.
641	will be fixed swiftly, though.	1731
		1732	Please refrain from using rt.cpan.org or any other bug reporting
		1733	service. I put the contact address into my modules for a reason.
642		1734
643	=cut	1735	=cut
644		1736
645	1;	1737	BEGIN {
		1738	*true = \$Types::Serialiser::true;
		1739	*true = \&Types::Serialiser::true;
		1740	*false = \$Types::Serialiser::false;
		1741	*false = \&Types::Serialiser::false;
		1742	*is_bool = \&Types::Serialiser::is_bool;
		1743
		1744	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
		1745	}
		1746
		1747	XSLoader::load "JSON::XS", $VERSION;
		1748
		1749	=head1 SEE ALSO
		1750
		1751	The F<json_xs> command line utility for quick experiments.
646		1752
647	=head1 AUTHOR	1753	=head1 AUTHOR
648		1754
649	Marc Lehmann <schmorp@schmorp.de>	1755	Marc Lehmann <schmorp@schmorp.de>
650	http://home.schmorp.de/	1756	http://home.schmorp.de/
651		1757
652	=cut	1758	=cut
653		1759
		1760	1
		1761

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