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Revision 1.13 by root, Fri Mar 23 18:37:30 2007 UTC vs.
Revision 1.140 by root, Thu Jun 27 11:45:17 2013 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
4		4
		5	=encoding utf-8
		6
		7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
8		13
9	# exported functions, croak on error	14	# exported functions, they croak on error
		15	# and expect/generate UTF-8
10		16
11	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
12	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
13		19
14	# oo-interface	20	# OO-interface
15		21
16	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
17	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
18	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
19		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
20	=head1 DESCRIPTION	34	=head1 DESCRIPTION
21		35
22	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
23	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
24	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overridden) with no overhead due to emulation (by inheriting constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
25		47
26	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
27	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
28	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
29	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
30	reports for other reasons.	52	reports for other reasons.
31		53
32	See COMPARISON, below, for a comparison to some other JSON modules.
33
34	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
35	vice versa.	55	vice versa.
36		56
37	=head2 FEATURES	57	=head2 FEATURES
38		58
39	=over 4	59	=over 4
40		60
41	=item * correct handling of unicode issues	61	=item * correct Unicode handling
42		62
43	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
44	it does so.	64	so, and even documents what "correct" means.
45		65
46	=item * round-trip integrity	66	=item * round-trip integrity
47		67
48	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
49	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
50	(e.g. the string "2.0" doesn't suddenly become "2").	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
		71	it looks like a number). There I<are> minor exceptions to this, read the
		72	MAPPING section below to learn about those.
51		73
52	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
53		75
54	There is no guessing, no generating of illegal JSON strings by default,	76	There is no guessing, no generating of illegal JSON texts by default,
55	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
56	feature).	78	feature).
57		79
58	=item * fast	80	=item * fast
59		81
60	Compared to other JSON modules, this module compares favourably in terms	82	Compared to other JSON modules and other serialisers such as Storable,
61	of speed, too.	83	this module usually compares favourably in terms of speed, too.
62		84
63	=item * simple to use	85	=item * simple to use
64		86
65	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
66	interface.	88	oriented interface.
67		89
68	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
69		91
70	You can choose between the most compact guarenteed single-line format	92	You can choose between the most compact guaranteed-single-line format
71	possible (nice for simple line-based protocols), a pure-ascii format (for	93	possible (nice for simple line-based protocols), a pure-ASCII format
72	when your transport is not 8-bit clean), or a pretty-printed format (for	94	(for when your transport is not 8-bit clean, still supports the whole
73	when you want to read that stuff). Or you can combine those features in	95	Unicode range), or a pretty-printed format (for when you want to read that
74	whatever way you like.	96	stuff). Or you can combine those features in whatever way you like.
75		97
76	=back	98	=back
77		99
78	=cut	100	=cut
79		101
80	package JSON::XS;	102	package JSON::XS;
81		103
82	BEGIN {	104	use common::sense;
		105
83	$VERSION = '0.3';	106	our $VERSION = 2.34;
84	@ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
85		108
86	@EXPORT = qw(to_json from_json);	109	our @EXPORT = qw(encode_json decode_json to_json from_json);
87	require Exporter;
88		110
		111	sub to_json($) {
89	require XSLoader;	112	require Carp;
90	XSLoader::load JSON::XS::, $VERSION;	113	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
91	}	114	}
92		115
		116	sub from_json($) {
		117	require Carp;
		118	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
		119	}
		120
		121	use Exporter;
		122	use XSLoader;
		123
93	=head1 FUNCTIONAL INTERFACE	124	=head1 FUNCTIONAL INTERFACE
94		125
95	The following convinience methods are provided by this module. They are	126	The following convenience methods are provided by this module. They are
96	exported by default:	127	exported by default:
97		128
98	=over 4	129	=over 4
99		130
100	=item $json_string = to_json $perl_scalar	131	=item $json_text = encode_json $perl_scalar
101		132
102	Converts the given Perl data structure (a simple scalar or a reference to	133	Converts the given Perl data structure to a UTF-8 encoded, binary string
103	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	134	(that is, the string contains octets only). Croaks on error.
104	octets only). Croaks on error.
105		135
106	This function call is functionally identical to C<< JSON::XS->new->utf8->encode ($perl_scalar) >>.	136	This function call is functionally identical to:
107		137
		138	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		139
		140	Except being faster.
		141
108	=item $perl_scalar = from_json $json_string	142	=item $perl_scalar = decode_json $json_text
109		143
110	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	144	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
111	parse that as an UTF-8 encoded JSON string, returning the resulting simple	145	to parse that as an UTF-8 encoded JSON text, returning the resulting
112	scalar or reference. Croaks on error.	146	reference. Croaks on error.
113		147
114	This function call is functionally identical to C<< JSON::XS->new->utf8->decode ($json_string) >>.	148	This function call is functionally identical to:
		149
		150	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		151
		152	Except being faster.
		153
		154	=item $is_boolean = JSON::XS::is_bool $scalar
		155
		156	Returns true if the passed scalar represents either JSON::XS::true or
		157	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		158	and are used to represent JSON C<true> and C<false> values in Perl.
		159
		160	See MAPPING, below, for more information on how JSON values are mapped to
		161	Perl.
115		162
116	=back	163	=back
		164
		165
		166	=head1 A FEW NOTES ON UNICODE AND PERL
		167
		168	Since this often leads to confusion, here are a few very clear words on
		169	how Unicode works in Perl, modulo bugs.
		170
		171	=over 4
		172
		173	=item 1. Perl strings can store characters with ordinal values > 255.
		174
		175	This enables you to store Unicode characters as single characters in a
		176	Perl string - very natural.
		177
		178	=item 2. Perl does I<not> associate an encoding with your strings.
		179
		180	... until you force it to, e.g. when matching it against a regex, or
		181	printing the scalar to a file, in which case Perl either interprets your
		182	string as locale-encoded text, octets/binary, or as Unicode, depending
		183	on various settings. In no case is an encoding stored together with your
		184	data, it is I<use> that decides encoding, not any magical meta data.
		185
		186	=item 3. The internal utf-8 flag has no meaning with regards to the
		187	encoding of your string.
		188
		189	Just ignore that flag unless you debug a Perl bug, a module written in
		190	XS or want to dive into the internals of perl. Otherwise it will only
		191	confuse you, as, despite the name, it says nothing about how your string
		192	is encoded. You can have Unicode strings with that flag set, with that
		193	flag clear, and you can have binary data with that flag set and that flag
		194	clear. Other possibilities exist, too.
		195
		196	If you didn't know about that flag, just the better, pretend it doesn't
		197	exist.
		198
		199	=item 4. A "Unicode String" is simply a string where each character can be
		200	validly interpreted as a Unicode code point.
		201
		202	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		203	Unicode string encoded in UTF-8, giving you a binary string.
		204
		205	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		206
		207	It's a fact. Learn to live with it.
		208
		209	=back
		210
		211	I hope this helps :)
		212
117		213
118	=head1 OBJECT-ORIENTED INTERFACE	214	=head1 OBJECT-ORIENTED INTERFACE
119		215
120	The object oriented interface lets you configure your own encoding or	216	The object oriented interface lets you configure your own encoding or
121	decoding style, within the limits of supported formats.	217	decoding style, within the limits of supported formats.
…		…
128	strings. All boolean flags described below are by default I<disabled>.	224	strings. All boolean flags described below are by default I<disabled>.
129		225
130	The mutators for flags all return the JSON object again and thus calls can	226	The mutators for flags all return the JSON object again and thus calls can
131	be chained:	227	be chained:
132		228
133	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	229	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
134	=> {"a": [1, 2]}	230	=> {"a": [1, 2]}
135		231
136	=item $json = $json->ascii ([$enable])	232	=item $json = $json->ascii ([$enable])
137		233
		234	=item $enabled = $json->get_ascii
		235
138	If C<$enable> is true (or missing), then the C<encode> method will	236	If C<$enable> is true (or missing), then the C<encode> method will not
139	not generate characters outside the code range C<0..127>. Any unicode	237	generate characters outside the code range C<0..127> (which is ASCII). Any
140	characters outside that range will be escaped using either a single	238	Unicode characters outside that range will be escaped using either a
141	\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per	239	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
142	RFC4627.	240	as per RFC4627. The resulting encoded JSON text can be treated as a native
		241	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		242	or any other superset of ASCII.
143		243
144	If C<$enable> is false, then the C<encode> method will not escape Unicode	244	If C<$enable> is false, then the C<encode> method will not escape Unicode
145	characters unless necessary.	245	characters unless required by the JSON syntax or other flags. This results
		246	in a faster and more compact format.
146		247
		248	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		249	document.
		250
		251	The main use for this flag is to produce JSON texts that can be
		252	transmitted over a 7-bit channel, as the encoded JSON texts will not
		253	contain any 8 bit characters.
		254
147	JSON::XS->new->ascii (1)->encode (chr 0x10401)	255	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
148	=> \ud801\udc01	256	=> ["\ud801\udc01"]
		257
		258	=item $json = $json->latin1 ([$enable])
		259
		260	=item $enabled = $json->get_latin1
		261
		262	If C<$enable> is true (or missing), then the C<encode> method will encode
		263	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		264	outside the code range C<0..255>. The resulting string can be treated as a
		265	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		266	will not be affected in any way by this flag, as C<decode> by default
		267	expects Unicode, which is a strict superset of latin1.
		268
		269	If C<$enable> is false, then the C<encode> method will not escape Unicode
		270	characters unless required by the JSON syntax or other flags.
		271
		272	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		273	document.
		274
		275	The main use for this flag is efficiently encoding binary data as JSON
		276	text, as most octets will not be escaped, resulting in a smaller encoded
		277	size. The disadvantage is that the resulting JSON text is encoded
		278	in latin1 (and must correctly be treated as such when storing and
		279	transferring), a rare encoding for JSON. It is therefore most useful when
		280	you want to store data structures known to contain binary data efficiently
		281	in files or databases, not when talking to other JSON encoders/decoders.
		282
		283	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		284	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
149		285
150	=item $json = $json->utf8 ([$enable])	286	=item $json = $json->utf8 ([$enable])
151		287
		288	=item $enabled = $json->get_utf8
		289
152	If C<$enable> is true (or missing), then the C<encode> method will encode	290	If C<$enable> is true (or missing), then the C<encode> method will encode
153	the JSON string into UTF-8, as required by many protocols, while the	291	the JSON result into UTF-8, as required by many protocols, while the
154	C<decode> method expects to be handled an UTF-8-encoded string. Please	292	C<decode> method expects to be handled an UTF-8-encoded string. Please
155	note that UTF-8-encoded strings do not contain any characters outside the	293	note that UTF-8-encoded strings do not contain any characters outside the
156	range C<0..255>, they are thus useful for bytewise/binary I/O.	294	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		295	versions, enabling this option might enable autodetection of the UTF-16
		296	and UTF-32 encoding families, as described in RFC4627.
157		297
158	If C<$enable> is false, then the C<encode> method will return the JSON	298	If C<$enable> is false, then the C<encode> method will return the JSON
159	string as a (non-encoded) unicode string, while C<decode> expects thus a	299	string as a (non-encoded) Unicode string, while C<decode> expects thus a
160	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	300	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
161	to be done yourself, e.g. using the Encode module.	301	to be done yourself, e.g. using the Encode module.
162		302
		303	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		304	document.
		305
163	Example, output UTF-16-encoded JSON:	306	Example, output UTF-16BE-encoded JSON:
		307
		308	use Encode;
		309	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		310
		311	Example, decode UTF-32LE-encoded JSON:
		312
		313	use Encode;
		314	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
164		315
165	=item $json = $json->pretty ([$enable])	316	=item $json = $json->pretty ([$enable])
166		317
167	This enables (or disables) all of the C<indent>, C<space_before> and	318	This enables (or disables) all of the C<indent>, C<space_before> and
168	C<space_after> (and in the future possibly more) flags in one call to	319	C<space_after> (and in the future possibly more) flags in one call to
…		…
179	]	330	]
180	}	331	}
181		332
182	=item $json = $json->indent ([$enable])	333	=item $json = $json->indent ([$enable])
183		334
		335	=item $enabled = $json->get_indent
		336
184	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	337	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
185	format as output, putting every array member or object/hash key-value pair	338	format as output, putting every array member or object/hash key-value pair
186	into its own line, identing them properly.	339	into its own line, indenting them properly.
187		340
188	If C<$enable> is false, no newlines or indenting will be produced, and the	341	If C<$enable> is false, no newlines or indenting will be produced, and the
189	resulting JSON strings is guarenteed not to contain any C<newlines>.	342	resulting JSON text is guaranteed not to contain any C<newlines>.
190		343
191	This setting has no effect when decoding JSON strings.	344	This setting has no effect when decoding JSON texts.
192		345
193	=item $json = $json->space_before ([$enable])	346	=item $json = $json->space_before ([$enable])
		347
		348	=item $enabled = $json->get_space_before
194		349
195	If C<$enable> is true (or missing), then the C<encode> method will add an extra	350	If C<$enable> is true (or missing), then the C<encode> method will add an extra
196	optional space before the C<:> separating keys from values in JSON objects.	351	optional space before the C<:> separating keys from values in JSON objects.
197		352
198	If C<$enable> is false, then the C<encode> method will not add any extra	353	If C<$enable> is false, then the C<encode> method will not add any extra
199	space at those places.	354	space at those places.
200		355
201	This setting has no effect when decoding JSON strings. You will also most	356	This setting has no effect when decoding JSON texts. You will also
202	likely combine this setting with C<space_after>.	357	most likely combine this setting with C<space_after>.
203		358
204	Example, space_before enabled, space_after and indent disabled:	359	Example, space_before enabled, space_after and indent disabled:
205		360
206	{"key" :"value"}	361	{"key" :"value"}
207		362
208	=item $json = $json->space_after ([$enable])	363	=item $json = $json->space_after ([$enable])
		364
		365	=item $enabled = $json->get_space_after
209		366
210	If C<$enable> is true (or missing), then the C<encode> method will add an extra	367	If C<$enable> is true (or missing), then the C<encode> method will add an extra
211	optional space after the C<:> separating keys from values in JSON objects	368	optional space after the C<:> separating keys from values in JSON objects
212	and extra whitespace after the C<,> separating key-value pairs and array	369	and extra whitespace after the C<,> separating key-value pairs and array
213	members.	370	members.
214		371
215	If C<$enable> is false, then the C<encode> method will not add any extra	372	If C<$enable> is false, then the C<encode> method will not add any extra
216	space at those places.	373	space at those places.
217		374
218	This setting has no effect when decoding JSON strings.	375	This setting has no effect when decoding JSON texts.
219		376
220	Example, space_before and indent disabled, space_after enabled:	377	Example, space_before and indent disabled, space_after enabled:
221		378
222	{"key": "value"}	379	{"key": "value"}
223		380
		381	=item $json = $json->relaxed ([$enable])
		382
		383	=item $enabled = $json->get_relaxed
		384
		385	If C<$enable> is true (or missing), then C<decode> will accept some
		386	extensions to normal JSON syntax (see below). C<encode> will not be
		387	affected in anyway. I<Be aware that this option makes you accept invalid
		388	JSON texts as if they were valid!>. I suggest only to use this option to
		389	parse application-specific files written by humans (configuration files,
		390	resource files etc.)
		391
		392	If C<$enable> is false (the default), then C<decode> will only accept
		393	valid JSON texts.
		394
		395	Currently accepted extensions are:
		396
		397	=over 4
		398
		399	=item * list items can have an end-comma
		400
		401	JSON I<separates> array elements and key-value pairs with commas. This
		402	can be annoying if you write JSON texts manually and want to be able to
		403	quickly append elements, so this extension accepts comma at the end of
		404	such items not just between them:
		405
		406	[
		407	1,
		408	2, <- this comma not normally allowed
		409	]
		410	{
		411	"k1": "v1",
		412	"k2": "v2", <- this comma not normally allowed
		413	}
		414
		415	=item * shell-style '#'-comments
		416
		417	Whenever JSON allows whitespace, shell-style comments are additionally
		418	allowed. They are terminated by the first carriage-return or line-feed
		419	character, after which more white-space and comments are allowed.
		420
		421	[
		422	1, # this comment not allowed in JSON
		423	# neither this one...
		424	]
		425
		426	=back
		427
224	=item $json = $json->canonical ([$enable])	428	=item $json = $json->canonical ([$enable])
		429
		430	=item $enabled = $json->get_canonical
225		431
226	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	432	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
227	by sorting their keys. This is adding a comparatively high overhead.	433	by sorting their keys. This is adding a comparatively high overhead.
228		434
229	If C<$enable> is false, then the C<encode> method will output key-value	435	If C<$enable> is false, then the C<encode> method will output key-value
230	pairs in the order Perl stores them (which will likely change between runs	436	pairs in the order Perl stores them (which will likely change between runs
231	of the same script).	437	of the same script, and can change even within the same run from 5.18
		438	onwards).
232		439
233	This option is useful if you want the same data structure to be encoded as	440	This option is useful if you want the same data structure to be encoded as
234	the same JSON string (given the same overall settings). If it is disabled,	441	the same JSON text (given the same overall settings). If it is disabled,
235	the same hash migh be encoded differently even if contains the same data,	442	the same hash might be encoded differently even if contains the same data,
236	as key-value pairs have no inherent ordering in Perl.	443	as key-value pairs have no inherent ordering in Perl.
237		444
238	This setting has no effect when decoding JSON strings.	445	This setting has no effect when decoding JSON texts.
		446
		447	This setting has currently no effect on tied hashes.
239		448
240	=item $json = $json->allow_nonref ([$enable])	449	=item $json = $json->allow_nonref ([$enable])
		450
		451	=item $enabled = $json->get_allow_nonref
241		452
242	If C<$enable> is true (or missing), then the C<encode> method can convert a	453	If C<$enable> is true (or missing), then the C<encode> method can convert a
243	non-reference into its corresponding string, number or null JSON value,	454	non-reference into its corresponding string, number or null JSON value,
244	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	455	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
245	values instead of croaking.	456	values instead of croaking.
246		457
247	If C<$enable> is false, then the C<encode> method will croak if it isn't	458	If C<$enable> is false, then the C<encode> method will croak if it isn't
248	passed an arrayref or hashref, as JSON strings must either be an object	459	passed an arrayref or hashref, as JSON texts must either be an object
249	or array. Likewise, C<decode> will croak if given something that is not a	460	or array. Likewise, C<decode> will croak if given something that is not a
250	JSON object or array.	461	JSON object or array.
251		462
252	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,	463	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
253	resulting in an invalid JSON text:	464	resulting in an invalid JSON text:
254		465
255	JSON::XS->new->allow_nonref->encode ("Hello, World!")	466	JSON::XS->new->allow_nonref->encode ("Hello, World!")
256	=> "Hello, World!"	467	=> "Hello, World!"
257		468
		469	=item $json = $json->allow_unknown ([$enable])
		470
		471	=item $enabled = $json->get_allow_unknown
		472
		473	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		474	exception when it encounters values it cannot represent in JSON (for
		475	example, filehandles) but instead will encode a JSON C<null> value. Note
		476	that blessed objects are not included here and are handled separately by
		477	c<allow_nonref>.
		478
		479	If C<$enable> is false (the default), then C<encode> will throw an
		480	exception when it encounters anything it cannot encode as JSON.
		481
		482	This option does not affect C<decode> in any way, and it is recommended to
		483	leave it off unless you know your communications partner.
		484
		485	=item $json = $json->allow_blessed ([$enable])
		486
		487	=item $enabled = $json->get_allow_blessed
		488
		489	If C<$enable> is true (or missing), then the C<encode> method will not
		490	barf when it encounters a blessed reference. Instead, the value of the
		491	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		492	disabled or no C<TO_JSON> method found) or a representation of the
		493	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		494	encoded. Has no effect on C<decode>.
		495
		496	If C<$enable> is false (the default), then C<encode> will throw an
		497	exception when it encounters a blessed object.
		498
		499	=item $json = $json->convert_blessed ([$enable])
		500
		501	=item $enabled = $json->get_convert_blessed
		502
		503	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		504	blessed object, will check for the availability of the C<TO_JSON> method
		505	on the object's class. If found, it will be called in scalar context
		506	and the resulting scalar will be encoded instead of the object. If no
		507	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		508	to do.
		509
		510	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		511	returns other blessed objects, those will be handled in the same
		512	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		513	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		514	methods called by the Perl core (== not by the user of the object) are
		515	usually in upper case letters and to avoid collisions with any C<to_json>
		516	function or method.
		517
		518	This setting does not yet influence C<decode> in any way, but in the
		519	future, global hooks might get installed that influence C<decode> and are
		520	enabled by this setting.
		521
		522	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		523	to do when a blessed object is found.
		524
		525	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		526
		527	When C<$coderef> is specified, it will be called from C<decode> each
		528	time it decodes a JSON object. The only argument is a reference to the
		529	newly-created hash. If the code references returns a single scalar (which
		530	need not be a reference), this value (i.e. a copy of that scalar to avoid
		531	aliasing) is inserted into the deserialised data structure. If it returns
		532	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		533	original deserialised hash will be inserted. This setting can slow down
		534	decoding considerably.
		535
		536	When C<$coderef> is omitted or undefined, any existing callback will
		537	be removed and C<decode> will not change the deserialised hash in any
		538	way.
		539
		540	Example, convert all JSON objects into the integer 5:
		541
		542	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		543	# returns [5]
		544	$js->decode ('[{}]')
		545	# throw an exception because allow_nonref is not enabled
		546	# so a lone 5 is not allowed.
		547	$js->decode ('{"a":1, "b":2}');
		548
		549	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		550
		551	Works remotely similar to C<filter_json_object>, but is only called for
		552	JSON objects having a single key named C<$key>.
		553
		554	This C<$coderef> is called before the one specified via
		555	C<filter_json_object>, if any. It gets passed the single value in the JSON
		556	object. If it returns a single value, it will be inserted into the data
		557	structure. If it returns nothing (not even C<undef> but the empty list),
		558	the callback from C<filter_json_object> will be called next, as if no
		559	single-key callback were specified.
		560
		561	If C<$coderef> is omitted or undefined, the corresponding callback will be
		562	disabled. There can only ever be one callback for a given key.
		563
		564	As this callback gets called less often then the C<filter_json_object>
		565	one, decoding speed will not usually suffer as much. Therefore, single-key
		566	objects make excellent targets to serialise Perl objects into, especially
		567	as single-key JSON objects are as close to the type-tagged value concept
		568	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		569	support this in any way, so you need to make sure your data never looks
		570	like a serialised Perl hash.
		571
		572	Typical names for the single object key are C<__class_whatever__>, or
		573	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		574	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		575	with real hashes.
		576
		577	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		578	into the corresponding C<< $WIDGET{<id>} >> object:
		579
		580	# return whatever is in $WIDGET{5}:
		581	JSON::XS
		582	->new
		583	->filter_json_single_key_object (__widget__ => sub {
		584	$WIDGET{ $_[0] }
		585	})
		586	->decode ('{"__widget__": 5')
		587
		588	# this can be used with a TO_JSON method in some "widget" class
		589	# for serialisation to json:
		590	sub WidgetBase::TO_JSON {
		591	my ($self) = @_;
		592
		593	unless ($self->{id}) {
		594	$self->{id} = ..get..some..id..;
		595	$WIDGET{$self->{id}} = $self;
		596	}
		597
		598	{ __widget__ => $self->{id} }
		599	}
		600
258	=item $json = $json->shrink ([$enable])	601	=item $json = $json->shrink ([$enable])
259		602
		603	=item $enabled = $json->get_shrink
		604
260	Perl usually over-allocates memory a bit when allocating space for	605	Perl usually over-allocates memory a bit when allocating space for
261	strings. This flag optionally resizes strings generated by either	606	strings. This flag optionally resizes strings generated by either
262	C<encode> or C<decode> to their minimum size possible. This can save	607	C<encode> or C<decode> to their minimum size possible. This can save
263	memory when your JSON strings are either very very long or you have many	608	memory when your JSON texts are either very very long or you have many
264	short strings. It will also try to downgrade any strings to octet-form	609	short strings. It will also try to downgrade any strings to octet-form
265	if possible: perl stores strings internally either in an encoding called	610	if possible: perl stores strings internally either in an encoding called
266	UTF-X or in octet-form. The latter cannot store everything but uses less	611	UTF-X or in octet-form. The latter cannot store everything but uses less
267	space in general.	612	space in general (and some buggy Perl or C code might even rely on that
		613	internal representation being used).
268		614
		615	The actual definition of what shrink does might change in future versions,
		616	but it will always try to save space at the expense of time.
		617
269	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	618	If C<$enable> is true (or missing), the string returned by C<encode> will
270	while all strings generated by C<decode> will also be shrunk-to-fit.	619	be shrunk-to-fit, while all strings generated by C<decode> will also be
		620	shrunk-to-fit.
271		621
272	If C<$enable> is false, then the normal perl allocation algorithms are used.	622	If C<$enable> is false, then the normal perl allocation algorithms are used.
273	If you work with your data, then this is likely to be faster.	623	If you work with your data, then this is likely to be faster.
274		624
275	In the future, this setting might control other things, such as converting	625	In the future, this setting might control other things, such as converting
276	strings that look like integers or floats into integers or floats	626	strings that look like integers or floats into integers or floats
277	internally (there is no difference on the Perl level), saving space.	627	internally (there is no difference on the Perl level), saving space.
278		628
		629	=item $json = $json->max_depth ([$maximum_nesting_depth])
		630
		631	=item $max_depth = $json->get_max_depth
		632
		633	Sets the maximum nesting level (default C<512>) accepted while encoding
		634	or decoding. If a higher nesting level is detected in JSON text or a Perl
		635	data structure, then the encoder and decoder will stop and croak at that
		636	point.
		637
		638	Nesting level is defined by number of hash- or arrayrefs that the encoder
		639	needs to traverse to reach a given point or the number of C<{> or C<[>
		640	characters without their matching closing parenthesis crossed to reach a
		641	given character in a string.
		642
		643	Setting the maximum depth to one disallows any nesting, so that ensures
		644	that the object is only a single hash/object or array.
		645
		646	If no argument is given, the highest possible setting will be used, which
		647	is rarely useful.
		648
		649	Note that nesting is implemented by recursion in C. The default value has
		650	been chosen to be as large as typical operating systems allow without
		651	crashing.
		652
		653	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		654
		655	=item $json = $json->max_size ([$maximum_string_size])
		656
		657	=item $max_size = $json->get_max_size
		658
		659	Set the maximum length a JSON text may have (in bytes) where decoding is
		660	being attempted. The default is C<0>, meaning no limit. When C<decode>
		661	is called on a string that is longer then this many bytes, it will not
		662	attempt to decode the string but throw an exception. This setting has no
		663	effect on C<encode> (yet).
		664
		665	If no argument is given, the limit check will be deactivated (same as when
		666	C<0> is specified).
		667
		668	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		669
279	=item $json_string = $json->encode ($perl_scalar)	670	=item $json_text = $json->encode ($perl_scalar)
280		671
281	Converts the given Perl data structure (a simple scalar or a reference	672	Converts the given Perl data structure (a simple scalar or a reference
282	to a hash or array) to its JSON representation. Simple scalars will be	673	to a hash or array) to its JSON representation. Simple scalars will be
283	converted into JSON string or number sequences, while references to arrays	674	converted into JSON string or number sequences, while references to arrays
284	become JSON arrays and references to hashes become JSON objects. Undefined	675	become JSON arrays and references to hashes become JSON objects. Undefined
285	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>	676	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
286	nor C<false> values will be generated.	677	nor C<false> values will be generated.
287		678
288	=item $perl_scalar = $json->decode ($json_string)	679	=item $perl_scalar = $json->decode ($json_text)
289		680
290	The opposite of C<encode>: expects a JSON string and tries to parse it,	681	The opposite of C<encode>: expects a JSON text and tries to parse it,
291	returning the resulting simple scalar or reference. Croaks on error.	682	returning the resulting simple scalar or reference. Croaks on error.
292		683
293	JSON numbers and strings become simple Perl scalars. JSON arrays become	684	JSON numbers and strings become simple Perl scalars. JSON arrays become
294	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	685	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
295	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	686	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
296		687
		688	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		689
		690	This works like the C<decode> method, but instead of raising an exception
		691	when there is trailing garbage after the first JSON object, it will
		692	silently stop parsing there and return the number of characters consumed
		693	so far.
		694
		695	This is useful if your JSON texts are not delimited by an outer protocol
		696	(which is not the brightest thing to do in the first place) and you need
		697	to know where the JSON text ends.
		698
		699	JSON::XS->new->decode_prefix ("[1] the tail")
		700	=> ([], 3)
		701
297	=back	702	=back
		703
		704
		705	=head1 INCREMENTAL PARSING
		706
		707	In some cases, there is the need for incremental parsing of JSON
		708	texts. While this module always has to keep both JSON text and resulting
		709	Perl data structure in memory at one time, it does allow you to parse a
		710	JSON stream incrementally. It does so by accumulating text until it has
		711	a full JSON object, which it then can decode. This process is similar to
		712	using C<decode_prefix> to see if a full JSON object is available, but
		713	is much more efficient (and can be implemented with a minimum of method
		714	calls).
		715
		716	JSON::XS will only attempt to parse the JSON text once it is sure it
		717	has enough text to get a decisive result, using a very simple but
		718	truly incremental parser. This means that it sometimes won't stop as
		719	early as the full parser, for example, it doesn't detect mismatched
		720	parentheses. The only thing it guarantees is that it starts decoding as
		721	soon as a syntactically valid JSON text has been seen. This means you need
		722	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		723	parsing in the presence if syntax errors.
		724
		725	The following methods implement this incremental parser.
		726
		727	=over 4
		728
		729	=item [void, scalar or list context] = $json->incr_parse ([$string])
		730
		731	This is the central parsing function. It can both append new text and
		732	extract objects from the stream accumulated so far (both of these
		733	functions are optional).
		734
		735	If C<$string> is given, then this string is appended to the already
		736	existing JSON fragment stored in the C<$json> object.
		737
		738	After that, if the function is called in void context, it will simply
		739	return without doing anything further. This can be used to add more text
		740	in as many chunks as you want.
		741
		742	If the method is called in scalar context, then it will try to extract
		743	exactly I<one> JSON object. If that is successful, it will return this
		744	object, otherwise it will return C<undef>. If there is a parse error,
		745	this method will croak just as C<decode> would do (one can then use
		746	C<incr_skip> to skip the erroneous part). This is the most common way of
		747	using the method.
		748
		749	And finally, in list context, it will try to extract as many objects
		750	from the stream as it can find and return them, or the empty list
		751	otherwise. For this to work, there must be no separators between the JSON
		752	objects or arrays, instead they must be concatenated back-to-back. If
		753	an error occurs, an exception will be raised as in the scalar context
		754	case. Note that in this case, any previously-parsed JSON texts will be
		755	lost.
		756
		757	Example: Parse some JSON arrays/objects in a given string and return
		758	them.
		759
		760	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		761
		762	=item $lvalue_string = $json->incr_text
		763
		764	This method returns the currently stored JSON fragment as an lvalue, that
		765	is, you can manipulate it. This I<only> works when a preceding call to
		766	C<incr_parse> in I<scalar context> successfully returned an object. Under
		767	all other circumstances you must not call this function (I mean it.
		768	although in simple tests it might actually work, it I<will> fail under
		769	real world conditions). As a special exception, you can also call this
		770	method before having parsed anything.
		771
		772	This function is useful in two cases: a) finding the trailing text after a
		773	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		774	(such as commas).
		775
		776	=item $json->incr_skip
		777
		778	This will reset the state of the incremental parser and will remove
		779	the parsed text from the input buffer so far. This is useful after
		780	C<incr_parse> died, in which case the input buffer and incremental parser
		781	state is left unchanged, to skip the text parsed so far and to reset the
		782	parse state.
		783
		784	The difference to C<incr_reset> is that only text until the parse error
		785	occurred is removed.
		786
		787	=item $json->incr_reset
		788
		789	This completely resets the incremental parser, that is, after this call,
		790	it will be as if the parser had never parsed anything.
		791
		792	This is useful if you want to repeatedly parse JSON objects and want to
		793	ignore any trailing data, which means you have to reset the parser after
		794	each successful decode.
		795
		796	=back
		797
		798	=head2 LIMITATIONS
		799
		800	All options that affect decoding are supported, except
		801	C<allow_nonref>. The reason for this is that it cannot be made to
		802	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		803	them back to back and still decode them perfectly. This does not hold true
		804	for JSON numbers, however.
		805
		806	For example, is the string C<1> a single JSON number, or is it simply the
		807	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		808	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		809	takes the conservative route and disallows this case.
		810
		811	=head2 EXAMPLES
		812
		813	Some examples will make all this clearer. First, a simple example that
		814	works similarly to C<decode_prefix>: We want to decode the JSON object at
		815	the start of a string and identify the portion after the JSON object:
		816
		817	my $text = "[1,2,3] hello";
		818
		819	my $json = new JSON::XS;
		820
		821	my $obj = $json->incr_parse ($text)
		822	or die "expected JSON object or array at beginning of string";
		823
		824	my $tail = $json->incr_text;
		825	# $tail now contains " hello"
		826
		827	Easy, isn't it?
		828
		829	Now for a more complicated example: Imagine a hypothetical protocol where
		830	you read some requests from a TCP stream, and each request is a JSON
		831	array, without any separation between them (in fact, it is often useful to
		832	use newlines as "separators", as these get interpreted as whitespace at
		833	the start of the JSON text, which makes it possible to test said protocol
		834	with C<telnet>...).
		835
		836	Here is how you'd do it (it is trivial to write this in an event-based
		837	manner):
		838
		839	my $json = new JSON::XS;
		840
		841	# read some data from the socket
		842	while (sysread $socket, my $buf, 4096) {
		843
		844	# split and decode as many requests as possible
		845	for my $request ($json->incr_parse ($buf)) {
		846	# act on the $request
		847	}
		848	}
		849
		850	Another complicated example: Assume you have a string with JSON objects
		851	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		852	[3]>). To parse them, we have to skip the commas between the JSON texts,
		853	and here is where the lvalue-ness of C<incr_text> comes in useful:
		854
		855	my $text = "[1],[2], [3]";
		856	my $json = new JSON::XS;
		857
		858	# void context, so no parsing done
		859	$json->incr_parse ($text);
		860
		861	# now extract as many objects as possible. note the
		862	# use of scalar context so incr_text can be called.
		863	while (my $obj = $json->incr_parse) {
		864	# do something with $obj
		865
		866	# now skip the optional comma
		867	$json->incr_text =~ s/^ \s* , //x;
		868	}
		869
		870	Now lets go for a very complex example: Assume that you have a gigantic
		871	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		872	but you cannot load it into memory fully (this has actually happened in
		873	the real world :).
		874
		875	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		876	can still help you: You implement a (very simple) array parser and let
		877	JSON decode the array elements, which are all full JSON objects on their
		878	own (this wouldn't work if the array elements could be JSON numbers, for
		879	example):
		880
		881	my $json = new JSON::XS;
		882
		883	# open the monster
		884	open my $fh, "<bigfile.json"
		885	or die "bigfile: $!";
		886
		887	# first parse the initial "["
		888	for (;;) {
		889	sysread $fh, my $buf, 65536
		890	or die "read error: $!";
		891	$json->incr_parse ($buf); # void context, so no parsing
		892
		893	# Exit the loop once we found and removed(!) the initial "[".
		894	# In essence, we are (ab-)using the $json object as a simple scalar
		895	# we append data to.
		896	last if $json->incr_text =~ s/^ \s* \[ //x;
		897	}
		898
		899	# now we have the skipped the initial "[", so continue
		900	# parsing all the elements.
		901	for (;;) {
		902	# in this loop we read data until we got a single JSON object
		903	for (;;) {
		904	if (my $obj = $json->incr_parse) {
		905	# do something with $obj
		906	last;
		907	}
		908
		909	# add more data
		910	sysread $fh, my $buf, 65536
		911	or die "read error: $!";
		912	$json->incr_parse ($buf); # void context, so no parsing
		913	}
		914
		915	# in this loop we read data until we either found and parsed the
		916	# separating "," between elements, or the final "]"
		917	for (;;) {
		918	# first skip whitespace
		919	$json->incr_text =~ s/^\s*//;
		920
		921	# if we find "]", we are done
		922	if ($json->incr_text =~ s/^\]//) {
		923	print "finished.\n";
		924	exit;
		925	}
		926
		927	# if we find ",", we can continue with the next element
		928	if ($json->incr_text =~ s/^,//) {
		929	last;
		930	}
		931
		932	# if we find anything else, we have a parse error!
		933	if (length $json->incr_text) {
		934	die "parse error near ", $json->incr_text;
		935	}
		936
		937	# else add more data
		938	sysread $fh, my $buf, 65536
		939	or die "read error: $!";
		940	$json->incr_parse ($buf); # void context, so no parsing
		941	}
		942
		943	This is a complex example, but most of the complexity comes from the fact
		944	that we are trying to be correct (bear with me if I am wrong, I never ran
		945	the above example :).
		946
		947
298		948
299	=head1 MAPPING	949	=head1 MAPPING
300		950
301	This section describes how JSON::XS maps Perl values to JSON values and	951	This section describes how JSON::XS maps Perl values to JSON values and
302	vice versa. These mappings are designed to "do the right thing" in most	952	vice versa. These mappings are designed to "do the right thing" in most
303	circumstances automatically, preserving round-tripping characteristics	953	circumstances automatically, preserving round-tripping characteristics
304	(what you put in comes out as something equivalent).	954	(what you put in comes out as something equivalent).
305		955
306	For the more enlightened: note that in the following descriptions,	956	For the more enlightened: note that in the following descriptions,
307	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	957	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
308	refers to the abstract Perl language itself.	958	refers to the abstract Perl language itself.
309		959
		960
310	=head2 JSON -> PERL	961	=head2 JSON -> PERL
311		962
312	=over 4	963	=over 4
313		964
314	=item object	965	=item object
315		966
316	A JSON object becomes a reference to a hash in Perl. No ordering of object	967	A JSON object becomes a reference to a hash in Perl. No ordering of object
317	keys is preserved.	968	keys is preserved (JSON does not preserve object key ordering itself).
318		969
319	=item array	970	=item array
320		971
321	A JSON array becomes a reference to an array in Perl.	972	A JSON array becomes a reference to an array in Perl.
322		973
…		…
326	are represented by the same codepoints in the Perl string, so no manual	977	are represented by the same codepoints in the Perl string, so no manual
327	decoding is necessary.	978	decoding is necessary.
328		979
329	=item number	980	=item number
330		981
331	A JSON number becomes either an integer or numeric (floating point)	982	A JSON number becomes either an integer, numeric (floating point) or
332	scalar in perl, depending on its range and any fractional parts. On the	983	string scalar in perl, depending on its range and any fractional parts. On
333	Perl level, there is no difference between those as Perl handles all the	984	the Perl level, there is no difference between those as Perl handles all
334	conversion details, but an integer may take slightly less memory and might	985	the conversion details, but an integer may take slightly less memory and
335	represent more values exactly than (floating point) numbers.	986	might represent more values exactly than floating point numbers.
		987
		988	If the number consists of digits only, JSON::XS will try to represent
		989	it as an integer value. If that fails, it will try to represent it as
		990	a numeric (floating point) value if that is possible without loss of
		991	precision. Otherwise it will preserve the number as a string value (in
		992	which case you lose roundtripping ability, as the JSON number will be
		993	re-encoded to a JSON string).
		994
		995	Numbers containing a fractional or exponential part will always be
		996	represented as numeric (floating point) values, possibly at a loss of
		997	precision (in which case you might lose perfect roundtripping ability, but
		998	the JSON number will still be re-encoded as a JSON number).
		999
		1000	Note that precision is not accuracy - binary floating point values cannot
		1001	represent most decimal fractions exactly, and when converting from and to
		1002	floating point, JSON::XS only guarantees precision up to but not including
		1003	the least significant bit.
336		1004
337	=item true, false	1005	=item true, false
338		1006
339	These JSON atoms become C<0>, C<1>, respectively. Information is lost in	1007	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
340	this process. Future versions might represent those values differently,	1008	respectively. They are overloaded to act almost exactly like the numbers
341	but they will be guarenteed to act like these integers would normally in	1009	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
342	Perl.	1010	the C<JSON::XS::is_bool> function.
343		1011
344	=item null	1012	=item null
345		1013
346	A JSON null atom becomes C<undef> in Perl.	1014	A JSON null atom becomes C<undef> in Perl.
347		1015
348	=back	1016	=back
		1017
349		1018
350	=head2 PERL -> JSON	1019	=head2 PERL -> JSON
351		1020
352	The mapping from Perl to JSON is slightly more difficult, as Perl is a	1021	The mapping from Perl to JSON is slightly more difficult, as Perl is a
353	truly typeless language, so we can only guess which JSON type is meant by	1022	truly typeless language, so we can only guess which JSON type is meant by
…		…
356	=over 4	1025	=over 4
357		1026
358	=item hash references	1027	=item hash references
359		1028
360	Perl hash references become JSON objects. As there is no inherent ordering	1029	Perl hash references become JSON objects. As there is no inherent ordering
361	in hash keys, they will usually be encoded in a pseudo-random order that	1030	in hash keys (or JSON objects), they will usually be encoded in a
362	can change between runs of the same program but stays generally the same	1031	pseudo-random order that can change between runs of the same program but
363	within the single run of a program. JSON::XS can optionally sort the hash	1032	stays generally the same within a single run of a program. JSON::XS can
364	keys (determined by the I<canonical> flag), so the same datastructure	1033	optionally sort the hash keys (determined by the I<canonical> flag), so
365	will serialise to the same JSON text (given same settings and version of	1034	the same datastructure will serialise to the same JSON text (given same
366	JSON::XS), but this incurs a runtime overhead.	1035	settings and version of JSON::XS), but this incurs a runtime overhead
		1036	and is only rarely useful, e.g. when you want to compare some JSON text
		1037	against another for equality.
367		1038
368	=item array references	1039	=item array references
369		1040
370	Perl array references become JSON arrays.	1041	Perl array references become JSON arrays.
371		1042
		1043	=item other references
		1044
		1045	Other unblessed references are generally not allowed and will cause an
		1046	exception to be thrown, except for references to the integers C<0> and
		1047	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		1048	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		1049
		1050	encode_json [\0, JSON::XS::true] # yields [false,true]
		1051
		1052	=item JSON::XS::true, JSON::XS::false
		1053
		1054	These special values become JSON true and JSON false values,
		1055	respectively. You can also use C<\1> and C<\0> directly if you want.
		1056
372	=item blessed objects	1057	=item blessed objects
373		1058
374	Blessed objects are not allowed. JSON::XS currently tries to encode their	1059	Blessed objects are not directly representable in JSON. See the
375	underlying representation (hash- or arrayref), but this behaviour might	1060	C<allow_blessed> and C<convert_blessed> methods on various options on
376	change in future versions.	1061	how to deal with this: basically, you can choose between throwing an
		1062	exception, encoding the reference as if it weren't blessed, or provide
		1063	your own serialiser method.
377		1064
378	=item simple scalars	1065	=item simple scalars
379		1066
380	Simple Perl scalars (any scalar that is not a reference) are the most	1067	Simple Perl scalars (any scalar that is not a reference) are the most
381	difficult objects to encode: JSON::XS will encode undefined scalars as	1068	difficult objects to encode: JSON::XS will encode undefined scalars as
382	JSON null value, scalars that have last been used in a string context	1069	JSON C<null> values, scalars that have last been used in a string context
383	before encoding as JSON strings and anything else as number value:	1070	before encoding as JSON strings, and anything else as number value:
384		1071
385	# dump as number	1072	# dump as number
386	to_json [2] # yields [2]	1073	encode_json [2] # yields [2]
387	to_json [-3.0e17] # yields [-3e+17]	1074	encode_json [-3.0e17] # yields [-3e+17]
388	my $value = 5; to_json [$value] # yields [5]	1075	my $value = 5; encode_json [$value] # yields [5]
389		1076
390	# used as string, so dump as string	1077	# used as string, so dump as string
391	print $value;	1078	print $value;
392	to_json [$value] # yields ["5"]	1079	encode_json [$value] # yields ["5"]
393		1080
394	# undef becomes null	1081	# undef becomes null
395	to_json [undef] # yields [null]	1082	encode_json [undef] # yields [null]
396		1083
397	You can force the type to be a string by stringifying it:	1084	You can force the type to be a JSON string by stringifying it:
398		1085
399	my $x = 3.1; # some variable containing a number	1086	my $x = 3.1; # some variable containing a number
400	"$x"; # stringified	1087	"$x"; # stringified
401	$x .= ""; # another, more awkward way to stringify	1088	$x .= ""; # another, more awkward way to stringify
402	print $x; # perl does it for you, too, quite often	1089	print $x; # perl does it for you, too, quite often
403		1090
404	You can force the type to be a number by numifying it:	1091	You can force the type to be a JSON number by numifying it:
405		1092
406	my $x = "3"; # some variable containing a string	1093	my $x = "3"; # some variable containing a string
407	$x += 0; # numify it, ensuring it will be dumped as a number	1094	$x += 0; # numify it, ensuring it will be dumped as a number
408	$x *= 1; # same thing, the choise is yours.	1095	$x *= 1; # same thing, the choice is yours.
409		1096
410	You can not currently output JSON booleans or force the type in other,	1097	You can not currently force the type in other, less obscure, ways. Tell me
411	less obscure, ways. Tell me if you need this capability.	1098	if you need this capability (but don't forget to explain why it's needed
		1099	:).
412		1100
413	=item circular data structures	1101	Note that numerical precision has the same meaning as under Perl (so
414		1102	binary to decimal conversion follows the same rules as in Perl, which
415	Those will be encoded until memory or stackspace runs out.	1103	can differ to other languages). Also, your perl interpreter might expose
		1104	extensions to the floating point numbers of your platform, such as
		1105	infinities or NaN's - these cannot be represented in JSON, and it is an
		1106	error to pass those in.
416		1107
417	=back	1108	=back
418		1109
419	=head1 COMPARISON
420		1110
421	As already mentioned, this module was created because none of the existing	1111	=head1 ENCODING/CODESET FLAG NOTES
422	JSON modules could be made to work correctly. First I will describe the	1112
423	problems (or pleasures) I encountered with various existing JSON modules,	1113	The interested reader might have seen a number of flags that signify
424	followed by some benchmark values. JSON::XS was designed not to suffer	1114	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
425	from any of these problems or limitations.	1115	some confusion on what these do, so here is a short comparison:
		1116
		1117	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1118	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1119	control whether C<encode> escapes character values outside their respective
		1120	codeset range. Neither of these flags conflict with each other, although
		1121	some combinations make less sense than others.
		1122
		1123	Care has been taken to make all flags symmetrical with respect to
		1124	C<encode> and C<decode>, that is, texts encoded with any combination of
		1125	these flag values will be correctly decoded when the same flags are used
		1126	- in general, if you use different flag settings while encoding vs. when
		1127	decoding you likely have a bug somewhere.
		1128
		1129	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1130	simply an abstract set of character-codepoint pairs, while an encoding
		1131	takes those codepoint numbers and I<encodes> them, in our case into
		1132	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1133	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1134	the same time, which can be confusing.
426		1135
427	=over 4	1136	=over 4
428		1137
429	=item JSON 1.07	1138	=item C<utf8> flag disabled
430		1139
431	Slow (but very portable, as it is written in pure Perl).	1140	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1141	and expect Unicode strings, that is, characters with high ordinal Unicode
		1142	values (> 255) will be encoded as such characters, and likewise such
		1143	characters are decoded as-is, no changes to them will be done, except
		1144	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1145	respectively (to Perl, these are the same thing in strings unless you do
		1146	funny/weird/dumb stuff).
432		1147
433	Undocumented/buggy Unicode handling (how JSON handles unicode values is	1148	This is useful when you want to do the encoding yourself (e.g. when you
434	undocumented. One can get far by feeding it unicode strings and doing	1149	want to have UTF-16 encoded JSON texts) or when some other layer does
435	en-/decoding oneself, but unicode escapes are not working properly).	1150	the encoding for you (for example, when printing to a terminal using a
		1151	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1152	to UTF-8 encode your data first and have Perl encode it another time).
436		1153
437	No roundtripping (strings get clobbered if they look like numbers, e.g.	1154	=item C<utf8> flag enabled
438	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
439	decode into the number 2.
440		1155
441	=item JSON::PC 0.01	1156	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1157	characters using the corresponding UTF-8 multi-byte sequence, and will
		1158	expect your input strings to be encoded as UTF-8, that is, no "character"
		1159	of the input string must have any value > 255, as UTF-8 does not allow
		1160	that.
442		1161
443	Very fast.	1162	The C<utf8> flag therefore switches between two modes: disabled means you
		1163	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1164	octet/binary string in Perl.
444		1165
445	Undocumented/buggy Unicode handling.	1166	=item C<latin1> or C<ascii> flags enabled
446		1167
447	No roundtripping.	1168	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1169	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1170	characters as specified by the C<utf8> flag.
448		1171
449	Has problems handling many Perl values (e.g. regex results and other magic	1172	If C<utf8> is disabled, then the result is also correctly encoded in those
450	values will make it croak).	1173	character sets (as both are proper subsets of Unicode, meaning that a
		1174	Unicode string with all character values < 256 is the same thing as a
		1175	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1176	the same thing as an ASCII string in Perl).
451		1177
452	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1178	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
453	which is not a valid JSON string.	1179	regardless of these flags, just some more characters will be escaped using
		1180	C<\uXXXX> then before.
454		1181
455	Unmaintained (maintainer unresponsive for many months, bugs are not	1182	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
456	getting fixed).	1183	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1184	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1185	a subset of Unicode), while ASCII is.
457		1186
458	=item JSON::Syck 0.21	1187	Surprisingly, C<decode> will ignore these flags and so treat all input
		1188	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1189	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1190	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
459		1191
460	Very buggy (often crashes).	1192	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1193	they only govern when the JSON output engine escapes a character or not.
461		1194
462	Very inflexible (no human-readable format supported, format pretty much	1195	The main use for C<latin1> is to relatively efficiently store binary data
463	undocumented. I need at least a format for easy reading by humans and a	1196	as JSON, at the expense of breaking compatibility with most JSON decoders.
464	single-line compact format for use in a protocol, and preferably a way to
465	generate ASCII-only JSON strings).
466		1197
467	Completely broken (and confusingly documented) Unicode handling (unicode	1198	The main use for C<ascii> is to force the output to not contain characters
468	escapes are not working properly, you need to set ImplicitUnicode to	1199	with values > 127, which means you can interpret the resulting string
469	I<different> values on en- and decoding to get symmetric behaviour).	1200	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
470		1201	8-bit-encoding, and still get the same data structure back. This is useful
471	No roundtripping (simple cases work, but this depends on wether the scalar	1202	when your channel for JSON transfer is not 8-bit clean or the encoding
472	value was used in a numeric context or not).	1203	might be mangled in between (e.g. in mail), and works because ASCII is a
473		1204	proper subset of most 8-bit and multibyte encodings in use in the world.
474	Dumping hashes may skip hash values depending on iterator state.
475
476	Unmaintained (maintainer unresponsive for many months, bugs are not
477	getting fixed).
478
479	Does not check input for validity (i.e. will accept non-JSON input and
480	return "something" instead of raising an exception. This is a security
481	issue: imagine two banks transfering money between each other using
482	JSON. One bank might parse a given non-JSON request and deduct money,
483	while the other might reject the transaction with a syntax error. While a
484	good protocol will at least recover, that is extra unnecessary work and
485	the transaction will still not succeed).
486
487	=item JSON::DWIW 0.04
488
489	Very fast. Very natural. Very nice.
490
491	Undocumented unicode handling (but the best of the pack. Unicode escapes
492	still don't get parsed properly).
493
494	Very inflexible.
495
496	No roundtripping.
497
498	Does not generate valid JSON (key strings are often unquoted, empty keys
499	result in nothing being output)
500
501	Does not check input for validity.
502		1205
503	=back	1206	=back
		1207
		1208
		1209	=head2 JSON and ECMAscript
		1210
		1211	JSON syntax is based on how literals are represented in javascript (the
		1212	not-standardised predecessor of ECMAscript) which is presumably why it is
		1213	called "JavaScript Object Notation".
		1214
		1215	However, JSON is not a subset (and also not a superset of course) of
		1216	ECMAscript (the standard) or javascript (whatever browsers actually
		1217	implement).
		1218
		1219	If you want to use javascript's C<eval> function to "parse" JSON, you
		1220	might run into parse errors for valid JSON texts, or the resulting data
		1221	structure might not be queryable:
		1222
		1223	One of the problems is that U+2028 and U+2029 are valid characters inside
		1224	JSON strings, but are not allowed in ECMAscript string literals, so the
		1225	following Perl fragment will not output something that can be guaranteed
		1226	to be parsable by javascript's C<eval>:
		1227
		1228	use JSON::XS;
		1229
		1230	print encode_json [chr 0x2028];
		1231
		1232	The right fix for this is to use a proper JSON parser in your javascript
		1233	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1234	F<json2.js> parser).
		1235
		1236	If this is not an option, you can, as a stop-gap measure, simply encode to
		1237	ASCII-only JSON:
		1238
		1239	use JSON::XS;
		1240
		1241	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1242
		1243	Note that this will enlarge the resulting JSON text quite a bit if you
		1244	have many non-ASCII characters. You might be tempted to run some regexes
		1245	to only escape U+2028 and U+2029, e.g.:
		1246
		1247	# DO NOT USE THIS!
		1248	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1249	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1250	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1251	print $json;
		1252
		1253	Note that I<this is a bad idea>: the above only works for U+2028 and
		1254	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1255	javascript implementations, however, have issues with other characters as
		1256	well - using C<eval> naively simply I<will> cause problems.
		1257
		1258	Another problem is that some javascript implementations reserve
		1259	some property names for their own purposes (which probably makes
		1260	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1261	C<__proto__> property name for its own purposes.
		1262
		1263	If that is a problem, you could parse try to filter the resulting JSON
		1264	output for these property strings, e.g.:
		1265
		1266	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1267
		1268	This works because C<__proto__> is not valid outside of strings, so every
		1269	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1270
		1271	If you know of other incompatibilities, please let me know.
		1272
		1273
		1274	=head2 JSON and YAML
		1275
		1276	You often hear that JSON is a subset of YAML. This is, however, a mass
		1277	hysteria(*) and very far from the truth (as of the time of this writing),
		1278	so let me state it clearly: I<in general, there is no way to configure
		1279	JSON::XS to output a data structure as valid YAML> that works in all
		1280	cases.
		1281
		1282	If you really must use JSON::XS to generate YAML, you should use this
		1283	algorithm (subject to change in future versions):
		1284
		1285	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1286	my $yaml = $to_yaml->encode ($ref) . "\n";
		1287
		1288	This will I<usually> generate JSON texts that also parse as valid
		1289	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1290	lengths that JSON doesn't have and also has different and incompatible
		1291	unicode character escape syntax, so you should make sure that your hash
		1292	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1293	and that you do not have characters with codepoint values outside the
		1294	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1295	sequences in strings (which JSON::XS does not I<currently> generate, but
		1296	other JSON generators might).
		1297
		1298	There might be other incompatibilities that I am not aware of (or the YAML
		1299	specification has been changed yet again - it does so quite often). In
		1300	general you should not try to generate YAML with a JSON generator or vice
		1301	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1302	high that you will run into severe interoperability problems when you
		1303	least expect it.
		1304
		1305	=over 4
		1306
		1307	=item (*)
		1308
		1309	I have been pressured multiple times by Brian Ingerson (one of the
		1310	authors of the YAML specification) to remove this paragraph, despite him
		1311	acknowledging that the actual incompatibilities exist. As I was personally
		1312	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1313	educate people about these issues, so others do not run into the same
		1314	problem again and again. After this, Brian called me a (quote)I<complete
		1315	and worthless idiot>(unquote).
		1316
		1317	In my opinion, instead of pressuring and insulting people who actually
		1318	clarify issues with YAML and the wrong statements of some of its
		1319	proponents, I would kindly suggest reading the JSON spec (which is not
		1320	that difficult or long) and finally make YAML compatible to it, and
		1321	educating users about the changes, instead of spreading lies about the
		1322	real compatibility for many I<years> and trying to silence people who
		1323	point out that it isn't true.
		1324
		1325	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1326	though the incompatibilities have been documented (and are known to Brian)
		1327	for many years and the spec makes explicit claims that YAML is a superset
		1328	of JSON. It would be so easy to fix, but apparently, bullying people and
		1329	corrupting userdata is so much easier.
		1330
		1331	=back
		1332
504		1333
505	=head2 SPEED	1334	=head2 SPEED
506		1335
507	It seems that JSON::XS is surprisingly fast, as shown in the following	1336	It seems that JSON::XS is surprisingly fast, as shown in the following
508	tables. They have been generated with the help of the C<eg/bench> program	1337	tables. They have been generated with the help of the C<eg/bench> program
509	in the JSON::XS distribution, to make it easy to compare on your own	1338	in the JSON::XS distribution, to make it easy to compare on your own
510	system.	1339	system.
511		1340
512	First comes a comparison between various modules using a very short JSON	1341	First comes a comparison between various modules using
513	string (83 bytes), showing the number of encodes/decodes per second	1342	a very short single-line JSON string (also available at
		1343	L<http://dist.schmorp.de/misc/json/short.json>).
		1344
		1345	{"method": "handleMessage", "params": ["user1",
		1346	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1347	1, 0]}
		1348
		1349	It shows the number of encodes/decodes per second (JSON::XS uses
514	(JSON::XS is the functional interface, while JSON::XS/2 is the OO	1350	the functional interface, while JSON::XS/2 uses the OO interface
515	interface with pretty-printing and hashkey sorting enabled). Higher is	1351	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
516	better:	1352	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1353	uses the from_json method). Higher is better:
517		1354
518	module | encode | decode |	1355	module | encode | decode |
519	-----------|------------|------------|	1356	--------------|------------|------------|
520	JSON | 14006 | 6820 |	1357	JSON::DWIW/DS | 86302.551 | 102300.098 |
521	JSON::DWIW | 200937 | 120386 |	1358	JSON::DWIW/FJ | 86302.551 | 75983.768 |
522	JSON::PC | 85065 | 129366 |	1359	JSON::PP | 15827.562 | 6638.658 |
523	JSON::Syck | 59898 | 44232 |	1360	JSON::Syck | 63358.066 | 47662.545 |
524	JSON::XS | 1171478 | 342435 |	1361	JSON::XS | 511500.488 | 511500.488 |
525	JSON::XS/2 | 730760 | 328714 |	1362	JSON::XS/2 | 291271.111 | 388361.481 |
		1363	JSON::XS/3 | 361577.931 | 361577.931 |
		1364	Storable | 66788.280 | 265462.278 |
526	-----------+------------+------------+	1365	--------------+------------+------------+
527		1366
528	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1367	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
529	times faster than JSON, even with pretty-printing and key sorting.	1368	about five times faster on decoding, and over thirty to seventy times
		1369	faster than JSON's pure perl implementation. It also compares favourably
		1370	to Storable for small amounts of data.
530		1371
531	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1372	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
532	search API (http://nanoref.com/yahooapis/mgPdGg):	1373	search API (L<http://dist.schmorp.de/misc/json/long.json>).
533		1374
534	module | encode | decode |	1375	module | encode | decode |
535	-----------|------------|------------|	1376	--------------|------------|------------|
536	JSON | 673 | 38 |	1377	JSON::DWIW/DS | 1647.927 | 2673.916 |
537	JSON::DWIW | 5271 | 770 |	1378	JSON::DWIW/FJ | 1630.249 | 2596.128 |
538	JSON::PC | 9901 | 2491 |	1379	JSON::PP | 400.640 | 62.311 |
539	JSON::Syck | 2360 | 786 |	1380	JSON::Syck | 1481.040 | 1524.869 |
540	JSON::XS | 37398 | 3202 |	1381	JSON::XS | 20661.596 | 9541.183 |
541	JSON::XS/2 | 13765 | 3153 |	1382	JSON::XS/2 | 10683.403 | 9416.938 |
		1383	JSON::XS/3 | 20661.596 | 9400.054 |
		1384	Storable | 19765.806 | 10000.725 |
542	-----------+------------+------------+	1385	--------------+------------+------------+
543		1386
544	Again, JSON::XS leads by far in the encoding case, while still beating	1387	Again, JSON::XS leads by far (except for Storable which non-surprisingly
545	every other module in the decoding case.	1388	decodes a bit faster).
546		1389
547	On large strings containing lots of unicode characters, some modules	1390	On large strings containing lots of high Unicode characters, some modules
548	(such as JSON::PC) decode faster than JSON::XS, but the result will be	1391	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
549	broken due to missing unicode handling. Others refuse to decode or encode	1392	will be broken due to missing (or wrong) Unicode handling. Others refuse
550	properly, so it was impossible to prepare a fair comparison table for that	1393	to decode or encode properly, so it was impossible to prepare a fair
551	case.	1394	comparison table for that case.
552		1395
553	=head1 RESOURCE LIMITS
554		1396
555	JSON::XS does not impose any limits on the size of JSON texts or Perl	1397	=head1 SECURITY CONSIDERATIONS
556	values they represent - if your machine can handle it, JSON::XS will	1398
557	encode or decode it. Future versions might optionally impose structure	1399	When you are using JSON in a protocol, talking to untrusted potentially
558	depth and memory use resource limits.	1400	hostile creatures requires relatively few measures.
		1401
		1402	First of all, your JSON decoder should be secure, that is, should not have
		1403	any buffer overflows. Obviously, this module should ensure that and I am
		1404	trying hard on making that true, but you never know.
		1405
		1406	Second, you need to avoid resource-starving attacks. That means you should
		1407	limit the size of JSON texts you accept, or make sure then when your
		1408	resources run out, that's just fine (e.g. by using a separate process that
		1409	can crash safely). The size of a JSON text in octets or characters is
		1410	usually a good indication of the size of the resources required to decode
		1411	it into a Perl structure. While JSON::XS can check the size of the JSON
		1412	text, it might be too late when you already have it in memory, so you
		1413	might want to check the size before you accept the string.
		1414
		1415	Third, JSON::XS recurses using the C stack when decoding objects and
		1416	arrays. The C stack is a limited resource: for instance, on my amd64
		1417	machine with 8MB of stack size I can decode around 180k nested arrays but
		1418	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1419	to free the temporary). If that is exceeded, the program crashes. To be
		1420	conservative, the default nesting limit is set to 512. If your process
		1421	has a smaller stack, you should adjust this setting accordingly with the
		1422	C<max_depth> method.
		1423
		1424	Something else could bomb you, too, that I forgot to think of. In that
		1425	case, you get to keep the pieces. I am always open for hints, though...
		1426
		1427	Also keep in mind that JSON::XS might leak contents of your Perl data
		1428	structures in its error messages, so when you serialise sensitive
		1429	information you might want to make sure that exceptions thrown by JSON::XS
		1430	will not end up in front of untrusted eyes.
		1431
		1432	If you are using JSON::XS to return packets to consumption
		1433	by JavaScript scripts in a browser you should have a look at
		1434	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
		1435	see whether you are vulnerable to some common attack vectors (which really
		1436	are browser design bugs, but it is still you who will have to deal with
		1437	it, as major browser developers care only for features, not about getting
		1438	security right).
		1439
		1440
		1441	=head1 THREADS
		1442
		1443	This module is I<not> guaranteed to be thread safe and there are no
		1444	plans to change this until Perl gets thread support (as opposed to the
		1445	horribly slow so-called "threads" which are simply slow and bloated
		1446	process simulations - use fork, it's I<much> faster, cheaper, better).
		1447
		1448	(It might actually work, but you have been warned).
		1449
		1450
		1451	=head1 THE PERILS OF SETLOCALE
		1452
		1453	Sometimes people avoid the Perl locale support and directly call the
		1454	system's setlocale function with C<LC_ALL>.
		1455
		1456	This breaks both perl and modules such as JSON::XS, as stringification of
		1457	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1458	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1459	perl to stringify numbers).
		1460
		1461	The solution is simple: don't call C<setlocale>, or use it for only those
		1462	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1463
		1464	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1465	actually needs it (avoiding stringification of numbers), and restore it
		1466	afterwards.
		1467
559		1468
560	=head1 BUGS	1469	=head1 BUGS
561		1470
562	While the goal of this module is to be correct, that unfortunately does	1471	While the goal of this module is to be correct, that unfortunately does
563	not mean its bug-free, only that I think its design is bug-free. It is	1472	not mean it's bug-free, only that I think its design is bug-free. If you
564	still very young and not well-tested. If you keep reporting bugs they will	1473	keep reporting bugs they will be fixed swiftly, though.
565	be fixed swiftly, though.	1474
		1475	Please refrain from using rt.cpan.org or any other bug reporting
		1476	service. I put the contact address into my modules for a reason.
566		1477
567	=cut	1478	=cut
568		1479
		1480	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1481	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1482
		1483	sub true() { $true }
		1484	sub false() { $false }
		1485
		1486	sub is_bool($) {
		1487	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1488	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1489	}
		1490
		1491	XSLoader::load "JSON::XS", $VERSION;
		1492
		1493	package JSON::XS::Boolean;
		1494
		1495	use overload
		1496	"0+" => sub { ${$_[0]} },
		1497	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1498	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1499	fallback => 1;
		1500
569	1;	1501	1;
		1502
		1503	=head1 SEE ALSO
		1504
		1505	The F<json_xs> command line utility for quick experiments.
570		1506
571	=head1 AUTHOR	1507	=head1 AUTHOR
572		1508
573	Marc Lehmann <schmorp@schmorp.de>	1509	Marc Lehmann <schmorp@schmorp.de>
574	http://home.schmorp.de/	1510	http://home.schmorp.de/

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