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Revision 1.15 by root, Sat Mar 24 01:15:22 2007 UTC vs.
Revision 1.104 by root, Thu May 8 15:33:06 2008 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
4		4
		5	=encoding utf-8
		6
		7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
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	overriden) with no overhead due to emulation (by inheritign 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
…		…
36		58
37	=head2 FEATURES	59	=head2 FEATURES
38		60
39	=over 4	61	=over 4
40		62
41	=item * correct handling of unicode issues	63	=item * correct Unicode handling
42		64
43	This module knows how to handle Unicode, and even documents how and when	65	This module knows how to handle Unicode, documents how and when it does
44	it does so.	66	so, and even documents what "correct" means.
45		67
46	=item * round-trip integrity	68	=item * round-trip integrity
47		69
48	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only datatypes supported
49	by JSON, the deserialised data structure is identical on the Perl level.	71	by JSON, the deserialised data structure is identical on the Perl level.
50	(e.g. the string "2.0" doesn't suddenly become "2").	72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
		73	like a number). There minor I<are> exceptions to this, read the MAPPING
		74	section below to learn about those.
51		75
52	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
53		77
54	There is no guessing, no generating of illegal JSON strings by default,	78	There is no guessing, no generating of illegal JSON texts by default,
55	and only JSON is accepted as input by default (the latter is a security	79	and only JSON is accepted as input by default (the latter is a security
56	feature).	80	feature).
57		81
58	=item * fast	82	=item * fast
59		83
60	Compared to other JSON modules, this module compares favourably in terms	84	Compared to other JSON modules and other serialisers such as Storable,
61	of speed, too.	85	this module usually compares favourably in terms of speed, too.
62		86
63	=item * simple to use	87	=item * simple to use
64		88
65	This module has both a simple functional interface as well as an OO	89	This module has both a simple functional interface as well as an objetc
66	interface.	90	oriented interface interface.
67		91
68	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
69		93
70	You can choose between the most compact guarenteed single-line format	94	You can choose between the most compact guaranteed-single-line format
71	possible (nice for simple line-based protocols), a pure-ascii format (for	95	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	96	(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	97	Unicode range), or a pretty-printed format (for when you want to read that
74	whatever way you like.	98	stuff). Or you can combine those features in whatever way you like.
75		99
76	=back	100	=back
77		101
78	=cut	102	=cut
79		103
80	package JSON::XS;	104	package JSON::XS;
81		105
82	BEGIN {	106	use strict;
		107
83	$VERSION = '0.31';	108	our $VERSION = '2.2';
84	@ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
85		110
86	@EXPORT = qw(to_json from_json);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
87	require Exporter;
88		112
		113	sub to_json($) {
89	require XSLoader;	114	require Carp;
90	XSLoader::load JSON::XS::, $VERSION;	115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
91	}	116	}
92		117
		118	sub from_json($) {
		119	require Carp;
		120	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
		121	}
		122
		123	use Exporter;
		124	use XSLoader;
		125
93	=head1 FUNCTIONAL INTERFACE	126	=head1 FUNCTIONAL INTERFACE
94		127
95	The following convinience methods are provided by this module. They are	128	The following convenience methods are provided by this module. They are
96	exported by default:	129	exported by default:
97		130
98	=over 4	131	=over 4
99		132
100	=item $json_string = to_json $perl_scalar	133	=item $json_text = encode_json $perl_scalar
101		134
102	Converts the given Perl data structure (a simple scalar or a reference to	135	Converts the given Perl data structure to a UTF-8 encoded, binary string
103	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	136	(that is, the string contains octets only). Croaks on error.
104	octets only). Croaks on error.
105		137
106	This function call is functionally identical to C<< JSON::XS->new->utf8->encode ($perl_scalar) >>.	138	This function call is functionally identical to:
107		139
		140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		141
		142	except being faster.
		143
108	=item $perl_scalar = from_json $json_string	144	=item $perl_scalar = decode_json $json_text
109		145
110	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
111	parse that as an UTF-8 encoded JSON string, returning the resulting simple	147	to parse that as an UTF-8 encoded JSON text, returning the resulting
112	scalar or reference. Croaks on error.	148	reference. Croaks on error.
113		149
114	This function call is functionally identical to C<< JSON::XS->new->utf8->decode ($json_string) >>.	150	This function call is functionally identical to:
		151
		152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		153
		154	except being faster.
		155
		156	=item $is_boolean = JSON::XS::is_bool $scalar
		157
		158	Returns true if the passed scalar represents either JSON::XS::true or
		159	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		160	and are used to represent JSON C<true> and C<false> values in Perl.
		161
		162	See MAPPING, below, for more information on how JSON values are mapped to
		163	Perl.
115		164
116	=back	165	=back
		166
		167
		168	=head1 A FEW NOTES ON UNICODE AND PERL
		169
		170	Since this often leads to confusion, here are a few very clear words on
		171	how Unicode works in Perl, modulo bugs.
		172
		173	=over 4
		174
		175	=item 1. Perl strings can store characters with ordinal values > 255.
		176
		177	This enables you to store Unicode characters as single characters in a
		178	Perl string - very natural.
		179
		180	=item 2. Perl does I<not> associate an encoding with your strings.
		181
		182	... until you force it to, e.g. when matching it against a regex, or
		183	printing the scalar to a file, in which case Perl either interprets your
		184	string as locale-encoded text, octets/binary, or as Unicode, depending
		185	on various settings. In no case is an encoding stored together with your
		186	data, it is I<use> that decides encoding, not any magical meta data.
		187
		188	=item 3. The internal utf-8 flag has no meaning with regards to the
		189	encoding of your string.
		190
		191	Just ignore that flag unless you debug a Perl bug, a module written in
		192	XS or want to dive into the internals of perl. Otherwise it will only
		193	confuse you, as, despite the name, it says nothing about how your string
		194	is encoded. You can have Unicode strings with that flag set, with that
		195	flag clear, and you can have binary data with that flag set and that flag
		196	clear. Other possibilities exist, too.
		197
		198	If you didn't know about that flag, just the better, pretend it doesn't
		199	exist.
		200
		201	=item 4. A "Unicode String" is simply a string where each character can be
		202	validly interpreted as a Unicode codepoint.
		203
		204	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		205	Unicode string encoded in UTF-8, giving you a binary string.
		206
		207	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		208
		209	It's a fact. Learn to live with it.
		210
		211	=back
		212
		213	I hope this helps :)
		214
117		215
118	=head1 OBJECT-ORIENTED INTERFACE	216	=head1 OBJECT-ORIENTED INTERFACE
119		217
120	The object oriented interface lets you configure your own encoding or	218	The object oriented interface lets you configure your own encoding or
121	decoding style, within the limits of supported formats.	219	decoding style, within the limits of supported formats.
…		…
128	strings. All boolean flags described below are by default I<disabled>.	226	strings. All boolean flags described below are by default I<disabled>.
129		227
130	The mutators for flags all return the JSON object again and thus calls can	228	The mutators for flags all return the JSON object again and thus calls can
131	be chained:	229	be chained:
132		230
133	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	231	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
134	=> {"a": [1, 2]}	232	=> {"a": [1, 2]}
135		233
136	=item $json = $json->ascii ([$enable])	234	=item $json = $json->ascii ([$enable])
137		235
		236	=item $enabled = $json->get_ascii
		237
138	If C<$enable> is true (or missing), then the C<encode> method will	238	If C<$enable> is true (or missing), then the C<encode> method will not
139	not generate characters outside the code range C<0..127>. Any unicode	239	generate characters outside the code range C<0..127> (which is ASCII). Any
140	characters outside that range will be escaped using either a single	240	Unicode characters outside that range will be escaped using either a
141	\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per	241	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
142	RFC4627.	242	as per RFC4627. The resulting encoded JSON text can be treated as a native
		243	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		244	or any other superset of ASCII.
143		245
144	If C<$enable> is false, then the C<encode> method will not escape Unicode	246	If C<$enable> is false, then the C<encode> method will not escape Unicode
145	characters unless necessary.	247	characters unless required by the JSON syntax or other flags. This results
		248	in a faster and more compact format.
146		249
		250	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		251	document.
		252
		253	The main use for this flag is to produce JSON texts that can be
		254	transmitted over a 7-bit channel, as the encoded JSON texts will not
		255	contain any 8 bit characters.
		256
147	JSON::XS->new->ascii (1)->encode (chr 0x10401)	257	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
148	=> \ud801\udc01	258	=> ["\ud801\udc01"]
		259
		260	=item $json = $json->latin1 ([$enable])
		261
		262	=item $enabled = $json->get_latin1
		263
		264	If C<$enable> is true (or missing), then the C<encode> method will encode
		265	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		266	outside the code range C<0..255>. The resulting string can be treated as a
		267	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		268	will not be affected in any way by this flag, as C<decode> by default
		269	expects Unicode, which is a strict superset of latin1.
		270
		271	If C<$enable> is false, then the C<encode> method will not escape Unicode
		272	characters unless required by the JSON syntax or other flags.
		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
		276
		277	The main use for this flag is efficiently encoding binary data as JSON
		278	text, as most octets will not be escaped, resulting in a smaller encoded
		279	size. The disadvantage is that the resulting JSON text is encoded
		280	in latin1 (and must correctly be treated as such when storing and
		281	transferring), a rare encoding for JSON. It is therefore most useful when
		282	you want to store data structures known to contain binary data efficiently
		283	in files or databases, not when talking to other JSON encoders/decoders.
		284
		285	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		286	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
149		287
150	=item $json = $json->utf8 ([$enable])	288	=item $json = $json->utf8 ([$enable])
151		289
		290	=item $enabled = $json->get_utf8
		291
152	If C<$enable> is true (or missing), then the C<encode> method will encode	292	If C<$enable> is true (or missing), then the C<encode> method will encode
153	the JSON string into UTF-8, as required by many protocols, while the	293	the JSON result into UTF-8, as required by many protocols, while the
154	C<decode> method expects to be handled an UTF-8-encoded string. Please	294	C<decode> method expects to be handled an UTF-8-encoded string. Please
155	note that UTF-8-encoded strings do not contain any characters outside the	295	note that UTF-8-encoded strings do not contain any characters outside the
156	range C<0..255>, they are thus useful for bytewise/binary I/O.	296	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		297	versions, enabling this option might enable autodetection of the UTF-16
		298	and UTF-32 encoding families, as described in RFC4627.
157		299
158	If C<$enable> is false, then the C<encode> method will return the JSON	300	If C<$enable> is false, then the C<encode> method will return the JSON
159	string as a (non-encoded) unicode string, while C<decode> expects thus a	301	string as a (non-encoded) Unicode string, while C<decode> expects thus a
160	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	302	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
161	to be done yourself, e.g. using the Encode module.	303	to be done yourself, e.g. using the Encode module.
162		304
		305	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		306	document.
		307
163	Example, output UTF-16-encoded JSON:	308	Example, output UTF-16BE-encoded JSON:
		309
		310	use Encode;
		311	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		312
		313	Example, decode UTF-32LE-encoded JSON:
		314
		315	use Encode;
		316	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
164		317
165	=item $json = $json->pretty ([$enable])	318	=item $json = $json->pretty ([$enable])
166		319
167	This enables (or disables) all of the C<indent>, C<space_before> and	320	This enables (or disables) all of the C<indent>, C<space_before> and
168	C<space_after> (and in the future possibly more) flags in one call to	321	C<space_after> (and in the future possibly more) flags in one call to
…		…
179	]	332	]
180	}	333	}
181		334
182	=item $json = $json->indent ([$enable])	335	=item $json = $json->indent ([$enable])
183		336
		337	=item $enabled = $json->get_indent
		338
184	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	339	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
185	format as output, putting every array member or object/hash key-value pair	340	format as output, putting every array member or object/hash key-value pair
186	into its own line, identing them properly.	341	into its own line, indenting them properly.
187		342
188	If C<$enable> is false, no newlines or indenting will be produced, and the	343	If C<$enable> is false, no newlines or indenting will be produced, and the
189	resulting JSON strings is guarenteed not to contain any C<newlines>.	344	resulting JSON text is guaranteed not to contain any C<newlines>.
190		345
191	This setting has no effect when decoding JSON strings.	346	This setting has no effect when decoding JSON texts.
192		347
193	=item $json = $json->space_before ([$enable])	348	=item $json = $json->space_before ([$enable])
		349
		350	=item $enabled = $json->get_space_before
194		351
195	If C<$enable> is true (or missing), then the C<encode> method will add an extra	352	If C<$enable> is true (or missing), then the C<encode> method will add an extra
196	optional space before the C<:> separating keys from values in JSON objects.	353	optional space before the C<:> separating keys from values in JSON objects.
197		354
198	If C<$enable> is false, then the C<encode> method will not add any extra	355	If C<$enable> is false, then the C<encode> method will not add any extra
199	space at those places.	356	space at those places.
200		357
201	This setting has no effect when decoding JSON strings. You will also most	358	This setting has no effect when decoding JSON texts. You will also
202	likely combine this setting with C<space_after>.	359	most likely combine this setting with C<space_after>.
203		360
204	Example, space_before enabled, space_after and indent disabled:	361	Example, space_before enabled, space_after and indent disabled:
205		362
206	{"key" :"value"}	363	{"key" :"value"}
207		364
208	=item $json = $json->space_after ([$enable])	365	=item $json = $json->space_after ([$enable])
		366
		367	=item $enabled = $json->get_space_after
209		368
210	If C<$enable> is true (or missing), then the C<encode> method will add an extra	369	If C<$enable> is true (or missing), then the C<encode> method will add an extra
211	optional space after the C<:> separating keys from values in JSON objects	370	optional space after the C<:> separating keys from values in JSON objects
212	and extra whitespace after the C<,> separating key-value pairs and array	371	and extra whitespace after the C<,> separating key-value pairs and array
213	members.	372	members.
214		373
215	If C<$enable> is false, then the C<encode> method will not add any extra	374	If C<$enable> is false, then the C<encode> method will not add any extra
216	space at those places.	375	space at those places.
217		376
218	This setting has no effect when decoding JSON strings.	377	This setting has no effect when decoding JSON texts.
219		378
220	Example, space_before and indent disabled, space_after enabled:	379	Example, space_before and indent disabled, space_after enabled:
221		380
222	{"key": "value"}	381	{"key": "value"}
223		382
		383	=item $json = $json->relaxed ([$enable])
		384
		385	=item $enabled = $json->get_relaxed
		386
		387	If C<$enable> is true (or missing), then C<decode> will accept some
		388	extensions to normal JSON syntax (see below). C<encode> will not be
		389	affected in anyway. I<Be aware that this option makes you accept invalid
		390	JSON texts as if they were valid!>. I suggest only to use this option to
		391	parse application-specific files written by humans (configuration files,
		392	resource files etc.)
		393
		394	If C<$enable> is false (the default), then C<decode> will only accept
		395	valid JSON texts.
		396
		397	Currently accepted extensions are:
		398
		399	=over 4
		400
		401	=item * list items can have an end-comma
		402
		403	JSON I<separates> array elements and key-value pairs with commas. This
		404	can be annoying if you write JSON texts manually and want to be able to
		405	quickly append elements, so this extension accepts comma at the end of
		406	such items not just between them:
		407
		408	[
		409	1,
		410	2, <- this comma not normally allowed
		411	]
		412	{
		413	"k1": "v1",
		414	"k2": "v2", <- this comma not normally allowed
		415	}
		416
		417	=item * shell-style '#'-comments
		418
		419	Whenever JSON allows whitespace, shell-style comments are additionally
		420	allowed. They are terminated by the first carriage-return or line-feed
		421	character, after which more white-space and comments are allowed.
		422
		423	[
		424	1, # this comment not allowed in JSON
		425	# neither this one...
		426	]
		427
		428	=back
		429
224	=item $json = $json->canonical ([$enable])	430	=item $json = $json->canonical ([$enable])
		431
		432	=item $enabled = $json->get_canonical
225		433
226	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	434	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
227	by sorting their keys. This is adding a comparatively high overhead.	435	by sorting their keys. This is adding a comparatively high overhead.
228		436
229	If C<$enable> is false, then the C<encode> method will output key-value	437	If C<$enable> is false, then the C<encode> method will output key-value
230	pairs in the order Perl stores them (which will likely change between runs	438	pairs in the order Perl stores them (which will likely change between runs
231	of the same script).	439	of the same script).
232		440
233	This option is useful if you want the same data structure to be encoded as	441	This option is useful if you want the same data structure to be encoded as
234	the same JSON string (given the same overall settings). If it is disabled,	442	the same JSON text (given the same overall settings). If it is disabled,
235	the same hash migh be encoded differently even if contains the same data,	443	the same hash might be encoded differently even if contains the same data,
236	as key-value pairs have no inherent ordering in Perl.	444	as key-value pairs have no inherent ordering in Perl.
237		445
238	This setting has no effect when decoding JSON strings.	446	This setting has no effect when decoding JSON texts.
239		447
240	=item $json = $json->allow_nonref ([$enable])	448	=item $json = $json->allow_nonref ([$enable])
		449
		450	=item $enabled = $json->get_allow_nonref
241		451
242	If C<$enable> is true (or missing), then the C<encode> method can convert a	452	If C<$enable> is true (or missing), then the C<encode> method can convert a
243	non-reference into its corresponding string, number or null JSON value,	453	non-reference into its corresponding string, number or null JSON value,
244	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	454	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
245	values instead of croaking.	455	values instead of croaking.
246		456
247	If C<$enable> is false, then the C<encode> method will croak if it isn't	457	If C<$enable> is false, then the C<encode> method will croak if it isn't
248	passed an arrayref or hashref, as JSON strings must either be an object	458	passed an arrayref or hashref, as JSON texts must either be an object
249	or array. Likewise, C<decode> will croak if given something that is not a	459	or array. Likewise, C<decode> will croak if given something that is not a
250	JSON object or array.	460	JSON object or array.
251		461
252	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,	462	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
253	resulting in an invalid JSON text:	463	resulting in an invalid JSON text:
254		464
255	JSON::XS->new->allow_nonref->encode ("Hello, World!")	465	JSON::XS->new->allow_nonref->encode ("Hello, World!")
256	=> "Hello, World!"	466	=> "Hello, World!"
257		467
		468	=item $json = $json->allow_unknown ([$enable])
		469
		470	=item $enabled = $json->get_allow_unknown
		471
		472	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		473	exception when it encounters values it cannot represent in JSON (for
		474	example, filehandles) but instead will encode a JSON C<null> value. Note
		475	that blessed objects are not included here and are handled separately by
		476	c<allow_nonref>.
		477
		478	If C<$enable> is false (the default), then C<encode> will throw an
		479	exception when it encounters anything it cannot encode as JSON.
		480
		481	This option does not affect C<decode> in any way, and it is recommended to
		482	leave it off unless you know your communications partner.
		483
		484	=item $json = $json->allow_blessed ([$enable])
		485
		486	=item $enabled = $json->get_allow_blessed
		487
		488	If C<$enable> is true (or missing), then the C<encode> method will not
		489	barf when it encounters a blessed reference. Instead, the value of the
		490	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		491	disabled or no C<TO_JSON> method found) or a representation of the
		492	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		493	encoded. Has no effect on C<decode>.
		494
		495	If C<$enable> is false (the default), then C<encode> will throw an
		496	exception when it encounters a blessed object.
		497
		498	=item $json = $json->convert_blessed ([$enable])
		499
		500	=item $enabled = $json->get_convert_blessed
		501
		502	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		503	blessed object, will check for the availability of the C<TO_JSON> method
		504	on the object's class. If found, it will be called in scalar context
		505	and the resulting scalar will be encoded instead of the object. If no
		506	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		507	to do.
		508
		509	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		510	returns other blessed objects, those will be handled in the same
		511	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		512	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		513	methods called by the Perl core (== not by the user of the object) are
		514	usually in upper case letters and to avoid collisions with any C<to_json>
		515	function or method.
		516
		517	This setting does not yet influence C<decode> in any way, but in the
		518	future, global hooks might get installed that influence C<decode> and are
		519	enabled by this setting.
		520
		521	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		522	to do when a blessed object is found.
		523
		524	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		525
		526	When C<$coderef> is specified, it will be called from C<decode> each
		527	time it decodes a JSON object. The only argument is a reference to the
		528	newly-created hash. If the code references returns a single scalar (which
		529	need not be a reference), this value (i.e. a copy of that scalar to avoid
		530	aliasing) is inserted into the deserialised data structure. If it returns
		531	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		532	original deserialised hash will be inserted. This setting can slow down
		533	decoding considerably.
		534
		535	When C<$coderef> is omitted or undefined, any existing callback will
		536	be removed and C<decode> will not change the deserialised hash in any
		537	way.
		538
		539	Example, convert all JSON objects into the integer 5:
		540
		541	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		542	# returns [5]
		543	$js->decode ('[{}]')
		544	# throw an exception because allow_nonref is not enabled
		545	# so a lone 5 is not allowed.
		546	$js->decode ('{"a":1, "b":2}');
		547
		548	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		549
		550	Works remotely similar to C<filter_json_object>, but is only called for
		551	JSON objects having a single key named C<$key>.
		552
		553	This C<$coderef> is called before the one specified via
		554	C<filter_json_object>, if any. It gets passed the single value in the JSON
		555	object. If it returns a single value, it will be inserted into the data
		556	structure. If it returns nothing (not even C<undef> but the empty list),
		557	the callback from C<filter_json_object> will be called next, as if no
		558	single-key callback were specified.
		559
		560	If C<$coderef> is omitted or undefined, the corresponding callback will be
		561	disabled. There can only ever be one callback for a given key.
		562
		563	As this callback gets called less often then the C<filter_json_object>
		564	one, decoding speed will not usually suffer as much. Therefore, single-key
		565	objects make excellent targets to serialise Perl objects into, especially
		566	as single-key JSON objects are as close to the type-tagged value concept
		567	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		568	support this in any way, so you need to make sure your data never looks
		569	like a serialised Perl hash.
		570
		571	Typical names for the single object key are C<__class_whatever__>, or
		572	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		573	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		574	with real hashes.
		575
		576	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		577	into the corresponding C<< $WIDGET{<id>} >> object:
		578
		579	# return whatever is in $WIDGET{5}:
		580	JSON::XS
		581	->new
		582	->filter_json_single_key_object (__widget__ => sub {
		583	$WIDGET{ $_[0] }
		584	})
		585	->decode ('{"__widget__": 5')
		586
		587	# this can be used with a TO_JSON method in some "widget" class
		588	# for serialisation to json:
		589	sub WidgetBase::TO_JSON {
		590	my ($self) = @_;
		591
		592	unless ($self->{id}) {
		593	$self->{id} = ..get..some..id..;
		594	$WIDGET{$self->{id}} = $self;
		595	}
		596
		597	{ __widget__ => $self->{id} }
		598	}
		599
258	=item $json = $json->shrink ([$enable])	600	=item $json = $json->shrink ([$enable])
259		601
		602	=item $enabled = $json->get_shrink
		603
260	Perl usually over-allocates memory a bit when allocating space for	604	Perl usually over-allocates memory a bit when allocating space for
261	strings. This flag optionally resizes strings generated by either	605	strings. This flag optionally resizes strings generated by either
262	C<encode> or C<decode> to their minimum size possible. This can save	606	C<encode> or C<decode> to their minimum size possible. This can save
263	memory when your JSON strings are either very very long or you have many	607	memory when your JSON texts are either very very long or you have many
264	short strings. It will also try to downgrade any strings to octet-form	608	short strings. It will also try to downgrade any strings to octet-form
265	if possible: perl stores strings internally either in an encoding called	609	if possible: perl stores strings internally either in an encoding called
266	UTF-X or in octet-form. The latter cannot store everything but uses less	610	UTF-X or in octet-form. The latter cannot store everything but uses less
267	space in general.	611	space in general (and some buggy Perl or C code might even rely on that
		612	internal representation being used).
268		613
		614	The actual definition of what shrink does might change in future versions,
		615	but it will always try to save space at the expense of time.
		616
269	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	617	If C<$enable> is true (or missing), the string returned by C<encode> will
270	while all strings generated by C<decode> will also be shrunk-to-fit.	618	be shrunk-to-fit, while all strings generated by C<decode> will also be
		619	shrunk-to-fit.
271		620
272	If C<$enable> is false, then the normal perl allocation algorithms are used.	621	If C<$enable> is false, then the normal perl allocation algorithms are used.
273	If you work with your data, then this is likely to be faster.	622	If you work with your data, then this is likely to be faster.
274		623
275	In the future, this setting might control other things, such as converting	624	In the future, this setting might control other things, such as converting
276	strings that look like integers or floats into integers or floats	625	strings that look like integers or floats into integers or floats
277	internally (there is no difference on the Perl level), saving space.	626	internally (there is no difference on the Perl level), saving space.
278		627
		628	=item $json = $json->max_depth ([$maximum_nesting_depth])
		629
		630	=item $max_depth = $json->get_max_depth
		631
		632	Sets the maximum nesting level (default C<512>) accepted while encoding
		633	or decoding. If a higher nesting level is detected in JSON text or a Perl
		634	data structure, then the encoder and decoder will stop and croak at that
		635	point.
		636
		637	Nesting level is defined by number of hash- or arrayrefs that the encoder
		638	needs to traverse to reach a given point or the number of C<{> or C<[>
		639	characters without their matching closing parenthesis crossed to reach a
		640	given character in a string.
		641
		642	Setting the maximum depth to one disallows any nesting, so that ensures
		643	that the object is only a single hash/object or array.
		644
		645	If no argument is given, the highest possible setting will be used, which
		646	is rarely useful.
		647
		648	Note that nesting is implemented by recursion in C. The default value has
		649	been chosen to be as large as typical operating systems allow without
		650	crashing.
		651
		652	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		653
		654	=item $json = $json->max_size ([$maximum_string_size])
		655
		656	=item $max_size = $json->get_max_size
		657
		658	Set the maximum length a JSON text may have (in bytes) where decoding is
		659	being attempted. The default is C<0>, meaning no limit. When C<decode>
		660	is called on a string that is longer then this many bytes, it will not
		661	attempt to decode the string but throw an exception. This setting has no
		662	effect on C<encode> (yet).
		663
		664	If no argument is given, the limit check will be deactivated (same as when
		665	C<0> is specified).
		666
		667	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		668
279	=item $json_string = $json->encode ($perl_scalar)	669	=item $json_text = $json->encode ($perl_scalar)
280		670
281	Converts the given Perl data structure (a simple scalar or a reference	671	Converts the given Perl data structure (a simple scalar or a reference
282	to a hash or array) to its JSON representation. Simple scalars will be	672	to a hash or array) to its JSON representation. Simple scalars will be
283	converted into JSON string or number sequences, while references to arrays	673	converted into JSON string or number sequences, while references to arrays
284	become JSON arrays and references to hashes become JSON objects. Undefined	674	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>	675	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
286	nor C<false> values will be generated.	676	nor C<false> values will be generated.
287		677
288	=item $perl_scalar = $json->decode ($json_string)	678	=item $perl_scalar = $json->decode ($json_text)
289		679
290	The opposite of C<encode>: expects a JSON string and tries to parse it,	680	The opposite of C<encode>: expects a JSON text and tries to parse it,
291	returning the resulting simple scalar or reference. Croaks on error.	681	returning the resulting simple scalar or reference. Croaks on error.
292		682
293	JSON numbers and strings become simple Perl scalars. JSON arrays become	683	JSON numbers and strings become simple Perl scalars. JSON arrays become
294	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	684	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>.	685	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
296		686
		687	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		688
		689	This works like the C<decode> method, but instead of raising an exception
		690	when there is trailing garbage after the first JSON object, it will
		691	silently stop parsing there and return the number of characters consumed
		692	so far.
		693
		694	This is useful if your JSON texts are not delimited by an outer protocol
		695	(which is not the brightest thing to do in the first place) and you need
		696	to know where the JSON text ends.
		697
		698	JSON::XS->new->decode_prefix ("[1] the tail")
		699	=> ([], 3)
		700
297	=back	701	=back
		702
		703
		704	=head1 INCREMENTAL PARSING
		705
		706	[This section and the API it details is still EXPERIMENTAL]
		707
		708	In some cases, there is the need for incremental parsing of JSON
		709	texts. While this module always has to keep both JSON text and resulting
		710	Perl data structure in memory at one time, it does allow you to parse a
		711	JSON stream incrementally. It does so by accumulating text until it has
		712	a full JSON object, which it then can decode. This process is similar to
		713	using C<decode_prefix> to see if a full JSON object is available, but is
		714	much more efficient (JSON::XS will only attempt to parse the JSON text
		715	once it is sure it has enough text to get a decisive result, using a very
		716	simple but truly incremental parser).
		717
		718	The following two methods deal with this.
		719
		720	=over 4
		721
		722	=item [void, scalar or list context] = $json->incr_parse ([$string])
		723
		724	This is the central parsing function. It can both append new text and
		725	extract objects from the stream accumulated so far (both of these
		726	functions are optional).
		727
		728	If C<$string> is given, then this string is appended to the already
		729	existing JSON fragment stored in the C<$json> object.
		730
		731	After that, if the function is called in void context, it will simply
		732	return without doing anything further. This can be used to add more text
		733	in as many chunks as you want.
		734
		735	If the method is called in scalar context, then it will try to extract
		736	exactly I<one> JSON object. If that is successful, it will return this
		737	object, otherwise it will return C<undef>. If there is a parse error,
		738	this method will croak just as C<decode> would do (one can then use
		739	C<incr_skip> to skip the errornous part). This is the most common way of
		740	using the method.
		741
		742	And finally, in list context, it will try to extract as many objects
		743	from the stream as it can find and return them, or the empty list
		744	otherwise. For this to work, there must be no separators between the JSON
		745	objects or arrays, instead they must be concatenated back-to-back. If
		746	an error occurs, an exception will be raised as in the scalar context
		747	case. Note that in this case, any previously-parsed JSON texts will be
		748	lost.
		749
		750	=item $lvalue_string = $json->incr_text
		751
		752	This method returns the currently stored JSON fragment as an lvalue, that
		753	is, you can manipulate it. This I<only> works when a preceding call to
		754	C<incr_parse> in I<scalar context> successfully returned an object. Under
		755	all other circumstances you must not call this function (I mean it.
		756	although in simple tests it might actually work, it I<will> fail under
		757	real world conditions). As a special exception, you can also call this
		758	method before having parsed anything.
		759
		760	This function is useful in two cases: a) finding the trailing text after a
		761	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		762	(such as commas).
		763
		764	=item $json->incr_skip
		765
		766	This will reset the state of the incremental parser and will remove the
		767	parsed text from the input buffer. This is useful after C<incr_parse>
		768	died, in which case the input buffer and incremental parser state is left
		769	unchanged, to skip the text parsed so far and to reset the parse state.
		770
		771	=back
		772
		773	=head2 LIMITATIONS
		774
		775	All options that affect decoding are supported, except
		776	C<allow_nonref>. The reason for this is that it cannot be made to
		777	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		778	them back to back and still decode them perfectly. This does not hold true
		779	for JSON numbers, however.
		780
		781	For example, is the string C<1> a single JSON number, or is it simply the
		782	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		783	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		784	takes the conservative route and disallows this case.
		785
		786	=head2 EXAMPLES
		787
		788	Some examples will make all this clearer. First, a simple example that
		789	works similarly to C<decode_prefix>: We want to decode the JSON object at
		790	the start of a string and identify the portion after the JSON object:
		791
		792	my $text = "[1,2,3] hello";
		793
		794	my $json = new JSON::XS;
		795
		796	my $obj = $json->incr_parse ($text)
		797	or die "expected JSON object or array at beginning of string";
		798
		799	my $tail = $json->incr_text;
		800	# $tail now contains " hello"
		801
		802	Easy, isn't it?
		803
		804	Now for a more complicated example: Imagine a hypothetical protocol where
		805	you read some requests from a TCP stream, and each request is a JSON
		806	array, without any separation between them (in fact, it is often useful to
		807	use newlines as "separators", as these get interpreted as whitespace at
		808	the start of the JSON text, which makes it possible to test said protocol
		809	with C<telnet>...).
		810
		811	Here is how you'd do it (it is trivial to write this in an event-based
		812	manner):
		813
		814	my $json = new JSON::XS;
		815
		816	# read some data from the socket
		817	while (sysread $socket, my $buf, 4096) {
		818
		819	# split and decode as many requests as possible
		820	for my $request ($json->incr_parse ($buf)) {
		821	# act on the $request
		822	}
		823	}
		824
		825	Another complicated example: Assume you have a string with JSON objects
		826	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		827	[3]>). To parse them, we have to skip the commas between the JSON texts,
		828	and here is where the lvalue-ness of C<incr_text> comes in useful:
		829
		830	my $text = "[1],[2], [3]";
		831	my $json = new JSON::XS;
		832
		833	# void context, so no parsing done
		834	$json->incr_parse ($text);
		835
		836	# now extract as many objects as possible. note the
		837	# use of scalar context so incr_text can be called.
		838	while (my $obj = $json->incr_parse) {
		839	# do something with $obj
		840
		841	# now skip the optional comma
		842	$json->incr_text =~ s/^ \s* , //x;
		843	}
		844
		845	Now lets go for a very complex example: Assume that you have a gigantic
		846	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		847	but you cannot load it into memory fully (this has actually happened in
		848	the real world :).
		849
		850	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		851	can still help you: You implement a (very simple) array parser and let
		852	JSON decode the array elements, which are all full JSON objects on their
		853	own (this wouldn't work if the array elements could be JSON numbers, for
		854	example):
		855
		856	my $json = new JSON::XS;
		857
		858	# open the monster
		859	open my $fh, "<bigfile.json"
		860	or die "bigfile: $!";
		861
		862	# first parse the initial "["
		863	for (;;) {
		864	sysread $fh, my $buf, 65536
		865	or die "read error: $!";
		866	$json->incr_parse ($buf); # void context, so no parsing
		867
		868	# Exit the loop once we found and removed(!) the initial "[".
		869	# In essence, we are (ab-)using the $json object as a simple scalar
		870	# we append data to.
		871	last if $json->incr_text =~ s/^ \s* \[ //x;
		872	}
		873
		874	# now we have the skipped the initial "[", so continue
		875	# parsing all the elements.
		876	for (;;) {
		877	# in this loop we read data until we got a single JSON object
		878	for (;;) {
		879	if (my $obj = $json->incr_parse) {
		880	# do something with $obj
		881	last;
		882	}
		883
		884	# add more data
		885	sysread $fh, my $buf, 65536
		886	or die "read error: $!";
		887	$json->incr_parse ($buf); # void context, so no parsing
		888	}
		889
		890	# in this loop we read data until we either found and parsed the
		891	# separating "," between elements, or the final "]"
		892	for (;;) {
		893	# first skip whitespace
		894	$json->incr_text =~ s/^\s*//;
		895
		896	# if we find "]", we are done
		897	if ($json->incr_text =~ s/^\]//) {
		898	print "finished.\n";
		899	exit;
		900	}
		901
		902	# if we find ",", we can continue with the next element
		903	if ($json->incr_text =~ s/^,//) {
		904	last;
		905	}
		906
		907	# if we find anything else, we have a parse error!
		908	if (length $json->incr_text) {
		909	die "parse error near ", $json->incr_text;
		910	}
		911
		912	# else add more data
		913	sysread $fh, my $buf, 65536
		914	or die "read error: $!";
		915	$json->incr_parse ($buf); # void context, so no parsing
		916	}
		917
		918	This is a complex example, but most of the complexity comes from the fact
		919	that we are trying to be correct (bear with me if I am wrong, I never ran
		920	the above example :).
		921
		922
298		923
299	=head1 MAPPING	924	=head1 MAPPING
300		925
301	This section describes how JSON::XS maps Perl values to JSON values and	926	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	927	vice versa. These mappings are designed to "do the right thing" in most
303	circumstances automatically, preserving round-tripping characteristics	928	circumstances automatically, preserving round-tripping characteristics
304	(what you put in comes out as something equivalent).	929	(what you put in comes out as something equivalent).
305		930
306	For the more enlightened: note that in the following descriptions,	931	For the more enlightened: note that in the following descriptions,
307	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	932	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
308	refers to the abstract Perl language itself.	933	refers to the abstract Perl language itself.
309		934
		935
310	=head2 JSON -> PERL	936	=head2 JSON -> PERL
311		937
312	=over 4	938	=over 4
313		939
314	=item object	940	=item object
315		941
316	A JSON object becomes a reference to a hash in Perl. No ordering of object	942	A JSON object becomes a reference to a hash in Perl. No ordering of object
317	keys is preserved (JSON does not preserver object key ordering itself).	943	keys is preserved (JSON does not preserve object key ordering itself).
318		944
319	=item array	945	=item array
320		946
321	A JSON array becomes a reference to an array in Perl.	947	A JSON array becomes a reference to an array in Perl.
322		948
…		…
326	are represented by the same codepoints in the Perl string, so no manual	952	are represented by the same codepoints in the Perl string, so no manual
327	decoding is necessary.	953	decoding is necessary.
328		954
329	=item number	955	=item number
330		956
331	A JSON number becomes either an integer or numeric (floating point)	957	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	958	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	959	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	960	the conversion details, but an integer may take slightly less memory and
335	represent more values exactly than (floating point) numbers.	961	might represent more values exactly than floating point numbers.
		962
		963	If the number consists of digits only, JSON::XS will try to represent
		964	it as an integer value. If that fails, it will try to represent it as
		965	a numeric (floating point) value if that is possible without loss of
		966	precision. Otherwise it will preserve the number as a string value (in
		967	which case you lose roundtripping ability, as the JSON number will be
		968	re-encoded toa JSON string).
		969
		970	Numbers containing a fractional or exponential part will always be
		971	represented as numeric (floating point) values, possibly at a loss of
		972	precision (in which case you might lose perfect roundtripping ability, but
		973	the JSON number will still be re-encoded as a JSON number).
336		974
337	=item true, false	975	=item true, false
338		976
339	These JSON atoms become C<0>, C<1>, respectively. Information is lost in	977	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
340	this process. Future versions might represent those values differently,	978	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	979	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
342	Perl.	980	the C<JSON::XS::is_bool> function.
343		981
344	=item null	982	=item null
345		983
346	A JSON null atom becomes C<undef> in Perl.	984	A JSON null atom becomes C<undef> in Perl.
347		985
348	=back	986	=back
		987
349		988
350	=head2 PERL -> JSON	989	=head2 PERL -> JSON
351		990
352	The mapping from Perl to JSON is slightly more difficult, as Perl is a	991	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	992	truly typeless language, so we can only guess which JSON type is meant by
…		…
356	=over 4	995	=over 4
357		996
358	=item hash references	997	=item hash references
359		998
360	Perl hash references become JSON objects. As there is no inherent ordering	999	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	1000	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	1001	pseudo-random order that can change between runs of the same program but
363	within a single run of a program. JSON::XS can optionally sort the hash	1002	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	1003	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	1004	the same datastructure will serialise to the same JSON text (given same
366	JSON::XS), but this incurs a runtime overhead.	1005	settings and version of JSON::XS), but this incurs a runtime overhead
		1006	and is only rarely useful, e.g. when you want to compare some JSON text
		1007	against another for equality.
367		1008
368	=item array references	1009	=item array references
369		1010
370	Perl array references become JSON arrays.	1011	Perl array references become JSON arrays.
371		1012
		1013	=item other references
		1014
		1015	Other unblessed references are generally not allowed and will cause an
		1016	exception to be thrown, except for references to the integers C<0> and
		1017	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		1018	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		1019
		1020	encode_json [\0, JSON::XS::true] # yields [false,true]
		1021
		1022	=item JSON::XS::true, JSON::XS::false
		1023
		1024	These special values become JSON true and JSON false values,
		1025	respectively. You can also use C<\1> and C<\0> directly if you want.
		1026
372	=item blessed objects	1027	=item blessed objects
373		1028
374	Blessed objects are not allowed. JSON::XS currently tries to encode their	1029	Blessed objects are not directly representable in JSON. See the
375	underlying representation (hash- or arrayref), but this behaviour might	1030	C<allow_blessed> and C<convert_blessed> methods on various options on
376	change in future versions.	1031	how to deal with this: basically, you can choose between throwing an
		1032	exception, encoding the reference as if it weren't blessed, or provide
		1033	your own serialiser method.
377		1034
378	=item simple scalars	1035	=item simple scalars
379		1036
380	Simple Perl scalars (any scalar that is not a reference) are the most	1037	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	1038	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	1039	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:	1040	before encoding as JSON strings, and anything else as number value:
384		1041
385	# dump as number	1042	# dump as number
386	to_json [2] # yields [2]	1043	encode_json [2] # yields [2]
387	to_json [-3.0e17] # yields [-3e+17]	1044	encode_json [-3.0e17] # yields [-3e+17]
388	my $value = 5; to_json [$value] # yields [5]	1045	my $value = 5; encode_json [$value] # yields [5]
389		1046
390	# used as string, so dump as string	1047	# used as string, so dump as string
391	print $value;	1048	print $value;
392	to_json [$value] # yields ["5"]	1049	encode_json [$value] # yields ["5"]
393		1050
394	# undef becomes null	1051	# undef becomes null
395	to_json [undef] # yields [null]	1052	encode_json [undef] # yields [null]
396		1053
397	You can force the type to be a string by stringifying it:	1054	You can force the type to be a JSON string by stringifying it:
398		1055
399	my $x = 3.1; # some variable containing a number	1056	my $x = 3.1; # some variable containing a number
400	"$x"; # stringified	1057	"$x"; # stringified
401	$x .= ""; # another, more awkward way to stringify	1058	$x .= ""; # another, more awkward way to stringify
402	print $x; # perl does it for you, too, quite often	1059	print $x; # perl does it for you, too, quite often
403		1060
404	You can force the type to be a number by numifying it:	1061	You can force the type to be a JSON number by numifying it:
405		1062
406	my $x = "3"; # some variable containing a string	1063	my $x = "3"; # some variable containing a string
407	$x += 0; # numify it, ensuring it will be dumped as a number	1064	$x += 0; # numify it, ensuring it will be dumped as a number
408	$x *= 1; # same thing, the choise is yours.	1065	$x *= 1; # same thing, the choice is yours.
409		1066
410	You can not currently output JSON booleans or force the type in other,	1067	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.	1068	if you need this capability (but don't forget to explain why it's needed
412		1069	:).
413	=item circular data structures
414
415	Those will be encoded until memory or stackspace runs out.
416		1070
417	=back	1071	=back
418		1072
419	=head1 COMPARISON
420		1073
421	As already mentioned, this module was created because none of the existing	1074	=head1 ENCODING/CODESET FLAG NOTES
422	JSON modules could be made to work correctly. First I will describe the	1075
423	problems (or pleasures) I encountered with various existing JSON modules,	1076	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	1077	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
425	from any of these problems or limitations.	1078	some confusion on what these do, so here is a short comparison:
		1079
		1080	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1081	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1082	control whether C<encode> escapes character values outside their respective
		1083	codeset range. Neither of these flags conflict with each other, although
		1084	some combinations make less sense than others.
		1085
		1086	Care has been taken to make all flags symmetrical with respect to
		1087	C<encode> and C<decode>, that is, texts encoded with any combination of
		1088	these flag values will be correctly decoded when the same flags are used
		1089	- in general, if you use different flag settings while encoding vs. when
		1090	decoding you likely have a bug somewhere.
		1091
		1092	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1093	simply an abstract set of character-codepoint pairs, while an encoding
		1094	takes those codepoint numbers and I<encodes> them, in our case into
		1095	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1096	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1097	the same time, which can be confusing.
426		1098
427	=over 4	1099	=over 4
428		1100
429	=item JSON 1.07	1101	=item C<utf8> flag disabled
430		1102
431	Slow (but very portable, as it is written in pure Perl).	1103	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1104	and expect Unicode strings, that is, characters with high ordinal Unicode
		1105	values (> 255) will be encoded as such characters, and likewise such
		1106	characters are decoded as-is, no canges to them will be done, except
		1107	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1108	respectively (to Perl, these are the same thing in strings unless you do
		1109	funny/weird/dumb stuff).
432		1110
433	Undocumented/buggy Unicode handling (how JSON handles unicode values is	1111	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	1112	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).	1113	the encoding for you (for example, when printing to a terminal using a
		1114	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1115	to UTF-8 encode your data first and have Perl encode it another time).
436		1116
437	No roundtripping (strings get clobbered if they look like numbers, e.g.	1117	=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		1118
441	=item JSON::PC 0.01	1119	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1120	characters using the corresponding UTF-8 multi-byte sequence, and will
		1121	expect your input strings to be encoded as UTF-8, that is, no "character"
		1122	of the input string must have any value > 255, as UTF-8 does not allow
		1123	that.
442		1124
443	Very fast.	1125	The C<utf8> flag therefore switches between two modes: disabled means you
		1126	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1127	octet/binary string in Perl.
444		1128
445	Undocumented/buggy Unicode handling.	1129	=item C<latin1> or C<ascii> flags enabled
446		1130
447	No roundtripping.	1131	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1132	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1133	characters as specified by the C<utf8> flag.
448		1134
449	Has problems handling many Perl values (e.g. regex results and other magic	1135	If C<utf8> is disabled, then the result is also correctly encoded in those
450	values will make it croak).	1136	character sets (as both are proper subsets of Unicode, meaning that a
		1137	Unicode string with all character values < 256 is the same thing as a
		1138	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1139	the same thing as an ASCII string in Perl).
451		1140
452	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1141	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
453	which is not a valid JSON string.	1142	regardless of these flags, just some more characters will be escaped using
		1143	C<\uXXXX> then before.
454		1144
455	Unmaintained (maintainer unresponsive for many months, bugs are not	1145	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
456	getting fixed).	1146	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1147	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1148	a subset of Unicode), while ASCII is.
457		1149
458	=item JSON::Syck 0.21	1150	Surprisingly, C<decode> will ignore these flags and so treat all input
		1151	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1152	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1153	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
459		1154
460	Very buggy (often crashes).	1155	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1156	they only govern when the JSON output engine escapes a character or not.
461		1157
462	Very inflexible (no human-readable format supported, format pretty much	1158	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	1159	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		1160
467	Completely broken (and confusingly documented) Unicode handling (unicode	1161	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	1162	with values > 127, which means you can interpret the resulting string
469	I<different> values on en- and decoding to get symmetric behaviour).	1163	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
470		1164	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	1165	when your channel for JSON transfer is not 8-bit clean or the encoding
472	value was used in a numeric context or not).	1166	might be mangled in between (e.g. in mail), and works because ASCII is a
473		1167	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		1168
503	=back	1169	=back
		1170
		1171
		1172	=head2 JSON and YAML
		1173
		1174	You often hear that JSON is a subset of YAML. This is, however, a mass
		1175	hysteria(*) and very far from the truth (as of the time of this writing),
		1176	so let me state it clearly: I<in general, there is no way to configure
		1177	JSON::XS to output a data structure as valid YAML> that works in all
		1178	cases.
		1179
		1180	If you really must use JSON::XS to generate YAML, you should use this
		1181	algorithm (subject to change in future versions):
		1182
		1183	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1184	my $yaml = $to_yaml->encode ($ref) . "\n";
		1185
		1186	This will I<usually> generate JSON texts that also parse as valid
		1187	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1188	lengths that JSON doesn't have and also has different and incompatible
		1189	unicode handling, so you should make sure that your hash keys are
		1190	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1191	you do not have characters with codepoint values outside the Unicode BMP
		1192	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1193	strings (which JSON::XS does not I<currently> generate, but other JSON
		1194	generators might).
		1195
		1196	There might be other incompatibilities that I am not aware of (or the YAML
		1197	specification has been changed yet again - it does so quite often). In
		1198	general you should not try to generate YAML with a JSON generator or vice
		1199	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1200	high that you will run into severe interoperability problems when you
		1201	least expect it.
		1202
		1203	=over 4
		1204
		1205	=item (*)
		1206
		1207	I have been pressured multiple times by Brian Ingerson (one of the
		1208	authors of the YAML specification) to remove this paragraph, despite him
		1209	acknowledging that the actual incompatibilities exist. As I was personally
		1210	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1211	educate people about these issues, so others do not run into the same
		1212	problem again and again. After this, Brian called me a (quote)I<complete
		1213	and worthless idiot>(unquote).
		1214
		1215	In my opinion, instead of pressuring and insulting people who actually
		1216	clarify issues with YAML and the wrong statements of some of its
		1217	proponents, I would kindly suggest reading the JSON spec (which is not
		1218	that difficult or long) and finally make YAML compatible to it, and
		1219	educating users about the changes, instead of spreading lies about the
		1220	real compatibility for many I<years> and trying to silence people who
		1221	point out that it isn't true.
		1222
		1223	=back
		1224
504		1225
505	=head2 SPEED	1226	=head2 SPEED
506		1227
507	It seems that JSON::XS is surprisingly fast, as shown in the following	1228	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	1229	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	1230	in the JSON::XS distribution, to make it easy to compare on your own
510	system.	1231	system.
511		1232
512	First comes a comparison between various modules using a very short JSON	1233	First comes a comparison between various modules using
513	string (83 bytes), showing the number of encodes/decodes per second	1234	a very short single-line JSON string (also available at
		1235	L<http://dist.schmorp.de/misc/json/short.json>).
		1236
		1237	{"method": "handleMessage", "params": ["user1",
		1238	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1239	true, false]}
		1240
		1241	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	1242	the functional interface, while JSON::XS/2 uses the OO interface
515	interface with pretty-printing and hashkey sorting enabled). Higher is	1243	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
516	better:	1244	shrink). Higher is better:
517		1245
518	module | encode | decode |	1246	module | encode | decode |
519	-----------|------------|------------|	1247	-----------|------------|------------|
520	JSON | 14006 | 6820 |	1248	JSON 1.x | 4990.842 | 4088.813 |
521	JSON::DWIW | 200937 | 120386 |	1249	JSON::DWIW | 51653.990 | 71575.154 |
522	JSON::PC | 85065 | 129366 |	1250	JSON::PC | 65948.176 | 74631.744 |
523	JSON::Syck | 59898 | 44232 |	1251	JSON::PP | 8931.652 | 3817.168 |
524	JSON::XS | 1171478 | 342435 |	1252	JSON::Syck | 24877.248 | 27776.848 |
525	JSON::XS/2 | 730760 | 328714 |	1253	JSON::XS | 388361.481 | 227951.304 |
		1254	JSON::XS/2 | 227951.304 | 218453.333 |
		1255	JSON::XS/3 | 338250.323 | 218453.333 |
		1256	Storable | 16500.016 | 135300.129 |
526	-----------+------------+------------+	1257	-----------+------------+------------+
527		1258
528	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1259	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
		1260	about three times faster on decoding, and over forty times faster
529	times faster than JSON, even with pretty-printing and key sorting.	1261	than JSON, even with pretty-printing and key sorting. It also compares
		1262	favourably to Storable for small amounts of data.
530		1263
531	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1264	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
532	search API (http://nanoref.com/yahooapis/mgPdGg):	1265	search API (L<http://dist.schmorp.de/misc/json/long.json>).
533		1266
534	module | encode | decode |	1267	module | encode | decode |
535	-----------|------------|------------|	1268	-----------|------------|------------|
536	JSON | 673 | 38 |	1269	JSON 1.x | 55.260 | 34.971 |
537	JSON::DWIW | 5271 | 770 |	1270	JSON::DWIW | 825.228 | 1082.513 |
538	JSON::PC | 9901 | 2491 |	1271	JSON::PC | 3571.444 | 2394.829 |
539	JSON::Syck | 2360 | 786 |	1272	JSON::PP | 210.987 | 32.574 |
540	JSON::XS | 37398 | 3202 |	1273	JSON::Syck | 552.551 | 787.544 |
541	JSON::XS/2 | 13765 | 3153 |	1274	JSON::XS | 5780.463 | 4854.519 |
		1275	JSON::XS/2 | 3869.998 | 4798.975 |
		1276	JSON::XS/3 | 5862.880 | 4798.975 |
		1277	Storable | 4445.002 | 5235.027 |
542	-----------+------------+------------+	1278	-----------+------------+------------+
543		1279
544	Again, JSON::XS leads by far in the encoding case, while still beating	1280	Again, JSON::XS leads by far (except for Storable which non-surprisingly
545	every other module in the decoding case.	1281	decodes faster).
546		1282
547	On large strings containing lots of unicode characters, some modules	1283	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	1284	(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	1285	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	1286	to decode or encode properly, so it was impossible to prepare a fair
551	case.	1287	comparison table for that case.
552		1288
553	=head1 RESOURCE LIMITS
554		1289
555	JSON::XS does not impose any limits on the size of JSON texts or Perl	1290	=head1 SECURITY CONSIDERATIONS
556	values they represent - if your machine can handle it, JSON::XS will	1291
557	encode or decode it. Future versions might optionally impose structure	1292	When you are using JSON in a protocol, talking to untrusted potentially
558	depth and memory use resource limits.	1293	hostile creatures requires relatively few measures.
		1294
		1295	First of all, your JSON decoder should be secure, that is, should not have
		1296	any buffer overflows. Obviously, this module should ensure that and I am
		1297	trying hard on making that true, but you never know.
		1298
		1299	Second, you need to avoid resource-starving attacks. That means you should
		1300	limit the size of JSON texts you accept, or make sure then when your
		1301	resources run out, that's just fine (e.g. by using a separate process that
		1302	can crash safely). The size of a JSON text in octets or characters is
		1303	usually a good indication of the size of the resources required to decode
		1304	it into a Perl structure. While JSON::XS can check the size of the JSON
		1305	text, it might be too late when you already have it in memory, so you
		1306	might want to check the size before you accept the string.
		1307
		1308	Third, JSON::XS recurses using the C stack when decoding objects and
		1309	arrays. The C stack is a limited resource: for instance, on my amd64
		1310	machine with 8MB of stack size I can decode around 180k nested arrays but
		1311	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1312	to free the temporary). If that is exceeded, the program crashes. To be
		1313	conservative, the default nesting limit is set to 512. If your process
		1314	has a smaller stack, you should adjust this setting accordingly with the
		1315	C<max_depth> method.
		1316
		1317	Something else could bomb you, too, that I forgot to think of. In that
		1318	case, you get to keep the pieces. I am always open for hints, though...
		1319
		1320	Also keep in mind that JSON::XS might leak contents of your Perl data
		1321	structures in its error messages, so when you serialise sensitive
		1322	information you might want to make sure that exceptions thrown by JSON::XS
		1323	will not end up in front of untrusted eyes.
		1324
		1325	If you are using JSON::XS to return packets to consumption
		1326	by JavaScript scripts in a browser you should have a look at
		1327	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1328	you are vulnerable to some common attack vectors (which really are browser
		1329	design bugs, but it is still you who will have to deal with it, as major
		1330	browser developers care only for features, not about getting security
		1331	right).
		1332
		1333
		1334	=head1 THREADS
		1335
		1336	This module is I<not> guaranteed to be thread safe and there are no
		1337	plans to change this until Perl gets thread support (as opposed to the
		1338	horribly slow so-called "threads" which are simply slow and bloated
		1339	process simulations - use fork, it's I<much> faster, cheaper, better).
		1340
		1341	(It might actually work, but you have been warned).
		1342
559		1343
560	=head1 BUGS	1344	=head1 BUGS
561		1345
562	While the goal of this module is to be correct, that unfortunately does	1346	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	1347	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	1348	keep reporting bugs they will be fixed swiftly, though.
565	be fixed swiftly, though.	1349
		1350	Please refrain from using rt.cpan.org or any other bug reporting
		1351	service. I put the contact address into my modules for a reason.
566		1352
567	=cut	1353	=cut
568		1354
		1355	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1356	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1357
		1358	sub true() { $true }
		1359	sub false() { $false }
		1360
		1361	sub is_bool($) {
		1362	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1363	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1364	}
		1365
		1366	XSLoader::load "JSON::XS", $VERSION;
		1367
		1368	package JSON::XS::Boolean;
		1369
		1370	use overload
		1371	"0+" => sub { ${$_[0]} },
		1372	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1373	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1374	fallback => 1;
		1375
569	1;	1376	1;
		1377
		1378	=head1 SEE ALSO
		1379
		1380	The F<json_xs> command line utility for quick experiments.
570		1381
571	=head1 AUTHOR	1382	=head1 AUTHOR
572		1383
573	Marc Lehmann <schmorp@schmorp.de>	1384	Marc Lehmann <schmorp@schmorp.de>
574	http://home.schmorp.de/	1385	http://home.schmorp.de/

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