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Revision 1.5 by root, Thu Mar 22 21:36:52 2007 UTC vs.
Revision 1.96 by root, Wed Mar 26 01:40:42 2008 UTC

1	=head1 NAME	1	=head1 NAME
2		2
		3	=encoding utf-8
		4
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	5	JSON::XS - JSON serialising/deserialising, done correctly and fast
4		6
		7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
		13
		14	# exported functions, they croak on error
		15	# and expect/generate UTF-8
		16
		17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
		18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
		19
		20	# OO-interface
		21
		22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
		23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
		24	$perl_scalar = $coder->decode ($unicode_json_text);
		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
8		33
9	=head1 DESCRIPTION	34	=head1 DESCRIPTION
10		35
11	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
12	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
13	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	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.
14		47
15	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
16	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
17	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
18	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
19	reports for other reasons.	52	reports for other reasons.
20		53
21	See COMPARISON, below, for a comparison to some other JSON modules.	54	See COMPARISON, below, for a comparison to some other JSON modules.
22		55
		56	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
		57	vice versa.
		58
23	=head2 FEATURES	59	=head2 FEATURES
24		60
25	=over 4	61	=over 4
26		62
27	=item * correct handling of unicode issues	63	=item * correct Unicode handling
28		64
29	This module knows how to handle Unicode, and even documents how it does so.	65	This module knows how to handle Unicode, documents how and when it does
		66	so, and even documents what "correct" means.
30		67
31	=item * round-trip integrity	68	=item * round-trip integrity
32		69
33	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only datatypes supported
34	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.
35	(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.
36		75
37	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
38		77
39	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,
40	and only JSON is accepted as input (the latter is a security feature).	79	and only JSON is accepted as input by default (the latter is a security
		80	feature).
41		81
42	=item * fast	82	=item * fast
43		83
44	compared to other JSON modules, this module compares favourably.	84	Compared to other JSON modules and other serialisers such as Storable,
		85	this module usually compares favourably in terms of speed, too.
45		86
46	=item * simple to use	87	=item * simple to use
47		88
48	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
49	interface.	90	oriented interface interface.
50		91
51	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
52		93
53	You can choose between the most compact format possible, a pure-ascii	94	You can choose between the most compact guaranteed-single-line format
54	format, or a pretty-printed format. Or you can combine those features in	95	possible (nice for simple line-based protocols), a pure-ascii format
55	whatever way you like.	96	(for when your transport is not 8-bit clean, still supports the whole
		97	Unicode range), or a pretty-printed format (for when you want to read that
		98	stuff). Or you can combine those features in whatever way you like.
56		99
57	=back	100	=back
58		101
59	=cut	102	=cut
60		103
61	package JSON::XS;	104	package JSON::XS;
62		105
63	BEGIN {	106	use strict;
		107
64	$VERSION = '0.1';	108	our $VERSION = '2.1';
65	@ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
66		110
67	@EXPORT = qw(to_json from_json);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
68	require Exporter;
69		112
		113	sub to_json($) {
70	require XSLoader;	114	require Carp;
71	XSLoader::load JSON::XS::, $VERSION;	115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
72	}	116	}
73		117
		118	sub from_json($) {
		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
74	=head1 FUNCTIONAL INTERFACE	126	=head1 FUNCTIONAL INTERFACE
75		127
76	The following convinience methods are provided by this module. They are	128	The following convenience methods are provided by this module. They are
77	exported by default:	129	exported by default:
78		130
79	=over 4	131	=over 4
80		132
81	=item $json_string = to_json $perl_scalar	133	=item $json_text = encode_json $perl_scalar
82		134
83	Converts the given Perl data structure (a simple scalar or a reference to	135	Converts the given Perl data structure to a UTF-8 encoded, binary string
84	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	136	(that is, the string contains octets only). Croaks on error.
85	octets only). Croaks on error.
86		137
87	This function call is functionally identical to C<< JSON::XS->new->utf8	138	This function call is functionally identical to:
88	(1)->encode ($perl_scalar) >>.
89		139
		140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		141
		142	except being faster.
		143
90	=item $perl_scalar = from_json $json_string	144	=item $perl_scalar = decode_json $json_text
91		145
92	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
93	parse that as an UTF-8 encoded JSON string, returning the resulting simple	147	to parse that as an UTF-8 encoded JSON text, returning the resulting
94	scalar or reference. Croaks on error.	148	reference. Croaks on error.
95		149
96	This function call is functionally identical to C<< JSON::XS->new->utf8	150	This function call is functionally identical to:
97	(1)->decode ($json_string) >>.	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.
98		164
99	=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
100		215
101	=head1 OBJECT-ORIENTED INTERFACE	216	=head1 OBJECT-ORIENTED INTERFACE
102		217
103	The object oriented interface lets you configure your own encoding or	218	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	219	decoding style, within the limits of supported formats.
…		…
111	strings. All boolean flags described below are by default I<disabled>.	226	strings. All boolean flags described below are by default I<disabled>.
112		227
113	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
114	be chained:	229	be chained:
115		230
116	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]})
117	=> {"a": [1, 2]}	232	=> {"a": [1, 2]}
118		233
119	=item $json = $json->ascii ($enable)	234	=item $json = $json->ascii ([$enable])
120		235
		236	=item $enabled = $json->get_ascii
		237
121	If C<$enable> is true, then the C<encode> method will not generate	238	If C<$enable> is true (or missing), then the C<encode> method will not
122	characters outside the code range C<0..127>. Any unicode characters	239	generate characters outside the code range C<0..127> (which is ASCII). Any
123	outside that range will be escaped using either a single \uXXXX (BMP	240	Unicode characters outside that range will be escaped using either a
124	characters) or a double \uHHHH\uLLLLL escape sequence, as per RFC4627.	241	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
		242	as per RFC4627. The resulting encoded JSON text can be treated as a native
		243	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		244	or any other superset of ASCII.
125		245
126	If C<$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
127	characters unless necessary.	247	characters unless required by the JSON syntax or other flags. This results
		248	in a faster and more compact format.
128		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
129	JSON::XS->new->ascii (1)->encode (chr 0x10401)	257	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
130	=> \ud801\udc01	258	=> ["\ud801\udc01"]
131		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)
		287
132	=item $json = $json->utf8 ($enable)	288	=item $json = $json->utf8 ([$enable])
133		289
		290	=item $enabled = $json->get_utf8
		291
134	If C<$enable> is true, then the C<encode> method will encode the JSON	292	If C<$enable> is true (or missing), then the C<encode> method will encode
135	string into UTF-8, as required by many protocols, while the C<decode>	293	the JSON result into UTF-8, as required by many protocols, while the
136	method expects to be handled an UTF-8-encoded string. Please note that	294	C<decode> method expects to be handled an UTF-8-encoded string. Please
137	UTF-8-encoded strings do not contain any characters outside the range	295	note that UTF-8-encoded strings do not contain any characters outside the
138	C<0..255>, they are thus useful for bytewise/binary I/O.	296	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		297	versions, enabling this option might enable autodetection of the UTF-16
		298	and UTF-32 encoding families, as described in RFC4627.
139		299
140	If C<$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
141	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
142	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
143	to be done yourself, e.g. using the Encode module.	303	to be done yourself, e.g. using the Encode module.
144		304
		305	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		306	document.
		307
		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);
		317
145	=item $json = $json->pretty ($enable)	318	=item $json = $json->pretty ([$enable])
146		319
147	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
148	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
149	generate the most readable (or most compact) form possible.	322	generate the most readable (or most compact) form possible.
		323
		324	Example, pretty-print some simple structure:
150		325
151	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})	326	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
152	=>	327	=>
153	{	328	{
154	"a" : [	329	"a" : [
155	1,	330	1,
156	2	331	2
157	]	332	]
158	}	333	}
159		334
160	=item $json = $json->indent ($enable)	335	=item $json = $json->indent ([$enable])
161		336
		337	=item $enabled = $json->get_indent
		338
162	If C<$enable> is true, then the C<encode> method will use a multiline	339	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
163	format as output, putting every array member or object/hash key-value pair	340	format as output, putting every array member or object/hash key-value pair
164	into its own line, identing them properly.	341	into its own line, indenting them properly.
165		342
166	If C<$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
167	resulting JSON strings is guarenteed not to contain any C<newlines>.	344	resulting JSON text is guaranteed not to contain any C<newlines>.
168		345
169	This setting has no effect when decoding JSON strings.	346	This setting has no effect when decoding JSON texts.
170		347
171	=item $json = $json->space_before ($enable)	348	=item $json = $json->space_before ([$enable])
172		349
		350	=item $enabled = $json->get_space_before
		351
173	If C<$enable> is true, then the C<encode> method will add an extra	352	If C<$enable> is true (or missing), then the C<encode> method will add an extra
174	optional space before the C<:> separating keys from values in JSON objects.	353	optional space before the C<:> separating keys from values in JSON objects.
175		354
176	If C<$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
177	space at those places.	356	space at those places.
178		357
179	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
180	likely combine this setting with C<space_after>.	359	most likely combine this setting with C<space_after>.
181		360
		361	Example, space_before enabled, space_after and indent disabled:
		362
		363	{"key" :"value"}
		364
182	=item $json = $json->space_after ($enable)	365	=item $json = $json->space_after ([$enable])
183		366
		367	=item $enabled = $json->get_space_after
		368
184	If C<$enable> is true, then the C<encode> method will add an extra	369	If C<$enable> is true (or missing), then the C<encode> method will add an extra
185	optional space after the C<:> separating keys from values in JSON objects	370	optional space after the C<:> separating keys from values in JSON objects
186	and extra whitespace after the C<,> separating key-value pairs and array	371	and extra whitespace after the C<,> separating key-value pairs and array
187	members.	372	members.
188		373
189	If C<$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
190	space at those places.	375	space at those places.
191		376
192	This setting has no effect when decoding JSON strings.	377	This setting has no effect when decoding JSON texts.
193		378
		379	Example, space_before and indent disabled, space_after enabled:
		380
		381	{"key": "value"}
		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
194	=item $json = $json->canonical ($enable)	430	=item $json = $json->canonical ([$enable])
195		431
		432	=item $enabled = $json->get_canonical
		433
196	If C<$enable> is true, then the C<encode> method will output JSON objects	434	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
197	by sorting their keys. This is adding a comparatively high overhead.	435	by sorting their keys. This is adding a comparatively high overhead.
198		436
199	If C<$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
200	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
201	of the same script).	439	of the same script).
202		440
203	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
204	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,
205	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,
206	as key-value pairs have no inherent ordering in Perl.	444	as key-value pairs have no inherent ordering in Perl.
207		445
208	This setting has no effect when decoding JSON strings.	446	This setting has no effect when decoding JSON texts.
209		447
210	=item $json = $json->allow_nonref ($enable)	448	=item $json = $json->allow_nonref ([$enable])
211		449
		450	=item $enabled = $json->get_allow_nonref
		451
212	If C<$enable> is true, then the C<encode> method can convert a	452	If C<$enable> is true (or missing), then the C<encode> method can convert a
213	non-reference into its corresponding string, number or null JSON value,	453	non-reference into its corresponding string, number or null JSON value,
214	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	454	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
215	values instead of croaking.	455	values instead of croaking.
216		456
217	If C<$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
218	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
219	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
220	JSON object or array.	460	JSON object or array.
221		461
		462	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
		463	resulting in an invalid JSON text:
		464
		465	JSON::XS->new->allow_nonref->encode ("Hello, World!")
		466	=> "Hello, World!"
		467
		468	=item $json = $json->allow_blessed ([$enable])
		469
		470	=item $enabled = $json->get_allow_blessed
		471
		472	If C<$enable> is true (or missing), then the C<encode> method will not
		473	barf when it encounters a blessed reference. Instead, the value of the
		474	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		475	disabled or no C<TO_JSON> method found) or a representation of the
		476	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		477	encoded. Has no effect on C<decode>.
		478
		479	If C<$enable> is false (the default), then C<encode> will throw an
		480	exception when it encounters a blessed object.
		481
		482	=item $json = $json->convert_blessed ([$enable])
		483
		484	=item $enabled = $json->get_convert_blessed
		485
		486	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		487	blessed object, will check for the availability of the C<TO_JSON> method
		488	on the object's class. If found, it will be called in scalar context
		489	and the resulting scalar will be encoded instead of the object. If no
		490	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		491	to do.
		492
		493	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		494	returns other blessed objects, those will be handled in the same
		495	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		496	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		497	methods called by the Perl core (== not by the user of the object) are
		498	usually in upper case letters and to avoid collisions with any C<to_json>
		499	function or method.
		500
		501	This setting does not yet influence C<decode> in any way, but in the
		502	future, global hooks might get installed that influence C<decode> and are
		503	enabled by this setting.
		504
		505	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		506	to do when a blessed object is found.
		507
		508	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		509
		510	When C<$coderef> is specified, it will be called from C<decode> each
		511	time it decodes a JSON object. The only argument is a reference to the
		512	newly-created hash. If the code references returns a single scalar (which
		513	need not be a reference), this value (i.e. a copy of that scalar to avoid
		514	aliasing) is inserted into the deserialised data structure. If it returns
		515	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		516	original deserialised hash will be inserted. This setting can slow down
		517	decoding considerably.
		518
		519	When C<$coderef> is omitted or undefined, any existing callback will
		520	be removed and C<decode> will not change the deserialised hash in any
		521	way.
		522
		523	Example, convert all JSON objects into the integer 5:
		524
		525	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		526	# returns [5]
		527	$js->decode ('[{}]')
		528	# throw an exception because allow_nonref is not enabled
		529	# so a lone 5 is not allowed.
		530	$js->decode ('{"a":1, "b":2}');
		531
		532	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		533
		534	Works remotely similar to C<filter_json_object>, but is only called for
		535	JSON objects having a single key named C<$key>.
		536
		537	This C<$coderef> is called before the one specified via
		538	C<filter_json_object>, if any. It gets passed the single value in the JSON
		539	object. If it returns a single value, it will be inserted into the data
		540	structure. If it returns nothing (not even C<undef> but the empty list),
		541	the callback from C<filter_json_object> will be called next, as if no
		542	single-key callback were specified.
		543
		544	If C<$coderef> is omitted or undefined, the corresponding callback will be
		545	disabled. There can only ever be one callback for a given key.
		546
		547	As this callback gets called less often then the C<filter_json_object>
		548	one, decoding speed will not usually suffer as much. Therefore, single-key
		549	objects make excellent targets to serialise Perl objects into, especially
		550	as single-key JSON objects are as close to the type-tagged value concept
		551	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		552	support this in any way, so you need to make sure your data never looks
		553	like a serialised Perl hash.
		554
		555	Typical names for the single object key are C<__class_whatever__>, or
		556	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		557	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		558	with real hashes.
		559
		560	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		561	into the corresponding C<< $WIDGET{<id>} >> object:
		562
		563	# return whatever is in $WIDGET{5}:
		564	JSON::XS
		565	->new
		566	->filter_json_single_key_object (__widget__ => sub {
		567	$WIDGET{ $_[0] }
		568	})
		569	->decode ('{"__widget__": 5')
		570
		571	# this can be used with a TO_JSON method in some "widget" class
		572	# for serialisation to json:
		573	sub WidgetBase::TO_JSON {
		574	my ($self) = @_;
		575
		576	unless ($self->{id}) {
		577	$self->{id} = ..get..some..id..;
		578	$WIDGET{$self->{id}} = $self;
		579	}
		580
		581	{ __widget__ => $self->{id} }
		582	}
		583
		584	=item $json = $json->shrink ([$enable])
		585
		586	=item $enabled = $json->get_shrink
		587
		588	Perl usually over-allocates memory a bit when allocating space for
		589	strings. This flag optionally resizes strings generated by either
		590	C<encode> or C<decode> to their minimum size possible. This can save
		591	memory when your JSON texts are either very very long or you have many
		592	short strings. It will also try to downgrade any strings to octet-form
		593	if possible: perl stores strings internally either in an encoding called
		594	UTF-X or in octet-form. The latter cannot store everything but uses less
		595	space in general (and some buggy Perl or C code might even rely on that
		596	internal representation being used).
		597
		598	The actual definition of what shrink does might change in future versions,
		599	but it will always try to save space at the expense of time.
		600
		601	If C<$enable> is true (or missing), the string returned by C<encode> will
		602	be shrunk-to-fit, while all strings generated by C<decode> will also be
		603	shrunk-to-fit.
		604
		605	If C<$enable> is false, then the normal perl allocation algorithms are used.
		606	If you work with your data, then this is likely to be faster.
		607
		608	In the future, this setting might control other things, such as converting
		609	strings that look like integers or floats into integers or floats
		610	internally (there is no difference on the Perl level), saving space.
		611
		612	=item $json = $json->max_depth ([$maximum_nesting_depth])
		613
		614	=item $max_depth = $json->get_max_depth
		615
		616	Sets the maximum nesting level (default C<512>) accepted while encoding
		617	or decoding. If the JSON text or Perl data structure has an equal or
		618	higher nesting level then this limit, then the encoder and decoder will
		619	stop and croak at that point.
		620
		621	Nesting level is defined by number of hash- or arrayrefs that the encoder
		622	needs to traverse to reach a given point or the number of C<{> or C<[>
		623	characters without their matching closing parenthesis crossed to reach a
		624	given character in a string.
		625
		626	Setting the maximum depth to one disallows any nesting, so that ensures
		627	that the object is only a single hash/object or array.
		628
		629	The argument to C<max_depth> will be rounded up to the next highest power
		630	of two. If no argument is given, the highest possible setting will be
		631	used, which is rarely useful.
		632
		633	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		634
		635	=item $json = $json->max_size ([$maximum_string_size])
		636
		637	=item $max_size = $json->get_max_size
		638
		639	Set the maximum length a JSON text may have (in bytes) where decoding is
		640	being attempted. The default is C<0>, meaning no limit. When C<decode>
		641	is called on a string longer then this number of characters it will not
		642	attempt to decode the string but throw an exception. This setting has no
		643	effect on C<encode> (yet).
		644
		645	The argument to C<max_size> will be rounded up to the next B<highest>
		646	power of two (so may be more than requested). If no argument is given, the
		647	limit check will be deactivated (same as when C<0> is specified).
		648
		649	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		650
222	=item $json_string = $json->encode ($perl_scalar)	651	=item $json_text = $json->encode ($perl_scalar)
223		652
224	Converts the given Perl data structure (a simple scalar or a reference	653	Converts the given Perl data structure (a simple scalar or a reference
225	to a hash or array) to its JSON representation. Simple scalars will be	654	to a hash or array) to its JSON representation. Simple scalars will be
226	converted into JSON string or number sequences, while references to arrays	655	converted into JSON string or number sequences, while references to arrays
227	become JSON arrays and references to hashes become JSON objects. Undefined	656	become JSON arrays and references to hashes become JSON objects. Undefined
228	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>	657	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
229	nor C<false> values will be generated.	658	nor C<false> values will be generated.
230		659
231	=item $perl_scalar = $json->decode ($json_string)	660	=item $perl_scalar = $json->decode ($json_text)
232		661
233	The opposite of C<encode>: expects a JSON string and tries to parse it,	662	The opposite of C<encode>: expects a JSON text and tries to parse it,
234	returning the resulting simple scalar or reference. Croaks on error.	663	returning the resulting simple scalar or reference. Croaks on error.
235		664
236	JSON numbers and strings become simple Perl scalars. JSON arrays become	665	JSON numbers and strings become simple Perl scalars. JSON arrays become
237	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	666	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
238	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	667	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
239		668
		669	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		670
		671	This works like the C<decode> method, but instead of raising an exception
		672	when there is trailing garbage after the first JSON object, it will
		673	silently stop parsing there and return the number of characters consumed
		674	so far.
		675
		676	This is useful if your JSON texts are not delimited by an outer protocol
		677	(which is not the brightest thing to do in the first place) and you need
		678	to know where the JSON text ends.
		679
		680	JSON::XS->new->decode_prefix ("[1] the tail")
		681	=> ([], 3)
		682
240	=back	683	=back
241		684
242	=head1 COMPARISON
243		685
244	As already mentioned, this module was created because none of the existing	686	=head1 INCREMENTAL PARSING
245	JSON modules could be made to work correctly. First I will describe the	687
246	problems (or pleasures) I encountered with various existing JSON modules,	688	[This section is still EXPERIMENTAL]
247	followed by some benchmark values. JSON::XS was designed not to suffer	689
248	from any of these problems or limitations.	690	In some cases, there is the need for incremental parsing of JSON
		691	texts. While this module always has to keep both JSON text and resulting
		692	Perl data structure in memory at one time, it does allow you to parse a
		693	JSON stream incrementally. It does so by accumulating text until it has
		694	a full JSON object, which it then can decode. This process is similar to
		695	using C<decode_prefix> to see if a full JSON object is available, but is
		696	much more efficient (JSON::XS will only attempt to parse the JSON text
		697	once it is sure it has enough text to get a decisive result, using a very
		698	simple but truly incremental parser).
		699
		700	The following two methods deal with this.
249		701
250	=over 4	702	=over 4
251		703
252	=item JSON 1.07	704	=item [void, scalar or list context] = $json->incr_parse ([$string])
253		705
254	Slow (but very portable, as it is written in pure Perl).	706	This is the central parsing function. It can both append new text and
		707	extract objects from the stream accumulated so far (both of these
		708	functions are optional).
255		709
256	Undocumented/buggy Unicode handling (how JSON handles unicode values is	710	If C<$string> is given, then this string is appended to the already
257	undocumented. One can get far by feeding it unicode strings and doing	711	existing JSON fragment stored in the C<$json> object.
258	en-/decoding oneself, but unicode escapes are not working properly).
259		712
260	No roundtripping (strings get clobbered if they look like numbers, e.g.	713	After that, if the function is called in void context, it will simply
261	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	714	return without doing anything further. This can be used to add more text
262	decode into the number 2.	715	in as many chunks as you want.
263		716
264	=item JSON::PC 0.01	717	If the method is called in scalar context, then it will try to extract
		718	exactly I<one> JSON object. If that is successful, it will return this
		719	object, otherwise it will return C<undef>. If there is a parse error,
		720	this method will croak just as C<decode> would do (one can then use
		721	C<incr_skip> to skip the errornous part). This is the most common way of
		722	using the method.
265		723
266	Very fast.	724	And finally, in list context, it will try to extract as many objects
		725	from the stream as it can find and return them, or the empty list
		726	otherwise. For this to work, there must be no separators between the JSON
		727	objects or arrays, instead they must be concatenated back-to-back. If
		728	an error occurs, an exception will be raised as in the scalar context
		729	case. Note that in this case, any previously-parsed JSON texts will be
		730	lost.
267		731
268	Undocumented/buggy Unicode handling.	732	If there is a parse
269		733
270	No roundtripping.	734	=item $lvalue_string = $json->incr_text
271		735
272	Has problems handling many Perl values (e.g. regex results and other magic	736	This method returns the currently stored JSON fragment as an lvalue, that
273	values will make it croak).	737	is, you can manipulate it. This I<only> works when a preceding call to
		738	C<incr_parse> in I<scalar context> successfully returned an object. Under
		739	all other circumstances you must not call this function (I mean it.
		740	although in simple tests it might actually work, it I<will> fail under
		741	real world conditions). As a special exception, you can also call this
		742	method before having parsed anything.
274		743
275	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	744	This function is useful in two cases: a) finding the trailing text after a
276	which is not a valid JSON string.	745	JSON object or b) parsing multiple JSON objects separated by non-JSON text
277		746	(such as commas).
278	Unmaintained (maintainer unresponsive for many months, bugs are not
279	getting fixed).
280
281	=item JSON::Syck 0.21
282
283	Very buggy (often crashes).
284
285	Very inflexible (no human-readable format supported, format pretty much
286	undocumented. I need at least a format for easy reading by humans and a
287	single-line compact format for use in a protocol, and preferably a way to
288	generate ASCII-only JSON strings).
289
290	Completely broken (and confusingly documented) Unicode handling (unicode
291	escapes are not working properly, you need to set ImplicitUnicode to
292	I<different> values on en- and decoding to get symmetric behaviour).
293
294	No roundtripping (simple cases work, but this depends on wether the scalar
295	value was used in a numeric context or not).
296
297	Dumping hashes may skip hash values depending on iterator state.
298
299	Unmaintained (maintainer unresponsive for many months, bugs are not
300	getting fixed).
301
302	Does not check input for validity (i.e. will accept non-JSON input and
303	return "something" instead of raising an exception. This is a security
304	issue: imagine two banks transfering money between each other using
305	JSON. One bank might parse a given non-JSON request and deduct money,
306	while the other might reject the transaction with a syntax error. While a
307	good protocol will at least recover, that is extra unnecessary work and
308	the transaction will still not succeed).
309
310	=item JSON::DWIW 0.04
311
312	Very fast. Very natural. Very nice.
313
314	Undocumented unicode handling (but the best of the pack. Unicode escapes
315	still don't get parsed properly).
316
317	Very inflexible.
318
319	No roundtripping.
320
321	Does not generate valid JSON (key strings are often unquoted, empty keys
322	result in nothing being output)
323
324	Does not check input for validity.
325		747
326	=back	748	=back
		749
		750	=head2 LIMITATIONS
		751
		752	All options that affect decoding are supported, except
		753	C<allow_nonref>. The reason for this is that it cannot be made to
		754	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		755	them back to back and still decode them perfectly. This does not hold true
		756	for JSON numbers, however.
		757
		758	For example, is the string C<1> a single JSON number, or is it simply the
		759	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		760	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		761	takes the conservative route and disallows this case.
		762
		763	=head2 EXAMPLES
		764
		765	Some examples will make all this clearer. First, a simple example that
		766	works similarly to C<decode_prefix>: We want to decode the JSON object at
		767	the start of a string and identify the portion after the JSON object:
		768
		769	my $text = "[1,2,3] hello";
		770
		771	my $json = new JSON::XS;
		772
		773	my $obj = $json->incr_parse ($text)
		774	or die "expected JSON object or array at beginning of string";
		775
		776	my $tail = $json->incr_text;
		777	# $tail now contains " hello"
		778
		779	Easy, isn't it?
		780
		781	Now for a more complicated example: Imagine a hypothetical protocol where
		782	you read some requests from a TCP stream, and each request is a JSON
		783	array, without any separation between them (in fact, it is often useful to
		784	use newlines as "separators", as these get interpreted as whitespace at
		785	the start of the JSON text, which makes it possible to test said protocol
		786	with C<telnet>...).
		787
		788	Here is how you'd do it (it is trivial to write this in an event-based
		789	manner):
		790
		791	my $json = new JSON::XS;
		792
		793	# read some data from the socket
		794	while (sysread $socket, my $buf, 4096) {
		795
		796	# split and decode as many requests as possible
		797	for my $request ($json->incr_parse ($buf)) {
		798	# act on the $request
		799	}
		800	}
		801
		802	Another complicated example: Assume you have a string with JSON objects
		803	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		804	[3]>). To parse them, we have to skip the commas between the JSON texts,
		805	and here is where the lvalue-ness of C<incr_text> comes in useful:
		806
		807	my $text = "[1],[2], [3]";
		808	my $json = new JSON::XS;
		809
		810	# void context, so no parsing done
		811	$json->incr_parse ($text);
		812
		813	# now extract as many objects as possible. note the
		814	# use of scalar context so incr_text can be called.
		815	while (my $obj = $json->incr_parse) {
		816	# do something with $obj
		817
		818	# now skip the optional comma
		819	$json->incr_text =~ s/^ \s* , //x;
		820	}
		821
		822	Now lets go for a very complex example: Assume that you have a gigantic
		823	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		824	but you cannot load it into memory fully (this has actually happened in
		825	the real world :).
		826
		827	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		828	can still help you: You implement a (very simple) array parser and let
		829	JSON decode the array elements, which are all full JSON objects on their
		830	own (this wouldn't work if the array elements could be JSON numbers, for
		831	example):
		832
		833	my $json = new JSON::XS;
		834
		835	# open the monster
		836	open my $fh, "<bigfile.json"
		837	or die "bigfile: $!";
		838
		839	# first parse the initial "["
		840	for (;;) {
		841	sysread $fh, my $buf, 65536
		842	or die "read error: $!";
		843	$json->incr_parse ($buf); # void context, so no parsing
		844
		845	# Exit the loop once we found and removed(!) the initial "[".
		846	# In essence, we are (ab-)using the $json object as a simple scalar
		847	# we append data to.
		848	last if $json->incr_text =~ s/^ \s* \[ //x;
		849	}
		850
		851	# now we have the skipped the initial "[", so continue
		852	# parsing all the elements.
		853	for (;;) {
		854	# in this loop we read data until we got a single JSON object
		855	for (;;) {
		856	if (my $obj = $json->incr_parse) {
		857	# do something with $obj
		858	last;
		859	}
		860
		861	# add more data
		862	sysread $fh, my $buf, 65536
		863	or die "read error: $!";
		864	$json->incr_parse ($buf); # void context, so no parsing
		865	}
		866
		867	# in this loop we read data until we either found and parsed the
		868	# separating "," between elements, or the final "]"
		869	for (;;) {
		870	# first skip whitespace
		871	$json->incr_text =~ s/^\s*//;
		872
		873	# if we find "]", we are done
		874	if ($json->incr_text =~ s/^\]//) {
		875	print "finished.\n";
		876	exit;
		877	}
		878
		879	# if we find ",", we can continue with the next element
		880	if ($json->incr_text =~ s/^,//) {
		881	last;
		882	}
		883
		884	# if we find anything else, we have a parse error!
		885	if (length $json->incr_text) {
		886	die "parse error near ", $json->incr_text;
		887	}
		888
		889	# else add more data
		890	sysread $fh, my $buf, 65536
		891	or die "read error: $!";
		892	$json->incr_parse ($buf); # void context, so no parsing
		893	}
		894
		895	This is a complex example, but most of the complexity comes from the fact
		896	that we are trying to be correct (bear with me if I am wrong, I never ran
		897	the above example :).
		898
		899
		900
		901	=head1 MAPPING
		902
		903	This section describes how JSON::XS maps Perl values to JSON values and
		904	vice versa. These mappings are designed to "do the right thing" in most
		905	circumstances automatically, preserving round-tripping characteristics
		906	(what you put in comes out as something equivalent).
		907
		908	For the more enlightened: note that in the following descriptions,
		909	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		910	refers to the abstract Perl language itself.
		911
		912
		913	=head2 JSON -> PERL
		914
		915	=over 4
		916
		917	=item object
		918
		919	A JSON object becomes a reference to a hash in Perl. No ordering of object
		920	keys is preserved (JSON does not preserve object key ordering itself).
		921
		922	=item array
		923
		924	A JSON array becomes a reference to an array in Perl.
		925
		926	=item string
		927
		928	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		929	are represented by the same codepoints in the Perl string, so no manual
		930	decoding is necessary.
		931
		932	=item number
		933
		934	A JSON number becomes either an integer, numeric (floating point) or
		935	string scalar in perl, depending on its range and any fractional parts. On
		936	the Perl level, there is no difference between those as Perl handles all
		937	the conversion details, but an integer may take slightly less memory and
		938	might represent more values exactly than floating point numbers.
		939
		940	If the number consists of digits only, JSON::XS will try to represent
		941	it as an integer value. If that fails, it will try to represent it as
		942	a numeric (floating point) value if that is possible without loss of
		943	precision. Otherwise it will preserve the number as a string value (in
		944	which case you lose roundtripping ability, as the JSON number will be
		945	re-encoded toa JSON string).
		946
		947	Numbers containing a fractional or exponential part will always be
		948	represented as numeric (floating point) values, possibly at a loss of
		949	precision (in which case you might lose perfect roundtripping ability, but
		950	the JSON number will still be re-encoded as a JSON number).
		951
		952	=item true, false
		953
		954	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
		955	respectively. They are overloaded to act almost exactly like the numbers
		956	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
		957	the C<JSON::XS::is_bool> function.
		958
		959	=item null
		960
		961	A JSON null atom becomes C<undef> in Perl.
		962
		963	=back
		964
		965
		966	=head2 PERL -> JSON
		967
		968	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		969	truly typeless language, so we can only guess which JSON type is meant by
		970	a Perl value.
		971
		972	=over 4
		973
		974	=item hash references
		975
		976	Perl hash references become JSON objects. As there is no inherent ordering
		977	in hash keys (or JSON objects), they will usually be encoded in a
		978	pseudo-random order that can change between runs of the same program but
		979	stays generally the same within a single run of a program. JSON::XS can
		980	optionally sort the hash keys (determined by the I<canonical> flag), so
		981	the same datastructure will serialise to the same JSON text (given same
		982	settings and version of JSON::XS), but this incurs a runtime overhead
		983	and is only rarely useful, e.g. when you want to compare some JSON text
		984	against another for equality.
		985
		986	=item array references
		987
		988	Perl array references become JSON arrays.
		989
		990	=item other references
		991
		992	Other unblessed references are generally not allowed and will cause an
		993	exception to be thrown, except for references to the integers C<0> and
		994	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		995	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		996
		997	encode_json [\0,JSON::XS::true] # yields [false,true]
		998
		999	=item JSON::XS::true, JSON::XS::false
		1000
		1001	These special values become JSON true and JSON false values,
		1002	respectively. You can also use C<\1> and C<\0> directly if you want.
		1003
		1004	=item blessed objects
		1005
		1006	Blessed objects are not directly representable in JSON. See the
		1007	C<allow_blessed> and C<convert_blessed> methods on various options on
		1008	how to deal with this: basically, you can choose between throwing an
		1009	exception, encoding the reference as if it weren't blessed, or provide
		1010	your own serialiser method.
		1011
		1012	=item simple scalars
		1013
		1014	Simple Perl scalars (any scalar that is not a reference) are the most
		1015	difficult objects to encode: JSON::XS will encode undefined scalars as
		1016	JSON C<null> values, scalars that have last been used in a string context
		1017	before encoding as JSON strings, and anything else as number value:
		1018
		1019	# dump as number
		1020	encode_json [2] # yields [2]
		1021	encode_json [-3.0e17] # yields [-3e+17]
		1022	my $value = 5; encode_json [$value] # yields [5]
		1023
		1024	# used as string, so dump as string
		1025	print $value;
		1026	encode_json [$value] # yields ["5"]
		1027
		1028	# undef becomes null
		1029	encode_json [undef] # yields [null]
		1030
		1031	You can force the type to be a JSON string by stringifying it:
		1032
		1033	my $x = 3.1; # some variable containing a number
		1034	"$x"; # stringified
		1035	$x .= ""; # another, more awkward way to stringify
		1036	print $x; # perl does it for you, too, quite often
		1037
		1038	You can force the type to be a JSON number by numifying it:
		1039
		1040	my $x = "3"; # some variable containing a string
		1041	$x += 0; # numify it, ensuring it will be dumped as a number
		1042	$x *= 1; # same thing, the choice is yours.
		1043
		1044	You can not currently force the type in other, less obscure, ways. Tell me
		1045	if you need this capability (but don't forget to explain why it's needed
		1046	:).
		1047
		1048	=back
		1049
		1050
		1051	=head1 ENCODING/CODESET FLAG NOTES
		1052
		1053	The interested reader might have seen a number of flags that signify
		1054	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1055	some confusion on what these do, so here is a short comparison:
		1056
		1057	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1058	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1059	control whether C<encode> escapes character values outside their respective
		1060	codeset range. Neither of these flags conflict with each other, although
		1061	some combinations make less sense than others.
		1062
		1063	Care has been taken to make all flags symmetrical with respect to
		1064	C<encode> and C<decode>, that is, texts encoded with any combination of
		1065	these flag values will be correctly decoded when the same flags are used
		1066	- in general, if you use different flag settings while encoding vs. when
		1067	decoding you likely have a bug somewhere.
		1068
		1069	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1070	simply an abstract set of character-codepoint pairs, while an encoding
		1071	takes those codepoint numbers and I<encodes> them, in our case into
		1072	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1073	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1074	the same time, which can be confusing.
		1075
		1076	=over 4
		1077
		1078	=item C<utf8> flag disabled
		1079
		1080	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1081	and expect Unicode strings, that is, characters with high ordinal Unicode
		1082	values (> 255) will be encoded as such characters, and likewise such
		1083	characters are decoded as-is, no canges to them will be done, except
		1084	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1085	respectively (to Perl, these are the same thing in strings unless you do
		1086	funny/weird/dumb stuff).
		1087
		1088	This is useful when you want to do the encoding yourself (e.g. when you
		1089	want to have UTF-16 encoded JSON texts) or when some other layer does
		1090	the encoding for you (for example, when printing to a terminal using a
		1091	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1092	to UTF-8 encode your data first and have Perl encode it another time).
		1093
		1094	=item C<utf8> flag enabled
		1095
		1096	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1097	characters using the corresponding UTF-8 multi-byte sequence, and will
		1098	expect your input strings to be encoded as UTF-8, that is, no "character"
		1099	of the input string must have any value > 255, as UTF-8 does not allow
		1100	that.
		1101
		1102	The C<utf8> flag therefore switches between two modes: disabled means you
		1103	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1104	octet/binary string in Perl.
		1105
		1106	=item C<latin1> or C<ascii> flags enabled
		1107
		1108	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1109	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1110	characters as specified by the C<utf8> flag.
		1111
		1112	If C<utf8> is disabled, then the result is also correctly encoded in those
		1113	character sets (as both are proper subsets of Unicode, meaning that a
		1114	Unicode string with all character values < 256 is the same thing as a
		1115	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1116	the same thing as an ASCII string in Perl).
		1117
		1118	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1119	regardless of these flags, just some more characters will be escaped using
		1120	C<\uXXXX> then before.
		1121
		1122	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1123	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1124	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1125	a subset of Unicode), while ASCII is.
		1126
		1127	Surprisingly, C<decode> will ignore these flags and so treat all input
		1128	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1129	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1130	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1131
		1132	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1133	they only govern when the JSON output engine escapes a character or not.
		1134
		1135	The main use for C<latin1> is to relatively efficiently store binary data
		1136	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1137
		1138	The main use for C<ascii> is to force the output to not contain characters
		1139	with values > 127, which means you can interpret the resulting string
		1140	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1141	8-bit-encoding, and still get the same data structure back. This is useful
		1142	when your channel for JSON transfer is not 8-bit clean or the encoding
		1143	might be mangled in between (e.g. in mail), and works because ASCII is a
		1144	proper subset of most 8-bit and multibyte encodings in use in the world.
		1145
		1146	=back
		1147
		1148
		1149	=head2 JSON and YAML
		1150
		1151	You often hear that JSON is a subset of YAML. This is, however, a mass
		1152	hysteria(*) and very far from the truth (as of the time of this writing),
		1153	so let me state it clearly: I<in general, there is no way to configure
		1154	JSON::XS to output a data structure as valid YAML> that works in all
		1155	cases.
		1156
		1157	If you really must use JSON::XS to generate YAML, you should use this
		1158	algorithm (subject to change in future versions):
		1159
		1160	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1161	my $yaml = $to_yaml->encode ($ref) . "\n";
		1162
		1163	This will I<usually> generate JSON texts that also parse as valid
		1164	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1165	lengths that JSON doesn't have and also has different and incompatible
		1166	unicode handling, so you should make sure that your hash keys are
		1167	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1168	you do not have characters with codepoint values outside the Unicode BMP
		1169	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1170	strings (which JSON::XS does not I<currently> generate, but other JSON
		1171	generators might).
		1172
		1173	There might be other incompatibilities that I am not aware of (or the YAML
		1174	specification has been changed yet again - it does so quite often). In
		1175	general you should not try to generate YAML with a JSON generator or vice
		1176	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1177	high that you will run into severe interoperability problems when you
		1178	least expect it.
		1179
		1180	=over 4
		1181
		1182	=item (*)
		1183
		1184	I have been pressured multiple times by Brian Ingerson (one of the
		1185	authors of the YAML specification) to remove this paragraph, despite him
		1186	acknowledging that the actual incompatibilities exist. As I was personally
		1187	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1188	educate people about these issues, so others do not run into the same
		1189	problem again and again. After this, Brian called me a (quote)I<complete
		1190	and worthless idiot>(unquote).
		1191
		1192	In my opinion, instead of pressuring and insulting people who actually
		1193	clarify issues with YAML and the wrong statements of some of its
		1194	proponents, I would kindly suggest reading the JSON spec (which is not
		1195	that difficult or long) and finally make YAML compatible to it, and
		1196	educating users about the changes, instead of spreading lies about the
		1197	real compatibility for many I<years> and trying to silence people who
		1198	point out that it isn't true.
		1199
		1200	=back
		1201
327		1202
328	=head2 SPEED	1203	=head2 SPEED
329		1204
330	It seems that JSON::XS is surprisingly fast, as shown in the following	1205	It seems that JSON::XS is surprisingly fast, as shown in the following
331	tables. They have been generated with the help of the C<eg/bench> program	1206	tables. They have been generated with the help of the C<eg/bench> program
332	in the JSON::XS distribution, to make it easy to compare on your own	1207	in the JSON::XS distribution, to make it easy to compare on your own
333	system.	1208	system.
334		1209
335	First is a comparison between various modules using a very simple JSON	1210	First comes a comparison between various modules using
		1211	a very short single-line JSON string (also available at
		1212	L<http://dist.schmorp.de/misc/json/short.json>).
		1213
		1214	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
		1215	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
		1216
336	string, showing the number of encodes/decodes per second (JSON::XS is	1217	It shows the number of encodes/decodes per second (JSON::XS uses
337	the functional interface, while JSON::XS/2 is the OO interface with	1218	the functional interface, while JSON::XS/2 uses the OO interface
338	pretty-printing and hashkey sorting enabled).	1219	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1220	shrink). Higher is better:
339		1221
340	module | encode | decode |	1222	module | encode | decode |
341	-----------|------------|------------|	1223	-----------|------------|------------|
342	JSON | 14006 | 6820 |	1224	JSON 1.x | 4990.842 | 4088.813 |
343	JSON::DWIW | 200937 | 120386 |	1225	JSON::DWIW | 51653.990 | 71575.154 |
344	JSON::PC | 85065 | 129366 |	1226	JSON::PC | 65948.176 | 74631.744 |
345	JSON::Syck | 59898 | 44232 |	1227	JSON::PP | 8931.652 | 3817.168 |
346	JSON::XS | 1171478 | 342435 |	1228	JSON::Syck | 24877.248 | 27776.848 |
347	JSON::XS/2 | 730760 | 328714 |	1229	JSON::XS | 388361.481 | 227951.304 |
		1230	JSON::XS/2 | 227951.304 | 218453.333 |
		1231	JSON::XS/3 | 338250.323 | 218453.333 |
		1232	Storable | 16500.016 | 135300.129 |
348	-----------+------------+------------+	1233	-----------+------------+------------+
349		1234
350	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1235	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
		1236	about three times faster on decoding, and over forty times faster
351	times faster than JSON, even with pretty-printing and key sorting.	1237	than JSON, even with pretty-printing and key sorting. It also compares
		1238	favourably to Storable for small amounts of data.
352		1239
353	Using a longer test string (roughly 8KB, generated from Yahoo! Locals	1240	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
354	search API (http://nanoref.com/yahooapis/mgPdGg):	1241	search API (L<http://dist.schmorp.de/misc/json/long.json>).
355		1242
356	module | encode | decode |	1243	module | encode | decode |
357	-----------|------------|------------|	1244	-----------|------------|------------|
358	JSON | 673 | 38 |	1245	JSON 1.x | 55.260 | 34.971 |
359	JSON::DWIW | 5271 | 770 |	1246	JSON::DWIW | 825.228 | 1082.513 |
360	JSON::PC | 9901 | 2491 |	1247	JSON::PC | 3571.444 | 2394.829 |
361	JSON::Syck | 2360 | 786 |	1248	JSON::PP | 210.987 | 32.574 |
362	JSON::XS | 37398 | 3202 |	1249	JSON::Syck | 552.551 | 787.544 |
363	JSON::XS/2 | 13765 | 3153 |	1250	JSON::XS | 5780.463 | 4854.519 |
		1251	JSON::XS/2 | 3869.998 | 4798.975 |
		1252	JSON::XS/3 | 5862.880 | 4798.975 |
		1253	Storable | 4445.002 | 5235.027 |
364	-----------+------------+------------+	1254	-----------+------------+------------+
365		1255
366	Again, JSON::XS leads by far in the encoding case, while still beating	1256	Again, JSON::XS leads by far (except for Storable which non-surprisingly
367	every other module in the decoding case.	1257	decodes faster).
368		1258
369	Last example is an almost 8MB large hash with many large binary values	1259	On large strings containing lots of high Unicode characters, some modules
370	(PNG files), resulting in a lot of escaping:	1260	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1261	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1262	to decode or encode properly, so it was impossible to prepare a fair
		1263	comparison table for that case.
		1264
		1265
		1266	=head1 SECURITY CONSIDERATIONS
		1267
		1268	When you are using JSON in a protocol, talking to untrusted potentially
		1269	hostile creatures requires relatively few measures.
		1270
		1271	First of all, your JSON decoder should be secure, that is, should not have
		1272	any buffer overflows. Obviously, this module should ensure that and I am
		1273	trying hard on making that true, but you never know.
		1274
		1275	Second, you need to avoid resource-starving attacks. That means you should
		1276	limit the size of JSON texts you accept, or make sure then when your
		1277	resources run out, that's just fine (e.g. by using a separate process that
		1278	can crash safely). The size of a JSON text in octets or characters is
		1279	usually a good indication of the size of the resources required to decode
		1280	it into a Perl structure. While JSON::XS can check the size of the JSON
		1281	text, it might be too late when you already have it in memory, so you
		1282	might want to check the size before you accept the string.
		1283
		1284	Third, JSON::XS recurses using the C stack when decoding objects and
		1285	arrays. The C stack is a limited resource: for instance, on my amd64
		1286	machine with 8MB of stack size I can decode around 180k nested arrays but
		1287	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1288	to free the temporary). If that is exceeded, the program crashes. To be
		1289	conservative, the default nesting limit is set to 512. If your process
		1290	has a smaller stack, you should adjust this setting accordingly with the
		1291	C<max_depth> method.
		1292
		1293	Something else could bomb you, too, that I forgot to think of. In that
		1294	case, you get to keep the pieces. I am always open for hints, though...
		1295
		1296	Also keep in mind that JSON::XS might leak contents of your Perl data
		1297	structures in its error messages, so when you serialise sensitive
		1298	information you might want to make sure that exceptions thrown by JSON::XS
		1299	will not end up in front of untrusted eyes.
		1300
		1301	If you are using JSON::XS to return packets to consumption
		1302	by JavaScript scripts in a browser you should have a look at
		1303	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1304	you are vulnerable to some common attack vectors (which really are browser
		1305	design bugs, but it is still you who will have to deal with it, as major
		1306	browser developers care only for features, not about getting security
		1307	right).
		1308
		1309
		1310	=head1 THREADS
		1311
		1312	This module is I<not> guaranteed to be thread safe and there are no
		1313	plans to change this until Perl gets thread support (as opposed to the
		1314	horribly slow so-called "threads" which are simply slow and bloated
		1315	process simulations - use fork, it's I<much> faster, cheaper, better).
		1316
		1317	(It might actually work, but you have been warned).
		1318
371		1319
372	=head1 BUGS	1320	=head1 BUGS
373		1321
374	While the goal of this module is to be correct, that unfortunately does	1322	While the goal of this module is to be correct, that unfortunately does
375	not mean its bug-free, only that I think its design is bug-free. It is	1323	not mean it's bug-free, only that I think its design is bug-free. It is
376	still very young and not well-tested. If you keep reporting bugs they will	1324	still relatively early in its development. If you keep reporting bugs they
377	be fixed swiftly, though.	1325	will be fixed swiftly, though.
		1326
		1327	Please refrain from using rt.cpan.org or any other bug reporting
		1328	service. I put the contact address into my modules for a reason.
378		1329
379	=cut	1330	=cut
380		1331
		1332	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1333	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1334
		1335	sub true() { $true }
		1336	sub false() { $false }
		1337
		1338	sub is_bool($) {
		1339	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1340	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1341	}
		1342
		1343	XSLoader::load "JSON::XS", $VERSION;
		1344
		1345	package JSON::XS::Boolean;
		1346
		1347	use overload
		1348	"0+" => sub { ${$_[0]} },
		1349	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1350	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1351	fallback => 1;
		1352
381	1;	1353	1;
		1354
		1355	=head1 SEE ALSO
		1356
		1357	The F<json_xs> command line utility for quick experiments.
382		1358
383	=head1 AUTHOR	1359	=head1 AUTHOR
384		1360
385	Marc Lehmann <schmorp@schmorp.de>	1361	Marc Lehmann <schmorp@schmorp.de>
386	http://home.schmorp.de/	1362	http://home.schmorp.de/

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