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Revision 1.2 by root, Thu Mar 22 17:28:50 2007 UTC vs.
Revision 1.110 by root, Sun Jul 20 17:55:19 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;
		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	overridden) with no overhead due to emulation (by inheriting constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
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 data types 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 object
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	no warnings;
64	$VERSION = '0.1';	107	use strict;
		108
		109	our $VERSION = '2.2222';
65	@ISA = qw(Exporter);	110	our @ISA = qw(Exporter);
66		111
67	@EXPORT = qw(to_json from_json);	112	our @EXPORT = qw(encode_json decode_json to_json from_json);
68	require Exporter;
69		113
		114	sub to_json($) {
70	require XSLoader;	115	require Carp;
71	XSLoader::load JSON::XS::, $VERSION;	116	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
72	}	117	}
73		118
		119	sub from_json($) {
		120	require Carp;
		121	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");
		122	}
		123
		124	use Exporter;
		125	use XSLoader;
		126
74	=head1 FUNCTIONAL INTERFACE	127	=head1 FUNCTIONAL INTERFACE
75		128
76	The following convinience methods are provided by this module. They are	129	The following convenience methods are provided by this module. They are
77	exported by default:	130	exported by default:
78		131
79	=over 4	132	=over 4
80		133
81	=item $json_string = to_json $perl_scalar	134	=item $json_text = encode_json $perl_scalar
82		135
83	Converts the given Perl data structure (a simple scalar or a reference to	136	Converts the given Perl data structure to a UTF-8 encoded, binary string
84	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	137	(that is, the string contains octets only). Croaks on error.
85	octets only). Croaks on error.
86		138
87	This function call is functionally identical to C<< JSON::XS->new->utf8	139	This function call is functionally identical to:
88	(1)->encode ($perl_scalar) >>.
89		140
		141	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		142
		143	Except being faster.
		144
90	=item $perl_scalar = from_json $json_string	145	=item $perl_scalar = decode_json $json_text
91		146
92	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	147	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
93	parse that as an UTF-8 encoded JSON string, returning the resulting simple	148	to parse that as an UTF-8 encoded JSON text, returning the resulting
94	scalar or reference. Croaks on error.	149	reference. Croaks on error.
95		150
96	This function call is functionally identical to C<< JSON::XS->new->utf8	151	This function call is functionally identical to:
97	(1)->decode ($json_string) >>.	152
		153	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		154
		155	Except being faster.
		156
		157	=item $is_boolean = JSON::XS::is_bool $scalar
		158
		159	Returns true if the passed scalar represents either JSON::XS::true or
		160	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		161	and are used to represent JSON C<true> and C<false> values in Perl.
		162
		163	See MAPPING, below, for more information on how JSON values are mapped to
		164	Perl.
98		165
99	=back	166	=back
		167
		168
		169	=head1 A FEW NOTES ON UNICODE AND PERL
		170
		171	Since this often leads to confusion, here are a few very clear words on
		172	how Unicode works in Perl, modulo bugs.
		173
		174	=over 4
		175
		176	=item 1. Perl strings can store characters with ordinal values > 255.
		177
		178	This enables you to store Unicode characters as single characters in a
		179	Perl string - very natural.
		180
		181	=item 2. Perl does I<not> associate an encoding with your strings.
		182
		183	... until you force it to, e.g. when matching it against a regex, or
		184	printing the scalar to a file, in which case Perl either interprets your
		185	string as locale-encoded text, octets/binary, or as Unicode, depending
		186	on various settings. In no case is an encoding stored together with your
		187	data, it is I<use> that decides encoding, not any magical meta data.
		188
		189	=item 3. The internal utf-8 flag has no meaning with regards to the
		190	encoding of your string.
		191
		192	Just ignore that flag unless you debug a Perl bug, a module written in
		193	XS or want to dive into the internals of perl. Otherwise it will only
		194	confuse you, as, despite the name, it says nothing about how your string
		195	is encoded. You can have Unicode strings with that flag set, with that
		196	flag clear, and you can have binary data with that flag set and that flag
		197	clear. Other possibilities exist, too.
		198
		199	If you didn't know about that flag, just the better, pretend it doesn't
		200	exist.
		201
		202	=item 4. A "Unicode String" is simply a string where each character can be
		203	validly interpreted as a Unicode code point.
		204
		205	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		206	Unicode string encoded in UTF-8, giving you a binary string.
		207
		208	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		209
		210	It's a fact. Learn to live with it.
		211
		212	=back
		213
		214	I hope this helps :)
		215
100		216
101	=head1 OBJECT-ORIENTED INTERFACE	217	=head1 OBJECT-ORIENTED INTERFACE
102		218
103	The object oriented interface lets you configure your own encoding or	219	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	220	decoding style, within the limits of supported formats.
…		…
111	strings. All boolean flags described below are by default I<disabled>.	227	strings. All boolean flags described below are by default I<disabled>.
112		228
113	The mutators for flags all return the JSON object again and thus calls can	229	The mutators for flags all return the JSON object again and thus calls can
114	be chained:	230	be chained:
115		231
116	my $json = JSON::XS->new->utf8(1)->pretty(1)->encode ({a => [1,2]})	232	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
117	=> {"a" : [1, 2]}	233	=> {"a": [1, 2]}
118		234
119	=item $json = $json->ascii ($enable)	235	=item $json = $json->ascii ([$enable])
120		236
		237	=item $enabled = $json->get_ascii
		238
121	If C<$enable> is true, then the C<encode> method will not generate	239	If C<$enable> is true (or missing), then the C<encode> method will not
122	characters outside the code range C<0..127>. Any unicode characters	240	generate characters outside the code range C<0..127> (which is ASCII). Any
123	outside that range will be escaped using either a single \uXXXX (BMP	241	Unicode characters outside that range will be escaped using either a
124	characters) or a double \uHHHH\uLLLLL escape sequence, as per RFC4627.	242	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
		243	as per RFC4627. The resulting encoded JSON text can be treated as a native
		244	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		245	or any other superset of ASCII.
125		246
126	If C<$enable> is false, then the C<encode> method will not escape Unicode	247	If C<$enable> is false, then the C<encode> method will not escape Unicode
127	characters unless necessary.	248	characters unless required by the JSON syntax or other flags. This results
		249	in a faster and more compact format.
128		250
		251	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		252	document.
		253
		254	The main use for this flag is to produce JSON texts that can be
		255	transmitted over a 7-bit channel, as the encoded JSON texts will not
		256	contain any 8 bit characters.
		257
		258	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
		259	=> ["\ud801\udc01"]
		260
		261	=item $json = $json->latin1 ([$enable])
		262
		263	=item $enabled = $json->get_latin1
		264
		265	If C<$enable> is true (or missing), then the C<encode> method will encode
		266	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		267	outside the code range C<0..255>. The resulting string can be treated as a
		268	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		269	will not be affected in any way by this flag, as C<decode> by default
		270	expects Unicode, which is a strict superset of latin1.
		271
		272	If C<$enable> is false, then the C<encode> method will not escape Unicode
		273	characters unless required by the JSON syntax or other flags.
		274
		275	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		276	document.
		277
		278	The main use for this flag is efficiently encoding binary data as JSON
		279	text, as most octets will not be escaped, resulting in a smaller encoded
		280	size. The disadvantage is that the resulting JSON text is encoded
		281	in latin1 (and must correctly be treated as such when storing and
		282	transferring), a rare encoding for JSON. It is therefore most useful when
		283	you want to store data structures known to contain binary data efficiently
		284	in files or databases, not when talking to other JSON encoders/decoders.
		285
		286	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		287	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
		288
129	=item $json = $json->utf8 ($enable)	289	=item $json = $json->utf8 ([$enable])
130		290
		291	=item $enabled = $json->get_utf8
		292
131	If C<$enable> is true, then the C<encode> method will encode the JSON	293	If C<$enable> is true (or missing), then the C<encode> method will encode
132	string into UTF-8, as required by many protocols, while the C<decode>	294	the JSON result into UTF-8, as required by many protocols, while the
133	method expects to be handled an UTF-8-encoded string. Please note that	295	C<decode> method expects to be handled an UTF-8-encoded string. Please
134	UTF-8-encoded strings do not contain any characters outside the range	296	note that UTF-8-encoded strings do not contain any characters outside the
135	C<0..255>, they are thus useful for bytewise/binary I/O.	297	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		298	versions, enabling this option might enable autodetection of the UTF-16
		299	and UTF-32 encoding families, as described in RFC4627.
136		300
137	If C<$enable> is false, then the C<encode> method will return the JSON	301	If C<$enable> is false, then the C<encode> method will return the JSON
138	string as a (non-encoded) unicode string, while C<decode> expects thus a	302	string as a (non-encoded) Unicode string, while C<decode> expects thus a
139	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	303	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
140	to be done yourself, e.g. using the Encode module.	304	to be done yourself, e.g. using the Encode module.
141		305
		306	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		307	document.
		308
		309	Example, output UTF-16BE-encoded JSON:
		310
		311	use Encode;
		312	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		313
		314	Example, decode UTF-32LE-encoded JSON:
		315
		316	use Encode;
		317	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
		318
142	=item $json = $json->pretty ($enabla)	319	=item $json = $json->pretty ([$enable])
143		320
144	This enables (or disables) all of the C<indent>, C<space_before> and	321	This enables (or disables) all of the C<indent>, C<space_before> and
145	C<space_after> (and in the future possibly more) settings in one call to	322	C<space_after> (and in the future possibly more) flags in one call to
146	generate the most readable (or most compact) form possible.	323	generate the most readable (or most compact) form possible.
147		324
		325	Example, pretty-print some simple structure:
		326
		327	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
		328	=>
		329	{
		330	"a" : [
		331	1,
		332	2
		333	]
		334	}
		335
148	=item $json = $json->indent ($enable)	336	=item $json = $json->indent ([$enable])
149		337
		338	=item $enabled = $json->get_indent
		339
150	If C<$enable> is true, then the C<encode> method will use a multiline	340	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
151	format as output, putting every array member or object/hash key-value pair	341	format as output, putting every array member or object/hash key-value pair
152	into its own line, identing them properly.	342	into its own line, indenting them properly.
153		343
154	If C<$enable> is false, no newlines or indenting will be produced, and the	344	If C<$enable> is false, no newlines or indenting will be produced, and the
155	resulting JSON strings is guarenteed not to contain any C<newlines>.	345	resulting JSON text is guaranteed not to contain any C<newlines>.
156		346
157	This setting has no effect when decoding JSON strings.	347	This setting has no effect when decoding JSON texts.
158		348
159	=item $json = $json->space_before ($enable)	349	=item $json = $json->space_before ([$enable])
160		350
		351	=item $enabled = $json->get_space_before
		352
161	If C<$enable> is true, then the C<encode> method will add an extra	353	If C<$enable> is true (or missing), then the C<encode> method will add an extra
162	optional space before the C<:> separating keys from values in JSON objects.	354	optional space before the C<:> separating keys from values in JSON objects.
163		355
164	If C<$enable> is false, then the C<encode> method will not add any extra	356	If C<$enable> is false, then the C<encode> method will not add any extra
165	space at those places.	357	space at those places.
166		358
167	This setting has no effect when decoding JSON strings. You will also most	359	This setting has no effect when decoding JSON texts. You will also
168	likely combine this setting with C<space_after>.	360	most likely combine this setting with C<space_after>.
169		361
		362	Example, space_before enabled, space_after and indent disabled:
		363
		364	{"key" :"value"}
		365
170	=item $json = $json->space_after ($enable)	366	=item $json = $json->space_after ([$enable])
171		367
		368	=item $enabled = $json->get_space_after
		369
172	If C<$enable> is true, then the C<encode> method will add an extra	370	If C<$enable> is true (or missing), then the C<encode> method will add an extra
173	optional space after the C<:> separating keys from values in JSON objects	371	optional space after the C<:> separating keys from values in JSON objects
174	and extra whitespace after the C<,> separating key-value pairs and array	372	and extra whitespace after the C<,> separating key-value pairs and array
175	members.	373	members.
176		374
177	If C<$enable> is false, then the C<encode> method will not add any extra	375	If C<$enable> is false, then the C<encode> method will not add any extra
178	space at those places.	376	space at those places.
179		377
180	This setting has no effect when decoding JSON strings.	378	This setting has no effect when decoding JSON texts.
181		379
		380	Example, space_before and indent disabled, space_after enabled:
		381
		382	{"key": "value"}
		383
		384	=item $json = $json->relaxed ([$enable])
		385
		386	=item $enabled = $json->get_relaxed
		387
		388	If C<$enable> is true (or missing), then C<decode> will accept some
		389	extensions to normal JSON syntax (see below). C<encode> will not be
		390	affected in anyway. I<Be aware that this option makes you accept invalid
		391	JSON texts as if they were valid!>. I suggest only to use this option to
		392	parse application-specific files written by humans (configuration files,
		393	resource files etc.)
		394
		395	If C<$enable> is false (the default), then C<decode> will only accept
		396	valid JSON texts.
		397
		398	Currently accepted extensions are:
		399
		400	=over 4
		401
		402	=item * list items can have an end-comma
		403
		404	JSON I<separates> array elements and key-value pairs with commas. This
		405	can be annoying if you write JSON texts manually and want to be able to
		406	quickly append elements, so this extension accepts comma at the end of
		407	such items not just between them:
		408
		409	[
		410	1,
		411	2, <- this comma not normally allowed
		412	]
		413	{
		414	"k1": "v1",
		415	"k2": "v2", <- this comma not normally allowed
		416	}
		417
		418	=item * shell-style '#'-comments
		419
		420	Whenever JSON allows whitespace, shell-style comments are additionally
		421	allowed. They are terminated by the first carriage-return or line-feed
		422	character, after which more white-space and comments are allowed.
		423
		424	[
		425	1, # this comment not allowed in JSON
		426	# neither this one...
		427	]
		428
		429	=back
		430
182	=item $json = $json->canonical ($enable)	431	=item $json = $json->canonical ([$enable])
183		432
		433	=item $enabled = $json->get_canonical
		434
184	If C<$enable> is true, then the C<encode> method will output JSON objects	435	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
185	by sorting their keys. This is adding a comparatively high overhead.	436	by sorting their keys. This is adding a comparatively high overhead.
186		437
187	If C<$enable> is false, then the C<encode> method will output key-value	438	If C<$enable> is false, then the C<encode> method will output key-value
188	pairs in the order Perl stores them (which will likely change between runs	439	pairs in the order Perl stores them (which will likely change between runs
189	of the same script).	440	of the same script).
190		441
191	This option is useful if you want the same data structure to be encoded as	442	This option is useful if you want the same data structure to be encoded as
192	the same JSON string (given the same overall settings). If it is disabled,	443	the same JSON text (given the same overall settings). If it is disabled,
193	the same hash migh be encoded differently even if contains the same data,	444	the same hash might be encoded differently even if contains the same data,
194	as key-value pairs have no inherent ordering in Perl.	445	as key-value pairs have no inherent ordering in Perl.
195		446
196	This setting has no effect when decoding JSON strings.	447	This setting has no effect when decoding JSON texts.
197		448
		449	=item $json = $json->allow_nonref ([$enable])
		450
		451	=item $enabled = $json->get_allow_nonref
		452
		453	If C<$enable> is true (or missing), then the C<encode> method can convert a
		454	non-reference into its corresponding string, number or null JSON value,
		455	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
		456	values instead of croaking.
		457
		458	If C<$enable> is false, then the C<encode> method will croak if it isn't
		459	passed an arrayref or hashref, as JSON texts must either be an object
		460	or array. Likewise, C<decode> will croak if given something that is not a
		461	JSON object or array.
		462
		463	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
		464	resulting in an invalid JSON text:
		465
		466	JSON::XS->new->allow_nonref->encode ("Hello, World!")
		467	=> "Hello, World!"
		468
		469	=item $json = $json->allow_unknown ([$enable])
		470
		471	=item $enabled = $json->get_allow_unknown
		472
		473	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		474	exception when it encounters values it cannot represent in JSON (for
		475	example, filehandles) but instead will encode a JSON C<null> value. Note
		476	that blessed objects are not included here and are handled separately by
		477	c<allow_nonref>.
		478
		479	If C<$enable> is false (the default), then C<encode> will throw an
		480	exception when it encounters anything it cannot encode as JSON.
		481
		482	This option does not affect C<decode> in any way, and it is recommended to
		483	leave it off unless you know your communications partner.
		484
		485	=item $json = $json->allow_blessed ([$enable])
		486
		487	=item $enabled = $json->get_allow_blessed
		488
		489	If C<$enable> is true (or missing), then the C<encode> method will not
		490	barf when it encounters a blessed reference. Instead, the value of the
		491	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		492	disabled or no C<TO_JSON> method found) or a representation of the
		493	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		494	encoded. Has no effect on C<decode>.
		495
		496	If C<$enable> is false (the default), then C<encode> will throw an
		497	exception when it encounters a blessed object.
		498
		499	=item $json = $json->convert_blessed ([$enable])
		500
		501	=item $enabled = $json->get_convert_blessed
		502
		503	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		504	blessed object, will check for the availability of the C<TO_JSON> method
		505	on the object's class. If found, it will be called in scalar context
		506	and the resulting scalar will be encoded instead of the object. If no
		507	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		508	to do.
		509
		510	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		511	returns other blessed objects, those will be handled in the same
		512	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		513	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		514	methods called by the Perl core (== not by the user of the object) are
		515	usually in upper case letters and to avoid collisions with any C<to_json>
		516	function or method.
		517
		518	This setting does not yet influence C<decode> in any way, but in the
		519	future, global hooks might get installed that influence C<decode> and are
		520	enabled by this setting.
		521
		522	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		523	to do when a blessed object is found.
		524
		525	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		526
		527	When C<$coderef> is specified, it will be called from C<decode> each
		528	time it decodes a JSON object. The only argument is a reference to the
		529	newly-created hash. If the code references returns a single scalar (which
		530	need not be a reference), this value (i.e. a copy of that scalar to avoid
		531	aliasing) is inserted into the deserialised data structure. If it returns
		532	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		533	original deserialised hash will be inserted. This setting can slow down
		534	decoding considerably.
		535
		536	When C<$coderef> is omitted or undefined, any existing callback will
		537	be removed and C<decode> will not change the deserialised hash in any
		538	way.
		539
		540	Example, convert all JSON objects into the integer 5:
		541
		542	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		543	# returns [5]
		544	$js->decode ('[{}]')
		545	# throw an exception because allow_nonref is not enabled
		546	# so a lone 5 is not allowed.
		547	$js->decode ('{"a":1, "b":2}');
		548
		549	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		550
		551	Works remotely similar to C<filter_json_object>, but is only called for
		552	JSON objects having a single key named C<$key>.
		553
		554	This C<$coderef> is called before the one specified via
		555	C<filter_json_object>, if any. It gets passed the single value in the JSON
		556	object. If it returns a single value, it will be inserted into the data
		557	structure. If it returns nothing (not even C<undef> but the empty list),
		558	the callback from C<filter_json_object> will be called next, as if no
		559	single-key callback were specified.
		560
		561	If C<$coderef> is omitted or undefined, the corresponding callback will be
		562	disabled. There can only ever be one callback for a given key.
		563
		564	As this callback gets called less often then the C<filter_json_object>
		565	one, decoding speed will not usually suffer as much. Therefore, single-key
		566	objects make excellent targets to serialise Perl objects into, especially
		567	as single-key JSON objects are as close to the type-tagged value concept
		568	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		569	support this in any way, so you need to make sure your data never looks
		570	like a serialised Perl hash.
		571
		572	Typical names for the single object key are C<__class_whatever__>, or
		573	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		574	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		575	with real hashes.
		576
		577	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		578	into the corresponding C<< $WIDGET{<id>} >> object:
		579
		580	# return whatever is in $WIDGET{5}:
		581	JSON::XS
		582	->new
		583	->filter_json_single_key_object (__widget__ => sub {
		584	$WIDGET{ $_[0] }
		585	})
		586	->decode ('{"__widget__": 5')
		587
		588	# this can be used with a TO_JSON method in some "widget" class
		589	# for serialisation to json:
		590	sub WidgetBase::TO_JSON {
		591	my ($self) = @_;
		592
		593	unless ($self->{id}) {
		594	$self->{id} = ..get..some..id..;
		595	$WIDGET{$self->{id}} = $self;
		596	}
		597
		598	{ __widget__ => $self->{id} }
		599	}
		600
		601	=item $json = $json->shrink ([$enable])
		602
		603	=item $enabled = $json->get_shrink
		604
		605	Perl usually over-allocates memory a bit when allocating space for
		606	strings. This flag optionally resizes strings generated by either
		607	C<encode> or C<decode> to their minimum size possible. This can save
		608	memory when your JSON texts are either very very long or you have many
		609	short strings. It will also try to downgrade any strings to octet-form
		610	if possible: perl stores strings internally either in an encoding called
		611	UTF-X or in octet-form. The latter cannot store everything but uses less
		612	space in general (and some buggy Perl or C code might even rely on that
		613	internal representation being used).
		614
		615	The actual definition of what shrink does might change in future versions,
		616	but it will always try to save space at the expense of time.
		617
		618	If C<$enable> is true (or missing), the string returned by C<encode> will
		619	be shrunk-to-fit, while all strings generated by C<decode> will also be
		620	shrunk-to-fit.
		621
		622	If C<$enable> is false, then the normal perl allocation algorithms are used.
		623	If you work with your data, then this is likely to be faster.
		624
		625	In the future, this setting might control other things, such as converting
		626	strings that look like integers or floats into integers or floats
		627	internally (there is no difference on the Perl level), saving space.
		628
		629	=item $json = $json->max_depth ([$maximum_nesting_depth])
		630
		631	=item $max_depth = $json->get_max_depth
		632
		633	Sets the maximum nesting level (default C<512>) accepted while encoding
		634	or decoding. If a higher nesting level is detected in JSON text or a Perl
		635	data structure, then the encoder and decoder will stop and croak at that
		636	point.
		637
		638	Nesting level is defined by number of hash- or arrayrefs that the encoder
		639	needs to traverse to reach a given point or the number of C<{> or C<[>
		640	characters without their matching closing parenthesis crossed to reach a
		641	given character in a string.
		642
		643	Setting the maximum depth to one disallows any nesting, so that ensures
		644	that the object is only a single hash/object or array.
		645
		646	If no argument is given, the highest possible setting will be used, which
		647	is rarely useful.
		648
		649	Note that nesting is implemented by recursion in C. The default value has
		650	been chosen to be as large as typical operating systems allow without
		651	crashing.
		652
		653	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		654
		655	=item $json = $json->max_size ([$maximum_string_size])
		656
		657	=item $max_size = $json->get_max_size
		658
		659	Set the maximum length a JSON text may have (in bytes) where decoding is
		660	being attempted. The default is C<0>, meaning no limit. When C<decode>
		661	is called on a string that is longer then this many bytes, it will not
		662	attempt to decode the string but throw an exception. This setting has no
		663	effect on C<encode> (yet).
		664
		665	If no argument is given, the limit check will be deactivated (same as when
		666	C<0> is specified).
		667
		668	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		669
198	=item $json_string = $json->encode ($perl_scalar)	670	=item $json_text = $json->encode ($perl_scalar)
199		671
200	Converts the given Perl data structure (a simple scalar or a reference	672	Converts the given Perl data structure (a simple scalar or a reference
201	to a hash or array) to its JSON representation. Simple scalars will be	673	to a hash or array) to its JSON representation. Simple scalars will be
202	converted into JSON string or number sequences, while references to arrays	674	converted into JSON string or number sequences, while references to arrays
203	become JSON arrays and references to hashes become JSON objects. Undefined	675	become JSON arrays and references to hashes become JSON objects. Undefined
204	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>	676	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
205	nor C<false> values will be generated.	677	nor C<false> values will be generated.
206		678
207	=item $perl_scalar = $json->decode ($json_string)	679	=item $perl_scalar = $json->decode ($json_text)
208		680
209	The opposite of C<encode>: expects a JSON string and tries to parse it,	681	The opposite of C<encode>: expects a JSON text and tries to parse it,
210	returning the resulting simple scalar or reference. Croaks on error.	682	returning the resulting simple scalar or reference. Croaks on error.
211		683
212	JSON numbers and strings become simple Perl scalars. JSON arrays become	684	JSON numbers and strings become simple Perl scalars. JSON arrays become
213	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	685	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
214	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	686	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
215		687
		688	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		689
		690	This works like the C<decode> method, but instead of raising an exception
		691	when there is trailing garbage after the first JSON object, it will
		692	silently stop parsing there and return the number of characters consumed
		693	so far.
		694
		695	This is useful if your JSON texts are not delimited by an outer protocol
		696	(which is not the brightest thing to do in the first place) and you need
		697	to know where the JSON text ends.
		698
		699	JSON::XS->new->decode_prefix ("[1] the tail")
		700	=> ([], 3)
		701
216	=back	702	=back
217		703
		704
		705	=head1 INCREMENTAL PARSING
		706
		707	In some cases, there is the need for incremental parsing of JSON
		708	texts. While this module always has to keep both JSON text and resulting
		709	Perl data structure in memory at one time, it does allow you to parse a
		710	JSON stream incrementally. It does so by accumulating text until it has
		711	a full JSON object, which it then can decode. This process is similar to
		712	using C<decode_prefix> to see if a full JSON object is available, but
		713	is much more efficient (and can be implemented with a minimum of method
		714	calls).
		715
		716	JSON::XS will only attempt to parse the JSON text once it is sure it
		717	has enough text to get a decisive result, using a very simple but
		718	truly incremental parser. This means that it sometimes won't stop as
		719	early as the full parser, for example, it doesn't detect parenthese
		720	mismatches. The only thing it guarantees is that it starts decoding as
		721	soon as a syntactically valid JSON text has been seen. This means you need
		722	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		723	parsing in the presence if syntax errors.
		724
		725	The following methods implement this incremental parser.
		726
		727	=over 4
		728
		729	=item [void, scalar or list context] = $json->incr_parse ([$string])
		730
		731	This is the central parsing function. It can both append new text and
		732	extract objects from the stream accumulated so far (both of these
		733	functions are optional).
		734
		735	If C<$string> is given, then this string is appended to the already
		736	existing JSON fragment stored in the C<$json> object.
		737
		738	After that, if the function is called in void context, it will simply
		739	return without doing anything further. This can be used to add more text
		740	in as many chunks as you want.
		741
		742	If the method is called in scalar context, then it will try to extract
		743	exactly I<one> JSON object. If that is successful, it will return this
		744	object, otherwise it will return C<undef>. If there is a parse error,
		745	this method will croak just as C<decode> would do (one can then use
		746	C<incr_skip> to skip the errornous part). This is the most common way of
		747	using the method.
		748
		749	And finally, in list context, it will try to extract as many objects
		750	from the stream as it can find and return them, or the empty list
		751	otherwise. For this to work, there must be no separators between the JSON
		752	objects or arrays, instead they must be concatenated back-to-back. If
		753	an error occurs, an exception will be raised as in the scalar context
		754	case. Note that in this case, any previously-parsed JSON texts will be
		755	lost.
		756
		757	=item $lvalue_string = $json->incr_text
		758
		759	This method returns the currently stored JSON fragment as an lvalue, that
		760	is, you can manipulate it. This I<only> works when a preceding call to
		761	C<incr_parse> in I<scalar context> successfully returned an object. Under
		762	all other circumstances you must not call this function (I mean it.
		763	although in simple tests it might actually work, it I<will> fail under
		764	real world conditions). As a special exception, you can also call this
		765	method before having parsed anything.
		766
		767	This function is useful in two cases: a) finding the trailing text after a
		768	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		769	(such as commas).
		770
		771	=item $json->incr_skip
		772
		773	This will reset the state of the incremental parser and will remove the
		774	parsed text from the input buffer. This is useful after C<incr_parse>
		775	died, in which case the input buffer and incremental parser state is left
		776	unchanged, to skip the text parsed so far and to reset the parse state.
		777
		778	=item $json->incr_reset
		779
		780	This completely resets the incremental parser, that is, after this call,
		781	it will be as if the parser had never parsed anything.
		782
		783	This is useful if you want ot repeatedly parse JSON objects and want to
		784	ignore any trailing data, which means you have to reset the parser after
		785	each successful decode.
		786
		787	=back
		788
		789	=head2 LIMITATIONS
		790
		791	All options that affect decoding are supported, except
		792	C<allow_nonref>. The reason for this is that it cannot be made to
		793	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		794	them back to back and still decode them perfectly. This does not hold true
		795	for JSON numbers, however.
		796
		797	For example, is the string C<1> a single JSON number, or is it simply the
		798	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		799	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		800	takes the conservative route and disallows this case.
		801
		802	=head2 EXAMPLES
		803
		804	Some examples will make all this clearer. First, a simple example that
		805	works similarly to C<decode_prefix>: We want to decode the JSON object at
		806	the start of a string and identify the portion after the JSON object:
		807
		808	my $text = "[1,2,3] hello";
		809
		810	my $json = new JSON::XS;
		811
		812	my $obj = $json->incr_parse ($text)
		813	or die "expected JSON object or array at beginning of string";
		814
		815	my $tail = $json->incr_text;
		816	# $tail now contains " hello"
		817
		818	Easy, isn't it?
		819
		820	Now for a more complicated example: Imagine a hypothetical protocol where
		821	you read some requests from a TCP stream, and each request is a JSON
		822	array, without any separation between them (in fact, it is often useful to
		823	use newlines as "separators", as these get interpreted as whitespace at
		824	the start of the JSON text, which makes it possible to test said protocol
		825	with C<telnet>...).
		826
		827	Here is how you'd do it (it is trivial to write this in an event-based
		828	manner):
		829
		830	my $json = new JSON::XS;
		831
		832	# read some data from the socket
		833	while (sysread $socket, my $buf, 4096) {
		834
		835	# split and decode as many requests as possible
		836	for my $request ($json->incr_parse ($buf)) {
		837	# act on the $request
		838	}
		839	}
		840
		841	Another complicated example: Assume you have a string with JSON objects
		842	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		843	[3]>). To parse them, we have to skip the commas between the JSON texts,
		844	and here is where the lvalue-ness of C<incr_text> comes in useful:
		845
		846	my $text = "[1],[2], [3]";
		847	my $json = new JSON::XS;
		848
		849	# void context, so no parsing done
		850	$json->incr_parse ($text);
		851
		852	# now extract as many objects as possible. note the
		853	# use of scalar context so incr_text can be called.
		854	while (my $obj = $json->incr_parse) {
		855	# do something with $obj
		856
		857	# now skip the optional comma
		858	$json->incr_text =~ s/^ \s* , //x;
		859	}
		860
		861	Now lets go for a very complex example: Assume that you have a gigantic
		862	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		863	but you cannot load it into memory fully (this has actually happened in
		864	the real world :).
		865
		866	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		867	can still help you: You implement a (very simple) array parser and let
		868	JSON decode the array elements, which are all full JSON objects on their
		869	own (this wouldn't work if the array elements could be JSON numbers, for
		870	example):
		871
		872	my $json = new JSON::XS;
		873
		874	# open the monster
		875	open my $fh, "<bigfile.json"
		876	or die "bigfile: $!";
		877
		878	# first parse the initial "["
		879	for (;;) {
		880	sysread $fh, my $buf, 65536
		881	or die "read error: $!";
		882	$json->incr_parse ($buf); # void context, so no parsing
		883
		884	# Exit the loop once we found and removed(!) the initial "[".
		885	# In essence, we are (ab-)using the $json object as a simple scalar
		886	# we append data to.
		887	last if $json->incr_text =~ s/^ \s* \[ //x;
		888	}
		889
		890	# now we have the skipped the initial "[", so continue
		891	# parsing all the elements.
		892	for (;;) {
		893	# in this loop we read data until we got a single JSON object
		894	for (;;) {
		895	if (my $obj = $json->incr_parse) {
		896	# do something with $obj
		897	last;
		898	}
		899
		900	# add more data
		901	sysread $fh, my $buf, 65536
		902	or die "read error: $!";
		903	$json->incr_parse ($buf); # void context, so no parsing
		904	}
		905
		906	# in this loop we read data until we either found and parsed the
		907	# separating "," between elements, or the final "]"
		908	for (;;) {
		909	# first skip whitespace
		910	$json->incr_text =~ s/^\s*//;
		911
		912	# if we find "]", we are done
		913	if ($json->incr_text =~ s/^\]//) {
		914	print "finished.\n";
		915	exit;
		916	}
		917
		918	# if we find ",", we can continue with the next element
		919	if ($json->incr_text =~ s/^,//) {
		920	last;
		921	}
		922
		923	# if we find anything else, we have a parse error!
		924	if (length $json->incr_text) {
		925	die "parse error near ", $json->incr_text;
		926	}
		927
		928	# else add more data
		929	sysread $fh, my $buf, 65536
		930	or die "read error: $!";
		931	$json->incr_parse ($buf); # void context, so no parsing
		932	}
		933
		934	This is a complex example, but most of the complexity comes from the fact
		935	that we are trying to be correct (bear with me if I am wrong, I never ran
		936	the above example :).
		937
		938
		939
		940	=head1 MAPPING
		941
		942	This section describes how JSON::XS maps Perl values to JSON values and
		943	vice versa. These mappings are designed to "do the right thing" in most
		944	circumstances automatically, preserving round-tripping characteristics
		945	(what you put in comes out as something equivalent).
		946
		947	For the more enlightened: note that in the following descriptions,
		948	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		949	refers to the abstract Perl language itself.
		950
		951
		952	=head2 JSON -> PERL
		953
		954	=over 4
		955
		956	=item object
		957
		958	A JSON object becomes a reference to a hash in Perl. No ordering of object
		959	keys is preserved (JSON does not preserve object key ordering itself).
		960
		961	=item array
		962
		963	A JSON array becomes a reference to an array in Perl.
		964
		965	=item string
		966
		967	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		968	are represented by the same codepoints in the Perl string, so no manual
		969	decoding is necessary.
		970
		971	=item number
		972
		973	A JSON number becomes either an integer, numeric (floating point) or
		974	string scalar in perl, depending on its range and any fractional parts. On
		975	the Perl level, there is no difference between those as Perl handles all
		976	the conversion details, but an integer may take slightly less memory and
		977	might represent more values exactly than floating point numbers.
		978
		979	If the number consists of digits only, JSON::XS will try to represent
		980	it as an integer value. If that fails, it will try to represent it as
		981	a numeric (floating point) value if that is possible without loss of
		982	precision. Otherwise it will preserve the number as a string value (in
		983	which case you lose roundtripping ability, as the JSON number will be
		984	re-encoded toa JSON string).
		985
		986	Numbers containing a fractional or exponential part will always be
		987	represented as numeric (floating point) values, possibly at a loss of
		988	precision (in which case you might lose perfect roundtripping ability, but
		989	the JSON number will still be re-encoded as a JSON number).
		990
		991	=item true, false
		992
		993	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
		994	respectively. They are overloaded to act almost exactly like the numbers
		995	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
		996	the C<JSON::XS::is_bool> function.
		997
		998	=item null
		999
		1000	A JSON null atom becomes C<undef> in Perl.
		1001
		1002	=back
		1003
		1004
		1005	=head2 PERL -> JSON
		1006
		1007	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		1008	truly typeless language, so we can only guess which JSON type is meant by
		1009	a Perl value.
		1010
		1011	=over 4
		1012
		1013	=item hash references
		1014
		1015	Perl hash references become JSON objects. As there is no inherent ordering
		1016	in hash keys (or JSON objects), they will usually be encoded in a
		1017	pseudo-random order that can change between runs of the same program but
		1018	stays generally the same within a single run of a program. JSON::XS can
		1019	optionally sort the hash keys (determined by the I<canonical> flag), so
		1020	the same datastructure will serialise to the same JSON text (given same
		1021	settings and version of JSON::XS), but this incurs a runtime overhead
		1022	and is only rarely useful, e.g. when you want to compare some JSON text
		1023	against another for equality.
		1024
		1025	=item array references
		1026
		1027	Perl array references become JSON arrays.
		1028
		1029	=item other references
		1030
		1031	Other unblessed references are generally not allowed and will cause an
		1032	exception to be thrown, except for references to the integers C<0> and
		1033	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		1034	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		1035
		1036	encode_json [\0, JSON::XS::true] # yields [false,true]
		1037
		1038	=item JSON::XS::true, JSON::XS::false
		1039
		1040	These special values become JSON true and JSON false values,
		1041	respectively. You can also use C<\1> and C<\0> directly if you want.
		1042
		1043	=item blessed objects
		1044
		1045	Blessed objects are not directly representable in JSON. See the
		1046	C<allow_blessed> and C<convert_blessed> methods on various options on
		1047	how to deal with this: basically, you can choose between throwing an
		1048	exception, encoding the reference as if it weren't blessed, or provide
		1049	your own serialiser method.
		1050
		1051	=item simple scalars
		1052
		1053	Simple Perl scalars (any scalar that is not a reference) are the most
		1054	difficult objects to encode: JSON::XS will encode undefined scalars as
		1055	JSON C<null> values, scalars that have last been used in a string context
		1056	before encoding as JSON strings, and anything else as number value:
		1057
		1058	# dump as number
		1059	encode_json [2] # yields [2]
		1060	encode_json [-3.0e17] # yields [-3e+17]
		1061	my $value = 5; encode_json [$value] # yields [5]
		1062
		1063	# used as string, so dump as string
		1064	print $value;
		1065	encode_json [$value] # yields ["5"]
		1066
		1067	# undef becomes null
		1068	encode_json [undef] # yields [null]
		1069
		1070	You can force the type to be a JSON string by stringifying it:
		1071
		1072	my $x = 3.1; # some variable containing a number
		1073	"$x"; # stringified
		1074	$x .= ""; # another, more awkward way to stringify
		1075	print $x; # perl does it for you, too, quite often
		1076
		1077	You can force the type to be a JSON number by numifying it:
		1078
		1079	my $x = "3"; # some variable containing a string
		1080	$x += 0; # numify it, ensuring it will be dumped as a number
		1081	$x *= 1; # same thing, the choice is yours.
		1082
		1083	You can not currently force the type in other, less obscure, ways. Tell me
		1084	if you need this capability (but don't forget to explain why it's needed
		1085	:).
		1086
		1087	=back
		1088
		1089
		1090	=head1 ENCODING/CODESET FLAG NOTES
		1091
		1092	The interested reader might have seen a number of flags that signify
		1093	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1094	some confusion on what these do, so here is a short comparison:
		1095
		1096	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1097	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1098	control whether C<encode> escapes character values outside their respective
		1099	codeset range. Neither of these flags conflict with each other, although
		1100	some combinations make less sense than others.
		1101
		1102	Care has been taken to make all flags symmetrical with respect to
		1103	C<encode> and C<decode>, that is, texts encoded with any combination of
		1104	these flag values will be correctly decoded when the same flags are used
		1105	- in general, if you use different flag settings while encoding vs. when
		1106	decoding you likely have a bug somewhere.
		1107
		1108	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1109	simply an abstract set of character-codepoint pairs, while an encoding
		1110	takes those codepoint numbers and I<encodes> them, in our case into
		1111	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1112	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1113	the same time, which can be confusing.
		1114
		1115	=over 4
		1116
		1117	=item C<utf8> flag disabled
		1118
		1119	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1120	and expect Unicode strings, that is, characters with high ordinal Unicode
		1121	values (> 255) will be encoded as such characters, and likewise such
		1122	characters are decoded as-is, no canges to them will be done, except
		1123	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1124	respectively (to Perl, these are the same thing in strings unless you do
		1125	funny/weird/dumb stuff).
		1126
		1127	This is useful when you want to do the encoding yourself (e.g. when you
		1128	want to have UTF-16 encoded JSON texts) or when some other layer does
		1129	the encoding for you (for example, when printing to a terminal using a
		1130	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1131	to UTF-8 encode your data first and have Perl encode it another time).
		1132
		1133	=item C<utf8> flag enabled
		1134
		1135	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1136	characters using the corresponding UTF-8 multi-byte sequence, and will
		1137	expect your input strings to be encoded as UTF-8, that is, no "character"
		1138	of the input string must have any value > 255, as UTF-8 does not allow
		1139	that.
		1140
		1141	The C<utf8> flag therefore switches between two modes: disabled means you
		1142	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1143	octet/binary string in Perl.
		1144
		1145	=item C<latin1> or C<ascii> flags enabled
		1146
		1147	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1148	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1149	characters as specified by the C<utf8> flag.
		1150
		1151	If C<utf8> is disabled, then the result is also correctly encoded in those
		1152	character sets (as both are proper subsets of Unicode, meaning that a
		1153	Unicode string with all character values < 256 is the same thing as a
		1154	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1155	the same thing as an ASCII string in Perl).
		1156
		1157	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1158	regardless of these flags, just some more characters will be escaped using
		1159	C<\uXXXX> then before.
		1160
		1161	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1162	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1163	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1164	a subset of Unicode), while ASCII is.
		1165
		1166	Surprisingly, C<decode> will ignore these flags and so treat all input
		1167	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1168	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1169	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1170
		1171	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1172	they only govern when the JSON output engine escapes a character or not.
		1173
		1174	The main use for C<latin1> is to relatively efficiently store binary data
		1175	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1176
		1177	The main use for C<ascii> is to force the output to not contain characters
		1178	with values > 127, which means you can interpret the resulting string
		1179	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1180	8-bit-encoding, and still get the same data structure back. This is useful
		1181	when your channel for JSON transfer is not 8-bit clean or the encoding
		1182	might be mangled in between (e.g. in mail), and works because ASCII is a
		1183	proper subset of most 8-bit and multibyte encodings in use in the world.
		1184
		1185	=back
		1186
		1187
		1188	=head2 JSON and YAML
		1189
		1190	You often hear that JSON is a subset of YAML. This is, however, a mass
		1191	hysteria(*) and very far from the truth (as of the time of this writing),
		1192	so let me state it clearly: I<in general, there is no way to configure
		1193	JSON::XS to output a data structure as valid YAML> that works in all
		1194	cases.
		1195
		1196	If you really must use JSON::XS to generate YAML, you should use this
		1197	algorithm (subject to change in future versions):
		1198
		1199	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1200	my $yaml = $to_yaml->encode ($ref) . "\n";
		1201
		1202	This will I<usually> generate JSON texts that also parse as valid
		1203	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1204	lengths that JSON doesn't have and also has different and incompatible
		1205	unicode handling, so you should make sure that your hash keys are
		1206	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1207	you do not have characters with codepoint values outside the Unicode BMP
		1208	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1209	strings (which JSON::XS does not I<currently> generate, but other JSON
		1210	generators might).
		1211
		1212	There might be other incompatibilities that I am not aware of (or the YAML
		1213	specification has been changed yet again - it does so quite often). In
		1214	general you should not try to generate YAML with a JSON generator or vice
		1215	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1216	high that you will run into severe interoperability problems when you
		1217	least expect it.
		1218
		1219	=over 4
		1220
		1221	=item (*)
		1222
		1223	I have been pressured multiple times by Brian Ingerson (one of the
		1224	authors of the YAML specification) to remove this paragraph, despite him
		1225	acknowledging that the actual incompatibilities exist. As I was personally
		1226	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1227	educate people about these issues, so others do not run into the same
		1228	problem again and again. After this, Brian called me a (quote)I<complete
		1229	and worthless idiot>(unquote).
		1230
		1231	In my opinion, instead of pressuring and insulting people who actually
		1232	clarify issues with YAML and the wrong statements of some of its
		1233	proponents, I would kindly suggest reading the JSON spec (which is not
		1234	that difficult or long) and finally make YAML compatible to it, and
		1235	educating users about the changes, instead of spreading lies about the
		1236	real compatibility for many I<years> and trying to silence people who
		1237	point out that it isn't true.
		1238
		1239	=back
		1240
		1241
		1242	=head2 SPEED
		1243
		1244	It seems that JSON::XS is surprisingly fast, as shown in the following
		1245	tables. They have been generated with the help of the C<eg/bench> program
		1246	in the JSON::XS distribution, to make it easy to compare on your own
		1247	system.
		1248
		1249	First comes a comparison between various modules using
		1250	a very short single-line JSON string (also available at
		1251	L<http://dist.schmorp.de/misc/json/short.json>).
		1252
		1253	{"method": "handleMessage", "params": ["user1",
		1254	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1255	true, false]}
		1256
		1257	It shows the number of encodes/decodes per second (JSON::XS uses
		1258	the functional interface, while JSON::XS/2 uses the OO interface
		1259	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1260	shrink). Higher is better:
		1261
		1262	module | encode | decode |
		1263	-----------|------------|------------|
		1264	JSON 1.x | 4990.842 | 4088.813 |
		1265	JSON::DWIW | 51653.990 | 71575.154 |
		1266	JSON::PC | 65948.176 | 74631.744 |
		1267	JSON::PP | 8931.652 | 3817.168 |
		1268	JSON::Syck | 24877.248 | 27776.848 |
		1269	JSON::XS | 388361.481 | 227951.304 |
		1270	JSON::XS/2 | 227951.304 | 218453.333 |
		1271	JSON::XS/3 | 338250.323 | 218453.333 |
		1272	Storable | 16500.016 | 135300.129 |
		1273	-----------+------------+------------+
		1274
		1275	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
		1276	about three times faster on decoding, and over forty times faster
		1277	than JSON, even with pretty-printing and key sorting. It also compares
		1278	favourably to Storable for small amounts of data.
		1279
		1280	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
		1281	search API (L<http://dist.schmorp.de/misc/json/long.json>).
		1282
		1283	module | encode | decode |
		1284	-----------|------------|------------|
		1285	JSON 1.x | 55.260 | 34.971 |
		1286	JSON::DWIW | 825.228 | 1082.513 |
		1287	JSON::PC | 3571.444 | 2394.829 |
		1288	JSON::PP | 210.987 | 32.574 |
		1289	JSON::Syck | 552.551 | 787.544 |
		1290	JSON::XS | 5780.463 | 4854.519 |
		1291	JSON::XS/2 | 3869.998 | 4798.975 |
		1292	JSON::XS/3 | 5862.880 | 4798.975 |
		1293	Storable | 4445.002 | 5235.027 |
		1294	-----------+------------+------------+
		1295
		1296	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1297	decodes faster).
		1298
		1299	On large strings containing lots of high Unicode characters, some modules
		1300	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1301	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1302	to decode or encode properly, so it was impossible to prepare a fair
		1303	comparison table for that case.
		1304
		1305
		1306	=head1 SECURITY CONSIDERATIONS
		1307
		1308	When you are using JSON in a protocol, talking to untrusted potentially
		1309	hostile creatures requires relatively few measures.
		1310
		1311	First of all, your JSON decoder should be secure, that is, should not have
		1312	any buffer overflows. Obviously, this module should ensure that and I am
		1313	trying hard on making that true, but you never know.
		1314
		1315	Second, you need to avoid resource-starving attacks. That means you should
		1316	limit the size of JSON texts you accept, or make sure then when your
		1317	resources run out, that's just fine (e.g. by using a separate process that
		1318	can crash safely). The size of a JSON text in octets or characters is
		1319	usually a good indication of the size of the resources required to decode
		1320	it into a Perl structure. While JSON::XS can check the size of the JSON
		1321	text, it might be too late when you already have it in memory, so you
		1322	might want to check the size before you accept the string.
		1323
		1324	Third, JSON::XS recurses using the C stack when decoding objects and
		1325	arrays. The C stack is a limited resource: for instance, on my amd64
		1326	machine with 8MB of stack size I can decode around 180k nested arrays but
		1327	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1328	to free the temporary). If that is exceeded, the program crashes. To be
		1329	conservative, the default nesting limit is set to 512. If your process
		1330	has a smaller stack, you should adjust this setting accordingly with the
		1331	C<max_depth> method.
		1332
		1333	Something else could bomb you, too, that I forgot to think of. In that
		1334	case, you get to keep the pieces. I am always open for hints, though...
		1335
		1336	Also keep in mind that JSON::XS might leak contents of your Perl data
		1337	structures in its error messages, so when you serialise sensitive
		1338	information you might want to make sure that exceptions thrown by JSON::XS
		1339	will not end up in front of untrusted eyes.
		1340
		1341	If you are using JSON::XS to return packets to consumption
		1342	by JavaScript scripts in a browser you should have a look at
		1343	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1344	you are vulnerable to some common attack vectors (which really are browser
		1345	design bugs, but it is still you who will have to deal with it, as major
		1346	browser developers care only for features, not about getting security
		1347	right).
		1348
		1349
		1350	=head1 THREADS
		1351
		1352	This module is I<not> guaranteed to be thread safe and there are no
		1353	plans to change this until Perl gets thread support (as opposed to the
		1354	horribly slow so-called "threads" which are simply slow and bloated
		1355	process simulations - use fork, it's I<much> faster, cheaper, better).
		1356
		1357	(It might actually work, but you have been warned).
		1358
		1359
		1360	=head1 BUGS
		1361
		1362	While the goal of this module is to be correct, that unfortunately does
		1363	not mean it's bug-free, only that I think its design is bug-free. If you
		1364	keep reporting bugs they will be fixed swiftly, though.
		1365
		1366	Please refrain from using rt.cpan.org or any other bug reporting
		1367	service. I put the contact address into my modules for a reason.
		1368
218	=cut	1369	=cut
219		1370
		1371	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1372	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1373
		1374	sub true() { $true }
		1375	sub false() { $false }
		1376
		1377	sub is_bool($) {
		1378	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1379	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1380	}
		1381
		1382	XSLoader::load "JSON::XS", $VERSION;
		1383
		1384	package JSON::XS::Boolean;
		1385
		1386	use overload
		1387	"0+" => sub { ${$_[0]} },
		1388	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1389	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1390	fallback => 1;
		1391
220	1;	1392	1;
		1393
		1394	=head1 SEE ALSO
		1395
		1396	The F<json_xs> command line utility for quick experiments.
221		1397
222	=head1 AUTHOR	1398	=head1 AUTHOR
223		1399
224	Marc Lehmann <schmorp@schmorp.de>	1400	Marc Lehmann <schmorp@schmorp.de>
225	http://home.schmorp.de/	1401	http://home.schmorp.de/

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