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Revision 1.15 by root, Sat Mar 24 01:15:22 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;
8		13
9	# exported functions, croak on error	14	# exported functions, they croak on error
		15	# and expect/generate UTF-8
10		16
11	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
12	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
13		19
14	# oo-interface	20	# OO-interface
15		21
16	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
17	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
18	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
19		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
		33
20	=head1 DESCRIPTION	34	=head1 DESCRIPTION
21		35
22	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
23	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
24	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overriden) with no overhead due to emulation (by inheritign constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
25		47
26	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
27	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
28	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
29	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
…		…
36		58
37	=head2 FEATURES	59	=head2 FEATURES
38		60
39	=over 4	61	=over 4
40		62
41	=item * correct handling of unicode issues	63	=item * correct Unicode handling
42		64
43	This module knows how to handle Unicode, and even documents how and when	65	This module knows how to handle Unicode, documents how and when it does
44	it does so.	66	so, and even documents what "correct" means.
45		67
46	=item * round-trip integrity	68	=item * round-trip integrity
47		69
48	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only datatypes supported
49	by JSON, the deserialised data structure is identical on the Perl level.	71	by JSON, the deserialised data structure is identical on the Perl level.
50	(e.g. the string "2.0" doesn't suddenly become "2").	72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
		73	like a number). There minor I<are> exceptions to this, read the MAPPING
		74	section below to learn about those.
51		75
52	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
53		77
54	There is no guessing, no generating of illegal JSON strings by default,	78	There is no guessing, no generating of illegal JSON texts by default,
55	and only JSON is accepted as input by default (the latter is a security	79	and only JSON is accepted as input by default (the latter is a security
56	feature).	80	feature).
57		81
58	=item * fast	82	=item * fast
59		83
60	Compared to other JSON modules, this module compares favourably in terms	84	Compared to other JSON modules and other serialisers such as Storable,
61	of speed, too.	85	this module usually compares favourably in terms of speed, too.
62		86
63	=item * simple to use	87	=item * simple to use
64		88
65	This module has both a simple functional interface as well as an OO	89	This module has both a simple functional interface as well as an objetc
66	interface.	90	oriented interface interface.
67		91
68	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
69		93
70	You can choose between the most compact guarenteed single-line format	94	You can choose between the most compact guaranteed-single-line format
71	possible (nice for simple line-based protocols), a pure-ascii format (for	95	possible (nice for simple line-based protocols), a pure-ascii format
72	when your transport is not 8-bit clean), or a pretty-printed format (for	96	(for when your transport is not 8-bit clean, still supports the whole
73	when you want to read that stuff). Or you can combine those features in	97	Unicode range), or a pretty-printed format (for when you want to read that
74	whatever way you like.	98	stuff). Or you can combine those features in whatever way you like.
75		99
76	=back	100	=back
77		101
78	=cut	102	=cut
79		103
80	package JSON::XS;	104	package JSON::XS;
81		105
82	BEGIN {	106	use strict;
		107
83	$VERSION = '0.31';	108	our $VERSION = '2.1';
84	@ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
85		110
86	@EXPORT = qw(to_json from_json);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
87	require Exporter;
88		112
		113	sub to_json($) {
89	require XSLoader;	114	require Carp;
90	XSLoader::load JSON::XS::, $VERSION;	115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
91	}	116	}
92		117
		118	sub from_json($) {
		119	require Carp;
		120	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
		121	}
		122
		123	use Exporter;
		124	use XSLoader;
		125
93	=head1 FUNCTIONAL INTERFACE	126	=head1 FUNCTIONAL INTERFACE
94		127
95	The following convinience methods are provided by this module. They are	128	The following convenience methods are provided by this module. They are
96	exported by default:	129	exported by default:
97		130
98	=over 4	131	=over 4
99		132
100	=item $json_string = to_json $perl_scalar	133	=item $json_text = encode_json $perl_scalar
101		134
102	Converts the given Perl data structure (a simple scalar or a reference to	135	Converts the given Perl data structure to a UTF-8 encoded, binary string
103	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	136	(that is, the string contains octets only). Croaks on error.
104	octets only). Croaks on error.
105		137
106	This function call is functionally identical to C<< JSON::XS->new->utf8->encode ($perl_scalar) >>.	138	This function call is functionally identical to:
107		139
		140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		141
		142	except being faster.
		143
108	=item $perl_scalar = from_json $json_string	144	=item $perl_scalar = decode_json $json_text
109		145
110	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
111	parse that as an UTF-8 encoded JSON string, returning the resulting simple	147	to parse that as an UTF-8 encoded JSON text, returning the resulting
112	scalar or reference. Croaks on error.	148	reference. Croaks on error.
113		149
114	This function call is functionally identical to C<< JSON::XS->new->utf8->decode ($json_string) >>.	150	This function call is functionally identical to:
		151
		152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		153
		154	except being faster.
		155
		156	=item $is_boolean = JSON::XS::is_bool $scalar
		157
		158	Returns true if the passed scalar represents either JSON::XS::true or
		159	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		160	and are used to represent JSON C<true> and C<false> values in Perl.
		161
		162	See MAPPING, below, for more information on how JSON values are mapped to
		163	Perl.
115		164
116	=back	165	=back
		166
		167
		168	=head1 A FEW NOTES ON UNICODE AND PERL
		169
		170	Since this often leads to confusion, here are a few very clear words on
		171	how Unicode works in Perl, modulo bugs.
		172
		173	=over 4
		174
		175	=item 1. Perl strings can store characters with ordinal values > 255.
		176
		177	This enables you to store Unicode characters as single characters in a
		178	Perl string - very natural.
		179
		180	=item 2. Perl does I<not> associate an encoding with your strings.
		181
		182	... until you force it to, e.g. when matching it against a regex, or
		183	printing the scalar to a file, in which case Perl either interprets your
		184	string as locale-encoded text, octets/binary, or as Unicode, depending
		185	on various settings. In no case is an encoding stored together with your
		186	data, it is I<use> that decides encoding, not any magical meta data.
		187
		188	=item 3. The internal utf-8 flag has no meaning with regards to the
		189	encoding of your string.
		190
		191	Just ignore that flag unless you debug a Perl bug, a module written in
		192	XS or want to dive into the internals of perl. Otherwise it will only
		193	confuse you, as, despite the name, it says nothing about how your string
		194	is encoded. You can have Unicode strings with that flag set, with that
		195	flag clear, and you can have binary data with that flag set and that flag
		196	clear. Other possibilities exist, too.
		197
		198	If you didn't know about that flag, just the better, pretend it doesn't
		199	exist.
		200
		201	=item 4. A "Unicode String" is simply a string where each character can be
		202	validly interpreted as a Unicode codepoint.
		203
		204	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		205	Unicode string encoded in UTF-8, giving you a binary string.
		206
		207	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		208
		209	It's a fact. Learn to live with it.
		210
		211	=back
		212
		213	I hope this helps :)
		214
117		215
118	=head1 OBJECT-ORIENTED INTERFACE	216	=head1 OBJECT-ORIENTED INTERFACE
119		217
120	The object oriented interface lets you configure your own encoding or	218	The object oriented interface lets you configure your own encoding or
121	decoding style, within the limits of supported formats.	219	decoding style, within the limits of supported formats.
…		…
128	strings. All boolean flags described below are by default I<disabled>.	226	strings. All boolean flags described below are by default I<disabled>.
129		227
130	The mutators for flags all return the JSON object again and thus calls can	228	The mutators for flags all return the JSON object again and thus calls can
131	be chained:	229	be chained:
132		230
133	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	231	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
134	=> {"a": [1, 2]}	232	=> {"a": [1, 2]}
135		233
136	=item $json = $json->ascii ([$enable])	234	=item $json = $json->ascii ([$enable])
137		235
		236	=item $enabled = $json->get_ascii
		237
138	If C<$enable> is true (or missing), then the C<encode> method will	238	If C<$enable> is true (or missing), then the C<encode> method will not
139	not generate characters outside the code range C<0..127>. Any unicode	239	generate characters outside the code range C<0..127> (which is ASCII). Any
140	characters outside that range will be escaped using either a single	240	Unicode characters outside that range will be escaped using either a
141	\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per	241	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
142	RFC4627.	242	as per RFC4627. The resulting encoded JSON text can be treated as a native
		243	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		244	or any other superset of ASCII.
143		245
144	If C<$enable> is false, then the C<encode> method will not escape Unicode	246	If C<$enable> is false, then the C<encode> method will not escape Unicode
145	characters unless necessary.	247	characters unless required by the JSON syntax or other flags. This results
		248	in a faster and more compact format.
146		249
		250	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		251	document.
		252
		253	The main use for this flag is to produce JSON texts that can be
		254	transmitted over a 7-bit channel, as the encoded JSON texts will not
		255	contain any 8 bit characters.
		256
147	JSON::XS->new->ascii (1)->encode (chr 0x10401)	257	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
148	=> \ud801\udc01	258	=> ["\ud801\udc01"]
		259
		260	=item $json = $json->latin1 ([$enable])
		261
		262	=item $enabled = $json->get_latin1
		263
		264	If C<$enable> is true (or missing), then the C<encode> method will encode
		265	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		266	outside the code range C<0..255>. The resulting string can be treated as a
		267	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		268	will not be affected in any way by this flag, as C<decode> by default
		269	expects Unicode, which is a strict superset of latin1.
		270
		271	If C<$enable> is false, then the C<encode> method will not escape Unicode
		272	characters unless required by the JSON syntax or other flags.
		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
		276
		277	The main use for this flag is efficiently encoding binary data as JSON
		278	text, as most octets will not be escaped, resulting in a smaller encoded
		279	size. The disadvantage is that the resulting JSON text is encoded
		280	in latin1 (and must correctly be treated as such when storing and
		281	transferring), a rare encoding for JSON. It is therefore most useful when
		282	you want to store data structures known to contain binary data efficiently
		283	in files or databases, not when talking to other JSON encoders/decoders.
		284
		285	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		286	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
149		287
150	=item $json = $json->utf8 ([$enable])	288	=item $json = $json->utf8 ([$enable])
151		289
		290	=item $enabled = $json->get_utf8
		291
152	If C<$enable> is true (or missing), then the C<encode> method will encode	292	If C<$enable> is true (or missing), then the C<encode> method will encode
153	the JSON string into UTF-8, as required by many protocols, while the	293	the JSON result into UTF-8, as required by many protocols, while the
154	C<decode> method expects to be handled an UTF-8-encoded string. Please	294	C<decode> method expects to be handled an UTF-8-encoded string. Please
155	note that UTF-8-encoded strings do not contain any characters outside the	295	note that UTF-8-encoded strings do not contain any characters outside the
156	range C<0..255>, they are thus useful for bytewise/binary I/O.	296	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		297	versions, enabling this option might enable autodetection of the UTF-16
		298	and UTF-32 encoding families, as described in RFC4627.
157		299
158	If C<$enable> is false, then the C<encode> method will return the JSON	300	If C<$enable> is false, then the C<encode> method will return the JSON
159	string as a (non-encoded) unicode string, while C<decode> expects thus a	301	string as a (non-encoded) Unicode string, while C<decode> expects thus a
160	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	302	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
161	to be done yourself, e.g. using the Encode module.	303	to be done yourself, e.g. using the Encode module.
162		304
		305	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		306	document.
		307
163	Example, output UTF-16-encoded JSON:	308	Example, output UTF-16BE-encoded JSON:
		309
		310	use Encode;
		311	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		312
		313	Example, decode UTF-32LE-encoded JSON:
		314
		315	use Encode;
		316	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
164		317
165	=item $json = $json->pretty ([$enable])	318	=item $json = $json->pretty ([$enable])
166		319
167	This enables (or disables) all of the C<indent>, C<space_before> and	320	This enables (or disables) all of the C<indent>, C<space_before> and
168	C<space_after> (and in the future possibly more) flags in one call to	321	C<space_after> (and in the future possibly more) flags in one call to
…		…
179	]	332	]
180	}	333	}
181		334
182	=item $json = $json->indent ([$enable])	335	=item $json = $json->indent ([$enable])
183		336
		337	=item $enabled = $json->get_indent
		338
184	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	339	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
185	format as output, putting every array member or object/hash key-value pair	340	format as output, putting every array member or object/hash key-value pair
186	into its own line, identing them properly.	341	into its own line, indenting them properly.
187		342
188	If C<$enable> is false, no newlines or indenting will be produced, and the	343	If C<$enable> is false, no newlines or indenting will be produced, and the
189	resulting JSON strings is guarenteed not to contain any C<newlines>.	344	resulting JSON text is guaranteed not to contain any C<newlines>.
190		345
191	This setting has no effect when decoding JSON strings.	346	This setting has no effect when decoding JSON texts.
192		347
193	=item $json = $json->space_before ([$enable])	348	=item $json = $json->space_before ([$enable])
		349
		350	=item $enabled = $json->get_space_before
194		351
195	If C<$enable> is true (or missing), then the C<encode> method will add an extra	352	If C<$enable> is true (or missing), then the C<encode> method will add an extra
196	optional space before the C<:> separating keys from values in JSON objects.	353	optional space before the C<:> separating keys from values in JSON objects.
197		354
198	If C<$enable> is false, then the C<encode> method will not add any extra	355	If C<$enable> is false, then the C<encode> method will not add any extra
199	space at those places.	356	space at those places.
200		357
201	This setting has no effect when decoding JSON strings. You will also most	358	This setting has no effect when decoding JSON texts. You will also
202	likely combine this setting with C<space_after>.	359	most likely combine this setting with C<space_after>.
203		360
204	Example, space_before enabled, space_after and indent disabled:	361	Example, space_before enabled, space_after and indent disabled:
205		362
206	{"key" :"value"}	363	{"key" :"value"}
207		364
208	=item $json = $json->space_after ([$enable])	365	=item $json = $json->space_after ([$enable])
		366
		367	=item $enabled = $json->get_space_after
209		368
210	If C<$enable> is true (or missing), then the C<encode> method will add an extra	369	If C<$enable> is true (or missing), then the C<encode> method will add an extra
211	optional space after the C<:> separating keys from values in JSON objects	370	optional space after the C<:> separating keys from values in JSON objects
212	and extra whitespace after the C<,> separating key-value pairs and array	371	and extra whitespace after the C<,> separating key-value pairs and array
213	members.	372	members.
214		373
215	If C<$enable> is false, then the C<encode> method will not add any extra	374	If C<$enable> is false, then the C<encode> method will not add any extra
216	space at those places.	375	space at those places.
217		376
218	This setting has no effect when decoding JSON strings.	377	This setting has no effect when decoding JSON texts.
219		378
220	Example, space_before and indent disabled, space_after enabled:	379	Example, space_before and indent disabled, space_after enabled:
221		380
222	{"key": "value"}	381	{"key": "value"}
223		382
		383	=item $json = $json->relaxed ([$enable])
		384
		385	=item $enabled = $json->get_relaxed
		386
		387	If C<$enable> is true (or missing), then C<decode> will accept some
		388	extensions to normal JSON syntax (see below). C<encode> will not be
		389	affected in anyway. I<Be aware that this option makes you accept invalid
		390	JSON texts as if they were valid!>. I suggest only to use this option to
		391	parse application-specific files written by humans (configuration files,
		392	resource files etc.)
		393
		394	If C<$enable> is false (the default), then C<decode> will only accept
		395	valid JSON texts.
		396
		397	Currently accepted extensions are:
		398
		399	=over 4
		400
		401	=item * list items can have an end-comma
		402
		403	JSON I<separates> array elements and key-value pairs with commas. This
		404	can be annoying if you write JSON texts manually and want to be able to
		405	quickly append elements, so this extension accepts comma at the end of
		406	such items not just between them:
		407
		408	[
		409	1,
		410	2, <- this comma not normally allowed
		411	]
		412	{
		413	"k1": "v1",
		414	"k2": "v2", <- this comma not normally allowed
		415	}
		416
		417	=item * shell-style '#'-comments
		418
		419	Whenever JSON allows whitespace, shell-style comments are additionally
		420	allowed. They are terminated by the first carriage-return or line-feed
		421	character, after which more white-space and comments are allowed.
		422
		423	[
		424	1, # this comment not allowed in JSON
		425	# neither this one...
		426	]
		427
		428	=back
		429
224	=item $json = $json->canonical ([$enable])	430	=item $json = $json->canonical ([$enable])
		431
		432	=item $enabled = $json->get_canonical
225		433
226	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	434	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
227	by sorting their keys. This is adding a comparatively high overhead.	435	by sorting their keys. This is adding a comparatively high overhead.
228		436
229	If C<$enable> is false, then the C<encode> method will output key-value	437	If C<$enable> is false, then the C<encode> method will output key-value
230	pairs in the order Perl stores them (which will likely change between runs	438	pairs in the order Perl stores them (which will likely change between runs
231	of the same script).	439	of the same script).
232		440
233	This option is useful if you want the same data structure to be encoded as	441	This option is useful if you want the same data structure to be encoded as
234	the same JSON string (given the same overall settings). If it is disabled,	442	the same JSON text (given the same overall settings). If it is disabled,
235	the same hash migh be encoded differently even if contains the same data,	443	the same hash might be encoded differently even if contains the same data,
236	as key-value pairs have no inherent ordering in Perl.	444	as key-value pairs have no inherent ordering in Perl.
237		445
238	This setting has no effect when decoding JSON strings.	446	This setting has no effect when decoding JSON texts.
239		447
240	=item $json = $json->allow_nonref ([$enable])	448	=item $json = $json->allow_nonref ([$enable])
		449
		450	=item $enabled = $json->get_allow_nonref
241		451
242	If C<$enable> is true (or missing), then the C<encode> method can convert a	452	If C<$enable> is true (or missing), then the C<encode> method can convert a
243	non-reference into its corresponding string, number or null JSON value,	453	non-reference into its corresponding string, number or null JSON value,
244	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	454	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
245	values instead of croaking.	455	values instead of croaking.
246		456
247	If C<$enable> is false, then the C<encode> method will croak if it isn't	457	If C<$enable> is false, then the C<encode> method will croak if it isn't
248	passed an arrayref or hashref, as JSON strings must either be an object	458	passed an arrayref or hashref, as JSON texts must either be an object
249	or array. Likewise, C<decode> will croak if given something that is not a	459	or array. Likewise, C<decode> will croak if given something that is not a
250	JSON object or array.	460	JSON object or array.
251		461
252	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,	462	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
253	resulting in an invalid JSON text:	463	resulting in an invalid JSON text:
254		464
255	JSON::XS->new->allow_nonref->encode ("Hello, World!")	465	JSON::XS->new->allow_nonref->encode ("Hello, World!")
256	=> "Hello, World!"	466	=> "Hello, World!"
257		467
		468	=item $json = $json->allow_blessed ([$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
258	=item $json = $json->shrink ([$enable])	584	=item $json = $json->shrink ([$enable])
259		585
		586	=item $enabled = $json->get_shrink
		587
260	Perl usually over-allocates memory a bit when allocating space for	588	Perl usually over-allocates memory a bit when allocating space for
261	strings. This flag optionally resizes strings generated by either	589	strings. This flag optionally resizes strings generated by either
262	C<encode> or C<decode> to their minimum size possible. This can save	590	C<encode> or C<decode> to their minimum size possible. This can save
263	memory when your JSON strings are either very very long or you have many	591	memory when your JSON texts are either very very long or you have many
264	short strings. It will also try to downgrade any strings to octet-form	592	short strings. It will also try to downgrade any strings to octet-form
265	if possible: perl stores strings internally either in an encoding called	593	if possible: perl stores strings internally either in an encoding called
266	UTF-X or in octet-form. The latter cannot store everything but uses less	594	UTF-X or in octet-form. The latter cannot store everything but uses less
267	space in general.	595	space in general (and some buggy Perl or C code might even rely on that
		596	internal representation being used).
268		597
		598	The actual definition of what shrink does might change in future versions,
		599	but it will always try to save space at the expense of time.
		600
269	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	601	If C<$enable> is true (or missing), the string returned by C<encode> will
270	while all strings generated by C<decode> will also be shrunk-to-fit.	602	be shrunk-to-fit, while all strings generated by C<decode> will also be
		603	shrunk-to-fit.
271		604
272	If C<$enable> is false, then the normal perl allocation algorithms are used.	605	If C<$enable> is false, then the normal perl allocation algorithms are used.
273	If you work with your data, then this is likely to be faster.	606	If you work with your data, then this is likely to be faster.
274		607
275	In the future, this setting might control other things, such as converting	608	In the future, this setting might control other things, such as converting
276	strings that look like integers or floats into integers or floats	609	strings that look like integers or floats into integers or floats
277	internally (there is no difference on the Perl level), saving space.	610	internally (there is no difference on the Perl level), saving space.
278		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
279	=item $json_string = $json->encode ($perl_scalar)	651	=item $json_text = $json->encode ($perl_scalar)
280		652
281	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
282	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
283	converted into JSON string or number sequences, while references to arrays	655	converted into JSON string or number sequences, while references to arrays
284	become JSON arrays and references to hashes become JSON objects. Undefined	656	become JSON arrays and references to hashes become JSON objects. Undefined
285	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>	657	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
286	nor C<false> values will be generated.	658	nor C<false> values will be generated.
287		659
288	=item $perl_scalar = $json->decode ($json_string)	660	=item $perl_scalar = $json->decode ($json_text)
289		661
290	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,
291	returning the resulting simple scalar or reference. Croaks on error.	663	returning the resulting simple scalar or reference. Croaks on error.
292		664
293	JSON numbers and strings become simple Perl scalars. JSON arrays become	665	JSON numbers and strings become simple Perl scalars. JSON arrays become
294	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	666	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
295	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	667	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
296		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
297	=back	683	=back
		684
		685
		686	=head1 INCREMENTAL PARSING
		687
		688	[This section is still EXPERIMENTAL]
		689
		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.
		701
		702	=over 4
		703
		704	=item [void, scalar or list context] = $json->incr_parse ([$string])
		705
		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).
		709
		710	If C<$string> is given, then this string is appended to the already
		711	existing JSON fragment stored in the C<$json> object.
		712
		713	After that, if the function is called in void context, it will simply
		714	return without doing anything further. This can be used to add more text
		715	in as many chunks as you want.
		716
		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.
		723
		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.
		731
		732	If there is a parse
		733
		734	=item $lvalue_string = $json->incr_text
		735
		736	This method returns the currently stored JSON fragment as an lvalue, that
		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.
		743
		744	This function is useful in two cases: a) finding the trailing text after a
		745	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		746	(such as commas).
		747
		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
298		900
299	=head1 MAPPING	901	=head1 MAPPING
300		902
301	This section describes how JSON::XS maps Perl values to JSON values and	903	This section describes how JSON::XS maps Perl values to JSON values and
302	vice versa. These mappings are designed to "do the right thing" in most	904	vice versa. These mappings are designed to "do the right thing" in most
303	circumstances automatically, preserving round-tripping characteristics	905	circumstances automatically, preserving round-tripping characteristics
304	(what you put in comes out as something equivalent).	906	(what you put in comes out as something equivalent).
305		907
306	For the more enlightened: note that in the following descriptions,	908	For the more enlightened: note that in the following descriptions,
307	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	909	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
308	refers to the abstract Perl language itself.	910	refers to the abstract Perl language itself.
309		911
		912
310	=head2 JSON -> PERL	913	=head2 JSON -> PERL
311		914
312	=over 4	915	=over 4
313		916
314	=item object	917	=item object
315		918
316	A JSON object becomes a reference to a hash in Perl. No ordering of object	919	A JSON object becomes a reference to a hash in Perl. No ordering of object
317	keys is preserved (JSON does not preserver object key ordering itself).	920	keys is preserved (JSON does not preserve object key ordering itself).
318		921
319	=item array	922	=item array
320		923
321	A JSON array becomes a reference to an array in Perl.	924	A JSON array becomes a reference to an array in Perl.
322		925
…		…
326	are represented by the same codepoints in the Perl string, so no manual	929	are represented by the same codepoints in the Perl string, so no manual
327	decoding is necessary.	930	decoding is necessary.
328		931
329	=item number	932	=item number
330		933
331	A JSON number becomes either an integer or numeric (floating point)	934	A JSON number becomes either an integer, numeric (floating point) or
332	scalar in perl, depending on its range and any fractional parts. On the	935	string scalar in perl, depending on its range and any fractional parts. On
333	Perl level, there is no difference between those as Perl handles all the	936	the Perl level, there is no difference between those as Perl handles all
334	conversion details, but an integer may take slightly less memory and might	937	the conversion details, but an integer may take slightly less memory and
335	represent more values exactly than (floating point) numbers.	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).
336		951
337	=item true, false	952	=item true, false
338		953
339	These JSON atoms become C<0>, C<1>, respectively. Information is lost in	954	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
340	this process. Future versions might represent those values differently,	955	respectively. They are overloaded to act almost exactly like the numbers
341	but they will be guarenteed to act like these integers would normally in	956	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
342	Perl.	957	the C<JSON::XS::is_bool> function.
343		958
344	=item null	959	=item null
345		960
346	A JSON null atom becomes C<undef> in Perl.	961	A JSON null atom becomes C<undef> in Perl.
347		962
348	=back	963	=back
		964
349		965
350	=head2 PERL -> JSON	966	=head2 PERL -> JSON
351		967
352	The mapping from Perl to JSON is slightly more difficult, as Perl is a	968	The mapping from Perl to JSON is slightly more difficult, as Perl is a
353	truly typeless language, so we can only guess which JSON type is meant by	969	truly typeless language, so we can only guess which JSON type is meant by
…		…
356	=over 4	972	=over 4
357		973
358	=item hash references	974	=item hash references
359		975
360	Perl hash references become JSON objects. As there is no inherent ordering	976	Perl hash references become JSON objects. As there is no inherent ordering
361	in hash keys, they will usually be encoded in a pseudo-random order that	977	in hash keys (or JSON objects), they will usually be encoded in a
362	can change between runs of the same program but stays generally the same	978	pseudo-random order that can change between runs of the same program but
363	within a single run of a program. JSON::XS can optionally sort the hash	979	stays generally the same within a single run of a program. JSON::XS can
364	keys (determined by the I<canonical> flag), so the same datastructure	980	optionally sort the hash keys (determined by the I<canonical> flag), so
365	will serialise to the same JSON text (given same settings and version of	981	the same datastructure will serialise to the same JSON text (given same
366	JSON::XS), but this incurs a runtime overhead.	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.
367		985
368	=item array references	986	=item array references
369		987
370	Perl array references become JSON arrays.	988	Perl array references become JSON arrays.
371		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
372	=item blessed objects	1004	=item blessed objects
373		1005
374	Blessed objects are not allowed. JSON::XS currently tries to encode their	1006	Blessed objects are not directly representable in JSON. See the
375	underlying representation (hash- or arrayref), but this behaviour might	1007	C<allow_blessed> and C<convert_blessed> methods on various options on
376	change in future versions.	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.
377		1011
378	=item simple scalars	1012	=item simple scalars
379		1013
380	Simple Perl scalars (any scalar that is not a reference) are the most	1014	Simple Perl scalars (any scalar that is not a reference) are the most
381	difficult objects to encode: JSON::XS will encode undefined scalars as	1015	difficult objects to encode: JSON::XS will encode undefined scalars as
382	JSON null value, scalars that have last been used in a string context	1016	JSON C<null> values, scalars that have last been used in a string context
383	before encoding as JSON strings and anything else as number value:	1017	before encoding as JSON strings, and anything else as number value:
384		1018
385	# dump as number	1019	# dump as number
386	to_json [2] # yields [2]	1020	encode_json [2] # yields [2]
387	to_json [-3.0e17] # yields [-3e+17]	1021	encode_json [-3.0e17] # yields [-3e+17]
388	my $value = 5; to_json [$value] # yields [5]	1022	my $value = 5; encode_json [$value] # yields [5]
389		1023
390	# used as string, so dump as string	1024	# used as string, so dump as string
391	print $value;	1025	print $value;
392	to_json [$value] # yields ["5"]	1026	encode_json [$value] # yields ["5"]
393		1027
394	# undef becomes null	1028	# undef becomes null
395	to_json [undef] # yields [null]	1029	encode_json [undef] # yields [null]
396		1030
397	You can force the type to be a string by stringifying it:	1031	You can force the type to be a JSON string by stringifying it:
398		1032
399	my $x = 3.1; # some variable containing a number	1033	my $x = 3.1; # some variable containing a number
400	"$x"; # stringified	1034	"$x"; # stringified
401	$x .= ""; # another, more awkward way to stringify	1035	$x .= ""; # another, more awkward way to stringify
402	print $x; # perl does it for you, too, quite often	1036	print $x; # perl does it for you, too, quite often
403		1037
404	You can force the type to be a number by numifying it:	1038	You can force the type to be a JSON number by numifying it:
405		1039
406	my $x = "3"; # some variable containing a string	1040	my $x = "3"; # some variable containing a string
407	$x += 0; # numify it, ensuring it will be dumped as a number	1041	$x += 0; # numify it, ensuring it will be dumped as a number
408	$x *= 1; # same thing, the choise is yours.	1042	$x *= 1; # same thing, the choice is yours.
409		1043
410	You can not currently output JSON booleans or force the type in other,	1044	You can not currently force the type in other, less obscure, ways. Tell me
411	less obscure, ways. Tell me if you need this capability.	1045	if you need this capability (but don't forget to explain why it's needed
412		1046	:).
413	=item circular data structures
414
415	Those will be encoded until memory or stackspace runs out.
416		1047
417	=back	1048	=back
418		1049
419	=head1 COMPARISON
420		1050
421	As already mentioned, this module was created because none of the existing	1051	=head1 ENCODING/CODESET FLAG NOTES
422	JSON modules could be made to work correctly. First I will describe the	1052
423	problems (or pleasures) I encountered with various existing JSON modules,	1053	The interested reader might have seen a number of flags that signify
424	followed by some benchmark values. JSON::XS was designed not to suffer	1054	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
425	from any of these problems or limitations.	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.
426		1075
427	=over 4	1076	=over 4
428		1077
429	=item JSON 1.07	1078	=item C<utf8> flag disabled
430		1079
431	Slow (but very portable, as it is written in pure Perl).	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).
432		1087
433	Undocumented/buggy Unicode handling (how JSON handles unicode values is	1088	This is useful when you want to do the encoding yourself (e.g. when you
434	undocumented. One can get far by feeding it unicode strings and doing	1089	want to have UTF-16 encoded JSON texts) or when some other layer does
435	en-/decoding oneself, but unicode escapes are not working properly).	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).
436		1093
437	No roundtripping (strings get clobbered if they look like numbers, e.g.	1094	=item C<utf8> flag enabled
438	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
439	decode into the number 2.
440		1095
441	=item JSON::PC 0.01	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.
442		1101
443	Very fast.	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.
444		1105
445	Undocumented/buggy Unicode handling.	1106	=item C<latin1> or C<ascii> flags enabled
446		1107
447	No roundtripping.	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.
448		1111
449	Has problems handling many Perl values (e.g. regex results and other magic	1112	If C<utf8> is disabled, then the result is also correctly encoded in those
450	values will make it croak).	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).
451		1117
452	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1118	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
453	which is not a valid JSON string.	1119	regardless of these flags, just some more characters will be escaped using
		1120	C<\uXXXX> then before.
454		1121
455	Unmaintained (maintainer unresponsive for many months, bugs are not	1122	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
456	getting fixed).	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.
457		1126
458	=item JSON::Syck 0.21	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.
459		1131
460	Very buggy (often crashes).	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.
461		1134
462	Very inflexible (no human-readable format supported, format pretty much	1135	The main use for C<latin1> is to relatively efficiently store binary data
463	undocumented. I need at least a format for easy reading by humans and a	1136	as JSON, at the expense of breaking compatibility with most JSON decoders.
464	single-line compact format for use in a protocol, and preferably a way to
465	generate ASCII-only JSON strings).
466		1137
467	Completely broken (and confusingly documented) Unicode handling (unicode	1138	The main use for C<ascii> is to force the output to not contain characters
468	escapes are not working properly, you need to set ImplicitUnicode to	1139	with values > 127, which means you can interpret the resulting string
469	I<different> values on en- and decoding to get symmetric behaviour).	1140	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
470		1141	8-bit-encoding, and still get the same data structure back. This is useful
471	No roundtripping (simple cases work, but this depends on wether the scalar	1142	when your channel for JSON transfer is not 8-bit clean or the encoding
472	value was used in a numeric context or not).	1143	might be mangled in between (e.g. in mail), and works because ASCII is a
473		1144	proper subset of most 8-bit and multibyte encodings in use in the world.
474	Dumping hashes may skip hash values depending on iterator state.
475
476	Unmaintained (maintainer unresponsive for many months, bugs are not
477	getting fixed).
478
479	Does not check input for validity (i.e. will accept non-JSON input and
480	return "something" instead of raising an exception. This is a security
481	issue: imagine two banks transfering money between each other using
482	JSON. One bank might parse a given non-JSON request and deduct money,
483	while the other might reject the transaction with a syntax error. While a
484	good protocol will at least recover, that is extra unnecessary work and
485	the transaction will still not succeed).
486
487	=item JSON::DWIW 0.04
488
489	Very fast. Very natural. Very nice.
490
491	Undocumented unicode handling (but the best of the pack. Unicode escapes
492	still don't get parsed properly).
493
494	Very inflexible.
495
496	No roundtripping.
497
498	Does not generate valid JSON (key strings are often unquoted, empty keys
499	result in nothing being output)
500
501	Does not check input for validity.
502		1145
503	=back	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
504		1202
505	=head2 SPEED	1203	=head2 SPEED
506		1204
507	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
508	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
509	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
510	system.	1208	system.
511		1209
512	First comes a comparison between various modules using a very short JSON	1210	First comes a comparison between various modules using
513	string (83 bytes), showing the number of encodes/decodes per second	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
		1217	It shows the number of encodes/decodes per second (JSON::XS uses
514	(JSON::XS is the functional interface, while JSON::XS/2 is the OO	1218	the functional interface, while JSON::XS/2 uses the OO interface
515	interface with pretty-printing and hashkey sorting enabled). Higher is	1219	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
516	better:	1220	shrink). Higher is better:
517		1221
518	module | encode | decode |	1222	module | encode | decode |
519	-----------|------------|------------|	1223	-----------|------------|------------|
520	JSON | 14006 | 6820 |	1224	JSON 1.x | 4990.842 | 4088.813 |
521	JSON::DWIW | 200937 | 120386 |	1225	JSON::DWIW | 51653.990 | 71575.154 |
522	JSON::PC | 85065 | 129366 |	1226	JSON::PC | 65948.176 | 74631.744 |
523	JSON::Syck | 59898 | 44232 |	1227	JSON::PP | 8931.652 | 3817.168 |
524	JSON::XS | 1171478 | 342435 |	1228	JSON::Syck | 24877.248 | 27776.848 |
525	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 |
526	-----------+------------+------------+	1233	-----------+------------+------------+
527		1234
528	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
529	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.
530		1239
531	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1240	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
532	search API (http://nanoref.com/yahooapis/mgPdGg):	1241	search API (L<http://dist.schmorp.de/misc/json/long.json>).
533		1242
534	module | encode | decode |	1243	module | encode | decode |
535	-----------|------------|------------|	1244	-----------|------------|------------|
536	JSON | 673 | 38 |	1245	JSON 1.x | 55.260 | 34.971 |
537	JSON::DWIW | 5271 | 770 |	1246	JSON::DWIW | 825.228 | 1082.513 |
538	JSON::PC | 9901 | 2491 |	1247	JSON::PC | 3571.444 | 2394.829 |
539	JSON::Syck | 2360 | 786 |	1248	JSON::PP | 210.987 | 32.574 |
540	JSON::XS | 37398 | 3202 |	1249	JSON::Syck | 552.551 | 787.544 |
541	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 |
542	-----------+------------+------------+	1254	-----------+------------+------------+
543		1255
544	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
545	every other module in the decoding case.	1257	decodes faster).
546		1258
547	On large strings containing lots of unicode characters, some modules	1259	On large strings containing lots of high Unicode characters, some modules
548	(such as JSON::PC) decode faster than JSON::XS, but the result will be	1260	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
549	broken due to missing unicode handling. Others refuse to decode or encode	1261	will be broken due to missing (or wrong) Unicode handling. Others refuse
550	properly, so it was impossible to prepare a fair comparison table for that	1262	to decode or encode properly, so it was impossible to prepare a fair
551	case.	1263	comparison table for that case.
552		1264
553	=head1 RESOURCE LIMITS
554		1265
555	JSON::XS does not impose any limits on the size of JSON texts or Perl	1266	=head1 SECURITY CONSIDERATIONS
556	values they represent - if your machine can handle it, JSON::XS will	1267
557	encode or decode it. Future versions might optionally impose structure	1268	When you are using JSON in a protocol, talking to untrusted potentially
558	depth and memory use resource limits.	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
559		1319
560	=head1 BUGS	1320	=head1 BUGS
561		1321
562	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
563	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
564	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
565	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.
566		1329
567	=cut	1330	=cut
568		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
569	1;	1353	1;
		1354
		1355	=head1 SEE ALSO
		1356
		1357	The F<json_xs> command line utility for quick experiments.
570		1358
571	=head1 AUTHOR	1359	=head1 AUTHOR
572		1360
573	Marc Lehmann <schmorp@schmorp.de>	1361	Marc Lehmann <schmorp@schmorp.de>
574	http://home.schmorp.de/	1362	http://home.schmorp.de/

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