[ViewVC] Diff of: cvs/JSON-XS/XS.pm

Comparing JSON-XS/XS.pm (file contents):
Revision 1.13 by root, Fri Mar 23 18:37:30 2007 UTC vs.
Revision 1.83 by root, Sun Jan 20 19:19:07 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	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		6	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		7
5	=head1 SYNOPSIS	8	=head1 SYNOPSIS
6		9
7	use JSON::XS;	10	use JSON::XS;
8		11
9	# exported functions, croak on error	12	# exported functions, they croak on error
		13	# and expect/generate UTF-8
10		14
11	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	15	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
12	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	16	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
13		17
14	# oo-interface	18	# OO-interface
15		19
16	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	20	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
17	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	21	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
18	$perl_scalar = $coder->decode ($unicode_json_text);	22	$perl_scalar = $coder->decode ($unicode_json_text);
19		23
		24	# Note that JSON version 2.0 and above will automatically use JSON::XS
		25	# if available, at virtually no speed overhead either, so you should
		26	# be able to just:
		27
		28	use JSON;
		29
		30	# and do the same things, except that you have a pure-perl fallback now.
		31
20	=head1 DESCRIPTION	32	=head1 DESCRIPTION
21		33
22	This module converts Perl data structures to JSON and vice versa. Its	34	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	35	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.	36	I<fast>. To reach the latter goal it was written in C.
		37
		38	Beginning with version 2.0 of the JSON module, when both JSON and
		39	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		40	overriden) with no overhead due to emulation (by inheritign constructor
		41	and methods). If JSON::XS is not available, it will fall back to the
		42	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		43	gives you a portable JSON API that can be fast when you need and doesn't
		44	require a C compiler when that is a problem.
25		45
26	As this is the n-th-something JSON module on CPAN, what was the reason	46	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	47	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	48	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	49	their maintainers are unresponsive, gone missing, or not listening to bug
36		56
37	=head2 FEATURES	57	=head2 FEATURES
38		58
39	=over 4	59	=over 4
40		60
41	=item * correct handling of unicode issues	61	=item * correct Unicode handling
42		62
43	This module knows how to handle Unicode, and even documents how and when	63	This module knows how to handle Unicode, and even documents how and when
44	it does so.	64	it does so.
45		65
46	=item * round-trip integrity	66	=item * round-trip integrity
47		67
48	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only datatypes supported
49	by JSON, the deserialised data structure is identical on the Perl level.	69	by JSON, the deserialised data structure is identical on the Perl level.
50	(e.g. the string "2.0" doesn't suddenly become "2").	70	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
		71	like a number).
51		72
52	=item * strict checking of JSON correctness	73	=item * strict checking of JSON correctness
53		74
54	There is no guessing, no generating of illegal JSON strings by default,	75	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	76	and only JSON is accepted as input by default (the latter is a security
56	feature).	77	feature).
57		78
58	=item * fast	79	=item * fast
59		80
…		…
65	This module has both a simple functional interface as well as an OO	86	This module has both a simple functional interface as well as an OO
66	interface.	87	interface.
67		88
68	=item * reasonably versatile output formats	89	=item * reasonably versatile output formats
69		90
70	You can choose between the most compact guarenteed single-line format	91	You can choose between the most compact guaranteed single-line format
71	possible (nice for simple line-based protocols), a pure-ascii format (for	92	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	93	(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	94	Unicode range), or a pretty-printed format (for when you want to read that
74	whatever way you like.	95	stuff). Or you can combine those features in whatever way you like.
75		96
76	=back	97	=back
77		98
78	=cut	99	=cut
79		100
80	package JSON::XS;	101	package JSON::XS;
81		102
82	BEGIN {	103	use strict;
		104
83	$VERSION = '0.3';	105	our $VERSION = '2.01';
84	@ISA = qw(Exporter);	106	our @ISA = qw(Exporter);
85		107
86	@EXPORT = qw(to_json from_json);	108	our @EXPORT = qw(encode_json decode_json to_json from_json);
87	require Exporter;
88		109
		110	sub to_json($) {
89	require XSLoader;	111	require Carp;
90	XSLoader::load JSON::XS::, $VERSION;	112	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
91	}	113	}
92		114
		115	sub from_json($) {
		116	require Carp;
		117	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");
		118	}
		119
		120	use Exporter;
		121	use XSLoader;
		122
93	=head1 FUNCTIONAL INTERFACE	123	=head1 FUNCTIONAL INTERFACE
94		124
95	The following convinience methods are provided by this module. They are	125	The following convenience methods are provided by this module. They are
96	exported by default:	126	exported by default:
97		127
98	=over 4	128	=over 4
99		129
100	=item $json_string = to_json $perl_scalar	130	=item $json_text = encode_json $perl_scalar
101		131
102	Converts the given Perl data structure (a simple scalar or a reference to	132	Converts the given Perl data structure to a UTF-8 encoded, binary string
103	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	133	(that is, the string contains octets only). Croaks on error.
104	octets only). Croaks on error.
105		134
106	This function call is functionally identical to C<< JSON::XS->new->utf8->encode ($perl_scalar) >>.	135	This function call is functionally identical to:
107		136
		137	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		138
		139	except being faster.
		140
108	=item $perl_scalar = from_json $json_string	141	=item $perl_scalar = decode_json $json_text
109		142
110	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	143	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
111	parse that as an UTF-8 encoded JSON string, returning the resulting simple	144	to parse that as an UTF-8 encoded JSON text, returning the resulting
112	scalar or reference. Croaks on error.	145	reference. Croaks on error.
113		146
114	This function call is functionally identical to C<< JSON::XS->new->utf8->decode ($json_string) >>.	147	This function call is functionally identical to:
		148
		149	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		150
		151	except being faster.
		152
		153	=item $is_boolean = JSON::XS::is_bool $scalar
		154
		155	Returns true if the passed scalar represents either JSON::XS::true or
		156	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		157	and are used to represent JSON C<true> and C<false> values in Perl.
		158
		159	See MAPPING, below, for more information on how JSON values are mapped to
		160	Perl.
115		161
116	=back	162	=back
		163
		164
		165	=head1 A FEW NOTES ON UNICODE AND PERL
		166
		167	Since this often leads to confusion, here are a few very clear words on
		168	how Unicode works in Perl, modulo bugs.
		169
		170	=over 4
		171
		172	=item 1. Perl strings can store characters with ordinal values > 255.
		173
		174	This enables you to store Unicode characters as single characters in a
		175	Perl string - very natural.
		176
		177	=item 2. Perl does I<not> associate an encoding with your strings.
		178
		179	Unless you force it to, e.g. when matching it against a regex, or printing
		180	the scalar to a file, in which case Perl either interprets your string as
		181	locale-encoded text, octets/binary, or as Unicode, depending on various
		182	settings. In no case is an encoding stored together with your data, it is
		183	I<use> that decides encoding, not any magical metadata.
		184
		185	=item 3. The internal utf-8 flag has no meaning with regards to the
		186	encoding of your string.
		187
		188	Just ignore that flag unless you debug a Perl bug, a module written in
		189	XS or want to dive into the internals of perl. Otherwise it will only
		190	confuse you, as, despite the name, it says nothing about how your string
		191	is encoded. You can have Unicode strings with that flag set, with that
		192	flag clear, and you can have binary data with that flag set and that flag
		193	clear. Other possibilities exist, too.
		194
		195	If you didn't know about that flag, just the better, pretend it doesn't
		196	exist.
		197
		198	=item 4. A "Unicode String" is simply a string where each character can be
		199	validly interpreted as a Unicode codepoint.
		200
		201	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		202	Unicode string encoded in UTF-8, giving you a binary string.
		203
		204	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		205
		206	It's a fact. Learn to live with it.
		207
		208	=back
		209
		210	I hope this helps :)
		211
117		212
118	=head1 OBJECT-ORIENTED INTERFACE	213	=head1 OBJECT-ORIENTED INTERFACE
119		214
120	The object oriented interface lets you configure your own encoding or	215	The object oriented interface lets you configure your own encoding or
121	decoding style, within the limits of supported formats.	216	decoding style, within the limits of supported formats.
…		…
128	strings. All boolean flags described below are by default I<disabled>.	223	strings. All boolean flags described below are by default I<disabled>.
129		224
130	The mutators for flags all return the JSON object again and thus calls can	225	The mutators for flags all return the JSON object again and thus calls can
131	be chained:	226	be chained:
132		227
133	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	228	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
134	=> {"a": [1, 2]}	229	=> {"a": [1, 2]}
135		230
136	=item $json = $json->ascii ([$enable])	231	=item $json = $json->ascii ([$enable])
137		232
		233	=item $enabled = $json->get_ascii
		234
138	If C<$enable> is true (or missing), then the C<encode> method will	235	If C<$enable> is true (or missing), then the C<encode> method will not
139	not generate characters outside the code range C<0..127>. Any unicode	236	generate characters outside the code range C<0..127> (which is ASCII). Any
140	characters outside that range will be escaped using either a single	237	Unicode characters outside that range will be escaped using either a
141	\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per	238	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
142	RFC4627.	239	as per RFC4627. The resulting encoded JSON text can be treated as a native
		240	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		241	or any other superset of ASCII.
143		242
144	If C<$enable> is false, then the C<encode> method will not escape Unicode	243	If C<$enable> is false, then the C<encode> method will not escape Unicode
145	characters unless necessary.	244	characters unless required by the JSON syntax or other flags. This results
		245	in a faster and more compact format.
146		246
		247	The main use for this flag is to produce JSON texts that can be
		248	transmitted over a 7-bit channel, as the encoded JSON texts will not
		249	contain any 8 bit characters.
		250
147	JSON::XS->new->ascii (1)->encode (chr 0x10401)	251	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
148	=> \ud801\udc01	252	=> ["\ud801\udc01"]
		253
		254	=item $json = $json->latin1 ([$enable])
		255
		256	=item $enabled = $json->get_latin1
		257
		258	If C<$enable> is true (or missing), then the C<encode> method will encode
		259	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		260	outside the code range C<0..255>. The resulting string can be treated as a
		261	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		262	will not be affected in any way by this flag, as C<decode> by default
		263	expects Unicode, which is a strict superset of latin1.
		264
		265	If C<$enable> is false, then the C<encode> method will not escape Unicode
		266	characters unless required by the JSON syntax or other flags.
		267
		268	The main use for this flag is efficiently encoding binary data as JSON
		269	text, as most octets will not be escaped, resulting in a smaller encoded
		270	size. The disadvantage is that the resulting JSON text is encoded
		271	in latin1 (and must correctly be treated as such when storing and
		272	transferring), a rare encoding for JSON. It is therefore most useful when
		273	you want to store data structures known to contain binary data efficiently
		274	in files or databases, not when talking to other JSON encoders/decoders.
		275
		276	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		277	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
149		278
150	=item $json = $json->utf8 ([$enable])	279	=item $json = $json->utf8 ([$enable])
151		280
		281	=item $enabled = $json->get_utf8
		282
152	If C<$enable> is true (or missing), then the C<encode> method will encode	283	If C<$enable> is true (or missing), then the C<encode> method will encode
153	the JSON string into UTF-8, as required by many protocols, while the	284	the JSON result into UTF-8, as required by many protocols, while the
154	C<decode> method expects to be handled an UTF-8-encoded string. Please	285	C<decode> method expects to be handled an UTF-8-encoded string. Please
155	note that UTF-8-encoded strings do not contain any characters outside the	286	note that UTF-8-encoded strings do not contain any characters outside the
156	range C<0..255>, they are thus useful for bytewise/binary I/O.	287	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		288	versions, enabling this option might enable autodetection of the UTF-16
		289	and UTF-32 encoding families, as described in RFC4627.
157		290
158	If C<$enable> is false, then the C<encode> method will return the JSON	291	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	292	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	293	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.	294	to be done yourself, e.g. using the Encode module.
162		295
163	Example, output UTF-16-encoded JSON:	296	Example, output UTF-16BE-encoded JSON:
		297
		298	use Encode;
		299	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		300
		301	Example, decode UTF-32LE-encoded JSON:
		302
		303	use Encode;
		304	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
164		305
165	=item $json = $json->pretty ([$enable])	306	=item $json = $json->pretty ([$enable])
166		307
167	This enables (or disables) all of the C<indent>, C<space_before> and	308	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	309	C<space_after> (and in the future possibly more) flags in one call to
…		…
179	]	320	]
180	}	321	}
181		322
182	=item $json = $json->indent ([$enable])	323	=item $json = $json->indent ([$enable])
183		324
		325	=item $enabled = $json->get_indent
		326
184	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	327	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
185	format as output, putting every array member or object/hash key-value pair	328	format as output, putting every array member or object/hash key-value pair
186	into its own line, identing them properly.	329	into its own line, indenting them properly.
187		330
188	If C<$enable> is false, no newlines or indenting will be produced, and the	331	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>.	332	resulting JSON text is guaranteed not to contain any C<newlines>.
190		333
191	This setting has no effect when decoding JSON strings.	334	This setting has no effect when decoding JSON texts.
192		335
193	=item $json = $json->space_before ([$enable])	336	=item $json = $json->space_before ([$enable])
		337
		338	=item $enabled = $json->get_space_before
194		339
195	If C<$enable> is true (or missing), then the C<encode> method will add an extra	340	If C<$enable> is true (or missing), then the C<encode> method will add an extra
196	optional space before the C<:> separating keys from values in JSON objects.	341	optional space before the C<:> separating keys from values in JSON objects.
197		342
198	If C<$enable> is false, then the C<encode> method will not add any extra	343	If C<$enable> is false, then the C<encode> method will not add any extra
199	space at those places.	344	space at those places.
200		345
201	This setting has no effect when decoding JSON strings. You will also most	346	This setting has no effect when decoding JSON texts. You will also
202	likely combine this setting with C<space_after>.	347	most likely combine this setting with C<space_after>.
203		348
204	Example, space_before enabled, space_after and indent disabled:	349	Example, space_before enabled, space_after and indent disabled:
205		350
206	{"key" :"value"}	351	{"key" :"value"}
207		352
208	=item $json = $json->space_after ([$enable])	353	=item $json = $json->space_after ([$enable])
		354
		355	=item $enabled = $json->get_space_after
209		356
210	If C<$enable> is true (or missing), then the C<encode> method will add an extra	357	If C<$enable> is true (or missing), then the C<encode> method will add an extra
211	optional space after the C<:> separating keys from values in JSON objects	358	optional space after the C<:> separating keys from values in JSON objects
212	and extra whitespace after the C<,> separating key-value pairs and array	359	and extra whitespace after the C<,> separating key-value pairs and array
213	members.	360	members.
214		361
215	If C<$enable> is false, then the C<encode> method will not add any extra	362	If C<$enable> is false, then the C<encode> method will not add any extra
216	space at those places.	363	space at those places.
217		364
218	This setting has no effect when decoding JSON strings.	365	This setting has no effect when decoding JSON texts.
219		366
220	Example, space_before and indent disabled, space_after enabled:	367	Example, space_before and indent disabled, space_after enabled:
221		368
222	{"key": "value"}	369	{"key": "value"}
223		370
		371	=item $json = $json->relaxed ([$enable])
		372
		373	=item $enabled = $json->get_relaxed
		374
		375	If C<$enable> is true (or missing), then C<decode> will accept some
		376	extensions to normal JSON syntax (see below). C<encode> will not be
		377	affected in anyway. I<Be aware that this option makes you accept invalid
		378	JSON texts as if they were valid!>. I suggest only to use this option to
		379	parse application-specific files written by humans (configuration files,
		380	resource files etc.)
		381
		382	If C<$enable> is false (the default), then C<decode> will only accept
		383	valid JSON texts.
		384
		385	Currently accepted extensions are:
		386
		387	=over 4
		388
		389	=item * list items can have an end-comma
		390
		391	JSON I<separates> array elements and key-value pairs with commas. This
		392	can be annoying if you write JSON texts manually and want to be able to
		393	quickly append elements, so this extension accepts comma at the end of
		394	such items not just between them:
		395
		396	[
		397	1,
		398	2, <- this comma not normally allowed
		399	]
		400	{
		401	"k1": "v1",
		402	"k2": "v2", <- this comma not normally allowed
		403	}
		404
		405	=item * shell-style '#'-comments
		406
		407	Whenever JSON allows whitespace, shell-style comments are additionally
		408	allowed. They are terminated by the first carriage-return or line-feed
		409	character, after which more white-space and comments are allowed.
		410
		411	[
		412	1, # this comment not allowed in JSON
		413	# neither this one...
		414	]
		415
		416	=back
		417
224	=item $json = $json->canonical ([$enable])	418	=item $json = $json->canonical ([$enable])
		419
		420	=item $enabled = $json->get_canonical
225		421
226	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	422	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
227	by sorting their keys. This is adding a comparatively high overhead.	423	by sorting their keys. This is adding a comparatively high overhead.
228		424
229	If C<$enable> is false, then the C<encode> method will output key-value	425	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	426	pairs in the order Perl stores them (which will likely change between runs
231	of the same script).	427	of the same script).
232		428
233	This option is useful if you want the same data structure to be encoded as	429	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,	430	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,	431	the same hash might be encoded differently even if contains the same data,
236	as key-value pairs have no inherent ordering in Perl.	432	as key-value pairs have no inherent ordering in Perl.
237		433
238	This setting has no effect when decoding JSON strings.	434	This setting has no effect when decoding JSON texts.
239		435
240	=item $json = $json->allow_nonref ([$enable])	436	=item $json = $json->allow_nonref ([$enable])
		437
		438	=item $enabled = $json->get_allow_nonref
241		439
242	If C<$enable> is true (or missing), then the C<encode> method can convert a	440	If C<$enable> is true (or missing), then the C<encode> method can convert a
243	non-reference into its corresponding string, number or null JSON value,	441	non-reference into its corresponding string, number or null JSON value,
244	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	442	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
245	values instead of croaking.	443	values instead of croaking.
246		444
247	If C<$enable> is false, then the C<encode> method will croak if it isn't	445	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	446	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	447	or array. Likewise, C<decode> will croak if given something that is not a
250	JSON object or array.	448	JSON object or array.
251		449
252	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,	450	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
253	resulting in an invalid JSON text:	451	resulting in an invalid JSON text:
254		452
255	JSON::XS->new->allow_nonref->encode ("Hello, World!")	453	JSON::XS->new->allow_nonref->encode ("Hello, World!")
256	=> "Hello, World!"	454	=> "Hello, World!"
257		455
		456	=item $json = $json->allow_blessed ([$enable])
		457
		458	=item $enabled = $json->get_allow_blessed
		459
		460	If C<$enable> is true (or missing), then the C<encode> method will not
		461	barf when it encounters a blessed reference. Instead, the value of the
		462	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		463	disabled or no C<TO_JSON> method found) or a representation of the
		464	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		465	encoded. Has no effect on C<decode>.
		466
		467	If C<$enable> is false (the default), then C<encode> will throw an
		468	exception when it encounters a blessed object.
		469
		470	=item $json = $json->convert_blessed ([$enable])
		471
		472	=item $enabled = $json->get_convert_blessed
		473
		474	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		475	blessed object, will check for the availability of the C<TO_JSON> method
		476	on the object's class. If found, it will be called in scalar context
		477	and the resulting scalar will be encoded instead of the object. If no
		478	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		479	to do.
		480
		481	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		482	returns other blessed objects, those will be handled in the same
		483	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		484	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		485	methods called by the Perl core (== not by the user of the object) are
		486	usually in upper case letters and to avoid collisions with any C<to_json>
		487	function or method.
		488
		489	This setting does not yet influence C<decode> in any way, but in the
		490	future, global hooks might get installed that influence C<decode> and are
		491	enabled by this setting.
		492
		493	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		494	to do when a blessed object is found.
		495
		496	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		497
		498	When C<$coderef> is specified, it will be called from C<decode> each
		499	time it decodes a JSON object. The only argument is a reference to the
		500	newly-created hash. If the code references returns a single scalar (which
		501	need not be a reference), this value (i.e. a copy of that scalar to avoid
		502	aliasing) is inserted into the deserialised data structure. If it returns
		503	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		504	original deserialised hash will be inserted. This setting can slow down
		505	decoding considerably.
		506
		507	When C<$coderef> is omitted or undefined, any existing callback will
		508	be removed and C<decode> will not change the deserialised hash in any
		509	way.
		510
		511	Example, convert all JSON objects into the integer 5:
		512
		513	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		514	# returns [5]
		515	$js->decode ('[{}]')
		516	# throw an exception because allow_nonref is not enabled
		517	# so a lone 5 is not allowed.
		518	$js->decode ('{"a":1, "b":2}');
		519
		520	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		521
		522	Works remotely similar to C<filter_json_object>, but is only called for
		523	JSON objects having a single key named C<$key>.
		524
		525	This C<$coderef> is called before the one specified via
		526	C<filter_json_object>, if any. It gets passed the single value in the JSON
		527	object. If it returns a single value, it will be inserted into the data
		528	structure. If it returns nothing (not even C<undef> but the empty list),
		529	the callback from C<filter_json_object> will be called next, as if no
		530	single-key callback were specified.
		531
		532	If C<$coderef> is omitted or undefined, the corresponding callback will be
		533	disabled. There can only ever be one callback for a given key.
		534
		535	As this callback gets called less often then the C<filter_json_object>
		536	one, decoding speed will not usually suffer as much. Therefore, single-key
		537	objects make excellent targets to serialise Perl objects into, especially
		538	as single-key JSON objects are as close to the type-tagged value concept
		539	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		540	support this in any way, so you need to make sure your data never looks
		541	like a serialised Perl hash.
		542
		543	Typical names for the single object key are C<__class_whatever__>, or
		544	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		545	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		546	with real hashes.
		547
		548	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		549	into the corresponding C<< $WIDGET{<id>} >> object:
		550
		551	# return whatever is in $WIDGET{5}:
		552	JSON::XS
		553	->new
		554	->filter_json_single_key_object (__widget__ => sub {
		555	$WIDGET{ $_[0] }
		556	})
		557	->decode ('{"__widget__": 5')
		558
		559	# this can be used with a TO_JSON method in some "widget" class
		560	# for serialisation to json:
		561	sub WidgetBase::TO_JSON {
		562	my ($self) = @_;
		563
		564	unless ($self->{id}) {
		565	$self->{id} = ..get..some..id..;
		566	$WIDGET{$self->{id}} = $self;
		567	}
		568
		569	{ __widget__ => $self->{id} }
		570	}
		571
258	=item $json = $json->shrink ([$enable])	572	=item $json = $json->shrink ([$enable])
259		573
		574	=item $enabled = $json->get_shrink
		575
260	Perl usually over-allocates memory a bit when allocating space for	576	Perl usually over-allocates memory a bit when allocating space for
261	strings. This flag optionally resizes strings generated by either	577	strings. This flag optionally resizes strings generated by either
262	C<encode> or C<decode> to their minimum size possible. This can save	578	C<encode> or C<decode> to their minimum size possible. This can save
263	memory when your JSON strings are either very very long or you have many	579	memory when your JSON texts are either very very long or you have many
264	short strings. It will also try to downgrade any strings to octet-form	580	short strings. It will also try to downgrade any strings to octet-form
265	if possible: perl stores strings internally either in an encoding called	581	if possible: perl stores strings internally either in an encoding called
266	UTF-X or in octet-form. The latter cannot store everything but uses less	582	UTF-X or in octet-form. The latter cannot store everything but uses less
267	space in general.	583	space in general (and some buggy Perl or C code might even rely on that
		584	internal representation being used).
268		585
		586	The actual definition of what shrink does might change in future versions,
		587	but it will always try to save space at the expense of time.
		588
269	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	589	If C<$enable> is true (or missing), the string returned by C<encode> will
270	while all strings generated by C<decode> will also be shrunk-to-fit.	590	be shrunk-to-fit, while all strings generated by C<decode> will also be
		591	shrunk-to-fit.
271		592
272	If C<$enable> is false, then the normal perl allocation algorithms are used.	593	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.	594	If you work with your data, then this is likely to be faster.
274		595
275	In the future, this setting might control other things, such as converting	596	In the future, this setting might control other things, such as converting
276	strings that look like integers or floats into integers or floats	597	strings that look like integers or floats into integers or floats
277	internally (there is no difference on the Perl level), saving space.	598	internally (there is no difference on the Perl level), saving space.
278		599
		600	=item $json = $json->max_depth ([$maximum_nesting_depth])
		601
		602	=item $max_depth = $json->get_max_depth
		603
		604	Sets the maximum nesting level (default C<512>) accepted while encoding
		605	or decoding. If the JSON text or Perl data structure has an equal or
		606	higher nesting level then this limit, then the encoder and decoder will
		607	stop and croak at that point.
		608
		609	Nesting level is defined by number of hash- or arrayrefs that the encoder
		610	needs to traverse to reach a given point or the number of C<{> or C<[>
		611	characters without their matching closing parenthesis crossed to reach a
		612	given character in a string.
		613
		614	Setting the maximum depth to one disallows any nesting, so that ensures
		615	that the object is only a single hash/object or array.
		616
		617	The argument to C<max_depth> will be rounded up to the next highest power
		618	of two. If no argument is given, the highest possible setting will be
		619	used, which is rarely useful.
		620
		621	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		622
		623	=item $json = $json->max_size ([$maximum_string_size])
		624
		625	=item $max_size = $json->get_max_size
		626
		627	Set the maximum length a JSON text may have (in bytes) where decoding is
		628	being attempted. The default is C<0>, meaning no limit. When C<decode>
		629	is called on a string longer then this number of characters it will not
		630	attempt to decode the string but throw an exception. This setting has no
		631	effect on C<encode> (yet).
		632
		633	The argument to C<max_size> will be rounded up to the next B<highest>
		634	power of two (so may be more than requested). If no argument is given, the
		635	limit check will be deactivated (same as when C<0> is specified).
		636
		637	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		638
279	=item $json_string = $json->encode ($perl_scalar)	639	=item $json_text = $json->encode ($perl_scalar)
280		640
281	Converts the given Perl data structure (a simple scalar or a reference	641	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	642	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	643	converted into JSON string or number sequences, while references to arrays
284	become JSON arrays and references to hashes become JSON objects. Undefined	644	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>	645	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
286	nor C<false> values will be generated.	646	nor C<false> values will be generated.
287		647
288	=item $perl_scalar = $json->decode ($json_string)	648	=item $perl_scalar = $json->decode ($json_text)
289		649
290	The opposite of C<encode>: expects a JSON string and tries to parse it,	650	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.	651	returning the resulting simple scalar or reference. Croaks on error.
292		652
293	JSON numbers and strings become simple Perl scalars. JSON arrays become	653	JSON numbers and strings become simple Perl scalars. JSON arrays become
294	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	654	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>.	655	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
296		656
		657	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		658
		659	This works like the C<decode> method, but instead of raising an exception
		660	when there is trailing garbage after the first JSON object, it will
		661	silently stop parsing there and return the number of characters consumed
		662	so far.
		663
		664	This is useful if your JSON texts are not delimited by an outer protocol
		665	(which is not the brightest thing to do in the first place) and you need
		666	to know where the JSON text ends.
		667
		668	JSON::XS->new->decode_prefix ("[1] the tail")
		669	=> ([], 3)
		670
297	=back	671	=back
		672
298		673
299	=head1 MAPPING	674	=head1 MAPPING
300		675
301	This section describes how JSON::XS maps Perl values to JSON values and	676	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	677	vice versa. These mappings are designed to "do the right thing" in most
303	circumstances automatically, preserving round-tripping characteristics	678	circumstances automatically, preserving round-tripping characteristics
304	(what you put in comes out as something equivalent).	679	(what you put in comes out as something equivalent).
305		680
306	For the more enlightened: note that in the following descriptions,	681	For the more enlightened: note that in the following descriptions,
307	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	682	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
308	refers to the abstract Perl language itself.	683	refers to the abstract Perl language itself.
309		684
		685
310	=head2 JSON -> PERL	686	=head2 JSON -> PERL
311		687
312	=over 4	688	=over 4
313		689
314	=item object	690	=item object
315		691
316	A JSON object becomes a reference to a hash in Perl. No ordering of object	692	A JSON object becomes a reference to a hash in Perl. No ordering of object
317	keys is preserved.	693	keys is preserved (JSON does not preserve object key ordering itself).
318		694
319	=item array	695	=item array
320		696
321	A JSON array becomes a reference to an array in Perl.	697	A JSON array becomes a reference to an array in Perl.
322		698
…		…
326	are represented by the same codepoints in the Perl string, so no manual	702	are represented by the same codepoints in the Perl string, so no manual
327	decoding is necessary.	703	decoding is necessary.
328		704
329	=item number	705	=item number
330		706
331	A JSON number becomes either an integer or numeric (floating point)	707	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	708	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	709	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	710	the conversion details, but an integer may take slightly less memory and
335	represent more values exactly than (floating point) numbers.	711	might represent more values exactly than (floating point) numbers.
		712
		713	If the number consists of digits only, JSON::XS will try to represent
		714	it as an integer value. If that fails, it will try to represent it as
		715	a numeric (floating point) value if that is possible without loss of
		716	precision. Otherwise it will preserve the number as a string value.
		717
		718	Numbers containing a fractional or exponential part will always be
		719	represented as numeric (floating point) values, possibly at a loss of
		720	precision.
		721
		722	This might create round-tripping problems as numbers might become strings,
		723	but as Perl is typeless there is no other way to do it.
336		724
337	=item true, false	725	=item true, false
338		726
339	These JSON atoms become C<0>, C<1>, respectively. Information is lost in	727	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
340	this process. Future versions might represent those values differently,	728	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	729	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
342	Perl.	730	the C<JSON::XS::is_bool> function.
343		731
344	=item null	732	=item null
345		733
346	A JSON null atom becomes C<undef> in Perl.	734	A JSON null atom becomes C<undef> in Perl.
347		735
348	=back	736	=back
		737
349		738
350	=head2 PERL -> JSON	739	=head2 PERL -> JSON
351		740
352	The mapping from Perl to JSON is slightly more difficult, as Perl is a	741	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	742	truly typeless language, so we can only guess which JSON type is meant by
…		…
356	=over 4	745	=over 4
357		746
358	=item hash references	747	=item hash references
359		748
360	Perl hash references become JSON objects. As there is no inherent ordering	749	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	750	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	751	pseudo-random order that can change between runs of the same program but
363	within the single run of a program. JSON::XS can optionally sort the hash	752	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	753	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	754	the same datastructure will serialise to the same JSON text (given same
366	JSON::XS), but this incurs a runtime overhead.	755	settings and version of JSON::XS), but this incurs a runtime overhead
		756	and is only rarely useful, e.g. when you want to compare some JSON text
		757	against another for equality.
367		758
368	=item array references	759	=item array references
369		760
370	Perl array references become JSON arrays.	761	Perl array references become JSON arrays.
371		762
		763	=item other references
		764
		765	Other unblessed references are generally not allowed and will cause an
		766	exception to be thrown, except for references to the integers C<0> and
		767	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		768	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		769
		770	encode_json [\0,JSON::XS::true] # yields [false,true]
		771
		772	=item JSON::XS::true, JSON::XS::false
		773
		774	These special values become JSON true and JSON false values,
		775	respectively. You can also use C<\1> and C<\0> directly if you want.
		776
372	=item blessed objects	777	=item blessed objects
373		778
374	Blessed objects are not allowed. JSON::XS currently tries to encode their	779	Blessed objects are not directly representable in JSON. See the
375	underlying representation (hash- or arrayref), but this behaviour might	780	C<allow_blessed> and C<convert_blessed> methods on various options on
376	change in future versions.	781	how to deal with this: basically, you can choose between throwing an
		782	exception, encoding the reference as if it weren't blessed, or provide
		783	your own serialiser method.
377		784
378	=item simple scalars	785	=item simple scalars
379		786
380	Simple Perl scalars (any scalar that is not a reference) are the most	787	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	788	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	789	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:	790	before encoding as JSON strings, and anything else as number value:
384		791
385	# dump as number	792	# dump as number
386	to_json [2] # yields [2]	793	encode_json [2] # yields [2]
387	to_json [-3.0e17] # yields [-3e+17]	794	encode_json [-3.0e17] # yields [-3e+17]
388	my $value = 5; to_json [$value] # yields [5]	795	my $value = 5; encode_json [$value] # yields [5]
389		796
390	# used as string, so dump as string	797	# used as string, so dump as string
391	print $value;	798	print $value;
392	to_json [$value] # yields ["5"]	799	encode_json [$value] # yields ["5"]
393		800
394	# undef becomes null	801	# undef becomes null
395	to_json [undef] # yields [null]	802	encode_json [undef] # yields [null]
396		803
397	You can force the type to be a string by stringifying it:	804	You can force the type to be a JSON string by stringifying it:
398		805
399	my $x = 3.1; # some variable containing a number	806	my $x = 3.1; # some variable containing a number
400	"$x"; # stringified	807	"$x"; # stringified
401	$x .= ""; # another, more awkward way to stringify	808	$x .= ""; # another, more awkward way to stringify
402	print $x; # perl does it for you, too, quite often	809	print $x; # perl does it for you, too, quite often
403		810
404	You can force the type to be a number by numifying it:	811	You can force the type to be a JSON number by numifying it:
405		812
406	my $x = "3"; # some variable containing a string	813	my $x = "3"; # some variable containing a string
407	$x += 0; # numify it, ensuring it will be dumped as a number	814	$x += 0; # numify it, ensuring it will be dumped as a number
408	$x *= 1; # same thing, the choise is yours.	815	$x *= 1; # same thing, the choice is yours.
409		816
410	You can not currently output JSON booleans or force the type in other,	817	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.	818	if you need this capability (but don't forget to explain why its needed
412		819	:).
413	=item circular data structures
414
415	Those will be encoded until memory or stackspace runs out.
416		820
417	=back	821	=back
		822
418		823
419	=head1 COMPARISON	824	=head1 COMPARISON
420		825
421	As already mentioned, this module was created because none of the existing	826	As already mentioned, this module was created because none of the existing
422	JSON modules could be made to work correctly. First I will describe the	827	JSON modules could be made to work correctly. First I will describe the
…		…
428		833
429	=item JSON 1.07	834	=item JSON 1.07
430		835
431	Slow (but very portable, as it is written in pure Perl).	836	Slow (but very portable, as it is written in pure Perl).
432		837
433	Undocumented/buggy Unicode handling (how JSON handles unicode values is	838	Undocumented/buggy Unicode handling (how JSON handles Unicode values is
434	undocumented. One can get far by feeding it unicode strings and doing	839	undocumented. One can get far by feeding it Unicode strings and doing
435	en-/decoding oneself, but unicode escapes are not working properly).	840	en-/decoding oneself, but Unicode escapes are not working properly).
436		841
437	No roundtripping (strings get clobbered if they look like numbers, e.g.	842	No round-tripping (strings get clobbered if they look like numbers, e.g.
438	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	843	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.	844	decode into the number 2.
440		845
441	=item JSON::PC 0.01	846	=item JSON::PC 0.01
442		847
443	Very fast.	848	Very fast.
444		849
445	Undocumented/buggy Unicode handling.	850	Undocumented/buggy Unicode handling.
446		851
447	No roundtripping.	852	No round-tripping.
448		853
449	Has problems handling many Perl values (e.g. regex results and other magic	854	Has problems handling many Perl values (e.g. regex results and other magic
450	values will make it croak).	855	values will make it croak).
451		856
452	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	857	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
453	which is not a valid JSON string.	858	which is not a valid JSON text.
454		859
455	Unmaintained (maintainer unresponsive for many months, bugs are not	860	Unmaintained (maintainer unresponsive for many months, bugs are not
456	getting fixed).	861	getting fixed).
457		862
458	=item JSON::Syck 0.21	863	=item JSON::Syck 0.21
…		…
460	Very buggy (often crashes).	865	Very buggy (often crashes).
461		866
462	Very inflexible (no human-readable format supported, format pretty much	867	Very inflexible (no human-readable format supported, format pretty much
463	undocumented. I need at least a format for easy reading by humans and a	868	undocumented. I need at least a format for easy reading by humans and a
464	single-line compact format for use in a protocol, and preferably a way to	869	single-line compact format for use in a protocol, and preferably a way to
465	generate ASCII-only JSON strings).	870	generate ASCII-only JSON texts).
466		871
467	Completely broken (and confusingly documented) Unicode handling (unicode	872	Completely broken (and confusingly documented) Unicode handling (Unicode
468	escapes are not working properly, you need to set ImplicitUnicode to	873	escapes are not working properly, you need to set ImplicitUnicode to
469	I<different> values on en- and decoding to get symmetric behaviour).	874	I<different> values on en- and decoding to get symmetric behaviour).
470		875
471	No roundtripping (simple cases work, but this depends on wether the scalar	876	No round-tripping (simple cases work, but this depends on whether the scalar
472	value was used in a numeric context or not).	877	value was used in a numeric context or not).
473		878
474	Dumping hashes may skip hash values depending on iterator state.	879	Dumping hashes may skip hash values depending on iterator state.
475		880
476	Unmaintained (maintainer unresponsive for many months, bugs are not	881	Unmaintained (maintainer unresponsive for many months, bugs are not
477	getting fixed).	882	getting fixed).
478		883
479	Does not check input for validity (i.e. will accept non-JSON input and	884	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	885	return "something" instead of raising an exception. This is a security
481	issue: imagine two banks transfering money between each other using	886	issue: imagine two banks transferring money between each other using
482	JSON. One bank might parse a given non-JSON request and deduct money,	887	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	888	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	889	good protocol will at least recover, that is extra unnecessary work and
485	the transaction will still not succeed).	890	the transaction will still not succeed).
486		891
487	=item JSON::DWIW 0.04	892	=item JSON::DWIW 0.04
488		893
489	Very fast. Very natural. Very nice.	894	Very fast. Very natural. Very nice.
490		895
491	Undocumented unicode handling (but the best of the pack. Unicode escapes	896	Undocumented Unicode handling (but the best of the pack. Unicode escapes
492	still don't get parsed properly).	897	still don't get parsed properly).
493		898
494	Very inflexible.	899	Very inflexible.
495		900
496	No roundtripping.	901	No round-tripping.
497		902
498	Does not generate valid JSON (key strings are often unquoted, empty keys	903	Does not generate valid JSON texts (key strings are often unquoted, empty keys
499	result in nothing being output)	904	result in nothing being output)
500		905
501	Does not check input for validity.	906	Does not check input for validity.
502		907
503	=back	908	=back
		909
		910
		911	=head2 JSON and YAML
		912
		913	You often hear that JSON is a subset of YAML. This is, however, a mass
		914	hysteria(*) and very far from the truth. In general, there is no way to
		915	configure JSON::XS to output a data structure as valid YAML that works for
		916	all cases.
		917
		918	If you really must use JSON::XS to generate YAML, you should use this
		919	algorithm (subject to change in future versions):
		920
		921	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		922	my $yaml = $to_yaml->encode ($ref) . "\n";
		923
		924	This will I<usually> generate JSON texts that also parse as valid
		925	YAML. Please note that YAML has hardcoded limits on (simple) object key
		926	lengths that JSON doesn't have and also has different and incompatible
		927	unicode handling, so you should make sure that your hash keys are
		928	noticeably shorter than the 1024 "stream characters" YAML allows and that
		929	you do not have codepoints with values outside the Unicode BMP (basic
		930	multilingual page). YAML also does not allow C<\/> sequences in strings
		931	(which JSON::XS does not I<currently> generate).
		932
		933	There might be other incompatibilities that I am not aware of (or the YAML
		934	specification has been changed yet again - it does so quite often). In
		935	general you should not try to generate YAML with a JSON generator or vice
		936	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		937	high that you will run into severe interoperability problems when you
		938	least expect it.
		939
		940	=over 4
		941
		942	=item (*)
		943
		944	This is spread actively by the YAML team, however. For many years now they
		945	claim YAML were a superset of JSON, even when proven otherwise.
		946
		947	Even the author of this manpage was at some point accused of providing
		948	"incorrect" information, despite the evidence presented (claims ranged
		949	from "your documentation contains inaccurate and negative statements about
		950	YAML" (the only negative comment is this footnote, and it didn't exist
		951	back then; the question on which claims were inaccurate was never answered
		952	etc.) to "the YAML spec is not up-to-date" (the real and supposedly
		953	JSON-compatible spec is apparently not currently publicly available)
		954	to actual requests to replace this section by incorrect information,
		955	suppressing information about the real problem).
		956
		957	So whenever you are told that YAML was a superset of JSON, first check
		958	wether it is really true (it might be when you check it, but it certainly
		959	was not true when this was written). I would much prefer if the YAML team
		960	would spent their time on actually making JSON compatibility a truth
		961	(JSON, after all, has a very small and simple specification) instead of
		962	trying to lobby/force people into reporting untruths.
		963
		964	=back
		965
504		966
505	=head2 SPEED	967	=head2 SPEED
506		968
507	It seems that JSON::XS is surprisingly fast, as shown in the following	969	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	970	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	971	in the JSON::XS distribution, to make it easy to compare on your own
510	system.	972	system.
511		973
512	First comes a comparison between various modules using a very short JSON	974	First comes a comparison between various modules using a very short
513	string (83 bytes), showing the number of encodes/decodes per second	975	single-line JSON string:
		976
		977	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
		978	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
		979
		980	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	981	the functional interface, while JSON::XS/2 uses the OO interface
515	interface with pretty-printing and hashkey sorting enabled). Higher is	982	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
516	better:	983	shrink). Higher is better:
517		984
518	module \| encode \| decode \|	985	module \| encode \| decode \|
519	-----------\|------------\|------------\|	986	-----------\|------------\|------------\|
520	JSON \| 14006 \| 6820 \|	987	JSON 1.x \| 4990.842 \| 4088.813 \|
521	JSON::DWIW \| 200937 \| 120386 \|	988	JSON::DWIW \| 51653.990 \| 71575.154 \|
522	JSON::PC \| 85065 \| 129366 \|	989	JSON::PC \| 65948.176 \| 74631.744 \|
523	JSON::Syck \| 59898 \| 44232 \|	990	JSON::PP \| 8931.652 \| 3817.168 \|
524	JSON::XS \| 1171478 \| 342435 \|	991	JSON::Syck \| 24877.248 \| 27776.848 \|
525	JSON::XS/2 \| 730760 \| 328714 \|	992	JSON::XS \| 388361.481 \| 227951.304 \|
		993	JSON::XS/2 \| 227951.304 \| 218453.333 \|
		994	JSON::XS/3 \| 338250.323 \| 218453.333 \|
		995	Storable \| 16500.016 \| 135300.129 \|
526	-----------+------------+------------+	996	-----------+------------+------------+
527		997
528	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	998	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
		999	about three times faster on decoding, and over forty times faster
529	times faster than JSON, even with pretty-printing and key sorting.	1000	than JSON, even with pretty-printing and key sorting. It also compares
		1001	favourably to Storable for small amounts of data.
530		1002
531	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1003	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
532	search API (http://nanoref.com/yahooapis/mgPdGg):	1004	search API (http://nanoref.com/yahooapis/mgPdGg):
533		1005
534	module \| encode \| decode \|	1006	module \| encode \| decode \|
535	-----------\|------------\|------------\|	1007	-----------\|------------\|------------\|
536	JSON \| 673 \| 38 \|	1008	JSON 1.x \| 55.260 \| 34.971 \|
537	JSON::DWIW \| 5271 \| 770 \|	1009	JSON::DWIW \| 825.228 \| 1082.513 \|
538	JSON::PC \| 9901 \| 2491 \|	1010	JSON::PC \| 3571.444 \| 2394.829 \|
539	JSON::Syck \| 2360 \| 786 \|	1011	JSON::PP \| 210.987 \| 32.574 \|
540	JSON::XS \| 37398 \| 3202 \|	1012	JSON::Syck \| 552.551 \| 787.544 \|
541	JSON::XS/2 \| 13765 \| 3153 \|	1013	JSON::XS \| 5780.463 \| 4854.519 \|
		1014	JSON::XS/2 \| 3869.998 \| 4798.975 \|
		1015	JSON::XS/3 \| 5862.880 \| 4798.975 \|
		1016	Storable \| 4445.002 \| 5235.027 \|
542	-----------+------------+------------+	1017	-----------+------------+------------+
543		1018
544	Again, JSON::XS leads by far in the encoding case, while still beating	1019	Again, JSON::XS leads by far (except for Storable which non-surprisingly
545	every other module in the decoding case.	1020	decodes faster).
546		1021
547	On large strings containing lots of unicode characters, some modules	1022	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	1023	(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	1024	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	1025	to decode or encode properly, so it was impossible to prepare a fair
551	case.	1026	comparison table for that case.
552		1027
553	=head1 RESOURCE LIMITS
554		1028
555	JSON::XS does not impose any limits on the size of JSON texts or Perl	1029	=head1 SECURITY CONSIDERATIONS
556	values they represent - if your machine can handle it, JSON::XS will	1030
557	encode or decode it. Future versions might optionally impose structure	1031	When you are using JSON in a protocol, talking to untrusted potentially
558	depth and memory use resource limits.	1032	hostile creatures requires relatively few measures.
		1033
		1034	First of all, your JSON decoder should be secure, that is, should not have
		1035	any buffer overflows. Obviously, this module should ensure that and I am
		1036	trying hard on making that true, but you never know.
		1037
		1038	Second, you need to avoid resource-starving attacks. That means you should
		1039	limit the size of JSON texts you accept, or make sure then when your
		1040	resources run out, that's just fine (e.g. by using a separate process that
		1041	can crash safely). The size of a JSON text in octets or characters is
		1042	usually a good indication of the size of the resources required to decode
		1043	it into a Perl structure. While JSON::XS can check the size of the JSON
		1044	text, it might be too late when you already have it in memory, so you
		1045	might want to check the size before you accept the string.
		1046
		1047	Third, JSON::XS recurses using the C stack when decoding objects and
		1048	arrays. The C stack is a limited resource: for instance, on my amd64
		1049	machine with 8MB of stack size I can decode around 180k nested arrays but
		1050	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1051	to free the temporary). If that is exceeded, the program crashes. To be
		1052	conservative, the default nesting limit is set to 512. If your process
		1053	has a smaller stack, you should adjust this setting accordingly with the
		1054	C<max_depth> method.
		1055
		1056	And last but least, something else could bomb you that I forgot to think
		1057	of. In that case, you get to keep the pieces. I am always open for hints,
		1058	though...
		1059
		1060	If you are using JSON::XS to return packets to consumption
		1061	by JavaScript scripts in a browser you should have a look at
		1062	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1063	you are vulnerable to some common attack vectors (which really are browser
		1064	design bugs, but it is still you who will have to deal with it, as major
		1065	browser developers care only for features, not about getting security
		1066	right).
		1067
		1068
		1069	=head1 THREADS
		1070
		1071	This module is I<not> guaranteed to be thread safe and there are no
		1072	plans to change this until Perl gets thread support (as opposed to the
		1073	horribly slow so-called "threads" which are simply slow and bloated
		1074	process simulations - use fork, its I<much> faster, cheaper, better).
		1075
		1076	(It might actually work, but you have been warned).
		1077
559		1078
560	=head1 BUGS	1079	=head1 BUGS
561		1080
562	While the goal of this module is to be correct, that unfortunately does	1081	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	1082	not mean its 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	1083	still relatively early in its development. If you keep reporting bugs they
565	be fixed swiftly, though.	1084	will be fixed swiftly, though.
		1085
		1086	Please refrain from using rt.cpan.org or any other bug reporting
		1087	service. I put the contact address into my modules for a reason.
566		1088
567	=cut	1089	=cut
		1090
		1091	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1092	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1093
		1094	sub true() { $true }
		1095	sub false() { $false }
		1096
		1097	sub is_bool($) {
		1098	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1099	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1100	}
		1101
		1102	XSLoader::load "JSON::XS", $VERSION;
		1103
		1104	package JSON::XS::Boolean;
		1105
		1106	use overload
		1107	"0+" => sub { ${$_[0]} },
		1108	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1109	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1110	fallback => 1;
568		1111
569	1;	1112	1;
570		1113
571	=head1 AUTHOR	1114	=head1 AUTHOR
572		1115

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Comparing JSON-XS/XS.pm (file contents): Revision 1.13 by root, Fri Mar 23 18:37:30 2007 UTC vs. Revision 1.83 by root, Sun Jan 20 19:19:07 2008 UTC

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Comparing JSON-XS/XS.pm (file contents):
Revision 1.13 by root, Fri Mar 23 18:37:30 2007 UTC vs.
Revision 1.83 by root, Sun Jan 20 19:19:07 2008 UTC