ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/JSON-XS/XS.pm

Comparing JSON-XS/XS.pm (file contents):
Revision 1.7 by root, Fri Mar 23 15:10:55 2007 UTC vs.
Revision 1.158 by root, Thu Sep 1 11:38:39 2016 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
4		4
		5	=encoding utf-8
		6
		7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
		13
		14	# exported functions, they croak on error
		15	# and expect/generate UTF-8
		16
		17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
		18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
		19
		20	# OO-interface
		21
		22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
		23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
		24	$perl_scalar = $coder->decode ($unicode_json_text);
		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
8		33
9	=head1 DESCRIPTION	34	=head1 DESCRIPTION
10		35
11	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
12	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
13	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overridden) with no overhead due to emulation (by inheriting constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
14		47
15	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
16	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
17	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
18	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
19	reports for other reasons.	52	reports for other reasons.
20		53
21	See COMPARISON, below, for a comparison to some other JSON modules.	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
		55	vice versa.
22		56
23	=head2 FEATURES	57	=head2 FEATURES
24		58
25	=over 4	59	=over 4
26		60
27	=item * correct handling of unicode issues	61	=item * correct Unicode handling
28		62
29	This module knows how to handle Unicode, and even documents how it does so.	63	This module knows how to handle Unicode, documents how and when it does
		64	so, and even documents what "correct" means.
30		65
31	=item * round-trip integrity	66	=item * round-trip integrity
32		67
33	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
34	by JSON, the deserialised data structure is identical on the Perl level.	69	by JSON and Perl, the deserialised data structure is identical on the Perl
35	(e.g. the string "2.0" doesn't suddenly become "2").	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
		71	it looks like a number). There I<are> minor exceptions to this, read the
		72	MAPPING section below to learn about those.
36		73
37	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
38		75
39	There is no guessing, no generating of illegal JSON strings by default,	76	There is no guessing, no generating of illegal JSON texts by default,
40	and only JSON is accepted as input (the latter is a security feature).	77	and only JSON is accepted as input by default (the latter is a security
		78	feature).
41		79
42	=item * fast	80	=item * fast
43		81
44	compared to other JSON modules, this module compares favourably.	82	Compared to other JSON modules and other serialisers such as Storable,
		83	this module usually compares favourably in terms of speed, too.
45		84
46	=item * simple to use	85	=item * simple to use
47		86
48	This module has both a simple functional interface as well as an OO	87	This module has both a simple functional interface as well as an object
49	interface.	88	oriented interface.
50		89
51	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
52		91
53	You can choose between the most compact format possible, a pure-ascii	92	You can choose between the most compact guaranteed-single-line format
54	format, or a pretty-printed format. Or you can combine those features in	93	possible (nice for simple line-based protocols), a pure-ASCII format
55	whatever way you like.	94	(for when your transport is not 8-bit clean, still supports the whole
		95	Unicode range), or a pretty-printed format (for when you want to read that
		96	stuff). Or you can combine those features in whatever way you like.
56		97
57	=back	98	=back
58		99
59	=cut	100	=cut
60		101
61	package JSON::XS;	102	package JSON::XS;
62		103
63	BEGIN {	104	use common::sense;
		105
64	$VERSION = '0.2';	106	our $VERSION = 3.02;
65	@ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
66		108
67	@EXPORT = qw(to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
68	require Exporter;
69		110
70	require XSLoader;	111	use Exporter;
71	XSLoader::load JSON::XS::, $VERSION;	112	use XSLoader;
72	}	113
		114	use Types::Serialiser ();
73		115
74	=head1 FUNCTIONAL INTERFACE	116	=head1 FUNCTIONAL INTERFACE
75		117
76	The following convinience methods are provided by this module. They are	118	The following convenience methods are provided by this module. They are
77	exported by default:	119	exported by default:
78		120
79	=over 4	121	=over 4
80		122
81	=item $json_string = to_json $perl_scalar	123	=item $json_text = encode_json $perl_scalar
82		124
83	Converts the given Perl data structure (a simple scalar or a reference to	125	Converts the given Perl data structure to a UTF-8 encoded, binary string
84	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	126	(that is, the string contains octets only). Croaks on error.
85	octets only). Croaks on error.
86		127
87	This function call is functionally identical to C<< JSON::XS->new->utf8	128	This function call is functionally identical to:
88	(1)->encode ($perl_scalar) >>.
89		129
		130	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		131
		132	Except being faster.
		133
90	=item $perl_scalar = from_json $json_string	134	=item $perl_scalar = decode_json $json_text
91		135
92	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	136	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
93	parse that as an UTF-8 encoded JSON string, returning the resulting simple	137	to parse that as an UTF-8 encoded JSON text, returning the resulting
94	scalar or reference. Croaks on error.	138	reference. Croaks on error.
95		139
96	This function call is functionally identical to C<< JSON::XS->new->utf8	140	This function call is functionally identical to:
97	(1)->decode ($json_string) >>.	141
		142	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		143
		144	Except being faster.
98		145
99	=back	146	=back
		147
		148
		149	=head1 A FEW NOTES ON UNICODE AND PERL
		150
		151	Since this often leads to confusion, here are a few very clear words on
		152	how Unicode works in Perl, modulo bugs.
		153
		154	=over 4
		155
		156	=item 1. Perl strings can store characters with ordinal values > 255.
		157
		158	This enables you to store Unicode characters as single characters in a
		159	Perl string - very natural.
		160
		161	=item 2. Perl does I<not> associate an encoding with your strings.
		162
		163	... until you force it to, e.g. when matching it against a regex, or
		164	printing the scalar to a file, in which case Perl either interprets your
		165	string as locale-encoded text, octets/binary, or as Unicode, depending
		166	on various settings. In no case is an encoding stored together with your
		167	data, it is I<use> that decides encoding, not any magical meta data.
		168
		169	=item 3. The internal utf-8 flag has no meaning with regards to the
		170	encoding of your string.
		171
		172	Just ignore that flag unless you debug a Perl bug, a module written in
		173	XS or want to dive into the internals of perl. Otherwise it will only
		174	confuse you, as, despite the name, it says nothing about how your string
		175	is encoded. You can have Unicode strings with that flag set, with that
		176	flag clear, and you can have binary data with that flag set and that flag
		177	clear. Other possibilities exist, too.
		178
		179	If you didn't know about that flag, just the better, pretend it doesn't
		180	exist.
		181
		182	=item 4. A "Unicode String" is simply a string where each character can be
		183	validly interpreted as a Unicode code point.
		184
		185	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		186	Unicode string encoded in UTF-8, giving you a binary string.
		187
		188	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		189
		190	It's a fact. Learn to live with it.
		191
		192	=back
		193
		194	I hope this helps :)
		195
100		196
101	=head1 OBJECT-ORIENTED INTERFACE	197	=head1 OBJECT-ORIENTED INTERFACE
102		198
103	The object oriented interface lets you configure your own encoding or	199	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	200	decoding style, within the limits of supported formats.
…		…
111	strings. All boolean flags described below are by default I<disabled>.	207	strings. All boolean flags described below are by default I<disabled>.
112		208
113	The mutators for flags all return the JSON object again and thus calls can	209	The mutators for flags all return the JSON object again and thus calls can
114	be chained:	210	be chained:
115		211
116	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	212	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
117	=> {"a": [1, 2]}	213	=> {"a": [1, 2]}
118		214
119	=item $json = $json->ascii ([$enable])	215	=item $json = $json->ascii ([$enable])
120		216
		217	=item $enabled = $json->get_ascii
		218
121	If C<$enable> is true (or missing), then the C<encode> method will	219	If C<$enable> is true (or missing), then the C<encode> method will not
122	not generate characters outside the code range C<0..127>. Any unicode	220	generate characters outside the code range C<0..127> (which is ASCII). Any
123	characters outside that range will be escaped using either a single	221	Unicode characters outside that range will be escaped using either a
124	\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per	222	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
125	RFC4627.	223	as per RFC4627. The resulting encoded JSON text can be treated as a native
		224	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		225	or any other superset of ASCII.
126		226
127	If C<$enable> is false, then the C<encode> method will not escape Unicode	227	If C<$enable> is false, then the C<encode> method will not escape Unicode
128	characters unless necessary.	228	characters unless required by the JSON syntax or other flags. This results
		229	in a faster and more compact format.
129		230
		231	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		232	document.
		233
		234	The main use for this flag is to produce JSON texts that can be
		235	transmitted over a 7-bit channel, as the encoded JSON texts will not
		236	contain any 8 bit characters.
		237
130	JSON::XS->new->ascii (1)->encode (chr 0x10401)	238	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
131	=> \ud801\udc01	239	=> ["\ud801\udc01"]
		240
		241	=item $json = $json->latin1 ([$enable])
		242
		243	=item $enabled = $json->get_latin1
		244
		245	If C<$enable> is true (or missing), then the C<encode> method will encode
		246	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		247	outside the code range C<0..255>. The resulting string can be treated as a
		248	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		249	will not be affected in any way by this flag, as C<decode> by default
		250	expects Unicode, which is a strict superset of latin1.
		251
		252	If C<$enable> is false, then the C<encode> method will not escape Unicode
		253	characters unless required by the JSON syntax or other flags.
		254
		255	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		256	document.
		257
		258	The main use for this flag is efficiently encoding binary data as JSON
		259	text, as most octets will not be escaped, resulting in a smaller encoded
		260	size. The disadvantage is that the resulting JSON text is encoded
		261	in latin1 (and must correctly be treated as such when storing and
		262	transferring), a rare encoding for JSON. It is therefore most useful when
		263	you want to store data structures known to contain binary data efficiently
		264	in files or databases, not when talking to other JSON encoders/decoders.
		265
		266	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		267	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
132		268
133	=item $json = $json->utf8 ([$enable])	269	=item $json = $json->utf8 ([$enable])
134		270
		271	=item $enabled = $json->get_utf8
		272
135	If C<$enable> is true (or missing), then the C<encode> method will encode	273	If C<$enable> is true (or missing), then the C<encode> method will encode
136	the JSON string into UTF-8, as required by many protocols, while the	274	the JSON result into UTF-8, as required by many protocols, while the
137	C<decode> method expects to be handled an UTF-8-encoded string. Please	275	C<decode> method expects to be handled an UTF-8-encoded string. Please
138	note that UTF-8-encoded strings do not contain any characters outside the	276	note that UTF-8-encoded strings do not contain any characters outside the
139	range C<0..255>, they are thus useful for bytewise/binary I/O.	277	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		278	versions, enabling this option might enable autodetection of the UTF-16
		279	and UTF-32 encoding families, as described in RFC4627.
140		280
141	If C<$enable> is false, then the C<encode> method will return the JSON	281	If C<$enable> is false, then the C<encode> method will return the JSON
142	string as a (non-encoded) unicode string, while C<decode> expects thus a	282	string as a (non-encoded) Unicode string, while C<decode> expects thus a
143	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	283	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
144	to be done yourself, e.g. using the Encode module.	284	to be done yourself, e.g. using the Encode module.
		285
		286	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		287	document.
		288
		289	Example, output UTF-16BE-encoded JSON:
		290
		291	use Encode;
		292	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		293
		294	Example, decode UTF-32LE-encoded JSON:
		295
		296	use Encode;
		297	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
145		298
146	=item $json = $json->pretty ([$enable])	299	=item $json = $json->pretty ([$enable])
147		300
148	This enables (or disables) all of the C<indent>, C<space_before> and	301	This enables (or disables) all of the C<indent>, C<space_before> and
149	C<space_after> (and in the future possibly more) flags in one call to	302	C<space_after> (and in the future possibly more) flags in one call to
150	generate the most readable (or most compact) form possible.	303	generate the most readable (or most compact) form possible.
		304
		305	Example, pretty-print some simple structure:
151		306
152	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})	307	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
153	=>	308	=>
154	{	309	{
155	"a" : [	310	"a" : [
…		…
158	]	313	]
159	}	314	}
160		315
161	=item $json = $json->indent ([$enable])	316	=item $json = $json->indent ([$enable])
162		317
		318	=item $enabled = $json->get_indent
		319
163	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	320	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
164	format as output, putting every array member or object/hash key-value pair	321	format as output, putting every array member or object/hash key-value pair
165	into its own line, identing them properly.	322	into its own line, indenting them properly.
166		323
167	If C<$enable> is false, no newlines or indenting will be produced, and the	324	If C<$enable> is false, no newlines or indenting will be produced, and the
168	resulting JSON strings is guarenteed not to contain any C<newlines>.	325	resulting JSON text is guaranteed not to contain any C<newlines>.
169		326
170	This setting has no effect when decoding JSON strings.	327	This setting has no effect when decoding JSON texts.
171		328
172	=item $json = $json->space_before ([$enable])	329	=item $json = $json->space_before ([$enable])
		330
		331	=item $enabled = $json->get_space_before
173		332
174	If C<$enable> is true (or missing), then the C<encode> method will add an extra	333	If C<$enable> is true (or missing), then the C<encode> method will add an extra
175	optional space before the C<:> separating keys from values in JSON objects.	334	optional space before the C<:> separating keys from values in JSON objects.
176		335
177	If C<$enable> is false, then the C<encode> method will not add any extra	336	If C<$enable> is false, then the C<encode> method will not add any extra
178	space at those places.	337	space at those places.
179		338
180	This setting has no effect when decoding JSON strings. You will also most	339	This setting has no effect when decoding JSON texts. You will also
181	likely combine this setting with C<space_after>.	340	most likely combine this setting with C<space_after>.
		341
		342	Example, space_before enabled, space_after and indent disabled:
		343
		344	{"key" :"value"}
182		345
183	=item $json = $json->space_after ([$enable])	346	=item $json = $json->space_after ([$enable])
		347
		348	=item $enabled = $json->get_space_after
184		349
185	If C<$enable> is true (or missing), then the C<encode> method will add an extra	350	If C<$enable> is true (or missing), then the C<encode> method will add an extra
186	optional space after the C<:> separating keys from values in JSON objects	351	optional space after the C<:> separating keys from values in JSON objects
187	and extra whitespace after the C<,> separating key-value pairs and array	352	and extra whitespace after the C<,> separating key-value pairs and array
188	members.	353	members.
189		354
190	If C<$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
191	space at those places.	356	space at those places.
192		357
193	This setting has no effect when decoding JSON strings.	358	This setting has no effect when decoding JSON texts.
		359
		360	Example, space_before and indent disabled, space_after enabled:
		361
		362	{"key": "value"}
		363
		364	=item $json = $json->relaxed ([$enable])
		365
		366	=item $enabled = $json->get_relaxed
		367
		368	If C<$enable> is true (or missing), then C<decode> will accept some
		369	extensions to normal JSON syntax (see below). C<encode> will not be
		370	affected in anyway. I<Be aware that this option makes you accept invalid
		371	JSON texts as if they were valid!>. I suggest only to use this option to
		372	parse application-specific files written by humans (configuration files,
		373	resource files etc.)
		374
		375	If C<$enable> is false (the default), then C<decode> will only accept
		376	valid JSON texts.
		377
		378	Currently accepted extensions are:
		379
		380	=over 4
		381
		382	=item * list items can have an end-comma
		383
		384	JSON I<separates> array elements and key-value pairs with commas. This
		385	can be annoying if you write JSON texts manually and want to be able to
		386	quickly append elements, so this extension accepts comma at the end of
		387	such items not just between them:
		388
		389	[
		390	1,
		391	2, <- this comma not normally allowed
		392	]
		393	{
		394	"k1": "v1",
		395	"k2": "v2", <- this comma not normally allowed
		396	}
		397
		398	=item * shell-style '#'-comments
		399
		400	Whenever JSON allows whitespace, shell-style comments are additionally
		401	allowed. They are terminated by the first carriage-return or line-feed
		402	character, after which more white-space and comments are allowed.
		403
		404	[
		405	1, # this comment not allowed in JSON
		406	# neither this one...
		407	]
		408
		409	=item * literal ASCII TAB characters in strings
		410
		411	Literal ASCII TAB characters are now allowed in strings (and treated as
		412	C<\t>).
		413
		414	[
		415	"Hello\tWorld",
		416	"Hello<TAB>World", # literal <TAB> would not normally be allowed
		417	]
		418
		419	=back
194		420
195	=item $json = $json->canonical ([$enable])	421	=item $json = $json->canonical ([$enable])
		422
		423	=item $enabled = $json->get_canonical
196		424
197	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	425	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
198	by sorting their keys. This is adding a comparatively high overhead.	426	by sorting their keys. This is adding a comparatively high overhead.
199		427
200	If C<$enable> is false, then the C<encode> method will output key-value	428	If C<$enable> is false, then the C<encode> method will output key-value
201	pairs in the order Perl stores them (which will likely change between runs	429	pairs in the order Perl stores them (which will likely change between runs
202	of the same script).	430	of the same script, and can change even within the same run from 5.18
		431	onwards).
203		432
204	This option is useful if you want the same data structure to be encoded as	433	This option is useful if you want the same data structure to be encoded as
205	the same JSON string (given the same overall settings). If it is disabled,	434	the same JSON text (given the same overall settings). If it is disabled,
206	the same hash migh be encoded differently even if contains the same data,	435	the same hash might be encoded differently even if contains the same data,
207	as key-value pairs have no inherent ordering in Perl.	436	as key-value pairs have no inherent ordering in Perl.
208		437
209	This setting has no effect when decoding JSON strings.	438	This setting has no effect when decoding JSON texts.
		439
		440	This setting has currently no effect on tied hashes.
210		441
211	=item $json = $json->allow_nonref ([$enable])	442	=item $json = $json->allow_nonref ([$enable])
		443
		444	=item $enabled = $json->get_allow_nonref
212		445
213	If C<$enable> is true (or missing), then the C<encode> method can convert a	446	If C<$enable> is true (or missing), then the C<encode> method can convert a
214	non-reference into its corresponding string, number or null JSON value,	447	non-reference into its corresponding string, number or null JSON value,
215	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	448	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
216	values instead of croaking.	449	values instead of croaking.
217		450
218	If C<$enable> is false, then the C<encode> method will croak if it isn't	451	If C<$enable> is false, then the C<encode> method will croak if it isn't
219	passed an arrayref or hashref, as JSON strings must either be an object	452	passed an arrayref or hashref, as JSON texts must either be an object
220	or array. Likewise, C<decode> will croak if given something that is not a	453	or array. Likewise, C<decode> will croak if given something that is not a
221	JSON object or array.	454	JSON object or array.
222		455
		456	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
		457	resulting in an invalid JSON text:
		458
		459	JSON::XS->new->allow_nonref->encode ("Hello, World!")
		460	=> "Hello, World!"
		461
		462	=item $json = $json->allow_unknown ([$enable])
		463
		464	=item $enabled = $json->get_allow_unknown
		465
		466	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		467	exception when it encounters values it cannot represent in JSON (for
		468	example, filehandles) but instead will encode a JSON C<null> value. Note
		469	that blessed objects are not included here and are handled separately by
		470	c<allow_nonref>.
		471
		472	If C<$enable> is false (the default), then C<encode> will throw an
		473	exception when it encounters anything it cannot encode as JSON.
		474
		475	This option does not affect C<decode> in any way, and it is recommended to
		476	leave it off unless you know your communications partner.
		477
		478	=item $json = $json->allow_blessed ([$enable])
		479
		480	=item $enabled = $json->get_allow_blessed
		481
		482	See L<OBJECT SERIALISATION> for details.
		483
		484	If C<$enable> is true (or missing), then the C<encode> method will not
		485	barf when it encounters a blessed reference that it cannot convert
		486	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
		487
		488	If C<$enable> is false (the default), then C<encode> will throw an
		489	exception when it encounters a blessed object that it cannot convert
		490	otherwise.
		491
		492	This setting has no effect on C<decode>.
		493
		494	=item $json = $json->convert_blessed ([$enable])
		495
		496	=item $enabled = $json->get_convert_blessed
		497
		498	See L<OBJECT SERIALISATION> for details.
		499
		500	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		501	blessed object, will check for the availability of the C<TO_JSON> method
		502	on the object's class. If found, it will be called in scalar context and
		503	the resulting scalar will be encoded instead of the object.
		504
		505	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		506	returns other blessed objects, those will be handled in the same
		507	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		508	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		509	methods called by the Perl core (== not by the user of the object) are
		510	usually in upper case letters and to avoid collisions with any C<to_json>
		511	function or method.
		512
		513	If C<$enable> is false (the default), then C<encode> will not consider
		514	this type of conversion.
		515
		516	This setting has no effect on C<decode>.
		517
		518	=item $json = $json->allow_tags ([$enable])
		519
		520	=item $enabled = $json->allow_tags
		521
		522	See L<OBJECT SERIALISATION> for details.
		523
		524	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		525	blessed object, will check for the availability of the C<FREEZE> method on
		526	the object's class. If found, it will be used to serialise the object into
		527	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		528
		529	It also causes C<decode> to parse such tagged JSON values and deserialise
		530	them via a call to the C<THAW> method.
		531
		532	If C<$enable> is false (the default), then C<encode> will not consider
		533	this type of conversion, and tagged JSON values will cause a parse error
		534	in C<decode>, as if tags were not part of the grammar.
		535
		536	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		537
		538	When C<$coderef> is specified, it will be called from C<decode> each
		539	time it decodes a JSON object. The only argument is a reference to the
		540	newly-created hash. If the code references returns a single scalar (which
		541	need not be a reference), this value (i.e. a copy of that scalar to avoid
		542	aliasing) is inserted into the deserialised data structure. If it returns
		543	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		544	original deserialised hash will be inserted. This setting can slow down
		545	decoding considerably.
		546
		547	When C<$coderef> is omitted or undefined, any existing callback will
		548	be removed and C<decode> will not change the deserialised hash in any
		549	way.
		550
		551	Example, convert all JSON objects into the integer 5:
		552
		553	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		554	# returns [5]
		555	$js->decode ('[{}]')
		556	# throw an exception because allow_nonref is not enabled
		557	# so a lone 5 is not allowed.
		558	$js->decode ('{"a":1, "b":2}');
		559
		560	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		561
		562	Works remotely similar to C<filter_json_object>, but is only called for
		563	JSON objects having a single key named C<$key>.
		564
		565	This C<$coderef> is called before the one specified via
		566	C<filter_json_object>, if any. It gets passed the single value in the JSON
		567	object. If it returns a single value, it will be inserted into the data
		568	structure. If it returns nothing (not even C<undef> but the empty list),
		569	the callback from C<filter_json_object> will be called next, as if no
		570	single-key callback were specified.
		571
		572	If C<$coderef> is omitted or undefined, the corresponding callback will be
		573	disabled. There can only ever be one callback for a given key.
		574
		575	As this callback gets called less often then the C<filter_json_object>
		576	one, decoding speed will not usually suffer as much. Therefore, single-key
		577	objects make excellent targets to serialise Perl objects into, especially
		578	as single-key JSON objects are as close to the type-tagged value concept
		579	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		580	support this in any way, so you need to make sure your data never looks
		581	like a serialised Perl hash.
		582
		583	Typical names for the single object key are C<__class_whatever__>, or
		584	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		585	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		586	with real hashes.
		587
		588	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		589	into the corresponding C<< $WIDGET{<id>} >> object:
		590
		591	# return whatever is in $WIDGET{5}:
		592	JSON::XS
		593	->new
		594	->filter_json_single_key_object (__widget__ => sub {
		595	$WIDGET{ $_[0] }
		596	})
		597	->decode ('{"__widget__": 5')
		598
		599	# this can be used with a TO_JSON method in some "widget" class
		600	# for serialisation to json:
		601	sub WidgetBase::TO_JSON {
		602	my ($self) = @_;
		603
		604	unless ($self->{id}) {
		605	$self->{id} = ..get..some..id..;
		606	$WIDGET{$self->{id}} = $self;
		607	}
		608
		609	{ __widget__ => $self->{id} }
		610	}
		611
223	=item $json = $json->shrink ([$enable])	612	=item $json = $json->shrink ([$enable])
224		613
		614	=item $enabled = $json->get_shrink
		615
225	Perl usually over-allocates memory a bit when allocating space for	616	Perl usually over-allocates memory a bit when allocating space for
226	strings. This flag optionally resizes strings generated by either	617	strings. This flag optionally resizes strings generated by either
227	C<encode> or C<decode> to their minimum size possible. This can save	618	C<encode> or C<decode> to their minimum size possible. This can save
228	memory when your JSON strings are either very very long or you have many	619	memory when your JSON texts are either very very long or you have many
229	short strings.	620	short strings. It will also try to downgrade any strings to octet-form
		621	if possible: perl stores strings internally either in an encoding called
		622	UTF-X or in octet-form. The latter cannot store everything but uses less
		623	space in general (and some buggy Perl or C code might even rely on that
		624	internal representation being used).
230		625
		626	The actual definition of what shrink does might change in future versions,
		627	but it will always try to save space at the expense of time.
		628
231	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	629	If C<$enable> is true (or missing), the string returned by C<encode> will
232	while all strings generated by C<decode> will also be shrunk-to-fit.	630	be shrunk-to-fit, while all strings generated by C<decode> will also be
		631	shrunk-to-fit.
233		632
234	If C<$enable> is false, then the normal perl allocation algorithms are used.	633	If C<$enable> is false, then the normal perl allocation algorithms are used.
235	If you work with your data, then this is likely to be faster.	634	If you work with your data, then this is likely to be faster.
236		635
237	In the future, this setting might control other things, such as converting	636	In the future, this setting might control other things, such as converting
238	strings that look like integers or floats into integers or floats	637	strings that look like integers or floats into integers or floats
239	internally (there is no difference on the Perl level), saving space.	638	internally (there is no difference on the Perl level), saving space.
240		639
		640	=item $json = $json->max_depth ([$maximum_nesting_depth])
		641
		642	=item $max_depth = $json->get_max_depth
		643
		644	Sets the maximum nesting level (default C<512>) accepted while encoding
		645	or decoding. If a higher nesting level is detected in JSON text or a Perl
		646	data structure, then the encoder and decoder will stop and croak at that
		647	point.
		648
		649	Nesting level is defined by number of hash- or arrayrefs that the encoder
		650	needs to traverse to reach a given point or the number of C<{> or C<[>
		651	characters without their matching closing parenthesis crossed to reach a
		652	given character in a string.
		653
		654	Setting the maximum depth to one disallows any nesting, so that ensures
		655	that the object is only a single hash/object or array.
		656
		657	If no argument is given, the highest possible setting will be used, which
		658	is rarely useful.
		659
		660	Note that nesting is implemented by recursion in C. The default value has
		661	been chosen to be as large as typical operating systems allow without
		662	crashing.
		663
		664	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		665
		666	=item $json = $json->max_size ([$maximum_string_size])
		667
		668	=item $max_size = $json->get_max_size
		669
		670	Set the maximum length a JSON text may have (in bytes) where decoding is
		671	being attempted. The default is C<0>, meaning no limit. When C<decode>
		672	is called on a string that is longer then this many bytes, it will not
		673	attempt to decode the string but throw an exception. This setting has no
		674	effect on C<encode> (yet).
		675
		676	If no argument is given, the limit check will be deactivated (same as when
		677	C<0> is specified).
		678
		679	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		680
241	=item $json_string = $json->encode ($perl_scalar)	681	=item $json_text = $json->encode ($perl_scalar)
242		682
243	Converts the given Perl data structure (a simple scalar or a reference	683	Converts the given Perl value or data structure to its JSON
244	to a hash or array) to its JSON representation. Simple scalars will be	684	representation. Croaks on error.
245	converted into JSON string or number sequences, while references to arrays
246	become JSON arrays and references to hashes become JSON objects. Undefined
247	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
248	nor C<false> values will be generated.
249		685
250	=item $perl_scalar = $json->decode ($json_string)	686	=item $perl_scalar = $json->decode ($json_text)
251		687
252	The opposite of C<encode>: expects a JSON string and tries to parse it,	688	The opposite of C<encode>: expects a JSON text and tries to parse it,
253	returning the resulting simple scalar or reference. Croaks on error.	689	returning the resulting simple scalar or reference. Croaks on error.
254		690
255	JSON numbers and strings become simple Perl scalars. JSON arrays become	691	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
256	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	692
257	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	693	This works like the C<decode> method, but instead of raising an exception
		694	when there is trailing garbage after the first JSON object, it will
		695	silently stop parsing there and return the number of characters consumed
		696	so far.
		697
		698	This is useful if your JSON texts are not delimited by an outer protocol
		699	and you need to know where the JSON text ends.
		700
		701	JSON::XS->new->decode_prefix ("[1] the tail")
		702	=> ([1], 3)
258		703
259	=back	704	=back
260		705
261	=head1 COMPARISON
262		706
263	As already mentioned, this module was created because none of the existing	707	=head1 INCREMENTAL PARSING
264	JSON modules could be made to work correctly. First I will describe the	708
265	problems (or pleasures) I encountered with various existing JSON modules,	709	In some cases, there is the need for incremental parsing of JSON
266	followed by some benchmark values. JSON::XS was designed not to suffer	710	texts. While this module always has to keep both JSON text and resulting
267	from any of these problems or limitations.	711	Perl data structure in memory at one time, it does allow you to parse a
		712	JSON stream incrementally. It does so by accumulating text until it has
		713	a full JSON object, which it then can decode. This process is similar to
		714	using C<decode_prefix> to see if a full JSON object is available, but
		715	is much more efficient (and can be implemented with a minimum of method
		716	calls).
		717
		718	JSON::XS will only attempt to parse the JSON text once it is sure it
		719	has enough text to get a decisive result, using a very simple but
		720	truly incremental parser. This means that it sometimes won't stop as
		721	early as the full parser, for example, it doesn't detect mismatched
		722	parentheses. The only thing it guarantees is that it starts decoding as
		723	soon as a syntactically valid JSON text has been seen. This means you need
		724	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		725	parsing in the presence if syntax errors.
		726
		727	The following methods implement this incremental parser.
268		728
269	=over 4	729	=over 4
270		730
271	=item JSON 1.07	731	=item [void, scalar or list context] = $json->incr_parse ([$string])
272		732
273	Slow (but very portable, as it is written in pure Perl).	733	This is the central parsing function. It can both append new text and
		734	extract objects from the stream accumulated so far (both of these
		735	functions are optional).
274		736
275	Undocumented/buggy Unicode handling (how JSON handles unicode values is	737	If C<$string> is given, then this string is appended to the already
276	undocumented. One can get far by feeding it unicode strings and doing	738	existing JSON fragment stored in the C<$json> object.
277	en-/decoding oneself, but unicode escapes are not working properly).
278		739
279	No roundtripping (strings get clobbered if they look like numbers, e.g.	740	After that, if the function is called in void context, it will simply
280	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	741	return without doing anything further. This can be used to add more text
281	decode into the number 2.	742	in as many chunks as you want.
282		743
283	=item JSON::PC 0.01	744	If the method is called in scalar context, then it will try to extract
		745	exactly I<one> JSON object. If that is successful, it will return this
		746	object, otherwise it will return C<undef>. If there is a parse error,
		747	this method will croak just as C<decode> would do (one can then use
		748	C<incr_skip> to skip the erroneous part). This is the most common way of
		749	using the method.
284		750
285	Very fast.	751	And finally, in list context, it will try to extract as many objects
		752	from the stream as it can find and return them, or the empty list
		753	otherwise. For this to work, there must be no separators (other than
		754	whitespace) between the JSON objects or arrays, instead they must be
		755	concatenated back-to-back. If an error occurs, an exception will be
		756	raised as in the scalar context case. Note that in this case, any
		757	previously-parsed JSON texts will be lost.
286		758
287	Undocumented/buggy Unicode handling.	759	Example: Parse some JSON arrays/objects in a given string and return
		760	them.
288		761
289	No roundtripping.	762	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
290		763
291	Has problems handling many Perl values (e.g. regex results and other magic	764	=item $lvalue_string = $json->incr_text
292	values will make it croak).
293		765
294	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	766	This method returns the currently stored JSON fragment as an lvalue, that
295	which is not a valid JSON string.	767	is, you can manipulate it. This I<only> works when a preceding call to
		768	C<incr_parse> in I<scalar context> successfully returned an object. Under
		769	all other circumstances you must not call this function (I mean it.
		770	although in simple tests it might actually work, it I<will> fail under
		771	real world conditions). As a special exception, you can also call this
		772	method before having parsed anything.
296		773
297	Unmaintained (maintainer unresponsive for many months, bugs are not	774	This function is useful in two cases: a) finding the trailing text after a
298	getting fixed).	775	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		776	(such as commas).
299		777
300	=item JSON::Syck 0.21	778	=item $json->incr_skip
301		779
302	Very buggy (often crashes).	780	This will reset the state of the incremental parser and will remove
		781	the parsed text from the input buffer so far. This is useful after
		782	C<incr_parse> died, in which case the input buffer and incremental parser
		783	state is left unchanged, to skip the text parsed so far and to reset the
		784	parse state.
303		785
304	Very inflexible (no human-readable format supported, format pretty much	786	The difference to C<incr_reset> is that only text until the parse error
305	undocumented. I need at least a format for easy reading by humans and a	787	occurred is removed.
306	single-line compact format for use in a protocol, and preferably a way to
307	generate ASCII-only JSON strings).
308		788
309	Completely broken (and confusingly documented) Unicode handling (unicode	789	=item $json->incr_reset
310	escapes are not working properly, you need to set ImplicitUnicode to
311	I<different> values on en- and decoding to get symmetric behaviour).
312		790
313	No roundtripping (simple cases work, but this depends on wether the scalar	791	This completely resets the incremental parser, that is, after this call,
314	value was used in a numeric context or not).	792	it will be as if the parser had never parsed anything.
315		793
316	Dumping hashes may skip hash values depending on iterator state.	794	This is useful if you want to repeatedly parse JSON objects and want to
317		795	ignore any trailing data, which means you have to reset the parser after
318	Unmaintained (maintainer unresponsive for many months, bugs are not	796	each successful decode.
319	getting fixed).
320
321	Does not check input for validity (i.e. will accept non-JSON input and
322	return "something" instead of raising an exception. This is a security
323	issue: imagine two banks transfering money between each other using
324	JSON. One bank might parse a given non-JSON request and deduct money,
325	while the other might reject the transaction with a syntax error. While a
326	good protocol will at least recover, that is extra unnecessary work and
327	the transaction will still not succeed).
328
329	=item JSON::DWIW 0.04
330
331	Very fast. Very natural. Very nice.
332
333	Undocumented unicode handling (but the best of the pack. Unicode escapes
334	still don't get parsed properly).
335
336	Very inflexible.
337
338	No roundtripping.
339
340	Does not generate valid JSON (key strings are often unquoted, empty keys
341	result in nothing being output)
342
343	Does not check input for validity.
344		797
345	=back	798	=back
		799
		800	=head2 LIMITATIONS
		801
		802	All options that affect decoding are supported, except
		803	C<allow_nonref>. The reason for this is that it cannot be made to work
		804	sensibly: JSON objects and arrays are self-delimited, i.e. you can
		805	concatenate them back to back and still decode them perfectly. This does
		806	not hold true for JSON numbers, however.
		807
		808	For example, is the string C<1> a single JSON number, or is it simply the
		809	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		810	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		811	takes the conservative route and disallows this case.
		812
		813	=head2 EXAMPLES
		814
		815	Some examples will make all this clearer. First, a simple example that
		816	works similarly to C<decode_prefix>: We want to decode the JSON object at
		817	the start of a string and identify the portion after the JSON object:
		818
		819	my $text = "[1,2,3] hello";
		820
		821	my $json = new JSON::XS;
		822
		823	my $obj = $json->incr_parse ($text)
		824	or die "expected JSON object or array at beginning of string";
		825
		826	my $tail = $json->incr_text;
		827	# $tail now contains " hello"
		828
		829	Easy, isn't it?
		830
		831	Now for a more complicated example: Imagine a hypothetical protocol where
		832	you read some requests from a TCP stream, and each request is a JSON
		833	array, without any separation between them (in fact, it is often useful to
		834	use newlines as "separators", as these get interpreted as whitespace at
		835	the start of the JSON text, which makes it possible to test said protocol
		836	with C<telnet>...).
		837
		838	Here is how you'd do it (it is trivial to write this in an event-based
		839	manner):
		840
		841	my $json = new JSON::XS;
		842
		843	# read some data from the socket
		844	while (sysread $socket, my $buf, 4096) {
		845
		846	# split and decode as many requests as possible
		847	for my $request ($json->incr_parse ($buf)) {
		848	# act on the $request
		849	}
		850	}
		851
		852	Another complicated example: Assume you have a string with JSON objects
		853	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		854	[3]>). To parse them, we have to skip the commas between the JSON texts,
		855	and here is where the lvalue-ness of C<incr_text> comes in useful:
		856
		857	my $text = "[1],[2], [3]";
		858	my $json = new JSON::XS;
		859
		860	# void context, so no parsing done
		861	$json->incr_parse ($text);
		862
		863	# now extract as many objects as possible. note the
		864	# use of scalar context so incr_text can be called.
		865	while (my $obj = $json->incr_parse) {
		866	# do something with $obj
		867
		868	# now skip the optional comma
		869	$json->incr_text =~ s/^ \s* , //x;
		870	}
		871
		872	Now lets go for a very complex example: Assume that you have a gigantic
		873	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		874	but you cannot load it into memory fully (this has actually happened in
		875	the real world :).
		876
		877	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		878	can still help you: You implement a (very simple) array parser and let
		879	JSON decode the array elements, which are all full JSON objects on their
		880	own (this wouldn't work if the array elements could be JSON numbers, for
		881	example):
		882
		883	my $json = new JSON::XS;
		884
		885	# open the monster
		886	open my $fh, "<bigfile.json"
		887	or die "bigfile: $!";
		888
		889	# first parse the initial "["
		890	for (;;) {
		891	sysread $fh, my $buf, 65536
		892	or die "read error: $!";
		893	$json->incr_parse ($buf); # void context, so no parsing
		894
		895	# Exit the loop once we found and removed(!) the initial "[".
		896	# In essence, we are (ab-)using the $json object as a simple scalar
		897	# we append data to.
		898	last if $json->incr_text =~ s/^ \s* \[ //x;
		899	}
		900
		901	# now we have the skipped the initial "[", so continue
		902	# parsing all the elements.
		903	for (;;) {
		904	# in this loop we read data until we got a single JSON object
		905	for (;;) {
		906	if (my $obj = $json->incr_parse) {
		907	# do something with $obj
		908	last;
		909	}
		910
		911	# add more data
		912	sysread $fh, my $buf, 65536
		913	or die "read error: $!";
		914	$json->incr_parse ($buf); # void context, so no parsing
		915	}
		916
		917	# in this loop we read data until we either found and parsed the
		918	# separating "," between elements, or the final "]"
		919	for (;;) {
		920	# first skip whitespace
		921	$json->incr_text =~ s/^\s*//;
		922
		923	# if we find "]", we are done
		924	if ($json->incr_text =~ s/^\]//) {
		925	print "finished.\n";
		926	exit;
		927	}
		928
		929	# if we find ",", we can continue with the next element
		930	if ($json->incr_text =~ s/^,//) {
		931	last;
		932	}
		933
		934	# if we find anything else, we have a parse error!
		935	if (length $json->incr_text) {
		936	die "parse error near ", $json->incr_text;
		937	}
		938
		939	# else add more data
		940	sysread $fh, my $buf, 65536
		941	or die "read error: $!";
		942	$json->incr_parse ($buf); # void context, so no parsing
		943	}
		944
		945	This is a complex example, but most of the complexity comes from the fact
		946	that we are trying to be correct (bear with me if I am wrong, I never ran
		947	the above example :).
		948
		949
		950
		951	=head1 MAPPING
		952
		953	This section describes how JSON::XS maps Perl values to JSON values and
		954	vice versa. These mappings are designed to "do the right thing" in most
		955	circumstances automatically, preserving round-tripping characteristics
		956	(what you put in comes out as something equivalent).
		957
		958	For the more enlightened: note that in the following descriptions,
		959	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		960	refers to the abstract Perl language itself.
		961
		962
		963	=head2 JSON -> PERL
		964
		965	=over 4
		966
		967	=item object
		968
		969	A JSON object becomes a reference to a hash in Perl. No ordering of object
		970	keys is preserved (JSON does not preserve object key ordering itself).
		971
		972	=item array
		973
		974	A JSON array becomes a reference to an array in Perl.
		975
		976	=item string
		977
		978	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		979	are represented by the same codepoints in the Perl string, so no manual
		980	decoding is necessary.
		981
		982	=item number
		983
		984	A JSON number becomes either an integer, numeric (floating point) or
		985	string scalar in perl, depending on its range and any fractional parts. On
		986	the Perl level, there is no difference between those as Perl handles all
		987	the conversion details, but an integer may take slightly less memory and
		988	might represent more values exactly than floating point numbers.
		989
		990	If the number consists of digits only, JSON::XS will try to represent
		991	it as an integer value. If that fails, it will try to represent it as
		992	a numeric (floating point) value if that is possible without loss of
		993	precision. Otherwise it will preserve the number as a string value (in
		994	which case you lose roundtripping ability, as the JSON number will be
		995	re-encoded to a JSON string).
		996
		997	Numbers containing a fractional or exponential part will always be
		998	represented as numeric (floating point) values, possibly at a loss of
		999	precision (in which case you might lose perfect roundtripping ability, but
		1000	the JSON number will still be re-encoded as a JSON number).
		1001
		1002	Note that precision is not accuracy - binary floating point values cannot
		1003	represent most decimal fractions exactly, and when converting from and to
		1004	floating point, JSON::XS only guarantees precision up to but not including
		1005	the least significant bit.
		1006
		1007	=item true, false
		1008
		1009	These JSON atoms become C<Types::Serialiser::true> and
		1010	C<Types::Serialiser::false>, respectively. They are overloaded to act
		1011	almost exactly like the numbers C<1> and C<0>. You can check whether
		1012	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1013	function (after C<use Types::Serialier>, of course).
		1014
		1015	=item null
		1016
		1017	A JSON null atom becomes C<undef> in Perl.
		1018
		1019	=item shell-style comments (C<< # I<text> >>)
		1020
		1021	As a nonstandard extension to the JSON syntax that is enabled by the
		1022	C<relaxed> setting, shell-style comments are allowed. They can start
		1023	anywhere outside strings and go till the end of the line.
		1024
		1025	=item tagged values (C<< (I<tag>)I<value> >>).
		1026
		1027	Another nonstandard extension to the JSON syntax, enabled with the
		1028	C<allow_tags> setting, are tagged values. In this implementation, the
		1029	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1030	I<value> must be a JSON array encoding optional constructor arguments.
		1031
		1032	See L<OBJECT SERIALISATION>, below, for details.
		1033
		1034	=back
		1035
		1036
		1037	=head2 PERL -> JSON
		1038
		1039	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		1040	truly typeless language, so we can only guess which JSON type is meant by
		1041	a Perl value.
		1042
		1043	=over 4
		1044
		1045	=item hash references
		1046
		1047	Perl hash references become JSON objects. As there is no inherent
		1048	ordering in hash keys (or JSON objects), they will usually be encoded
		1049	in a pseudo-random order. JSON::XS can optionally sort the hash keys
		1050	(determined by the I<canonical> flag), so the same datastructure will
		1051	serialise to the same JSON text (given same settings and version of
		1052	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
		1053	e.g. when you want to compare some JSON text against another for equality.
		1054
		1055	=item array references
		1056
		1057	Perl array references become JSON arrays.
		1058
		1059	=item other references
		1060
		1061	Other unblessed references are generally not allowed and will cause an
		1062	exception to be thrown, except for references to the integers C<0> and
		1063	C<1>, which get turned into C<false> and C<true> atoms in JSON.
		1064
		1065	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1066	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1067	and C<Types::Serialiser::true> to improve readability.
		1068
		1069	use Types::Serialiser;
		1070	encode_json [\0, Types::Serialiser::true] # yields [false,true]
		1071
		1072	=item Types::Serialiser::true, Types::Serialiser::false
		1073
		1074	These special values from the L<Types::Serialiser> module become JSON true
		1075	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1076	directly if you want.
		1077
		1078	=item blessed objects
		1079
		1080	Blessed objects are not directly representable in JSON, but C<JSON::XS>
		1081	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
		1082	below, for details.
		1083
		1084	=item simple scalars
		1085
		1086	Simple Perl scalars (any scalar that is not a reference) are the most
		1087	difficult objects to encode: JSON::XS will encode undefined scalars as
		1088	JSON C<null> values, scalars that have last been used in a string context
		1089	before encoding as JSON strings, and anything else as number value:
		1090
		1091	# dump as number
		1092	encode_json [2] # yields [2]
		1093	encode_json [-3.0e17] # yields [-3e+17]
		1094	my $value = 5; encode_json [$value] # yields [5]
		1095
		1096	# used as string, so dump as string
		1097	print $value;
		1098	encode_json [$value] # yields ["5"]
		1099
		1100	# undef becomes null
		1101	encode_json [undef] # yields [null]
		1102
		1103	You can force the type to be a JSON string by stringifying it:
		1104
		1105	my $x = 3.1; # some variable containing a number
		1106	"$x"; # stringified
		1107	$x .= ""; # another, more awkward way to stringify
		1108	print $x; # perl does it for you, too, quite often
		1109
		1110	You can force the type to be a JSON number by numifying it:
		1111
		1112	my $x = "3"; # some variable containing a string
		1113	$x += 0; # numify it, ensuring it will be dumped as a number
		1114	$x *= 1; # same thing, the choice is yours.
		1115
		1116	You can not currently force the type in other, less obscure, ways. Tell me
		1117	if you need this capability (but don't forget to explain why it's needed
		1118	:).
		1119
		1120	Note that numerical precision has the same meaning as under Perl (so
		1121	binary to decimal conversion follows the same rules as in Perl, which
		1122	can differ to other languages). Also, your perl interpreter might expose
		1123	extensions to the floating point numbers of your platform, such as
		1124	infinities or NaN's - these cannot be represented in JSON, and it is an
		1125	error to pass those in.
		1126
		1127	=back
		1128
		1129	=head2 OBJECT SERIALISATION
		1130
		1131	As JSON cannot directly represent Perl objects, you have to choose between
		1132	a pure JSON representation (without the ability to deserialise the object
		1133	automatically again), and a nonstandard extension to the JSON syntax,
		1134	tagged values.
		1135
		1136	=head3 SERIALISATION
		1137
		1138	What happens when C<JSON::XS> encounters a Perl object depends on the
		1139	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
		1140	used in this order:
		1141
		1142	=over 4
		1143
		1144	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
		1145
		1146	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1147	serialisation protocol to create a tagged JSON value, using a nonstandard
		1148	extension to the JSON syntax.
		1149
		1150	This works by invoking the C<FREEZE> method on the object, with the first
		1151	argument being the object to serialise, and the second argument being the
		1152	constant string C<JSON> to distinguish it from other serialisers.
		1153
		1154	The C<FREEZE> method can return any number of values (i.e. zero or
		1155	more). These values and the paclkage/classname of the object will then be
		1156	encoded as a tagged JSON value in the following format:
		1157
		1158	("classname")[FREEZE return values...]
		1159
		1160	e.g.:
		1161
		1162	("URI")["http://www.google.com/"]
		1163	("MyDate")[2013,10,29]
		1164	("ImageData::JPEG")["Z3...VlCg=="]
		1165
		1166	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1167	objects C<type> and C<id> members to encode the object:
		1168
		1169	sub My::Object::FREEZE {
		1170	my ($self, $serialiser) = @_;
		1171
		1172	($self->{type}, $self->{id})
		1173	}
		1174
		1175	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
		1176
		1177	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1178	context. It must return a single scalar that can be directly encoded into
		1179	JSON. This scalar replaces the object in the JSON text.
		1180
		1181	For example, the following C<TO_JSON> method will convert all L<URI>
		1182	objects to JSON strings when serialised. The fatc that these values
		1183	originally were L<URI> objects is lost.
		1184
		1185	sub URI::TO_JSON {
		1186	my ($uri) = @_;
		1187	$uri->as_string
		1188	}
		1189
		1190	=item 3. C<allow_blessed> is enabled.
		1191
		1192	The object will be serialised as a JSON null value.
		1193
		1194	=item 4. none of the above
		1195
		1196	If none of the settings are enabled or the respective methods are missing,
		1197	C<JSON::XS> throws an exception.
		1198
		1199	=back
		1200
		1201	=head3 DESERIALISATION
		1202
		1203	For deserialisation there are only two cases to consider: either
		1204	nonstandard tagging was used, in which case C<allow_tags> decides,
		1205	or objects cannot be automatically be deserialised, in which
		1206	case you can use postprocessing or the C<filter_json_object> or
		1207	C<filter_json_single_key_object> callbacks to get some real objects our of
		1208	your JSON.
		1209
		1210	This section only considers the tagged value case: I a tagged JSON object
		1211	is encountered during decoding and C<allow_tags> is disabled, a parse
		1212	error will result (as if tagged values were not part of the grammar).
		1213
		1214	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1215	of the package/classname used during serialisation (it will not attempt
		1216	to load the package as a Perl module). If there is no such method, the
		1217	decoding will fail with an error.
		1218
		1219	Otherwise, the C<THAW> method is invoked with the classname as first
		1220	argument, the constant string C<JSON> as second argument, and all the
		1221	values from the JSON array (the values originally returned by the
		1222	C<FREEZE> method) as remaining arguments.
		1223
		1224	The method must then return the object. While technically you can return
		1225	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1226	make that work in all cases, so better return an actual blessed reference.
		1227
		1228	As an example, let's implement a C<THAW> function that regenerates the
		1229	C<My::Object> from the C<FREEZE> example earlier:
		1230
		1231	sub My::Object::THAW {
		1232	my ($class, $serialiser, $type, $id) = @_;
		1233
		1234	$class->new (type => $type, id => $id)
		1235	}
		1236
		1237
		1238	=head1 ENCODING/CODESET FLAG NOTES
		1239
		1240	The interested reader might have seen a number of flags that signify
		1241	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1242	some confusion on what these do, so here is a short comparison:
		1243
		1244	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1245	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1246	control whether C<encode> escapes character values outside their respective
		1247	codeset range. Neither of these flags conflict with each other, although
		1248	some combinations make less sense than others.
		1249
		1250	Care has been taken to make all flags symmetrical with respect to
		1251	C<encode> and C<decode>, that is, texts encoded with any combination of
		1252	these flag values will be correctly decoded when the same flags are used
		1253	- in general, if you use different flag settings while encoding vs. when
		1254	decoding you likely have a bug somewhere.
		1255
		1256	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1257	simply an abstract set of character-codepoint pairs, while an encoding
		1258	takes those codepoint numbers and I<encodes> them, in our case into
		1259	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1260	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1261	the same time, which can be confusing.
		1262
		1263	=over 4
		1264
		1265	=item C<utf8> flag disabled
		1266
		1267	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1268	and expect Unicode strings, that is, characters with high ordinal Unicode
		1269	values (> 255) will be encoded as such characters, and likewise such
		1270	characters are decoded as-is, no changes to them will be done, except
		1271	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1272	respectively (to Perl, these are the same thing in strings unless you do
		1273	funny/weird/dumb stuff).
		1274
		1275	This is useful when you want to do the encoding yourself (e.g. when you
		1276	want to have UTF-16 encoded JSON texts) or when some other layer does
		1277	the encoding for you (for example, when printing to a terminal using a
		1278	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1279	to UTF-8 encode your data first and have Perl encode it another time).
		1280
		1281	=item C<utf8> flag enabled
		1282
		1283	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1284	characters using the corresponding UTF-8 multi-byte sequence, and will
		1285	expect your input strings to be encoded as UTF-8, that is, no "character"
		1286	of the input string must have any value > 255, as UTF-8 does not allow
		1287	that.
		1288
		1289	The C<utf8> flag therefore switches between two modes: disabled means you
		1290	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1291	octet/binary string in Perl.
		1292
		1293	=item C<latin1> or C<ascii> flags enabled
		1294
		1295	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1296	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1297	characters as specified by the C<utf8> flag.
		1298
		1299	If C<utf8> is disabled, then the result is also correctly encoded in those
		1300	character sets (as both are proper subsets of Unicode, meaning that a
		1301	Unicode string with all character values < 256 is the same thing as a
		1302	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1303	the same thing as an ASCII string in Perl).
		1304
		1305	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1306	regardless of these flags, just some more characters will be escaped using
		1307	C<\uXXXX> then before.
		1308
		1309	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1310	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1311	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1312	a subset of Unicode), while ASCII is.
		1313
		1314	Surprisingly, C<decode> will ignore these flags and so treat all input
		1315	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1316	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1317	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1318
		1319	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1320	they only govern when the JSON output engine escapes a character or not.
		1321
		1322	The main use for C<latin1> is to relatively efficiently store binary data
		1323	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1324
		1325	The main use for C<ascii> is to force the output to not contain characters
		1326	with values > 127, which means you can interpret the resulting string
		1327	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1328	8-bit-encoding, and still get the same data structure back. This is useful
		1329	when your channel for JSON transfer is not 8-bit clean or the encoding
		1330	might be mangled in between (e.g. in mail), and works because ASCII is a
		1331	proper subset of most 8-bit and multibyte encodings in use in the world.
		1332
		1333	=back
		1334
		1335
		1336	=head2 JSON and ECMAscript
		1337
		1338	JSON syntax is based on how literals are represented in javascript (the
		1339	not-standardised predecessor of ECMAscript) which is presumably why it is
		1340	called "JavaScript Object Notation".
		1341
		1342	However, JSON is not a subset (and also not a superset of course) of
		1343	ECMAscript (the standard) or javascript (whatever browsers actually
		1344	implement).
		1345
		1346	If you want to use javascript's C<eval> function to "parse" JSON, you
		1347	might run into parse errors for valid JSON texts, or the resulting data
		1348	structure might not be queryable:
		1349
		1350	One of the problems is that U+2028 and U+2029 are valid characters inside
		1351	JSON strings, but are not allowed in ECMAscript string literals, so the
		1352	following Perl fragment will not output something that can be guaranteed
		1353	to be parsable by javascript's C<eval>:
		1354
		1355	use JSON::XS;
		1356
		1357	print encode_json [chr 0x2028];
		1358
		1359	The right fix for this is to use a proper JSON parser in your javascript
		1360	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1361	F<json2.js> parser).
		1362
		1363	If this is not an option, you can, as a stop-gap measure, simply encode to
		1364	ASCII-only JSON:
		1365
		1366	use JSON::XS;
		1367
		1368	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1369
		1370	Note that this will enlarge the resulting JSON text quite a bit if you
		1371	have many non-ASCII characters. You might be tempted to run some regexes
		1372	to only escape U+2028 and U+2029, e.g.:
		1373
		1374	# DO NOT USE THIS!
		1375	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1376	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1377	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1378	print $json;
		1379
		1380	Note that I<this is a bad idea>: the above only works for U+2028 and
		1381	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1382	javascript implementations, however, have issues with other characters as
		1383	well - using C<eval> naively simply I<will> cause problems.
		1384
		1385	Another problem is that some javascript implementations reserve
		1386	some property names for their own purposes (which probably makes
		1387	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1388	C<__proto__> property name for its own purposes.
		1389
		1390	If that is a problem, you could parse try to filter the resulting JSON
		1391	output for these property strings, e.g.:
		1392
		1393	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1394
		1395	This works because C<__proto__> is not valid outside of strings, so every
		1396	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1397
		1398	If you know of other incompatibilities, please let me know.
		1399
		1400
		1401	=head2 JSON and YAML
		1402
		1403	You often hear that JSON is a subset of YAML. This is, however, a mass
		1404	hysteria(*) and very far from the truth (as of the time of this writing),
		1405	so let me state it clearly: I<in general, there is no way to configure
		1406	JSON::XS to output a data structure as valid YAML> that works in all
		1407	cases.
		1408
		1409	If you really must use JSON::XS to generate YAML, you should use this
		1410	algorithm (subject to change in future versions):
		1411
		1412	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1413	my $yaml = $to_yaml->encode ($ref) . "\n";
		1414
		1415	This will I<usually> generate JSON texts that also parse as valid
		1416	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1417	lengths that JSON doesn't have and also has different and incompatible
		1418	unicode character escape syntax, so you should make sure that your hash
		1419	keys are noticeably shorter than the 1024 "stream characters" YAML allows
		1420	and that you do not have characters with codepoint values outside the
		1421	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
		1422	sequences in strings (which JSON::XS does not I<currently> generate, but
		1423	other JSON generators might).
		1424
		1425	There might be other incompatibilities that I am not aware of (or the YAML
		1426	specification has been changed yet again - it does so quite often). In
		1427	general you should not try to generate YAML with a JSON generator or vice
		1428	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1429	high that you will run into severe interoperability problems when you
		1430	least expect it.
		1431
		1432	=over 4
		1433
		1434	=item (*)
		1435
		1436	I have been pressured multiple times by Brian Ingerson (one of the
		1437	authors of the YAML specification) to remove this paragraph, despite him
		1438	acknowledging that the actual incompatibilities exist. As I was personally
		1439	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1440	educate people about these issues, so others do not run into the same
		1441	problem again and again. After this, Brian called me a (quote)I<complete
		1442	and worthless idiot>(unquote).
		1443
		1444	In my opinion, instead of pressuring and insulting people who actually
		1445	clarify issues with YAML and the wrong statements of some of its
		1446	proponents, I would kindly suggest reading the JSON spec (which is not
		1447	that difficult or long) and finally make YAML compatible to it, and
		1448	educating users about the changes, instead of spreading lies about the
		1449	real compatibility for many I<years> and trying to silence people who
		1450	point out that it isn't true.
		1451
		1452	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1453	though the incompatibilities have been documented (and are known to Brian)
		1454	for many years and the spec makes explicit claims that YAML is a superset
		1455	of JSON. It would be so easy to fix, but apparently, bullying people and
		1456	corrupting userdata is so much easier.
		1457
		1458	=back
		1459
346		1460
347	=head2 SPEED	1461	=head2 SPEED
348		1462
349	It seems that JSON::XS is surprisingly fast, as shown in the following	1463	It seems that JSON::XS is surprisingly fast, as shown in the following
350	tables. They have been generated with the help of the C<eg/bench> program	1464	tables. They have been generated with the help of the C<eg/bench> program
351	in the JSON::XS distribution, to make it easy to compare on your own	1465	in the JSON::XS distribution, to make it easy to compare on your own
352	system.	1466	system.
353		1467
354	First is a comparison between various modules using a very simple JSON	1468	First comes a comparison between various modules using
		1469	a very short single-line JSON string (also available at
		1470	L<http://dist.schmorp.de/misc/json/short.json>).
		1471
		1472	{"method": "handleMessage", "params": ["user1",
		1473	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1474	1, 0]}
		1475
355	string, showing the number of encodes/decodes per second (JSON::XS is	1476	It shows the number of encodes/decodes per second (JSON::XS uses
356	the functional interface, while JSON::XS/2 is the OO interface with	1477	the functional interface, while JSON::XS/2 uses the OO interface
357	pretty-printing and hashkey sorting enabled).	1478	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1479	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1480	uses the from_json method). Higher is better:
358		1481
359	module | encode | decode |	1482	module | encode | decode |
360	-----------|------------|------------|	1483	--------------|------------|------------|
361	JSON | 14006 | 6820 |	1484	JSON::DWIW/DS | 86302.551 | 102300.098 |
362	JSON::DWIW | 200937 | 120386 |	1485	JSON::DWIW/FJ | 86302.551 | 75983.768 |
363	JSON::PC | 85065 | 129366 |	1486	JSON::PP | 15827.562 | 6638.658 |
364	JSON::Syck | 59898 | 44232 |	1487	JSON::Syck | 63358.066 | 47662.545 |
365	JSON::XS | 1171478 | 342435 |	1488	JSON::XS | 511500.488 | 511500.488 |
366	JSON::XS/2 | 730760 | 328714 |	1489	JSON::XS/2 | 291271.111 | 388361.481 |
		1490	JSON::XS/3 | 361577.931 | 361577.931 |
		1491	Storable | 66788.280 | 265462.278 |
367	-----------+------------+------------+	1492	--------------+------------+------------+
368		1493
369	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1494	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
370	times faster than JSON, even with pretty-printing and key sorting.	1495	about five times faster on decoding, and over thirty to seventy times
		1496	faster than JSON's pure perl implementation. It also compares favourably
		1497	to Storable for small amounts of data.
371		1498
372	Using a longer test string (roughly 8KB, generated from Yahoo! Locals	1499	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
373	search API (http://nanoref.com/yahooapis/mgPdGg):	1500	search API (L<http://dist.schmorp.de/misc/json/long.json>).
374		1501
375	module | encode | decode |	1502	module | encode | decode |
376	-----------|------------|------------|	1503	--------------|------------|------------|
377	JSON | 673 | 38 |	1504	JSON::DWIW/DS | 1647.927 | 2673.916 |
378	JSON::DWIW | 5271 | 770 |	1505	JSON::DWIW/FJ | 1630.249 | 2596.128 |
379	JSON::PC | 9901 | 2491 |	1506	JSON::PP | 400.640 | 62.311 |
380	JSON::Syck | 2360 | 786 |	1507	JSON::Syck | 1481.040 | 1524.869 |
381	JSON::XS | 37398 | 3202 |	1508	JSON::XS | 20661.596 | 9541.183 |
382	JSON::XS/2 | 13765 | 3153 |	1509	JSON::XS/2 | 10683.403 | 9416.938 |
		1510	JSON::XS/3 | 20661.596 | 9400.054 |
		1511	Storable | 19765.806 | 10000.725 |
383	-----------+------------+------------+	1512	--------------+------------+------------+
384		1513
385	Again, JSON::XS leads by far in the encoding case, while still beating	1514	Again, JSON::XS leads by far (except for Storable which non-surprisingly
386	every other module in the decoding case.	1515	decodes a bit faster).
387		1516
388	Last example is an almost 8MB large hash with many large binary values	1517	On large strings containing lots of high Unicode characters, some modules
389	(PNG files), resulting in a lot of escaping:	1518	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1519	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1520	to decode or encode properly, so it was impossible to prepare a fair
		1521	comparison table for that case.
		1522
		1523
		1524	=head1 SECURITY CONSIDERATIONS
		1525
		1526	When you are using JSON in a protocol, talking to untrusted potentially
		1527	hostile creatures requires relatively few measures.
		1528
		1529	First of all, your JSON decoder should be secure, that is, should not have
		1530	any buffer overflows. Obviously, this module should ensure that and I am
		1531	trying hard on making that true, but you never know.
		1532
		1533	Second, you need to avoid resource-starving attacks. That means you should
		1534	limit the size of JSON texts you accept, or make sure then when your
		1535	resources run out, that's just fine (e.g. by using a separate process that
		1536	can crash safely). The size of a JSON text in octets or characters is
		1537	usually a good indication of the size of the resources required to decode
		1538	it into a Perl structure. While JSON::XS can check the size of the JSON
		1539	text, it might be too late when you already have it in memory, so you
		1540	might want to check the size before you accept the string.
		1541
		1542	Third, JSON::XS recurses using the C stack when decoding objects and
		1543	arrays. The C stack is a limited resource: for instance, on my amd64
		1544	machine with 8MB of stack size I can decode around 180k nested arrays but
		1545	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1546	to free the temporary). If that is exceeded, the program crashes. To be
		1547	conservative, the default nesting limit is set to 512. If your process
		1548	has a smaller stack, you should adjust this setting accordingly with the
		1549	C<max_depth> method.
		1550
		1551	Something else could bomb you, too, that I forgot to think of. In that
		1552	case, you get to keep the pieces. I am always open for hints, though...
		1553
		1554	Also keep in mind that JSON::XS might leak contents of your Perl data
		1555	structures in its error messages, so when you serialise sensitive
		1556	information you might want to make sure that exceptions thrown by JSON::XS
		1557	will not end up in front of untrusted eyes.
		1558
		1559	If you are using JSON::XS to return packets to consumption
		1560	by JavaScript scripts in a browser you should have a look at
		1561	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
		1562	see whether you are vulnerable to some common attack vectors (which really
		1563	are browser design bugs, but it is still you who will have to deal with
		1564	it, as major browser developers care only for features, not about getting
		1565	security right).
		1566
		1567
		1568	=head1 "OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)
		1569
		1570	TL;DR: Due to security concerns, JSON::XS will not allow scalar data in
		1571	JSON texts by default - you need to create your own JSON::XS object and
		1572	enable C<allow_nonref>:
		1573
		1574
		1575	my $json = JSON::XS->new->allow_nonref;
		1576
		1577	$text = $json->encode ($data);
		1578	$data = $json->decode ($text);
		1579
		1580	The long version: JSON being an important and supposedly stable format,
		1581	the IETF standardised it as RFC 4627 in 2006. Unfortunately, the inventor
		1582	of JSON, Dougles Crockford, unilaterally changed the definition of JSON in
		1583	javascript. Rather than create a fork, the IETF decided to standardise the
		1584	new syntax (apparently, so Iw as told, without finding it very amusing).
		1585
		1586	The biggest difference between thed original JSON and the new JSON is that
		1587	the new JSON supports scalars (anything other than arrays and objects) at
		1588	the toplevel of a JSON text. While this is strictly backwards compatible
		1589	to older versions, it breaks a number of protocols that relied on sending
		1590	JSON back-to-back, and is a minor security concern.
		1591
		1592	For example, imagine you have two banks communicating, and on one side,
		1593	trhe JSON coder gets upgraded. Two messages, such as C<10> and C<1000>
		1594	might then be confused to mean C<101000>, something that couldn't happen
		1595	in the original JSON, because niether of these messages would be valid
		1596	JSON.
		1597
		1598	If one side accepts these messages, then an upgrade in the coder on either
		1599	side could result in this becoming exploitable.
		1600
		1601	This module has always allowed these messages as an optional extension, by
		1602	default disabled. The security concerns are the reason why the default is
		1603	still disabled, but future versions might/will likely upgrade to the newer
		1604	RFC as default format, so you are advised to check your implementation
		1605	and/or override the default with C<< ->allow_nonref (0) >> to ensure that
		1606	future versions are safe.
		1607
		1608
		1609	=head1 INTEROPERABILITY WITH OTHER MODULES
		1610
		1611	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1612	constants. That means that the JSON true and false values will be
		1613	comaptible to true and false values of iother modules that do the same,
		1614	such as L<JSON::PP> and L<CBOR::XS>.
		1615
		1616
		1617	=head1 INTEROPERABILITY WITH OTHER JSON DECODERS
		1618
		1619	As long as you only serialise data that can be directly expressed in JSON,
		1620	C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs,
		1621	but C<JSON::XS> has found more bugs in the official JSON testsuite (1)
		1622	than the official JSON testsuite has found in C<JSON::XS> (0)).
		1623
		1624	When you have trouble decoding JSON generated by this module using other
		1625	decoders, then it is very likely that you have an encoding mismatch or the
		1626	other decoder is broken.
		1627
		1628	When decoding, C<JSON::XS> is strict by default and will likely catch all
		1629	errors. There are currently two settings that change this: C<relaxed>
		1630	makes C<JSON::XS> accept (but not generate) some non-standard extensions,
		1631	and C<allow_tags> will allow you to encode and decode Perl objects, at the
		1632	cost of not outputting valid JSON anymore.
		1633
		1634	=head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
		1635
		1636	When you use C<allow_tags> to use the extended (and also nonstandard and
		1637	invalid) JSON syntax for serialised objects, and you still want to decode
		1638	the generated When you want to serialise objects, you can run a regex
		1639	to replace the tagged syntax by standard JSON arrays (it only works for
		1640	"normal" packagesnames without comma, newlines or single colons). First,
		1641	the readable Perl version:
		1642
		1643	# if your FREEZE methods return no values, you need this replace first:
		1644	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
		1645
		1646	# this works for non-empty constructor arg lists:
		1647	$json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
		1648
		1649	And here is a less readable version that is easy to adapt to other
		1650	languages:
		1651
		1652	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
		1653
		1654	Here is an ECMAScript version (same regex):
		1655
		1656	json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
		1657
		1658	Since this syntax converts to standard JSON arrays, it might be hard to
		1659	distinguish serialised objects from normal arrays. You can prepend a
		1660	"magic number" as first array element to reduce chances of a collision:
		1661
		1662	$json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
		1663
		1664	And after decoding the JSON text, you could walk the data
		1665	structure looking for arrays with a first element of
		1666	C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>.
		1667
		1668	The same approach can be used to create the tagged format with another
		1669	encoder. First, you create an array with the magic string as first member,
		1670	the classname as second, and constructor arguments last, encode it as part
		1671	of your JSON structure, and then:
		1672
		1673	$json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
		1674
		1675	Again, this has some limitations - the magic string must not be encoded
		1676	with character escapes, and the constructor arguments must be non-empty.
		1677
		1678
		1679	=head1 RFC7159
		1680
		1681	Since this module was written, Google has written a new JSON RFC, RFC 7159
		1682	(and RFC7158). Unfortunately, this RFC breaks compatibility with both the
		1683	original JSON specification on www.json.org and RFC4627.
		1684
		1685	As far as I can see, you can get partial compatibility when parsing by
		1686	using C<< ->allow_nonref >>. However, consider thew security implications
		1687	of doing so.
		1688
		1689	I haven't decided yet when to break compatibility with RFC4627 by default
		1690	(and potentially leave applications insecure) and change the default to
		1691	follow RFC7159, but application authors are well advised to call C<<
		1692	->allow_nonref(0) >> even if this is the current default, if they cannot
		1693	handle non-reference values, in preparation for the day when the4 default
		1694	will change.
		1695
		1696
		1697	=head1 THREADS
		1698
		1699	This module is I<not> guaranteed to be thread safe and there are no
		1700	plans to change this until Perl gets thread support (as opposed to the
		1701	horribly slow so-called "threads" which are simply slow and bloated
		1702	process simulations - use fork, it's I<much> faster, cheaper, better).
		1703
		1704	(It might actually work, but you have been warned).
		1705
		1706
		1707	=head1 THE PERILS OF SETLOCALE
		1708
		1709	Sometimes people avoid the Perl locale support and directly call the
		1710	system's setlocale function with C<LC_ALL>.
		1711
		1712	This breaks both perl and modules such as JSON::XS, as stringification of
		1713	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1714	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1715	perl to stringify numbers).
		1716
		1717	The solution is simple: don't call C<setlocale>, or use it for only those
		1718	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1719
		1720	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1721	actually needs it (avoiding stringification of numbers), and restore it
		1722	afterwards.
		1723
390		1724
391	=head1 BUGS	1725	=head1 BUGS
392		1726
393	While the goal of this module is to be correct, that unfortunately does	1727	While the goal of this module is to be correct, that unfortunately does
394	not mean its bug-free, only that I think its design is bug-free. It is	1728	not mean it's bug-free, only that I think its design is bug-free. If you
395	still very young and not well-tested. If you keep reporting bugs they will	1729	keep reporting bugs they will be fixed swiftly, though.
396	be fixed swiftly, though.	1730
		1731	Please refrain from using rt.cpan.org or any other bug reporting
		1732	service. I put the contact address into my modules for a reason.
397		1733
398	=cut	1734	=cut
399		1735
400	1;	1736	BEGIN {
		1737	*true = \$Types::Serialiser::true;
		1738	*true = \&Types::Serialiser::true;
		1739	*false = \$Types::Serialiser::false;
		1740	*false = \&Types::Serialiser::false;
		1741	*is_bool = \&Types::Serialiser::is_bool;
		1742
		1743	*JSON::XS::Boolean:: = *Types::Serialiser::Boolean::;
		1744	}
		1745
		1746	XSLoader::load "JSON::XS", $VERSION;
		1747
		1748	=head1 SEE ALSO
		1749
		1750	The F<json_xs> command line utility for quick experiments.
401		1751
402	=head1 AUTHOR	1752	=head1 AUTHOR
403		1753
404	Marc Lehmann <schmorp@schmorp.de>	1754	Marc Lehmann <schmorp@schmorp.de>
405	http://home.schmorp.de/	1755	http://home.schmorp.de/
406		1756
407	=cut	1757	=cut
408		1758
		1759	1
		1760

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines