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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.3 by root, Thu Mar 22 18:10:29 2007 UTC vs.
Revision 1.91 by root, Thu Mar 20 02:11:21 2008 UTC

…		…
		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	5	JSON::XS - JSON serialising/deserialising, done correctly and fast
4		6
		7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
		13
		14	# exported functions, they croak on error
		15	# and expect/generate UTF-8
		16
		17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
		18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
		19
		20	# OO-interface
		21
		22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
		23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
		24	$perl_scalar = $coder->decode ($unicode_json_text);
		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
8		33
9	=head1 DESCRIPTION	34	=head1 DESCRIPTION
10		35
11	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
12	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
13	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overriden) with no overhead due to emulation (by inheritign constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
14		47
15	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
16	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
17	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
18	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
19	reports for other reasons.	52	reports for other reasons.
20		53
21	See COMPARISON, below, for a comparison to some other JSON modules.	54	See COMPARISON, below, for a comparison to some other JSON modules.
22		55
		56	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
		57	vice versa.
		58
23	=head2 FEATURES	59	=head2 FEATURES
24		60
25	=over 4	61	=over 4
26		62
27	=item * correct handling of unicode issues	63	=item * correct Unicode handling
28		64
29	This module knows how to handle Unicode, and even documents how it does so.	65	This module knows how to handle Unicode, documents how and when it does
		66	so, and even documents what "correct" means.
30		67
31	=item * round-trip integrity	68	=item * round-trip integrity
32		69
33	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only datatypes supported
34	by JSON, the deserialised data structure is identical on the Perl level.	71	by JSON, the deserialised data structure is identical on the Perl level.
35	(e.g. the string "2.0" doesn't suddenly become "2").	72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
		73	like a number). There minor I<are> exceptions to this, read the MAPPING
		74	section below to learn about those.
36		75
37	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
38		77
39	There is no guessing, no generating of illegal JSON strings by default,	78	There is no guessing, no generating of illegal JSON texts by default,
40	and only JSON is accepted as input (the latter is a security feature).	79	and only JSON is accepted as input by default (the latter is a security
		80	feature).
41		81
42	=item * fast	82	=item * fast
43		83
44	compared to other JSON modules, this module compares favourably.	84	Compared to other JSON modules and other serialisers such as Storable,
		85	this module usually compares favourably in terms of speed, too.
45		86
46	=item * simple to use	87	=item * simple to use
47		88
48	This module has both a simple functional interface as well as an OO	89	This module has both a simple functional interface as well as an objetc
49	interface.	90	oriented interface interface.
50		91
51	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
52		93
53	You can choose between the most compact format possible, a pure-ascii	94	You can choose between the most compact guaranteed-single-line format
54	format, or a pretty-printed format. Or you can combine those features in	95	possible (nice for simple line-based protocols), a pure-ascii format
55	whatever way you like.	96	(for when your transport is not 8-bit clean, still supports the whole
		97	Unicode range), or a pretty-printed format (for when you want to read that
		98	stuff). Or you can combine those features in whatever way you like.
56		99
57	=back	100	=back
58		101
59	=cut	102	=cut
60		103
61	package JSON::XS;	104	package JSON::XS;
62		105
63	BEGIN {	106	use strict;
		107
64	$VERSION = '0.1';	108	our $VERSION = '2.1';
65	@ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
66		110
67	@EXPORT = qw(to_json from_json);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
68	require Exporter;
69		112
		113	sub to_json($) {
70	require XSLoader;	114	require Carp;
71	XSLoader::load JSON::XS::, $VERSION;	115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
72	}	116	}
73		117
		118	sub from_json($) {
		119	require Carp;
		120	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
		121	}
		122
		123	use Exporter;
		124	use XSLoader;
		125
74	=head1 FUNCTIONAL INTERFACE	126	=head1 FUNCTIONAL INTERFACE
75		127
76	The following convinience methods are provided by this module. They are	128	The following convenience methods are provided by this module. They are
77	exported by default:	129	exported by default:
78		130
79	=over 4	131	=over 4
80		132
81	=item $json_string = to_json $perl_scalar	133	=item $json_text = encode_json $perl_scalar
82		134
83	Converts the given Perl data structure (a simple scalar or a reference to	135	Converts the given Perl data structure to a UTF-8 encoded, binary string
84	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	136	(that is, the string contains octets only). Croaks on error.
85	octets only). Croaks on error.
86		137
87	This function call is functionally identical to C<< JSON::XS->new->utf8	138	This function call is functionally identical to:
88	(1)->encode ($perl_scalar) >>.
89		139
		140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		141
		142	except being faster.
		143
90	=item $perl_scalar = from_json $json_string	144	=item $perl_scalar = decode_json $json_text
91		145
92	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
93	parse that as an UTF-8 encoded JSON string, returning the resulting simple	147	to parse that as an UTF-8 encoded JSON text, returning the resulting
94	scalar or reference. Croaks on error.	148	reference. Croaks on error.
95		149
96	This function call is functionally identical to C<< JSON::XS->new->utf8	150	This function call is functionally identical to:
97	(1)->decode ($json_string) >>.	151
		152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		153
		154	except being faster.
		155
		156	=item $is_boolean = JSON::XS::is_bool $scalar
		157
		158	Returns true if the passed scalar represents either JSON::XS::true or
		159	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		160	and are used to represent JSON C<true> and C<false> values in Perl.
		161
		162	See MAPPING, below, for more information on how JSON values are mapped to
		163	Perl.
98		164
99	=back	165	=back
		166
		167
		168	=head1 A FEW NOTES ON UNICODE AND PERL
		169
		170	Since this often leads to confusion, here are a few very clear words on
		171	how Unicode works in Perl, modulo bugs.
		172
		173	=over 4
		174
		175	=item 1. Perl strings can store characters with ordinal values > 255.
		176
		177	This enables you to store Unicode characters as single characters in a
		178	Perl string - very natural.
		179
		180	=item 2. Perl does I<not> associate an encoding with your strings.
		181
		182	... until you force it to, e.g. when matching it against a regex, or
		183	printing the scalar to a file, in which case Perl either interprets your
		184	string as locale-encoded text, octets/binary, or as Unicode, depending
		185	on various settings. In no case is an encoding stored together with your
		186	data, it is I<use> that decides encoding, not any magical meta data.
		187
		188	=item 3. The internal utf-8 flag has no meaning with regards to the
		189	encoding of your string.
		190
		191	Just ignore that flag unless you debug a Perl bug, a module written in
		192	XS or want to dive into the internals of perl. Otherwise it will only
		193	confuse you, as, despite the name, it says nothing about how your string
		194	is encoded. You can have Unicode strings with that flag set, with that
		195	flag clear, and you can have binary data with that flag set and that flag
		196	clear. Other possibilities exist, too.
		197
		198	If you didn't know about that flag, just the better, pretend it doesn't
		199	exist.
		200
		201	=item 4. A "Unicode String" is simply a string where each character can be
		202	validly interpreted as a Unicode codepoint.
		203
		204	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		205	Unicode string encoded in UTF-8, giving you a binary string.
		206
		207	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		208
		209	It's a fact. Learn to live with it.
		210
		211	=back
		212
		213	I hope this helps :)
		214
100		215
101	=head1 OBJECT-ORIENTED INTERFACE	216	=head1 OBJECT-ORIENTED INTERFACE
102		217
103	The object oriented interface lets you configure your own encoding or	218	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	219	decoding style, within the limits of supported formats.
111	strings. All boolean flags described below are by default I<disabled>.	226	strings. All boolean flags described below are by default I<disabled>.
112		227
113	The mutators for flags all return the JSON object again and thus calls can	228	The mutators for flags all return the JSON object again and thus calls can
114	be chained:	229	be chained:
115		230
116	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	231	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
117	=> {"a": [1, 2]}	232	=> {"a": [1, 2]}
118		233
119	=item $json = $json->ascii ($enable)	234	=item $json = $json->ascii ([$enable])
120		235
		236	=item $enabled = $json->get_ascii
		237
121	If C<$enable> is true, then the C<encode> method will not generate	238	If C<$enable> is true (or missing), then the C<encode> method will not
122	characters outside the code range C<0..127>. Any unicode characters	239	generate characters outside the code range C<0..127> (which is ASCII). Any
123	outside that range will be escaped using either a single \uXXXX (BMP	240	Unicode characters outside that range will be escaped using either a
124	characters) or a double \uHHHH\uLLLLL escape sequence, as per RFC4627.	241	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
		242	as per RFC4627. The resulting encoded JSON text can be treated as a native
		243	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		244	or any other superset of ASCII.
125		245
126	If C<$enable> is false, then the C<encode> method will not escape Unicode	246	If C<$enable> is false, then the C<encode> method will not escape Unicode
127	characters unless necessary.	247	characters unless required by the JSON syntax or other flags. This results
		248	in a faster and more compact format.
128		249
		250	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		251	document.
		252
		253	The main use for this flag is to produce JSON texts that can be
		254	transmitted over a 7-bit channel, as the encoded JSON texts will not
		255	contain any 8 bit characters.
		256
129	JSON::XS->new->ascii (1)->encode (chr 0x10401)	257	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
130	=> \ud801\udc01	258	=> ["\ud801\udc01"]
131		259
		260	=item $json = $json->latin1 ([$enable])
		261
		262	=item $enabled = $json->get_latin1
		263
		264	If C<$enable> is true (or missing), then the C<encode> method will encode
		265	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		266	outside the code range C<0..255>. The resulting string can be treated as a
		267	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		268	will not be affected in any way by this flag, as C<decode> by default
		269	expects Unicode, which is a strict superset of latin1.
		270
		271	If C<$enable> is false, then the C<encode> method will not escape Unicode
		272	characters unless required by the JSON syntax or other flags.
		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
		276
		277	The main use for this flag is efficiently encoding binary data as JSON
		278	text, as most octets will not be escaped, resulting in a smaller encoded
		279	size. The disadvantage is that the resulting JSON text is encoded
		280	in latin1 (and must correctly be treated as such when storing and
		281	transferring), a rare encoding for JSON. It is therefore most useful when
		282	you want to store data structures known to contain binary data efficiently
		283	in files or databases, not when talking to other JSON encoders/decoders.
		284
		285	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		286	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
		287
132	=item $json = $json->utf8 ($enable)	288	=item $json = $json->utf8 ([$enable])
133		289
		290	=item $enabled = $json->get_utf8
		291
134	If C<$enable> is true, then the C<encode> method will encode the JSON	292	If C<$enable> is true (or missing), then the C<encode> method will encode
135	string into UTF-8, as required by many protocols, while the C<decode>	293	the JSON result into UTF-8, as required by many protocols, while the
136	method expects to be handled an UTF-8-encoded string. Please note that	294	C<decode> method expects to be handled an UTF-8-encoded string. Please
137	UTF-8-encoded strings do not contain any characters outside the range	295	note that UTF-8-encoded strings do not contain any characters outside the
138	C<0..255>, they are thus useful for bytewise/binary I/O.	296	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		297	versions, enabling this option might enable autodetection of the UTF-16
		298	and UTF-32 encoding families, as described in RFC4627.
139		299
140	If C<$enable> is false, then the C<encode> method will return the JSON	300	If C<$enable> is false, then the C<encode> method will return the JSON
141	string as a (non-encoded) unicode string, while C<decode> expects thus a	301	string as a (non-encoded) Unicode string, while C<decode> expects thus a
142	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	302	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
143	to be done yourself, e.g. using the Encode module.	303	to be done yourself, e.g. using the Encode module.
144		304
		305	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		306	document.
		307
		308	Example, output UTF-16BE-encoded JSON:
		309
		310	use Encode;
		311	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		312
		313	Example, decode UTF-32LE-encoded JSON:
		314
		315	use Encode;
		316	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
		317
145	=item $json = $json->pretty ($enable)	318	=item $json = $json->pretty ([$enable])
146		319
147	This enables (or disables) all of the C<indent>, C<space_before> and	320	This enables (or disables) all of the C<indent>, C<space_before> and
148	C<space_after> (and in the future possibly more) flags in one call to	321	C<space_after> (and in the future possibly more) flags in one call to
149	generate the most readable (or most compact) form possible.	322	generate the most readable (or most compact) form possible.
		323
		324	Example, pretty-print some simple structure:
150		325
151	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})	326	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
152	=>	327	=>
153	{	328	{
154	"a" : [	329	"a" : [
155	1,	330	1,
156	2	331	2
157	]	332	]
158	}	333	}
159		334
160	=item $json = $json->indent ($enable)	335	=item $json = $json->indent ([$enable])
161		336
		337	=item $enabled = $json->get_indent
		338
162	If C<$enable> is true, then the C<encode> method will use a multiline	339	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
163	format as output, putting every array member or object/hash key-value pair	340	format as output, putting every array member or object/hash key-value pair
164	into its own line, identing them properly.	341	into its own line, indenting them properly.
165		342
166	If C<$enable> is false, no newlines or indenting will be produced, and the	343	If C<$enable> is false, no newlines or indenting will be produced, and the
167	resulting JSON strings is guarenteed not to contain any C<newlines>.	344	resulting JSON text is guaranteed not to contain any C<newlines>.
168		345
169	This setting has no effect when decoding JSON strings.	346	This setting has no effect when decoding JSON texts.
170		347
171	=item $json = $json->space_before ($enable)	348	=item $json = $json->space_before ([$enable])
172		349
		350	=item $enabled = $json->get_space_before
		351
173	If C<$enable> is true, then the C<encode> method will add an extra	352	If C<$enable> is true (or missing), then the C<encode> method will add an extra
174	optional space before the C<:> separating keys from values in JSON objects.	353	optional space before the C<:> separating keys from values in JSON objects.
175		354
176	If C<$enable> is false, then the C<encode> method will not add any extra	355	If C<$enable> is false, then the C<encode> method will not add any extra
177	space at those places.	356	space at those places.
178		357
179	This setting has no effect when decoding JSON strings. You will also most	358	This setting has no effect when decoding JSON texts. You will also
180	likely combine this setting with C<space_after>.	359	most likely combine this setting with C<space_after>.
181		360
		361	Example, space_before enabled, space_after and indent disabled:
		362
		363	{"key" :"value"}
		364
182	=item $json = $json->space_after ($enable)	365	=item $json = $json->space_after ([$enable])
183		366
		367	=item $enabled = $json->get_space_after
		368
184	If C<$enable> is true, then the C<encode> method will add an extra	369	If C<$enable> is true (or missing), then the C<encode> method will add an extra
185	optional space after the C<:> separating keys from values in JSON objects	370	optional space after the C<:> separating keys from values in JSON objects
186	and extra whitespace after the C<,> separating key-value pairs and array	371	and extra whitespace after the C<,> separating key-value pairs and array
187	members.	372	members.
188		373
189	If C<$enable> is false, then the C<encode> method will not add any extra	374	If C<$enable> is false, then the C<encode> method will not add any extra
190	space at those places.	375	space at those places.
191		376
192	This setting has no effect when decoding JSON strings.	377	This setting has no effect when decoding JSON texts.
193		378
		379	Example, space_before and indent disabled, space_after enabled:
		380
		381	{"key": "value"}
		382
		383	=item $json = $json->relaxed ([$enable])
		384
		385	=item $enabled = $json->get_relaxed
		386
		387	If C<$enable> is true (or missing), then C<decode> will accept some
		388	extensions to normal JSON syntax (see below). C<encode> will not be
		389	affected in anyway. I<Be aware that this option makes you accept invalid
		390	JSON texts as if they were valid!>. I suggest only to use this option to
		391	parse application-specific files written by humans (configuration files,
		392	resource files etc.)
		393
		394	If C<$enable> is false (the default), then C<decode> will only accept
		395	valid JSON texts.
		396
		397	Currently accepted extensions are:
		398
		399	=over 4
		400
		401	=item * list items can have an end-comma
		402
		403	JSON I<separates> array elements and key-value pairs with commas. This
		404	can be annoying if you write JSON texts manually and want to be able to
		405	quickly append elements, so this extension accepts comma at the end of
		406	such items not just between them:
		407
		408	[
		409	1,
		410	2, <- this comma not normally allowed
		411	]
		412	{
		413	"k1": "v1",
		414	"k2": "v2", <- this comma not normally allowed
		415	}
		416
		417	=item * shell-style '#'-comments
		418
		419	Whenever JSON allows whitespace, shell-style comments are additionally
		420	allowed. They are terminated by the first carriage-return or line-feed
		421	character, after which more white-space and comments are allowed.
		422
		423	[
		424	1, # this comment not allowed in JSON
		425	# neither this one...
		426	]
		427
		428	=back
		429
194	=item $json = $json->canonical ($enable)	430	=item $json = $json->canonical ([$enable])
195		431
		432	=item $enabled = $json->get_canonical
		433
196	If C<$enable> is true, then the C<encode> method will output JSON objects	434	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
197	by sorting their keys. This is adding a comparatively high overhead.	435	by sorting their keys. This is adding a comparatively high overhead.
198		436
199	If C<$enable> is false, then the C<encode> method will output key-value	437	If C<$enable> is false, then the C<encode> method will output key-value
200	pairs in the order Perl stores them (which will likely change between runs	438	pairs in the order Perl stores them (which will likely change between runs
201	of the same script).	439	of the same script).
202		440
203	This option is useful if you want the same data structure to be encoded as	441	This option is useful if you want the same data structure to be encoded as
204	the same JSON string (given the same overall settings). If it is disabled,	442	the same JSON text (given the same overall settings). If it is disabled,
205	the same hash migh be encoded differently even if contains the same data,	443	the same hash might be encoded differently even if contains the same data,
206	as key-value pairs have no inherent ordering in Perl.	444	as key-value pairs have no inherent ordering in Perl.
207		445
208	This setting has no effect when decoding JSON strings.	446	This setting has no effect when decoding JSON texts.
209		447
210	=item $json = $json->allow_nonref ($enable)	448	=item $json = $json->allow_nonref ([$enable])
211		449
		450	=item $enabled = $json->get_allow_nonref
		451
212	If C<$enable> is true, then the C<encode> method can convert a	452	If C<$enable> is true (or missing), then the C<encode> method can convert a
213	non-reference into its corresponding string, number or null JSON value,	453	non-reference into its corresponding string, number or null JSON value,
214	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	454	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
215	values instead of croaking.	455	values instead of croaking.
216		456
217	If C<$enable> is false, then the C<encode> method will croak if it isn't	457	If C<$enable> is false, then the C<encode> method will croak if it isn't
218	passed an arrayref or hashref, as JSON strings must either be an object	458	passed an arrayref or hashref, as JSON texts must either be an object
219	or array. Likewise, C<decode> will croak if given something that is not a	459	or array. Likewise, C<decode> will croak if given something that is not a
220	JSON object or array.	460	JSON object or array.
221		461
		462	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
		463	resulting in an invalid JSON text:
		464
		465	JSON::XS->new->allow_nonref->encode ("Hello, World!")
		466	=> "Hello, World!"
		467
		468	=item $json = $json->allow_blessed ([$enable])
		469
		470	=item $enabled = $json->get_allow_blessed
		471
		472	If C<$enable> is true (or missing), then the C<encode> method will not
		473	barf when it encounters a blessed reference. Instead, the value of the
		474	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		475	disabled or no C<TO_JSON> method found) or a representation of the
		476	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		477	encoded. Has no effect on C<decode>.
		478
		479	If C<$enable> is false (the default), then C<encode> will throw an
		480	exception when it encounters a blessed object.
		481
		482	=item $json = $json->convert_blessed ([$enable])
		483
		484	=item $enabled = $json->get_convert_blessed
		485
		486	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		487	blessed object, will check for the availability of the C<TO_JSON> method
		488	on the object's class. If found, it will be called in scalar context
		489	and the resulting scalar will be encoded instead of the object. If no
		490	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		491	to do.
		492
		493	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		494	returns other blessed objects, those will be handled in the same
		495	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		496	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		497	methods called by the Perl core (== not by the user of the object) are
		498	usually in upper case letters and to avoid collisions with any C<to_json>
		499	function or method.
		500
		501	This setting does not yet influence C<decode> in any way, but in the
		502	future, global hooks might get installed that influence C<decode> and are
		503	enabled by this setting.
		504
		505	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		506	to do when a blessed object is found.
		507
		508	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		509
		510	When C<$coderef> is specified, it will be called from C<decode> each
		511	time it decodes a JSON object. The only argument is a reference to the
		512	newly-created hash. If the code references returns a single scalar (which
		513	need not be a reference), this value (i.e. a copy of that scalar to avoid
		514	aliasing) is inserted into the deserialised data structure. If it returns
		515	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		516	original deserialised hash will be inserted. This setting can slow down
		517	decoding considerably.
		518
		519	When C<$coderef> is omitted or undefined, any existing callback will
		520	be removed and C<decode> will not change the deserialised hash in any
		521	way.
		522
		523	Example, convert all JSON objects into the integer 5:
		524
		525	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		526	# returns [5]
		527	$js->decode ('[{}]')
		528	# throw an exception because allow_nonref is not enabled
		529	# so a lone 5 is not allowed.
		530	$js->decode ('{"a":1, "b":2}');
		531
		532	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		533
		534	Works remotely similar to C<filter_json_object>, but is only called for
		535	JSON objects having a single key named C<$key>.
		536
		537	This C<$coderef> is called before the one specified via
		538	C<filter_json_object>, if any. It gets passed the single value in the JSON
		539	object. If it returns a single value, it will be inserted into the data
		540	structure. If it returns nothing (not even C<undef> but the empty list),
		541	the callback from C<filter_json_object> will be called next, as if no
		542	single-key callback were specified.
		543
		544	If C<$coderef> is omitted or undefined, the corresponding callback will be
		545	disabled. There can only ever be one callback for a given key.
		546
		547	As this callback gets called less often then the C<filter_json_object>
		548	one, decoding speed will not usually suffer as much. Therefore, single-key
		549	objects make excellent targets to serialise Perl objects into, especially
		550	as single-key JSON objects are as close to the type-tagged value concept
		551	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		552	support this in any way, so you need to make sure your data never looks
		553	like a serialised Perl hash.
		554
		555	Typical names for the single object key are C<__class_whatever__>, or
		556	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		557	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		558	with real hashes.
		559
		560	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		561	into the corresponding C<< $WIDGET{<id>} >> object:
		562
		563	# return whatever is in $WIDGET{5}:
		564	JSON::XS
		565	->new
		566	->filter_json_single_key_object (__widget__ => sub {
		567	$WIDGET{ $_[0] }
		568	})
		569	->decode ('{"__widget__": 5')
		570
		571	# this can be used with a TO_JSON method in some "widget" class
		572	# for serialisation to json:
		573	sub WidgetBase::TO_JSON {
		574	my ($self) = @_;
		575
		576	unless ($self->{id}) {
		577	$self->{id} = ..get..some..id..;
		578	$WIDGET{$self->{id}} = $self;
		579	}
		580
		581	{ __widget__ => $self->{id} }
		582	}
		583
		584	=item $json = $json->shrink ([$enable])
		585
		586	=item $enabled = $json->get_shrink
		587
		588	Perl usually over-allocates memory a bit when allocating space for
		589	strings. This flag optionally resizes strings generated by either
		590	C<encode> or C<decode> to their minimum size possible. This can save
		591	memory when your JSON texts are either very very long or you have many
		592	short strings. It will also try to downgrade any strings to octet-form
		593	if possible: perl stores strings internally either in an encoding called
		594	UTF-X or in octet-form. The latter cannot store everything but uses less
		595	space in general (and some buggy Perl or C code might even rely on that
		596	internal representation being used).
		597
		598	The actual definition of what shrink does might change in future versions,
		599	but it will always try to save space at the expense of time.
		600
		601	If C<$enable> is true (or missing), the string returned by C<encode> will
		602	be shrunk-to-fit, while all strings generated by C<decode> will also be
		603	shrunk-to-fit.
		604
		605	If C<$enable> is false, then the normal perl allocation algorithms are used.
		606	If you work with your data, then this is likely to be faster.
		607
		608	In the future, this setting might control other things, such as converting
		609	strings that look like integers or floats into integers or floats
		610	internally (there is no difference on the Perl level), saving space.
		611
		612	=item $json = $json->max_depth ([$maximum_nesting_depth])
		613
		614	=item $max_depth = $json->get_max_depth
		615
		616	Sets the maximum nesting level (default C<512>) accepted while encoding
		617	or decoding. If the JSON text or Perl data structure has an equal or
		618	higher nesting level then this limit, then the encoder and decoder will
		619	stop and croak at that point.
		620
		621	Nesting level is defined by number of hash- or arrayrefs that the encoder
		622	needs to traverse to reach a given point or the number of C<{> or C<[>
		623	characters without their matching closing parenthesis crossed to reach a
		624	given character in a string.
		625
		626	Setting the maximum depth to one disallows any nesting, so that ensures
		627	that the object is only a single hash/object or array.
		628
		629	The argument to C<max_depth> will be rounded up to the next highest power
		630	of two. If no argument is given, the highest possible setting will be
		631	used, which is rarely useful.
		632
		633	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		634
		635	=item $json = $json->max_size ([$maximum_string_size])
		636
		637	=item $max_size = $json->get_max_size
		638
		639	Set the maximum length a JSON text may have (in bytes) where decoding is
		640	being attempted. The default is C<0>, meaning no limit. When C<decode>
		641	is called on a string longer then this number of characters it will not
		642	attempt to decode the string but throw an exception. This setting has no
		643	effect on C<encode> (yet).
		644
		645	The argument to C<max_size> will be rounded up to the next B<highest>
		646	power of two (so may be more than requested). If no argument is given, the
		647	limit check will be deactivated (same as when C<0> is specified).
		648
		649	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		650
222	=item $json_string = $json->encode ($perl_scalar)	651	=item $json_text = $json->encode ($perl_scalar)
223		652
224	Converts the given Perl data structure (a simple scalar or a reference	653	Converts the given Perl data structure (a simple scalar or a reference
225	to a hash or array) to its JSON representation. Simple scalars will be	654	to a hash or array) to its JSON representation. Simple scalars will be
226	converted into JSON string or number sequences, while references to arrays	655	converted into JSON string or number sequences, while references to arrays
227	become JSON arrays and references to hashes become JSON objects. Undefined	656	become JSON arrays and references to hashes become JSON objects. Undefined
228	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>	657	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
229	nor C<false> values will be generated.	658	nor C<false> values will be generated.
230		659
231	=item $perl_scalar = $json->decode ($json_string)	660	=item $perl_scalar = $json->decode ($json_text)
232		661
233	The opposite of C<encode>: expects a JSON string and tries to parse it,	662	The opposite of C<encode>: expects a JSON text and tries to parse it,
234	returning the resulting simple scalar or reference. Croaks on error.	663	returning the resulting simple scalar or reference. Croaks on error.
235		664
236	JSON numbers and strings become simple Perl scalars. JSON arrays become	665	JSON numbers and strings become simple Perl scalars. JSON arrays become
237	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	666	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
238	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	667	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
239		668
		669	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		670
		671	This works like the C<decode> method, but instead of raising an exception
		672	when there is trailing garbage after the first JSON object, it will
		673	silently stop parsing there and return the number of characters consumed
		674	so far.
		675
		676	This is useful if your JSON texts are not delimited by an outer protocol
		677	(which is not the brightest thing to do in the first place) and you need
		678	to know where the JSON text ends.
		679
		680	JSON::XS->new->decode_prefix ("[1] the tail")
		681	=> ([], 3)
		682
240	=back	683	=back
		684
		685
		686	=head1 MAPPING
		687
		688	This section describes how JSON::XS maps Perl values to JSON values and
		689	vice versa. These mappings are designed to "do the right thing" in most
		690	circumstances automatically, preserving round-tripping characteristics
		691	(what you put in comes out as something equivalent).
		692
		693	For the more enlightened: note that in the following descriptions,
		694	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		695	refers to the abstract Perl language itself.
		696
		697
		698	=head2 JSON -> PERL
		699
		700	=over 4
		701
		702	=item object
		703
		704	A JSON object becomes a reference to a hash in Perl. No ordering of object
		705	keys is preserved (JSON does not preserve object key ordering itself).
		706
		707	=item array
		708
		709	A JSON array becomes a reference to an array in Perl.
		710
		711	=item string
		712
		713	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		714	are represented by the same codepoints in the Perl string, so no manual
		715	decoding is necessary.
		716
		717	=item number
		718
		719	A JSON number becomes either an integer, numeric (floating point) or
		720	string scalar in perl, depending on its range and any fractional parts. On
		721	the Perl level, there is no difference between those as Perl handles all
		722	the conversion details, but an integer may take slightly less memory and
		723	might represent more values exactly than floating point numbers.
		724
		725	If the number consists of digits only, JSON::XS will try to represent
		726	it as an integer value. If that fails, it will try to represent it as
		727	a numeric (floating point) value if that is possible without loss of
		728	precision. Otherwise it will preserve the number as a string value (in
		729	which case you lose roundtripping ability, as the JSON number will be
		730	re-encoded toa JSON string).
		731
		732	Numbers containing a fractional or exponential part will always be
		733	represented as numeric (floating point) values, possibly at a loss of
		734	precision (in which case you might lose perfect roundtripping ability, but
		735	the JSON number will still be re-encoded as a JSON number).
		736
		737	=item true, false
		738
		739	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
		740	respectively. They are overloaded to act almost exactly like the numbers
		741	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
		742	the C<JSON::XS::is_bool> function.
		743
		744	=item null
		745
		746	A JSON null atom becomes C<undef> in Perl.
		747
		748	=back
		749
		750
		751	=head2 PERL -> JSON
		752
		753	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		754	truly typeless language, so we can only guess which JSON type is meant by
		755	a Perl value.
		756
		757	=over 4
		758
		759	=item hash references
		760
		761	Perl hash references become JSON objects. As there is no inherent ordering
		762	in hash keys (or JSON objects), they will usually be encoded in a
		763	pseudo-random order that can change between runs of the same program but
		764	stays generally the same within a single run of a program. JSON::XS can
		765	optionally sort the hash keys (determined by the I<canonical> flag), so
		766	the same datastructure will serialise to the same JSON text (given same
		767	settings and version of JSON::XS), but this incurs a runtime overhead
		768	and is only rarely useful, e.g. when you want to compare some JSON text
		769	against another for equality.
		770
		771	=item array references
		772
		773	Perl array references become JSON arrays.
		774
		775	=item other references
		776
		777	Other unblessed references are generally not allowed and will cause an
		778	exception to be thrown, except for references to the integers C<0> and
		779	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		780	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		781
		782	encode_json [\0,JSON::XS::true] # yields [false,true]
		783
		784	=item JSON::XS::true, JSON::XS::false
		785
		786	These special values become JSON true and JSON false values,
		787	respectively. You can also use C<\1> and C<\0> directly if you want.
		788
		789	=item blessed objects
		790
		791	Blessed objects are not directly representable in JSON. See the
		792	C<allow_blessed> and C<convert_blessed> methods on various options on
		793	how to deal with this: basically, you can choose between throwing an
		794	exception, encoding the reference as if it weren't blessed, or provide
		795	your own serialiser method.
		796
		797	=item simple scalars
		798
		799	Simple Perl scalars (any scalar that is not a reference) are the most
		800	difficult objects to encode: JSON::XS will encode undefined scalars as
		801	JSON C<null> values, scalars that have last been used in a string context
		802	before encoding as JSON strings, and anything else as number value:
		803
		804	# dump as number
		805	encode_json [2] # yields [2]
		806	encode_json [-3.0e17] # yields [-3e+17]
		807	my $value = 5; encode_json [$value] # yields [5]
		808
		809	# used as string, so dump as string
		810	print $value;
		811	encode_json [$value] # yields ["5"]
		812
		813	# undef becomes null
		814	encode_json [undef] # yields [null]
		815
		816	You can force the type to be a JSON string by stringifying it:
		817
		818	my $x = 3.1; # some variable containing a number
		819	"$x"; # stringified
		820	$x .= ""; # another, more awkward way to stringify
		821	print $x; # perl does it for you, too, quite often
		822
		823	You can force the type to be a JSON number by numifying it:
		824
		825	my $x = "3"; # some variable containing a string
		826	$x += 0; # numify it, ensuring it will be dumped as a number
		827	$x *= 1; # same thing, the choice is yours.
		828
		829	You can not currently force the type in other, less obscure, ways. Tell me
		830	if you need this capability (but don't forget to explain why it's needed
		831	:).
		832
		833	=back
		834
		835
		836	=head1 ENCODING/CODESET FLAG NOTES
		837
		838	The interested reader might have seen a number of flags that signify
		839	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		840	some confusion on what these do, so here is a short comparison:
		841
		842	C<utf8> controls whether the JSON text created by C<encode> (and expected
		843	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		844	control whether C<encode> escapes character values outside their respective
		845	codeset range. Neither of these flags conflict with each other, although
		846	some combinations make less sense than others.
		847
		848	Care has been taken to make all flags symmetrical with respect to
		849	C<encode> and C<decode>, that is, texts encoded with any combination of
		850	these flag values will be correctly decoded when the same flags are used
		851	- in general, if you use different flag settings while encoding vs. when
		852	decoding you likely have a bug somewhere.
		853
		854	Below comes a verbose discussion of these flags. Note that a "codeset" is
		855	simply an abstract set of character-codepoint pairs, while an encoding
		856	takes those codepoint numbers and I<encodes> them, in our case into
		857	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		858	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		859	the same time, which can be confusing.
		860
		861	=over 4
		862
		863	=item C<utf8> flag disabled
		864
		865	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		866	and expect Unicode strings, that is, characters with high ordinal Unicode
		867	values (> 255) will be encoded as such characters, and likewise such
		868	characters are decoded as-is, no canges to them will be done, except
		869	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		870	respectively (to Perl, these are the same thing in strings unless you do
		871	funny/weird/dumb stuff).
		872
		873	This is useful when you want to do the encoding yourself (e.g. when you
		874	want to have UTF-16 encoded JSON texts) or when some other layer does
		875	the encoding for you (for example, when printing to a terminal using a
		876	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		877	to UTF-8 encode your data first and have Perl encode it another time).
		878
		879	=item C<utf8> flag enabled
		880
		881	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		882	characters using the corresponding UTF-8 multi-byte sequence, and will
		883	expect your input strings to be encoded as UTF-8, that is, no "character"
		884	of the input string must have any value > 255, as UTF-8 does not allow
		885	that.
		886
		887	The C<utf8> flag therefore switches between two modes: disabled means you
		888	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		889	octet/binary string in Perl.
		890
		891	=item C<latin1> or C<ascii> flags enabled
		892
		893	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		894	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		895	characters as specified by the C<utf8> flag.
		896
		897	If C<utf8> is disabled, then the result is also correctly encoded in those
		898	character sets (as both are proper subsets of Unicode, meaning that a
		899	Unicode string with all character values < 256 is the same thing as a
		900	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		901	the same thing as an ASCII string in Perl).
		902
		903	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		904	regardless of these flags, just some more characters will be escaped using
		905	C<\uXXXX> then before.
		906
		907	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		908	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		909	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		910	a subset of Unicode), while ASCII is.
		911
		912	Surprisingly, C<decode> will ignore these flags and so treat all input
		913	values as governed by the C<utf8> flag. If it is disabled, this allows you
		914	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		915	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		916
		917	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		918	they only govern when the JSON output engine escapes a character or not.
		919
		920	The main use for C<latin1> is to relatively efficiently store binary data
		921	as JSON, at the expense of breaking compatibility with most JSON decoders.
		922
		923	The main use for C<ascii> is to force the output to not contain characters
		924	with values > 127, which means you can interpret the resulting string
		925	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		926	8-bit-encoding, and still get the same data structure back. This is useful
		927	when your channel for JSON transfer is not 8-bit clean or the encoding
		928	might be mangled in between (e.g. in mail), and works because ASCII is a
		929	proper subset of most 8-bit and multibyte encodings in use in the world.
		930
		931	=back
		932
241		933
242	=head1 COMPARISON	934	=head1 COMPARISON
243		935
244	As already mentioned, this module was created because none of the existing	936	As already mentioned, this module was created because none of the existing
245	JSON modules could be made to work correctly. First I will describe the	937	JSON modules could be made to work correctly. First I will describe the
246	problems (or pleasures) I encountered with various existing JSON modules,	938	problems (or pleasures) I encountered with various existing JSON modules,
247	followed by some benchmark values.	939	followed by some benchmark values. JSON::XS was designed not to suffer
		940	from any of these problems or limitations.
248		941
249	=over 4	942	=over 4
250		943
251	=item JSON	944	=item JSON 2.xx
		945
		946	A marvellous piece of engineering, this module either uses JSON::XS
		947	directly when available (so will be 100% compatible with it, including
		948	speed), or it uses JSON::PP, which is basically JSON::XS translated to
		949	Pure Perl, which should be 100% compatible with JSON::XS, just a bit
		950	slower.
		951
		952	You cannot really lose by using this module, especially as it tries very
		953	hard to work even with ancient Perl versions, while JSON::XS does not.
		954
		955	=item JSON 1.07
252		956
253	Slow (but very portable, as it is written in pure Perl).	957	Slow (but very portable, as it is written in pure Perl).
254		958
255	Undocumented/buggy Unicode handling (how JSON handles unicode values is	959	Undocumented/buggy Unicode handling (how JSON handles Unicode values is
256	undocumented. One can get far by feeding it unicode strings and doing	960	undocumented. One can get far by feeding it Unicode strings and doing
257	en-/decoding oneself, but unicode escapes are not working properly).	961	en-/decoding oneself, but Unicode escapes are not working properly).
258		962
259	No roundtripping (strings get clobbered if they look like numbers, e.g.	963	No round-tripping (strings get clobbered if they look like numbers, e.g.
260	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	964	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
261	decode into the number 2.	965	decode into the number 2.
262		966
263	=item JSON::PC	967	=item JSON::PC 0.01
264		968
265	Very fast.	969	Very fast.
		970
		971	Undocumented/buggy Unicode handling.
		972
		973	No round-tripping.
		974
		975	Has problems handling many Perl values (e.g. regex results and other magic
		976	values will make it croak).
		977
		978	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
		979	which is not a valid JSON text.
		980
		981	Unmaintained (maintainer unresponsive for many months, bugs are not
		982	getting fixed).
		983
		984	=item JSON::Syck 0.21
		985
		986	Very buggy (often crashes).
266		987
267	Very inflexible (no human-readable format supported, format pretty much	988	Very inflexible (no human-readable format supported, format pretty much
268	undocumented. I need at least a format for easy reading by humans and a	989	undocumented. I need at least a format for easy reading by humans and a
269	single-line compact format for use in a protocol, and preferably a way to	990	single-line compact format for use in a protocol, and preferably a way to
270	generate ASCII-only JSON strings).	991	generate ASCII-only JSON texts).
271		992
272	Undocumented/buggy Unicode handling.	993	Completely broken (and confusingly documented) Unicode handling (Unicode
		994	escapes are not working properly, you need to set ImplicitUnicode to
		995	I<different> values on en- and decoding to get symmetric behaviour).
273		996
274	No roundtripping.	997	No round-tripping (simple cases work, but this depends on whether the scalar
		998	value was used in a numeric context or not).
275		999
276	Has problems handling many Perl values.	1000	Dumping hashes may skip hash values depending on iterator state.
277
278	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
279	which is not a valid JSON string.
280		1001
281	Unmaintained (maintainer unresponsive for many months, bugs are not	1002	Unmaintained (maintainer unresponsive for many months, bugs are not
282	getting fixed).	1003	getting fixed).
283		1004
284	=item JSON::Syck
285
286	Very buggy (often crashes).
287
288	Very inflexible.
289
290	Completely broken (and confusingly documented) Unicode handling (unicode
291	escapes are not working properly, you need to set ImplicitUnicode to
292	I<different> values on en- and decoding to get symmetric behaviour).
293
294	No roundtripping (simple cases work, but this depends on wether the scalar
295	value was used in a numeric context or not).
296
297	Dumping hashes may skip hash values depending on iterator state.
298
299	Unmaintained (maintainer unresponsive for many months, bugs are not
300	getting fixed).
301
302	Does not check input for validity (i.e. will accept non-JSON input and	1005	Does not check input for validity (i.e. will accept non-JSON input and
303	return "something" instead of raising an exception. This is a security	1006	return "something" instead of raising an exception. This is a security
304	issue: imagine two banks transfering money between each other using	1007	issue: imagine two banks transferring money between each other using
305	JSON. One bank might parse a given non-JSON request and deduct money,	1008	JSON. One bank might parse a given non-JSON request and deduct money,
306	while the other might reject the transaction with a syntax error. While a	1009	while the other might reject the transaction with a syntax error. While a
307	good protocol will at least recover, that is extra unnecessary work and	1010	good protocol will at least recover, that is extra unnecessary work and
308	the transaction will still not succeed).	1011	the transaction will still not succeed).
309		1012
310	=item JSON::DWIW	1013	=item JSON::DWIW 0.04
311		1014
312	Very fast. Very natural. Very nice.	1015	Very fast. Very natural. Very nice.
313		1016
314	Undocumented unicode handling (but the best of the pack. Unicode escapes	1017	Undocumented Unicode handling (but the best of the pack. Unicode escapes
315	still don't get parsed properly).	1018	still don't get parsed properly).
316		1019
317	Very inflexible.	1020	Very inflexible.
318		1021
319	No roundtripping.	1022	No round-tripping.
		1023
		1024	Does not generate valid JSON texts (key strings are often unquoted, empty keys
		1025	result in nothing being output)
320		1026
321	Does not check input for validity.	1027	Does not check input for validity.
322		1028
323	=back	1029	=back
324		1030
		1031
		1032	=head2 JSON and YAML
		1033
		1034	You often hear that JSON is a subset of YAML. This is, however, a mass
		1035	hysteria(*) and very far from the truth (as of the time of this writing),
		1036	so let me state it clearly: I<in general, there is no way to configure
		1037	JSON::XS to output a data structure as valid YAML> that works in all
		1038	cases.
		1039
		1040	If you really must use JSON::XS to generate YAML, you should use this
		1041	algorithm (subject to change in future versions):
		1042
		1043	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1044	my $yaml = $to_yaml->encode ($ref) . "\n";
		1045
		1046	This will I<usually> generate JSON texts that also parse as valid
		1047	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1048	lengths that JSON doesn't have and also has different and incompatible
		1049	unicode handling, so you should make sure that your hash keys are
		1050	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1051	you do not have characters with codepoint values outside the Unicode BMP
		1052	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1053	strings (which JSON::XS does not I<currently> generate, but other JSON
		1054	generators might).
		1055
		1056	There might be other incompatibilities that I am not aware of (or the YAML
		1057	specification has been changed yet again - it does so quite often). In
		1058	general you should not try to generate YAML with a JSON generator or vice
		1059	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1060	high that you will run into severe interoperability problems when you
		1061	least expect it.
		1062
		1063	=over 4
		1064
		1065	=item (*)
		1066
		1067	I have been pressured multiple times by Brian Ingerson (one of the
		1068	authors of the YAML specification) to remove this paragraph, despite him
		1069	acknowledging that the actual incompatibilities exist. As I was personally
		1070	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1071	educate people about these issues, so others do not run into the same
		1072	problem again and again. After this, Brian called me a (quote)I<complete
		1073	and worthless idiot>(unquote).
		1074
		1075	In my opinion, instead of pressuring and insulting people who actually
		1076	clarify issues with YAML and the wrong statements of some of its
		1077	proponents, I would kindly suggest reading the JSON spec (which is not
		1078	that difficult or long) and finally make YAML compatible to it, and
		1079	educating users about the changes, instead of spreading lies about the
		1080	real compatibility for many I<years> and trying to silence people who
		1081	point out that it isn't true.
		1082
		1083	=back
		1084
		1085
325	=head2 SPEED	1086	=head2 SPEED
326		1087
		1088	It seems that JSON::XS is surprisingly fast, as shown in the following
		1089	tables. They have been generated with the help of the C<eg/bench> program
		1090	in the JSON::XS distribution, to make it easy to compare on your own
		1091	system.
		1092
		1093	First comes a comparison between various modules using
		1094	a very short single-line JSON string (also available at
		1095	L<http://dist.schmorp.de/misc/json/short.json>).
		1096
		1097	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
		1098	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
		1099
		1100	It shows the number of encodes/decodes per second (JSON::XS uses
		1101	the functional interface, while JSON::XS/2 uses the OO interface
		1102	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1103	shrink). Higher is better:
		1104
		1105	module \| encode \| decode \|
		1106	-----------\|------------\|------------\|
		1107	JSON 1.x \| 4990.842 \| 4088.813 \|
		1108	JSON::DWIW \| 51653.990 \| 71575.154 \|
		1109	JSON::PC \| 65948.176 \| 74631.744 \|
		1110	JSON::PP \| 8931.652 \| 3817.168 \|
		1111	JSON::Syck \| 24877.248 \| 27776.848 \|
		1112	JSON::XS \| 388361.481 \| 227951.304 \|
		1113	JSON::XS/2 \| 227951.304 \| 218453.333 \|
		1114	JSON::XS/3 \| 338250.323 \| 218453.333 \|
		1115	Storable \| 16500.016 \| 135300.129 \|
		1116	-----------+------------+------------+
		1117
		1118	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
		1119	about three times faster on decoding, and over forty times faster
		1120	than JSON, even with pretty-printing and key sorting. It also compares
		1121	favourably to Storable for small amounts of data.
		1122
		1123	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
		1124	search API (L<http://dist.schmorp.de/misc/json/long.json>).
		1125
		1126	module \| encode \| decode \|
		1127	-----------\|------------\|------------\|
		1128	JSON 1.x \| 55.260 \| 34.971 \|
		1129	JSON::DWIW \| 825.228 \| 1082.513 \|
		1130	JSON::PC \| 3571.444 \| 2394.829 \|
		1131	JSON::PP \| 210.987 \| 32.574 \|
		1132	JSON::Syck \| 552.551 \| 787.544 \|
		1133	JSON::XS \| 5780.463 \| 4854.519 \|
		1134	JSON::XS/2 \| 3869.998 \| 4798.975 \|
		1135	JSON::XS/3 \| 5862.880 \| 4798.975 \|
		1136	Storable \| 4445.002 \| 5235.027 \|
		1137	-----------+------------+------------+
		1138
		1139	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1140	decodes faster).
		1141
		1142	On large strings containing lots of high Unicode characters, some modules
		1143	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1144	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1145	to decode or encode properly, so it was impossible to prepare a fair
		1146	comparison table for that case.
		1147
		1148
		1149	=head1 SECURITY CONSIDERATIONS
		1150
		1151	When you are using JSON in a protocol, talking to untrusted potentially
		1152	hostile creatures requires relatively few measures.
		1153
		1154	First of all, your JSON decoder should be secure, that is, should not have
		1155	any buffer overflows. Obviously, this module should ensure that and I am
		1156	trying hard on making that true, but you never know.
		1157
		1158	Second, you need to avoid resource-starving attacks. That means you should
		1159	limit the size of JSON texts you accept, or make sure then when your
		1160	resources run out, that's just fine (e.g. by using a separate process that
		1161	can crash safely). The size of a JSON text in octets or characters is
		1162	usually a good indication of the size of the resources required to decode
		1163	it into a Perl structure. While JSON::XS can check the size of the JSON
		1164	text, it might be too late when you already have it in memory, so you
		1165	might want to check the size before you accept the string.
		1166
		1167	Third, JSON::XS recurses using the C stack when decoding objects and
		1168	arrays. The C stack is a limited resource: for instance, on my amd64
		1169	machine with 8MB of stack size I can decode around 180k nested arrays but
		1170	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1171	to free the temporary). If that is exceeded, the program crashes. To be
		1172	conservative, the default nesting limit is set to 512. If your process
		1173	has a smaller stack, you should adjust this setting accordingly with the
		1174	C<max_depth> method.
		1175
		1176	Something else could bomb you, too, that I forgot to think of. In that
		1177	case, you get to keep the pieces. I am always open for hints, though...
		1178
		1179	Also keep in mind that JSON::XS might leak contents of your Perl data
		1180	structures in its error messages, so when you serialise sensitive
		1181	information you might want to make sure that exceptions thrown by JSON::XS
		1182	will not end up in front of untrusted eyes.
		1183
		1184	If you are using JSON::XS to return packets to consumption
		1185	by JavaScript scripts in a browser you should have a look at
		1186	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1187	you are vulnerable to some common attack vectors (which really are browser
		1188	design bugs, but it is still you who will have to deal with it, as major
		1189	browser developers care only for features, not about getting security
		1190	right).
		1191
		1192
		1193	=head1 THREADS
		1194
		1195	This module is I<not> guaranteed to be thread safe and there are no
		1196	plans to change this until Perl gets thread support (as opposed to the
		1197	horribly slow so-called "threads" which are simply slow and bloated
		1198	process simulations - use fork, it's I<much> faster, cheaper, better).
		1199
		1200	(It might actually work, but you have been warned).
		1201
		1202
		1203	=head1 BUGS
		1204
		1205	While the goal of this module is to be correct, that unfortunately does
		1206	not mean it's bug-free, only that I think its design is bug-free. It is
		1207	still relatively early in its development. If you keep reporting bugs they
		1208	will be fixed swiftly, though.
		1209
		1210	Please refrain from using rt.cpan.org or any other bug reporting
		1211	service. I put the contact address into my modules for a reason.
		1212
327	=cut	1213	=cut
		1214
		1215	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1216	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1217
		1218	sub true() { $true }
		1219	sub false() { $false }
		1220
		1221	sub is_bool($) {
		1222	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1223	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1224	}
		1225
		1226	XSLoader::load "JSON::XS", $VERSION;
		1227
		1228	package JSON::XS::Boolean;
		1229
		1230	use overload
		1231	"0+" => sub { ${$_[0]} },
		1232	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1233	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1234	fallback => 1;
328		1235
329	1;	1236	1;
330		1237
331	=head1 AUTHOR	1238	=head1 AUTHOR
332		1239

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Revision 1.3 by root, Thu Mar 22 18:10:29 2007 UTC vs.
Revision 1.91 by root, Thu Mar 20 02:11:21 2008 UTC