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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.14 by root, Fri Mar 23 19:02:02 2007 UTC vs.
Revision 1.90 by root, Wed Mar 19 22:28:43 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;
8		13
9	# exported functions, croak on error	14	# exported functions, they croak on error
		15	# and expect/generate UTF-8
10		16
11	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
12	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
13		19
14	# oo-interface	20	# OO-interface
15		21
16	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
17	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
18	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
19		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
		33
20	=head1 DESCRIPTION	34	=head1 DESCRIPTION
21		35
22	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
23	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
24	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overriden) with no overhead due to emulation (by inheritign constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
25		47
26	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
27	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
28	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
29	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
36		58
37	=head2 FEATURES	59	=head2 FEATURES
38		60
39	=over 4	61	=over 4
40		62
41	=item * correct handling of unicode issues	63	=item * correct Unicode handling
42		64
43	This module knows how to handle Unicode, and even documents how and when	65	This module knows how to handle Unicode, documents how and when it does
44	it does so.	66	so, and even documents what "correct" means.
45		67
46	=item * round-trip integrity	68	=item * round-trip integrity
47		69
48	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only datatypes supported
49	by JSON, the deserialised data structure is identical on the Perl level.	71	by JSON, the deserialised data structure is identical on the Perl level.
50	(e.g. the string "2.0" doesn't suddenly become "2").	72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
		73	like a number). There minor I<are> exceptions to this, read the MAPPING
		74	section below to learn about those.
51		75
52	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
53		77
54	There is no guessing, no generating of illegal JSON strings by default,	78	There is no guessing, no generating of illegal JSON texts by default,
55	and only JSON is accepted as input by default (the latter is a security	79	and only JSON is accepted as input by default (the latter is a security
56	feature).	80	feature).
57		81
58	=item * fast	82	=item * fast
59		83
60	Compared to other JSON modules, this module compares favourably in terms	84	Compared to other JSON modules and other serialisers such as Storable,
61	of speed, too.	85	this module usually compares favourably in terms of speed, too.
62		86
63	=item * simple to use	87	=item * simple to use
64		88
65	This module has both a simple functional interface as well as an OO	89	This module has both a simple functional interface as well as an objetc
66	interface.	90	oriented interface interface.
67		91
68	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
69		93
70	You can choose between the most compact guarenteed single-line format	94	You can choose between the most compact guaranteed-single-line format
71	possible (nice for simple line-based protocols), a pure-ascii format (for	95	possible (nice for simple line-based protocols), a pure-ascii format
72	when your transport is not 8-bit clean), or a pretty-printed format (for	96	(for when your transport is not 8-bit clean, still supports the whole
73	when you want to read that stuff). Or you can combine those features in	97	Unicode range), or a pretty-printed format (for when you want to read that
74	whatever way you like.	98	stuff). Or you can combine those features in whatever way you like.
75		99
76	=back	100	=back
77		101
78	=cut	102	=cut
79		103
80	package JSON::XS;	104	package JSON::XS;
81		105
82	BEGIN {	106	use strict;
		107
83	$VERSION = '0.3';	108	our $VERSION = '2.1';
84	@ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
85		110
86	@EXPORT = qw(to_json from_json);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
87	require Exporter;
88		112
		113	sub to_json($) {
89	require XSLoader;	114	require Carp;
90	XSLoader::load JSON::XS::, $VERSION;	115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
91	}	116	}
92		117
		118	sub from_json($) {
		119	require Carp;
		120	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
		121	}
		122
		123	use Exporter;
		124	use XSLoader;
		125
93	=head1 FUNCTIONAL INTERFACE	126	=head1 FUNCTIONAL INTERFACE
94		127
95	The following convinience methods are provided by this module. They are	128	The following convenience methods are provided by this module. They are
96	exported by default:	129	exported by default:
97		130
98	=over 4	131	=over 4
99		132
100	=item $json_string = to_json $perl_scalar	133	=item $json_text = encode_json $perl_scalar
101		134
102	Converts the given Perl data structure (a simple scalar or a reference to	135	Converts the given Perl data structure to a UTF-8 encoded, binary string
103	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	136	(that is, the string contains octets only). Croaks on error.
104	octets only). Croaks on error.
105		137
106	This function call is functionally identical to C<< JSON::XS->new->utf8->encode ($perl_scalar) >>.	138	This function call is functionally identical to:
107		139
		140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		141
		142	except being faster.
		143
108	=item $perl_scalar = from_json $json_string	144	=item $perl_scalar = decode_json $json_text
109		145
110	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
111	parse that as an UTF-8 encoded JSON string, returning the resulting simple	147	to parse that as an UTF-8 encoded JSON text, returning the resulting
112	scalar or reference. Croaks on error.	148	reference. Croaks on error.
113		149
114	This function call is functionally identical to C<< JSON::XS->new->utf8->decode ($json_string) >>.	150	This function call is functionally identical to:
		151
		152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		153
		154	except being faster.
		155
		156	=item $is_boolean = JSON::XS::is_bool $scalar
		157
		158	Returns true if the passed scalar represents either JSON::XS::true or
		159	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		160	and are used to represent JSON C<true> and C<false> values in Perl.
		161
		162	See MAPPING, below, for more information on how JSON values are mapped to
		163	Perl.
115		164
116	=back	165	=back
		166
		167
		168	=head1 A FEW NOTES ON UNICODE AND PERL
		169
		170	Since this often leads to confusion, here are a few very clear words on
		171	how Unicode works in Perl, modulo bugs.
		172
		173	=over 4
		174
		175	=item 1. Perl strings can store characters with ordinal values > 255.
		176
		177	This enables you to store Unicode characters as single characters in a
		178	Perl string - very natural.
		179
		180	=item 2. Perl does I<not> associate an encoding with your strings.
		181
		182	... until you force it to, e.g. when matching it against a regex, or
		183	printing the scalar to a file, in which case Perl either interprets your
		184	string as locale-encoded text, octets/binary, or as Unicode, depending
		185	on various settings. In no case is an encoding stored together with your
		186	data, it is I<use> that decides encoding, not any magical meta data.
		187
		188	=item 3. The internal utf-8 flag has no meaning with regards to the
		189	encoding of your string.
		190
		191	Just ignore that flag unless you debug a Perl bug, a module written in
		192	XS or want to dive into the internals of perl. Otherwise it will only
		193	confuse you, as, despite the name, it says nothing about how your string
		194	is encoded. You can have Unicode strings with that flag set, with that
		195	flag clear, and you can have binary data with that flag set and that flag
		196	clear. Other possibilities exist, too.
		197
		198	If you didn't know about that flag, just the better, pretend it doesn't
		199	exist.
		200
		201	=item 4. A "Unicode String" is simply a string where each character can be
		202	validly interpreted as a Unicode codepoint.
		203
		204	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		205	Unicode string encoded in UTF-8, giving you a binary string.
		206
		207	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		208
		209	It's a fact. Learn to live with it.
		210
		211	=back
		212
		213	I hope this helps :)
		214
117		215
118	=head1 OBJECT-ORIENTED INTERFACE	216	=head1 OBJECT-ORIENTED INTERFACE
119		217
120	The object oriented interface lets you configure your own encoding or	218	The object oriented interface lets you configure your own encoding or
121	decoding style, within the limits of supported formats.	219	decoding style, within the limits of supported formats.
…		…
128	strings. All boolean flags described below are by default I<disabled>.	226	strings. All boolean flags described below are by default I<disabled>.
129		227
130	The mutators for flags all return the JSON object again and thus calls can	228	The mutators for flags all return the JSON object again and thus calls can
131	be chained:	229	be chained:
132		230
133	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	231	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
134	=> {"a": [1, 2]}	232	=> {"a": [1, 2]}
135		233
136	=item $json = $json->ascii ([$enable])	234	=item $json = $json->ascii ([$enable])
137		235
		236	=item $enabled = $json->get_ascii
		237
138	If C<$enable> is true (or missing), then the C<encode> method will	238	If C<$enable> is true (or missing), then the C<encode> method will not
139	not generate characters outside the code range C<0..127>. Any unicode	239	generate characters outside the code range C<0..127> (which is ASCII). Any
140	characters outside that range will be escaped using either a single	240	Unicode characters outside that range will be escaped using either a
141	\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per	241	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
142	RFC4627.	242	as per RFC4627. The resulting encoded JSON text can be treated as a native
		243	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		244	or any other superset of ASCII.
143		245
144	If C<$enable> is false, then the C<encode> method will not escape Unicode	246	If C<$enable> is false, then the C<encode> method will not escape Unicode
145	characters unless necessary.	247	characters unless required by the JSON syntax or other flags. This results
		248	in a faster and more compact format.
146		249
		250	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		251	document.
		252
		253	The main use for this flag is to produce JSON texts that can be
		254	transmitted over a 7-bit channel, as the encoded JSON texts will not
		255	contain any 8 bit characters.
		256
147	JSON::XS->new->ascii (1)->encode (chr 0x10401)	257	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
148	=> \ud801\udc01	258	=> ["\ud801\udc01"]
		259
		260	=item $json = $json->latin1 ([$enable])
		261
		262	=item $enabled = $json->get_latin1
		263
		264	If C<$enable> is true (or missing), then the C<encode> method will encode
		265	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		266	outside the code range C<0..255>. The resulting string can be treated as a
		267	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		268	will not be affected in any way by this flag, as C<decode> by default
		269	expects Unicode, which is a strict superset of latin1.
		270
		271	If C<$enable> is false, then the C<encode> method will not escape Unicode
		272	characters unless required by the JSON syntax or other flags.
		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
		276
		277	The main use for this flag is efficiently encoding binary data as JSON
		278	text, as most octets will not be escaped, resulting in a smaller encoded
		279	size. The disadvantage is that the resulting JSON text is encoded
		280	in latin1 (and must correctly be treated as such when storing and
		281	transferring), a rare encoding for JSON. It is therefore most useful when
		282	you want to store data structures known to contain binary data efficiently
		283	in files or databases, not when talking to other JSON encoders/decoders.
		284
		285	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		286	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
149		287
150	=item $json = $json->utf8 ([$enable])	288	=item $json = $json->utf8 ([$enable])
151		289
		290	=item $enabled = $json->get_utf8
		291
152	If C<$enable> is true (or missing), then the C<encode> method will encode	292	If C<$enable> is true (or missing), then the C<encode> method will encode
153	the JSON string into UTF-8, as required by many protocols, while the	293	the JSON result into UTF-8, as required by many protocols, while the
154	C<decode> method expects to be handled an UTF-8-encoded string. Please	294	C<decode> method expects to be handled an UTF-8-encoded string. Please
155	note that UTF-8-encoded strings do not contain any characters outside the	295	note that UTF-8-encoded strings do not contain any characters outside the
156	range C<0..255>, they are thus useful for bytewise/binary I/O.	296	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		297	versions, enabling this option might enable autodetection of the UTF-16
		298	and UTF-32 encoding families, as described in RFC4627.
157		299
158	If C<$enable> is false, then the C<encode> method will return the JSON	300	If C<$enable> is false, then the C<encode> method will return the JSON
159	string as a (non-encoded) unicode string, while C<decode> expects thus a	301	string as a (non-encoded) Unicode string, while C<decode> expects thus a
160	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	302	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
161	to be done yourself, e.g. using the Encode module.	303	to be done yourself, e.g. using the Encode module.
162		304
		305	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		306	document.
		307
163	Example, output UTF-16-encoded JSON:	308	Example, output UTF-16BE-encoded JSON:
		309
		310	use Encode;
		311	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		312
		313	Example, decode UTF-32LE-encoded JSON:
		314
		315	use Encode;
		316	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
164		317
165	=item $json = $json->pretty ([$enable])	318	=item $json = $json->pretty ([$enable])
166		319
167	This enables (or disables) all of the C<indent>, C<space_before> and	320	This enables (or disables) all of the C<indent>, C<space_before> and
168	C<space_after> (and in the future possibly more) flags in one call to	321	C<space_after> (and in the future possibly more) flags in one call to
…		…
179	]	332	]
180	}	333	}
181		334
182	=item $json = $json->indent ([$enable])	335	=item $json = $json->indent ([$enable])
183		336
		337	=item $enabled = $json->get_indent
		338
184	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	339	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
185	format as output, putting every array member or object/hash key-value pair	340	format as output, putting every array member or object/hash key-value pair
186	into its own line, identing them properly.	341	into its own line, indenting them properly.
187		342
188	If C<$enable> is false, no newlines or indenting will be produced, and the	343	If C<$enable> is false, no newlines or indenting will be produced, and the
189	resulting JSON strings is guarenteed not to contain any C<newlines>.	344	resulting JSON text is guaranteed not to contain any C<newlines>.
190		345
191	This setting has no effect when decoding JSON strings.	346	This setting has no effect when decoding JSON texts.
192		347
193	=item $json = $json->space_before ([$enable])	348	=item $json = $json->space_before ([$enable])
		349
		350	=item $enabled = $json->get_space_before
194		351
195	If C<$enable> is true (or missing), then the C<encode> method will add an extra	352	If C<$enable> is true (or missing), then the C<encode> method will add an extra
196	optional space before the C<:> separating keys from values in JSON objects.	353	optional space before the C<:> separating keys from values in JSON objects.
197		354
198	If C<$enable> is false, then the C<encode> method will not add any extra	355	If C<$enable> is false, then the C<encode> method will not add any extra
199	space at those places.	356	space at those places.
200		357
201	This setting has no effect when decoding JSON strings. You will also most	358	This setting has no effect when decoding JSON texts. You will also
202	likely combine this setting with C<space_after>.	359	most likely combine this setting with C<space_after>.
203		360
204	Example, space_before enabled, space_after and indent disabled:	361	Example, space_before enabled, space_after and indent disabled:
205		362
206	{"key" :"value"}	363	{"key" :"value"}
207		364
208	=item $json = $json->space_after ([$enable])	365	=item $json = $json->space_after ([$enable])
		366
		367	=item $enabled = $json->get_space_after
209		368
210	If C<$enable> is true (or missing), then the C<encode> method will add an extra	369	If C<$enable> is true (or missing), then the C<encode> method will add an extra
211	optional space after the C<:> separating keys from values in JSON objects	370	optional space after the C<:> separating keys from values in JSON objects
212	and extra whitespace after the C<,> separating key-value pairs and array	371	and extra whitespace after the C<,> separating key-value pairs and array
213	members.	372	members.
214		373
215	If C<$enable> is false, then the C<encode> method will not add any extra	374	If C<$enable> is false, then the C<encode> method will not add any extra
216	space at those places.	375	space at those places.
217		376
218	This setting has no effect when decoding JSON strings.	377	This setting has no effect when decoding JSON texts.
219		378
220	Example, space_before and indent disabled, space_after enabled:	379	Example, space_before and indent disabled, space_after enabled:
221		380
222	{"key": "value"}	381	{"key": "value"}
223		382
		383	=item $json = $json->relaxed ([$enable])
		384
		385	=item $enabled = $json->get_relaxed
		386
		387	If C<$enable> is true (or missing), then C<decode> will accept some
		388	extensions to normal JSON syntax (see below). C<encode> will not be
		389	affected in anyway. I<Be aware that this option makes you accept invalid
		390	JSON texts as if they were valid!>. I suggest only to use this option to
		391	parse application-specific files written by humans (configuration files,
		392	resource files etc.)
		393
		394	If C<$enable> is false (the default), then C<decode> will only accept
		395	valid JSON texts.
		396
		397	Currently accepted extensions are:
		398
		399	=over 4
		400
		401	=item * list items can have an end-comma
		402
		403	JSON I<separates> array elements and key-value pairs with commas. This
		404	can be annoying if you write JSON texts manually and want to be able to
		405	quickly append elements, so this extension accepts comma at the end of
		406	such items not just between them:
		407
		408	[
		409	1,
		410	2, <- this comma not normally allowed
		411	]
		412	{
		413	"k1": "v1",
		414	"k2": "v2", <- this comma not normally allowed
		415	}
		416
		417	=item * shell-style '#'-comments
		418
		419	Whenever JSON allows whitespace, shell-style comments are additionally
		420	allowed. They are terminated by the first carriage-return or line-feed
		421	character, after which more white-space and comments are allowed.
		422
		423	[
		424	1, # this comment not allowed in JSON
		425	# neither this one...
		426	]
		427
		428	=back
		429
224	=item $json = $json->canonical ([$enable])	430	=item $json = $json->canonical ([$enable])
		431
		432	=item $enabled = $json->get_canonical
225		433
226	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	434	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
227	by sorting their keys. This is adding a comparatively high overhead.	435	by sorting their keys. This is adding a comparatively high overhead.
228		436
229	If C<$enable> is false, then the C<encode> method will output key-value	437	If C<$enable> is false, then the C<encode> method will output key-value
230	pairs in the order Perl stores them (which will likely change between runs	438	pairs in the order Perl stores them (which will likely change between runs
231	of the same script).	439	of the same script).
232		440
233	This option is useful if you want the same data structure to be encoded as	441	This option is useful if you want the same data structure to be encoded as
234	the same JSON string (given the same overall settings). If it is disabled,	442	the same JSON text (given the same overall settings). If it is disabled,
235	the same hash migh be encoded differently even if contains the same data,	443	the same hash might be encoded differently even if contains the same data,
236	as key-value pairs have no inherent ordering in Perl.	444	as key-value pairs have no inherent ordering in Perl.
237		445
238	This setting has no effect when decoding JSON strings.	446	This setting has no effect when decoding JSON texts.
239		447
240	=item $json = $json->allow_nonref ([$enable])	448	=item $json = $json->allow_nonref ([$enable])
		449
		450	=item $enabled = $json->get_allow_nonref
241		451
242	If C<$enable> is true (or missing), then the C<encode> method can convert a	452	If C<$enable> is true (or missing), then the C<encode> method can convert a
243	non-reference into its corresponding string, number or null JSON value,	453	non-reference into its corresponding string, number or null JSON value,
244	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	454	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
245	values instead of croaking.	455	values instead of croaking.
246		456
247	If C<$enable> is false, then the C<encode> method will croak if it isn't	457	If C<$enable> is false, then the C<encode> method will croak if it isn't
248	passed an arrayref or hashref, as JSON strings must either be an object	458	passed an arrayref or hashref, as JSON texts must either be an object
249	or array. Likewise, C<decode> will croak if given something that is not a	459	or array. Likewise, C<decode> will croak if given something that is not a
250	JSON object or array.	460	JSON object or array.
251		461
252	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,	462	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
253	resulting in an invalid JSON text:	463	resulting in an invalid JSON text:
254		464
255	JSON::XS->new->allow_nonref->encode ("Hello, World!")	465	JSON::XS->new->allow_nonref->encode ("Hello, World!")
256	=> "Hello, World!"	466	=> "Hello, World!"
257		467
		468	=item $json = $json->allow_blessed ([$enable])
		469
		470	=item $enabled = $json->get_allow_blessed
		471
		472	If C<$enable> is true (or missing), then the C<encode> method will not
		473	barf when it encounters a blessed reference. Instead, the value of the
		474	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		475	disabled or no C<TO_JSON> method found) or a representation of the
		476	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		477	encoded. Has no effect on C<decode>.
		478
		479	If C<$enable> is false (the default), then C<encode> will throw an
		480	exception when it encounters a blessed object.
		481
		482	=item $json = $json->convert_blessed ([$enable])
		483
		484	=item $enabled = $json->get_convert_blessed
		485
		486	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		487	blessed object, will check for the availability of the C<TO_JSON> method
		488	on the object's class. If found, it will be called in scalar context
		489	and the resulting scalar will be encoded instead of the object. If no
		490	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		491	to do.
		492
		493	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		494	returns other blessed objects, those will be handled in the same
		495	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		496	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		497	methods called by the Perl core (== not by the user of the object) are
		498	usually in upper case letters and to avoid collisions with any C<to_json>
		499	function or method.
		500
		501	This setting does not yet influence C<decode> in any way, but in the
		502	future, global hooks might get installed that influence C<decode> and are
		503	enabled by this setting.
		504
		505	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		506	to do when a blessed object is found.
		507
		508	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		509
		510	When C<$coderef> is specified, it will be called from C<decode> each
		511	time it decodes a JSON object. The only argument is a reference to the
		512	newly-created hash. If the code references returns a single scalar (which
		513	need not be a reference), this value (i.e. a copy of that scalar to avoid
		514	aliasing) is inserted into the deserialised data structure. If it returns
		515	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		516	original deserialised hash will be inserted. This setting can slow down
		517	decoding considerably.
		518
		519	When C<$coderef> is omitted or undefined, any existing callback will
		520	be removed and C<decode> will not change the deserialised hash in any
		521	way.
		522
		523	Example, convert all JSON objects into the integer 5:
		524
		525	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		526	# returns [5]
		527	$js->decode ('[{}]')
		528	# throw an exception because allow_nonref is not enabled
		529	# so a lone 5 is not allowed.
		530	$js->decode ('{"a":1, "b":2}');
		531
		532	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		533
		534	Works remotely similar to C<filter_json_object>, but is only called for
		535	JSON objects having a single key named C<$key>.
		536
		537	This C<$coderef> is called before the one specified via
		538	C<filter_json_object>, if any. It gets passed the single value in the JSON
		539	object. If it returns a single value, it will be inserted into the data
		540	structure. If it returns nothing (not even C<undef> but the empty list),
		541	the callback from C<filter_json_object> will be called next, as if no
		542	single-key callback were specified.
		543
		544	If C<$coderef> is omitted or undefined, the corresponding callback will be
		545	disabled. There can only ever be one callback for a given key.
		546
		547	As this callback gets called less often then the C<filter_json_object>
		548	one, decoding speed will not usually suffer as much. Therefore, single-key
		549	objects make excellent targets to serialise Perl objects into, especially
		550	as single-key JSON objects are as close to the type-tagged value concept
		551	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		552	support this in any way, so you need to make sure your data never looks
		553	like a serialised Perl hash.
		554
		555	Typical names for the single object key are C<__class_whatever__>, or
		556	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		557	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		558	with real hashes.
		559
		560	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		561	into the corresponding C<< $WIDGET{<id>} >> object:
		562
		563	# return whatever is in $WIDGET{5}:
		564	JSON::XS
		565	->new
		566	->filter_json_single_key_object (__widget__ => sub {
		567	$WIDGET{ $_[0] }
		568	})
		569	->decode ('{"__widget__": 5')
		570
		571	# this can be used with a TO_JSON method in some "widget" class
		572	# for serialisation to json:
		573	sub WidgetBase::TO_JSON {
		574	my ($self) = @_;
		575
		576	unless ($self->{id}) {
		577	$self->{id} = ..get..some..id..;
		578	$WIDGET{$self->{id}} = $self;
		579	}
		580
		581	{ __widget__ => $self->{id} }
		582	}
		583
258	=item $json = $json->shrink ([$enable])	584	=item $json = $json->shrink ([$enable])
259		585
		586	=item $enabled = $json->get_shrink
		587
260	Perl usually over-allocates memory a bit when allocating space for	588	Perl usually over-allocates memory a bit when allocating space for
261	strings. This flag optionally resizes strings generated by either	589	strings. This flag optionally resizes strings generated by either
262	C<encode> or C<decode> to their minimum size possible. This can save	590	C<encode> or C<decode> to their minimum size possible. This can save
263	memory when your JSON strings are either very very long or you have many	591	memory when your JSON texts are either very very long or you have many
264	short strings. It will also try to downgrade any strings to octet-form	592	short strings. It will also try to downgrade any strings to octet-form
265	if possible: perl stores strings internally either in an encoding called	593	if possible: perl stores strings internally either in an encoding called
266	UTF-X or in octet-form. The latter cannot store everything but uses less	594	UTF-X or in octet-form. The latter cannot store everything but uses less
267	space in general.	595	space in general (and some buggy Perl or C code might even rely on that
		596	internal representation being used).
268		597
		598	The actual definition of what shrink does might change in future versions,
		599	but it will always try to save space at the expense of time.
		600
269	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	601	If C<$enable> is true (or missing), the string returned by C<encode> will
270	while all strings generated by C<decode> will also be shrunk-to-fit.	602	be shrunk-to-fit, while all strings generated by C<decode> will also be
		603	shrunk-to-fit.
271		604
272	If C<$enable> is false, then the normal perl allocation algorithms are used.	605	If C<$enable> is false, then the normal perl allocation algorithms are used.
273	If you work with your data, then this is likely to be faster.	606	If you work with your data, then this is likely to be faster.
274		607
275	In the future, this setting might control other things, such as converting	608	In the future, this setting might control other things, such as converting
276	strings that look like integers or floats into integers or floats	609	strings that look like integers or floats into integers or floats
277	internally (there is no difference on the Perl level), saving space.	610	internally (there is no difference on the Perl level), saving space.
278		611
		612	=item $json = $json->max_depth ([$maximum_nesting_depth])
		613
		614	=item $max_depth = $json->get_max_depth
		615
		616	Sets the maximum nesting level (default C<512>) accepted while encoding
		617	or decoding. If the JSON text or Perl data structure has an equal or
		618	higher nesting level then this limit, then the encoder and decoder will
		619	stop and croak at that point.
		620
		621	Nesting level is defined by number of hash- or arrayrefs that the encoder
		622	needs to traverse to reach a given point or the number of C<{> or C<[>
		623	characters without their matching closing parenthesis crossed to reach a
		624	given character in a string.
		625
		626	Setting the maximum depth to one disallows any nesting, so that ensures
		627	that the object is only a single hash/object or array.
		628
		629	The argument to C<max_depth> will be rounded up to the next highest power
		630	of two. If no argument is given, the highest possible setting will be
		631	used, which is rarely useful.
		632
		633	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		634
		635	=item $json = $json->max_size ([$maximum_string_size])
		636
		637	=item $max_size = $json->get_max_size
		638
		639	Set the maximum length a JSON text may have (in bytes) where decoding is
		640	being attempted. The default is C<0>, meaning no limit. When C<decode>
		641	is called on a string longer then this number of characters it will not
		642	attempt to decode the string but throw an exception. This setting has no
		643	effect on C<encode> (yet).
		644
		645	The argument to C<max_size> will be rounded up to the next B<highest>
		646	power of two (so may be more than requested). If no argument is given, the
		647	limit check will be deactivated (same as when C<0> is specified).
		648
		649	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		650
279	=item $json_string = $json->encode ($perl_scalar)	651	=item $json_text = $json->encode ($perl_scalar)
280		652
281	Converts the given Perl data structure (a simple scalar or a reference	653	Converts the given Perl data structure (a simple scalar or a reference
282	to a hash or array) to its JSON representation. Simple scalars will be	654	to a hash or array) to its JSON representation. Simple scalars will be
283	converted into JSON string or number sequences, while references to arrays	655	converted into JSON string or number sequences, while references to arrays
284	become JSON arrays and references to hashes become JSON objects. Undefined	656	become JSON arrays and references to hashes become JSON objects. Undefined
285	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>	657	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
286	nor C<false> values will be generated.	658	nor C<false> values will be generated.
287		659
288	=item $perl_scalar = $json->decode ($json_string)	660	=item $perl_scalar = $json->decode ($json_text)
289		661
290	The opposite of C<encode>: expects a JSON string and tries to parse it,	662	The opposite of C<encode>: expects a JSON text and tries to parse it,
291	returning the resulting simple scalar or reference. Croaks on error.	663	returning the resulting simple scalar or reference. Croaks on error.
292		664
293	JSON numbers and strings become simple Perl scalars. JSON arrays become	665	JSON numbers and strings become simple Perl scalars. JSON arrays become
294	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	666	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
295	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	667	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
296		668
		669	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		670
		671	This works like the C<decode> method, but instead of raising an exception
		672	when there is trailing garbage after the first JSON object, it will
		673	silently stop parsing there and return the number of characters consumed
		674	so far.
		675
		676	This is useful if your JSON texts are not delimited by an outer protocol
		677	(which is not the brightest thing to do in the first place) and you need
		678	to know where the JSON text ends.
		679
		680	JSON::XS->new->decode_prefix ("[1] the tail")
		681	=> ([], 3)
		682
297	=back	683	=back
		684
298		685
299	=head1 MAPPING	686	=head1 MAPPING
300		687
301	This section describes how JSON::XS maps Perl values to JSON values and	688	This section describes how JSON::XS maps Perl values to JSON values and
302	vice versa. These mappings are designed to "do the right thing" in most	689	vice versa. These mappings are designed to "do the right thing" in most
303	circumstances automatically, preserving round-tripping characteristics	690	circumstances automatically, preserving round-tripping characteristics
304	(what you put in comes out as something equivalent).	691	(what you put in comes out as something equivalent).
305		692
306	For the more enlightened: note that in the following descriptions,	693	For the more enlightened: note that in the following descriptions,
307	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	694	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
308	refers to the abstract Perl language itself.	695	refers to the abstract Perl language itself.
309		696
		697
310	=head2 JSON -> PERL	698	=head2 JSON -> PERL
311		699
312	=over 4	700	=over 4
313		701
314	=item object	702	=item object
315		703
316	A JSON object becomes a reference to a hash in Perl. No ordering of object	704	A JSON object becomes a reference to a hash in Perl. No ordering of object
317	keys is preserved (JSON does not preserver object key ordering itself).	705	keys is preserved (JSON does not preserve object key ordering itself).
318		706
319	=item array	707	=item array
320		708
321	A JSON array becomes a reference to an array in Perl.	709	A JSON array becomes a reference to an array in Perl.
322		710
…		…
326	are represented by the same codepoints in the Perl string, so no manual	714	are represented by the same codepoints in the Perl string, so no manual
327	decoding is necessary.	715	decoding is necessary.
328		716
329	=item number	717	=item number
330		718
331	A JSON number becomes either an integer or numeric (floating point)	719	A JSON number becomes either an integer, numeric (floating point) or
332	scalar in perl, depending on its range and any fractional parts. On the	720	string scalar in perl, depending on its range and any fractional parts. On
333	Perl level, there is no difference between those as Perl handles all the	721	the Perl level, there is no difference between those as Perl handles all
334	conversion details, but an integer may take slightly less memory and might	722	the conversion details, but an integer may take slightly less memory and
335	represent more values exactly than (floating point) numbers.	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).
336		736
337	=item true, false	737	=item true, false
338		738
339	These JSON atoms become C<0>, C<1>, respectively. Information is lost in	739	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
340	this process. Future versions might represent those values differently,	740	respectively. They are overloaded to act almost exactly like the numbers
341	but they will be guarenteed to act like these integers would normally in	741	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
342	Perl.	742	the C<JSON::XS::is_bool> function.
343		743
344	=item null	744	=item null
345		745
346	A JSON null atom becomes C<undef> in Perl.	746	A JSON null atom becomes C<undef> in Perl.
347		747
348	=back	748	=back
		749
349		750
350	=head2 PERL -> JSON	751	=head2 PERL -> JSON
351		752
352	The mapping from Perl to JSON is slightly more difficult, as Perl is a	753	The mapping from Perl to JSON is slightly more difficult, as Perl is a
353	truly typeless language, so we can only guess which JSON type is meant by	754	truly typeless language, so we can only guess which JSON type is meant by
…		…
356	=over 4	757	=over 4
357		758
358	=item hash references	759	=item hash references
359		760
360	Perl hash references become JSON objects. As there is no inherent ordering	761	Perl hash references become JSON objects. As there is no inherent ordering
361	in hash keys, they will usually be encoded in a pseudo-random order that	762	in hash keys (or JSON objects), they will usually be encoded in a
362	can change between runs of the same program but stays generally the same	763	pseudo-random order that can change between runs of the same program but
363	within a single run of a program. JSON::XS can optionally sort the hash	764	stays generally the same within a single run of a program. JSON::XS can
364	keys (determined by the I<canonical> flag), so the same datastructure	765	optionally sort the hash keys (determined by the I<canonical> flag), so
365	will serialise to the same JSON text (given same settings and version of	766	the same datastructure will serialise to the same JSON text (given same
366	JSON::XS), but this incurs a runtime overhead.	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.
367		770
368	=item array references	771	=item array references
369		772
370	Perl array references become JSON arrays.	773	Perl array references become JSON arrays.
371		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
372	=item blessed objects	789	=item blessed objects
373		790
374	Blessed objects are not allowed. JSON::XS currently tries to encode their	791	Blessed objects are not directly representable in JSON. See the
375	underlying representation (hash- or arrayref), but this behaviour might	792	C<allow_blessed> and C<convert_blessed> methods on various options on
376	change in future versions.	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.
377		796
378	=item simple scalars	797	=item simple scalars
379		798
380	Simple Perl scalars (any scalar that is not a reference) are the most	799	Simple Perl scalars (any scalar that is not a reference) are the most
381	difficult objects to encode: JSON::XS will encode undefined scalars as	800	difficult objects to encode: JSON::XS will encode undefined scalars as
382	JSON null value, scalars that have last been used in a string context	801	JSON C<null> values, scalars that have last been used in a string context
383	before encoding as JSON strings and anything else as number value:	802	before encoding as JSON strings, and anything else as number value:
384		803
385	# dump as number	804	# dump as number
386	to_json [2] # yields [2]	805	encode_json [2] # yields [2]
387	to_json [-3.0e17] # yields [-3e+17]	806	encode_json [-3.0e17] # yields [-3e+17]
388	my $value = 5; to_json [$value] # yields [5]	807	my $value = 5; encode_json [$value] # yields [5]
389		808
390	# used as string, so dump as string	809	# used as string, so dump as string
391	print $value;	810	print $value;
392	to_json [$value] # yields ["5"]	811	encode_json [$value] # yields ["5"]
393		812
394	# undef becomes null	813	# undef becomes null
395	to_json [undef] # yields [null]	814	encode_json [undef] # yields [null]
396		815
397	You can force the type to be a string by stringifying it:	816	You can force the type to be a JSON string by stringifying it:
398		817
399	my $x = 3.1; # some variable containing a number	818	my $x = 3.1; # some variable containing a number
400	"$x"; # stringified	819	"$x"; # stringified
401	$x .= ""; # another, more awkward way to stringify	820	$x .= ""; # another, more awkward way to stringify
402	print $x; # perl does it for you, too, quite often	821	print $x; # perl does it for you, too, quite often
403		822
404	You can force the type to be a number by numifying it:	823	You can force the type to be a JSON number by numifying it:
405		824
406	my $x = "3"; # some variable containing a string	825	my $x = "3"; # some variable containing a string
407	$x += 0; # numify it, ensuring it will be dumped as a number	826	$x += 0; # numify it, ensuring it will be dumped as a number
408	$x *= 1; # same thing, the choise is yours.	827	$x *= 1; # same thing, the choice is yours.
409		828
410	You can not currently output JSON booleans or force the type in other,	829	You can not currently force the type in other, less obscure, ways. Tell me
411	less obscure, ways. Tell me if you need this capability.	830	if you need this capability (but don't forget to explain why its needed
412		831	:).
413	=item circular data structures
414
415	Those will be encoded until memory or stackspace runs out.
416		832
417	=back	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 wether 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 wether 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
418		933
419	=head1 COMPARISON	934	=head1 COMPARISON
420		935
421	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
422	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
…		…
424	followed by some benchmark values. JSON::XS was designed not to suffer	939	followed by some benchmark values. JSON::XS was designed not to suffer
425	from any of these problems or limitations.	940	from any of these problems or limitations.
426		941
427	=over 4	942	=over 4
428		943
		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
429	=item JSON 1.07	955	=item JSON 1.07
430		956
431	Slow (but very portable, as it is written in pure Perl).	957	Slow (but very portable, as it is written in pure Perl).
432		958
433	Undocumented/buggy Unicode handling (how JSON handles unicode values is	959	Undocumented/buggy Unicode handling (how JSON handles Unicode values is
434	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
435	en-/decoding oneself, but unicode escapes are not working properly).	961	en-/decoding oneself, but Unicode escapes are not working properly).
436		962
437	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.
438	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
439	decode into the number 2.	965	decode into the number 2.
440		966
441	=item JSON::PC 0.01	967	=item JSON::PC 0.01
442		968
443	Very fast.	969	Very fast.
444		970
445	Undocumented/buggy Unicode handling.	971	Undocumented/buggy Unicode handling.
446		972
447	No roundtripping.	973	No round-tripping.
448		974
449	Has problems handling many Perl values (e.g. regex results and other magic	975	Has problems handling many Perl values (e.g. regex results and other magic
450	values will make it croak).	976	values will make it croak).
451		977
452	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	978	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
453	which is not a valid JSON string.	979	which is not a valid JSON text.
454		980
455	Unmaintained (maintainer unresponsive for many months, bugs are not	981	Unmaintained (maintainer unresponsive for many months, bugs are not
456	getting fixed).	982	getting fixed).
457		983
458	=item JSON::Syck 0.21	984	=item JSON::Syck 0.21
…		…
460	Very buggy (often crashes).	986	Very buggy (often crashes).
461		987
462	Very inflexible (no human-readable format supported, format pretty much	988	Very inflexible (no human-readable format supported, format pretty much
463	undocumented. I need at least a format for easy reading by humans and a	989	undocumented. I need at least a format for easy reading by humans and a
464	single-line compact format for use in a protocol, and preferably a way to	990	single-line compact format for use in a protocol, and preferably a way to
465	generate ASCII-only JSON strings).	991	generate ASCII-only JSON texts).
466		992
467	Completely broken (and confusingly documented) Unicode handling (unicode	993	Completely broken (and confusingly documented) Unicode handling (Unicode
468	escapes are not working properly, you need to set ImplicitUnicode to	994	escapes are not working properly, you need to set ImplicitUnicode to
469	I<different> values on en- and decoding to get symmetric behaviour).	995	I<different> values on en- and decoding to get symmetric behaviour).
470		996
471	No roundtripping (simple cases work, but this depends on wether the scalar	997	No round-tripping (simple cases work, but this depends on whether the scalar
472	value was used in a numeric context or not).	998	value was used in a numeric context or not).
473		999
474	Dumping hashes may skip hash values depending on iterator state.	1000	Dumping hashes may skip hash values depending on iterator state.
475		1001
476	Unmaintained (maintainer unresponsive for many months, bugs are not	1002	Unmaintained (maintainer unresponsive for many months, bugs are not
477	getting fixed).	1003	getting fixed).
478		1004
479	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
480	return "something" instead of raising an exception. This is a security	1006	return "something" instead of raising an exception. This is a security
481	issue: imagine two banks transfering money between each other using	1007	issue: imagine two banks transferring money between each other using
482	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,
483	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
484	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
485	the transaction will still not succeed).	1011	the transaction will still not succeed).
486		1012
487	=item JSON::DWIW 0.04	1013	=item JSON::DWIW 0.04
488		1014
489	Very fast. Very natural. Very nice.	1015	Very fast. Very natural. Very nice.
490		1016
491	Undocumented unicode handling (but the best of the pack. Unicode escapes	1017	Undocumented Unicode handling (but the best of the pack. Unicode escapes
492	still don't get parsed properly).	1018	still don't get parsed properly).
493		1019
494	Very inflexible.	1020	Very inflexible.
495		1021
496	No roundtripping.	1022	No round-tripping.
497		1023
498	Does not generate valid JSON (key strings are often unquoted, empty keys	1024	Does not generate valid JSON texts (key strings are often unquoted, empty keys
499	result in nothing being output)	1025	result in nothing being output)
500		1026
501	Does not check input for validity.	1027	Does not check input for validity.
502		1028
503	=back	1029	=back
		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
504		1085
505	=head2 SPEED	1086	=head2 SPEED
506		1087
507	It seems that JSON::XS is surprisingly fast, as shown in the following	1088	It seems that JSON::XS is surprisingly fast, as shown in the following
508	tables. They have been generated with the help of the C<eg/bench> program	1089	tables. They have been generated with the help of the C<eg/bench> program
509	in the JSON::XS distribution, to make it easy to compare on your own	1090	in the JSON::XS distribution, to make it easy to compare on your own
510	system.	1091	system.
511		1092
512	First comes a comparison between various modules using a very short JSON	1093	First comes a comparison between various modules using
513	string (83 bytes), showing the number of encodes/decodes per second	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
514	(JSON::XS is the functional interface, while JSON::XS/2 is the OO	1101	the functional interface, while JSON::XS/2 uses the OO interface
515	interface with pretty-printing and hashkey sorting enabled). Higher is	1102	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
516	better:	1103	shrink). Higher is better:
517		1104
518	module \| encode \| decode \|	1105	module \| encode \| decode \|
519	-----------\|------------\|------------\|	1106	-----------\|------------\|------------\|
520	JSON \| 14006 \| 6820 \|	1107	JSON 1.x \| 4990.842 \| 4088.813 \|
521	JSON::DWIW \| 200937 \| 120386 \|	1108	JSON::DWIW \| 51653.990 \| 71575.154 \|
522	JSON::PC \| 85065 \| 129366 \|	1109	JSON::PC \| 65948.176 \| 74631.744 \|
523	JSON::Syck \| 59898 \| 44232 \|	1110	JSON::PP \| 8931.652 \| 3817.168 \|
524	JSON::XS \| 1171478 \| 342435 \|	1111	JSON::Syck \| 24877.248 \| 27776.848 \|
525	JSON::XS/2 \| 730760 \| 328714 \|	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 \|
526	-----------+------------+------------+	1116	-----------+------------+------------+
527		1117
528	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	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
529	times faster than JSON, even with pretty-printing and key sorting.	1120	than JSON, even with pretty-printing and key sorting. It also compares
		1121	favourably to Storable for small amounts of data.
530		1122
531	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1123	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
532	search API (http://nanoref.com/yahooapis/mgPdGg):	1124	search API (L<http://dist.schmorp.de/misc/json/long.json>).
533		1125
534	module \| encode \| decode \|	1126	module \| encode \| decode \|
535	-----------\|------------\|------------\|	1127	-----------\|------------\|------------\|
536	JSON \| 673 \| 38 \|	1128	JSON 1.x \| 55.260 \| 34.971 \|
537	JSON::DWIW \| 5271 \| 770 \|	1129	JSON::DWIW \| 825.228 \| 1082.513 \|
538	JSON::PC \| 9901 \| 2491 \|	1130	JSON::PC \| 3571.444 \| 2394.829 \|
539	JSON::Syck \| 2360 \| 786 \|	1131	JSON::PP \| 210.987 \| 32.574 \|
540	JSON::XS \| 37398 \| 3202 \|	1132	JSON::Syck \| 552.551 \| 787.544 \|
541	JSON::XS/2 \| 13765 \| 3153 \|	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 \|
542	-----------+------------+------------+	1137	-----------+------------+------------+
543		1138
544	Again, JSON::XS leads by far in the encoding case, while still beating	1139	Again, JSON::XS leads by far (except for Storable which non-surprisingly
545	every other module in the decoding case.	1140	decodes faster).
546		1141
547	On large strings containing lots of unicode characters, some modules	1142	On large strings containing lots of high Unicode characters, some modules
548	(such as JSON::PC) decode faster than JSON::XS, but the result will be	1143	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
549	broken due to missing unicode handling. Others refuse to decode or encode	1144	will be broken due to missing (or wrong) Unicode handling. Others refuse
550	properly, so it was impossible to prepare a fair comparison table for that	1145	to decode or encode properly, so it was impossible to prepare a fair
551	case.	1146	comparison table for that case.
552		1147
553	=head1 RESOURCE LIMITS
554		1148
555	JSON::XS does not impose any limits on the size of JSON texts or Perl	1149	=head1 SECURITY CONSIDERATIONS
556	values they represent - if your machine can handle it, JSON::XS will	1150
557	encode or decode it. Future versions might optionally impose structure	1151	When you are using JSON in a protocol, talking to untrusted potentially
558	depth and memory use resource limits.	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, its I<much> faster, cheaper, better).
		1199
		1200	(It might actually work, but you have been warned).
		1201
559		1202
560	=head1 BUGS	1203	=head1 BUGS
561		1204
562	While the goal of this module is to be correct, that unfortunately does	1205	While the goal of this module is to be correct, that unfortunately does
563	not mean its bug-free, only that I think its design is bug-free. It is	1206	not mean its bug-free, only that I think its design is bug-free. It is
564	still very young and not well-tested. If you keep reporting bugs they will	1207	still relatively early in its development. If you keep reporting bugs they
565	be fixed swiftly, though.	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.
566		1212
567	=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;
568		1235
569	1;	1236	1;
570		1237
571	=head1 AUTHOR	1238	=head1 AUTHOR
572		1239

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Comparing JSON-XS/XS.pm (file contents): Revision 1.14 by root, Fri Mar 23 19:02:02 2007 UTC vs. Revision 1.90 by root, Wed Mar 19 22:28:43 2008 UTC

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Revision 1.14 by root, Fri Mar 23 19:02:02 2007 UTC vs.
Revision 1.90 by root, Wed Mar 19 22:28:43 2008 UTC