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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.30 by root, Mon Apr 9 06:37:40 2007 UTC vs.
Revision 1.86 by root, Wed Mar 19 03:17:38 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
		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)
4		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
8		13
9	# exported functions, they croak on error	14	# exported functions, they croak on error
10	# and expect/generate UTF-8	15	# and expect/generate UTF-8
11		16
12	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
13	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
14
15	# objToJson and jsonToObj aliases to to_json and from_json
16	# are exported for compatibility to the JSON module,
17	# but should not be used in new code.
18		19
19	# OO-interface	20	# OO-interface
20		21
21	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
22	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
23	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
24		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
25	=head1 DESCRIPTION	34	=head1 DESCRIPTION
26		35
27	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
28	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
29	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.
30		47
31	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
32	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
33	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
34	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
41		58
42	=head2 FEATURES	59	=head2 FEATURES
43		60
44	=over 4	61	=over 4
45		62
46	=item * correct unicode handling	63	=item * correct Unicode handling
47		64
48	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
49	it does so.	66	so, and even documents what "correct" means.
50		67
51	=item * round-trip integrity	68	=item * round-trip integrity
52		69
53	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only datatypes supported
54	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.
55	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
56	like a number).	73	like a number). There minor I<are> exceptions to this, read the MAPPING
		74	section below to learn about those.
57		75
58	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
59		77
60	There is no guessing, no generating of illegal JSON texts by default,	78	There is no guessing, no generating of illegal JSON texts by default,
61	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
62	feature).	80	feature).
63		81
64	=item * fast	82	=item * fast
65		83
66	Compared to other JSON modules, this module compares favourably in terms	84	Compared to other JSON modules and other serialisers such as Storable,
67	of speed, too.	85	this module usually compares favourably in terms of speed, too.
68		86
69	=item * simple to use	87	=item * simple to use
70		88
71	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
72	interface.	90	oriented interface interface.
73		91
74	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
75		93
76	You can choose between the most compact guarenteed single-line format	94	You can choose between the most compact guaranteed-single-line format
77	possible (nice for simple line-based protocols), a pure-ascii format	95	possible (nice for simple line-based protocols), a pure-ascii format
78	(for when your transport is not 8-bit clean, still supports the whole	96	(for when your transport is not 8-bit clean, still supports the whole
79	unicode range), or a pretty-printed format (for when you want to read that	97	Unicode range), or a pretty-printed format (for when you want to read that
80	stuff). Or you can combine those features in whatever way you like.	98	stuff). Or you can combine those features in whatever way you like.
81		99
82	=back	100	=back
83		101
84	=cut	102	=cut
85		103
86	package JSON::XS;	104	package JSON::XS;
87		105
88	use strict;	106	use strict;
89		107
90	BEGIN {
91	our $VERSION = '1.11';	108	our $VERSION = '2.01';
92	our @ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
93		110
94	our @EXPORT = qw(to_json from_json objToJson jsonToObj);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
95	require Exporter;
96		112
		113	sub to_json($) {
97	require XSLoader;	114	require Carp;
98	XSLoader::load JSON::XS::, $VERSION;	115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
99	}	116	}
100		117
		118	sub from_json($) {
		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
101	=head1 FUNCTIONAL INTERFACE	126	=head1 FUNCTIONAL INTERFACE
102		127
103	The following convinience methods are provided by this module. They are	128	The following convenience methods are provided by this module. They are
104	exported by default:	129	exported by default:
105		130
106	=over 4	131	=over 4
107		132
108	=item $json_text = to_json $perl_scalar	133	=item $json_text = encode_json $perl_scalar
109		134
110	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
111	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.
112	octets only). Croaks on error.
113		137
114	This function call is functionally identical to:	138	This function call is functionally identical to:
115		139
116	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
117		141
118	except being faster.	142	except being faster.
119		143
120	=item $perl_scalar = from_json $json_text	144	=item $perl_scalar = decode_json $json_text
121		145
122	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
123	parse that as an UTF-8 encoded JSON text, returning the resulting simple	147	to parse that as an UTF-8 encoded JSON text, returning the resulting
124	scalar or reference. Croaks on error.	148	reference. Croaks on error.
125		149
126	This function call is functionally identical to:	150	This function call is functionally identical to:
127		151
128	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
129		153
130	except being faster.	154	except being faster.
131		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.
		164
132	=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 :)
133		214
134		215
135	=head1 OBJECT-ORIENTED INTERFACE	216	=head1 OBJECT-ORIENTED INTERFACE
136		217
137	The object oriented interface lets you configure your own encoding or	218	The object oriented interface lets you configure your own encoding or
…		…
150	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	231	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
151	=> {"a": [1, 2]}	232	=> {"a": [1, 2]}
152		233
153	=item $json = $json->ascii ([$enable])	234	=item $json = $json->ascii ([$enable])
154		235
		236	=item $enabled = $json->get_ascii
		237
155	If C<$enable> is true (or missing), then the C<encode> method will not	238	If C<$enable> is true (or missing), then the C<encode> method will not
156	generate characters outside the code range C<0..127> (which is ASCII). Any	239	generate characters outside the code range C<0..127> (which is ASCII). Any
157	unicode characters outside that range will be escaped using either a	240	Unicode characters outside that range will be escaped using either a
158	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,	241	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
159	as per RFC4627.	242	as per RFC4627. The resulting encoded JSON text can be treated as a native
		243	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		244	or any other superset of ASCII.
160		245
161	If C<$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
162	characters unless required by the JSON syntax. This results in a faster	247	characters unless required by the JSON syntax or other flags. This results
163	and more compact format.	248	in a faster and more compact format.
		249
		250	The main use for this flag is to produce JSON texts that can be
		251	transmitted over a 7-bit channel, as the encoded JSON texts will not
		252	contain any 8 bit characters.
164		253
165	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	254	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
166	=> ["\ud801\udc01"]	255	=> ["\ud801\udc01"]
167		256
		257	=item $json = $json->latin1 ([$enable])
		258
		259	=item $enabled = $json->get_latin1
		260
		261	If C<$enable> is true (or missing), then the C<encode> method will encode
		262	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		263	outside the code range C<0..255>. The resulting string can be treated as a
		264	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		265	will not be affected in any way by this flag, as C<decode> by default
		266	expects Unicode, which is a strict superset of latin1.
		267
		268	If C<$enable> is false, then the C<encode> method will not escape Unicode
		269	characters unless required by the JSON syntax or other flags.
		270
		271	The main use for this flag is efficiently encoding binary data as JSON
		272	text, as most octets will not be escaped, resulting in a smaller encoded
		273	size. The disadvantage is that the resulting JSON text is encoded
		274	in latin1 (and must correctly be treated as such when storing and
		275	transferring), a rare encoding for JSON. It is therefore most useful when
		276	you want to store data structures known to contain binary data efficiently
		277	in files or databases, not when talking to other JSON encoders/decoders.
		278
		279	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		280	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
		281
168	=item $json = $json->utf8 ([$enable])	282	=item $json = $json->utf8 ([$enable])
		283
		284	=item $enabled = $json->get_utf8
169		285
170	If C<$enable> is true (or missing), then the C<encode> method will encode	286	If C<$enable> is true (or missing), then the C<encode> method will encode
171	the JSON result into UTF-8, as required by many protocols, while the	287	the JSON result into UTF-8, as required by many protocols, while the
172	C<decode> method expects to be handled an UTF-8-encoded string. Please	288	C<decode> method expects to be handled an UTF-8-encoded string. Please
173	note that UTF-8-encoded strings do not contain any characters outside the	289	note that UTF-8-encoded strings do not contain any characters outside the
174	range C<0..255>, they are thus useful for bytewise/binary I/O. In future	290	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
175	versions, enabling this option might enable autodetection of the UTF-16	291	versions, enabling this option might enable autodetection of the UTF-16
176	and UTF-32 encoding families, as described in RFC4627.	292	and UTF-32 encoding families, as described in RFC4627.
177		293
178	If C<$enable> is false, then the C<encode> method will return the JSON	294	If C<$enable> is false, then the C<encode> method will return the JSON
179	string as a (non-encoded) unicode string, while C<decode> expects thus a	295	string as a (non-encoded) Unicode string, while C<decode> expects thus a
180	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	296	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
181	to be done yourself, e.g. using the Encode module.	297	to be done yourself, e.g. using the Encode module.
182		298
183	Example, output UTF-16BE-encoded JSON:	299	Example, output UTF-16BE-encoded JSON:
184		300
185	use Encode;	301	use Encode;
…		…
207	]	323	]
208	}	324	}
209		325
210	=item $json = $json->indent ([$enable])	326	=item $json = $json->indent ([$enable])
211		327
		328	=item $enabled = $json->get_indent
		329
212	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	330	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
213	format as output, putting every array member or object/hash key-value pair	331	format as output, putting every array member or object/hash key-value pair
214	into its own line, identing them properly.	332	into its own line, indenting them properly.
215		333
216	If C<$enable> is false, no newlines or indenting will be produced, and the	334	If C<$enable> is false, no newlines or indenting will be produced, and the
217	resulting JSON text is guarenteed not to contain any C<newlines>.	335	resulting JSON text is guaranteed not to contain any C<newlines>.
218		336
219	This setting has no effect when decoding JSON texts.	337	This setting has no effect when decoding JSON texts.
220		338
221	=item $json = $json->space_before ([$enable])	339	=item $json = $json->space_before ([$enable])
		340
		341	=item $enabled = $json->get_space_before
222		342
223	If C<$enable> is true (or missing), then the C<encode> method will add an extra	343	If C<$enable> is true (or missing), then the C<encode> method will add an extra
224	optional space before the C<:> separating keys from values in JSON objects.	344	optional space before the C<:> separating keys from values in JSON objects.
225		345
226	If C<$enable> is false, then the C<encode> method will not add any extra	346	If C<$enable> is false, then the C<encode> method will not add any extra
…		…
232	Example, space_before enabled, space_after and indent disabled:	352	Example, space_before enabled, space_after and indent disabled:
233		353
234	{"key" :"value"}	354	{"key" :"value"}
235		355
236	=item $json = $json->space_after ([$enable])	356	=item $json = $json->space_after ([$enable])
		357
		358	=item $enabled = $json->get_space_after
237		359
238	If C<$enable> is true (or missing), then the C<encode> method will add an extra	360	If C<$enable> is true (or missing), then the C<encode> method will add an extra
239	optional space after the C<:> separating keys from values in JSON objects	361	optional space after the C<:> separating keys from values in JSON objects
240	and extra whitespace after the C<,> separating key-value pairs and array	362	and extra whitespace after the C<,> separating key-value pairs and array
241	members.	363	members.
…		…
247		369
248	Example, space_before and indent disabled, space_after enabled:	370	Example, space_before and indent disabled, space_after enabled:
249		371
250	{"key": "value"}	372	{"key": "value"}
251		373
		374	=item $json = $json->relaxed ([$enable])
		375
		376	=item $enabled = $json->get_relaxed
		377
		378	If C<$enable> is true (or missing), then C<decode> will accept some
		379	extensions to normal JSON syntax (see below). C<encode> will not be
		380	affected in anyway. I<Be aware that this option makes you accept invalid
		381	JSON texts as if they were valid!>. I suggest only to use this option to
		382	parse application-specific files written by humans (configuration files,
		383	resource files etc.)
		384
		385	If C<$enable> is false (the default), then C<decode> will only accept
		386	valid JSON texts.
		387
		388	Currently accepted extensions are:
		389
		390	=over 4
		391
		392	=item * list items can have an end-comma
		393
		394	JSON I<separates> array elements and key-value pairs with commas. This
		395	can be annoying if you write JSON texts manually and want to be able to
		396	quickly append elements, so this extension accepts comma at the end of
		397	such items not just between them:
		398
		399	[
		400	1,
		401	2, <- this comma not normally allowed
		402	]
		403	{
		404	"k1": "v1",
		405	"k2": "v2", <- this comma not normally allowed
		406	}
		407
		408	=item * shell-style '#'-comments
		409
		410	Whenever JSON allows whitespace, shell-style comments are additionally
		411	allowed. They are terminated by the first carriage-return or line-feed
		412	character, after which more white-space and comments are allowed.
		413
		414	[
		415	1, # this comment not allowed in JSON
		416	# neither this one...
		417	]
		418
		419	=back
		420
252	=item $json = $json->canonical ([$enable])	421	=item $json = $json->canonical ([$enable])
		422
		423	=item $enabled = $json->get_canonical
253		424
254	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	425	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
255	by sorting their keys. This is adding a comparatively high overhead.	426	by sorting their keys. This is adding a comparatively high overhead.
256		427
257	If C<$enable> is false, then the C<encode> method will output key-value	428	If C<$enable> is false, then the C<encode> method will output key-value
258	pairs in the order Perl stores them (which will likely change between runs	429	pairs in the order Perl stores them (which will likely change between runs
259	of the same script).	430	of the same script).
260		431
261	This option is useful if you want the same data structure to be encoded as	432	This option is useful if you want the same data structure to be encoded as
262	the same JSON text (given the same overall settings). If it is disabled,	433	the same JSON text (given the same overall settings). If it is disabled,
263	the same hash migh be encoded differently even if contains the same data,	434	the same hash might be encoded differently even if contains the same data,
264	as key-value pairs have no inherent ordering in Perl.	435	as key-value pairs have no inherent ordering in Perl.
265		436
266	This setting has no effect when decoding JSON texts.	437	This setting has no effect when decoding JSON texts.
267		438
268	=item $json = $json->allow_nonref ([$enable])	439	=item $json = $json->allow_nonref ([$enable])
		440
		441	=item $enabled = $json->get_allow_nonref
269		442
270	If C<$enable> is true (or missing), then the C<encode> method can convert a	443	If C<$enable> is true (or missing), then the C<encode> method can convert a
271	non-reference into its corresponding string, number or null JSON value,	444	non-reference into its corresponding string, number or null JSON value,
272	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	445	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
273	values instead of croaking.	446	values instead of croaking.
…		…
281	resulting in an invalid JSON text:	454	resulting in an invalid JSON text:
282		455
283	JSON::XS->new->allow_nonref->encode ("Hello, World!")	456	JSON::XS->new->allow_nonref->encode ("Hello, World!")
284	=> "Hello, World!"	457	=> "Hello, World!"
285		458
		459	=item $json = $json->allow_blessed ([$enable])
		460
		461	=item $enabled = $json->get_allow_blessed
		462
		463	If C<$enable> is true (or missing), then the C<encode> method will not
		464	barf when it encounters a blessed reference. Instead, the value of the
		465	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		466	disabled or no C<TO_JSON> method found) or a representation of the
		467	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		468	encoded. Has no effect on C<decode>.
		469
		470	If C<$enable> is false (the default), then C<encode> will throw an
		471	exception when it encounters a blessed object.
		472
		473	=item $json = $json->convert_blessed ([$enable])
		474
		475	=item $enabled = $json->get_convert_blessed
		476
		477	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		478	blessed object, will check for the availability of the C<TO_JSON> method
		479	on the object's class. If found, it will be called in scalar context
		480	and the resulting scalar will be encoded instead of the object. If no
		481	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		482	to do.
		483
		484	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		485	returns other blessed objects, those will be handled in the same
		486	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		487	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		488	methods called by the Perl core (== not by the user of the object) are
		489	usually in upper case letters and to avoid collisions with any C<to_json>
		490	function or method.
		491
		492	This setting does not yet influence C<decode> in any way, but in the
		493	future, global hooks might get installed that influence C<decode> and are
		494	enabled by this setting.
		495
		496	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		497	to do when a blessed object is found.
		498
		499	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		500
		501	When C<$coderef> is specified, it will be called from C<decode> each
		502	time it decodes a JSON object. The only argument is a reference to the
		503	newly-created hash. If the code references returns a single scalar (which
		504	need not be a reference), this value (i.e. a copy of that scalar to avoid
		505	aliasing) is inserted into the deserialised data structure. If it returns
		506	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		507	original deserialised hash will be inserted. This setting can slow down
		508	decoding considerably.
		509
		510	When C<$coderef> is omitted or undefined, any existing callback will
		511	be removed and C<decode> will not change the deserialised hash in any
		512	way.
		513
		514	Example, convert all JSON objects into the integer 5:
		515
		516	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		517	# returns [5]
		518	$js->decode ('[{}]')
		519	# throw an exception because allow_nonref is not enabled
		520	# so a lone 5 is not allowed.
		521	$js->decode ('{"a":1, "b":2}');
		522
		523	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		524
		525	Works remotely similar to C<filter_json_object>, but is only called for
		526	JSON objects having a single key named C<$key>.
		527
		528	This C<$coderef> is called before the one specified via
		529	C<filter_json_object>, if any. It gets passed the single value in the JSON
		530	object. If it returns a single value, it will be inserted into the data
		531	structure. If it returns nothing (not even C<undef> but the empty list),
		532	the callback from C<filter_json_object> will be called next, as if no
		533	single-key callback were specified.
		534
		535	If C<$coderef> is omitted or undefined, the corresponding callback will be
		536	disabled. There can only ever be one callback for a given key.
		537
		538	As this callback gets called less often then the C<filter_json_object>
		539	one, decoding speed will not usually suffer as much. Therefore, single-key
		540	objects make excellent targets to serialise Perl objects into, especially
		541	as single-key JSON objects are as close to the type-tagged value concept
		542	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		543	support this in any way, so you need to make sure your data never looks
		544	like a serialised Perl hash.
		545
		546	Typical names for the single object key are C<__class_whatever__>, or
		547	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		548	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		549	with real hashes.
		550
		551	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		552	into the corresponding C<< $WIDGET{<id>} >> object:
		553
		554	# return whatever is in $WIDGET{5}:
		555	JSON::XS
		556	->new
		557	->filter_json_single_key_object (__widget__ => sub {
		558	$WIDGET{ $_[0] }
		559	})
		560	->decode ('{"__widget__": 5')
		561
		562	# this can be used with a TO_JSON method in some "widget" class
		563	# for serialisation to json:
		564	sub WidgetBase::TO_JSON {
		565	my ($self) = @_;
		566
		567	unless ($self->{id}) {
		568	$self->{id} = ..get..some..id..;
		569	$WIDGET{$self->{id}} = $self;
		570	}
		571
		572	{ __widget__ => $self->{id} }
		573	}
		574
286	=item $json = $json->shrink ([$enable])	575	=item $json = $json->shrink ([$enable])
		576
		577	=item $enabled = $json->get_shrink
287		578
288	Perl usually over-allocates memory a bit when allocating space for	579	Perl usually over-allocates memory a bit when allocating space for
289	strings. This flag optionally resizes strings generated by either	580	strings. This flag optionally resizes strings generated by either
290	C<encode> or C<decode> to their minimum size possible. This can save	581	C<encode> or C<decode> to their minimum size possible. This can save
291	memory when your JSON texts are either very very long or you have many	582	memory when your JSON texts are either very very long or you have many
…		…
309	strings that look like integers or floats into integers or floats	600	strings that look like integers or floats into integers or floats
310	internally (there is no difference on the Perl level), saving space.	601	internally (there is no difference on the Perl level), saving space.
311		602
312	=item $json = $json->max_depth ([$maximum_nesting_depth])	603	=item $json = $json->max_depth ([$maximum_nesting_depth])
313		604
		605	=item $max_depth = $json->get_max_depth
		606
314	Sets the maximum nesting level (default C<512>) accepted while encoding	607	Sets the maximum nesting level (default C<512>) accepted while encoding
315	or decoding. If the JSON text or Perl data structure has an equal or	608	or decoding. If the JSON text or Perl data structure has an equal or
316	higher nesting level then this limit, then the encoder and decoder will	609	higher nesting level then this limit, then the encoder and decoder will
317	stop and croak at that point.	610	stop and croak at that point.
318		611
…		…
322	given character in a string.	615	given character in a string.
323		616
324	Setting the maximum depth to one disallows any nesting, so that ensures	617	Setting the maximum depth to one disallows any nesting, so that ensures
325	that the object is only a single hash/object or array.	618	that the object is only a single hash/object or array.
326		619
327	The argument to C<max_depth> will be rounded up to the next nearest power	620	The argument to C<max_depth> will be rounded up to the next highest power
328	of two.	621	of two. If no argument is given, the highest possible setting will be
		622	used, which is rarely useful.
		623
		624	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		625
		626	=item $json = $json->max_size ([$maximum_string_size])
		627
		628	=item $max_size = $json->get_max_size
		629
		630	Set the maximum length a JSON text may have (in bytes) where decoding is
		631	being attempted. The default is C<0>, meaning no limit. When C<decode>
		632	is called on a string longer then this number of characters it will not
		633	attempt to decode the string but throw an exception. This setting has no
		634	effect on C<encode> (yet).
		635
		636	The argument to C<max_size> will be rounded up to the next B<highest>
		637	power of two (so may be more than requested). If no argument is given, the
		638	limit check will be deactivated (same as when C<0> is specified).
329		639
330	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	640	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
331		641
332	=item $json_text = $json->encode ($perl_scalar)	642	=item $json_text = $json->encode ($perl_scalar)
333		643
…		…
345		655
346	JSON numbers and strings become simple Perl scalars. JSON arrays become	656	JSON numbers and strings become simple Perl scalars. JSON arrays become
347	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	657	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
348	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	658	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
349		659
		660	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		661
		662	This works like the C<decode> method, but instead of raising an exception
		663	when there is trailing garbage after the first JSON object, it will
		664	silently stop parsing there and return the number of characters consumed
		665	so far.
		666
		667	This is useful if your JSON texts are not delimited by an outer protocol
		668	(which is not the brightest thing to do in the first place) and you need
		669	to know where the JSON text ends.
		670
		671	JSON::XS->new->decode_prefix ("[1] the tail")
		672	=> ([], 3)
		673
350	=back	674	=back
351		675
352		676
353	=head1 MAPPING	677	=head1 MAPPING
354		678
…		…
356	vice versa. These mappings are designed to "do the right thing" in most	680	vice versa. These mappings are designed to "do the right thing" in most
357	circumstances automatically, preserving round-tripping characteristics	681	circumstances automatically, preserving round-tripping characteristics
358	(what you put in comes out as something equivalent).	682	(what you put in comes out as something equivalent).
359		683
360	For the more enlightened: note that in the following descriptions,	684	For the more enlightened: note that in the following descriptions,
361	lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>	685	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
362	refers to the abstract Perl language itself.	686	refers to the abstract Perl language itself.
363		687
		688
364	=head2 JSON -> PERL	689	=head2 JSON -> PERL
365		690
366	=over 4	691	=over 4
367		692
368	=item object	693	=item object
369		694
370	A JSON object becomes a reference to a hash in Perl. No ordering of object	695	A JSON object becomes a reference to a hash in Perl. No ordering of object
371	keys is preserved (JSON does not preserver object key ordering itself).	696	keys is preserved (JSON does not preserve object key ordering itself).
372		697
373	=item array	698	=item array
374		699
375	A JSON array becomes a reference to an array in Perl.	700	A JSON array becomes a reference to an array in Perl.
376		701
…		…
380	are represented by the same codepoints in the Perl string, so no manual	705	are represented by the same codepoints in the Perl string, so no manual
381	decoding is necessary.	706	decoding is necessary.
382		707
383	=item number	708	=item number
384		709
385	A JSON number becomes either an integer or numeric (floating point)	710	A JSON number becomes either an integer, numeric (floating point) or
386	scalar in perl, depending on its range and any fractional parts. On the	711	string scalar in perl, depending on its range and any fractional parts. On
387	Perl level, there is no difference between those as Perl handles all the	712	the Perl level, there is no difference between those as Perl handles all
388	conversion details, but an integer may take slightly less memory and might	713	the conversion details, but an integer may take slightly less memory and
389	represent more values exactly than (floating point) numbers.	714	might represent more values exactly than floating point numbers.
		715
		716	If the number consists of digits only, JSON::XS will try to represent
		717	it as an integer value. If that fails, it will try to represent it as
		718	a numeric (floating point) value if that is possible without loss of
		719	precision. Otherwise it will preserve the number as a string value (in
		720	which case you lose roundtripping ability, as the JSON number will be
		721	re-encoded toa JSON string).
		722
		723	Numbers containing a fractional or exponential part will always be
		724	represented as numeric (floating point) values, possibly at a loss of
		725	precision (in which case you might lose perfect roundtripping ability, but
		726	the JSON number will still be re-encoded as a JSON number).
390		727
391	=item true, false	728	=item true, false
392		729
393	These JSON atoms become C<0>, C<1>, respectively. Information is lost in	730	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
394	this process. Future versions might represent those values differently,	731	respectively. They are overloaded to act almost exactly like the numbers
395	but they will be guarenteed to act like these integers would normally in	732	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
396	Perl.	733	the C<JSON::XS::is_bool> function.
397		734
398	=item null	735	=item null
399		736
400	A JSON null atom becomes C<undef> in Perl.	737	A JSON null atom becomes C<undef> in Perl.
401		738
402	=back	739	=back
		740
403		741
404	=head2 PERL -> JSON	742	=head2 PERL -> JSON
405		743
406	The mapping from Perl to JSON is slightly more difficult, as Perl is a	744	The mapping from Perl to JSON is slightly more difficult, as Perl is a
407	truly typeless language, so we can only guess which JSON type is meant by	745	truly typeless language, so we can only guess which JSON type is meant by
…		…
430	Other unblessed references are generally not allowed and will cause an	768	Other unblessed references are generally not allowed and will cause an
431	exception to be thrown, except for references to the integers C<0> and	769	exception to be thrown, except for references to the integers C<0> and
432	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	770	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
433	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.	771	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
434		772
435	to_json [\0,JSON::XS::true] # yields [false,true]	773	encode_json [\0,JSON::XS::true] # yields [false,true]
		774
		775	=item JSON::XS::true, JSON::XS::false
		776
		777	These special values become JSON true and JSON false values,
		778	respectively. You can also use C<\1> and C<\0> directly if you want.
436		779
437	=item blessed objects	780	=item blessed objects
438		781
439	Blessed objects are not allowed. JSON::XS currently tries to encode their	782	Blessed objects are not directly representable in JSON. See the
440	underlying representation (hash- or arrayref), but this behaviour might	783	C<allow_blessed> and C<convert_blessed> methods on various options on
441	change in future versions.	784	how to deal with this: basically, you can choose between throwing an
		785	exception, encoding the reference as if it weren't blessed, or provide
		786	your own serialiser method.
442		787
443	=item simple scalars	788	=item simple scalars
444		789
445	Simple Perl scalars (any scalar that is not a reference) are the most	790	Simple Perl scalars (any scalar that is not a reference) are the most
446	difficult objects to encode: JSON::XS will encode undefined scalars as	791	difficult objects to encode: JSON::XS will encode undefined scalars as
447	JSON null value, scalars that have last been used in a string context	792	JSON C<null> values, scalars that have last been used in a string context
448	before encoding as JSON strings and anything else as number value:	793	before encoding as JSON strings, and anything else as number value:
449		794
450	# dump as number	795	# dump as number
451	to_json [2] # yields [2]	796	encode_json [2] # yields [2]
452	to_json [-3.0e17] # yields [-3e+17]	797	encode_json [-3.0e17] # yields [-3e+17]
453	my $value = 5; to_json [$value] # yields [5]	798	my $value = 5; encode_json [$value] # yields [5]
454		799
455	# used as string, so dump as string	800	# used as string, so dump as string
456	print $value;	801	print $value;
457	to_json [$value] # yields ["5"]	802	encode_json [$value] # yields ["5"]
458		803
459	# undef becomes null	804	# undef becomes null
460	to_json [undef] # yields [null]	805	encode_json [undef] # yields [null]
461		806
462	You can force the type to be a string by stringifying it:	807	You can force the type to be a JSON string by stringifying it:
463		808
464	my $x = 3.1; # some variable containing a number	809	my $x = 3.1; # some variable containing a number
465	"$x"; # stringified	810	"$x"; # stringified
466	$x .= ""; # another, more awkward way to stringify	811	$x .= ""; # another, more awkward way to stringify
467	print $x; # perl does it for you, too, quite often	812	print $x; # perl does it for you, too, quite often
468		813
469	You can force the type to be a number by numifying it:	814	You can force the type to be a JSON number by numifying it:
470		815
471	my $x = "3"; # some variable containing a string	816	my $x = "3"; # some variable containing a string
472	$x += 0; # numify it, ensuring it will be dumped as a number	817	$x += 0; # numify it, ensuring it will be dumped as a number
473	$x *= 1; # same thing, the choise is yours.	818	$x *= 1; # same thing, the choice is yours.
474		819
475	You can not currently output JSON booleans or force the type in other,	820	You can not currently force the type in other, less obscure, ways. Tell me
476	less obscure, ways. Tell me if you need this capability.	821	if you need this capability (but don't forget to explain why its needed
		822	:).
		823
		824	=back
		825
		826
		827	=head1 ENCODING/CODESET FLAG NOTES
		828
		829	The interested reader might have seen a number of flags that signify
		830	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		831	some confusion on what these do, so here is a short comparison:
		832
		833	C<utf8> controls wether the JSON text created by C<encode> (and expected
		834	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		835	control wether C<encode> escapes character values outside their respective
		836	codeset range. Neither of these flags conflict with each other, although
		837	some combinations make less sense than others.
		838
		839	Care has been taken to make all flags symmetrical with respect to
		840	C<encode> and C<decode>, that is, texts encoded with any combination of
		841	these flag values will be correctly decoded when the same flags are used
		842	- in general, if you use different flag settings while encoding vs. when
		843	decoding you likely have a bug somewhere.
		844
		845	Below comes a verbose discussion of these flags. Note that a "codeset" is
		846	simply an abstract set of character-codepoint pairs, while an encoding
		847	takes those codepoint numbers and I<encodes> them, in our case into
		848	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		849	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		850	the same time, which can be confusing.
		851
		852	=over 4
		853
		854	=item C<utf8> flag disabled
		855
		856	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		857	and expect Unicode strings, that is, characters with high ordinal Unicode
		858	values (> 255) will be encoded as such characters, and likewise such
		859	characters are decoded as-is, no canges to them will be done, except
		860	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		861	respectively (to Perl, these are the same thing in strings unless you do
		862	funny/weird/dumb stuff).
		863
		864	This is useful when you want to do the encoding yourself (e.g. when you
		865	want to have UTF-16 encoded JSON texts) or when some other layer does
		866	the encoding for you (for example, when printing to a terminal using a
		867	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		868	to UTF-8 encode your data first and have Perl encode it another time).
		869
		870	=item C<utf8> flag enabled
		871
		872	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		873	characters using the corresponding UTF-8 multi-byte sequence, and will
		874	expect your input strings to be encoded as UTF-8, that is, no "character"
		875	of the input string must have any value > 255, as UTF-8 does not allow
		876	that.
		877
		878	The C<utf8> flag therefore switches between two modes: disabled means you
		879	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		880	octet/binary string in Perl.
		881
		882	=item C<latin1> or C<ascii> flags enabled
		883
		884	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		885	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		886	characters as specified by the C<utf8> flag.
		887
		888	If C<utf8> is disabled, then the result is also correctly encoded in those
		889	character sets (as both are proper subsets of Unicode, meaning that a
		890	Unicode string with all character values < 256 is the same thing as a
		891	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		892	the same thing as an ASCII string in Perl).
		893
		894	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		895	regardless of these flags, just some more characters will be escaped using
		896	C<\uXXXX> then before.
		897
		898	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		899	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		900	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		901	a subset of Unicode), while ASCII is.
		902
		903	Surprisingly, C<decode> will ignore these flags and so treat all input
		904	values as governed by the C<utf8> flag. If it is disabled, this allows you
		905	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		906	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		907
		908	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		909	they only govern when the JSON output engine escapes a character or not.
		910
		911	The main use for C<latin1> is to relatively efficiently store binary data
		912	as JSON, at the expense of breaking compatibility with most JSON decoders.
		913
		914	The main use for C<ascii> is to force the output to not contain characters
		915	with values > 127, which means you can interpret the resulting string
		916	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		917	8-bit-encoding, and still get the same data structure back. This is useful
		918	when your channel for JSON transfer is not 8-bit clean or the encoding
		919	might be mangled in between (e.g. in mail), and works because ASCII is a
		920	proper subset of most 8-bit and multibyte encodings in use in the world.
477		921
478	=back	922	=back
479		923
480		924
481	=head1 COMPARISON	925	=head1 COMPARISON
…		…
486	followed by some benchmark values. JSON::XS was designed not to suffer	930	followed by some benchmark values. JSON::XS was designed not to suffer
487	from any of these problems or limitations.	931	from any of these problems or limitations.
488		932
489	=over 4	933	=over 4
490		934
		935	=item JSON 2.xx
		936
		937	A marvellous piece of engineering, this module either uses JSON::XS
		938	directly when available (so will be 100% compatible with it, including
		939	speed), or it uses JSON::PP, which is basically JSON::XS translated to
		940	Pure Perl, which should be 100% compatible with JSON::XS, just a bit
		941	slower.
		942
		943	You cannot really lose by using this module, especially as it tries very
		944	hard to work even with ancient Perl versions, while JSON::XS does not.
		945
491	=item JSON 1.07	946	=item JSON 1.07
492		947
493	Slow (but very portable, as it is written in pure Perl).	948	Slow (but very portable, as it is written in pure Perl).
494		949
495	Undocumented/buggy Unicode handling (how JSON handles unicode values is	950	Undocumented/buggy Unicode handling (how JSON handles Unicode values is
496	undocumented. One can get far by feeding it unicode strings and doing	951	undocumented. One can get far by feeding it Unicode strings and doing
497	en-/decoding oneself, but unicode escapes are not working properly).	952	en-/decoding oneself, but Unicode escapes are not working properly).
498		953
499	No roundtripping (strings get clobbered if they look like numbers, e.g.	954	No round-tripping (strings get clobbered if they look like numbers, e.g.
500	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	955	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
501	decode into the number 2.	956	decode into the number 2.
502		957
503	=item JSON::PC 0.01	958	=item JSON::PC 0.01
504		959
505	Very fast.	960	Very fast.
506		961
507	Undocumented/buggy Unicode handling.	962	Undocumented/buggy Unicode handling.
508		963
509	No roundtripping.	964	No round-tripping.
510		965
511	Has problems handling many Perl values (e.g. regex results and other magic	966	Has problems handling many Perl values (e.g. regex results and other magic
512	values will make it croak).	967	values will make it croak).
513		968
514	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	969	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
…		…
524	Very inflexible (no human-readable format supported, format pretty much	979	Very inflexible (no human-readable format supported, format pretty much
525	undocumented. I need at least a format for easy reading by humans and a	980	undocumented. I need at least a format for easy reading by humans and a
526	single-line compact format for use in a protocol, and preferably a way to	981	single-line compact format for use in a protocol, and preferably a way to
527	generate ASCII-only JSON texts).	982	generate ASCII-only JSON texts).
528		983
529	Completely broken (and confusingly documented) Unicode handling (unicode	984	Completely broken (and confusingly documented) Unicode handling (Unicode
530	escapes are not working properly, you need to set ImplicitUnicode to	985	escapes are not working properly, you need to set ImplicitUnicode to
531	I<different> values on en- and decoding to get symmetric behaviour).	986	I<different> values on en- and decoding to get symmetric behaviour).
532		987
533	No roundtripping (simple cases work, but this depends on wether the scalar	988	No round-tripping (simple cases work, but this depends on whether the scalar
534	value was used in a numeric context or not).	989	value was used in a numeric context or not).
535		990
536	Dumping hashes may skip hash values depending on iterator state.	991	Dumping hashes may skip hash values depending on iterator state.
537		992
538	Unmaintained (maintainer unresponsive for many months, bugs are not	993	Unmaintained (maintainer unresponsive for many months, bugs are not
539	getting fixed).	994	getting fixed).
540		995
541	Does not check input for validity (i.e. will accept non-JSON input and	996	Does not check input for validity (i.e. will accept non-JSON input and
542	return "something" instead of raising an exception. This is a security	997	return "something" instead of raising an exception. This is a security
543	issue: imagine two banks transfering money between each other using	998	issue: imagine two banks transferring money between each other using
544	JSON. One bank might parse a given non-JSON request and deduct money,	999	JSON. One bank might parse a given non-JSON request and deduct money,
545	while the other might reject the transaction with a syntax error. While a	1000	while the other might reject the transaction with a syntax error. While a
546	good protocol will at least recover, that is extra unnecessary work and	1001	good protocol will at least recover, that is extra unnecessary work and
547	the transaction will still not succeed).	1002	the transaction will still not succeed).
548		1003
549	=item JSON::DWIW 0.04	1004	=item JSON::DWIW 0.04
550		1005
551	Very fast. Very natural. Very nice.	1006	Very fast. Very natural. Very nice.
552		1007
553	Undocumented unicode handling (but the best of the pack. Unicode escapes	1008	Undocumented Unicode handling (but the best of the pack. Unicode escapes
554	still don't get parsed properly).	1009	still don't get parsed properly).
555		1010
556	Very inflexible.	1011	Very inflexible.
557		1012
558	No roundtripping.	1013	No round-tripping.
559		1014
560	Does not generate valid JSON texts (key strings are often unquoted, empty keys	1015	Does not generate valid JSON texts (key strings are often unquoted, empty keys
561	result in nothing being output)	1016	result in nothing being output)
562		1017
563	Does not check input for validity.	1018	Does not check input for validity.
564		1019
565	=back	1020	=back
		1021
		1022
		1023	=head2 JSON and YAML
		1024
		1025	You often hear that JSON is a subset of YAML. This is, however, a mass
		1026	hysteria(*) and very far from the truth. In general, there is no way to
		1027	configure JSON::XS to output a data structure as valid YAML that works for
		1028	all cases.
		1029
		1030	If you really must use JSON::XS to generate YAML, you should use this
		1031	algorithm (subject to change in future versions):
		1032
		1033	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1034	my $yaml = $to_yaml->encode ($ref) . "\n";
		1035
		1036	This will I<usually> generate JSON texts that also parse as valid
		1037	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1038	lengths that JSON doesn't have and also has different and incompatible
		1039	unicode handling, so you should make sure that your hash keys are
		1040	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1041	you do not have codepoints with values outside the Unicode BMP (basic
		1042	multilingual page). YAML also does not allow C<\/> sequences in strings
		1043	(which JSON::XS does not I<currently> generate).
		1044
		1045	There might be other incompatibilities that I am not aware of (or the YAML
		1046	specification has been changed yet again - it does so quite often). In
		1047	general you should not try to generate YAML with a JSON generator or vice
		1048	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1049	high that you will run into severe interoperability problems when you
		1050	least expect it.
		1051
		1052	=over 4
		1053
		1054	=item (*)
		1055
		1056	This is spread actively by the YAML team, however. For many years now they
		1057	claim YAML were a superset of JSON, even when proven otherwise.
		1058
		1059	Even the author of this manpage was at some point accused of providing
		1060	"incorrect" information, despite the evidence presented (claims ranged
		1061	from "your documentation contains inaccurate and negative statements about
		1062	YAML" (the only negative comment is this footnote, and it didn't exist
		1063	back then; the question on which claims were inaccurate was never answered
		1064	etc.) to "the YAML spec is not up-to-date" (the real and supposedly
		1065	JSON-compatible spec is apparently not currently publicly available)
		1066	to actual requests to replace this section by incorrect information,
		1067	suppressing information about the real problem).
		1068
		1069	So whenever you are told that YAML was a superset of JSON, first check
		1070	wether it is really true (it might be when you check it, but it certainly
		1071	was not true when this was written). I would much prefer if the YAML team
		1072	would spent their time on actually making JSON compatibility a truth
		1073	(JSON, after all, has a very small and simple specification) instead of
		1074	trying to lobby/force people into reporting untruths.
		1075
		1076	=back
		1077
566		1078
567	=head2 SPEED	1079	=head2 SPEED
568		1080
569	It seems that JSON::XS is surprisingly fast, as shown in the following	1081	It seems that JSON::XS is surprisingly fast, as shown in the following
570	tables. They have been generated with the help of the C<eg/bench> program	1082	tables. They have been generated with the help of the C<eg/bench> program
571	in the JSON::XS distribution, to make it easy to compare on your own	1083	in the JSON::XS distribution, to make it easy to compare on your own
572	system.	1084	system.
573		1085
574	First comes a comparison between various modules using a very short JSON	1086	First comes a comparison between various modules using a very short
575	string:	1087	single-line JSON string:
576		1088
577	{"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null}	1089	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
		1090	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
578		1091
579	It shows the number of encodes/decodes per second (JSON::XS uses the	1092	It shows the number of encodes/decodes per second (JSON::XS uses
580	functional interface, while JSON::XS/2 uses the OO interface with	1093	the functional interface, while JSON::XS/2 uses the OO interface
581	pretty-printing and hashkey sorting enabled). Higher is better:	1094	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1095	shrink). Higher is better:
582		1096
583	module \| encode \| decode \|	1097	module \| encode \| decode \|
584	-----------\|------------\|------------\|	1098	-----------\|------------\|------------\|
585	JSON \| 11488.516 \| 7823.035 \|	1099	JSON 1.x \| 4990.842 \| 4088.813 \|
586	JSON::DWIW \| 94708.054 \| 129094.260 \|	1100	JSON::DWIW \| 51653.990 \| 71575.154 \|
587	JSON::PC \| 63884.157 \| 128528.212 \|	1101	JSON::PC \| 65948.176 \| 74631.744 \|
588	JSON::Syck \| 34898.677 \| 42096.911 \|	1102	JSON::PP \| 8931.652 \| 3817.168 \|
589	JSON::XS \| 654027.064 \| 396423.669 \|	1103	JSON::Syck \| 24877.248 \| 27776.848 \|
590	JSON::XS/2 \| 371564.190 \| 371725.613 \|	1104	JSON::XS \| 388361.481 \| 227951.304 \|
		1105	JSON::XS/2 \| 227951.304 \| 218453.333 \|
		1106	JSON::XS/3 \| 338250.323 \| 218453.333 \|
		1107	Storable \| 16500.016 \| 135300.129 \|
591	-----------+------------+------------+	1108	-----------+------------+------------+
592		1109
593	That is, JSON::XS is more than six times faster than JSON::DWIW on	1110	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
594	encoding, more than three times faster on decoding, and about thirty times	1111	about three times faster on decoding, and over forty times faster
595	faster than JSON, even with pretty-printing and key sorting.	1112	than JSON, even with pretty-printing and key sorting. It also compares
		1113	favourably to Storable for small amounts of data.
596		1114
597	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1115	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
598	search API (http://nanoref.com/yahooapis/mgPdGg):	1116	search API (http://nanoref.com/yahooapis/mgPdGg):
599		1117
600	module \| encode \| decode \|	1118	module \| encode \| decode \|
601	-----------\|------------\|------------\|	1119	-----------\|------------\|------------\|
602	JSON \| 273.023 \| 44.674 \|	1120	JSON 1.x \| 55.260 \| 34.971 \|
603	JSON::DWIW \| 1089.383 \| 1145.704 \|	1121	JSON::DWIW \| 825.228 \| 1082.513 \|
604	JSON::PC \| 3097.419 \| 2393.921 \|	1122	JSON::PC \| 3571.444 \| 2394.829 \|
605	JSON::Syck \| 514.060 \| 843.053 \|	1123	JSON::PP \| 210.987 \| 32.574 \|
606	JSON::XS \| 6479.668 \| 3636.364 \|	1124	JSON::Syck \| 552.551 \| 787.544 \|
607	JSON::XS/2 \| 3774.221 \| 3599.124 \|	1125	JSON::XS \| 5780.463 \| 4854.519 \|
		1126	JSON::XS/2 \| 3869.998 \| 4798.975 \|
		1127	JSON::XS/3 \| 5862.880 \| 4798.975 \|
		1128	Storable \| 4445.002 \| 5235.027 \|
608	-----------+------------+------------+	1129	-----------+------------+------------+
609		1130
610	Again, JSON::XS leads by far.	1131	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1132	decodes faster).
611		1133
612	On large strings containing lots of high unicode characters, some modules	1134	On large strings containing lots of high Unicode characters, some modules
613	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1135	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
614	will be broken due to missing (or wrong) unicode handling. Others refuse	1136	will be broken due to missing (or wrong) Unicode handling. Others refuse
615	to decode or encode properly, so it was impossible to prepare a fair	1137	to decode or encode properly, so it was impossible to prepare a fair
616	comparison table for that case.	1138	comparison table for that case.
617		1139
618		1140
619	=head1 SECURITY CONSIDERATIONS	1141	=head1 SECURITY CONSIDERATIONS
…		…
625	any buffer overflows. Obviously, this module should ensure that and I am	1147	any buffer overflows. Obviously, this module should ensure that and I am
626	trying hard on making that true, but you never know.	1148	trying hard on making that true, but you never know.
627		1149
628	Second, you need to avoid resource-starving attacks. That means you should	1150	Second, you need to avoid resource-starving attacks. That means you should
629	limit the size of JSON texts you accept, or make sure then when your	1151	limit the size of JSON texts you accept, or make sure then when your
630	resources run out, thats just fine (e.g. by using a separate process that	1152	resources run out, that's just fine (e.g. by using a separate process that
631	can crash safely). The size of a JSON text in octets or characters is	1153	can crash safely). The size of a JSON text in octets or characters is
632	usually a good indication of the size of the resources required to decode	1154	usually a good indication of the size of the resources required to decode
633	it into a Perl structure.	1155	it into a Perl structure. While JSON::XS can check the size of the JSON
		1156	text, it might be too late when you already have it in memory, so you
		1157	might want to check the size before you accept the string.
634		1158
635	Third, JSON::XS recurses using the C stack when decoding objects and	1159	Third, JSON::XS recurses using the C stack when decoding objects and
636	arrays. The C stack is a limited resource: for instance, on my amd64	1160	arrays. The C stack is a limited resource: for instance, on my amd64
637	machine with 8MB of stack size I can decode around 180k nested arrays but	1161	machine with 8MB of stack size I can decode around 180k nested arrays but
638	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1162	only 14k nested JSON objects (due to perl itself recursing deeply on croak
639	to free the temporary). If that is exceeded, the program crashes. to be	1163	to free the temporary). If that is exceeded, the program crashes. To be
640	conservative, the default nesting limit is set to 512. If your process	1164	conservative, the default nesting limit is set to 512. If your process
641	has a smaller stack, you should adjust this setting accordingly with the	1165	has a smaller stack, you should adjust this setting accordingly with the
642	C<max_depth> method.	1166	C<max_depth> method.
643		1167
644	And last but least, something else could bomb you that I forgot to think	1168	Something else could bomb you, too, that I forgot to think of. In that
645	of. In that case, you get to keep the pieces. I am always open for hints,	1169	case, you get to keep the pieces. I am always open for hints, though...
646	though...	1170
		1171	Also keep in mind that JSON::XS might leak contents of your Perl data
		1172	structures in its error messages, so when you serialise sensitive
		1173	information you might want to make sure that exceptions thrown by JSON::XS
		1174	will not end up in front of untrusted eyes.
		1175
		1176	If you are using JSON::XS to return packets to consumption
		1177	by JavaScript scripts in a browser you should have a look at
		1178	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1179	you are vulnerable to some common attack vectors (which really are browser
		1180	design bugs, but it is still you who will have to deal with it, as major
		1181	browser developers care only for features, not about getting security
		1182	right).
		1183
		1184
		1185	=head1 THREADS
		1186
		1187	This module is I<not> guaranteed to be thread safe and there are no
		1188	plans to change this until Perl gets thread support (as opposed to the
		1189	horribly slow so-called "threads" which are simply slow and bloated
		1190	process simulations - use fork, its I<much> faster, cheaper, better).
		1191
		1192	(It might actually work, but you have been warned).
647		1193
648		1194
649	=head1 BUGS	1195	=head1 BUGS
650		1196
651	While the goal of this module is to be correct, that unfortunately does	1197	While the goal of this module is to be correct, that unfortunately does
652	not mean its bug-free, only that I think its design is bug-free. It is	1198	not mean its bug-free, only that I think its design is bug-free. It is
653	still relatively early in its development. If you keep reporting bugs they	1199	still relatively early in its development. If you keep reporting bugs they
654	will be fixed swiftly, though.	1200	will be fixed swiftly, though.
655		1201
		1202	Please refrain from using rt.cpan.org or any other bug reporting
		1203	service. I put the contact address into my modules for a reason.
		1204
656	=cut	1205	=cut
657		1206
		1207	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1208	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1209
658	sub true() { \1 }	1210	sub true() { $true }
659	sub false() { \0 }	1211	sub false() { $false }
		1212
		1213	sub is_bool($) {
		1214	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1215	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1216	}
		1217
		1218	XSLoader::load "JSON::XS", $VERSION;
		1219
		1220	package JSON::XS::Boolean;
		1221
		1222	use overload
		1223	"0+" => sub { ${$_[0]} },
		1224	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1225	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1226	fallback => 1;
660		1227
661	1;	1228	1;
662		1229
663	=head1 AUTHOR	1230	=head1 AUTHOR
664		1231

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Comparing JSON-XS/XS.pm (file contents): Revision 1.30 by root, Mon Apr 9 06:37:40 2007 UTC vs. Revision 1.86 by root, Wed Mar 19 03:17:38 2008 UTC

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Comparing JSON-XS/XS.pm (file contents):
Revision 1.30 by root, Mon Apr 9 06:37:40 2007 UTC vs.
Revision 1.86 by root, Wed Mar 19 03:17:38 2008 UTC