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Revision 1.39 by root, Tue Oct 29 15:55:49 2013 UTC

1	NAME	1	NAME
2	JSON::XS - JSON serialising/deserialising, done correctly and fast	2	JSON::XS - JSON serialising/deserialising, done correctly and fast
3		3
		4	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		5	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		6
4	SYNOPSIS	7	SYNOPSIS
5	use JSON::XS;	8	use JSON::XS;
6		9
7	# exported functions, they croak on error	10	# exported functions, they croak on error
8	# and expect/generate UTF-8	11	# and expect/generate UTF-8
9		12
10	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	13	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
11	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	14	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
12		15
13	# OO-interface	16	# OO-interface
14		17
15	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	18	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
16	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	19	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
17	$perl_scalar = $coder->decode ($unicode_json_text);	20	$perl_scalar = $coder->decode ($unicode_json_text);
		21
		22	# Note that JSON version 2.0 and above will automatically use JSON::XS
		23	# if available, at virtually no speed overhead either, so you should
		24	# be able to just:
		25
		26	use JSON;
		27
		28	# and do the same things, except that you have a pure-perl fallback now.
18		29
19	DESCRIPTION	30	DESCRIPTION
20	This module converts Perl data structures to JSON and vice versa. Its	31	This module converts Perl data structures to JSON and vice versa. Its
21	primary goal is to be *correct* and its secondary goal is to be *fast*.	32	primary goal is to be *correct* and its secondary goal is to be *fast*.
22	To reach the latter goal it was written in C.	33	To reach the latter goal it was written in C.
		34
		35	Beginning with version 2.0 of the JSON module, when both JSON and
		36	JSON::XS are installed, then JSON will fall back on JSON::XS (this can
		37	be overridden) with no overhead due to emulation (by inheriting
		38	constructor and methods). If JSON::XS is not available, it will fall
		39	back to the compatible JSON::PP module as backend, so using JSON instead
		40	of JSON::XS gives you a portable JSON API that can be fast when you need
		41	and doesn't require a C compiler when that is a problem.
23		42
24	As this is the n-th-something JSON module on CPAN, what was the reason	43	As this is the n-th-something JSON module on CPAN, what was the reason
25	to write yet another JSON module? While it seems there are many JSON	44	to write yet another JSON module? While it seems there are many JSON
26	modules, none of them correctly handle all corner cases, and in most	45	modules, none of them correctly handle all corner cases, and in most
27	cases their maintainers are unresponsive, gone missing, or not listening	46	cases their maintainers are unresponsive, gone missing, or not listening
28	to bug reports for other reasons.	47	to bug reports for other reasons.
29		48
30	See COMPARISON, below, for a comparison to some other JSON modules.
31
32	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	49	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
33	vice versa.	50	vice versa.
34		51
35	FEATURES	52	FEATURES
36	* correct unicode handling	53	* correct Unicode handling
		54
37	This module knows how to handle Unicode, and even documents how and	55	This module knows how to handle Unicode, documents how and when it
38	when it does so.	56	does so, and even documents what "correct" means.
39		57
40	* round-trip integrity	58	* round-trip integrity
		59
41	When you serialise a perl data structure using only datatypes	60	When you serialise a perl data structure using only data types
42	supported by JSON, the deserialised data structure is identical on	61	supported by JSON and Perl, the deserialised data structure is
43	the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"	62	identical on the Perl level. (e.g. the string "2.0" doesn't suddenly
44	just because it looks like a number).	63	become "2" just because it looks like a number). There *are* minor
		64	exceptions to this, read the MAPPING section below to learn about
		65	those.
45		66
46	* strict checking of JSON correctness	67	* strict checking of JSON correctness
		68
47	There is no guessing, no generating of illegal JSON texts by	69	There is no guessing, no generating of illegal JSON texts by
48	default, and only JSON is accepted as input by default (the latter	70	default, and only JSON is accepted as input by default (the latter
49	is a security feature).	71	is a security feature).
50		72
51	* fast	73	* fast
52	Compared to other JSON modules, this module compares favourably in
53	terms of speed, too.
54		74
		75	Compared to other JSON modules and other serialisers such as
		76	Storable, this module usually compares favourably in terms of speed,
		77	too.
		78
55	* simple to use	79	* simple to use
		80
56	This module has both a simple functional interface as well as an OO	81	This module has both a simple functional interface as well as an
57	interface.	82	object oriented interface.
58		83
59	* reasonably versatile output formats	84	* reasonably versatile output formats
		85
60	You can choose between the most compact guarenteed single-line	86	You can choose between the most compact guaranteed-single-line
61	format possible (nice for simple line-based protocols), a pure-ascii	87	format possible (nice for simple line-based protocols), a pure-ASCII
62	format (for when your transport is not 8-bit clean, still supports	88	format (for when your transport is not 8-bit clean, still supports
63	the whole unicode range), or a pretty-printed format (for when you	89	the whole Unicode range), or a pretty-printed format (for when you
64	want to read that stuff). Or you can combine those features in	90	want to read that stuff). Or you can combine those features in
65	whatever way you like.	91	whatever way you like.
66		92
67	FUNCTIONAL INTERFACE	93	FUNCTIONAL INTERFACE
68	The following convinience methods are provided by this module. They are	94	The following convenience methods are provided by this module. They are
69	exported by default:	95	exported by default:
70		96
71	$json_text = to_json $perl_scalar	97	$json_text = encode_json $perl_scalar
72	Converts the given Perl data structure (a simple scalar or a	98	Converts the given Perl data structure to a UTF-8 encoded, binary
73	reference to a hash or array) to a UTF-8 encoded, binary string
74	(that is, the string contains octets only). Croaks on error.	99	string (that is, the string contains octets only). Croaks on error.
75		100
76	This function call is functionally identical to:	101	This function call is functionally identical to:
77		102
78	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	103	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
79		104
80	except being faster.	105	Except being faster.
81		106
82	$perl_scalar = from_json $json_text	107	$perl_scalar = decode_json $json_text
83	The opposite of "to_json": expects an UTF-8 (binary) string and	108	The opposite of "encode_json": expects an UTF-8 (binary) string and
84	tries to parse that as an UTF-8 encoded JSON text, returning the	109	tries to parse that as an UTF-8 encoded JSON text, returning the
85	resulting simple scalar or reference. Croaks on error.	110	resulting reference. Croaks on error.
86		111
87	This function call is functionally identical to:	112	This function call is functionally identical to:
88		113
89	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	114	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
90		115
91	except being faster.	116	Except being faster.
92		117
93	$is_boolean = JSON::XS::is_bool $scalar	118	A FEW NOTES ON UNICODE AND PERL
94	Returns true if the passed scalar represents either JSON::XS::true	119	Since this often leads to confusion, here are a few very clear words on
95	or JSON::XS::false, two constants that act like 1 and 0,	120	how Unicode works in Perl, modulo bugs.
96	respectively and are used to represent JSON "true" and "false"
97	values in Perl.
98		121
99	See MAPPING, below, for more information on how JSON values are	122	1. Perl strings can store characters with ordinal values > 255.
100	mapped to Perl.	123	This enables you to store Unicode characters as single characters in
		124	a Perl string - very natural.
		125
		126	2. Perl does *not* associate an encoding with your strings.
		127	... until you force it to, e.g. when matching it against a regex, or
		128	printing the scalar to a file, in which case Perl either interprets
		129	your string as locale-encoded text, octets/binary, or as Unicode,
		130	depending on various settings. In no case is an encoding stored
		131	together with your data, it is *use* that decides encoding, not any
		132	magical meta data.
		133
		134	3. The internal utf-8 flag has no meaning with regards to the encoding
		135	of your string.
		136	Just ignore that flag unless you debug a Perl bug, a module written
		137	in XS or want to dive into the internals of perl. Otherwise it will
		138	only confuse you, as, despite the name, it says nothing about how
		139	your string is encoded. You can have Unicode strings with that flag
		140	set, with that flag clear, and you can have binary data with that
		141	flag set and that flag clear. Other possibilities exist, too.
		142
		143	If you didn't know about that flag, just the better, pretend it
		144	doesn't exist.
		145
		146	4. A "Unicode String" is simply a string where each character can be
		147	validly interpreted as a Unicode code point.
		148	If you have UTF-8 encoded data, it is no longer a Unicode string,
		149	but a Unicode string encoded in UTF-8, giving you a binary string.
		150
		151	5. A string containing "high" (> 255) character values is *not* a UTF-8
		152	string.
		153	It's a fact. Learn to live with it.
		154
		155	I hope this helps :)
101		156
102	OBJECT-ORIENTED INTERFACE	157	OBJECT-ORIENTED INTERFACE
103	The object oriented interface lets you configure your own encoding or	158	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	159	decoding style, within the limits of supported formats.
105		160
…		…
113		168
114	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	169	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
115	=> {"a": [1, 2]}	170	=> {"a": [1, 2]}
116		171
117	$json = $json->ascii ([$enable])	172	$json = $json->ascii ([$enable])
		173	$enabled = $json->get_ascii
118	If $enable is true (or missing), then the "encode" method will not	174	If $enable is true (or missing), then the "encode" method will not
119	generate characters outside the code range 0..127 (which is ASCII).	175	generate characters outside the code range 0..127 (which is ASCII).
120	Any unicode characters outside that range will be escaped using	176	Any Unicode characters outside that range will be escaped using
121	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL	177	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
122	escape sequence, as per RFC4627. The resulting encoded JSON text can	178	escape sequence, as per RFC4627. The resulting encoded JSON text can
123	be treated as a native unicode string, an ascii-encoded,	179	be treated as a native Unicode string, an ascii-encoded,
124	latin1-encoded or UTF-8 encoded string, or any other superset of	180	latin1-encoded or UTF-8 encoded string, or any other superset of
125	ASCII.	181	ASCII.
126		182
127	If $enable is false, then the "encode" method will not escape	183	If $enable is false, then the "encode" method will not escape
128	Unicode characters unless required by the JSON syntax or other	184	Unicode characters unless required by the JSON syntax or other
129	flags. This results in a faster and more compact format.	185	flags. This results in a faster and more compact format.
130		186
		187	See also the section *ENCODING/CODESET FLAG NOTES* later in this
		188	document.
		189
131	The main use for this flag is to produce JSON texts that can be	190	The main use for this flag is to produce JSON texts that can be
132	transmitted over a 7-bit channel, as the encoded JSON texts will not	191	transmitted over a 7-bit channel, as the encoded JSON texts will not
133	contain any 8 bit characters.	192	contain any 8 bit characters.
134		193
135	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	194	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
136	=> ["\ud801\udc01"]	195	=> ["\ud801\udc01"]
137		196
138	$json = $json->latin1 ([$enable])	197	$json = $json->latin1 ([$enable])
		198	$enabled = $json->get_latin1
139	If $enable is true (or missing), then the "encode" method will	199	If $enable is true (or missing), then the "encode" method will
140	encode the resulting JSON text as latin1 (or iso-8859-1), escaping	200	encode the resulting JSON text as latin1 (or iso-8859-1), escaping
141	any characters outside the code range 0..255. The resulting string	201	any characters outside the code range 0..255. The resulting string
142	can be treated as a latin1-encoded JSON text or a native unicode	202	can be treated as a latin1-encoded JSON text or a native Unicode
143	string. The "decode" method will not be affected in any way by this	203	string. The "decode" method will not be affected in any way by this
144	flag, as "decode" by default expects unicode, which is a strict	204	flag, as "decode" by default expects Unicode, which is a strict
145	superset of latin1.	205	superset of latin1.
146		206
147	If $enable is false, then the "encode" method will not escape	207	If $enable is false, then the "encode" method will not escape
148	Unicode characters unless required by the JSON syntax or other	208	Unicode characters unless required by the JSON syntax or other
149	flags.	209	flags.
		210
		211	See also the section *ENCODING/CODESET FLAG NOTES* later in this
		212	document.
150		213
151	The main use for this flag is efficiently encoding binary data as	214	The main use for this flag is efficiently encoding binary data as
152	JSON text, as most octets will not be escaped, resulting in a	215	JSON text, as most octets will not be escaped, resulting in a
153	smaller encoded size. The disadvantage is that the resulting JSON	216	smaller encoded size. The disadvantage is that the resulting JSON
154	text is encoded in latin1 (and must correctly be treated as such	217	text is encoded in latin1 (and must correctly be treated as such
155	when storing and transfering), a rare encoding for JSON. It is	218	when storing and transferring), a rare encoding for JSON. It is
156	therefore most useful when you want to store data structures known	219	therefore most useful when you want to store data structures known
157	to contain binary data efficiently in files or databases, not when	220	to contain binary data efficiently in files or databases, not when
158	talking to other JSON encoders/decoders.	221	talking to other JSON encoders/decoders.
159		222
160	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	223	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
161	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	224	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
162		225
163	$json = $json->utf8 ([$enable])	226	$json = $json->utf8 ([$enable])
		227	$enabled = $json->get_utf8
164	If $enable is true (or missing), then the "encode" method will	228	If $enable is true (or missing), then the "encode" method will
165	encode the JSON result into UTF-8, as required by many protocols,	229	encode the JSON result into UTF-8, as required by many protocols,
166	while the "decode" method expects to be handled an UTF-8-encoded	230	while the "decode" method expects to be handled an UTF-8-encoded
167	string. Please note that UTF-8-encoded strings do not contain any	231	string. Please note that UTF-8-encoded strings do not contain any
168	characters outside the range 0..255, they are thus useful for	232	characters outside the range 0..255, they are thus useful for
169	bytewise/binary I/O. In future versions, enabling this option might	233	bytewise/binary I/O. In future versions, enabling this option might
170	enable autodetection of the UTF-16 and UTF-32 encoding families, as	234	enable autodetection of the UTF-16 and UTF-32 encoding families, as
171	described in RFC4627.	235	described in RFC4627.
172		236
173	If $enable is false, then the "encode" method will return the JSON	237	If $enable is false, then the "encode" method will return the JSON
174	string as a (non-encoded) unicode string, while "decode" expects	238	string as a (non-encoded) Unicode string, while "decode" expects
175	thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or	239	thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
176	UTF-16) needs to be done yourself, e.g. using the Encode module.	240	UTF-16) needs to be done yourself, e.g. using the Encode module.
		241
		242	See also the section *ENCODING/CODESET FLAG NOTES* later in this
		243	document.
177		244
178	Example, output UTF-16BE-encoded JSON:	245	Example, output UTF-16BE-encoded JSON:
179		246
180	use Encode;	247	use Encode;
181	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	248	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
200	2	267	2
201	]	268	]
202	}	269	}
203		270
204	$json = $json->indent ([$enable])	271	$json = $json->indent ([$enable])
		272	$enabled = $json->get_indent
205	If $enable is true (or missing), then the "encode" method will use a	273	If $enable is true (or missing), then the "encode" method will use a
206	multiline format as output, putting every array member or	274	multiline format as output, putting every array member or
207	object/hash key-value pair into its own line, identing them	275	object/hash key-value pair into its own line, indenting them
208	properly.	276	properly.
209		277
210	If $enable is false, no newlines or indenting will be produced, and	278	If $enable is false, no newlines or indenting will be produced, and
211	the resulting JSON text is guarenteed not to contain any "newlines".	279	the resulting JSON text is guaranteed not to contain any "newlines".
212		280
213	This setting has no effect when decoding JSON texts.	281	This setting has no effect when decoding JSON texts.
214		282
215	$json = $json->space_before ([$enable])	283	$json = $json->space_before ([$enable])
		284	$enabled = $json->get_space_before
216	If $enable is true (or missing), then the "encode" method will add	285	If $enable is true (or missing), then the "encode" method will add
217	an extra optional space before the ":" separating keys from values	286	an extra optional space before the ":" separating keys from values
218	in JSON objects.	287	in JSON objects.
219		288
220	If $enable is false, then the "encode" method will not add any extra	289	If $enable is false, then the "encode" method will not add any extra
…		…
226	Example, space_before enabled, space_after and indent disabled:	295	Example, space_before enabled, space_after and indent disabled:
227		296
228	{"key" :"value"}	297	{"key" :"value"}
229		298
230	$json = $json->space_after ([$enable])	299	$json = $json->space_after ([$enable])
		300	$enabled = $json->get_space_after
231	If $enable is true (or missing), then the "encode" method will add	301	If $enable is true (or missing), then the "encode" method will add
232	an extra optional space after the ":" separating keys from values in	302	an extra optional space after the ":" separating keys from values in
233	JSON objects and extra whitespace after the "," separating key-value	303	JSON objects and extra whitespace after the "," separating key-value
234	pairs and array members.	304	pairs and array members.
235		305
…		…
240		310
241	Example, space_before and indent disabled, space_after enabled:	311	Example, space_before and indent disabled, space_after enabled:
242		312
243	{"key": "value"}	313	{"key": "value"}
244		314
		315	$json = $json->relaxed ([$enable])
		316	$enabled = $json->get_relaxed
		317	If $enable is true (or missing), then "decode" will accept some
		318	extensions to normal JSON syntax (see below). "encode" will not be
		319	affected in anyway. *Be aware that this option makes you accept
		320	invalid JSON texts as if they were valid!*. I suggest only to use
		321	this option to parse application-specific files written by humans
		322	(configuration files, resource files etc.)
		323
		324	If $enable is false (the default), then "decode" will only accept
		325	valid JSON texts.
		326
		327	Currently accepted extensions are:
		328
		329	* list items can have an end-comma
		330
		331	JSON *separates* array elements and key-value pairs with commas.
		332	This can be annoying if you write JSON texts manually and want
		333	to be able to quickly append elements, so this extension accepts
		334	comma at the end of such items not just between them:
		335
		336	[
		337	1,
		338	2, <- this comma not normally allowed
		339	]
		340	{
		341	"k1": "v1",
		342	"k2": "v2", <- this comma not normally allowed
		343	}
		344
		345	* shell-style '#'-comments
		346
		347	Whenever JSON allows whitespace, shell-style comments are
		348	additionally allowed. They are terminated by the first
		349	carriage-return or line-feed character, after which more
		350	white-space and comments are allowed.
		351
		352	[
		353	1, # this comment not allowed in JSON
		354	# neither this one...
		355	]
		356
245	$json = $json->canonical ([$enable])	357	$json = $json->canonical ([$enable])
		358	$enabled = $json->get_canonical
246	If $enable is true (or missing), then the "encode" method will	359	If $enable is true (or missing), then the "encode" method will
247	output JSON objects by sorting their keys. This is adding a	360	output JSON objects by sorting their keys. This is adding a
248	comparatively high overhead.	361	comparatively high overhead.
249		362
250	If $enable is false, then the "encode" method will output key-value	363	If $enable is false, then the "encode" method will output key-value
251	pairs in the order Perl stores them (which will likely change	364	pairs in the order Perl stores them (which will likely change
252	between runs of the same script).	365	between runs of the same script, and can change even within the same
		366	run from 5.18 onwards).
253		367
254	This option is useful if you want the same data structure to be	368	This option is useful if you want the same data structure to be
255	encoded as the same JSON text (given the same overall settings). If	369	encoded as the same JSON text (given the same overall settings). If
256	it is disabled, the same hash migh be encoded differently even if	370	it is disabled, the same hash might be encoded differently even if
257	contains the same data, as key-value pairs have no inherent ordering	371	contains the same data, as key-value pairs have no inherent ordering
258	in Perl.	372	in Perl.
259		373
260	This setting has no effect when decoding JSON texts.	374	This setting has no effect when decoding JSON texts.
261		375
		376	This setting has currently no effect on tied hashes.
		377
262	$json = $json->allow_nonref ([$enable])	378	$json = $json->allow_nonref ([$enable])
		379	$enabled = $json->get_allow_nonref
263	If $enable is true (or missing), then the "encode" method can	380	If $enable is true (or missing), then the "encode" method can
264	convert a non-reference into its corresponding string, number or	381	convert a non-reference into its corresponding string, number or
265	null JSON value, which is an extension to RFC4627. Likewise,	382	null JSON value, which is an extension to RFC4627. Likewise,
266	"decode" will accept those JSON values instead of croaking.	383	"decode" will accept those JSON values instead of croaking.
267		384
…		…
274	"allow_nonref", resulting in an invalid JSON text:	391	"allow_nonref", resulting in an invalid JSON text:
275		392
276	JSON::XS->new->allow_nonref->encode ("Hello, World!")	393	JSON::XS->new->allow_nonref->encode ("Hello, World!")
277	=> "Hello, World!"	394	=> "Hello, World!"
278		395
		396	$json = $json->allow_unknown ([$enable])
		397	$enabled = $json->get_allow_unknown
		398	If $enable is true (or missing), then "encode" will *not* throw an
		399	exception when it encounters values it cannot represent in JSON (for
		400	example, filehandles) but instead will encode a JSON "null" value.
		401	Note that blessed objects are not included here and are handled
		402	separately by c<allow_nonref>.
		403
		404	If $enable is false (the default), then "encode" will throw an
		405	exception when it encounters anything it cannot encode as JSON.
		406
		407	This option does not affect "decode" in any way, and it is
		408	recommended to leave it off unless you know your communications
		409	partner.
		410
279	$json = $json->allow_blessed ([$enable])	411	$json = $json->allow_blessed ([$enable])
		412	$enabled = $json->get_allow_blessed
		413	See "OBJECT SERIALISATION" for details.
		414
280	If $enable is true (or missing), then the "encode" method will not	415	If $enable is true (or missing), then the "encode" method will not
281	barf when it encounters a blessed reference. Instead, the value of	416	barf when it encounters a blessed reference that it cannot convert
282	the convert_blessed option will decide wether "null"	417	otherwise. Instead, a JSON "null" value is encoded instead of the
283	("convert_blessed" disabled or no "to_json" method found) or a	418	object.
284	representation of the object ("convert_blessed" enabled and
285	"to_json" method found) is being encoded. Has no effect on "decode".
286		419
287	If $enable is false (the default), then "encode" will throw an	420	If $enable is false (the default), then "encode" will throw an
288	exception when it encounters a blessed object.	421	exception when it encounters a blessed object that it cannot convert
		422	otherwise.
		423
		424	This setting has no effect on "decode".
289		425
290	$json = $json->convert_blessed ([$enable])	426	$json = $json->convert_blessed ([$enable])
		427	$enabled = $json->get_convert_blessed
		428	See "OBJECT SERIALISATION" for details.
		429
291	If $enable is true (or missing), then "encode", upon encountering a	430	If $enable is true (or missing), then "encode", upon encountering a
292	blessed object, will check for the availability of the "TO_JSON"	431	blessed object, will check for the availability of the "TO_JSON"
293	method on the object's class. If found, it will be called in scalar	432	method on the object's class. If found, it will be called in scalar
294	context and the resulting scalar will be encoded instead of the	433	context and the resulting scalar will be encoded instead of the
295	object. If no "TO_JSON" method is found, the value of	434	object.
296	"allow_blessed" will decide what to do.
297		435
298	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"	436	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
299	returns other blessed objects, those will be handled in the same	437	returns other blessed objects, those will be handled in the same
300	way. "TO_JSON" must take care of not causing an endless recursion	438	way. "TO_JSON" must take care of not causing an endless recursion
301	cycle (== crash) in this case. The name of "TO_JSON" was chosen	439	cycle (== crash) in this case. The name of "TO_JSON" was chosen
302	because other methods called by the Perl core (== not by the user of	440	because other methods called by the Perl core (== not by the user of
303	the object) are usually in upper case letters and to avoid	441	the object) are usually in upper case letters and to avoid
304	collisions with the "to_json" function.	442	collisions with any "to_json" function or method.
305		443
306	This setting does not yet influence "decode" in any way, but in the	444	If $enable is false (the default), then "encode" will not consider
307	future, global hooks might get installed that influence "decode" and	445	this type of conversion.
308	are enabled by this setting.
309		446
310	If $enable is false, then the "allow_blessed" setting will decide	447	This setting has no effect on "decode".
311	what to do when a blessed object is found.	448
		449	$json = $json->allow_tags ([$enable])
		450	$enabled = $json->allow_tags
		451	See "OBJECT SERIALISATION" for details.
		452
		453	If $enable is true (or missing), then "encode", upon encountering a
		454	blessed object, will check for the availability of the "FREEZE"
		455	method on the object's class. If found, it will be used to serialise
		456	the object into a nonstandard tagged JSON value (that JSON decoders
		457	cannot decode).
		458
		459	It also causes "decode" to parse such tagged JSON values and
		460	deserialise them via a call to the "THAW" method.
		461
		462	If $enable is false (the default), then "encode" will not consider
		463	this type of conversion, and tagged JSON values will cause a parse
		464	error in "decode", as if tags were not part of the grammar.
312		465
313	$json = $json->filter_json_object ([$coderef->($hashref)])	466	$json = $json->filter_json_object ([$coderef->($hashref)])
314	When $coderef is specified, it will be called from "decode" each	467	When $coderef is specified, it will be called from "decode" each
315	time it decodes a JSON object. The only argument is a reference to	468	time it decodes a JSON object. The only argument is a reference to
316	the newly-created hash. If the code references returns a single	469	the newly-created hash. If the code references returns a single
…		…
350		503
351	As this callback gets called less often then the	504	As this callback gets called less often then the
352	"filter_json_object" one, decoding speed will not usually suffer as	505	"filter_json_object" one, decoding speed will not usually suffer as
353	much. Therefore, single-key objects make excellent targets to	506	much. Therefore, single-key objects make excellent targets to
354	serialise Perl objects into, especially as single-key JSON objects	507	serialise Perl objects into, especially as single-key JSON objects
355	are as close to the type-tagged value concept as JSON gets (its	508	are as close to the type-tagged value concept as JSON gets (it's
356	basically an ID/VALUE tuple). Of course, JSON does not support this	509	basically an ID/VALUE tuple). Of course, JSON does not support this
357	in any way, so you need to make sure your data never looks like a	510	in any way, so you need to make sure your data never looks like a
358	serialised Perl hash.	511	serialised Perl hash.
359		512
360	Typical names for the single object key are "__class_whatever__", or	513	Typical names for the single object key are "__class_whatever__", or
…		…
385		538
386	{ __widget__ => $self->{id} }	539	{ __widget__ => $self->{id} }
387	}	540	}
388		541
389	$json = $json->shrink ([$enable])	542	$json = $json->shrink ([$enable])
		543	$enabled = $json->get_shrink
390	Perl usually over-allocates memory a bit when allocating space for	544	Perl usually over-allocates memory a bit when allocating space for
391	strings. This flag optionally resizes strings generated by either	545	strings. This flag optionally resizes strings generated by either
392	"encode" or "decode" to their minimum size possible. This can save	546	"encode" or "decode" to their minimum size possible. This can save
393	memory when your JSON texts are either very very long or you have	547	memory when your JSON texts are either very very long or you have
394	many short strings. It will also try to downgrade any strings to	548	many short strings. It will also try to downgrade any strings to
…		…
412	converting strings that look like integers or floats into integers	566	converting strings that look like integers or floats into integers
413	or floats internally (there is no difference on the Perl level),	567	or floats internally (there is no difference on the Perl level),
414	saving space.	568	saving space.
415		569
416	$json = $json->max_depth ([$maximum_nesting_depth])	570	$json = $json->max_depth ([$maximum_nesting_depth])
		571	$max_depth = $json->get_max_depth
417	Sets the maximum nesting level (default 512) accepted while encoding	572	Sets the maximum nesting level (default 512) accepted while encoding
418	or decoding. If the JSON text or Perl data structure has an equal or	573	or decoding. If a higher nesting level is detected in JSON text or a
419	higher nesting level then this limit, then the encoder and decoder	574	Perl data structure, then the encoder and decoder will stop and
420	will stop and croak at that point.	575	croak at that point.
421		576
422	Nesting level is defined by number of hash- or arrayrefs that the	577	Nesting level is defined by number of hash- or arrayrefs that the
423	encoder needs to traverse to reach a given point or the number of	578	encoder needs to traverse to reach a given point or the number of
424	"{" or "[" characters without their matching closing parenthesis	579	"{" or "[" characters without their matching closing parenthesis
425	crossed to reach a given character in a string.	580	crossed to reach a given character in a string.
426		581
427	Setting the maximum depth to one disallows any nesting, so that	582	Setting the maximum depth to one disallows any nesting, so that
428	ensures that the object is only a single hash/object or array.	583	ensures that the object is only a single hash/object or array.
429		584
430	The argument to "max_depth" will be rounded up to the next highest
431	power of two. If no argument is given, the highest possible setting	585	If no argument is given, the highest possible setting will be used,
432	will be used, which is rarely useful.	586	which is rarely useful.
		587
		588	Note that nesting is implemented by recursion in C. The default
		589	value has been chosen to be as large as typical operating systems
		590	allow without crashing.
433		591
434	See SECURITY CONSIDERATIONS, below, for more info on why this is	592	See SECURITY CONSIDERATIONS, below, for more info on why this is
435	useful.	593	useful.
436		594
437	$json = $json->max_size ([$maximum_string_size])	595	$json = $json->max_size ([$maximum_string_size])
		596	$max_size = $json->get_max_size
438	Set the maximum length a JSON text may have (in bytes) where	597	Set the maximum length a JSON text may have (in bytes) where
439	decoding is being attempted. The default is 0, meaning no limit.	598	decoding is being attempted. The default is 0, meaning no limit.
440	When "decode" is called on a string longer then this number of	599	When "decode" is called on a string that is longer then this many
441	characters it will not attempt to decode the string but throw an	600	bytes, it will not attempt to decode the string but throw an
442	exception. This setting has no effect on "encode" (yet).	601	exception. This setting has no effect on "encode" (yet).
443		602
444	The argument to "max_size" will be rounded up to the next highest
445	power of two (so may be more than requested). If no argument is
446	given, the limit check will be deactivated (same as when 0 is	603	If no argument is given, the limit check will be deactivated (same
447	specified).	604	as when 0 is specified).
448		605
449	See SECURITY CONSIDERATIONS, below, for more info on why this is	606	See SECURITY CONSIDERATIONS, below, for more info on why this is
450	useful.	607	useful.
451		608
452	$json_text = $json->encode ($perl_scalar)	609	$json_text = $json->encode ($perl_scalar)
453	Converts the given Perl data structure (a simple scalar or a	610	Converts the given Perl value or data structure to its JSON
454	reference to a hash or array) to its JSON representation. Simple	611	representation. Croaks on error.
455	scalars will be converted into JSON string or number sequences,
456	while references to arrays become JSON arrays and references to
457	hashes become JSON objects. Undefined Perl values (e.g. "undef")
458	become JSON "null" values. Neither "true" nor "false" values will be
459	generated.
460		612
461	$perl_scalar = $json->decode ($json_text)	613	$perl_scalar = $json->decode ($json_text)
462	The opposite of "encode": expects a JSON text and tries to parse it,	614	The opposite of "encode": expects a JSON text and tries to parse it,
463	returning the resulting simple scalar or reference. Croaks on error.	615	returning the resulting simple scalar or reference. Croaks on error.
464
465	JSON numbers and strings become simple Perl scalars. JSON arrays
466	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
467	becomes 1, "false" becomes 0 and "null" becomes "undef".
468		616
469	($perl_scalar, $characters) = $json->decode_prefix ($json_text)	617	($perl_scalar, $characters) = $json->decode_prefix ($json_text)
470	This works like the "decode" method, but instead of raising an	618	This works like the "decode" method, but instead of raising an
471	exception when there is trailing garbage after the first JSON	619	exception when there is trailing garbage after the first JSON
472	object, it will silently stop parsing there and return the number of	620	object, it will silently stop parsing there and return the number of
473	characters consumed so far.	621	characters consumed so far.
474		622
475	This is useful if your JSON texts are not delimited by an outer	623	This is useful if your JSON texts are not delimited by an outer
476	protocol (which is not the brightest thing to do in the first place)
477	and you need to know where the JSON text ends.	624	protocol and you need to know where the JSON text ends.
478		625
479	JSON::XS->new->decode_prefix ("[1] the tail")	626	JSON::XS->new->decode_prefix ("[1] the tail")
480	=> ([], 3)	627	=> ([], 3)
		628
		629	INCREMENTAL PARSING
		630	In some cases, there is the need for incremental parsing of JSON texts.
		631	While this module always has to keep both JSON text and resulting Perl
		632	data structure in memory at one time, it does allow you to parse a JSON
		633	stream incrementally. It does so by accumulating text until it has a
		634	full JSON object, which it then can decode. This process is similar to
		635	using "decode_prefix" to see if a full JSON object is available, but is
		636	much more efficient (and can be implemented with a minimum of method
		637	calls).
		638
		639	JSON::XS will only attempt to parse the JSON text once it is sure it has
		640	enough text to get a decisive result, using a very simple but truly
		641	incremental parser. This means that it sometimes won't stop as early as
		642	the full parser, for example, it doesn't detect mismatched parentheses.
		643	The only thing it guarantees is that it starts decoding as soon as a
		644	syntactically valid JSON text has been seen. This means you need to set
		645	resource limits (e.g. "max_size") to ensure the parser will stop parsing
		646	in the presence if syntax errors.
		647
		648	The following methods implement this incremental parser.
		649
		650	[void, scalar or list context] = $json->incr_parse ([$string])
		651	This is the central parsing function. It can both append new text
		652	and extract objects from the stream accumulated so far (both of
		653	these functions are optional).
		654
		655	If $string is given, then this string is appended to the already
		656	existing JSON fragment stored in the $json object.
		657
		658	After that, if the function is called in void context, it will
		659	simply return without doing anything further. This can be used to
		660	add more text in as many chunks as you want.
		661
		662	If the method is called in scalar context, then it will try to
		663	extract exactly *one* JSON object. If that is successful, it will
		664	return this object, otherwise it will return "undef". If there is a
		665	parse error, this method will croak just as "decode" would do (one
		666	can then use "incr_skip" to skip the erroneous part). This is the
		667	most common way of using the method.
		668
		669	And finally, in list context, it will try to extract as many objects
		670	from the stream as it can find and return them, or the empty list
		671	otherwise. For this to work, there must be no separators between the
		672	JSON objects or arrays, instead they must be concatenated
		673	back-to-back. If an error occurs, an exception will be raised as in
		674	the scalar context case. Note that in this case, any
		675	previously-parsed JSON texts will be lost.
		676
		677	Example: Parse some JSON arrays/objects in a given string and return
		678	them.
		679
		680	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		681
		682	$lvalue_string = $json->incr_text
		683	This method returns the currently stored JSON fragment as an lvalue,
		684	that is, you can manipulate it. This *only* works when a preceding
		685	call to "incr_parse" in *scalar context* successfully returned an
		686	object. Under all other circumstances you must not call this
		687	function (I mean it. although in simple tests it might actually
		688	work, it *will* fail under real world conditions). As a special
		689	exception, you can also call this method before having parsed
		690	anything.
		691
		692	This function is useful in two cases: a) finding the trailing text
		693	after a JSON object or b) parsing multiple JSON objects separated by
		694	non-JSON text (such as commas).
		695
		696	$json->incr_skip
		697	This will reset the state of the incremental parser and will remove
		698	the parsed text from the input buffer so far. This is useful after
		699	"incr_parse" died, in which case the input buffer and incremental
		700	parser state is left unchanged, to skip the text parsed so far and
		701	to reset the parse state.
		702
		703	The difference to "incr_reset" is that only text until the parse
		704	error occurred is removed.
		705
		706	$json->incr_reset
		707	This completely resets the incremental parser, that is, after this
		708	call, it will be as if the parser had never parsed anything.
		709
		710	This is useful if you want to repeatedly parse JSON objects and want
		711	to ignore any trailing data, which means you have to reset the
		712	parser after each successful decode.
		713
		714	LIMITATIONS
		715	All options that affect decoding are supported, except "allow_nonref".
		716	The reason for this is that it cannot be made to work sensibly: JSON
		717	objects and arrays are self-delimited, i.e. you can concatenate them
		718	back to back and still decode them perfectly. This does not hold true
		719	for JSON numbers, however.
		720
		721	For example, is the string 1 a single JSON number, or is it simply the
		722	start of 12? Or is 12 a single JSON number, or the concatenation of 1
		723	and 2? In neither case you can tell, and this is why JSON::XS takes the
		724	conservative route and disallows this case.
		725
		726	EXAMPLES
		727	Some examples will make all this clearer. First, a simple example that
		728	works similarly to "decode_prefix": We want to decode the JSON object at
		729	the start of a string and identify the portion after the JSON object:
		730
		731	my $text = "[1,2,3] hello";
		732
		733	my $json = new JSON::XS;
		734
		735	my $obj = $json->incr_parse ($text)
		736	or die "expected JSON object or array at beginning of string";
		737
		738	my $tail = $json->incr_text;
		739	# $tail now contains " hello"
		740
		741	Easy, isn't it?
		742
		743	Now for a more complicated example: Imagine a hypothetical protocol
		744	where you read some requests from a TCP stream, and each request is a
		745	JSON array, without any separation between them (in fact, it is often
		746	useful to use newlines as "separators", as these get interpreted as
		747	whitespace at the start of the JSON text, which makes it possible to
		748	test said protocol with "telnet"...).
		749
		750	Here is how you'd do it (it is trivial to write this in an event-based
		751	manner):
		752
		753	my $json = new JSON::XS;
		754
		755	# read some data from the socket
		756	while (sysread $socket, my $buf, 4096) {
		757
		758	# split and decode as many requests as possible
		759	for my $request ($json->incr_parse ($buf)) {
		760	# act on the $request
		761	}
		762	}
		763
		764	Another complicated example: Assume you have a string with JSON objects
		765	or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
		766	[3]"). To parse them, we have to skip the commas between the JSON texts,
		767	and here is where the lvalue-ness of "incr_text" comes in useful:
		768
		769	my $text = "[1],[2], [3]";
		770	my $json = new JSON::XS;
		771
		772	# void context, so no parsing done
		773	$json->incr_parse ($text);
		774
		775	# now extract as many objects as possible. note the
		776	# use of scalar context so incr_text can be called.
		777	while (my $obj = $json->incr_parse) {
		778	# do something with $obj
		779
		780	# now skip the optional comma
		781	$json->incr_text =~ s/^ \s* , //x;
		782	}
		783
		784	Now lets go for a very complex example: Assume that you have a gigantic
		785	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		786	but you cannot load it into memory fully (this has actually happened in
		787	the real world :).
		788
		789	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		790	can still help you: You implement a (very simple) array parser and let
		791	JSON decode the array elements, which are all full JSON objects on their
		792	own (this wouldn't work if the array elements could be JSON numbers, for
		793	example):
		794
		795	my $json = new JSON::XS;
		796
		797	# open the monster
		798	open my $fh, "<bigfile.json"
		799	or die "bigfile: $!";
		800
		801	# first parse the initial "["
		802	for (;;) {
		803	sysread $fh, my $buf, 65536
		804	or die "read error: $!";
		805	$json->incr_parse ($buf); # void context, so no parsing
		806
		807	# Exit the loop once we found and removed(!) the initial "[".
		808	# In essence, we are (ab-)using the $json object as a simple scalar
		809	# we append data to.
		810	last if $json->incr_text =~ s/^ \s* \[ //x;
		811	}
		812
		813	# now we have the skipped the initial "[", so continue
		814	# parsing all the elements.
		815	for (;;) {
		816	# in this loop we read data until we got a single JSON object
		817	for (;;) {
		818	if (my $obj = $json->incr_parse) {
		819	# do something with $obj
		820	last;
		821	}
		822
		823	# add more data
		824	sysread $fh, my $buf, 65536
		825	or die "read error: $!";
		826	$json->incr_parse ($buf); # void context, so no parsing
		827	}
		828
		829	# in this loop we read data until we either found and parsed the
		830	# separating "," between elements, or the final "]"
		831	for (;;) {
		832	# first skip whitespace
		833	$json->incr_text =~ s/^\s*//;
		834
		835	# if we find "]", we are done
		836	if ($json->incr_text =~ s/^\]//) {
		837	print "finished.\n";
		838	exit;
		839	}
		840
		841	# if we find ",", we can continue with the next element
		842	if ($json->incr_text =~ s/^,//) {
		843	last;
		844	}
		845
		846	# if we find anything else, we have a parse error!
		847	if (length $json->incr_text) {
		848	die "parse error near ", $json->incr_text;
		849	}
		850
		851	# else add more data
		852	sysread $fh, my $buf, 65536
		853	or die "read error: $!";
		854	$json->incr_parse ($buf); # void context, so no parsing
		855	}
		856
		857	This is a complex example, but most of the complexity comes from the
		858	fact that we are trying to be correct (bear with me if I am wrong, I
		859	never ran the above example :).
481		860
482	MAPPING	861	MAPPING
483	This section describes how JSON::XS maps Perl values to JSON values and	862	This section describes how JSON::XS maps Perl values to JSON values and
484	vice versa. These mappings are designed to "do the right thing" in most	863	vice versa. These mappings are designed to "do the right thing" in most
485	circumstances automatically, preserving round-tripping characteristics	864	circumstances automatically, preserving round-tripping characteristics
486	(what you put in comes out as something equivalent).	865	(what you put in comes out as something equivalent).
487		866
488	For the more enlightened: note that in the following descriptions,	867	For the more enlightened: note that in the following descriptions,
489	lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl*	868	lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
490	refers to the abstract Perl language itself.	869	refers to the abstract Perl language itself.
491		870
492	JSON -> PERL	871	JSON -> PERL
493	object	872	object
494	A JSON object becomes a reference to a hash in Perl. No ordering of	873	A JSON object becomes a reference to a hash in Perl. No ordering of
495	object keys is preserved (JSON does not preserver object key	874	object keys is preserved (JSON does not preserve object key ordering
496	ordering itself).	875	itself).
497		876
498	array	877	array
499	A JSON array becomes a reference to an array in Perl.	878	A JSON array becomes a reference to an array in Perl.
500		879
501	string	880	string
502	A JSON string becomes a string scalar in Perl - Unicode codepoints	881	A JSON string becomes a string scalar in Perl - Unicode codepoints
503	in JSON are represented by the same codepoints in the Perl string,	882	in JSON are represented by the same codepoints in the Perl string,
504	so no manual decoding is necessary.	883	so no manual decoding is necessary.
505		884
506	number	885	number
507	A JSON number becomes either an integer or numeric (floating point)	886	A JSON number becomes either an integer, numeric (floating point) or
508	scalar in perl, depending on its range and any fractional parts. On	887	string scalar in perl, depending on its range and any fractional
509	the Perl level, there is no difference between those as Perl handles	888	parts. On the Perl level, there is no difference between those as
510	all the conversion details, but an integer may take slightly less	889	Perl handles all the conversion details, but an integer may take
511	memory and might represent more values exactly than (floating point)	890	slightly less memory and might represent more values exactly than
		891	floating point numbers.
		892
		893	If the number consists of digits only, JSON::XS will try to
		894	represent it as an integer value. If that fails, it will try to
		895	represent it as a numeric (floating point) value if that is possible
		896	without loss of precision. Otherwise it will preserve the number as
		897	a string value (in which case you lose roundtripping ability, as the
		898	JSON number will be re-encoded to a JSON string).
		899
		900	Numbers containing a fractional or exponential part will always be
		901	represented as numeric (floating point) values, possibly at a loss
		902	of precision (in which case you might lose perfect roundtripping
		903	ability, but the JSON number will still be re-encoded as a JSON
512	numbers.	904	number).
		905
		906	Note that precision is not accuracy - binary floating point values
		907	cannot represent most decimal fractions exactly, and when converting
		908	from and to floating point, JSON::XS only guarantees precision up to
		909	but not including the least significant bit.
513		910
514	true, false	911	true, false
515	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",	912	These JSON atoms become "Types::Serialiser::true" and
516	respectively. They are overloaded to act almost exactly like the	913	"Types::Serialiser::false", respectively. They are overloaded to act
517	numbers 1 and 0. You can check wether a scalar is a JSON boolean by	914	almost exactly like the numbers 1 and 0. You can check whether a
518	using the "JSON::XS::is_bool" function.	915	scalar is a JSON boolean by using the "Types::Serialiser::is_bool"
		916	function (after "use Types::Serialier", of course).
519		917
520	null	918	null
521	A JSON null atom becomes "undef" in Perl.	919	A JSON null atom becomes "undef" in Perl.
		920
		921	shell-style comments ("# *text*")
		922	As a nonstandard extension to the JSON syntax that is enabled by the
		923	"relaxed" setting, shell-style comments are allowed. They can start
		924	anywhere outside strings and go till the end of the line.
		925
		926	tagged values ("(*tag*)*value*").
		927	Another nonstandard extension to the JSON syntax, enabled with the
		928	"allow_tags" setting, are tagged values. In this implementation, the
		929	*tag* must be a perl package/class name encoded as a JSON string,
		930	and the *value* must be a JSON array encoding optional constructor
		931	arguments.
		932
		933	See "OBJECT SERIALISATION", below, for details.
522		934
523	PERL -> JSON	935	PERL -> JSON
524	The mapping from Perl to JSON is slightly more difficult, as Perl is a	936	The mapping from Perl to JSON is slightly more difficult, as Perl is a
525	truly typeless language, so we can only guess which JSON type is meant	937	truly typeless language, so we can only guess which JSON type is meant
526	by a Perl value.	938	by a Perl value.
527		939
528	hash references	940	hash references
529	Perl hash references become JSON objects. As there is no inherent	941	Perl hash references become JSON objects. As there is no inherent
530	ordering in hash keys (or JSON objects), they will usually be	942	ordering in hash keys (or JSON objects), they will usually be
531	encoded in a pseudo-random order that can change between runs of the	943	encoded in a pseudo-random order. JSON::XS can optionally sort the
532	same program but stays generally the same within a single run of a	944	hash keys (determined by the *canonical* flag), so the same
533	program. JSON::XS can optionally sort the hash keys (determined by	945	datastructure will serialise to the same JSON text (given same
534	the *canonical* flag), so the same datastructure will serialise to	946	settings and version of JSON::XS), but this incurs a runtime
535	the same JSON text (given same settings and version of JSON::XS),	947	overhead and is only rarely useful, e.g. when you want to compare
536	but this incurs a runtime overhead and is only rarely useful, e.g.	948	some JSON text against another for equality.
537	when you want to compare some JSON text against another for
538	equality.
539		949
540	array references	950	array references
541	Perl array references become JSON arrays.	951	Perl array references become JSON arrays.
542		952
543	other references	953	other references
544	Other unblessed references are generally not allowed and will cause	954	Other unblessed references are generally not allowed and will cause
545	an exception to be thrown, except for references to the integers 0	955	an exception to be thrown, except for references to the integers 0
546	and 1, which get turned into "false" and "true" atoms in JSON. You	956	and 1, which get turned into "false" and "true" atoms in JSON.
547	can also use "JSON::XS::false" and "JSON::XS::true" to improve	957
		958	Since "JSON::XS" uses the boolean model from Types::Serialiser, you
		959	can also "use Types::Serialiser" and then use
		960	"Types::Serialiser::false" and "Types::Serialiser::true" to improve
548	readability.	961	readability.
549		962
		963	use Types::Serialiser;
550	to_json [\0,JSON::XS::true] # yields [false,true]	964	encode_json [\0, Types::Serialiser::true] # yields [false,true]
551		965
552	JSON::XS::true, JSON::XS::false	966	Types::Serialiser::true, Types::Serialiser::false
553	These special values become JSON true and JSON false values,	967	These special values from the Types::Serialiser module become JSON
554	respectively. You cna alos use "\1" and "\0" directly if you want.	968	true and JSON false values, respectively. You can also use "\1" and
		969	"\0" directly if you want.
555		970
556	blessed objects	971	blessed objects
557	Blessed objects are not allowed. JSON::XS currently tries to encode	972	Blessed objects are not directly representable in JSON, but
558	their underlying representation (hash- or arrayref), but this	973	"JSON::XS" allows various ways of handling objects. See "OBJECT
559	behaviour might change in future versions.	974	SERIALISATION", below, for details.
560		975
561	simple scalars	976	simple scalars
562	Simple Perl scalars (any scalar that is not a reference) are the	977	Simple Perl scalars (any scalar that is not a reference) are the
563	most difficult objects to encode: JSON::XS will encode undefined	978	most difficult objects to encode: JSON::XS will encode undefined
564	scalars as JSON null value, scalars that have last been used in a	979	scalars as JSON "null" values, scalars that have last been used in a
565	string context before encoding as JSON strings and anything else as	980	string context before encoding as JSON strings, and anything else as
566	number value:	981	number value:
567		982
568	# dump as number	983	# dump as number
569	to_json [2] # yields [2]	984	encode_json [2] # yields [2]
570	to_json [-3.0e17] # yields [-3e+17]	985	encode_json [-3.0e17] # yields [-3e+17]
571	my $value = 5; to_json [$value] # yields [5]	986	my $value = 5; encode_json [$value] # yields [5]
572		987
573	# used as string, so dump as string	988	# used as string, so dump as string
574	print $value;	989	print $value;
575	to_json [$value] # yields ["5"]	990	encode_json [$value] # yields ["5"]
576		991
577	# undef becomes null	992	# undef becomes null
578	to_json [undef] # yields [null]	993	encode_json [undef] # yields [null]
579		994
580	You can force the type to be a string by stringifying it:	995	You can force the type to be a JSON string by stringifying it:
581		996
582	my $x = 3.1; # some variable containing a number	997	my $x = 3.1; # some variable containing a number
583	"$x"; # stringified	998	"$x"; # stringified
584	$x .= ""; # another, more awkward way to stringify	999	$x .= ""; # another, more awkward way to stringify
585	print $x; # perl does it for you, too, quite often	1000	print $x; # perl does it for you, too, quite often
586		1001
587	You can force the type to be a number by numifying it:	1002	You can force the type to be a JSON number by numifying it:
588		1003
589	my $x = "3"; # some variable containing a string	1004	my $x = "3"; # some variable containing a string
590	$x += 0; # numify it, ensuring it will be dumped as a number	1005	$x += 0; # numify it, ensuring it will be dumped as a number
591	$x *= 1; # same thing, the choise is yours.	1006	$x *= 1; # same thing, the choice is yours.
592		1007
593	You can not currently output JSON booleans or force the type in	1008	You can not currently force the type in other, less obscure, ways.
594	other, less obscure, ways. Tell me if you need this capability.	1009	Tell me if you need this capability (but don't forget to explain why
		1010	it's needed :).
595		1011
596	COMPARISON	1012	Note that numerical precision has the same meaning as under Perl (so
597	As already mentioned, this module was created because none of the	1013	binary to decimal conversion follows the same rules as in Perl,
598	existing JSON modules could be made to work correctly. First I will	1014	which can differ to other languages). Also, your perl interpreter
599	describe the problems (or pleasures) I encountered with various existing	1015	might expose extensions to the floating point numbers of your
600	JSON modules, followed by some benchmark values. JSON::XS was designed	1016	platform, such as infinities or NaN's - these cannot be represented
601	not to suffer from any of these problems or limitations.	1017	in JSON, and it is an error to pass those in.
602		1018
603	JSON 1.07	1019	OBJECT SERIALISATION
604	Slow (but very portable, as it is written in pure Perl).	1020	As JSON cannot directly represent Perl objects, you have to choose
		1021	between a pure JSON representation (without the ability to deserialise
		1022	the object automatically again), and a nonstandard extension to the JSON
		1023	syntax, tagged values.
605		1024
606	Undocumented/buggy Unicode handling (how JSON handles unicode values	1025	SERIALISATION
607	is undocumented. One can get far by feeding it unicode strings and	1026	What happens when "JSON::XS" encounters a Perl object depends on the
608	doing en-/decoding oneself, but unicode escapes are not working	1027	"allow_blessed", "convert_blessed" and "allow_tags" settings, which are
		1028	used in this order:
		1029
		1030	1. "allow_tags" is enabled and the object has a "FREEZE" method.
		1031	In this case, "JSON::XS" uses the Types::Serialiser object
		1032	serialisation protocol to create a tagged JSON value, using a
		1033	nonstandard extension to the JSON syntax.
		1034
		1035	This works by invoking the "FREEZE" method on the object, with the
		1036	first argument being the object to serialise, and the second
		1037	argument being the constant string "JSON" to distinguish it from
		1038	other serialisers.
		1039
		1040	The "FREEZE" method can return any number of values (i.e. zero or
		1041	more). These values and the paclkage/classname of the object will
		1042	then be encoded as a tagged JSON value in the following format:
		1043
		1044	("classname")[FREEZE return values...]
		1045
		1046	e.g.:
		1047
		1048	("URI")["http://www.google.com/"]
		1049	("MyDate")[2013,10,29]
		1050	("ImageData::JPEG")["Z3...VlCg=="]
		1051
		1052	For example, the hypothetical "My::Object" "FREEZE" method might use
		1053	the objects "type" and "id" members to encode the object:
		1054
		1055	sub My::Object::FREEZE {
		1056	my ($self, $serialiser) = @_;
		1057
		1058	($self->{type}, $self->{id})
		1059	}
		1060
		1061	2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
		1062	In this case, the "TO_JSON" method of the object is invoked in
		1063	scalar context. It must return a single scalar that can be directly
		1064	encoded into JSON. This scalar replaces the object in the JSON text.
		1065
		1066	For example, the following "TO_JSON" method will convert all URI
		1067	objects to JSON strings when serialised. The fatc that these values
		1068	originally were URI objects is lost.
		1069
		1070	sub URI::TO_JSON {
		1071	my ($uri) = @_;
		1072	$uri->as_string
		1073	}
		1074
		1075	3. "allow_blessed" is enabled.
		1076	The object will be serialised as a JSON null value.
		1077
		1078	4. none of the above
		1079	If none of the settings are enabled or the respective methods are
		1080	missing, "JSON::XS" throws an exception.
		1081
		1082	DESERIALISATION
		1083	For deserialisation there are only two cases to consider: either
		1084	nonstandard tagging was used, in which case "allow_tags" decides, or
		1085	objects cannot be automatically be deserialised, in which case you can
		1086	use postprocessing or the "filter_json_object" or
		1087	"filter_json_single_key_object" callbacks to get some real objects our
		1088	of your JSON.
		1089
		1090	This section only considers the tagged value case: I a tagged JSON
		1091	object is encountered during decoding and "allow_tags" is disabled, a
		1092	parse error will result (as if tagged values were not part of the
		1093	grammar).
		1094
		1095	If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of
		1096	the package/classname used during serialisation (it will not attempt to
		1097	load the package as a Perl module). If there is no such method, the
		1098	decoding will fail with an error.
		1099
		1100	Otherwise, the "THAW" method is invoked with the classname as first
		1101	argument, the constant string "JSON" as second argument, and all the
		1102	values from the JSON array (the values originally returned by the
		1103	"FREEZE" method) as remaining arguments.
		1104
		1105	The method must then return the object. While technically you can return
		1106	any Perl scalar, you might have to enable the "enable_nonref" setting to
		1107	make that work in all cases, so better return an actual blessed
		1108	reference.
		1109
		1110	As an example, let's implement a "THAW" function that regenerates the
		1111	"My::Object" from the "FREEZE" example earlier:
		1112
		1113	sub My::Object::THAW {
		1114	my ($class, $serialiser, $type, $id) = @_;
		1115
		1116	$class->new (type => $type, id => $id)
		1117	}
		1118
		1119	ENCODING/CODESET FLAG NOTES
		1120	The interested reader might have seen a number of flags that signify
		1121	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
		1122	some confusion on what these do, so here is a short comparison:
		1123
		1124	"utf8" controls whether the JSON text created by "encode" (and expected
		1125	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
		1126	control whether "encode" escapes character values outside their
		1127	respective codeset range. Neither of these flags conflict with each
		1128	other, although some combinations make less sense than others.
		1129
		1130	Care has been taken to make all flags symmetrical with respect to
		1131	"encode" and "decode", that is, texts encoded with any combination of
		1132	these flag values will be correctly decoded when the same flags are used
		1133	- in general, if you use different flag settings while encoding vs. when
		1134	decoding you likely have a bug somewhere.
		1135
		1136	Below comes a verbose discussion of these flags. Note that a "codeset"
		1137	is simply an abstract set of character-codepoint pairs, while an
		1138	encoding takes those codepoint numbers and *encodes* them, in our case
		1139	into octets. Unicode is (among other things) a codeset, UTF-8 is an
		1140	encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
		1141	encodings at the same time, which can be confusing.
		1142
		1143	"utf8" flag disabled
		1144	When "utf8" is disabled (the default), then "encode"/"decode"
		1145	generate and expect Unicode strings, that is, characters with high
		1146	ordinal Unicode values (> 255) will be encoded as such characters,
		1147	and likewise such characters are decoded as-is, no changes to them
		1148	will be done, except "(re-)interpreting" them as Unicode codepoints
		1149	or Unicode characters, respectively (to Perl, these are the same
		1150	thing in strings unless you do funny/weird/dumb stuff).
		1151
		1152	This is useful when you want to do the encoding yourself (e.g. when
		1153	you want to have UTF-16 encoded JSON texts) or when some other layer
		1154	does the encoding for you (for example, when printing to a terminal
		1155	using a filehandle that transparently encodes to UTF-8 you certainly
		1156	do NOT want to UTF-8 encode your data first and have Perl encode it
		1157	another time).
		1158
		1159	"utf8" flag enabled
		1160	If the "utf8"-flag is enabled, "encode"/"decode" will encode all
		1161	characters using the corresponding UTF-8 multi-byte sequence, and
		1162	will expect your input strings to be encoded as UTF-8, that is, no
		1163	"character" of the input string must have any value > 255, as UTF-8
		1164	does not allow that.
		1165
		1166	The "utf8" flag therefore switches between two modes: disabled means
		1167	you will get a Unicode string in Perl, enabled means you get an
		1168	UTF-8 encoded octet/binary string in Perl.
		1169
		1170	"latin1" or "ascii" flags enabled
		1171	With "latin1" (or "ascii") enabled, "encode" will escape characters
		1172	with ordinal values > 255 (> 127 with "ascii") and encode the
		1173	remaining characters as specified by the "utf8" flag.
		1174
		1175	If "utf8" is disabled, then the result is also correctly encoded in
		1176	those character sets (as both are proper subsets of Unicode, meaning
		1177	that a Unicode string with all character values < 256 is the same
		1178	thing as a ISO-8859-1 string, and a Unicode string with all
		1179	character values < 128 is the same thing as an ASCII string in
609	properly).	1180	Perl).
610		1181
611	No roundtripping (strings get clobbered if they look like numbers,	1182	If "utf8" is enabled, you still get a correct UTF-8-encoded string,
612	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	1183	regardless of these flags, just some more characters will be escaped
613	will decode into the number 2.	1184	using "\uXXXX" then before.
614		1185
615	JSON::PC 0.01	1186	Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
616	Very fast.	1187	encoding, while ASCII-encoded strings are. That is because the
		1188	ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
		1189	*codeset* being a subset of Unicode), while ASCII is.
617		1190
618	Undocumented/buggy Unicode handling.	1191	Surprisingly, "decode" will ignore these flags and so treat all
		1192	input values as governed by the "utf8" flag. If it is disabled, this
		1193	allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
		1194	strict subsets of Unicode. If it is enabled, you can correctly
		1195	decode UTF-8 encoded strings.
619		1196
620	No roundtripping.	1197	So neither "latin1" nor "ascii" are incompatible with the "utf8"
		1198	flag - they only govern when the JSON output engine escapes a
		1199	character or not.
621		1200
622	Has problems handling many Perl values (e.g. regex results and other	1201	The main use for "latin1" is to relatively efficiently store binary
623	magic values will make it croak).	1202	data as JSON, at the expense of breaking compatibility with most
		1203	JSON decoders.
624		1204
625	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1205	The main use for "ascii" is to force the output to not contain
626	which is not a valid JSON text.	1206	characters with values > 127, which means you can interpret the
		1207	resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
		1208	any character set and 8-bit-encoding, and still get the same data
		1209	structure back. This is useful when your channel for JSON transfer
		1210	is not 8-bit clean or the encoding might be mangled in between (e.g.
		1211	in mail), and works because ASCII is a proper subset of most 8-bit
		1212	and multibyte encodings in use in the world.
627		1213
628	Unmaintained (maintainer unresponsive for many months, bugs are not	1214	JSON and ECMAscript
629	getting fixed).	1215	JSON syntax is based on how literals are represented in javascript (the
		1216	not-standardised predecessor of ECMAscript) which is presumably why it
		1217	is called "JavaScript Object Notation".
630		1218
631	JSON::Syck 0.21	1219	However, JSON is not a subset (and also not a superset of course) of
632	Very buggy (often crashes).	1220	ECMAscript (the standard) or javascript (whatever browsers actually
		1221	implement).
633		1222
634	Very inflexible (no human-readable format supported, format pretty	1223	If you want to use javascript's "eval" function to "parse" JSON, you
635	much undocumented. I need at least a format for easy reading by	1224	might run into parse errors for valid JSON texts, or the resulting data
636	humans and a single-line compact format for use in a protocol, and	1225	structure might not be queryable:
637	preferably a way to generate ASCII-only JSON texts).
638		1226
639	Completely broken (and confusingly documented) Unicode handling	1227	One of the problems is that U+2028 and U+2029 are valid characters
640	(unicode escapes are not working properly, you need to set	1228	inside JSON strings, but are not allowed in ECMAscript string literals,
641	ImplicitUnicode to *different* values on en- and decoding to get	1229	so the following Perl fragment will not output something that can be
642	symmetric behaviour).	1230	guaranteed to be parsable by javascript's "eval":
643		1231
644	No roundtripping (simple cases work, but this depends on wether the	1232	use JSON::XS;
645	scalar value was used in a numeric context or not).
646		1233
647	Dumping hashes may skip hash values depending on iterator state.	1234	print encode_json [chr 0x2028];
648		1235
649	Unmaintained (maintainer unresponsive for many months, bugs are not	1236	The right fix for this is to use a proper JSON parser in your javascript
650	getting fixed).	1237	programs, and not rely on "eval" (see for example Douglas Crockford's
		1238	json2.js parser).
651		1239
652	Does not check input for validity (i.e. will accept non-JSON input	1240	If this is not an option, you can, as a stop-gap measure, simply encode
653	and return "something" instead of raising an exception. This is a	1241	to ASCII-only JSON:
654	security issue: imagine two banks transfering money between each
655	other using JSON. One bank might parse a given non-JSON request and
656	deduct money, while the other might reject the transaction with a
657	syntax error. While a good protocol will at least recover, that is
658	extra unnecessary work and the transaction will still not succeed).
659		1242
660	JSON::DWIW 0.04	1243	use JSON::XS;
661	Very fast. Very natural. Very nice.
662		1244
663	Undocumented unicode handling (but the best of the pack. Unicode	1245	print JSON::XS->new->ascii->encode ([chr 0x2028]);
664	escapes still don't get parsed properly).
665		1246
666	Very inflexible.	1247	Note that this will enlarge the resulting JSON text quite a bit if you
		1248	have many non-ASCII characters. You might be tempted to run some regexes
		1249	to only escape U+2028 and U+2029, e.g.:
667		1250
668	No roundtripping.	1251	# DO NOT USE THIS!
		1252	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1253	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1254	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1255	print $json;
669		1256
670	Does not generate valid JSON texts (key strings are often unquoted,	1257	Note that *this is a bad idea*: the above only works for U+2028 and
671	empty keys result in nothing being output)	1258	U+2029 and thus only for fully ECMAscript-compliant parsers. Many
		1259	existing javascript implementations, however, have issues with other
		1260	characters as well - using "eval" naively simply *will* cause problems.
672		1261
673	Does not check input for validity.	1262	Another problem is that some javascript implementations reserve some
		1263	property names for their own purposes (which probably makes them
		1264	non-ECMAscript-compliant). For example, Iceweasel reserves the
		1265	"__proto__" property name for its own purposes.
		1266
		1267	If that is a problem, you could parse try to filter the resulting JSON
		1268	output for these property strings, e.g.:
		1269
		1270	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1271
		1272	This works because "__proto__" is not valid outside of strings, so every
		1273	occurrence of ""__proto__"\s*:" must be a string used as property name.
		1274
		1275	If you know of other incompatibilities, please let me know.
674		1276
675	JSON and YAML	1277	JSON and YAML
676	You often hear that JSON is a subset (or a close subset) of YAML. This	1278	You often hear that JSON is a subset of YAML. This is, however, a mass
677	is, however, a mass hysteria and very far from the truth. In general,	1279	hysteria(*) and very far from the truth (as of the time of this
678	there is no way to configure JSON::XS to output a data structure as	1280	writing), so let me state it clearly: *in general, there is no way to
679	valid YAML.	1281	configure JSON::XS to output a data structure as valid YAML* that works
		1282	in all cases.
680		1283
681	If you really must use JSON::XS to generate YAML, you should use this	1284	If you really must use JSON::XS to generate YAML, you should use this
682	algorithm (subject to change in future versions):	1285	algorithm (subject to change in future versions):
683		1286
684	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1287	my $to_yaml = JSON::XS->new->utf8->space_after (1);
685	my $yaml = $to_yaml->encode ($ref) . "\n";	1288	my $yaml = $to_yaml->encode ($ref) . "\n";
686		1289
687	This will usually generate JSON texts that also parse as valid YAML.	1290	This will *usually* generate JSON texts that also parse as valid YAML.
688	Please note that YAML has hardcoded limits on (simple) object key	1291	Please note that YAML has hardcoded limits on (simple) object key
689	lengths that JSON doesn't have, so you should make sure that your hash	1292	lengths that JSON doesn't have and also has different and incompatible
		1293	unicode character escape syntax, so you should make sure that your hash
690	keys are noticably shorter than the 1024 characters YAML allows.	1294	keys are noticeably shorter than the 1024 "stream characters" YAML
		1295	allows and that you do not have characters with codepoint values outside
		1296	the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
		1297	sequences in strings (which JSON::XS does not *currently* generate, but
		1298	other JSON generators might).
691		1299
692	There might be other incompatibilities that I am not aware of. In	1300	There might be other incompatibilities that I am not aware of (or the
		1301	YAML specification has been changed yet again - it does so quite often).
693	general you should not try to generate YAML with a JSON generator or	1302	In general you should not try to generate YAML with a JSON generator or
694	vice versa, or try to parse JSON with a YAML parser or vice versa:	1303	vice versa, or try to parse JSON with a YAML parser or vice versa:
695	chances are high that you will run into severe interoperability	1304	chances are high that you will run into severe interoperability problems
696	problems.	1305	when you least expect it.
		1306
		1307	(*) I have been pressured multiple times by Brian Ingerson (one of the
		1308	authors of the YAML specification) to remove this paragraph, despite
		1309	him acknowledging that the actual incompatibilities exist. As I was
		1310	personally bitten by this "JSON is YAML" lie, I refused and said I
		1311	will continue to educate people about these issues, so others do not
		1312	run into the same problem again and again. After this, Brian called
		1313	me a (quote)*complete and worthless idiot*(unquote).
		1314
		1315	In my opinion, instead of pressuring and insulting people who
		1316	actually clarify issues with YAML and the wrong statements of some
		1317	of its proponents, I would kindly suggest reading the JSON spec
		1318	(which is not that difficult or long) and finally make YAML
		1319	compatible to it, and educating users about the changes, instead of
		1320	spreading lies about the real compatibility for many *years* and
		1321	trying to silence people who point out that it isn't true.
		1322
		1323	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
		1324	even though the incompatibilities have been documented (and are
		1325	known to Brian) for many years and the spec makes explicit claims
		1326	that YAML is a superset of JSON. It would be so easy to fix, but
		1327	apparently, bullying people and corrupting userdata is so much
		1328	easier.
697		1329
698	SPEED	1330	SPEED
699	It seems that JSON::XS is surprisingly fast, as shown in the following	1331	It seems that JSON::XS is surprisingly fast, as shown in the following
700	tables. They have been generated with the help of the "eg/bench" program	1332	tables. They have been generated with the help of the "eg/bench" program
701	in the JSON::XS distribution, to make it easy to compare on your own	1333	in the JSON::XS distribution, to make it easy to compare on your own
702	system.	1334	system.
703		1335
704	First comes a comparison between various modules using a very short	1336	First comes a comparison between various modules using a very short
705	single-line JSON string:	1337	single-line JSON string (also available at
		1338	<http://dist.schmorp.de/misc/json/short.json>).
706		1339
707	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1340	{"method": "handleMessage", "params": ["user1",
708	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1341	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1342	1, 0]}
709		1343
710	It shows the number of encodes/decodes per second (JSON::XS uses the	1344	It shows the number of encodes/decodes per second (JSON::XS uses the
711	functional interface, while JSON::XS/2 uses the OO interface with	1345	functional interface, while JSON::XS/2 uses the OO interface with
712	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).	1346	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
713	Higher is better:	1347	JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
		1348	the from_json method). Higher is better:
714		1349
715	Storable | 15779.925 | 14169.946 |
716	-----------+------------+------------+
717	module | encode | decode |	1350	module | encode | decode |
718	-----------|------------|------------|	1351	--------------|------------|------------|
719	JSON | 4990.842 | 4088.813 |	1352	JSON::DWIW/DS | 86302.551 | 102300.098 |
720	JSON::DWIW | 51653.990 | 71575.154 |	1353	JSON::DWIW/FJ | 86302.551 | 75983.768 |
721	JSON::PC | 65948.176 | 74631.744 |	1354	JSON::PP | 15827.562 | 6638.658 |
722	JSON::PP | 8931.652 | 3817.168 |	1355	JSON::Syck | 63358.066 | 47662.545 |
723	JSON::Syck | 24877.248 | 27776.848 |	1356	JSON::XS | 511500.488 | 511500.488 |
724	JSON::XS | 388361.481 | 227951.304 |	1357	JSON::XS/2 | 291271.111 | 388361.481 |
725	JSON::XS/2 | 227951.304 | 218453.333 |	1358	JSON::XS/3 | 361577.931 | 361577.931 |
726	JSON::XS/3 | 338250.323 | 218453.333 |	1359	Storable | 66788.280 | 265462.278 |
727	Storable | 16500.016 | 135300.129 |
728	-----------+------------+------------+	1360	--------------+------------+------------+
729		1361
730	That is, JSON::XS is about five times faster than JSON::DWIW on	1362	That is, JSON::XS is almost six times faster than JSON::DWIW on
731	encoding, about three times faster on decoding, and over fourty times	1363	encoding, about five times faster on decoding, and over thirty to
732	faster than JSON, even with pretty-printing and key sorting. It also	1364	seventy times faster than JSON's pure perl implementation. It also
733	compares favourably to Storable for small amounts of data.	1365	compares favourably to Storable for small amounts of data.
734		1366
735	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1367	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
736	search API (http://nanoref.com/yahooapis/mgPdGg):	1368	search API (<http://dist.schmorp.de/misc/json/long.json>).
737		1369
738	module | encode | decode |	1370	module | encode | decode |
739	-----------|------------|------------|	1371	--------------|------------|------------|
740	JSON | 55.260 | 34.971 |	1372	JSON::DWIW/DS | 1647.927 | 2673.916 |
741	JSON::DWIW | 825.228 | 1082.513 |	1373	JSON::DWIW/FJ | 1630.249 | 2596.128 |
742	JSON::PC | 3571.444 | 2394.829 |
743	JSON::PP | 210.987 | 32.574 |	1374	JSON::PP | 400.640 | 62.311 |
744	JSON::Syck | 552.551 | 787.544 |	1375	JSON::Syck | 1481.040 | 1524.869 |
745	JSON::XS | 5780.463 | 4854.519 |	1376	JSON::XS | 20661.596 | 9541.183 |
746	JSON::XS/2 | 3869.998 | 4798.975 |	1377	JSON::XS/2 | 10683.403 | 9416.938 |
747	JSON::XS/3 | 5862.880 | 4798.975 |	1378	JSON::XS/3 | 20661.596 | 9400.054 |
748	Storable | 4445.002 | 5235.027 |	1379	Storable | 19765.806 | 10000.725 |
749	-----------+------------+------------+	1380	--------------+------------+------------+
750		1381
751	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1382	Again, JSON::XS leads by far (except for Storable which non-surprisingly
752	decodes faster).	1383	decodes a bit faster).
753		1384
754	On large strings containing lots of high unicode characters, some	1385	On large strings containing lots of high Unicode characters, some
755	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1386	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
756	result will be broken due to missing (or wrong) unicode handling. Others	1387	result will be broken due to missing (or wrong) Unicode handling. Others
757	refuse to decode or encode properly, so it was impossible to prepare a	1388	refuse to decode or encode properly, so it was impossible to prepare a
758	fair comparison table for that case.	1389	fair comparison table for that case.
759		1390
760	SECURITY CONSIDERATIONS	1391	SECURITY CONSIDERATIONS
761	When you are using JSON in a protocol, talking to untrusted potentially	1392	When you are using JSON in a protocol, talking to untrusted potentially
…		…
765	have any buffer overflows. Obviously, this module should ensure that and	1396	have any buffer overflows. Obviously, this module should ensure that and
766	I am trying hard on making that true, but you never know.	1397	I am trying hard on making that true, but you never know.
767		1398
768	Second, you need to avoid resource-starving attacks. That means you	1399	Second, you need to avoid resource-starving attacks. That means you
769	should limit the size of JSON texts you accept, or make sure then when	1400	should limit the size of JSON texts you accept, or make sure then when
770	your resources run out, thats just fine (e.g. by using a separate	1401	your resources run out, that's just fine (e.g. by using a separate
771	process that can crash safely). The size of a JSON text in octets or	1402	process that can crash safely). The size of a JSON text in octets or
772	characters is usually a good indication of the size of the resources	1403	characters is usually a good indication of the size of the resources
773	required to decode it into a Perl structure. While JSON::XS can check	1404	required to decode it into a Perl structure. While JSON::XS can check
774	the size of the JSON text, it might be too late when you already have it	1405	the size of the JSON text, it might be too late when you already have it
775	in memory, so you might want to check the size before you accept the	1406	in memory, so you might want to check the size before you accept the
…		…
778	Third, JSON::XS recurses using the C stack when decoding objects and	1409	Third, JSON::XS recurses using the C stack when decoding objects and
779	arrays. The C stack is a limited resource: for instance, on my amd64	1410	arrays. The C stack is a limited resource: for instance, on my amd64
780	machine with 8MB of stack size I can decode around 180k nested arrays	1411	machine with 8MB of stack size I can decode around 180k nested arrays
781	but only 14k nested JSON objects (due to perl itself recursing deeply on	1412	but only 14k nested JSON objects (due to perl itself recursing deeply on
782	croak to free the temporary). If that is exceeded, the program crashes.	1413	croak to free the temporary). If that is exceeded, the program crashes.
783	to be conservative, the default nesting limit is set to 512. If your	1414	To be conservative, the default nesting limit is set to 512. If your
784	process has a smaller stack, you should adjust this setting accordingly	1415	process has a smaller stack, you should adjust this setting accordingly
785	with the "max_depth" method.	1416	with the "max_depth" method.
786		1417
787	And last but least, something else could bomb you that I forgot to think	1418	Something else could bomb you, too, that I forgot to think of. In that
788	of. In that case, you get to keep the pieces. I am always open for	1419	case, you get to keep the pieces. I am always open for hints, though...
789	hints, though...
790		1420
		1421	Also keep in mind that JSON::XS might leak contents of your Perl data
		1422	structures in its error messages, so when you serialise sensitive
		1423	information you might want to make sure that exceptions thrown by
		1424	JSON::XS will not end up in front of untrusted eyes.
		1425
791	If you are using JSON::XS to return packets to consumption by javascript	1426	If you are using JSON::XS to return packets to consumption by JavaScript
792	scripts in a browser you should have a look at	1427	scripts in a browser you should have a look at
793	<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether	1428	<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
794	you are vulnerable to some common attack vectors (which really are	1429	to see whether you are vulnerable to some common attack vectors (which
795	browser design bugs, but it is still you who will have to deal with it,	1430	really are browser design bugs, but it is still you who will have to
796	as major browser developers care only for features, not about doing	1431	deal with it, as major browser developers care only for features, not
797	security right).	1432	about getting security right).
		1433
		1434	INTEROPERABILITY WITH OTHER MODULES
		1435	"JSON::XS" uses the Types::Serialiser module to provide boolean
		1436	constants. That means that the JSON true and false values will be
		1437	comaptible to true and false values of iother modules that do the same,
		1438	such as JSON::PP and CBOR::XS.
		1439
		1440	THREADS
		1441	This module is *not* guaranteed to be thread safe and there are no plans
		1442	to change this until Perl gets thread support (as opposed to the
		1443	horribly slow so-called "threads" which are simply slow and bloated
		1444	process simulations - use fork, it's *much* faster, cheaper, better).
		1445
		1446	(It might actually work, but you have been warned).
		1447
		1448	THE PERILS OF SETLOCALE
		1449	Sometimes people avoid the Perl locale support and directly call the
		1450	system's setlocale function with "LC_ALL".
		1451
		1452	This breaks both perl and modules such as JSON::XS, as stringification
		1453	of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
		1454	might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
		1455	on perl to stringify numbers).
		1456
		1457	The solution is simple: don't call "setlocale", or use it for only those
		1458	categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
		1459
		1460	If you need "LC_NUMERIC", you should enable it only around the code that
		1461	actually needs it (avoiding stringification of numbers), and restore it
		1462	afterwards.
798		1463
799	BUGS	1464	BUGS
800	While the goal of this module is to be correct, that unfortunately does	1465	While the goal of this module is to be correct, that unfortunately does
801	not mean its bug-free, only that I think its design is bug-free. It is	1466	not mean it's bug-free, only that I think its design is bug-free. If you
802	still relatively early in its development. If you keep reporting bugs
803	they will be fixed swiftly, though.	1467	keep reporting bugs they will be fixed swiftly, though.
		1468
		1469	Please refrain from using rt.cpan.org or any other bug reporting
		1470	service. I put the contact address into my modules for a reason.
		1471
		1472	SEE ALSO
		1473	The json_xs command line utility for quick experiments.
804		1474
805	AUTHOR	1475	AUTHOR
806	Marc Lehmann <schmorp@schmorp.de>	1476	Marc Lehmann <schmorp@schmorp.de>
807	http://home.schmorp.de/	1477	http://home.schmorp.de/
808		1478

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