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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
13	# objToJson and jsonToObj aliases to to_json and from_json
14	# are exported for compatibility to the JSON module,
15	# but should not be used in new code.
16		15
17	# OO-interface	16	# OO-interface
18		17
19	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	18	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
20	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	19	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
21	$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.
22		29
23	DESCRIPTION	30	DESCRIPTION
24	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
25	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*.
26	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.
27		42
28	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
29	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
30	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
31	cases their maintainers are unresponsive, gone missing, or not listening	46	cases their maintainers are unresponsive, gone missing, or not listening
32	to bug reports for other reasons.	47	to bug reports for other reasons.
33		48
34	See COMPARISON, below, for a comparison to some other JSON modules.
35
36	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
37	vice versa.	50	vice versa.
38		51
39	FEATURES	52	FEATURES
40	* correct unicode handling	53	* correct Unicode handling
		54
41	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
42	when it does so.	56	does so, and even documents what "correct" means.
43		57
44	* round-trip integrity	58	* round-trip integrity
		59
45	When you serialise a perl data structure using only datatypes	60	When you serialise a perl data structure using only data types
46	supported by JSON, the deserialised data structure is identical on	61	supported by JSON and Perl, the deserialised data structure is
47	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
48	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.
49		66
50	* strict checking of JSON correctness	67	* strict checking of JSON correctness
		68
51	There is no guessing, no generating of illegal JSON texts by	69	There is no guessing, no generating of illegal JSON texts by
52	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
53	is a security feature).	71	is a security feature).
54		72
55	* fast	73	* fast
56	Compared to other JSON modules, this module compares favourably in
57	terms of speed, too.
58		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
59	* simple to use	79	* simple to use
		80
60	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
61	interface.	82	object oriented interface.
62		83
63	* reasonably versatile output formats	84	* reasonably versatile output formats
		85
64	You can choose between the most compact guarenteed single-line	86	You can choose between the most compact guaranteed-single-line
65	format possible (nice for simple line-based protocols), a pure-ascii	87	format possible (nice for simple line-based protocols), a pure-ASCII
66	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
67	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
68	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
69	whatever way you like.	91	whatever way you like.
70		92
71	FUNCTIONAL INTERFACE	93	FUNCTIONAL INTERFACE
72	The following convinience methods are provided by this module. They are	94	The following convenience methods are provided by this module. They are
73	exported by default:	95	exported by default:
74		96
75	$json_text = to_json $perl_scalar	97	$json_text = encode_json $perl_scalar
76	Converts the given Perl data structure (a simple scalar or a	98	Converts the given Perl data structure to a UTF-8 encoded, binary
77	reference to a hash or array) to a UTF-8 encoded, binary string
78	(that is, the string contains octets only). Croaks on error.	99	string (that is, the string contains octets only). Croaks on error.
79		100
80	This function call is functionally identical to:	101	This function call is functionally identical to:
81		102
82	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	103	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
83		104
84	except being faster.	105	Except being faster.
85		106
86	$perl_scalar = from_json $json_text	107	$perl_scalar = decode_json $json_text
87	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
88	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
89	resulting simple scalar or reference. Croaks on error.	110	resulting reference. Croaks on error.
90		111
91	This function call is functionally identical to:	112	This function call is functionally identical to:
92		113
93	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	114	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
94		115
95	except being faster.	116	Except being faster.
		117
		118	A FEW NOTES ON UNICODE AND PERL
		119	Since this often leads to confusion, here are a few very clear words on
		120	how Unicode works in Perl, modulo bugs.
		121
		122	1. Perl strings can store characters with ordinal values > 255.
		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 :)
96		156
97	OBJECT-ORIENTED INTERFACE	157	OBJECT-ORIENTED INTERFACE
98	The object oriented interface lets you configure your own encoding or	158	The object oriented interface lets you configure your own encoding or
99	decoding style, within the limits of supported formats.	159	decoding style, within the limits of supported formats.
100		160
…		…
108		168
109	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]})
110	=> {"a": [1, 2]}	170	=> {"a": [1, 2]}
111		171
112	$json = $json->ascii ([$enable])	172	$json = $json->ascii ([$enable])
		173	$enabled = $json->get_ascii
113	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
114	generate characters outside the code range 0..127 (which is ASCII).	175	generate characters outside the code range 0..127 (which is ASCII).
115	Any unicode characters outside that range will be escaped using	176	Any Unicode characters outside that range will be escaped using
116	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL	177	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
117	escape sequence, as per RFC4627. The resulting encoded JSON text can	178	escape sequence, as per RFC4627. The resulting encoded JSON text can
118	be treated as a native unicode string, an ascii-encoded,	179	be treated as a native Unicode string, an ascii-encoded,
119	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
120	ASCII.	181	ASCII.
121		182
122	If $enable is false, then the "encode" method will not escape	183	If $enable is false, then the "encode" method will not escape
123	Unicode characters unless required by the JSON syntax or other	184	Unicode characters unless required by the JSON syntax or other
124	flags. This results in a faster and more compact format.	185	flags. This results in a faster and more compact format.
125		186
		187	See also the section *ENCODING/CODESET FLAG NOTES* later in this
		188	document.
		189
126	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
127	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
128	contain any 8 bit characters.	192	contain any 8 bit characters.
129		193
130	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	194	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
131	=> ["\ud801\udc01"]	195	=> ["\ud801\udc01"]
132		196
133	$json = $json->latin1 ([$enable])	197	$json = $json->latin1 ([$enable])
		198	$enabled = $json->get_latin1
134	If $enable is true (or missing), then the "encode" method will	199	If $enable is true (or missing), then the "encode" method will
135	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
136	any characters outside the code range 0..255. The resulting string	201	any characters outside the code range 0..255. The resulting string
137	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
138	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
139	flag, as "decode" by default expects unicode, which is a strict	204	flag, as "decode" by default expects Unicode, which is a strict
140	superset of latin1.	205	superset of latin1.
141		206
142	If $enable is false, then the "encode" method will not escape	207	If $enable is false, then the "encode" method will not escape
143	Unicode characters unless required by the JSON syntax or other	208	Unicode characters unless required by the JSON syntax or other
144	flags.	209	flags.
		210
		211	See also the section *ENCODING/CODESET FLAG NOTES* later in this
		212	document.
145		213
146	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
147	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
148	smaller encoded size. The disadvantage is that the resulting JSON	216	smaller encoded size. The disadvantage is that the resulting JSON
149	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
150	when storing and transfering), a rare encoding for JSON. It is	218	when storing and transferring), a rare encoding for JSON. It is
151	therefore most useful when you want to store data structures known	219	therefore most useful when you want to store data structures known
152	to contain binary data efficiently in files or databases, not when	220	to contain binary data efficiently in files or databases, not when
153	talking to other JSON encoders/decoders.	221	talking to other JSON encoders/decoders.
154		222
155	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	223	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
156	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	224	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
157		225
158	$json = $json->utf8 ([$enable])	226	$json = $json->utf8 ([$enable])
		227	$enabled = $json->get_utf8
159	If $enable is true (or missing), then the "encode" method will	228	If $enable is true (or missing), then the "encode" method will
160	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,
161	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
162	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
163	characters outside the range 0..255, they are thus useful for	232	characters outside the range 0..255, they are thus useful for
164	bytewise/binary I/O. In future versions, enabling this option might	233	bytewise/binary I/O. In future versions, enabling this option might
165	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
166	described in RFC4627.	235	described in RFC4627.
167		236
168	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
169	string as a (non-encoded) unicode string, while "decode" expects	238	string as a (non-encoded) Unicode string, while "decode" expects
170	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
171	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.
172		244
173	Example, output UTF-16BE-encoded JSON:	245	Example, output UTF-16BE-encoded JSON:
174		246
175	use Encode;	247	use Encode;
176	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	248	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
195	2	267	2
196	]	268	]
197	}	269	}
198		270
199	$json = $json->indent ([$enable])	271	$json = $json->indent ([$enable])
		272	$enabled = $json->get_indent
200	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
201	multiline format as output, putting every array member or	274	multiline format as output, putting every array member or
202	object/hash key-value pair into its own line, identing them	275	object/hash key-value pair into its own line, indenting them
203	properly.	276	properly.
204		277
205	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
206	the resulting JSON text is guarenteed not to contain any "newlines".	279	the resulting JSON text is guaranteed not to contain any "newlines".
207		280
208	This setting has no effect when decoding JSON texts.	281	This setting has no effect when decoding JSON texts.
209		282
210	$json = $json->space_before ([$enable])	283	$json = $json->space_before ([$enable])
		284	$enabled = $json->get_space_before
211	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
212	an extra optional space before the ":" separating keys from values	286	an extra optional space before the ":" separating keys from values
213	in JSON objects.	287	in JSON objects.
214		288
215	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
…		…
221	Example, space_before enabled, space_after and indent disabled:	295	Example, space_before enabled, space_after and indent disabled:
222		296
223	{"key" :"value"}	297	{"key" :"value"}
224		298
225	$json = $json->space_after ([$enable])	299	$json = $json->space_after ([$enable])
		300	$enabled = $json->get_space_after
226	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
227	an extra optional space after the ":" separating keys from values in	302	an extra optional space after the ":" separating keys from values in
228	JSON objects and extra whitespace after the "," separating key-value	303	JSON objects and extra whitespace after the "," separating key-value
229	pairs and array members.	304	pairs and array members.
230		305
…		…
235		310
236	Example, space_before and indent disabled, space_after enabled:	311	Example, space_before and indent disabled, space_after enabled:
237		312
238	{"key": "value"}	313	{"key": "value"}
239		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
240	$json = $json->canonical ([$enable])	357	$json = $json->canonical ([$enable])
		358	$enabled = $json->get_canonical
241	If $enable is true (or missing), then the "encode" method will	359	If $enable is true (or missing), then the "encode" method will
242	output JSON objects by sorting their keys. This is adding a	360	output JSON objects by sorting their keys. This is adding a
243	comparatively high overhead.	361	comparatively high overhead.
244		362
245	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
246	pairs in the order Perl stores them (which will likely change	364	pairs in the order Perl stores them (which will likely change
247	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).
248		367
249	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
250	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
251	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
252	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
253	in Perl.	372	in Perl.
254		373
255	This setting has no effect when decoding JSON texts.	374	This setting has no effect when decoding JSON texts.
256		375
		376	This setting has currently no effect on tied hashes.
		377
257	$json = $json->allow_nonref ([$enable])	378	$json = $json->allow_nonref ([$enable])
		379	$enabled = $json->get_allow_nonref
258	If $enable is true (or missing), then the "encode" method can	380	If $enable is true (or missing), then the "encode" method can
259	convert a non-reference into its corresponding string, number or	381	convert a non-reference into its corresponding string, number or
260	null JSON value, which is an extension to RFC4627. Likewise,	382	null JSON value, which is an extension to RFC4627. Likewise,
261	"decode" will accept those JSON values instead of croaking.	383	"decode" will accept those JSON values instead of croaking.
262		384
…		…
269	"allow_nonref", resulting in an invalid JSON text:	391	"allow_nonref", resulting in an invalid JSON text:
270		392
271	JSON::XS->new->allow_nonref->encode ("Hello, World!")	393	JSON::XS->new->allow_nonref->encode ("Hello, World!")
272	=> "Hello, World!"	394	=> "Hello, World!"
273		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
		411	$json = $json->allow_blessed ([$enable])
		412	$enabled = $json->get_allow_blessed
		413	See "OBJECT SERIALISATION" for details.
		414
		415	If $enable is true (or missing), then the "encode" method will not
		416	barf when it encounters a blessed reference that it cannot convert
		417	otherwise. Instead, a JSON "null" value is encoded instead of the
		418	object.
		419
		420	If $enable is false (the default), then "encode" will throw an
		421	exception when it encounters a blessed object that it cannot convert
		422	otherwise.
		423
		424	This setting has no effect on "decode".
		425
		426	$json = $json->convert_blessed ([$enable])
		427	$enabled = $json->get_convert_blessed
		428	See "OBJECT SERIALISATION" for details.
		429
		430	If $enable is true (or missing), then "encode", upon encountering a
		431	blessed object, will check for the availability of the "TO_JSON"
		432	method on the object's class. If found, it will be called in scalar
		433	context and the resulting scalar will be encoded instead of the
		434	object.
		435
		436	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
		437	returns other blessed objects, those will be handled in the same
		438	way. "TO_JSON" must take care of not causing an endless recursion
		439	cycle (== crash) in this case. The name of "TO_JSON" was chosen
		440	because other methods called by the Perl core (== not by the user of
		441	the object) are usually in upper case letters and to avoid
		442	collisions with any "to_json" function or method.
		443
		444	If $enable is false (the default), then "encode" will not consider
		445	this type of conversion.
		446
		447	This setting has no effect on "decode".
		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.
		465
		466	$json = $json->filter_json_object ([$coderef->($hashref)])
		467	When $coderef is specified, it will be called from "decode" each
		468	time it decodes a JSON object. The only argument is a reference to
		469	the newly-created hash. If the code references returns a single
		470	scalar (which need not be a reference), this value (i.e. a copy of
		471	that scalar to avoid aliasing) is inserted into the deserialised
		472	data structure. If it returns an empty list (NOTE: *not* "undef",
		473	which is a valid scalar), the original deserialised hash will be
		474	inserted. This setting can slow down decoding considerably.
		475
		476	When $coderef is omitted or undefined, any existing callback will be
		477	removed and "decode" will not change the deserialised hash in any
		478	way.
		479
		480	Example, convert all JSON objects into the integer 5:
		481
		482	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		483	# returns [5]
		484	$js->decode ('[{}]')
		485	# throw an exception because allow_nonref is not enabled
		486	# so a lone 5 is not allowed.
		487	$js->decode ('{"a":1, "b":2}');
		488
		489	$json = $json->filter_json_single_key_object ($key [=>
		490	$coderef->($value)])
		491	Works remotely similar to "filter_json_object", but is only called
		492	for JSON objects having a single key named $key.
		493
		494	This $coderef is called before the one specified via
		495	"filter_json_object", if any. It gets passed the single value in the
		496	JSON object. If it returns a single value, it will be inserted into
		497	the data structure. If it returns nothing (not even "undef" but the
		498	empty list), the callback from "filter_json_object" will be called
		499	next, as if no single-key callback were specified.
		500
		501	If $coderef is omitted or undefined, the corresponding callback will
		502	be disabled. There can only ever be one callback for a given key.
		503
		504	As this callback gets called less often then the
		505	"filter_json_object" one, decoding speed will not usually suffer as
		506	much. Therefore, single-key objects make excellent targets to
		507	serialise Perl objects into, especially as single-key JSON objects
		508	are as close to the type-tagged value concept as JSON gets (it's
		509	basically an ID/VALUE tuple). Of course, JSON does not support this
		510	in any way, so you need to make sure your data never looks like a
		511	serialised Perl hash.
		512
		513	Typical names for the single object key are "__class_whatever__", or
		514	"$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
		515	things like "__class_md5sum(classname)__", to reduce the risk of
		516	clashing with real hashes.
		517
		518	Example, decode JSON objects of the form "{ "__widget__" => <id> }"
		519	into the corresponding $WIDGET{<id>} object:
		520
		521	# return whatever is in $WIDGET{5}:
		522	JSON::XS
		523	->new
		524	->filter_json_single_key_object (__widget__ => sub {
		525	$WIDGET{ $_[0] }
		526	})
		527	->decode ('{"__widget__": 5')
		528
		529	# this can be used with a TO_JSON method in some "widget" class
		530	# for serialisation to json:
		531	sub WidgetBase::TO_JSON {
		532	my ($self) = @_;
		533
		534	unless ($self->{id}) {
		535	$self->{id} = ..get..some..id..;
		536	$WIDGET{$self->{id}} = $self;
		537	}
		538
		539	{ __widget__ => $self->{id} }
		540	}
		541
274	$json = $json->shrink ([$enable])	542	$json = $json->shrink ([$enable])
		543	$enabled = $json->get_shrink
275	Perl usually over-allocates memory a bit when allocating space for	544	Perl usually over-allocates memory a bit when allocating space for
276	strings. This flag optionally resizes strings generated by either	545	strings. This flag optionally resizes strings generated by either
277	"encode" or "decode" to their minimum size possible. This can save	546	"encode" or "decode" to their minimum size possible. This can save
278	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
279	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
…		…
297	converting strings that look like integers or floats into integers	566	converting strings that look like integers or floats into integers
298	or floats internally (there is no difference on the Perl level),	567	or floats internally (there is no difference on the Perl level),
299	saving space.	568	saving space.
300		569
301	$json = $json->max_depth ([$maximum_nesting_depth])	570	$json = $json->max_depth ([$maximum_nesting_depth])
		571	$max_depth = $json->get_max_depth
302	Sets the maximum nesting level (default 512) accepted while encoding	572	Sets the maximum nesting level (default 512) accepted while encoding
303	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
304	higher nesting level then this limit, then the encoder and decoder	574	Perl data structure, then the encoder and decoder will stop and
305	will stop and croak at that point.	575	croak at that point.
306		576
307	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
308	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
309	"{" or "[" characters without their matching closing parenthesis	579	"{" or "[" characters without their matching closing parenthesis
310	crossed to reach a given character in a string.	580	crossed to reach a given character in a string.
311		581
312	Setting the maximum depth to one disallows any nesting, so that	582	Setting the maximum depth to one disallows any nesting, so that
313	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.
314		584
315	The argument to "max_depth" will be rounded up to the next nearest	585	If no argument is given, the highest possible setting will be used,
316	power of two.	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.
317		591
318	See SECURITY CONSIDERATIONS, below, for more info on why this is	592	See SECURITY CONSIDERATIONS, below, for more info on why this is
319	useful.	593	useful.
320		594
		595	$json = $json->max_size ([$maximum_string_size])
		596	$max_size = $json->get_max_size
		597	Set the maximum length a JSON text may have (in bytes) where
		598	decoding is being attempted. The default is 0, meaning no limit.
		599	When "decode" is called on a string that is longer then this many
		600	bytes, it will not attempt to decode the string but throw an
		601	exception. This setting has no effect on "encode" (yet).
		602
		603	If no argument is given, the limit check will be deactivated (same
		604	as when 0 is specified).
		605
		606	See SECURITY CONSIDERATIONS, below, for more info on why this is
		607	useful.
		608
321	$json_text = $json->encode ($perl_scalar)	609	$json_text = $json->encode ($perl_scalar)
322	Converts the given Perl data structure (a simple scalar or a	610	Converts the given Perl value or data structure to its JSON
323	reference to a hash or array) to its JSON representation. Simple	611	representation. Croaks on error.
324	scalars will be converted into JSON string or number sequences,
325	while references to arrays become JSON arrays and references to
326	hashes become JSON objects. Undefined Perl values (e.g. "undef")
327	become JSON "null" values. Neither "true" nor "false" values will be
328	generated.
329		612
330	$perl_scalar = $json->decode ($json_text)	613	$perl_scalar = $json->decode ($json_text)
331	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,
332	returning the resulting simple scalar or reference. Croaks on error.	615	returning the resulting simple scalar or reference. Croaks on error.
333
334	JSON numbers and strings become simple Perl scalars. JSON arrays
335	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
336	becomes 1, "false" becomes 0 and "null" becomes "undef".
337		616
338	($perl_scalar, $characters) = $json->decode_prefix ($json_text)	617	($perl_scalar, $characters) = $json->decode_prefix ($json_text)
339	This works like the "decode" method, but instead of raising an	618	This works like the "decode" method, but instead of raising an
340	exception when there is trailing garbage after the first JSON	619	exception when there is trailing garbage after the first JSON
341	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
342	characters consumed so far.	621	characters consumed so far.
343		622
344	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
345	protocol (which is not the brightest thing to do in the first place)
346	and you need to know where the JSON text ends.	624	protocol and you need to know where the JSON text ends.
347		625
348	JSON::XS->new->decode_prefix ("[1] the tail")	626	JSON::XS->new->decode_prefix ("[1] the tail")
349	=> ([], 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 :).
350		860
351	MAPPING	861	MAPPING
352	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
353	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
354	circumstances automatically, preserving round-tripping characteristics	864	circumstances automatically, preserving round-tripping characteristics
355	(what you put in comes out as something equivalent).	865	(what you put in comes out as something equivalent).
356		866
357	For the more enlightened: note that in the following descriptions,	867	For the more enlightened: note that in the following descriptions,
358	lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl*	868	lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
359	refers to the abstract Perl language itself.	869	refers to the abstract Perl language itself.
360		870
361	JSON -> PERL	871	JSON -> PERL
362	object	872	object
363	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
364	object keys is preserved (JSON does not preserver object key	874	object keys is preserved (JSON does not preserve object key ordering
365	ordering itself).	875	itself).
366		876
367	array	877	array
368	A JSON array becomes a reference to an array in Perl.	878	A JSON array becomes a reference to an array in Perl.
369		879
370	string	880	string
371	A JSON string becomes a string scalar in Perl - Unicode codepoints	881	A JSON string becomes a string scalar in Perl - Unicode codepoints
372	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,
373	so no manual decoding is necessary.	883	so no manual decoding is necessary.
374		884
375	number	885	number
376	A JSON number becomes either an integer or numeric (floating point)	886	A JSON number becomes either an integer, numeric (floating point) or
377	scalar in perl, depending on its range and any fractional parts. On	887	string scalar in perl, depending on its range and any fractional
378	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
379	all the conversion details, but an integer may take slightly less	889	Perl handles all the conversion details, but an integer may take
380	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
381	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.
382		910
383	true, false	911	true, false
384	These JSON atoms become 0, 1, respectively. Information is lost in	912	These JSON atoms become "Types::Serialiser::true" and
385	this process. Future versions might represent those values	913	"Types::Serialiser::false", respectively. They are overloaded to act
386	differently, but they will be guarenteed to act like these integers	914	almost exactly like the numbers 1 and 0. You can check whether a
387	would normally in Perl.	915	scalar is a JSON boolean by using the "Types::Serialiser::is_bool"
		916	function (after "use Types::Serialier", of course).
388		917
389	null	918	null
390	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.
391		934
392	PERL -> JSON	935	PERL -> JSON
393	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
394	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
395	by a Perl value.	938	by a Perl value.
396		939
397	hash references	940	hash references
398	Perl hash references become JSON objects. As there is no inherent	941	Perl hash references become JSON objects. As there is no inherent
399	ordering in hash keys (or JSON objects), they will usually be	942	ordering in hash keys (or JSON objects), they will usually be
400	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
401	same program but stays generally the same within a single run of a	944	hash keys (determined by the *canonical* flag), so the same
402	program. JSON::XS can optionally sort the hash keys (determined by	945	datastructure will serialise to the same JSON text (given same
403	the *canonical* flag), so the same datastructure will serialise to	946	settings and version of JSON::XS), but this incurs a runtime
404	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
405	but this incurs a runtime overhead and is only rarely useful, e.g.	948	some JSON text against another for equality.
406	when you want to compare some JSON text against another for
407	equality.
408		949
409	array references	950	array references
410	Perl array references become JSON arrays.	951	Perl array references become JSON arrays.
411		952
412	other references	953	other references
413	Other unblessed references are generally not allowed and will cause	954	Other unblessed references are generally not allowed and will cause
414	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
415	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.
416	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
417	readability.	961	readability.
418		962
		963	use Types::Serialiser;
419	to_json [\0,JSON::XS::true] # yields [false,true]	964	encode_json [\0, Types::Serialiser::true] # yields [false,true]
		965
		966	Types::Serialiser::true, Types::Serialiser::false
		967	These special values from the Types::Serialiser module become JSON
		968	true and JSON false values, respectively. You can also use "\1" and
		969	"\0" directly if you want.
420		970
421	blessed objects	971	blessed objects
422	Blessed objects are not allowed. JSON::XS currently tries to encode	972	Blessed objects are not directly representable in JSON, but
423	their underlying representation (hash- or arrayref), but this	973	"JSON::XS" allows various ways of handling objects. See "OBJECT
424	behaviour might change in future versions.	974	SERIALISATION", below, for details.
425		975
426	simple scalars	976	simple scalars
427	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
428	most difficult objects to encode: JSON::XS will encode undefined	978	most difficult objects to encode: JSON::XS will encode undefined
429	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
430	string context before encoding as JSON strings and anything else as	980	string context before encoding as JSON strings, and anything else as
431	number value:	981	number value:
432		982
433	# dump as number	983	# dump as number
434	to_json [2] # yields [2]	984	encode_json [2] # yields [2]
435	to_json [-3.0e17] # yields [-3e+17]	985	encode_json [-3.0e17] # yields [-3e+17]
436	my $value = 5; to_json [$value] # yields [5]	986	my $value = 5; encode_json [$value] # yields [5]
437		987
438	# used as string, so dump as string	988	# used as string, so dump as string
439	print $value;	989	print $value;
440	to_json [$value] # yields ["5"]	990	encode_json [$value] # yields ["5"]
441		991
442	# undef becomes null	992	# undef becomes null
443	to_json [undef] # yields [null]	993	encode_json [undef] # yields [null]
444		994
445	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:
446		996
447	my $x = 3.1; # some variable containing a number	997	my $x = 3.1; # some variable containing a number
448	"$x"; # stringified	998	"$x"; # stringified
449	$x .= ""; # another, more awkward way to stringify	999	$x .= ""; # another, more awkward way to stringify
450	print $x; # perl does it for you, too, quite often	1000	print $x; # perl does it for you, too, quite often
451		1001
452	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:
453		1003
454	my $x = "3"; # some variable containing a string	1004	my $x = "3"; # some variable containing a string
455	$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
456	$x *= 1; # same thing, the choise is yours.	1006	$x *= 1; # same thing, the choice is yours.
457		1007
458	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.
459	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 :).
460		1011
461	COMPARISON	1012	Note that numerical precision has the same meaning as under Perl (so
462	As already mentioned, this module was created because none of the	1013	binary to decimal conversion follows the same rules as in Perl,
463	existing JSON modules could be made to work correctly. First I will	1014	which can differ to other languages). Also, your perl interpreter
464	describe the problems (or pleasures) I encountered with various existing	1015	might expose extensions to the floating point numbers of your
465	JSON modules, followed by some benchmark values. JSON::XS was designed	1016	platform, such as infinities or NaN's - these cannot be represented
466	not to suffer from any of these problems or limitations.	1017	in JSON, and it is an error to pass those in.
467		1018
468	JSON 1.07	1019	OBJECT SERIALISATION
469	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.
470		1024
471	Undocumented/buggy Unicode handling (how JSON handles unicode values	1025	SERIALISATION
472	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
473	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	For example, the hypothetical "My::Object" "FREEZE" method might use
		1047	the objects "type" and "id" members to encode the object:
		1048
		1049	sub My::Object::FREEZE {
		1050	my ($self, $serialiser) = @_;
		1051
		1052	($self->{type}, $self->{id})
		1053	}
		1054
		1055	2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
		1056	In this case, the "TO_JSON" method of the object is invoked in
		1057	scalar context. It must return a single scalar that can be directly
		1058	encoded into JSON. This scalar replaces the object in the JSON text.
		1059
		1060	For example, the following "TO_JSON" method will convert all URI
		1061	objects to JSON strings when serialised. The fatc that these values
		1062	originally were URI objects is lost.
		1063
		1064	sub URI::TO_JSON {
		1065	my ($uri) = @_;
		1066	$uri->as_string
		1067	}
		1068
		1069	3. "allow_blessed" is enabled.
		1070	The object will be serialised as a JSON null value.
		1071
		1072	4. none of the above
		1073	If none of the settings are enabled or the respective methods are
		1074	missing, "JSON::XS" throws an exception.
		1075
		1076	DESERIALISATION
		1077	For deserialisation there are only two cases to consider: either
		1078	nonstandard tagging was used, in which case "allow_tags" decides, or
		1079	objects cannot be automatically be deserialised, in which case you can
		1080	use postprocessing or the "filter_json_object" or
		1081	"filter_json_single_key_object" callbacks to get some real objects our
		1082	of your JSON.
		1083
		1084	This section only considers the tagged value case: I a tagged JSON
		1085	object is encountered during decoding and "allow_tags" is disabled, a
		1086	parse error will result (as if tagged values were not part of the
		1087	grammar).
		1088
		1089	If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of
		1090	the package/classname used during serialisation (it will not attempt to
		1091	load the package as a Perl module). If there is no such method, the
		1092	decoding will fail with an error.
		1093
		1094	Otherwise, the "THAW" method is invoked with the classname as first
		1095	argument, the constant string "JSON" as second argument, and all the
		1096	values from the JSON array (the values originally returned by the
		1097	"FREEZE" method) as remaining arguments.
		1098
		1099	The method must then return the object. While technically you can return
		1100	any Perl scalar, you might have to enable the "enable_nonref" setting to
		1101	make that work in all cases, so better return an actual blessed
		1102	reference.
		1103
		1104	As an example, let's implement a "THAW" function that regenerates the
		1105	"My::Object" from the "FREEZE" example earlier:
		1106
		1107	sub My::Object::THAW {
		1108	my ($class, $serialiser, $type, $id) = @_;
		1109
		1110	$class->new (type => $type, id => $id)
		1111	}
		1112
		1113	ENCODING/CODESET FLAG NOTES
		1114	The interested reader might have seen a number of flags that signify
		1115	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
		1116	some confusion on what these do, so here is a short comparison:
		1117
		1118	"utf8" controls whether the JSON text created by "encode" (and expected
		1119	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
		1120	control whether "encode" escapes character values outside their
		1121	respective codeset range. Neither of these flags conflict with each
		1122	other, although some combinations make less sense than others.
		1123
		1124	Care has been taken to make all flags symmetrical with respect to
		1125	"encode" and "decode", that is, texts encoded with any combination of
		1126	these flag values will be correctly decoded when the same flags are used
		1127	- in general, if you use different flag settings while encoding vs. when
		1128	decoding you likely have a bug somewhere.
		1129
		1130	Below comes a verbose discussion of these flags. Note that a "codeset"
		1131	is simply an abstract set of character-codepoint pairs, while an
		1132	encoding takes those codepoint numbers and *encodes* them, in our case
		1133	into octets. Unicode is (among other things) a codeset, UTF-8 is an
		1134	encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
		1135	encodings at the same time, which can be confusing.
		1136
		1137	"utf8" flag disabled
		1138	When "utf8" is disabled (the default), then "encode"/"decode"
		1139	generate and expect Unicode strings, that is, characters with high
		1140	ordinal Unicode values (> 255) will be encoded as such characters,
		1141	and likewise such characters are decoded as-is, no changes to them
		1142	will be done, except "(re-)interpreting" them as Unicode codepoints
		1143	or Unicode characters, respectively (to Perl, these are the same
		1144	thing in strings unless you do funny/weird/dumb stuff).
		1145
		1146	This is useful when you want to do the encoding yourself (e.g. when
		1147	you want to have UTF-16 encoded JSON texts) or when some other layer
		1148	does the encoding for you (for example, when printing to a terminal
		1149	using a filehandle that transparently encodes to UTF-8 you certainly
		1150	do NOT want to UTF-8 encode your data first and have Perl encode it
		1151	another time).
		1152
		1153	"utf8" flag enabled
		1154	If the "utf8"-flag is enabled, "encode"/"decode" will encode all
		1155	characters using the corresponding UTF-8 multi-byte sequence, and
		1156	will expect your input strings to be encoded as UTF-8, that is, no
		1157	"character" of the input string must have any value > 255, as UTF-8
		1158	does not allow that.
		1159
		1160	The "utf8" flag therefore switches between two modes: disabled means
		1161	you will get a Unicode string in Perl, enabled means you get an
		1162	UTF-8 encoded octet/binary string in Perl.
		1163
		1164	"latin1" or "ascii" flags enabled
		1165	With "latin1" (or "ascii") enabled, "encode" will escape characters
		1166	with ordinal values > 255 (> 127 with "ascii") and encode the
		1167	remaining characters as specified by the "utf8" flag.
		1168
		1169	If "utf8" is disabled, then the result is also correctly encoded in
		1170	those character sets (as both are proper subsets of Unicode, meaning
		1171	that a Unicode string with all character values < 256 is the same
		1172	thing as a ISO-8859-1 string, and a Unicode string with all
		1173	character values < 128 is the same thing as an ASCII string in
474	properly).	1174	Perl).
475		1175
476	No roundtripping (strings get clobbered if they look like numbers,	1176	If "utf8" is enabled, you still get a correct UTF-8-encoded string,
477	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	1177	regardless of these flags, just some more characters will be escaped
478	will decode into the number 2.	1178	using "\uXXXX" then before.
479		1179
480	JSON::PC 0.01	1180	Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
481	Very fast.	1181	encoding, while ASCII-encoded strings are. That is because the
		1182	ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
		1183	*codeset* being a subset of Unicode), while ASCII is.
482		1184
483	Undocumented/buggy Unicode handling.	1185	Surprisingly, "decode" will ignore these flags and so treat all
		1186	input values as governed by the "utf8" flag. If it is disabled, this
		1187	allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
		1188	strict subsets of Unicode. If it is enabled, you can correctly
		1189	decode UTF-8 encoded strings.
484		1190
485	No roundtripping.	1191	So neither "latin1" nor "ascii" are incompatible with the "utf8"
		1192	flag - they only govern when the JSON output engine escapes a
		1193	character or not.
486		1194
487	Has problems handling many Perl values (e.g. regex results and other	1195	The main use for "latin1" is to relatively efficiently store binary
488	magic values will make it croak).	1196	data as JSON, at the expense of breaking compatibility with most
		1197	JSON decoders.
489		1198
490	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1199	The main use for "ascii" is to force the output to not contain
491	which is not a valid JSON text.	1200	characters with values > 127, which means you can interpret the
		1201	resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
		1202	any character set and 8-bit-encoding, and still get the same data
		1203	structure back. This is useful when your channel for JSON transfer
		1204	is not 8-bit clean or the encoding might be mangled in between (e.g.
		1205	in mail), and works because ASCII is a proper subset of most 8-bit
		1206	and multibyte encodings in use in the world.
492		1207
493	Unmaintained (maintainer unresponsive for many months, bugs are not	1208	JSON and ECMAscript
494	getting fixed).	1209	JSON syntax is based on how literals are represented in javascript (the
		1210	not-standardised predecessor of ECMAscript) which is presumably why it
		1211	is called "JavaScript Object Notation".
495		1212
496	JSON::Syck 0.21	1213	However, JSON is not a subset (and also not a superset of course) of
497	Very buggy (often crashes).	1214	ECMAscript (the standard) or javascript (whatever browsers actually
		1215	implement).
498		1216
499	Very inflexible (no human-readable format supported, format pretty	1217	If you want to use javascript's "eval" function to "parse" JSON, you
500	much undocumented. I need at least a format for easy reading by	1218	might run into parse errors for valid JSON texts, or the resulting data
501	humans and a single-line compact format for use in a protocol, and	1219	structure might not be queryable:
502	preferably a way to generate ASCII-only JSON texts).
503		1220
504	Completely broken (and confusingly documented) Unicode handling	1221	One of the problems is that U+2028 and U+2029 are valid characters
505	(unicode escapes are not working properly, you need to set	1222	inside JSON strings, but are not allowed in ECMAscript string literals,
506	ImplicitUnicode to *different* values on en- and decoding to get	1223	so the following Perl fragment will not output something that can be
507	symmetric behaviour).	1224	guaranteed to be parsable by javascript's "eval":
508		1225
509	No roundtripping (simple cases work, but this depends on wether the	1226	use JSON::XS;
510	scalar value was used in a numeric context or not).
511		1227
512	Dumping hashes may skip hash values depending on iterator state.	1228	print encode_json [chr 0x2028];
513		1229
514	Unmaintained (maintainer unresponsive for many months, bugs are not	1230	The right fix for this is to use a proper JSON parser in your javascript
515	getting fixed).	1231	programs, and not rely on "eval" (see for example Douglas Crockford's
		1232	json2.js parser).
516		1233
517	Does not check input for validity (i.e. will accept non-JSON input	1234	If this is not an option, you can, as a stop-gap measure, simply encode
518	and return "something" instead of raising an exception. This is a	1235	to ASCII-only JSON:
519	security issue: imagine two banks transfering money between each
520	other using JSON. One bank might parse a given non-JSON request and
521	deduct money, while the other might reject the transaction with a
522	syntax error. While a good protocol will at least recover, that is
523	extra unnecessary work and the transaction will still not succeed).
524		1236
525	JSON::DWIW 0.04	1237	use JSON::XS;
526	Very fast. Very natural. Very nice.
527		1238
528	Undocumented unicode handling (but the best of the pack. Unicode	1239	print JSON::XS->new->ascii->encode ([chr 0x2028]);
529	escapes still don't get parsed properly).
530		1240
531	Very inflexible.	1241	Note that this will enlarge the resulting JSON text quite a bit if you
		1242	have many non-ASCII characters. You might be tempted to run some regexes
		1243	to only escape U+2028 and U+2029, e.g.:
532		1244
533	No roundtripping.	1245	# DO NOT USE THIS!
		1246	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1247	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1248	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1249	print $json;
534		1250
535	Does not generate valid JSON texts (key strings are often unquoted,	1251	Note that *this is a bad idea*: the above only works for U+2028 and
536	empty keys result in nothing being output)	1252	U+2029 and thus only for fully ECMAscript-compliant parsers. Many
		1253	existing javascript implementations, however, have issues with other
		1254	characters as well - using "eval" naively simply *will* cause problems.
537		1255
538	Does not check input for validity.	1256	Another problem is that some javascript implementations reserve some
		1257	property names for their own purposes (which probably makes them
		1258	non-ECMAscript-compliant). For example, Iceweasel reserves the
		1259	"__proto__" property name for its own purposes.
		1260
		1261	If that is a problem, you could parse try to filter the resulting JSON
		1262	output for these property strings, e.g.:
		1263
		1264	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1265
		1266	This works because "__proto__" is not valid outside of strings, so every
		1267	occurrence of ""__proto__"\s*:" must be a string used as property name.
		1268
		1269	If you know of other incompatibilities, please let me know.
		1270
		1271	JSON and YAML
		1272	You often hear that JSON is a subset of YAML. This is, however, a mass
		1273	hysteria(*) and very far from the truth (as of the time of this
		1274	writing), so let me state it clearly: *in general, there is no way to
		1275	configure JSON::XS to output a data structure as valid YAML* that works
		1276	in all cases.
		1277
		1278	If you really must use JSON::XS to generate YAML, you should use this
		1279	algorithm (subject to change in future versions):
		1280
		1281	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1282	my $yaml = $to_yaml->encode ($ref) . "\n";
		1283
		1284	This will *usually* generate JSON texts that also parse as valid YAML.
		1285	Please note that YAML has hardcoded limits on (simple) object key
		1286	lengths that JSON doesn't have and also has different and incompatible
		1287	unicode character escape syntax, so you should make sure that your hash
		1288	keys are noticeably shorter than the 1024 "stream characters" YAML
		1289	allows and that you do not have characters with codepoint values outside
		1290	the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
		1291	sequences in strings (which JSON::XS does not *currently* generate, but
		1292	other JSON generators might).
		1293
		1294	There might be other incompatibilities that I am not aware of (or the
		1295	YAML specification has been changed yet again - it does so quite often).
		1296	In general you should not try to generate YAML with a JSON generator or
		1297	vice versa, or try to parse JSON with a YAML parser or vice versa:
		1298	chances are high that you will run into severe interoperability problems
		1299	when you least expect it.
		1300
		1301	(*) I have been pressured multiple times by Brian Ingerson (one of the
		1302	authors of the YAML specification) to remove this paragraph, despite
		1303	him acknowledging that the actual incompatibilities exist. As I was
		1304	personally bitten by this "JSON is YAML" lie, I refused and said I
		1305	will continue to educate people about these issues, so others do not
		1306	run into the same problem again and again. After this, Brian called
		1307	me a (quote)*complete and worthless idiot*(unquote).
		1308
		1309	In my opinion, instead of pressuring and insulting people who
		1310	actually clarify issues with YAML and the wrong statements of some
		1311	of its proponents, I would kindly suggest reading the JSON spec
		1312	(which is not that difficult or long) and finally make YAML
		1313	compatible to it, and educating users about the changes, instead of
		1314	spreading lies about the real compatibility for many *years* and
		1315	trying to silence people who point out that it isn't true.
		1316
		1317	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
		1318	even though the incompatibilities have been documented (and are
		1319	known to Brian) for many years and the spec makes explicit claims
		1320	that YAML is a superset of JSON. It would be so easy to fix, but
		1321	apparently, bullying people and corrupting userdata is so much
		1322	easier.
539		1323
540	SPEED	1324	SPEED
541	It seems that JSON::XS is surprisingly fast, as shown in the following	1325	It seems that JSON::XS is surprisingly fast, as shown in the following
542	tables. They have been generated with the help of the "eg/bench" program	1326	tables. They have been generated with the help of the "eg/bench" program
543	in the JSON::XS distribution, to make it easy to compare on your own	1327	in the JSON::XS distribution, to make it easy to compare on your own
544	system.	1328	system.
545		1329
546	First comes a comparison between various modules using a very short	1330	First comes a comparison between various modules using a very short
547	single-line JSON string:	1331	single-line JSON string (also available at
		1332	<http://dist.schmorp.de/misc/json/short.json>).
548		1333
549	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1334	{"method": "handleMessage", "params": ["user1",
550	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1335	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1336	1, 0]}
551		1337
552	It shows the number of encodes/decodes per second (JSON::XS uses the	1338	It shows the number of encodes/decodes per second (JSON::XS uses the
553	functional interface, while JSON::XS/2 uses the OO interface with	1339	functional interface, while JSON::XS/2 uses the OO interface with
554	pretty-printing and hashkey sorting enabled). Higher is better:	1340	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
		1341	JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
		1342	the from_json method). Higher is better:
555		1343
556	module | encode | decode |	1344	module | encode | decode |
557	-----------|------------|------------|	1345	--------------|------------|------------|
558	JSON | 7645.468 | 4208.613 |	1346	JSON::DWIW/DS | 86302.551 | 102300.098 |
559	JSON::DWIW | 68534.379 | 79437.576 |	1347	JSON::DWIW/FJ | 86302.551 | 75983.768 |
560	JSON::PC | 65948.176 | 78251.940 |	1348	JSON::PP | 15827.562 | 6638.658 |
561	JSON::Syck | 23379.621 | 28416.694 |	1349	JSON::Syck | 63358.066 | 47662.545 |
562	JSON::XS | 388361.481 | 199728.762 |	1350	JSON::XS | 511500.488 | 511500.488 |
563	JSON::XS/2 | 218453.333 | 192399.266 |	1351	JSON::XS/2 | 291271.111 | 388361.481 |
564	JSON::XS/3 | 338250.323 | 192399.266 |	1352	JSON::XS/3 | 361577.931 | 361577.931 |
565	Storable | 15732.573 | 28571.553 |	1353	Storable | 66788.280 | 265462.278 |
566	-----------+------------+------------+	1354	--------------+------------+------------+
567		1355
568	That is, JSON::XS is about five times faster than JSON::DWIW on	1356	That is, JSON::XS is almost six times faster than JSON::DWIW on
569	encoding, about three times faster on decoding, and over fourty times	1357	encoding, about five times faster on decoding, and over thirty to
570	faster than JSON, even with pretty-printing and key sorting. It also	1358	seventy times faster than JSON's pure perl implementation. It also
571	compares favourably to Storable for small amounts of data.	1359	compares favourably to Storable for small amounts of data.
572		1360
573	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1361	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
574	search API (http://nanoref.com/yahooapis/mgPdGg):	1362	search API (<http://dist.schmorp.de/misc/json/long.json>).
575		1363
576	module | encode | decode |	1364	module | encode | decode |
577	-----------|------------|------------|	1365	--------------|------------|------------|
578	JSON | 254.685 | 37.665 |	1366	JSON::DWIW/DS | 1647.927 | 2673.916 |
579	JSON::DWIW | 1014.244 | 1087.678 |	1367	JSON::DWIW/FJ | 1630.249 | 2596.128 |
580	JSON::PC | 3602.116 | 2307.352 |	1368	JSON::PP | 400.640 | 62.311 |
581	JSON::Syck | 558.035 | 776.263 |	1369	JSON::Syck | 1481.040 | 1524.869 |
582	JSON::XS | 5747.196 | 3543.684 |	1370	JSON::XS | 20661.596 | 9541.183 |
583	JSON::XS/2 | 3968.121 | 3589.170 |	1371	JSON::XS/2 | 10683.403 | 9416.938 |
584	JSON::XS/3 | 6105.246 | 3561.134 |	1372	JSON::XS/3 | 20661.596 | 9400.054 |
585	Storable | 4456.337 | 5320.020 |	1373	Storable | 19765.806 | 10000.725 |
586	-----------+------------+------------+	1374	--------------+------------+------------+
587		1375
588	Again, JSON::XS leads by far.	1376	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1377	decodes a bit faster).
589		1378
590	On large strings containing lots of high unicode characters, some	1379	On large strings containing lots of high Unicode characters, some
591	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1380	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
592	result will be broken due to missing (or wrong) unicode handling. Others	1381	result will be broken due to missing (or wrong) Unicode handling. Others
593	refuse to decode or encode properly, so it was impossible to prepare a	1382	refuse to decode or encode properly, so it was impossible to prepare a
594	fair comparison table for that case.	1383	fair comparison table for that case.
595		1384
596	SECURITY CONSIDERATIONS	1385	SECURITY CONSIDERATIONS
597	When you are using JSON in a protocol, talking to untrusted potentially	1386	When you are using JSON in a protocol, talking to untrusted potentially
…		…
601	have any buffer overflows. Obviously, this module should ensure that and	1390	have any buffer overflows. Obviously, this module should ensure that and
602	I am trying hard on making that true, but you never know.	1391	I am trying hard on making that true, but you never know.
603		1392
604	Second, you need to avoid resource-starving attacks. That means you	1393	Second, you need to avoid resource-starving attacks. That means you
605	should limit the size of JSON texts you accept, or make sure then when	1394	should limit the size of JSON texts you accept, or make sure then when
606	your resources run out, thats just fine (e.g. by using a separate	1395	your resources run out, that's just fine (e.g. by using a separate
607	process that can crash safely). The size of a JSON text in octets or	1396	process that can crash safely). The size of a JSON text in octets or
608	characters is usually a good indication of the size of the resources	1397	characters is usually a good indication of the size of the resources
609	required to decode it into a Perl structure.	1398	required to decode it into a Perl structure. While JSON::XS can check
		1399	the size of the JSON text, it might be too late when you already have it
		1400	in memory, so you might want to check the size before you accept the
		1401	string.
610		1402
611	Third, JSON::XS recurses using the C stack when decoding objects and	1403	Third, JSON::XS recurses using the C stack when decoding objects and
612	arrays. The C stack is a limited resource: for instance, on my amd64	1404	arrays. The C stack is a limited resource: for instance, on my amd64
613	machine with 8MB of stack size I can decode around 180k nested arrays	1405	machine with 8MB of stack size I can decode around 180k nested arrays
614	but only 14k nested JSON objects (due to perl itself recursing deeply on	1406	but only 14k nested JSON objects (due to perl itself recursing deeply on
615	croak to free the temporary). If that is exceeded, the program crashes.	1407	croak to free the temporary). If that is exceeded, the program crashes.
616	to be conservative, the default nesting limit is set to 512. If your	1408	To be conservative, the default nesting limit is set to 512. If your
617	process has a smaller stack, you should adjust this setting accordingly	1409	process has a smaller stack, you should adjust this setting accordingly
618	with the "max_depth" method.	1410	with the "max_depth" method.
619		1411
620	And last but least, something else could bomb you that I forgot to think	1412	Something else could bomb you, too, that I forgot to think of. In that
621	of. In that case, you get to keep the pieces. I am always open for	1413	case, you get to keep the pieces. I am always open for hints, though...
622	hints, though...	1414
		1415	Also keep in mind that JSON::XS might leak contents of your Perl data
		1416	structures in its error messages, so when you serialise sensitive
		1417	information you might want to make sure that exceptions thrown by
		1418	JSON::XS will not end up in front of untrusted eyes.
		1419
		1420	If you are using JSON::XS to return packets to consumption by JavaScript
		1421	scripts in a browser you should have a look at
		1422	<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
		1423	to see whether you are vulnerable to some common attack vectors (which
		1424	really are browser design bugs, but it is still you who will have to
		1425	deal with it, as major browser developers care only for features, not
		1426	about getting security right).
		1427
		1428	INTEROPERABILITY WITH OTHER MODULES
		1429	"JSON::XS" uses the Types::Serialiser module to provide boolean
		1430	constants. That means that the JSON true and false values will be
		1431	comaptible to true and false values of iother modules that do the same,
		1432	such as JSON::PP and CBOR::XS.
		1433
		1434	THREADS
		1435	This module is *not* guaranteed to be thread safe and there are no plans
		1436	to change this until Perl gets thread support (as opposed to the
		1437	horribly slow so-called "threads" which are simply slow and bloated
		1438	process simulations - use fork, it's *much* faster, cheaper, better).
		1439
		1440	(It might actually work, but you have been warned).
		1441
		1442	THE PERILS OF SETLOCALE
		1443	Sometimes people avoid the Perl locale support and directly call the
		1444	system's setlocale function with "LC_ALL".
		1445
		1446	This breaks both perl and modules such as JSON::XS, as stringification
		1447	of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
		1448	might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
		1449	on perl to stringify numbers).
		1450
		1451	The solution is simple: don't call "setlocale", or use it for only those
		1452	categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
		1453
		1454	If you need "LC_NUMERIC", you should enable it only around the code that
		1455	actually needs it (avoiding stringification of numbers), and restore it
		1456	afterwards.
623		1457
624	BUGS	1458	BUGS
625	While the goal of this module is to be correct, that unfortunately does	1459	While the goal of this module is to be correct, that unfortunately does
626	not mean its bug-free, only that I think its design is bug-free. It is	1460	not mean it's bug-free, only that I think its design is bug-free. If you
627	still relatively early in its development. If you keep reporting bugs
628	they will be fixed swiftly, though.	1461	keep reporting bugs they will be fixed swiftly, though.
		1462
		1463	Please refrain from using rt.cpan.org or any other bug reporting
		1464	service. I put the contact address into my modules for a reason.
		1465
		1466	SEE ALSO
		1467	The json_xs command line utility for quick experiments.
629		1468
630	AUTHOR	1469	AUTHOR
631	Marc Lehmann <schmorp@schmorp.de>	1470	Marc Lehmann <schmorp@schmorp.de>
632	http://home.schmorp.de/	1471	http://home.schmorp.de/
633		1472

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