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Revision 1.5 by root, Sat Mar 24 01:15:22 2007 UTC vs.
Revision 1.29 by root, Thu Feb 19 01:13:46 2009 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, croak on error	10	# exported functions, they croak on error
		11	# and expect/generate UTF-8
8		12
9	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	13	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
10	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	14	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
11		15
12	# oo-interface	16	# OO-interface
13		17
14	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	18	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
15	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	19	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
16	$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.
17		29
18	DESCRIPTION	30	DESCRIPTION
19	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
20	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.
21	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.
22		42
23	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
24	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
25	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
26	cases their maintainers are unresponsive, gone missing, or not listening	46	cases their maintainers are unresponsive, gone missing, or not listening
27	to bug reports for other reasons.	47	to bug reports for other reasons.
28		48
29	See COMPARISON, below, for a comparison to some other JSON modules.
30
31	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
32	vice versa.	50	vice versa.
33		51
34	FEATURES	52	FEATURES
35	* correct handling of unicode issues	53	* correct Unicode handling
		54
36	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
37	when it does so.	56	does so, and even documents what "correct" means.
38		57
39	* round-trip integrity	58	* round-trip integrity
		59
40	When you serialise a perl data structure using only datatypes	60	When you serialise a perl data structure using only data types
41	supported by JSON, the deserialised data structure is identical on	61	supported by JSON, the deserialised data structure is identical on
42	the Perl level. (e.g. the string "2.0" doesn't suddenly become "2").	62	the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
		63	just because it looks like a number). There minor are exceptions
		64	to this, read the MAPPING section below to learn about those.
43		65
44	* strict checking of JSON correctness	66	* strict checking of JSON correctness
		67
45	There is no guessing, no generating of illegal JSON strings by	68	There is no guessing, no generating of illegal JSON texts by
46	default, and only JSON is accepted as input by default (the latter	69	default, and only JSON is accepted as input by default (the latter
47	is a security feature).	70	is a security feature).
48		71
49	* fast	72	* fast
50	Compared to other JSON modules, this module compares favourably in
51	terms of speed, too.
52		73
		74	Compared to other JSON modules and other serialisers such as
		75	Storable, this module usually compares favourably in terms of speed,
		76	too.
		77
53	* simple to use	78	* simple to use
		79
54	This module has both a simple functional interface as well as an OO	80	This module has both a simple functional interface as well as an
55	interface.	81	object oriented interface interface.
56		82
57	* reasonably versatile output formats	83	* reasonably versatile output formats
		84
58	You can choose between the most compact guarenteed single-line	85	You can choose between the most compact guaranteed-single-line
59	format possible (nice for simple line-based protocols), a pure-ascii	86	format possible (nice for simple line-based protocols), a pure-ASCII
60	format (for when your transport is not 8-bit clean), or a	87	format (for when your transport is not 8-bit clean, still supports
61	pretty-printed format (for when you want to read that stuff). Or you	88	the whole Unicode range), or a pretty-printed format (for when you
62	can combine those features in whatever way you like.	89	want to read that stuff). Or you can combine those features in
		90	whatever way you like.
63		91
64	FUNCTIONAL INTERFACE	92	FUNCTIONAL INTERFACE
65	The following convinience methods are provided by this module. They are	93	The following convenience methods are provided by this module. They are
66	exported by default:	94	exported by default:
67		95
68	$json_string = to_json $perl_scalar	96	$json_text = encode_json $perl_scalar
69	Converts the given Perl data structure (a simple scalar or a	97	Converts the given Perl data structure to a UTF-8 encoded, binary
70	reference to a hash or array) to a UTF-8 encoded, binary string
71	(that is, the string contains octets only). Croaks on error.	98	string (that is, the string contains octets only). Croaks on error.
72		99
73	This function call is functionally identical to	100	This function call is functionally identical to:
		101
74	"JSON::XS->new->utf8->encode ($perl_scalar)".	102	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
75		103
		104	Except being faster.
		105
76	$perl_scalar = from_json $json_string	106	$perl_scalar = decode_json $json_text
77	The opposite of "to_json": expects an UTF-8 (binary) string and	107	The opposite of "encode_json": expects an UTF-8 (binary) string and
78	tries to parse that as an UTF-8 encoded JSON string, returning the	108	tries to parse that as an UTF-8 encoded JSON text, returning the
79	resulting simple scalar or reference. Croaks on error.	109	resulting reference. Croaks on error.
80		110
81	This function call is functionally identical to	111	This function call is functionally identical to:
		112
82	"JSON::XS->new->utf8->decode ($json_string)".	113	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		114
		115	Except being faster.
		116
		117	$is_boolean = JSON::XS::is_bool $scalar
		118	Returns true if the passed scalar represents either JSON::XS::true
		119	or JSON::XS::false, two constants that act like 1 and 0,
		120	respectively and are used to represent JSON "true" and "false"
		121	values in Perl.
		122
		123	See MAPPING, below, for more information on how JSON values are
		124	mapped to Perl.
		125
		126	A FEW NOTES ON UNICODE AND PERL
		127	Since this often leads to confusion, here are a few very clear words on
		128	how Unicode works in Perl, modulo bugs.
		129
		130	1. Perl strings can store characters with ordinal values > 255.
		131	This enables you to store Unicode characters as single characters in
		132	a Perl string - very natural.
		133
		134	2. Perl does not associate an encoding with your strings.
		135	... until you force it to, e.g. when matching it against a regex, or
		136	printing the scalar to a file, in which case Perl either interprets
		137	your string as locale-encoded text, octets/binary, or as Unicode,
		138	depending on various settings. In no case is an encoding stored
		139	together with your data, it is use that decides encoding, not any
		140	magical meta data.
		141
		142	3. The internal utf-8 flag has no meaning with regards to the encoding
		143	of your string.
		144	Just ignore that flag unless you debug a Perl bug, a module written
		145	in XS or want to dive into the internals of perl. Otherwise it will
		146	only confuse you, as, despite the name, it says nothing about how
		147	your string is encoded. You can have Unicode strings with that flag
		148	set, with that flag clear, and you can have binary data with that
		149	flag set and that flag clear. Other possibilities exist, too.
		150
		151	If you didn't know about that flag, just the better, pretend it
		152	doesn't exist.
		153
		154	4. A "Unicode String" is simply a string where each character can be
		155	validly interpreted as a Unicode code point.
		156	If you have UTF-8 encoded data, it is no longer a Unicode string,
		157	but a Unicode string encoded in UTF-8, giving you a binary string.
		158
		159	5. A string containing "high" (> 255) character values is not a UTF-8
		160	string.
		161	It's a fact. Learn to live with it.
		162
		163	I hope this helps :)
83		164
84	OBJECT-ORIENTED INTERFACE	165	OBJECT-ORIENTED INTERFACE
85	The object oriented interface lets you configure your own encoding or	166	The object oriented interface lets you configure your own encoding or
86	decoding style, within the limits of supported formats.	167	decoding style, within the limits of supported formats.
87		168
91	disabled.	172	disabled.
92		173
93	The mutators for flags all return the JSON object again and thus	174	The mutators for flags all return the JSON object again and thus
94	calls can be chained:	175	calls can be chained:
95		176
96	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	177	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
97	=> {"a": [1, 2]}	178	=> {"a": [1, 2]}
98		179
99	$json = $json->ascii ([$enable])	180	$json = $json->ascii ([$enable])
		181	$enabled = $json->get_ascii
100	If $enable is true (or missing), then the "encode" method will not	182	If $enable is true (or missing), then the "encode" method will not
101	generate characters outside the code range 0..127. Any unicode	183	generate characters outside the code range 0..127 (which is ASCII).
102	characters outside that range will be escaped using either a single	184	Any Unicode characters outside that range will be escaped using
103	\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,	185	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
104	as per RFC4627.	186	escape sequence, as per RFC4627. The resulting encoded JSON text can
		187	be treated as a native Unicode string, an ascii-encoded,
		188	latin1-encoded or UTF-8 encoded string, or any other superset of
		189	ASCII.
105		190
106	If $enable is false, then the "encode" method will not escape	191	If $enable is false, then the "encode" method will not escape
107	Unicode characters unless necessary.	192	Unicode characters unless required by the JSON syntax or other
		193	flags. This results in a faster and more compact format.
108		194
		195	See also the section ENCODING/CODESET FLAG NOTES later in this
		196	document.
		197
		198	The main use for this flag is to produce JSON texts that can be
		199	transmitted over a 7-bit channel, as the encoded JSON texts will not
		200	contain any 8 bit characters.
		201
109	JSON::XS->new->ascii (1)->encode (chr 0x10401)	202	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
110	=> \ud801\udc01	203	=> ["\ud801\udc01"]
		204
		205	$json = $json->latin1 ([$enable])
		206	$enabled = $json->get_latin1
		207	If $enable is true (or missing), then the "encode" method will
		208	encode the resulting JSON text as latin1 (or iso-8859-1), escaping
		209	any characters outside the code range 0..255. The resulting string
		210	can be treated as a latin1-encoded JSON text or a native Unicode
		211	string. The "decode" method will not be affected in any way by this
		212	flag, as "decode" by default expects Unicode, which is a strict
		213	superset of latin1.
		214
		215	If $enable is false, then the "encode" method will not escape
		216	Unicode characters unless required by the JSON syntax or other
		217	flags.
		218
		219	See also the section ENCODING/CODESET FLAG NOTES later in this
		220	document.
		221
		222	The main use for this flag is efficiently encoding binary data as
		223	JSON text, as most octets will not be escaped, resulting in a
		224	smaller encoded size. The disadvantage is that the resulting JSON
		225	text is encoded in latin1 (and must correctly be treated as such
		226	when storing and transferring), a rare encoding for JSON. It is
		227	therefore most useful when you want to store data structures known
		228	to contain binary data efficiently in files or databases, not when
		229	talking to other JSON encoders/decoders.
		230
		231	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		232	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
111		233
112	$json = $json->utf8 ([$enable])	234	$json = $json->utf8 ([$enable])
		235	$enabled = $json->get_utf8
113	If $enable is true (or missing), then the "encode" method will	236	If $enable is true (or missing), then the "encode" method will
114	encode the JSON string into UTF-8, as required by many protocols,	237	encode the JSON result into UTF-8, as required by many protocols,
115	while the "decode" method expects to be handled an UTF-8-encoded	238	while the "decode" method expects to be handled an UTF-8-encoded
116	string. Please note that UTF-8-encoded strings do not contain any	239	string. Please note that UTF-8-encoded strings do not contain any
117	characters outside the range 0..255, they are thus useful for	240	characters outside the range 0..255, they are thus useful for
118	bytewise/binary I/O.	241	bytewise/binary I/O. In future versions, enabling this option might
		242	enable autodetection of the UTF-16 and UTF-32 encoding families, as
		243	described in RFC4627.
119		244
120	If $enable is false, then the "encode" method will return the JSON	245	If $enable is false, then the "encode" method will return the JSON
121	string as a (non-encoded) unicode string, while "decode" expects	246	string as a (non-encoded) Unicode string, while "decode" expects
122	thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or	247	thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
123	UTF-16) needs to be done yourself, e.g. using the Encode module.	248	UTF-16) needs to be done yourself, e.g. using the Encode module.
124		249
		250	See also the section ENCODING/CODESET FLAG NOTES later in this
		251	document.
		252
125	Example, output UTF-16-encoded JSON:	253	Example, output UTF-16BE-encoded JSON:
		254
		255	use Encode;
		256	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		257
		258	Example, decode UTF-32LE-encoded JSON:
		259
		260	use Encode;
		261	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
126		262
127	$json = $json->pretty ([$enable])	263	$json = $json->pretty ([$enable])
128	This enables (or disables) all of the "indent", "space_before" and	264	This enables (or disables) all of the "indent", "space_before" and
129	"space_after" (and in the future possibly more) flags in one call to	265	"space_after" (and in the future possibly more) flags in one call to
130	generate the most readable (or most compact) form possible.	266	generate the most readable (or most compact) form possible.
…		…
139	2	275	2
140	]	276	]
141	}	277	}
142		278
143	$json = $json->indent ([$enable])	279	$json = $json->indent ([$enable])
		280	$enabled = $json->get_indent
144	If $enable is true (or missing), then the "encode" method will use a	281	If $enable is true (or missing), then the "encode" method will use a
145	multiline format as output, putting every array member or	282	multiline format as output, putting every array member or
146	object/hash key-value pair into its own line, identing them	283	object/hash key-value pair into its own line, indenting them
147	properly.	284	properly.
148		285
149	If $enable is false, no newlines or indenting will be produced, and	286	If $enable is false, no newlines or indenting will be produced, and
150	the resulting JSON strings is guarenteed not to contain any	287	the resulting JSON text is guaranteed not to contain any "newlines".
151	"newlines".
152		288
153	This setting has no effect when decoding JSON strings.	289	This setting has no effect when decoding JSON texts.
154		290
155	$json = $json->space_before ([$enable])	291	$json = $json->space_before ([$enable])
		292	$enabled = $json->get_space_before
156	If $enable is true (or missing), then the "encode" method will add	293	If $enable is true (or missing), then the "encode" method will add
157	an extra optional space before the ":" separating keys from values	294	an extra optional space before the ":" separating keys from values
158	in JSON objects.	295	in JSON objects.
159		296
160	If $enable is false, then the "encode" method will not add any extra	297	If $enable is false, then the "encode" method will not add any extra
161	space at those places.	298	space at those places.
162		299
163	This setting has no effect when decoding JSON strings. You will also	300	This setting has no effect when decoding JSON texts. You will also
164	most likely combine this setting with "space_after".	301	most likely combine this setting with "space_after".
165		302
166	Example, space_before enabled, space_after and indent disabled:	303	Example, space_before enabled, space_after and indent disabled:
167		304
168	{"key" :"value"}	305	{"key" :"value"}
169		306
170	$json = $json->space_after ([$enable])	307	$json = $json->space_after ([$enable])
		308	$enabled = $json->get_space_after
171	If $enable is true (or missing), then the "encode" method will add	309	If $enable is true (or missing), then the "encode" method will add
172	an extra optional space after the ":" separating keys from values in	310	an extra optional space after the ":" separating keys from values in
173	JSON objects and extra whitespace after the "," separating key-value	311	JSON objects and extra whitespace after the "," separating key-value
174	pairs and array members.	312	pairs and array members.
175		313
176	If $enable is false, then the "encode" method will not add any extra	314	If $enable is false, then the "encode" method will not add any extra
177	space at those places.	315	space at those places.
178		316
179	This setting has no effect when decoding JSON strings.	317	This setting has no effect when decoding JSON texts.
180		318
181	Example, space_before and indent disabled, space_after enabled:	319	Example, space_before and indent disabled, space_after enabled:
182		320
183	{"key": "value"}	321	{"key": "value"}
184		322
		323	$json = $json->relaxed ([$enable])
		324	$enabled = $json->get_relaxed
		325	If $enable is true (or missing), then "decode" will accept some
		326	extensions to normal JSON syntax (see below). "encode" will not be
		327	affected in anyway. *Be aware that this option makes you accept
		328	invalid JSON texts as if they were valid!*. I suggest only to use
		329	this option to parse application-specific files written by humans
		330	(configuration files, resource files etc.)
		331
		332	If $enable is false (the default), then "decode" will only accept
		333	valid JSON texts.
		334
		335	Currently accepted extensions are:
		336
		337	* list items can have an end-comma
		338
		339	JSON separates array elements and key-value pairs with commas.
		340	This can be annoying if you write JSON texts manually and want
		341	to be able to quickly append elements, so this extension accepts
		342	comma at the end of such items not just between them:
		343
		344	[
		345	1,
		346	2, <- this comma not normally allowed
		347	]
		348	{
		349	"k1": "v1",
		350	"k2": "v2", <- this comma not normally allowed
		351	}
		352
		353	* shell-style '#'-comments
		354
		355	Whenever JSON allows whitespace, shell-style comments are
		356	additionally allowed. They are terminated by the first
		357	carriage-return or line-feed character, after which more
		358	white-space and comments are allowed.
		359
		360	[
		361	1, # this comment not allowed in JSON
		362	# neither this one...
		363	]
		364
185	$json = $json->canonical ([$enable])	365	$json = $json->canonical ([$enable])
		366	$enabled = $json->get_canonical
186	If $enable is true (or missing), then the "encode" method will	367	If $enable is true (or missing), then the "encode" method will
187	output JSON objects by sorting their keys. This is adding a	368	output JSON objects by sorting their keys. This is adding a
188	comparatively high overhead.	369	comparatively high overhead.
189		370
190	If $enable is false, then the "encode" method will output key-value	371	If $enable is false, then the "encode" method will output key-value
191	pairs in the order Perl stores them (which will likely change	372	pairs in the order Perl stores them (which will likely change
192	between runs of the same script).	373	between runs of the same script).
193		374
194	This option is useful if you want the same data structure to be	375	This option is useful if you want the same data structure to be
195	encoded as the same JSON string (given the same overall settings).	376	encoded as the same JSON text (given the same overall settings). If
196	If it is disabled, the same hash migh be encoded differently even if	377	it is disabled, the same hash might be encoded differently even if
197	contains the same data, as key-value pairs have no inherent ordering	378	contains the same data, as key-value pairs have no inherent ordering
198	in Perl.	379	in Perl.
199		380
200	This setting has no effect when decoding JSON strings.	381	This setting has no effect when decoding JSON texts.
201		382
202	$json = $json->allow_nonref ([$enable])	383	$json = $json->allow_nonref ([$enable])
		384	$enabled = $json->get_allow_nonref
203	If $enable is true (or missing), then the "encode" method can	385	If $enable is true (or missing), then the "encode" method can
204	convert a non-reference into its corresponding string, number or	386	convert a non-reference into its corresponding string, number or
205	null JSON value, which is an extension to RFC4627. Likewise,	387	null JSON value, which is an extension to RFC4627. Likewise,
206	"decode" will accept those JSON values instead of croaking.	388	"decode" will accept those JSON values instead of croaking.
207		389
208	If $enable is false, then the "encode" method will croak if it isn't	390	If $enable is false, then the "encode" method will croak if it isn't
209	passed an arrayref or hashref, as JSON strings must either be an	391	passed an arrayref or hashref, as JSON texts must either be an
210	object or array. Likewise, "decode" will croak if given something	392	object or array. Likewise, "decode" will croak if given something
211	that is not a JSON object or array.	393	that is not a JSON object or array.
212		394
213	Example, encode a Perl scalar as JSON value with enabled	395	Example, encode a Perl scalar as JSON value with enabled
214	"allow_nonref", resulting in an invalid JSON text:	396	"allow_nonref", resulting in an invalid JSON text:
215		397
216	JSON::XS->new->allow_nonref->encode ("Hello, World!")	398	JSON::XS->new->allow_nonref->encode ("Hello, World!")
217	=> "Hello, World!"	399	=> "Hello, World!"
218		400
		401	$json = $json->allow_unknown ([$enable])
		402	$enabled = $json->get_allow_unknown
		403	If $enable is true (or missing), then "encode" will not throw an
		404	exception when it encounters values it cannot represent in JSON (for
		405	example, filehandles) but instead will encode a JSON "null" value.
		406	Note that blessed objects are not included here and are handled
		407	separately by c<allow_nonref>.
		408
		409	If $enable is false (the default), then "encode" will throw an
		410	exception when it encounters anything it cannot encode as JSON.
		411
		412	This option does not affect "decode" in any way, and it is
		413	recommended to leave it off unless you know your communications
		414	partner.
		415
		416	$json = $json->allow_blessed ([$enable])
		417	$enabled = $json->get_allow_blessed
		418	If $enable is true (or missing), then the "encode" method will not
		419	barf when it encounters a blessed reference. Instead, the value of
		420	the convert_blessed option will decide whether "null"
		421	("convert_blessed" disabled or no "TO_JSON" method found) or a
		422	representation of the object ("convert_blessed" enabled and
		423	"TO_JSON" method found) is being encoded. Has no effect on "decode".
		424
		425	If $enable is false (the default), then "encode" will throw an
		426	exception when it encounters a blessed object.
		427
		428	$json = $json->convert_blessed ([$enable])
		429	$enabled = $json->get_convert_blessed
		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. If no "TO_JSON" method is found, the value of
		435	"allow_blessed" will decide what to do.
		436
		437	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
		438	returns other blessed objects, those will be handled in the same
		439	way. "TO_JSON" must take care of not causing an endless recursion
		440	cycle (== crash) in this case. The name of "TO_JSON" was chosen
		441	because other methods called by the Perl core (== not by the user of
		442	the object) are usually in upper case letters and to avoid
		443	collisions with any "to_json" function or method.
		444
		445	This setting does not yet influence "decode" in any way, but in the
		446	future, global hooks might get installed that influence "decode" and
		447	are enabled by this setting.
		448
		449	If $enable is false, then the "allow_blessed" setting will decide
		450	what to do when a blessed object is found.
		451
		452	$json = $json->filter_json_object ([$coderef->($hashref)])
		453	When $coderef is specified, it will be called from "decode" each
		454	time it decodes a JSON object. The only argument is a reference to
		455	the newly-created hash. If the code references returns a single
		456	scalar (which need not be a reference), this value (i.e. a copy of
		457	that scalar to avoid aliasing) is inserted into the deserialised
		458	data structure. If it returns an empty list (NOTE: not "undef",
		459	which is a valid scalar), the original deserialised hash will be
		460	inserted. This setting can slow down decoding considerably.
		461
		462	When $coderef is omitted or undefined, any existing callback will be
		463	removed and "decode" will not change the deserialised hash in any
		464	way.
		465
		466	Example, convert all JSON objects into the integer 5:
		467
		468	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		469	# returns [5]
		470	$js->decode ('[{}]')
		471	# throw an exception because allow_nonref is not enabled
		472	# so a lone 5 is not allowed.
		473	$js->decode ('{"a":1, "b":2}');
		474
		475	$json = $json->filter_json_single_key_object ($key [=>
		476	$coderef->($value)])
		477	Works remotely similar to "filter_json_object", but is only called
		478	for JSON objects having a single key named $key.
		479
		480	This $coderef is called before the one specified via
		481	"filter_json_object", if any. It gets passed the single value in the
		482	JSON object. If it returns a single value, it will be inserted into
		483	the data structure. If it returns nothing (not even "undef" but the
		484	empty list), the callback from "filter_json_object" will be called
		485	next, as if no single-key callback were specified.
		486
		487	If $coderef is omitted or undefined, the corresponding callback will
		488	be disabled. There can only ever be one callback for a given key.
		489
		490	As this callback gets called less often then the
		491	"filter_json_object" one, decoding speed will not usually suffer as
		492	much. Therefore, single-key objects make excellent targets to
		493	serialise Perl objects into, especially as single-key JSON objects
		494	are as close to the type-tagged value concept as JSON gets (it's
		495	basically an ID/VALUE tuple). Of course, JSON does not support this
		496	in any way, so you need to make sure your data never looks like a
		497	serialised Perl hash.
		498
		499	Typical names for the single object key are "__class_whatever__", or
		500	"$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
		501	things like "__class_md5sum(classname)__", to reduce the risk of
		502	clashing with real hashes.
		503
		504	Example, decode JSON objects of the form "{ "__widget__" => <id> }"
		505	into the corresponding $WIDGET{<id>} object:
		506
		507	# return whatever is in $WIDGET{5}:
		508	JSON::XS
		509	->new
		510	->filter_json_single_key_object (__widget__ => sub {
		511	$WIDGET{ $_[0] }
		512	})
		513	->decode ('{"__widget__": 5')
		514
		515	# this can be used with a TO_JSON method in some "widget" class
		516	# for serialisation to json:
		517	sub WidgetBase::TO_JSON {
		518	my ($self) = @_;
		519
		520	unless ($self->{id}) {
		521	$self->{id} = ..get..some..id..;
		522	$WIDGET{$self->{id}} = $self;
		523	}
		524
		525	{ __widget__ => $self->{id} }
		526	}
		527
219	$json = $json->shrink ([$enable])	528	$json = $json->shrink ([$enable])
		529	$enabled = $json->get_shrink
220	Perl usually over-allocates memory a bit when allocating space for	530	Perl usually over-allocates memory a bit when allocating space for
221	strings. This flag optionally resizes strings generated by either	531	strings. This flag optionally resizes strings generated by either
222	"encode" or "decode" to their minimum size possible. This can save	532	"encode" or "decode" to their minimum size possible. This can save
223	memory when your JSON strings are either very very long or you have	533	memory when your JSON texts are either very very long or you have
224	many short strings. It will also try to downgrade any strings to	534	many short strings. It will also try to downgrade any strings to
225	octet-form if possible: perl stores strings internally either in an	535	octet-form if possible: perl stores strings internally either in an
226	encoding called UTF-X or in octet-form. The latter cannot store	536	encoding called UTF-X or in octet-form. The latter cannot store
227	everything but uses less space in general.	537	everything but uses less space in general (and some buggy Perl or C
		538	code might even rely on that internal representation being used).
		539
		540	The actual definition of what shrink does might change in future
		541	versions, but it will always try to save space at the expense of
		542	time.
228		543
229	If $enable is true (or missing), the string returned by "encode"	544	If $enable is true (or missing), the string returned by "encode"
230	will be shrunk-to-fit, while all strings generated by "decode" will	545	will be shrunk-to-fit, while all strings generated by "decode" will
231	also be shrunk-to-fit.	546	also be shrunk-to-fit.
232		547
…		…
236	In the future, this setting might control other things, such as	551	In the future, this setting might control other things, such as
237	converting strings that look like integers or floats into integers	552	converting strings that look like integers or floats into integers
238	or floats internally (there is no difference on the Perl level),	553	or floats internally (there is no difference on the Perl level),
239	saving space.	554	saving space.
240		555
		556	$json = $json->max_depth ([$maximum_nesting_depth])
		557	$max_depth = $json->get_max_depth
		558	Sets the maximum nesting level (default 512) accepted while encoding
		559	or decoding. If a higher nesting level is detected in JSON text or a
		560	Perl data structure, then the encoder and decoder will stop and
		561	croak at that point.
		562
		563	Nesting level is defined by number of hash- or arrayrefs that the
		564	encoder needs to traverse to reach a given point or the number of
		565	"{" or "[" characters without their matching closing parenthesis
		566	crossed to reach a given character in a string.
		567
		568	Setting the maximum depth to one disallows any nesting, so that
		569	ensures that the object is only a single hash/object or array.
		570
		571	If no argument is given, the highest possible setting will be used,
		572	which is rarely useful.
		573
		574	Note that nesting is implemented by recursion in C. The default
		575	value has been chosen to be as large as typical operating systems
		576	allow without crashing.
		577
		578	See SECURITY CONSIDERATIONS, below, for more info on why this is
		579	useful.
		580
		581	$json = $json->max_size ([$maximum_string_size])
		582	$max_size = $json->get_max_size
		583	Set the maximum length a JSON text may have (in bytes) where
		584	decoding is being attempted. The default is 0, meaning no limit.
		585	When "decode" is called on a string that is longer then this many
		586	bytes, it will not attempt to decode the string but throw an
		587	exception. This setting has no effect on "encode" (yet).
		588
		589	If no argument is given, the limit check will be deactivated (same
		590	as when 0 is specified).
		591
		592	See SECURITY CONSIDERATIONS, below, for more info on why this is
		593	useful.
		594
241	$json_string = $json->encode ($perl_scalar)	595	$json_text = $json->encode ($perl_scalar)
242	Converts the given Perl data structure (a simple scalar or a	596	Converts the given Perl data structure (a simple scalar or a
243	reference to a hash or array) to its JSON representation. Simple	597	reference to a hash or array) to its JSON representation. Simple
244	scalars will be converted into JSON string or number sequences,	598	scalars will be converted into JSON string or number sequences,
245	while references to arrays become JSON arrays and references to	599	while references to arrays become JSON arrays and references to
246	hashes become JSON objects. Undefined Perl values (e.g. "undef")	600	hashes become JSON objects. Undefined Perl values (e.g. "undef")
247	become JSON "null" values. Neither "true" nor "false" values will be	601	become JSON "null" values. Neither "true" nor "false" values will be
248	generated.	602	generated.
249		603
250	$perl_scalar = $json->decode ($json_string)	604	$perl_scalar = $json->decode ($json_text)
251	The opposite of "encode": expects a JSON string and tries to parse	605	The opposite of "encode": expects a JSON text and tries to parse it,
252	it, returning the resulting simple scalar or reference. Croaks on	606	returning the resulting simple scalar or reference. Croaks on error.
253	error.
254		607
255	JSON numbers and strings become simple Perl scalars. JSON arrays	608	JSON numbers and strings become simple Perl scalars. JSON arrays
256	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"	609	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
257	becomes 1, "false" becomes 0 and "null" becomes "undef".	610	becomes 1, "false" becomes 0 and "null" becomes "undef".
		611
		612	($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		613	This works like the "decode" method, but instead of raising an
		614	exception when there is trailing garbage after the first JSON
		615	object, it will silently stop parsing there and return the number of
		616	characters consumed so far.
		617
		618	This is useful if your JSON texts are not delimited by an outer
		619	protocol (which is not the brightest thing to do in the first place)
		620	and you need to know where the JSON text ends.
		621
		622	JSON::XS->new->decode_prefix ("[1] the tail")
		623	=> ([], 3)
		624
		625	INCREMENTAL PARSING
		626	In some cases, there is the need for incremental parsing of JSON texts.
		627	While this module always has to keep both JSON text and resulting Perl
		628	data structure in memory at one time, it does allow you to parse a JSON
		629	stream incrementally. It does so by accumulating text until it has a
		630	full JSON object, which it then can decode. This process is similar to
		631	using "decode_prefix" to see if a full JSON object is available, but is
		632	much more efficient (and can be implemented with a minimum of method
		633	calls).
		634
		635	JSON::XS will only attempt to parse the JSON text once it is sure it has
		636	enough text to get a decisive result, using a very simple but truly
		637	incremental parser. This means that it sometimes won't stop as early as
		638	the full parser, for example, it doesn't detect parenthese mismatches.
		639	The only thing it guarantees is that it starts decoding as soon as a
		640	syntactically valid JSON text has been seen. This means you need to set
		641	resource limits (e.g. "max_size") to ensure the parser will stop parsing
		642	in the presence if syntax errors.
		643
		644	The following methods implement this incremental parser.
		645
		646	[void, scalar or list context] = $json->incr_parse ([$string])
		647	This is the central parsing function. It can both append new text
		648	and extract objects from the stream accumulated so far (both of
		649	these functions are optional).
		650
		651	If $string is given, then this string is appended to the already
		652	existing JSON fragment stored in the $json object.
		653
		654	After that, if the function is called in void context, it will
		655	simply return without doing anything further. This can be used to
		656	add more text in as many chunks as you want.
		657
		658	If the method is called in scalar context, then it will try to
		659	extract exactly one JSON object. If that is successful, it will
		660	return this object, otherwise it will return "undef". If there is a
		661	parse error, this method will croak just as "decode" would do (one
		662	can then use "incr_skip" to skip the errornous part). This is the
		663	most common way of using the method.
		664
		665	And finally, in list context, it will try to extract as many objects
		666	from the stream as it can find and return them, or the empty list
		667	otherwise. For this to work, there must be no separators between the
		668	JSON objects or arrays, instead they must be concatenated
		669	back-to-back. If an error occurs, an exception will be raised as in
		670	the scalar context case. Note that in this case, any
		671	previously-parsed JSON texts will be lost.
		672
		673	$lvalue_string = $json->incr_text
		674	This method returns the currently stored JSON fragment as an lvalue,
		675	that is, you can manipulate it. This only works when a preceding
		676	call to "incr_parse" in scalar context successfully returned an
		677	object. Under all other circumstances you must not call this
		678	function (I mean it. although in simple tests it might actually
		679	work, it will fail under real world conditions). As a special
		680	exception, you can also call this method before having parsed
		681	anything.
		682
		683	This function is useful in two cases: a) finding the trailing text
		684	after a JSON object or b) parsing multiple JSON objects separated by
		685	non-JSON text (such as commas).
		686
		687	$json->incr_skip
		688	This will reset the state of the incremental parser and will remove
		689	the parsed text from the input buffer so far. This is useful after
		690	"incr_parse" died, in which case the input buffer and incremental
		691	parser state is left unchanged, to skip the text parsed so far and
		692	to reset the parse state.
		693
		694	The difference to "incr_reset" is that only text until the parse
		695	error occured is removed.
		696
		697	$json->incr_reset
		698	This completely resets the incremental parser, that is, after this
		699	call, it will be as if the parser had never parsed anything.
		700
		701	This is useful if you want to repeatedly parse JSON objects and want
		702	to ignore any trailing data, which means you have to reset the
		703	parser after each successful decode.
		704
		705	LIMITATIONS
		706	All options that affect decoding are supported, except "allow_nonref".
		707	The reason for this is that it cannot be made to work sensibly: JSON
		708	objects and arrays are self-delimited, i.e. you can concatenate them
		709	back to back and still decode them perfectly. This does not hold true
		710	for JSON numbers, however.
		711
		712	For example, is the string 1 a single JSON number, or is it simply the
		713	start of 12? Or is 12 a single JSON number, or the concatenation of 1
		714	and 2? In neither case you can tell, and this is why JSON::XS takes the
		715	conservative route and disallows this case.
		716
		717	EXAMPLES
		718	Some examples will make all this clearer. First, a simple example that
		719	works similarly to "decode_prefix": We want to decode the JSON object at
		720	the start of a string and identify the portion after the JSON object:
		721
		722	my $text = "[1,2,3] hello";
		723
		724	my $json = new JSON::XS;
		725
		726	my $obj = $json->incr_parse ($text)
		727	or die "expected JSON object or array at beginning of string";
		728
		729	my $tail = $json->incr_text;
		730	# $tail now contains " hello"
		731
		732	Easy, isn't it?
		733
		734	Now for a more complicated example: Imagine a hypothetical protocol
		735	where you read some requests from a TCP stream, and each request is a
		736	JSON array, without any separation between them (in fact, it is often
		737	useful to use newlines as "separators", as these get interpreted as
		738	whitespace at the start of the JSON text, which makes it possible to
		739	test said protocol with "telnet"...).
		740
		741	Here is how you'd do it (it is trivial to write this in an event-based
		742	manner):
		743
		744	my $json = new JSON::XS;
		745
		746	# read some data from the socket
		747	while (sysread $socket, my $buf, 4096) {
		748
		749	# split and decode as many requests as possible
		750	for my $request ($json->incr_parse ($buf)) {
		751	# act on the $request
		752	}
		753	}
		754
		755	Another complicated example: Assume you have a string with JSON objects
		756	or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
		757	[3]"). To parse them, we have to skip the commas between the JSON texts,
		758	and here is where the lvalue-ness of "incr_text" comes in useful:
		759
		760	my $text = "[1],[2], [3]";
		761	my $json = new JSON::XS;
		762
		763	# void context, so no parsing done
		764	$json->incr_parse ($text);
		765
		766	# now extract as many objects as possible. note the
		767	# use of scalar context so incr_text can be called.
		768	while (my $obj = $json->incr_parse) {
		769	# do something with $obj
		770
		771	# now skip the optional comma
		772	$json->incr_text =~ s/^ \s* , //x;
		773	}
		774
		775	Now lets go for a very complex example: Assume that you have a gigantic
		776	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		777	but you cannot load it into memory fully (this has actually happened in
		778	the real world :).
		779
		780	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		781	can still help you: You implement a (very simple) array parser and let
		782	JSON decode the array elements, which are all full JSON objects on their
		783	own (this wouldn't work if the array elements could be JSON numbers, for
		784	example):
		785
		786	my $json = new JSON::XS;
		787
		788	# open the monster
		789	open my $fh, "<bigfile.json"
		790	or die "bigfile: $!";
		791
		792	# first parse the initial "["
		793	for (;;) {
		794	sysread $fh, my $buf, 65536
		795	or die "read error: $!";
		796	$json->incr_parse ($buf); # void context, so no parsing
		797
		798	# Exit the loop once we found and removed(!) the initial "[".
		799	# In essence, we are (ab-)using the $json object as a simple scalar
		800	# we append data to.
		801	last if $json->incr_text =~ s/^ \s* \[ //x;
		802	}
		803
		804	# now we have the skipped the initial "[", so continue
		805	# parsing all the elements.
		806	for (;;) {
		807	# in this loop we read data until we got a single JSON object
		808	for (;;) {
		809	if (my $obj = $json->incr_parse) {
		810	# do something with $obj
		811	last;
		812	}
		813
		814	# add more data
		815	sysread $fh, my $buf, 65536
		816	or die "read error: $!";
		817	$json->incr_parse ($buf); # void context, so no parsing
		818	}
		819
		820	# in this loop we read data until we either found and parsed the
		821	# separating "," between elements, or the final "]"
		822	for (;;) {
		823	# first skip whitespace
		824	$json->incr_text =~ s/^\s*//;
		825
		826	# if we find "]", we are done
		827	if ($json->incr_text =~ s/^\]//) {
		828	print "finished.\n";
		829	exit;
		830	}
		831
		832	# if we find ",", we can continue with the next element
		833	if ($json->incr_text =~ s/^,//) {
		834	last;
		835	}
		836
		837	# if we find anything else, we have a parse error!
		838	if (length $json->incr_text) {
		839	die "parse error near ", $json->incr_text;
		840	}
		841
		842	# else add more data
		843	sysread $fh, my $buf, 65536
		844	or die "read error: $!";
		845	$json->incr_parse ($buf); # void context, so no parsing
		846	}
		847
		848	This is a complex example, but most of the complexity comes from the
		849	fact that we are trying to be correct (bear with me if I am wrong, I
		850	never ran the above example :).
258		851
259	MAPPING	852	MAPPING
260	This section describes how JSON::XS maps Perl values to JSON values and	853	This section describes how JSON::XS maps Perl values to JSON values and
261	vice versa. These mappings are designed to "do the right thing" in most	854	vice versa. These mappings are designed to "do the right thing" in most
262	circumstances automatically, preserving round-tripping characteristics	855	circumstances automatically, preserving round-tripping characteristics
263	(what you put in comes out as something equivalent).	856	(what you put in comes out as something equivalent).
264		857
265	For the more enlightened: note that in the following descriptions,	858	For the more enlightened: note that in the following descriptions,
266	lowercase perl refers to the Perl interpreter, while uppcercase Perl	859	lowercase perl refers to the Perl interpreter, while uppercase Perl
267	refers to the abstract Perl language itself.	860	refers to the abstract Perl language itself.
268		861
269	JSON -> PERL	862	JSON -> PERL
270	object	863	object
271	A JSON object becomes a reference to a hash in Perl. No ordering of	864	A JSON object becomes a reference to a hash in Perl. No ordering of
272	object keys is preserved (JSON does not preserver object key	865	object keys is preserved (JSON does not preserve object key ordering
273	ordering itself).	866	itself).
274		867
275	array	868	array
276	A JSON array becomes a reference to an array in Perl.	869	A JSON array becomes a reference to an array in Perl.
277		870
278	string	871	string
279	A JSON string becomes a string scalar in Perl - Unicode codepoints	872	A JSON string becomes a string scalar in Perl - Unicode codepoints
280	in JSON are represented by the same codepoints in the Perl string,	873	in JSON are represented by the same codepoints in the Perl string,
281	so no manual decoding is necessary.	874	so no manual decoding is necessary.
282		875
283	number	876	number
284	A JSON number becomes either an integer or numeric (floating point)	877	A JSON number becomes either an integer, numeric (floating point) or
285	scalar in perl, depending on its range and any fractional parts. On	878	string scalar in perl, depending on its range and any fractional
286	the Perl level, there is no difference between those as Perl handles	879	parts. On the Perl level, there is no difference between those as
287	all the conversion details, but an integer may take slightly less	880	Perl handles all the conversion details, but an integer may take
288	memory and might represent more values exactly than (floating point)	881	slightly less memory and might represent more values exactly than
		882	floating point numbers.
		883
		884	If the number consists of digits only, JSON::XS will try to
		885	represent it as an integer value. If that fails, it will try to
		886	represent it as a numeric (floating point) value if that is possible
		887	without loss of precision. Otherwise it will preserve the number as
		888	a string value (in which case you lose roundtripping ability, as the
		889	JSON number will be re-encoded toa JSON string).
		890
		891	Numbers containing a fractional or exponential part will always be
		892	represented as numeric (floating point) values, possibly at a loss
		893	of precision (in which case you might lose perfect roundtripping
		894	ability, but the JSON number will still be re-encoded as a JSON
289	numbers.	895	number).
290		896
291	true, false	897	true, false
292	These JSON atoms become 0, 1, respectively. Information is lost in	898	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
293	this process. Future versions might represent those values	899	respectively. They are overloaded to act almost exactly like the
294	differently, but they will be guarenteed to act like these integers	900	numbers 1 and 0. You can check whether a scalar is a JSON boolean by
295	would normally in Perl.	901	using the "JSON::XS::is_bool" function.
296		902
297	null	903	null
298	A JSON null atom becomes "undef" in Perl.	904	A JSON null atom becomes "undef" in Perl.
299		905
300	PERL -> JSON	906	PERL -> JSON
…		…
302	truly typeless language, so we can only guess which JSON type is meant	908	truly typeless language, so we can only guess which JSON type is meant
303	by a Perl value.	909	by a Perl value.
304		910
305	hash references	911	hash references
306	Perl hash references become JSON objects. As there is no inherent	912	Perl hash references become JSON objects. As there is no inherent
307	ordering in hash keys, they will usually be encoded in a	913	ordering in hash keys (or JSON objects), they will usually be
308	pseudo-random order that can change between runs of the same program	914	encoded in a pseudo-random order that can change between runs of the
309	but stays generally the same within a single run of a program.	915	same program but stays generally the same within a single run of a
310	JSON::XS can optionally sort the hash keys (determined by the	916	program. JSON::XS can optionally sort the hash keys (determined by
311	canonical flag), so the same datastructure will serialise to the	917	the canonical flag), so the same datastructure will serialise to
312	same JSON text (given same settings and version of JSON::XS), but	918	the same JSON text (given same settings and version of JSON::XS),
313	this incurs a runtime overhead.	919	but this incurs a runtime overhead and is only rarely useful, e.g.
		920	when you want to compare some JSON text against another for
		921	equality.
314		922
315	array references	923	array references
316	Perl array references become JSON arrays.	924	Perl array references become JSON arrays.
317		925
		926	other references
		927	Other unblessed references are generally not allowed and will cause
		928	an exception to be thrown, except for references to the integers 0
		929	and 1, which get turned into "false" and "true" atoms in JSON. You
		930	can also use "JSON::XS::false" and "JSON::XS::true" to improve
		931	readability.
		932
		933	encode_json [\0, JSON::XS::true] # yields [false,true]
		934
		935	JSON::XS::true, JSON::XS::false
		936	These special values become JSON true and JSON false values,
		937	respectively. You can also use "\1" and "\0" directly if you want.
		938
318	blessed objects	939	blessed objects
319	Blessed objects are not allowed. JSON::XS currently tries to encode	940	Blessed objects are not directly representable in JSON. See the
320	their underlying representation (hash- or arrayref), but this	941	"allow_blessed" and "convert_blessed" methods on various options on
321	behaviour might change in future versions.	942	how to deal with this: basically, you can choose between throwing an
		943	exception, encoding the reference as if it weren't blessed, or
		944	provide your own serialiser method.
322		945
323	simple scalars	946	simple scalars
324	Simple Perl scalars (any scalar that is not a reference) are the	947	Simple Perl scalars (any scalar that is not a reference) are the
325	most difficult objects to encode: JSON::XS will encode undefined	948	most difficult objects to encode: JSON::XS will encode undefined
326	scalars as JSON null value, scalars that have last been used in a	949	scalars as JSON "null" values, scalars that have last been used in a
327	string context before encoding as JSON strings and anything else as	950	string context before encoding as JSON strings, and anything else as
328	number value:	951	number value:
329		952
330	# dump as number	953	# dump as number
331	to_json [2] # yields [2]	954	encode_json [2] # yields [2]
332	to_json [-3.0e17] # yields [-3e+17]	955	encode_json [-3.0e17] # yields [-3e+17]
333	my $value = 5; to_json [$value] # yields [5]	956	my $value = 5; encode_json [$value] # yields [5]
334		957
335	# used as string, so dump as string	958	# used as string, so dump as string
336	print $value;	959	print $value;
337	to_json [$value] # yields ["5"]	960	encode_json [$value] # yields ["5"]
338		961
339	# undef becomes null	962	# undef becomes null
340	to_json [undef] # yields [null]	963	encode_json [undef] # yields [null]
341		964
342	You can force the type to be a string by stringifying it:	965	You can force the type to be a JSON string by stringifying it:
343		966
344	my $x = 3.1; # some variable containing a number	967	my $x = 3.1; # some variable containing a number
345	"$x"; # stringified	968	"$x"; # stringified
346	$x .= ""; # another, more awkward way to stringify	969	$x .= ""; # another, more awkward way to stringify
347	print $x; # perl does it for you, too, quite often	970	print $x; # perl does it for you, too, quite often
348		971
349	You can force the type to be a number by numifying it:	972	You can force the type to be a JSON number by numifying it:
350		973
351	my $x = "3"; # some variable containing a string	974	my $x = "3"; # some variable containing a string
352	$x += 0; # numify it, ensuring it will be dumped as a number	975	$x += 0; # numify it, ensuring it will be dumped as a number
353	$x *= 1; # same thing, the choise is yours.	976	$x *= 1; # same thing, the choice is yours.
354		977
355	You can not currently output JSON booleans or force the type in	978	You can not currently force the type in other, less obscure, ways.
356	other, less obscure, ways. Tell me if you need this capability.	979	Tell me if you need this capability (but don't forget to explain why
		980	it's needed :).
357		981
358	circular data structures	982	ENCODING/CODESET FLAG NOTES
359	Those will be encoded until memory or stackspace runs out.	983	The interested reader might have seen a number of flags that signify
		984	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
		985	some confusion on what these do, so here is a short comparison:
360		986
361	COMPARISON	987	"utf8" controls whether the JSON text created by "encode" (and expected
362	As already mentioned, this module was created because none of the	988	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
363	existing JSON modules could be made to work correctly. First I will	989	control whether "encode" escapes character values outside their
364	describe the problems (or pleasures) I encountered with various existing	990	respective codeset range. Neither of these flags conflict with each
365	JSON modules, followed by some benchmark values. JSON::XS was designed	991	other, although some combinations make less sense than others.
366	not to suffer from any of these problems or limitations.
367		992
368	JSON 1.07	993	Care has been taken to make all flags symmetrical with respect to
369	Slow (but very portable, as it is written in pure Perl).	994	"encode" and "decode", that is, texts encoded with any combination of
		995	these flag values will be correctly decoded when the same flags are used
		996	- in general, if you use different flag settings while encoding vs. when
		997	decoding you likely have a bug somewhere.
370		998
371	Undocumented/buggy Unicode handling (how JSON handles unicode values	999	Below comes a verbose discussion of these flags. Note that a "codeset"
372	is undocumented. One can get far by feeding it unicode strings and	1000	is simply an abstract set of character-codepoint pairs, while an
373	doing en-/decoding oneself, but unicode escapes are not working	1001	encoding takes those codepoint numbers and encodes them, in our case
		1002	into octets. Unicode is (among other things) a codeset, UTF-8 is an
		1003	encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
		1004	encodings at the same time, which can be confusing.
		1005
		1006	"utf8" flag disabled
		1007	When "utf8" is disabled (the default), then "encode"/"decode"
		1008	generate and expect Unicode strings, that is, characters with high
		1009	ordinal Unicode values (> 255) will be encoded as such characters,
		1010	and likewise such characters are decoded as-is, no canges to them
		1011	will be done, except "(re-)interpreting" them as Unicode codepoints
		1012	or Unicode characters, respectively (to Perl, these are the same
		1013	thing in strings unless you do funny/weird/dumb stuff).
		1014
		1015	This is useful when you want to do the encoding yourself (e.g. when
		1016	you want to have UTF-16 encoded JSON texts) or when some other layer
		1017	does the encoding for you (for example, when printing to a terminal
		1018	using a filehandle that transparently encodes to UTF-8 you certainly
		1019	do NOT want to UTF-8 encode your data first and have Perl encode it
		1020	another time).
		1021
		1022	"utf8" flag enabled
		1023	If the "utf8"-flag is enabled, "encode"/"decode" will encode all
		1024	characters using the corresponding UTF-8 multi-byte sequence, and
		1025	will expect your input strings to be encoded as UTF-8, that is, no
		1026	"character" of the input string must have any value > 255, as UTF-8
		1027	does not allow that.
		1028
		1029	The "utf8" flag therefore switches between two modes: disabled means
		1030	you will get a Unicode string in Perl, enabled means you get an
		1031	UTF-8 encoded octet/binary string in Perl.
		1032
		1033	"latin1" or "ascii" flags enabled
		1034	With "latin1" (or "ascii") enabled, "encode" will escape characters
		1035	with ordinal values > 255 (> 127 with "ascii") and encode the
		1036	remaining characters as specified by the "utf8" flag.
		1037
		1038	If "utf8" is disabled, then the result is also correctly encoded in
		1039	those character sets (as both are proper subsets of Unicode, meaning
		1040	that a Unicode string with all character values < 256 is the same
		1041	thing as a ISO-8859-1 string, and a Unicode string with all
		1042	character values < 128 is the same thing as an ASCII string in
374	properly).	1043	Perl).
375		1044
376	No roundtripping (strings get clobbered if they look like numbers,	1045	If "utf8" is enabled, you still get a correct UTF-8-encoded string,
377	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	1046	regardless of these flags, just some more characters will be escaped
378	will decode into the number 2.	1047	using "\uXXXX" then before.
379		1048
380	JSON::PC 0.01	1049	Note that ISO-8859-1-encoded strings are not compatible with UTF-8
381	Very fast.	1050	encoding, while ASCII-encoded strings are. That is because the
		1051	ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
		1052	codeset being a subset of Unicode), while ASCII is.
382		1053
383	Undocumented/buggy Unicode handling.	1054	Surprisingly, "decode" will ignore these flags and so treat all
		1055	input values as governed by the "utf8" flag. If it is disabled, this
		1056	allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
		1057	strict subsets of Unicode. If it is enabled, you can correctly
		1058	decode UTF-8 encoded strings.
384		1059
385	No roundtripping.	1060	So neither "latin1" nor "ascii" are incompatible with the "utf8"
		1061	flag - they only govern when the JSON output engine escapes a
		1062	character or not.
386		1063
387	Has problems handling many Perl values (e.g. regex results and other	1064	The main use for "latin1" is to relatively efficiently store binary
388	magic values will make it croak).	1065	data as JSON, at the expense of breaking compatibility with most
		1066	JSON decoders.
389		1067
390	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1068	The main use for "ascii" is to force the output to not contain
391	which is not a valid JSON string.	1069	characters with values > 127, which means you can interpret the
		1070	resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
		1071	any character set and 8-bit-encoding, and still get the same data
		1072	structure back. This is useful when your channel for JSON transfer
		1073	is not 8-bit clean or the encoding might be mangled in between (e.g.
		1074	in mail), and works because ASCII is a proper subset of most 8-bit
		1075	and multibyte encodings in use in the world.
392		1076
393	Unmaintained (maintainer unresponsive for many months, bugs are not	1077	JSON and ECMAscript
394	getting fixed).	1078	JSON syntax is based on how literals are represented in javascript (the
		1079	not-standardised predecessor of ECMAscript) which is presumably why it
		1080	is called "JavaScript Object Notation".
395		1081
396	JSON::Syck 0.21	1082	However, JSON is not a subset (and also not a superset of course) of
397	Very buggy (often crashes).	1083	ECMAscript (the standard) or javascript (whatever browsers actually
		1084	implement).
398		1085
399	Very inflexible (no human-readable format supported, format pretty	1086	If you want to use javascript's "eval" function to "parse" JSON, you
400	much undocumented. I need at least a format for easy reading by	1087	might run into parse errors for valid JSON texts, or the resulting data
401	humans and a single-line compact format for use in a protocol, and	1088	structure might not be queryable:
402	preferably a way to generate ASCII-only JSON strings).
403		1089
404	Completely broken (and confusingly documented) Unicode handling	1090	One of the problems is that U+2028 and U+2029 are valid characters
405	(unicode escapes are not working properly, you need to set	1091	inside JSON strings, but are not allowed in ECMAscript string literals,
406	ImplicitUnicode to different values on en- and decoding to get	1092	so the following Perl fragment will not output something that can be
407	symmetric behaviour).	1093	guaranteed to be parsable by javascript's "eval":
408		1094
409	No roundtripping (simple cases work, but this depends on wether the	1095	use JSON::XS;
410	scalar value was used in a numeric context or not).
411		1096
412	Dumping hashes may skip hash values depending on iterator state.	1097	print encode_json [chr 0x2028];
413		1098
414	Unmaintained (maintainer unresponsive for many months, bugs are not	1099	The right fix for this is to use a proper JSON parser in your javascript
415	getting fixed).	1100	programs, and not rely on "eval" (see for example Douglas Crockford's
		1101	json2.js parser).
416		1102
417	Does not check input for validity (i.e. will accept non-JSON input	1103	If this is not an option, you can, as a stop-gap measure, simply encode
418	and return "something" instead of raising an exception. This is a	1104	to ASCII-only JSON:
419	security issue: imagine two banks transfering money between each
420	other using JSON. One bank might parse a given non-JSON request and
421	deduct money, while the other might reject the transaction with a
422	syntax error. While a good protocol will at least recover, that is
423	extra unnecessary work and the transaction will still not succeed).
424		1105
425	JSON::DWIW 0.04	1106	use JSON::XS;
426	Very fast. Very natural. Very nice.
427		1107
428	Undocumented unicode handling (but the best of the pack. Unicode	1108	print JSON::XS->new->ascii->encode ([chr 0x2028]);
429	escapes still don't get parsed properly).
430		1109
431	Very inflexible.	1110	Note that this will enlarge the resulting JSON text quite a bit if you
		1111	have many non-ASCII characters. You might be tempted to run some regexes
		1112	to only escape U+2028 and U+2029, e.g.:
432		1113
433	No roundtripping.	1114	# DO NOT USE THIS!
		1115	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1116	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1117	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1118	print $json;
434		1119
435	Does not generate valid JSON (key strings are often unquoted, empty	1120	Note that this is a bad idea: the above only works for U+2028 and
436	keys result in nothing being output)	1121	U+2029 and thus only for fully ECMAscript-compliant parsers. Many
		1122	existing javascript implementations, however, have issues with other
		1123	characters as well - using "eval" naively simply will cause problems.
437		1124
438	Does not check input for validity.	1125	Another problem is that some javascript implementations reserve some
		1126	property names for their own purposes (which probably makes them
		1127	non-ECMAscript-compliant). For example, Iceweasel reserves the
		1128	"__proto__" property name for it's own purposes.
		1129
		1130	If that is a problem, you could parse try to filter the resulting JSON
		1131	output for these property strings, e.g.:
		1132
		1133	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1134
		1135	This works because "__proto__" is not valid outside of strings, so every
		1136	occurence of ""__proto__"\s*:" must be a string used as property name.
		1137
		1138	If you know of other incompatibilities, please let me know.
		1139
		1140	JSON and YAML
		1141	You often hear that JSON is a subset of YAML. This is, however, a mass
		1142	hysteria(*) and very far from the truth (as of the time of this
		1143	writing), so let me state it clearly: *in general, there is no way to
		1144	configure JSON::XS to output a data structure as valid YAML* that works
		1145	in all cases.
		1146
		1147	If you really must use JSON::XS to generate YAML, you should use this
		1148	algorithm (subject to change in future versions):
		1149
		1150	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1151	my $yaml = $to_yaml->encode ($ref) . "\n";
		1152
		1153	This will usually generate JSON texts that also parse as valid YAML.
		1154	Please note that YAML has hardcoded limits on (simple) object key
		1155	lengths that JSON doesn't have and also has different and incompatible
		1156	unicode handling, so you should make sure that your hash keys are
		1157	noticeably shorter than the 1024 "stream characters" YAML allows and
		1158	that you do not have characters with codepoint values outside the
		1159	Unicode BMP (basic multilingual page). YAML also does not allow "\/"
		1160	sequences in strings (which JSON::XS does not currently generate, but
		1161	other JSON generators might).
		1162
		1163	There might be other incompatibilities that I am not aware of (or the
		1164	YAML specification has been changed yet again - it does so quite often).
		1165	In general you should not try to generate YAML with a JSON generator or
		1166	vice versa, or try to parse JSON with a YAML parser or vice versa:
		1167	chances are high that you will run into severe interoperability problems
		1168	when you least expect it.
		1169
		1170	(*) I have been pressured multiple times by Brian Ingerson (one of the
		1171	authors of the YAML specification) to remove this paragraph, despite
		1172	him acknowledging that the actual incompatibilities exist. As I was
		1173	personally bitten by this "JSON is YAML" lie, I refused and said I
		1174	will continue to educate people about these issues, so others do not
		1175	run into the same problem again and again. After this, Brian called
		1176	me a (quote)complete and worthless idiot(unquote).
		1177
		1178	In my opinion, instead of pressuring and insulting people who
		1179	actually clarify issues with YAML and the wrong statements of some
		1180	of its proponents, I would kindly suggest reading the JSON spec
		1181	(which is not that difficult or long) and finally make YAML
		1182	compatible to it, and educating users about the changes, instead of
		1183	spreading lies about the real compatibility for many years and
		1184	trying to silence people who point out that it isn't true.
439		1185
440	SPEED	1186	SPEED
441	It seems that JSON::XS is surprisingly fast, as shown in the following	1187	It seems that JSON::XS is surprisingly fast, as shown in the following
442	tables. They have been generated with the help of the "eg/bench" program	1188	tables. They have been generated with the help of the "eg/bench" program
443	in the JSON::XS distribution, to make it easy to compare on your own	1189	in the JSON::XS distribution, to make it easy to compare on your own
444	system.	1190	system.
445		1191
446	First comes a comparison between various modules using a very short JSON	1192	First comes a comparison between various modules using a very short
447	string (83 bytes), showing the number of encodes/decodes per second	1193	single-line JSON string (also available at
448	(JSON::XS is the functional interface, while JSON::XS/2 is the OO	1194	<http://dist.schmorp.de/misc/json/short.json>).
449	interface with pretty-printing and hashkey sorting enabled). Higher is	1195
450	better:	1196	{"method": "handleMessage", "params": ["user1",
		1197	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1198	true, false]}
		1199
		1200	It shows the number of encodes/decodes per second (JSON::XS uses the
		1201	functional interface, while JSON::XS/2 uses the OO interface with
		1202	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
		1203	Higher is better:
451		1204
452	module \| encode \| decode \|	1205	module \| encode \| decode \|
453	-----------\|------------\|------------\|	1206	-----------\|------------\|------------\|
454	JSON \| 14006 \| 6820 \|	1207	JSON 1.x \| 4990.842 \| 4088.813 \|
455	JSON::DWIW \| 200937 \| 120386 \|	1208	JSON::DWIW \| 51653.990 \| 71575.154 \|
456	JSON::PC \| 85065 \| 129366 \|	1209	JSON::PC \| 65948.176 \| 74631.744 \|
457	JSON::Syck \| 59898 \| 44232 \|	1210	JSON::PP \| 8931.652 \| 3817.168 \|
458	JSON::XS \| 1171478 \| 342435 \|	1211	JSON::Syck \| 24877.248 \| 27776.848 \|
459	JSON::XS/2 \| 730760 \| 328714 \|	1212	JSON::XS \| 388361.481 \| 227951.304 \|
		1213	JSON::XS/2 \| 227951.304 \| 218453.333 \|
		1214	JSON::XS/3 \| 338250.323 \| 218453.333 \|
		1215	Storable \| 16500.016 \| 135300.129 \|
460	-----------+------------+------------+	1216	-----------+------------+------------+
461		1217
462	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1218	That is, JSON::XS is about five times faster than JSON::DWIW on
		1219	encoding, about three times faster on decoding, and over forty times
463	times faster than JSON, even with pretty-printing and key sorting.	1220	faster than JSON, even with pretty-printing and key sorting. It also
		1221	compares favourably to Storable for small amounts of data.
464		1222
465	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1223	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
466	search API (http://nanoref.com/yahooapis/mgPdGg):	1224	search API (<http://dist.schmorp.de/misc/json/long.json>).
467		1225
468	module \| encode \| decode \|	1226	module \| encode \| decode \|
469	-----------\|------------\|------------\|	1227	-----------\|------------\|------------\|
470	JSON \| 673 \| 38 \|	1228	JSON 1.x \| 55.260 \| 34.971 \|
471	JSON::DWIW \| 5271 \| 770 \|	1229	JSON::DWIW \| 825.228 \| 1082.513 \|
		1230	JSON::PC \| 3571.444 \| 2394.829 \|
472	JSON::PC \| 9901 \| 2491 \|	1231	JSON::PP \| 210.987 \| 32.574 \|
473	JSON::Syck \| 2360 \| 786 \|	1232	JSON::Syck \| 552.551 \| 787.544 \|
474	JSON::XS \| 37398 \| 3202 \|	1233	JSON::XS \| 5780.463 \| 4854.519 \|
475	JSON::XS/2 \| 13765 \| 3153 \|	1234	JSON::XS/2 \| 3869.998 \| 4798.975 \|
		1235	JSON::XS/3 \| 5862.880 \| 4798.975 \|
		1236	Storable \| 4445.002 \| 5235.027 \|
476	-----------+------------+------------+	1237	-----------+------------+------------+
477		1238
478	Again, JSON::XS leads by far in the encoding case, while still beating	1239	Again, JSON::XS leads by far (except for Storable which non-surprisingly
479	every other module in the decoding case.	1240	decodes faster).
480		1241
481	On large strings containing lots of unicode characters, some modules	1242	On large strings containing lots of high Unicode characters, some
482	(such as JSON::PC) decode faster than JSON::XS, but the result will be	1243	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
483	broken due to missing unicode handling. Others refuse to decode or	1244	result will be broken due to missing (or wrong) Unicode handling. Others
484	encode properly, so it was impossible to prepare a fair comparison table	1245	refuse to decode or encode properly, so it was impossible to prepare a
485	for that case.	1246	fair comparison table for that case.
486		1247
487	RESOURCE LIMITS	1248	SECURITY CONSIDERATIONS
488	JSON::XS does not impose any limits on the size of JSON texts or Perl	1249	When you are using JSON in a protocol, talking to untrusted potentially
489	values they represent - if your machine can handle it, JSON::XS will	1250	hostile creatures requires relatively few measures.
490	encode or decode it. Future versions might optionally impose structure	1251
491	depth and memory use resource limits.	1252	First of all, your JSON decoder should be secure, that is, should not
		1253	have any buffer overflows. Obviously, this module should ensure that and
		1254	I am trying hard on making that true, but you never know.
		1255
		1256	Second, you need to avoid resource-starving attacks. That means you
		1257	should limit the size of JSON texts you accept, or make sure then when
		1258	your resources run out, that's just fine (e.g. by using a separate
		1259	process that can crash safely). The size of a JSON text in octets or
		1260	characters is usually a good indication of the size of the resources
		1261	required to decode it into a Perl structure. While JSON::XS can check
		1262	the size of the JSON text, it might be too late when you already have it
		1263	in memory, so you might want to check the size before you accept the
		1264	string.
		1265
		1266	Third, JSON::XS recurses using the C stack when decoding objects and
		1267	arrays. The C stack is a limited resource: for instance, on my amd64
		1268	machine with 8MB of stack size I can decode around 180k nested arrays
		1269	but only 14k nested JSON objects (due to perl itself recursing deeply on
		1270	croak to free the temporary). If that is exceeded, the program crashes.
		1271	To be conservative, the default nesting limit is set to 512. If your
		1272	process has a smaller stack, you should adjust this setting accordingly
		1273	with the "max_depth" method.
		1274
		1275	Something else could bomb you, too, that I forgot to think of. In that
		1276	case, you get to keep the pieces. I am always open for hints, though...
		1277
		1278	Also keep in mind that JSON::XS might leak contents of your Perl data
		1279	structures in its error messages, so when you serialise sensitive
		1280	information you might want to make sure that exceptions thrown by
		1281	JSON::XS will not end up in front of untrusted eyes.
		1282
		1283	If you are using JSON::XS to return packets to consumption by JavaScript
		1284	scripts in a browser you should have a look at
		1285	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1286	you are vulnerable to some common attack vectors (which really are
		1287	browser design bugs, but it is still you who will have to deal with it,
		1288	as major browser developers care only for features, not about getting
		1289	security right).
		1290
		1291	THREADS
		1292	This module is not guaranteed to be thread safe and there are no plans
		1293	to change this until Perl gets thread support (as opposed to the
		1294	horribly slow so-called "threads" which are simply slow and bloated
		1295	process simulations - use fork, it's much faster, cheaper, better).
		1296
		1297	(It might actually work, but you have been warned).
492		1298
493	BUGS	1299	BUGS
494	While the goal of this module is to be correct, that unfortunately does	1300	While the goal of this module is to be correct, that unfortunately does
495	not mean its bug-free, only that I think its design is bug-free. It is	1301	not mean it's bug-free, only that I think its design is bug-free. If you
496	still very young and not well-tested. If you keep reporting bugs they	1302	keep reporting bugs they will be fixed swiftly, though.
497	will be fixed swiftly, though.	1303
		1304	Please refrain from using rt.cpan.org or any other bug reporting
		1305	service. I put the contact address into my modules for a reason.
		1306
		1307	SEE ALSO
		1308	The json_xs command line utility for quick experiments.
498		1309
499	AUTHOR	1310	AUTHOR
500	Marc Lehmann <schmorp@schmorp.de>	1311	Marc Lehmann <schmorp@schmorp.de>
501	http://home.schmorp.de/	1312	http://home.schmorp.de/
502		1313

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Comparing JSON-XS/README (file contents): Revision 1.5 by root, Sat Mar 24 01:15:22 2007 UTC vs. Revision 1.29 by root, Thu Feb 19 01:13:46 2009 UTC

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Comparing JSON-XS/README (file contents):
Revision 1.5 by root, Sat Mar 24 01:15:22 2007 UTC vs.
Revision 1.29 by root, Thu Feb 19 01:13:46 2009 UTC