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Comparing JSON-XS/README (file contents):
Revision 1.10 by root, Wed Apr 4 00:01:44 2007 UTC vs.
Revision 1.27 by root, Tue Jul 15 11:29:29 2008 UTC

…		…
1	NAME	1	NAME
2	JSON::XS - JSON serialising/deserialising, done correctly and fast	2	JSON::XS - JSON serialising/deserialising, done correctly and fast
3		3
		4	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		5	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		6
4	SYNOPSIS	7	SYNOPSIS
5	use JSON::XS;	8	use JSON::XS;
6		9
7	# exported functions, they croak on error	10	# exported functions, they croak on error
8	# and expect/generate UTF-8	11	# and expect/generate UTF-8
9		12
10	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	13	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
11	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	14	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
12
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
35		50
36	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	51	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
37	vice versa.	52	vice versa.
38		53
39	FEATURES	54	FEATURES
40	* correct unicode handling	55	* correct Unicode handling
		56
41	This module knows how to handle Unicode, and even documents how and	57	This module knows how to handle Unicode, documents how and when it
42	when it does so.	58	does so, and even documents what "correct" means.
43		59
44	* round-trip integrity	60	* round-trip integrity
		61
45	When you serialise a perl data structure using only datatypes	62	When you serialise a perl data structure using only data types
46	supported by JSON, the deserialised data structure is identical on	63	supported by JSON, the deserialised data structure is identical on
47	the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"	64	the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
48	just because it looks like a number).	65	just because it looks like a number). There minor are exceptions
		66	to this, read the MAPPING section below to learn about those.
49		67
50	* strict checking of JSON correctness	68	* strict checking of JSON correctness
		69
51	There is no guessing, no generating of illegal JSON texts by	70	There is no guessing, no generating of illegal JSON texts by
52	default, and only JSON is accepted as input by default (the latter	71	default, and only JSON is accepted as input by default (the latter
53	is a security feature).	72	is a security feature).
54		73
55	* fast	74	* fast
56	Compared to other JSON modules, this module compares favourably in
57	terms of speed, too.
58		75
		76	Compared to other JSON modules and other serialisers such as
		77	Storable, this module usually compares favourably in terms of speed,
		78	too.
		79
59	* simple to use	80	* simple to use
		81
60	This module has both a simple functional interface as well as an OO	82	This module has both a simple functional interface as well as an
61	interface.	83	object oriented interface interface.
62		84
63	* reasonably versatile output formats	85	* reasonably versatile output formats
		86
64	You can choose between the most compact guarenteed single-line	87	You can choose between the most compact guaranteed-single-line
65	format possible (nice for simple line-based protocols), a pure-ascii	88	format possible (nice for simple line-based protocols), a pure-ASCII
66	format (for when your transport is not 8-bit clean, still supports	89	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	90	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	91	want to read that stuff). Or you can combine those features in
69	whatever way you like.	92	whatever way you like.
70		93
71	FUNCTIONAL INTERFACE	94	FUNCTIONAL INTERFACE
72	The following convinience methods are provided by this module. They are	95	The following convenience methods are provided by this module. They are
73	exported by default:	96	exported by default:
74		97
75	$json_text = to_json $perl_scalar	98	$json_text = encode_json $perl_scalar
76	Converts the given Perl data structure (a simple scalar or a	99	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.	100	string (that is, the string contains octets only). Croaks on error.
79		101
80	This function call is functionally identical to:	102	This function call is functionally identical to:
81		103
82	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	104	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
83		105
84	except being faster.	106	Except being faster.
85		107
86	$perl_scalar = from_json $json_text	108	$perl_scalar = decode_json $json_text
87	The opposite of "to_json": expects an UTF-8 (binary) string and	109	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	110	tries to parse that as an UTF-8 encoded JSON text, returning the
89	resulting simple scalar or reference. Croaks on error.	111	resulting reference. Croaks on error.
90		112
91	This function call is functionally identical to:	113	This function call is functionally identical to:
92		114
93	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	115	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
94		116
95	except being faster.	117	Except being faster.
		118
		119	$is_boolean = JSON::XS::is_bool $scalar
		120	Returns true if the passed scalar represents either JSON::XS::true
		121	or JSON::XS::false, two constants that act like 1 and 0,
		122	respectively and are used to represent JSON "true" and "false"
		123	values in Perl.
		124
		125	See MAPPING, below, for more information on how JSON values are
		126	mapped to Perl.
		127
		128	A FEW NOTES ON UNICODE AND PERL
		129	Since this often leads to confusion, here are a few very clear words on
		130	how Unicode works in Perl, modulo bugs.
		131
		132	1. Perl strings can store characters with ordinal values > 255.
		133	This enables you to store Unicode characters as single characters in
		134	a Perl string - very natural.
		135
		136	2. Perl does not associate an encoding with your strings.
		137	... until you force it to, e.g. when matching it against a regex, or
		138	printing the scalar to a file, in which case Perl either interprets
		139	your string as locale-encoded text, octets/binary, or as Unicode,
		140	depending on various settings. In no case is an encoding stored
		141	together with your data, it is use that decides encoding, not any
		142	magical meta data.
		143
		144	3. The internal utf-8 flag has no meaning with regards to the encoding
		145	of your string.
		146	Just ignore that flag unless you debug a Perl bug, a module written
		147	in XS or want to dive into the internals of perl. Otherwise it will
		148	only confuse you, as, despite the name, it says nothing about how
		149	your string is encoded. You can have Unicode strings with that flag
		150	set, with that flag clear, and you can have binary data with that
		151	flag set and that flag clear. Other possibilities exist, too.
		152
		153	If you didn't know about that flag, just the better, pretend it
		154	doesn't exist.
		155
		156	4. A "Unicode String" is simply a string where each character can be
		157	validly interpreted as a Unicode code point.
		158	If you have UTF-8 encoded data, it is no longer a Unicode string,
		159	but a Unicode string encoded in UTF-8, giving you a binary string.
		160
		161	5. A string containing "high" (> 255) character values is not a UTF-8
		162	string.
		163	It's a fact. Learn to live with it.
		164
		165	I hope this helps :)
96		166
97	OBJECT-ORIENTED INTERFACE	167	OBJECT-ORIENTED INTERFACE
98	The object oriented interface lets you configure your own encoding or	168	The object oriented interface lets you configure your own encoding or
99	decoding style, within the limits of supported formats.	169	decoding style, within the limits of supported formats.
100		170
…		…
108		178
109	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	179	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
110	=> {"a": [1, 2]}	180	=> {"a": [1, 2]}
111		181
112	$json = $json->ascii ([$enable])	182	$json = $json->ascii ([$enable])
		183	$enabled = $json->get_ascii
113	If $enable is true (or missing), then the "encode" method will not	184	If $enable is true (or missing), then the "encode" method will not
114	generate characters outside the code range 0..127 (which is ASCII).	185	generate characters outside the code range 0..127 (which is ASCII).
115	Any unicode characters outside that range will be escaped using	186	Any Unicode characters outside that range will be escaped using
116	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL	187	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
117	escape sequence, as per RFC4627.	188	escape sequence, as per RFC4627. The resulting encoded JSON text can
		189	be treated as a native Unicode string, an ascii-encoded,
		190	latin1-encoded or UTF-8 encoded string, or any other superset of
		191	ASCII.
118		192
119	If $enable is false, then the "encode" method will not escape	193	If $enable is false, then the "encode" method will not escape
120	Unicode characters unless required by the JSON syntax. This results	194	Unicode characters unless required by the JSON syntax or other
121	in a faster and more compact format.	195	flags. This results in a faster and more compact format.
		196
		197	See also the section ENCODING/CODESET FLAG NOTES later in this
		198	document.
		199
		200	The main use for this flag is to produce JSON texts that can be
		201	transmitted over a 7-bit channel, as the encoded JSON texts will not
		202	contain any 8 bit characters.
122		203
123	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	204	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
124	=> ["\ud801\udc01"]	205	=> ["\ud801\udc01"]
125		206
		207	$json = $json->latin1 ([$enable])
		208	$enabled = $json->get_latin1
		209	If $enable is true (or missing), then the "encode" method will
		210	encode the resulting JSON text as latin1 (or iso-8859-1), escaping
		211	any characters outside the code range 0..255. The resulting string
		212	can be treated as a latin1-encoded JSON text or a native Unicode
		213	string. The "decode" method will not be affected in any way by this
		214	flag, as "decode" by default expects Unicode, which is a strict
		215	superset of latin1.
		216
		217	If $enable is false, then the "encode" method will not escape
		218	Unicode characters unless required by the JSON syntax or other
		219	flags.
		220
		221	See also the section ENCODING/CODESET FLAG NOTES later in this
		222	document.
		223
		224	The main use for this flag is efficiently encoding binary data as
		225	JSON text, as most octets will not be escaped, resulting in a
		226	smaller encoded size. The disadvantage is that the resulting JSON
		227	text is encoded in latin1 (and must correctly be treated as such
		228	when storing and transferring), a rare encoding for JSON. It is
		229	therefore most useful when you want to store data structures known
		230	to contain binary data efficiently in files or databases, not when
		231	talking to other JSON encoders/decoders.
		232
		233	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		234	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
		235
126	$json = $json->utf8 ([$enable])	236	$json = $json->utf8 ([$enable])
		237	$enabled = $json->get_utf8
127	If $enable is true (or missing), then the "encode" method will	238	If $enable is true (or missing), then the "encode" method will
128	encode the JSON result into UTF-8, as required by many protocols,	239	encode the JSON result into UTF-8, as required by many protocols,
129	while the "decode" method expects to be handled an UTF-8-encoded	240	while the "decode" method expects to be handled an UTF-8-encoded
130	string. Please note that UTF-8-encoded strings do not contain any	241	string. Please note that UTF-8-encoded strings do not contain any
131	characters outside the range 0..255, they are thus useful for	242	characters outside the range 0..255, they are thus useful for
132	bytewise/binary I/O. In future versions, enabling this option might	243	bytewise/binary I/O. In future versions, enabling this option might
133	enable autodetection of the UTF-16 and UTF-32 encoding families, as	244	enable autodetection of the UTF-16 and UTF-32 encoding families, as
134	described in RFC4627.	245	described in RFC4627.
135		246
136	If $enable is false, then the "encode" method will return the JSON	247	If $enable is false, then the "encode" method will return the JSON
137	string as a (non-encoded) unicode string, while "decode" expects	248	string as a (non-encoded) Unicode string, while "decode" expects
138	thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or	249	thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
139	UTF-16) needs to be done yourself, e.g. using the Encode module.	250	UTF-16) needs to be done yourself, e.g. using the Encode module.
		251
		252	See also the section ENCODING/CODESET FLAG NOTES later in this
		253	document.
140		254
141	Example, output UTF-16BE-encoded JSON:	255	Example, output UTF-16BE-encoded JSON:
142		256
143	use Encode;	257	use Encode;
144	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	258	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
163	2	277	2
164	]	278	]
165	}	279	}
166		280
167	$json = $json->indent ([$enable])	281	$json = $json->indent ([$enable])
		282	$enabled = $json->get_indent
168	If $enable is true (or missing), then the "encode" method will use a	283	If $enable is true (or missing), then the "encode" method will use a
169	multiline format as output, putting every array member or	284	multiline format as output, putting every array member or
170	object/hash key-value pair into its own line, identing them	285	object/hash key-value pair into its own line, indenting them
171	properly.	286	properly.
172		287
173	If $enable is false, no newlines or indenting will be produced, and	288	If $enable is false, no newlines or indenting will be produced, and
174	the resulting JSON text is guarenteed not to contain any "newlines".	289	the resulting JSON text is guaranteed not to contain any "newlines".
175		290
176	This setting has no effect when decoding JSON texts.	291	This setting has no effect when decoding JSON texts.
177		292
178	$json = $json->space_before ([$enable])	293	$json = $json->space_before ([$enable])
		294	$enabled = $json->get_space_before
179	If $enable is true (or missing), then the "encode" method will add	295	If $enable is true (or missing), then the "encode" method will add
180	an extra optional space before the ":" separating keys from values	296	an extra optional space before the ":" separating keys from values
181	in JSON objects.	297	in JSON objects.
182		298
183	If $enable is false, then the "encode" method will not add any extra	299	If $enable is false, then the "encode" method will not add any extra
…		…
189	Example, space_before enabled, space_after and indent disabled:	305	Example, space_before enabled, space_after and indent disabled:
190		306
191	{"key" :"value"}	307	{"key" :"value"}
192		308
193	$json = $json->space_after ([$enable])	309	$json = $json->space_after ([$enable])
		310	$enabled = $json->get_space_after
194	If $enable is true (or missing), then the "encode" method will add	311	If $enable is true (or missing), then the "encode" method will add
195	an extra optional space after the ":" separating keys from values in	312	an extra optional space after the ":" separating keys from values in
196	JSON objects and extra whitespace after the "," separating key-value	313	JSON objects and extra whitespace after the "," separating key-value
197	pairs and array members.	314	pairs and array members.
198		315
…		…
203		320
204	Example, space_before and indent disabled, space_after enabled:	321	Example, space_before and indent disabled, space_after enabled:
205		322
206	{"key": "value"}	323	{"key": "value"}
207		324
		325	$json = $json->relaxed ([$enable])
		326	$enabled = $json->get_relaxed
		327	If $enable is true (or missing), then "decode" will accept some
		328	extensions to normal JSON syntax (see below). "encode" will not be
		329	affected in anyway. *Be aware that this option makes you accept
		330	invalid JSON texts as if they were valid!*. I suggest only to use
		331	this option to parse application-specific files written by humans
		332	(configuration files, resource files etc.)
		333
		334	If $enable is false (the default), then "decode" will only accept
		335	valid JSON texts.
		336
		337	Currently accepted extensions are:
		338
		339	* list items can have an end-comma
		340
		341	JSON separates array elements and key-value pairs with commas.
		342	This can be annoying if you write JSON texts manually and want
		343	to be able to quickly append elements, so this extension accepts
		344	comma at the end of such items not just between them:
		345
		346	[
		347	1,
		348	2, <- this comma not normally allowed
		349	]
		350	{
		351	"k1": "v1",
		352	"k2": "v2", <- this comma not normally allowed
		353	}
		354
		355	* shell-style '#'-comments
		356
		357	Whenever JSON allows whitespace, shell-style comments are
		358	additionally allowed. They are terminated by the first
		359	carriage-return or line-feed character, after which more
		360	white-space and comments are allowed.
		361
		362	[
		363	1, # this comment not allowed in JSON
		364	# neither this one...
		365	]
		366
208	$json = $json->canonical ([$enable])	367	$json = $json->canonical ([$enable])
		368	$enabled = $json->get_canonical
209	If $enable is true (or missing), then the "encode" method will	369	If $enable is true (or missing), then the "encode" method will
210	output JSON objects by sorting their keys. This is adding a	370	output JSON objects by sorting their keys. This is adding a
211	comparatively high overhead.	371	comparatively high overhead.
212		372
213	If $enable is false, then the "encode" method will output key-value	373	If $enable is false, then the "encode" method will output key-value
214	pairs in the order Perl stores them (which will likely change	374	pairs in the order Perl stores them (which will likely change
215	between runs of the same script).	375	between runs of the same script).
216		376
217	This option is useful if you want the same data structure to be	377	This option is useful if you want the same data structure to be
218	encoded as the same JSON text (given the same overall settings). If	378	encoded as the same JSON text (given the same overall settings). If
219	it is disabled, the same hash migh be encoded differently even if	379	it is disabled, the same hash might be encoded differently even if
220	contains the same data, as key-value pairs have no inherent ordering	380	contains the same data, as key-value pairs have no inherent ordering
221	in Perl.	381	in Perl.
222		382
223	This setting has no effect when decoding JSON texts.	383	This setting has no effect when decoding JSON texts.
224		384
225	$json = $json->allow_nonref ([$enable])	385	$json = $json->allow_nonref ([$enable])
		386	$enabled = $json->get_allow_nonref
226	If $enable is true (or missing), then the "encode" method can	387	If $enable is true (or missing), then the "encode" method can
227	convert a non-reference into its corresponding string, number or	388	convert a non-reference into its corresponding string, number or
228	null JSON value, which is an extension to RFC4627. Likewise,	389	null JSON value, which is an extension to RFC4627. Likewise,
229	"decode" will accept those JSON values instead of croaking.	390	"decode" will accept those JSON values instead of croaking.
230		391
…		…
237	"allow_nonref", resulting in an invalid JSON text:	398	"allow_nonref", resulting in an invalid JSON text:
238		399
239	JSON::XS->new->allow_nonref->encode ("Hello, World!")	400	JSON::XS->new->allow_nonref->encode ("Hello, World!")
240	=> "Hello, World!"	401	=> "Hello, World!"
241		402
		403	$json = $json->allow_unknown ([$enable])
		404	$enabled = $json->get_allow_unknown
		405	If $enable is true (or missing), then "encode" will not throw an
		406	exception when it encounters values it cannot represent in JSON (for
		407	example, filehandles) but instead will encode a JSON "null" value.
		408	Note that blessed objects are not included here and are handled
		409	separately by c<allow_nonref>.
		410
		411	If $enable is false (the default), then "encode" will throw an
		412	exception when it encounters anything it cannot encode as JSON.
		413
		414	This option does not affect "decode" in any way, and it is
		415	recommended to leave it off unless you know your communications
		416	partner.
		417
		418	$json = $json->allow_blessed ([$enable])
		419	$enabled = $json->get_allow_blessed
		420	If $enable is true (or missing), then the "encode" method will not
		421	barf when it encounters a blessed reference. Instead, the value of
		422	the convert_blessed option will decide whether "null"
		423	("convert_blessed" disabled or no "TO_JSON" method found) or a
		424	representation of the object ("convert_blessed" enabled and
		425	"TO_JSON" method found) is being encoded. Has no effect on "decode".
		426
		427	If $enable is false (the default), then "encode" will throw an
		428	exception when it encounters a blessed object.
		429
		430	$json = $json->convert_blessed ([$enable])
		431	$enabled = $json->get_convert_blessed
		432	If $enable is true (or missing), then "encode", upon encountering a
		433	blessed object, will check for the availability of the "TO_JSON"
		434	method on the object's class. If found, it will be called in scalar
		435	context and the resulting scalar will be encoded instead of the
		436	object. If no "TO_JSON" method is found, the value of
		437	"allow_blessed" will decide what to do.
		438
		439	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
		440	returns other blessed objects, those will be handled in the same
		441	way. "TO_JSON" must take care of not causing an endless recursion
		442	cycle (== crash) in this case. The name of "TO_JSON" was chosen
		443	because other methods called by the Perl core (== not by the user of
		444	the object) are usually in upper case letters and to avoid
		445	collisions with any "to_json" function or method.
		446
		447	This setting does not yet influence "decode" in any way, but in the
		448	future, global hooks might get installed that influence "decode" and
		449	are enabled by this setting.
		450
		451	If $enable is false, then the "allow_blessed" setting will decide
		452	what to do when a blessed object is found.
		453
		454	$json = $json->filter_json_object ([$coderef->($hashref)])
		455	When $coderef is specified, it will be called from "decode" each
		456	time it decodes a JSON object. The only argument is a reference to
		457	the newly-created hash. If the code references returns a single
		458	scalar (which need not be a reference), this value (i.e. a copy of
		459	that scalar to avoid aliasing) is inserted into the deserialised
		460	data structure. If it returns an empty list (NOTE: not "undef",
		461	which is a valid scalar), the original deserialised hash will be
		462	inserted. This setting can slow down decoding considerably.
		463
		464	When $coderef is omitted or undefined, any existing callback will be
		465	removed and "decode" will not change the deserialised hash in any
		466	way.
		467
		468	Example, convert all JSON objects into the integer 5:
		469
		470	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		471	# returns [5]
		472	$js->decode ('[{}]')
		473	# throw an exception because allow_nonref is not enabled
		474	# so a lone 5 is not allowed.
		475	$js->decode ('{"a":1, "b":2}');
		476
		477	$json = $json->filter_json_single_key_object ($key [=>
		478	$coderef->($value)])
		479	Works remotely similar to "filter_json_object", but is only called
		480	for JSON objects having a single key named $key.
		481
		482	This $coderef is called before the one specified via
		483	"filter_json_object", if any. It gets passed the single value in the
		484	JSON object. If it returns a single value, it will be inserted into
		485	the data structure. If it returns nothing (not even "undef" but the
		486	empty list), the callback from "filter_json_object" will be called
		487	next, as if no single-key callback were specified.
		488
		489	If $coderef is omitted or undefined, the corresponding callback will
		490	be disabled. There can only ever be one callback for a given key.
		491
		492	As this callback gets called less often then the
		493	"filter_json_object" one, decoding speed will not usually suffer as
		494	much. Therefore, single-key objects make excellent targets to
		495	serialise Perl objects into, especially as single-key JSON objects
		496	are as close to the type-tagged value concept as JSON gets (it's
		497	basically an ID/VALUE tuple). Of course, JSON does not support this
		498	in any way, so you need to make sure your data never looks like a
		499	serialised Perl hash.
		500
		501	Typical names for the single object key are "__class_whatever__", or
		502	"$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
		503	things like "__class_md5sum(classname)__", to reduce the risk of
		504	clashing with real hashes.
		505
		506	Example, decode JSON objects of the form "{ "__widget__" => <id> }"
		507	into the corresponding $WIDGET{<id>} object:
		508
		509	# return whatever is in $WIDGET{5}:
		510	JSON::XS
		511	->new
		512	->filter_json_single_key_object (__widget__ => sub {
		513	$WIDGET{ $_[0] }
		514	})
		515	->decode ('{"__widget__": 5')
		516
		517	# this can be used with a TO_JSON method in some "widget" class
		518	# for serialisation to json:
		519	sub WidgetBase::TO_JSON {
		520	my ($self) = @_;
		521
		522	unless ($self->{id}) {
		523	$self->{id} = ..get..some..id..;
		524	$WIDGET{$self->{id}} = $self;
		525	}
		526
		527	{ __widget__ => $self->{id} }
		528	}
		529
242	$json = $json->shrink ([$enable])	530	$json = $json->shrink ([$enable])
		531	$enabled = $json->get_shrink
243	Perl usually over-allocates memory a bit when allocating space for	532	Perl usually over-allocates memory a bit when allocating space for
244	strings. This flag optionally resizes strings generated by either	533	strings. This flag optionally resizes strings generated by either
245	"encode" or "decode" to their minimum size possible. This can save	534	"encode" or "decode" to their minimum size possible. This can save
246	memory when your JSON texts are either very very long or you have	535	memory when your JSON texts are either very very long or you have
247	many short strings. It will also try to downgrade any strings to	536	many short strings. It will also try to downgrade any strings to
…		…
265	converting strings that look like integers or floats into integers	554	converting strings that look like integers or floats into integers
266	or floats internally (there is no difference on the Perl level),	555	or floats internally (there is no difference on the Perl level),
267	saving space.	556	saving space.
268		557
269	$json = $json->max_depth ([$maximum_nesting_depth])	558	$json = $json->max_depth ([$maximum_nesting_depth])
		559	$max_depth = $json->get_max_depth
270	Sets the maximum nesting level (default 512) accepted while encoding	560	Sets the maximum nesting level (default 512) accepted while encoding
271	or decoding. If the JSON text or Perl data structure has an equal or	561	or decoding. If a higher nesting level is detected in JSON text or a
272	higher nesting level then this limit, then the encoder and decoder	562	Perl data structure, then the encoder and decoder will stop and
273	will stop and croak at that point.	563	croak at that point.
274		564
275	Nesting level is defined by number of hash- or arrayrefs that the	565	Nesting level is defined by number of hash- or arrayrefs that the
276	encoder needs to traverse to reach a given point or the number of	566	encoder needs to traverse to reach a given point or the number of
277	"{" or "[" characters without their matching closing parenthesis	567	"{" or "[" characters without their matching closing parenthesis
278	crossed to reach a given character in a string.	568	crossed to reach a given character in a string.
279		569
280	Setting the maximum depth to one disallows any nesting, so that	570	Setting the maximum depth to one disallows any nesting, so that
281	ensures that the object is only a single hash/object or array.	571	ensures that the object is only a single hash/object or array.
282		572
283	The argument to "max_depth" will be rounded up to the next nearest	573	If no argument is given, the highest possible setting will be used,
284	power of two.	574	which is rarely useful.
		575
		576	Note that nesting is implemented by recursion in C. The default
		577	value has been chosen to be as large as typical operating systems
		578	allow without crashing.
		579
		580	See SECURITY CONSIDERATIONS, below, for more info on why this is
		581	useful.
		582
		583	$json = $json->max_size ([$maximum_string_size])
		584	$max_size = $json->get_max_size
		585	Set the maximum length a JSON text may have (in bytes) where
		586	decoding is being attempted. The default is 0, meaning no limit.
		587	When "decode" is called on a string that is longer then this many
		588	bytes, it will not attempt to decode the string but throw an
		589	exception. This setting has no effect on "encode" (yet).
		590
		591	If no argument is given, the limit check will be deactivated (same
		592	as when 0 is specified).
285		593
286	See SECURITY CONSIDERATIONS, below, for more info on why this is	594	See SECURITY CONSIDERATIONS, below, for more info on why this is
287	useful.	595	useful.
288		596
289	$json_text = $json->encode ($perl_scalar)	597	$json_text = $json->encode ($perl_scalar)
…		…
301		609
302	JSON numbers and strings become simple Perl scalars. JSON arrays	610	JSON numbers and strings become simple Perl scalars. JSON arrays
303	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"	611	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
304	becomes 1, "false" becomes 0 and "null" becomes "undef".	612	becomes 1, "false" becomes 0 and "null" becomes "undef".
305		613
		614	($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		615	This works like the "decode" method, but instead of raising an
		616	exception when there is trailing garbage after the first JSON
		617	object, it will silently stop parsing there and return the number of
		618	characters consumed so far.
		619
		620	This is useful if your JSON texts are not delimited by an outer
		621	protocol (which is not the brightest thing to do in the first place)
		622	and you need to know where the JSON text ends.
		623
		624	JSON::XS->new->decode_prefix ("[1] the tail")
		625	=> ([], 3)
		626
		627	INCREMENTAL PARSING
		628	In some cases, there is the need for incremental parsing of JSON texts.
		629	While this module always has to keep both JSON text and resulting Perl
		630	data structure in memory at one time, it does allow you to parse a JSON
		631	stream incrementally. It does so by accumulating text until it has a
		632	full JSON object, which it then can decode. This process is similar to
		633	using "decode_prefix" to see if a full JSON object is available, but is
		634	much more efficient (and can be implemented with a minimum of method
		635	calls).
		636
		637	JSON::XS will only attempt to parse the JSON text once it is sure it has
		638	enough text to get a decisive result, using a very simple but truly
		639	incremental parser. This means that it sometimes won't stop as early as
		640	the full parser, for example, it doesn't detect parenthese mismatches.
		641	The only thing it guarantees is that it starts decoding as soon as a
		642	syntactically valid JSON text has been seen. This means you need to set
		643	resource limits (e.g. "max_size") to ensure the parser will stop parsing
		644	in the presence if syntax errors.
		645
		646	The following methods implement this incremental parser.
		647
		648	[void, scalar or list context] = $json->incr_parse ([$string])
		649	This is the central parsing function. It can both append new text
		650	and extract objects from the stream accumulated so far (both of
		651	these functions are optional).
		652
		653	If $string is given, then this string is appended to the already
		654	existing JSON fragment stored in the $json object.
		655
		656	After that, if the function is called in void context, it will
		657	simply return without doing anything further. This can be used to
		658	add more text in as many chunks as you want.
		659
		660	If the method is called in scalar context, then it will try to
		661	extract exactly one JSON object. If that is successful, it will
		662	return this object, otherwise it will return "undef". If there is a
		663	parse error, this method will croak just as "decode" would do (one
		664	can then use "incr_skip" to skip the errornous part). This is the
		665	most common way of using the method.
		666
		667	And finally, in list context, it will try to extract as many objects
		668	from the stream as it can find and return them, or the empty list
		669	otherwise. For this to work, there must be no separators between the
		670	JSON objects or arrays, instead they must be concatenated
		671	back-to-back. If an error occurs, an exception will be raised as in
		672	the scalar context case. Note that in this case, any
		673	previously-parsed JSON texts will be lost.
		674
		675	$lvalue_string = $json->incr_text
		676	This method returns the currently stored JSON fragment as an lvalue,
		677	that is, you can manipulate it. This only works when a preceding
		678	call to "incr_parse" in scalar context successfully returned an
		679	object. Under all other circumstances you must not call this
		680	function (I mean it. although in simple tests it might actually
		681	work, it will fail under real world conditions). As a special
		682	exception, you can also call this method before having parsed
		683	anything.
		684
		685	This function is useful in two cases: a) finding the trailing text
		686	after a JSON object or b) parsing multiple JSON objects separated by
		687	non-JSON text (such as commas).
		688
		689	$json->incr_skip
		690	This will reset the state of the incremental parser and will remove
		691	the parsed text from the input buffer. This is useful after
		692	"incr_parse" died, in which case the input buffer and incremental
		693	parser state is left unchanged, to skip the text parsed so far and
		694	to reset the parse state.
		695
		696	$json->incr_reset
		697	This completely resets the incremental parser, that is, after this
		698	call, it will be as if the parser had never parsed anything.
		699
		700	This is useful if you want ot repeatedly parse JSON objects and want
		701	to ignore any trailing data, which means you have to reset the
		702	parser after each successful decode.
		703
		704	LIMITATIONS
		705	All options that affect decoding are supported, except "allow_nonref".
		706	The reason for this is that it cannot be made to work sensibly: JSON
		707	objects and arrays are self-delimited, i.e. you can concatenate them
		708	back to back and still decode them perfectly. This does not hold true
		709	for JSON numbers, however.
		710
		711	For example, is the string 1 a single JSON number, or is it simply the
		712	start of 12? Or is 12 a single JSON number, or the concatenation of 1
		713	and 2? In neither case you can tell, and this is why JSON::XS takes the
		714	conservative route and disallows this case.
		715
		716	EXAMPLES
		717	Some examples will make all this clearer. First, a simple example that
		718	works similarly to "decode_prefix": We want to decode the JSON object at
		719	the start of a string and identify the portion after the JSON object:
		720
		721	my $text = "[1,2,3] hello";
		722
		723	my $json = new JSON::XS;
		724
		725	my $obj = $json->incr_parse ($text)
		726	or die "expected JSON object or array at beginning of string";
		727
		728	my $tail = $json->incr_text;
		729	# $tail now contains " hello"
		730
		731	Easy, isn't it?
		732
		733	Now for a more complicated example: Imagine a hypothetical protocol
		734	where you read some requests from a TCP stream, and each request is a
		735	JSON array, without any separation between them (in fact, it is often
		736	useful to use newlines as "separators", as these get interpreted as
		737	whitespace at the start of the JSON text, which makes it possible to
		738	test said protocol with "telnet"...).
		739
		740	Here is how you'd do it (it is trivial to write this in an event-based
		741	manner):
		742
		743	my $json = new JSON::XS;
		744
		745	# read some data from the socket
		746	while (sysread $socket, my $buf, 4096) {
		747
		748	# split and decode as many requests as possible
		749	for my $request ($json->incr_parse ($buf)) {
		750	# act on the $request
		751	}
		752	}
		753
		754	Another complicated example: Assume you have a string with JSON objects
		755	or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
		756	[3]"). To parse them, we have to skip the commas between the JSON texts,
		757	and here is where the lvalue-ness of "incr_text" comes in useful:
		758
		759	my $text = "[1],[2], [3]";
		760	my $json = new JSON::XS;
		761
		762	# void context, so no parsing done
		763	$json->incr_parse ($text);
		764
		765	# now extract as many objects as possible. note the
		766	# use of scalar context so incr_text can be called.
		767	while (my $obj = $json->incr_parse) {
		768	# do something with $obj
		769
		770	# now skip the optional comma
		771	$json->incr_text =~ s/^ \s* , //x;
		772	}
		773
		774	Now lets go for a very complex example: Assume that you have a gigantic
		775	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		776	but you cannot load it into memory fully (this has actually happened in
		777	the real world :).
		778
		779	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		780	can still help you: You implement a (very simple) array parser and let
		781	JSON decode the array elements, which are all full JSON objects on their
		782	own (this wouldn't work if the array elements could be JSON numbers, for
		783	example):
		784
		785	my $json = new JSON::XS;
		786
		787	# open the monster
		788	open my $fh, "<bigfile.json"
		789	or die "bigfile: $!";
		790
		791	# first parse the initial "["
		792	for (;;) {
		793	sysread $fh, my $buf, 65536
		794	or die "read error: $!";
		795	$json->incr_parse ($buf); # void context, so no parsing
		796
		797	# Exit the loop once we found and removed(!) the initial "[".
		798	# In essence, we are (ab-)using the $json object as a simple scalar
		799	# we append data to.
		800	last if $json->incr_text =~ s/^ \s* \[ //x;
		801	}
		802
		803	# now we have the skipped the initial "[", so continue
		804	# parsing all the elements.
		805	for (;;) {
		806	# in this loop we read data until we got a single JSON object
		807	for (;;) {
		808	if (my $obj = $json->incr_parse) {
		809	# do something with $obj
		810	last;
		811	}
		812
		813	# add more data
		814	sysread $fh, my $buf, 65536
		815	or die "read error: $!";
		816	$json->incr_parse ($buf); # void context, so no parsing
		817	}
		818
		819	# in this loop we read data until we either found and parsed the
		820	# separating "," between elements, or the final "]"
		821	for (;;) {
		822	# first skip whitespace
		823	$json->incr_text =~ s/^\s*//;
		824
		825	# if we find "]", we are done
		826	if ($json->incr_text =~ s/^\]//) {
		827	print "finished.\n";
		828	exit;
		829	}
		830
		831	# if we find ",", we can continue with the next element
		832	if ($json->incr_text =~ s/^,//) {
		833	last;
		834	}
		835
		836	# if we find anything else, we have a parse error!
		837	if (length $json->incr_text) {
		838	die "parse error near ", $json->incr_text;
		839	}
		840
		841	# else add more data
		842	sysread $fh, my $buf, 65536
		843	or die "read error: $!";
		844	$json->incr_parse ($buf); # void context, so no parsing
		845	}
		846
		847	This is a complex example, but most of the complexity comes from the
		848	fact that we are trying to be correct (bear with me if I am wrong, I
		849	never ran the above example :).
		850
306	MAPPING	851	MAPPING
307	This section describes how JSON::XS maps Perl values to JSON values and	852	This section describes how JSON::XS maps Perl values to JSON values and
308	vice versa. These mappings are designed to "do the right thing" in most	853	vice versa. These mappings are designed to "do the right thing" in most
309	circumstances automatically, preserving round-tripping characteristics	854	circumstances automatically, preserving round-tripping characteristics
310	(what you put in comes out as something equivalent).	855	(what you put in comes out as something equivalent).
311		856
312	For the more enlightened: note that in the following descriptions,	857	For the more enlightened: note that in the following descriptions,
313	lowercase perl refers to the Perl interpreter, while uppcercase Perl	858	lowercase perl refers to the Perl interpreter, while uppercase Perl
314	refers to the abstract Perl language itself.	859	refers to the abstract Perl language itself.
315		860
316	JSON -> PERL	861	JSON -> PERL
317	object	862	object
318	A JSON object becomes a reference to a hash in Perl. No ordering of	863	A JSON object becomes a reference to a hash in Perl. No ordering of
319	object keys is preserved (JSON does not preserver object key	864	object keys is preserved (JSON does not preserve object key ordering
320	ordering itself).	865	itself).
321		866
322	array	867	array
323	A JSON array becomes a reference to an array in Perl.	868	A JSON array becomes a reference to an array in Perl.
324		869
325	string	870	string
326	A JSON string becomes a string scalar in Perl - Unicode codepoints	871	A JSON string becomes a string scalar in Perl - Unicode codepoints
327	in JSON are represented by the same codepoints in the Perl string,	872	in JSON are represented by the same codepoints in the Perl string,
328	so no manual decoding is necessary.	873	so no manual decoding is necessary.
329		874
330	number	875	number
331	A JSON number becomes either an integer or numeric (floating point)	876	A JSON number becomes either an integer, numeric (floating point) or
332	scalar in perl, depending on its range and any fractional parts. On	877	string scalar in perl, depending on its range and any fractional
333	the Perl level, there is no difference between those as Perl handles	878	parts. On the Perl level, there is no difference between those as
334	all the conversion details, but an integer may take slightly less	879	Perl handles all the conversion details, but an integer may take
335	memory and might represent more values exactly than (floating point)	880	slightly less memory and might represent more values exactly than
		881	floating point numbers.
		882
		883	If the number consists of digits only, JSON::XS will try to
		884	represent it as an integer value. If that fails, it will try to
		885	represent it as a numeric (floating point) value if that is possible
		886	without loss of precision. Otherwise it will preserve the number as
		887	a string value (in which case you lose roundtripping ability, as the
		888	JSON number will be re-encoded toa JSON string).
		889
		890	Numbers containing a fractional or exponential part will always be
		891	represented as numeric (floating point) values, possibly at a loss
		892	of precision (in which case you might lose perfect roundtripping
		893	ability, but the JSON number will still be re-encoded as a JSON
336	numbers.	894	number).
337		895
338	true, false	896	true, false
339	These JSON atoms become 0, 1, respectively. Information is lost in	897	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
340	this process. Future versions might represent those values	898	respectively. They are overloaded to act almost exactly like the
341	differently, but they will be guarenteed to act like these integers	899	numbers 1 and 0. You can check whether a scalar is a JSON boolean by
342	would normally in Perl.	900	using the "JSON::XS::is_bool" function.
343		901
344	null	902	null
345	A JSON null atom becomes "undef" in Perl.	903	A JSON null atom becomes "undef" in Perl.
346		904
347	PERL -> JSON	905	PERL -> JSON
…		…
369	an exception to be thrown, except for references to the integers 0	927	an exception to be thrown, except for references to the integers 0
370	and 1, which get turned into "false" and "true" atoms in JSON. You	928	and 1, which get turned into "false" and "true" atoms in JSON. You
371	can also use "JSON::XS::false" and "JSON::XS::true" to improve	929	can also use "JSON::XS::false" and "JSON::XS::true" to improve
372	readability.	930	readability.
373		931
374	to_json [\0,JSON::XS::true] # yields [false,true]	932	encode_json [\0, JSON::XS::true] # yields [false,true]
		933
		934	JSON::XS::true, JSON::XS::false
		935	These special values become JSON true and JSON false values,
		936	respectively. You can also use "\1" and "\0" directly if you want.
375		937
376	blessed objects	938	blessed objects
377	Blessed objects are not allowed. JSON::XS currently tries to encode	939	Blessed objects are not directly representable in JSON. See the
378	their underlying representation (hash- or arrayref), but this	940	"allow_blessed" and "convert_blessed" methods on various options on
379	behaviour might change in future versions.	941	how to deal with this: basically, you can choose between throwing an
		942	exception, encoding the reference as if it weren't blessed, or
		943	provide your own serialiser method.
380		944
381	simple scalars	945	simple scalars
382	Simple Perl scalars (any scalar that is not a reference) are the	946	Simple Perl scalars (any scalar that is not a reference) are the
383	most difficult objects to encode: JSON::XS will encode undefined	947	most difficult objects to encode: JSON::XS will encode undefined
384	scalars as JSON null value, scalars that have last been used in a	948	scalars as JSON "null" values, scalars that have last been used in a
385	string context before encoding as JSON strings and anything else as	949	string context before encoding as JSON strings, and anything else as
386	number value:	950	number value:
387		951
388	# dump as number	952	# dump as number
389	to_json [2] # yields [2]	953	encode_json [2] # yields [2]
390	to_json [-3.0e17] # yields [-3e+17]	954	encode_json [-3.0e17] # yields [-3e+17]
391	my $value = 5; to_json [$value] # yields [5]	955	my $value = 5; encode_json [$value] # yields [5]
392		956
393	# used as string, so dump as string	957	# used as string, so dump as string
394	print $value;	958	print $value;
395	to_json [$value] # yields ["5"]	959	encode_json [$value] # yields ["5"]
396		960
397	# undef becomes null	961	# undef becomes null
398	to_json [undef] # yields [null]	962	encode_json [undef] # yields [null]
399		963
400	You can force the type to be a string by stringifying it:	964	You can force the type to be a JSON string by stringifying it:
401		965
402	my $x = 3.1; # some variable containing a number	966	my $x = 3.1; # some variable containing a number
403	"$x"; # stringified	967	"$x"; # stringified
404	$x .= ""; # another, more awkward way to stringify	968	$x .= ""; # another, more awkward way to stringify
405	print $x; # perl does it for you, too, quite often	969	print $x; # perl does it for you, too, quite often
406		970
407	You can force the type to be a number by numifying it:	971	You can force the type to be a JSON number by numifying it:
408		972
409	my $x = "3"; # some variable containing a string	973	my $x = "3"; # some variable containing a string
410	$x += 0; # numify it, ensuring it will be dumped as a number	974	$x += 0; # numify it, ensuring it will be dumped as a number
411	$x *= 1; # same thing, the choise is yours.	975	$x *= 1; # same thing, the choice is yours.
412		976
413	You can not currently output JSON booleans or force the type in	977	You can not currently force the type in other, less obscure, ways.
414	other, less obscure, ways. Tell me if you need this capability.	978	Tell me if you need this capability (but don't forget to explain why
		979	it's needed :).
415		980
416	COMPARISON	981	ENCODING/CODESET FLAG NOTES
417	As already mentioned, this module was created because none of the	982	The interested reader might have seen a number of flags that signify
418	existing JSON modules could be made to work correctly. First I will	983	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
419	describe the problems (or pleasures) I encountered with various existing	984	some confusion on what these do, so here is a short comparison:
420	JSON modules, followed by some benchmark values. JSON::XS was designed
421	not to suffer from any of these problems or limitations.
422		985
423	JSON 1.07	986	"utf8" controls whether the JSON text created by "encode" (and expected
424	Slow (but very portable, as it is written in pure Perl).	987	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
		988	control whether "encode" escapes character values outside their
		989	respective codeset range. Neither of these flags conflict with each
		990	other, although some combinations make less sense than others.
425		991
426	Undocumented/buggy Unicode handling (how JSON handles unicode values	992	Care has been taken to make all flags symmetrical with respect to
427	is undocumented. One can get far by feeding it unicode strings and	993	"encode" and "decode", that is, texts encoded with any combination of
428	doing en-/decoding oneself, but unicode escapes are not working	994	these flag values will be correctly decoded when the same flags are used
		995	- in general, if you use different flag settings while encoding vs. when
		996	decoding you likely have a bug somewhere.
		997
		998	Below comes a verbose discussion of these flags. Note that a "codeset"
		999	is simply an abstract set of character-codepoint pairs, while an
		1000	encoding takes those codepoint numbers and encodes them, in our case
		1001	into octets. Unicode is (among other things) a codeset, UTF-8 is an
		1002	encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
		1003	encodings at the same time, which can be confusing.
		1004
		1005	"utf8" flag disabled
		1006	When "utf8" is disabled (the default), then "encode"/"decode"
		1007	generate and expect Unicode strings, that is, characters with high
		1008	ordinal Unicode values (> 255) will be encoded as such characters,
		1009	and likewise such characters are decoded as-is, no canges to them
		1010	will be done, except "(re-)interpreting" them as Unicode codepoints
		1011	or Unicode characters, respectively (to Perl, these are the same
		1012	thing in strings unless you do funny/weird/dumb stuff).
		1013
		1014	This is useful when you want to do the encoding yourself (e.g. when
		1015	you want to have UTF-16 encoded JSON texts) or when some other layer
		1016	does the encoding for you (for example, when printing to a terminal
		1017	using a filehandle that transparently encodes to UTF-8 you certainly
		1018	do NOT want to UTF-8 encode your data first and have Perl encode it
		1019	another time).
		1020
		1021	"utf8" flag enabled
		1022	If the "utf8"-flag is enabled, "encode"/"decode" will encode all
		1023	characters using the corresponding UTF-8 multi-byte sequence, and
		1024	will expect your input strings to be encoded as UTF-8, that is, no
		1025	"character" of the input string must have any value > 255, as UTF-8
		1026	does not allow that.
		1027
		1028	The "utf8" flag therefore switches between two modes: disabled means
		1029	you will get a Unicode string in Perl, enabled means you get an
		1030	UTF-8 encoded octet/binary string in Perl.
		1031
		1032	"latin1" or "ascii" flags enabled
		1033	With "latin1" (or "ascii") enabled, "encode" will escape characters
		1034	with ordinal values > 255 (> 127 with "ascii") and encode the
		1035	remaining characters as specified by the "utf8" flag.
		1036
		1037	If "utf8" is disabled, then the result is also correctly encoded in
		1038	those character sets (as both are proper subsets of Unicode, meaning
		1039	that a Unicode string with all character values < 256 is the same
		1040	thing as a ISO-8859-1 string, and a Unicode string with all
		1041	character values < 128 is the same thing as an ASCII string in
429	properly).	1042	Perl).
430		1043
431	No roundtripping (strings get clobbered if they look like numbers,	1044	If "utf8" is enabled, you still get a correct UTF-8-encoded string,
432	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	1045	regardless of these flags, just some more characters will be escaped
433	will decode into the number 2.	1046	using "\uXXXX" then before.
434		1047
435	JSON::PC 0.01	1048	Note that ISO-8859-1-encoded strings are not compatible with UTF-8
436	Very fast.	1049	encoding, while ASCII-encoded strings are. That is because the
		1050	ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
		1051	codeset being a subset of Unicode), while ASCII is.
437		1052
438	Undocumented/buggy Unicode handling.	1053	Surprisingly, "decode" will ignore these flags and so treat all
		1054	input values as governed by the "utf8" flag. If it is disabled, this
		1055	allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
		1056	strict subsets of Unicode. If it is enabled, you can correctly
		1057	decode UTF-8 encoded strings.
439		1058
440	No roundtripping.	1059	So neither "latin1" nor "ascii" are incompatible with the "utf8"
		1060	flag - they only govern when the JSON output engine escapes a
		1061	character or not.
441		1062
442	Has problems handling many Perl values (e.g. regex results and other	1063	The main use for "latin1" is to relatively efficiently store binary
443	magic values will make it croak).	1064	data as JSON, at the expense of breaking compatibility with most
		1065	JSON decoders.
444		1066
445	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1067	The main use for "ascii" is to force the output to not contain
446	which is not a valid JSON text.	1068	characters with values > 127, which means you can interpret the
		1069	resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
		1070	any character set and 8-bit-encoding, and still get the same data
		1071	structure back. This is useful when your channel for JSON transfer
		1072	is not 8-bit clean or the encoding might be mangled in between (e.g.
		1073	in mail), and works because ASCII is a proper subset of most 8-bit
		1074	and multibyte encodings in use in the world.
447		1075
448	Unmaintained (maintainer unresponsive for many months, bugs are not	1076	JSON and YAML
449	getting fixed).	1077	You often hear that JSON is a subset of YAML. This is, however, a mass
		1078	hysteria(*) and very far from the truth (as of the time of this
		1079	writing), so let me state it clearly: *in general, there is no way to
		1080	configure JSON::XS to output a data structure as valid YAML* that works
		1081	in all cases.
450		1082
451	JSON::Syck 0.21	1083	If you really must use JSON::XS to generate YAML, you should use this
452	Very buggy (often crashes).	1084	algorithm (subject to change in future versions):
453		1085
454	Very inflexible (no human-readable format supported, format pretty	1086	my $to_yaml = JSON::XS->new->utf8->space_after (1);
455	much undocumented. I need at least a format for easy reading by	1087	my $yaml = $to_yaml->encode ($ref) . "\n";
456	humans and a single-line compact format for use in a protocol, and
457	preferably a way to generate ASCII-only JSON texts).
458		1088
459	Completely broken (and confusingly documented) Unicode handling	1089	This will usually generate JSON texts that also parse as valid YAML.
460	(unicode escapes are not working properly, you need to set	1090	Please note that YAML has hardcoded limits on (simple) object key
461	ImplicitUnicode to different values on en- and decoding to get	1091	lengths that JSON doesn't have and also has different and incompatible
462	symmetric behaviour).	1092	unicode handling, so you should make sure that your hash keys are
		1093	noticeably shorter than the 1024 "stream characters" YAML allows and
		1094	that you do not have characters with codepoint values outside the
		1095	Unicode BMP (basic multilingual page). YAML also does not allow "\/"
		1096	sequences in strings (which JSON::XS does not currently generate, but
		1097	other JSON generators might).
463		1098
464	No roundtripping (simple cases work, but this depends on wether the	1099	There might be other incompatibilities that I am not aware of (or the
465	scalar value was used in a numeric context or not).	1100	YAML specification has been changed yet again - it does so quite often).
		1101	In general you should not try to generate YAML with a JSON generator or
		1102	vice versa, or try to parse JSON with a YAML parser or vice versa:
		1103	chances are high that you will run into severe interoperability problems
		1104	when you least expect it.
466		1105
467	Dumping hashes may skip hash values depending on iterator state.	1106	(*) I have been pressured multiple times by Brian Ingerson (one of the
		1107	authors of the YAML specification) to remove this paragraph, despite
		1108	him acknowledging that the actual incompatibilities exist. As I was
		1109	personally bitten by this "JSON is YAML" lie, I refused and said I
		1110	will continue to educate people about these issues, so others do not
		1111	run into the same problem again and again. After this, Brian called
		1112	me a (quote)complete and worthless idiot(unquote).
468		1113
469	Unmaintained (maintainer unresponsive for many months, bugs are not	1114	In my opinion, instead of pressuring and insulting people who
470	getting fixed).	1115	actually clarify issues with YAML and the wrong statements of some
471		1116	of its proponents, I would kindly suggest reading the JSON spec
472	Does not check input for validity (i.e. will accept non-JSON input	1117	(which is not that difficult or long) and finally make YAML
473	and return "something" instead of raising an exception. This is a	1118	compatible to it, and educating users about the changes, instead of
474	security issue: imagine two banks transfering money between each	1119	spreading lies about the real compatibility for many years and
475	other using JSON. One bank might parse a given non-JSON request and	1120	trying to silence people who point out that it isn't true.
476	deduct money, while the other might reject the transaction with a
477	syntax error. While a good protocol will at least recover, that is
478	extra unnecessary work and the transaction will still not succeed).
479
480	JSON::DWIW 0.04
481	Very fast. Very natural. Very nice.
482
483	Undocumented unicode handling (but the best of the pack. Unicode
484	escapes still don't get parsed properly).
485
486	Very inflexible.
487
488	No roundtripping.
489
490	Does not generate valid JSON texts (key strings are often unquoted,
491	empty keys result in nothing being output)
492
493	Does not check input for validity.
494		1121
495	SPEED	1122	SPEED
496	It seems that JSON::XS is surprisingly fast, as shown in the following	1123	It seems that JSON::XS is surprisingly fast, as shown in the following
497	tables. They have been generated with the help of the "eg/bench" program	1124	tables. They have been generated with the help of the "eg/bench" program
498	in the JSON::XS distribution, to make it easy to compare on your own	1125	in the JSON::XS distribution, to make it easy to compare on your own
499	system.	1126	system.
500		1127
501	First comes a comparison between various modules using a very short JSON	1128	First comes a comparison between various modules using a very short
502	string:	1129	single-line JSON string (also available at
		1130	<http://dist.schmorp.de/misc/json/short.json>).
503		1131
504	{"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null}	1132	{"method": "handleMessage", "params": ["user1",
		1133	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1134	true, false]}
505		1135
506	It shows the number of encodes/decodes per second (JSON::XS uses the	1136	It shows the number of encodes/decodes per second (JSON::XS uses the
507	functional interface, while JSON::XS/2 uses the OO interface with	1137	functional interface, while JSON::XS/2 uses the OO interface with
508	pretty-printing and hashkey sorting enabled). Higher is better:	1138	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
		1139	Higher is better:
509		1140
510	module \| encode \| decode \|	1141	module \| encode \| decode \|
511	-----------\|------------\|------------\|	1142	-----------\|------------\|------------\|
512	JSON \| 11488.516 \| 7823.035 \|	1143	JSON 1.x \| 4990.842 \| 4088.813 \|
513	JSON::DWIW \| 94708.054 \| 129094.260 \|	1144	JSON::DWIW \| 51653.990 \| 71575.154 \|
514	JSON::PC \| 63884.157 \| 128528.212 \|	1145	JSON::PC \| 65948.176 \| 74631.744 \|
		1146	JSON::PP \| 8931.652 \| 3817.168 \|
515	JSON::Syck \| 34898.677 \| 42096.911 \|	1147	JSON::Syck \| 24877.248 \| 27776.848 \|
516	JSON::XS \| 654027.064 \| 396423.669 \|	1148	JSON::XS \| 388361.481 \| 227951.304 \|
517	JSON::XS/2 \| 371564.190 \| 371725.613 \|	1149	JSON::XS/2 \| 227951.304 \| 218453.333 \|
		1150	JSON::XS/3 \| 338250.323 \| 218453.333 \|
		1151	Storable \| 16500.016 \| 135300.129 \|
518	-----------+------------+------------+	1152	-----------+------------+------------+
519		1153
520	That is, JSON::XS is more than six times faster than JSON::DWIW on	1154	That is, JSON::XS is about five times faster than JSON::DWIW on
521	encoding, more than three times faster on decoding, and about thirty	1155	encoding, about three times faster on decoding, and over forty times
522	times faster than JSON, even with pretty-printing and key sorting.	1156	faster than JSON, even with pretty-printing and key sorting. It also
		1157	compares favourably to Storable for small amounts of data.
523		1158
524	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1159	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
525	search API (http://nanoref.com/yahooapis/mgPdGg):	1160	search API (<http://dist.schmorp.de/misc/json/long.json>).
526		1161
527	module \| encode \| decode \|	1162	module \| encode \| decode \|
528	-----------\|------------\|------------\|	1163	-----------\|------------\|------------\|
529	JSON \| 273.023 \| 44.674 \|	1164	JSON 1.x \| 55.260 \| 34.971 \|
530	JSON::DWIW \| 1089.383 \| 1145.704 \|	1165	JSON::DWIW \| 825.228 \| 1082.513 \|
531	JSON::PC \| 3097.419 \| 2393.921 \|	1166	JSON::PC \| 3571.444 \| 2394.829 \|
532	JSON::Syck \| 514.060 \| 843.053 \|	1167	JSON::PP \| 210.987 \| 32.574 \|
533	JSON::XS \| 6479.668 \| 3636.364 \|	1168	JSON::Syck \| 552.551 \| 787.544 \|
534	JSON::XS/2 \| 3774.221 \| 3599.124 \|	1169	JSON::XS \| 5780.463 \| 4854.519 \|
		1170	JSON::XS/2 \| 3869.998 \| 4798.975 \|
		1171	JSON::XS/3 \| 5862.880 \| 4798.975 \|
		1172	Storable \| 4445.002 \| 5235.027 \|
535	-----------+------------+------------+	1173	-----------+------------+------------+
536		1174
537	Again, JSON::XS leads by far.	1175	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1176	decodes faster).
538		1177
539	On large strings containing lots of high unicode characters, some	1178	On large strings containing lots of high Unicode characters, some
540	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1179	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
541	result will be broken due to missing (or wrong) unicode handling. Others	1180	result will be broken due to missing (or wrong) Unicode handling. Others
542	refuse to decode or encode properly, so it was impossible to prepare a	1181	refuse to decode or encode properly, so it was impossible to prepare a
543	fair comparison table for that case.	1182	fair comparison table for that case.
544		1183
545	SECURITY CONSIDERATIONS	1184	SECURITY CONSIDERATIONS
546	When you are using JSON in a protocol, talking to untrusted potentially	1185	When you are using JSON in a protocol, talking to untrusted potentially
…		…
550	have any buffer overflows. Obviously, this module should ensure that and	1189	have any buffer overflows. Obviously, this module should ensure that and
551	I am trying hard on making that true, but you never know.	1190	I am trying hard on making that true, but you never know.
552		1191
553	Second, you need to avoid resource-starving attacks. That means you	1192	Second, you need to avoid resource-starving attacks. That means you
554	should limit the size of JSON texts you accept, or make sure then when	1193	should limit the size of JSON texts you accept, or make sure then when
555	your resources run out, thats just fine (e.g. by using a separate	1194	your resources run out, that's just fine (e.g. by using a separate
556	process that can crash safely). The size of a JSON text in octets or	1195	process that can crash safely). The size of a JSON text in octets or
557	characters is usually a good indication of the size of the resources	1196	characters is usually a good indication of the size of the resources
558	required to decode it into a Perl structure.	1197	required to decode it into a Perl structure. While JSON::XS can check
		1198	the size of the JSON text, it might be too late when you already have it
		1199	in memory, so you might want to check the size before you accept the
		1200	string.
559		1201
560	Third, JSON::XS recurses using the C stack when decoding objects and	1202	Third, JSON::XS recurses using the C stack when decoding objects and
561	arrays. The C stack is a limited resource: for instance, on my amd64	1203	arrays. The C stack is a limited resource: for instance, on my amd64
562	machine with 8MB of stack size I can decode around 180k nested arrays	1204	machine with 8MB of stack size I can decode around 180k nested arrays
563	but only 14k nested JSON objects (due to perl itself recursing deeply on	1205	but only 14k nested JSON objects (due to perl itself recursing deeply on
564	croak to free the temporary). If that is exceeded, the program crashes.	1206	croak to free the temporary). If that is exceeded, the program crashes.
565	to be conservative, the default nesting limit is set to 512. If your	1207	To be conservative, the default nesting limit is set to 512. If your
566	process has a smaller stack, you should adjust this setting accordingly	1208	process has a smaller stack, you should adjust this setting accordingly
567	with the "max_depth" method.	1209	with the "max_depth" method.
568		1210
569	And last but least, something else could bomb you that I forgot to think	1211	Something else could bomb you, too, that I forgot to think of. In that
570	of. In that case, you get to keep the pieces. I am alway sopen for	1212	case, you get to keep the pieces. I am always open for hints, though...
571	hints, though...	1213
		1214	Also keep in mind that JSON::XS might leak contents of your Perl data
		1215	structures in its error messages, so when you serialise sensitive
		1216	information you might want to make sure that exceptions thrown by
		1217	JSON::XS will not end up in front of untrusted eyes.
		1218
		1219	If you are using JSON::XS to return packets to consumption by JavaScript
		1220	scripts in a browser you should have a look at
		1221	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1222	you are vulnerable to some common attack vectors (which really are
		1223	browser design bugs, but it is still you who will have to deal with it,
		1224	as major browser developers care only for features, not about getting
		1225	security right).
		1226
		1227	THREADS
		1228	This module is not guaranteed to be thread safe and there are no plans
		1229	to change this until Perl gets thread support (as opposed to the
		1230	horribly slow so-called "threads" which are simply slow and bloated
		1231	process simulations - use fork, it's much faster, cheaper, better).
		1232
		1233	(It might actually work, but you have been warned).
572		1234
573	BUGS	1235	BUGS
574	While the goal of this module is to be correct, that unfortunately does	1236	While the goal of this module is to be correct, that unfortunately does
575	not mean its bug-free, only that I think its design is bug-free. It is	1237	not mean it's bug-free, only that I think its design is bug-free. If you
576	still relatively early in its development. If you keep reporting bugs
577	they will be fixed swiftly, though.	1238	keep reporting bugs they will be fixed swiftly, though.
		1239
		1240	Please refrain from using rt.cpan.org or any other bug reporting
		1241	service. I put the contact address into my modules for a reason.
		1242
		1243	SEE ALSO
		1244	The json_xs command line utility for quick experiments.
578		1245
579	AUTHOR	1246	AUTHOR
580	Marc Lehmann <schmorp@schmorp.de>	1247	Marc Lehmann <schmorp@schmorp.de>
581	http://home.schmorp.de/	1248	http://home.schmorp.de/
582		1249

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Comparing JSON-XS/README (file contents):
Revision 1.10 by root, Wed Apr 4 00:01:44 2007 UTC vs.
Revision 1.27 by root, Tue Jul 15 11:29:29 2008 UTC