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Comparing JSON-XS/README (file contents):
Revision 1.8 by root, Sun Mar 25 22:11:06 2007 UTC vs.
Revision 1.25 by root, Wed Apr 16 18:38:38 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 overriden) with no overhead due to emulation (by inheritign
		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 datatypes
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	objetc 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 codepoint.
		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
248	octet-form if possible: perl stores strings internally either in an	537	octet-form if possible: perl stores strings internally either in an
249	encoding called UTF-X or in octet-form. The latter cannot store	538	encoding called UTF-X or in octet-form. The latter cannot store
250	everything but uses less space in general.	539	everything but uses less space in general (and some buggy Perl or C
		540	code might even rely on that internal representation being used).
		541
		542	The actual definition of what shrink does might change in future
		543	versions, but it will always try to save space at the expense of
		544	time.
251		545
252	If $enable is true (or missing), the string returned by "encode"	546	If $enable is true (or missing), the string returned by "encode"
253	will be shrunk-to-fit, while all strings generated by "decode" will	547	will be shrunk-to-fit, while all strings generated by "decode" will
254	also be shrunk-to-fit.	548	also be shrunk-to-fit.
255		549
…		…
260	converting strings that look like integers or floats into integers	554	converting strings that look like integers or floats into integers
261	or floats internally (there is no difference on the Perl level),	555	or floats internally (there is no difference on the Perl level),
262	saving space.	556	saving space.
263		557
264	$json = $json->max_depth ([$maximum_nesting_depth])	558	$json = $json->max_depth ([$maximum_nesting_depth])
		559	$max_depth = $json->get_max_depth
265	Sets the maximum nesting level (default 8192) accepted while	560	Sets the maximum nesting level (default 512) accepted while encoding
266	encoding or decoding. If the JSON text or Perl data structure has an	561	or decoding. If a higher nesting level is detected in JSON text or a
267	equal or higher nesting level then this limit, then the encoder and	562	Perl data structure, then the encoder and decoder will stop and
268	decoder will stop and croak at that point.	563	croak at that point.
269		564
270	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
271	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
272	"{" or "[" characters without their matching closing parenthesis	567	"{" or "[" characters without their matching closing parenthesis
273	crossed to reach a given character in a string.	568	crossed to reach a given character in a string.
274		569
275	Setting the maximum depth to one disallows any nesting, so that	570	Setting the maximum depth to one disallows any nesting, so that
276	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.
277		572
278	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,
279	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).
280		593
281	See SECURITY CONSIDERATIONS, below, for more info on why this is	594	See SECURITY CONSIDERATIONS, below, for more info on why this is
282	useful.	595	useful.
283		596
284	$json_text = $json->encode ($perl_scalar)	597	$json_text = $json->encode ($perl_scalar)
…		…
296		609
297	JSON numbers and strings become simple Perl scalars. JSON arrays	610	JSON numbers and strings become simple Perl scalars. JSON arrays
298	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"	611	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
299	becomes 1, "false" becomes 0 and "null" becomes "undef".	612	becomes 1, "false" becomes 0 and "null" becomes "undef".
300		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	[This section and the API it details is still EXPERIMENTAL]
		629
		630	In some cases, there is the need for incremental parsing of JSON texts.
		631	While this module always has to keep both JSON text and resulting Perl
		632	data structure in memory at one time, it does allow you to parse a JSON
		633	stream incrementally. It does so by accumulating text until it has a
		634	full JSON object, which it then can decode. This process is similar to
		635	using "decode_prefix" to see if a full JSON object is available, but is
		636	much more efficient (JSON::XS will only attempt to parse the JSON text
		637	once it is sure it has enough text to get a decisive result, using a
		638	very simple but truly incremental parser).
		639
		640	The following two methods deal with this.
		641
		642	[void, scalar or list context] = $json->incr_parse ([$string])
		643	This is the central parsing function. It can both append new text
		644	and extract objects from the stream accumulated so far (both of
		645	these functions are optional).
		646
		647	If $string is given, then this string is appended to the already
		648	existing JSON fragment stored in the $json object.
		649
		650	After that, if the function is called in void context, it will
		651	simply return without doing anything further. This can be used to
		652	add more text in as many chunks as you want.
		653
		654	If the method is called in scalar context, then it will try to
		655	extract exactly one JSON object. If that is successful, it will
		656	return this object, otherwise it will return "undef". If there is a
		657	parse error, this method will croak just as "decode" would do (one
		658	can then use "incr_skip" to skip the errornous part). This is the
		659	most common way of using the method.
		660
		661	And finally, in list context, it will try to extract as many objects
		662	from the stream as it can find and return them, or the empty list
		663	otherwise. For this to work, there must be no separators between the
		664	JSON objects or arrays, instead they must be concatenated
		665	back-to-back. If an error occurs, an exception will be raised as in
		666	the scalar context case. Note that in this case, any
		667	previously-parsed JSON texts will be lost.
		668
		669	$lvalue_string = $json->incr_text
		670	This method returns the currently stored JSON fragment as an lvalue,
		671	that is, you can manipulate it. This only works when a preceding
		672	call to "incr_parse" in scalar context successfully returned an
		673	object. Under all other circumstances you must not call this
		674	function (I mean it. although in simple tests it might actually
		675	work, it will fail under real world conditions). As a special
		676	exception, you can also call this method before having parsed
		677	anything.
		678
		679	This function is useful in two cases: a) finding the trailing text
		680	after a JSON object or b) parsing multiple JSON objects separated by
		681	non-JSON text (such as commas).
		682
		683	$json->incr_skip
		684	This will reset the state of the incremental parser and will remove
		685	the parsed text from the input buffer. This is useful after
		686	"incr_parse" died, in which case the input buffer and incremental
		687	parser state is left unchanged, to skip the text parsed so far and
		688	to reset the parse state.
		689
		690	LIMITATIONS
		691	All options that affect decoding are supported, except "allow_nonref".
		692	The reason for this is that it cannot be made to work sensibly: JSON
		693	objects and arrays are self-delimited, i.e. you can concatenate them
		694	back to back and still decode them perfectly. This does not hold true
		695	for JSON numbers, however.
		696
		697	For example, is the string 1 a single JSON number, or is it simply the
		698	start of 12? Or is 12 a single JSON number, or the concatenation of 1
		699	and 2? In neither case you can tell, and this is why JSON::XS takes the
		700	conservative route and disallows this case.
		701
		702	EXAMPLES
		703	Some examples will make all this clearer. First, a simple example that
		704	works similarly to "decode_prefix": We want to decode the JSON object at
		705	the start of a string and identify the portion after the JSON object:
		706
		707	my $text = "[1,2,3] hello";
		708
		709	my $json = new JSON::XS;
		710
		711	my $obj = $json->incr_parse ($text)
		712	or die "expected JSON object or array at beginning of string";
		713
		714	my $tail = $json->incr_text;
		715	# $tail now contains " hello"
		716
		717	Easy, isn't it?
		718
		719	Now for a more complicated example: Imagine a hypothetical protocol
		720	where you read some requests from a TCP stream, and each request is a
		721	JSON array, without any separation between them (in fact, it is often
		722	useful to use newlines as "separators", as these get interpreted as
		723	whitespace at the start of the JSON text, which makes it possible to
		724	test said protocol with "telnet"...).
		725
		726	Here is how you'd do it (it is trivial to write this in an event-based
		727	manner):
		728
		729	my $json = new JSON::XS;
		730
		731	# read some data from the socket
		732	while (sysread $socket, my $buf, 4096) {
		733
		734	# split and decode as many requests as possible
		735	for my $request ($json->incr_parse ($buf)) {
		736	# act on the $request
		737	}
		738	}
		739
		740	Another complicated example: Assume you have a string with JSON objects
		741	or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
		742	[3]"). To parse them, we have to skip the commas between the JSON texts,
		743	and here is where the lvalue-ness of "incr_text" comes in useful:
		744
		745	my $text = "[1],[2], [3]";
		746	my $json = new JSON::XS;
		747
		748	# void context, so no parsing done
		749	$json->incr_parse ($text);
		750
		751	# now extract as many objects as possible. note the
		752	# use of scalar context so incr_text can be called.
		753	while (my $obj = $json->incr_parse) {
		754	# do something with $obj
		755
		756	# now skip the optional comma
		757	$json->incr_text =~ s/^ \s* , //x;
		758	}
		759
		760	Now lets go for a very complex example: Assume that you have a gigantic
		761	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		762	but you cannot load it into memory fully (this has actually happened in
		763	the real world :).
		764
		765	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		766	can still help you: You implement a (very simple) array parser and let
		767	JSON decode the array elements, which are all full JSON objects on their
		768	own (this wouldn't work if the array elements could be JSON numbers, for
		769	example):
		770
		771	my $json = new JSON::XS;
		772
		773	# open the monster
		774	open my $fh, "<bigfile.json"
		775	or die "bigfile: $!";
		776
		777	# first parse the initial "["
		778	for (;;) {
		779	sysread $fh, my $buf, 65536
		780	or die "read error: $!";
		781	$json->incr_parse ($buf); # void context, so no parsing
		782
		783	# Exit the loop once we found and removed(!) the initial "[".
		784	# In essence, we are (ab-)using the $json object as a simple scalar
		785	# we append data to.
		786	last if $json->incr_text =~ s/^ \s* \[ //x;
		787	}
		788
		789	# now we have the skipped the initial "[", so continue
		790	# parsing all the elements.
		791	for (;;) {
		792	# in this loop we read data until we got a single JSON object
		793	for (;;) {
		794	if (my $obj = $json->incr_parse) {
		795	# do something with $obj
		796	last;
		797	}
		798
		799	# add more data
		800	sysread $fh, my $buf, 65536
		801	or die "read error: $!";
		802	$json->incr_parse ($buf); # void context, so no parsing
		803	}
		804
		805	# in this loop we read data until we either found and parsed the
		806	# separating "," between elements, or the final "]"
		807	for (;;) {
		808	# first skip whitespace
		809	$json->incr_text =~ s/^\s*//;
		810
		811	# if we find "]", we are done
		812	if ($json->incr_text =~ s/^\]//) {
		813	print "finished.\n";
		814	exit;
		815	}
		816
		817	# if we find ",", we can continue with the next element
		818	if ($json->incr_text =~ s/^,//) {
		819	last;
		820	}
		821
		822	# if we find anything else, we have a parse error!
		823	if (length $json->incr_text) {
		824	die "parse error near ", $json->incr_text;
		825	}
		826
		827	# else add more data
		828	sysread $fh, my $buf, 65536
		829	or die "read error: $!";
		830	$json->incr_parse ($buf); # void context, so no parsing
		831	}
		832
		833	This is a complex example, but most of the complexity comes from the
		834	fact that we are trying to be correct (bear with me if I am wrong, I
		835	never ran the above example :).
		836
301	MAPPING	837	MAPPING
302	This section describes how JSON::XS maps Perl values to JSON values and	838	This section describes how JSON::XS maps Perl values to JSON values and
303	vice versa. These mappings are designed to "do the right thing" in most	839	vice versa. These mappings are designed to "do the right thing" in most
304	circumstances automatically, preserving round-tripping characteristics	840	circumstances automatically, preserving round-tripping characteristics
305	(what you put in comes out as something equivalent).	841	(what you put in comes out as something equivalent).
306		842
307	For the more enlightened: note that in the following descriptions,	843	For the more enlightened: note that in the following descriptions,
308	lowercase perl refers to the Perl interpreter, while uppcercase Perl	844	lowercase perl refers to the Perl interpreter, while uppercase Perl
309	refers to the abstract Perl language itself.	845	refers to the abstract Perl language itself.
310		846
311	JSON -> PERL	847	JSON -> PERL
312	object	848	object
313	A JSON object becomes a reference to a hash in Perl. No ordering of	849	A JSON object becomes a reference to a hash in Perl. No ordering of
314	object keys is preserved (JSON does not preserver object key	850	object keys is preserved (JSON does not preserve object key ordering
315	ordering itself).	851	itself).
316		852
317	array	853	array
318	A JSON array becomes a reference to an array in Perl.	854	A JSON array becomes a reference to an array in Perl.
319		855
320	string	856	string
321	A JSON string becomes a string scalar in Perl - Unicode codepoints	857	A JSON string becomes a string scalar in Perl - Unicode codepoints
322	in JSON are represented by the same codepoints in the Perl string,	858	in JSON are represented by the same codepoints in the Perl string,
323	so no manual decoding is necessary.	859	so no manual decoding is necessary.
324		860
325	number	861	number
326	A JSON number becomes either an integer or numeric (floating point)	862	A JSON number becomes either an integer, numeric (floating point) or
327	scalar in perl, depending on its range and any fractional parts. On	863	string scalar in perl, depending on its range and any fractional
328	the Perl level, there is no difference between those as Perl handles	864	parts. On the Perl level, there is no difference between those as
329	all the conversion details, but an integer may take slightly less	865	Perl handles all the conversion details, but an integer may take
330	memory and might represent more values exactly than (floating point)	866	slightly less memory and might represent more values exactly than
		867	floating point numbers.
		868
		869	If the number consists of digits only, JSON::XS will try to
		870	represent it as an integer value. If that fails, it will try to
		871	represent it as a numeric (floating point) value if that is possible
		872	without loss of precision. Otherwise it will preserve the number as
		873	a string value (in which case you lose roundtripping ability, as the
		874	JSON number will be re-encoded toa JSON string).
		875
		876	Numbers containing a fractional or exponential part will always be
		877	represented as numeric (floating point) values, possibly at a loss
		878	of precision (in which case you might lose perfect roundtripping
		879	ability, but the JSON number will still be re-encoded as a JSON
331	numbers.	880	number).
332		881
333	true, false	882	true, false
334	These JSON atoms become 0, 1, respectively. Information is lost in	883	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
335	this process. Future versions might represent those values	884	respectively. They are overloaded to act almost exactly like the
336	differently, but they will be guarenteed to act like these integers	885	numbers 1 and 0. You can check whether a scalar is a JSON boolean by
337	would normally in Perl.	886	using the "JSON::XS::is_bool" function.
338		887
339	null	888	null
340	A JSON null atom becomes "undef" in Perl.	889	A JSON null atom becomes "undef" in Perl.
341		890
342	PERL -> JSON	891	PERL -> JSON
…		…
344	truly typeless language, so we can only guess which JSON type is meant	893	truly typeless language, so we can only guess which JSON type is meant
345	by a Perl value.	894	by a Perl value.
346		895
347	hash references	896	hash references
348	Perl hash references become JSON objects. As there is no inherent	897	Perl hash references become JSON objects. As there is no inherent
349	ordering in hash keys, they will usually be encoded in a	898	ordering in hash keys (or JSON objects), they will usually be
350	pseudo-random order that can change between runs of the same program	899	encoded in a pseudo-random order that can change between runs of the
351	but stays generally the same within a single run of a program.	900	same program but stays generally the same within a single run of a
352	JSON::XS can optionally sort the hash keys (determined by the	901	program. JSON::XS can optionally sort the hash keys (determined by
353	canonical flag), so the same datastructure will serialise to the	902	the canonical flag), so the same datastructure will serialise to
354	same JSON text (given same settings and version of JSON::XS), but	903	the same JSON text (given same settings and version of JSON::XS),
355	this incurs a runtime overhead.	904	but this incurs a runtime overhead and is only rarely useful, e.g.
		905	when you want to compare some JSON text against another for
		906	equality.
356		907
357	array references	908	array references
358	Perl array references become JSON arrays.	909	Perl array references become JSON arrays.
359		910
		911	other references
		912	Other unblessed references are generally not allowed and will cause
		913	an exception to be thrown, except for references to the integers 0
		914	and 1, which get turned into "false" and "true" atoms in JSON. You
		915	can also use "JSON::XS::false" and "JSON::XS::true" to improve
		916	readability.
		917
		918	encode_json [\0,JSON::XS::true] # yields [false,true]
		919
		920	JSON::XS::true, JSON::XS::false
		921	These special values become JSON true and JSON false values,
		922	respectively. You can also use "\1" and "\0" directly if you want.
		923
360	blessed objects	924	blessed objects
361	Blessed objects are not allowed. JSON::XS currently tries to encode	925	Blessed objects are not directly representable in JSON. See the
362	their underlying representation (hash- or arrayref), but this	926	"allow_blessed" and "convert_blessed" methods on various options on
363	behaviour might change in future versions.	927	how to deal with this: basically, you can choose between throwing an
		928	exception, encoding the reference as if it weren't blessed, or
		929	provide your own serialiser method.
364		930
365	simple scalars	931	simple scalars
366	Simple Perl scalars (any scalar that is not a reference) are the	932	Simple Perl scalars (any scalar that is not a reference) are the
367	most difficult objects to encode: JSON::XS will encode undefined	933	most difficult objects to encode: JSON::XS will encode undefined
368	scalars as JSON null value, scalars that have last been used in a	934	scalars as JSON "null" values, scalars that have last been used in a
369	string context before encoding as JSON strings and anything else as	935	string context before encoding as JSON strings, and anything else as
370	number value:	936	number value:
371		937
372	# dump as number	938	# dump as number
373	to_json [2] # yields [2]	939	encode_json [2] # yields [2]
374	to_json [-3.0e17] # yields [-3e+17]	940	encode_json [-3.0e17] # yields [-3e+17]
375	my $value = 5; to_json [$value] # yields [5]	941	my $value = 5; encode_json [$value] # yields [5]
376		942
377	# used as string, so dump as string	943	# used as string, so dump as string
378	print $value;	944	print $value;
379	to_json [$value] # yields ["5"]	945	encode_json [$value] # yields ["5"]
380		946
381	# undef becomes null	947	# undef becomes null
382	to_json [undef] # yields [null]	948	encode_json [undef] # yields [null]
383		949
384	You can force the type to be a string by stringifying it:	950	You can force the type to be a JSON string by stringifying it:
385		951
386	my $x = 3.1; # some variable containing a number	952	my $x = 3.1; # some variable containing a number
387	"$x"; # stringified	953	"$x"; # stringified
388	$x .= ""; # another, more awkward way to stringify	954	$x .= ""; # another, more awkward way to stringify
389	print $x; # perl does it for you, too, quite often	955	print $x; # perl does it for you, too, quite often
390		956
391	You can force the type to be a number by numifying it:	957	You can force the type to be a JSON number by numifying it:
392		958
393	my $x = "3"; # some variable containing a string	959	my $x = "3"; # some variable containing a string
394	$x += 0; # numify it, ensuring it will be dumped as a number	960	$x += 0; # numify it, ensuring it will be dumped as a number
395	$x *= 1; # same thing, the choise is yours.	961	$x *= 1; # same thing, the choice is yours.
396		962
397	You can not currently output JSON booleans or force the type in	963	You can not currently force the type in other, less obscure, ways.
398	other, less obscure, ways. Tell me if you need this capability.	964	Tell me if you need this capability (but don't forget to explain why
		965	it's needed :).
399		966
400	circular data structures	967	ENCODING/CODESET FLAG NOTES
401	Those will be encoded until memory or stackspace runs out.	968	The interested reader might have seen a number of flags that signify
		969	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
		970	some confusion on what these do, so here is a short comparison:
402		971
403	COMPARISON	972	"utf8" controls whether the JSON text created by "encode" (and expected
404	As already mentioned, this module was created because none of the	973	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
405	existing JSON modules could be made to work correctly. First I will	974	control whether "encode" escapes character values outside their
406	describe the problems (or pleasures) I encountered with various existing	975	respective codeset range. Neither of these flags conflict with each
407	JSON modules, followed by some benchmark values. JSON::XS was designed	976	other, although some combinations make less sense than others.
408	not to suffer from any of these problems or limitations.
409		977
410	JSON 1.07	978	Care has been taken to make all flags symmetrical with respect to
411	Slow (but very portable, as it is written in pure Perl).	979	"encode" and "decode", that is, texts encoded with any combination of
		980	these flag values will be correctly decoded when the same flags are used
		981	- in general, if you use different flag settings while encoding vs. when
		982	decoding you likely have a bug somewhere.
412		983
413	Undocumented/buggy Unicode handling (how JSON handles unicode values	984	Below comes a verbose discussion of these flags. Note that a "codeset"
414	is undocumented. One can get far by feeding it unicode strings and	985	is simply an abstract set of character-codepoint pairs, while an
415	doing en-/decoding oneself, but unicode escapes are not working	986	encoding takes those codepoint numbers and encodes them, in our case
		987	into octets. Unicode is (among other things) a codeset, UTF-8 is an
		988	encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
		989	encodings at the same time, which can be confusing.
		990
		991	"utf8" flag disabled
		992	When "utf8" is disabled (the default), then "encode"/"decode"
		993	generate and expect Unicode strings, that is, characters with high
		994	ordinal Unicode values (> 255) will be encoded as such characters,
		995	and likewise such characters are decoded as-is, no canges to them
		996	will be done, except "(re-)interpreting" them as Unicode codepoints
		997	or Unicode characters, respectively (to Perl, these are the same
		998	thing in strings unless you do funny/weird/dumb stuff).
		999
		1000	This is useful when you want to do the encoding yourself (e.g. when
		1001	you want to have UTF-16 encoded JSON texts) or when some other layer
		1002	does the encoding for you (for example, when printing to a terminal
		1003	using a filehandle that transparently encodes to UTF-8 you certainly
		1004	do NOT want to UTF-8 encode your data first and have Perl encode it
		1005	another time).
		1006
		1007	"utf8" flag enabled
		1008	If the "utf8"-flag is enabled, "encode"/"decode" will encode all
		1009	characters using the corresponding UTF-8 multi-byte sequence, and
		1010	will expect your input strings to be encoded as UTF-8, that is, no
		1011	"character" of the input string must have any value > 255, as UTF-8
		1012	does not allow that.
		1013
		1014	The "utf8" flag therefore switches between two modes: disabled means
		1015	you will get a Unicode string in Perl, enabled means you get an
		1016	UTF-8 encoded octet/binary string in Perl.
		1017
		1018	"latin1" or "ascii" flags enabled
		1019	With "latin1" (or "ascii") enabled, "encode" will escape characters
		1020	with ordinal values > 255 (> 127 with "ascii") and encode the
		1021	remaining characters as specified by the "utf8" flag.
		1022
		1023	If "utf8" is disabled, then the result is also correctly encoded in
		1024	those character sets (as both are proper subsets of Unicode, meaning
		1025	that a Unicode string with all character values < 256 is the same
		1026	thing as a ISO-8859-1 string, and a Unicode string with all
		1027	character values < 128 is the same thing as an ASCII string in
416	properly).	1028	Perl).
417		1029
418	No roundtripping (strings get clobbered if they look like numbers,	1030	If "utf8" is enabled, you still get a correct UTF-8-encoded string,
419	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	1031	regardless of these flags, just some more characters will be escaped
420	will decode into the number 2.	1032	using "\uXXXX" then before.
421		1033
422	JSON::PC 0.01	1034	Note that ISO-8859-1-encoded strings are not compatible with UTF-8
423	Very fast.	1035	encoding, while ASCII-encoded strings are. That is because the
		1036	ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
		1037	codeset being a subset of Unicode), while ASCII is.
424		1038
425	Undocumented/buggy Unicode handling.	1039	Surprisingly, "decode" will ignore these flags and so treat all
		1040	input values as governed by the "utf8" flag. If it is disabled, this
		1041	allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
		1042	strict subsets of Unicode. If it is enabled, you can correctly
		1043	decode UTF-8 encoded strings.
426		1044
427	No roundtripping.	1045	So neither "latin1" nor "ascii" are incompatible with the "utf8"
		1046	flag - they only govern when the JSON output engine escapes a
		1047	character or not.
428		1048
429	Has problems handling many Perl values (e.g. regex results and other	1049	The main use for "latin1" is to relatively efficiently store binary
430	magic values will make it croak).	1050	data as JSON, at the expense of breaking compatibility with most
		1051	JSON decoders.
431		1052
432	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1053	The main use for "ascii" is to force the output to not contain
433	which is not a valid JSON text.	1054	characters with values > 127, which means you can interpret the
		1055	resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
		1056	any character set and 8-bit-encoding, and still get the same data
		1057	structure back. This is useful when your channel for JSON transfer
		1058	is not 8-bit clean or the encoding might be mangled in between (e.g.
		1059	in mail), and works because ASCII is a proper subset of most 8-bit
		1060	and multibyte encodings in use in the world.
434		1061
435	Unmaintained (maintainer unresponsive for many months, bugs are not	1062	JSON and YAML
436	getting fixed).	1063	You often hear that JSON is a subset of YAML. This is, however, a mass
		1064	hysteria(*) and very far from the truth (as of the time of this
		1065	writing), so let me state it clearly: *in general, there is no way to
		1066	configure JSON::XS to output a data structure as valid YAML* that works
		1067	in all cases.
437		1068
438	JSON::Syck 0.21	1069	If you really must use JSON::XS to generate YAML, you should use this
439	Very buggy (often crashes).	1070	algorithm (subject to change in future versions):
440		1071
441	Very inflexible (no human-readable format supported, format pretty	1072	my $to_yaml = JSON::XS->new->utf8->space_after (1);
442	much undocumented. I need at least a format for easy reading by	1073	my $yaml = $to_yaml->encode ($ref) . "\n";
443	humans and a single-line compact format for use in a protocol, and
444	preferably a way to generate ASCII-only JSON texts).
445		1074
446	Completely broken (and confusingly documented) Unicode handling	1075	This will usually generate JSON texts that also parse as valid YAML.
447	(unicode escapes are not working properly, you need to set	1076	Please note that YAML has hardcoded limits on (simple) object key
448	ImplicitUnicode to different values on en- and decoding to get	1077	lengths that JSON doesn't have and also has different and incompatible
449	symmetric behaviour).	1078	unicode handling, so you should make sure that your hash keys are
		1079	noticeably shorter than the 1024 "stream characters" YAML allows and
		1080	that you do not have characters with codepoint values outside the
		1081	Unicode BMP (basic multilingual page). YAML also does not allow "\/"
		1082	sequences in strings (which JSON::XS does not currently generate, but
		1083	other JSON generators might).
450		1084
451	No roundtripping (simple cases work, but this depends on wether the	1085	There might be other incompatibilities that I am not aware of (or the
452	scalar value was used in a numeric context or not).	1086	YAML specification has been changed yet again - it does so quite often).
		1087	In general you should not try to generate YAML with a JSON generator or
		1088	vice versa, or try to parse JSON with a YAML parser or vice versa:
		1089	chances are high that you will run into severe interoperability problems
		1090	when you least expect it.
453		1091
454	Dumping hashes may skip hash values depending on iterator state.	1092	(*) I have been pressured multiple times by Brian Ingerson (one of the
		1093	authors of the YAML specification) to remove this paragraph, despite
		1094	him acknowledging that the actual incompatibilities exist. As I was
		1095	personally bitten by this "JSON is YAML" lie, I refused and said I
		1096	will continue to educate people about these issues, so others do not
		1097	run into the same problem again and again. After this, Brian called
		1098	me a (quote)complete and worthless idiot(unquote).
455		1099
456	Unmaintained (maintainer unresponsive for many months, bugs are not	1100	In my opinion, instead of pressuring and insulting people who
457	getting fixed).	1101	actually clarify issues with YAML and the wrong statements of some
458		1102	of its proponents, I would kindly suggest reading the JSON spec
459	Does not check input for validity (i.e. will accept non-JSON input	1103	(which is not that difficult or long) and finally make YAML
460	and return "something" instead of raising an exception. This is a	1104	compatible to it, and educating users about the changes, instead of
461	security issue: imagine two banks transfering money between each	1105	spreading lies about the real compatibility for many years and
462	other using JSON. One bank might parse a given non-JSON request and	1106	trying to silence people who point out that it isn't true.
463	deduct money, while the other might reject the transaction with a
464	syntax error. While a good protocol will at least recover, that is
465	extra unnecessary work and the transaction will still not succeed).
466
467	JSON::DWIW 0.04
468	Very fast. Very natural. Very nice.
469
470	Undocumented unicode handling (but the best of the pack. Unicode
471	escapes still don't get parsed properly).
472
473	Very inflexible.
474
475	No roundtripping.
476
477	Does not generate valid JSON texts (key strings are often unquoted,
478	empty keys result in nothing being output)
479
480	Does not check input for validity.
481		1107
482	SPEED	1108	SPEED
483	It seems that JSON::XS is surprisingly fast, as shown in the following	1109	It seems that JSON::XS is surprisingly fast, as shown in the following
484	tables. They have been generated with the help of the "eg/bench" program	1110	tables. They have been generated with the help of the "eg/bench" program
485	in the JSON::XS distribution, to make it easy to compare on your own	1111	in the JSON::XS distribution, to make it easy to compare on your own
486	system.	1112	system.
487		1113
488	First comes a comparison between various modules using a very short JSON	1114	First comes a comparison between various modules using a very short
489	string:	1115	single-line JSON string (also available at
		1116	<http://dist.schmorp.de/misc/json/short.json>).
490		1117
491	{"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null}	1118	{"method": "handleMessage", "params": ["user1",
		1119	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1120	true, false]}
492		1121
493	It shows the number of encodes/decodes per second (JSON::XS uses the	1122	It shows the number of encodes/decodes per second (JSON::XS uses the
494	functional interface, while JSON::XS/2 uses the OO interface with	1123	functional interface, while JSON::XS/2 uses the OO interface with
495	pretty-printing and hashkey sorting enabled). Higher is better:	1124	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
		1125	Higher is better:
496		1126
497	module \| encode \| decode \|	1127	module \| encode \| decode \|
498	-----------\|------------\|------------\|	1128	-----------\|------------\|------------\|
499	JSON \| 11488.516 \| 7823.035 \|	1129	JSON 1.x \| 4990.842 \| 4088.813 \|
500	JSON::DWIW \| 94708.054 \| 129094.260 \|	1130	JSON::DWIW \| 51653.990 \| 71575.154 \|
501	JSON::PC \| 63884.157 \| 128528.212 \|	1131	JSON::PC \| 65948.176 \| 74631.744 \|
		1132	JSON::PP \| 8931.652 \| 3817.168 \|
502	JSON::Syck \| 34898.677 \| 42096.911 \|	1133	JSON::Syck \| 24877.248 \| 27776.848 \|
503	JSON::XS \| 654027.064 \| 396423.669 \|	1134	JSON::XS \| 388361.481 \| 227951.304 \|
504	JSON::XS/2 \| 371564.190 \| 371725.613 \|	1135	JSON::XS/2 \| 227951.304 \| 218453.333 \|
		1136	JSON::XS/3 \| 338250.323 \| 218453.333 \|
		1137	Storable \| 16500.016 \| 135300.129 \|
505	-----------+------------+------------+	1138	-----------+------------+------------+
506		1139
507	That is, JSON::XS is more than six times faster than JSON::DWIW on	1140	That is, JSON::XS is about five times faster than JSON::DWIW on
508	encoding, more than three times faster on decoding, and about thirty	1141	encoding, about three times faster on decoding, and over forty times
509	times faster than JSON, even with pretty-printing and key sorting.	1142	faster than JSON, even with pretty-printing and key sorting. It also
		1143	compares favourably to Storable for small amounts of data.
510		1144
511	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1145	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
512	search API (http://nanoref.com/yahooapis/mgPdGg):	1146	search API (<http://dist.schmorp.de/misc/json/long.json>).
513		1147
514	module \| encode \| decode \|	1148	module \| encode \| decode \|
515	-----------\|------------\|------------\|	1149	-----------\|------------\|------------\|
516	JSON \| 273.023 \| 44.674 \|	1150	JSON 1.x \| 55.260 \| 34.971 \|
517	JSON::DWIW \| 1089.383 \| 1145.704 \|	1151	JSON::DWIW \| 825.228 \| 1082.513 \|
518	JSON::PC \| 3097.419 \| 2393.921 \|	1152	JSON::PC \| 3571.444 \| 2394.829 \|
519	JSON::Syck \| 514.060 \| 843.053 \|	1153	JSON::PP \| 210.987 \| 32.574 \|
520	JSON::XS \| 6479.668 \| 3636.364 \|	1154	JSON::Syck \| 552.551 \| 787.544 \|
521	JSON::XS/2 \| 3774.221 \| 3599.124 \|	1155	JSON::XS \| 5780.463 \| 4854.519 \|
		1156	JSON::XS/2 \| 3869.998 \| 4798.975 \|
		1157	JSON::XS/3 \| 5862.880 \| 4798.975 \|
		1158	Storable \| 4445.002 \| 5235.027 \|
522	-----------+------------+------------+	1159	-----------+------------+------------+
523		1160
524	Again, JSON::XS leads by far.	1161	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1162	decodes faster).
525		1163
526	On large strings containing lots of high unicode characters, some	1164	On large strings containing lots of high Unicode characters, some
527	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1165	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
528	result will be broken due to missing (or wrong) unicode handling. Others	1166	result will be broken due to missing (or wrong) Unicode handling. Others
529	refuse to decode or encode properly, so it was impossible to prepare a	1167	refuse to decode or encode properly, so it was impossible to prepare a
530	fair comparison table for that case.	1168	fair comparison table for that case.
531		1169
532	SECURITY CONSIDERATIONS	1170	SECURITY CONSIDERATIONS
533	When you are using JSON in a protocol, talking to untrusted potentially	1171	When you are using JSON in a protocol, talking to untrusted potentially
…		…
537	have any buffer overflows. Obviously, this module should ensure that and	1175	have any buffer overflows. Obviously, this module should ensure that and
538	I am trying hard on making that true, but you never know.	1176	I am trying hard on making that true, but you never know.
539		1177
540	Second, you need to avoid resource-starving attacks. That means you	1178	Second, you need to avoid resource-starving attacks. That means you
541	should limit the size of JSON texts you accept, or make sure then when	1179	should limit the size of JSON texts you accept, or make sure then when
542	your resources run out, thats just fine (e.g. by using a separate	1180	your resources run out, that's just fine (e.g. by using a separate
543	process that can crash safely). The size of a JSON text in octets or	1181	process that can crash safely). The size of a JSON text in octets or
544	characters is usually a good indication of the size of the resources	1182	characters is usually a good indication of the size of the resources
545	required to decode it into a Perl structure.	1183	required to decode it into a Perl structure. While JSON::XS can check
		1184	the size of the JSON text, it might be too late when you already have it
		1185	in memory, so you might want to check the size before you accept the
		1186	string.
546		1187
547	Third, JSON::XS recurses using the C stack when decoding objects and	1188	Third, JSON::XS recurses using the C stack when decoding objects and
548	arrays. The C stack is a limited resource: for instance, on my amd64	1189	arrays. The C stack is a limited resource: for instance, on my amd64
549	machine with 8MB of stack size I can decode around 180k nested arrays	1190	machine with 8MB of stack size I can decode around 180k nested arrays
550	but only 14k nested JSON objects. If that is exceeded, the program	1191	but only 14k nested JSON objects (due to perl itself recursing deeply on
		1192	croak to free the temporary). If that is exceeded, the program crashes.
551	crashes. Thats why the default nesting limit is set to 8192. If your	1193	To be conservative, the default nesting limit is set to 512. If your
552	process has a smaller stack, you should adjust this setting accordingly	1194	process has a smaller stack, you should adjust this setting accordingly
553	with the "max_depth" method.	1195	with the "max_depth" method.
554		1196
555	And last but least, something else could bomb you that I forgot to think	1197	Something else could bomb you, too, that I forgot to think of. In that
556	of. In that case, you get to keep the pieces. I am alway sopen for	1198	case, you get to keep the pieces. I am always open for hints, though...
557	hints, though...	1199
		1200	Also keep in mind that JSON::XS might leak contents of your Perl data
		1201	structures in its error messages, so when you serialise sensitive
		1202	information you might want to make sure that exceptions thrown by
		1203	JSON::XS will not end up in front of untrusted eyes.
		1204
		1205	If you are using JSON::XS to return packets to consumption by JavaScript
		1206	scripts in a browser you should have a look at
		1207	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1208	you are vulnerable to some common attack vectors (which really are
		1209	browser design bugs, but it is still you who will have to deal with it,
		1210	as major browser developers care only for features, not about getting
		1211	security right).
		1212
		1213	THREADS
		1214	This module is not guaranteed to be thread safe and there are no plans
		1215	to change this until Perl gets thread support (as opposed to the
		1216	horribly slow so-called "threads" which are simply slow and bloated
		1217	process simulations - use fork, it's much faster, cheaper, better).
		1218
		1219	(It might actually work, but you have been warned).
558		1220
559	BUGS	1221	BUGS
560	While the goal of this module is to be correct, that unfortunately does	1222	While the goal of this module is to be correct, that unfortunately does
561	not mean its bug-free, only that I think its design is bug-free. It is	1223	not mean it's bug-free, only that I think its design is bug-free. It is
562	still relatively early in its development. If you keep reporting bugs	1224	still relatively early in its development. If you keep reporting bugs
563	they will be fixed swiftly, though.	1225	they will be fixed swiftly, though.
		1226
		1227	Please refrain from using rt.cpan.org or any other bug reporting
		1228	service. I put the contact address into my modules for a reason.
		1229
		1230	SEE ALSO
		1231	The json_xs command line utility for quick experiments.
564		1232
565	AUTHOR	1233	AUTHOR
566	Marc Lehmann <schmorp@schmorp.de>	1234	Marc Lehmann <schmorp@schmorp.de>
567	http://home.schmorp.de/	1235	http://home.schmorp.de/
568		1236

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Comparing JSON-XS/README (file contents):
Revision 1.8 by root, Sun Mar 25 22:11:06 2007 UTC vs.
Revision 1.25 by root, Wed Apr 16 18:38:38 2008 UTC