[ViewVC] Diff of: cvs/JSON-XS/README

Comparing JSON-XS/README (file contents):
Revision 1.12 by root, Wed Jun 6 18:17:13 2007 UTC vs.
Revision 1.23 by root, Wed Mar 19 22:31:00 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. The resulting encoded JSON text can	188	escape sequence, as per RFC4627. The resulting encoded JSON text can
118	be treated as a native unicode string, an ascii-encoded,	189	be treated as a native Unicode string, an ascii-encoded,
119	latin1-encoded or UTF-8 encoded string, or any other superset of	190	latin1-encoded or UTF-8 encoded string, or any other superset of
120	ASCII.	191	ASCII.
121		192
122	If $enable is false, then the "encode" method will not escape	193	If $enable is false, then the "encode" method will not escape
123	Unicode characters unless required by the JSON syntax or other	194	Unicode characters unless required by the JSON syntax or other
124	flags. This results in a faster and more compact format.	195	flags. This results in a faster and more compact format.
125		196
		197	See also the section ENCODING/CODESET FLAG NOTES later in this
		198	document.
		199
126	The main use for this flag is to produce JSON texts that can be	200	The main use for this flag is to produce JSON texts that can be
127	transmitted over a 7-bit channel, as the encoded JSON texts will not	201	transmitted over a 7-bit channel, as the encoded JSON texts will not
128	contain any 8 bit characters.	202	contain any 8 bit characters.
129		203
130	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	204	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
131	=> ["\ud801\udc01"]	205	=> ["\ud801\udc01"]
132		206
133	$json = $json->latin1 ([$enable])	207	$json = $json->latin1 ([$enable])
		208	$enabled = $json->get_latin1
134	If $enable is true (or missing), then the "encode" method will	209	If $enable is true (or missing), then the "encode" method will
135	encode the resulting JSON text as latin1 (or iso-8859-1), escaping	210	encode the resulting JSON text as latin1 (or iso-8859-1), escaping
136	any characters outside the code range 0..255. The resulting string	211	any characters outside the code range 0..255. The resulting string
137	can be treated as a latin1-encoded JSON text or a native unicode	212	can be treated as a latin1-encoded JSON text or a native Unicode
138	string. The "decode" method will not be affected in any way by this	213	string. The "decode" method will not be affected in any way by this
139	flag, as "decode" by default expects unicode, which is a strict	214	flag, as "decode" by default expects Unicode, which is a strict
140	superset of latin1.	215	superset of latin1.
141		216
142	If $enable is false, then the "encode" method will not escape	217	If $enable is false, then the "encode" method will not escape
143	Unicode characters unless required by the JSON syntax or other	218	Unicode characters unless required by the JSON syntax or other
144	flags.	219	flags.
		220
		221	See also the section ENCODING/CODESET FLAG NOTES later in this
		222	document.
145		223
146	The main use for this flag is efficiently encoding binary data as	224	The main use for this flag is efficiently encoding binary data as
147	JSON text, as most octets will not be escaped, resulting in a	225	JSON text, as most octets will not be escaped, resulting in a
148	smaller encoded size. The disadvantage is that the resulting JSON	226	smaller encoded size. The disadvantage is that the resulting JSON
149	text is encoded in latin1 (and must correctly be treated as such	227	text is encoded in latin1 (and must correctly be treated as such
150	when storing and transfering), a rare encoding for JSON. It is	228	when storing and transferring), a rare encoding for JSON. It is
151	therefore most useful when you want to store data structures known	229	therefore most useful when you want to store data structures known
152	to contain binary data efficiently in files or databases, not when	230	to contain binary data efficiently in files or databases, not when
153	talking to other JSON encoders/decoders.	231	talking to other JSON encoders/decoders.
154		232
155	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	233	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
156	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	234	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
157		235
158	$json = $json->utf8 ([$enable])	236	$json = $json->utf8 ([$enable])
		237	$enabled = $json->get_utf8
159	If $enable is true (or missing), then the "encode" method will	238	If $enable is true (or missing), then the "encode" method will
160	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,
161	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
162	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
163	characters outside the range 0..255, they are thus useful for	242	characters outside the range 0..255, they are thus useful for
164	bytewise/binary I/O. In future versions, enabling this option might	243	bytewise/binary I/O. In future versions, enabling this option might
165	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
166	described in RFC4627.	245	described in RFC4627.
167		246
168	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
169	string as a (non-encoded) unicode string, while "decode" expects	248	string as a (non-encoded) Unicode string, while "decode" expects
170	thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or	249	thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
171	UTF-16) needs to be done yourself, e.g. using the Encode module.	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.
172		254
173	Example, output UTF-16BE-encoded JSON:	255	Example, output UTF-16BE-encoded JSON:
174		256
175	use Encode;	257	use Encode;
176	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	258	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
195	2	277	2
196	]	278	]
197	}	279	}
198		280
199	$json = $json->indent ([$enable])	281	$json = $json->indent ([$enable])
		282	$enabled = $json->get_indent
200	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
201	multiline format as output, putting every array member or	284	multiline format as output, putting every array member or
202	object/hash key-value pair into its own line, identing them	285	object/hash key-value pair into its own line, indenting them
203	properly.	286	properly.
204		287
205	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
206	the resulting JSON text is guarenteed not to contain any "newlines".	289	the resulting JSON text is guaranteed not to contain any "newlines".
207		290
208	This setting has no effect when decoding JSON texts.	291	This setting has no effect when decoding JSON texts.
209		292
210	$json = $json->space_before ([$enable])	293	$json = $json->space_before ([$enable])
		294	$enabled = $json->get_space_before
211	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
212	an extra optional space before the ":" separating keys from values	296	an extra optional space before the ":" separating keys from values
213	in JSON objects.	297	in JSON objects.
214		298
215	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
…		…
221	Example, space_before enabled, space_after and indent disabled:	305	Example, space_before enabled, space_after and indent disabled:
222		306
223	{"key" :"value"}	307	{"key" :"value"}
224		308
225	$json = $json->space_after ([$enable])	309	$json = $json->space_after ([$enable])
		310	$enabled = $json->get_space_after
226	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
227	an extra optional space after the ":" separating keys from values in	312	an extra optional space after the ":" separating keys from values in
228	JSON objects and extra whitespace after the "," separating key-value	313	JSON objects and extra whitespace after the "," separating key-value
229	pairs and array members.	314	pairs and array members.
230		315
…		…
235		320
236	Example, space_before and indent disabled, space_after enabled:	321	Example, space_before and indent disabled, space_after enabled:
237		322
238	{"key": "value"}	323	{"key": "value"}
239		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
240	$json = $json->canonical ([$enable])	367	$json = $json->canonical ([$enable])
		368	$enabled = $json->get_canonical
241	If $enable is true (or missing), then the "encode" method will	369	If $enable is true (or missing), then the "encode" method will
242	output JSON objects by sorting their keys. This is adding a	370	output JSON objects by sorting their keys. This is adding a
243	comparatively high overhead.	371	comparatively high overhead.
244		372
245	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
246	pairs in the order Perl stores them (which will likely change	374	pairs in the order Perl stores them (which will likely change
247	between runs of the same script).	375	between runs of the same script).
248		376
249	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
250	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
251	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
252	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
253	in Perl.	381	in Perl.
254		382
255	This setting has no effect when decoding JSON texts.	383	This setting has no effect when decoding JSON texts.
256		384
257	$json = $json->allow_nonref ([$enable])	385	$json = $json->allow_nonref ([$enable])
		386	$enabled = $json->get_allow_nonref
258	If $enable is true (or missing), then the "encode" method can	387	If $enable is true (or missing), then the "encode" method can
259	convert a non-reference into its corresponding string, number or	388	convert a non-reference into its corresponding string, number or
260	null JSON value, which is an extension to RFC4627. Likewise,	389	null JSON value, which is an extension to RFC4627. Likewise,
261	"decode" will accept those JSON values instead of croaking.	390	"decode" will accept those JSON values instead of croaking.
262		391
…		…
269	"allow_nonref", resulting in an invalid JSON text:	398	"allow_nonref", resulting in an invalid JSON text:
270		399
271	JSON::XS->new->allow_nonref->encode ("Hello, World!")	400	JSON::XS->new->allow_nonref->encode ("Hello, World!")
272	=> "Hello, World!"	401	=> "Hello, World!"
273		402
		403	$json = $json->allow_blessed ([$enable])
		404	$enabled = $json->get_allow_blessed
		405	If $enable is true (or missing), then the "encode" method will not
		406	barf when it encounters a blessed reference. Instead, the value of
		407	the convert_blessed option will decide whether "null"
		408	("convert_blessed" disabled or no "TO_JSON" method found) or a
		409	representation of the object ("convert_blessed" enabled and
		410	"TO_JSON" method found) is being encoded. Has no effect on "decode".
		411
		412	If $enable is false (the default), then "encode" will throw an
		413	exception when it encounters a blessed object.
		414
		415	$json = $json->convert_blessed ([$enable])
		416	$enabled = $json->get_convert_blessed
		417	If $enable is true (or missing), then "encode", upon encountering a
		418	blessed object, will check for the availability of the "TO_JSON"
		419	method on the object's class. If found, it will be called in scalar
		420	context and the resulting scalar will be encoded instead of the
		421	object. If no "TO_JSON" method is found, the value of
		422	"allow_blessed" will decide what to do.
		423
		424	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
		425	returns other blessed objects, those will be handled in the same
		426	way. "TO_JSON" must take care of not causing an endless recursion
		427	cycle (== crash) in this case. The name of "TO_JSON" was chosen
		428	because other methods called by the Perl core (== not by the user of
		429	the object) are usually in upper case letters and to avoid
		430	collisions with any "to_json" function or method.
		431
		432	This setting does not yet influence "decode" in any way, but in the
		433	future, global hooks might get installed that influence "decode" and
		434	are enabled by this setting.
		435
		436	If $enable is false, then the "allow_blessed" setting will decide
		437	what to do when a blessed object is found.
		438
		439	$json = $json->filter_json_object ([$coderef->($hashref)])
		440	When $coderef is specified, it will be called from "decode" each
		441	time it decodes a JSON object. The only argument is a reference to
		442	the newly-created hash. If the code references returns a single
		443	scalar (which need not be a reference), this value (i.e. a copy of
		444	that scalar to avoid aliasing) is inserted into the deserialised
		445	data structure. If it returns an empty list (NOTE: not "undef",
		446	which is a valid scalar), the original deserialised hash will be
		447	inserted. This setting can slow down decoding considerably.
		448
		449	When $coderef is omitted or undefined, any existing callback will be
		450	removed and "decode" will not change the deserialised hash in any
		451	way.
		452
		453	Example, convert all JSON objects into the integer 5:
		454
		455	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		456	# returns [5]
		457	$js->decode ('[{}]')
		458	# throw an exception because allow_nonref is not enabled
		459	# so a lone 5 is not allowed.
		460	$js->decode ('{"a":1, "b":2}');
		461
		462	$json = $json->filter_json_single_key_object ($key [=>
		463	$coderef->($value)])
		464	Works remotely similar to "filter_json_object", but is only called
		465	for JSON objects having a single key named $key.
		466
		467	This $coderef is called before the one specified via
		468	"filter_json_object", if any. It gets passed the single value in the
		469	JSON object. If it returns a single value, it will be inserted into
		470	the data structure. If it returns nothing (not even "undef" but the
		471	empty list), the callback from "filter_json_object" will be called
		472	next, as if no single-key callback were specified.
		473
		474	If $coderef is omitted or undefined, the corresponding callback will
		475	be disabled. There can only ever be one callback for a given key.
		476
		477	As this callback gets called less often then the
		478	"filter_json_object" one, decoding speed will not usually suffer as
		479	much. Therefore, single-key objects make excellent targets to
		480	serialise Perl objects into, especially as single-key JSON objects
		481	are as close to the type-tagged value concept as JSON gets (it's
		482	basically an ID/VALUE tuple). Of course, JSON does not support this
		483	in any way, so you need to make sure your data never looks like a
		484	serialised Perl hash.
		485
		486	Typical names for the single object key are "__class_whatever__", or
		487	"$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
		488	things like "__class_md5sum(classname)__", to reduce the risk of
		489	clashing with real hashes.
		490
		491	Example, decode JSON objects of the form "{ "__widget__" => <id> }"
		492	into the corresponding $WIDGET{<id>} object:
		493
		494	# return whatever is in $WIDGET{5}:
		495	JSON::XS
		496	->new
		497	->filter_json_single_key_object (__widget__ => sub {
		498	$WIDGET{ $_[0] }
		499	})
		500	->decode ('{"__widget__": 5')
		501
		502	# this can be used with a TO_JSON method in some "widget" class
		503	# for serialisation to json:
		504	sub WidgetBase::TO_JSON {
		505	my ($self) = @_;
		506
		507	unless ($self->{id}) {
		508	$self->{id} = ..get..some..id..;
		509	$WIDGET{$self->{id}} = $self;
		510	}
		511
		512	{ __widget__ => $self->{id} }
		513	}
		514
274	$json = $json->shrink ([$enable])	515	$json = $json->shrink ([$enable])
		516	$enabled = $json->get_shrink
275	Perl usually over-allocates memory a bit when allocating space for	517	Perl usually over-allocates memory a bit when allocating space for
276	strings. This flag optionally resizes strings generated by either	518	strings. This flag optionally resizes strings generated by either
277	"encode" or "decode" to their minimum size possible. This can save	519	"encode" or "decode" to their minimum size possible. This can save
278	memory when your JSON texts are either very very long or you have	520	memory when your JSON texts are either very very long or you have
279	many short strings. It will also try to downgrade any strings to	521	many short strings. It will also try to downgrade any strings to
…		…
297	converting strings that look like integers or floats into integers	539	converting strings that look like integers or floats into integers
298	or floats internally (there is no difference on the Perl level),	540	or floats internally (there is no difference on the Perl level),
299	saving space.	541	saving space.
300		542
301	$json = $json->max_depth ([$maximum_nesting_depth])	543	$json = $json->max_depth ([$maximum_nesting_depth])
		544	$max_depth = $json->get_max_depth
302	Sets the maximum nesting level (default 512) accepted while encoding	545	Sets the maximum nesting level (default 512) accepted while encoding
303	or decoding. If the JSON text or Perl data structure has an equal or	546	or decoding. If the JSON text or Perl data structure has an equal or
304	higher nesting level then this limit, then the encoder and decoder	547	higher nesting level then this limit, then the encoder and decoder
305	will stop and croak at that point.	548	will stop and croak at that point.
306		549
…		…
310	crossed to reach a given character in a string.	553	crossed to reach a given character in a string.
311		554
312	Setting the maximum depth to one disallows any nesting, so that	555	Setting the maximum depth to one disallows any nesting, so that
313	ensures that the object is only a single hash/object or array.	556	ensures that the object is only a single hash/object or array.
314		557
315	The argument to "max_depth" will be rounded up to the next nearest	558	The argument to "max_depth" will be rounded up to the next highest
316	power of two.	559	power of two. If no argument is given, the highest possible setting
		560	will be used, which is rarely useful.
		561
		562	See SECURITY CONSIDERATIONS, below, for more info on why this is
		563	useful.
		564
		565	$json = $json->max_size ([$maximum_string_size])
		566	$max_size = $json->get_max_size
		567	Set the maximum length a JSON text may have (in bytes) where
		568	decoding is being attempted. The default is 0, meaning no limit.
		569	When "decode" is called on a string longer then this number of
		570	characters it will not attempt to decode the string but throw an
		571	exception. This setting has no effect on "encode" (yet).
		572
		573	The argument to "max_size" will be rounded up to the next highest
		574	power of two (so may be more than requested). If no argument is
		575	given, the limit check will be deactivated (same as when 0 is
		576	specified).
317		577
318	See SECURITY CONSIDERATIONS, below, for more info on why this is	578	See SECURITY CONSIDERATIONS, below, for more info on why this is
319	useful.	579	useful.
320		580
321	$json_text = $json->encode ($perl_scalar)	581	$json_text = $json->encode ($perl_scalar)
…		…
353	vice versa. These mappings are designed to "do the right thing" in most	613	vice versa. These mappings are designed to "do the right thing" in most
354	circumstances automatically, preserving round-tripping characteristics	614	circumstances automatically, preserving round-tripping characteristics
355	(what you put in comes out as something equivalent).	615	(what you put in comes out as something equivalent).
356		616
357	For the more enlightened: note that in the following descriptions,	617	For the more enlightened: note that in the following descriptions,
358	lowercase perl refers to the Perl interpreter, while uppcercase Perl	618	lowercase perl refers to the Perl interpreter, while uppercase Perl
359	refers to the abstract Perl language itself.	619	refers to the abstract Perl language itself.
360		620
361	JSON -> PERL	621	JSON -> PERL
362	object	622	object
363	A JSON object becomes a reference to a hash in Perl. No ordering of	623	A JSON object becomes a reference to a hash in Perl. No ordering of
364	object keys is preserved (JSON does not preserver object key	624	object keys is preserved (JSON does not preserve object key ordering
365	ordering itself).	625	itself).
366		626
367	array	627	array
368	A JSON array becomes a reference to an array in Perl.	628	A JSON array becomes a reference to an array in Perl.
369		629
370	string	630	string
371	A JSON string becomes a string scalar in Perl - Unicode codepoints	631	A JSON string becomes a string scalar in Perl - Unicode codepoints
372	in JSON are represented by the same codepoints in the Perl string,	632	in JSON are represented by the same codepoints in the Perl string,
373	so no manual decoding is necessary.	633	so no manual decoding is necessary.
374		634
375	number	635	number
376	A JSON number becomes either an integer or numeric (floating point)	636	A JSON number becomes either an integer, numeric (floating point) or
377	scalar in perl, depending on its range and any fractional parts. On	637	string scalar in perl, depending on its range and any fractional
378	the Perl level, there is no difference between those as Perl handles	638	parts. On the Perl level, there is no difference between those as
379	all the conversion details, but an integer may take slightly less	639	Perl handles all the conversion details, but an integer may take
380	memory and might represent more values exactly than (floating point)	640	slightly less memory and might represent more values exactly than
		641	floating point numbers.
		642
		643	If the number consists of digits only, JSON::XS will try to
		644	represent it as an integer value. If that fails, it will try to
		645	represent it as a numeric (floating point) value if that is possible
		646	without loss of precision. Otherwise it will preserve the number as
		647	a string value (in which case you lose roundtripping ability, as the
		648	JSON number will be re-encoded toa JSON string).
		649
		650	Numbers containing a fractional or exponential part will always be
		651	represented as numeric (floating point) values, possibly at a loss
		652	of precision (in which case you might lose perfect roundtripping
		653	ability, but the JSON number will still be re-encoded as a JSON
381	numbers.	654	number).
382		655
383	true, false	656	true, false
384	These JSON atoms become 0, 1, respectively. Information is lost in	657	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
385	this process. Future versions might represent those values	658	respectively. They are overloaded to act almost exactly like the
386	differently, but they will be guarenteed to act like these integers	659	numbers 1 and 0. You can check whether a scalar is a JSON boolean by
387	would normally in Perl.	660	using the "JSON::XS::is_bool" function.
388		661
389	null	662	null
390	A JSON null atom becomes "undef" in Perl.	663	A JSON null atom becomes "undef" in Perl.
391		664
392	PERL -> JSON	665	PERL -> JSON
…		…
414	an exception to be thrown, except for references to the integers 0	687	an exception to be thrown, except for references to the integers 0
415	and 1, which get turned into "false" and "true" atoms in JSON. You	688	and 1, which get turned into "false" and "true" atoms in JSON. You
416	can also use "JSON::XS::false" and "JSON::XS::true" to improve	689	can also use "JSON::XS::false" and "JSON::XS::true" to improve
417	readability.	690	readability.
418		691
419	to_json [\0,JSON::XS::true] # yields [false,true]	692	encode_json [\0,JSON::XS::true] # yields [false,true]
		693
		694	JSON::XS::true, JSON::XS::false
		695	These special values become JSON true and JSON false values,
		696	respectively. You can also use "\1" and "\0" directly if you want.
420		697
421	blessed objects	698	blessed objects
422	Blessed objects are not allowed. JSON::XS currently tries to encode	699	Blessed objects are not directly representable in JSON. See the
423	their underlying representation (hash- or arrayref), but this	700	"allow_blessed" and "convert_blessed" methods on various options on
424	behaviour might change in future versions.	701	how to deal with this: basically, you can choose between throwing an
		702	exception, encoding the reference as if it weren't blessed, or
		703	provide your own serialiser method.
425		704
426	simple scalars	705	simple scalars
427	Simple Perl scalars (any scalar that is not a reference) are the	706	Simple Perl scalars (any scalar that is not a reference) are the
428	most difficult objects to encode: JSON::XS will encode undefined	707	most difficult objects to encode: JSON::XS will encode undefined
429	scalars as JSON null value, scalars that have last been used in a	708	scalars as JSON "null" values, scalars that have last been used in a
430	string context before encoding as JSON strings and anything else as	709	string context before encoding as JSON strings, and anything else as
431	number value:	710	number value:
432		711
433	# dump as number	712	# dump as number
434	to_json [2] # yields [2]	713	encode_json [2] # yields [2]
435	to_json [-3.0e17] # yields [-3e+17]	714	encode_json [-3.0e17] # yields [-3e+17]
436	my $value = 5; to_json [$value] # yields [5]	715	my $value = 5; encode_json [$value] # yields [5]
437		716
438	# used as string, so dump as string	717	# used as string, so dump as string
439	print $value;	718	print $value;
440	to_json [$value] # yields ["5"]	719	encode_json [$value] # yields ["5"]
441		720
442	# undef becomes null	721	# undef becomes null
443	to_json [undef] # yields [null]	722	encode_json [undef] # yields [null]
444		723
445	You can force the type to be a string by stringifying it:	724	You can force the type to be a JSON string by stringifying it:
446		725
447	my $x = 3.1; # some variable containing a number	726	my $x = 3.1; # some variable containing a number
448	"$x"; # stringified	727	"$x"; # stringified
449	$x .= ""; # another, more awkward way to stringify	728	$x .= ""; # another, more awkward way to stringify
450	print $x; # perl does it for you, too, quite often	729	print $x; # perl does it for you, too, quite often
451		730
452	You can force the type to be a number by numifying it:	731	You can force the type to be a JSON number by numifying it:
453		732
454	my $x = "3"; # some variable containing a string	733	my $x = "3"; # some variable containing a string
455	$x += 0; # numify it, ensuring it will be dumped as a number	734	$x += 0; # numify it, ensuring it will be dumped as a number
456	$x *= 1; # same thing, the choise is yours.	735	$x *= 1; # same thing, the choice is yours.
457		736
458	You can not currently output JSON booleans or force the type in	737	You can not currently force the type in other, less obscure, ways.
459	other, less obscure, ways. Tell me if you need this capability.	738	Tell me if you need this capability (but don't forget to explain why
		739	its needed :).
		740
		741	ENCODING/CODESET FLAG NOTES
		742	The interested reader might have seen a number of flags that signify
		743	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
		744	some confusion on what these do, so here is a short comparison:
		745
		746	"utf8" controls wether the JSON text created by "encode" (and expected
		747	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
		748	control wether "encode" escapes character values outside their
		749	respective codeset range. Neither of these flags conflict with each
		750	other, although some combinations make less sense than others.
		751
		752	Care has been taken to make all flags symmetrical with respect to
		753	"encode" and "decode", that is, texts encoded with any combination of
		754	these flag values will be correctly decoded when the same flags are used
		755	- in general, if you use different flag settings while encoding vs. when
		756	decoding you likely have a bug somewhere.
		757
		758	Below comes a verbose discussion of these flags. Note that a "codeset"
		759	is simply an abstract set of character-codepoint pairs, while an
		760	encoding takes those codepoint numbers and encodes them, in our case
		761	into octets. Unicode is (among other things) a codeset, UTF-8 is an
		762	encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
		763	encodings at the same time, which can be confusing.
		764
		765	"utf8" flag disabled
		766	When "utf8" is disabled (the default), then "encode"/"decode"
		767	generate and expect Unicode strings, that is, characters with high
		768	ordinal Unicode values (> 255) will be encoded as such characters,
		769	and likewise such characters are decoded as-is, no canges to them
		770	will be done, except "(re-)interpreting" them as Unicode codepoints
		771	or Unicode characters, respectively (to Perl, these are the same
		772	thing in strings unless you do funny/weird/dumb stuff).
		773
		774	This is useful when you want to do the encoding yourself (e.g. when
		775	you want to have UTF-16 encoded JSON texts) or when some other layer
		776	does the encoding for you (for example, when printing to a terminal
		777	using a filehandle that transparently encodes to UTF-8 you certainly
		778	do NOT want to UTF-8 encode your data first and have Perl encode it
		779	another time).
		780
		781	"utf8" flag enabled
		782	If the "utf8"-flag is enabled, "encode"/"decode" will encode all
		783	characters using the corresponding UTF-8 multi-byte sequence, and
		784	will expect your input strings to be encoded as UTF-8, that is, no
		785	"character" of the input string must have any value > 255, as UTF-8
		786	does not allow that.
		787
		788	The "utf8" flag therefore switches between two modes: disabled means
		789	you will get a Unicode string in Perl, enabled means you get an
		790	UTF-8 encoded octet/binary string in Perl.
		791
		792	"latin1" or "ascii" flags enabled
		793	With "latin1" (or "ascii") enabled, "encode" will escape characters
		794	with ordinal values > 255 (> 127 with "ascii") and encode the
		795	remaining characters as specified by the "utf8" flag.
		796
		797	If "utf8" is disabled, then the result is also correctly encoded in
		798	those character sets (as both are proper subsets of Unicode, meaning
		799	that a Unicode string with all character values < 256 is the same
		800	thing as a ISO-8859-1 string, and a Unicode string with all
		801	character values < 128 is the same thing as an ASCII string in
		802	Perl).
		803
		804	If "utf8" is enabled, you still get a correct UTF-8-encoded string,
		805	regardless of these flags, just some more characters will be escaped
		806	using "\uXXXX" then before.
		807
		808	Note that ISO-8859-1-encoded strings are not compatible with UTF-8
		809	encoding, while ASCII-encoded strings are. That is because the
		810	ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
		811	codeset being a subset of Unicode), while ASCII is.
		812
		813	Surprisingly, "decode" will ignore these flags and so treat all
		814	input values as governed by the "utf8" flag. If it is disabled, this
		815	allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
		816	strict subsets of Unicode. If it is enabled, you can correctly
		817	decode UTF-8 encoded strings.
		818
		819	So neither "latin1" nor "ascii" are incompatible with the "utf8"
		820	flag - they only govern when the JSON output engine escapes a
		821	character or not.
		822
		823	The main use for "latin1" is to relatively efficiently store binary
		824	data as JSON, at the expense of breaking compatibility with most
		825	JSON decoders.
		826
		827	The main use for "ascii" is to force the output to not contain
		828	characters with values > 127, which means you can interpret the
		829	resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
		830	any character set and 8-bit-encoding, and still get the same data
		831	structure back. This is useful when your channel for JSON transfer
		832	is not 8-bit clean or the encoding might be mangled in between (e.g.
		833	in mail), and works because ASCII is a proper subset of most 8-bit
		834	and multibyte encodings in use in the world.
460		835
461	COMPARISON	836	COMPARISON
462	As already mentioned, this module was created because none of the	837	As already mentioned, this module was created because none of the
463	existing JSON modules could be made to work correctly. First I will	838	existing JSON modules could be made to work correctly. First I will
464	describe the problems (or pleasures) I encountered with various existing	839	describe the problems (or pleasures) I encountered with various existing
465	JSON modules, followed by some benchmark values. JSON::XS was designed	840	JSON modules, followed by some benchmark values. JSON::XS was designed
466	not to suffer from any of these problems or limitations.	841	not to suffer from any of these problems or limitations.
467		842
		843	JSON 2.xx
		844	A marvellous piece of engineering, this module either uses JSON::XS
		845	directly when available (so will be 100% compatible with it,
		846	including speed), or it uses JSON::PP, which is basically JSON::XS
		847	translated to Pure Perl, which should be 100% compatible with
		848	JSON::XS, just a bit slower.
		849
		850	You cannot really lose by using this module, especially as it tries
		851	very hard to work even with ancient Perl versions, while JSON::XS
		852	does not.
		853
468	JSON 1.07	854	JSON 1.07
469	Slow (but very portable, as it is written in pure Perl).	855	Slow (but very portable, as it is written in pure Perl).
470		856
471	Undocumented/buggy Unicode handling (how JSON handles unicode values	857	Undocumented/buggy Unicode handling (how JSON handles Unicode values
472	is undocumented. One can get far by feeding it unicode strings and	858	is undocumented. One can get far by feeding it Unicode strings and
473	doing en-/decoding oneself, but unicode escapes are not working	859	doing en-/decoding oneself, but Unicode escapes are not working
474	properly).	860	properly).
475		861
476	No roundtripping (strings get clobbered if they look like numbers,	862	No round-tripping (strings get clobbered if they look like numbers,
477	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	863	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
478	will decode into the number 2.	864	will decode into the number 2.
479		865
480	JSON::PC 0.01	866	JSON::PC 0.01
481	Very fast.	867	Very fast.
482		868
483	Undocumented/buggy Unicode handling.	869	Undocumented/buggy Unicode handling.
484		870
485	No roundtripping.	871	No round-tripping.
486		872
487	Has problems handling many Perl values (e.g. regex results and other	873	Has problems handling many Perl values (e.g. regex results and other
488	magic values will make it croak).	874	magic values will make it croak).
489		875
490	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	876	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
…		…
500	much undocumented. I need at least a format for easy reading by	886	much undocumented. I need at least a format for easy reading by
501	humans and a single-line compact format for use in a protocol, and	887	humans and a single-line compact format for use in a protocol, and
502	preferably a way to generate ASCII-only JSON texts).	888	preferably a way to generate ASCII-only JSON texts).
503		889
504	Completely broken (and confusingly documented) Unicode handling	890	Completely broken (and confusingly documented) Unicode handling
505	(unicode escapes are not working properly, you need to set	891	(Unicode escapes are not working properly, you need to set
506	ImplicitUnicode to different values on en- and decoding to get	892	ImplicitUnicode to different values on en- and decoding to get
507	symmetric behaviour).	893	symmetric behaviour).
508		894
509	No roundtripping (simple cases work, but this depends on wether the	895	No round-tripping (simple cases work, but this depends on whether
510	scalar value was used in a numeric context or not).	896	the scalar value was used in a numeric context or not).
511		897
512	Dumping hashes may skip hash values depending on iterator state.	898	Dumping hashes may skip hash values depending on iterator state.
513		899
514	Unmaintained (maintainer unresponsive for many months, bugs are not	900	Unmaintained (maintainer unresponsive for many months, bugs are not
515	getting fixed).	901	getting fixed).
516		902
517	Does not check input for validity (i.e. will accept non-JSON input	903	Does not check input for validity (i.e. will accept non-JSON input
518	and return "something" instead of raising an exception. This is a	904	and return "something" instead of raising an exception. This is a
519	security issue: imagine two banks transfering money between each	905	security issue: imagine two banks transferring money between each
520	other using JSON. One bank might parse a given non-JSON request and	906	other using JSON. One bank might parse a given non-JSON request and
521	deduct money, while the other might reject the transaction with a	907	deduct money, while the other might reject the transaction with a
522	syntax error. While a good protocol will at least recover, that is	908	syntax error. While a good protocol will at least recover, that is
523	extra unnecessary work and the transaction will still not succeed).	909	extra unnecessary work and the transaction will still not succeed).
524		910
525	JSON::DWIW 0.04	911	JSON::DWIW 0.04
526	Very fast. Very natural. Very nice.	912	Very fast. Very natural. Very nice.
527		913
528	Undocumented unicode handling (but the best of the pack. Unicode	914	Undocumented Unicode handling (but the best of the pack. Unicode
529	escapes still don't get parsed properly).	915	escapes still don't get parsed properly).
530		916
531	Very inflexible.	917	Very inflexible.
532		918
533	No roundtripping.	919	No round-tripping.
534		920
535	Does not generate valid JSON texts (key strings are often unquoted,	921	Does not generate valid JSON texts (key strings are often unquoted,
536	empty keys result in nothing being output)	922	empty keys result in nothing being output)
537		923
538	Does not check input for validity.	924	Does not check input for validity.
		925
		926	JSON and YAML
		927	You often hear that JSON is a subset of YAML. This is, however, a mass
		928	hysteria(*) and very far from the truth (as of the time of this
		929	writing), so let me state it clearly: *in general, there is no way to
		930	configure JSON::XS to output a data structure as valid YAML* that works
		931	in all cases.
		932
		933	If you really must use JSON::XS to generate YAML, you should use this
		934	algorithm (subject to change in future versions):
		935
		936	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		937	my $yaml = $to_yaml->encode ($ref) . "\n";
		938
		939	This will usually generate JSON texts that also parse as valid YAML.
		940	Please note that YAML has hardcoded limits on (simple) object key
		941	lengths that JSON doesn't have and also has different and incompatible
		942	unicode handling, so you should make sure that your hash keys are
		943	noticeably shorter than the 1024 "stream characters" YAML allows and
		944	that you do not have characters with codepoint values outside the
		945	Unicode BMP (basic multilingual page). YAML also does not allow "\/"
		946	sequences in strings (which JSON::XS does not currently generate, but
		947	other JSON generators might).
		948
		949	There might be other incompatibilities that I am not aware of (or the
		950	YAML specification has been changed yet again - it does so quite often).
		951	In general you should not try to generate YAML with a JSON generator or
		952	vice versa, or try to parse JSON with a YAML parser or vice versa:
		953	chances are high that you will run into severe interoperability problems
		954	when you least expect it.
		955
		956	(*) I have been pressured multiple times by Brian Ingerson (one of the
		957	authors of the YAML specification) to remove this paragraph, despite
		958	him acknowledging that the actual incompatibilities exist. As I was
		959	personally bitten by this "JSON is YAML" lie, I refused and said I
		960	will continue to educate people about these issues, so others do not
		961	run into the same problem again and again. After this, Brian called
		962	me a (quote)complete and worthless idiot(unquote).
		963
		964	In my opinion, instead of pressuring and insulting people who
		965	actually clarify issues with YAML and the wrong statements of some
		966	of its proponents, I would kindly suggest reading the JSON spec
		967	(which is not that difficult or long) and finally make YAML
		968	compatible to it, and educating users about the changes, instead of
		969	spreading lies about the real compatibility for many years and
		970	trying to silence people who point out that it isn't true.
539		971
540	SPEED	972	SPEED
541	It seems that JSON::XS is surprisingly fast, as shown in the following	973	It seems that JSON::XS is surprisingly fast, as shown in the following
542	tables. They have been generated with the help of the "eg/bench" program	974	tables. They have been generated with the help of the "eg/bench" program
543	in the JSON::XS distribution, to make it easy to compare on your own	975	in the JSON::XS distribution, to make it easy to compare on your own
544	system.	976	system.
545		977
546	First comes a comparison between various modules using a very short	978	First comes a comparison between various modules using a very short
547	single-line JSON string:	979	single-line JSON string (also available at
		980	<http://dist.schmorp.de/misc/json/short.json>).
548		981
549	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	982	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
550	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	983	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
551		984
552	It shows the number of encodes/decodes per second (JSON::XS uses the	985	It shows the number of encodes/decodes per second (JSON::XS uses the
553	functional interface, while JSON::XS/2 uses the OO interface with	986	functional interface, while JSON::XS/2 uses the OO interface with
554	pretty-printing and hashkey sorting enabled). Higher is better:	987	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
		988	Higher is better:
555		989
556	module \| encode \| decode \|	990	module \| encode \| decode \|
557	-----------\|------------\|------------\|	991	-----------\|------------\|------------\|
558	JSON \| 7645.468 \| 4208.613 \|	992	JSON 1.x \| 4990.842 \| 4088.813 \|
559	JSON::DWIW \| 68534.379 \| 79437.576 \|	993	JSON::DWIW \| 51653.990 \| 71575.154 \|
560	JSON::PC \| 65948.176 \| 78251.940 \|	994	JSON::PC \| 65948.176 \| 74631.744 \|
561	JSON::Syck \| 23379.621 \| 28416.694 \|	995	JSON::PP \| 8931.652 \| 3817.168 \|
		996	JSON::Syck \| 24877.248 \| 27776.848 \|
562	JSON::XS \| 388361.481 \| 199728.762 \|	997	JSON::XS \| 388361.481 \| 227951.304 \|
563	JSON::XS/2 \| 218453.333 \| 192399.266 \|	998	JSON::XS/2 \| 227951.304 \| 218453.333 \|
564	JSON::XS/3 \| 338250.323 \| 192399.266 \|	999	JSON::XS/3 \| 338250.323 \| 218453.333 \|
565	Storable \| 15732.573 \| 28571.553 \|	1000	Storable \| 16500.016 \| 135300.129 \|
566	-----------+------------+------------+	1001	-----------+------------+------------+
567		1002
568	That is, JSON::XS is about five times faster than JSON::DWIW on	1003	That is, JSON::XS is about five times faster than JSON::DWIW on
569	encoding, about three times faster on decoding, and over fourty times	1004	encoding, about three times faster on decoding, and over forty times
570	faster than JSON, even with pretty-printing and key sorting. It also	1005	faster than JSON, even with pretty-printing and key sorting. It also
571	compares favourably to Storable for small amounts of data.	1006	compares favourably to Storable for small amounts of data.
572		1007
573	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1008	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
574	search API (http://nanoref.com/yahooapis/mgPdGg):	1009	search API (<http://dist.schmorp.de/misc/json/long.json>).
575		1010
576	module \| encode \| decode \|	1011	module \| encode \| decode \|
577	-----------\|------------\|------------\|	1012	-----------\|------------\|------------\|
578	JSON \| 254.685 \| 37.665 \|	1013	JSON 1.x \| 55.260 \| 34.971 \|
579	JSON::DWIW \| 1014.244 \| 1087.678 \|	1014	JSON::DWIW \| 825.228 \| 1082.513 \|
580	JSON::PC \| 3602.116 \| 2307.352 \|	1015	JSON::PC \| 3571.444 \| 2394.829 \|
581	JSON::Syck \| 558.035 \| 776.263 \|	1016	JSON::PP \| 210.987 \| 32.574 \|
582	JSON::XS \| 5747.196 \| 3543.684 \|	1017	JSON::Syck \| 552.551 \| 787.544 \|
583	JSON::XS/2 \| 3968.121 \| 3589.170 \|	1018	JSON::XS \| 5780.463 \| 4854.519 \|
584	JSON::XS/3 \| 6105.246 \| 3561.134 \|	1019	JSON::XS/2 \| 3869.998 \| 4798.975 \|
585	Storable \| 4456.337 \| 5320.020 \|	1020	JSON::XS/3 \| 5862.880 \| 4798.975 \|
		1021	Storable \| 4445.002 \| 5235.027 \|
586	-----------+------------+------------+	1022	-----------+------------+------------+
587		1023
588	Again, JSON::XS leads by far.	1024	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1025	decodes faster).
589		1026
590	On large strings containing lots of high unicode characters, some	1027	On large strings containing lots of high Unicode characters, some
591	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1028	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
592	result will be broken due to missing (or wrong) unicode handling. Others	1029	result will be broken due to missing (or wrong) Unicode handling. Others
593	refuse to decode or encode properly, so it was impossible to prepare a	1030	refuse to decode or encode properly, so it was impossible to prepare a
594	fair comparison table for that case.	1031	fair comparison table for that case.
595		1032
596	SECURITY CONSIDERATIONS	1033	SECURITY CONSIDERATIONS
597	When you are using JSON in a protocol, talking to untrusted potentially	1034	When you are using JSON in a protocol, talking to untrusted potentially
…		…
601	have any buffer overflows. Obviously, this module should ensure that and	1038	have any buffer overflows. Obviously, this module should ensure that and
602	I am trying hard on making that true, but you never know.	1039	I am trying hard on making that true, but you never know.
603		1040
604	Second, you need to avoid resource-starving attacks. That means you	1041	Second, you need to avoid resource-starving attacks. That means you
605	should limit the size of JSON texts you accept, or make sure then when	1042	should limit the size of JSON texts you accept, or make sure then when
606	your resources run out, thats just fine (e.g. by using a separate	1043	your resources run out, that's just fine (e.g. by using a separate
607	process that can crash safely). The size of a JSON text in octets or	1044	process that can crash safely). The size of a JSON text in octets or
608	characters is usually a good indication of the size of the resources	1045	characters is usually a good indication of the size of the resources
609	required to decode it into a Perl structure.	1046	required to decode it into a Perl structure. While JSON::XS can check
		1047	the size of the JSON text, it might be too late when you already have it
		1048	in memory, so you might want to check the size before you accept the
		1049	string.
610		1050
611	Third, JSON::XS recurses using the C stack when decoding objects and	1051	Third, JSON::XS recurses using the C stack when decoding objects and
612	arrays. The C stack is a limited resource: for instance, on my amd64	1052	arrays. The C stack is a limited resource: for instance, on my amd64
613	machine with 8MB of stack size I can decode around 180k nested arrays	1053	machine with 8MB of stack size I can decode around 180k nested arrays
614	but only 14k nested JSON objects (due to perl itself recursing deeply on	1054	but only 14k nested JSON objects (due to perl itself recursing deeply on
615	croak to free the temporary). If that is exceeded, the program crashes.	1055	croak to free the temporary). If that is exceeded, the program crashes.
616	to be conservative, the default nesting limit is set to 512. If your	1056	To be conservative, the default nesting limit is set to 512. If your
617	process has a smaller stack, you should adjust this setting accordingly	1057	process has a smaller stack, you should adjust this setting accordingly
618	with the "max_depth" method.	1058	with the "max_depth" method.
619		1059
620	And last but least, something else could bomb you that I forgot to think	1060	Something else could bomb you, too, that I forgot to think of. In that
621	of. In that case, you get to keep the pieces. I am always open for	1061	case, you get to keep the pieces. I am always open for hints, though...
622	hints, though...	1062
		1063	Also keep in mind that JSON::XS might leak contents of your Perl data
		1064	structures in its error messages, so when you serialise sensitive
		1065	information you might want to make sure that exceptions thrown by
		1066	JSON::XS will not end up in front of untrusted eyes.
		1067
		1068	If you are using JSON::XS to return packets to consumption by JavaScript
		1069	scripts in a browser you should have a look at
		1070	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1071	you are vulnerable to some common attack vectors (which really are
		1072	browser design bugs, but it is still you who will have to deal with it,
		1073	as major browser developers care only for features, not about getting
		1074	security right).
		1075
		1076	THREADS
		1077	This module is not guaranteed to be thread safe and there are no plans
		1078	to change this until Perl gets thread support (as opposed to the
		1079	horribly slow so-called "threads" which are simply slow and bloated
		1080	process simulations - use fork, its much faster, cheaper, better).
		1081
		1082	(It might actually work, but you have been warned).
623		1083
624	BUGS	1084	BUGS
625	While the goal of this module is to be correct, that unfortunately does	1085	While the goal of this module is to be correct, that unfortunately does
626	not mean its bug-free, only that I think its design is bug-free. It is	1086	not mean its bug-free, only that I think its design is bug-free. It is
627	still relatively early in its development. If you keep reporting bugs	1087	still relatively early in its development. If you keep reporting bugs
628	they will be fixed swiftly, though.	1088	they will be fixed swiftly, though.
629		1089
		1090	Please refrain from using rt.cpan.org or any other bug reporting
		1091	service. I put the contact address into my modules for a reason.
		1092
630	AUTHOR	1093	AUTHOR
631	Marc Lehmann <schmorp@schmorp.de>	1094	Marc Lehmann <schmorp@schmorp.de>
632	http://home.schmorp.de/	1095	http://home.schmorp.de/
633		1096

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Comparing JSON-XS/README (file contents): Revision 1.12 by root, Wed Jun 6 18:17:13 2007 UTC vs. Revision 1.23 by root, Wed Mar 19 22:31:00 2008 UTC

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Comparing JSON-XS/README (file contents):
Revision 1.12 by root, Wed Jun 6 18:17:13 2007 UTC vs.
Revision 1.23 by root, Wed Mar 19 22:31:00 2008 UTC