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

Comparing JSON-XS/README (file contents):
Revision 1.14 by root, Sat Jun 23 23:50:03 2007 UTC vs.
Revision 1.24 by root, Thu Mar 27 06:37:35 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
…		…
101	values in Perl.	123	values in Perl.
102		124
103	See MAPPING, below, for more information on how JSON values are	125	See MAPPING, below, for more information on how JSON values are
104	mapped to Perl.	126	mapped to Perl.
105		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 :)
		166
106	OBJECT-ORIENTED INTERFACE	167	OBJECT-ORIENTED INTERFACE
107	The object oriented interface lets you configure your own encoding or	168	The object oriented interface lets you configure your own encoding or
108	decoding style, within the limits of supported formats.	169	decoding style, within the limits of supported formats.
109		170
110	$json = new JSON::XS	171	$json = new JSON::XS
…		…
117		178
118	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]})
119	=> {"a": [1, 2]}	180	=> {"a": [1, 2]}
120		181
121	$json = $json->ascii ([$enable])	182	$json = $json->ascii ([$enable])
		183	$enabled = $json->get_ascii
122	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
123	generate characters outside the code range 0..127 (which is ASCII).	185	generate characters outside the code range 0..127 (which is ASCII).
124	Any unicode characters outside that range will be escaped using	186	Any Unicode characters outside that range will be escaped using
125	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL	187	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
126	escape sequence, as per RFC4627. The resulting encoded JSON text can	188	escape sequence, as per RFC4627. The resulting encoded JSON text can
127	be treated as a native unicode string, an ascii-encoded,	189	be treated as a native Unicode string, an ascii-encoded,
128	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
129	ASCII.	191	ASCII.
130		192
131	If $enable is false, then the "encode" method will not escape	193	If $enable is false, then the "encode" method will not escape
132	Unicode characters unless required by the JSON syntax or other	194	Unicode characters unless required by the JSON syntax or other
133	flags. This results in a faster and more compact format.	195	flags. This results in a faster and more compact format.
134		196
		197	See also the section ENCODING/CODESET FLAG NOTES later in this
		198	document.
		199
135	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
136	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
137	contain any 8 bit characters.	202	contain any 8 bit characters.
138		203
139	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	204	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
140	=> ["\ud801\udc01"]	205	=> ["\ud801\udc01"]
141		206
142	$json = $json->latin1 ([$enable])	207	$json = $json->latin1 ([$enable])
		208	$enabled = $json->get_latin1
143	If $enable is true (or missing), then the "encode" method will	209	If $enable is true (or missing), then the "encode" method will
144	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
145	any characters outside the code range 0..255. The resulting string	211	any characters outside the code range 0..255. The resulting string
146	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
147	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
148	flag, as "decode" by default expects unicode, which is a strict	214	flag, as "decode" by default expects Unicode, which is a strict
149	superset of latin1.	215	superset of latin1.
150		216
151	If $enable is false, then the "encode" method will not escape	217	If $enable is false, then the "encode" method will not escape
152	Unicode characters unless required by the JSON syntax or other	218	Unicode characters unless required by the JSON syntax or other
153	flags.	219	flags.
		220
		221	See also the section ENCODING/CODESET FLAG NOTES later in this
		222	document.
154		223
155	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
156	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
157	smaller encoded size. The disadvantage is that the resulting JSON	226	smaller encoded size. The disadvantage is that the resulting JSON
158	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
159	when storing and transfering), a rare encoding for JSON. It is	228	when storing and transferring), a rare encoding for JSON. It is
160	therefore most useful when you want to store data structures known	229	therefore most useful when you want to store data structures known
161	to contain binary data efficiently in files or databases, not when	230	to contain binary data efficiently in files or databases, not when
162	talking to other JSON encoders/decoders.	231	talking to other JSON encoders/decoders.
163		232
164	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]	233	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
165	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)	234	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
166		235
167	$json = $json->utf8 ([$enable])	236	$json = $json->utf8 ([$enable])
		237	$enabled = $json->get_utf8
168	If $enable is true (or missing), then the "encode" method will	238	If $enable is true (or missing), then the "encode" method will
169	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,
170	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
171	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
172	characters outside the range 0..255, they are thus useful for	242	characters outside the range 0..255, they are thus useful for
173	bytewise/binary I/O. In future versions, enabling this option might	243	bytewise/binary I/O. In future versions, enabling this option might
174	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
175	described in RFC4627.	245	described in RFC4627.
176		246
177	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
178	string as a (non-encoded) unicode string, while "decode" expects	248	string as a (non-encoded) Unicode string, while "decode" expects
179	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
180	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.
181		254
182	Example, output UTF-16BE-encoded JSON:	255	Example, output UTF-16BE-encoded JSON:
183		256
184	use Encode;	257	use Encode;
185	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	258	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
204	2	277	2
205	]	278	]
206	}	279	}
207		280
208	$json = $json->indent ([$enable])	281	$json = $json->indent ([$enable])
		282	$enabled = $json->get_indent
209	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
210	multiline format as output, putting every array member or	284	multiline format as output, putting every array member or
211	object/hash key-value pair into its own line, identing them	285	object/hash key-value pair into its own line, indenting them
212	properly.	286	properly.
213		287
214	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
215	the resulting JSON text is guarenteed not to contain any "newlines".	289	the resulting JSON text is guaranteed not to contain any "newlines".
216		290
217	This setting has no effect when decoding JSON texts.	291	This setting has no effect when decoding JSON texts.
218		292
219	$json = $json->space_before ([$enable])	293	$json = $json->space_before ([$enable])
		294	$enabled = $json->get_space_before
220	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
221	an extra optional space before the ":" separating keys from values	296	an extra optional space before the ":" separating keys from values
222	in JSON objects.	297	in JSON objects.
223		298
224	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
…		…
230	Example, space_before enabled, space_after and indent disabled:	305	Example, space_before enabled, space_after and indent disabled:
231		306
232	{"key" :"value"}	307	{"key" :"value"}
233		308
234	$json = $json->space_after ([$enable])	309	$json = $json->space_after ([$enable])
		310	$enabled = $json->get_space_after
235	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
236	an extra optional space after the ":" separating keys from values in	312	an extra optional space after the ":" separating keys from values in
237	JSON objects and extra whitespace after the "," separating key-value	313	JSON objects and extra whitespace after the "," separating key-value
238	pairs and array members.	314	pairs and array members.
239		315
…		…
244		320
245	Example, space_before and indent disabled, space_after enabled:	321	Example, space_before and indent disabled, space_after enabled:
246		322
247	{"key": "value"}	323	{"key": "value"}
248		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
249	$json = $json->canonical ([$enable])	367	$json = $json->canonical ([$enable])
		368	$enabled = $json->get_canonical
250	If $enable is true (or missing), then the "encode" method will	369	If $enable is true (or missing), then the "encode" method will
251	output JSON objects by sorting their keys. This is adding a	370	output JSON objects by sorting their keys. This is adding a
252	comparatively high overhead.	371	comparatively high overhead.
253		372
254	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
255	pairs in the order Perl stores them (which will likely change	374	pairs in the order Perl stores them (which will likely change
256	between runs of the same script).	375	between runs of the same script).
257		376
258	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
259	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
260	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
261	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
262	in Perl.	381	in Perl.
263		382
264	This setting has no effect when decoding JSON texts.	383	This setting has no effect when decoding JSON texts.
265		384
266	$json = $json->allow_nonref ([$enable])	385	$json = $json->allow_nonref ([$enable])
		386	$enabled = $json->get_allow_nonref
267	If $enable is true (or missing), then the "encode" method can	387	If $enable is true (or missing), then the "encode" method can
268	convert a non-reference into its corresponding string, number or	388	convert a non-reference into its corresponding string, number or
269	null JSON value, which is an extension to RFC4627. Likewise,	389	null JSON value, which is an extension to RFC4627. Likewise,
270	"decode" will accept those JSON values instead of croaking.	390	"decode" will accept those JSON values instead of croaking.
271		391
…		…
278	"allow_nonref", resulting in an invalid JSON text:	398	"allow_nonref", resulting in an invalid JSON text:
279		399
280	JSON::XS->new->allow_nonref->encode ("Hello, World!")	400	JSON::XS->new->allow_nonref->encode ("Hello, World!")
281	=> "Hello, World!"	401	=> "Hello, World!"
282		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
283	$json = $json->shrink ([$enable])	515	$json = $json->shrink ([$enable])
		516	$enabled = $json->get_shrink
284	Perl usually over-allocates memory a bit when allocating space for	517	Perl usually over-allocates memory a bit when allocating space for
285	strings. This flag optionally resizes strings generated by either	518	strings. This flag optionally resizes strings generated by either
286	"encode" or "decode" to their minimum size possible. This can save	519	"encode" or "decode" to their minimum size possible. This can save
287	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
288	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
…		…
306	converting strings that look like integers or floats into integers	539	converting strings that look like integers or floats into integers
307	or floats internally (there is no difference on the Perl level),	540	or floats internally (there is no difference on the Perl level),
308	saving space.	541	saving space.
309		542
310	$json = $json->max_depth ([$maximum_nesting_depth])	543	$json = $json->max_depth ([$maximum_nesting_depth])
		544	$max_depth = $json->get_max_depth
311	Sets the maximum nesting level (default 512) accepted while encoding	545	Sets the maximum nesting level (default 512) accepted while encoding
312	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
313	higher nesting level then this limit, then the encoder and decoder	547	higher nesting level then this limit, then the encoder and decoder
314	will stop and croak at that point.	548	will stop and croak at that point.
315		549
…		…
319	crossed to reach a given character in a string.	553	crossed to reach a given character in a string.
320		554
321	Setting the maximum depth to one disallows any nesting, so that	555	Setting the maximum depth to one disallows any nesting, so that
322	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.
323		557
324	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
325	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).
326		577
327	See SECURITY CONSIDERATIONS, below, for more info on why this is	578	See SECURITY CONSIDERATIONS, below, for more info on why this is
328	useful.	579	useful.
329		580
330	$json_text = $json->encode ($perl_scalar)	581	$json_text = $json->encode ($perl_scalar)
…		…
355	and you need to know where the JSON text ends.	606	and you need to know where the JSON text ends.
356		607
357	JSON::XS->new->decode_prefix ("[1] the tail")	608	JSON::XS->new->decode_prefix ("[1] the tail")
358	=> ([], 3)	609	=> ([], 3)
359		610
		611	INCREMENTAL PARSING
		612	[This section and the API it details is still EXPERIMENTAL]
		613
		614	In some cases, there is the need for incremental parsing of JSON texts.
		615	While this module always has to keep both JSON text and resulting Perl
		616	data structure in memory at one time, it does allow you to parse a JSON
		617	stream incrementally. It does so by accumulating text until it has a
		618	full JSON object, which it then can decode. This process is similar to
		619	using "decode_prefix" to see if a full JSON object is available, but is
		620	much more efficient (JSON::XS will only attempt to parse the JSON text
		621	once it is sure it has enough text to get a decisive result, using a
		622	very simple but truly incremental parser).
		623
		624	The following two methods deal with this.
		625
		626	[void, scalar or list context] = $json->incr_parse ([$string])
		627	This is the central parsing function. It can both append new text
		628	and extract objects from the stream accumulated so far (both of
		629	these functions are optional).
		630
		631	If $string is given, then this string is appended to the already
		632	existing JSON fragment stored in the $json object.
		633
		634	After that, if the function is called in void context, it will
		635	simply return without doing anything further. This can be used to
		636	add more text in as many chunks as you want.
		637
		638	If the method is called in scalar context, then it will try to
		639	extract exactly one JSON object. If that is successful, it will
		640	return this object, otherwise it will return "undef". If there is a
		641	parse error, this method will croak just as "decode" would do (one
		642	can then use "incr_skip" to skip the errornous part). This is the
		643	most common way of using the method.
		644
		645	And finally, in list context, it will try to extract as many objects
		646	from the stream as it can find and return them, or the empty list
		647	otherwise. For this to work, there must be no separators between the
		648	JSON objects or arrays, instead they must be concatenated
		649	back-to-back. If an error occurs, an exception will be raised as in
		650	the scalar context case. Note that in this case, any
		651	previously-parsed JSON texts will be lost.
		652
		653	$lvalue_string = $json->incr_text
		654	This method returns the currently stored JSON fragment as an lvalue,
		655	that is, you can manipulate it. This only works when a preceding
		656	call to "incr_parse" in scalar context successfully returned an
		657	object. Under all other circumstances you must not call this
		658	function (I mean it. although in simple tests it might actually
		659	work, it will fail under real world conditions). As a special
		660	exception, you can also call this method before having parsed
		661	anything.
		662
		663	This function is useful in two cases: a) finding the trailing text
		664	after a JSON object or b) parsing multiple JSON objects separated by
		665	non-JSON text (such as commas).
		666
		667	$json->incr_skip
		668	This will reset the state of the incremental parser and will remove
		669	the parsed text from the input buffer. This is useful after
		670	"incr_parse" died, in which case the input buffer and incremental
		671	parser state is left unchanged, to skip the text parsed so far and
		672	to reset the parse state.
		673
		674	LIMITATIONS
		675	All options that affect decoding are supported, except "allow_nonref".
		676	The reason for this is that it cannot be made to work sensibly: JSON
		677	objects and arrays are self-delimited, i.e. you can concatenate them
		678	back to back and still decode them perfectly. This does not hold true
		679	for JSON numbers, however.
		680
		681	For example, is the string 1 a single JSON number, or is it simply the
		682	start of 12? Or is 12 a single JSON number, or the concatenation of 1
		683	and 2? In neither case you can tell, and this is why JSON::XS takes the
		684	conservative route and disallows this case.
		685
		686	EXAMPLES
		687	Some examples will make all this clearer. First, a simple example that
		688	works similarly to "decode_prefix": We want to decode the JSON object at
		689	the start of a string and identify the portion after the JSON object:
		690
		691	my $text = "[1,2,3] hello";
		692
		693	my $json = new JSON::XS;
		694
		695	my $obj = $json->incr_parse ($text)
		696	or die "expected JSON object or array at beginning of string";
		697
		698	my $tail = $json->incr_text;
		699	# $tail now contains " hello"
		700
		701	Easy, isn't it?
		702
		703	Now for a more complicated example: Imagine a hypothetical protocol
		704	where you read some requests from a TCP stream, and each request is a
		705	JSON array, without any separation between them (in fact, it is often
		706	useful to use newlines as "separators", as these get interpreted as
		707	whitespace at the start of the JSON text, which makes it possible to
		708	test said protocol with "telnet"...).
		709
		710	Here is how you'd do it (it is trivial to write this in an event-based
		711	manner):
		712
		713	my $json = new JSON::XS;
		714
		715	# read some data from the socket
		716	while (sysread $socket, my $buf, 4096) {
		717
		718	# split and decode as many requests as possible
		719	for my $request ($json->incr_parse ($buf)) {
		720	# act on the $request
		721	}
		722	}
		723
		724	Another complicated example: Assume you have a string with JSON objects
		725	or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
		726	[3]"). To parse them, we have to skip the commas between the JSON texts,
		727	and here is where the lvalue-ness of "incr_text" comes in useful:
		728
		729	my $text = "[1],[2], [3]";
		730	my $json = new JSON::XS;
		731
		732	# void context, so no parsing done
		733	$json->incr_parse ($text);
		734
		735	# now extract as many objects as possible. note the
		736	# use of scalar context so incr_text can be called.
		737	while (my $obj = $json->incr_parse) {
		738	# do something with $obj
		739
		740	# now skip the optional comma
		741	$json->incr_text =~ s/^ \s* , //x;
		742	}
		743
		744	Now lets go for a very complex example: Assume that you have a gigantic
		745	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		746	but you cannot load it into memory fully (this has actually happened in
		747	the real world :).
		748
		749	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		750	can still help you: You implement a (very simple) array parser and let
		751	JSON decode the array elements, which are all full JSON objects on their
		752	own (this wouldn't work if the array elements could be JSON numbers, for
		753	example):
		754
		755	my $json = new JSON::XS;
		756
		757	# open the monster
		758	open my $fh, "<bigfile.json"
		759	or die "bigfile: $!";
		760
		761	# first parse the initial "["
		762	for (;;) {
		763	sysread $fh, my $buf, 65536
		764	or die "read error: $!";
		765	$json->incr_parse ($buf); # void context, so no parsing
		766
		767	# Exit the loop once we found and removed(!) the initial "[".
		768	# In essence, we are (ab-)using the $json object as a simple scalar
		769	# we append data to.
		770	last if $json->incr_text =~ s/^ \s* \[ //x;
		771	}
		772
		773	# now we have the skipped the initial "[", so continue
		774	# parsing all the elements.
		775	for (;;) {
		776	# in this loop we read data until we got a single JSON object
		777	for (;;) {
		778	if (my $obj = $json->incr_parse) {
		779	# do something with $obj
		780	last;
		781	}
		782
		783	# add more data
		784	sysread $fh, my $buf, 65536
		785	or die "read error: $!";
		786	$json->incr_parse ($buf); # void context, so no parsing
		787	}
		788
		789	# in this loop we read data until we either found and parsed the
		790	# separating "," between elements, or the final "]"
		791	for (;;) {
		792	# first skip whitespace
		793	$json->incr_text =~ s/^\s*//;
		794
		795	# if we find "]", we are done
		796	if ($json->incr_text =~ s/^\]//) {
		797	print "finished.\n";
		798	exit;
		799	}
		800
		801	# if we find ",", we can continue with the next element
		802	if ($json->incr_text =~ s/^,//) {
		803	last;
		804	}
		805
		806	# if we find anything else, we have a parse error!
		807	if (length $json->incr_text) {
		808	die "parse error near ", $json->incr_text;
		809	}
		810
		811	# else add more data
		812	sysread $fh, my $buf, 65536
		813	or die "read error: $!";
		814	$json->incr_parse ($buf); # void context, so no parsing
		815	}
		816
		817	This is a complex example, but most of the complexity comes from the
		818	fact that we are trying to be correct (bear with me if I am wrong, I
		819	never ran the above example :).
		820
360	MAPPING	821	MAPPING
361	This section describes how JSON::XS maps Perl values to JSON values and	822	This section describes how JSON::XS maps Perl values to JSON values and
362	vice versa. These mappings are designed to "do the right thing" in most	823	vice versa. These mappings are designed to "do the right thing" in most
363	circumstances automatically, preserving round-tripping characteristics	824	circumstances automatically, preserving round-tripping characteristics
364	(what you put in comes out as something equivalent).	825	(what you put in comes out as something equivalent).
365		826
366	For the more enlightened: note that in the following descriptions,	827	For the more enlightened: note that in the following descriptions,
367	lowercase perl refers to the Perl interpreter, while uppcercase Perl	828	lowercase perl refers to the Perl interpreter, while uppercase Perl
368	refers to the abstract Perl language itself.	829	refers to the abstract Perl language itself.
369		830
370	JSON -> PERL	831	JSON -> PERL
371	object	832	object
372	A JSON object becomes a reference to a hash in Perl. No ordering of	833	A JSON object becomes a reference to a hash in Perl. No ordering of
373	object keys is preserved (JSON does not preserver object key	834	object keys is preserved (JSON does not preserve object key ordering
374	ordering itself).	835	itself).
375		836
376	array	837	array
377	A JSON array becomes a reference to an array in Perl.	838	A JSON array becomes a reference to an array in Perl.
378		839
379	string	840	string
380	A JSON string becomes a string scalar in Perl - Unicode codepoints	841	A JSON string becomes a string scalar in Perl - Unicode codepoints
381	in JSON are represented by the same codepoints in the Perl string,	842	in JSON are represented by the same codepoints in the Perl string,
382	so no manual decoding is necessary.	843	so no manual decoding is necessary.
383		844
384	number	845	number
385	A JSON number becomes either an integer or numeric (floating point)	846	A JSON number becomes either an integer, numeric (floating point) or
386	scalar in perl, depending on its range and any fractional parts. On	847	string scalar in perl, depending on its range and any fractional
387	the Perl level, there is no difference between those as Perl handles	848	parts. On the Perl level, there is no difference between those as
388	all the conversion details, but an integer may take slightly less	849	Perl handles all the conversion details, but an integer may take
389	memory and might represent more values exactly than (floating point)	850	slightly less memory and might represent more values exactly than
		851	floating point numbers.
		852
		853	If the number consists of digits only, JSON::XS will try to
		854	represent it as an integer value. If that fails, it will try to
		855	represent it as a numeric (floating point) value if that is possible
		856	without loss of precision. Otherwise it will preserve the number as
		857	a string value (in which case you lose roundtripping ability, as the
		858	JSON number will be re-encoded toa JSON string).
		859
		860	Numbers containing a fractional or exponential part will always be
		861	represented as numeric (floating point) values, possibly at a loss
		862	of precision (in which case you might lose perfect roundtripping
		863	ability, but the JSON number will still be re-encoded as a JSON
390	numbers.	864	number).
391		865
392	true, false	866	true, false
393	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",	867	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
394	respectively. They are overloaded to act almost exactly like the	868	respectively. They are overloaded to act almost exactly like the
395	numbers 1 and 0. You can check wether a scalar is a JSON boolean by	869	numbers 1 and 0. You can check whether a scalar is a JSON boolean by
396	using the "JSON::XS::is_bool" function.	870	using the "JSON::XS::is_bool" function.
397		871
398	null	872	null
399	A JSON null atom becomes "undef" in Perl.	873	A JSON null atom becomes "undef" in Perl.
400		874
…		…
423	an exception to be thrown, except for references to the integers 0	897	an exception to be thrown, except for references to the integers 0
424	and 1, which get turned into "false" and "true" atoms in JSON. You	898	and 1, which get turned into "false" and "true" atoms in JSON. You
425	can also use "JSON::XS::false" and "JSON::XS::true" to improve	899	can also use "JSON::XS::false" and "JSON::XS::true" to improve
426	readability.	900	readability.
427		901
428	to_json [\0,JSON::XS::true] # yields [false,true]	902	encode_json [\0,JSON::XS::true] # yields [false,true]
429		903
430	JSON::XS::true, JSON::XS::false	904	JSON::XS::true, JSON::XS::false
431	These special values become JSON true and JSON false values,	905	These special values become JSON true and JSON false values,
432	respectively. You cna alos use "\1" and "\0" directly if you want.	906	respectively. You can also use "\1" and "\0" directly if you want.
433		907
434	blessed objects	908	blessed objects
435	Blessed objects are not allowed. JSON::XS currently tries to encode	909	Blessed objects are not directly representable in JSON. See the
436	their underlying representation (hash- or arrayref), but this	910	"allow_blessed" and "convert_blessed" methods on various options on
437	behaviour might change in future versions.	911	how to deal with this: basically, you can choose between throwing an
		912	exception, encoding the reference as if it weren't blessed, or
		913	provide your own serialiser method.
438		914
439	simple scalars	915	simple scalars
440	Simple Perl scalars (any scalar that is not a reference) are the	916	Simple Perl scalars (any scalar that is not a reference) are the
441	most difficult objects to encode: JSON::XS will encode undefined	917	most difficult objects to encode: JSON::XS will encode undefined
442	scalars as JSON null value, scalars that have last been used in a	918	scalars as JSON "null" values, scalars that have last been used in a
443	string context before encoding as JSON strings and anything else as	919	string context before encoding as JSON strings, and anything else as
444	number value:	920	number value:
445		921
446	# dump as number	922	# dump as number
447	to_json [2] # yields [2]	923	encode_json [2] # yields [2]
448	to_json [-3.0e17] # yields [-3e+17]	924	encode_json [-3.0e17] # yields [-3e+17]
449	my $value = 5; to_json [$value] # yields [5]	925	my $value = 5; encode_json [$value] # yields [5]
450		926
451	# used as string, so dump as string	927	# used as string, so dump as string
452	print $value;	928	print $value;
453	to_json [$value] # yields ["5"]	929	encode_json [$value] # yields ["5"]
454		930
455	# undef becomes null	931	# undef becomes null
456	to_json [undef] # yields [null]	932	encode_json [undef] # yields [null]
457		933
458	You can force the type to be a string by stringifying it:	934	You can force the type to be a JSON string by stringifying it:
459		935
460	my $x = 3.1; # some variable containing a number	936	my $x = 3.1; # some variable containing a number
461	"$x"; # stringified	937	"$x"; # stringified
462	$x .= ""; # another, more awkward way to stringify	938	$x .= ""; # another, more awkward way to stringify
463	print $x; # perl does it for you, too, quite often	939	print $x; # perl does it for you, too, quite often
464		940
465	You can force the type to be a number by numifying it:	941	You can force the type to be a JSON number by numifying it:
466		942
467	my $x = "3"; # some variable containing a string	943	my $x = "3"; # some variable containing a string
468	$x += 0; # numify it, ensuring it will be dumped as a number	944	$x += 0; # numify it, ensuring it will be dumped as a number
469	$x *= 1; # same thing, the choise is yours.	945	$x *= 1; # same thing, the choice is yours.
470		946
471	You can not currently output JSON booleans or force the type in	947	You can not currently force the type in other, less obscure, ways.
472	other, less obscure, ways. Tell me if you need this capability.	948	Tell me if you need this capability (but don't forget to explain why
		949	it's needed :).
473		950
474	COMPARISON	951	ENCODING/CODESET FLAG NOTES
475	As already mentioned, this module was created because none of the	952	The interested reader might have seen a number of flags that signify
476	existing JSON modules could be made to work correctly. First I will	953	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
477	describe the problems (or pleasures) I encountered with various existing	954	some confusion on what these do, so here is a short comparison:
478	JSON modules, followed by some benchmark values. JSON::XS was designed
479	not to suffer from any of these problems or limitations.
480		955
481	JSON 1.07	956	"utf8" controls whether the JSON text created by "encode" (and expected
482	Slow (but very portable, as it is written in pure Perl).	957	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
		958	control whether "encode" escapes character values outside their
		959	respective codeset range. Neither of these flags conflict with each
		960	other, although some combinations make less sense than others.
483		961
484	Undocumented/buggy Unicode handling (how JSON handles unicode values	962	Care has been taken to make all flags symmetrical with respect to
485	is undocumented. One can get far by feeding it unicode strings and	963	"encode" and "decode", that is, texts encoded with any combination of
486	doing en-/decoding oneself, but unicode escapes are not working	964	these flag values will be correctly decoded when the same flags are used
		965	- in general, if you use different flag settings while encoding vs. when
		966	decoding you likely have a bug somewhere.
		967
		968	Below comes a verbose discussion of these flags. Note that a "codeset"
		969	is simply an abstract set of character-codepoint pairs, while an
		970	encoding takes those codepoint numbers and encodes them, in our case
		971	into octets. Unicode is (among other things) a codeset, UTF-8 is an
		972	encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
		973	encodings at the same time, which can be confusing.
		974
		975	"utf8" flag disabled
		976	When "utf8" is disabled (the default), then "encode"/"decode"
		977	generate and expect Unicode strings, that is, characters with high
		978	ordinal Unicode values (> 255) will be encoded as such characters,
		979	and likewise such characters are decoded as-is, no canges to them
		980	will be done, except "(re-)interpreting" them as Unicode codepoints
		981	or Unicode characters, respectively (to Perl, these are the same
		982	thing in strings unless you do funny/weird/dumb stuff).
		983
		984	This is useful when you want to do the encoding yourself (e.g. when
		985	you want to have UTF-16 encoded JSON texts) or when some other layer
		986	does the encoding for you (for example, when printing to a terminal
		987	using a filehandle that transparently encodes to UTF-8 you certainly
		988	do NOT want to UTF-8 encode your data first and have Perl encode it
		989	another time).
		990
		991	"utf8" flag enabled
		992	If the "utf8"-flag is enabled, "encode"/"decode" will encode all
		993	characters using the corresponding UTF-8 multi-byte sequence, and
		994	will expect your input strings to be encoded as UTF-8, that is, no
		995	"character" of the input string must have any value > 255, as UTF-8
		996	does not allow that.
		997
		998	The "utf8" flag therefore switches between two modes: disabled means
		999	you will get a Unicode string in Perl, enabled means you get an
		1000	UTF-8 encoded octet/binary string in Perl.
		1001
		1002	"latin1" or "ascii" flags enabled
		1003	With "latin1" (or "ascii") enabled, "encode" will escape characters
		1004	with ordinal values > 255 (> 127 with "ascii") and encode the
		1005	remaining characters as specified by the "utf8" flag.
		1006
		1007	If "utf8" is disabled, then the result is also correctly encoded in
		1008	those character sets (as both are proper subsets of Unicode, meaning
		1009	that a Unicode string with all character values < 256 is the same
		1010	thing as a ISO-8859-1 string, and a Unicode string with all
		1011	character values < 128 is the same thing as an ASCII string in
487	properly).	1012	Perl).
488		1013
489	No roundtripping (strings get clobbered if they look like numbers,	1014	If "utf8" is enabled, you still get a correct UTF-8-encoded string,
490	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	1015	regardless of these flags, just some more characters will be escaped
491	will decode into the number 2.	1016	using "\uXXXX" then before.
492		1017
493	JSON::PC 0.01	1018	Note that ISO-8859-1-encoded strings are not compatible with UTF-8
494	Very fast.	1019	encoding, while ASCII-encoded strings are. That is because the
		1020	ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
		1021	codeset being a subset of Unicode), while ASCII is.
495		1022
496	Undocumented/buggy Unicode handling.	1023	Surprisingly, "decode" will ignore these flags and so treat all
		1024	input values as governed by the "utf8" flag. If it is disabled, this
		1025	allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
		1026	strict subsets of Unicode. If it is enabled, you can correctly
		1027	decode UTF-8 encoded strings.
497		1028
498	No roundtripping.	1029	So neither "latin1" nor "ascii" are incompatible with the "utf8"
		1030	flag - they only govern when the JSON output engine escapes a
		1031	character or not.
499		1032
500	Has problems handling many Perl values (e.g. regex results and other	1033	The main use for "latin1" is to relatively efficiently store binary
501	magic values will make it croak).	1034	data as JSON, at the expense of breaking compatibility with most
		1035	JSON decoders.
502		1036
503	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1037	The main use for "ascii" is to force the output to not contain
504	which is not a valid JSON text.	1038	characters with values > 127, which means you can interpret the
505		1039	resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
506	Unmaintained (maintainer unresponsive for many months, bugs are not	1040	any character set and 8-bit-encoding, and still get the same data
507	getting fixed).	1041	structure back. This is useful when your channel for JSON transfer
508		1042	is not 8-bit clean or the encoding might be mangled in between (e.g.
509	JSON::Syck 0.21	1043	in mail), and works because ASCII is a proper subset of most 8-bit
510	Very buggy (often crashes).	1044	and multibyte encodings in use in the world.
511
512	Very inflexible (no human-readable format supported, format pretty
513	much undocumented. I need at least a format for easy reading by
514	humans and a single-line compact format for use in a protocol, and
515	preferably a way to generate ASCII-only JSON texts).
516
517	Completely broken (and confusingly documented) Unicode handling
518	(unicode escapes are not working properly, you need to set
519	ImplicitUnicode to different values on en- and decoding to get
520	symmetric behaviour).
521
522	No roundtripping (simple cases work, but this depends on wether the
523	scalar value was used in a numeric context or not).
524
525	Dumping hashes may skip hash values depending on iterator state.
526
527	Unmaintained (maintainer unresponsive for many months, bugs are not
528	getting fixed).
529
530	Does not check input for validity (i.e. will accept non-JSON input
531	and return "something" instead of raising an exception. This is a
532	security issue: imagine two banks transfering money between each
533	other using JSON. One bank might parse a given non-JSON request and
534	deduct money, while the other might reject the transaction with a
535	syntax error. While a good protocol will at least recover, that is
536	extra unnecessary work and the transaction will still not succeed).
537
538	JSON::DWIW 0.04
539	Very fast. Very natural. Very nice.
540
541	Undocumented unicode handling (but the best of the pack. Unicode
542	escapes still don't get parsed properly).
543
544	Very inflexible.
545
546	No roundtripping.
547
548	Does not generate valid JSON texts (key strings are often unquoted,
549	empty keys result in nothing being output)
550
551	Does not check input for validity.
552		1045
553	JSON and YAML	1046	JSON and YAML
554	You often hear that JSON is a subset (or a close subset) of YAML. This	1047	You often hear that JSON is a subset of YAML. This is, however, a mass
555	is, however, a mass hysteria and very far from the truth. In general,	1048	hysteria(*) and very far from the truth (as of the time of this
556	there is no way to configure JSON::XS to output a data structure as	1049	writing), so let me state it clearly: *in general, there is no way to
557	valid YAML.	1050	configure JSON::XS to output a data structure as valid YAML* that works
		1051	in all cases.
558		1052
559	If you really must use JSON::XS to generate YAML, you should use this	1053	If you really must use JSON::XS to generate YAML, you should use this
560	algorithm (subject to change in future versions):	1054	algorithm (subject to change in future versions):
561		1055
562	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1056	my $to_yaml = JSON::XS->new->utf8->space_after (1);
563	my $yaml = $to_yaml->encode ($ref) . "\n";	1057	my $yaml = $to_yaml->encode ($ref) . "\n";
564		1058
565	This will usually generate JSON texts that also parse as valid YAML.	1059	This will usually generate JSON texts that also parse as valid YAML.
566	Please note that YAML has hardcoded limits on (simple) object key	1060	Please note that YAML has hardcoded limits on (simple) object key
567	lengths that JSON doesn't have, so you should make sure that your hash	1061	lengths that JSON doesn't have and also has different and incompatible
		1062	unicode handling, so you should make sure that your hash keys are
568	keys are noticably shorter than the 1024 characters YAML allows.	1063	noticeably shorter than the 1024 "stream characters" YAML allows and
		1064	that you do not have characters with codepoint values outside the
		1065	Unicode BMP (basic multilingual page). YAML also does not allow "\/"
		1066	sequences in strings (which JSON::XS does not currently generate, but
		1067	other JSON generators might).
569		1068
570	There might be other incompatibilities that I am not aware of. In	1069	There might be other incompatibilities that I am not aware of (or the
		1070	YAML specification has been changed yet again - it does so quite often).
571	general you should not try to generate YAML with a JSON generator or	1071	In general you should not try to generate YAML with a JSON generator or
572	vice versa, or try to parse JSON with a YAML parser or vice versa:	1072	vice versa, or try to parse JSON with a YAML parser or vice versa:
573	chances are high that you will run into severe interoperability	1073	chances are high that you will run into severe interoperability problems
574	problems.	1074	when you least expect it.
		1075
		1076	(*) I have been pressured multiple times by Brian Ingerson (one of the
		1077	authors of the YAML specification) to remove this paragraph, despite
		1078	him acknowledging that the actual incompatibilities exist. As I was
		1079	personally bitten by this "JSON is YAML" lie, I refused and said I
		1080	will continue to educate people about these issues, so others do not
		1081	run into the same problem again and again. After this, Brian called
		1082	me a (quote)complete and worthless idiot(unquote).
		1083
		1084	In my opinion, instead of pressuring and insulting people who
		1085	actually clarify issues with YAML and the wrong statements of some
		1086	of its proponents, I would kindly suggest reading the JSON spec
		1087	(which is not that difficult or long) and finally make YAML
		1088	compatible to it, and educating users about the changes, instead of
		1089	spreading lies about the real compatibility for many years and
		1090	trying to silence people who point out that it isn't true.
575		1091
576	SPEED	1092	SPEED
577	It seems that JSON::XS is surprisingly fast, as shown in the following	1093	It seems that JSON::XS is surprisingly fast, as shown in the following
578	tables. They have been generated with the help of the "eg/bench" program	1094	tables. They have been generated with the help of the "eg/bench" program
579	in the JSON::XS distribution, to make it easy to compare on your own	1095	in the JSON::XS distribution, to make it easy to compare on your own
580	system.	1096	system.
581		1097
582	First comes a comparison between various modules using a very short	1098	First comes a comparison between various modules using a very short
583	single-line JSON string:	1099	single-line JSON string (also available at
		1100	<http://dist.schmorp.de/misc/json/short.json>).
584		1101
585	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1102	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
586	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1103	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
587		1104
588	It shows the number of encodes/decodes per second (JSON::XS uses the	1105	It shows the number of encodes/decodes per second (JSON::XS uses the
…		…
590	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).	1107	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
591	Higher is better:	1108	Higher is better:
592		1109
593	module \| encode \| decode \|	1110	module \| encode \| decode \|
594	-----------\|------------\|------------\|	1111	-----------\|------------\|------------\|
595	JSON \| 7645.468 \| 4208.613 \|	1112	JSON 1.x \| 4990.842 \| 4088.813 \|
596	JSON::DWIW \| 40721.398 \| 77101.176 \|	1113	JSON::DWIW \| 51653.990 \| 71575.154 \|
597	JSON::PC \| 65948.176 \| 78251.940 \|	1114	JSON::PC \| 65948.176 \| 74631.744 \|
598	JSON::Syck \| 22844.793 \| 26479.192 \|	1115	JSON::PP \| 8931.652 \| 3817.168 \|
		1116	JSON::Syck \| 24877.248 \| 27776.848 \|
599	JSON::XS \| 388361.481 \| 199728.762 \|	1117	JSON::XS \| 388361.481 \| 227951.304 \|
600	JSON::XS/2 \| 218453.333 \| 192399.266 \|	1118	JSON::XS/2 \| 227951.304 \| 218453.333 \|
601	JSON::XS/3 \| 338250.323 \| 192399.266 \|	1119	JSON::XS/3 \| 338250.323 \| 218453.333 \|
602	Storable \| 15779.925 \| 14169.946 \|	1120	Storable \| 16500.016 \| 135300.129 \|
603	-----------+------------+------------+	1121	-----------+------------+------------+
604		1122
605	That is, JSON::XS is about five times faster than JSON::DWIW on	1123	That is, JSON::XS is about five times faster than JSON::DWIW on
606	encoding, about three times faster on decoding, and over fourty times	1124	encoding, about three times faster on decoding, and over forty times
607	faster than JSON, even with pretty-printing and key sorting. It also	1125	faster than JSON, even with pretty-printing and key sorting. It also
608	compares favourably to Storable for small amounts of data.	1126	compares favourably to Storable for small amounts of data.
609		1127
610	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1128	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
611	search API (http://nanoref.com/yahooapis/mgPdGg):	1129	search API (<http://dist.schmorp.de/misc/json/long.json>).
612		1130
613	module \| encode \| decode \|	1131	module \| encode \| decode \|
614	-----------\|------------\|------------\|	1132	-----------\|------------\|------------\|
615	JSON \| 254.685 \| 37.665 \|	1133	JSON 1.x \| 55.260 \| 34.971 \|
616	JSON::DWIW \| 843.343 \| 1049.731 \|	1134	JSON::DWIW \| 825.228 \| 1082.513 \|
617	JSON::PC \| 3602.116 \| 2307.352 \|	1135	JSON::PC \| 3571.444 \| 2394.829 \|
		1136	JSON::PP \| 210.987 \| 32.574 \|
618	JSON::Syck \| 505.107 \| 787.899 \|	1137	JSON::Syck \| 552.551 \| 787.544 \|
619	JSON::XS \| 5747.196 \| 3690.220 \|	1138	JSON::XS \| 5780.463 \| 4854.519 \|
620	JSON::XS/2 \| 3968.121 \| 3676.634 \|	1139	JSON::XS/2 \| 3869.998 \| 4798.975 \|
621	JSON::XS/3 \| 6105.246 \| 3662.508 \|	1140	JSON::XS/3 \| 5862.880 \| 4798.975 \|
622	Storable \| 4417.337 \| 5285.161 \|	1141	Storable \| 4445.002 \| 5235.027 \|
623	-----------+------------+------------+	1142	-----------+------------+------------+
624		1143
625	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1144	Again, JSON::XS leads by far (except for Storable which non-surprisingly
626	decodes faster).	1145	decodes faster).
627		1146
628	On large strings containing lots of high unicode characters, some	1147	On large strings containing lots of high Unicode characters, some
629	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1148	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
630	result will be broken due to missing (or wrong) unicode handling. Others	1149	result will be broken due to missing (or wrong) Unicode handling. Others
631	refuse to decode or encode properly, so it was impossible to prepare a	1150	refuse to decode or encode properly, so it was impossible to prepare a
632	fair comparison table for that case.	1151	fair comparison table for that case.
633		1152
634	SECURITY CONSIDERATIONS	1153	SECURITY CONSIDERATIONS
635	When you are using JSON in a protocol, talking to untrusted potentially	1154	When you are using JSON in a protocol, talking to untrusted potentially
…		…
639	have any buffer overflows. Obviously, this module should ensure that and	1158	have any buffer overflows. Obviously, this module should ensure that and
640	I am trying hard on making that true, but you never know.	1159	I am trying hard on making that true, but you never know.
641		1160
642	Second, you need to avoid resource-starving attacks. That means you	1161	Second, you need to avoid resource-starving attacks. That means you
643	should limit the size of JSON texts you accept, or make sure then when	1162	should limit the size of JSON texts you accept, or make sure then when
644	your resources run out, thats just fine (e.g. by using a separate	1163	your resources run out, that's just fine (e.g. by using a separate
645	process that can crash safely). The size of a JSON text in octets or	1164	process that can crash safely). The size of a JSON text in octets or
646	characters is usually a good indication of the size of the resources	1165	characters is usually a good indication of the size of the resources
647	required to decode it into a Perl structure.	1166	required to decode it into a Perl structure. While JSON::XS can check
		1167	the size of the JSON text, it might be too late when you already have it
		1168	in memory, so you might want to check the size before you accept the
		1169	string.
648		1170
649	Third, JSON::XS recurses using the C stack when decoding objects and	1171	Third, JSON::XS recurses using the C stack when decoding objects and
650	arrays. The C stack is a limited resource: for instance, on my amd64	1172	arrays. The C stack is a limited resource: for instance, on my amd64
651	machine with 8MB of stack size I can decode around 180k nested arrays	1173	machine with 8MB of stack size I can decode around 180k nested arrays
652	but only 14k nested JSON objects (due to perl itself recursing deeply on	1174	but only 14k nested JSON objects (due to perl itself recursing deeply on
653	croak to free the temporary). If that is exceeded, the program crashes.	1175	croak to free the temporary). If that is exceeded, the program crashes.
654	to be conservative, the default nesting limit is set to 512. If your	1176	To be conservative, the default nesting limit is set to 512. If your
655	process has a smaller stack, you should adjust this setting accordingly	1177	process has a smaller stack, you should adjust this setting accordingly
656	with the "max_depth" method.	1178	with the "max_depth" method.
657		1179
658	And last but least, something else could bomb you that I forgot to think	1180	Something else could bomb you, too, that I forgot to think of. In that
659	of. In that case, you get to keep the pieces. I am always open for	1181	case, you get to keep the pieces. I am always open for hints, though...
660	hints, though...
661		1182
		1183	Also keep in mind that JSON::XS might leak contents of your Perl data
		1184	structures in its error messages, so when you serialise sensitive
		1185	information you might want to make sure that exceptions thrown by
		1186	JSON::XS will not end up in front of untrusted eyes.
		1187
662	If you are using JSON::XS to return packets to consumption by javascript	1188	If you are using JSON::XS to return packets to consumption by JavaScript
663	scripts in a browser you should have a look at	1189	scripts in a browser you should have a look at
664	<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether	1190	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
665	you are vulnerable to some common attack vectors (which really are	1191	you are vulnerable to some common attack vectors (which really are
666	browser design bugs, but it is still you who will have to deal with it,	1192	browser design bugs, but it is still you who will have to deal with it,
667	as major browser developers care only for features, not about doing	1193	as major browser developers care only for features, not about getting
668	security right).	1194	security right).
		1195
		1196	THREADS
		1197	This module is not guaranteed to be thread safe and there are no plans
		1198	to change this until Perl gets thread support (as opposed to the
		1199	horribly slow so-called "threads" which are simply slow and bloated
		1200	process simulations - use fork, it's much faster, cheaper, better).
		1201
		1202	(It might actually work, but you have been warned).
669		1203
670	BUGS	1204	BUGS
671	While the goal of this module is to be correct, that unfortunately does	1205	While the goal of this module is to be correct, that unfortunately does
672	not mean its bug-free, only that I think its design is bug-free. It is	1206	not mean it's bug-free, only that I think its design is bug-free. It is
673	still relatively early in its development. If you keep reporting bugs	1207	still relatively early in its development. If you keep reporting bugs
674	they will be fixed swiftly, though.	1208	they will be fixed swiftly, though.
		1209
		1210	Please refrain from using rt.cpan.org or any other bug reporting
		1211	service. I put the contact address into my modules for a reason.
		1212
		1213	SEE ALSO
		1214	The json_xs command line utility for quick experiments.
675		1215
676	AUTHOR	1216	AUTHOR
677	Marc Lehmann <schmorp@schmorp.de>	1217	Marc Lehmann <schmorp@schmorp.de>
678	http://home.schmorp.de/	1218	http://home.schmorp.de/
679		1219

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Comparing JSON-XS/README (file contents): Revision 1.14 by root, Sat Jun 23 23:50:03 2007 UTC vs. Revision 1.24 by root, Thu Mar 27 06:37:35 2008 UTC

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Comparing JSON-XS/README (file contents):
Revision 1.14 by root, Sat Jun 23 23:50:03 2007 UTC vs.
Revision 1.24 by root, Thu Mar 27 06:37:35 2008 UTC