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Comparing JSON-XS/README (file contents):
Revision 1.10 by root, Wed Apr 4 00:01:44 2007 UTC vs.
Revision 1.28 by root, Mon Sep 29 03:09:27 2008 UTC

…		…
1	NAME	1	NAME
2	JSON::XS - JSON serialising/deserialising, done correctly and fast	2	JSON::XS - JSON serialising/deserialising, done correctly and fast
3		3
		4	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		5	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		6
4	SYNOPSIS	7	SYNOPSIS
5	use JSON::XS;	8	use JSON::XS;
6		9
7	# exported functions, they croak on error	10	# exported functions, they croak on error
8	# and expect/generate UTF-8	11	# and expect/generate UTF-8
9		12
10	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	13	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
11	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	14	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
12
13	# objToJson and jsonToObj aliases to to_json and from_json
14	# are exported for compatibility to the JSON module,
15	# but should not be used in new code.
16		15
17	# OO-interface	16	# OO-interface
18		17
19	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	18	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
20	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	19	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
21	$perl_scalar = $coder->decode ($unicode_json_text);	20	$perl_scalar = $coder->decode ($unicode_json_text);
		21
		22	# Note that JSON version 2.0 and above will automatically use JSON::XS
		23	# if available, at virtually no speed overhead either, so you should
		24	# be able to just:
		25
		26	use JSON;
		27
		28	# and do the same things, except that you have a pure-perl fallback now.
22		29
23	DESCRIPTION	30	DESCRIPTION
24	This module converts Perl data structures to JSON and vice versa. Its	31	This module converts Perl data structures to JSON and vice versa. Its
25	primary goal is to be correct and its secondary goal is to be fast.	32	primary goal is to be correct and its secondary goal is to be fast.
26	To reach the latter goal it was written in C.	33	To reach the latter goal it was written in C.
		34
		35	Beginning with version 2.0 of the JSON module, when both JSON and
		36	JSON::XS are installed, then JSON will fall back on JSON::XS (this can
		37	be overridden) with no overhead due to emulation (by inheriting
		38	constructor and methods). If JSON::XS is not available, it will fall
		39	back to the compatible JSON::PP module as backend, so using JSON instead
		40	of JSON::XS gives you a portable JSON API that can be fast when you need
		41	and doesn't require a C compiler when that is a problem.
27		42
28	As this is the n-th-something JSON module on CPAN, what was the reason	43	As this is the n-th-something JSON module on CPAN, what was the reason
29	to write yet another JSON module? While it seems there are many JSON	44	to write yet another JSON module? While it seems there are many JSON
30	modules, none of them correctly handle all corner cases, and in most	45	modules, none of them correctly handle all corner cases, and in most
31	cases their maintainers are unresponsive, gone missing, or not listening	46	cases their maintainers are unresponsive, gone missing, or not listening
32	to bug reports for other reasons.	47	to bug reports for other reasons.
33		48
34	See COMPARISON, below, for a comparison to some other JSON modules.
35
36	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	49	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
37	vice versa.	50	vice versa.
38		51
39	FEATURES	52	FEATURES
40	* correct unicode handling	53	* correct Unicode handling
		54
41	This module knows how to handle Unicode, and even documents how and	55	This module knows how to handle Unicode, documents how and when it
42	when it does so.	56	does so, and even documents what "correct" means.
43		57
44	* round-trip integrity	58	* round-trip integrity
		59
45	When you serialise a perl data structure using only datatypes	60	When you serialise a perl data structure using only data types
46	supported by JSON, the deserialised data structure is identical on	61	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"	62	the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
48	just because it looks like a number).	63	just because it looks like a number). There minor are exceptions
		64	to this, read the MAPPING section below to learn about those.
49		65
50	* strict checking of JSON correctness	66	* strict checking of JSON correctness
		67
51	There is no guessing, no generating of illegal JSON texts by	68	There is no guessing, no generating of illegal JSON texts by
52	default, and only JSON is accepted as input by default (the latter	69	default, and only JSON is accepted as input by default (the latter
53	is a security feature).	70	is a security feature).
54		71
55	* fast	72	* fast
56	Compared to other JSON modules, this module compares favourably in
57	terms of speed, too.
58		73
		74	Compared to other JSON modules and other serialisers such as
		75	Storable, this module usually compares favourably in terms of speed,
		76	too.
		77
59	* simple to use	78	* simple to use
		79
60	This module has both a simple functional interface as well as an OO	80	This module has both a simple functional interface as well as an
61	interface.	81	object oriented interface interface.
62		82
63	* reasonably versatile output formats	83	* reasonably versatile output formats
		84
64	You can choose between the most compact guarenteed single-line	85	You can choose between the most compact guaranteed-single-line
65	format possible (nice for simple line-based protocols), a pure-ascii	86	format possible (nice for simple line-based protocols), a pure-ASCII
66	format (for when your transport is not 8-bit clean, still supports	87	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	88	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	89	want to read that stuff). Or you can combine those features in
69	whatever way you like.	90	whatever way you like.
70		91
71	FUNCTIONAL INTERFACE	92	FUNCTIONAL INTERFACE
72	The following convinience methods are provided by this module. They are	93	The following convenience methods are provided by this module. They are
73	exported by default:	94	exported by default:
74		95
75	$json_text = to_json $perl_scalar	96	$json_text = encode_json $perl_scalar
76	Converts the given Perl data structure (a simple scalar or a	97	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.	98	string (that is, the string contains octets only). Croaks on error.
79		99
80	This function call is functionally identical to:	100	This function call is functionally identical to:
81		101
82	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	102	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
83		103
84	except being faster.	104	Except being faster.
85		105
86	$perl_scalar = from_json $json_text	106	$perl_scalar = decode_json $json_text
87	The opposite of "to_json": expects an UTF-8 (binary) string and	107	The opposite of "encode_json": expects an UTF-8 (binary) string and
88	tries to parse that as an UTF-8 encoded JSON text, returning the	108	tries to parse that as an UTF-8 encoded JSON text, returning the
89	resulting simple scalar or reference. Croaks on error.	109	resulting reference. Croaks on error.
90		110
91	This function call is functionally identical to:	111	This function call is functionally identical to:
92		112
93	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	113	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
94		114
95	except being faster.	115	Except being faster.
		116
		117	$is_boolean = JSON::XS::is_bool $scalar
		118	Returns true if the passed scalar represents either JSON::XS::true
		119	or JSON::XS::false, two constants that act like 1 and 0,
		120	respectively and are used to represent JSON "true" and "false"
		121	values in Perl.
		122
		123	See MAPPING, below, for more information on how JSON values are
		124	mapped to Perl.
		125
		126	A FEW NOTES ON UNICODE AND PERL
		127	Since this often leads to confusion, here are a few very clear words on
		128	how Unicode works in Perl, modulo bugs.
		129
		130	1. Perl strings can store characters with ordinal values > 255.
		131	This enables you to store Unicode characters as single characters in
		132	a Perl string - very natural.
		133
		134	2. Perl does not associate an encoding with your strings.
		135	... until you force it to, e.g. when matching it against a regex, or
		136	printing the scalar to a file, in which case Perl either interprets
		137	your string as locale-encoded text, octets/binary, or as Unicode,
		138	depending on various settings. In no case is an encoding stored
		139	together with your data, it is use that decides encoding, not any
		140	magical meta data.
		141
		142	3. The internal utf-8 flag has no meaning with regards to the encoding
		143	of your string.
		144	Just ignore that flag unless you debug a Perl bug, a module written
		145	in XS or want to dive into the internals of perl. Otherwise it will
		146	only confuse you, as, despite the name, it says nothing about how
		147	your string is encoded. You can have Unicode strings with that flag
		148	set, with that flag clear, and you can have binary data with that
		149	flag set and that flag clear. Other possibilities exist, too.
		150
		151	If you didn't know about that flag, just the better, pretend it
		152	doesn't exist.
		153
		154	4. A "Unicode String" is simply a string where each character can be
		155	validly interpreted as a Unicode code point.
		156	If you have UTF-8 encoded data, it is no longer a Unicode string,
		157	but a Unicode string encoded in UTF-8, giving you a binary string.
		158
		159	5. A string containing "high" (> 255) character values is not a UTF-8
		160	string.
		161	It's a fact. Learn to live with it.
		162
		163	I hope this helps :)
96		164
97	OBJECT-ORIENTED INTERFACE	165	OBJECT-ORIENTED INTERFACE
98	The object oriented interface lets you configure your own encoding or	166	The object oriented interface lets you configure your own encoding or
99	decoding style, within the limits of supported formats.	167	decoding style, within the limits of supported formats.
100		168
108		176
109	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})	177	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
110	=> {"a": [1, 2]}	178	=> {"a": [1, 2]}
111		179
112	$json = $json->ascii ([$enable])	180	$json = $json->ascii ([$enable])
		181	$enabled = $json->get_ascii
113	If $enable is true (or missing), then the "encode" method will not	182	If $enable is true (or missing), then the "encode" method will not
114	generate characters outside the code range 0..127 (which is ASCII).	183	generate characters outside the code range 0..127 (which is ASCII).
115	Any unicode characters outside that range will be escaped using	184	Any Unicode characters outside that range will be escaped using
116	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL	185	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
117	escape sequence, as per RFC4627.	186	escape sequence, as per RFC4627. The resulting encoded JSON text can
		187	be treated as a native Unicode string, an ascii-encoded,
		188	latin1-encoded or UTF-8 encoded string, or any other superset of
		189	ASCII.
118		190
119	If $enable is false, then the "encode" method will not escape	191	If $enable is false, then the "encode" method will not escape
120	Unicode characters unless required by the JSON syntax. This results	192	Unicode characters unless required by the JSON syntax or other
121	in a faster and more compact format.	193	flags. This results in a faster and more compact format.
		194
		195	See also the section ENCODING/CODESET FLAG NOTES later in this
		196	document.
		197
		198	The main use for this flag is to produce JSON texts that can be
		199	transmitted over a 7-bit channel, as the encoded JSON texts will not
		200	contain any 8 bit characters.
122		201
123	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	202	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
124	=> ["\ud801\udc01"]	203	=> ["\ud801\udc01"]
125		204
		205	$json = $json->latin1 ([$enable])
		206	$enabled = $json->get_latin1
		207	If $enable is true (or missing), then the "encode" method will
		208	encode the resulting JSON text as latin1 (or iso-8859-1), escaping
		209	any characters outside the code range 0..255. The resulting string
		210	can be treated as a latin1-encoded JSON text or a native Unicode
		211	string. The "decode" method will not be affected in any way by this
		212	flag, as "decode" by default expects Unicode, which is a strict
		213	superset of latin1.
		214
		215	If $enable is false, then the "encode" method will not escape
		216	Unicode characters unless required by the JSON syntax or other
		217	flags.
		218
		219	See also the section ENCODING/CODESET FLAG NOTES later in this
		220	document.
		221
		222	The main use for this flag is efficiently encoding binary data as
		223	JSON text, as most octets will not be escaped, resulting in a
		224	smaller encoded size. The disadvantage is that the resulting JSON
		225	text is encoded in latin1 (and must correctly be treated as such
		226	when storing and transferring), a rare encoding for JSON. It is
		227	therefore most useful when you want to store data structures known
		228	to contain binary data efficiently in files or databases, not when
		229	talking to other JSON encoders/decoders.
		230
		231	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		232	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
		233
126	$json = $json->utf8 ([$enable])	234	$json = $json->utf8 ([$enable])
		235	$enabled = $json->get_utf8
127	If $enable is true (or missing), then the "encode" method will	236	If $enable is true (or missing), then the "encode" method will
128	encode the JSON result into UTF-8, as required by many protocols,	237	encode the JSON result into UTF-8, as required by many protocols,
129	while the "decode" method expects to be handled an UTF-8-encoded	238	while the "decode" method expects to be handled an UTF-8-encoded
130	string. Please note that UTF-8-encoded strings do not contain any	239	string. Please note that UTF-8-encoded strings do not contain any
131	characters outside the range 0..255, they are thus useful for	240	characters outside the range 0..255, they are thus useful for
132	bytewise/binary I/O. In future versions, enabling this option might	241	bytewise/binary I/O. In future versions, enabling this option might
133	enable autodetection of the UTF-16 and UTF-32 encoding families, as	242	enable autodetection of the UTF-16 and UTF-32 encoding families, as
134	described in RFC4627.	243	described in RFC4627.
135		244
136	If $enable is false, then the "encode" method will return the JSON	245	If $enable is false, then the "encode" method will return the JSON
137	string as a (non-encoded) unicode string, while "decode" expects	246	string as a (non-encoded) Unicode string, while "decode" expects
138	thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or	247	thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
139	UTF-16) needs to be done yourself, e.g. using the Encode module.	248	UTF-16) needs to be done yourself, e.g. using the Encode module.
		249
		250	See also the section ENCODING/CODESET FLAG NOTES later in this
		251	document.
140		252
141	Example, output UTF-16BE-encoded JSON:	253	Example, output UTF-16BE-encoded JSON:
142		254
143	use Encode;	255	use Encode;
144	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	256	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
163	2	275	2
164	]	276	]
165	}	277	}
166		278
167	$json = $json->indent ([$enable])	279	$json = $json->indent ([$enable])
		280	$enabled = $json->get_indent
168	If $enable is true (or missing), then the "encode" method will use a	281	If $enable is true (or missing), then the "encode" method will use a
169	multiline format as output, putting every array member or	282	multiline format as output, putting every array member or
170	object/hash key-value pair into its own line, identing them	283	object/hash key-value pair into its own line, indenting them
171	properly.	284	properly.
172		285
173	If $enable is false, no newlines or indenting will be produced, and	286	If $enable is false, no newlines or indenting will be produced, and
174	the resulting JSON text is guarenteed not to contain any "newlines".	287	the resulting JSON text is guaranteed not to contain any "newlines".
175		288
176	This setting has no effect when decoding JSON texts.	289	This setting has no effect when decoding JSON texts.
177		290
178	$json = $json->space_before ([$enable])	291	$json = $json->space_before ([$enable])
		292	$enabled = $json->get_space_before
179	If $enable is true (or missing), then the "encode" method will add	293	If $enable is true (or missing), then the "encode" method will add
180	an extra optional space before the ":" separating keys from values	294	an extra optional space before the ":" separating keys from values
181	in JSON objects.	295	in JSON objects.
182		296
183	If $enable is false, then the "encode" method will not add any extra	297	If $enable is false, then the "encode" method will not add any extra
…		…
189	Example, space_before enabled, space_after and indent disabled:	303	Example, space_before enabled, space_after and indent disabled:
190		304
191	{"key" :"value"}	305	{"key" :"value"}
192		306
193	$json = $json->space_after ([$enable])	307	$json = $json->space_after ([$enable])
		308	$enabled = $json->get_space_after
194	If $enable is true (or missing), then the "encode" method will add	309	If $enable is true (or missing), then the "encode" method will add
195	an extra optional space after the ":" separating keys from values in	310	an extra optional space after the ":" separating keys from values in
196	JSON objects and extra whitespace after the "," separating key-value	311	JSON objects and extra whitespace after the "," separating key-value
197	pairs and array members.	312	pairs and array members.
198		313
…		…
203		318
204	Example, space_before and indent disabled, space_after enabled:	319	Example, space_before and indent disabled, space_after enabled:
205		320
206	{"key": "value"}	321	{"key": "value"}
207		322
		323	$json = $json->relaxed ([$enable])
		324	$enabled = $json->get_relaxed
		325	If $enable is true (or missing), then "decode" will accept some
		326	extensions to normal JSON syntax (see below). "encode" will not be
		327	affected in anyway. *Be aware that this option makes you accept
		328	invalid JSON texts as if they were valid!*. I suggest only to use
		329	this option to parse application-specific files written by humans
		330	(configuration files, resource files etc.)
		331
		332	If $enable is false (the default), then "decode" will only accept
		333	valid JSON texts.
		334
		335	Currently accepted extensions are:
		336
		337	* list items can have an end-comma
		338
		339	JSON separates array elements and key-value pairs with commas.
		340	This can be annoying if you write JSON texts manually and want
		341	to be able to quickly append elements, so this extension accepts
		342	comma at the end of such items not just between them:
		343
		344	[
		345	1,
		346	2, <- this comma not normally allowed
		347	]
		348	{
		349	"k1": "v1",
		350	"k2": "v2", <- this comma not normally allowed
		351	}
		352
		353	* shell-style '#'-comments
		354
		355	Whenever JSON allows whitespace, shell-style comments are
		356	additionally allowed. They are terminated by the first
		357	carriage-return or line-feed character, after which more
		358	white-space and comments are allowed.
		359
		360	[
		361	1, # this comment not allowed in JSON
		362	# neither this one...
		363	]
		364
208	$json = $json->canonical ([$enable])	365	$json = $json->canonical ([$enable])
		366	$enabled = $json->get_canonical
209	If $enable is true (or missing), then the "encode" method will	367	If $enable is true (or missing), then the "encode" method will
210	output JSON objects by sorting their keys. This is adding a	368	output JSON objects by sorting their keys. This is adding a
211	comparatively high overhead.	369	comparatively high overhead.
212		370
213	If $enable is false, then the "encode" method will output key-value	371	If $enable is false, then the "encode" method will output key-value
214	pairs in the order Perl stores them (which will likely change	372	pairs in the order Perl stores them (which will likely change
215	between runs of the same script).	373	between runs of the same script).
216		374
217	This option is useful if you want the same data structure to be	375	This option is useful if you want the same data structure to be
218	encoded as the same JSON text (given the same overall settings). If	376	encoded as the same JSON text (given the same overall settings). If
219	it is disabled, the same hash migh be encoded differently even if	377	it is disabled, the same hash might be encoded differently even if
220	contains the same data, as key-value pairs have no inherent ordering	378	contains the same data, as key-value pairs have no inherent ordering
221	in Perl.	379	in Perl.
222		380
223	This setting has no effect when decoding JSON texts.	381	This setting has no effect when decoding JSON texts.
224		382
225	$json = $json->allow_nonref ([$enable])	383	$json = $json->allow_nonref ([$enable])
		384	$enabled = $json->get_allow_nonref
226	If $enable is true (or missing), then the "encode" method can	385	If $enable is true (or missing), then the "encode" method can
227	convert a non-reference into its corresponding string, number or	386	convert a non-reference into its corresponding string, number or
228	null JSON value, which is an extension to RFC4627. Likewise,	387	null JSON value, which is an extension to RFC4627. Likewise,
229	"decode" will accept those JSON values instead of croaking.	388	"decode" will accept those JSON values instead of croaking.
230		389
…		…
237	"allow_nonref", resulting in an invalid JSON text:	396	"allow_nonref", resulting in an invalid JSON text:
238		397
239	JSON::XS->new->allow_nonref->encode ("Hello, World!")	398	JSON::XS->new->allow_nonref->encode ("Hello, World!")
240	=> "Hello, World!"	399	=> "Hello, World!"
241		400
		401	$json = $json->allow_unknown ([$enable])
		402	$enabled = $json->get_allow_unknown
		403	If $enable is true (or missing), then "encode" will not throw an
		404	exception when it encounters values it cannot represent in JSON (for
		405	example, filehandles) but instead will encode a JSON "null" value.
		406	Note that blessed objects are not included here and are handled
		407	separately by c<allow_nonref>.
		408
		409	If $enable is false (the default), then "encode" will throw an
		410	exception when it encounters anything it cannot encode as JSON.
		411
		412	This option does not affect "decode" in any way, and it is
		413	recommended to leave it off unless you know your communications
		414	partner.
		415
		416	$json = $json->allow_blessed ([$enable])
		417	$enabled = $json->get_allow_blessed
		418	If $enable is true (or missing), then the "encode" method will not
		419	barf when it encounters a blessed reference. Instead, the value of
		420	the convert_blessed option will decide whether "null"
		421	("convert_blessed" disabled or no "TO_JSON" method found) or a
		422	representation of the object ("convert_blessed" enabled and
		423	"TO_JSON" method found) is being encoded. Has no effect on "decode".
		424
		425	If $enable is false (the default), then "encode" will throw an
		426	exception when it encounters a blessed object.
		427
		428	$json = $json->convert_blessed ([$enable])
		429	$enabled = $json->get_convert_blessed
		430	If $enable is true (or missing), then "encode", upon encountering a
		431	blessed object, will check for the availability of the "TO_JSON"
		432	method on the object's class. If found, it will be called in scalar
		433	context and the resulting scalar will be encoded instead of the
		434	object. If no "TO_JSON" method is found, the value of
		435	"allow_blessed" will decide what to do.
		436
		437	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
		438	returns other blessed objects, those will be handled in the same
		439	way. "TO_JSON" must take care of not causing an endless recursion
		440	cycle (== crash) in this case. The name of "TO_JSON" was chosen
		441	because other methods called by the Perl core (== not by the user of
		442	the object) are usually in upper case letters and to avoid
		443	collisions with any "to_json" function or method.
		444
		445	This setting does not yet influence "decode" in any way, but in the
		446	future, global hooks might get installed that influence "decode" and
		447	are enabled by this setting.
		448
		449	If $enable is false, then the "allow_blessed" setting will decide
		450	what to do when a blessed object is found.
		451
		452	$json = $json->filter_json_object ([$coderef->($hashref)])
		453	When $coderef is specified, it will be called from "decode" each
		454	time it decodes a JSON object. The only argument is a reference to
		455	the newly-created hash. If the code references returns a single
		456	scalar (which need not be a reference), this value (i.e. a copy of
		457	that scalar to avoid aliasing) is inserted into the deserialised
		458	data structure. If it returns an empty list (NOTE: not "undef",
		459	which is a valid scalar), the original deserialised hash will be
		460	inserted. This setting can slow down decoding considerably.
		461
		462	When $coderef is omitted or undefined, any existing callback will be
		463	removed and "decode" will not change the deserialised hash in any
		464	way.
		465
		466	Example, convert all JSON objects into the integer 5:
		467
		468	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		469	# returns [5]
		470	$js->decode ('[{}]')
		471	# throw an exception because allow_nonref is not enabled
		472	# so a lone 5 is not allowed.
		473	$js->decode ('{"a":1, "b":2}');
		474
		475	$json = $json->filter_json_single_key_object ($key [=>
		476	$coderef->($value)])
		477	Works remotely similar to "filter_json_object", but is only called
		478	for JSON objects having a single key named $key.
		479
		480	This $coderef is called before the one specified via
		481	"filter_json_object", if any. It gets passed the single value in the
		482	JSON object. If it returns a single value, it will be inserted into
		483	the data structure. If it returns nothing (not even "undef" but the
		484	empty list), the callback from "filter_json_object" will be called
		485	next, as if no single-key callback were specified.
		486
		487	If $coderef is omitted or undefined, the corresponding callback will
		488	be disabled. There can only ever be one callback for a given key.
		489
		490	As this callback gets called less often then the
		491	"filter_json_object" one, decoding speed will not usually suffer as
		492	much. Therefore, single-key objects make excellent targets to
		493	serialise Perl objects into, especially as single-key JSON objects
		494	are as close to the type-tagged value concept as JSON gets (it's
		495	basically an ID/VALUE tuple). Of course, JSON does not support this
		496	in any way, so you need to make sure your data never looks like a
		497	serialised Perl hash.
		498
		499	Typical names for the single object key are "__class_whatever__", or
		500	"$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
		501	things like "__class_md5sum(classname)__", to reduce the risk of
		502	clashing with real hashes.
		503
		504	Example, decode JSON objects of the form "{ "__widget__" => <id> }"
		505	into the corresponding $WIDGET{<id>} object:
		506
		507	# return whatever is in $WIDGET{5}:
		508	JSON::XS
		509	->new
		510	->filter_json_single_key_object (__widget__ => sub {
		511	$WIDGET{ $_[0] }
		512	})
		513	->decode ('{"__widget__": 5')
		514
		515	# this can be used with a TO_JSON method in some "widget" class
		516	# for serialisation to json:
		517	sub WidgetBase::TO_JSON {
		518	my ($self) = @_;
		519
		520	unless ($self->{id}) {
		521	$self->{id} = ..get..some..id..;
		522	$WIDGET{$self->{id}} = $self;
		523	}
		524
		525	{ __widget__ => $self->{id} }
		526	}
		527
242	$json = $json->shrink ([$enable])	528	$json = $json->shrink ([$enable])
		529	$enabled = $json->get_shrink
243	Perl usually over-allocates memory a bit when allocating space for	530	Perl usually over-allocates memory a bit when allocating space for
244	strings. This flag optionally resizes strings generated by either	531	strings. This flag optionally resizes strings generated by either
245	"encode" or "decode" to their minimum size possible. This can save	532	"encode" or "decode" to their minimum size possible. This can save
246	memory when your JSON texts are either very very long or you have	533	memory when your JSON texts are either very very long or you have
247	many short strings. It will also try to downgrade any strings to	534	many short strings. It will also try to downgrade any strings to
…		…
265	converting strings that look like integers or floats into integers	552	converting strings that look like integers or floats into integers
266	or floats internally (there is no difference on the Perl level),	553	or floats internally (there is no difference on the Perl level),
267	saving space.	554	saving space.
268		555
269	$json = $json->max_depth ([$maximum_nesting_depth])	556	$json = $json->max_depth ([$maximum_nesting_depth])
		557	$max_depth = $json->get_max_depth
270	Sets the maximum nesting level (default 512) accepted while encoding	558	Sets the maximum nesting level (default 512) accepted while encoding
271	or decoding. If the JSON text or Perl data structure has an equal or	559	or decoding. If a higher nesting level is detected in JSON text or a
272	higher nesting level then this limit, then the encoder and decoder	560	Perl data structure, then the encoder and decoder will stop and
273	will stop and croak at that point.	561	croak at that point.
274		562
275	Nesting level is defined by number of hash- or arrayrefs that the	563	Nesting level is defined by number of hash- or arrayrefs that the
276	encoder needs to traverse to reach a given point or the number of	564	encoder needs to traverse to reach a given point or the number of
277	"{" or "[" characters without their matching closing parenthesis	565	"{" or "[" characters without their matching closing parenthesis
278	crossed to reach a given character in a string.	566	crossed to reach a given character in a string.
279		567
280	Setting the maximum depth to one disallows any nesting, so that	568	Setting the maximum depth to one disallows any nesting, so that
281	ensures that the object is only a single hash/object or array.	569	ensures that the object is only a single hash/object or array.
282		570
283	The argument to "max_depth" will be rounded up to the next nearest	571	If no argument is given, the highest possible setting will be used,
284	power of two.	572	which is rarely useful.
		573
		574	Note that nesting is implemented by recursion in C. The default
		575	value has been chosen to be as large as typical operating systems
		576	allow without crashing.
		577
		578	See SECURITY CONSIDERATIONS, below, for more info on why this is
		579	useful.
		580
		581	$json = $json->max_size ([$maximum_string_size])
		582	$max_size = $json->get_max_size
		583	Set the maximum length a JSON text may have (in bytes) where
		584	decoding is being attempted. The default is 0, meaning no limit.
		585	When "decode" is called on a string that is longer then this many
		586	bytes, it will not attempt to decode the string but throw an
		587	exception. This setting has no effect on "encode" (yet).
		588
		589	If no argument is given, the limit check will be deactivated (same
		590	as when 0 is specified).
285		591
286	See SECURITY CONSIDERATIONS, below, for more info on why this is	592	See SECURITY CONSIDERATIONS, below, for more info on why this is
287	useful.	593	useful.
288		594
289	$json_text = $json->encode ($perl_scalar)	595	$json_text = $json->encode ($perl_scalar)
…		…
301		607
302	JSON numbers and strings become simple Perl scalars. JSON arrays	608	JSON numbers and strings become simple Perl scalars. JSON arrays
303	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"	609	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
304	becomes 1, "false" becomes 0 and "null" becomes "undef".	610	becomes 1, "false" becomes 0 and "null" becomes "undef".
305		611
		612	($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		613	This works like the "decode" method, but instead of raising an
		614	exception when there is trailing garbage after the first JSON
		615	object, it will silently stop parsing there and return the number of
		616	characters consumed so far.
		617
		618	This is useful if your JSON texts are not delimited by an outer
		619	protocol (which is not the brightest thing to do in the first place)
		620	and you need to know where the JSON text ends.
		621
		622	JSON::XS->new->decode_prefix ("[1] the tail")
		623	=> ([], 3)
		624
		625	INCREMENTAL PARSING
		626	In some cases, there is the need for incremental parsing of JSON texts.
		627	While this module always has to keep both JSON text and resulting Perl
		628	data structure in memory at one time, it does allow you to parse a JSON
		629	stream incrementally. It does so by accumulating text until it has a
		630	full JSON object, which it then can decode. This process is similar to
		631	using "decode_prefix" to see if a full JSON object is available, but is
		632	much more efficient (and can be implemented with a minimum of method
		633	calls).
		634
		635	JSON::XS will only attempt to parse the JSON text once it is sure it has
		636	enough text to get a decisive result, using a very simple but truly
		637	incremental parser. This means that it sometimes won't stop as early as
		638	the full parser, for example, it doesn't detect parenthese mismatches.
		639	The only thing it guarantees is that it starts decoding as soon as a
		640	syntactically valid JSON text has been seen. This means you need to set
		641	resource limits (e.g. "max_size") to ensure the parser will stop parsing
		642	in the presence if syntax errors.
		643
		644	The following methods implement this incremental parser.
		645
		646	[void, scalar or list context] = $json->incr_parse ([$string])
		647	This is the central parsing function. It can both append new text
		648	and extract objects from the stream accumulated so far (both of
		649	these functions are optional).
		650
		651	If $string is given, then this string is appended to the already
		652	existing JSON fragment stored in the $json object.
		653
		654	After that, if the function is called in void context, it will
		655	simply return without doing anything further. This can be used to
		656	add more text in as many chunks as you want.
		657
		658	If the method is called in scalar context, then it will try to
		659	extract exactly one JSON object. If that is successful, it will
		660	return this object, otherwise it will return "undef". If there is a
		661	parse error, this method will croak just as "decode" would do (one
		662	can then use "incr_skip" to skip the errornous part). This is the
		663	most common way of using the method.
		664
		665	And finally, in list context, it will try to extract as many objects
		666	from the stream as it can find and return them, or the empty list
		667	otherwise. For this to work, there must be no separators between the
		668	JSON objects or arrays, instead they must be concatenated
		669	back-to-back. If an error occurs, an exception will be raised as in
		670	the scalar context case. Note that in this case, any
		671	previously-parsed JSON texts will be lost.
		672
		673	$lvalue_string = $json->incr_text
		674	This method returns the currently stored JSON fragment as an lvalue,
		675	that is, you can manipulate it. This only works when a preceding
		676	call to "incr_parse" in scalar context successfully returned an
		677	object. Under all other circumstances you must not call this
		678	function (I mean it. although in simple tests it might actually
		679	work, it will fail under real world conditions). As a special
		680	exception, you can also call this method before having parsed
		681	anything.
		682
		683	This function is useful in two cases: a) finding the trailing text
		684	after a JSON object or b) parsing multiple JSON objects separated by
		685	non-JSON text (such as commas).
		686
		687	$json->incr_skip
		688	This will reset the state of the incremental parser and will remove
		689	the parsed text from the input buffer. This is useful after
		690	"incr_parse" died, in which case the input buffer and incremental
		691	parser state is left unchanged, to skip the text parsed so far and
		692	to reset the parse state.
		693
		694	$json->incr_reset
		695	This completely resets the incremental parser, that is, after this
		696	call, it will be as if the parser had never parsed anything.
		697
		698	This is useful if you want ot repeatedly parse JSON objects and want
		699	to ignore any trailing data, which means you have to reset the
		700	parser after each successful decode.
		701
		702	LIMITATIONS
		703	All options that affect decoding are supported, except "allow_nonref".
		704	The reason for this is that it cannot be made to work sensibly: JSON
		705	objects and arrays are self-delimited, i.e. you can concatenate them
		706	back to back and still decode them perfectly. This does not hold true
		707	for JSON numbers, however.
		708
		709	For example, is the string 1 a single JSON number, or is it simply the
		710	start of 12? Or is 12 a single JSON number, or the concatenation of 1
		711	and 2? In neither case you can tell, and this is why JSON::XS takes the
		712	conservative route and disallows this case.
		713
		714	EXAMPLES
		715	Some examples will make all this clearer. First, a simple example that
		716	works similarly to "decode_prefix": We want to decode the JSON object at
		717	the start of a string and identify the portion after the JSON object:
		718
		719	my $text = "[1,2,3] hello";
		720
		721	my $json = new JSON::XS;
		722
		723	my $obj = $json->incr_parse ($text)
		724	or die "expected JSON object or array at beginning of string";
		725
		726	my $tail = $json->incr_text;
		727	# $tail now contains " hello"
		728
		729	Easy, isn't it?
		730
		731	Now for a more complicated example: Imagine a hypothetical protocol
		732	where you read some requests from a TCP stream, and each request is a
		733	JSON array, without any separation between them (in fact, it is often
		734	useful to use newlines as "separators", as these get interpreted as
		735	whitespace at the start of the JSON text, which makes it possible to
		736	test said protocol with "telnet"...).
		737
		738	Here is how you'd do it (it is trivial to write this in an event-based
		739	manner):
		740
		741	my $json = new JSON::XS;
		742
		743	# read some data from the socket
		744	while (sysread $socket, my $buf, 4096) {
		745
		746	# split and decode as many requests as possible
		747	for my $request ($json->incr_parse ($buf)) {
		748	# act on the $request
		749	}
		750	}
		751
		752	Another complicated example: Assume you have a string with JSON objects
		753	or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
		754	[3]"). To parse them, we have to skip the commas between the JSON texts,
		755	and here is where the lvalue-ness of "incr_text" comes in useful:
		756
		757	my $text = "[1],[2], [3]";
		758	my $json = new JSON::XS;
		759
		760	# void context, so no parsing done
		761	$json->incr_parse ($text);
		762
		763	# now extract as many objects as possible. note the
		764	# use of scalar context so incr_text can be called.
		765	while (my $obj = $json->incr_parse) {
		766	# do something with $obj
		767
		768	# now skip the optional comma
		769	$json->incr_text =~ s/^ \s* , //x;
		770	}
		771
		772	Now lets go for a very complex example: Assume that you have a gigantic
		773	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		774	but you cannot load it into memory fully (this has actually happened in
		775	the real world :).
		776
		777	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		778	can still help you: You implement a (very simple) array parser and let
		779	JSON decode the array elements, which are all full JSON objects on their
		780	own (this wouldn't work if the array elements could be JSON numbers, for
		781	example):
		782
		783	my $json = new JSON::XS;
		784
		785	# open the monster
		786	open my $fh, "<bigfile.json"
		787	or die "bigfile: $!";
		788
		789	# first parse the initial "["
		790	for (;;) {
		791	sysread $fh, my $buf, 65536
		792	or die "read error: $!";
		793	$json->incr_parse ($buf); # void context, so no parsing
		794
		795	# Exit the loop once we found and removed(!) the initial "[".
		796	# In essence, we are (ab-)using the $json object as a simple scalar
		797	# we append data to.
		798	last if $json->incr_text =~ s/^ \s* \[ //x;
		799	}
		800
		801	# now we have the skipped the initial "[", so continue
		802	# parsing all the elements.
		803	for (;;) {
		804	# in this loop we read data until we got a single JSON object
		805	for (;;) {
		806	if (my $obj = $json->incr_parse) {
		807	# do something with $obj
		808	last;
		809	}
		810
		811	# add more data
		812	sysread $fh, my $buf, 65536
		813	or die "read error: $!";
		814	$json->incr_parse ($buf); # void context, so no parsing
		815	}
		816
		817	# in this loop we read data until we either found and parsed the
		818	# separating "," between elements, or the final "]"
		819	for (;;) {
		820	# first skip whitespace
		821	$json->incr_text =~ s/^\s*//;
		822
		823	# if we find "]", we are done
		824	if ($json->incr_text =~ s/^\]//) {
		825	print "finished.\n";
		826	exit;
		827	}
		828
		829	# if we find ",", we can continue with the next element
		830	if ($json->incr_text =~ s/^,//) {
		831	last;
		832	}
		833
		834	# if we find anything else, we have a parse error!
		835	if (length $json->incr_text) {
		836	die "parse error near ", $json->incr_text;
		837	}
		838
		839	# else add more data
		840	sysread $fh, my $buf, 65536
		841	or die "read error: $!";
		842	$json->incr_parse ($buf); # void context, so no parsing
		843	}
		844
		845	This is a complex example, but most of the complexity comes from the
		846	fact that we are trying to be correct (bear with me if I am wrong, I
		847	never ran the above example :).
		848
306	MAPPING	849	MAPPING
307	This section describes how JSON::XS maps Perl values to JSON values and	850	This section describes how JSON::XS maps Perl values to JSON values and
308	vice versa. These mappings are designed to "do the right thing" in most	851	vice versa. These mappings are designed to "do the right thing" in most
309	circumstances automatically, preserving round-tripping characteristics	852	circumstances automatically, preserving round-tripping characteristics
310	(what you put in comes out as something equivalent).	853	(what you put in comes out as something equivalent).
311		854
312	For the more enlightened: note that in the following descriptions,	855	For the more enlightened: note that in the following descriptions,
313	lowercase perl refers to the Perl interpreter, while uppcercase Perl	856	lowercase perl refers to the Perl interpreter, while uppercase Perl
314	refers to the abstract Perl language itself.	857	refers to the abstract Perl language itself.
315		858
316	JSON -> PERL	859	JSON -> PERL
317	object	860	object
318	A JSON object becomes a reference to a hash in Perl. No ordering of	861	A JSON object becomes a reference to a hash in Perl. No ordering of
319	object keys is preserved (JSON does not preserver object key	862	object keys is preserved (JSON does not preserve object key ordering
320	ordering itself).	863	itself).
321		864
322	array	865	array
323	A JSON array becomes a reference to an array in Perl.	866	A JSON array becomes a reference to an array in Perl.
324		867
325	string	868	string
326	A JSON string becomes a string scalar in Perl - Unicode codepoints	869	A JSON string becomes a string scalar in Perl - Unicode codepoints
327	in JSON are represented by the same codepoints in the Perl string,	870	in JSON are represented by the same codepoints in the Perl string,
328	so no manual decoding is necessary.	871	so no manual decoding is necessary.
329		872
330	number	873	number
331	A JSON number becomes either an integer or numeric (floating point)	874	A JSON number becomes either an integer, numeric (floating point) or
332	scalar in perl, depending on its range and any fractional parts. On	875	string scalar in perl, depending on its range and any fractional
333	the Perl level, there is no difference between those as Perl handles	876	parts. On the Perl level, there is no difference between those as
334	all the conversion details, but an integer may take slightly less	877	Perl handles all the conversion details, but an integer may take
335	memory and might represent more values exactly than (floating point)	878	slightly less memory and might represent more values exactly than
		879	floating point numbers.
		880
		881	If the number consists of digits only, JSON::XS will try to
		882	represent it as an integer value. If that fails, it will try to
		883	represent it as a numeric (floating point) value if that is possible
		884	without loss of precision. Otherwise it will preserve the number as
		885	a string value (in which case you lose roundtripping ability, as the
		886	JSON number will be re-encoded toa JSON string).
		887
		888	Numbers containing a fractional or exponential part will always be
		889	represented as numeric (floating point) values, possibly at a loss
		890	of precision (in which case you might lose perfect roundtripping
		891	ability, but the JSON number will still be re-encoded as a JSON
336	numbers.	892	number).
337		893
338	true, false	894	true, false
339	These JSON atoms become 0, 1, respectively. Information is lost in	895	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
340	this process. Future versions might represent those values	896	respectively. They are overloaded to act almost exactly like the
341	differently, but they will be guarenteed to act like these integers	897	numbers 1 and 0. You can check whether a scalar is a JSON boolean by
342	would normally in Perl.	898	using the "JSON::XS::is_bool" function.
343		899
344	null	900	null
345	A JSON null atom becomes "undef" in Perl.	901	A JSON null atom becomes "undef" in Perl.
346		902
347	PERL -> JSON	903	PERL -> JSON
…		…
369	an exception to be thrown, except for references to the integers 0	925	an exception to be thrown, except for references to the integers 0
370	and 1, which get turned into "false" and "true" atoms in JSON. You	926	and 1, which get turned into "false" and "true" atoms in JSON. You
371	can also use "JSON::XS::false" and "JSON::XS::true" to improve	927	can also use "JSON::XS::false" and "JSON::XS::true" to improve
372	readability.	928	readability.
373		929
374	to_json [\0,JSON::XS::true] # yields [false,true]	930	encode_json [\0, JSON::XS::true] # yields [false,true]
		931
		932	JSON::XS::true, JSON::XS::false
		933	These special values become JSON true and JSON false values,
		934	respectively. You can also use "\1" and "\0" directly if you want.
375		935
376	blessed objects	936	blessed objects
377	Blessed objects are not allowed. JSON::XS currently tries to encode	937	Blessed objects are not directly representable in JSON. See the
378	their underlying representation (hash- or arrayref), but this	938	"allow_blessed" and "convert_blessed" methods on various options on
379	behaviour might change in future versions.	939	how to deal with this: basically, you can choose between throwing an
		940	exception, encoding the reference as if it weren't blessed, or
		941	provide your own serialiser method.
380		942
381	simple scalars	943	simple scalars
382	Simple Perl scalars (any scalar that is not a reference) are the	944	Simple Perl scalars (any scalar that is not a reference) are the
383	most difficult objects to encode: JSON::XS will encode undefined	945	most difficult objects to encode: JSON::XS will encode undefined
384	scalars as JSON null value, scalars that have last been used in a	946	scalars as JSON "null" values, scalars that have last been used in a
385	string context before encoding as JSON strings and anything else as	947	string context before encoding as JSON strings, and anything else as
386	number value:	948	number value:
387		949
388	# dump as number	950	# dump as number
389	to_json [2] # yields [2]	951	encode_json [2] # yields [2]
390	to_json [-3.0e17] # yields [-3e+17]	952	encode_json [-3.0e17] # yields [-3e+17]
391	my $value = 5; to_json [$value] # yields [5]	953	my $value = 5; encode_json [$value] # yields [5]
392		954
393	# used as string, so dump as string	955	# used as string, so dump as string
394	print $value;	956	print $value;
395	to_json [$value] # yields ["5"]	957	encode_json [$value] # yields ["5"]
396		958
397	# undef becomes null	959	# undef becomes null
398	to_json [undef] # yields [null]	960	encode_json [undef] # yields [null]
399		961
400	You can force the type to be a string by stringifying it:	962	You can force the type to be a JSON string by stringifying it:
401		963
402	my $x = 3.1; # some variable containing a number	964	my $x = 3.1; # some variable containing a number
403	"$x"; # stringified	965	"$x"; # stringified
404	$x .= ""; # another, more awkward way to stringify	966	$x .= ""; # another, more awkward way to stringify
405	print $x; # perl does it for you, too, quite often	967	print $x; # perl does it for you, too, quite often
406		968
407	You can force the type to be a number by numifying it:	969	You can force the type to be a JSON number by numifying it:
408		970
409	my $x = "3"; # some variable containing a string	971	my $x = "3"; # some variable containing a string
410	$x += 0; # numify it, ensuring it will be dumped as a number	972	$x += 0; # numify it, ensuring it will be dumped as a number
411	$x *= 1; # same thing, the choise is yours.	973	$x *= 1; # same thing, the choice is yours.
412		974
413	You can not currently output JSON booleans or force the type in	975	You can not currently force the type in other, less obscure, ways.
414	other, less obscure, ways. Tell me if you need this capability.	976	Tell me if you need this capability (but don't forget to explain why
		977	it's needed :).
415		978
416	COMPARISON	979	ENCODING/CODESET FLAG NOTES
417	As already mentioned, this module was created because none of the	980	The interested reader might have seen a number of flags that signify
418	existing JSON modules could be made to work correctly. First I will	981	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
419	describe the problems (or pleasures) I encountered with various existing	982	some confusion on what these do, so here is a short comparison:
420	JSON modules, followed by some benchmark values. JSON::XS was designed
421	not to suffer from any of these problems or limitations.
422		983
423	JSON 1.07	984	"utf8" controls whether the JSON text created by "encode" (and expected
424	Slow (but very portable, as it is written in pure Perl).	985	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
		986	control whether "encode" escapes character values outside their
		987	respective codeset range. Neither of these flags conflict with each
		988	other, although some combinations make less sense than others.
425		989
426	Undocumented/buggy Unicode handling (how JSON handles unicode values	990	Care has been taken to make all flags symmetrical with respect to
427	is undocumented. One can get far by feeding it unicode strings and	991	"encode" and "decode", that is, texts encoded with any combination of
428	doing en-/decoding oneself, but unicode escapes are not working	992	these flag values will be correctly decoded when the same flags are used
		993	- in general, if you use different flag settings while encoding vs. when
		994	decoding you likely have a bug somewhere.
		995
		996	Below comes a verbose discussion of these flags. Note that a "codeset"
		997	is simply an abstract set of character-codepoint pairs, while an
		998	encoding takes those codepoint numbers and encodes them, in our case
		999	into octets. Unicode is (among other things) a codeset, UTF-8 is an
		1000	encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and
		1001	encodings at the same time, which can be confusing.
		1002
		1003	"utf8" flag disabled
		1004	When "utf8" is disabled (the default), then "encode"/"decode"
		1005	generate and expect Unicode strings, that is, characters with high
		1006	ordinal Unicode values (> 255) will be encoded as such characters,
		1007	and likewise such characters are decoded as-is, no canges to them
		1008	will be done, except "(re-)interpreting" them as Unicode codepoints
		1009	or Unicode characters, respectively (to Perl, these are the same
		1010	thing in strings unless you do funny/weird/dumb stuff).
		1011
		1012	This is useful when you want to do the encoding yourself (e.g. when
		1013	you want to have UTF-16 encoded JSON texts) or when some other layer
		1014	does the encoding for you (for example, when printing to a terminal
		1015	using a filehandle that transparently encodes to UTF-8 you certainly
		1016	do NOT want to UTF-8 encode your data first and have Perl encode it
		1017	another time).
		1018
		1019	"utf8" flag enabled
		1020	If the "utf8"-flag is enabled, "encode"/"decode" will encode all
		1021	characters using the corresponding UTF-8 multi-byte sequence, and
		1022	will expect your input strings to be encoded as UTF-8, that is, no
		1023	"character" of the input string must have any value > 255, as UTF-8
		1024	does not allow that.
		1025
		1026	The "utf8" flag therefore switches between two modes: disabled means
		1027	you will get a Unicode string in Perl, enabled means you get an
		1028	UTF-8 encoded octet/binary string in Perl.
		1029
		1030	"latin1" or "ascii" flags enabled
		1031	With "latin1" (or "ascii") enabled, "encode" will escape characters
		1032	with ordinal values > 255 (> 127 with "ascii") and encode the
		1033	remaining characters as specified by the "utf8" flag.
		1034
		1035	If "utf8" is disabled, then the result is also correctly encoded in
		1036	those character sets (as both are proper subsets of Unicode, meaning
		1037	that a Unicode string with all character values < 256 is the same
		1038	thing as a ISO-8859-1 string, and a Unicode string with all
		1039	character values < 128 is the same thing as an ASCII string in
429	properly).	1040	Perl).
430		1041
431	No roundtripping (strings get clobbered if they look like numbers,	1042	If "utf8" is enabled, you still get a correct UTF-8-encoded string,
432	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	1043	regardless of these flags, just some more characters will be escaped
433	will decode into the number 2.	1044	using "\uXXXX" then before.
434		1045
435	JSON::PC 0.01	1046	Note that ISO-8859-1-encoded strings are not compatible with UTF-8
436	Very fast.	1047	encoding, while ASCII-encoded strings are. That is because the
		1048	ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
		1049	codeset being a subset of Unicode), while ASCII is.
437		1050
438	Undocumented/buggy Unicode handling.	1051	Surprisingly, "decode" will ignore these flags and so treat all
		1052	input values as governed by the "utf8" flag. If it is disabled, this
		1053	allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
		1054	strict subsets of Unicode. If it is enabled, you can correctly
		1055	decode UTF-8 encoded strings.
439		1056
440	No roundtripping.	1057	So neither "latin1" nor "ascii" are incompatible with the "utf8"
		1058	flag - they only govern when the JSON output engine escapes a
		1059	character or not.
441		1060
442	Has problems handling many Perl values (e.g. regex results and other	1061	The main use for "latin1" is to relatively efficiently store binary
443	magic values will make it croak).	1062	data as JSON, at the expense of breaking compatibility with most
		1063	JSON decoders.
444		1064
445	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1065	The main use for "ascii" is to force the output to not contain
446	which is not a valid JSON text.	1066	characters with values > 127, which means you can interpret the
		1067	resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
		1068	any character set and 8-bit-encoding, and still get the same data
		1069	structure back. This is useful when your channel for JSON transfer
		1070	is not 8-bit clean or the encoding might be mangled in between (e.g.
		1071	in mail), and works because ASCII is a proper subset of most 8-bit
		1072	and multibyte encodings in use in the world.
447		1073
448	Unmaintained (maintainer unresponsive for many months, bugs are not	1074	JSON and YAML
449	getting fixed).	1075	You often hear that JSON is a subset of YAML. This is, however, a mass
		1076	hysteria(*) and very far from the truth (as of the time of this
		1077	writing), so let me state it clearly: *in general, there is no way to
		1078	configure JSON::XS to output a data structure as valid YAML* that works
		1079	in all cases.
450		1080
451	JSON::Syck 0.21	1081	If you really must use JSON::XS to generate YAML, you should use this
452	Very buggy (often crashes).	1082	algorithm (subject to change in future versions):
453		1083
454	Very inflexible (no human-readable format supported, format pretty	1084	my $to_yaml = JSON::XS->new->utf8->space_after (1);
455	much undocumented. I need at least a format for easy reading by	1085	my $yaml = $to_yaml->encode ($ref) . "\n";
456	humans and a single-line compact format for use in a protocol, and
457	preferably a way to generate ASCII-only JSON texts).
458		1086
459	Completely broken (and confusingly documented) Unicode handling	1087	This will usually generate JSON texts that also parse as valid YAML.
460	(unicode escapes are not working properly, you need to set	1088	Please note that YAML has hardcoded limits on (simple) object key
461	ImplicitUnicode to different values on en- and decoding to get	1089	lengths that JSON doesn't have and also has different and incompatible
462	symmetric behaviour).	1090	unicode handling, so you should make sure that your hash keys are
		1091	noticeably shorter than the 1024 "stream characters" YAML allows and
		1092	that you do not have characters with codepoint values outside the
		1093	Unicode BMP (basic multilingual page). YAML also does not allow "\/"
		1094	sequences in strings (which JSON::XS does not currently generate, but
		1095	other JSON generators might).
463		1096
464	No roundtripping (simple cases work, but this depends on wether the	1097	There might be other incompatibilities that I am not aware of (or the
465	scalar value was used in a numeric context or not).	1098	YAML specification has been changed yet again - it does so quite often).
		1099	In general you should not try to generate YAML with a JSON generator or
		1100	vice versa, or try to parse JSON with a YAML parser or vice versa:
		1101	chances are high that you will run into severe interoperability problems
		1102	when you least expect it.
466		1103
467	Dumping hashes may skip hash values depending on iterator state.	1104	(*) I have been pressured multiple times by Brian Ingerson (one of the
		1105	authors of the YAML specification) to remove this paragraph, despite
		1106	him acknowledging that the actual incompatibilities exist. As I was
		1107	personally bitten by this "JSON is YAML" lie, I refused and said I
		1108	will continue to educate people about these issues, so others do not
		1109	run into the same problem again and again. After this, Brian called
		1110	me a (quote)complete and worthless idiot(unquote).
468		1111
469	Unmaintained (maintainer unresponsive for many months, bugs are not	1112	In my opinion, instead of pressuring and insulting people who
470	getting fixed).	1113	actually clarify issues with YAML and the wrong statements of some
471		1114	of its proponents, I would kindly suggest reading the JSON spec
472	Does not check input for validity (i.e. will accept non-JSON input	1115	(which is not that difficult or long) and finally make YAML
473	and return "something" instead of raising an exception. This is a	1116	compatible to it, and educating users about the changes, instead of
474	security issue: imagine two banks transfering money between each	1117	spreading lies about the real compatibility for many years and
475	other using JSON. One bank might parse a given non-JSON request and	1118	trying to silence people who point out that it isn't true.
476	deduct money, while the other might reject the transaction with a
477	syntax error. While a good protocol will at least recover, that is
478	extra unnecessary work and the transaction will still not succeed).
479
480	JSON::DWIW 0.04
481	Very fast. Very natural. Very nice.
482
483	Undocumented unicode handling (but the best of the pack. Unicode
484	escapes still don't get parsed properly).
485
486	Very inflexible.
487
488	No roundtripping.
489
490	Does not generate valid JSON texts (key strings are often unquoted,
491	empty keys result in nothing being output)
492
493	Does not check input for validity.
494		1119
495	SPEED	1120	SPEED
496	It seems that JSON::XS is surprisingly fast, as shown in the following	1121	It seems that JSON::XS is surprisingly fast, as shown in the following
497	tables. They have been generated with the help of the "eg/bench" program	1122	tables. They have been generated with the help of the "eg/bench" program
498	in the JSON::XS distribution, to make it easy to compare on your own	1123	in the JSON::XS distribution, to make it easy to compare on your own
499	system.	1124	system.
500		1125
501	First comes a comparison between various modules using a very short JSON	1126	First comes a comparison between various modules using a very short
502	string:	1127	single-line JSON string (also available at
		1128	<http://dist.schmorp.de/misc/json/short.json>).
503		1129
504	{"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null}	1130	{"method": "handleMessage", "params": ["user1",
		1131	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1132	true, false]}
505		1133
506	It shows the number of encodes/decodes per second (JSON::XS uses the	1134	It shows the number of encodes/decodes per second (JSON::XS uses the
507	functional interface, while JSON::XS/2 uses the OO interface with	1135	functional interface, while JSON::XS/2 uses the OO interface with
508	pretty-printing and hashkey sorting enabled). Higher is better:	1136	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
		1137	Higher is better:
509		1138
510	module \| encode \| decode \|	1139	module \| encode \| decode \|
511	-----------\|------------\|------------\|	1140	-----------\|------------\|------------\|
512	JSON \| 11488.516 \| 7823.035 \|	1141	JSON 1.x \| 4990.842 \| 4088.813 \|
513	JSON::DWIW \| 94708.054 \| 129094.260 \|	1142	JSON::DWIW \| 51653.990 \| 71575.154 \|
514	JSON::PC \| 63884.157 \| 128528.212 \|	1143	JSON::PC \| 65948.176 \| 74631.744 \|
		1144	JSON::PP \| 8931.652 \| 3817.168 \|
515	JSON::Syck \| 34898.677 \| 42096.911 \|	1145	JSON::Syck \| 24877.248 \| 27776.848 \|
516	JSON::XS \| 654027.064 \| 396423.669 \|	1146	JSON::XS \| 388361.481 \| 227951.304 \|
517	JSON::XS/2 \| 371564.190 \| 371725.613 \|	1147	JSON::XS/2 \| 227951.304 \| 218453.333 \|
		1148	JSON::XS/3 \| 338250.323 \| 218453.333 \|
		1149	Storable \| 16500.016 \| 135300.129 \|
518	-----------+------------+------------+	1150	-----------+------------+------------+
519		1151
520	That is, JSON::XS is more than six times faster than JSON::DWIW on	1152	That is, JSON::XS is about five times faster than JSON::DWIW on
521	encoding, more than three times faster on decoding, and about thirty	1153	encoding, about three times faster on decoding, and over forty times
522	times faster than JSON, even with pretty-printing and key sorting.	1154	faster than JSON, even with pretty-printing and key sorting. It also
		1155	compares favourably to Storable for small amounts of data.
523		1156
524	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1157	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
525	search API (http://nanoref.com/yahooapis/mgPdGg):	1158	search API (<http://dist.schmorp.de/misc/json/long.json>).
526		1159
527	module \| encode \| decode \|	1160	module \| encode \| decode \|
528	-----------\|------------\|------------\|	1161	-----------\|------------\|------------\|
529	JSON \| 273.023 \| 44.674 \|	1162	JSON 1.x \| 55.260 \| 34.971 \|
530	JSON::DWIW \| 1089.383 \| 1145.704 \|	1163	JSON::DWIW \| 825.228 \| 1082.513 \|
531	JSON::PC \| 3097.419 \| 2393.921 \|	1164	JSON::PC \| 3571.444 \| 2394.829 \|
532	JSON::Syck \| 514.060 \| 843.053 \|	1165	JSON::PP \| 210.987 \| 32.574 \|
533	JSON::XS \| 6479.668 \| 3636.364 \|	1166	JSON::Syck \| 552.551 \| 787.544 \|
534	JSON::XS/2 \| 3774.221 \| 3599.124 \|	1167	JSON::XS \| 5780.463 \| 4854.519 \|
		1168	JSON::XS/2 \| 3869.998 \| 4798.975 \|
		1169	JSON::XS/3 \| 5862.880 \| 4798.975 \|
		1170	Storable \| 4445.002 \| 5235.027 \|
535	-----------+------------+------------+	1171	-----------+------------+------------+
536		1172
537	Again, JSON::XS leads by far.	1173	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1174	decodes faster).
538		1175
539	On large strings containing lots of high unicode characters, some	1176	On large strings containing lots of high Unicode characters, some
540	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1177	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
541	result will be broken due to missing (or wrong) unicode handling. Others	1178	result will be broken due to missing (or wrong) Unicode handling. Others
542	refuse to decode or encode properly, so it was impossible to prepare a	1179	refuse to decode or encode properly, so it was impossible to prepare a
543	fair comparison table for that case.	1180	fair comparison table for that case.
544		1181
545	SECURITY CONSIDERATIONS	1182	SECURITY CONSIDERATIONS
546	When you are using JSON in a protocol, talking to untrusted potentially	1183	When you are using JSON in a protocol, talking to untrusted potentially
…		…
550	have any buffer overflows. Obviously, this module should ensure that and	1187	have any buffer overflows. Obviously, this module should ensure that and
551	I am trying hard on making that true, but you never know.	1188	I am trying hard on making that true, but you never know.
552		1189
553	Second, you need to avoid resource-starving attacks. That means you	1190	Second, you need to avoid resource-starving attacks. That means you
554	should limit the size of JSON texts you accept, or make sure then when	1191	should limit the size of JSON texts you accept, or make sure then when
555	your resources run out, thats just fine (e.g. by using a separate	1192	your resources run out, that's just fine (e.g. by using a separate
556	process that can crash safely). The size of a JSON text in octets or	1193	process that can crash safely). The size of a JSON text in octets or
557	characters is usually a good indication of the size of the resources	1194	characters is usually a good indication of the size of the resources
558	required to decode it into a Perl structure.	1195	required to decode it into a Perl structure. While JSON::XS can check
		1196	the size of the JSON text, it might be too late when you already have it
		1197	in memory, so you might want to check the size before you accept the
		1198	string.
559		1199
560	Third, JSON::XS recurses using the C stack when decoding objects and	1200	Third, JSON::XS recurses using the C stack when decoding objects and
561	arrays. The C stack is a limited resource: for instance, on my amd64	1201	arrays. The C stack is a limited resource: for instance, on my amd64
562	machine with 8MB of stack size I can decode around 180k nested arrays	1202	machine with 8MB of stack size I can decode around 180k nested arrays
563	but only 14k nested JSON objects (due to perl itself recursing deeply on	1203	but only 14k nested JSON objects (due to perl itself recursing deeply on
564	croak to free the temporary). If that is exceeded, the program crashes.	1204	croak to free the temporary). If that is exceeded, the program crashes.
565	to be conservative, the default nesting limit is set to 512. If your	1205	To be conservative, the default nesting limit is set to 512. If your
566	process has a smaller stack, you should adjust this setting accordingly	1206	process has a smaller stack, you should adjust this setting accordingly
567	with the "max_depth" method.	1207	with the "max_depth" method.
568		1208
569	And last but least, something else could bomb you that I forgot to think	1209	Something else could bomb you, too, that I forgot to think of. In that
570	of. In that case, you get to keep the pieces. I am alway sopen for	1210	case, you get to keep the pieces. I am always open for hints, though...
571	hints, though...	1211
		1212	Also keep in mind that JSON::XS might leak contents of your Perl data
		1213	structures in its error messages, so when you serialise sensitive
		1214	information you might want to make sure that exceptions thrown by
		1215	JSON::XS will not end up in front of untrusted eyes.
		1216
		1217	If you are using JSON::XS to return packets to consumption by JavaScript
		1218	scripts in a browser you should have a look at
		1219	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1220	you are vulnerable to some common attack vectors (which really are
		1221	browser design bugs, but it is still you who will have to deal with it,
		1222	as major browser developers care only for features, not about getting
		1223	security right).
		1224
		1225	THREADS
		1226	This module is not guaranteed to be thread safe and there are no plans
		1227	to change this until Perl gets thread support (as opposed to the
		1228	horribly slow so-called "threads" which are simply slow and bloated
		1229	process simulations - use fork, it's much faster, cheaper, better).
		1230
		1231	(It might actually work, but you have been warned).
572		1232
573	BUGS	1233	BUGS
574	While the goal of this module is to be correct, that unfortunately does	1234	While the goal of this module is to be correct, that unfortunately does
575	not mean its bug-free, only that I think its design is bug-free. It is	1235	not mean it's bug-free, only that I think its design is bug-free. If you
576	still relatively early in its development. If you keep reporting bugs
577	they will be fixed swiftly, though.	1236	keep reporting bugs they will be fixed swiftly, though.
		1237
		1238	Please refrain from using rt.cpan.org or any other bug reporting
		1239	service. I put the contact address into my modules for a reason.
		1240
		1241	SEE ALSO
		1242	The json_xs command line utility for quick experiments.
578		1243
579	AUTHOR	1244	AUTHOR
580	Marc Lehmann <schmorp@schmorp.de>	1245	Marc Lehmann <schmorp@schmorp.de>
581	http://home.schmorp.de/	1246	http://home.schmorp.de/
582		1247

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Comparing JSON-XS/README (file contents): Revision 1.10 by root, Wed Apr 4 00:01:44 2007 UTC vs. Revision 1.28 by root, Mon Sep 29 03:09:27 2008 UTC

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Comparing JSON-XS/README (file contents):
Revision 1.10 by root, Wed Apr 4 00:01:44 2007 UTC vs.
Revision 1.28 by root, Mon Sep 29 03:09:27 2008 UTC